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In metal and nonmetal mines, measurement of the carbonaceous diesel par- ticulate fraction of respirable dust aerosol is accomplished using common sampling techniques and laboratory analysis. In coal mines, measurement is complicated by the carbonaceous nature of the coal. In such cases, special sampling and analytical tech- niques must be used to distinguish between diesel and respirable coal dust aerosol. The objective of this Bureau of Mines paper is to review some of the techniques that can be used to measure the diesel particulate fraction of respirable aerosol in the mine environment. In addition, the regulatory requirements for respirable dust in U.S. mines and the physical and chemical characteristics of diesel aerosols are reviewed in the larger context of ambient aerosol in the mine. Current regulatory and experimental measure- ment protocols for respirable mine aerosols are discussed. These include the use of filtra- tion, inertial impaction, and optical detection methods. In each case, the methodology is evaluated for the information that can be derived from the technique about the diesel fraction of the measured aerosol. Concluding the paper are recommendations on the use of dichotomous samplers to derive qualitative information on exposure to diesel aerosol in a mine. Also discussed are some of the Bureau's current research plans with regard to measurement of diesel emissions aerosol. INTRODUCTION Extensive use of diesels in the mining industry has given rise to questions concerning the exposure of miners to diesel aerosol emissions. Primary among these is, To what mass concentration levels of diesel aerosol are miners ex- posed? A secondary, but important, question being posed is, What fraction of the measured respirable aerosol originates from diesel equipment in the mine? Answering such questions accurately depends on the type of mine under consideration and the aerosol measurement methods that are employed. 'Research physicist, Twin Cities Research Center, Bureau of Mines, Min- neapolis, MN. "Physical scientist, Twin Cities Research Center. 'Supervisory physical scientist, Pittsburgh Research Center, Pittsburgh, PA. 'Public health officer, National Institute for Occupational Safety and Health, Morgantown, WV. This paper reviews the problems associated with monitoring and measurement of the diesel component of mine aerosol. It focuses on the instrumentation used to determine the contribution that diesel emission aerosols make to respirable aerosol concentrations in the mine en- vironment. The paper summarizes regulatory requirements for respirable aerosol in U.S. mines. The physical and chemical characteristics of diesel aerosols are also discussed in relation to their effect on the methods used to both monitor and measure the diesel fraction of respirable mine aerosol. The paper then reviews both those measurement methods currently used to monitor respirable dust in mines and those used for mine aerosol research. In each case an attempt is made to summarize the type of information that the technique can provide on the diesel fraction of the respirable aerosol as measured. 19 REGULATORY REQUIREMENTS— METAL AND NONMETAL The Mine Safety and Health Administration (MSHA) regulates health and safety conditions and practices in metal and nonmetal mines and mills under the authority of the Federal Mine Safety and Health Act of 1977 (I). 5 The specific regulations are found in the Code of Federal Regula- tions, title 30 (2). Standards in these regulations for airborne contaminants and physical agents were adopted from the 1973 recommended threshold limit values (TLV's) of the American Conference of Governmental Industrial Hygienists (ACGIH) (3). Compliance with these regulations is determined by the collection of environmental samples by MSHA inspectors. For respirable dust, a sample is collected on a filter after the aerosol has passed through a cyclone preclassifier at a flow rate of 1.7 L/min. The TLV for respirable dust con- taining quartz is determined by collecting a respirable dust sample, analyzing for quartz content, 8 and calculating the TLV using the formula: 10 mg/m 3 percent respirable quartz + 2 when the quartz content (percent respirable quartz) is greater than 1 pet (3). The resultant TLV is expressed in milligrams per cubic meter. For a given exposure level the magnitude of the toxicity is proportional to the quartz con- tent (4). The factor 2 in the denominator of the TLV for- mula ensures that dust exposures will not be excessively high when the quartz content is less than 5 pet and effec- tively limits the dust concentration to 5 mg/m 3 when no quartz is present in the sample. In 1983 MSHA proposed to revise many of the existing health regulations (5). Included in these revisions was a pro- posed change in the respirable dust standard. The propos- ed new standard, which is still undergoing review, is 100 Mg/m 3 of respirable quartz. REGULATORY REQUIREMENTS— COAL In 1970 a mandatory respirable dust standard of 3.0 mg/m 3 was established for underground coal mines under the Federal Coal Mine Health and Safety Act of 1969. This standard was subsequently lowered in 1972 to 2.0 mg/m 3 . Mandatory dust standards for surface work areas of underground coal mines and surface mines also became ef- fective in 1972. These regulations were continued under the Federal Mine Safety and Health Act of 1977 (6), which amended the 1969 coal act and merged coal and noncoal regulations into one law. In the 1969 act, "concentration of respirable dust" was defined as a measurement made with a Mining Research Establishment (MRE) Casella model 113A sampling instrument shown in figure 1 or such equivalent concentration measured with another device. This instrument was designed to have a sampling efficiency equivalent to the respirable response curve specified by the British Medical Research Council (BMRC) and shown in figure 2. The 1977 act changed the definition "concentra- tion of respirable dust" to be the "average concentration of respirable dust measured with a device approved by the Secretary (of Labor) and the Secretary of Health Education and Welfare." The device approved for measuring respirable dust uses a Dorr-Oliver 10-mm nylon cyclone, sampling at 2 L/min, to remove the nonrespirable fraction of dust samples. Measurements made with this device are con- verted to equivalent MRE concentrations by multiplying by an accommodation factor of 1.38 (7). Specific regulations detailing the collection of respirable dust samples by mine operators are found in the Code of Federal Regulations, title 30, (2). From the BMRC sampling efficiency curve of figure 2, it can be seen that all aerosol less than about 7 /ma aerodynamic diameter are included in the definition of respirable dust. As a result, diesel emissions aerosol, which 'Italic numbers in parentheses refer to items in the list of references at the end of this paper. ■Quartz content is determined by X-ray diffraction after the filter has been weighed. are mostly in this size range (8), are a major component of the aerosol sampled for compliance measurement of respirable dust in a coal mine. This diesel component of the sampled aerosol can affect the measurement in several ways. It can contribute out of proportion to its actual con- centration to the measured respirable aerosol in a mine because the accommodation factor used to correct com- pliance measurements overcorrects for aerosols less than 1 /im. Also, for mines with quartz concentrations greater than the minimums specified by the current regulations, the diesel component can dilute the collected respirable aerosol sample leading to a false low concentration for the quartz fraction of the mineral dust portion of the aerosol. Figure 1.— MRE gravimetric dust sampler. 20 100 90 ^^1 1 1 1 1 1 1 80 — — 70 — £ 60 — z o t 50 or UJ lj 40 Q_ KEY — 30 n Mr?r V — 20 \ — 10 l 1 1 1 J 1 \ I 2 3 4 5 6 7 PARTICLE AERODYNAMIC DIAMETER (D p ), M m 8 Figure 2.— BMRC respirable penetration curve. 21 REVIEW OF MINE AEROSOL CHARACTERISTICS To this point in the discussion, the terms dust, dust aerosol, diesel emissions aerosol, and diesel aerosol have been used loosely. More properly, the terms dust or par- ticulate refer to finely divided material wherever it is found. The term aerosol refers to such finely divided material suspended in air. When referring to air suspensions of par- ticulates, the proper terminology is aerosol. In a mine, sources of such aerosols include mining activities in the face area; e.g., drilling, operation of continuous mining machines, conventional mining methods, etc.; materials handling procedures such as use of breaker heads on con- veyor roads; and the diesel-powered equipment necessary to perform these tasks. Secondary sources of aerosol include dust entrainment during load-haul- dump operations, dust reentrainment from floor and walls caused by mine traffic, and dust from special procedures such as rock dusting. Aerosols from each of these sources have size distributions, chemical properties, and trace element compositions that are characteristic of the source emission or parent material from which the aerosol is formed. These characteristics are briefly discussed in the following subsections. AEROSOL SIZE RANGES Mine aerosols arise from a variety of sources and, as shown in figure 3, the shape of the aerosol size distribution can be influenced by these sources. The figure also displays the physical mechanisms such as condensation and coagula- tion that transfer aerosol mass from one size to another. There are three distinct aerosol size ranges that can be iden- tified from features in measured size distributions. The smallest of these, from 0.001 to 0.08 fan, is the Aitken nuclei range, which contains primary aerosol from combustion sources, such as diesel engines, and secondary aerosol form- ed from coagulation of primary aerosols to form chain ag- gregates. The next size range, from 0.08 to approximately 1.0 fan, termed the accumulation range, contains emissions in this size range plus aerosol accumulated by mass transfer through coagulation and condensation processes from the nuclei range. The last range, 1.0 to approximately 40 fan, is termed the coarse-aerosol range. Aerosols within this size fraction are generally the result of mechanical processes such as a rock fracture and bulk material handling. Mineral dust aerosol reentrained by mine haulage vehicles during the load-haul-dump cycle is an example of an in -mine emis- sion that will contribute aerosol to this size range. For convenience, the Aitken nuclei and the accumula- tion range are combined in a single "fine" aerosol range. A division is usually made between this range and the "coarse" aerosol at 1.0 fan. This distinction is possible because sources of aerosol in the two ranges are usually dif- ferent, and the coarse-aerosol range contains very little mass transferred from the accumulation range by coagula- tion. Respirable aerosol, as defined by the penetration effi- ciency curve of figure 2, include aerosols from about 10 fan and down in size. The respirable aerosol size range therefore includes a portion of the coarse aerosol range and all of the accumulation and nuclei aerosol ranges. MODAL STRUCTURE AND GRAPHICAL DISPLAY CONVENTION In each of the ranges mentioned, the size distribution of mine aerosol can exhibit a maximum, or mode, which takes its name from the size range in which it occurs. Hence, the maximum in the accumulation particle range is term- ed the accumulation particle mode. Figure 4 presents a typical size distribution of aerosol mass concentration measured near a feeder-breaker conveyor head in a diesel- equipped mine. Here the modal character of the size distribution is discernible even though the nuclei mode is suppressed compared with the accumulation mode. In con- trast, figure 5 shows a mass size distribution measured near a feeder-breaker conveyor in an all-electric-equipped mine. Here the accumulation mode is much smaller than the coarse particle mode. Taken together the figures indicate that diesel aerosols make a strong contribution to accumula- tion mode aerosol in a diesel-equipped mine. In both figures, the mass concentration histograms are plotted as AC/A(log Dp) versus D p on a log scale, where AC is the concentration in each size interval and D p is the aerosol's aerodynamic diameter. Using this convention, the area of each block of the histogram is proportional to the fraction of the mass concentration in the indicated aerosol size interval. CHEMICAL AND ELEMENTAL ANALYSIS TECHNIQUES FOR DIESEL AEROSOL Another distinguishing characteristic of mine aerosol is its chemical nature including the distribution of trace elements. In a diesel-equipped mine, diesel emission and mineral dust aerosol are mixed and are not separated when collected using a simple filter sampler. In metal and nonmetal mines, determining the amount of the diesel frac- tion on such a filter sample is relatively straightforward. A common analysis method relies on combustion techniques to determine the total combustible fraction as a measure of the mostly carbon diesel aerosol in the sample (9). For coal mine aerosol samples such analysis is not applicable since both types of aerosol involved are primarily carbon. To determine the diesel fraction of mixed carbonaceous aerosol from collected samples requires rather complicated and relatively expensive analytical procedures. Two such procedures have been developed under Bureau sponsorship. These are analysis using Raman spectroscopy and chemical mass balance (CMB) modeling. The first, by Johnson (9), is measurement of diesel and coal fractions of particulate matter using Raman spectral parameters. The second method is source apportionment based on the elemental analysis of both the collected aerosol and the source of the aerosol. For diesel-equipped mines the primary sources are the coal and diesel aerosol emissions. CMB analysis per- mits relating of elements or chemical components in an aerosol sample to those same components in the sources of the aerosol. The model is based on the following assump- tions, summarized by Watson (10): 22 Hot vapor ~r Condensation k Primary particles • • • m I Coagulation I Chain aggregates Mineral fracture aerosol + Comminution aeroso + Reentrained dust + Rock dust 0.002 0.01 0.1 I 2 PARTICLE DIAMETER, ^m 10 00 Transient nuclei or_ Aitken nuclei range Accumulation range Fine particles Mechanically generated aerosol range Coarse particles Figure 3.— Summary of in-mine aerosol characteristics exhibiting the modal character of the size distribution and the conven- tional terminology for their description. 23 E E Q O) O < 2.00 1.50 - 1.00 - .50 .00 I Accumulation mode I i 0.01 Coarse mode ■ I'"" 0.1 1 10 100 AERODYNAMIC DIAMETER (D p ),//m Figure 4.— Mass size distribution collected at a breaker site in a diesel-equipped coal mine. 24 2.00 1.50 E Q O) O 1.00 .50 .00 Accumulation mode Coarse mode i i i wm m c 1¥m I l I II li 0.01 0.1 1 10 AERODYNAMIC DIAMETER (D p ),//m 100 Figure 5.— Mass size distribution collected at a breaker site in an all-electric-equipped coal mine. 1. Compositions of elemental and chemical components of source emissions are constant. 2. Components do not react with each other. 3. p identified sources contribute to aerosol concentra- tions in the sample, i.e., they add linearly. 4. The number of sources, p, is less than or equal to the number of components, n. 5. The compositions of all p sources are linearly indepen- dent of each other. The model is expressed as Here, C„ is the mass concentration of the i'* elemental or chemical component of the sample, in /*g/m 3 , a y is the frac- tional amount of component i in emissions from source j, and S> is the total contribution of source j to the sample. Apportionment of the source is achieved by first characteriz- ing the aerosol sources, obtaining values for a w then analyz- ing the aerosol in the sample for the same components and, finally solving for the S y . A least squares regression analysis is used to determine the S, of the overdetermined system of equations expressed by equation 1 . C = I a tf S,. (1) 25 DIESEL AEROSOL MEASUREMENT TECHNIQUES An aerosol measurement can be separated into two parts: (1) collection or confinement of the aerosol into a specific location and (2) application of an analysis method that is specific for the aerosol characteristic of interest. Com- mercially available instruments used to perform such measurements on diesel aerosol emissions in a mine can be grouped in two categories: (1) instruments that provide an integrated sample of the mine aerosol for subsequent analysis and (2) those that provide continuous or quasi- continuous direct measurement of aerosol in the mine en- vironment. It should be remembered that each of the in- struments discussed in these categories was designed for specific functions that are not necessarily compatible with measurement of diesel emissions in the mine. MEASUREMENTS WITH COLLECTED AEROSOL SAMPLES These techniques depend on collection of sufficient aerosol mass for gravimetric or other analysis. The length of sampling time depends on the sensitivity of the analysis method and the rate at which air is sampled. Two such measurement systems applicable to the measurement of the diesel fraction of collected aerosol are discussed here. The first is the personal cassette filter sampling system and the second is the Bosch smoke meter. Filter Sampler The personal cassette sampling system is used for respirable dust compliance monitoring. It is a filter follow- ing a cyclone that acts as an aerosol preseparator. Analysis of the collected samples to complete the measurement pro- tocol consists of determining the change in weight of the filter and yields the mass concentration of respirable aerosol at the sampling site. This, however, provides no informa- tion on the diesel component of the aerosol sample. This information may be obtained using either Raman or CMB analysis. Although these techniques show promise for yielding the required information, they are costly and are as yet in the research stage. As such they cannot be relied on for definitive analysis of samples containing diesel aerosols. Another drawback for these methods is high cost per sample. Until these problems are resolved, other, more indirect, methods must be used to estimate diesel aerosol concentration in mine aerosol. Smoke Meter Measurements The Bosch smoke meter utilizes filter reflectance as a method of measurement. It consists of two components: a manual, spring-operated piston pump for collecting sample aerosol on a filter and a separate optical reader consisting of a light source and a sensor. In practice, a clean filter is inserted into the pump and a sample of the exhaust is col- lected, a process that takes about a minute. The filter is removed and a reflectance measurement is made of the filter using the optical reader. The Bosch meter does not provide direct measurements of diesel aerosol mass concentration. Instead, readings are given as Bosch units. Approximate, empirical methods are available for converting Bosch units to mass concentration. One such relationship (11) is given by the following equation: A lnQO/UO-BJ) 1 - 206 . (2) Here C is the concentration, in mg/m 3 , B„ is the Bosch number, and A is en empirical coefficient. A suggested value for A is about 500 to 600 mg/m 3 . In other work, Homan (12) has provided means for converting Bosch readings to other smoke meter readings. Athough the Bosch meter is not a continuous, real-time monitor, it can provide smoke concentration estimates every few minutes and can be used for in-mine, tailpipe measurements where the only source of carbon in the measured aerosol is diesel aerosol. For example, it can be used to evaluate relative engine condition, as it affects aerosol emissions, by sampling the exhaust with the engine running at full load and comparing the result with prior measurements from the same engine or those from another engine operating at the condition under test. Engine con- dition could be tracked over time with a Bosch meter to determine when emissions are excessive and engine maintenance required. The instrument could also conceivably be used for soot measurements in the workplace. When no other dusts are present, or have been removed from the sample air, and when the diesel soot is diluted by mine ventilation, the on- ly operational modification would be the need for sufficient pump cycles to obtain an adequate filter sample for the op- tical reader. Even if other dusts are present, the instrument may conceivably be used because the light absorption characteristics of some mineral dusts may not interfere significantly with light absorption by soot carbon. CONTINUOUS PHOTOMETRIC MEASUREMENTS A number of photometric instruments are available from different manufacturers for real-time, continuous monitoring of dust aerosols. These are of two types: the first utilizes light scattering to detect aerosol and the second employs light absorption. Light Scattering Instruments The GCA RAMI and MINIRAM, Sibata P5, TM-digital, and Simslin II all use a light source to illuminate the dust aerosol and a light sensor to measure the scattered light, which can then be related to the mass concentration of the aerosol. There are many differences among these in- struments. For example, some are certified for underground coal mine use. All, except the TM-digital and the MINIRAM, use a pump for air movement through the in- strument. Various means, such as cyclones or optical techniques, are used to provide output proportional to the respirable dust concentration. These light scattering aerosol monitors have been characterized in the laboratory for dif- ferent dusts by Kuusisto (13), Marple (14), Keeton (15), and Williams (16). Except for the work by Keeton, none of the laboratory research has involved diesel exhaust particulate. In all cases the relationship of instrument response to aerosol concentration is not simple but depends on particle size, particle composition, and on instrument design and 26 manufacturing differences. Usually these instruments must be calibrated to the specific dust being monitored, although this is not necessary for cases where only relative measures are needed and the particle properties do not change significantly during tbe measurement period. Most of the Bureau's work with real-time, photometric instruments has been with the GCA RAMI and MINIRAM devices. Because they were initially designed for use in the mine environment, versions can be certified for underground coal mine use and can be operated with the Dorr-Oliver 10-mm cyclone to measure respirable dust. The RAM is a light-scattering aerosol monitor of the nephelometric type; i.e., the instrument continuously senses the combined scattering from the cloud of particles within its sensing volume. The instrument uses a pulsed gallium- arsenide light-emitting source that generates a narrow-band emission centered at 875 nm. Radiation scattered by air- borne particles in the view volume is collected over an angular range of approximately 45° to 95° from the for- ward direction by means of a silicon light detector. The fraction of incident light per unit particle mass col- lected by the RAM-1 detector can be estimated as a func- tion of aerosol size using a Mie scattering calculation for spherical aerosols with an index of refraction close to that measured for carbon. Figure 6 shows the results of such a calculation for an index of refraction (n)=2.0-il.O and a monochromatic incident light wavelength of 875 nm. The key feature to note is the dramatic decrease in scattered light with a decrease in aerosol size from 0.2 to 0.05 /im. To scatter an appreciable amount of light, most of the diesel aerosol would need to be greater than 0.1 jun. Because of insufficient time for coagulation, laboratory measurements of diesel aerosol size yield smaller values than this for some engine operating conditions. In these cases, the RAM would not seem to be a reliable instrument for diesel aerosol monitoring. Index of refraction(n)= 2.0 - i 1.0 Wavelength = 875 nm 0.01 0.10 1.00 AEROSOL DIAMETER, //m 10.00 Figure 6.— Theoretically predicted mass sensitivity of GCA RAM-1 to carbon aerosol. In-mine experience with these monitors for mineral dusts is extensive, but little published data are available for diesel aerosol. The National Institute for Occupational Safety and Health (NIOSH) (17) has obtained correlations of 92 pet between coal mine MINIRAM measurements and a gravimetric sampler fitted with an intake impactor to restrict penetration of particles larger than 1 jim. Analysis of the collected sample was accomplished using respirable combustible dust (RCD) measurements. This successful com- parison between diesel aerosol and the response of a RAM type instrument holds promise that it might be used to monitor diesel aerosol in a coal mine environment. Response of the RAM-1 and MINIRAM to diesel aerosol in the laboratory has also been reported by Zeller (18-19). Figure 7 shows the recorded response during these tests of two MINTRAM's and three RAM's for diesel exhaust aerosol from a Caterpillar 3304 engine operated at different com- binations of steady-state speeds and loads. The exhaust was diluted, about 25:1, with clean air prior to measurement. The mass concentrations are from simultaneously collected filter samples. Data shown in figure 7A exhibit five distinct trends in- dicating that each instrument responds differently to diesel aerosol. This instrument bias is normal and has been observed by Marple (14) for rock and coal dusts. Manufac- turing tolerances are the sources of these differences in in- strument response functions. Figure IB shows these same data adjusted for instrument bias by multiplying the instru- ment responses by a value that is constant for each instru- ment. The data now lie on a line with only moderate scat- ter attributed to imprecision or random error. In the case of the RAM's, the manufacturer provides in- ternal adjustments to compensate for instrument bias. All the results in figure 7 were obtained with the instruments adjusted according to the factory calibration, which is based on a standard silica dust. An alternative to this procedure would be to expose the instruments to a known concentra- tion of diesel aerosol and determine a new internal adjust- ment specifically for diesel aerosol. If this had been done for these tests, then it is expected that the instrument responses would appear as depicted in figure IB without any need for a mathematical adjustment of the data. Light Absorption Instruments Opacity meters are widely used as continuous monitors for diesel emissions, but their sensitivity is not adequate for measuring soot concentrations diluted by mine ventila- tion. Standardized calibration and operating procedures for several commercial instruments are given in the SAE Hand- book (20). As with the Bosch meter, opacity smoke meters do not provide output directly proportional to mass concen- tration. Instead the output is percent opacity, which is related to mass concentration by N = 100(l-exp(-KL)). Here, N is the opacity, in pet, K is the extinction coefficient, in units of reciprocal length, and L is the path length in units of length. K is the parameter that is directly related to diesel aerosol concentration. Bureau staff have had considerable experience with the Celesco model 107 opacity meter used in the diesel emis- sions test facility (18). Representative data from a portable in-line meter are displayed in figure 8. The results are ad- 27 15 e E u in o 0. in UJ a: 5 - KEY • MINIRAM I v MINIRAM 2 d RAM I O RAM 2 A RAM 3 D A O O V A A O o v V 5 10 DIESEL AEROSEL CONCENTRATION, mg/m 3 Figure 7.— RAM and MINIRAM response to diesel soot. A, actual instrument response; B, same data adjusted for instrument bias. 28 100 200 300 GRAVIMETRIC CONCENTRATION, mg/m 3 400 Figure 8.— Comparison of opacity with gravimetrically measured aerosol concentration. justed to standard conditions of 75 ° F and 1 atm. The ap- parent linearity of the opacity data with gravimetric measurements is typical of this instrument for a wide range of engine operating conditions. However, close examination of the data labeled solid plus volatiles in figure 9, shows that the opacity meter underestimates aerosol concentra- tion at concentrations, below about 80 mg/m 3 , with the magnitude of the underestimation increasing as soot con- centration decreases. The response of most optically based instruments, including opacity meters, is dependent on both particle size and composition (14,18-19). When the opacity data are plotted against only the solid or carbon fraction of the aerosol (fig. 9), the degree of underestimation decreases. This result is consistent with the results of other investigators (21-23); who concluded that opacity meters primarily respond to the carbon component in diesel aerosols. One application for opacity meters in mines is diesel emissions monitoring of equipment to determine when engine maintenance is required for acceptable emissions control. Portable, battery-operated opacity meters, which are designed for pipe-end measurements, are available for this purpose (24). A second application of these instruments is validation of the use of other instruments as continuous monitors of soot mass concentrations. Figure 10 illustrates the precision that can be expected for light-scattering in- struments such as the RAM-1. The RAM-1 data are com- pared with those from the in-line opacity meter used in the Bureau's diesel emissions test facility. To obtain this com- parison the RAM-1 readings were adjusted so that the areas under the two curves are equal; the opacity data were cor- rected from exhaust to room (RAM) temperature. The result is excellent tracking of the two instruments. The correla- tion between the two instruments is actually better than illustrated because some of the discrepancies are the result of deficiencies and limitations of the data acquisition system. The fact that these instruments correlate so well simplifies the task of comparing results from the two and assures that they will complement one another in in-mine evaluations. CRITIQUE OF DIESEL EMISSIONS AEROSOL MEASUREMENT METHODS The main criticism concerning in-mine aerosol sampling and measurement techniques for diesel emissions is that the sampled aerosol is mixed thus creating an ambiguous analytical situation. For metal-no nmetal mines, chemical analysis can separate the diesel component but the presence of another carbonaceous aerosol in the mixture will cause interference in the analytical procedure. This is particularly true in the case of coal mine aerosol measurements. To determine relative diesel and dust aerosol fractions in this latter case requires even more cumbersome and expensive analytical techniques. Sampling techniques such as the Bosch smoke meter also suffer from the same problem when coal dust aerosol is involved. Reflectance measurements of 29 £3 D 1 1 1 1 1 o KEY Q. n Solid and volatile •o 20 ~~ E □ Solid only \ o> E v — * o r- < 15 ~o — or D >- B D H o % D „ < o O Q_ ? 10 D ™e 8 — o or 8 o 8 °0 ° D D D o ^ % 8 8 i- o ° LxJ 2 > o < 5 — or o 1 1 1 i i 50 100 150 200 250 GRAVIMETRIC CONCENTRATION, mg/m^ Figure 9.— Variation in opacity response as a function of gravimetrically measured aerosol concentration. 300 30 J2 o UJ > UJ o CO o cc UJ < TIME, min Figure 10.— Comparison of GCA RAM-1 and opacity measurement of diesel aerosol emissions during a standard test cycle. in-mine diesel aerosol admixed with coal dust aerosol are unreliable because of interference. The response of the optically based instruments depends on the light-scattering and absorption properties of aerosols. A serious limitation on the use of such instruments is un- predictable response caused by changes in aerosol composi- tion or size which, in turn, affect optical properties. For in-mine applications, these aerosol property changes can result from numerous causes. Major engine-related causes include engine type, engine condition, operating duty cycle, use of fuel additives, and exhaust emission controls. Mine-related effects on diesel aerosol properties include ef- fects of ventilation, dilution factors, aerosol age, and in- terferences from other aerosols such as coal dusts. To address these problems, use is being made of the size characteristics of the diesel and mine dust aerosol. A series of sampler modifications and new designs are now being used that employ size selective sampling techniques to separate diesel and mineral dust aerosol during sampling. SIZE SELECTIVE MONITORS FOR DIESEL AEROSOL SAMPLING The contribution of diesel aerosol emissions to total respirable aerosol in coal mines using diesel-powered equip- ment is not easily determined by chemical means. Since diesel aerosols are expected to be predominately sub- micrometer in size, while mechanically generated dust aerosols are generally larger than 1 ftm, a solution for this problem is to physically separate these aerosol fractions on the basis of aerosol size during sampling. Under sponsor- ship of the Bureau and NIOSH, aerosol samplers employ- ing such techniques are now being developed to obtain size- dependent information on respirable aerosol containing a diesel component. These can be grouped into two categories: (1) samplers that separate the mine aerosol into a series of several size intervals during sampling, yielding a dif- ferential size distribution of the aerosol, and (2) samplers that separate the sampled aerosol into two or three size in- tervals in an attempt to isolate the diesel and dust aerosol fractions. Samplers of the first category are used to obtain 31 general information about aerosol size distributions and thereby establish the sampling criteria for the second category of samplers. INERTIAL IMPACTORS Many size selective sampling devices use inertial im- paction to select for specific sizes during sampling. The theory of inertial impactors has been described by Ranz (25) and, more recently, by Marple (26) and Fuchs ( 27). An in- ertial impactor is a device that classifies aerosol particles by their aerodynamic diameter. This is accomplished, as shown in figure 11, by directing a jet of particle-laden air at an impaction or collection plate. Particles with sufficient inertia will impact on the plate while smaller, lower iner- tia particles will not impact but remain suspended in the airstream. The size of the aerosol at which this inertial selection occurs is termed the cutoff size of the impactor. DIFFERENTIAL SIZE SELECTIVE SAMPLING TECHNIQUES Differential size selective sampling is achieved by cascading several of the impaction stages so that they act on the sample air sequentially. By designing each successive stage with a smaller cutoff size the net effect is to divide the sampled aerosols into contiguous size interval samples. Gravimetric analysis of substrates placed on the impaction plates will yield a mass weighted size distribution for the sampled aerosol. Marple Personal Sampler A differential size selective sampling technique that has found use for in-mine measurement of both diesel and mineral dust aerosol is the Marple personal impactor (MPS) manufactured by Anderson/Sierra as the series 290 sampler. This is a compact, radial-slot cascade impactor designed to Nozzle < >^_Trajectory of ^/ impacted particle 7 Impaction plate Trajectory of particle to smal I to impact Figure 1 1 .—Streamlines and particle trajectories for a typical impactor. 32 be worn as a personal sampler. The impactor, pictured in figure 12, can be used in several configurations with up to eight impactor stages plus an afterfilter. Nominal size separations for these stages are 21, 15, 10, 6.0, 3.5, 2.0, 0.9, and 0.5 jim. The impactor operates with a flow rate of 2 L/min and uses the same sample pump as the personal cassette sampler. The MPS was originally designed for NIOSH as a wood- dust sampler by Rubow (28). More recently, it has been used in surveys of diesel-equipped mines and by the Bureau and NIOSH as a device for size characterization of diesel and dust aerosol (17). These surveys compared the operation of the cascade impactor with that of the standard cassette sampler and a simplified dichotomous sampler that uses a single impaction stage. Figure 13 gives a typical size distribution measured during the survey using the MPS. This distribution was obtained from an average of several full shift samples collected in a haulage road of a diesel- equipped coal mine. It shows a distinct coarse particle mode and a smaller submicrometer mode. These can be used to estimate average levels of diesel and mineral dust aerosol during a working shift. Micro-Orifice, Uniform-Deposit Impactor The micro-orifice, uniform-deposit impactor (MOUDI) holds promise for use in measuring the size distribution of mine aerosol over the size range in which diesel aerosol is expected to predominate (29). The basic sampler is an eight- stage cascade impactor designed for a flow rate of 30 L/min. A picture of the device is shown in figure 14. Each stage of the impactor consists of an impaction plate for the stage above it and a nozzle plate for the stage below. When alter- nate stages are rotated, the impaction plates of all stages are rotated relative to the nozzle plates, creating a uniform deposit on the impaction plate. Four of the stages are of micro-orifice design with 2,000 nozzles in each stage. An electric motor and gear assembly can be used to rotate the stages to obtain the uniform deposits on the impactor substrates. Nominal size separations for the impactor are 18.7, 10.0, 4.9, 2.6, 1.0, 0.60, 0.23, and 0.10 pm. The MOUDI has been used during in-mine field sampling experiments (30) to evaluate its ability to separate diesel aerosol from dust aerosol on the basis of their size distribution. In addition to the MOUDI, a two-stage Figure 12.— Marple personal sampler. M 33 2.00 1.50- E E < "N, O < 1.00- 0.01 0.1 1.0 10 AERODYNAMIC DIAMETER (D p ), pm Figure 13.— Mass size distribution collected in a return airway with a Marple personal sampler. respirable impactor, with the second size separation at 0.6 \aa., was also used to provide samples of submicrometer and supermicrometer aerosol for elemental analysis. The field evaluation was conducted in three underground mines; in one mine, which used only electric-powered mining equip- ment, and in two others that used diesel-powered mining equipment. For each mine visited, sampling was conducted in secondary return airways near mine conveyor systems, in primary ventilation returns, and in primary intakes. Mass size distributions of aerosol measured in the dieselized mines using the MOUDI and exemplified in figure 4 show two distinct maximums; one submicrometer and the other greater than a micrometer in size. To pro- vide a measure of the distribution of diesel aerosol between these two size ranges, the samples collected with the respirable impactor were analyzed using CMB model source apportionment analysis. Trace element concentrations used in this analysis were obtained using instrumental neutron activation. Results of these analyses, given in table 1 for the two diesel mines, confirm that diesel emission aerosols in the dieselized mines studied are predominantly sub- micrometer in size. The diesel associated submicrometer aerosol accounted for approximately 40 to 60 pet of the respirable aerosol mass concentration. For respirable aerosol concentrations less than 2 mg/m 3 , 10 pet or less of the submicrometer aerosol mass was dust associated. In con- trast, aerosol size measurements in the all-electric equip- ment coal mine, typified by figure 5, exhibit no sub- micrometer maximums and less than 10 pet of the measured respirable aerosol mass was in the submicrometer size range. Based on the success of the MOUDI in separating the two aerosol fractions, a simpler, two-stage sampler with size separation at 0.8 fan can be recommended for sampling diesel and dust aerosol in mines. The MOUDI, with a weight of approximately 10 lb and sample pump requirements of 150 H 2 at 30 L/min, is not suitable for routine in-mine monitoring. Its use has been as a research tool for characterization of diesel aerosol. Table 1 .—Average source apportionment analysis results for two coal mines, percent Source Fine Coarse MINE A Coal Rock dust 7 ±8 .4 ± .2 87 ± 7 13 ± 7 Diesel fuel 92 ± 8 <8 MINEB Coal Rock dust 25 ±4 .2 ± .1 92 ± 5 8 ± 2 Diesel fuel 75 ± 3 1.0 ftm- Aerosol < 1.0 /i.m- Final filter T Vacuum /.Nonre Nonrespirable fraction Figure 1 5.— Dichotomous sampler with cyclone preseparator. Foil substrate E ■s. a> E < a: o O O rr o H O < a. o a: 0. I.O 0.5 I.O I.5 2.0 DICHOTOMOUS SAMPLER CONCENTRATION, mg/m 3 Figure 16. — Comparison of submicrometer aerosol mass concentrations measured with the dichotomous sampler to that measured using the Marple personal sampler. 36 PROPOSED MONITORS FOR REAL-TIME MEASUREMENTS OF DIESEL AEROSOL The following sections describe two prospective in- struments for real-time measurement of both laboratory- generated and in-mine diesel aerosol. Each of these in- struments is proposed for use as a continuous aerosol detec- tor in place of the afterfilter in a dichotomous sampling train similar to that discussed in the previous section. Use of the preliminary impaction stage enhances the response of the instrument to diesel aerosol by removing the majority of mineral dust aerosol from the sample. The instruments thus configured will be particularly useful for real-time mass concentration measurement of diesel exhaust aerosol in laboratory tests of engines operated in transient modes; especially those involving fast transients intended to simulate the duty cycles of load-haul-dump equipment as described by Alcock (32) and other Bureau work. 7 In addition to laboratory needs, real-time diesel aerosol mass concentration instruments would also be useful in mines for the following: (1) identify and prioritize problem areas such as changes in control equipment efficiency, (2) quickly assess the benefits of diesel aerosol control changes to determine cost effectiveness, (3) evaluate the diesel aerosol control effectiveness of engine maintenance pro- grams, and (4) determine relative importance of diesel aerosol and mineral dust sources so that resources can be directed at the most significant problems. Photodetector CONDENSATION NUCLEI COUNTER A method that is specific for detection of submicrometer aerosol and hence diesel emissions is the condensation nuclei counter (CNC). This device, described by Aitken in 1888 (33), operates by condensing water or other vapor on nuclei particles. These aerosols grow to a uniform size and are then detected using an optical particle detector operated as either a single particle detector or as a forward scatter- ing nephelometer. The instrument output is the integral of aerosol number over its range of sensitivity. This range is usually 0.003 to 0.5 jim, just the range where most of the diesel emissions contribution is made to in-mine respirable aerosol. Figure 17 shows a schematic of a TSI model 3204 CNC. This device uses alcohol vapor to increase the sam- ple aerosol size and employs both single particle and nephelometric detection modes for measurement depending on the number concentrations of the aerosol. The resultant data are expressed in number per cubic centimeter. Although this measurement is accurate for number, the correlation with aerosol mass is highly dependent on the operating mode of the diesel source. This is because the size distribution changes continually with the operating mode; e.g., an equivalent nuclei mode mass can be achieved with much fewer accumulation mode aerosols. For coal mine aerosol not dominated by an immediate diesel source, this may not be a serious drawback because measurements, such as those reported in figure 4, indicate a relatively stable submicrometer aerosol. This stable relationship between number and mass permits conversion of aerosol number measurement to mass concentration, though it must still be measured in each case where the CNC is used. 'Contract J0100010, "Study of Duty Cycles of Diesel Vehicles Used in Mines." -To flowmeter and pump -Slit (0 1 by 2mm| Collecting lens Alcohol pool Figure 17.— TSI model 3204 condensation nucleus counter (top) and schematic (bottom). TAPERED ELEMENT MASS MONITOR The tapered element oscillating microbalance (TEOM) technique was developed to measure the mass concentra- tion of various types of airborne respirable dust. This tech- nique uses the inertial behavior of a vibrating tapered ele- ment to directly measure the mass of a sampled dust, thus avoiding measurement errors associated with other parti- cle characteristics. Other TEOM dust monitors have been used to measure diesel equipment exhaust emissions (34-35), atmospheric aerosols (36), and stack emissions (37). The 37 Respirable dust on j collection filter ,LED Amplifier Photo- transistor Counter Hollow glass tapered element Data processing SECTION A-A' SECTIONAL SIDE VIEW Figure 18— TEOM sample analysis. Bureau and the NIOSH cosponsored the development of a prototype TEOM dust monitor for measuring respirable coal mine dust mass concentrations (38). The original objective was to develop a personal sampler that used the tapered element oscillating microbalance measurement technique. The active element of the system, shown in figure 18 mounted in a sampling canister, is a specially tapered hollow tube constructed of elastic, glasslike material. The wide end of the tube is firmly mounted on an appropriate base plate, while the narrow end supports a replaceable filter and is permitted to oscillate. As the filter collects dust, the mass increases thereby decreasing the frequency of oscillation. The frequency of oscillation is detected by using a light- emitting diode (LED>phototransistor pair aligned perpen- dicular to the plane of oscillation of the tapered element as depicted in figure 18. The output signal of the phototran- sistor is modulated by the light-blocking effect of the oscillating element positioned between the phototransistor and the LED. This signal is amplified. Part of the amplified signal is applied to a conductive coating on the outside of the tapered element. In the presence of constant electric field plates, this signal provides sufficient force to keep the tapered element in oscillation. In other words, part of the amplified signal from the LED- phototransistor pair is used in an electrical feedback loop to overcome any amplitude damping of the tapered element oscillation. In use as a submicrometer aerosol sampler, a canister containing the sensing cone and filter is connected to a 10-mm Dorr-Oliver nylon cyclone and single-stage impac- tor. By using a typical personal sampling pump operating at 2 L/min, air can be drawn through the cyclone. The cyclone removes large particles, passing respirable dust to the impactor and finally the filter mounted atop the tapered element. The filtered air passes through the tapered ele- ment to the sampling pump. During sample collection the canister is used like any filter that might be used in gravimetric personal samplers. A time-resolved measurement of diesel aerosol emis- sions collected, using the TEOM alone, during a heavy-duty test cycle is given in figure 19. Here, the transient emis- sions from the engine are clearly evident with a time resolu- tion of about 1 min. In laboratory tests by the Bureau, the TEOM had a mass resolution of 1.6 fig. Its response to a large sudden change in relative humidity is a change of less than 0.02 fig/min in its zero reading. Orientation of the device during readout does not appear to affect readings. Other than the sensitivity to relative humidity, the TEOM seems suited to use as a diesel aerosol mass detector. 38 in LJ < 2.0 1.51- 1.0 .5 -5 L 2.0 1.5 1.0 .5 in m o -.5 L 2.0 1.5 1.0 .5 -.5 KEY Mass rate Total mass -,225 175 125 75 25 -25 i225 175 125 75 25 1 -25 225 175 125 75 25 -25 en in in < O l- Figure 19— Triplicate hot-start particulate emission rate over the U.S. Federal heavy duty transient cycle. 39 SUMMARY OF MINE AEROSOL MEASUREMENT TECHNIQUES Accurate measurement of diesel aerosol emissions in a mine environment depends to a large extent on the man- ner in which the sampling or measurement device exploits the physical and chemical characteristics of the aerosol. Diesel aerosol is primarily carbonaceous and predominantly submicrometer in size as opposed to the mineral dust aerosol fraction which is predominantly greater than 1 pm. The trace elemental and chemical composition of diesel aerosol has been found to be sufficiently different from most mineral dust aerosol so that special analytical techniques can be used to resolve diesel and mineral dust components of a col- lected aerosol sample. This is even true for mineral dust aerosols like coal, which are also primarily carbonaceous. A review of the aerosol sampling techniques currently used in mines for compliance monitoring reveal that without modification they are, at best, marginally useful for diesel aerosol measurement. Because all of these techni- ques were designed to sample respirable dust, in diesel- equipped mines they provide mixed aerosol samples for subsequent analysis. Analyses of these samples for the diesel fraction require special analytical techniques that are of a research nature and hence unavailable to most mine operators. The Bureau and other agencies such as NIOSH are cur- rently sponsoring development of aerosol samplers design- ed to selectively sample the diesel aerosol component of mine dust aerosol. For the most part, these samplers employ physical size selective sampling using inertial impaction to achieve this end. The goal of these development studies is to produce and validate a simplified sampler for mine owners that will provide separate measurement of diesel and mineral dust aerosol mass concentrations in the mine environment. As a collateral development, the Bureau is also evaluating designs for a real-time diesel aerosol monitor for in-mine use. All of the proposed instruments are design- ed to accommodate a size-selective sample inlet that will eliminate the mineral dust fraction of the aerosol sample before it is introduced into the detector mechanism. This separate development is admittedly for research purposes but could be adapted for compliance monitoring should the need ever arise in the future. REFERENCES 1. U.S. Congress. The Federal Mine Safety and Health Act of 1977. Public Law 91-173, as amended by Public Law 95-164, Nov. 9, 1977, 83 Stat. 803. 2. U.S. Code of Federal Regulations. Title 30-Mineral Resources; Chapter 1— Mine Safety and Health Administration, Department of Labor. July 1, 1985. 3. American Conference of Governmental Industrial Hygienists. (Cincinnati, OH). TLV's-Threshold Limit Values for Chemical Substances in Workroom Air Adopted by the ACGIH in 1973. 1973, 54 pp. 4. . Documentation of the Threshold Limit Values. 4th ed., 1980, pp. 364-365. 5. U.S. Mine Safety and Health Administration. Preproposal Draft Air Quality Standards. 1983, 61 pp; available from Health Div. for Metal and Nonmetal Safety and Health, MSHA, Arlington, VA. 6. U.S. Congress. The Federal Mine Safety and Health Act of 1977. Public Law 91-173, as amended by Public Law 95-164, Nov. 9, 1977, 91 Stat. 1291 and 1299. 7. Treaftis, H.N., A.J. Gero, P.M. Kacsmar, and T.F. Tomb. Comparison of Mass Concentrations Determined With Personal Respirable Coal Mine Dust Samplers Operating at 1.2 Liters Per Minute and the Casella 113 A Gravimetric Sampler (MRE). Am. Ind. Hyg. Assoc. J., v. 45, No. 12, 1984, pp. 826-832. 8. Kittelson, D.B., D. Dolan, R.B. Diver, and E. Aufderheide. Diesel Exhaust Particle Size Distributions— Fuel and Additive Ef- fects. Sec. in The Measurement and Control of Diesel Particulate Emissions. SAE/PT-79/17, 1979, pp. 233-244. 9. Johnson, J.H., D.H. Carlson, M.D. Osborne, E.O. Reinbold, B.C. Cornilsen, and V. Lorprayoon. Monitoring and Control of Mine Air Diesel Pollutants: Tailpipe Emissions Measurements, After- treatment Device Evaluation and Quantification of Particulate Matter With Raman Spectroscopy (contract J0199125, MI Technol. Univ.). BuMines OFR 150-84, 1982, 182 pp.; NTIS PB 84-239151. 10. Watson, J.G. Overview of Receptor Model Principles. APCA J., v. 34, No. 6 June 1984, pp. 619-623. 11. Alkidas, A.C. Relationships Between Smoke Measurements and Particulate Measurements. SAE paper 840412, 1984, 9 pp. 12. Homan, H.S. Conversion Factors Among Smoke Measurements. SAE paper 850267, 1985, 15 pp. 13. Kuusisto, P. Evaluation of the Direct Reading Instruments for the Measurement of Aerosols. Am. Ind. Hyg. Assoc. J., v. 44, No. 11, 1983, pp. 863-874. 14. Marple, V.A., and K.L. Rubow. Instruments and Techniques for Dynamic Particle Size Measurement of Coal Dust (contract H0177026, Univ. MN). BuMines OFR 173-83, 1981, 242 pp.; NTIS PB 83-262360. 15. Keeton, S.C. Carbon Particulate Measurements in a Diesel Engine. Sandia Lab. Publ. SAND 79-8210, June 1979, 45 pp. 16. Williams, K.L., and R.J. Timko. Performance Evaluation of a Real-Time Aerosol Monitor. BuMines IC 8968, 1984, 20 pp. 17. National Institutes for Occupational Safety and Health. Diesel Particulate Measurement Techniques Applied to Ventila- tion Control Strategies in Underground Coal Mines. Ongoing BuMines contract J0145006; for inf., contact D.M. Doyle-Coombs, BuMines, Pittsburgh, PA. 18. Zeller, H.W. Effects of Barium-Based Additive on Diesel Ex- haust Particulate. BuMines RI 9090, 1987 (in press). 19. Measurement of the Effects of Fuel Additive on Diesel Soot Emissions. 9th paper in this Information Circular. 20. Society of Automotive Engineers (Warrendale, PA). SAE Handbook: Engines, Fuels, Lubricants, Emissions, and Noise. V. 3, 1982. 21. Japar, S.M., and A.C. Szkarlat. Real Time Measurements of Diesel Vehicle Exhaust Particulate Using Photoacoustic Spec- troscopy and Total Light Extinction. SAE paper 811184, 1981, 8 pp. 22. MacDonald, J.S., N.J. Barsic, G.P. Gross, S.P. Shahed, and J.H. Johnson. Status of Diesel Particulate Measurement Methods. SAE paper 840345, 1984, 20 pp. 23. Scherrer, H.C., D.B. Kittelson, and D.F. Dolan. Light Absorp- tion Measurements of Diesel Particulate Matter. SAE paper 810181, 1981, 7 pp. 24. Johnson J.H., E.O. Reinbold, and D.H. Carlson. The Engineer- ing Control of Diesel Pollutants in Underground Mining. SAE paper 810684, 1981, 46 pp. 25. Ranz, W.E., and J.B. Wong. Impaction of Dust and Smoke Particles. Ind. Eng. Chem., v. 44, 1952, p. 1371. 26. Marple, V.A., and B.Y.H. Liu. Characteristics of Laminar Jet Impactors. Environ. Sci. Tech., v. 8, 1974, pp. 648-654. 27. Fuchs, N.A. Aerosol Impactors. Ch. in Fundamentals of Aerosol Science, ed. by D.T. Shaw. Wiley, 1978, pp. 1-85. 28. Rubow, K.L., V.A. Marple, J. Olin, and M.A. McCawley. A 40 Personal Cascade Impactor: Design, Evaluation and Calibration. Univ. MN, Dep. Mech. Eng. Particle Technol. Lab. Publ. 469, 1985, 19 pp. 29. Marple, V _A., and K.L. Rubow. Development of a Micro-Orifice Uniform Deposit Impactor. U.S. Dep. Energy Rep. DOE/PC/61255, Aug. 1984, 31 pp. 30. Cantrell, B.K., K.L. Rubow, and J. Cocalis. In-Mine Measure- ment of Diesel and Dust Aerosol Size Distributions Using a Micro- Orifice, Uniform Deposit Impactor. Pres. at AJHA Conf., Dallas, TX, May 18-20, 1986, 15 pp.; available from B. Cantrell, BuMines/Minneapolis, MN. 31. Jones, W., J. Jankovic, and P. Baron. Design, Construction, and Evaluation of a Multi-Stage "Cassette" Impactor. Am. Ind. Hyg. Assoc. J., v. 44b, p. 409. 32. Alcock, K. Duty Cycles and Load Factors of Diesel-Powered Vehicles in Underground Mines. Am. Min. Congr., Washington, DC, p. 19L. 33. Aitken, J. On the Number of Dust Particles in the At- mosphere. Trans Roy. Soc. Edinburgh, v. 35, 1888, pp. 1-20. 34. MacDonald, J., N. Barsic, G. Gross, S. Shahed, and J. Johnson. Status of Diesel Particulate Measurement Methods, SAE paper 840345, 1984, 20 pp. 35. Whitby, R., R. Gibbs, R. Johnson, B. Hill, S. Shimpi, and R. Jorgenson. Real-Time Diesel Particulate Measurement Using a Tapered Element Oscillating Microbalance. SAE paper 820463, 1982, pp. 267-283. 36. Patashnick, H., and G. Rupprecht. The Tapered Element Oscillating Microbalance— A Monitor for Short-Term Measurement of Fine Aerosol Mass Concentration. EPA-699/2-81-146, Aug. 1981, 34 pp. 37. Wang, J., H. Patashnick, and G. Rupprecht. Recent Developments on a Real-Time Particulate Mass Monitor for Stack Emission Applications. J. APCA, v. 31, No. 11, Nov. 1981, pp. 1194-1196. 38. Patashnick, H., and G. Rupprecht. Personal Dust Exposure Monitor Based on the Tapered Element Oscillating Microbalance, (contract H0308106, Rupprecht & Patashnick Co. Inc.). BuMines OFR 56-84, 1983, 89 pp.; NTIS PB 84-173749. 41 MEASURING GASEOUS POLLUTANTS FROM DIESEL EXHAUST IN UNDERGROUND MINES By Kenneth L. Williams, 1 J. Emery Chilton, 2 Donald P. Tuchman, 3 and Anna F. Cohen 4 ABSTRACT Several techniques are available today for measuring gaseous pollutants from diesel exhaust such as carbon monoxide, carbon dioxide, nitric oxide, nitrogen dioxide, and sulfur dioxide. Four gas-sensing techniques are discussed: electrochemical, infrared, detector tubes, and passive samplers. For each technique, the general operating prin- ciples are described, and a discussion of measurement range, response time, accuracy, interferences, power requirements, life, and cost is included. Selecting the most ap- propriate technique is challenging. Each of the four techniques have benefits and short- comings that must be evaluated in light of the sampling objective. At present, no "recom- mended" sampling or measurement protocol is available. A complete discussion of the problem of measuring gases present in diesel exhaust would require several large volumes. This paper is intended as an introduction to the problem. INTRODUCTION Exhaust from diesel equipment used in mines contains a wide variety of pollutants, both gaseous and particulate in nature. The health implications and related industrial hygiene issues arising from the use of diesel equipment are discussed in another paper in this Information Circular (IC). Measurement of particulate pollutants will also be discussed elsewhere in this IC. This paper will discuss measurement techniques and instruments for measuring gaseous pollutants from diesel exhaust, including carbon monoxide (CO), carbon dioxide (COj), nitric oxide (NO), nitrogen diox- ide (N0 2 ), and sulfur dioxide (S0 2 ). Four gas-sensing techniques will be discussed: elec- trochemical, infrared, detector tubes, and passive sampler tubes. For each technique, the general operating principles will be described, and then a discussion of measurement range, response time, accuracy, interferences, power re- quirements, life, and cost will be included. This paper will not attempt to provide a buying guide by listing every available monitor suitable for measurement in underground mines and discussing specific features. Rather, the text will review commonly used sensing technologies and the associated benefits and pitfalls of each. Reports that discuss specific equipment and list manufacturers for measuring diesel exhaust gases can be found in the literature (l-3). s Other reports list gas measur- ing equipment that has been approved by the Mine Safety and Health Administration (MSHA) for operation in gassy mines (4). MEASUREMENT CONSIDERATIONS A myriad of instruments exist on the market today for measuring diesel exhaust gases. However, a necessary first step in any data-gathering episode is to develop some type of monitoring strategy. Examples of possible objectives are determining average exposure of workers to a particular contaminant, alarming workers to an imminent hazard, 'Supervisory physical scientist. •Research chemist. "Industrial hygienist. 'Physicist. Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. monitoring the performance of a diesel engine or of a con- taminant control system, collecting exposure data for use in epidemiological studies, etc. Selecting an objective leads to important questions about the way data are collected. For example, will the average of several intermittent grab samples supply the in- formation that is needed, or is the time-resolved history of continuous sampling necessary? Is immediate indication of 'Italic numbers in parentheses refer to items in the list of references preceding the "Typical Chemical Reactions in Electrochemical Cells" sec- tion at the end of this paper. 42 contaminant levels necessary (perhaps even an alarm), or can the data be analyzed remotely at a later time? Should samplers be attached to or carried by each individual worker, or can they be placed at an appropriate location at the work site? The answers to these questions, as well as other con- siderations such as the ruggedness and explosiveness of the environment or the range of contaminant levels that could be encountered, comprise the sampling protocol. The pro- tocol in turn makes certain requirements that help deter- mine the appropriateness of particular sampling- measurement devices. Developing monitoring strategies is beyond the scope of this paper; however, a detailed scheme for developing a monitoring strategy for air contaminants from diesel exhaust was formulated in 1983 by the Rocky Mountain Center for Occupational and Environmental Health (5). This reference also contains a helpful review and summary of measurement methods, and an extensive bibliography on the subject of diesel pollutant health issues and measurement methods. ELECTROCHEMICAL An electrochemical gas cell consists of at least two elec- trodes that are in contact with an electrolyte. Electrodes are solid electrical conductors that allow electric current to enter and leave an electrolyte. The electrolyte is a substance (either liquid or solid) that dissociates into negatively and positively charged ions. Electrochemical cells exist in a variety of configurations; however, figure 1 illustrates features that are common to most. This illustration shows the sensing electrode (also referred to as an active or working electrode), a counter elec- trode, and a reference electrode. Sensing electrode L Reference electrode Gas permeable membrane walls Electrolyte Counter electrode Figure 1 .—Electrochemical cell. To operate the cell, an external electrical potential is applied across the sensing and counter electrodes. The voltage between the reference electrode and the sensing electrode is maintained constant by an appropriate power supply and control circuit. The gas to be measured must be allowed to contact the sensing electrode. This contact is often accomplished by a porous membrane that allows the gas to pass through to the electrode while preventing the electrolyte from leaking out of the cell. A chemical reac- tion takes place at the sensing electrode that produces elec- trons that move through the electric circuit and ions that are free to move through the electrolyte. Because of the elec- tric potential imposed between the electrodes, charged ions flow through the electrolyte from one electrode to the other. The number of electrons created by the reaction is propor- tional to the concentration of gas passing through the mem- brane. This current is measured and displayed on a meter as gas concentration in engineering units. When designing an electrochemical cell to detect a cer- tain gas, the manufacturer must select appropriate materials for the electrodes, electrolyte, and porous mem- brane, and must apply the appropriate voltage to the elec- trodes to allow the ion flow to take place. As an example, consider a typical CO electrochemical cell. Design parameters must be selected so that CO diffusing to the sen- sing electrode (anode) reacts with water in the electrolyte according to CO + H 2 = C0 2 +2H + + 2e At the counter electrode the reaction is % 2 + 2H + + 2e~ = H 2 0. (1) (2) The oxygen required for the reaction in equation 2 is sup- plied from the ambient air by diffusion to the cell. In the reaction with CO described here, the sensing elec- trode served as an oxidizing electrode where CO was ox- idized to C0 2 . A sensing electrode can also be used as a reduction electrode, 6 as in the case of an electrochemical N0 2 cell. Details of numerous electrochemical gas sensing instruments are available throughout the literature (6-8). Numerous patents are now held for designs of elec- trochemical CO, C0 2 , NO, N0 2 , and S0 2 gas detecting sen- sors (9-10). RANGE Any discussion of the measurement range of mine gas instruments would be meaningless without information about typically expected gas concentration levels. In that context, several terms shall be defined. Table 1 lists threshold limit values (TLV's) (11) or exposure standards for CO, C0 2 , NO, N0 2 , and S0 2 . TWA means time weighted average and refers to the maximum allowable average gas level over an 8-h working shift. STEL means short-term ex- posure level and refers to the maximum allowable average gas level over a 15-min period. IDLH (12) refers to the gas level that is immediately dangerous to life or health; that is, the maximum gas concentration from which a person can escape within 30 min without any escape-impairing symptoms or irreversible health effects. Table 2 lists gas "Typical chemical reactions in electrochemical cells are given at the end of this paper. Table 1. — TLV exposure standards, parts per million Gas TWA STEL IDLH CO... 50 400 1,500 co 2 .. 5,000 30,000 50,000 NO... 25 1 35 100 N0 2 .. 3 5 50 S0 2 ... 2 5 100 'Value for 1985-86; deleted in table for 1986-87 (11). 43 Table 2.— Typical diesel exhaust gas concentrations in mines, parts per million Gas Diesel Diluted exhaust in exhaust mine atmosphere CO 200- 2,500 10 - 20 C0 2 8,000-10,000 1,000 -5,000 NO 500- 1,000 2 - 10 N0 2 12- 20 .5- 1 S0 2 NA NA NA Not available. concentrations representative of those that have been measured by Bureau of Mines researchers in diesel engine exhaust and in the atmospheres of underground mines downstream from diesel equipment. Electrochemical sensors capable of detecting CO, C0 2 , NO, N0 2 , and S0 2 have been developed and at least one commercial instrument using electrochemical cells exists for each gas. The measurement ranges listed in table 3 for each of the five gases were compiled from manufacturers' specification literature and are typical of commercial elec- trochemical gas instruments; however, instruments with higher or lower measurement ranges are also available. To measure these gases at the tailpipe with such monitors, dilu- tion may be required. In general, electrochemical gas monitors are available with measurement ranges adequate for monitoring CO, C0 2 , NO, N0 2 , and S0 2 in underground mines that use diesel equipment. Table 3.— Typical measurement ranges for electrochemical gas monitors, parts per million Sensor type CO 0- 2,000 C0 2 0-10,000 NO - - 0- 1 ,000 N0 2 0- 100 S0 2 0- 100 RESPONSE TIME The response time of a gas instrument is usually defined as the time required for the instrument to reach 90 pet of its final reading when challenged with a step change in gas concentration. According to most manufacturers, the response time for diffusion-type electrochemical gas monitors is typically less than 2 min. This information is important only when compared to the expected magnitude and rate of change of gas concentration and to the time re- quired for the concentration of gas being measured to cause harm to those exposed. Consider, for example, a sudden ex- posure to 5 pet CO. At such levels, unconsciousness and death can occur within minutes. Obviously, any monitor used to alert workers to this situation must have a very short alarm time. On the other hand, table 2 indicates that typical gas levels in underground mines that use diesel equipment with adequate ventilation are far below levels that would pose immediate hazards to workers. In that case, the response time of electrochemical gas monitors will be adequate for measuring gas concentrations that normally result from the use of diesels in underground mines. ACCURACY As discussed earlier, electrochemical sensors produce an electrical signal proportional to the amount of gas available for the chemical reaction. That electrical signal is amplified and used to operate a meter that indicates gas concentration in engineering units. Electrochemical gas monitors can be calibrated by exposing them to a known concentration of gas and then adjusting the gain of the amplifier circuit so that the meter indicates the concentra- tion of the challenge gas. To calibrate electrochemical in- struments underground, supplies of stable gases at the con- centration levels of interest must be used. Such gases are available in small metal cylinders for CO in air, C0 2 in air, and NO in nitrogen. On the other hand, sufficiently low con- centration mixtures of N0 2 and S0 2 (2 to 5 ppm) are generally not available in such cylinders, making field calibration difficult. Laboratory calibration of N0 2 and S0 2 instruments can be accomplished, however, using accurate, low-concentration mixtures obtained from a permeation tube system. Because of certain changes in the electrochemical cell when used, or simply because of aging, electrochemical gas monitors must be periodically recalibrated. Environmen- tal factors such as changes in temperature and barometric pressure can also affect the accuracy of electrochemical gas sensors. Manufacturers normally incorporate some means of compensating for variations in temperature. A calibra- tion period of once every 30 days of operation is required by MSHA for underground fixed-point carbon monoxide monitors (13). Once calibrated, however, typical accuracy cited by manufacturers of electrochemical gas monitors is ±2 pet of the reading. Typical sensor output drift is less than 2 pet of full scale per month. INTERFERENTS OR CROSS-SENSITIVITY Occasionally, other gases present in the atmosphere can enter into the chemical reaction and either enhance or diminish the electrical signal produced. These gases are called interferents. For example, according to the manufac- turer's specification literature for a particular commercial electrochemical CO monitor, 100 ppm of hydrogen (H 2 ) will cause the monitor to indicate 30 ppm of CO. If 10 ppm of CO is present with the 100 ppm of H 2 , the monitor will in- dicate a total of 40 ppm CO. This positive interference causes falsely high readings of CO, possibly resulting in false alarms. On the other hand, 10 ppm of N0 2 will cause the monitor to indicate -6 ppm CO. This negative in- terference results in falsely low readings of CO. In this case, workers may unknowingly be exposed to excessive levels of CO. Table 4 was compiled from specification literature from various manufacturers and lists common interferents for CO, C0 2 , NO, N0 2 , and S0 2 electrochemical sensors that could be found in underground mines that use diesel equip- ment. In some cases, interferents can be removed by chemical filters that allow only the gas of interest to r c ~ Ii the sensor. Fortunately, NO and N0 2 , common pollutants in diesel exhaust and interferents for electrochemical CO sensors, as well as ethylene and hydrogen sulfide are easily removed by chemical filters. On the other hand, H 2 cannot Table 4.— Interferents possibly found in underground mines for electrochemical sensors Sensor type CO H 2 , C 2 H 2 , C 2 H 4 , NO, N0 2 , H 2 S, S0 2 . co 2 so 2 . NO H 2 S, N0 2 . N0 2 S0 2 . S0 2 H 2 S, N0 2 . 44 be removed by any known chemical filter. Thus if CO measurements must be made in the presence of hydrogen, a falsely high reading could result. Furthermore, some chemical filters become less effective with use. Before pur- chasing any electrochemical instrument, prospective buyers are strongly urged to consult manufacturers for specific in- formation about interferents and the effectiveness of filters that might be incorporated. POWER Most electrochemical cells require very little current (typically a few microamperes) and very little voltage (4 V or less). Control circuitry, amplification of signals, etc., would require additional power. Such low-current, low- power electrochemical gas sensing cells are incorporated in battery-operated, handheld, and portable instruments as well as larger, ac-powered monitors intended for operation at fixed monitoring sites. Many of the battery-operated in- struments are designed to be intrinsically safe for use in explosive methane-air mixtures found in underground coal mines. LIFE Most portable and handheld electrochemical gas monitors are warranted for 1 yr. In practice, however, operating life of CO, NO, N0 2 , and S0 2 sensors is expected to be 1 to 2 yr. COST Handheld electrochemical gas instruments typically range from $500 to $1,000. Portable monitors intended for monitoring at a fixed location may cost up to $2,000, depend- ing in part on the measurement range and whether more than one measurement range is included. Annual sensor replacement costs can range from $100 to $300 per instru- ment. Batteries usually need replacement semiannually, and some additional costs will be incurred for calibration equipment and standard tank gas replacement. INFRARED Light is comprised of radiation over a wide range of wavelengths. All materials, including gases from most chemical groups, are capable of absorbing certain wavelengths of light. If infrared light (say from 2.5- to 15-jan wavelength) is passed through a gas, light of specific wavelengths within that range will be absorbed. 7 If one measures and graphs the intensity of light passing through a gas versus the wavelengths, the wavelengths at which light is absorbed will be apparent. This graph of peaks and valleys is referred to as an absorption spectrum. The specific wavelengths of light that a substance absorbs depend on the particular construction of its molecules. The energy of infrared light absorbed by a gas causes increases in molecular vibration or rotation. Simple compounds such as CO, C0 2 , NO, N0 2 , and S0 2 have simple absorption spec- tra, each with a few pronounced valleys at wavelengths where the greatest absorptions occur. These valleys are called absorption wavelengths or absorption bands. The spectra are simple because the molecules themselves have simple structures. To measure the airborne presence of any of the preceding gases, one must identify a convenient absorption band in its infrared spectrum, that is, a wavelength of in- frared light that is absorbed. However, more is involved in building an infrared detection system than making a choice on the wavelength to be used. Care must be taken that no other airborne gas or material in the light path absorbs the wavelength of interest to any substantial degree. If such an additional absorption occurs, the detection system will respond to the presence of the secondary material as well as the gas one intends to measure. This obscuring, overlap- ping absorption is a spectral interference. Detection in- struments can correct for some interferences by elec- tronically subtracting the absorption signal from a reference light path that is not open to the atmosphere. However, if two or more gases in the environment absorb the same in- 7 Hydrogen does not absorb in the usual infrared working region, but this is an exception (14). frared band, the instrument will measure them as being the same substance and the interference is not easily correctable. While it would not be very useful to discuss the mathematics associated with light absorbance, noting some basic physical principles will be helpful. First, absorbance of light by a gas sample is dependent on the path length that the light takes through the sample cell. Second, ab- sorbance is also proportional to the concentration of the in- teracting gas in the instrument's sample cell. Lastly, ab- sorbance is proportional to a property called absorbtivity, which varies with every combination of gas and chosen wavelength. It represents a measure of a material's effi- ciency in absorbing light. If the gas one intends to measure has a low absorbtivity, and if the instrument incorporates only a short light path, the gas concentration will have to be high before the in- strument detects it. That is, the instrument's detection limit may be inappropriately high and one may not be able to measure low concentrations of gas. The absorbtivity of a gas is an unchangeable property of nature. If one wishes to measure low concentrations of a gas with low absorb- tivity, one is forced to design an instrument with a long light path, and possibly use mirrors in the sample cell to ac- complish this. Another fact that can affect instrument performance is related to sample handling. Some infrared instruments are intended for handheld portable use; others are intended for mounting at a fixed location. Many of these instruments use a pump to draw air through the sample cell. Any direct connection between the sample cell and the mine at- mosphere would require use of an air filter to prevent dust from soiling or damaging the optical components of the instrument. Frequent cleaning and servicing would other- wise be necessary. An alternative procedure is to carry a container of mine air to a laboratory for off-site analysis. Infrared gas detectors have limited versatility and ruggedness, but they can be used for environmental evalua- tion in mines with the proper planning and forethought. RANGE The measurement range for an infrared-based gas monitor varies with the specifics of design and usage. The absorption behavior of the specific gas measured, the design of the sample cell, and choices in electrical signal modifica- tion determine the response range of the instrument. Instruments are usually designed with one or two given concentration ranges reflecting a particular buyer's measurement interests. They may be built to accurately measure high concentrations or low concentrations, but usually not both. The upper detection limit can be up to 100 pet; the lower detection limit is usually a few hundred parts per million. Lower limits are achievable with careful design that may require specialized, long-path-length sample cells. In general, an instrument can be built for any concentra- tion range of interest. The greatest challenges, however, toward satisfying an instrument user's wishes are at or below the exposure standard level for a particular gas. In- frared instruments have been manufactured that can measure levels of 10 to 20 ppm CO, for alarm use in con- junction with early fire detection. RESPONSE TIME Manufacturer literature states that infrared detectors respond very quickly, and any change in gas composition would normally be indicated within 5 to 10 s. Some delay would occur if the gas were sampled from a remote site through tubing. Whatever time the gas spent in transit would have to be added to the instrument response time. If the delay is acceptable, a very long tube could be attached to the detector inlet and an auxiliary pump used to draw the gas. ACCURACY As was the case for electrochemical gas monitors, the accuracy of infrared gas monitors depends heavily on how 45 recently the instrument was calibrated. Manufacturers generally report the performance specifications of the prod- uct under ideal circumstances. However, even when careful- ly handled, manufacturers still typically record drifts in readings of 2 pet of full scale in 1 day. Precision for infrared instruments (reproducibility of a reading under set condi- tions) is typically given as 1 pet of full scale. Instruments should be calibrated before each shift, or as often as ex- perience dictates. Field experience with an instrument can vary with the quality and condition of the product, care in calibration, experience of the operator, and the exact means and circumstances of use. Generally, an instrument should measure the concentration of a gas with a total deviation of no more than several percent. Exact accuracy or preci- sion requirements, however, depend strongly on the objec- tive of the sampling. Typically available infrared instruments (with one or two small-length sample cells) would not be of sufficient sen- sitivity to measure S0 2 , N0 2 , and NO over the concentra- tion ranges of health interest (see table 2), especially at the low end. For example, for S0 2 , using a 90-cm-path-length column, the full scale concentration range is 2,000 ppm. With an accuracy of ± 1 pet full scale, readings below 20 ppm have an uncertainty of ±20 ppm, which is much greater than the allowed TLV of 2 ppm for S0 2 . INTERFERENTS OR CROSS-SENSITIVITY By one means or another, every instrument designed to detect a particular gas must attempt to view the wavelength or wavelengths of light absorbed by that gas. Some instruments use a filter that allows only that nar- row band of wavelengths to reach the detector (fig. 2). Another option is to use filters to produce a specific wavelength of light that passes through the gas to the detec- tor (fig. 3). Unfortunately, CO and C0 2 absorb light at wavelengths that are quite close to each other on the in- frared spectrum (15). In fact, an instrument that views a Sample gas source t /? \ ►- Optical filter •»■ Detector »»■ Display o o o U Figure 2.— Infrared sensor with filter immediately before detector. Sample gas IR source ^TS Detector ^- Display o o o Figure 3.— Infrared sensor with filter immediately after light source. ■^H 46 spectral bandwidth of more than a fraction of l^m may con- fuse the two gases. The same situation exists with SO a and methane (CH<) (15). Thus, an important factor that will determine whether one gas will interfere with the detec- tion of another is called the instrument's slit width. The slit width is that range of the infrared spectrum that an instrument examines for absorption. The narrower the slit width for an instrument, the more likely only one absorp- tion band from one gas will be measured. The broader the slit width, the more likely that absorption caused by more than one gas will be measured by the instrument. To in- crease instrument specificity, the slit width should be nar- row. On the other hand, to increase signal strength and to avoid background noise in the absorption signal, the slit width should be broad. The design of the instrument must balance the need for specific gas detection with stable ab- sorption signals. It is general knowledge that some gases, such as water vapor, absorb infrared light in such broad bands that an interference is quite likely if the vapor is present and care is not exercised during instrument choice and design. Many instruments incorporate a reference cell to correct for the undesired absorbance. Using a second wavelength not ab- sorbed by the gas of interest but absorbed by the water vapor only, may provide another means to correct the ab- sorption signal. Special care is sometimes taken in instru- ment design to see that no part of the light path traverses air outside the sample cell. This prevents ambient water vapor outside the sample cell from causing an interference. Chemical interferences are also possible for infrared as well as other types of instruments. For this type of problem, the reactivity or instability of the gas examined would be the main cause of concern. For example, oxides of nitrogen (NO, N0 2 , and N 2 4 ) are in dynamic equilibrium (16-18). Depending on temperature, pressure, and especially con- centration, the gas molecules may transform into other nitrogen-based substances. These types of reactions tend to be slow at low concentrations (near TLV's), but the general chemistry of nitrogen compounds should be understood before a measurement program is started. Of particular con- cern are measurements made near the tailpipe of diesel engines. The gases are concentrated and fresh at that point, and prone to change until some stabilizing interaction is reached with the surrounding environment. POWER Much of the power required to operate an infrared gas monitor is used to produce infrared light. The present technology used to produce infrared energy requires con- siderably more power than that required for electrochemical sensors. For instruments that are line operated, power re- quirements are not a problem. However, if the unit is por- table and uses battery power, the batteries will normally have to be recharged at least every shift, but more typically after 4 to 6 h of use. Because of this power requirement, most available infrared instruments are line operated, designed primarily for operation at a fixed measurement location. Infrared instruments are generally not designed to be intrinsically safe, but can be used in nongassy mines or in fresh air locations in gassy mines. LIFE The concept of shelf life does not apply to infrared detec- tion instruments. Each component, and the instrument as a whole, may be stored indefinitely without loss of perform- ance. As for operating life, almost all infrared instruments are marketed with a 1-yr warranty; however, these in- struments may be expected to operate for much longer periods. Over a number of years, some repairs may be necessary. The device's light source or light detector may fail. Other electrical components may need service after long use. Damage to the instrument from the mine environ- ment is generally of more concern than aging. Deployment in a mine setting may be considered severe use that may not be covered by the manufacturer's warranty. In less rigorous circumstances, infrared instruments are extremely reliable and are more often replaced because of obsolescence rather than malfunction. COST The cost of infrared instrumentation is generally much greater than other types of instruments reviewed in this paper. Devices configured for on-site measurement of gases, either for portable, handheld use or for fixed station monitoring, are available for up to $3,000. Custom designs or construction will obviously cost more. For example, sam- ple cells for detection of gases at very low concentration (parts per billion level) may cost several thousand dollars each. Some additional costs will be incurred for calibration equipment and standard gas replacement. Periodic battery replacement costs must be considered for portable, battery- powered units. GAS DETECTOR TUBES A gas detector tube is a small, portable device used to provide direct readings of gas concentrations (19). Three types of detector tubes are used in mines today: short-term pumped, long-term pumped, and diffusion. All consist of a small glass tube containing a chemically impregnated granular packing (fig. 4). As gas passes through the tube, it reacts with the chemical and produces a color change. The spread of the color change down the length of the tube is related to a given amount of gas drawn or diffusing through the tube. Other gas detector tubes or badges are available that indicate gas concentration by a change in color intensity; however, this type was not considered for diesel exhaust application. For short-term (several minute) average measurements (grab samples) of a gas concentration at a given site, the tube is broken open at both ends and is fitted into the hand- operated pump or syringe (fig. 5). A certain number of pumps or strokes are performed according to the manufac- turer's specifications, drawing a given volume of air through the tube at a given flow rate. An estimation of gas concen- tration can be read directly by noting where the length of color stain ends on a scale (in parts per million) on the side of the tube. For work-shift average measurements, a second type of detector tube is used with a battery-powered air pump to draw a gas sample through the tube. An estimation of the 47 Tip — Inert packing Interferent filter Glass tube Granular indicating reagent Gas sample flow Inert packing Figure 4.— Gas detector (stain tube). average gas concentration over the work shift can be calculated at the end of the shift using the reading of the length of stain on the scale (in microliters) on the side of the tube. A third type of detector tube uses no pump but depends on gas diffusing into a tube with only one open end. An average gas exposure over the sampling period is obtained by measuring the length of stain with a scale (in parts per million). By dividing this reading by the time of exposure (in hours), the average concentration of gas during the sampling period can be calculated. RANGE Stain tubes have been used for many years to measure average gas concentrations. As a result, a wide assortment of tubes are available to measure a number of gases. Table 5 was compiled from specification literature from several manufacturers and lists typical measurement ranges for tubes designed to measure the five gases of interest. The Table 5.— Typical detection ranges for stain tubes, parts per million Gas Short-term Long-term Diffusion CO 5 - 15 2.5-25 6 - 75 100 - 700 6.3- 63 CO z 100 -3,000 250 -1,500 1,200 -40,000 1,000 -12,000 5,000 -60,000 NO 1 .5- 10 1.3- 12.5 ( 2 ) NO z .5- 10 1 .3- 13 1.3- 25 SQ 2 .5- 5 1.3-13 .6- 20 1 This tube actually measures NO,. To determine NO, one must assume that only NO and N0 2 are present, measure N0 2 separately, and then subtract the value for N0 2 from the value for NO„ "None available. il-.-.U-: 'I. ■•'-'• ' '■ - : - m Stain tube Stain tube Figure 5.— Hand-operated bellows (top) and syringe (bottom) pump. 48 table lists separately information about tubes designed for short-term (several minutes), long-term (4-8 h) average measurements, and about diffusion tubes. Once again, pro- spective buyers are encouraged to check with tube manufac- turers because new tubes are occasionally made available as new needs arise. ±35 pet of the correct value at concentrations equal to one- half of the TLV, and to within ±25 pet for concentrations within 1, 2, and 5 times the TLV (19). INTERFERENTS OR CROSS-SENSITIVITY RESPONSE TIME Detector tubes are intended for average measurements of gas concentration or exposure. As discussed earlier, short- term tubes that use a hand-operated pump collect samples over several-minute periods. Long-term tubes that use battery-powered pumps collect samples over periods lasting 4 to 8 h. Finally, tubes that depend on diffusion of the gas into the tube usually collect samples over an 8-h work-shift period. ACCURACY Unlike electrochemical or infrared instruments, detec- tor tubes are usually not calibrated by the user. If properly manufactured, no calibration is needed. Since conveniently portable sources of stable calibration gases are not available for gases such as S0 2 and N0 2 , stain tubes and sampler tubes might be used in preference to electronic instruments that require periodic calibration. To assure accuracy, however, the tube manufacturer must maintain adequate control during the production proc- ess to form reproducible detector tubes. The tube must be evenly packed throughout the entire measuring length with granules of uniform size that are evenly coated with the reactive chemicals. The color change must be of sufficient intensity so that a well-defined interface is formed between the reacted or color-developed tube section and the unreacted section. A well-defined interface is necessary so the stain length can be visually estimated with some cer- tainty. Finally, the manufacturer must be sure of the con- centration and purity of the standard gas used to test the tubes during fabrication. The accuracy of measurements made using tubes that require pumped samples also depends on the care taken by the operator to draw the proper volume of gas through the tube. Hand-operated pumps must be operated the proper number of strokes, and the flow rate of battery-powered pumps must be properly calibrated and periodically checked. The gas sample should be free of water droplets and high concentrations of dust particles. Finally, detector tubes are usually manufactured to read properly at 25 ° C and at 1 atm barometric pressure. Measurements made at other than these standard conditions must be corrected us- ing the following equation: C = (C M XT)/298(P), where C = the corrected reading, C M = the reading from the tube, T = the temperature, K, measured at the sampling site, and P = the barometric pressure, atm, measured at the sampling site. Detector tubes previously certified by the National In- stitute of Safety and Health (NIOSH) are to indicate within The chemical reaction chosen for the color change should be sufficiently specific so that indications obtained from the tube can be attributed to the gas of interest in a given gas mixture. An experimental assessment of the use of detec- tor tubes for measuring gaseous pollutants from diesel ex- haust concluded that the constituents of diesel exhaust in- clude many potent interferents to the measurement of CO, C0 2 , NO, N0 2 , and S0 2 (20). In this work, the detector tubes were found to yield measurements with interference error greater than +35 pet in 40 pet of the CO measurements, and errors greater than -35 pet in 65 pet of the S0 2 measurements. Many of the chemical reactions used in detector tubes are such that many types of gases will react with a single tube. For example, a tube used to detect CO contains iodine pentoxide, selenium dioxide, and fuming sulfuric acid. In this tube, CO is converted to C0 2 , iodine is formed, and a color change from white to brownish green is observed. Other gases that are easily oxidized will also form iodine in this reaction. These gases include acetylene, ethylene, benzene, toluene, trichloroethylene, and hydrogen sulfide. In order to improve the specificity of the CO detector tube, an initial reacting layer is included in some tubes to preox- idize the organic compounds and hydrogen sulfide while passing the CO through. The capacity of the initial react- ing layer is limited, of course. If large quantities of interfer- ing gases are present, they may use up the initial reacting layer and pass into the indicating portion of the tube. If large amounts of interfering gases are expected, a tube con- taining activated charcoal may be placed in front of the CO detecting tube during measurement to remove limited quan- tities of chloro-organic compounds and many of the higher molecular weight interfering hydrocarbons. Large quan- tities of water vapor in the air sample can lead to positive errors in the CO determination. At higher concentrations of CO, above 200 ppm, negative errors may occur from direct reaction of the CO with the selenium dioxide in the tube. The preceding information indicates that in spite of the broad acceptance of the validity of detector tube concentra- tion measurements in industrial hygiene air monitoring, further studies into calibration and interference errors are necessary. POWER No electrical power is required to use detector tubes unless a battery-operated pump is used to draw a gas sam- ple through the tube. Note that many pumps available for this application are not intrinsically safe for operation in potentially explosive atmospheres underground. LIFE Detector tubes are used for a single measurement and are then discarded. Shelf life is generally listed as 2 yr. Cer- tain tubes, such as some CO detector tubes, require refrigeration «20° C), and shelf life is usually listed as 1 yr. COST Detector tubes cost from $2 to $3 each. For a small number of diesel exhaust analyses, stain tubes and sampler tubes may be very useful. For large numbers of analyses, say hundreds per month, electronic instruments such as 49 electrochemical or infrared types may be more cost effec- tive. The initial cost of the hand-operated pump can be as much as $150. Battery-powered pumps can cost several hun- dred dollars. Thus, the cost of using detector tubes depends upon the total number of gas samples needed, and must be weighed against the cost of purchasing and maintaining electronic gas detectors over a number of years. PASSIVE SAMPLER TUBES Passive sampler or diffusion tubes, called Palmes-type samplers after their inventor (21), consist of a tube that is open at one end into which a gas may diffuse (fig. 6). The gas to be analyzed collects on a screen coated with an ad- sorbent material at the other end of the tube. To collect N0 2 or S0 2 , an alkaline adsorbent called triethanolamine is used. Upon adsorbtion, N0 2 is converted into a nitrite ion. After the sampling period is over, the Palmes-type sampler is taken to a separate facility for analysis. The adsorbed nitrite ion is mixed with a chemical reagent to form a deep red color. The concentration of the red color complex and thus the nitrite ion is determined by measuring the adsor- bance of light by the solution using a colorimeter. The number of moles of N0 2 collected is then equal to the measured nitrite ion concentration. The average N0 2 con- centration is then calculated using the number of moles of N0 2 collected in the equation for Fick's first diffusion law (21): C = [(dm/dtXLXRXT)/(D)(AXP)] x 10" 6 , (4) where C = the gas concentration, ppm, dm = the number of moles of N0 2 collected in the sampler, dt = the sampling period, s, L = the tube diffusion length, cm, R = the gas constant, T = the temperature, D = the diffusion coefficient for N0 2 in air, cm 2 /s, A = the tube cross section area, cm*, and P = the barometric pressure. Thus, the concentration of gas in parts per million is pro- portional to the moles of nitrogen dioxide collected per unit time for a given tube geometry. RANGE Palmes-type samplers have successfully been used to measure both NO x and N0 2 up to 20 ppm (21). RESPONSE TIME Palmes-type samplers are intended for average measurements of gas concentration or exposure. Samples are usually collected over an 8-h working shift. Unless con- centrations of gas are very high, at least 1 h of sampling would be necessary. ACCURACY Accuracy has been estimated at ± 10 pet at 10 ppm (21). Top cap Bottom cap Stainless steel screens Acrylic tube Figure 6.— Passive sampler (Palmes-type). 50 INTERFERENTS OR CROSS-SENSITIVITY COST At this time, no interferents have been identified (21). LIFE Studies of shelf life have not been conducted; however, tubes should be prepared within several days of scheduled sampling and stored in sealed containers. Palmes sampler tubes are no longer commercially available; however, they are relatively easy to make (21). The body of the sampler can be made simply by cutting lengths of acrylic tubing. The small, round stainless steel screens (fig. 6) can be cut from sheets of stainless steel screen material using a large hole punch. Other assorted parts such as plastic caps and metallic clips can be purchased from supply houses. Complete samplers can be made for less than $1 per unit. Additional cost would be incurred for the col- orimetric analyses. SUMMARY Intrinsically safe, mine-worthy electrochemical in- struments for detecting CO, C0 2 , NO, N0 2 , and S0 2 have been developed and one or more commercial instruments using electrochemical cells exists for each gas. For CO, elec- trochemical sensor-based instruments are leading con- tenders for fulfilling several of the monitoring objectives mentioned at the start of this paper. Intrinsically safe in- struments exist that can measure CO concentrations to an accuracy of 2 pet of full scale or better. NO and N0 2 , com- mon pollutants in diesel exhaust and interferents for elec- trochemical CO sensors, as well as ethylene and hydrogen sulfide are easily removed by chemical filters. On the other hand, H, is an interferent to electrochemical CO in- struments and is not removed by any known chemical filter. In cases with high interferent concentrations, infrared techniques could be used instead of electrochemical in- strumentation for measuring CO. Stable gases are available in small, portable metal cylinders for convenient on-site calibration of the CO, C0 2 , and NO instruments. On the other hand, low concentration mixtures of N0 2 and S0 2 (2 to 5 ppm) are generally not available in such cylinders, mak- ing field calibration difficult. Suitable infrared instruments are generally not intrin- sically safe but can be used in fresh air locations in gassy mines. Infrared instruments are available for in-mine CO and C0 2 concentration measurement; however, infrared in- struments are more costly than electrochemical in- struments. Generally, portable infrared instruments can- not measure NO, N0 2 , or S0 2 at the low levels required by exposure standards. Stain tubes and passive sampler tubes, especially for measurement of S0 2 and N0 2 at low parts per million con- centrations, may be very useful for characterizing air qual- ity. Stain tubes and passive samplers are the only tech- niques not requiring extensive use of calibration gases. At costs of $2 to $3 per tube, this technique can also be quite cost effective when only a small number of diesel exhaust analyses are required. On the other hand, for measurement requiring accuracy better than ±25 pet or when large numbers of samples must be taken, electrochemical or in- frared instrumentation is preferred. REFERENCES 1. Liouy, P.J., and M. J.Y. Liouy (ed.). Air Sampling Instruments for Evaluation of Atmospheric Contaminants. ACGlH, 6th ed., 1983, 537 pp. 2. Carlson, D.H., and J.H. Johnson. Monitoring Diesel Pollutants in Underground Mines. Soc. Min. Eng. AIME preprint 74-69, 1979, 47 pp. 3. Ferber, B.I., and A.H. Wieser. Instruments for Detecting Gases in Underground Mines and Tunnels. BuMines IC 8548, 1972, 16 pp. 4. Schnakenberg, G.H., and F.N. Kissell. Ventilation Monitor- ing Instrumentation. Sec. in Underground Mining Methods Hand- book, ed. by W.A. Hustrulid. Soc. Min. Eng. AIME, 1982, pp. 1669-1673. 5. Rocky Mountain Center for Occupational and Environmen- tal Health. Development of a Mine Air Contaminant Measurement Program— Diesels and Explosives (contract J0100004). BuMines OFR 80-84, 1983, 74 pp.; NTIS PB 84-183078. 6. Verdin, A. Gas Analysis Instrumentation. McMillan, Halstead, 1973, pp. 187-230. 7. Nader, J.S., T.F. Lauderdale, and C.S. McCammon. Direct Reading Instruments for Analyzing Airborne Gases and Vapors; Air Sampling Instruments for Evaluation of Atmospheric Con- taminants. ACGffl, 6th ed., 1983, pp. VI -VI 18. 8. LaConti, A., and H. Maget. Electrochemical Detection of CO, H,, and Hydrocarbons in Inert or Oxygen Atmospheres. J. Elec- trochem. Soc., v. 118, 1971, p. 506. 9. Blazhennova, A.N., G.I. Krukov, and R.N. Saifi. An Ap- paratus for Electrochemical Analysis (3-electrode gas sensor). United Kingdom Pat. UK 1,101,101, Jan. 31, 1968. 10. Osborn, H.G., and K.F. Blurton. Electrochemical Detection Cell. U.S. Pat. 3,776, 832, Nov. 10, 1970. 11. American Conference of Industrial Hygienists (Cincinnati, OH). Threshold Limit Values and Biological Exposure Indices for 1986-1987, 1986, 111 pp. 12. National Institute for Occupational Safety and Health. NIOSH Pocket Guide to Chemical Hazards. Publ. 78-210, Sept. 1985, 250 pp. 13. Mine Safety and Health Administration. Petitions for Modification of MSHA Mandatory Safety Standards. Mine Safety and Health Reporter, v. 8, No. 13, 1986, p. 304. 14. Skoog, D.A., and D.M. West. Principles of Instrumental Analysis. Saunders College-Holt, Rinehart & Winston, 2d ed., 1980, pp. 113-167, 209-261. 15. Zeller, M.V. Reference Spectra of Gases. Ch. 8 in Infrared Methods in Air Analysis. Perkin-Elmer Corp. Publ. 993-9236, ca. 1976, pp. 68-93. 16. American Conference of Governmental Industrial Hygienists. Documentation of the Threshold Limit Values. 4th ed., 1980, pp. 301-305. 17. Braker, W., and A.L. Mossman. Matheson Gas Data Book. Matheson Gas Products, 5th ed., 1971, pp. 407-408. 18. Zeller, M.V. Infrared Spectra of Nitrogen Oxides. Ch. 5 in 51 Infrared Methods in Air Analysis. Perkin-Elmer Corp. Publ. 993-9236, ca. 1976, pp. 31-44. 19. Saltzman, B.E. Direct Reading Colorimetric Indicators in Air Sampling Instrumentation. ACGIH, 6th ed., 1983, pp. T-2-T-29. 20. Carlson, D.H., M.D. Osborne, and J.H. Johnson. The Develop- ment and Application to Detector Tubes of a Laboratory Method to Assess Accuracy of Occupational Diesel Pollutant Concentra- tion Measurements. AIHA J., v. 43, No. 4, 1982, pp. 275-285. 21. Palmes, E.D., A.F. Gunnison, J. Dimattio, and C. Tomezyk. Personal Sampler for Nitrogen Dioxide. ADIA J., v. 37, 1976, pp. 570-577. TYPICAL CHEMICAL REACTIONS IN ELECTROCHEMICAL CELLS 2- or 3-Electrode CO Cell The reaction at the sensing electrode is CO + H 2 = C0 2 + 2H + + 2e~ The reaction at the counter electrode is Vz 2 + 2H + + 2e~ = H 2 0. NO Cell The reaction at the sensing electrode is NO + H 2 = N0 2 + 2H + + 2e" The reaction at the counter electrode is % 2 + 2H + + 2e~ = H 2 0. N0 2 Cell The reaction at the sensing electrode is N0 2 + 2H + + 2e~ = NO + H 2 0. The reaction at the counter electrode is H 2 = % 2 + 2H + + 2e~. S0 2 Cell The reaction at the sensing electrode is S0 2 + 2H 2 = H 2 S0 4 + 2H + + 2e~ The reaction at the counter electrode is Ms0 2 + 2H + + 2e~ = H 2 0. ^^■i 52 CARBON DIOXIDE AS AN INDEX OF DIESEL POLLUTANTS By J. Harrison Daniel, Jr. 1 ABSTRACT The underground use of diesel equipment in hard-rock mines is well established, and the use of the equipment in underground coal mines is increasing. As the number of diesel units and their power ratings increase, concern over the health effects of the exhaust emissions becomes more significant. A monitoring methodology to assess underground air quality in mines using diesel equipment is needed along with the development of emission control technology. The Bureau of Mines has been developing a methodology that provides an assessment of air quality by measuring only ambient carbon dioxide (COj) concentrations after the relationships between C0 2 and the other pollutants have been established. The concept involves determining the ratios of the other pollutants to C0 2 under actual equipment operating conditions, using an air qual- ity index to establish a single C0 2 concentration below which other pollutants are con- sidered below harmful levels, and verifying if engine operating conditions have changed such that maintenance is required. INTRODUCTION The exhaust pollutants emitted from the combustion process of diesel engines represent a principal concern over the use of the equipment in underground mines. Because of increasing mechanization, underground mining has become less dependent on large, concentrated work forces. Many operations have a few persons working in many dif- ferent and scattered sections, which makes the mobility of diesel-powered equipment very attractive in mine feasibility and design studies. The versatility of the equipment is also an advantage since a single piece of equipment can be modified to perform the many different functions required of loading and hauling of both workers and supplies. The issue of proper control of diesel exhaust emissions is complex. The operating mode and condition of the engine, the mine environment, and the equipment operator's habits all influence the concentration and composition of the ex- haust emissions. The Mine Safety and Health Administra- tion (MSHA) in April 1986, along with the National In- stitutes for Occupational Safety and Health (NIOSH) and the Bureau of Mines completed a study of the health and safety implications of the use of diesels in underground coal mines. This interagency study did not find conclusive evidence that indicates that uncontrolled diesel exposure poses no health risk, and states that sensitivity toward this 'Staff engineer, Division of Health and Safety Technology, Bureau of Mines, Washington, DC. This paper was submitted to the University of Idaho, College of Mines and Earth Resources, Moscow, ID, as partial fulfill- ment of Mining 600. ■Italic numbers in parentheses refer to items in the list of references at the end of this paper. issue and a conservative approach toward control of diesel exhaust exposure is warranted (l). 2 It is not practical to measure all the constituents of diesel exhaust in the underground mining environment. A selective monitoring methodology is therefore required that will accurately assess the overall air quality when diesels are used. The Bureau has been developing a monitoring methodology that requires only the measurement of CO, to assess the mine atmosphere. Once the relationship be- tween the other pollutants and C0 2 has been established for the specific equipment and mine conditions, C0 2 becomes a surrogate for the other pollutants. C0 2 remains a reliable indicator of overall air quality as long as the equipment operating conditions and mine ventilation do not significantly change. The monitoring methodology makes use of an air quality index to provide a relative, numerical value to assess air quality. This index combines the in- dividual and combined health effects of the pollutants. References dealing with underground mining operations have suggested that C0 2 concentrations could allow ac- curate prediction of the levels of other exhaust con- taminants (2-4). Other references have described the monitoring methodology used with the air quality index (5-7). The feasibility of using the C0 2 monitoring methodology with the air quality index has been demonstrated in three mines in the United States and two in Canada— Homestake gold mine, Lead, SD (8), White Pine copper mine, White Pine, MI, and Brushy Creek lead-zinc mine, Vibirnum, MO (9), Ojibway salt mine, Windsor, On- tario, Canada (10), and Sullivan lead- zinc mine, Kimberley, British Columbia, Canada (11). 53 NEED FOR A MONITORING METHODOLOGY The policies of various organizations are split concern- ing the underground use of diesel equipment. This dif- ference is popularly termed the diesel debate. The United Mine Workers of America is opposed to the present use of diesel equipment in underground operations, while the American Mining Congress, an industry association, sup- ports the use of underground diesel equipment (12-13). Com- plicating the issue is the fact that attempts to control only one of the emission pollutants can often result in an unac- ceptable increase in the concentration of a number of the remaining pollutants. It is necessary to control all the pollutants below harmful concentrations. The operating mode and condition of the engine, the mine environment, and the equipment operator's habits all influence the con- centration and composition of the exhaust emissions. The proper control of diesel exhaust emissions is thus a sensitive and complex issue. Bureau studies in the 1950's concluded that diesels could be operated safely from an air quality perspective, provided the engine is properly maintained and adjusted, the tailpipe exhaust flow is immediately diluted, and ade- quate positive mechanical ventilation is provided to dilute and remove the exhaust from the mine and to restore ox- ygen used in the combustion process (14). To assure that these conditions are fulfilled and to address the complex operational variables that influence exhaust concentration and composition, a monitoring methodology is needed that will not only assess the worker's atmosphere where diesels are operated, but will also evaluate the mine ventilation and equipment condition. In April 1986 as a result of a joint diesel task group, MSHA recommended that any requirements concerning air quality should consist of an approach that integrates the control of emissions through mine ventilation practices and periodic sampling of both the workplace and equipment (1). It was further recommended that the three components af- fecting air quality— the emissions, the ventilation, and the sampling strategy— are interrelated and must be considered as a system. The monitoring methodology is needed even with the development of emission control systems mounted on board the mobile equipment. Emission control systems by themselves do not insure compliance with mine atmosphere regulations because specific uses of the equipment or con- ditions under which the equipment operates may exceed the design capabilities of the emission control device. The con- trols that will be developed to reduce contaminant levels may also require periodic maintenance and inspection to ensure that they are functioning properly. It is also likely that these on-board controls will produce a back pressure on the combustion process of the engine, which may ad- versely affect both performance and emissions. Finally, it is essential to consider the engine type, the task the equipment performs, and the specific mine condi- tions under which the equipment operates in selecting emis- sion control alternatives. The degree and the sophistication of the emission controls required for each unit are a func- tion of these parameters. In some sections of underground mines, mine ventilation may be adequate to allow the safe use of properly maintained equipment without emission controls; however, in other sections mine ventilation may not be adequate to allow safe operation, depending on the task and the number of units operating. Each condition must be investigated for proper worker protection. An ef- fective monitoring methodology will determine the degree of control required. THE MONITORING METHODOLOGY GENERAL The monitoring methodology described provides an assessment of air quality when underground diesel equip- ment is used by measuring only ambient C0 2 concentra- tions on board the equipment after the relationships be- tween C0 2 and the other pollutants have been determin- ed. It also provides a means to evaluate both the adequacy of mine ventilation to remove exhaust pollutants and the operating condition of the engine. Since it is based on pollu- tant ratios established under site-specific mine conditions, once it has been established it does not have to be corrected for altitude effects. The methodology has evolved from Bureau in-house research and contract work with Michigan Technological University in Houghton, MI (2, 15). The methodology involves the following three phases: (1) establishing pollutant characteristic curves for specific diesel equipment and ventilation conditions that illustrate the relationship between the concentration of the exhaust pollutants and the concentration of C0 2 measured at the same location and over the same period of time, (2) using an air quality index to establish a single C0 2 concentra- tion below which the other diesel pollutants are considered below harmful levels, and (3) measuring periodically the tailpipe emissions of the engine to verify if engine operating conditions have changed. The concepts involved in the methodology will be developed in the following subsections. C0 2 AS AN INDICATOR OF OTHER POLLUTANTS Measurements of C0 2 concentrations can provide a basis for estimating concentrations of the other combustion prod- ucts from diesel engines— CO, NO, N0 2 , S0 2 , and par- ticulate matter. The amount of C0 2 produced during the combustion of liquid hydrocarbon fuels, such as diesel oil, is directly related to the amount of fuel burned. The power output and/or loading of the compression ignition (diesel) engine is controlled by the amount of fuel that is directly injected into the cylinders. The power at any given moment is related to that fuel consumption by a nearly constant fac- tor, the brake specific fuel consumption (bsfc) given in pounds per horsepower-hour. The precise metering of the fuel by the fuel injectors, which individually control each cylinder, accounts for the nearly constant bsfc. In addition, the carbon content of the various engine-quality fuels is very constant so that the C0 2 concentrations in the exhaust vary 54 in nearly direct proportion to the engine duty cycle and load. The CO, concentrations are also less affected than those of the other pollutants by improper adjustment of the fuel system, combustion chamber design, and imperfections in fuel injection nozzles. CO, is present in the exhaust gases in the highest con- centration of any of the pollutants; therefore, making it easier to detect and measure than many of the gases. Table 1 shows the combustion products of diesel fuel on a volumetric basis (16). The combustion products shown are for complete combustion of the fuel with the chemically cor- rect ratio of air to fuel to completely oxidize all the fuel. The threshold limit value (TLV) of C0 2 is 0.5 pet, or 5,000 ppm by volume. This value is 2,500 times the TLV for S0 2 , 1,667 times the TLV for NO,, 200 times the TLV for NO, and 100 times the TLV for CO, as shown in table 2 (17). Table 1 .—Products of combustion of diesel fuel, volumetric basis, percent Complete combustion products: Nitrogen (NJ 73 Carbon dioxide (CO plus oxygen 13 Water (H 2 0) 13 Incomplete combustion products (pollutants): Hydrocarbons (HC) <1 Carbon monoxide (CO) <1 Nitric oxide (NO) <1 Nitrogen dioxide (N0 2 ) <1 Carbon (C) or smoke <1 Sulfur dioxide (SOJ <1 Total 100 Table 2.— 1986-87 ACGIH TLV's for selected substances TWA* STEL2 CO ppm ... 50 400 C0 2 pet 0.5 3.0 NO ppm... 25 NAp N0 2 ppm ... 3 5 S0 2 ppm... 2 5 Dust, mg/m 3 : Coal 32 NAp Metal-nonmetal 4 10 NAp NAp Not applicable. STEL Short-term-exposure limit. TWA Time-weighted average. '8- or 10-h shift. Veiling limit that is not to be exceeded. Excursions above the TWA up to the STEL are allowed for up to 15 min as long as there is at least 1 h between such excursions. 3 Respirable size; if >5 pet quartz, the standard is (10 divided by percent of respirable quartz). 4 Total dust; if >1 pet quartz, the standard is set for the respirable fraction instead and is [10 divided by (percent respirable quartz plus 2)]. There is no TLV specifically for diesel particulates, although the diesel particulate is collected in the 10-mm nylon cyclone respirable dust sampler, which is used to monitor respirable dust on a full-shift (8-h) gravimetric or mass basis. This cyclone sampler, which collects respirable- sized particles without regard to the source of the particles or dust, is used by MSHA to enforce Federal dust standards. The diesel particulate is thus included with the respirable dust TLV or standard. Regulations (18) also cite that "ab- normal smoke production should be sufficient reason for removing a locomotive from service until this condition has been corrected." C0 2 is the only stable and nonreactive pollutant in the exhaust that is unaffected to any appreciable extent by time, emission control devices, or engine wear. Typically, CO,, S0 2 , and NO, (NO and NO,) accompany C0 2 as combustion products. The production of CO and NO, can be markedly suppressed, but for a given amount of fuel burned, the pro- duction of C0 2 cannot be reduced. Accuracy of air quality measurements is dependent upon the zero stability and resolution of the instruments, the other airborne contaminants that interfere with the detection principle of the instruments, as well as the pu- j rity of the gases used to calibrate the instruments. Because of these impacts on accuracy of measurements, the use of C0 2 measurements to estimate the concentrations of the other gaseous pollutants may give greater accuracy and reliability than direct underground measurements of the concentrations of the other pollutants. This conclusion can be attributed principally to both the difficulties of measur- ing the very low concentrations (as low as 1 ppm) of the other pollutants in the very humid, dusty, confined, and often hot underground mine environment, and the lack of availability of accurate, portable, commercial instrumen- tation for these measurements. However, portable and ac- curate commercial instrumentation to measure C0 2 concen- trations in the underground mine environment is available. These portable instruments can be calibrated outside the mine and are not required for continuous, extended opera- tion in the mine environment. POLLUTANT CHARACTERISTIC CURVES Pollutant characteristic curves are plots of the in- dividual time-weighted average (TWA) concentrations of diesel pollutants versus the corresponding C0 2 concentra- tions found at the same location and measured over the same period of time. These plots illustrate the relationship between the concentration of the exhaust pollutants and the concentration of C0 2 . There is a separate plot for each pollutant— CO, NO, N0 2 , S0 2 , and particulate matter. These curves are determined for each piece of diesel equipment and are used to estimate the exhaust pollutant concentra- tions. After the curves have been established, the exhaust pollutants can be estimated by measuring only the ambient C0 2 levels on board the equipment and reading the pollu- tant concentration from the curves. A representative curve is shown in figure 1. The operating points shown are TWA measurements of the pollutant measured on board the piece of diesel equipment versus the C0 2 values. The dashed, horizontal line represents a TLV below which the pollutant must be kept. A corresponding limiting C0 2 level above which the pollutant exceeds its TLV is read from the x-axis. 0.1 0.2 0.3 0.4 CO, CONCENTRATION, pet Figure 1.— Pollutant characteristic curve. 55 Dilution of each exhaust gas pollutant concentration with fresh air is equal for all pollutants and thus does not . alter the ratio of the concentration of the pollutants to each other or to the C0 2 concentration. This ratio of pollutant concentration to the C0 2 concentration is the slope of the curves; hence, the curves ideally represent straight lines that pass through the origin. It is possible that the fuel-air combustion process over a wide range of C0 2 values, that is different fuel rates, will not approximate a straight-line plot. However, over the range of C0 2 values of concern, the mass of C0 2 produced by the fuel- injected, compression- ignited diesel cycle is expected to be directly related to the mass of fuel burned. The numerical value of the slope is a function of the type of engine and its condition, the exhaust emission control devices, the duty cycle of the engine, the operator's habits, and the mine environment. All these interrelating variables affect the quality of exhaust emissions so that the curves must be determined from actual underground conditions. These curves, once established, will be altered by changes in engine condition. Thus, the periodic assessment of the engine tailpipe emissions to ensure that the engine has not degraded becomes an essential part of the methodology. If more than one diesel unit is operating in a single ven- tilation split, a cumulative pollutant characteristic curve can be established for that split, which includes the con- tribution of all the exhaust pollutants from all units. A fixed-point monitoring position characteristic of the overall air quality of the split can then be used for monitoring purposes. AIR QUALITY INDEX TO DETERMINE C0 2 CONTROL LEVEL An air quality index (AQD is required to establish a single C0 2 concentration at which the other diesel pollutants are considered below harmful levels. Such an in- dex is necessary to combine the effects of the pollutants in- to a single number that is used to assess air quality. The index selected is the only one known to have been developed that incorporates the additive effects of the pollutants when found in combination. It was defined in 1978 by Ian W. French and Associates, Ontario, Canada, as a means of quantitatively evaluating underground hard-rock mine at- mospheres (19). It involves the measurement of five exhaust pollutants, CO, NO, S0 2 , N0 2 , and respirable combustible dust (RCD), on a TWA basis. This RCD term is an estimate of diesel particulate (carbon-based particles) in hard-rock mines that do not contain carbon in the host rock. The values of the pollutants measured underground are used to calculate a numerical value for the AQI using the follow- ing formula: AQI = (COV50 + (NO)/25 + (RCD)/2 + 1.5[S0 2 )/3 + (RCD)/2] + 1.2[(N0 2 )/5 + (RCD)/2], where the concentration of RCD is expressed in milligrams per cubic meter and all other concentrations are expressed in parts per million. If the concentration of S0 2 or N0 2 is zero, the appropriate bracketed term is omitted. This original 1978 version of the AQI uses the TLV's that were in effect at the time. In summing the five terms of the equation, the AQI ac- counts for possible interactions and synergistic effects be- tween the various exhaust components. The value contained in the denominator of each exhaust gas term is the TLV for that exhaust component adopted by the ACGIH in 1978. The TLV for RCD is the value for respirable dust in underground coal mines containing less than 5 pet quartz in the host rock. French and Associates indicate that an AQI value be- tween 3.0 and 4.0 poses a moderate threat to health, which could be alleviated by personnel protective measures such as respirators or filters. A value in excess of 4.0 indicates a health hazard level and the need for increased ventila- tion or pollutant source controls to bring the value back to less than 3.0. It is further recommended that these values need to be lowered in mines where the host rock contains over 20 pet quartz, and that an additional term be added to the equation in the case of very dusty mines. The AQI and values suggested are recommendations based on extensive review of available published data on mine atmospheric contaminant concentrations along with an assessment of scientific and medical knowledge of health effects of the contaminants at the time. This medical knowledge is incomplete with the investigations done to date. In developing the AQI, French and Associates had assumed the public health attitude and approach that it is prudent to reduce all exposures to as low a level as possi- ble, at least until valid scientific data are available upon which more precise limits of exposure can be based. In 1984, this AQI was modified by French and Associates into a two-part index to resolve criticisms from some health researchers and to include findings from con- tinual review of the world literature relating to the car- cinogenicity, mutagenicity, and toxicity of diesel emissions (20). The two principal criticisms of the AQI were (1) that the ACGIH recommends that the additive approach for toxic compounds only be used when the components exert their toxicity by similar mechanisms— mainly, the respirable dust and gaseous terms might be considered separately, and (2) that the synergism factors 1.5 and 1.2 for S0 2 and N0 2 , respectively, were not supported by scientific evidence. It is now suggested that two independent equations, one for the gases and one for the respirable dust and S0 2 and N0 2 components be used as follows: AQI(gas) = (CO)/TLV for CO + (NO)/TLV for NO + (N0 2 )/TLV for N0 2 . The AQI(gas) should not exceed 1, and no individual com- ponent should exceed its TLV, and AQKparticulate) = (RCD)/TLV for RCD + [(S0 2 )/TLV for S0 2 + (RCD)/TLV for RCD] + [(N0 2 )/TLV for N0 2 + (RCD)/TLV for RCD]. ^^H 56 It is recommended that the AQI(p articulate) value should not exceed 2.0, and no single component should exceed its TLV, as dictated by current ACGIH values. If the concen- tration of SO, or NO, is zero, the appropriate bracketed term is omitted. These terms are included to address the synergistic effects of the SO, and NO, with RCD. An AQI summary graph of all the pollutants showing the contribution of each pollutant to the AQI is obtained from the characteristic curves and the AQI formula. Values are plotted versus CO, concentration. A representative graph is shown in figure 2. The plot labeled Total in figure 2 combines the individual pollutant contributions to the AQI and is the summary plot. From this total plot, underground air quality can be assessed from the TWA measurements of CO, taken on board the diesel equipment with a portable instrument. Figure 2 shows that a CO, con- centration of 0.09 yields an air quality of 3, which indicates the upper CO, level for safe operation in this representative example. X LLI Q < o DC < 0.1 0.2 0.3 0.4 C0 2 CONCENTRATION, pet Figure 2.— AQI and contributing characteristic curves. INDUSTRY USE OF THE METHODOLOGY For the methodology to be useful to the mining industry, the following conditions are required: (1) it must be reduced to a procedure that mining personnel can implement without continual assistance of personnel trained in com- plicated instrumentation and analysis techniques, (2) agen- cies responsible for establishing health standards must ap- prove the AQI and its limiting values, and (3) a method that can be implemented by mine workers to assess engine con- dition in the underground environment must be developed. Establishing the pollutant characteristic curves involves specialized and expensive instrumentation, as well as trained personnel to collect and analyze the data. It can- not be done by present mining staffs, but must be ac- complished by consultants or service organizations. However, the CO, monitoring required to assess air quali- ty after the characteristic curves have been established can be performed by mining personnel with little additional training required. To evaluate quantitatively the health aspects indicated in the AQI, field investigations are necessary under mine conditions that have a record of the health effects from diesel engine operation. Such epidemiological health effects evaluations at occupational exposure levels would take perhaps 20 to 30 yr to prove any possible adverse health effects on humans. The Canadian Department of Energy, Mines and Resources (CANMET) has examined the AQI concept with the findings of a number of animal diesel- exposure studies. CANMET researchers found that the limits associated with the one-part AQI expression com- pared very favorably with the health effects observed dur- ing two extensive animal studies conducted by General Motors Research Laboratories and by Lovelace Biomedical and Environmental Research Institute (21). The studies showed that the animals did not experience adverse health effects at exposure levels below the AQI limit, and did ex- perience adverse health effects at levels greater than the ! limit. In comparing the one-part AQI with the two-part AQI, CANMET researchers showed a correlation coefficient of 0.953 between the two AQI expressions in testing eight diesel engines. The Bureau of Mines and Michigan Technology University in the United States, as well as CANMET, have been using the AQI concept to compare the relative effectiveness of exhaust control concepts (22). Changing engine conditions due to wear, mal- adjustments, and improper maintenance will alter the slope of the pollutant characteristic curves so that actual engine pollutant correlations with CO, will no longer be represen- tative of the curves established at the original operating conditions. A simple tailpipe exhaust analysis method is necessary to indicate changes in engine condition so that the engine may be restored to its operating condition under which the characteristic curves were established. Because of the widely varying and harsh conditions under which diesels are operated in underground mines, a typical time period for scheduled maintenance is impossible to predict, thus requiring this exhaust analysis. This time period will be determined for each specific case of diesel use and may only involve periodic measurement of the CO, level at the tailpipe of the engine. Portable instruments exist for this type of evaluation. Finally, the cost effectiveness of the methodology depends greatly on the time interval over which the on- board CO, measurements need to be taken to assure a healthy environment. This time interval may be thousands of hours if both mine and engine conditions remain constant. This interval will have to be determined as the methodology is evaluated. CONCLUSION With the attractiveness of considering the use of highly mobile diesel equipment during the planning phase of designing a profitable mine and the continuing research into both exhaust controls and health effects of diesel par- ticulates, the diesel debate is expected to continue. The monitoring methodology described in this paper is being 57 developed as a means to assure the safe use of diesels underground from an air quality standpoint. Phases of it may seem rigorous from an industry perspective, but the complexities will be reduced as it continues to be developed and demonstrated. It is important to note that the methodology is more applicable to mines that operate a number of active diesel sections on a single ventilation split. In mines that employ a single diesel vehicle per split and where the air volume is adequate, the methodology may not be necessary. This is particularly true if the mine is operating under more stringent dust standards, which are applicable when respirable-sized silica or quartz particles are present in the mine air. The methodology described will provide a means to determine the degree of exhaust con- trols required. The Bureau is developing an alternative methodology to assess mine air quality in mines using diesel equipment in addition to the concept of monitoring C0 2 . This alter- native methodology is based on monitoring only the diesel particulate present in the mine atmosphere. The concept is based on the fact that the diesel particulates are predominantly less than 1 /im in aerodynamic diameter; hence, represent the most severe health hazard of the com- bustion products since they can be inhaled and retained in the lungs. Their small size also allows them to be selectively differentiated from other dusts such as coal, rock, and mineral dusts present in the mine atmosphere. This is par- ticularly important in coal operations where it is important to know whether the carbon-based, respirable-size dust aerosols are diesel combustion products or coal particles so that effective dust control technology can be implemented. This concept of monitoring diesel particulates is described in another paper of this Information Circular. REFERENCES 1. Mine Safety and Health Administration. The Health and Safety Implications of the Use of Diesel -Powered Equipment in Underground Coal Mines, A Report by an Interagency Task Group. Apr. 1986, 160 pp. 2. Holtz, J.C., and R.W. Dalzell. Diesel Exhaust Contamina- tion of Tunnel Air. BuMines RI 7074, 1968, 23 pp. 3. Hurn, R.W. Diesel Emissions Measurement and Control. Paper in Proceedings of the Symposium on the Use of Diesel- Powered Equipment in Underground Mining, Pittsburgh, Pa., Jan. 30-31, 1973, comp. by B.F. Grant and D.F. Friedman. BuMines IC 8666, 1975, pp. 47-58. 4. Stewart, D.B., P. Mogan, and E.D. Dainty. Diesel Emissions and Mine Ventilation. CIM Bull., v. 71, No. 791, 1978, pp. 144-151. 5. Schnakenberg, G.H. Use of C0 2 Measurement in Monitor- ing Air Quality in Dead End Drifts. Paper in Proceedings of Third International Mine Ventilation Congress, Harrogate, England, June 13-19, 1984, ed. by M.J. Jones, pp. 383-389. 6. Johnson, J.H., D.H. Carlson, and M.K. Schimmelman. Monitoring and Control of Mine Air Diesel Pollutants: Mine Measurements and Interpretation Relative to Standards and Con- trol Technology, Design and Development of a Tailpipe Emission Measurement Apparatus, and On-board Drift Ventilation System Evaluation (contract J01 99125, MI Technol. Univ.). BuMines OFR 43-86, 1984, 450 pp.; NTIS PB 86-204104. 7. Johnson, J.H. Monitoring Methods for Underground Diesel Pollutants. Paper in Diesels in Mining. World Mining/World Coal, Miller Freeman, Nov. 1982, pp. D29-D33. 8. Daniel, J.H., Jr. Diesels in Underground Mining: A Review and an Evaluation of an Advanced Air Quality Monitoring Methodology. BuMines RI 8884, 1984, 36 pp. 9. Johnson, J.H. Overview of Monitoring and Control Methods for Diesel Pollutants in Underground Mines Using Diesel Equip- ment. CIM Bull., v. 73, No. 819, July 1980, pp. 73-87. 10. Johnson, J.H., and D.H. Carlson. The Application of Advanced Measurement and Control Technology To Diesel Powered Vehicles in an Underground Salt Mine. Presented at 86th Ann. Gen. Meeting of CIM-1984, Ottawa, Canada, Apr. 15-19, 1984, 58 pp.; available from J.H. Johnson, MI Technol. Univ., Houghton, MI. 11. Gangal, M.K., E.D. Dainty, L. Weitzel, and M. Bapty. Evalua- tion of Diesel Emissions Control Technology at Cominco's Sullivan Mine. Paper in Heavy-Duty Diesel Emission Control: A Review of Technology. CIM Spec. Vol. 36, 1986, pp. 332-347. 12. Weeks, J.L. UMWA Speaks-Keep Diesels Out. Coal Min. Process., v. 20, Dec. 1983, pp. 37, 66. 13. American Mining Congress. Statement— Meeting of the Diesel Subgroups, NIOSH Mine Health Research Advisory Com- mittee. Washington, DC, Jan. 18, 1985, 2 pp., available upon re- quest from J.H. Daniel, BuMines, Washington, DC. 14. Holtz, J.C. Safety With Mobile Diesel-Powered Equipment Underground. BuMines RI 5616, 1960, 87 pp. 15. Johnson, J.H., E.O. Reinbold, and D.H. Carlson. The Engineering Control of Diesel Pollutants in Underground Mining. SAE Tech. Pap. Series, 810684, 1981, 46 pp. 16. Johnson, J.H. Diesel Engine Design, Performance, and Emis- sion Characteristics. Paper in Proceedings of the Symposium on the Use of Diesel-Powered Equipment in Underground Mining, Pittsburgh, Pa. Jan. 30-31, 1973, comp. by B.F. Grant and D.F. Friedman. BuMines IC 8666, 1975, pp. 9-46. 17. American Conference of Governmental Industrial Hygienists. Threshold Limit Values and Biological Exposure Indices for 1986-1987. 1986, 111 pp. 18. U.S. Code of Federal Regulations. Title 30— Mineral Resources: Parts to 199; 1985, 732 pp. 19. Ian W. French and Associates Ltd. (Claremont, Ontario). An Annotated Bibliography Relative to the Health Implications of Ex- posure of Underground Mine Workers to Diesel Exhaust Emissions (contract 16SQ. 23440-6-9095). Rep. to the Dep. of Energy, Mines and Resources, Ottawa, Canada, Dec. 11, 1978, 350 pp. 20. Health Implications of Exposure of Underground Mine Workers to Diesel Exhaust Emissions— An Update (contract OSQ82-00121). Rep. to the Dep. of Energy, Mines and Resources, Ottawa, Canada, Apr. 1984, 607 pp. 21. Mogan, J.P., and E.D. Dainty. Development of the AQI/EQI Concept— A Ventilation Performance Standard for Dieselized Underground Mines. Ann. ACGIH, v. 14, 1986, pp. 245-247. 22. Mitchell, E.W. (ed). Heavy-Duty Diesel Emissions Control: A Review of Technology. CIM Spec. Vol. 36, 1986, 480 pp. mi^am 58 SURVEY OF GASEOUS DIESEL POLLUTANTS IN UNDERGROUND COAL MINES By Diane M. Doyle-Coombs 1 ABSTRACT The Bureau of Mines surveyed working sections in seven diesel-equipped underground coal mines to obtain data on gaseous diesel pollutant concentrations. Typical production shifts were monitored to determine if the ventilation was adequate to maintain the pollutant concentrations below their respective threshold limit values (TLV's). The sections surveyed were in coal seams located in different geographic regions of the United States, and which had different section ventilation patterns, production rates, and diesel equipment types. Laboratory analysis provided concentration levels of the following gases: carbon dioxide (CO.j), carbon monoxide (CO), nitrogen dioxide (NOJ, and oxides of nitrogen (NO*). Some general findings on ventilation can be concluded from this study. The ventila- tion on all sections was adequate to dilute the C0 2 , CO, N0 2 , and NO* exhaust gases to well below TLV's. The amount of air prescribed by the Mine Safety and Health Ad- ministration (MSHA) diesel approval plates was in excess of what was necessary to main- tain pollutants below required levels. In terms of exposure to pollutants, the C0 2 levels were highest at the miner operator location, but even the maximum of these was only 38 pet of the TLV. INTRODUCTION The Bureau of Mines recently completed a survey of seven diesel equipped underground coal mines to provide information on typical C0 2 , CO, N0 2 , and NO, concentra- tions found on continuous miner development sections. The objectives of the survey were to (1) identify ventilation prob- lem areas on a dieselized section, (2) determine if the ex- isting face ventilation techniques were adequate to provide the operator with sufficient dilution air to keep exhaust con- centrations below specified levels, and (3) obtain data on typical CO,, CO, N0 2 , and No, concentrations for coal mine diesel sections. Diesel equipment usage has increased in U.S. coal mines in the past 10 yr because of its enhanced safety potential and its flexibility. However, there remains a serious con- cern over the possible health hazards associated with diesel pollutants in the underground environment. MSHA has established required ventilation rates 2 for each type of diesel equipment. These minimum rates are based on the un- diluted tailpipe exhaust emissions of a single diesel engine operating at full power and requires that sufficient air is 1 Mining engineer, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. * U.S. Code of Federal Regulations. Title 30— Mineral Resources; Chapter 1— Mine Safety and Health Administration, Department of Labor; Sub- chapter E— Mechanical Equipment for Mines; Tests for Permissibility and Suitability; Fees; Part 31— Diesel Mine Locomotives; July 1, 1985. available to dilute the various exhaust contaminants to one- half of their TLV's. MSHA tests each type of diesel engine to determine its characteristic exhaust emissions and assigns a required ventilation rate accordingly. Diesels operated at elevations of 3,000 to 10,000 ft have a greater potential for polluting the mine environment because at higher elevations the stoichiometry of the fuel-air ratio is different; the atmosphere is less dense and a lower weight of air is drawn into the diesel engines. Therefore, either more ventilation air is needed or the maximum fuel injec- tion rate of the engine must be reduced to prevent excessive generation of exhaust gases. The MSHA ventilation re- quirements for diesel-powered equipment have been established to limit the concentration of various exhaust gas components. In practice, this generally means that the exhaust must be diluted to one-half the TLV for only NO x and CO. Assuming a maximum NO, emission at full load of 735 ppm or 0.0735 pet and an engine exhaust flow rate of 300 ft 3 /min, the airflow necessary to dilute NO, to its TLV of 25 ppm or 0.0025 pet is 8,820 ftVmin. The airflow based on MSHA regulations, 30 CFR 36.45, requires NO, to be reduc- ed to one-half its TLV or 12.5 ppm, meaning a ventilation quantity of 17,640 ftVmin is required. If more than one diesel unit operates in the same split of intake air the ventilation rate becomes additive. A 1981 59 MSHA policy memorandum established a formula for the minimum air quantity requirements provided that the air- borne contaminants were below the TLV's. The minimum air volume formula is expressed as Q t = 100 pet Q, + 75 pet Q 2 . . . + 50 pet Q„, where: Q, = total air quality required, ft 3 /min, Q x = permissible volume rating for the largest diesel rated unit, ft 3 /min, Q 2 = permissible volume rating for the next largest rated diesel unit, fWmin, and Q„ = combined permissible volume ratings for each addi- tional diesel unit, ft 3 /min. Contamination of underground air by the exhaust of diesel equipment is related to the air velocity, equipment speeds, the number of trips during an air change in the en- try, the engine adjustments, and the engine loads. It is estimated that 32,000 ft 3 /min would be required under MSHA regulations to ventilate two shuttle cars and a scoop in the face area of a section. In 112-ft 2 (16- by 7-ft) entries, this represents an air velocity of 286 ft/min. Table 1 presents the range of calculated undiluted ex- haust constituents 3 and their associated TLV's and the ceil- ing limit values. The undiluted values represent tailpipe exhaust concentration prior to mixing with the ventilation air. The TLV's, which have been established by the 1986-87 American Conference of Governmental Industrial Hygienists (ACGIH), are time-weighted average concentra- tions. This value may be exceeded provided the exposure to the high concentration is compensated for by exposure to a concentration below the threshold limit for an ap- propriate period of time. A short-term exposure limit (STEL) is defined as a 15-min time-weighted average exposure, which should not be exceeded at any time during a work- day if the 8-h time-weighted average is within the TLV. Table 1.— Pollutant concentrations in diesel exhaust, parts per million P°»"tan» U ?a d nge 6d TLV CO 114-513 50 C0 2 '6.1-7.2 5,000 NO 225-735 25 NQ 2 36-84 3__ NAp Not applicable. TLV Threshold limit value. 1 Percent. Ceiling limits 77 NAp 37.5 5 ACKNOWLEDGMENTS The author appreciates the efforts of Robert J. Timko, physical scientist, Jon Volkwein, physical scientist, Pitts- burgh Research Center, Bureau of Mines, and Joseph Cocalis, mining engineer, Michael McCawley, industrial hygienist, National Institutes for Occupational Safety and Health, for their help in the underground field surveys. SURVEY DESCRIPTION Air samples were collected by the Bureau in seven underground coal mines. The sections surveyed were in coal seams located in different geographic regions of the United States, with different ventilation schemes, entry layouts, ventilation quantities, and production rates. To determine how the ventilation system dilutes and distributes diesel exhaust gases throughout a working section, bottle samples of the mine atmosphere were taken in the intakes, returns, at the feeder breaker (section transfer point where the face haulage car dumps the car for transport out of the mine), approximately 50 ft inby the feeder breaker in the haulage road and face areas. A sample of fresh air was collected out- side the mine intake portal for analysis of the background concentrations of C0 2 and CO. Fixed point samplers were placed about 5 ft from the floor of the mine entry, away from direct interference with equipment moves, and on-board samplers were attached directly to the section equipment. Since short-duration grab sampling tends to isolate localized activity and is not indicative of long-term average concentrations on the working section, a sampling arrange- ment was developed using an accumulator consisting of a 4-L chamber through which the mine air is pumped at a flow rate approximating 0.27 L/min. This chamber pump assembly resulted in nominally one air change in the con- tainer every 15 min. Air changes within the chamber are a function of the chamber volume and pump flow rate. This allows the samples to be integrated with respect to time. By using a syringe and a clean evacuated test tube, an air sample was drawn from the accumulator every 15 min. The air sample was then returned to the laboratory for C0 2 and CO analysis on a gas chromatograph. Continuous sampling of C0 2 and CO in the manner described yielded time-weighed average (TWA), throughout the entire shift. Passive, diffusion-type, Palmes samplers were used to collect N0 2 and NO, samples 4 at the continuous miner, sec- tion intakes, section returns, feeder -breaker, and haulage road. Samplers were assembled and capped 1 to 2 days prior to their use, uncapped at the beginning of the sampling * Wagner, W.L. The Use of Diesel Equipment in Underground Coal Min- ing. Paper in Proceedings From the NIOSH Workshop, Morgantown, WV. 1977, p. 48. * Palmes, E.D., A.F. Gunnison, J. DiMattio, and C. Tomczyk. Personal Sampler for Nitrogen Dioxide. Am. Ind. Hyg. Assoc. J., v. 37, 1976, pp. 570-577. Palmes, E.D., and C. Tomczyk. Personal Sampler for NO,. Am. Ind. Hyg. Assoc. J., v. 40, 1979, pp. 1588-1597. H^H^M 60 period, and recapped at the end. Three samplers for NO, and NO, were required at each sampling location. The NO, and NO, samplers were returned to the laboratory and analyzed by colorimetric techniques. Ventilation schemes, air quantities, and diesel equip- ment information was also collected for each section surveyed. Mining parameters, such as haulage travelways, number of diesel vehicles, location of feeder breaker, and the use of support and supply equipment outby the section were obtained to establish their impact, if any, on CO,, CO, NO,, and NO, contaminant levels to which miners are exposed. Each mine was surveyed for a 2- to 5-day period to ob- tain gas samples. The seven developing continuous mining sections had seam heights ranging from 5 to 10 ft. Diesel face haulage equipment was used in all mines. All mines used electric continuous mining machines at the face and some mines used diesel support and supply equipment throughout the mine. Each mine evaluated during this survey is discussed separately in the following section. The effects of the ven- tilation scheme on the distribution of the pollutants are presented for each mine and specific findings for that mine are given. DESCRIPTION OF MINES SURVEYED MINE A Sampling was conducted at a location where five entries were driven perpendicular to the main entry. Two 10-st ram cars were used to transport coal from the face to a belt line. Electric rail haulage was used to transport personnel and supplies to the working section. Ventilation at the face was controlled by a blowing brattice curtain. Because rooms were being driven off the mains, the section feeder breaker was in the main entry as shown in figure 1. One fresh air intake brought air to the working section. D D D l Ull lll l ll llH l l ll ll ll l lll lll l l l l l l lll l QChO □ D □ □ -y — SE zr Air duct Truck Figure 1.— Schematic of crosscut showing the location of the truck and loader with respect to sampling sections 90, 140, and 190 ft from the muckpile. 68 TRUCK CYCLE 100 z o £ (r (- z LlJ o z o o o o Q Ld N o o o o 3 I CO o cr uu Mill 1 III 1 1 Mil 1 IIMMIIII II 80 ^->* 60 40 "* "t" - 20 - 1 1 i 100 200 TIME, min 300 TRUCK CYCLE i n iiiiiii n i KEY Distance above floor, ft ■ 5 • 15 A 25 100 200 TIME, min 300 Figure 2.— Concentrations of C0 2 normalized to peak measured value versus time during simulated mucking operations. Figure 3.— Concentrations of CO normalized to peak measured value versus time during simulated mucking operations. ~ S2 o Q. Z o r- < i- z UJ o z o o X o Q UJ M en o z o TRUCK CYCLE mi him Minimi KEY Distance above floor, ft ■ 5 • 15 A 25 z o Q I- X to o z> rr \- TRUCK CYCLE Mill llllllllll 100 200 TIME, min 300 00 200 TIME, min 300 Figure 4.— Concentrations of NO, normalized to peak measured value versus time during simulated mucking operations. Figure 5. — Concentrations of NO normalized to peak measured value versus time during simulated mucking operations. 69 Vertical stratification of the pollutants because of the density difference between ventilation air and the hot ex- haust was clearly shown by the data in figures 2 through 5. Table 1 lists the time-weighted-average (TWA) concen- trations, normalized to the highest TWA value for each pollutant to provide a relative measure of the stratification. Concentrations at 5 ft above the floor varied between 28 and 64 pet of the concentrations measured at 25 ft above the floor. The normalized TWA values indicated that leav- ing the truck idling during loading increased the pollutant levels. Table 1. — Relative difference in TWA concentration at various heights Normalized cone x iqq,i pet Truck shut down Truck idling 72 48 22 68 55 36 75 52 23 82 56 24 100 64 42 100 84 64 100 57 28 100 58 28 Height above floor, ft C0 2 : 25 15 5 CO: 25 15 5 NO,: 25 15 5 NO: 25 15 5 formalized to peak TWA value. Stratification of diesel particulates because of the buoy- ancy of the hot exhaust was also observed. The concentra- tion of diesel particulates (aerodynamic particle diameters less than 0.69 /im) at 5 ft above the floor were 66 pet of the concentration measured at 12 ft above the floor. The air temperature was also measured throughout the room to establish the degree of temperature stratification. The data are presented in figure 6, using a format similar to the concentration data. Time-weighted-average tem- perature for the steady -state portions of the data are listed in table 2 for sections 90, 140, and 190, and indicate that temperatures at 28 ft above the floor averaged 3.9 ° F higher than at 10 ft above the floor, because of stratification of the hot exhaust. The data indicated that thermally induced stratifica- tion of the pollutants acted to enhance face ventilation ef- fectiveness. Pollutants tended to be transported at higher concentrations near the roof, thereby reducing the concen- tration at lower heights where personnel were exposed. Mix- ing was uniform throughout the plan area of the room, in- dicating that ventilation flow rates sufficient to dilute the diesel fumes would also provide sufficient turbulence in full- size operations. Table 2. — TWA temperatures during loading, degrees Fahrenheit Height above Section Section Section floor, ft 90 140 190 10 52.7 52.0 52.0 ?0 54.7 56.0 55.0 ?5 56.3 57.5 57.1 ?8 55.6 56.0 56.7 65 60 - TRUCK CYCLE irr 1 1 1 1 lit lllllllllll Mill KEY Distance above floor, ft ■ 10 Section 90 j f 65 o oc Z> UJ Q_ Id r- "I I UIIIIMI II Mill I lllllllllll Start mucking cycle Section 190 100 200 TIME, min 300 Figure 6.— Temperature versus time during the mucking simulation. 70 TRACER GAS CHARACTERIZATION OF FACE VENTILATION SYSTEMS Two candidate ventilation systems were fabricated and then tested in the test room to compare operating characteristics. Sulfur hexafluoride (SF 6 ) gas was used to compare ventilation effectiveness in identical test condi- tions. These tests are reported in detail by Brechtel. 4 The candidate ventilation systems were— A free-standing jet fan consisting of a 52-in-diameter fan with a two-speed, 75-kW motor, A reversible fan with rigid duct consisting of a 52-in- diameter, two-stage fan with two 93-kW motors connected to a 54-in-diameter round steel duct. Both systems were designed to deliver 100,000 ft 3 /min in dead-end heading ventilation illustrated by figure 7. Fresh air Jet fan -320'- ^k Rigid duct *<£ "-- Reversible ventilation fan — Ducted fan-blowing mode Fresh air £ 320'- Rigid duct z.T^Reversible / J ventilation fan *i r Ducted fan- exhaust mode LEGEND Intake air -« — 30 ft from face: 6 289±41 227±11 o z UJ 40 ft from face: 5 320±40 346±32 o 15 315±46 375±71 25 310±31 328±52 U- Mean 315±39 350±56 UJ 80 ft from face: 5 287±52 295± 9 z 15 265±58 292±18 o 25 265±48 285±11 r- Mean 272±52 290±14 ^ 200 ft from face: _l 5 268± 3 259± 9 Q 15 266±15 252±10 25 236±29 244±11 Mean 256±25 245±18 Overall mean 282 288 could be fully simulated using tracer gas if the heated airstream flow rate was similar to the output of the large engine. The tracer gas results indicated that both fan systems delivered uniform mixing at high efficiency. This result is similar to results of the mucking simulation, except that vertical stratification of the magnitude observed in the 20 "i 1 1 ' 1 ' r Hot exhaust test, 40 ft from face TWA=0.7I Face fan, SF 6 release started at time i I L. Ideal dilution=IOO pet J u 20 40 60 TIME, min 80 100 Figure 10.— Comparison of the performance of the jet fan and ducted fan for the hot exhaust test at 40 ft from the face. mucking simulation served to enhance ventiliation effec- tiveness by reducing pollutant concentration at floor level where personnel are exposed. CONCLUSIONS These tests indicated that conventional face ventilation systems operating at the high flow rates necessary to ven- tilate diesel equipment in the 600- to-700-hp range could provide effective mixing as far as 300 ft from the fan in large rooms. The mixing of pollutants was very uniform in the horizontal plane, and vertical stratification of air flow due to the large room size was not observed. Vertical stratifica- tion of pollutants due to thermally induced buoyancy of the exhaust fumes was observed, but tended to improve air quality at room heights where personnel would be working. SF 6 tracer gas was effective in characterizing the mix- ing uniformity in the test rooms, but did not simulate the thermal stratification because of the low flow rate of the heated air. The tracer gas tests provided an effective method to compare the performance of the different fans and to measure their capacity to ventilate steady-state pollutant production similar to diesel exhaust. 72 AN OVERVIEW OF THE EFFECTS OF DIESEL ENGINE MAINTENANCE ON EMISSIONS AND PERFORMANCE By Robert W. Waytulonis 1 ABSTRACT Diesel engines are a source of mine air contamination and can be a safety hazard if misused. Safe and healthful use of diesel-powered equipment depends primarily on proper maintenance of the engine, rapid dilution of the exhaust, adequate ventilation to dilute and remove the exhaust from the mine and to restore oxygen used in the com- bustion process, and a mine air monitoring program to insure pollutant concentrations are below Federal standards. The objective of this paper is to outline the diesel engine maintenance practices affecting emissions and performance. This information is based on research sponsored by the Bureau of Mines, which investigated current use patterns of diesels in underground mines and the effects of engine maintenance on exhaust emissions. The paper is organized so that practical maintenance recommendations appear in a form that can be readily applied by a mine operator. The major findings essential for safe equipment use and long engine life are use indirect injection engines, read and apply the information in the equipment manuals, shut down engines when ventilation is interrupted, use low-sulfur fuel, keep all fluids entering the engine clean, do not overheat engines, do not idle longer than 5 min, do not lug the engine, keep the fuel-to-air ratio within specifications, and shut down engines if black smoke appears in the exhaust. If the maintenance practices described in this paper are enacted, reduced emissions will result, thus improving the air quality in areas where diesel-powered equipment is used. Additionally, these practices also reduce the chance of accidents occurring because of equipment failure, or fire and explosions, thus mine safety is improved. INTRODUCTION Diesel-powered equipment was first introduced into U.S. underground metal and nonmetal mines in 1939 (l), 2 and today they are heavily relied upon to move personnel, materials, and ore. Use of diesels in underground coal mines has steadily increased from less than 200 units in 1973 to about 1,200 units in 1985 (2). A historical perspective of the Bureau's research on diesels in underground mines is presented in Bureau reports {3-4). Diesel equipment has disadvantages that must be over- come to ensure that the equipment does not present addi- tional hazards in the mine environment. Diesel engines are a fire and explosion hazard (1, 5-6) because of their high surface and exhaust temperatures, and the possibility of engine backfires. Additionally, diesel exhaust is a source 'Supervisory physical scientist, Twin Cities Research Center, Bureau of Mines, Minneapolis, MN. 'Italic numbers in parentheses refer to items in the list of references at the end of this paper. of noxious gases and particulate matter (1, 5), which must be controlled to ensure a healthful work environment. The increased use of diesels, and the concern for the safety and health of miners, led the Bureau of Mines to spon- sor research with the objective of defining current use pat- terns of equipment, and relationships among engine condition, maintenance practices, and emissions (7). Addi- tional in-depth data analysis (8-9) was undertaken, which further defined the effects of maintenance on exhaust emis- sions and time in service. One way to ensure safe operation and reduce emissions is to perform regular engine maintenance. Although it has been recognized for some time that properly adjusted engines and ventilation were necessary for safe operation, the objective of this paper is to outline the diesel engine maintenance practices affecting emissions and performance in a way that is useful to the mine operator. 73 BACKGROUND DIESEL ENGINE OPERATION All diesel engines operate on the compression-ignition principle in which air is compressed and liquid fuel is in- jected under high pressure in the form of a spray. This mix of fuel and air ignites by the heat of compression, resulting in power output from the engine. Diesel engines are either naturally aspirated (NA) or turbocharged (TC). In NA engines, air is taken in from the atmosphere without external assistance. The amount of air taken in depends on engine speed. In TC engines, exhaust energy is used to power a turbine air compressor that in- creases the amount of air inducted per piston stroke. The amount of fuel injected determines the power output. An engine's fuel-air (F-A) ratio is the mass of fuel con- sumed divided by the mass of air. For each gallon of fuel, approximately 12,500 gal of air is required. An F-A ratio of about 0.01 occurs at idle; at high power output the ratio is closer to 0.05. The chemically correct F-A ratio is 0.067. This is achieved when the correct amount of fuel is injected to chemically react with all the available oxygen in the com- bustion chamber. Because of incomplete mixing of the fuel with air, it is impractical to operate at this condition and, therefore, all diesel engines operate fuel lean (or air rich), making it a comparatively low-emission power source. DIESEL ENGINE EMISSIONS The majority of the gaseous emissions are composed of oxygen, nitrogen, and water vapor. A small percentage of the total is made up of the products of incomplete combus- tion, i.e., carbon monoxide (CO), carbon dioxide (C0 2 ), hydrocarbons (HC), oxides of nitrogen (NOJ, oxides of sulfur (SOJ, and exhaust particulates (smoke or soot). Although small by comparison to the total exhaust volume, these pollutants are important because of the large amount of ex- haust flow and the limited fresh air available for dilution in underground mines. Typically, a 100-hp engine will emit in excess of 1,000 ft 3 /min of exhaust at full speed. Measures must be taken to minimize worker exposure to these contaminants. Diesel exhaust-gas composition is related chiefly to the F-A ratio. There is a range of F-A ratios within which the generation of CO is relatively low (5, 10). When any diesel engine is adjusted for maximum power output, the F-A ratio is in the rich range. The volume of CO and objectional gases, particularly NO x , are affected both by the F-A ratio at which the engine is operated and the design of the combustion chamber. An important product of incomplete combustion is par- ticulate emissions, which are composed primarily of small carbon particles with absorbed HC's and other gases. Dif- ferent types of particles are emitted from diesel engines under different modes and operating conditions. About 95 pet, by mass, of the smoke particles are submicrometer in size (11). These types of particulate emissions are 1. White smoke.— Results when the engine is cold or under low load. Liquid particles appear as white clouds of vapor emitted under cold starting, idling, and low loads. These consist mainly of water vapor, unburned fuel, and a small portion of lubricating oil (12). These white clouds disappear as the load is increased and the engine warms. 2. Black smoke (soot).— Is a sign of overfueling or a rich F-A ratio. Soot or black smoke is unburned carbon particles emitted as a product of the incomplete combustion process, particularly at maximum loads (12). 3. Other particles.— White and/or blue-black smoke par- ticles result from lubrication oil finding its way into the combustion chamber because of wear or leaks. Typically the oil passes by worn valve guides and piston rings. REGULATIONS Title 30 of the Code of Federal Regulations (13) contains the health and safety regulations governing diesels in mines. Under part 32 (14), CO emissions are regulated to 2,500 ppm in the undiluted exhaust and 3,000 ppm under part 36 (15). Once an engine is submitted by a manufac- turer to the Mine Safety and Health Administration (MSHA) for certification, the maximum F-A ratio, whereby these CO values are not exceeded, is determined and set. Next, the engine is run throughout its operating range and NO„ C0 2 , and CO are measured. The quantity of air re- quired to dilute each pollutant to less than its threshold limit value (TLV) is calculated to establish the ventilation rate for the engine. NO, is usually the pollutant that governs the amount of ventilation required. For NA prechamber engines, the worst operating condition for NO, is usually at part load-peak torque speed. Exhaust par- ticulate emissions per se, are not regulated; however, these regulations state that equipment should be shut down when "black smoke" appears. An important determination made during certification testing by the MSHA is the maximum allowable fuel- injection rate needed to avoid excessive generation of CO. The results of engine tests are used to determine maximum fuel injection rate at or below which CO can be controlled by a reasonable ventilation rate and smoke is essentially eliminated. This fuel rate must be adjusted to the altitude at which the engine will be operating (5). DIESEL ENGINE MAINTENANCE The objective of diesel engine maintenance is to keep engines in good operating condition to maximize produc- tivity and engine life. Once equipment is put into opera- tion, it is the responsibility of the mine operator to keep it in good condition. Preventive maintenance, periodic repairs, and adjustments are all part of a basic maintenance program. Maintenance can prolong or restore near-original efficiency of the engine (16). A brief discussion of the six major systems pertaining to the maintenance of diesel engines used in underground mines follows. AIR INTAKE SYSTEM The high compression ratios and close tolerances of diesel engines require that airborne particles be removed 74 from the large volumes of air consumed, in order to prevent abrasion of internal engine surfaces. This requirement demands a well-maintained air intake system. Dust-laden mine air causes intake air filters to become filled with dust, creating a restriction that may exceed the manufacturer's recommended limit. Intake air filters should be replaced when the pressure drop across the filter exceeds the manufacturer's specification, usually 20 to 25 in H 2 0. A dirty intake filter, if not quickly replaced, will result in increased emissions and decreased performance. Loose clamps, small cracks in hose or piping, poorly connected slip joints, or defective seals must be repaired to keep out dirty air. Installation of intake restriction indicators downstream of the air cleaner is recommended. However, installation should not compromise permissibility features on ap- proved equipment. Equipment operators should carry spare filter elements for replacement when the gauge indicates a saturated filter. Used filter elements should be dis- carded. Not all air intake system failures can be detected by pressure drop indicators, e.g., a broken intake air duct or punctured filter will not be detected. The best method presently available for detection of these failures is a visual inspection of the air intake system. Premature engine failures are often traced to dust in- take. Dual element air filters and proper service intervals provide an excellent defense. COOLING SYSTEM The loss of engine cooling leads to scuffed cylinder walls and pistons, cracked heads, and burned valves. These con- ditions directly affect emission production and output power. A liquid-cooled engine relies on transfer of heat from the coolant to the radiator, and from the radiator to ambient air. Internal coolant passages of the engine and radiator must be kept free of mineral and rust deposits for effective heat transfer. Mine water is generally high in minerals and salts, rendering it unfit for use in engine cooling systems (17). Ideally, a 50-pct mixture of distilled water and an- tifreeze should be used. Not only necessary for cold weather operation, antifreeze will prevent rust formation and also provide lubrication for the water pump, and increase the boiling temperature of the coolant. Air-cooled engines reject heat via cooling fins, which are an integral part of the engine. During normal operation these fins become coated with oil and dust, which bakes on to form an insulating layer. If this layer is allowed to build on the engine, overheating will result. Periodic steam or pressure cleaning will delay development of this condition. Whether the engine is air- or liquid-cooled, the causes of overheating of diesels include the following: 1. Dirt deposits blocking airflow through the radiator or bent cooling fins; damaged fins and shrouds reduce airflow and contribute to overheating. 2. Engine faults, such as retarded fuel injection timing and overfueling. These increase combustion and exhaust- gas temperatures, putting additional heat load on the cool- ing system. 3. Incorrect coolant solution; a 50-pct antifreeze and dis- tilled water solution is optimum. Also, internal scale build- up caused by use of water with high mineral content reduces cooling system performance. 4. Slipping fan and pump belts, which reduce air and coolant flow. FUEL QUALITY AND HANDLING DF 2 (sometimes designated 2-D) diesel fuel should be used whenever ambient temperatures are above the cloud point (approximately 37 ° F) of the fuel. DF 2 possesses bet- ter lubrication properties than DF 1 (1-D) and tends to ex- tend fuel injection system component life. Additionally, DF 2 has a higher energy content per gallon (18). Sulfur content should be as low as possible, preferably less than 0.2 pet by weight. If the sulfur content of the only available fuel is known to be above 0.2 pet, the engine oil should be changed more frequently. The sulfur present in all diesel fuels directly affects the emissions of particulate sulfates and accelerates engine wear (19). Much of the sulfur will pass through the engine and reappear as SO, emissions (20). Sulfur in the fuel combines with moisture in the engine to produce sulfuric acid, which is corrosive to parts, bear- ings, and seals. The quality of fuel delivered to the mine should be controlled by placing specifications on the pur- chase order. Fuel contamination causes accelerated engine wear, because of extremely close tolerances, often 0.00008 in, of the injection equipment (21). Most fuels hold a small amount of sediment and abrasives in suspension that should be removed. Most engines include one or more filters to pro- tect the injection system from dirty fuel. In addition to routine cleaning or replacement of filters, there should be periodic cleaning or draining of the vehicle fuel tanks. Prop- er fuel handling can reduce fuel contamination. It is im- portant to minimize the number of fuel transfers and to store the fuel in tightly sealed containers that are clearly labeled. Water is a common contaminant. It condenses in storage tanks, especially if the tanks are partially full and are at high humidity, or water may be in the delivered fuel. The best method to remove water is to install fuel-water separators on all equipment, minimize fuel transfer points, and keep fuel storage tanks full. There are three places where a fuel filter and water separator would be used in a good fuel handling system: (1) at the outlet of the surface storage tank, (2) at the pump side of the portable fuel trailers, and (3) on the engine. FUEL INJECTION SYSTEM The engine fuel flow rate is usually set at the factory or at an authorized service shop, and is based on the MSHA horsepower and ventilation rating. Seals to discourage tampering are installed on the fuel pump because of the critical relationship between F-A ratio and emissions. Operation of any diesel engine at F-A ratios greater than 0.05 produces excessive quantities of CO and particles that requires an impractical ventilation rate (5). The function of the injection nozzles is critical to good fuel economy. Injectors act to mechanically atomize the li- quid fuel by forcing it under very high pressure through small holes at a certain time in the combustion cycle. Whatever happens during operation to alter spray pattern, injection timing, or fuel charge, will alter engine perform- ance and emissions. If the nozzles are dirty, improperly ad- justed, or worn beyond tolerances, the engine will waste fuel. Very small particles of dirt in the fuel can damage the injectors, and can result in increased CO, HC's, and par- ticulate emissions. Carbon buildup on injector tips results in loss of power and requires more fuel to accomplish a given 75 amount of work. Improperly adjusted nozzle opening pressures can affect the spray pattern, resulting in a poor F-A mixture and loss of fuel efficiency. Malfunctioning in- jectors cause smoking, uneven engine operation, and high CO and HC emissions (7-9). If a fuel injector problem is the suspected cause of ex- cessive smoke, the following items should be inspected: fuel injector and nozzles for leakage, opening pressure, nozzle valve sticking, spray pattern, and correct nozzle part number. To check injectors, they must be removed and placed in a special test fixture. A simple apparatus can be used to check spray pattern and nozzle opening pressure. More sophisticated bench-test equipment should be used by specially trained technicians to flow-balance and match in- jector delivery rate, spray pattern, and penetration. It is advisable to inspect injectors on a routine basis, as specified in the engine manual (21). Unless manually adjusted, diesel injection timing generally remains constant over long service intervals. Tim- ing could be improperly adjusted at the factory or by a ser- viceperson, or otherwise altered to yield higher output horsepower. Engine manufacturers usually allow a 1° deviation from the recommended setting. Induced fault testing has shown that injection timing (advanced or retarded) will affect all emissions (7-9). CO will increase whether timing is advanced or retarded from the factory setting, particles will tend to decrease slightly with retarded timing and increase with advanced timing, and NO x increases when timing is advanced and decreases when it's retarded. Once properly set, fuel injection timing does not require frequent adjustment. LUBRICATION SYSTEM Failure of the lubrication system usually results in catastrophic engine failure. System failures are often caused by a component failure, such as seized bearings, lubricant breakdown or contamination, or engine overheating. To con- trol these failures it is important to keep the crankcase lubricant at the recommended level, free of solid and liquid contamination, and maintain the engine's cooling system. If an engine becomes excessively hot, the oil viscosity is lowered and oil consumption increases, resulting in loss of lubricity and accelerated engine wear (23). EXHAUST SYSTEM Excessive exhaust gas restriction or backpressure can result from either a partially plugged water scrubber, flame trap, catalytic converter, or dented exhaust pipe. Engine manufacturers generally consider 2 to 3 in Hg to be the ac- ceptable limit. Excessive backpressure causes increased emission of some pollutants and decreased power output. Periodic inspection and cleaning of the exhaust system com- ponents will preclude excessive backpressure. RECOMMENDATIONS The following is a list and description of 10 recommen- dations for safe use of diesel equipment in underground mines: 1. Use indirect injection (IDI) combustion chamber engines. The first step a mine operator can take to reduce emissions is to select prechamber or H)I engines, which have lower emissions than direct injection (DI) engines of equivalent power. These engines emit about one-half as much CO and particle emissions as do DI engines, thus re- quiring less ventilating air. The DI combustion chamber design is used almost ex- clusively in over-the-road and other surface vehicles. It has an advantage of slightly less fuel consumption, but has a penalty of higher levels of pollutants in the exhaust. Figure 1 is a plot of the ventilation requirements for three engines in the 135 to 150-hp range. The Isuzu QD 145 is a DI engine requiring 156 (ft 3 /min)/hp. The Deutz F6L 413 and the Caterpillar 3306 PCNA are IDI engines requir- ing 86 and 103 (ft 3 /min)/hp, respectively. These engines have been tested and certified by MSHA for use in underground mines. It is clear that the IDI engines have an important advantage by requiring significantly less ventilation air to dilute their exhaust pollutants to less than the current TLV's. 2. Read operation and maintenance manuals. The operator's manuals should be made required reading to learn the correct operation of the vehicle and engine. The engine manual should be followed for service intervals and other vital information. Manufacturers have developed engines to be a balance between performance, durability, and emissions. Deviation from proper servicing methods and intervals will result in degraded performance and emis- sions, and shortened engine life. 3. No ventilation, no operation. If ventilation is inter- rupted for any reason, all diesel equipment should be shut down until fresh airflow is resumed. If more than one diesel is used in a split of air, 100 pet of the largest ventilation air quantity requirement plus 75 pet of the second largest ventilation requirement, plus 50 pet each of the remaining diesel unit's requirement, determines the total quantity of ventilating air for the diesel equipment. 4. Use low sulfur fuel It is especially important to limit the amount of sulfur in the fuel. Low sulfur content is im- portant for maximum engine life, lubrication, and fuel economy. Also, sulfate emissions are controlled by limiting the amount of sulfur in the fuel. 5. Keep it clean. Dirt is very detrimental to engines. Regular checks and maintenance of the machine's air in- duction system are necessary to peak engine performance. The diesel consumes large volumes of air to function. If the volume of air is restricted or insufficient, the engine will perform poorly and emit large quantities of particulates and other pollutants, which indicate that the fuel is not burn- ing completely. One of the most common causes of excessive and dark smoke is intake air restriction caused by plugged air cleaners. The most effective way to improve engine life is to frequently and correctly service air cleaners. 6. Keep it cool Engine overheating is a frequent cause of premature engine failures. Insure that lubrication oil is the correct viscosity and kept at the recommended level. Keep all heat exchangers free of accumulated dirt and open to circulating air. 7. No extended idling. An established tradition of diesel engine operation is idling engines for long periods, which wastes fuel. Fuel consumption is not the only problem; engines at idle tend to overcool with operating temperatures 76 or Id o 0_ LU CO tr o X ncomplete combustion CO, particles, exhaust trend- — Power re 0.032 0.05 0.067 0.10 ENGINE FUEL-AIR (F-A)RATIO Figure 1 .—Ventilation requirements for one direct (Ol) and two indirect (IDI) injection engines in the 135- to 150-hp range. well below ranges recommended by the manufacturers. This results in incomplete combustion, which leads to varnish and sludge formation. Unburned fuel washing down cylinder walls removes the protective film of lubricant and results in accelerated wear (23). Once fuel mixes with crankcase oil, dilution further reduces effectiveness of the lubricant. Planning for cold starts and shut down of engines for work breaks is now regarded as much more economical and less damaging to engines than prolonged idling. Engines should be shut down if idle periods are expected to exceed 5 min. 8. No lugging. Engine lugging or operating the engine at high load-low speed will significantly increase CO and particle emissions, and increase operating temperatures. Lugging should be avoided in order to operate at the lowest CO and particulate emission range. Operators should shift gears to operate the engine at a higher rotational speed or lessen the engine load, rather than lug the engine. Figure 2 illustrates this by showing typical horsepower curves at 1,200 and 2,000 r/min. If a certain amount of power is re- quired to perform the task at hand (as indicated by the dot- ted line intersecting the y-axis), this level of power can be attained at two different F-A ratios. By operating at the lower F-A ratio of 0.032 at 2,000 r/min, CO, particulate, and exhaust-gas temperatures will all be lower than at the cor- responding F-A ratio of 0.05 at 1,200 r/min. 9. No overpowering. The fuel injection pump governor must be set according to manufacturer's specifications. Engines have a specific engine high idle, full load, and, in some cases, torque converter stall speeds. The governor set- ting should never be set to exceed these limits. The engine's F-A ratio is set and locked, and should remain that way un- til adjustment by an authorized person. Derating the engine limits the maximum fuel rate and promotes oxidization of HC's and CO to HjO, and more complete burning of the fuel. Fuel system tampering sometimes occurs in an attempt to increase output horsepower. Changing the calibration of the fuel pump or installing larger capacity injectors af- fects the F-A ratio and results in greater pollutant produc- tion and possible engine damage. These changes increase combustion pressures and engine temperatures. The in- crease in combustion pressure will be felt throughout the entire engine. More stress is placed on liners, rings, pistons, bearings, valves, camshafts, and cam followers. The types of damage that can eventually occur are cracked or burned pistons, scored liners, accelerated bearing wear, broken or sticking valves, and broken rings (7). The damage caused by increased combustion pressures may not be apparent for some time. Air density decreases with an increase in elevation, therefore the F-A ratio will change as altitude increases. If the engine is to be operated at altitudes above 1,000 ft, 77 200 i- Q. C 'E UJ UJ or 5 o UJ or z o »- < _) UJ > 150 - 100 - 50 - 156 103 / // engine // 86 '// IDI // // // , engine ' // — / // IDI // // engine ^/ / DEUTZ F6L 413 139 hp CAT 3306 PCNA 150 hp ISUZU QD 145 135 hp Figure 2.— Typical horsepower curves and corresponding fuel-air ratios for 1 ,200 and 2,000 r/min. the fuel rate must be reduced by 3 pet for each 1,000 ft above 1,000 ft. An engine operating at 7,000-ft elevation, for ex- ample, would be limited to consume 18 pet less fuel at full load-rated speed. An engine adjusted for sea-level operation, but operating at 4,000 ft, is overfueled by about 10 pet, and if operating at 7,000 ft, is overfueled by 20 pet. Only a trained and certified person should set fuel pumps and once set, leave it alone. Failure to derate will greatly increase fuel consumption and exhaust pollutants. Turbocharged engines can exceed 1,000-ft altitude before deration due to the excessive quantities of air available from the turbocharger. For example, a Caterpillar 3306 PCTA engine can operate up to 6,500-ft elevation before deration is required. 10. Beware of black smoke. Dark smoke from a diesel engine exhaust is a result of an improper F-A ratio. This is a dangerous condition because of high CO and particles in the exhaust. Equipment emitting black smoke should be shut down and taken to a maintenance area for diagnosis and repair. Black smoke may indicate incorrect governor setting, air cleaner restrictions, incorrect fuel delivery, improper injection pump timing or cam valve timing, defective in- jectors or nozzles, poor compression, or incorrect timing advances. CONCLUSIONS Exhaust pollutants can be held to very low levels through proper and sustained engine maintenance. A good engine maintenance program will reduce the diesel's burden on the mine ventilation system and help sustain good air quality. Additionally, the added benefit of high equipment availability and good performance with minimum fuel con- sumption can be realized. The safe and healthful use of diesel-powered mine equip- ment can be promoted by adherence to the following four basic guidelines: ^^mm 78 1. Use equipment approved by MSHA; this assures that equipment workmanship and materials pertinent to main- taining permissibility, have been scrutinized, and a safe maximum fuel rate and corresponding ventilation rate has been established for the vehicle. 2. Perform proper and timely engine maintenance specified by the manufacturer; this is essential for satisfac- tory engine life and performance, and minimum fuel con- sumption and emissions. 3. Assure adequate ventilation; this is necessary for good air quality in areas where diesels are operating, to dilute and remove the exhaust gas, and replenish oxygen. 4. Perform regular air monitoring; contaminants such as CO and total respirable dust must be regularly sampled to determine if air quality is being maintained at acceptable levels. REFERENCES 1. Harrington, D.E., and J.H. East, Jr. Diesel Equipment in Underground Mining. BuMines IC 7406, 1947, 87 pp. 2. Turcic, P. (MSHA). Private communication, 1986; available upon request from R.W. Waytulonis, BuMines, Minneapolis, MN. 3. Elliott, MA. Review of Bureau of Mines Work on Use of Diesel Engines Underground. BuMines RI 4381, 1948, 28 pp. 4. Daniel, J.H., Jr. Diesels in Underground Mining: A Review and an Evaluation of an Air Quality Monitoring Methodology. BuMines RI 8884, 1984, 36 pp. 5. Holtz, H.C. Safety With Mobile Diesel-Powered Equipment Underground. BuMines RI 5616, 1960, 87 pp. 6. Mine Safety and Health Administration (U.S. Dep. Labor). The Health and Safety Implications of the Use of Diesel-Powered Equip- ment in Underground Coal Mines. Report to the Assistant Secretary, Apr. 1986, 160 pp. 7. Branstetter, R., R. Burrahm, and H. Dietzmann. Relationship of Underground Diesel Engine Maintenance to Emissions. Volume I and Volume II (contract H0292009, SW Res. Inst.). BuMines OFR 110(l)-84, 1983, 104 pp.; NTTS PB 84-195510 and BuMines OFR 110(2)-84, 217 pp.; NTIS PB 84-195528. 8. Waytulonis, R.W. The Effects of Diesel Engine Maintenance on Emissions. CIM preprint 101, 1984, 31 pp. 9. Waytulonis, R.W. The Effects of Maintenance and Time-in- Service on Diesel Engine Exhaust Emissions. Paper in the Pro- ceedings of the 2d U.S. Mine Ventilation Symposium, ed. by P. Moussett-Jones, A.A. Balkema, 1985, pp. 609-617. 10. Obert, E.F. Internal Combustion Engines. Intext Educational Publ., 3d ed., 1973, 740 pp. 11. Lipkea, W.H., J.H. Johnson, and C.T. Vuk. The Physical and Chemical Character of Diesel Particulate Emissions— Measurement Techniques and Fundamental Considerations. SAE Progress in Technology Series 17, 1979, pp. 1-57. 12. Springer, K.J. Smoke. Heavy Duty Equipment Maintenance. Jan./Feb. 1973, 6 pp. 13. U.S. Code of Federal Regulations. Title 30-Mineral Resources; Parts to 199, Chapter 1— Mine Safety and Health Ad- ministration, Department of Labor, July 1, 1985, 732 pp. 14. Title 30— Mineral Resources; Chapter 1— Mine Safety and Health Administration, Department of Labor; Subchapter E— Mechanical Equipment for Mines; Tests for Permissibility and Suitability; Fees; Part 32— Mobile Diesel-Powered Equipment for Noncoal Mines, July 1, 1985, pp. 210-222. 15. Title 30— Mineral Resources; Chapter 1— Mine Safety and Health Administration, Department of Labor; Subchapter E— Mechanical Equipment for Mines; Tests for Permissibility and Suitability; Fees; Part 36— Mobile Diesel-Powered Transportation Equipment for Gassy Noncoal Mines and Tunnels, July 1, 1985, pp. 237-249. 16. Springer, K.J. Transportation, Trucks, and Fuel Conserva- tion. Pres. at IV Interamerican Conf. on Materials Technology, Caracas, Venezuela, June 29-July 4, 1975, 7 pp.; available from R.W. Waytulonis, BuMines, Minneapolis, MN. 17. Waytulonis, R.W., S.D. Smith, and L.C. Mejia. Failure Analysis of Diesel Exhaust-Gas Water Scrubbers. BuMines RI 8682, 1982, 19 pp. 18. Lilly, L.C.R. (ed.). Part 1-Theory, Section 4— Fuels and Com- bustion in Diesel Engine Reference Book. Butterworth, 1984. 19. Weaver, C.S., C. Miller, W.A. Johnson, and T.S. Higgins. Reducing the Sulfur and Aromatic Content of Diesel Fuel: Costs, Benefits, and Effectiveness for Emissions Control. SAE Technical Paper Series 860622, 1986, 16 pp. 20. Khatri, N.J., J.H. Johnson, and D.G. Leddy. The Characterization of Hydrocarbon and Sulfate Fractions of Diesel Particulate Matter. SAE Progress in Technology Series 17, 1979, pp. 73-96. 21. Lilly, L.C.R. (ed.). Part 2— Engine Design Practice, Section 10— Fuel Injection Systems in Diesel Engine Reference Book. But- terworth, 1984. 22. Part 8 — Maintenance, Section 32— Maintenance and Overhaul Procedure and Workshop Equipment in Diesel Engine Reference Book. Butterworth, 1984. 23. Part 3— Lubrication, Section 16— Lubrication and Lubricating Oil, Part 2— Engine Design Practice in Diesel Engine Reference Book. Butterworth, 1984. 79 MEASUREMENT OF THE EFFECTS OF A FUEL ADDITIVE ON DIESEL SOOT EMISSIONS By H.W. Zelleri ABSTRACT The Bureau of Mines is conducting research to reduce exhaust emissions from diesel- powered equipment used underground. Reported here is recently conducted laboratory research to determine the potential of a barium-based fuel additive for reducing soot from diesels. These tests were conducted at steady-state engine operating conditions. The objective of this paper is to use the steady-state emissions data to predict engine emissions and the effects of fuel additives for representative equipment duty cycles. A significant finding is that the effect of the additive on carbon reduction is independ- ent of additive content in the fuel between half and double the manufacturer's recom- mended concentration. The addition is capable of reducing particulate emissions by over 30 pet when used at half the manufacturer's recommended concentration. INTRODUCTION PROBLEM SIGNIFICANCE Exposure to contaminants in diesel exhaust is a poten- tial health problem for underground miners. Diesel particulates are composed of a carbon core surrounded by adsorbed organic compounds produced as a result of in- complete combustion (23). 2 Chemical analyses have iden- tified hundreds of different compounds, including known carcinogens, in particulate extracts (10, 14, 24, 31). The com- position and mutagenic activity of these extracts varies with engine type, operating conditions, fuel type, exhaust con- trols, and ambient conditions (1 7). Most of the soot mass is smaller than 1.0 yon.; therefore, all diesel particulates are in the respirable size range and are easily transported into the deep regions of the lungs. Mine operators are instructed to shut down equipment when "black smoke" becomes apparent (28). The Mine Health Research Advisory Committee recommends that mines using diesel-powered equipment should employ con- trols to minimize miner exposure to diesel exhaust (29). By measuring the carbon-hydrogen-nitrogen content of dust samples, Reinbold (20) estimated diesel particulate to be 60 to 90 pet of the respirable dust at two underground mines. Measured concentrations of respirable, combustible dust of up to 1.5 mg/m 3 were observed by Reinbold. At such levels diesel soot can contribute significantly to the respirable dust load in coal mines. 1 Physical scientist, Twin Cities Research Center, Bureau of Mines, Min- neapolis, Minnesota. * Italic numbers in parentheses refer to items in the list of references preceding the "Calculation of Load Factors" section of the end of this paper. STATUS OF RESEARCH ON FUEL ADDITIVES There are many types of commercially available fuel ad- ditives that are designed to perform a variety of functions. "Preflame" additives correct problems that occur prior to burning (i.e. , storage stability, flow in cold weather, water contamination) and include dispersants, pour-point depressants, and emulsifiers. "Flame" additives promote complete burning of fuel in the combustion chamber and include atomizers and combustion catalysts. "Postflame" additives are designed to reduce engine deposits, gaseous emissions, and are used for visible smoke control in over- the-road vehicles. This approach may also be appropriate for mine operations not requiring, or as an alternative to, the high-efficiency diesel particulate filters (DPF) currently under development and evaluation. However, the effec- tiveness of fuel additives for controlling soot mass from diesel-powered mining equipment has not yet been demonstrated. The use of postflame fuel additives in over-the-road vehicles has been widely reported. Norman (19), Miller (18), Golothan (11), Tessier (25), Turley (27), and Apostolescu (3-4) all showed that barium-based additives reduced visible smoke from diesel engines. In most cases the soot measurements were done using smoke meters— either light transmission (opacity) or filter reflectance (Bosch). However, other research studies have reported conflict- ing results. Truex (26) determined that a barium additive reduced smoke opacity by 30 to 40 pet, but that particulate mass, measured gravimetrically, was relatively unaffected. Kittleson (15) and Hare (13) found that smoke, measured with a reflectance smoke meter, was reduced by additive- 80 treated fuels, but total particulate emissions, measured gravimetrically, were increased. Kittleson noted that one effect of the additive was to reduce the particle size of diesel smoke. Because the response per unit mass of optical smoke meters often decreases with decreasing particle size, the smoke meters underestimated soot mass. For the purpose of predicting additive effectiveness for reducing soot in mining equipment, much of the earlier research is considered deficient in at least two general areas: The engines tested were not representative of those used underground and there was too much emphasis on visible smoke reduction and not enough attention was given to measuring the actual soot mass concentration emitted. The Bureau of Mines evaluated Lubrizol 565, a postflame fuel additive, to determine effects on diesel par- ticulate emissions in a typical engine used in mining equip- ment (32). It is a commercially available, barium-containing additive and is sold as a smoke suppressant. All the work was carried out in the diesel engine emis- sions test facility located at the Bureau's Twin Cities (Minnesota) Research Center (TCRC). Gaseous and par- ticulate emissions were measured for both barium-treated and untreated fuels. The particulate emissions were monitored to determine mass concentration and particle size distributions. Limited chemical and physical analyses of the soot samples were carried out to determine the major soot components. The data were analyzed to determine the effectiveness of different additive concentrations for reduc- ing soot, to assess the effect of the additive on gaseous emissions, to help explain why certain types of mass con- centration instruments furnished unreliable measurements for treated fuels, and to evaluate changes in emissions that might affect the health of miners. Additional details on test procedures and results for steady-state engine operation are given by Zeller (32). In this paper the steady-state data are further analyzed to predict additive effectiveness when used in engines operated at assumed duty cycles and load factors. SOOT EMISSIONS CHARACTERISTICS FOR UNTREATED FUELS In this section the results of the Bureau's steady-state tests are used to predict soot emissions from mining equip- ment operated at assumed duty cycles. estimate compares with measurements of respirable com- bustible dust (assumed to be mainly diesel soot) in two mines ranging between 0.2 and 1.5 mg/m 3 (20). STEADY STATE OPERATING CONDITIONS Test Variables and Measured Soot Levels The Bureau's tests were conducted on a four-cylinder, 7-L diesel engine (Caterpillar 3304 PCNA) rated for 85 hp at 1,800 r/min. It is a four-cycle, water-cooled, prechamber engine. Engines of this type, which have been certified by the Mine Health and Safety Administration (MSHA), are used in underground coal mines. The test conditions and soot emission levels are summarized in table 1. The soot levels are also plotted in figure 1. Table 1. — Soot mass concentrations measured at five steady-state loads and 1,200 r/min for a Caterpillar 3304 Test mode 1 Engine parameters: BMEP psi Load pet of full Power hp Torque ft-lb Fuel rate Ib/h Fuel-air ratio Av soot emissions: Cone ' mg/m 3 Rate 2 g/h 7.5 7 4.6 20 5.72 0.012 15.4 2.8 49.0 50 33 145 13.3 0.027 36.1 6.6 74.4 75 49 217 19.2 0.039 57.0 10.5 90.5 90 60 261 22.2 0.046 92.4 17.0 103.9 100 66 290 27.9 0.056 222 40.7 BMEP Brake mean effective pressure. 1 Raw exhaust adjusted to a temperature of 75° F and 1 atm. 2 Based on 107-ft 3 /min volume flow from engine. These results show that pipe-end soot concentrations ranged from 15 mg/m 3 (2.8 g/h) at idle to 222 mg/m 3 (40.7 g/h) at full load. Even when diluted by ventilation, these high levels of emissions from diesel -powered equipment can significantly increase particulate levels in mines. For ex- ample, assuming 100 fVVmin of ventilation air per horsepower, based on MSHA ventilation recommendations for diesel-powered equipment (28), estimated in-mine levels for the tested engine range between 0.2 to 3 mg/m 3 . This Air Density or Altitude Effects on Soot Levels Soot emissions are affected by changes in air density resulting from either pressure (altitude) or temperature changes. The laboratory test data plotted in figure 2, for the Caterpillar 3304 engine, show how particulate emis- sions increase by almost a factor of 2 for less than a 10-pct reduction in oxygen concentration. This change in oxygen concentration is equivalent to an altitude change of about 3,000 ft. Also, a temperature increase of about 45° F, at constant pressure, would have the same effect. It is important to realize that the factor in common for these data is mainly the engine's fuel-air (F-A) ratio. Cer- tification tests of diesel engines require that the maximum F-A ratio be determined based on CO emissions. The barometric pressure at which these tests are conducted is recorded also. For operation at significantly lower barometric pressures, such as those at mines in moun- tainous areas, regulations (28) require engine adjustment (i.e., the engine is derated) so that this maximum F-A air ratio is not exceeded. Effects of Engine Speed and Load on Soot Levels Diesel exhaust-gas composition is related chiefly to the engine's F-A ratio. Lower F-A ratio values result in lower CO and soot emissions. The engine speed and load deter- mines the F-A ratio. An F-A ratio of about 0.01 is present during idle, but at higher power output the ratio is closer to 0.05. Waytulonis (30) recommends that engines be operated at higher speeds, rather than lower speeds, to avoid rich or high F-A ratios. For a given load, operating at the highest speed that will accomplish the required work results in a lower F-A ratio. Operating at a low speed under high load is defined as lugging the engine. This condition should be 81 250 200 - £ o 150 - < tr h- z UJ o z o o o o in 100 - 50 v!;!v!v!v!v!v!v; 50 75 90 STEADY-STATE ENGINE LOAD, pet of f u I 100 Figure 1.— Diesel soot levels from a Caterpillar 3304 engine at five steady-state loads and a speed of 1 ,200 r/min. 3,000 350 I00 0.0 1 45 EQUIVALENT ALTITUDE ABOVE SEA LEVEL, ft 2,000 1 ,000 0.0 1 5 OXYGEN CONCENTRATION, lb/ft 0.0 1 55 3 0.0 1 6 Figure 2.— Air density or altitude effects on soot levels at full engine load and 1,200 r/min. ^HHHB 82 avoided to minimize CO and soot emissions. This is con- firmed by the test results shown in table 1. It can be seen that as the F-A ratio increases from 0.012 at mode 1 to 0.056 at mode 5, average soot concentrations increase from 15.4 mg/m 1 to 222 mg/m s . EFFECT OF DUTY CYCLES AND ENGINE LOAD FACTORS The importance of this discussion is that the concepts of duty cycles and load factors are essential to analyzing the production and full-shift effects of additives on soot emissions. Description of Duty Cycles The duty cycles for diesel-powered equipment in underground mines consist of many combinations of com- plex modes of operation (I). For each type of equipment- production, haulage, and utility— a specific, repetitive se- quence of operations is usually apparent and is referred to as the machine's duty cycle. Only a few specific operational modes, out of an infinite number of speeds and loads, are necessary to describe the duty cycle of a piece of equipment. Alcock (i) determined that 90 pet of a load-haul-dump (LHD) duty cycle is ade- quately accounted for by combinations of the eight modes listed in table 2. Except for idle conditions, note that engine speed does not fall below 80 pet of the full rated speed. Mode 8, transient, is that part of a duty cycle in which engine speed and load change continuously. equipment averaged SLF's of 30 to 40 pet and PLF's of 60 to 70 pet. The effects of soot emissions of different duty cycles, all at the same load factor of 50 pet, are illustrated in figure 3. (Note that the soot concentration scales differ in figures 3A-3D.) These calculated emissions are based on the steady- state data in figure 1 and table 1. The unusual duty cycles in figures 3A and 3D were selected because they represent two extremes: the duty cycles corresponding to the minimum and maximum emis- sions for a load factor of 50 pet. For any load factor, minimum soot emissions occur for the duty cycle consisting simply of steady-state operation at the engine load that is numerically equal to the load factor. For the 50-pct load fac- tor in figure 3A, this means operation at an engine load of 50 pet of full load for the total duration of the duty cycle. Any other duty cycle, having a 50-pct load factor, will result in greater soot emissions. The duty cycle having the maximum emissions, for any load factor, is that which consists of the maximum possi- ble operating time at full engine load. The remaining time is spent at the minimum engine load condition. The opera- tion times for the duty cycle for maximum emissions are calculated from the following simultaneous equations: t^ELi) + t 2 (EL 2 ) = LF t, + t, = 100, (1) (2) where t = time, EL = emission level, and LF = load factor. Table 2.— Load-haul-dump equipment operating modes, percent of full rated Engine speed Engine load 100 100 100 75 100 50 100 25 90 100 80 100 Idle (') None 0) Mode 1 2 3 4 5 6 7 8 1 Transient. Specific duty cycles are determined by the amount of time equipment operates in each of the modes in table 2. Once a machine's duty cycle is approximated, it is possible to calculate its load factor (LF), which is defined as the ratio of the actual work performed by a machine to the maximum work that could be performed in an 8-h shift. The exact calculation of load factors is presented in the section follow- ing the references of this paper. As a practical matter, a load factor can be approximated by the time- weighted-average fuel rate divided by the fuel rate at the full-speed, full-rated load. This method tends to underestimate load factors because fuel consumption is not exactly proportional to power developed at high loads. It is sometimes convenient to define two types of load factors: a shift load factor (SLF) corresponding to a full-shift or 8-h duty cycle and a production load factor (PLF), which is based on the time that the machine is engaged in actual production. Alcock (1) found that SLF's generally range be- tween 50 and 80 pet of PLF's because most mining equip- ment is engaged in actual productive work for only 4 to 7 h of an 8-h work shift. In hard-rock mines, for example, LHD For EL, = 7 pet of full load, EL 2 = 100 pet of full load, and LF = 50 pet, the equations are solved to give tj = 53 pet and t 2 = 47 pet, the values displayed in figure 3D. In general, soot emissions increase with increasing distribution or spread of operating modes around the engine load numerically equal to the load factor. This trend is ap- parent in figure 3, which shows emissions increasing from the minimum of 36 mg/m 3 (6.61 g/h), figure 3A, to 110 mg/m 3 (20.3 g/h) in figure 3D. Soot Envelopes The emissions data (figure 1 and table 1) for the Cater- pillar 3304 are plotted in figure 4. Based on the discussion in the previous section, the points are connected by a smooth curve that defines the minimum soot emissions for all load factors. The duty cycles corresponding to maximum emis- sions for each load factor are calculated from equations 1 and 2. The maximum emissions determined from these duty cycles all lie on the straight line connecting the maximum and minimum loads. The two lines in figure 4 define the boundaries of the soot emissions envelope for the tested engine. In other words, the soot emissions from this engine, for any arbitrary duty cycle, all fall within the envelope in figure 4. For ex- ample, the data in figure 3 for a 50-pct load factor are plot- ted in figure 4 to illustrate emission's envelope characteristics. Limitations on Use of Envelope Concept Unfortunately, there are limitations on the applicability of the emissions envelope in figure 4. For example, this 83 £ < cc LU o z o o I- o o - 1 1 1 1 1 1 1 1 1 1 I 1 1 150 E 100 90 75 50 25 7 ENGINE LOAD, pet of full Soot 100 90 75 50 25 7 ENGINE LOAD, pet of full 100 o < or 50 uj o z o u I- o Soot Figure pet. The 250 3.— Soot emissions, calculated from steady-state data, for four duty cycles and for a constant engine load factor of 50 lengths of the stacked segments in the emissions bars are proportional to the soot levels for the indicated engine loads. 200 CD < 50 UJ ^ 100 o o o o CO KEY ° Steady-state emissions A Duty-cycle emissions 50 - _L 20 40 60 ENGINE LOAD FACTOR, pet 80 100 Figure 4.— Soot emissions envelope, calculated from steady-state data, for the Caterpillar 3304 engine, 1,200 r/min, and untreated fuel. l^l^M 84 envelope is for operation only at an engine speed of 1,200 r/min. Operation at other engine speeds would likely pro- duce different emissions envelopes. Also, average emission values were used for the full-load tests because of the varia- tion (fig. 2) observed for air density changes. In general, an infinite number of emission envelopes could be defined for all combinations of engine adjustment (such as maximum power setting), engine speeds, and ambient pressure (altitude). Finally, an assumption in developing these con- cepts is that emissions for transient or multimode opera- tion of diesel engines can be calculated from steady-state data. There is some evidence that this is not always true (8-9). TREATED FUELS— EFFECTS ON ENGINES AND EMISSIONS Even though these fuel additives reduce soot emissions, their use may also have some undesirable consequences. The purpose of this section is to review the experience of the Bureau and others concerning the effects of barium- based fuel additives on engines, soot measuring in- struments, gaseous emissions, and soot composition. ENGINE OPERATION AND MAINTENANCE Engine Deposits Barium-based smoke suppressants added to the fuel definitely increase engine deposits. Brandes (7), using 0.50 vol pet of additive, weighed engine parts (truck engines ranging between 240 and 480 hp) before and after periods of operation. He determined that deposit mass for treated fuels was greatly increased over that measured for un- treated fuels. However, Brandes did not observe any prob- lems of wear or maintenance attributable to these deposits. Golothan (11) found that engines, prone to injector clog- ging, exhibited some performance deterioration when fuel additives were used. Cleaning the injectors restored performance. Golothan also noted that the use of an uniden- tified dispersant in the fuel eliminated the clogging problem. Saito (22) measured increased deposits in bus diesels for 60,000 miles of operation but did not observe any excessive engine wear, fuel consumption or injection problems, or adverse lubrication effects. Norman (19) conducted exten- sive tests in the laboratory and over the road on engines ranging between 43 and 2,700 hp. He concluded that the additives actually promoted engine cleanliness. Miller (18) found that additives reduced piston ring wear because car- bon deposits were reduced. Ziejewski (33) also determined that barium additives promoted engine cleanliness in ex- periments with vegetable-based fuels (sunflower oil). For these experimental fuels treated with barium and compared with untreated fuels, he noted that carbon deposits in com- bustion chambers and injector deposits were both reduced. Ziejewski also observed a modest horsepower increase, but Apostolescu (3-4) observed no effect of fuel additives on engine performance. Compatibility Neither the Bureau nor other researchers experienced any compatibility problems between the additive tested and fuels, lubricants, or other additives. Nevertheless, whenever additives are used in fuels and lubricants, the operator must be concerned about compatibility. Regarding fuels, Miller (18) claimed that barium-based fuel additives promoted "... better storage stability, im- proved antistatic properties, and antibacterial protection." Regarding lubricants, researchers have not observed any problems with fuel additives, but work by Rounds (21) in- dicates that soot itself inhibits the antiwear additives con- tained in lubricants as determined in laboratory wear tests ' (four-ball test). This effect was not observed in engines. Tessier (25) claimed that additives reduced clogging and therefore extended service intervals for catalytic mufflers used on bus engines. The converters had to be cleaned regularly when the engines were operated with untreated fuels. When barium-treated fuels were used, further clog- ging and backpressure buildup was prevented and the prior clogging and backpressure was significantly reduced. GASEOUS EMISSIONS NO, In the Bureau's additive tests, the only gaseous emis- sion measured was NO x . The results, in figure 5, show that NO x emissions are not affected significantly Oess than 10 pet change) when barium -treated fuels are used. Figure 5 shows only the results for the manufacturer's recom- mended concentration of 0.36 wt pet, but the results at other tested concentrations were similar. Other studies (3-4, 11) came to similar conclusions concerning NO, and other emis- sions such as CO and C0 2 . This is a positive result in the sense that it appears that barium can be used for soot reduc- tion without concern for adverse effects on other emissions. Volatiles Figure 6 shows the effect on volatiles of the barium ad- ditive used at the manufacturer's recommended concentra- tion of 0.36 wt pet. Except for the minimum engine load of 7 pet of full load, additive usage produced some reduc- tion in volatiles. The significance of this result is unclear, but it is considered to be a positive result because the volatile fraction contains many carcinogenic and mutagenic substances that are potentially harmful (14). SMOKE AND SOOT MEASURING INSTRUMENTS The response of three different types of aerosol monitor- ing instruments are shown in figure 7. Two of the in- struments, the Bosch and opacity meters, are intended specifically for monitoring diesel exhaust. The third instru- ment, the GCA RAM-1, is intended for monitoring respirable mineral dusts and is factory-calibrated for silica dusts. The responses of these instruments were compared with gravimetric measurements of diesel soot concentration. Ex- cept for the Bosch response at 0.18 wt pet, all three in- struments underestimate the concentration of diesel ex- haust from barium-treated fuels. Furthermore, the percent 800 E a a z" o I- < 600 - 400 UJ o z o o 200 85 KEY Untreated Treated 50 75 90 ENGINE LOAD, pet of full 100 Figure 5.— The effect on steady-state NO, emissions of a barium-based fuel additive used at the manufacturer's recommended concentration of 0.36 wt pet. 12 E z" o I- < or t- z UJ u z o o UJ o > 10 KEY Untreated ^^j Treated 50 75 90 ENGINE LOAD, pet of full 100 Figure 6.— The effect on steady-state hydrocarbon (volatile) emissions of a barium-based fuel additive used at the manufacturer's recommended concentration of 0.36 wt pet. ^l^^^H 86 1.2 1.0 < Z> t .8 < UJ I- z < .6 .4 itive KEY concentration, wt pet i-xSii o.i8 ■I 0.36 Hi 0.72 BOSCH SPOT OPACITY TYPE OF OPTICAL INSTRUMENT 6CA RAM- I Figure 7.— Increasing additive concentration in the fuel causes a reduction in response of three different types of optically based, particulate concentration measuring instruments. of underestimation is directly related to the barium con- centration in the fuels— the higher the concentration of barium, the greater is the degree of underestimation. The reasons for this are related to both size and composition changes of the soot particles as discussed by Zeller (32) and others (12, 15-16). Many studies of additive effectiveness for soot reduction relied on either the Bosch or opacity meters. This soot measuring bias explains why such studies (11, 18-19) con- cluded that additives appeared more effective for reducing smoke than other studies (6, 15, 32), which measured soot using gravimetric methods. It should be apparent that these types of instruments must be used with care when measur- ing soot emissions from engines using treated fuels. HEALTH Bureau (32) results show that up to half the barium in- troduced into the fuel ends up in the exhaust in the form of respirable barium compounds, which can have two adverse effects: (1) the added particulate in the form of barium compounds adds to the general dust loading in coal mines and increases compliance problems with dust stand- ards and (2) up to 25 pet of the emitted barium compounds are soluble and therefore toxic. The Bureau's results also show that the maximum con- centration of barium in the raw exhaust from the Cater- pillar 3304 engine, at full load, is about 25 mg/m 3 when the recommended additive concentration of 0.36 wt pet is used in the fuel. The assumptions of a maximum limit (11) of 25 pet as soluble barium and a worst-case dilution of 20:1 (5) results in 0.31 mg/m 3 toxic barium in the mine atmosphere for the tested engine at full load (100 pet load factor). This is less than the full-shift, time- weighted TLV of 0.5 mg/m 3 (2), but there is little margin for error. If more than one piece of equipment is operating in a drift with limited ventila- tion the TLV could be exceeded even allowing for less than full-load operation. The preceding is certainly a worst case situation. There are a number of controls available for substantially reduc- ing soot emissions: (1) ventilation factors of at least 60:1, (2) a load factor of 40 to 60 pet instead of the 100-pct value assumed, and (3) use of the additive at half the recom- mended concentration. By such means, a mine operator should be able to control the concentration of soluble barium from a single piece of equipment to less than 10 pet of the TLV. Additional diesel-powered equipment would, of course, increase the amount of emitted barium. PARTICULATE SOOT EMISSIONS Most of the results in this section are for a specific engine (Caterpillar 3304), at one speed (1,200 r/min), and steady-state loads. Other engines, speeds, and duty cycles might lead to different results and conclusions. At this time the Bureau has insufficient information available for estimating the effects of different engines. 87 Steady State Engine Load and Additive Concentration Effects The measured soot emissions from a Caterpillar 3304 engine for both untreated and barium-treated fuel are presented in figure 8. Tests were conducted at three additive concentrations: 0.18 wt pet, 0.36 wt pet (manufacturer's recommended concentration), and 0.72 wt pet. Considering only the treated fuel results in figure 8, increasing additive concentration generally increased soot levels at the same engine load. The additive appears to be generally more ef- fective at high engine loads than at light loads. Only at full load were particulate soot emissions actually reduced for fuel treated with either the manufacturer's recommended concentration or double that concentration compared with untreated fuel. At engine loads equal to or less than 90 pet of full load, these two fuel treatments actually increased soot emissions over those for untreated fuel because the barium compounds added to the exhaust were greater than the carbon level reduction. For fuel treated with 0.18 wt pet additive, half the recommended concentration, soot reductions were measured at the three highest engine loads, although the reduction at 75 pet load was small. Soot Composition Soot particulate from untreated fuels consists of two ma- jor components— solid carbon and volatiles. When fuels are treated with barium, an additional soot component, con- sisting of barium compounds, is added. The data in figure 8 are replotted in figure 9 to explicitly show the concentra- tions of both the carbon (solid carbon plus volatiles) and barium compound fractions. The data for 75-pct load are not shown in figure 9 because barium concentration data were not available. The following trends are apparent: (1) The barium com- pound fraction for the treated fuels generally increases with increasing additive concentration in the fuel; (2) for all four engine loads, reduced carbon was observed for treated ver- sus untreated fuels, and (3) the carbon concentration is nearly independent of additive concentration at each of the four engine loads for treated fuels. In figure 10 the carbon fraction data are plotted against additive concentration to emphasize that additive effec- tiveness for reducing carbon was independent of additive concentration. This result suggests that the additive con- centration could be reduced below the minimum tested level of 0.18 wt pet and still achieve significant carbon reduction and also reduce the undesirable concentration of barium compounds. Duty Cycle and Load Factor All of the results in the previous section were for steady- state engine operating conditions. In this section the effects of equipment duty cycles are considered. 250 T T 200 e o 150 < uj o o o o en 100 50 KEY Additive concentration, wt pet I Untreated 0.18 0.36 0.72 50 75 ENGINE LOADS, pet of ful 90 100 Figure 8.— Additive concentration effects on steady-state soot emissions from a Caterpillar 3304 engine for five engine loads at 1,200 r/min. 88 250 200 150 100 50 -~i 1 r 100 pet E z* o < o ■z. o o h- o o (A) 1 r KEY Barium Carbon 90 pet 75 pet 7 pet J_ 0.18 0.36 0.72 0.18 0.36 072 0.18 0.36 0.72 ADDITIVE CONCENTRATION, wt pet 0.18 0.36 0.72 Figure 9.— Effect of barium fuel additive concentration on the carbon and barium compound soot components for four engine loads at 1 ,200 r/min. 250 200 E ■£ o < cr l- z UJ o o o CD CC < 0.2 0.4 0.6 0.8 BARIUM ADDITIVE CONCENTRATION, wt pet Figure 10. — Carbon concentration in exhaust soot is nearly independent of the concentration of the barium-based fuel additive. 89 Manufacturer's Recommended Concentration In figure 11 the emissions envelope for the manufac- turer's recommended concentration, based on the data in figure 8, is shown together with the soot envelope for un- treated fuel from figure 4. Note that there are a number of intersections of these envelopes about which certain properties can be inferred. For all load factors smaller than that associated with the intersection at A (LF = 13 pet), treated-fuel operation will always produce greater emissions than untreated fuel. For all load factors greater than that associated with the intersection at D (LF = 94 pet), treated fuel will always produce decreased particulate emissions compared wth untreated fuel. Note that these observations depend only on the value of the load factor and are independ- ent of the actual duty cycle or distribution of engine loads. For all the load factors between B and C, mixed results will be observed. For those duty cycles consisting of large percentages of full-power or near full -power operation, some emissions reduction will result for treated fuel. For duty cycles consisting of narrow distributions of operational modes around the numerically equivalent engine load, emis- sions will increase for treated fuels. The interpretations for load factors between A and B and between C and D are as follows: For those load factors between A and B, treated fuel will produce greater emis- sions when the duty cycles are identical for the two fuel con- ditions. Between C and D, treated fuel will produce re- duced emissions for identical duty cycles. Double and Half the Manufacturer's Recommended Concentration The soot envelope for double the manufacturer's recom- mended concentration is shown in figure 12. For load fac- tors less than about 40 pet, an additive concentration of 0.72 wt pet will increase soot emissions compared with untreated fuel for identical duty cycles. Even at near full-power opera- tion for the full shift, soot reduction is only on the order of 13 pet (from 222 down to 190 mg/m 3 ). As noted pre- viously, the use of double the manufacturer's recommended concentration is generally counterproductive. The results for half the manufacturer's recommended concentration in figure 13 are more promising. They show that for similar duty cycles and for load factors greater than about 65 pet that soot reductions are expected. Furthermore, for any duty cycle consisting of substantial time at or near full-power output, a decrease in soot emissions is anticipated for load factors greater than about 15 pet. Only if the duty cycle consists of a narrow distribution of operational modes around the engine load numerically equal to the duty cy- cle are particulate emissions likely to increase for treated fuels. 250 •*> 200 E ■£ o < cr i- UJ (J z o o h- o o (J) 150 100 KEY d Untreated o Treated 50 20 40 60 ENGINE LOAD FACTOR, pet 80 100 Figure 1 1 .—Soot emissions envelopes for untreated fuel and for fuel treated with the manufacturer's recommended additive con- centration of 0.36 wt pet. Interpretation of meaning of intersections at A, B, C, and D are discussed in text. 90 250 200 - E O 150 - H < o z o u H o o 100 - 50 - 1 1 1 KEY o Untreated 1 - o Treated y^^^ / 1 - - i i i i 20 40 60 ENGINE LOAD FACTOR, pet 80 100 Figure 1 2.— Comparison of soot emissions envelopes for untreated fuel and for fuel treated with twice (0.72 wt pet) the manufac- turer's recommended additive concentration. CZ3KJ 200 l 1 1 1 KEY yS \ o E a Untreated / \ E o Treated / o 1 50 - H < a. i- 2 UJ <~> 100 ^r ^^"^ / / - z o o t- o o 6 X O [I 5 o Ixl a. C/5 l±J < tr GO Prechamber diesel 1,600 r/min Hydrogen engine at 1,400-2,200 r/min 100 200 300 400 500 600 BRAKE MEAN EFFECTIVE PRESSURE, kPa 700 800 Figure 1 .—Brake specific oxides of nitrogen versus brake mean effective pressure for the hydrogen-fueled Caterpillar 3304 engine compared to two prechamber diesel engines. 110 particularly at extremely lean air-fuel mixtures (5-6). Hydrogen peroxide is not encountered at the hydrogen equivalency rates at which the converted engine normally operates, and any unburned hydrogen is removed by a catalytic converter placed in the exbaust. The phase III activities included the fabrication and testing of a unique hydrogen storage system using metal hydrides. The system was tested under a wide range of engine operating conditions in the engine test cell (7). Also during phase HI, novel heat transfer designs were explored to reduce the hydrogen leakage potential of the hydrides in case of accidental damage. This paper focuses on phase IV, the transfer of the previously developed components to a test vehicle and the construction of additional fuel modules with advanced heat transfer capabilities (8). VEHICLE DESCRIPTION The vehicle used in this program is an EIMCO 975 utility truck. The truck (figure 2) is an articulated four- wheel-drive general-purpose vehicle with a 4,550-kg payload capacity. It is normally used to transport personnel and material underground. There are several reasons why the EIMCO 975 was selected for this conversion. The previous engine development work had been applied to a Caterpillar 3304 engine. The EIMCO 975 series vehicles are often sup- plied with 3304 engines, which deliver adequate power for this machine. This also provides a familiar basis for com- parison for experienced operators of diesel-powered utility trucks. The EIMCO 975 utility truck is a member of a fami- ly of vehicles including shotcrete machines, personnel car- riers, and lubrication trucks, so the test results may be ex- trapolated to a variety of uses. A utility truck is also a good choice for future underground demonstration activities because new technology in underground mining should first be proven in a noncritical support vehicle, rather than in a production machine. As received from the factory, the vehicle was equipped with a 57-kW Deutz F6L 912 W air-cooled diesel engine. The substitution of the Caterpillar water-cooled hydrogen engine for the Deutz air-cooled engine required several modifications to the vehicle. Two identical, heavy-duty radiators were mounted in series ahead of the hydrogen engine; one for engine cool- ing and the other for intake charge-air cooling. The fan was downsized from the standard Caterpillar unit to reduce noise levels, and since about half of the engine's cooling load is absorbed by the hydride fuel system, the higher perform- Figure 2.— Photograph of the EIMCO 975 utility vehicle converted to hydride fuel. Ill ance fan is not required. The radiator mounts, air ducting, and fan shrouding were custom fabricated. The forward radiator dissipates heat from the aftercooler. Coolant is cir- culated between the aftercooler and radiator by an accessory pump adapted to a magneto drive gear. This coolant loop is entirely separate from the engine's coolant. The inlet air temperature is regulated at 40° C by a thermostat, which controls the circulation rate in the charge-air coolant loop. A transmission oil cooler was also added to the liquid cooling system of the hydrogen engine to replace the air-cooled Deutz unit. ENGINE MODIFICATIONS The engine, developed during phase II, was essentially unchanged from its dynamometer test configuration. A belt- driven air pump was installed to provide positive ventila- tion for the crankcase as shown in figure 3. The airflow from this pump dilutes blow -by gases with fresh air to maintain low hydrogen concentrations in the crankcase. This air is filtered by a filter cartridge mounted to the side of the cylinder block. The air flows into the gear case at the front of the engine, through the crankcase, up through the push- Power unit Articulation joint Exhaust Underhood Catalyst Crankcase air pump Thermostat Filter Turbocharger Exhaust Coolant supply \ Coo la nL retur n Engine Oil dropout j Cronkcose Iter LL Vapor loop Governor _'._ Engine fuel pressure regulator After- cooler X0-o|- ! (* V ir cleaner Venti "^^Inlet Coolant_ return "\ L& Manual Solenoid shutoff shutoff W act Cold-stort coolant supply Main fuel coolant supply Flexible lines Figure 3.— Crankcase ventilation system and governor circuit on the prototype vehicle. 112 rod passages, and out through the rocker cover vent. As the air goes through the engine, it picks up a significant amount of oil mist, especially at near-peak engine speeds. To solve this problem, a coalescing filter was installed to condense this mist and return it to the oil sump before crankcase ven- tilation air is discharged into the engine's intake system. Figure 4 shows the performance of the ventilation system relative to the minimum flow (dashed line) required to pre- vent dangerous hydrogen buildup. The turbocharger used during phase I engine tests was modified by increasing the area-to-radius (A-R) of the tur- bine from 0.43 to 0.51. With the previous turbine, boost was supplied at engine speeds as low as 700 r/min. The torque converter on the truck will not transmit high torque at such low engine speed. The larger turbine provides ample low- speed torque and reduces exhaust backpressure at high engine speeds. This engine is limited by a speed switch attached to the tachometer drive. This dual-point unit operates one set of points at 2,150 r/min and the other at 2,400 r/min. The first set is connected to a solenoid valve on the dome of the hydrogen regulator, as shown in figure 3. When the engine speed exceeds 2,150 r/min, the air pressure above the diaphragm is relieved and fuel pressure falls to 1 atm regardless of turbocharger boost. Engine torque is thereby limited to naturally aspirated levels (approximately 400 kPa BMEP) until the speed drops below 2,150 r/min. The second set of points is connected to the main hydrogen sup- ply solenoid valve. If the engine speed exceeds 2,400 r/min (9 pet overspeed), the fuel supply is interrupted. This two- stage governor provides smooth control of the engine torque at 2,150 r/min under most operating conditions and precludes operation beyond 2,400 r/min. 900 800 700 E 600 Ll) f- < ac 500 z o r- < _l 400 K Z UJ > 300 ir < 200 100 T Measured airflow from air pump with filter Minimum required for dilution to below flammability limit Idle / Y 400 _L 600 800 1,000 1,200 1,400 1,600 1,800 2,000 2,200 ENGINE SPEED, r/mln Figure 4.— Performance of crankcase ventilation system showing that dilution rates exceed minimum requirements. 113 The electrical modifications to the engine are shown in figure 5. The main hydrogen supply solenoid valve also con- trols the start-stop sequences. A procedure, always followed during engine tests, has proven effective at preventing in- take backfires and exhaust afterfires. A three-step starting sequence of cranking the engine, energizing the magneto, and then supplying the fuel assures that no unburned fuel- air mixtures accumulate in the engine before starting. To accomplish this, an oil pressure switch is installed in the ignition and hydrogen solenoid circuits. When cranking is begun, the oil pressure is zero. This allows the oil pressure switch to remain in its relaxed position, with the magneto grounded and the hydrogen solenoid closed. When the oil pressure reaches 35 kPa the switch opens the magneto ground circuit and completes the hydrogen solenoid circuit. The magneto instantly begins firing the spark plugs, and a second or so later, the engine starts when fuel arrives in the combustion chambers. The engine is stopped by switching off the hydrogen solenoid valve via the standard key switch on the operator panel. The fuel flow stops, but the magneto continues firing until the engine stops and oil pressure falls below 35 kPa. This is the inverse of the sequence followed during start- up. It assures that no unburned fuel-air mixture remains in the engine or intake system after shutdown. Other benefits of this oil pressure interlock are that the engine cannot be started without oil pressure and if the engine dies, fuel flow automatically stops. HYDRIDE FUEL SYSTEM The prototype vehicle is equipped with a metal hydride fuel storage system with 8 kg of hydrogen capacity. The hydrogen diffuses into the crystal structure of metal powders where it exists as an interstitial chemical com- pound (9). The powdered hydrides are contained in heat ex- changers that utilize waste heat from the engine's cooling system to break the chemical bonds, releasing the hydrogen fuel for the engine (10). The hydrides may be recharged by applying hydrogen pressure while they are being cooled. The total mass of the metal hydrides and their containers when filled with engine coolant is 1,226 kg. Underground mining vehicles may occasionally be operated in poorly ventilated areas. This places severe safety constraints on the design of hydride containers for underground service. The maximum accidental leakage potential of the hydride system should be less than the amount required to create an explosive atmosphere in a typical mining environment. One way to restrict the leakage potential of hydrides is to select alloys whose equilibrium hydrogen pressure at Governor Hydrogen solenoid Ignition itch ^d Kill Magneto Zl Oil pressure switch Figure 5.— Electrical circuit used to sequence engine start-stop procedure. 114 ambient temperature is less than atmospheric pressure. Such alloys can leak little or no hydrogen until they are heated by engine coolant. If small segments of the fuel storage system are heated, one at a time, then only the heated segments can release significant amounts of hydrogen during an accident. After each segment is depleted, it can no longer release hydrogen. This concept emerged during the early phases of the project, and many design decisions were influenced by it. For example, the choice of parallel induction over competing methods of fuel injection was made because it has a lower fuel pressure re- quirement than the others (11). The engine can achieve full power with as little as 275 kPa of hydrogen pressure upstream of the final fuel regulator. The modular configuration of the hydride system, built in phase HI, also recognized the need for segmenting fuel storage. Figure 6 shows the resulting design. The main difficulty in implementing a modular mine- safe hydride system is that each module must be large enough to supply pressurized hydrogen at the engine's fuel demand rate. Hydrides can only release hydrogen if heat is supplied to balance the endothermic decomposition reac- tion (12). At the outset of phase HI, the state of the art in hydride fuel containers did not permit large enough heat exchange rates in containers small enough to be mine safe. Despite this shortcoming, the project went forward using state-of-the-art hydride containers, while studying advanced heat transfer methods. Therefore, the first 14 hydride modules were built with inadequate heat transfer capabilities to allow segmentation. Several had to be heated in parallel to meet the pressure and flow requirements of the engine at full rated power. To make matters worse, hydrides with pressure well above 1 atm were needed to meet some transient conditions. The hydrides chosen for the phase III work had 25° C isotherms as shown in figure 7. Of the 14 modules built dur- ing this phase, 2 contained the cold-start hydride (upper curve); the remaining 12 formed the main bed (middle curve). Altogether, the 14 modules contained 6 kg of hydrogen. The phase HI system worked well during dynamometer tests (3), but it cannot be considered mine safe because its potential for hydrogen release is too great. Toward the end of phase HI, an improved module had been developed with nearly four times the heat transfer capabilities of the earlier design. Most of the components were the same as in figure 6. The differences are found in- side the tubes. Figure 8 is a cross section of a tube in a heat- transfer-enhanced module. The copper brush bristles are added to conduct heat radially and at much higher rates than hydrides alone. The hydride powder is mixed with tetrafluoroethylene (TFE) powder (used as a flow aid) to im- part fluidlike properties. This is effective in preventing tube strain when the hydrides expand by 20 pet to 25 pet during recharge (13-14). The hydrogen flows in and out through a polypropylene filter, supported by a perforated stainless steel tube. One heat-transfer-enhanced module, containing the cold-start hydride, was built and tested during the latter portion of phase HI. It is capable of starting the engine at temperatures below 4° C and sustaining light engine loads until the coolant reaches operating temperature (71 ° C). An additional six modules were constructed during phase IV. These modules contained copper brushes (see figure 8) and hydrides with less than 1 atm pressure at am- bient temperature. This brought the total number of modules for the prototype truck to 21, with just over 8 kg of hydrogen content. Water jacket with inlet -outlet fittings Inlet fitting- Figure 6.— Construction schematic of heat-exchanger modules for the prototype mining vehicle. 115 100 0) 3 O W -Q O E o UJ X T KEY Absorption Desorption 10 Cold-start hydride .5 0.2 0.4 0.6 0.8 1.0 HYDROGEN/METAL, atom ratio Figure 7.— Twenty-five degree Celsius desorption (solid curves) and absorption isotherms for hydrides used on the prototype vehicle. 116 Porous plastic Filter support Hydride and TFE Copper bristles •Brush stem Figure 8.— Cross section of a heat exchanger tube with copper brush, flow-aid TFE powder, and filter. The 25 ° C desorption isotherm for the phase IV hydride is the bottom curve in figure 7. It is apparent that most of the hydrogen in the phase IV main bed is contained at less than 1 atm at 25 ° C. This means that very little hydrogen can escape in a mining accident. A ruptured hydride con- tainer cools itself to a temperature where the equilibrium hydrogen pressure equals atmospheric air pressure. The amount of hydrogen released is approximately proportional to the temperature change during the cooling process. The three hydrides used on the prototype truck have 1 atm equilibrium temperature (Tlatm) as listed in table 1. The subatmospheric hydride in the phase IV mine-safe modules has a Tlatm value greater than normal ambient temperature. Table 1.— Metal hydride thermal properties Fuel system Phase III cold start Phase III main bed Phase IV main bed P-desorption at 25° C, atm Tlatm, «C 10.3 3.4 .8 -28.6 -4.1 +30.0 Hydrogen Leak Simulation Hydrogen fuel release was simulated by discharging hydrogen as fast as it would flow from each of the three hydrides shown in figure 7. Three meters of 8-mm-ID tub- ing connected each test module to a large-diameter vent stack through a 9.5-mm manually operated ball valve. Prior to each test, the hydride was saturated with hydrogen at five times the midisotherm absorption pressure or 3.45 Pa, whichever was less. Tap water at 14° C was used to cool the modules during charging and to standardize the initial test conditions. At time zero, the ball valve was opened and hydrogen was discharged to the vent stack as rapidly as the plumb- ing would permit. After various periods of time (usually 15, 30, 45, or 60 min) the ball valve was closed and the test module was recharged from a calibrated volume (44.1 ± 0.3 L). The pressure change in the calibrated volume was noted, and compressibility and temperature corrections were made to reduce the amount of hydrogen absorbed dur- ing recharge. These data were used to determine the amount of hydrogen lost during each discharge test. The results are shown in figure 9. The hydrogen mass intercepts of each line indicate the amount of gas that could escape instantly in a catastrophic failure of each module. The slope of each line indicates the hydrogen release rate after the initial surge. As expected, the cold-start modules release the largest amount of gas., The 169-g initial discharge is about 41 pet of the module's hydrogen content. A hydrogen pressure tank or a liquid hydrogen Dewar could lose 100 pet of its contents, so even the cold-start hydride at its 41 pet loss potential is safer than these two conventional hydrogen storage techniques. The prototype truck contains three cold-start modules that, 117 280 240 200 Q LlI to < UJ _l LU tr LU o o rr o > X 60 120 80 40 KEY A Cold-start module □ Main module o Mine-safe module ■O" 1 1 ± 10 20 30 40 50 DISCHARGE PERIOD, min Figure 9.— Hydrogen released during simulated rupture of hydride modules. 60 70 together, could release 0.5 kg of hydrogen. About 150 m 3 of air would be needed to dilute the hydrogen below the lower flammability limit (4 pet by volume). Phase HI main modules can lose 89 g of hydrogen in- stantly in an accident. This is just over 20 pet of the con- tent; although this is very good compared with other hydrogen storage methods, if all 12 of the main modules were discharged, over 320 m 3 of air would be required to dilute the gas below the flammability limit. The mine-safe phase IV modules instantly released only 9 g of hydrogen; 3 pet of the content. If all six of these modules were discharged, 16 m 3 of air would dilute the hydrogen below the flammability limit. If all 21 modules were mine safe, the dilution air requirement would be only 56 m 3 . The prototype vehicle's hydride system, however, can release 1.63 kg of hydrogen, requiring 486 m 3 of dilution air. When the system is heated by engine coolant during normal operation, the potential hydrogen release is greater yet. The present hydride system cannot be considered mine safe except in well-ventilated tunnels. After the initial surge of hydrogen has escaped, and the hydrides have cooled to Tlatm, additional hydrogen flow is directly related to the influx of heat from the surroun- dings. Adjacent hydride modules, the support structure, and ambient air are cooled by the discharging module. During the tests that produced figure 9, the modules were in place, under the bed of the truck. The 1-in fiberglass insulation and sheet metal panels, which normally enclosed the hydrides, were not installed at the time of the test. Therefore, the test results show greater release rates than 118 would have occurred if the insulation were in place (see figure 10). The greatest leak rate was observed from the phase III main module. This is an unexpected result because the main module does not get as cold as the cold-start module. This is probably the result of better air convection past the main module because of its slightly different location on the vehicle. The total leak rate of the 21 modules on the prototype truck is 0.31 nrVmin. A very modest ventilation rate of 7.8 m 3 /min would dilute this flow to less than the 4 pet flam- mability limit. The phase III modules will eventually discharge virtually all of their hydrogen, because their am- bient temperature desorption pressures are greater than 1 atm. The mine-safe phase IV modules will release approx- imately 20 pet of their content over a period of about 40 h at normal ambient temperatures. Refueling Refueling tests during development showed that the 14 modules without heat-transfer enhancement required about 15 min for 90 pet recharge under typical conditions. The heat-transfer-enhanced, mine-safe modules are extremely fast owing in part to the more stable hydrides contained in them. With 2.75 MPa of hydrogen pressure and 47 L/min of cooling water at 20° C, the mine-safe modules refuel in 90s. The prototype vehicle is recharged using a small pump and heat exchanger circulating 38 L/min of engine coolant (30 pet antifreeze solution) through the shell, while 42 L/min of tap water at 10 ° C flows through the tubes. The recharg- ing cooler is shown in the lower left corner of figure 11. Two snap couplings connect the cooler to the vehicle. A third snap coupling (a different type for safety reasons) connects the hydrogen supply hose to the vehicle. Refuel- ing commences when pressure is applied. The heat of the exothermic absorption process is rejected to the cooler. Figure 12 charts the progress of a refueling operation at the vehicle test site. About 20 pet of the fuel is trans- ferred immediately. During this initial stage of charging, the heat of reaction is largely absorbed by the hydrides themselves as their temperature rises. Thereafter, the hydrogen is absorbed as rapidly as the relatively small recharge cooler can carry heat away. A larger cooler and pump would allow more rapid refueling if a greater flow of cooling water was available. The hydride fuel system has performed well during refueling and in supplying the engine with hydrogen fuel. The vehicle has been cold-started after overnight exposure to temperatures down to -9° C. There has been no measurable loss of hydrogen capacity in any of the 21 hydride modules. Some of the modules have been refueled over 50 times. Figure 13 is a schematic of the engine and hydride controls of the prototype vehicle. Figure 10.— Rear view of vehicle showing all hydride modules. 119 refueled (prior to installation of rear bumper). 120 90 1 1 1 1 1 1 II l_______L 80 - jf 70 60 o a. 2 50 o or < X ° 40 30 20 10 1 1 1 1 1 1 1 1 1 1 10 20 30 40 50 60 70 80 90 100 110 TIME, mm Figure 12.— Slow recharge of the hydride system using a small portable cooler. The dashed line indicates a 90 pet charge can be attained in less than 60 min. Cold-start coolant supply Main fuel coolant supply Flemble lines Figure 13.— Schematic of prototype vehicle power and fuel system. 121 SUMMARY The hydrogen-converted vehicle has accumulated over 200 h of surface operation. The hydrogen engine in its tur- bocharged, intercooled, spark-ignition configuration pro- duces adequate power (approximately 75 kW) for the EIMCO 975 utility vehicle. Much modification was required to properly interface the engine-hydride fuel system to the prototype vehicle. The engine required a double-radiator system: one for engine cooling and the other for charge-air cooling. An air pump system was also added to provide dilution air in the crankcase to keep the hydrogen concentration below its flammability limit. A speed control system was incorporated to prevent engine overspeed and to provide smooth engine and torque transfer to the torque converter when the vehi- cle is operated at or near engine rated speeds. Many structural changes were also made to accom- modate the 21 hydride heat exchangers within the frame rails of the utility bed. Six of these hydride containers have enhanced heat transfer capabilities to provide for more ef- ficient vehicle refueling and to meet the hydrogen demands of the engine. These heat-transfer-enhanced, mine-safe units also contain subatmospheric hydrides that minimize poten- tially dangerous hydrogen leakage. Discharge tests confirm that the maximum accidental hydrogen release from the advanced mine-safe hydride modules is within the limits tentatively established for underground mines. The hydrogen leakage tests showed that the overall hydride fuel system could release 20 pet of its hydrogen content. Part of the system that has the ad- vance mine-safe design only released 3 pet of its content under a simulated fuel system rupture. The phase HI hydride modules do not meet these safety guidelines and should therefore be replaced before the prototype vehicle is operated underground. REFERENCES 1. Baker, N.,L. Houston, F. Lynch, L. Olavson, and G. Sandrock. A Clean Internal Combustion Engine for Underground Mining Machinery. A Technical Assessment and Program Plan. Final Phase I Report (contract H0202034, EIMCO Min. Mach. Int.). BuMines OFR 86-82, 1981, 232 pp.; NTIS PB 82-244724. 2. Baker, N., and F. Lynch. A Hydrogen Engine Induction Tech- nique for Backfire-Free Operation (contract H0202034, EIMCO Min. Mach. Int.). BuMines OFR 94-83, 1982, 46 pp.; NTIS PB 83-205443. 3. Rogowski, A.R. Elements of Internal Combustion Engines. McGraw Hill, 1953, 234 pp. 4. Obert, E.F. Internal Combustion Engines and Air Pollution. Harper and Row, 1973, 740 pp. 5. Levi, J., and D.B. Kittelson. Further Studies With the Hydrogen Engine (Pres. at the 1978 Int. Cong, and Expo., Detroit, MI, Feb. 27-Mar 3, 1978). SAE paper 780233, 1978, 12 pp. 6. Escher, W.J.D. Hydrogen Fueled Internal Combustion Engines— A Technical Survey of Contemporary U.S. Projects. U.S. Dep. Commerce, TEC-7 5/005, 1975, 110 pp. 7. Baker, N., and F. Lynch. Development of a Hydride Fuel System for Underground Mine Use (contract H0202034, EIMCO Min. Mach. Int.). BuMines OFR 79-84, 1983, 56 pp; NTIS PB 84-182773. 8 A Prototype Hydride Powered Underground Mining Vehicle. Ongoing BuMines contract H0202034; for inf., contact R.W. Waytulonis, TPO, BuMines Minneapolis, MN. 9. Reilly, J.J., and G. Sandrock. Hydrogen Storage in Metal Hydrides. Sci. Am., v. 242, No. 2 , pp. 118-129, 1980. 10. Lynch, F., and E. Snape. The Role of Metal Hydrides in Hydrogen Storage and Utilization. Paper in Hydrogen Energy Systems (Proc. 2d World Hydrogen Energy Conference, Zurich). Pergamon, v. 3, 1978, pp. 1475-1524. 11. Lynch, F.E. Parallel Induction. J. of Hydrogen Energy (Great Britain), v. 8, No. 9, 1983, pp. 721-730 12. Mueller, W.M., J.P. Blackledge, and G.G. Libowitz (ed.). Metal Hydrides. Academic, 1968. 13. Schlapbach, L.A. Seiler, F. Stucki, P. Zurcher, and P. Fisher. How FeTi Absorbs Hydrogen. U.S. Dep. Energy (Oak Ridge, TN), Rep. 79042000, 1979, 20 pp. 14. Adt, R.R., Jr., M.R. Swain, and J.M. Pappas. Hydrogen Engine Performance Analysis Project. Univ. Miami, Coral Gables, FL, Se- cond Annual Report SAN-1212-T1, 1980, 448 pp. 122 Organization, objectives and achievements of a three-government collaborative program on diesel emissions reduction research and development E.D. DAINTY Research Scientist, Canadian Explosive Atmospheres Laboratory Canada Centre for Mineral and Energy Technology, EMR Ottawa, Ontario, Canada E.W. MITCHELL Research Coordinator, Mining Health and Safety Branch Ontario Ministry of Labour Toronto, Ontario, Canada G.H. SCHNAKENBERG, JR. Supervisory Physical Scientist U.S. Bureau of Mines Pittsburgh, Pennsylvania, U.S.A. ABSTRACT The historical development of the collaboration among three funding agencies: the United States Bureau of Mines (USBM), the Canada Centre for Mineral and Energy Technology (CANMET), and the Ontario Ministry of Labour (MOD, and numerous private sector contractors, is briefly discussed in this paper. Each government agency has had a diesel-related program in place for some time in recognition of the need to better understand the impact of diesel emissions on the underground worker. Official collaboration began on December 1, 1981 with the signing of a Memorandum of Understanding by all three govern- ments. The program officially ends in June 9 of 1987, the termination date given in that document. The result of this Memorandum was the formation of the "Collaborative Diesel Research Advisory Panel" (CDRAP), which undertook the resolution of a number of issues including: (1) the use of a criterion by which to evaluate the comprehensive toxicity of the major components of diesel exhaust, and the consequent provision of a tool for ventilation prescription and engineering economic studies, (2) research and development to produce add-on exhaust hard- ware and study of other techniques to reduce emissions from diesel engines, (3) development of the means of measuring the impact of such devices on the underground environment for the benefit of regulatory agencies and mine opera- tors, and finally, (4) synthesis of the principles learned into an overall strategy by which to improve mine environments, reduce ventilation costs, increase productivity and improve safety underground, depending on the circum- stances of each case. These matters are elaborated in general in this paper, amplified in the other five papers of this series, and further detailed in the reprinted papers and annotated bibliography of this compendium. Ke>word: diesel emissions. Mineral and Energy Technology, Mining Research Laboratories, Division Report M&ET86-19(OP, J); for presentation to the C1M/AGM, Montreal, May 14, 1986. 123 INTRODUCTION Diesel-powered machines were gradually introduced into underground mines in Europe in the 1940s to improve some aspects of coal mining opera- tions. Their introduction into North American mines began in earnest in the 1950' s. By the early 1960s, many North American non-coal mines were employing diesel machinery, but their use in coal mines remained limited. The general perception has been that untethered diesel machines pro- vide flexibility which in turn fosters improved operating efficiency and in- creased productivity. This perception persists to date, but not without voices that question this viewpoint when the entire mining system is consid- ered. There is also a current view that a combination of fixed and flexible machines may prove to be a better system for some mining operations. To cope with the increasing use of diesel machines, regulatory agen- cies in the major mining nations undertook R&D for the development of stand- ards for the use of such machines underground. Notable among these efforts was the work of John C. Holtz et al. at the United States Bureau of Mines (USBM) in Pittsburgh. This work was well-defined by I960 in (1), providing supporting data for the ventilation provisions of the several USBM-fostered standards for diesel application in several types of mines (2). The energy crisis of the Mid-1970s caused the Western nations to review the use of the entire spectrum of petroleum-based products. The high thermal efficiency of diesel engines suggested an increase in their use rela- tive to others in all applications, in turn raising the fear that a many-fold increase in urban air-borne particulate matter could result, potentially pro- ducing a severe health impact. These circumstances stimulated renewed interest on the part of gov- ernment regulatory authorities in North America, and was the catalyst for the R&D collaboration of three mining-oriented agencies: the United States Bureau of Mines, the Ministry of Labour (MOD of the Province of Ontario, and the Canada Centre for Mineral and Energy Technology (CANMET). INITIATION OF THE THREE-GOVERNMENT COLLABORATION In an effort to protect the health of mine workers in Canada's heav- ily dLeselized mining industry ( 27% of the free world's estimated 15 000 machines) , a comprehensive plan for diesel-related health and safety R&D was formulated during 1977 (3). This timing coincided with the availability of Canadian Government funding as a direct result of the energy crisis. The plan confirmed two initiatives taken the year before and placed them into a con- tinuing program which suggested the need for inter-government collaboration. These two initiatives were: (a) the formulation of a comprehensive criterion for evaluating the combined impact of the several toxic constituents of diesel exhaust leading to the Air Quality Index expression described below, and (b) the determination of the performance of the then-current water scrubbers and catalytic purifiers. Because two thirds (i.e., 2700 machines) of the Canadian underground diesel machine fleet were in the jurisdiction of the province of Ontario, 124 there was likewise considerable concern on the part of that provincial govern- ment, sensitive to the mounting criticism of the use of diesels by the miners themselves. Consequently, because of these concerns, because the raining sector makes a substantial contribution to Canada's overall economy, and because much of the mining industry was dieselized, the perception grew in Canada that the time was right to launch a major study. The U.S. Bureau of Mines' original initiatives in this field were de- scribed above. In addition to those strong beginnings, efforts on the part of the Bureau resulted in the achievement of a significant milestone in January of 1973. This milestone, the Pittsburgh Symposium (4) on the use of diesel- powered equipment in underground mining, along with a number of other impor- tant matters relating to this evolving study, are described by Schnakenberg (5). That reference describes the cooperation of the U.S. Bureau of Mines and its sister agencies: the Mining Enforcement and Safety Administration, now called the Mining Safety and Health Administration (MSHA), the National Insti- tute of Safety and Health (NIOSH), and also the American Conference of Govern- mental Industrial Hygienists (ACGIH), for the period from 1973 to 1978. That cooperation fostered the evolution of the view that further research into diesel exhaust control and health impact studies were necessary. At the ACGIH November 1978 Industrial Hygiene Symposium the CANMET Air Quality Index approach, formulated by I.W. French and A. Mildon (6) an 1 discussed in the next section, was first presented, the initial results of th- Bureau's environment monitoring efforts performed by Michigan Technological University were described, and the MSHA/NIOSH silica/diesel exhaust study was presented. All these important developments preceded an informal discussion between representatives from Canada and the United States at the 1979 Inter- national Conference of Safety in Mines Research Institutes, which proposed a joint research program for the development of hardware to substantially reduce diesel emissions, as well as the continued development of environmental as- sessment techniques. Similar discussions at the 1980 American Mining Congress reinforced the need for a joint R&D program. These discussions were followed by a meeting in 1980 of three funding agencies in Pittsburgh: USBM, MOL, and CANMET, along with a major contractor, the Ontario Research Foundation (ORF). The purpose of the meeting was to report the status of diesel emissions R&D and to lay plans for formal collaboration. Such a cooperative program was instituted by the signing of a Memorandum of Understanding during December of 1981, and the Collaborative Diesel Research Advisory Panel (CDRAP) was formed. Among the first matters undertaken was the installation of an ad- vanced engine test facility at the Ontario Research Foundation, with major support from the Ontario Ministry of Labour. This facility featured: (1) computer-controlled dynamometers to simulate vehicle duty cycles, (2) a dilu- tion tunnel sampling system to cope with dynamic sampling of particulate matter, (3) sophisticated analytical equipment necessary for monitoring the several gaseous, liquid and solid constituents in diesel exhaust, and (4) development of Ames mutagenic assessment capacity to flag potential occurrence of carcinogens. 125 The Panel has subsequently been the vehicle for the sharing of R&D results not only among the funding agencies, but also among the several con- tractors and contributing private sector manufacturers, equipment users, and regulatory agencies. The Panel has also been the vehicle for consultation on the directions that future R&D should take to achieve the four main objectives listed in the abstract. The minutes of the Panel meetings have been widely distributed throughout the mining community to inform all concerned of the activities and progress. The highlights of the achievement of these objectives are described briefly in the remainder of this paper, and in greater detail in the following five papers of this compendium. SELECTION OF THE MEASURE OF PROGRESS Diesel emissions contain a number of constituents which are toxic to those exposed to high enough concentrations for long enough periods of time. Discovering the safe levels and periods of exposure is a process, and percep- tions as to appropriate values of these parameters change as experience and understanding grow. Of the many constituents in diesel exhaust, six are the cause of varying degrees of concern: carbon monoxide (CO), nitrogen dioxide (N02)» nitric oxide (NO), sulphur dioxide (SO2), aldehydes and soot. Table 1 indi- cates their general order of present concern from least to greatest and the reduction in the general magnitudes of these tail-pipe levels over time (for the higher range of levels for full load/speed conditions). These reductions are due to the developments in two-stage combustion or indirect injection of fuel (IDI) relative to direct injection (DI) over the last 20 years. Finally, the table gives the dilution ratios necessary to reduce these tail-pipe levels to the ACGIH TLVs or other appropriate levels. Table 1 - Undiluted contaminant levels in diesel exhaust at full load/speed engine operation Prior Present Present generation generation TLV or dilution engine engine other ratio Constituent Units levels (DI) levels (IDI) limit required CO ppm 2000 300 50 6 NO 2 ppm - U8 3 16 NO ppm 1500 700 25 28 S0 2 * ppm 80 80 2*** M0 soot mg/m3 1000 75 1.5° 50 EQI - - 232 3«« 77 •0.2056 sulphur in the fuel, ••proposed in (6). •••note that the TLV for SO2 remains 3 ppm when used in the EQI expression defined below. 126 CO, formerly of great concern, now has become much less of a concern relative to other constituents as our knowledge of their health effects has increased: NO2 is generally not a controlling constituent, although concen- trations tend to rise at lower loads; NO produces moderate concern; SO2 has perhaps become the individual gas of greatest concern because its TLV has recently been reduced to 2 ppm - if the fuel sulphur is below 0.2/&, it is of less concern; the aldehydes are generally kept below their TLVs when the other constituents are controlled; and soot would appear to require the greatest fresh air dilution given a limit value of 1.5 mg/m3. Diesel soot is visible and has always been perceived as objection- able, and possibly noxious by miners. However, widespread concern for its relative effect on health has been clearly expressed only in the last decade. The Environmental Protection Agency (EPA) in the United States and the Cana- dian Environment Department both anticipate similar substantial reductions in soot emissions from surface diesels by 1991 relative to the present to neu- tralize the health consequences. Recent studies indicate that, while coal dust exposure was characterized by normally activated alveolar macrophages (as would be expected as a result of the invasion of a hostile particulate) the appearance of the microphage population on exposure to diesel soot suggested poisoning with consequent degradation in function (7). I.W. French and Asso- ciates, contractors to CANMET, after studying 1500 citations in the literature in 1978 (6), concluded that diesel soot was the most potentially hazardous component in diesel exhaust, suggesting an emphasis with respect to its con- trol. In general, when engine adjustments such as injection timing are made, the relative proportions of these various constituents change. Changes in these constituents due to malfunction, wear and maladjustment have been addressed in detail by Waytulonis (8) in a major effort performed on behalf of the U.S* Bureau of Mines Twin Cities Research Center in Minneapolis. Some- times these changes compensate - as one constituent increases another de- creases. Further, derating an engine, i.e., reducing the maximum fuel rate, can reduce the soot emissions to below the 'smoke point', perhaps interchang- ing the governing constituents in the exhaust. Finally, addition of emission control devices can greatly alter the relative constituent concentrations. These facts present all segments of the mining industry with a di- lemma: by what criterion should adequacy of ventilation, i.e., air quality, be assessed? Such a criterion would ideally: (a) take into account the changing nature of the constituents, (b) assess comprehensively the toxicity of the exhaust constituents of major concern, (c) give credit for any air quality improvements allowing engineering economic tradeoffs to be made, and (d) allow regulatory agencies to prescribe ventilation consistent with items (a), (b), and (c), and permit compliance measurements to be made. At a meeting of the participants in Pittsburgh in 1980, the above aspects were considered and it was decided that the Health Effects Index (HEI), then renamed the Air Quality Index (AQI) , was the best criterion in existence by which to accomplish the above objectives and particularly to measure the progress of control technology developments on the reduction of overall diesel emissions. 127 At the same meeting, CDRAP decided to use the reduced emissions IDI Deutz engines* for application of emission control equipment because of their widespread use by the U.S. and Canadian mining industries. Although some R&D had already been carried out on the F8L714 engine, particularly the successful water-in-fuel emulsion work to reduce soot and NO, the 413FW series was chosen because of its introduction in 1976 to ultimately replace the 714 version. Unfortunately, the water in fuel emulsion system did not prove to be effective when applied to the new 413FW series. Except for minor and beneficial changes, the relative concentration of the components of diesel exhaust are unaffected by dilution. Therefore, the French-Mildon criterion, intended for the evaluation of the diluted or ambient air, and known as the Ventilation Index, the Health Effects Index or preferably the AQI , can be used to evaluate the potential toxicity of undi- luted diesel exhaust. When used for this purpose it is referred to as the Exhaust Quality Index (EQI). The French-Mildon literature study recommended a maximum value for the AQI of 3, above which some control measure was sug- gested. The mathematical expression recommended was: Afvr CO NO RCD H 2 S °4 _ _ f S °2 RCD 1 . . [~ N °2 RCD 1 EQI or AQI = - + - + — + — j- + 1.5 |_— + — J + 1.2 [ — + —J where the ppm concentration for each gas is divided by its ACGIH TLV at the time of the formulation of the expression, and RCD is Respirable Combustible Dust having a limit of 2 mg/m3. In addition, it should be pointed out that no constituent should be permitted to rise above its own individual limit, and that the sum of the gaseous terms (CO, NO, and NO2 relative to their respec- tive TLVs) should be less than 1. A minimum ventilation dilution ratio then can be calculated from EQI/AQI max = EQI/3, and the minimum ventilation prescription equation is: ventilation rate = undiluted dry exhaust gas rate x EQI/3 Assuming sulphur in the fuel to be 0.20%, and applying the above maximum values for the various constituents, produces typically an EQI value of 232, which when divided by AQI max = 3, yields a dilution ratio of 77. Therefore, the comprehensive EQI value, if employed, will govern ventilation prescription in most circumstances, rather than any of the individual constituents as indi- cated in Table 1. There is a further development of this criterion which separates the gas effects from the RCD effects by the formulation of two independent expres- sions each with its own limit. The reader is referred to (9) for further elaboration. For the purposes of control technology performance assessment however, CDRAP has continued to use the above single equation for consistency as both equation systems give virtually identical results from the standpoint of fresh air dilution ratio. •Reference to specific brands, equipment or trade names in this paper is made to facilitate understanding and does not imply endorsement by the government agencies. 128 It should also be noted that the use of AQI = 3 in the single equa- tion relation generally increases the prescribed ventilation rate for un- treated exhaust only slightly relative to the use of the U.S. criterion: N0 X (as equivalent NO2) divided by a limit of 12.5, as prescribed in Part 36 (2). Therefore, with respect to the objectives stated above, this crite- rion takes into account the changing relationship of the constituents and assesses their overall effects. With respect to giving credit for air quality improvements, the addition of a device that is 90% efficient in reducing par- ticulate emissions, reduces the EQI by say 30 to 50% depending on the circum- stances as is evident from inspection of the AQI expression. Therefore, a balance can be struck between realizing a total benefit in improved air qual- ity from the use of such a device and maintaining ventilation as before on the one hand, and by realizing an economic benefit on the other hand by reducing ventilation to the appropriate level determined by the maximum limit of the AQI or of the individual constituents. Likewise, the buying of low sulphur fuel will have an effect which is easily assessed, etc. Further, technology has been evolving as described below, which per- mits the underground ambient assessment of these major constituents using time-weight-average field measurement devices permitting calculation of the AQI levels. This in turn permits operators or regulatory authorities to evaluate the on-site performance of engines, and/or treatment devices or sys- tems, in order to assure adequate levels of ventilation in a given circum- stance. Thus all four requirements by which to evaluate progress listed (a) to (d) on page 4 above, are addressed by the use of such a criterion. In addition to applying this AQI criterion for equipment performance determination, CDRAP has applied an additional assay - the Ames test. The mutagenic activity, as determined by the use of the Ames microbial assay, has demonstrated a high positive correlation with a number of other tests (in- vitro and in-vivo) of mutagenicity and carcinogenicity for the soluble frac- tion of diesel particulate (10). Thus the Ames assay provides an inexpensive, convenient and relevant means of comparing diesel-derived contaminants from engine to engine and/or among treatment devices, permitting engineering judge- ments to be made regarding which R&D avenues to pursue, emphasize or discard. DEVELOPMENT OF EXHAUST TREATMENT DEVICES Exhaust treatment devices such as those developed in connection with the CDRAP program, can be applied to diesel emissions reduction in all types of underground workings: coal mines, other types of gassy mines, metal mines, and all other non-gassy types of underground workings. In the case of gassy mines, further developments to reduce the fire and explosion hazards are re- quired. Traditionally, water scrubbing equipment has been employed in gassy mines to assist in avoiding this hazard. A decade ago, however, they were common in metal mines. In this connection, the original 1977 CANMET contract with the Ontario Research Foundation described in (11), detailed, evidently for the first time in the published- literature, the performances of two then- current water scrubbers, and a once-through catalytic purifier all employed in metal mines. The scrubbers removed a respectable 40 to 65% of the sulphur oxides (SO2 and SO3 - an important point to note in view of the recent TLV re- duction for SO2 from 3 to 2), but only 30% or so of the soot. The catalytic 129 purifier reduced 90% of the CO to carbon dioxide (COp), but converted signifi- cant amounts of the SO2 to SO3 and NO to NO2 (SO3 and NO2 are the more toxic forms). These early results suggested that there was room for improvement, particularly in the capture of soot. Consequently, control technology devel- opment work was begun. As part of this development program, a CANMET Research Agreement with the University of Waterloo was implemented to study materials by which soot could be filtered from diesel exhaust. This study continued for 3 years (1977-79), and showed that six materials were potential candidates. The USBM and CANMET studied the two most promising materials by the building, and in- house testing, of prototype systems with modest success. At this point, the Corning Glass Works representatives approached CANMET and the USBM to assess the potential of the ceramic wall-flow filter element as an underground diesel emission control system. Initial trials were successful. As the unit appeared to offer considerable advantages in terms of bulk, maintenance and regeneration potential, further development of the Waterloo materials was suspended. These initial studies have subsequently led to the study by CDRAP of the following array of emissions reduction equipment options: 1. (a) a simple optimized baffle-type water scrubber design, and (b) a high efficiency venturi-type water scrubbing system. 2. several ceramic wall-flow diesel particulate filter options (DPFs) : (a) simple DPFs for high exhaust gas temperature levels fostering unas- sisted soot auto-regeneration (combustion), resulting in acceptable equilibrium backpressures, (b) the use of fuel additives in conjunction with the above DPF unit, significantly depressing the soot auto-ignition temperature and fur- ther widening the filter applicability or further ensuring untended, passive auto-regeneration of the filter, (c) the use of noble catalyst-impregnated DPFs further depressing the soot auto-ignition temperature relative to (b), useful particularly for low sulphur fuels. Recent preliminary work indicates negligible conver- sion of SO? to SO3 for one noble catalyst formulation, perhaps elimi- nating this concern when fuels with moderate fuel sulphur levels are employed, (d) the use of non-noble catalyst formulations which, it is hoped will demonstrate helpful soot ignition temperature depression and similar insensitivity to fuel sulphur levels, (e) the use of combinations of the above, such as applications of the simple DPF unit at non-auto-regenerating exhaust temperature levels, thus requiring some means of out-of -service regeneration such as is possible with the addition of auxiliary heat [for example, the face heater described in (12)], 3. a wire mesh catalytic trap oxidizer (CTO) filter unit (13), 130 4. exhaust gas recirculation (EGR) for NO control in connection with DPF use (14), 5. water-in-fuel emulsions for NO and soot control (15), and 6. emissions effects of varying types of fuels and emulsions (16). The following sections describe highlights of the first two develop- ment thrusts. For the remainder, the attention of the reader is directed to the references indicated at the end of each item. WATER SCRUBBING SYSTEMS In-house CANMET assessment of commercial water scrubber performance over several years indicated a variation from 10 to nearly 50% removal of soot. Further, scrubbers built to some non-Canadian specifications were often either heavy or costly to import or both. Because of this fact, the Beaver Construction Group approached CANMET in 1981 to design and test a series of simple, low-cost, baffle-type, flameproof water scrubbers. These were to be used to drive the development heading to the Donkin-Morien seam of the Cape Breton Development Company in Cape Breton, Nova Scotia. The outcome was that design principles were established and two scrubber sizes were drawn, built and tested by Beaver, Hovey and Associates (1979), and CANMET in collaboration. Careful use of a water separation crite- rion resulted in a 40 to 49% (maximum) soot removal efficiency, plus other beneficial effects including the absorption of some of the acid gases. The performance matched or exceeded the best of available scrubbers at reduced cost. Such performance may represent a limit for basic uncomplicated designs. In 1981 CANMET scientists' realized that momentum-transfer, and conse- quent impact of soot particles with water droplets in a water-injected venturi throat inserted into an exhaust system, could be optimized for soot capture using a mathematical model. This resulted in the design, manufacture and testing of a venturi system mounted in the exhaust system of a Deutz F6L 912W engine. This unit captured 70% of the soot, some of the sulphur oxides, and 19% of the NO2, utilizing a backpressure of 10 kPa. Such a performance re- duces the EQI by a substantial 50 to 60% depending on the backpressure, sug- gesting beneficial application to coal mine vehicles where the prescribed air- borne soot plus coal dust levels are difficult to attain, and in non-coal mines where humidity is not a problem. These water scrubbing developments are amplified in paper 2 of this series. CERAMIC FILTER SYSTEMS The filtering element in such filters is a porous ceramic material, the configuration of which is shown in (17) - see paper 3 of this series, and in (18,19). The porosity can be varied so that the degree of soot trapping can be tailored to the need and coupled with tradeoffs in size and shape, filtering surface area, and soot-free backpressure, etc. 131 The rapid optimization of the ceramic element size to the gas rates of six and eight cylinder Deutz engines, for a nominal trapping efficiency of 90% , led quickly to several development directions including underground tests described in (20) - see paper 4 of this series, and to the option definition process of the above list. These option developments are described briefly as follows. In essence the successful application of ceramic filters depends on the capability of the filter to handle the collected soot: (1) over a useful operating period, and (2) in such a manner that the backpressure buildup does not jeopardize engine warranty or mine safety. Thus methods for promoting and enhancing the handling/disposing of the collected soot, were held in high priority by the CDRAP and investigated. The method appropriate for the ceramic DPF is the combustion of the collected soot while it remains in the DPF. The most advantageous circumstances would be to have the collected soot burn off as collected, a so-called auto-regeneration. Auto-regeneration of soot results from the inter-related effects of several parameters including the amount of carbon deposited on the filter surfaces and in the pores, the oxygen content of the exhaust gases passing through the ceramic element, and perhaps most important, the temperature of the exhaust gases. Cyclic dynamometer tests at ORF, simulating Load-Haul-Dump (LHD) machine operation, have approximately defined the average values of some of these parameters as reported in Table 2. Table 2 - Ceramic filter regeneration threshold parameters Noble Unassisted Additive catalyst Option filter assisted assisted minimum average load {%) CO2/O2 concentrations {%) fuel/air ratio (-) average exhaust (°C) temperature (°F) 77 54 48 8.0/9.7 6.0/12.2 5.4/13.0 0.037 0.028 0.025 427 365 349 800 690 660 The application of these three regenerating options of Table 2 to specific types of vehicles powered by conventional four-stroke engines, ap- pears initially to be a question of exhaust gas temperature characteristic determination. Such tests have been completed in the field at INCO Limited (21). These confirm the above LHD dynamometer results for the unassisted auto-regenerating filter from the standpoints of average exhaust temperature and also confirmation of the necessity of temperature excursions in excess of the 500°C (932°F) soot ignition temperature for sufficient periods to initiate combustion. There have been examples of runaway regeneration which have resulted in damage, i.e., melting through or channelling of the ceramic matrix of the filter, the metal can remaining unaffected (22). This appears to have resulted when excessive amounts of soot are deposited in the filter and ultimately sub- jected to sufficient oxygen and temperature to produce continuous high inten- sity combustion. The result is that soot removal virtually ceases and filter pressure drop decreases to a lower value with little immediate safety hazard. 132 The INCO experience (21), indicates that high exhaust gas temperature operation, which fosters continuous regeneration, maintains the backpressure at an acceptable equilibrium limit of 4 kPa (20 in H 2 0) for a Deutz F8L 714 engine. Under these conditions the filter neither self-destructs nor results in apparent significant thermal overstressing for periods up to 1830 h of operation. The key to safe operation seems to be the limiting of the amount of soot in the filter. To limit the amount of combustible material, and thus foster filter integrity, it is prudent to mount a backpressure sensor before the filter and arrange for a signal to illuminate a dash light when the back- pressure is constantly in excess of a given upper limit, say 7.5 kPa (30 in H 2 0). Unreported in-house CANMET experiments using a Deutz F6L 912W engine in connection with electric face heater development studies, showed that soot ignition did not occur when a filter loaded to a 5 kPa backpressure level was heat-soaked at high exhaust temperature (but below the soot ignition tempera- ture) and suddenly exposed to the high oxygen concentration associated with low speed idle conditions. It should also be noted that the use of additives or catalysts depresses the soot ignition temperature significantly, appreci- ably reducing the likelihood of soot accumulation. While it appears that the type of operation described above results in safety thus far, safety research is currently continuing at the Twin Cities Research Center of the United States Bureau of Mines. In addition to safety considerations, extensive studies of exhaust treatment devices have been made both in the laboratory and in the field to indirectly gauge the health effects of diesel pollutants. These studies have been in the form of polynuclear aromatic hydrocarbon (PAHs or PNAs) analyses to determine the levels of known carcinogens, and Ames mutagenic assessments, to flag their apparent collective carcinogenic potential relative to presently applied technologies. This latter aspect is detailed in (10) - see paper 5 of this series, which indicates that a significant reduction in Ames muta- genicity levels occurs as a result of the use of novel emission control op- tions such as those developed in connection with the CDRAP program. As a result of this multi-facetted examination of these filtration systems, it is estimated that they can be applied to most LHD machines and a portion of haulage trucks (say a total of 50% of the underground fleet), thus coping with by far the greater part of diesel vehicle soot contributions to underground environment contamination. Other applications would require peri- odic induced regeneration, either off or on the vehicle, prompted by a panel- mounted warning light, indicating backpressure buildup due to soot deposition. DEVELOPMENT 0. FIELD ENVIRONMENT ASSESSMENT TECHNIQUES The U.S. Bureau of Mines has had an on-going environmental assessment program in place for some time, involving study of such concepts as: (a) tube bundle continuous monitoring (23), (b) in-mine array of sensors relaying sig- nals to the surface, (c) a Mine Air Quality Laboratory (MAQL) for in-mine deployment where possible (24) and (25) - see paper 6 in this volume, and (d) a portable analysis equipment array carried into the mine to monitor environ- mental contaminants in order to provide both time-weighted-average (TWA) and instantaneous levels of five contaminants (26). 133 While each of these can be related to mine diesel technology, the latter two have been of most assistance to the CDRAP diesel program. The MAQL has been and continues to be employed by Michigan Technological University (MTU) under contract to the Bureau of Mines to evaluate some of the options listed above. Among these are the catalyst and fuel additive filter options installed in a Wagner Mining Equipment Company Scooptram. The venturi water scrubbing system, and some ceramic filter options are being evaluated in the same facility employing an LHD machine furnished by the Jarvis Clark Company Limited supported by the Mining Industry Research Organization of Canada (MIROC). This work is performed in an underground experimental mine heading in Hancock, Michigan, designed to duplicate real world conditions for an LHD mucking cycle, while at the same time permitting careful control of all the experimental conditions relating to ventilation, multi-component sampling, analytical precision, and vehicle cycle repetition, so difficult to realize in the dynamics of an operating mine. Results of this option testing program are described in (25). The portable analysis system has been developed by MTU and employed by an MTU team and /or a CANMET team for a number of mine environmental assess- ments including coal, salt, nickel, zinc and potash mines, to evaluate the impact of new diesel emissions reduction concepts on the environment and to evaluate the contaminant levels. Some aspects of four such studies are de- tailed in (20) - see paper 4 in this volume. The result of applying these portable systems is the determination of the time -weighted -average values (TWAs) of CO2, CO, NO and NO2 gases (in % of ppm) , plus the respirable combustible dust (RCD) in mg/m3, for however many sampling stations are employed in a given investigation. These are the neces- sary values for characterizing the comprehensive toxicity of all the major components of diesel exhaust using the AQI described above, and relating such values to the CO2 concentration. Instantaneous, real-time concentrations of the four gases are also determined at one sampling station for confirming com- parisons to the TWA values, and for assisting in the definition of the varia- tions of the machine operating cycle. By 3uch field measurements, comparative evaluation of the air quality can be made, with and without control devices for example. The studies re- ported in (20) indicate environmental improvements due to ceramic filter application of 35 to 65% relative to catalytic purifiers as measured by the AQI criterion. There are several important generalizations which emerge from this detailed environmental assessment work, a summary of which follows: 1. Examination of < voluminous constituent concentrations in the MAQL has led to the conclusion that the CO2 concentration is a direct surrogate for all the other measured pollutants. This is most useful for an engineering approach to environmental control, which approach is described in relative detail by Schnakenberg (27) of the Pittsburgh Research Center, and Daniel (28) of the Washington D.C. Office of the Bureau of Mines, Department of the Interior. 134 2. TWA values of N0 X and NO2 are presently determined by the easy in-mine deployment of Palmes diffusion-type samplers. These simple devices can, when care is exercised, produce an in-sample variation generally well within plus or minus 20% of the mean, and levels that compare well with integration of constituent con- centrations derived from real-time traces generated by portable laboratory-type analyzers (20). The Palmes sampler approach is acceptable but it requires considerable pre-test preparation time arid post-test analysis time plus some laboratory analytical equipment. TWA values of CO2 and CO are determined by bag sam- pling and post-test analysis using the same type of portable laboratory zero/span analyzers, likewise involving some addi- tional time before the answer emerges. Long-term stain tubes (CO21 CO, N0 X , and NO2), plus associated pumps, are now available to provide immediate answers at the end of the testing period without further effort. While pump failure and NO2 sensitivity are present difficulties (20), it would appear that further development of long-term stain tubes will reduce the effort to make spot AQI and individual constituent assessments underground by an estimated 40% relative to the use of the present array of equipment. 3. Soot, assumed to comprise 75% of the RCD, is composed of solid carbon plus varying amounts of adsorbed hydrocarbons. The hydro- carbon fraction has been a source of difficulty in assessing the efficiency of ceramic filters in the underground environment. Dynamometer-derived efficiencies of the order of 90% were not confirmed by the results of a number of underground assessments which suggested a 40% or so level of filtration efficiency. MTU personnel were asked to look into this lack of agreement. Pre- liminary considerations, quoted from an MTU progress report show- ing that "half an ounce of oil (leakage) per hour could offset the test results and lower the MAQL (emissions) system effi- ciencies from 78% to 36% due to this additional particulate source", were confirmed in (25) - see paper 6 of this series. It appears that leakage of fuel, hydraulic oil, etc., onto hot surfaces, can add substantially to the air-borne contributors to the RCD measurement in addition to exhaust-generated soot; a point that must be kept in mind not only when field assessments are made, but also as a source of unwanted respirable particulate matter and hydrocarbon vapours even though the limits for the latter may be higher than that for suggested for soot. 4. Over reasonable periods of time assuming proper maintenance and small variations in the vehicle duty cycle, the components of diesel exhaust remain in relatively constant proportion with one another and CO2. The AQI for such periods is therefore in rela- tively direct and constant proportion to the CO2. Consequently, easy measurements of CO2 can then provide quick estimates of the suitability of the ventilation keeping in mind the following proviso. Changes in emission levels due to engine wear, fuel system adjustments, malfunctions, etc., can change the relativity of the various constituent levels of CO2. Thus, undiluted ex- haust levels of the constituents and CO2 should be monitored from 135 time to time to determine such changes, re-establish the appro- priate dilution ratio and adjust the ventilation accordingly. In the short term, assuming no significant changes in engine emissions or ventilation rate and an AQI = 3, the easily-measured CO2 control limit can be determined by using the ratio of the measured CO2 and AQI values for the ambient environment. As long as the CO2 remains at or below this control limit, the AQI can be assumed to be 3 or less. For example, during one filter evalua- tion described in (29), an AQI value of 0.51 and a CO2 value of 0.05/6 were determined for the LHD operator's station. Because the AQI, of all of the possible limiting items, was closest to its limit of 3 (both the SO2 and the NO concentrations were simi- larly close to their respective limits) , the ventilation could theoretically be reduced by a factor of six, to produce a C0 2 value of 0. 3% (i.e., 0.05 x 3.0/0.51), assuming that other diffi- culties would not result. Therefore, suitably accurate measurement techniques are available to assess all the constituents normally necessary for environmental assessment. While some aspects of these techniques presently require time and capital, developments in the near future should minimize both of these aspects. Once such measurements are made, they will facilitate the making of engineering judgements regarding ventilation acceptability by virtue of the direct rela- tionship of easily-measured CO2 with each of the toxic constituents and/or the AQI, ratioing each to its respective limit and keeping in mind the assump- tions stated. CONCLUSIONS RETROSPECT AND PROSPECT It has been estimated that there are some 5000 to 6000 diesel vehi- cles in the underground mining fleet in all types of mines in the U.S.A. Similarly, there are between 3000 and 4000 such vehicles in underground ser- vice in Canadian mines (30). In very approximate terms, this means that the North American mining industry has a substantial capital investment of between 0.5 and 0.75 billion dollars directly in such equipment, to say nothing of the indirectly related investments. This substantial sum suggests on the one hand, that such equipment might have a minimum life to say 10 years perhaps longer before writeoff. At such a time it would be replaced when and if superior, proven technologies emerge that can be applied. Therefore the application of the control technology produced by this program would appear to be suitable for a commensurate period of time. It is likely on the other hand, that a residual number of diesel vehicles will always be required for some raining tasks, by virtue of their flexibility of operation. Therefore, emissions technology may have a considerable lifetime of applicability in excess of the 10-year period. It would also appear that sharper definition of the health effects of diesel emissions, as well as the development of reduced emissions technolo- gies, can reduce the legitimate fears and lessen the perception on the part of some members of the mining community, of the necessity of discarding diesel 136 equipment technology, making it more feasible to extend the lifetime at least to the point of investment recovery and perhaps longer. SPECIFIC OUTCOMES There is a view expressed in connection with the listing of technolo- gies necessary to meet the 1991 EPA soot standards for surface diesels vehi- cles, that engine development has already contributed the maximum possible to the reduction of emission levels with no significant engineering breakthrough in sight. Therefore, it is assumed that major reductions can only come from exhaust treatment, fuel alterations, etc. To this end the CDRAP collaborators have advanced two water scrubbing systems (venturi and baffle types) suitable particularly for coal mines, to the demonstration and application stages, respectively. In addition, mainly for non-gassy mines, six ceramic filter options including EGR, have been studied as listed above. These are variously applicable depending on the circumstances. Extended field durability tests of approximately 1830 h in service, suggest that filtration is a strong option with which to either reduce the toxicity of the environment or reduce costly ventilation, or to strike a compromise, depending on the stance taken by the appropriate regulatory authority. It is estimated that these filter options are applicable to up to 50/6 of the underground diesel fleet of which the con- tribution to the underground contaminants is thought to be 70% of the total. The AQI/EQI concept, while not presently promulgated as a standard, does provide a means of assessing the comprehensive toxicity of emissions. Use of the AQI as a ventilation criterion generally only slightly increases the ventilation prescription resulting from use of the N0 X /12.5 criterion. In general, the order of ventilation-governing items is: (1) the AQI, (2) soot concentration, and (3) SO2. In cases where the fuel sulphur exceeds 0.3$i SO2 may be the governing constituent. Therefore, use of the EQI/AQI concept and the principle that CO2 con- centration is an easily-measured surrogate for the AQI or each contaminating constituent, rationalizes choice of engine, treatment option selection, venti- lation system and mine design, and makes possible the ultimate closing of the loop, i.e., the establishment of automated control of ventilation and related systems, based on continuous sensing of CO2 or the individual contaminants and the ventilation parameters in order to effect considerable operating cost reductions. THE POWER OF COLLABORATION The willing cooperation of the various segments of the mining commu- nity in North America has resulted in the numerous significant developments described above. The large number (approximately 3D of collaborating organi- zations attests to the power that has been brought to bear on the emissions problem by this active cooperation of all parties, public and private, par- ticipating in the CDRAP programs. Gratitude for these efforts is extended to all the participants in the acknowledgement section of this compendium. 137 REFERENCES 1. Holtz, J.C. "Safety with mobile diesel-powered equipment underground"; U.S. Bureau of Mines Report on Investigations 5616; I960. 2. U.S.A. Federal Code of Regulations: Part 31 - Diesel Mine Locomotives (Sen 22). Part 32 - Mobile Diesel-Powered Equipment for Non-Coal Mines. Part 36 - Mobile Diesel-Powered Transportation Equipment for Gassy, Non- Coal Mines (Sen 3D. 3. Dainty, E.D. "A five-year cooperative plan for underground diesel ma- chine safety and emissions R&D"; Internal Report MRP/ERP/MRL 77-135(TR); Mining Research Laboratories; CANMET, Energy, Mines and Resources Canada; December 1977. 4. Grant, B. and Friedman, D.F. "Proceedings on the use of diesel-powered equipment in underground mining"; USBM Information Circular IC 8666; 1975. 5. Schnakenberg, G.H. , Jr. "Current state-of-the-art of diesel emissions control - an overview"; USBM Pittsburgh Research Center; Presented to the Third Theodore Hatch Symposium, International Conference on the Health of Miners; Pittsburgh, PA; June 1985. 6. French, I.W. and Mildon, M.A. "Health implications of exposure of under- ground workers to diesel exhaust emissions"; CANMET, Energy, Mines and Resources Canada; Contract No. 16. SQ. 23440-6-9025; 350 pp; 1978. 7. Castranova, V., Bowmann, L. , Reasor, M.J., Lewis, T. , Tucker, J. and Miles, P.R. "The response of rat alveolar macrophages to chronic inhala- tion of coal dust and/or diesel exhaust"; Environment Research; Vol. 36, 405-419 pp; 1985. 8. Waytulonis, R.W. "The effects of diesel engine maintenance on emis- sions"; USBM Twin Cities Research Center; Presented to the 86th Annual General Meeting of the Canadian Institute for Mining and Metallurgy; 30 pp; Ottawa, Canada; 1984. 9. French, I.W. and Mildon, M.A. "Health implications of exposure of under- ground workers to diesel exhaust emissions - an update"; CANMET, Energy, Mines and Resources Canada; Contract No. 0SQ. 82-00121; 607 pp; April 1984. 10. Mogan, J.P. , Horton, A. J. , Vergeer, H.C. and Westaway, K.C. "A compari- son of laboratory and underground mutagen levels for treated and un- treated diesel exhaust"; Presented to the CIM/AGM Session on Heavy Duty Emission Control, Montreal; Published by the Canadian Institute of Mining and Metallurgy; See paper No. 5 in this series; May 1986. 11. Lawson, A. and Vergeer, H.C. "Analysis of diesel exhaust emitted from water scrubbers and exhaust purifiers"; Performed by the Ontario Research Foundation under contract to the Department of Energy, Mines and Resour- ces Canada; Contract No. 0SQ. 76-00014; 115 pp; May 1977. 138 12. Vergeer, H.C., Gulati, S.T., Mogan, J. P. and Dainty, E.D. "Electrical regeneration of ceramic wall-flow diesel filters for underground mining applications"; SAE International Congress and Exposition; Special Publi- cation P-158 - Diesel Particulate Control; 143-151 pp; SAE No. 850152; Detroit, Michigan; February 1985. 13. Mogan, J. P., Vergeer, H.C., Westaway, K.C. , Weglo, J.K., Lawson, A., Dainty, E.D. and Thomas, L.R. "Investigation of the CTO emission control system applied to heavy-duty diesel engines used in underground mining equipment"; SAE International Congress and Exposition; Special Publica- tion P-158 - Diesel Particulate Control; 131-142 pp; SAE No. 850151; Detroit, Michigan; February 1985. 14. Stawsky, A., Lawson, A., Vergeer, H.C. and Sharp, F.A. ""Evaluation of an underground emissions control strategy for underground diesel mining equipment"; SAE International Congress and Exposition; SAE Paper No. 840176; Detroit, Michigan; February 1984. 15. Lawson, A., Vergeer, H.C, Mitchell, E. and Dainty, E.D. "Update of water/fuel emulsification effects on diesel emissions reduction"; Pre- sented to the 86th Annual General Meeting of the Canadian Institute of Mining and Metallurgy; 15 pp; Ottawa, Canada; 1984. 16. "Control of diesel exhaust emissions in underground coal mines - fuel modification"; U.S. Bureau of Mines Contract No. J0188157; Performed by Southwest Research Institute of San Antonio, Texas; Technical Project Officer - R. Waytulonis, of the U.S. Bureau of Mines, Twin Cities Re- search Center; Minneapolis, Minnesota; 1980-1986. 17. Lawson, A., Vergeer, H.C, Roach, M.H. and Stawsky, A. "Evaluation of ceramic and wire mesh filters for reducing diesel particulate emis- sions"; Presented to the CIM/AGM Session on Heavy Duty Emission Control, Montreal; Published by the Canadian Institute of Mining and Metallurgy; See paper 3 in this volume; May 1986. 18. Howitt, J.S., Elliott, W.T., Mogan, J. P. and Dainty, E.D. "Application of a ceramic wall-flow filter to underground diesel emissions reduction"; SAE International Congress and Exposition; Special Publication SP-537 - Diesel Particulate Control; 131-139 pp; SAE No. 830181; Detroit, Michi- gan; February 1983. 19. Dainty, E.D. , Mogan, J. P., Lawson, A. and Mitchell, E. "The status of total diesel exhaust filter development for underground mines"; Presented to and published in the Proceedings by the XXIst International Conference of Safety in Mines Research Institutes; 8 pp; Sydney, Australia; October 1985. 20. Dainty, E.D. , Gangal, M.K., Vergeer, H.C, Carlson, D.H., Stawsky, A. and Mitchell, E.W. "A summary of underground mine investigations of ceramic diesel particulate filters and catalytic purifiers"; Presented to the CIM/AGM Session on Heavy Duty Emission Control, Montreal; Published by the Canadian Institute of Mining and Metallurgy; See paper No. 4 in this volume; May 1986. 139 21. Dainty, E.D. , Bourre, C. and Elliott, W.T. "Characterization of ceramic diesel exhaust filter auto-regeneration in a hard rock mine"; Presented to and Published by the Mines Accident Prevention Association of Ontario; Annual General Meeting; 26 pp; Toronto; May 1985. 22. Ludecke, O.A. and Dimick, D.L. "Diesel exhaust particulate control sys- tem development"; SAE paper No. 830085; SAE International Congress and Exposition; Detroit, Michigan; February 1983. 23. Fries, E.F. "Progress report on the Bureau of Mines monitoring systems at the Black River and Bruceton Safety Research Mines"; Published in the Proceedings of the Sixth WVU Conference on Coal Electrotechnology (Bureau of Mines Contract Report J0123017); 361-377 pp; November 1982. 24. Keski-Hynnila, D.E., Reinbold, E.O. and Johnson, .H. "An underground mine air quality laboratory for studying ventilation, vehicle and diesel engine pollutant control techniques"; The Canadian Mining and Metallurgi- cal Bulletin; Vol. 74, No. 835, 74-83 pp; See paper No. 50 in this volume; November 19 81. 25. Carlson, D.H., Bucheger, D. , Patton, M. , Johnson, J.H. and Schnakenberg, G.H. "The evaluation of a ceramic diesel particulate filter in an under- ground mine laboratory"; Presented to the CIM/AGM Session on Heavy Duty Emission Control; Published by the Canadian Institute of Mining and Metallurgy; See paper No. 6 in this volume; Montreal; May 1986. 26. Johnson, J.H. , Carlson, D.H. and Bunting, B.G. "The application of advanced air monitoring techniques to mines using diesel-powered equip- ment"; Annual Report to the United States Department of the Interior by Michigan Technological University; Bureau of Mines Grant Agreement No. G0166027; NTIS Springfield Virginia 22161; January 1977. 27. Schnakenberg, G.H., Jr. "An approach to air quality control for diesel mucking in underground mines"; Annals of the American Conference of Industrial Hygienists; Vol. 8, 107-117 pp; 1984. 28. Daniel, J.H. , Jr. "Diesels in underground mining: a review and an evaluation of an air quality monitoring methodology"; U.S. Bureau of Mines Report of Investigation RI 8884; pp 36; 1984. 29. Gangal, M.K. , Dainty, E.D. , Weitzel, L. and Bapty, M. "Evaluation of diesel emission control technology at COMINCO's Sullivan Mine"; Presented to the IVth Mechanical/Electrical Engineering Symposium of the Ministry of Energy, Mines and Petroleum Resources; 27 pp; Victoria, British Columbia; February 1985. 30. Stewart, D.B. "Breakdown of diesel-powered equipment used in Canadian underground mines"; Internal Report MRP/MRL 77-92(TR); Mining Research Laboratories; CANMET, Energy, Mines and Resources Canada; Appended update by E. Mitchell of the Ontario Ministry of Labour; August 1977. 140 Diesel emission control catalyst — friend or foe J. P. MOGAN and E.D. DAINTY CANMET, Energy, Mines and Resources Ottawa, Ontario, Canada ABSTRACT The paper describes the role of noble metal oxidation catalysts in the treatment of diesel exhaust in underground mines. Benefits, such as a reduction in carbon monoxide, various classes of hydrocarbons, and odour, are described, both as they apply to earlier diesels, and to the current generation of underground engines. Potentially negative impacts, such as the oxidation of sulphur dioxide, and an apparent increase in mutagen concentration (five-fold for monoliths, 500-fold or greater with pelletted units) are also described. INTRODUCTION Noble metnl. oxidation catalysts supported on alumina spheres or honeycombs have been routinely employed for many years for emission control of diesel engines used as a source of underground power. Their role has been the oxidation of carbon monoxide plus unburned and partly oxidized hydrocar- bons, and as a result, a considerable reduction in diesel odour. During the early stages of dieselization of underground mining operations, these func- tions were highly significant. Holtz (1), reported carbon monoxide levels of 800 to 1000 parts per million (ppm), and Elliot and Davis (2) found aldehyde levels of 100 ppm in some indirect injection (IDI) diesel engines in common use underground. Bailey, Javes and Lock (3), reported total aldehyde levels as high as 1440 ppm for a direct injection "road" engine in "poor" condition, and 700 ppm for one in "good" condition. Formaldehyde contributed 64 ppm of the 700. Marshall and Hum (4) quote carbon monoxide levels as high as 2600 ppm and Pischinger and Carterellieri (5) show unburned hydrocarbon (UBHC) levels up to 850 ppm. Fresh air required to dilute these exhaust constituents to the recommended Threshold Limit Values (TLV's) of the era could reach 2600/100 = 26 times the raw exhaust volume in the case of carbon monoxide, 64/2 = 32 times for formaldehyde, and 850/50* s 17 times for unburned hydro- carbons. Use of exhaust treatment devices such as oxidation catalysts or water bath scrubbers was therefore recommended to reduce the levels of these noxious exhaust constituents. Maximum levels of exhaust components found with modern IDI diesel engines in common use underground, as reported by Lawson and Vergeer (7), Reyl (8), and Vergeer (9) amount to 330 ppm carbon monoxide, 84 ppm unburned hydro- carbons, 25 ppm total aldehydes, 14 ppm formaldehyde, 740 ppm nitric oxide, *TLV of cumene, suggested as a representative diesel exhaust hydrocarbon (6). Kt.wvord: catalyst. Presented at ihc 86th Annual General Meeting of CIM, Ottawa, April 1984. 141 and 9.9? carbon dioxide. The ratio of raw exhaust to fresh dilution air re- quired to reduce these levels to current TLV's would be: CO 330/50 = 6.6 UBHC 84/50* = 1.7 HCHO 14/1 14 NO 740/25 = 29.6 C0 2 9.9/0.5 = 19.8 This demonstrates that the fresh air requirement to dilute the exhaust con- stituents which are not reduced by the catalyst (nitric oxide and carbon di- oxide) considerably exceeds that of those that are, thereby lessening the value of catalytic exhaust treatment for this class of engine. Identification of a sulphur dioxide to sulphur trioxide conversion problem with automobile catalysts in the early 70 's prompted similar inves- tigations of the diesel catalysts. Work such as that by Marshall (10), Marshall, Seizinger and Freedman (11), and Lawson and Vergeer (7) provided ample evidence that oxidation catalysts can convert up to 85? of the sulphur dioxide in diesel exhaust to sulphur trioxide in a laboratory setting. This sulphur trioxide, if not converted to sulphate in the exhaust train, could then be emitted as the more toxic sulphuric acid mist. A potential benefit to counterbalance this demonstrated acid forma- tion could be the oxidation (to harmless carbon dioxide and water) of the small quantities of known carcinogens (such as benzo-a-pyrene) which have been shown to be present in untreated diesel exhaust (12, 13). Recent research sponsored by CANMET has provided considerable insight in this aspect of cata- lytic purifier performance, and has thus prompted the following constituent- by-constituent review of the role of the oxidation catalyst as an underground emission control device. CARBON MONOXIDE Noble metal catalysts for diesel emission control have been shown to exhibit "light-off" temperatures of 175° to 250°C, above which 50 to 90 per cent of the exhaust carbon monoxide is oxidized to carbon dioxide (7,10,11). This temperature will be exceeded for a good portion of the operating cycle of haulage trucks and Load-Haul-Dump (LHD) units (14). Service trucks and personnel vehicles, however, would need a supplementary heat source for effec- tive full time CO oxidation, particularly when operating down-ramp (14). •TLV of cumene, suggested as a representative diesel exhaust hydrocarbon (6). 142 HYDROCARBONS Exhaust hydrocarbon, monitored by a flame ionization hydrocarbon analyzer (as methane equivalent), is reduced 50 to 80% on passing through oxi- dation catalysts (7,10,11). Some work suggests that the "light-off" tempera- ture is less significant for hydrocarbon oxidation, with some conversion occurring at quite low loads. PARTLY OXIDIZED HYDROCARBONS Marshall, Seizinger and Freedman (11), report oxidation of 30 to 70 per cent of the raw exhaust formaldehyde, 30 to 90 per cent of acrolein, and 25 to 90 per cent of the higher aldehydes, depending on catalyst formulation. As with carbon monoxide, effective aldehyde oxidation cannot be expected at ■11 times with lightly-loaded service vehicles and consequent low average catalyst temperatures. ODOUR As may be expected from the above, catalysts were found to exert a •arkedly beneficial effect on exhaust odour, reducing the raw exhaust inten- sity of 7.0 odour units to levels as low as 2.2 (11). This may not, however, be entirely desirable in cases in which the untreated diesel exhaust has a tolerable odour: an increase in odour intensity may be the best early warning of reduced ventilation levels. Marshall and Hum (15) showed rapid build up (10 min) of carbon monoxide to lethal concentrations when a diesel engine rebreathes its own exhaust, as may occur during total or partial failure of the ventilating air supply to a panel. SOOT Oxidation catalysts were found to have almost no effect on the soot content of the exhaust (7,16). Using a preconditioning procedure, the authors (17) were able to infer that apparent soot removal by a pelletted style cata- lyst was actually a storage- release phenomenon. NITROGEN OXIDES Nitric oxide generally passed through the oxidation catalyst un- changed (7,18). Lawson and Vergeer (7), however, found up to 40 per cent con- 143 version of nitric oxide (TLV 25) to the more toxic nitrogen dioxide (TLV 3) at some engine load-speed combinations. Later work with the same engine-catalyst system (19), exhibited much reduced conversion, suggesting that significant nitric oxide oxidation may only occur with fresh highly active catalyst. The low level of nitrogen dioxide found in operating mines (20) supports this con- jecture. SULPHUR OXIDES Laboratory studies (21), have shown that virtually all of the fuel sulphur emerges as sulphur dioxide in the raw exhaust, but considerable oxida- tion to sulphur trioxide occurs on passing through the catalyst. Combining the S0 ? conversion vs temperature plots of reference (7) with the temperature profiles of reference (14) suggests a conversion of S0 2 to SO- in the neigh- bourhood of 30 per cent for a typical LHD operation. With 0.2 per cent sul- phur fuel this represents about 20 ppm SO, in the raw exhaust and 0.3 ppm SO, equivalent or 1.2 mg/m sulphuric acid mist in the mine air at normal under- ground ventilation rates (about seventy times the raw exhaust volume). Kirk 3 and Seymour (22) reported 0.5 to 1.1 mg/m of sulphate ion in an LHD heading for similar quantities of ventilating air with 0.2 per cent sulphur fuel. The current CGSB (Canadian General Standards Board) diesel fuel standard permits up to 0.7 per cent sulphur. The soon- to- issued CGSB standard for mining fuel specifies 0.5 per cent for the regular grade, and 0.25 for the special grade. Use of 0.6 per cent sulphur fuel in a catalyst equipped LHD, 3 for example, could result in a mine air ambient concentration of 3.6 mg/m of sulphuric acid mist (unless conversion to the less harmful sulphate occurs), 3 which is well above the TLV of 1 mg/m . P0LYNUCLEAR AROMATIC HYDROCARBONS AND MUTAGENS Many polynuclear aromatic hydrocarbons (PNA's), some of which are known carcinogens (13), have been shown to be present in small quantities in diesel soot extracts (12). Nitration products of these base PNA's (such as the mono- and dinitro-pyrenes) apparently contribute much of the mutagenic activity observed with untreated diesel soot extracts (23). Given the effi- ciency with which catalytic purifiers have been shown to oxidize unburned hydrocarbons and aldehydes, it might be expected that a similar beneficial oxidation would occur with PNA's. Assay of the PNA content of extracts of particulate samples collected in an underground LHD heading, however, showed little difference between untreated and honeycomb-purifier equipped machines 144 (24). When the same machine was fitted with a pelletted purifier, a substan- tial decrease in PNA content was observed. Examination of the mutagen concen- tration, however, (as determined by the Ames salmonella assay - an indication of a possible increase in carcinogen concentration) showed a 100- to 500-fold increase over average ambient levels when no exhaust treatment was used. This decrease in PNA concentration accompanied by an increase in mutagenic activity has been shown to result from nitration of the PNA's by as little as 0.96 ppm of nitrogen dioxide (25). The storage-release phenomenon observed with a pelletted purifier (17) could provide ample time for the nitration reaction to occur. Seemingly, the only logical explanation for this large increase in mutagenic activity, considering the concentrations of PNA's measured, would be the formation of very strong mutagens such as the dinitropyrenes. Since preliminary animal studies (sub-cutaneous injection) suggest that the dinitro- pyrenes are roughly similar in carcinogenic potential to the strong carcino- gen, benzo-a-pyrene (BAP) (26), the mine air samples when pelletted purifiers were fitted may have contained 5 to 40 times as much BAP-equivalent carcinogen (compared to average BAP levels when no purifier was used). On the same basis, the mine air BAP equivalent could have increased about 1.7 times with the honeycomb unit. The health hazard level resulting from these low concen- trations of PNA's measured and nitro PNA's postulated is, as yet, undefined. DISCUSSION Current information thus appears to support Reyl's view (8): "Cata- lytic afterburners and exhaust gas cleaners are not recommended by us because of their dubious advantages and obvious disadvantages" - when modern well- maintained IDI diesel engines are used underground. If this class of engine is not fitted, or in remote locations where rigorous maintenance practices are not achievable (it might be hoped that noxious exhaust constituent levels a*s high as those reported by Bailey, Javes, and Lock are not encountered), an oxidation catalyst would seem to have considerable value for the reduction of aldehydes, carbon monoxide and odour. The formaldehyde level in the exhaust of a modern IDI engine in new condition did not exceed 14 ppm at typical LHD engine loadings (9). The amount of dilution air required to reduce the oxides of nitrogen and soot to their recommended ambient concentrations would therefore reduce formaldehyde levels to considerably below the current proposed TLV of 1 ppm (27), without catalytic exhaust treatment. If the recommendation of Kane and Allerie for a formaldehyde TLV of 0.03 to 0.3 (28) were to be adopted, however, there would obviously be less margin for safe operation when allowance is made for degra- 145 dation of the engine performance because of age, or between routine mainte- nance check-ups. Further, if the normal ventilation requirement is reduced because of the application of emission control measures such as soot traps and exhaust gas recirculation, formaldehyde, with a potential TLV of 0.3, may well be the critical exhaust constituent. The oxidation of raw exhaust sulphur dioxide by emission control catalysts has been well documented, but the resultant impact on the health of exposed workers is less well established. The work with catalytic purifiers in series with wet scrubbers (7), provides evidence that the sulphur trioxide (or sulphuric acid) which is produced is tightly bound to the soot particles. Whether this provides a site for formation of less toxic sulphates or a mecha- nism for the transport of additional acid past the upper respiratory tract defences is not likely to be resolved without costly animal exposure studies. Lacking these, it would seem prudent to use only low sulphur fuel (less than 0.2$ by weight) when exhaust treatment by catalytic purifier is indicated, so that potential sulphuric acid exposure will remain below the TLV at current ventilation air prescriptions. Similarly, the impact on health signalled by the increased mutagen concentration observed when catalysts are fitted has not been established. Further, it has not been definitively determined whether support configuration or catalyst formulation, both, or some other factor engenders the observed increase in Ames activity. None-the-less, an assessment of the potential to increase mutagen concentration should obviously be included when catalysts are chosen for underground applications. In summary, it appears that a modern well maintained indirect injec- tion diesel engine can be safely operated underground without a catalytic purifier. When other types of engines are fitted, and/or there are fewer opportunities for rigorous maintenance, the oxidation catalyst has a definite role in reducing the health impact of diesel emissions. When use of a cata- lyst is indicated, however, it is prudent to use only low sulphur fuel, and choose catalytic units with due consideration of the potential for mutagenic enhancement. ACKNOWLEDGEMENT The authors would like to thank Professor H.S. Rosenkranz of Case Western Reserve University for providing information on the significance of mutagenic response which was used to calculate of the potential hazard signal- led by the increased mutagen concentration observed with oxidation catalysts. 146 A NEW ROLE FOR OXIDATION CATALYSTS! A number of recent health studies have identified soot as the compo- nent of diesel exhaust with the greatest potential impact on health. Ceramic filters have been shown (in both laboratory and underground studies) to effec- tively trap 90% of the soot. The trapped soot, if allowed to accumulate, would inevitably cause the exhaust back-pressure to increase to unacceptable levels, so some means of removing the soot must be devised. If the engine load is sufficiently higher - in a mine with steeply ramped haulage or when loading heavy ore - the soot undergoes continuous spontaneous ignition (re- generation) so that exhaust back-pressure is maintained at an acceptable equilibrium level. At lower engine loads, encompassing many Load-Haul-Dump vehicles and haulage trucks, and virtually all service vehicles, some means of assisted regeneration must be adopted. Laboratory and underground studies have deter- mined that three regeneration strategies are effective: 1. Off-line by an externally supplied source of heat (furnace, in situ electric heater, or heated air flow) . 2. Mixing of a catalytic additive with the fuel. 3. Coating the ceramic filter with an oxidation catalyst. Of the three, the catalyst coating is the least labour intensive and obviously involves the least disruption of normal mine operating practices. New catalyst coatings (and the additive), have been shown to exhibit the advantages of the currently used emission control catalysts - reduction in the levels of hydrocarbons, aldehydes, and odour. More significantly, two recent coating formulations have achieved appreciable reduction in regeneration tem- perature (as compared to the uncatalyzed filter), while converting negligible SOp to sulphuric acid (29). These are promising developments which could ultimately eliminate some of the negative aspects of catalyst use, both in their present role, and as applied to ceramic fillers. REFERENCES 1. Holtz, J.C. "Safety with mobile diesel powered equipment underground"; Report of Investigations 5616, U.S. Bureau of Mines; I960. 2. Elliot, M.A. and Davis, R.F. "Composition of diesel exhaust gas"; SAE Quarterly Transactions ; 4, 3; 1950. 147 3. Bailey, C.L. , Javes, A.R. and Lock, J.K. "Investigation into the composi- tion of diesel engine exhaust"; Proceedings of The Fifth World Petroleum Congress ; June 3, 1959, New York, 209-226; 1959. 4. Marshall, W.F. and Hum, R.W. "Factors influencing diesel emissions"; SAE Reprint 680528; August, 1968. 5. Pischinger, R. and Cartellieri, W. "Combustion system parameters, and their effect upon diesel engine exhaust emissions"; SAE Reprint 720756; 1972. 6. Stokinger, H.E. "Toxicology of diesel emission"; Information Circular 8666, U.S. Bureau of Mines, Proceedings of the Symposium on the Use of Diesel Powered Equipment in Underground Mining, January 30, 1973, Pitts- burgh, 147-158; 1973. 7. Lawson, A. and Vergeer H. "Analysis of diesel exhaust emitted from water scrubbers and catalytic purifiers"; Contract Report ORF 77-01 for con- tract 0SQ 76-00014; CANMET, Department of Energy, Mines and Resources. 8. Reyl, G. "Deutz diesel engines operating in underground mines"; Publica- tion W0 999-94E, Klockner-Humboldt-Deutz AG. 9. Vergeer, H. P ersonal Communication , Ontario Research Foundation; Decem- ber, 1983. 10. Marshall, W.F. "Emission control for diesels operated underground: cata- lytic converters"; Report of Investigations 75/8, Bartlesville Energy Research Center; 1975. 11. Marshall, W.F., Seizinger, D.E. and Freedman, R.W. "Effects of catalytic reactors on diesel exhaust composition"; Technical Progress Report 105, U.S. Bureau of Mines; 1978. 12. Bricklemyer, B.A. and Spindt, R.S. "Measurement of polynuclear aromatic hydrocarbons in diesel exhaust gases"; SAE Reprint 780115; March 1978. 13. Menster, M. and Sharkey, A.G. "Chemical characterization of diesel ex- haust particulates"; Report of Investigations 77/5, Pittsburgh Energy Research Center; 1977. 148 14. Stewart, D.B., Ebersole, J.A.D. and Mogan, J. P. "Measurement of exhaust temperatures on operating underground diesel equipment"; Can. Min. Metall. Bull. 70, 801, 70-79; 1979. 15. Marshall, W.F. and Hum, R.W. "Hazard from engines rebreathing exhaust in confined space"; Report of Investigations 7757, U.S. Bureau of Mines; 1973. 16. Acres, G.J.K. "Platinum catalysts for diesel exhaust purification"; Platinum Metals Review 14, 78; 1970. 17. Mogan, J.P. , Stewart, D.B. and Dainty, E.D. "Analyzing LHD exhausts"; Can. Min. J. 95, 4, 35-36; 1974. 18. Sercorabe, E.J. "Exhaust purifiers for compression ignition engines"; Platinum Metals Review 19, 2; 1975. 19. Lawson, A., Simmons, E.W. and Piett, M. "Emission control of a Deutz F6L714 diesel engine, derated for underground use, by application of water/oil fuel emulsions"; Final Report 2722/02 for Contract ISQ 78- 00022; CANMET, Department of Energy, Mines and Resources; 1979. 20. Fontana, A. "Health Effects Index - a practical tool for atmospheric evaluation in highly dieselized underground mining operations"; Can. Min Metall. Bull. 75, 842, 69-72; 1982. 21. Lawson, A., Simmons, E.W. , Piett, M. and Chips, K. "Sulphate emission from catalyst equipped diesel engines"; Addendum to ORF Report No. 2722/ 02 for Contract ISQ 78-002; CANMET, Department of Energy, Mines and Resources; 1979* 22. Kirk, B. and Seymour, R. "Sulphuric acid production by diesel mine equip- ment"; Technical Report MRP/MRL 78-45, Mining Research Laboratories; CANMET, Department of Energy, Mines and Resources; 1978. 23. Nishioka, M.G. , Petersen, B.A. and Lewtas, J. "Comparison of nitro-PNA content and mutagenity of diesel exhaust"; Abstracts , EPA 1981 Diesel Emissions Symposium, Rayleigh, N.C.; October, 1981. 24. Mogan, J.P., Westaway, K.C., Horton, A.J. and Dainty, E.D. "Polynuclear aromatic hydrocarbons in the air of underground dieselized mines"; Pro- 149 ceedings of The Specialized Meeting of The Tenth World Congress on The Prevention of Occupational Accidents and Diseases , Ottawa; May, 1983. 25. Lofroth, G. , Toftgard, R. , Carlstedt-Duke, J., Gustafsson, J. A., Brorstrora, E. , Grennfelt, P. and Lindskog, A. "Effects of ozone and nitrogen dioxide present during sampling of genuine particulate matter as detected by two biological test systems and analysis of polycyclic aromatic hydrocarbons"; Abstract s, EPA 1981 Diesel Emissions Symposium, Raleigh, N.C.; October, 1981. 26. Sato, F. "Carcinogenicity of nitroarenes" ; U.S. -Japan Cooperative Pro- gram, Workshop on Carcinogens and Environmental Factors, Dedhara, Mass.; March, 1983. 27. Threshold Limit Values for Chemical Substances and Physical Agents in the Work Environment with Intended Changes for 1983-84. American Conference of Governmental Industrial Hygienists. 28. Supplemental Documentation of The Threshold Limit Values, 1981, American Conference of Governmental Industrial Hygienists. 29. Manicom, B. "Preliminary Results of the Evaluation of Catalyzed DPFs 34c, 35c" and "Preliminary Results - Catalyzed DPFs 36, 3 7 c"; Presented to the Collaborative Diesel Research Advisory Panel Meeting , Ottawa, Canada, February, 1986. 150 Characterization of ceramic diesel exhaust filter — regeneration in a hard rock mine E.D. DAINTY CANMET, Energy, Mines and Resources Ottawa, Ontario, Canada C. BOURRE and W.T. ELLIOT Inco Limited Copper Cliff, Ontario, Canada ABSTRACT During January of 1985, CANMET/MRL, in collaboration with Inco Metals Company, undertook the measurement of exhaust temperatures during both production and utility operating cycles of a J A RCO 500 LHD on the 1400-ft level of Little Stobie Mine in Sudbury. Vie apparent corroboration of laboratory and field test results suggests that load-haul-dump (LHD) cycles characterized by average temperature levels above 430"C (805°F), and sufficient high temperature excursions such as encountered during the studies reported, will auto-regenerate ceramic wall-flow filters. This process involves minimal apparent filter damage for hundreds of hours (approaching 1500 hours as of November 1985) of operation, yielding significant improvements in the operating environment and in several other mine operating parameters as derived from this and other work, and itemized below. 1. virtual absence of soot in the headings, 2. consequent reduction in toxicity of the environment: a) 30 to 50% relative to 'raw' untreated exhaust, or b) up to 75% relative to a widely-used catalytic purifier, as measured by the Exhaust Quality/Air Quality (EOIAQI) Indices, 3. considerably improved visibility, promoting safely and potentially increasing productivity, particularly in areas where production is ventilation limited, and 4. substantial reductions in machine noise — up to 14 dbA, performing the engine exhaust muffing function. INTRODUCTION Development of the ceramic honey-comb wall flow filter for the heavy duty underground mining application was undertaken by CANMET, in collaboration with the Corning Glass works, early in 1981. Since then, considerable R&D effort has been focussed on this device by three collaborating funding agen- cies: the United States Bureau of Mines, the Ministry of Labour of Ontario, and CANMET. The status of this collaborative development work has been sum- marized in (1) for publication in October 1985. The outcome, as of May 1985, is that the beneficial environmental effects of filter have been demonstrated both in the laboratory (1), and underground (2). Further, progress has been such that systems incorporating this filter unit may be commercially available by the end of 1986. One of the major aspects of the studies has been the characterization of soot ignition temperatures under varying conditions of operation. This is a fundamentally important matter because continuous deposition of soot in the filter could raise the engine backpressure to unacceptable levels within 1 to 3 shifts of LHD operation. Such levels would require the application of some Keywords: diesel emissions, load cycles, sool, filters. Presenied at the 54th Annual Meeting and Technical Sessions of the Mines Accident Prevention Association of Ontario, May 1985. Reprinted with permission of the MAPAO. 151 means of combusting the accumulated soot in order to return the filter to suitable operating condition, safely, easily and reasonably quickly. Under- ground studies at INCO have begun to shed light on this and other issues. The surprising point that emerged early from these tests, was the fact that the filters were auto-generating, and did not therefore, require remedial attention of any kind during normal operation. Evidently, the LHD service to which they were subjected underground was of such a 'nature' that the backpressures for high speed idle engine operating conditions, rose from a value of around 2.5 kPa (10 in HO) for new, unsooted filters, to approxi- mately 5 kPa (20 in H ? 0) after some hours of operation, remaining at that equilibrium level for hundreds of operating hours thereafter. This positive result provided a strong incentive to define, in real world circumstances, not only the nature of these auto-regenerating condi- tions, but also if possible, the regeneration temperature threshold of soot generated with no fuel additives or catalysts involved. Additives and cata- lysts have been shown to lower the soot ignition temperature (1,3). If suc- cessful, such studies would therefore outline the application regime for unassisted auto-regeneration of ceramic filters. The following is a descrip- tion of a successful effort to pin-point these conditions underground thanks to unforeseen unusual engine operating conditions. FIELD TEST EQUIPMENT DESCRIPTION THE FILTER CONFIGURATION The filter units are composed of a honey-comb ceramic material and configuration designated by Corning as EX-47, 100/17. This ceramic structure is characterized by a large number of parallel channels alternately plugged at both ends so that soot-burdened exhaust gas entering each channel must traverse the membrane wall in order to exit from an adjacent channel. This principle is illustrated schematically in Fig. 1. In the process of passing through the ceramic membra-"^ wall, 90$ of the soot is removed from the ex- haust. When a filter cf sufficient size for use on a Deutz 8-cy Under mining engine (F8LM13FW or F8L71M) is assembled, its overall configuration is illus- trated in Fig. 2. The ceramic element is 'canned' with a sealant material around its periphery to prevent leakage and to fix the ceramic in place, and diffusing and converging cones are fitted to the inlet and outlet of the unit for convenient connection to the exhaust system. The units can be supplied with rugged quick-release, over-centre flange locking systems for rapid, easy removal when necessary. ■B^^^^KL 152 OPERATING HISTORY OF THE FIELD-TESTED FILTERS Beginning in 1982 and continuing to the present, INCO has mounted three pairs of filter units on a JARCO 500 LHD. These pairs were designated: (a) #4 and #5, (b) #24 and #25, and (c) #18 and #19, by the collaborating agencies. These filter sets saw 267, 850 and 396 h of vehicle operation re- spectively before increasing backpressures were noted. During these periods, records were kept of backpressure changes at high speed idle engine operating conditions. The first set suffered some damage and was retired from service after the 267 h. The design and adaptation aspects of the second and third sets were improved however, and these are continuing in service. Set (c) has seen an additional 394 h since off -machine regeneration, giving an approximate total for that set of 790 h at time of writing (March 85). The increases in backpressure for pairs 24/25 and 18/19 were asso- ciated in both cases with significant periods of machine shutdown of the order of one month. While such shutdowns are perhaps not the greatest contributor to the pressure drop increase, it appears to be prudent to avoid long-term shutdowns, or regenerate the filter before storage. After noting increased backpressure at the end of these long operating periods, both sets of filters were shipped to the Ontario Research Foundation (ORF) for dynamometer assess- ment of backpressures, filtration efficiency checks, and for regeneration of the filters by high temperature operation of the engine (3 to 4 min) as was the case for filter number 24; or by slower ? diffusion-controlled electric oven regeneration (eight hours at 510°C or 950°F) for filter numbers 18, 19 and 25. The dynamometer-determined backpressures and soot filtration effi- ciencies for specified engine operating conditions, are given in Tables 1 and 2 respectively, for both pre- and post-regeneration runs. The results re- ported here are derived from (4) and discussed below. Subsequently, filters 18/19 were returned to the mine and re-in- stalled on the same machine. They had an additional 40 h of operation after the ORF regeneration at 396 h, when the temperature traces for the three cycles described below were produced during January 1985. Further operation of this set has resulted in a total of 790 h of use, as mentioned above. At the 790 h point, one filter again experienced a pressure drop change (#19). This unit was removed for inspection and possible further test- ing later, and filters 24/25 were shipped to INCO from ORF to continue the program. As discussed in detail below, all of these pressure drop increases appear to be due, in the main, to an unusually large bank-to-bank exhaust temperature differential resulting in soot build-up on the non-regenerating 153 cold side. INSTRUMENTING AND EQUIPPING THE JARCO 500 LHP A Priraeline 6723, two-pen portable recorder with an Omega TAC386-K converter was mounted on the top of the JARCO 500 LHD (INCO #55*0 equipped with a Deutz F8L714 engine which had 5000 plus hours of operation since re- build. The recorder inputs were each connected to a 0.125-in. diam. sheathed thermocouple (standard for this work), inserted into the inlet of each ceramic filter. The filters were adapted directly to the exhaust manifold via a metal, accordion-type vibration isolation coupling, and fixed rigidly to the frame of the vehicle by angle-iron brackets welded in place. Filter #19 was mounted on the RHS engine bank (when viewed from behind the engine end of the machine, looking forward to the bucket at the front end); and filter #18 on the LHS bank. The machine was performing normal LHD production functions plus util- ity service on the lUOO-ft level of the Little Stobie Mine. The plan view of this level is shown to scale in a number of the figures defining the machine cycle referred to below. TEMPERATURE FINGER-PRINTING THE CYCLES The operation of the machine was, where possible, observed directly and notes were made regarding the specifics of the several path3 that the machine followed. The temperature traces taken, along with the cycle time and distance measurements, defined the three types of production cycle that the machine performed plus preliminary warm-up periods (4 to 5 production cycles to equi- librium from start-up), and also defined some periods when the machine was used for utility purposes (materials handling, muck cleanup, toe of wall dressing, and floor scraping). The time and distance aspects of the three cycles, styled A, B and C ; are defined in Tables 3, 4 and 5 respectively. Cycles A and C are well-defined because the vehicle could be kept in sight during its entire cycle. Cycle B is mostly inferred because only the end points at the mucking and storage sites were time-measured along with the 20$ ramp data. Figures 3, 4 and 5 show the scale plan view of the A, B and C cycle routes respectively. Figures 6 and 7 are reduced reproductions of the RHS (hotter) tem- perature traces only. These traces, read from right to left, were examined using an area planimeter in order to determine average cycle temperatures and times above U82°C (900°F) so that the regeneration potential of the cycle 154 could be evaluated. The results for both the LHS and RHS filters are given in Tables 6 and 7. The latter table provides an estimate of 'overall' tem- peratures including not only the production cycles, but the utility and warm- up periods as well. These were all included in an attempt to characterize the entire operation of the machine in such circumstances. DISCUSSION OF THE RESULTS DYNAMOMETER EVALUATION OF FIELD-TESTED FILTERS From Table 1 derived from (4), it is clear that after 396 h, only filter #18 required regeneration because of a moderately high backpressure of 8.4 kPa (33.6 in H_0). The pre-regeneration pressure of #19 was somewhat low at 3.7 kPa (14.6 in HO). Both filters were carefully regenerated in an oven for 8 h at 510°C (950°F). Filter #18 was regenerated back to a high idle value of 3.0 kPa (11.8 in HJD). On regeneration the backpressure for #19 unaccountably increased from 3-7 to 4.9 kPa (14.6 to 19.4 in H^O). This latter value was confirmed by the on-board field value recorded in Table 9 as discussed below. Table 2 records soluble, insoluble and overall soot filtration effi- ciencies, before and after regeneration for a high speed, non-auto-regenerat- ing, steady-state load; and for a lightly-loaded LHD cycle (called the Michi- gan Technological University - MTU cycle). Notice that the insoluble fraction (solid carbon) efficiencies remain high, but the soluble fraction (liquid hydrocarbon) efficiencies have decreased after regeneration. This effect could be a sign of some minor ceramic pore structure change. However, because of the known affinity of hydrocarbons for soot, this efficiency should in- crease with a small am6unt of soot deposition after re-installation, as the pre-regeneration numbers in Table 2 suggest. Thus, even after 396 h the fil- tration remains substantial. This same outcome was also true for the 24/25 pair after 850 h. It should be noted that the 389°C (733°F) overall INCO LHD tempera- ture measured in this study (see RHS trace Table 7) is similar to the steady- state dynamometer loading temperature in Table 2, i.e., 400°C (750°F), and that the field filtration efficiency is similarly likely to remain at the 90% plus level for a sooted filter demonstrated by the dynamometer results. As far as dynamometer definition of the ignition temperature of field-deposited soot is concerned, the ORF studies (4) showed that the diesel particulate ignition temperature, as determined by step increases in load with noted zero change in backpressure, varied between 431 to 452°C (807 to 846°F). This result is compared to the field results below. That this result is con- siderably below the 482 to 496°C (900 to 925°F) range known for soot regenera- 155 tion in new filters (1), is perhaps because of modest catalytic action by the non-noble metal deposits from fuel ash and lubricating oil additives and ash. Apparently, soot regeneration temperature reduces with use. FIELD CYCLE DEFINITION Tables 3, 4 and 5 record data for cycles A, B and C respectively. The location points in the mine, used to define the various segments of each cycle, are indicated in Figs. 3, 4 and 5 respectively. The cycles measured vary in total cycle time from 87 to 228 s, involving round trip distances of 147 to 285 m (482 to 934 ft) and having average machine speeds of between 1.5 to 2.4 m/s (5.0 to 8.0 fps). If a detailed examination of cycle 8 of the A-type (see Fig. 6) is made, the results can be presented in the form of Table 8 and Fig. 8. It is not a surprise that travelling up-grade produces high temperatures, and down grade-low temperatures for example. The contribution of all the other aspects of the example cycle can be clearly defined as in Table 8, and the other types of cycles similarly detailed. These tables and figures provide detailed information potentially useful for predicting suitable applications of simple non-auto-regenerating filter to planned LHD cycles in a given mine layout. The result of planimeter analysis of the traces documented in Table 6, is that the regenerating RHS bank exhibited temperatures above 482°C (900°F) for periods ranging from 24 to 53% of the time.. The corresponding peak temperatures varied between 507 and 528°C (945 and 982°F), and the aver- age temperatures between 435 to 468°C (815 to 874°F). These RHS levels are evidently required for regeneration; the LHS levels do not regenerate. Note that Table 6 suggests that where a catalyst or fuel additive is to be em- ployed, it is likely that even the cold bank would auto-regenerate. DEFINITION OF AUTO-REG ENE RATION TEMPERATURE IN THE FIELD The go/no go relation of the RHS/LHS respectively was the fortunate result of the engine in question being near the end of its life prior to re- build (5000 plus hours), and exhibiting an unusual temperature differential between left and right banks. This differential varied between 68 and 91°C (122 and 164°F) for the peak temperatures, and 56 and 80°C (100 and 144°F) for the average temperatures of Table 6. This is a high differential relative to CANMET dynamometer experience, and Henninger Diesel of Sudbury suggests that the differential should be approximately 14°C (25°F). Evidently, some fuel- ling system component required some adjustment. As pointed out above, it is clear that the colder LHS filter #18 was 156 not regenerating, and the hotter RHS filter #19 was. This is evident from backpressure data gathered from the time of re-installation at 396 h to the present (March 1985). This data is recorded in Table 9 and plotted in Fig. 9. The backpressure values were determined by reading a pressure gauge inserted between the filter and the manifold during check periods only and for which the engine was operated at full speed no load. When the LHS filter had built up to a backpressure of 15 kPa (60 in H ? 0) after 108 h of operation after ORF regeneration (approximately 2f shifts - a slow buildup), it was decided to exchange filters side to Side. The result was that in about eight hours the high backpressure filter #18, returned to the equilibrium backpressure 4.5 kPa (18 in H p 0) which pressure remained unchanged thereafter. Figure 9 indicates a gradual increase in back- pressure for filter #19 after it was placed on the colder LHS. Quite clearly, the cycle temperature variations from bank-to-bank, bracket the 'real world 1 soot auto-regeneration conditions. As recorded in Table 6, cycle A generated the lowest RHS (hot) average temperature - 435°C (815°F); cycle C generated the highest LHS (cold) cycle temperature - 408°C (766°F). Note that the RHS field temperature exceeds the J*31°C (807°F) mini- mum dynamometer-determined value quoted above (**), and the LHS value falls below. Thus laboratory and field data appear to corroborate one another sug- gesting that average temperatures in excess of 430°C (805°F) are likely to auto-regenerate diesel soot in ceramic filters. These and other underground filter tests (2) resulted in very evident environmental improvements which have impressed the miners working in the test areas to the point where the removal of the filters for other tests has met with resistance. This is because of positive subjective impressions, which are in some cases backed by direct evidence, as follows: 1. virtual absence of soot in the headings (2), 2. consequent reductions in toxicity of the environment: a) 30 to 50% relative 'raw' untreated exhaust (1), or b) up to 75% relative to a widely-used catalytic purifier (2), as measured by the Exhaust Quality/Air Quality (EQI/AQI) Indi- ces, 3. considerably improved visibility, promoting safety and potential- ly increasing productivity, 4. substantial reductions in machine noise - up to 14 dbA (5), per- forming the muffling function well. 157 CONCLUSIONS The apparent corroboration of laboratory and field test results sug- gests that LHD cycles characterized by average temperature levels above 430°C (805°F), and sufficient high temperature excursions such as encountered during the studies reported, will auto-regenerate ceramic wall-flow filters. This process involves minimal apparent filter damage for hundreds of hours of un- tended operation, yielding significant improvements in the operating environ- ment and in several other mine operating parameters. ACKNOWLEDGEMENTS The efforts of the following contributors to this study are grate- fully acknowledged : M. Szabo and B. Manicom of the Ontario Research Foundation, for dyna- mometer evaluation of field-tested filters, and J. Vallieres and J. Ebersole of CANMET for careful attention to the calibration and operation of the temperature recording equipment, and management and operators of INCO Ltd. for their cooperation and assistance. REFERENCES 1. Dainty, E.O., Mogan, J. P., Lawson, A. and Mitchell, E.W. "The status of total diesel exhaust filter development for underground mines"; XXIst International Conference of Safety in Mines Research Institutes; Sydney, Australia; October 1985. 2. Gangal, M.K., Dainty, E.D., Weitzel, L. and Bapty, M. "Evaluation of diesel emission control technology at COMINCO's Sullivan. Mine"; Presented to the Mechanical/Electrical Symposium under. the sponsorship of the B.C. Ministry of Energy, Mines and Petroleum Resources; Victoria, B.C.; February 1985. 3. Lawson, A., Vergeer, H.C., Drummond, W., Mogan, J. P. and Dainty, E.D. "Performance of a ceramic diesel particulate trap over typical mining duty cycles using fuel additives"; SAE paper 850150; SAE International Congress and Symposium; Detroit, Michigan, USA; February /March 1985. k. Vergeer, H.C. "Results of the evaluation of four DPFs used in the INCO mining operation"; Presentation by the Ontario Research Foundation to the Underground Diesel Emissions Planning Group at Washington Office of the United States Bureau of Mines; February 1985- 5. Howitt, J.S., Elliott, W.T., Mogan, J. P. and Dainty, E.D. "Application of a ceramic wall-flow filter to underground diesel emissions reduction"; SAE paper 830181; SAE International Congress and Exposition; Detroit, Michigan, USA; February /March 1983- 158 V O 0» -* o» •o eg - X ■ 03 1 m I pn en ■ P» 1 r. oc c o ■ p- as cn O CJ a. z it * 1 p- 1 as I CM 1 s z O as o IM CM X IM 1 p» O m e- o» » ■3- > pg on *«i » «■< M Pg ■^ S a i. o ffl p» in P- a «■ CO pg o a. » as o o a. (M J< ST CM p» CM as cn pn m Pg a O r- p- O z CM o vO 1 p- as 1 l I I ^ t M PU e a l o o S IM o> e IM a. M X » 1 VO pg I i I I O pn o so no as d) TJ >> O C Cm 0> C o •H ■P O O o o> .■-• ro t- co D. >> t- o Jj ro t- o x> ro CVJ to H c o •H J-> ro r_ a> c V V I- t- o Cm a> m t— CVJ MO 00 00 in o <* t- oo o\ o m (M 1 a- o cy> cj> Ov CO o in vo 0> 0^ l>- in in in a- in oo m oo O CO VO 00 Ov o a- Cn Cn OO o^ vo m t- Cn VO •H fH in CM CM OO cn av cn ON OV Cn On bO C •H *s ro L 0) Q. O 0) c •H bO c u 0) • *> o pH 2 CM cn Cn a- 00 Cn VO CO 00 o> CO VO o >> o * o o CM X a- J •»v 1 o =5 o H CM z CM CM O >> o a x i 3 H in CM o CM sr o o CM CM O >> ° o Q CM x -a- J ^ I o =» p t- CM O >. o a x j i H O in r- o o X 0) 4J z o CM sr •o c CO E a t- o o CM CM Table 3 - Measured definition of LHD cycle A (see Fig. 3) 159 Location Description of function Approx, time (sees) Approx. distance (m) Approx. average velocity (m/s) (mph) 1-1 mucking period 30 1-2 hauling loaded up 20$ grade 11 2-3 hauling loaded on level 22 3-1 hauling loaded up 10$ grade 20 1-5 hauling loaded down 10$ grade 15 5-6 hauling loaded on level 10 6-6 dumping period 12 6-5 hauling empty on level 11 5-1 tramming empty up 10$ grade 15 1-3 tramming empty down 10$ grade 10 3-2 tramming empty on level 15 2-1 tramming empty down 20$ grade 2l_ 10 26 18 31 21 21 31 18 26 10 0.91 2.0 1.2 2.7 0.?1 2.0 2.2 5.0 2.1 5.5 2.2 5.0 2.2 5.0 1.8 1.1 1.7 3.9 1.7 3.8 overall cycle 228 28'l 1.25 iA Table 1 - Inferred definition of LHD cycle B (see Fig. 1) Location Description of function 6-6 6-7 7-5 5-8 8-9 9-9 9-8 8-5 5-7 7-6 dumping period tramming empty bucket direction reversal on level tramming up 20$ grade empty tramming empty up 2$ grade mucking period hauling loaded down 2$ grade hauling loaded down 20$ grade bucket direction reversal on level hauling loaded on level Approx. Approx. Approx. average time distance (m) velocity (sees)* (m/s) (mph) 12 - - - 18 17 0.9 2.1 7 15 2.1 1.7 35«« 30 0.9 2.0 20 19 2.1 5.5 25 - - - 15 19 3.2 7.2 7«*« 30 1.3 9.7 8 15 1.8 1.1 12 17 1.1 3.2 overall cycle 159 222 1.8 1.0 •cycle No. 5 of cycle 13 **C Bourre measured 19 sees, average »»«C Bourre measured 6.5 sees, average 160 Table 5 - Measured definition of LHD cycle C (see Fig. 5) Location Description of function Approx. Approx. Approx. average time distance (m) velocity (sees)" (m/a) (mph) 17 - - - 8 17 2.1 4.8 in 38 2.7 6.1 12 18 1.5 3.4 10 - - - 9 18 2.0 4.6 10 38 3.8 8.5 7 17 2.4 5.5 6-6 mucking from stored pile 6-7 bucket direction reversal on level 7-4 hauling loaded up 10% grade 4-3 hauling loaded down 10% grade 3-3 dumping into ore cars 3-4 tramming empty up 10% grade 4-7 tramming empty down 10% grade 7-6 moving into stored muck pile overall cycle 87 146 2.4 5.5 Table 6 - Regeneration and cycle temperature measurements Type of cycle A B C Filter location LHS RHS LHS RHS LHS RHS maximum cycle temp. (°C) (°F) 416 781 507 945 452 846 528 982 440 824 508 946 time above 900°F/482°C (%) 24 53 37 average cycle temp. (°C) (°F) 359 435 402 468 408 464 671 815 756 874 766 867 apparent auto-regeneration? yes yes no yes projected additive-assisted regeneration? ' yes yes yes yes yes *350 to 366°C (660 to 690°F) dynamometer-defined minimum average temperature for regeneration with catalyst coating or additive in the fuel. Table 7 - Time-weighted average exhaust temperatures including production and utility LHD duty Type cf duty ■ Cycle A Cycle B Cycle C Utility Warmup Overall RHS average temperature (°F) CO 815 435 874 467 867 464 579 304 554 290 473 245 733 389 LHS average temperature (°F) (°C> 671 355 756 402 766 408 500 260 625 329 Time contribution of duty (%) 29 23 8 22 18 100 161 Table 8 - Detailed time-temperature analysis of production cycle 8 of cycle type A Accumulated Time time Tempera ture Location Description of function (sec) (sec) (°C) (°F) 1 start of mucking 302 576 1 end of mucking 15 15 112 828 2 top of 20$ upgrade 140 85 508 916 3 end of level 20 105 120 788 1 top of 10$ grade 25 130 500 932 5 bottom of 10$ grade 15 115 365 689 6 end of horizontal tramming 10 155 160 860 6 end of dumping 13 168 180 896 5 end of horizontal tr amming 12 180 118 838 1 top of 10$ grade 15 195 187 909 3 bottom of 10$ grade 10 205 392 738 2 top of 20$ grade 15 220 120 788 1 bottom of 20$ grade 25 215 308 586 Table 9 - Filter regeneration by cold to hot side exchange - high idle backpressure variation with time Variable backp "essure rilter location (see text) LHS RHS Relative exhaust temperature level colder hotter Filter identification number initially //18 #19 units (kPa) (in H 2 0) (kPa) (in H 2 0) Accumulated time (h) installation of regenerated filter on LHD 1.5 18 7.0 26 10.0 10 11.3 15 15.0 60+ filter numbers after exchange 1.5 5.0 5.0 5.5 5.0 18 20 20 22 20 019 #18 5.0 1.5 5.0 6.0 6.2 20 18 20 21 25 15.0 12.5 1.5 1.5 1.5 60+ 50 18 18 18 10.2 67 91 108 2 8 28 -3J_ 6.5 7.5 7.5 10.0 9.5 • 26 30 30 10 38 1.5 t) o 1.5 1.5 1.5 18 18 18 18 39 68 112 119 211 286 •Probable gauge problems. 162 Fig. 1 - Ceramic filter - principle of operation Entronce cone Seal Fig. 2 - Heavy duty ceramic filter configuration 0& n'°"tf 3 q o ° Q5 ^0 o iiji torage Garage Seals-, m 1 1 1 1 10 20 30 1 i i i i | i i i i | 50 100 Scol«ft Muck point Fig. 3 - Plan of Little Stobie's 1400 ft level showing route for cycle A 163 Muck point r — cfe^ CD Q {/ 3 £ Hx£^ 8 r """W I / iV& /Storage M ill tlM I MMHM I I HHMM l HH I MM t Scale m I 1 1 1 10 20 30 I t I i i | i I i I | 50 100 Scole:ft Fig. 4 - Plan of Little Stobie's 1400 ft level showing route for cycle B Garage Gorage I i i i i l i i i i | 50 100 Scale:ft Fig. 5 - Plan of Little Stobie's 1400 ft level showing route for cycle C 164 Temp (°C) ^ ^^^^^^^^^^^^^^^ ^ 600 500 400 300 200 100 15 13 Utility vehicleuse o q csi u |se 3 cycles (A) r: u c x> >» O w ® « 12 4 cycles 7cycles (A) (A) 1 + •^ a icycle I ° Mucking cycle no. Preliminary use m q csi o q in o O cvi 6 o o q •n cvi K) cvi Fig. 6 - RHS (hot) temperature traces for cycle A and utility use Tffl ttff ! W\i ^fnfypA M\h-A m n plFf Iff m& i::::: * 6 5 4 3 lO o c k o - 6cycl 215 4 3 2 1 65 •> 3 > es 5 cycles |= 6( 4 321 :ycles 3 cycles Utility 9 8 7 6 5 9 eye 4 3 2 les i Preliminary 2 4 O O a 3 k. o " (O (B) R (C) (B) vehicle use (G 1) use in Temp (°C) 600 500 400 300 200 100 Fig. 7 - RHS (hot) temperature traces for cycles B and C and utility use 165 T3 a o c 3 a> •o o O O C 3 O C "i E ■0 3? O c 0) TJ O k. E « c E E ■D O ■0 c E E e O k. 9 O •> TJ O k. 35 ai > a> •0 3? 38 k. O T3 Q. 3 k> k. k. e * O M O k. O CM O a. a. O O. a CM c • O C O N T3 • ■O O O O O O c 9 c a. O c ■0 ■0 ■0 3 at ■0 O at ■0 3 ■o a> "O c 1000 _ IA w k. E k. ■0 SJ 9 O C "c O 3 O 3 O I 3 3 X O ^ -1 _l _l -1 2 900 u. t, 800 9 L. \ 3 o 700 i- 01 Q. « 600 1- Cycle 8 of cycle type A expanded \ 500 400 ^ i i . . .. 1 L. 1 ...1 ■ ' _j 1 t500 o c V k. 3 O - 400 a> CL E 40 . u_ 3 CO 35 to 0) 30 / ■— a. 25 U O 20 jQ 15 - 0) c 10 m Hot side o» c b UJ 1 1 • Filter no. 18 x Filter no. 19 ii5 Time of side toside exchange _1_L - 10 40 80 120 160 200 240 280 320 Elapsed time (hours) 360 400 Fig. 9 - Filter regeneration by cold to hot side exchange - high idle backpressure variation with time O 0. 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