Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924003951773 Date Due 5 1924 003 951 773 - ^3%^o involves friction. Friction will eventually bring the moving bodies, whatever they be, to rest and the kinetic mechanical energy will then have been entirely converted into heat energy. The reverse of this process is not in general as easily accomplished — in fact rather elaborate devices are required when it is desired to continuously convert heat into me- chanical energy. Such devices are known as heat power plants, several types of which wall be discussed in a later chapter. The operation of such a power plant can be illustrated diagrammatically as in Fig. 1. In this figure A represents a source of heat; that is, anything in which heat is made available at a comparatively high temperature T-. The ordinary boiler furnace is a good example. B repre- sents the device in which heat is converted into mechanical energy — in engineering language it is an engine or a heat engine. The body C is anything which can be maintained at a comparatively low temperature, T 2 , and which can receive heat from the engine. The combination of A, B, and C constitutes a heat power plant and operates roughly in the following manner. I. THE HEAT ENGINE PROBLEM 5 Heat flows from A to the engine B in quantities repre- sented by the width of stream a. All this heat enters the engine B and part of it is there converted into mechanical energy, leaving the engine as represented by stream b. The part of the heat stream a which is not converted into mechanical energy remains in the form of heat energy and passes from the engine to the body C as shown by stream c. In all heat power plants the following two conditions exist : 1. The heat leaving the engine in stream c is at a lower Heat in Steam \^__ Atmosphere Heat in (Cold Body) Steam (CJ (T,) Cold Body Fig. 1. temperature than that entering the engine in stream a and 2. The sum of the quantities of mechanical and heat energy leaving the engine, i.e., the sum of the streams c and b, must equal the heat energy entering the engine as represented by stream a. It is obvious that the best plant will be the one which converts the maximum amount of heat stream a into mechanical energy as represented by stream 6. A measure of the performance of a plant is therefore obtained by dividing the quantity of mechanical energy (b) leaving by 6 GAS POWER the quantity of heat energy (a) entering. This quotient is called the thermal efficiency of the plant — that is . Mechanical Energy made available Heat Supplied The nearer this fraction approaches unity the more nearly does the plant convert into mechanical energy all of the heat supplied and, therefore, the better it is as a power plant. It can be shown that a theoretically perfect power plant can under no circumstances have an efficiency as high as unity — because it must always reject heat as heat. Real plants do not, of course, give as good results as theoretical considerations indicate to be possible, and real power plant 1 35 efficiencies range from — to about , that is, from b 100 100 1 to 35 per cent. The best real plants thus convert into mechanical energy about 35 per cent of the heat supplied and reject at low temperatrure the other (>."> per cent. The practical bearing of these considerations on the gas power field will appear in later chapters. CHAPTER II. FUELS. In Chapter I, the general term fuel was explained, and various familiar examples cited. It was shown that for man's purposes, it is more convenient to utilize the heat stored in fuels than to make a direct conversion of the sun's rays. The so-called fuels fall into logical groups, which will be described briefly here, while those bearing more directly on gas power work will be considered in more detail in later chapters. Solid Fuels. 5. Wood and Vegetable Fibres. The processes of vege- table growth closely resemble processes which occur in a mod- ern chemical laboratory. AVater, drawn from the earth by the plant, and carbon, in the form of CO2, drawn from the atmosphere, combine under the action of the sun's rays to form chemical combinations of which cellulose is the most familiar example. The chemical composition of pure cellulose is, C = 44.44 per cent; H = 6.17 per cent; = 49.39 per cent. Cellulose and other similar compounds, in combina- tion with plant juices and small quantities of mineral salts and other substances, form vegetable materials such as wood, leaves, grasses, ferns, mosses, etc., which can be used as fuel after proper treatment. Wood, which is one of the most familiar examples, often contains as much as 40 per 7 8 GAS POWER cent of water when felled, and must be dried for satisfactory use. When wood is heated under conditions which partly or entirely prevent oxidation, destructive distillation occurs, which, if continued to a sufficient extent, converts the wood into what is known as charcoal, a material containing practically only carbon and the mineral salts originally present in the wood itself. 6. Coal. It has been clearly proven that coal is formed from vegetable materials, such as those just described* which accumulated in thick layers on the earth's surface ages ago, and were later buried under deposits of silt and other earthy matter. The process of formation of coal is complex, but in brief we may say that coal is the result of the distillation of the original vegetable matter under the action of the natural heat of the earth and the heat generated in decomposition. Its ultimate composition is dependent upon the amount of hydrogen and other gases which have been able to escape from the decomposing mass. Thousands of years ago a piece of coal was a mass of damp vegetable fibre, a portion of a peat-bog. During successive geologic ages the peat-bog was submerged and overlaid with mud which hardened into slate. This was covered with glacial and alluvial drift, and may have been tilted and upheaved by volcanic action or subsidence of the earth's crust. It was subjected to great pressures and high temperatures, and underwent a more or less complete destructive distillation under pressure. The products of the distillation vary in different localities, and with dif- ferent histories, so that we now find materials varying all the way from the original peat, through the lignites, bitumi- nous and anthracite coals, to graphitic coal. The last named found in Rhode Island, has had nearly all the volatile hydro- carbon gases and oxygen driven off from it, leaving prac- tically only fixed carbon and ash. This carbon is in a form II. FUELS 9 which is so hard to burn that it finds no extensive use as a commercial fuel. Coals are classified in many ways, the most common being according to the relative percentages of carbon and volatile matter contained in the combustible portion. The following outline will serve to indicate both the line of development and the general classification of coals: 1. Wood. Fresh vegetable material, cellulose, starch, water. 2. Peat. Vegetable matter, consisting generally of mosses more or less decomposed under water. Generally dried by weathering or pressure or both before use. 3. Brown Lignite. Carbon, complex paraffin hydro- carbons and carbohydrates, water. 4. Black Lignite. Like the brown lignite but with more elementary carbon. 5. Sub-Bituminous. Intermediate in grade between the black lignite and bituminous proper. 6. Bituminous. Carbon, complex hydrocarbons, with carbohydrates and no hygroscopic water. 7. Semi-Bituminous. Between bituminous and semi- anthracite. 8. Semi-Anthracite. More elementary carbon than (7) and no carbohydrates; less of hydrocarbons and these simpler. 9. Anthracite. Elementary carbon and simple hydro- carbons. 10. Graphitic Anthracite. Very few hydrocarbons left, and some of the elementary carbon transformed into graphite. 11. Graphite. Final result. A study of the map of the U. S. will show the remark- able way in which the coal deposits of this country follow in general the table of gradations outlined above, viz., the deposit in Rhode Island and Massachusetts of hard graphitic coal, high in carbon content and low in ash, mois- 10 GAS POWER ture and volatile matter; followed in Eastern Pennsylvania by the great anthracite beds which grade off as we pass on to the Susquehanna River to the semi-anthracite fields. These in turn are succeeded by the large bituminous deposits of Western Pennsylvania, Eastern Kentucky and Ohio, extending down into Tennessee and Alabama; while the fields of Indiana, Illinois and Western Kentucky belong to this same classification. Passing the Mississippi, we find a constantly decreasing quality of coal from the standpoint of carbon content, which finally grades into the lignites and peats of the Pacific Coast regions. While this broad statement is true in gen- eral, it must not be taken too literally, as there are numerous small fields of various qualities, erratically distributed over the country; but the best of the higher grade coals of the West do not compare favorably with those of the Appalachian Mountain system. In Alaska, bituminous and anthracite deposits of good quality are being opened. 7. Solid Wastes. Other possible solid fuels are manu- facturing and city waste, sawdust, straw, shavings, bagasse and tan-bark, etc., which materials can be burned under boilers in vicinities where such use results in actual financial returns. The modern methods used in producing gas from these solid fuels, to be used for power purposes in an engine cylinder, will be fully discussed in a later chapter. Liquid Fuels. 8. Petroleum Products. The most important liquid fuels to-day in gas-engine work are the petroleum products which are obtained from " oil " wells situated in various parts of the world, as Russia, Pennsylvania, Ohio, West Virginia, California, and Texas. Crude Petroleum, as it comes out of the earth, is a mechan- ical mixture of many different hydrocarbons, with some II. FUELS 11 sulphur and other impurities. Hence it is to be expected that crude oils from various fields will show compositions which differ considerably. By the process called refining, which is accomplished by fractional distillation, a series of distillates is obtained running from the very light vapors and oils down through the heavier liquids, to the final thick, tarry residues. Each succeeding product, therefore, contains a number of hydro- carbons with contiguous boiling-points. Of these oils, the various gasolines, kerosenes, and the so-called ." dis- tillates," besides crude oil itself, are widely used for gas- engine fuels. The first results of crude oil distillation are very light products, which are easily vaporized, and very dangerous because an explosive mixture is quickly made when they are exposed to air. They have, therefore, not been used to any extent for internal combustion engines. Following the distillation of the above mentioned light products, we obtain a series of gasolines of varying gravities and flash points. The first of these is about 86° Be. gasoline,* which is now seldom used for power purposes because of the small quantity available. This is followed by gasoline of higher specific gravity (lower Be. number) and lower flash point. Most of the gasolines used in engines at the present time are in the neighborhood of 60 to 65 Be. The next heavier distillate following the gasolines is kerosene, which is not used for gas engines in this country as extensively as is gasoline. It will not so readily form an explosive mixture with air at ordinary temperatures, and therefore requires more elaborate apparatus when used as a fuel in internal combustion engines. There is another group of refinery products called distillates. These are not as well refined as kerosene, * This is read 86° Baume gasoline, and means that an instrument which is called a Baum<5 hydrometer will sink in the liquid to a point marked 86 on an arbitrary scale attached to the instrument. 12 GAS POWER but resemble it in their general properties. They are handled in the same way for gas-engine work. Table No. 1 gives average values of the analyses of American fuel oils, as determined in a recent investiga- tion by the authors. Table I AVERAGE VALUES OF ANALYSES OF AMERICAN FUEL OILS Gasoline Kero- sene. Crude Oil. Fuel Oil. Baum6 gravity Specific gravity Per cent carbon Per cent hydrogen Calorific value per lb. (calcu- \ "High lated) J Low Calorific value per lb. (actual ] High by test) / Low Theoretical air, cubic ft. per pound. Calorific value per cubic foot 1 High of mixture, theoretical air . . J Low Oxygen +nitrogen Per cent nitrogen Per cent oxygen Per cent sulphur Calorific value per cubic foot mixture (low), calculated with given excess coeffi- cient Boiling-point Flash point 70 2° 0.704 82 . 54 14.91 21,271 19,818 19,740 18,500 193.5 109.2 102 4.3 1.93 31 09 93 85.2 78.8 73 2 68.2 167° 47° 0.863 84.00 14.14 20,892 19,600 20,849 18,755 189 110.3 103.6 2.3 1 . 838 2.0 0.23 94.3 86.3 79.7 74.0 69.0 437° 130° 18.3° . S77 84.24 13.44 20,162 19,160 19,560 18,636 187 111.7 102.3 3.1 0.2 1.93 0.823 93 2 85.3 7:-! 6S 0.939 83.04 11.58 19,183 18,183 19,121 178 110.2 102 0.60 2.82 0.90 92.7 85.0 78.5 73.0 68.2 * When the heat of the vaporization of the water vapor present in the product.* of combustion is not included in the calorific or heating value per pound or per cubic foot of the?e gases, the result is known as " The Lower Heating Value " " The Higher Heating Value " includes this extra heat. 9. Alcohol. Ethyl alcohol is not used to any extent in this country as a gas-engine fuel, but is the most likely successor of the petroleum products as these become scarcer. II. FUELS 13 Results of tests show that a higher thermal efficiency can be obtained from alcohol, due to the higher compression pressures that can be used. It is also much safer than gasoline as regards fire risks. Ethyl alcohol or grain alcohol is made from the fermentation of grape sugar, grain, potatoes, and such substances. It should not be confused with methyl or wood alcohol, which results from the distillation of wood. The heating value (heat liberated per pound of alcohol burned) of ethyl alcohol cannot be accurately computed from its chemical composition, and it is therefore deter- mined by means of the calorimeter. The value of 11,664 B.t.u. per pound is most frequently used. Absolute or 100 per cent ethyl alcohol has a specific gravity of 0.7946 at 15° C. or 59° F., so that one gallon of pure alcohol weighs 6.625 lbs. One pound of absolute ethyl alcohol requires 9 lbs. of air for its combustion; or 111.5 cu.ft. at 62° F. Absolute ethyl alcohol is never sold for fuel purposes, but is always diluted with water and certain " denatur- ing " substances. This material is sold as " denatured " alcohol, and generally contains about 10 per cent of water and small quantities of methyl alcohol and hydrocarbons with an unpleasant odor. Gaseous Fuels. 10. Natural Gas. This gas, which issues from the interior of the earth in many parts of the world, especially in the vicinity of oil-fields, is very well adapted for use in gas engines. It is extensively used for this purpose in the natural gas regions around Pittsburgh, Buffalo, Indianapolis, and in the State of Ohio. Its chief constituent is marsh gas (CH 4 ), with small amounts of hydrogen, carbon monoxide, and unsaturated hydrocarbons. Natural gas is also found in West Virginia, Kentucky, Tennessee, Colorado and California. Like the petroleum U GAS POWER products, its composition varies constantly, even in the same well, and due to the large amounts that have been and are still being wasted, the supply is rapidly diminishing. The average values of analyses of American natural gases, as given in Table II, show the wide variation in the composition of this fuel. 11. Artificial Gases. In addition to natural gas, the following artificial gases are used for gas engine fuels: (a) Producer gas; (b) Blast-furnace gas; (c) Illuminat- ing gases; (d) Coke-oven gas; (e) Oil gas. These may be roughly divided into two classes according to the proc- ess of manufacture as, (1) Producer gases, or those made by combustion processes and (2) Retort gases, or those made by processes involving destructive distillation. The more important of these gases are described in the following sections. 12. Producer Gas. This is the name given to that group of gases which are generated by the passage of oxygen (present cither in air or in a mixture of steam and air) through an incandescent bed of carbon. The gases com- monly known as suction gas, Dowson, Riche, Mond, Siemens, etc., are all in this class and similar in character. Ordinary producer gas is made continuously by passing a mixture of air and steam through the fuel, in correct proportions to maintain a sufficient amount of heat to enable chemical action to take place. Producer gas may be made from: (1) anthracite coal; (2) bituminous coal; (3) coke; (4) lignite; C3) oil; (6) peat; (7; wood. Its manufacture will be discussed in detail in a later chapter. The compositions and heating values of this gas as made from different fuels are given in Table II, the values given representing the final average of a large number of determinations. 13. Blast-furnace Gas. This is the gas obtained as a by-product during the making of pig iron from iron ore. II. FUELS 15 Table II AVERAGE VALUES OF ANALYSES OF AMERICAN GASES Gas. Average Constituents of Gas in Per CVnt, Volume. CCV CO. H. CH 4 . CsHe. C2H4. OH* N Calorific Value by Test per Cubic Foot. High. Low, Producer: Anthracite. . . . 6.03 22.38 13.38 1.96 0.36 55 . 65 0.803 142 131.3 Bituminous . . 9.12 17.54 11.73 4.2S 0.36 0.424 57.24 0.265 154 130 Coke 4 90 27.30 in 07 1.18 56 60 0.550 133.7 (125) Lignite 9.43 18.90 15.13 3.65 52 . 50 0.582 150.4 *134 Oil 4.10 11.40 5.57 5.87 3.1o: 06 . 90 3 . 060 *176 *151 Peat 12.40 21.00 18.50 2.20 0.40 ... . 45 . 50 0.000 175 |*141 Wood 13.90 20.03 21.00 2.79 0.60 | 41.80 0.185|13S.7J*128 Illuminating: Water 4.72 34.8 48.81 4.06 1.97 7.16 0.503 329 278 Carbureted water 2.07 24.1 32.40 23.40 12.52 3.75 0.510 677 632 Coal or bench. 1.21 6.18 43.94 37.78 5.87 4.16 3.50 0.502 655 592 Natural: Average 684 0.647 10.89 79.67 1.26 6.40 5.S9J0.79 965 S5.3 Hi?h hvdro^en 0.580 0.730 20 . 56 50.30 2.07 5.S8 8.80 1.13 895 810 Low O.SOO 0.525 1.92 91.40 0.515 3.25 0.50 971 862 Blast-furnace... 11.80 26 . 75 3.40 0.30 0.182 9S.7 *95 2 Coke oven 2.1 6.51 51 . 56 32.9 (1.4) 2.5 4.0 0.36 598 . 500 2.79 4.96 17.70 23.60jlS.7S 5.53 37.55 0.702 662 *542 * Theoretical value. 16 GAS POWER The blast furnace may be regarded as nothing more than a large producer, the coke or coal used with the iron ore being partly burned to carbon monoxide by the oxygen in the air blast. The gas given off from the blast furnace contains from 23 to 34 per cent of carbon monoxide, a small amount of hydrogen and hydrocarbons from the dissociation of water and volatile matter in the fuel, some carbon dioxide, and a large amount of nitrogen. Because of the small content of carbon monoxide, prac- tically the only combustible constituent, blast-furnace gas is always of low calorific value, and requires a much greater cylinder capacity than other gases. However, its use in gas engines has led to great savings in plants where it was originally either wasted or burned under steam boilers. Its calorific value (heat liberated per cu.ft. of gas burned) varies from about 85 to 105 B.t.u. per cu.ft. 14. Water Gas. This gas is produced by passing steam through a bed of incandescent carbon (coke), which has first been raised to a high temperature by a forced blast of air. The steam, passing through the fuel bed, breaks up, forming hydrogen, carbon monoxide and carbon dioxide. This breaking up is accompanied by the absorption of heat and tends to reduce the temperature so that the process must be an intermittent one. 15. Mixed Gas or Air and Water Gas. This gas may be divided into two parts: that made during the " blow," during which air only is passed through the fuel, and that made during the " make," during which the fuel is supplied with steam only. The " blow " is a heating period and the " make " a cooling period. Toward the end of the " blow " the gas formed contains a large proportion of car- bon monoxide and is therefore combustible. It is some- times caught and used under the name of air gas. The gas formed during the "make," consisting largely of hydrogen and carbon monoxide, is properly known as II. FUELS 17 water gas. Air gas and water gas are frequently mixed and used under the name of mixed gas. 16. Carbureted Water Gas. This gas is produced in much the same way as plain water gas, except for the addi- tion of oil gas, which is formed by spraying oil into a heated brick chamber, through which the water gas passes. This addition is made for the purpose of giving the latter illu- minating power. 17. Retort Gases. These comprise those gases which are generated by destructive distillation in closed retorts, some being manufactured for fuel and power purposes only, and others primarily as illuminating gases. The two principal retort gases are briefly described in the fol- lowing paragraphs : (a) Bench gas, also known as coal gas, town gas, or illuminating gas, is one of the most important of this class, and results from the distillation of bituminous coal in fire- clay retorts. Its calorific value varies with the fuel and the process of manufacture, but generally lies between 525 and 650 B.t.u. per cubic foot. (6) Coke-oven gas is a by-product obtained during the manufacture of coke in retort coke-ovens. It is the part of the gas generated which need not be reburned for heating the ovens. So far as its properties are concerned it is practically identical with the gas already described as bench gas. 18. Oil Gas. This name is applied rather indiscrimi- nately to the gases made from crude or unrefined oil, by a number of different processes. The principal ones may be roughly divided into producer gas processes, water-gas processes, and retort-gas processes. The first of these, namely the producer-gas process, will be considered in a later chapter. The second very closely resembles the carbureted water gas already described, except that no solid fuel is used. The gas has a high 18 GAS POWER calorific value, and a high hydrogen content, and is not well adapted for use as a power gas, although it has been rather extensively applied for this purpose on the Pacific Coast. The retort process is carried out by properly heating crude or partly refined petroleum, or any other oil composed of hydrocarbons, in a closed retort, so that " cracking " (partial decomposition) results and hydrocarbons, which are gaseous at atmospheric pressure and temperature, are obtained while solid carbon is left behind in the retort. By the proper regulation of the time and temperature, the process of decomposition can be stopped at any desired point. Oil gas is not the same as vaporized oil, since in the latter the hydrocarbons are unchanged, and, if the vapor is cooler a liquid will result. CHAPTER III. COMPARISON OF THE EXTERNAL AND INTERNAL COMBUSTION PRINCIPLES. 19. External Combustion. Heat engines may, in gen- eral, be divided into two great classes, viz., those in which the combustion of the fuel is made to occur in a receptacle outside the engine itself, and those in which combustion takes place directly within the engine. The steam power plant is an example of the first method. In such plants, fuel is burned on a grate under, or within, a boiler, and part of the heat liberated is transferred to and absorbed by the contained water. When the temperature corresponding to the desired pressure is reached, boiling occurs and steam, containing the heat it has received from the fuel, passes through a pipe line into an engine cylinder. This steam now acts upon a piston in the cylinder and part of its heat energy is converted into mechanical energy, part is radiated, and part is discharged in the exhaust steam. In some plants the steam is exhausted into the atmosphere and allowed to waste, while in others it is condensed in an apparatus known as a condenser, returned by means of a pump to the boiler, where it is reconverted into steam, and then again started on the series of events above described. Fig. 2 shows an elementary steam power plant in which the cycle of operations just described can be clearly followed. The energy stream, shown on the figure, represents to an approximate scale the various losses occurring in an external combustion plant. 19 20 GAS POWER III. EXTERNAL AND INTERNAL COMBUSTION 23 expect an internal combustion engine of this type to have a higher thermal efficiency than that of a steam plant. That this is really true in practice is shown by the fact that engines of this kind give thermal efficiencies ranging from 15 to 30 per cent. Now consider a complete producer-gas power plant, where the fuel gas is artificially manufactured in a producer, then cleaned thoroughly to eliminate all dust, and either " , ; ".-i.'^'^y "-*-B ^^i^>^. e i -: ~^~~-~-Jl~ — ^~~~~~~ t *-s.f? v^__ / — [y Clearance I C Vol. J Fig. 10. — Modifications of Ideal Otto Diagram. The gases now expand behind the piston on the third stroke, until the point c' is reached, at about 85 to 90 per cent of the out-stroke, where the exhaust valve must start to open in order to be fully opened before the end of the stroke is reached and to allow the greater part of the charge to escape before the return stroke starts. The point d' is slightly above atmospheric pressure, because as the pis- ton returns on its fourth stroke, the passages and parts offer a slight resistance to the gases, thus necessitating a 40 GAS POWER pressure greater than atmospheric to cause flow. The Velocity of the gases through the exhaust port varies from 80 to 125 feet or more per second, and to produce this, the exhaust pressure line must be from one to three pounds above atmospheric. The area of the " lower-loop," represents the work (force X distance) done upon the gas by the piston and consequently must be subtracted from the total positive work (or the area of the upper loop of the card) in order to obtain the net useful work of the engine. The lower loop area, however, is so small on an actual card that it is usually neglected, in determining the I.H.P. (indicated horse- power) of a real engine. 31. Practical Modifications of Four-stroke Diagram. In Fig. 11 is given the perfect diagram of Fig. 10 with cards, such as might be obtained from practice, superimposed on it to show the discrepancies often existing between the actual and the ideal. In an actual engine it is found that, for best operation, ignition of the compressed charge should occur before the piston has reached the end of its stroke, as at m in the figure, because combustion does not occur instantaneously. With a proper mixture and correct setting of the spark, a combustion line such as a'b' will result, which is practi- cally a vertical line or is slightly inclined to the right, thus approximating the constant volume line of the theoretical cycle. If the spark is too early, the line nn' will result, while a late setting of the spark will give combustion lines like a' b", a' b'", a' b"", etc. Due to imperfect or slow burning of the charge, many cards have a rounded top, expansion beginning after the piston has already passed over an appreciable distance on its return stroke. Also, it will be found that in practice there is an actual transfer of heat to and from the cylinder walls during the various events, so that the expansion and compression curves do not coincide with the corresponding V. FOUR- AND TWO-STROKE OPERATION 41 curves of the ideal cycle. This means that the curves follow some law expressed by the equation PV n = constant instead of the law PV y = constant, which is the law of the adiabatic change. For a detailed discussion of these laws of gases, refer to any good text-book on Thermody- namics. In theory it is assumed that ignition is perfect, that the composition of the charge is uniform, and that combustion is complete and perfect. None of these things, however, obtain in practice, and all the variations have their influence upon the engine performance. Fig. 11. — Modifications of Ideal Otto Diagram. Numerous other changes may be made in the diagrams obtained from real engines by improper setting of valves, leaky pistons, and many other things. These will be dis- cussed in a later chapter. 32. Two-stroke Operation, Otto Cycle. The chief difference between four- and two-stroke operation is in the method of charging the cylinder and then exhausting the burned gases. The other events are practically the same in both types. This difference results from the fact that 42 GAS POWER the two-stroke engine uses a charging pump to do the pump- ing work done by the engine piston in four-stroke operation. In Fig. 12 is shown a diagrammatic representation of the two-stroke egine. The pump cylinder, which is represented as being entirely separate from the power cylinder, has an admission valve, A, and a discharge valve, J, the latter also acting as an inlet valve to the power cylinder. This cylinder has a ring of ports, E, cut through the walls at such a point r ?w Pump Cylinder Fiq. 12. — Idealized Two-stroke Otto Engine. that the piston, by uncovering them near the end of its stroke, acts as an exhaust valve. Now consider the power cylinder filled with mixture at atmospheric pressure d, Fig. 12a, the piston just cover- ing ports E. The first stroke is to the left, causing com- pression of the charge along the line da. Combustion produces the line ab, followed by the expansion line be. At c the ports are uncovered, allowing exhaust to occur along a sloping exhaust line cc'. We now assume that the power piston moves from c' to d while the auxiliary pump, which has already drawn in a charge of mixture V. FOUR- AND TWO-STROKE OPERATION 43 through valve A, forces it into the power cylinder through valve J. This new charge is supposed to push the burnt gases ahead of it and out through the ports E, and the piston is operated to close these ports just as the new mixture reaches them. Conditions are now the same as at the beginning and the cycle is repeated. Line ef, Fig. 12(b) is the line formed in the pump cylin- der (ideal case) when the charge is drawn in at atmospheric pressure. Line fe is the line formed when the charge is forced into the power cylinder under the same conditions. These coincide in the ideal case and therefore cancel, leaving the area abc c'd as the net area of the power diagram, which is practically the same as in the four-stroke operation already described. Theoretically, by making the ports of zero length, or by using an auxiliary exhaust valve, such as a sleeve, outside the ports, the two-stroke diagram could have been made identical with that of the four- stroke operation. The principal difference in the two methods of operation is that the pumping strokes ef and fe are accomplished outside the power cylinder in two-stroke operation while in the four-stroke engine, the power cylinder itself does the -pumping. The operations as ordinarily carried out are shown in Fig. 13, where the heavy lines represent an actual two- stroke card. The exhaust port opens at a and part of the exhaust gases escape. Scavenging (cleaning .the cylinder a' burned gases) begins about b; charging commences between 6 and c and continues to some point d, where compression begins. There are some modifications of this, but these are special cases. It is obvious, therefore, that the exhaust, scavenging and charging operations, must be accomplished while the piston is moving from a to c and back to d or, roughly, during about 10 per cent of the stroke. This gives a very short time for these important operations and the difficulty of preventing the mixing of burned gases and fresh charge, 44 GAS POWER and of precluding the loss of combustible mixture through the exhaust openings is very great. With high-speed engines conditions are naturally worse. After the admission port is closed at d, the charge is compressed to e, where it is ignited and burned. The intrinsic energy of this high-pressure gas now causes expan- sion on the second stroke down to point a, after which the cycle is repeated. It will be noted, therefore, that the more perfect the scavenging of the cylinder of burned gases, the better will Fig. 13. — Actual Two-stroke Diagram. be the operation of a two-stroke engine. This must be accomplished in a very short period of time, as shown above, requiring an exhaust port of ample size. The quantity of the new charge, and its combustibility, are directly dependent on the throughness of the scavenging operation. By the time point c is reached, the exhaust gases should be at approximately atmospheric pressure, since the volume of the gases remaining in the cylinder as well as the work done in displacing them is thus reduced. For this reason an exhaust valve is generally eliminated and a ring of ports, uncovered each stroke by the piston, is used instead. FOUR- AND TWO-STROKE OPERATION 45 The two agents used for scavenging are pure air and fuel mixture, and these are furnished in three ways, viz: (1) By independent pumps, Fig. 14 (a). (2) By designing some part of the engine, as one end of a cylinder or the barrel holding the crosshead guides, to act as a pump, Fig. 14, (b), (c) and (d). W Power Cylinder f- T \\^r \JI r IC^r -&- \ ' Pump Cylinder Fig. 14(a). 3- Power Cylinder Pump Cylinder Fig. 14(6). (3) By using the crank case and the front side of the piston, Fig. 14 (e). It has been found that the scavenging agent should be at a low and, if possible, a constant pressure, which will prevent the incoming air from bursting through the 46 GAS POWER *H L Power Cylinder *=." T it -€t J Crossbead and ' Compression Piston Fig. 14(c). e} Power Cylinder V tfCu. ^ Fig. 14 d) Pump Cylinder Fig. 14(e). V. FOUR- AND TWO-STROKE OPERATION 47 burned gases and breaking them up, but will cause it to act as a more or less solid wall pushing the exhaust gases out ahead of it. In nearly all of the small two-stroke engines the crank case is used as a pump for the fresh charge, raising the pressure to 6 or 8 pounds above atmospheric on the out stroke of the piston. This pressure is just enough to force the gases through the passages and into the cylinder the moment the admission port is uncovered by the piston. This method, however, is not used in large engines, but instead, separate pumps for the air and gas are installed directly on the frame, and outside the cylinder proper. a Y' ^fT> At mo.-. ^ ^ — — " "=s= c d Fig. 15. — Pump Diagram; Two-cycle Engine. Thus it is clear that in order to show all the phases passed through by the charge, during each cycle, at least two indicator diagrams are necessary: one for the power cylinder and one for the pump, the latter being part of the engine or separate. Referring to Fig. 15, which shows a pump diagram, the piston begins at c to draw a fresh charge into the pump cylinder and continues along the line c-d, which falls slightly below atmospheric pressure due to the partial vacuum formed. The piston is now driven forward by the explosion in the power end of the cylinder, and the mixture in the pump cylinder is compressed along d-a until at a the piston uncovers the inlet port of the cylinder, when the charge is released 48 GAS POWEK on entering the cylinder along a-b and drops in pressure to b. The piston now returns, and the pressure in the pump chamber drops rapidly to c, where the cylinder port is covered, preventing further escape of the mixture. Further movement of the piston causes a drop below atmospheric pressure when the succeeding card is formed. 33. Practical Modification of the Two-stroke Diagram. In practice, the actual card would not coincide with the theoretical, the maximum explosion pressure being at some point / below /', Fig. 13. The expansion and compression lines as in the four-stroke diagram would also obey laws other than the ideal. 34. Comparison of Four-stroke and Two-stroke Oper- ation. It has been shown that the diagrams of events for four-stroke and two-stroke operation are practically alike, the modifications of the toe of the diagram in the latter type being so small as to be negligible. On the basis of the theoretical diagrams there is therefore little, if any, choice between the two types. There are, however, certain practical considerations which should be noted. On a basis of power obtained from a given size of cylinder, two-stroke operation would seem to be preferable. In this type a complete cycle is obtained every revolution, whereas it takes two revolutions with the other method to complete a cycle and produce the same amount of power in the same sized cylinder. This would indicate that a two-stroke engine should give twice the power of a four-stroke engine with the same piston displacement and running at the same speed. Practically, however, this is not the case, and the power actually obtained varies from about 1.3 to 1.7 of that obtained from similar four-stroke engines. This is due to a number of causes, but principally to the difficulty of obtaining perfect scavenging and a pure charge, so that the real two-stroke diagram does not generally approximate its ideal as closely as does the four-stroke. V. FOUR- AND TWO-STROKE OPERATION 49 In the better and larger types of two-stroke engines, separate pump cylinders are always used. These, when coupled with proper design, may be made to give very perfect scavenging, but experience shows that they then entail friction losses of such magnitude as to cut down the useful work delivered by the engine, so that the ideal of double the power of a similar four-stroke engine is never realized. So far as thermal efficiency is concerned, theory would indicate both methods of operation to be equally desirable. Practically, however, two-stroke operation does not give as high thermal efficiencies as the other method. In the smaller, simpler types, this is due to the poor scavenging and to the loss of unburned fuel through the exhaust ports during scavenging. In the larger and more complicated types, losses of this kind are diminished, but the added friction losses, due to the presence of elaborate pumps, partly or wholly counterbalance the more perfect cylinder action. Many two-stroke engines are much more sensitive in operation than similar four-stroke machines, because of the great difficulty experienced in exhausting, scavenging, and charging in the short time available. This fact has prejudiced many against two-stroke operation, but the excel- lent and consistent performance of many engines operating in this way proves that such difficulties are not insurmount- able and that the operation of such engines can be made just as certain as that of the other type. It should also be observed that in designs in which the crank case or some similar part of the engine is used as a pump, the elaborate cam shafts and valves of the four- stroke engine may be partly or wholly omitted, and this same sort of simplicity can be more or less incorporated in even larger and more elaborate types. As a result of these and other similar considerations, practice has been standardized in general along the follow- ing lines: 50 GAS POWER (a) Where cheapness, simplicity, and light weight for a given power are controlling factors, particularly for small powers, two-stroke operation is very extensively used. Thus a great many of the smaller farm engines operate in this way. Similarly small motor boat engines are very commonly built to operate on the two-stroke principle. For the same reasons, the smaller engines built for opera- tion in the oil and natural gas fields utilize this method. (b) On the other hand, where great and rapid variations of load are expected and where high thermal efficiency is desired, four-stroke operation is generally given the preference. Thus most automobile engines operate in this way, although it must be admitted that at least one two-stroke engine has proven itself fully the equal of the more elaborate four-stroke engine for this service. Again, nearly all large engines use the four-stroke method because of the higher thermal efficiency and the greater simplicity resulting from the omission of separate pumping cylinders. Here again, however, it is worthy of note' that some of the large two-stroke constructions have shown themselves fully the equal of their more popular rivals. (c) There is one field in which the two-stroke method is preeminently successful. In all liquid fuel engines in which the fuel is sprayed into the cylinder at the end of the compression stroke, air only (and not combustible mixture) is admitted to the cylinder and compressed therein. Such engines may, therefore, operate on the two-stroke principle without danger of losing fuel through the exhaust port and, if sufficient scavenging air is available, almost complete expulsion of the exhaust gases is possible. For small engines of this type two-stroke operation is therefore advisable because the lack of valves and the increased power for a given weight reduce initial cost, while the thermal efficiency is not lowered by loss of fuel through the exhaust ports. For large engines of this type, two-stroke operation brings the added advantage of reducing the size of cvlinders V. FOUR- AND TWO-STROKE OPERATION 51 required for a given power. This is a very important consideration, particularly in the case of large Diesel engines, in which the high gas pressures make the successful con- struction and operation of large cylinders a very difficult matter. 35. The Diesel Engine. Having described in detail the operation of the four- and two-stroke Otto cycles, it is pertinent at this point to show briefly the method of opera- tion of the Diesel engine, which is being used so extensively in Europe at the present time. The real Diesel cycle may be completed in two or four strokes, and the mechanical operations within the power cylinder are very similar to those of the Otto engine. In the four-stroke engine, the cylinder is charged with air during the suction stroke, and this is compressed on the return stroke into a very small clearance volume, resulting in a very high terminal pressure of 500 pounds per square inch or more. The corresponding temperature is also very high, in fact it reaches such a point that it will ignite liquid fuel injected into it in a fine spray. At about the end of the compression stroke, a- small quantity of finely atomized liquid fuel is blown into the clearance space by means of an air blast, at a pressure of about 100 to 500 pounds above the compression pressure in the cylinder. This high pressure air-blast carries the completely atomized particles into the highly compressed and heated air in the cylinder, where they are immediately vaporized and ignited. Injec- tion continues during the first part of the stroke of the piston, ceasing at about 10 per cent of stroke at rated load. Thus combustion is effected without pressure rise, the fuel being admitted and burned at such a rate as to maintain almost a constant pressure during the first part of the out- stroke. In Fig. 16 are shown an ideal and a real Diesel four- stroke card superimposed, with the lower loop slightly exaggerated. 52 GAS POWER The thermal efficiency, which for any engine is equal Heat converted into mechanical energy . to _, ^ . , — — , is especially Total neat supplied high in the Diesel engine, running to 30 or 32 per cent or more, measured at the brake. The Diesel motor has found very wide application abroad both in stationary and marine Fig. 16. — Diesel Cards. practice. Because of the method employed in compress- ing the air alone to a high temperature and pressure, it lends itself readily to the use of liquid fuels, and it will readily handle many of the heavier petroleum oils and a number of by-product tars. CHAPTER VI. METHODS OF COOLING. 36. Necessity of Cooling. It will be shown in a later chapter that practically all internal combustion engines must be supplied with from 7500 to 14,000 B.t.u. per effective, or shaft, horse-power per hour. Of this the greater part is actually liberated by combustion in the cylinder, but only about 25 to 35 per cent is converted into useful work. The remainder, being energy and there- fore indestructible, must be dissipated in other ways. It is lost in three ways: (a) part passes off in the hot exhaust gases expelled from the cylinder; (6) part is lost by friction in the mechanism, heating the moving parts and being radiated into space; and (c) the rest is carried off by some cooling medium. Unless this were clone the cylinder and connected parts would ultimately attain a very high tem- perature and would then radiate heat rapidly enough to main- tain a balance between supply and waste unless the engine ceased operation because of mechanical difficulties before this condition was reached. To prevent this overheating, which would preclude satisfactory lubrication and mechani- cal operation, all internal combustion engines are artificially cooled m some way. In the smaller engines, only the cylinder or the cylinder and the cylinder head need be cooled, but in the largest double-acting types, it is customary to cool the cylinders, cylinder heads, exhaust valves, pistons, and piston rods. In general, from 25 to 40 per cent of all the heat supplied the engine is dissipated by this artificial cooling. Assuming 53 54 GAS POWER that the average engine requires about 10,000 B.t.u. per effective horse-power hour, and that 30 per cent of this is carried away by cooling, we have about 3000 B.t.u. per horse-power hour, to dispose of. In a 1000 h.p. engine, this would, be 3,000,000 B.t.u. per hour, or about 10 per cent more than the amount converted into useful power, and the equivalent of about 90 boiler horse-power. This will give an idea of the enormous waste which occurs in this way. 37. Methods of Cooling. The methods in use for cooling internal combustion engines are divisible into two general classes which may be called: (1) Air cooling, and (2) Liquid cooling. These will be separately considered in the succeeding paragraphs. Air Cooling is effected, as the name suggests, by a stream of air which passes over the surfaces to be cooled. When an engine is to be cooled in this way, the cylinder and cylinder head are generally cast with webs as shown in Fig. 17, or have similar webs shrunk on. The circulation of air may be: (1) natural, that is simply due to the rising of the heated air which is in contact with the engine and its replacement by air from the surrounding atmosphere; or (2) it may be forced by the use of a fan or similar blower, driven from the engine, as shown in the figure. The forced circulation is preferable in all but the very smallest units, because it has been found by experience that if natural circulation is depended on, the cylinder will under some circumstances attain a higher temperature than is consistent with good lubrication and satisfactory operation. Natural circulation is, therefore, seldom used on engines developing more than about two or three horse- power and generally only on still smaller sizes. Theoretically there is no limit to the size of engine which can be satisfactorily cooled by forced circulation of air, as it is merely a question of circulating enough air at a high enough velocity to remove the necessary amount of heat. VI. METHODS OF COOLING 55 Practically, however, there is a commercial limit, set by the cost of the pumping mechanism and its operation, beyond which it does not pay to go under any given circumstances. Thus few stationary engines larger than 5 h.p. are built for air-cooling even with forced circulation, and most of them are still smaller. One very notable example of forced-air circulation is that used on the Franklin automobile engine. Each cyl- inder of this engine is capable of developing about 6 h.p., and the air cooling has proved satisfactory. A very elab- orate sheet-metal casing is used to direct the air over the [ Fig. 17. — Air-cooled Engine. parts to be cooled, the circulation being maintained by a well-designed, high-speed blower driven from the engine. There are several marked advantages of air cooling in comparison with water cooling, which is the most common example of liquid cooling. The principal ones are: 1. No charge for the cooling medium, as air is free to all and available in all places. 2. No danger of rupture of the engine cylinder and other cooled parts by freezing, as in the case of water cooling if the jacket is not drained when the engine stands idle in freezing weather. 56 GAS POWER 3. No danger of damaging the engine by forgetting to turn on the supply of cooling medium when starting the engine, as air cooling is automatic. 4. Simplicity, if properly designed. 5. Low cost, as the castings are simpler and there are no piping and other auxiliaries to pay for. 6. No necessity for cleaning out restricted jacket spaces as is the ease with water cooling when using water carrying scale-forming material or mud in solution or suspension. 7. Light weight. To partially balance these advantages are the following disadvantages: 1. The method is applicable only to small sizes. 2. There is practically no positive control over the temperature of the engine, so that it generally runs cooler than necessary in cold weather and at too high a temper- ature in warm weather or when operated in restricted spaces which prevent the inflow of a continuous supply of cold air. 3. The exhaust is smoky in warm weather, due to the cracking and burning of the cylinder lubricating oil in a hot cylinder. 4. Rapid fouling of piston rings, piston, and combustion space occurs through the deposit of carbon formed by the cracking and partial combustion of the cylinder oil. Water Cooling may be called the standard method, as it is with few exceptions the method used with the better engines, and is the only method available for use in all but the smallest sizes. Oil cooling has been used on some engines, but has not found extensive application. As with air cooling, there are two distinctly different methods of water cooling in use, namely: natural circulation, depend- ing on the density changes accompanying temperature changes, and forced circulation, depending on a natural or artificially created head of water. Natural Circulation is applied in two different ways: one system is known as hopper cooling; the other as tank VI. METHODS OF COOLING 57 cooling. A hopper-cooled engine is shown in Fig. 18. As the water is heated by contact with the hot walls of the cylinder it is forced upward and its place is taken by cooler water descending from the hopper as shown. Naturally, the isolated body of water contained in the jacket and hopper tends to attain higher and higher temperatures as it is supplied with heat. This tendency is more or less balanced by the lowering of temperature by the radiation of heat from the exterior of the jacket and hopper; by conduction to and radiation from the other parts of the M i 4 ^ 4 [a) SECTION ON A-B SHOWING CIRCULATION (0) SECTIONAL ELEVATION ((.") SECTION ON C-D Fia. 18. — Hopper-cooled Engine. engine; and by vaporization from the exposed surface of water in the hopper. In any case, a very definite limit to the maximum tem- perature attainable is naturally set. The water cannot be raised to a temperature higher than boiling temperature at atmospheric pressure, so that, as long as the jacket and hopper contain water, the temperature is limited to about 212° F. For small engines and even for engines develop- ing 25 h.p., such a temperature is permissible though not desirable. Hopper cooling has several advantages over other types of water cooling; the principal ones are: 58 GAS POWER 1. Cheapness in first cost because of simplicity of arrangement. 2. Cheapness in operation because the water is prac- tically used up (evaporated) instead of being run through the jacket and allowed to run to waste as in most forced water circulating systems. 3. Safety against damage by freezing because of the free expansion possible in the hopper. 4. Light weight when used with a portable engine because the amount of water which must be carried is reduced to a minimum. Fig. 19. — Tank-cooled Engine. The principal disadvantages are: 1. Inability to control the temperature of the engine, as it runs cool when carrying a light load and runs hot when carrying a heavy load. 2. Danger of damage to the engine through failure to replace the water which has evaporated from the hopper. Tank Cooling is shown in Fig. 19, in which the natural circulation is shown by arrows. This method is older than hopper cooling and is now being largely replaced by the latter, particularly for portable work. It is possible to maintain a more even temperature by using a large tank VI. METHODS OF COOLING 59 to facilitate cooling and large diameter of pipes to facilitate circulation; but with tanks and pipes as ordinarily supplied, the method has little advantage over the simpler hopper. A method of tank cooling with forced circulation is shown in Fig. 20, where the water flows over a conical screen before entering the tank. Forced Water Circulation is used on all large engines and on many of the smaller sizes when intended for sta- tionary work. An example illustrating its application to an ordinary type of horizontal engine is shown in Fig. 21. Fig. 20. — Cooling Tower, with Screen for Cooling Water. When this method of cooling is used, it is customary to control the flow of water so as to maintain any desired temperature. Thus with small and medium-sized engines, the discharged water is generally maintained at a temper- ature of about 160° F., while on larger engines, temperatures between 125° and 140° are more common. With large, double-acting engines, the cylinder, cylinder head, exhaust valve, and the piston systems are generally each on a sepa- rate line — that is have independent supply and discharge — and it is customary to determine the best temperature for each system by actual operating results. 60 GAS POWER The piping system for forced circulation should have a shut-off valve on the pressure side of the engine, a throttle valve on the discharge side for controlling the flow, and a drain valve at the lowest point of the system for draining when the engine is standing idle in freezing weather. This is illustrated in Fig. 21. It is very important to note that the discharge pipe must connect to the highest point of the jacket space in order that any air liberated as the water is heated may pass out of the system and not remain caught in a pocket, thus eventually causing local overheating. Fig. 21. — Forced ^'ater Circulations, Showing External Piping .System. All water-jacketed engines should be so arranged that the jacket space can easily be cleaned out. This is necessary because mud and various salts are deposited in this space just as they are in a steam boiler, and, with bad water, it does not take long to seriously decrease the effectiveness of the jacket. It is not at all uncommon to find engines in which the jacket space is almost entirely filled with scale and mud, and many failures have been due to this cause. Cleaning is generally provided for by means of hand holes which are closed with cover plates during operation. VI. METHODS OF COOLING 61 38. Reclamation of Cooling Water. It is not generally realized that the amount of cooling water required by a gas plant is a relatively large quantity. To obtain an idea of the amount required, consider a 1000 h.p. engine receiving water at a temperature of 60° F. and discharging it at 130° F. Every pound of water circulated will then absorb about 70 B.t.u. The engine will probably require about 10,000 B.t.u. per horse-power hour, and at least 25 per cent of this will have to be carried away by the jacket. The jacket must then remove about 2500 B.t.u. per brake horse-power hour which will require about 2500-^70 = about 35+ pounds of water per brake horse-power hour. When it is remembered that an ordinary steam plant of this size running non-condensing can deliver a brake horse- power hour on less than this amount of steam the importance of the cooling water consumption becomes apparent. For the purpose of having an ample supply to meet contingencies it is common practice to assume that a gas engine will require from 4.5 to 9 gallons of water per brake horse-power hour, depending on the type, fuel used, etc. This corresponds to from 37.6 lbs. to 75.2 lbs. per brake horse-power hour. It sometimes happens that cooling water is available at a negligibly small cost, but this is seldom the case. In general it must be pumped or purchased, and in either event its cost must be charged against the power generated. To keep down the cost to the lowest possible figure, it is customary in many large plants to cool the water coming from the jackets so that it can be used over and over again. This cooling is generally effected by a combination of radia- tion and evaporation. In the simplest plan for cooling the water so that it may be used again, the water is run through exposed pipes to an open pond or tank. Some cooling occurs by radia- tion from the pipes and the rest is clue to radiation and evaporation from the exposed surface of the tank or pond. This simple method is not applicable to very large stations, 62 GAS POWER as the exposed surface would have to be prohibitively extensive in order to cool the required quantity of water. For larger iastallations, some method of exposing a greater surface without using too much ground area must be devised. There are practically two methods in use. In one, the water is sprayed over a pond from a great num- ber of small nozzles. Part of it evaporates, cooling the remainder, which falls and collects in the pond. The latter serves principally as a storage reservoir. In the other method, some form of cooling tower such as is used for cooling condensing water in steam plants is utilized. In some small portable plants a modified and diminutive form of cooling tower is used. One variety is shown in Fig. 20. This arrangement gives all the advantages of tank cooling and has the further advantages that the cooling can be made more effective and that a smaller weight of water need be carried with the plant. All these methods result in a constant loss of water by evaporation and by windage. This amount will vary between about 2 and 10 per cent, depending upon the highest temperature attained by the water, the condition of the atmosphere, the strength of the wind, etc. Even in the worst cases, however, it is far cheaper to do the necessary pumping and to pay interest and depreciation charges on pumping and cooling equipment when the price of water is at all high, as it is in many cities. There is another incidental advantage attained by cool- ing and recirculating the jacket water. It has already been shown that the deposition of mud and scale in jackets is an important consideration. When a given supply of water is continuously circulated through the system the deposit of mud and similar material is reduced to a minimum, as only that brought in by the make-up water (from 2 to 10 per cent of the whole) is available for deposition. CHAPTER VII. GOVERNING AND GOVERNORS. 39. Explanation of Governing. When an engine is in normal operation there is a balance between the power it is generating and the power which is being used. If an engine were to develop more power within its cylinders than is required to overcome its own friction and similar losses and to do the work called for at its shaft, it would have to speed up to absorb the excess power. The only limit to this would be final rupture under the great stresses induced. Similarly, if it were to develop less power than required, its speed would decrease until it ultimately came to rest. Maintaining a proper balance between power generation and power demand is called governing. The function of governing may be further complicated by the addition of other requirements as well as the main- tenance of a balance between the power generated and the power demanded. Thus it may be necessary to be able to operate at various speeds while maintaining the above balance, as with automobile and motor-boat engines. In every case, however, the problem of governing, in the last analysis, is the maintaining of this balance between supply and demand. In most stationary engines it is desirable to maintain an approximately constant speed of rotation no matter what the power demand. Thus if the engine drives the line shafting of a mill or shop, it is generally desirable to have that shafting run at about the same speed no matter how much power is being taken from it; 63 64 GAS POWER or, if the engine drives an electric generator, the speed of rotation must generally be approximately the same at all loads. This demand for practically constant speed is so com- mon that most people are apt to think of the governing problem as that of maintaining a constant speed. To show the fallacy of this, it may be well to cite a few examples in which this is not the case. Assume a gas engine driving a water-works pump; the quantity of water pumped varies practically as the speed at which the pump is operated. In most water works, the demand for water is very variable, and therefore the pump must be operated at different speeds to meet this variable demand. At each speed, the governor has to regulate the power output of the engine to the power demand of the pump; the variable speed is merely an added requirement. The case of an air compressor is similar. Many air compressors vary their speed to suit the demand for air, and the engine must, of course, do likewise. The automobile engine and the motor boat engine have already been cited as example- of variable speed requirements. This balance between supply and demand may be maintained manually, as in the automobile and marine engine; or it may be maintained automatically by appropriate mechanism, as in the ordinary power engine; or it may be maintained by a combination of these two methods, as is often the case with pumping engines in which the mechanism is set by hand for a certain speed and then maintains the required power balance to preserve this speed until again adjusted by hand for another set of conditions. 40. Methods Available. The power made available in an engine cylinder is dependent directly upon: (1) The net work supplied to the piston by the working substance per cycle, and (2) the number of cycles performed per unit of time. To vary the power made available, we mav then VII. GOVERNING AND GOVERNORS 65 vary the net work supplied the piston per cycle, or we may vary the number of cycles per unit of time, or we may do both in conjunction. The commercial methods of govern- ing are all based upon such changes. 41. Hit and Miss Governing. One of the commonest methods of governing is called Hit and Miss governing. This method operates on the second possibility enumerated above; that is, it varies the number of cycles per unit of time. It is generally used only on engines which are expected to operate at about constant speed, and it preserves the required power balance by decreasing the number of work- ing cycles per unit of time whenever the engine tends to speed up because of excess power made available. The name, hit and miss, is derived from the type of mechanism used to effect this kind of governing. This mechanism is so constructed that while the speed of the engine does not exceed the normal value (i.e., while the power being made available does not exceed the demand) some part of the mechanism " hits " another part neces- sary to produce a working cycle; when the speed exceeds normal, that is, when the engine is making available more power than is demanded, some part of the mechanism " misses " another part and prevents the occurrence of a working cycle. There are, in general, a number of possible methods of preventing the production of a working cycle, i.e., causing a " miss." Very few are, however, in actual use. The most common method is to hold the inlet valve closed and the exhaust valve open when a " miss " is desired. The engine then merely pumps the burned gases from the exhaust pipe into its cylinder and back into the pipe again until normal operation is resumed by allowing the valves to function properly. The control of the valves is generally effected either by a pendulum governor or by a centrifugal governor. Examples of pendulum governors are shown in Fig. 22 (a), (b) and (c). 66 GAS TOWER Examples of flyball governors as applied to throttling gov- erning, which will be explained in a later paragraph, are shown in Fig. 23, (a) and(6). The hit and miss method of governing has two marked advantages; they are: 1. It is a comparatively simple and cheap method, and 2. It gives a high thermal efficiency at fractional loads. The latter point is worthy of note both because of its practical bearing and because it corresponds with theoretical deductions. Theoretically an internal combustion engine D (b) (c) Fie;. 22. — Simple Forms of Pendulum Governors. operating on the Otto cycle gives its highest efficiency when producing approximately its maximum power cycle. It is obvious that with hit-and-miss governing the engine either produces its maximum cycle or no cycle at all, and hence all heat used is, in theory at least, converted with maximum efficiency. In practice, the cooling of the cylinder during missed cycles, and the disturbance of the fuel, air and burned gas ratios cause a falling off in efficiency at fractional loads. To counterbalance the advantages enumerated above, this method of governing is open to the objection that VII. GOVERNING AND GOVERNORS 67 it is difficult to maintain as even a speed as with other methods unless an excessively heavy flywheel is used. This is due to the fact that when in operation the engine gives erratically distributed impulses of comparatively great magnitude instead of an evenly distributed set of impulses each grad- uated to suit the instantaneous requirement. Even with the other methods of governing, the flywheel must be made very heavy when close speed regulation is desired, so that (o) Regulating Butterfly Throttle. (6) Regulating Grid Throttle Valve. Fig. 23. — Flyball Governors. hit and miss governing is generally used only when very close regulation is not required. 42. Methods Involving Variation of Cycle. With the number of cycles per unit of time remaining constant, the power made available may be varied by changing the amount of work done on the piston per cycle; i.e., by changing the work value of a cycle. This can be done in three dis- tinctly different ways; they are: (1) Changing the relative proportions of gas and air (i.e., the quality of the mixture). This is known as quality governing. (2) Changing the weight of constant quality mixture 68 GAS POWER drawn into the cylinder per cycle. This is known as quan- tity governing. (3) Changing the time of ignition. Governing by changing the time of ignition is not desir- able because there is a certain best time of ignition for each engine operating under a given set of conditions. When governing is effected by changing the time, it simply amounts to improper ignition, thus causing a loss of power and efficiency. This method is, therefore, not to be rec- ommended where economy and good operation are desired. It is often used as a temporary means of control in the case of automobile and small marine engines, and such use is justifiable on the grounds of convenience even though it is not efficient. Schemes involving quality and quantity changes are both extensively used commercially and are the standard methods of governing all but the smaller and cheaper engines. They are often called " precision " forms of gov- erning in comparison with the less precise hit-and-miss method. 43. Quality Governing. Since the internal combustion engine is a heat engine, the quantity of work which it makes available in a given time must, in a general way, be proportional to the heat energy supplied it; that is, to the quantity of fuel supplied in that time. It follows from the above that, if the energy made avail- able i- to be decreased, it is only necessary to decrease the quantity of fuel burned per cycle; while an increase in the amount of fuel in the mixture will cause an increase in the energy made available provided sufficient air is present to burn it all. A series of indicator diagrams showing the variation in size accompanying a variation in the fuel supply i> given in Fig. 24. The area of each cycle is, of course, proportional to the work done upon the piston during that cycle, and hence is a measure of the energy made available. The largest diagram corresponds to the rated VII. GOVERNING AND GOVERNORS 69 load, with very nearly the maximum proportion of fuel in the mixture. The smaller diagrams correspond to smaller loads and smaller proportions of fuel, or, as it is commonly expressed, " leaner " mixtures. It will be observed that the compression pressure remains the same for all cycles, indicating that a full charge is drawn in at all loads. Any diminution in the fuel charge is bal- anced by a corresponding increase in the air charge. The- oretically, this is advantageous, as the efficiency of the I 1 1 1 /' \l Atmos. Y V i<-eiv-sH<- -Bisplaeement- Fig. 24. — Indicator Diagrams for Quality Governing. Otto cycle depends on the terminal compression pressure if the initial pressure remains constant. From the theoretical view point this method of govern- ing should, therefore, give a constant efficiency for all loads. Practically, this is not the case because as the mixture becomes leaner it burns more and more slowly, as is indicated by the gradual tipping of the combustion lines in Fig. 24. This results in greater loss to the jacket water at fractional loads, and ultimately, to the exhaust of incompletely burned charges at very light loads. The efficiency, therefore, actually decreases as the load decreases. 70 GAS POWER This can be partly counterbalanced in two ways, neither of which has met with extended practical success. As the mixture becomes slower burning, the time at which ignition occurs can be advanced (made earlier) with reference to the rest of the cycle. This is often done by hand when an engine has to run for long periods of time at reduced loads, but has not yet been generally adapted to governor control so that the time of ignition can be made to follow a variable load. The other method is to draw in air only during the first part of the suction stroke on fractional loads, and to follow this with mixture of the best proportions in sufficient quantity to give the power required at the instant. Dur- ing the last part of the suction stroke and all of the com- pression stroke, this mixture will have an opportunity to mix with the air drawn in first, but this action is far from perfect and a comparatively rich charge will remain next to the cylinder head and around the igniters. The result is that, although the proportions of air and fuel are such as to give the lean mixture required for the load, most of the fuel exists in a fairly rich mixture which will burn rapidly. The use of this method has been attempted in several different way-;, but lias always seemed to lead to greater complications than were warranted by the results attained. The advantages and disadvantages of quality regulation will be considered in connection with the method next described. 44. Quantity Regulation. When carrying full load an internal combustion engine draws into its cylinder enough air to practically completely burn the fuel charge. It was seen that in quality regulation this quantity is increased when the amount of fuel is decreased to obtain fractional loads; hence with that method there is more than enough air present at all but the maximum load and a slower burn- ing mixture results. In quantity regulation this is obviated by decreasing the air supply with the fuel supply so that the mixture has VII. GOVERNING AND GOVERNORS 71 practically the same proportions or quality for all loads, but varies in quantity to suit the demand. This variation is generally effected by throttling the enter- ing charge of mixture, and engines operated in this way are often called throttling engines. There is, however, another method of varying the quantity which is known as the cut-off method of governing. The mixture is drawn in during the first part of the suction stroke as though full load were to be carried, but when enough has entered to supply the existing demand, the charge is cut off. That already in the cylinder simply expands behind the piston (a) "Cut-off." (b) "Throttling." Fig. 25. — Indicator Diagrams for Quantity Governing. during the remainder of the suction stroke, and is then compressed as in normal operation. Of the two methods, the straight throttling is generally preferred, as it leads to simple governors and valve gear. Diagrams for each type of quantity governing are given in Fig. 25 (a), (b). The former shows a diagram with cut- off governing, the latter with straight throttling. Theoretically, the efficiency of engines governed by the quantity method should decrease as the load falls off, because of the decreasing compression pressure which would cause slower burning of the charge. Practically, the efficiency falls for this reason and also because of the 72 GAS POWER increasing negative work of the lower loop of the diagram, which grows larger as the throttling increases. 45. Advantages and Disadvantages of Precision Govern- ing. Both quantity and quality methods give regularly distributed impulses so that practically the same weight of flywheel can be used for both, although there is the- oretically a slight advantage in favor of quantity governing. Quality governing is almost ideal for the higher loads, but with low loads the lean mixtures required are apt to be slow burning and always give more or less erratic ignition phenomena. On the other hand, quantity governing is best at light loads because the mixture of most rapid-burning proportions may be used and, if the compression has not been too greatly reduced, there will be no difficulty in effecting ignition. 46. Mixed Methods. Many builders have attempted, more or less successfully, to combine two or three methods of governing so as to attain the maximum number of advan- tages with the fewest undesirable features. Most of these combinations have been of questionable merit because of the added complications involved, but some of the more recent have proved highly successful. One practical example of this mixed method is that used by the Buckeye Engine Company (see p. 146), which is so arranged that the governing is practically effected by quality changes for the higher loads, while for the lower loads the quality is maintained approximately constant and the quantity changed. In this way, no slow-burning mixtures are obtained, and the compression pressure does not vary greatly during the entire range. This company has also devised a successful method of shifting the time of ignition by means of the governor so that the charge is ignited at the time best suited to its characteristics. CHAPTER VIII IGNITION SYSTEMS 47. Historical. Some of the first gas engines built were equipped with electric ignition, but this rapidly gave way to what was known as the open-flame ignition, which Avas used in one form or another on all the early Otto engines. This method depended on the maintaining of an open flame in an auxiliary chamber so arranged that it could be opened into the engine cylinder at the end of compression, thus igniting the charge. The violent pressure changes generally extinguished the open flame, but this was sub- sequently relighted by means of an auxiliary jet which burned continuously. The method was costly, as it often consumed as much as 10 per cent of all the fuel used by the engine and was unsatisfactory because of its uncertainty, the flames frequently being extinguished by drafts and other unavoidable occurrences. The open-flame method was followed by the hot tube, and later, by the earlier forms of electric igniters. As all of these are still in use in modified form they will be sepa- rately considered in the following paragraphs. 48. Hot-tube Ignition. With this method, ignition is caused by bringing the compressed charge into contact with a heated tube. One form of the apparatus is shown in Fig. 26, and will serve to illustrate the description. The tube a, which is made either of porcelain or of a nickel alloy, communicates at one end with the combustion cham- 73 74 GAS POWER ber as shown. It is heated near its closed end by means of the Bunsen burner b. After an exhaust stroke has been completed, the clearance space, of which the tube forms a part, is always filled with burned gases. During the suction stroke of the piston, the gases in the tube remain practically stagnant and do not mix to any appreciable extent with the fresh charge being Fig. 26. — Hot Tube Ignition. admitted. During the following compression stroke, some of the fresh charge is compressed into the tube, partly com- pressing the burned gases ahead of it and partly mixing with them. Ultimately, an ignitable mixture will arrive at a point in the tube which is at a high enough tem- perature to fire it. When this occurs, the flame strikes back along the tube and ignites the compressed charge in the clearance. By properly regulating the location of the hot zone on VIII. IGNITION SYSTEMS 75 the tube and its temperature, the ignition can be made to occur at any desired point near the end of the compression stroke. Such timing is effected by sliding the burner and chimney in or out on the post c, to set the location of the hot zone, and by regulating the burner to fix the tem- perature. The hot zone is nearly always maintained at about a dull red. Hot-tube ignition possesses the advantages of being very simple and very certain, but it is open to the two fol- lowing serious objections: It entails the use of 5 per cent or more of all the heat supplied a small engine, and timing can never be very exact because of varying degrees of churn- ing of the gases, varying temperatures, and varying propor- tions or quality of mixture. Several attempts have been made to obtain exact timing by the use of some sort of valve which would close the tube off from the combustion space until ignition was desired, but these constructions have generally been abandoned because of the mechanical dif- ficulties encountered. Hot-tube ignition is now seldom used, as such, in this country, having been superseded by the more exact, and almost equally reliable, electrical methods. It is, how- ever, occasionally found on engines used where fuel is plentiful, as in the natural-gas fields, because of its low first and maintenance costs and because of its great sim- plicity. A modified type of hot-tube ignition which in its various forms may be called hot-head, hot-bulb, or hot-disk igni- tion, is used to a considerable extent with oil engines and will be described in connection with such apparatus in Chapter XIII. 49. Electric Ignition. There are a great number of kinds or systems of electric ignition but the scope of this book does not permit of more than a very cursory examina- tion of the field. For this purpose we shall first divide the numerous systems into two classes which may be called 76 GAS POWER low-tension and high-tension methods. Typical simple examples of each class are given in the following para- graphs. (a) Low-tension Ignition. In all low-tension ignition systems, a low-voltage source of electrical energy is used. This source may be anything from the simplest of dry batteries to the most complicated small electric generator or dynamo or the most expensive form of low-voltage magneto. The tension which must be available in the average case is about five to six volts, and the resistance of the circuit is such that from one to two Fin ger Blad e Moving Electrode.tn electrical contact ^rith. metal ofeuginn .Reactance or Kick.C. Stationary electrode insulated from — ,, metal of engine ~=~ Battery Circuit through metal of engine.^ ^ T Movable grounded electrode Fig. -Low-tension Ignition System. amperes, or in extreme cases as high as five amperes, flow when the circuit is closed. In Fig. 27 are shown the essential parts of a low-tension system of the simplest type. AVith the switch closed, current will flow through the circuit whenever the " elec- trodes " which are enclosed in the combustion space of the engine are brought into contact. When such a condition exists, the sudden breaking of contact between the electrodes will cause a spark to pass between them, and if this occurs near the end of the compression stroke when the electrodes are surrounded by highly compressed combustible mixture, ignition will be effected. VIII. IGNITION SYSTEMS 77 The passing of the spark is due to the action of the coil which is variously known as a " reactance," an " intensify- ing," or a " kick " coil. This consists essentially of a num- ber of turns of insulated wire around a soft iron core. On account of the inductive action of such a coil a momentary increase of voltage is caused when the circuit is broken by the motion of the moving electrode. Systems of this type are often designated as " make- and-break " ignition systems, because of the action of the electrodes. It will be observed that the apparatus of the make-and break system is electrically very simple. Mechanically it is more or less complicated, in the real case, by the appara- tus necessary to give proper motion to the electrode and by the devices which must be used in order to prevent leakage of the compressed mixture around the movable electrode where it enters the cylinder. For high engine speed, extremely refined design is required in order that inertia effects may not prevent the satisfactory operation of the moving electrode. In Fig. 28 is shown a typical igniter of the make-and- break type, together with the method of operating it. The contact is made between the points on the electrodes when the flipper F moving to the left (in the figure) engages the hammer trigger, overtravel being permitted by the spring S, which fastens the hammer trigger to the movable elec- trode. When the flipper F has traveled so far to the left that it disengages the hammer trigger, the spring S' rotates the movable electrode, thus suddenly breaking the circuit at the contact points within the cylinder. Timing is effected by sliding the block B along the rod R and fastening it at an appropriate position by means of the screw shown. Igniters in which the electrodes make and break contact in the way shown in these figures are often called hammer " make-and-break " igniters to distinguish them from 78 GAS POWER a variety described in the next paragraph. There is, how- ever, some uncertainty in the use of this term, as it is used by many to designate a type similar to that just described, but operating in such a way that the electrodes are separated by the hammer action of a spring-actuated piece striking a trigger on the movable electrode. ^ Movable Electrode Insulated Electrode Insulating Washers Valve and Igniter Shaft T0, .Movable Electrode - (W (6) Method of Operation on Engine Insulated Electrode Steel - Stop Pin Contact. Pointa Fig. 28. — Hammer Type — " Make-and-Break " Igniter. There is another type of make-and-break igniter plug- known as a wipe-spark plug, one example of which is shown in Fig. 29. This is the type used by the Foos Gas Engine Company, and is favored by this company on the ground that the rubbing of one electrode over the other keeps both clean and free from carbon, oil and other deposits, which with the type already described may cause imperfect action. There are also a number of magnetically (or electrically) operated make-and-break plugs designed to make the VIII. IGNITION SYSTEMS 79 plug a self-contained mechanism, which need only be wired to the source of the current and a timing device, thus eliminating push rods, cams, and other light, but numerous mechanical parts. This type of igniter is generally constructed in such a way that the electric circuit energizes an electro-magnet which causes the motion Fig. 29.— The Foos Patent Wiping Contact Igniter. of the electrode and also serves as a kick or reactance coil. One example of such a plug as made by the Bosch Magneto Company, for operation in connection with certain - heat + heat, or . (11) 2H 2 + C = 2H 2 -r-C0 2 -heat, .... (12) when hydrogen and carbon dioxide result. X. GAS PRODUCERS 101 In both the above cases, the formation of the CO or CO2 produces heat, but the decomposition of the steam absorbs a much greater amount, and the net effect is an absorption of heat, with a much lower temperature in the bed and gas. Thus the steam not only reduces the excessive heat in the producer, but it also increases the amount of com- bustible in the gas and the calorific power per unit volume, by replacing N with H or with H and CO. The amount of steam employed depends upon the type of fuel and producer and the purpose for which the gas is to be used. For average conditions in an ordinary pro- ducer, 6 per cent of the weight of the blast or 10 per cent by volume may be steam; sometimes 25 per cent more steam may be used-. The quantity of steam required is often assumed as f to f of the coal gasified. The average theoretical composition of wet-blast gas is about CO = 40 per cent, H = 17 per cent and X = 43 per cent, and its heating value per cubic foot is 195.6 B.t.u., which would indicate an efficiency of about 93 per cent. Carbon dioxide is sometimes used as a cooling agent instead of steam, giving the following reaction: C0 2 + C = CO+CO-heat (13) As CO2 must result when producer gas is burned, this method of cooling is effected by returning to the producer part of the burned gases from the engine or other consumer. This, however, also involves a return of all the nitrogen accompanying this C0 2 , so that there is more N in the gas issuing from the producer, and therefore a greater loss in the form of sensible heat, in the issuing gas. Moreover, as this sensible heat is not used for the generation of steam, for which there is no use in this method of cooling, it cannot be recovered, and hence represents a loss. Cooling with CO2 has, however, certain advantages when the gas is to be used in a gas engine because it produces a gas of very 102 GAS POWER uniform properties at all loads and thus simplifies the operation of the engine, particularly with regard to govern- ing and regulation of the time of ignition. 57. Types of Producers. The various real producers used to carry out the processes which have just been outlined are divisible into types in several different ways. The most common division is based on direction of draft through the producer and the way in which that draft is created. Exam- ples will be given in subsequent paragraphs. Another method of classification is on the basis of fuel utilized; thus there are hard coal producers, bituminous or soft coal producers, peat producers, and such. Again, the method used for supporting the fuel column is often used as a basis for classification. Thus there are grate-bottom producers in which this column is supported on a grate of some sort, and there are water-bottom pro- ducers in which the fuel column rests on a pile of its own ash contained in a water-filled saucer in the floor of the producer house. These and other classifications will be better appreciated after a study of the description of producers which follows: (a) Suction Producers. In Fig. 39 is shown a typical suction producer as made by Fairbanks, Morse and Company. The name of suction producer is applied to all plants in which the draft through the producer is created by the suction of the engine. The plant shown would be completely described by calling it an updraft, grate-bottom, suction producer. Its method of operation should be evident from the figure. Such producers as are here shown are well fitted for the gasification of such fuels as anthracite coal and coke, but unless considerably modified they cannot be used with fuels high in volatile material for reasons which are indicated in the following paragraphs. X. GAS PRODUCERS 103 c a o 104 GAS POWER Fig. 40 (a). — R. D. Wood Pressure Producer. X. (JAS PRODUCERS 105 They are ideally simple, comparatively cheap, and easy to operate when properly designed. They are built in sizes ranging from about ten to several hundred horse- power, the rating being based on the engine horse-power which they can supply. With average fuels it is generally safe to figure on a consumption of from 1 to 1.2 pounds of fuel per brake-horse-power hour, and better figures have been obtained in many instances. A ^Slla^Sk !#*! Wp (b) Pressure Producers. In Fig. 40 (n) is shown a section of a pressure producer manufactured by R. D. Wood & Co. All producers in which the draft is created by some form of blower which raises the pressure at the entering side or end of the fuel column are called pressure producers. This is usually done by means of a steam jet blower desig- nated by b in the figure and shown in greater detail in Fig. 40 (b). A fairly complete description of the producer here shown would be given by calling it an updraft, grate-bottom pressure producer. The particular type illustrated is furnished with an automatic feed and a rotating, self-cleaning ash table. Both of these devices serve to maintain approximately constant conditions and hence constant com- position of the gas. They are often used, in one form or another, on the Fig. 40 (b). j producers. Steam Blower. ° r . , ■ The updraft, pressure type is limited with regard to the character of fuel in much the 106 GAS POWER same way as is the updraft suction producer, as will appear in the paragraphs immediately following. (c) Modifications of the Producer for Different Fuels. In the elementary discussion it was assumed that pure carbon only was used in the producer for the manufacture of gas and the various chemical changes were calculated on this assumption. However, in practice we find that actual fuels contain other constituents than carbon, and when heated give off more or less volatile material. Each fresh charge is heated and subjected to this process of dis- tillation before it descends into the zone where partial combustion occurs. Thus in an updraft producer we obtain a mixture of the volatile substances that are distilled off, and of the gas resulting from the residue which is left after the raw fuel has been more or less completely deprived of its volatile constituents by the action of heat. These volatile constituents consist partly of gases and partly of condensihle vapors. The latter, if allowed to pass out with the gas, must generally be condensed and separated from the producer gas before it can be used in a gas engine. In the case of fuels like anthracite, which con- tain little volatile material, no difficulty is met from this source, but in the case of fuels rich in oxygen and hydrogen, as bituminous or semi-bituminous coals, lignite, peat, etc., the thermal efficiency of the producer gas process may be decreased from 12 to 20 per cent by the removal of the tarry vapors from the gas. To prevent this loss, which is inevitable if such fuels are gasified in the simple type of apparatus already described, producers are also arranged to burn the tarry vapors in the producer itself or decompose or convert them into com- bustible gases which will not condense at ordinary temper- atures. X. (! VS PRODUCERS 107 (d) Downdraft Producers. Producers operating on the " downdraft " principle were early tried as a means of fixing the tarr}- vapors. These were fairly successful, and had the advantage of doing away with all smoke during the charging of the coal. One of the best-known American types of downdraft producer is the Loomis-Pettibone, shown in Fig. 41. Thr- plant consists of the producer or generator, an economizer, a wet and a dry scrubber, an exhauster and a gas holder. Coal is charged through the doors at the top as shown at m into the annular space between the air inlet nozzle and the firebrick lining. Air enters the economizer at b around the pipe e through which the hot gases are drawn from the producer. It is heated by passing over the tubes e' and t, and is mixed with the steam which results from the water entering through d and being vaporized as it trickles down the outside of the central tube e', the function of which is that of a flash boiler. The air and steam then pass over into the drum / and down through the fuel bed and grate .L and through the pipe e because of the suction produced by the exhauster C. The hot gases next pass through the wet scrubber B, where they are cooled and exhausted into the dry scrubber D, which still further cleans and dries the gases, after which they pass into the gas holder E. The amount of gas in the holder E is regulated automat- ically by means of a by-pass not shown. A wire rope connects the top of the holder to valves so located that when the holder is full of gas and in its top position the exhauster simply pumps its discharge back into its own suction through the by-pass. As the holder drops, the by- pass is gradually shut off so that the exhauster draws on the producer. When starting up, the valve k is closed and the valve A is opened, so that the exhauster can discharge to the 108 CAS POWER J ! X. GAS PRODUCERS 109 atmosphere through the purge pipe p until the gas made is of such quality that it can be sent to the holder. Whenever the fuel bed becomes stopped up with clinkers, etc., the valve between the economizer and wet scrubber is closed and high-pressure gas is forced up through the grate /I, breaking up the fuel bed thoroughly. Any fuel containing large amounts of volatile matter, as bituminous coal, wood, etc., can be successfully gasified in this producer. All the gases and tarry matter distilled from the fresh-fuel magazine are mixed with air, and partly burned and partly "cracked" as they pass downward through the bed of incandescent fuel from which they issue as fixed or non-condensible combustible gases. In starting this producer, a bed of incandescent coke or similar material is first built upon the grate. This bed serves to fix the tarry vapors distilled off from the first coal supplied. Since all the ash which does not fall through the brick arch must remain within the fuel column, the producer does not permit of continuous operation. In practice it is found that the accumulation of ash generally necessitates shutting down and completely cleaning about once a week. In Fig. 42 is shown a section of the Ackerlund Bituminous Gas Producer, which is distinguished by being one of the first successful downdraft producers to permit of continuous operation. The principal parts of the apparatus and the" method of operation are clearly shown in the figure, the distinguish- ing feature being the water bottom which makes it possible to operate continuously. 110 GAS POWER o -a SfSX X. GAS PRODUCERS 111 (I) Double-zone Producers. The Westinghouse Producer for bituminous fuels and lignite shown in Fig. 43 is of the double-zone type. Fig. 43. — Westinghouse Double-zone Producer. About the center of the producer is a hollow annular casting, called the vaporizer, which is kept nearly filled 112 GAS I'dWEK with water. The hot gases drawn from the top and bottom beds pass under this casting and vaporize the water. Air enters through the pipe a and circulates over the surface of the hot-water in the vaporizer, mixing with the steam, and passing off through the pipes on the left to the top and bottom fuel beds, to effect combustion. The amount is regulated by means of the valves c and c' in the pipes. There is no grate in this producer, the bottom being submerged in a water seal formed by a basin in the con- crete foundation. Ash arid clinkers can be removed easily through the opening between the bottom of the producer shell and the bottom of the water basin. It will be observed that the upper part of this apparatus is merely a downdraft producer with its own incandescent zone, in which the vapors, distilled from the fuel fed in on top, are fixed. The coke formed in this upper zone works downward and ultimately becomes the fuel gasified in the updraft producer, which forms the lower part of the apparatus. 58. Cleaning Apparatus. When producer gas is burned in furnaces used in metallurgical processes, impurities, such as tar, dust and ashes, do not, in general, prevent its successful utilization. Therefore expensive gas-cleaning equipment is unnecessary, ami the gases reach the furnace at a high temperature, resulting in an increased efficiency, because of the retention of sensible heat and the tarn- vapors which are easily burned, thereby adding materially to the total quantity of heat derived. When, however, the gas is to be used in an engine, it is absolutely necessary to remove all tarry products which would collect in the valves and in the passages leading to the engine, and all dust and grit which would score the cylinder walls. Therefore the gas must be thoroughly cleaned, and, incidentally, cooled before entering the engine. The most common process for removing the X. GAS PRODUCERS 113 impurities is called scr-ubbing and ordinary forms of wet and dry scrubbers are shown in Fig. 41. In the wet scrubber, the hot gases enter at the bottom and pass upward through a bed of coke or other convenient material, over which water i.s sprayed. The water and gas thus come into intimate contact, the particles of dust are washed out and the tarry vapors are condensed and removed. The gas is cooled and passed on through dry- scrubbers containing excelsior or through other water sepa- rators, for the purpose of removing the excess moisture and remaining traces of dust and tar. For bituminous coals, lignite, peat and other tarn- fuels in updraft producers, the above scrubbing process is not alone sufficient, so mechanical tar extractors are often used. The chief disadvantages, however, of this method are loss of heat value due to the removal of the tar from the gas, the loss of power required to operate the tar extractors, and the fact that the tar is a disagreeable substance to handle around a plant and often difficult to dispose of. 59. Blast-furnace as Gas Producer. The blast furnace is one of the most common types of gas producer, although not built primarily for this purpose, the gas being a by- product. In making pig iron from ore, coke, or anthracite coal, . iron ore and limestone or similar flux are charged so as to form a deep bed within the furnace. This may be regarded as nothing more than a bed of fuel with an extremely high ash content, and the blast of air introduced at the bottom of the furnace causes the formation of producer gas in practically the same way as occurs in an ordinary updraft producer. The gas given off has a low heating value, averaging, generally, from 80 to 90 B.t.u. per cubic foot, but occasion- ally running over 100. The cleaning apparatus must be large and expensive, due to the large amount of dust carried by the gas. But 114 (.JA.-5 POWER even with the high cot of cleaning it is found economical to use this by-product, which would otherwise be wasted. The most notable installations in this country are tho>e at the Lackawanna Steel Company's plant at Buffalo, X. Y., and the Indiana Steel Company's plant at Gary, Ind. The former develops 40,000 h.p. by means of 2-cycle gas engines in units of 1000 and 2000 h.p., and the latter con- sists of 17 units of 2000 kw. rating* each, and 16 blowing engines of about the same capacity. Six new units of 3000 kw. each have recently been ordered and are being installed. Experience has shown that after all the necessary gas has been used for heating the hot blast and operating the gas-driven blowing engines there still remains enough gas to produce about 3000 h.p. continuously for every 100 tons (if pig iron made per twenty-four hours. CHAPTER XI CLASSIFICATION AND TYPES OF MODERN ENGINES 60. Multiplicity of Classifications. The various types of modern internal combustion engines may be classified according to the following: [■ (a) Otto (1) As to cycle i (b) Diesel I (c) Intermediate (2) As to method of operation. (3) As to fuel used . (a) Two-stroke (b) Four-stroke (a) Gasoline (fo) Kerosene (1) Illuminating (2) Natural (3) Produce]' (4) Blast-furnace (d) Oil. Kerosene, through all the intervening distillates to crude oil (c) Gas (a) Stationary (6) Portable (4) As to use i (c) Automobile I (d) Marine I (e) Aeroplane J C (a) Vertical (5) As to position of axis \ (b) Horizontal I (c) Inclined (6) As to action . (a) Single acting (trunk piston) (b) Double acting 115 116 GAS POWER (7) As to cylinder arrangement (8) As to governing. (a) Twin (2 parallel cylinders with separate frames) (b) Multicylinder engine 2, 3, etc., to any number of parallel cyl- inders with combined frame (c) Tandem (2 co-axial cylinders on same side of crank shaft) (d) Opposed (2 co-axial cylinders on opposite sides of crank shaft) (a) Hit-and-miss (b) Throttling, etc. 61. Division on Basis of Fuel Used. Engines operating on illuminating gas are built in sizes from 2 to about 160 developed horse-power (d.h.p.) per cylinder, per end, and these may be considered as the limits for engines using this type of gas, although, because of its high cost, this gas is seldom used in engines larger than 50 h.p. in this country. There is on record, however, a 4'2"X60", double- acting, twin-tandem, horizontal engine, SS r.p.m., built by the Snow Steam Pump Company, using illuminating gas and rated at 40(10 d.h.p. total, which means 500 d.h.p. per cylinder end. This engine was installed to meet very peculiar conditions. For engines operating on natural gas the limits of sizes as built in America to-day are from about 2 to about 625 d.h.p. per cylinder per end. For single-acting engines of this type, the upper limit runs from 180 to 200 d.h.p. per cylinder per end. Typical dimensions of double-acting, tandem, horizontal engines operating on natural gas arc from 11"X12" to 43"X60", developing horse-powers from 60 total or 15 per cylinder end, to 2500 total or 625 per cylinder end, the corresponding speeds varying from 250 to 90 r.p.m. For engines operating on -producer gas the average limits of sizes as built in America to-day are from I5 to 200 or 250 d.h.p. per cylinder per end. Exceptions to these sizes again are found in double-acting engines built by various XL CLASSIFICATION AND TYPES OF ENOIXKS 117 companies ranging from 12|"X12" to 48"X60" and developing 60 total h.p. or 15 per cylinder end, to 2500 h.p. total or 625 per cylinder end, with corresponding r.p.m. of 250 to 90. Engines operating on blast furnace gas are built in sizes from 100 d.h.p. up to about 500 d.h.p. per cylinder end. Typical dimensions of the larger sizes as installed in several of the steel plants are 30"X42" twin-tandem, double-acting, developing 1500 h.p. total or 187.5 per cylinder end; 42"X60" and 42"X80" engines for gas- blowing purposes; a 42"X70" twin-tandem, developing 3600 h.p. total or 450 h.p. per cylinder end; a 44"X60" twin-tandem, double-acting, at 83.3 r.p.m., developing about 4000 h.p. Gasoline engines are built in sizes from j h.p. to 60 h.p. per cylinder end, while a few are built up to 90 h.p. or over. Single-acting, horizontal, single-cylinder engines up to 22"X28", developing 125 h.p. per cylinder end at 150 r.p.m. have been installed. Because of the high cost of this fuel, such engines are usually bought only when special conditions are to be met. Kerosene and heavy oil engine* operating on the Otto cycle are built in sizes ranging from 2 h.p. to 125 h.p. per cylinder end. Typical dimensions of this type run from 5^"X10", developing 7 h.p., to 14"X24". developing 90 h.p., operating on the California distillates. The Diesel engine is now often built in sizes even as largo as 225 h.p. per cylinder end, and three cylinder units are very common for stationary work. Diesel engines are seldom built smaller than 10 h.p. per cylinder per end. Recent experi- mental work by European firms indicates the possibility of obtaining 1000 to 1500 h.p. per double-acting, two-stroke, cylinder. 62. Division on Basis of Use. Under this heading we may divide internal combustion engines into four classes: (1) Stationary engines, or those which are used exclusively 118 i;as POWER in " power plants," as for electric lighting, pumping, operat- ing machine shops, manufacturing plants, etc. These may vary in size from the smallest to the largest tandem and twin-tandem engines mentioned above and with few exceptions operate on the four-stroke principle. (2) Portable engines, which are built only in the smaller sizes to be easily and quickly transported as on trucks, road rollers, traction engines, etc., from place to place or used for various purposes about a farm. Gasoline and kerosene engines of this type and adapted especially to farm use are finding a tremendous field, and the industry i^ rapidly becoming a large one. (3 J Automobile or Auto engines, which were developed primarily for use in the gasoline automobile. They are almost exclusively built in four, and six-cylinder vertical units, and most of them operate on the four-stroke principle. There are, however, a few notable exceptions to the last statement. The auto type is now being extensively applied to heavy truck and tractor work, to high-powered fire engines, and to a number of allied uses. It 1 UIS also found extensive applica- tion in small and medium-powered, high-speed motor boats. (4) Marine engines, which an- similar in general construc- tion to the auto-engine, save that in small units we find the two-stroke type widely used in the motor-boat industry, because of its simplicity, cheapness, and ease of operation. For larger motor boats and launches, etc., the four-stroke vertical engine in one-, two-, three- and four-cylinder units, is common, because of the more severe requirements, necessitating durability, reliability, and speed. The modern Diesel oil engine is now being installed abroad in almost even - type of vessel, and bids fair to rival steam for marine iw, because of the higher powers to be obtained for the space now occupied by a steam plant, the elimination of boilers, and the reduction in space required to cany the fuel oil. XI. CLASSIFICATION AND TYPES OF ENGINES 119 Irrespective of fuel and type, sizes from 1 to 25 h.p. are suitable for the various types of small motor boats ; those from 25 to 100 or more horse-power for larger boats and small yachts; and those up to 1000 h.p. for small cruisers, tugs, ferry-boats, torpedo-boats and destroyers. Marine motors are generally of heavier construction than the corresponding auto-engine, because of the wear and tear incident to continuous operation under full power, which is seldom required of an automobile engine. (5) A fifth type may be mentioned, namely the aero- typc motor, which has been but recently developed, to meet the requirements of great strength and reliability, very light weight and high speed, necessitated by this particular industry. 63. Mechanical Construction. To summarize briefly the leading features of engine design, with their advantages and disadvantages, we may say that small engines, almost without exception, are built single-acting, and when more power is required, the number of cylinders is increased. The single-acting engine, either vertical or horizontal, has the obvious advantage of great simplicity of manufacture and therefore small first cost. The trunk piston with its obvious disadvantages, which, however, can be overcome successfully in the smaller and intermediate sizes, is used almost exclusively, thereby obviating the necessity of the crosshead and guides, ex- pensive water-cooled pistons, and piston-rods, etc. For large machines the trunk piston (without crosshead) is practically impossible, because of the great weight to be supported, the necessity of obtaining accurate fits to prevent leakage of gases past the piston, the difficulty of proper lubrication, and such. Medium sizes, from one to several hundred horse-power, are commonly built single-acting with cylinders in tandem and pistons and rods supported by crossheads, but all the larger sizes are built double-acting, with two cylinders in 120 CAS POWER tandem. This arrangement is " twinned " for the largest powers. Much can be said with regard to the relative advantages and disadvantages of horizontal and vertical engines. Small engines are commonly built both horizontal and vertical, often by the same manufacturer. The vertical type lias the advantage of a smaller and lighter founda- tion, as well as of allowing a more uniform lubrication of the cylinders. It is also claimed that the wear on the cylinder wall i- less in the case of the vertical machine. The box frame with enclosed crank case, using splash lubrication, affords a cheap construction and simple but >atisfactory lubrication and is a favorite form with this type of engine. In the medium and larger sizes of vertical machines there are the additional advantages of being able to dis- mount them more easily than the horizontal type by means of the overhead crane, and the fact that vertical constructions occupy less floor space than do horizontal engines of like power. The commercial limit to the size of vertical engines has been set principally by the difficulties met in attempting to make them double-acting and thus increasing the power per cylinder and per unit of weight. The chief difficulty is that of getting a satisfactory location of the valves for the lower end of the cylinder. The horizontal machine has the advantage of being more easily handled and operated, since all climbing and mount- ing of platforms, excepting in the largest sizes, are obviated. Also, the operator can watch his machine more closely, as all parts are practically on one level. It is also easier, in the case of horizontal engines using artificial power gases, winch contain a certain amount of dust, to pass this through and out of the cylinder than is the case in a vertical machine, since the exhaust valve can be located at the bottom of the cylinder. The cylinder arrangement varies according to the sizes XI. CLASSIFICATION AND TYPES OF ENGINES 121 of engines employed and the requirements of the service. In the small and intermediate sizes of vertical engines, as mentioned above, the power may be increased by placing two, three, or more cylinders on the same shaft, which is termed multi-cylinder construction. In horizontal engine practice two cylinders may be placed side by side on separate frames (known as " twin arrangement "), or they may be fastened together in " tan- dem," which would necessitate only one connecting rod. Two tandems may be placed together in parallel and con- nected to the same crank shaft, giving what is known as a " twin-tandem " engine. In small sizes a duplex arrange- ment is sometimes used, two cylinders being placed side by side and fastened to the same frame. When two cylinders are placed horizontally on opposite sides of a main shaft with the connecting rods fastened to the same or adjacent crank pins, the arrangement is known as " two-cylinder opposed." This may be duplicated to form a " four-cylinder opposed " type. The opposed arrangement is no longer used except for the small sizes; it is favored at the present time by some tractor manufacturers because of the automatic balance which it gives. The advantage of one type over another depends upon the class of work for which it is to be used, the relative cost, the floor space and head-room available, the type of fuel, character of attendance, and a number of other considera- tions. CHAPTER XII MODERN TYPES OF CIAS AND GASOLINE ENGINES 64. The Pierce Arrow Automobile Engine. This engine- is built by the Pierce Arrow Motor Car Company, for use in the cars of the same name. It is shown in Figs. 44 la), (b) and (c). The first figure gives a longitudinal section along the centre line of the engine, the second a vertical cross-section through the centre of the cylinder which is shown at the left in Fig. 44 (), by two cam shafts N and iS" gear-driven from the crank shaft. Two separate iytiiliun xi/xtcmx are provided. One is operated by a battery, and is connected to the plugs D. Jt is controlled by the timer T, which is gear-driven from the inlet shaft. The other system is operated by a high- tension magneto and is connected to the plugs F. The XII. TYPES OF GAS AND GASOLINE ENGINES 123 124 GAS POWER Fig. 44 (&).— Pierce-Arrow Automobile Engine, Vertical Secti XII. TYPES OF GAS AND GASOLINE ENGINES 125 systems can be used separately or both can be used at the same time. The location of the plugs in the inlet cavity assures their points being scrubbed by the incoming mixture, thus keeping them free of oil and carbon. It also insures the presence of pure, and therefore readily ignitable, mixture in their immediate neighborhood. The cooling water is circulated by a small centrifugal pump which is gear-driven from the exhaust cam-shaft Oil Gauge on Dash. Oil Pump Fig. 44 (c). — Part Section of Pierce-Arrow Automobile Engine. system. This pump receives cooled water from the radiator, forces it through the jackets, and through the pipe G in Fig. 44 (a), back to the radiator. The fan shown in the same figure is driven by a belt from the crank shaft. It serves to assist the circulation of air through the radiator and about the cylinders of the engine and thus assists in the cooling. ■ Lubrication is forced by a small pump as shown in Fig. 44 (c) . The oil is delivered to the main bearings and travels through drilled holes in the shaft to the crank pins. The 126 <;as power wrist pins are lubricated by oil carried from the crank pin by means of a small pipe fastened to the connecting rod as shown. The engine can be started by a hand crank in the ordinary way, or by high-pressure air which is controlled from the seat. This air is prepared, while the engine is in operation, by a small four-cylinder pump under the control of the operator and is stored in a tank. .rft. *h ,f^i rf: Fit;. 45 (a). Elcvut ion of Fairbanks-Morse Marine Engine. 65. The Fairbanks-Morse Marine Engine. The engine illustrated in Fins. 4o (a), (6) and (c) and described in the following paragraphs is one of several types of marine engines marketed by Fairbanks, Morse & Co. It is a single-cylinder, single-acting engine, operating on the two- stroke principle and using crank-case compression. Because of the number and arrangement of the ports, which are XII. TYPES OF GAS AND GASOLINE ENGINES 127 controlled by the piston, it is further known as a three- port engine. Starting the description of the method of operation with the piston in the position shown in Fig. 45 (c), the burned gases of the expansion which has just been completed are passing out through the exhaust port, and the new charge, which was compressed in the crank case during the down- Fig. 45 (6). — End Elevation of Fairbanks-Morse Marine Engine. stroke, is passing into the cylinder through the inlet or transfer port. During the next up-stroke, this charge, mixed with such burned gases as remain in the cylinder, is compressed. It is then burned at about the end of the stroke and expands on the next down-stroke, thus completing the working cycle. During the up-stroke, a partial vacuum is created in the crank case until the piston uncovers the third port. 128 GAS POWER When this occurs, air rushes through the carbureter and this port into the crank case, where it is compressed by the returning piston. In engines of this type, difficulty is often experienced because of back fires, or ignition of the compressed charge in the crank case, at the time when the piston uncovers the transfer port. The charge burned in the crank case is obviously useless as a producer of power and hence such t JtodBuahin? I'ppet Ualf .Lo-erllnlf *er Cranli Case - CunDcctiog KoJ lap Fn;. 45 (c). — Sectional Elevation of Fairbanks-Morse Marine Engine. combustion means a missed cycle, if nothing more. Back firing is due to the ignition of the mixture entering the cylinder, ignition being produced by the hot gases of the previous charge or by glowing carbon on the face of the piston. When the incoming stream is thus ignited, the flame strikes back, traveling down the transfer passage and into the crank case causing a " crank case explosion." To prevent such action, the transfer passage in this engine contains a piece of wire screen pleated in such a way XII. TYPES OP GAS AND GASOLINE ENGINES 129 as to present a large surface to the gas in the passage. This screen acts in the same way as that surrounding a miner's safety lamp, that is, it serves as- a quick absorber of heat in case of a strike-back, thus reducing the temperature of the burning gases to so low a value that the flame is extinguished and does not reach the mixture still left in the crank case. Cooling of the engine is effected by drawing water from outside of the boat and forcing it through the jackets. This pumping is done by means of the small plunger pump P, Fig. 45 (a), which is operated by an eccentric E on the crank shaft. The pump discharges into the lower part of the cylinder jacket through the pipe .4, the water flowing up through the jacket, then through the by-pass into the head as shown in Fig. 45 (c), and from the head to the jacket around the, exhaust pipe. Ignition is by a make-and-break igniter located in the side of the clearance space as shown in Fig. 45 (&). The movable electrode is operated by an extension of the pump plunger as shown. The time of ignition is con- trolled by means of a hand lever indicated by (7 in Fig. 45 (6). The main bearings are lubricated by compression grease cups, while the moving parts within the engine are lubricated by oil fed from the cup shown in Fig. 45 (a). One of the leads from this cup enters the cylinder wall and supplies oil to the piston and the hollow piston pin. From the latter, the oil flows to the exterior of the pin through a hole drilled at right angles to the bore. The other lead from the cup enters the wall of the crank case and is arranged to drop oil into the interior of a centrifugal or ring oiler, not shown in the figures. This ring is fastened to the crank cheek with its centre in line with that of the crank shaft. A groove is turned on its inner circumference so that when in rotation any oil which gets into this groove will be pressed against the surface of the groove with a definite pressure due to the centrifugal action. This oil passes through a hole in the ring into a 130 GAS POWEK c c XII. TYPES OF (IAS AND GASOLINE ENGINES 131 hole along the centre line of the crank pin and then through a hole at right angles to the surface of the pin. 66. The Foos Single-cylinder Horizontal Engine. This engine, constructed by the company of the same name, is built substantially as shown in Figs. 46 (a), (b), (c) and (d), in sizes from 3 to 90 h.p. to operate on the ordinary T Fig. 46 (b). — The Foos Gas Engine, Half-time Mechanism. gas and liquid fuels. It operates on the four-stroke Otto cycle and is governed either by hit-and-miss or by throttling methods, depending upon the purpose for which power is supplied. The inlet and exhaust valves are operated positively by the cams T' and U, Fig. 46 (b), respectively. These cams push on rollers as shown in Fig. 46 (6), and the motiosn 132 GA.S POWER given to these rollers are transmitted through cranks and rods within the frame of the engine until finally imparted to the valves by the bell cranks shown in Figs. 46 (a) and (c). The cams are fastened to the shaft of the large spur gear G, Fig. 46 (6), which meshes with the pinion on the crank shaft as shown. The ratio of diameters for these Fig. 46 (c),— The Foos Gas Engine, Section Showing the Valves. gears is two to one, giving the half speed required at the cams for four-stroke operation. Hit-and-mis* governing is effected by cutting out fuel only and allowing the inlet and exhaust valves to function as usual. The rod J, shown in Fig. 46 (d), causes the admission of fuel when it is pushed toward the cylinder XII. TYPES OF GA.S AND UA8ULIXE ENGINES 133 by the plate F on the arm C, which in turn is operated by a cam on the engine tide of the half-time gear G. The plate F imparts motion to the rod J through the hinged block B, which, whenever a miss is to occur, is forced toward the engine and out of the path of F by means of the finger A, operated by the governor. Excessive speed causes the Fig. 46 (d). — Fuos Gas Engine, Governing Mechanism. weights of the governor G to move out, drawing the spindle of the governor toward the gears and pressing on a roller D at the upper end of finger .4. The speed of the engine can be regulated while in operation by turning the milled wheel H, which changes the position of the pin on which .1 swings. 134 GAS POWER The ignition apparatus is of the wipe jump-spark type and was described and illustrated in Chapter VIII. 67. The Bessemer Gas Engine. One form of this engine, which is manufactured by the Bessemer Gas Engine Company, is shown in Figs. 47 (a) and (b). The former is an elevation of the operating side, the latter a longitudinal section on the centre line of the engine. It is a single-acting engine, operating on the two-stroke principle, is built with a crosshead, and, in the form shown, has an enclosed crank case. The open side of the piston is used for the precompres- sion so that, while the head end of the cylinder is the work- ing end as usual, the crank end is really a charging pump. During the instroke of the piston — toward the left in Fig. 47 (b) — air flows into the charging pump through the air pipe .4 and the automatic admission valve V. The seat of this valve is drilled as shown, the holes connecting with the gas pipe indicated by G in Fig. 47 (a). The valve therefore serves as a mixing valve, admitting gas to the air flowing through it so that, at the end of the instroke of the piston, the charging pump is filled with a combustible mixture. This mixture is compressed during" the outstroke until the piston uncovers the inlet port / Fig. 47 (6), at which time the new charge begins to flow from the pump to the engine cylinder through the passage P, and to more or less perfectly replace the burned gases of the previous stroke, which flow out through the exhaust port E. The piston compresses this new charge into the combus- tion chamber on the next instroke and ignition and expan- sion follow in the usual way, the next cylinder charge being drawn into and compressed in the charging pump, while the charge we have been following is being compressed and expanded in the engine cylinder. Ignition is effected by a make-and-break igniter placed in the center of the head of the cylinder and operated from the crank shaft by means of the push rod indicated by R in Fig. 47 (a). XII. TYPES OF GAS AND GASOLINE ENGINES 135 -a bo ft O w g c 3 136 GAS POWER XII. TYPES OF GAS AND GASOLINE ENGINES 137 The engine is governed by the quality method, the supply of gas to the admission valve, 1', Fig. 47 (6), being eontrollcd by the throttle valve, T, Fig. 47 (), the engine is built with a crosshead and with enclosed guides and crank case. The closed construction greatly simplifies the lubrication, at the same time giving a more cleanly engine and engine room. It will be observed that the part of the piston rod which connects the two pistons must pass through the cylinder head of the forward cylinder. This necessitates some form of packing to prevent leakage of high-pressure gas from this cylinder. The long water-cooled sleeve which surrounds the rod is bored to give small clearance and serves to cool any gas leaking along the rod, and thus reduce the pressure. Further leakage of this cooled gas is then practically entirely eliminated by cast-iron rings in a stuffing-box fitted to the outside of the head as shown. Starting is effected by compressed air operating on the rear piston and admitted through the valve shown in the rear cylinder head. The cam shaft or half-time shaft is driven by spiral gears from the crank shaft, and the inlet and exhaust 138 GAS POWER '- XII. TYPES OF GAS AND GASOLINK ENGINES 139 i4 -3 3 140 OA.S POWER valves arc both operated by one cam on this shaft as shown in Figs. 48 (c) and 4 X S Hl60 u y ,,^ E » A s ^ ty -ft~V & 140 _C ft ^ $ o S%4 w ft^> 1W 30 20 10 ii ^ ►V -^ 13 4 ^ ^ y ^ y G» 5> ir i 2 In ^ * fo g © § o o a o ~ y ^ A, ^oo 4 o © ©" o ^/g p. 00 QO ji? y •a Is 40 « 20 r^. y ^ y AVERAGE CURVES FOR ALL FUELS ooooooooooooooo XoSocpooooooooo© c5 tt «o oo o cm ■v r~ — r —i* ^T ca~ tV c*" ci c*~ eo" Values of d 2 Jn. Fig. 57. product d 2 ln (as abscissa), against normal rated d.h.p. per working cylinder end (as ordinates). The equation of each average curve is given below:* * All curves and equations are for stationary four-stroke Otto cycle engines only. 180 GAS POWER For engines using producer gas: ■ d 2 ln (1) d.h.p. = 7^^777:— 2.0 (average, all values). . . . (14) ,„, ,, _ d 2 ln _ (average, single-acting hor. , . {Z) a.h.p.- 17Q0Q i.u andvert engines) ■• U6J ,„, , , d 2 ln . . (average, double-acting .,„. (3) d.h.p. = s ? r7^7;-4.0 . . ' , • ■, B . . . (16) 20,600 horizontal engines) For engines using natural gas: d.h.p. =-^^7^. — 5.0 (average all arrangements). . (17) For engines using illuminating gas: d 2 ln (average, single-acting hori- ,,„. d.h.p. = -2.0 ° ' b ? . (18) 15, /00 zontal and vertical) For engines using blast-furnace gas: _ d 2 ln _ (average, double-acting P ' "21,000 horizontal) " ' For engines using gasoline: , . d 2 fa _ (average, single-acting hori- 16,400 zontal and vertical) For engines using oils and distillates: (19) (20) dh = d 2 ln Q 75 (average, single-acting hori- 21,875 zontal and vertical) Where d.h.p. = rated brake horse-power per working cylin- der end; d = cylinder diameter in inches; 1 = length of stroke in inches; n = r.p.m. XV. RATING OF INTERNAL-COMBUSTION ENGINES 181 Thus it is evident that the normal rated brake horse-power of an engine can be determined when the cylinder diameter, stroke, r.p.m., and kind of fuel are known. 80. To Determine Bore, Stroke, and r.p.m. The following steps are convenient in determining the speed and dimensions of an engine to deliver a certain power with a given fuel: (a) To find the r.p.m. The investigation referred to showed that the average curve for each type of engine takes the form of a rectangular hyperbola, the equation of which can be readily determined. The results are as follows : For single- and multi-cylinder, single-acting, vertical engines: r -p- m -=difSr4 +176 < 22 > For single-cylinder, single-acting, horizontal engines: (1) r.p.m. = . , , 77 + 128 (for gasoline). . (23) d.h.p.+9 (2) r.p.m. = dh 6 ^ 21 + 131 (for gases). . (24) For single-acting tandem engines: r -P- m -=d3f+T5+ 156 ™ For double-acting horizontal power engines (not applicable to blowing engines): r -P- m - = dlff29+ 72 ™ Having determined from the equations the r.p.m. for the assumed b.h.p. and fuel, substitutions in the proper 182 GAS POWER one of the equations numbered 14 through 21 will give d 2 l for the desired engine; so that it now remains merely to properly proportion the cylinder diameter, d, and the stroke, I. (b) Relation of Stroke to Diameter. The definite rela- tion between the cylinder diameter d in inches (ordinate) and the length of stroke I in inches (abscissae), is shown in Fig. 58, from which the following equations were derived. 36 a o 30 ~28 ^24 S20 &18 ""16 ^ A a- < 4 , » , V 1^ -• U ,» < *■» !P W > y i° . *" .£<£*■ O * /Y* > c v^ ja y ^ $* <& N ■t$ 't-i y ^ 3 *• ^ 2 J 6 3 10 12 14 16 18 20 a 21 26 28 30 32 3-1 36 38 40 42 44 46 48 50 52 54 56 58 60 Length of Stroke U) Inches P'lG. 58. For single- and multi-cylinder, single-acting, vertical engines: d = 0.9U-0A5 (27) For single-cylinder, single acting, horizontal engines: d = 0.667Z+0.4 (28) For single-acting tandem engines: d = 0.772^+0.55 (29) XV. EATING OF INTERNAL-COMBUSTION ENGINES 183 For double-acting horizontal engines: (1) d = 0.533J+4.0 (natural gas). . . . (30) (2) d = 0.667^+2.0 (producer gas) . . . (31) Problem. Assume a 100 d.h.p. single-cylinder, single-acting, horizontal engine, operating on producer gas, and running at its normal speed for rated load. Determine the dimensions of the above engine by means of the preceding equations. The steps would be as follows : From Eq. (1), giving dHn „ „ 100 =I8^T 2 - ' and from this dHn = 1,887,000 (a) But from Eq. (24) 6580 r.p.m. =— — - + 131, d.h.p. +21 giving and therefore r -p- m -=ddSi +i3i = i86 > (6) ,, 1,887,000 ,„„, p W- ' =10,145. ..... (c) 186 Now from Eq. (28) d =0.6671+0.4, which gives Z = 1.5rf-0.6, 184 GAS POWER and substituting this for I in Eq. (c) above gives, after rearrange- ment, d>-0.4d*= 6766 .715, from which d = 19 inches (approx.). Therefore Z = 1.5d-0.6=2S inches. Hence the required engine dimensions are: Cylinder diameter = 19" ; Stroke = 2>"; r.p.m. =186"; d.h.p. =100 (total). CHAPTER XVI METHODS OF TESTING 81. Object of Tests. When the size of the engine permits, tests are usually made in the factory to ascertain the proper setting of the governor for speed regulation; the correct timing of the igniter apparatus; the correct amount of compression; the proper timing of the valves; and also to bring out any defects in material or operation before placing the machine on the market. The common objects of commercial tests as made by purchasers are, however, the determination of the power which the engine is capable of developing and the fuel consumptions at full and fractional loads, i.e., the fulfillment of contract. If a still more exact knowledge is desired, not only of the engine performance, but also of the intricate heat inter- changes, losses, etc., a careful laboratory test must be made by a trained engineer. The necessary data of such a test vary with the objects of the test, but a number are common to all tests in which economy must be determined. The data listed below are those which would be obtained in a complete commercial test: (1) Quantity of fuel supplied. (2) Calorific value of fuel. (3) Indicated power. (4) Developed power. (5) Quantity of jacket water. (6) Entering and exit temperatures of jacket water. 185 186 GAS POWER (7) Air temperature. (8) Fuel temperature at engine. (9) Temperature of exhaust gases at engine. (10) Barometric pressure. (11) Pressure in gas and air pipes at engine. (12) Speed of engine. (13) Variation of speed with changes of load. It is outside the province of this book to describe in detail the various pieces of apparatus used for obtaining the data. For such descriptions the reader is referred to text-books on Experimental Engineering. It is, however, advisable to call attention to certain points which are of great importance and which are commonly met in com- mercial testing. These are: (a) Calorific Value of Fuel. Since the determination of the quantity of heat consumed by the engine depends entirely upon the measurement of the quantity of fuel, and the determination of its heating value, it follows that considerable accuracy is necessary at this point. It is never safe to assume that the calorific value of a fuel during any tost is equal to the average for that particular type; nor is it safe to assume it equal to what it was on some previous occasion. This is particularly true in the case of all artificial gases. A fuel calorimeter should therefore be used, and moreover it should be operated by one skilled in the art and should be supplied with average samples, at regular and frequent intervals. It is not at all difficult to make an error of 10 per cent by careless sampling and improper use of the calorimeter. (6) Quantity of Fuel. As just indicated, the determina- tion of the quantity of fuel is just as important as that of the calorific value. Liquid fuels are commonly measured by weighing, but some sort of meter or equivalent must be used with gases. With small engines, gas meters of the ordinary type XVI. METHODS OF TESTING 187 may be made to give satisfactory results if proper precau- tions are taken, but, with large engines, the quantity of fuel used becomes so great as to necessitate some other form of measuring device. The most accurate method is probably that of using a Venturi meter, though good results may be obtained with Pitot tubes in skilled hands, and by the more common " holder drop " method, when a gas holder forms part of the installation. In the " holder drop " or displace- ment method, the gas holder is calibrated as to contents for each position of the bell. The time required to lower the bell from one position to another is then determined, and from this measurement the true consumption can be calculated. It should be particularly noted that all volume methods of measuring gases are materially influenced by the tem- perature and pressure of the gas being measured, and proper precautions should be taken during measurements and calculations to eliminate error from this source. It is also important to see that consumption and calorific value are reduced to the same temperature and pressure condi- tions before multiplying to obtain the heat supplied. (c) Measurement of Developed Horse-power. The direct measurement of the developed horse-power of engines of moderate size running at moderate speeds is easily effected by means of the Prony brake or other similar dynamometer. But for small engines running at high speeds and for large engines, such apparatus is not satisfactory. For small high-speed engines such as auto engines, it is best to use a water, fan, or electric dynamometer, especially constructed for such purposes. In the case of large engines, it is generally impossible to obtain a direct measurement of this item, and some roundabout means must then be employed, as, for instance, the measurement of the output of a direct-con- nected generator of known efficiency. (d) Method of Stating Results. The economy of engines is often stated in terms of the quantity of fuel used per brake 188 GAS POWER horse-power hour, or other convenient unit. It is, however, more exact and more satisfactory, particularly in the case of gaseous fuels, to state the consumption in terms of B.t.u. consumed per developed horse-power hour (or kilowatt hour), stating, if necessary, a minimum calorific value below which the fuel should not fall. Governor regulation is generally stated in terms of a percentage variation from normal speed and particular care is necessary to define what is meant. Some engineers and builders refer to a percentage variation each side of the normal, whereas others will speak of a percentage variation in the same way, when they mean total varia- tion, counting that on both sides of the normal. It is obvious that the variation covered by the first method is approximately twice that covered by the second. CHAPTER XVII PERFORMANCE OF AMERICAN ENGINES 82. Fuel Consumption. During a recent investiga- tion * the following data, showing the guarantees on the fuel consumption of their engines, were obtained from American manufacturers. In almost all cases the values are on the safe side, as actual tests show much better results. This underrating the economy of engines is the tendency of nearly all American builders to-day, as experience has shown it to be the safest course. These guarantees have the following ranges for the various types of fuels: (a) Producer Gas. (1) At full load: 9370 B.t.u. to 13,500 B.t.u. per d.h.p. hour. 75 to 100 cu.ft. gas per d.h.p. hour. 1.12 lbs. to 1.25 lbs. coal as fired. (2) At f load: 11,000 B.t.u. to 13,000 B.t.u. per d.h.p. hour. (3) At \ load: 12,250 B.t.u. to 16,000 B.t.u. per d.h.p. hour. (4) At i load: 17,000 B.t.u. up, per d.h.p. hour. (b) Natural Gas. (1) At full load : 8000 B.t.u. to 15,300 B.t.u. per d.h.p. hour. 10 to 18 cu.ft. gas per d.h.p. hour. * See footnote page 178. 189 190 GAS POWER (2) At | load: 10,700 B.t.u. to 12,000 B.t.u. per d.h.p. hour. (3) At i load: 12,250 B.t.u. to 16,000 B.t.u. per d.h.p. hour. (4) At | load. 17,000 B.t.u. up, per d.h.p. hour. (c) Illuminating Gas. (1) At full load: 10,000 B.t.u. to 13,000 B.t.u. per d.h.p. hour. 15 to 20 cu.ft. gas per d.h.p. hour. (2) At f load: 11,000 B.t.u. to 12,000 B.t.u. per d.h.p. hour. (3) Atf load: 13,000 to 16,000 B.t.u. per d.h.p. hour. (d) Blast Furnace Gas. (1) At full load: 10,500 B.t.u. per d.h.p. hour. (2) At | load: 11,500 B.t.u. per d.h.p. hour. (3) At §load: 13,600 B.t.u. per d.h.p. hour. (e) Kerosene. At full load: 13,240 B.t.u. to 16,150 B.t.u. per d.h.p. hour. tV gal. or 0.75 lb. to 0.84 lb. per d.h.p. hour for small engines. 0.56 lb. to 0.65 lb. per d.h.p. hour for large engines. 0.725 pint to 0.901 pint per d.h.p. hour. (f) Gasoline. At full load: 10,820 B.t.u. to 15,500 B.t.u. per d.h.p. hour. | gal. to tV gal. per d.h.p. hour. 0.586 lb. to 0.968 lb. per d.h.p. hour. 0.80 pint to 1.10 pint per d.h.p. hour. XVII. PERFORMANCE OF AMERICAN ENGINES 191 (g) Fuel Oils in Otto Cycle Engines. At full load: 8720 B.t.u. to 13,320 B.t.u. per d.h.p. hour. 0.100 gal. to 0.128 gal., per d.h.p. hour. 0.393 lb. to 0.74 lb. per d.h.p. hour. 1 pint average per d.h.p. hour. (h) Fuel Oils in Diesel and Diesel Type Engines. At full load: 9029 B.t.u. to 11,200 b.t.u. per d.h.p. hour. 0.0608 gal. to 0.0784 gal. per d.h.p. hour. 0.447 lb. to 0.588 lb. per d.h.p. hour. 30 &26 a -224 o e Si 18 16 11 Xiiti ral ;r -P inliu Die ,ol *#*= -Tllu nina ing -^ 1^' ^ N^ xiUid' Utf '/ Kerc sene / ,' .^ ^ .10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 D.H.P. per Cylinder Per End Fig. 59.— Thermal Efficiency Curves (on Brake). 83. Thermal Efficiency Curves. From the data given in the preceding article, thermal efficiencies on the brake were calculated (in most cases) from the formula, 2545 . , Thermal efficiency = — — • . . (32) B.t.u. per d.h.p. and the results plotted as in Fig. 59. * * A recent comprehensive test on a " Pierce- Arrow " 48-h.p. auto- mobile motor, showed a maximum thermal efficiency at from 1100 to 1400 r.p.m., of 17.8 per cent with muffler on and throttle wide open. With the throttle one-third open the thermal efficiency was 15.1 per cent; and 6.2 per cent with throttle one-sixth open. 192 GAS POWER 84. Consumption of Lubricating Oils. It is customary to allow a consumption of from 0.0015 to 0.010 pint of cylinder lubricating oil, per horse-power hour and of 0.001 to 0.030 pint of ordinary lubricating oil for bearings, etc. per horse-power hour. The great variation in these figures is due to the difference in types of engines, methods of lubrication, and personal equations of the attendants. The smaller figures are obtained when the oil is recovered, filtered and re-used. 85. Cooling Water. The consumption of cooling water has already been discussed in Chapter VI, in which it was shown that average consumptions range from 37 to 75 lbs. per d.h.p. hour, in cases where the water is allowed to run to waste. CHAPTER XVIII PRACTICAL OPERATION 86. Sensitiveness of Engine. Internal combustion en- gines have always had the reputation of being unreliable, but public opinion in this respect is rapidly changing in view of the remarkable reliability shown by the modern auto and marine engines, and by the better class of sta- tionary engines. It must be admitted that the internal combustion engine is more sensitive to maladjustment than are those of the external combustion type, but exper- ience has shown that intelligent attendance is all that is required to counteract this weakness. It has often been said in favor of internal combustion, that such engines are so sensitive to maladjustment that if they operate at all it must be at the highest efficiency possible, while with external combustion engines, operation can be continued under almost any conditions of efficiency. The first part of this statement is greatly exaggerated, as the following paragraphs will show. 87. Effect of Jacket Temperature. Most engines can be operated at widely different jacket temperatures by simply changing the amount of water circulated. For each engine, however, there is some best temperature which should be approximately maintained. Determination of the value of this temperature is largely a matter of experience, but certain guiding principles can be set down. (a) Other things being equal, the higher the jacket tem- perature, the higher should be the thermal efficiency of the engine because of the better combustion phenomena and the 193 194 GAS POWER decreased loss to the jacket. The thermal efficiency does not, however, increase as rapidly as might be expected, because increased jacket temperature causes increased loss in the exhaust, and, beyond a certain point, increased friction losses. (6) With fuels subject to preignition and used in engines with high compression, a high jacket temperature may cause trouble because of insufficient cooling during compression. Thus engines which compress a mixture of air and liquid petroleum fuels call for a low jacket temperature if high compression is to be used. The temperature cannot be kept too low, however, as there would then be trouble from condensation of the fuel on the cool cylinder walls just as water condenses from the air upon a cold surface. (c) The power capacity of an engine will generally be slightly increased as the jacket temperature is raised from very low to higher values because of improved com- bustion phenomena in the warmer cylinder, but great increase of temperature will often cause a reversal of this phenomenon because of heating of the charge during suc- tion, thus decreasing the weight per cycle. (d) Small engines can generally be operated with higher jacket temperatures than large ones for the two following reasons: first, in the small sizes a larger cooling surface exists in proportion to the cylinder content and therefore the cooling is more effective; second, the castings of large engines are generally more complicated than those of small ones and they are more subject to casting strains of a serious nature; they are also operated under much higher stresses. It is, therefore, desirable to maintain a comparatively low temperature in order that stresses due to uneven cooling and differential expansion may be kept as small as possible. 88. Effect of Varying Time of Ignition. Experience has shown that ignition must occur before the end of the compression in all engines in order that combustion may be nearly completed by the time the expansion curve starts. XVIII. PRACTICAL OPERATION 195 This is because of the fact that it takes an appreciable time for the flame to spread through the entire charge. The greater the quantity of hydrogen or light hydrocarbons in the fuel, the more rapid is the flame propagation and the later may ignition occur. The more nearly the combustible constituent approaches pure carbon monoxide the slower the propagation and the earlier ignition must occur. The time element and the size of cylinder are obviously the controlling features with any given mixture. With high speed, the time available is short and ignition must occur very early, while with a large cylinder diameter, the flame must travel a great distance and hence early p P p i CI «- N. — » oJ\ Nv — » (a) Normal Ignition (b) Early Ignition (c) Late Ignition Fig. 60. — Effect of Varying the Time of Ignition. ignition is required. These effects can be partly overcome by igniting at two or more points at the same time, so that the distance through which the flame must be transmitted is correspondingly reduced. Such multiple ignition arrange- ments nearly always produce a gain in the thermal efficiency of the engine because of the more rapid combustion and the smaller loss to the jackets. The diagrams obtained with varying times of ignition have been briefly discussed in Chapter V, and have been illustrated in Fig. 11. In Fig. 60 are given three diagrams obtained in an actual test. The first shows a normal time of ignition, the second extremely early ignition, and the third very late ignition. 196 GAS POWER The quality of the mixture also has an effect upon the correct time of ignition. Extremely lean and very rich mixtures are both slower burning than the normal charge, and both, therefore, require early ignition. Such mixtures, even when properly ignited, will often continue burning after the opening of the exhaust valve, and in some instances, such combustion may continue until after the opening of the admission valve. This phenom- enon often results in back firing, that is, in ignition of the incoming charge. 89. Effect of Leaky Piston and Valves. The efficiency of internal combustion engines depends on the compression pressure if the pressure at the beginning of the compression stroke remains constant, and, therefore, anything which lowers the compression pressure lowers the thermal efficiency. Leaky pistons and valves must then result in lowered thermal efficiency. There may be a further loss of efficiency due to the actual loss of fuel to the atmosphere in the case of a leaky piston or exhaust valve. Leaky parts will also decrease the power of the engine both by loss of charge before ignition and by loss of high pressure gases after ignition. Further results of leaky pistons and valves are often found in erratic back firing and explosions in the exhaust pipe and muffler. The first can be caused by an inlet valve overheated by the leakage of gases, combined with the effect of the hot gases themselves; the second by the ignition of an unburned charge which has leaked by the exhaust valve. 90. Effect of Excessive Cylinder Lubrication. The in- terior of the cylinder walls of internal combustion engines requires lubrication on the parts traversed by the piston in order that friction and wear may be reduced to a min- imum. The thin film of oil which is spread over these walls is exposed to hot gases during every expansion stroke, and as a result is partly burned and partly " cracked." XVIII. PRACTICAL OPERATION 197 The cracking results in the formation of carbon and heavy viscous liquids which will ultimately impair, or even pre- vent, the operation of the engine. Such material collect- ing in the combustion space generally acquires a high tem- perature and will ultimately cause preignition; collecting in the piston ring grooves it will prevent the free motion of the rings and cause leakage. That part of the oil which burns must take its oxygen from the air in the combustible mixture and it is obvious that there is therefore a limit to the amount which can be burned in this way. An excessive supply of oil must then result in the retention of considerable quantities within the cylinder and the ultimate cracking thereof. The result will be a smoky exhaust, preignitions, carbon deposits, and inoperative piston rings. When horizontal engines are arranged with the exhaust valve at the bottom of the cylinder, most of the loose car- bon collecting in the clearance space will be blown out automatically with the exhaust. When these valves are not so located, it is customary to install a blowoff cock at the lowest point so that loose carbon can be blown out periodically. 91. Timing of Valves. In earlier chapters it was assumed that admission and exhaust valves could be opened suddenly and to their full extent, at the ends of the various strokes, and that satisfactory operation would result. Such is, how- ever, far from true; the valves of real engines seldom open and close exactly at the ends of the stroke and never open or close suddenly to their full extent. The fact that the exhaust valve is opened early (from 85 to 90 per cent of stroke) has already been mentioned. This is done to allow some of the gas to blow out under the driving force of its own high pressure and thus reduce the pressure and negative work during the return stroke. It has the further advantage of giving a fairly large valve opening by the beginning of the exhaust stroke, thus de- 198 GAS POWER creasing the throttling loss during the early part of that stroke. The exhaust valve, in practice, is seldom completely closed at the end of the exhaust stroke, such closure not occurring until the crank has rotated a number of degrees by dead centre. The burned gases acquire a high velocity during the exhaust period and by leaving the valve open in this way the outflow will continue because of the inertia of the gas column even after the piston has started on the next (suction) stroke. More perfect scavenging is effected in this way. In the case of engines in which the valves are widely separated it is very common practice to open the inlet valve before the exhaust valve has closed, in many cases even before the exhaust stroke is completed. This permits of wider opening of the valve in the early part of the suction stroke and also takes advantage of the inertia of the exhaust gases, the outrush of which will often lower the pressure within the cylinder to a sufficient extent to assist in over- coming the inertia of the new charge. Similarly, the inlet valve does not close at the end of the suction stroke, but remains open until the piston has started its return. In this way advantage is taken of the inertia of the incoming column of gas, thus allowing it to pack itself into the cylinder by virtue of its own momentum. The amount of overlap in the valve timing, that is, the length of time during which both valves are open, is deter- mined by the valve location and by the speed. It is greatest with valves widely separated and with highest engine speeds for obvious reasons. INDEX A , PAGE Acetylene mixture 174 Aero-type engines 119 Air and water gas 15 Air cooling (see Cooling) 54 Alcohol 12 American Car Wheel Co., engine 137-142 American fuel oils, table of average values 12 American practice in the rating of internal combustion engines . 178-184 Anthracite coal 9 Artificial gases (see Fuels, gaseous) 14 Auto engines 118 Auxilaries, gas engine 173-177 Average analyses of American fuel oils (Table I) 12 Average analyses of American gases (Table II) 18 B Back-firing 128 Baum6 hydrometer 11 Beau de Rochas' cycle 26 Bench gas 16 Bessemer gas engine 134-137 Bituminous coal 9 Blast-furnace as gas producer 113 Blast-furnace gas 14 Blower, steam 104 Bore, determination of cylinder 181-184 Bosch, make and break plug 79 199 200 INDEX PAGE Brake horse-power, ratings of American engines 179-181 Brayton engine 29 British Thermal Unit 2 Bruce-Macbeth engine , 142-145 Bubbling carbureters 86 Buckeye engine 146-152 Busch-Sulzer Diesel engine 168-172 Calorific value of fuel 186 Carbureters 85-95 bubbling 86 gasoline 85 jet 86 carbureting valve 87 " float-feed " 89 necessity for 85 puddle carbureters 86, 91 wick carbureters 86 Carbureting kerosene 91 difficulties of 92 Use of water in 93 Carbureting valve 87 Carbureted water gas 16 Charcoal 8 Chemistry of producer gas 97-102 Classification of modern engines 115-121 On basis of fuel used 116, 117 On basis of use 117, 118 Cleaning apparatus for producers 112 Clerk engine 33 Coal 8 Classification 9 Coke-oven gas 16 Cold gas efficiency 99 Combustion, external 19 Combustion, internal 21 Compressed-air starting , 173 Construction, mechanical, of modern engines 119 Consumption of fuel, by American engines 189-191 INDEX 201 PAGE Consumption of lubricating oils by American engines 192 Conversion of heat energy into mechanical energy 2 Cooling, Methods of 54 Air cooling 54 advantages /55 disadvantages \56 forced 54 natural 54 Forced circulation 59 Oil cooling 56 water cooling 56 hopper-cooling 57 natural circulation 56 advantages of /'57 , disadvantages ^5iL'' tank cooling ( 58 Cooling of gas producers 99 Cooling water 192 reclamation of 61 " Cracking " 93 Crude petroleum 10 Cut-off governing (sec Governing) 71 Cycle, Beau de Rochas' 26 Cylinder arrangement 120 Cylinder, lubrication, excessive 196-197 D Diesel cycle, thermal efficiency 52 Diesel oil engine 33, 51, 168-172 Distillates , 11 Double-zone producers (see Producers) Ill Down-draft producers (see Producers) 107 Dowson producer gas 14 E Efficiency, Cold gas, producer 99 Thermal 6, 21, 52 American engines 191 Diesel engines 52 Otto cycle 38 Overall 21 202 INDEX PAOE Electric ignition (see Ignition) 75 Electrical starting device 174 Elyria oil engine 163-168 Engines, heat 4 Brayton 29 Clerk 33 Diesel 33, 51 Free-piston 28 Gunpowder 25 Lenoir 26 Otto 31 Otto and Langen 28 Engine operation 193 Effect of excessive cylinder lubrication 196-197 effect of jacket temperature 193-194 effect of leaky piston and valves 196 effect of varying time of ignition 194-195 Timing of valves '. 197-198 Engine, sensitiveness of 193 Engine, testing 185-188 Engine types, Areo-type 119 Auto 119 Marine 118 Portable 118 Stationary 117 External combustion 19 F Fairbanks-Morse Marine engine 126-131 " Float-feed " carbureter 89 Fly-ball governor 66 Foos gas engine 131-134 Foot-pound, unit of work 3 Formulae on rating of American engines 179-181 Four-stroke, actual indicator card 38 Four-stroke, comparison with two-stroke 48 Four-stroke, diagram, modifications 40 Four-stroke, Otto cycle 34 Free-piston engine 28 INDEX 203 PAGE Fuel, a source of heat 3 , calorific value 186 consumption 189-192 Fuels, solid, Charcoal 8 Coal 8 Solid wastes 10 Wood and vegetable fibres 7 Liquid Petroleum products 10 Crude petroleum 10 Distillates 11 Gasoline 11 Kerosene 11 Alcohol 12 Fuels, gaseous, Natural gas 13 Artificial gases 14 Blast-furnace 14 Coke-oven 14 Illuminating 14 Oil gas 14 Producer 14 " Fuel-mixture "-starting device 174 Fuel oils, table of average American values 12 G Gas and gasoline engines, modern types (see Modern types). . . . 122-152 Gas engine auxiliaries 173-177 ■Gas engine rating 178-184 Gas producers 96-114 Gaseous fuels 13-17 Gases (see Fuels, gaseous) 13 Gasoline carbureters (see Carbureters) 85-95 Gasolines 11 Governing 63 methods 64 Hit and miss 65-67 Methods involving cycle variation 67 Quality 67-70, 72 204 INDEX PAGE Governing methods, quantity 67, 70 cut-off 71, 72 throttling 71 mixed 72 purpose 63 Governors, fly-ball 66 pendulum 65 Graphite 9 Gunpowder engines 25 H Heat energy converted into mechanical energy 2 Heat engines and heat power plants 4 Heat from fuel 3 Heat unit, B.t.u 2 High-tension system 80-84 Higher heating value of gases 12 Hit and miss governing 65 Hornsby-Akroyd oil engine 157-161 Horse-power, rating on brake 178-184 Hot-tube ignition 73 I Igniters, hammer " make-and-break " 77, 78 Ignition, effect of varying time of 194-195 Ignition systems 73 electric 75 low tension 76 make-and-break 77 hammer 77 wipe-spark 78 high tension 80 with trembler coil 82 hot-tube 73 open-flame 73 Indicator card, actual, four-stroke 38 Internal combustion 21 INDEX 205 J PAGE Jacket temperatures, effect of 193-194 Jet carbureters 86 Joule's equivalent 3 K Kerosene 11 Kerosene carbureting of (see Carbureting) 91 Leaky piston and valves 196 Lenoir engine 26 Lignite, brown and black 9 Liquid fuel problem 85 Liquid fuels 10-13 alcohol 12 distillates 11 gasoline 11 kerosene 11 light products 11 petroleum products 10 Lower heating value of gases 12 Low tension ignition 76 Lubricating oils, consumption of 192 Lubrication, excessive cylinder 196-197 M Make-and-break ignition (see Ignition) 77 Marine engines 118 Measurement of D.H.P 187 Mechanical construction of modern engines 119 Mechanical energy, from heat energy 2 Methods of governing (see Governing) 64 Methods of stating results of engine tests 187-188 Mixed gas, or air and water gas 15 Mixed governing 72 206 INDEX PAGE Modern types of gas and gasoline engines 122-152 American Car Wheel Co 137-142 Bessemer, two-stroke 134-137 Bruce-Macbeth gas 142-145 Buckeye 146-152 Fairbanks-Morse marine 126-131 Foos horizontal 131-134 Pierce-Arrow auto engine 122-126 Modern types of oil engines 153-172 Diesel oil 168-172 Elyria oil 163-168 Hornsby-Akroyd oil 157-161 Muncie oil 161-163 Peterson kerosene 153-157 Modifications, four-stroke diagram 40 Modifications, two-stroke diagram 48 Modification of producer for different fuels 106 Mond producer gas 14 Mufflers 175-177 types of 176 Muncie oil engine 161-163 X Natural gas 13 Need of mechanical power 1 Oil cooling 54 Oil engines, modern types 153-172 Oil gas 16 Oils, lubricating, consumption of 192 Oil gas tig, vaporized oil 17 Open-flame ignition 73 Operation, practical 193-198 Otto cycle: four-stroke 34 thermal efficiency 38 two-stroke 41 Otto engine 31 Otto and Langen engine 2S Over-all thermal efficiency 21 INDEX 207 P PAGE Peat 9 Pendulum governor 65 Peterson kerosene engines 153-157 Petroleum products 10 Pierce-Arrow auto engine 122-126 Piston, leaky 196 Portable engines 118 Power starting 174, 175 Practical operation 193-198 Precision governing, advantages and disadvantages (see Govern- ing) 72 Producer cleaning apparatus 112 Producer gas 14, 96 Producer, modified for different fuels 106 Producer, types of 102-1 14 Ackerlund 109, 1 10 double-zone Ill down-draft 107 Fairbanks-Morse 103 Loomis-Pettibone 108 pressure 104 R. D. Wood 105 suction 102 Westinghouse 111-112 Puddle carbureters 86, 91 Q Quality governing (see Governing) 60-70, 72 Quantity governing (see Governing) 67, 70 Quantity of fuel used in testing engines (measurement of ) . . . 186, 187 R R.P.M. determination of 181-184 Rating of American engines 178-184 Rated brake horse-power 179-181 Reactions of producer gas 97-99 Reclamation of cooling water 61 208 INDEX PAGE Refining 11 Relation of stroke to diameter 182 Retort gases 14, 16 bench gas 16 coke-oven gas 16 Retort process 17 Riche\ producer gas 14 S Scavenging 45 Sensitiveness of engines 193 Siemens producer gas 14 Solid fuels 7-10 Solid wastes 10 Source of heat, fuel 3 Starting devices 173-174 Stationary engines 117 Steam blower 104 Stroke, determination of 181-184 Suction producer, (see Producer) 102 Table 1 12 Table II 18 Testing of engines 185-188 calorific value of fuel 186 measurement of D.H.P 187 method of stating results 187-188 necessary data 185-186 object 185 quantity of fuel 186-187 Thermal efficiency 6, 21, 52 curves 191 Otto cycle 3S Throttling governing (see Governing) 71 Timing, adjustment of S4 Timing of valves 197-198 INDEX 209 PAGE Two-stroke diagram 48 comparison with four-stroke 48 modification 48 Two-stroke operation, Otto cycle 41 U Unit of heat, B.t.u 2 Unit of work, foot-pound 3 V Valves, leaky 196 Valves, timing 197-198 Vaporized oil vs. oil gas 17 Vegetable fibres 7 \Y Wastes, solid 10 Water cooling (see Cooling) 56 Water gas 15 carbureted 16 Water used for cooling 192 Wet-blast gas 101 Wick carbureters 86 Wipe-spark ignition plug 78 Wood 9 Wood and vegetables 7 Work 2 THE WILEY TECHNICAL SERIES EDITED BY J. M. JAMESON A series of carefully adapted texts for use in technical, vocational and industrial schools. The subjects treated will include Applied Science; Industrial, Household, and Agricultural Chemistry; Electricity; Electrical Power and Machinery; Applied Mechanics; Drafting and Design; Steam; Gas Engines; Shop Practice; Applied Mathematics; Agriculture; Household Science, etc. The following texts are announced; others are being added rapidly. THE ESSENTIALS OF ELECTRICITY; A Textbook for Wire- men and the Electrical Trades. By W. H. Timbie, Head of Department of Applied Science, Wentworth Institute. 12mo, flexible covers, pocket size, xiii+271 pages, 224 figures, $1.25 net. HEAT; A Textbook for Technical and Industrial Students. By J.A.Randall, Instructor in Mechanics and Heat, Pratt Institute. Large 12mo, xiv+331 pages, 80 figures. $1.50 net. GAS POWER. By Professor C. F. Hirshfeld and T. C. Ulbricht, Sibley College, Cornell University. Large 12mo, viii+209 pages, 60 figures. $1.25 net. THE ELEMENTS OF ELECTRICITY; For Technical Students. By W. H. Tembie, Head of Department of Applied Science, Went- worth Institute. Large 12mo, xi+556 pages, 415 figures. $2.00 net. MACHINE SHOP PRACTICE. By W. J. Kaup, Westinghouse Electric and Manufacturing Company, Pittsburgh. Large 12mo, ix+227 pages, 185 figures. $1.25 net. CONTINUOUS AND ALTERNATING CURRENT MACHIN- ERY. By Professor J. H. Morecroft, Columbia University. {Ready in Fall, 1913.) ALTERNATING CURRENTS. By W H. Timbie, Head of Depart- ment of Applied Science, and H. H. Higbie, Head of Department of Applied Electricity, Wentworth Institute. (Ready in Fall, 1913.) HEAT AND LIGHT IN THE HOUSEHOLD. By W. G. Whitman, State Normal School, Salem, Mass. (In preparation.) ELECTRIC LIGHTING. By H. H. Higbie, Head of Department of Applied Electricity, Wentworth Institute. (In preparation.) PATTERN MAKING. By Frederick W. Turner and Daniel G. Town, Mechanics Arts High School, Boston. (Ready inFall, 1913.) INTRODUCTION TO INDUSTRIAL ELECTRICITY. By W. H. Timbie, Head of Department of Applied Science, Wentworth Institute. (Ready in Fall, 1913.) APPLIED MATHEMATICS. In preparation by carefully selected specialists. (a) Elementary Applied Mathematics. lb) Mathematics for Machinists. (c) Mathematics for the Woodworking Trades. (d) Mathematics for the Electrical Trades. (V) Mathematics for the Metal Trades. THE LOOSE LEAF FIELD AND LABORATORY MANUAL. A series of carefully selected exercises to accompany the texts of the Series, covering every subject in which laboratory or field work may be given. Each exercise is complete in itself, and is printed sep- arately. These will be sold by the single sheet, or assembled in any number and order desired, with or without covers. Exercises in General Chemistry. By Charles M. Allen, Head of Department of Chemistry, Pratt Institute. An intro- ductory course in Applied Chemistry, covering a year's labora- tory work on the acid-forming and metallic elements and compounds. 4to, 02 pages, 61 exercises. Selected exercises, as desired, to fit an ordinary binder, two cents each. Complete, in paper cover, $1 net. Exercises for the Applied Mechanics Laboratory. By J. P. Kottcamp, M. E., Instructor in Steam and Strength of Materials, Pratt Institute. Steam, Strength of Materials, Gas Engines, and Hydraulics. 4to, 54 exercises, with numerous cuts and tables. Selected exercises as desired, to fit an ordinary binder, two cents each. Complete, in paper cover, $1 net. Studies of Trees; Their Diseases and Care. By J. J. Levison, M. F., Lecturer on Ornamental and Shade Tree.-, Yale University Forest School, Forester to the Department of Parks, Brooklyn, N. Y. (In press. Ready in Spring, 1913.) Exercises in Farm Dairying. By Professor C. Larsen, Department of Dairy Husbandry, South Dakota State College. (Ready in Fall, 1913.) Studies of Plants. By Professor Mel T. Cook, New Jersey State College of Agriculture. (In preparation.) Wiring Exercises. By H. A. Calderwood, Carnegie Institute of Technology. (In preparation.) Exercises in Industrial Chemistry. By Dr. Allen Rogers, Instructor in Industrial Chemistry, Pratt Institute. (In preparation.) Technical Chemical Analysis. By R. H. H. Atjngst, In- structor in Technical Chemistry, Pratt Institute. (Ready in Fall, 1913.) Qualitative Chemical Analysis. By C. E. Bivins, Instructor in Qualitative Analysis, Pratt Institute. (In preparation .) Exercises in Electricity, A. C. and D. C. By W. H. Timbie, Head of Department of Applied Science, Wentworth Institute. (Ready in Spring, 1913.) DRAFTING AND DESIGN. By Charles B. Howe, Stuyvesant Technical High School, New York, and associated specialists. (a) Mechanical Drafting. (b) Engineering Drafting. (c) Agricultural Drafting. By Charles B. Howe, Member of Society of Agiicultural Engineers. (Ready in Spring, 1913.) (d) Architectural Drafting. By Charles B. Howe and A. B. Greenberg, Stuyvesant Technical High School, New York. (Ready in Fall, 1913.) (e) Drafting for Plumbers. (f) Drafting for Steam Fitters. (g) Electrical Drafting. (h) Drafting for Sheet Metal Workers and Boiler Makers. (i) Drafting for the Heating and Ventilating Trades. THE LOOSE LEAF DRAFTING MANUAL. Reference and Prob- lem Sheets to accompany the texts in Drafting and Design. These will be furnished singly as selected, and are designed to enable the instructor to adapt his problems closely to the needs of his class. (In preparation.)