hJ/\c(\r-ix RB No. E4I27 NATIONAL ADVISORy COMMITTEE FOR AERONAUTICS WARTIME REPORT ORIGINALLY ISSUED September 1944 as Restricted Bulletin E4I27 END -ZONE WATER INJECTION AS A MEANS OF SUPPRESSING KNOCK IN A SPARK-IGNITION ENGINE By Rinaldo J. Brun, H. Lowell Olsen, and Cearcy D. Miller Aircraft Engine Research Laboratory Cleveland, Ohio NACA WASHINGTON NACA WARTIME REPORTS are reprints of papers originally issued to provide rapid distribution of advance research results to an authorized group requiring them for the war effort. They were pre- viously held under a security status but are now unclassified. Some of these reports were not tech- nically edited. All have been reproduced without change in order to expedite general distribution. E-72 DOCUMEMTS DEPARTMENT HACA R3 No. EUI27 NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS RESTRICTED BULLETIN END-ZONE WATER INJECTION ..S A MEAI-IS OF SUPPRESSING KNOCK IN A SPiVRX-IGNITION ENGEIE By Rinaldo J. Brun, H. Lowell Olsen, and Cearcy D. Killer SUlfMARY An investigation has baen made of the effnctiveness of vmter injection into the combustion end 7,one of a spark-ignition engine cylinder for the suppression of knock. Pressure-time records obtained show that injection of vfater at 60"^ B.T.C. on the com- pression stroke at a water- fuel ratio^of Q.;) rendered M-^j fuel as £ood as S-J fuel from an antik/iock consideration. The optii.iura crank angle for injection of v,':i,--er into the en'i zone was found to be critical. As tlie injection ".ngle v;a3 increased beyond the optimum, the quantity of v.atci required to auopress knock increased to '^,6 Avatcr-fuel ratio a.^ 1^'-"'' P.T.C. The water quantity could not be increased beyond 3.6 water-fuel ratio because of injection- pump limitations; however, a furtiier increase in the injection angle up to the earliest angle obtainable, wlii.-;h ^vas 20"'* A.T.C. on the intake stroke, continuously increLised the jraock intojnsity. The engine operating, conditions of the tests did -lot simulate those encountered in flight, especially v/ith regard to the oper- ating speed of 570 rpm. For this reason the results should only be regarded as of theoretical importance untiJ further investiga- tion has been made. I?n.'R0DUC.TI0N The investigation herein described was suggested by observation of high-speed photographs of coiribastion i.n a spark-ignition engine cylinder taken with the i'lACA high-speed camera at the rate of ij.U,000 frames per second (reference 1;. These j-jhotographs con- firmed the prevailing opinion that the combustion end zone involved in the knock reaction includes otily a small fraction of the itiass of the total cylinder charge. T]ie photographs also indicated that this small fraction of the mass of the total charge is ?.o;.iprossed into an extreriely siiiall and well-defined volume before knock occurs. 2 NAGA R3 No. £1^2? A study of the photographs sucgestoJ that a great savinjj in anti- knock additive might bo effected by injecting the additive exclu- sively into the ond zone, pr-ssumably the only region in which it 1.3 needed. Introd'jction oi water into the corbustion char.ber of the internal- coir^ustion engine for the purpose oi" s lopressing knock or cooling of the engine parts is v„ry old. In 1913' Hopkinson (reference 2) reported successful results cf extensive tests v.ith large gas engines with which the cooling was entirely by water spray on tlie inner ourfaces of the combustion chamber. In 1921 Clerk (reference 3) indicated tnat he had used vrat ^r to suppress extremely violent knock in the year 1830* More recent investigations of the effect of water and other liquids introluceci into t!ie fuel-rdr mixture before a^taission into the cylinder on Icnook-liiLited and tf-niperature-limited power output are described in refcronccG U and 5» The water or oth-jr liquids used in this manner are tei'med "i;.'t'>rnal coolant." The object of the tests repor'"ed herein was to determine the value of injection of vrater into the end ^one as an antikriock agent. The engine used in these tests could not bo superchcurged and the inlet-ail' temperature could not b-.; raised above room feniperaturej therefore, the effjctiveness of the water was determined by lowering the aritiknock value of the fuel. The engine operating speed was far belov.' the speeds used in flight. The results should bo consid- ered only on a theoretical basis jntil further investigations have been made more closely appr achin, the operating conditions of fligiit. Tnis vfarning is particularly important because difficjlty may be expei-ieiiced in applying the- inetiiod to high-speed engine operation. The tests were perfonned at th"^ Aircraft Engine Research Labo- ratory of the National Advisory Committee for Aeronautics d^aring late 19'-t5 engaged at the beginning of the firing cycle betvjean the engine crankshaft and an accessory sliaft to inject a single charp;e of fuel into the cylinder on the intake stroke, ignite the charge at tnc-; proper tin^.e, and inject water at t,lie predetermined injection anfle. The cylinder tenipera- tiue was maintained by circulating heated glycerin through the engine jackets. Three spark plW;S were used to brin^ the end zone inbo the desii'ed position in front of the water-injection nozzle. The ignition timing was so set that t!ie coiTipletion of burning mth S-3 fuel occurred near top center. The water used for injection into the cylinder v;as deaerated in order to avoid the fo.miatJ.on of gas bubbles in the injection valve. The fuel-air ratio was set slightly richer than that required i'o\- inaxim-iim Icnock with S-J fuel. T^ffo valves vrere used, each serving for both intake and ex.haust. Press'.aro-tinie records were obtained by paotographing an oscillo- scope screen. The input to the vertical nlates of the oscilloscope was r'i'oduced by a piczoelectrj.c prer.sii;-e dck?.ip installed in the engine. Engine conditions held con3tar:t were: Engine speed, rom , 570 Fuel injection (intake stroxke), degrees A.T.G 20 Fuel-air ratio (approxiiiate) 0.U72 Cylinder tenioeratiare, '^F , 2,!|2±2 Go.-ripi'ession ratio 7.1 Intake pressure atrnosoheric Exnaust pressure at.aosoheric Intake teinj ;rat ire, °F 65-70 (room temperature) Spark tiirdng, degrees B.T.C.: Earliest plug 5011 Later plugs 26+1 RES-'.JLT:; AMD iHSCUSSIQAl A photograph of about one-i'.alT the coniDustion chamber at the time all the water spray had entered int/o the chamber is shoT;n in figiir'T 1. The dashed cj.rcle shoves the conbusti on-chamber outline as viewed froi.i the top. The letter G in the figure indicates the position of the earliost-fired spark plug, E and F the positions of the later-fired spark plug's; J indicates the position of the vrater-injoction no'^-lc, H the position of the fnel-injection nozzle, and I the oosition of the piezoelectric pressure oickup. MACA P3 No. Em27 A photOi^raph of the end zone a fev: e:agif.e crank-angle degrees before the end of combustion is shown in figure 2. Tiie end zone as seen in figure I is somewhat larger than the knocking end zone under the most severe condition^ in'-Dosed in the tests. The photographs in figures 1 and 2 are single frames from two series of pictures taken at UO^OUO irar'ies per second vri. th the NACA high-speed camera and srjow the develo-onent of the v^ater spray from the aozr.le and the burning ox the charr^e in the ctiojiiber, respectively. In figure 2, the Tfater-cpray outline obta:Lned ji-om f ij:ure 1 has b'3en di'avn in to shovf its location -with reopect bo the end zone. Pressure-time records of firing cycles are shown in fi^'ures 3 to ^. Tho lovfest trace in each li.-jure is a motoring trace taken j'ost before the firin^^ cycles. The traces of tv.'o coiisecutivs firing cycles superiimosed on t!ie sane fi]m are ■jiicwn in fij-'ure J. The trace with the violent knock, designated "unquenched ll-^i" in the fi£;urs, vfas taken A-ith IJ-3 fuel vjithout water injection. The trace vlth incipient knock and larger area under the trace, designated "quenched li-jj" in the figure, Vfas taken vdth M-^ fuel v.c.th injection of xvater at ^9^ B.T.G. on the cornpressioa stroke. The weight of vfat^r injected was three-tenths of the fuel weig'.it. All of tne operating condi- tions of the engine and osciiloscoe were th',. saine foi' the two runs of figure 3 except the vv-ater injecion. The amplitude of the vibra- tions registered on tho qucnciiei trace was considered to be indica- tive of incipient knock because a lower axiplitade of vibrations was not readily detect3a visually on the oscilloscope. The ■'.'.'ater-fuel ratio of 0,3 with injectioji at t/ie optiir.uiri crank angle consistantly gavo incipient knock or no knock. The 0.;? water-fuel ratio v/as the lowest obtainable .vith tho water-injection systeir.; therefore, the siTiailest water quantity necessary to quench the knock v;as not deter- mined iii this investigation. High-speed Motion t;icturcs of the quenched cor^buction of M-3 fuel indicated that the knock did not, occur in that part of the end zone permeated by the water, -.ut that the incipient knock such as registered on tii.. quenched trace in figui-e 3 came from a v^ry snail fraction of the charge located on either side of the ■^^'^ter spray near th.e cylhider wa].l. If bhi small pockets of gas near the water- injection nozzle alor^gside the cylir.der v^all could have been sprayed with vfater, possibly all traces oi knock '©uld have been removed. The pov/er loss resulting from severe k:iock is shown in f ir- ure 3^ The tn"0 traces are nearly identical aporoximately to the point -;;here knock occurred in the unquenched trace. Th2 loss of energy witli ..heavy knock cannot be acco^ontcd for as being involved •)'•': 4 CA RB No. EUI27 in the energy ci vibratioA of the gases, because even after the vibrations have been nearly damped out the unquenched pressure- time tr'ice remains about the same distance below the quenched trace, borne of the energy may be lost in the highei- heat transfer through the cylinder walls with hea\^ Vrnock because of the greater scrubbing action of the gases on the chamber Avails, as suggested by iDitlirow and Rassweiler (reference 7). The greatest portion of the energy loss might be accountable in the form of unreleased energy in unburnsd carbon. During every violent knocking run made in these tests, the engine released a large quantity of black smoke on the exV'iaust stroke, Vilrien the knock was reduced to the incipient level, eitiier by quenching or by increasing the antikiiock value of the fuel, no traces of smoke v»-ere noted, KacCoull (reference 3) has presented nieasurements of power loss with heavy knock. The traces of ti/vo firi.ng cycles were super impose.i in figure h to siiow tfiat quenched M-J fuel pi'oducea as much power as unquenched S-3 fuel. The octane ratings of I'-';;, and S-3 fuels, as obtained from the A.S.T.M. (Motor) Method, are about 20 and 100, respectively. The quenched trace in figure Ij. has a shar'p rise ap'oroximately at the point where fciock v;oulJ occur in an- unquenched cycle. The sudden rise in pressure at that jjoint is charactei'istic of all quenched M-3 i-iins. Kotiou pictures of thci-si; runs, ho-^'revor, do not show the cliaracteristic vibrations in vhe b'.irned gases I'.'hich accompany kiiodc. The trace for unquenched S-3 fuel in figure h siiows about the same amplitude of knocking vibrations a3 does the trace iu the same figure for quenched M-3 fuel. The traces shown in figures 3 ^nd J4 are representative of more than 50 traces taken -onder the same test condJtions. The reproduc- ibility of the test data was very goodj furtiiermore, the order of taking the tvro traces on the carJs vv'as reversed many times and identical resaits were obtained. The ootimuiii angle for start of water injection with resoect to knock was found to be critical; under the conditions oi" the tests, the optimum angle was fx'om $0° to 60° B.T.C. on the compression stroke. The total time require.! lor injection 01 i/vater, as indicated by the high-speed photographs, was S'-* to 10° of crank angle. Start of injection even as late as 10^ B.T.C. did not give good results regardless of the quantity of water injected up to the capacity of tlie water-injection t;ystem., which was 3,6 tiip.es -i-he fuel quantity, or 12 times the water used at the optimum angle. The large time lapse between knock an..l injection (50^'' irdnimum angle) is not encour- aging from Uie consideration nf applying the listhod to the conditions of flighit. If ttie mj.nimuifi time between water injection and com- pletion of burning remains constcu'it for different engine speeds, the miniinuia anfle of injection foi' good resists v.-ill inci-'ease from 50'^ at KACA R3 No. EUI27 570 rpm to 2h$° at 2800 rpm. The Droblerr' of injectinr: water when the r)istcn is near bottom center in such :.!anner that it will ba concentrated in tiie end zone when the piston is at top center will be diificult. With injection of water betvr en 6vO° and 13:?'^ B.T.C., the quan- tity of vrater req'iired to prevent t.ie M-3 fuel fi'or:i exoeoding tho incipient feock limit increased rapidly fi'oti. O.3 to y.b water-fuel ratio. As the injeoi-ioii angle was advanced beyond 13^'^ 3.T.C. on the cojT.pression stroke tc 20° A.T.G. on thf; intalte str-^ke, the knock ijiteasity conbinaouol.y increased at u constant water-fuel ratio of ^,6; also, the H.-aiie speed deci-eased and Icnock occurred later in the cycle. The slower rate of b-jrninc lowered the cycle efficiency considerably. Fr--"thei.T;i.i"a, so.rie cycles vrere drovvned out with the 3.6 watci'-iuel ratio injected at 20° A.T.G. on the intake stn ke . Injection earlier than 20° A.T.G. on the intake stroke was not possible b&ca ise of mechanical lindtatioas. Injection at this angle was as nearlj'' oompprable ■viith introducing the coolant into the manifold near the intake valve as possible with the apparatus used. In other engines, depending on the operating conJitioas, introducing the coolant into thn manifold near the intake valve will require different wat-.3r quantities for the same effective knock reduction. The 3.6 water-fuel ratio used on this apparatus, therefore, sho'old now b'j used in making connarisons witli other engines. In order to assiu'e as thorough a raixinp of the water and the fu'3l-air ciiarge as possible, the plain valves used in the runs of figures 3 =^nd '4. were reolaced by shrouded valves for the run of figure 5. The shrouded valves i;icreased the turbulence, -.)artic- ularly durLug t^£ air intake. Figure 5> is =1 pressure-time 'trace taken v.ith M-3 fuel, J). 6 v/ater-fu^l ratio, water injection at 20 A.T.G. on the intake stroke, u^d all oth^r conditions the same as for the other runs. The knock intensity was not reduced appre- ciably from that produced by unquenched 11-3 fuel, as shown in fig- ure 3- The rate of pressure rise durin<.; combustion was appreciably reduced as coirspared with the pressure rise at the optimum injection angle (figs. 3 and U), particularly during th'.^ earlier stages of combustion, uith shrouded valves, the rate oi' nrrssure rise v;as considerably greater than vath pl.n.n valvos at tho earliest injec- tion angle and the largest quantity 01 -■'.'atei-. NACA RB No. EUl27 SmMAEY CF RESULTS The follovdng res'iLts wore obtained from limited water-injection tests ccndactid on the NAGA combustion apparatus at an Oinginc oper- ating speed of 570 rpra: 1. Injectinf^ vrater into the end zone with a v/ater-fusl ratio of 0.5 reduced the knock intensit.';- of L-3 fuel to that of S-J fuel without water. 2. The considerable power loss associated with violent knock was prevented in the cycles in which, the knock v.^as quenched by .end-zone viater injection. 3. The optimum uxir'/ie of water injection was critical. Aircraft Engine Research Laboratory, National Advisory Gvomndttee i'or Aeronautics, Cleveland, Ohio. RZlFEPJiMCES 1. Miller, Gearcy D. : A Study by Hifh-Speed Photography of Combus- tion and Knock in a Spar k-Ifnit ion Engine, NACA Rep. Ur, 727, 19l;2. 2. Hopkinson, Bertrar.: A New Met.iod of Coolirip Gas-Engines. Inst, Mech. Eng, (Proc.j, PLs. 5-li., July 1913, pp. o79-71!j. 3. Clerk, Dufjald: Cylinder Actions in Gas and Gasoline Engines. SAE J.jur., vol. VIII, no. 6, June 19^1, pp. 52>-539. .'4.. Rothrock, Addison M. , Krsek, Alois, Jr., and Jones, Anthony YJ.: Summary Report on the Induction of Water to tlie Inlet Air as a Means of Intei'nal Cool-Lng :i 1 Aircraft Engine Cylinders. NACA MiTi, AiiG. 1042. 5. KiJiring, M. S.: V/ater and Wat-;r-Alcohol Injection in a Super— cliarged Jaguar ''urcrait EngLne. Canadian Jour. Res., sec. A, vol. 16, Aug. iry], op. lli9-i7o. 6. Rothrock, A. !vi., anl Spencer, R. C.; A Photographic Study of Goribustion and Knock j.n a Spar'/-Ir.nitioa Engine. NAGA Rep. No. 622, I93S. VikCk RB No. Shl27 7. Withrowj Lloyd, and Rassvrei.ler, Ger-ild M,: Slor Ijiotion Shows Knocking and Non-Knocking Sxolosions. 3A£ Joii'., vol. y9, no. 2, Auj-. l?3.j, pp. 297-303, 312. 3. MacGouil, Neil: Power Loss Accompanjanj^ Detonation. 3AE Joiir., vol. Ui, no. Ij., A.rril 1?39, -o.' l^^-lbo. NACA RB No. E4I27 Fig. I Early spark plug Piezoelectric pressure pi ckup- Fuel-i nject ion nozzi e- -Outline of combust ion chamber C>639l Uoter-inject Ion nozzle Figure 1. - Photograph of uoter spray in combust ion chamber after uater injection uas complete. Combust ion has not token place. Exposure time, 25 microseconds- NACA RB No. E4I27 Early spark plug Plezoelecfrf c pressure pi ckup Fig. e Fuel-Inject Ion noz? le- NACA C* 6 39 2 Flame-' , ^ Flame End zone Vater-lnject Ion nozzle Figure 2. - Location and shape of end zone a feu engine crank-angle degrees before comp let Ion of burning. Exposure time, 25 microseconds; relative position of uoter spray, shoun by dotted lines, uas obtained from figure 1. NACA RB No. E4I27 Fig. 3 CO o »- r) ^ >-< to cz SI . oo "•^ -^ mac w. 1 to c; LU to v.^ ^< ♦-too ^ o o K 1 -^ a lATIO TTE 1 * <0 to "^ w ^i to «^., *. a t en S , Oh- o I o o:t o «« >a. o •. . to c to-. H- a— to •^ W ties to tH* ts CJ «e to fc « t: .. •- o o c a c •- a o to ■». i. < a o w o.to"t) •--.to - = o cc-< k o z 1 ■»> c/jO -c I. «o _ oc •►. ^ >UJ •^ ♦. t Q-< ago >< a— . OC ^ «o i^ — 'O ^ 'i. 10 Q> ^"^ a o ■C -^ 1 o O XJotO c •• c * fc CS « a a — Cr k. t tkot) -^"^ C % «. •- ^ O k. O «) •. O C '^C ck. to c a e a "^ k. OO 1 O k."0 to to «o . >•* .c to— o o o to a c e> a to w.H^ ., a ■^ Or\ o- f»> . R to 1 o ^ «Co •^ ■»- ti o . 1 to--^ Jto-c ♦- . k. o e»— a c c . «o to «ft «o a — to e- to« k. fc avo «*. aH~«o 2J NACA RB No. E4I27 Fig. 5 o q: < oz (n o > < < UJ < a: o O lij o o «^«o C) • «> cvx >s * w o Q> a «>. • t)^ CJ k. • ♦. •«b • c Qa-^ a Q) •k-O -^ 1 o o V.OSI >\ ^ o 4^ ^ o — ^ Q«a «> t -* •Mlk •« o k^cn k. •". 1 '«>. H» * CO C3 * « ^ «* «0 Q> o t :3 «. — «. U. fc a •^. O ^ <: • Q> •^ *^. % «o«o o C C o o o i. «.. c c o o Q> •«. •^ ^ «> '•l. •«. o o '*> q> % 1 •-^ •-% % c k: k. •^ a 1 1 V) i. V. «0 Q> 09 «> '*.. «_ k. o cs •i. 3 a UNIVERSITY OF FLORIDA 3 1262 08104 951 1 IhSlTY OF FLORIDA ■■-f^^S QEPARTMEMT Srosv^ SCIENCE U6RARY ■■.^.j.'-ja iiroii GAINBSVIkLE. FL 32611-7011 USA 1