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'REPORT No. 756

THE INDUCTION OF WATER TO THE INLET Am AS A MEANS OF INTERNAL COOLINGAmCRAFT -ENGINE CYLINDERS

By ADDISON M. ROTHROCK, ALOIS KRsEK, Jr., and ANTHONY W. JONES

SUMMARYInvestigations w ere conducted on a full-scale air-cooled air-

craft-engine cylin iler oj O !J-cubic-inch displacement todetermine the effede oj internal cool ing by wa te r in du ctio n onth e maeimum perm issib le power and output oj an internal-eombustica: engine . For a range oj fuel-air an d water-fuelra tio s, th e en gin e inlet pressure was i nc re as ed un til lc no ck wasdetected aural ly , th e power was then. decreased 7 p er ce nt h old in gth e r atio s c on sta nt. 1e data indicated tha t water was a veryeffective internal coolant, perm itting large increases in enginepower as lim ited by either k n o c k or by c yl in d er t emper at ur es .

INTRODUCTIONThe induction of water into the inlet air of an internal-combustion engine has been.investigated by various personsas a means of improving engine cooling. P~escott in a papergiven in Chicago in 1933, presented data for extremely highpermissible power outputs obtained by the use of inductedwater to suppress knock. (See reference 1.) Kuhring (refer-

ence 2) determined the effect of induction of water and ofwater-alcohol mixtures on the temperatures of a full-scaleaircraft engine. Heron and Beatty (reference 3) have shownthat water-alcohol mixtures decrease the temperature of aliquid-cooled single-cylinder test engine. Hives and Smith(reference 4) present brief evidence of the increase of per-missible brake mean effective pressure as limited by knockwhen water is inducted with the incoming air. The effec-tiveness of water and water-alcohol mixtures as internalcoolants in a multicylinder engine has also been investigatedat Wright Field. The results of these various investigationsshow that water is an effective internal coolant.The use of water as an internal coolant is of particularinterest if a suitable aftercooler of the exhaust gases can bedesigned that will permit the recovery of water formed duringthe combustion process. Investigations at Langley Memo-rial Aeronautical Laboratory show that the weight of waterformed at a fuel-air ratio of 0.067 is 1.25 (based on exhaust-gas analysis) times the weight of the fuel burned, as com-pared with an estimated weiglit of water 1.34 (based onhydrogen-carbon ratio) times the weight of the fuel burned.Consequently, the amount of water in the exhaust is sufficientfor appreciable internal cooling of the engine.

If a satisfactory water-recovery apparatus can be designed,several advantages will result:

1. The permissible output from the fuel could be mateincreased or the octane number of the fuel required coumaterially decreased.2. The water-recovery apparatus may be mountedaircraft wing and used as a wing de-icer.3. The exhaust flame or glow would be eliminated.4. Intercoolers or aftercoolers in the supercharging symight be eliminated.The disadvantages of the system are:1. Increased weight.2. Bulkiness of water-recovery apparatus.3. Increased drag.4. Difficulties inpreventing freezing of water.5. Difficulties if used in conjunction with turbosucharger.6. Difficulties if installed in conjunction with exhaupropulsion.Information on weights of an aftercooler is given in

ence 5, in which Kohr presents data on a water-recoapparatus built for a small airship. The following infotion is taken from Kohr's data:Duration of tests, hours__________________________________Average airspeed, miles per hour__________________________Average air temperature, F______________________________Total weight of fuel used, poundsTotal weight of water collected, poundsWater collected, percent of fueL__________________________Engine horsepower (estimated) ___Weight condenser less suspension, pounds__________________The horsepower listed is based on the assumption thabrake specific fuel consumption of the engine was 0.6 p

per horsepower-hour. The weight of the aftercooler is1.42 pounds per horsepower. Improved design sappreciably decrease this weight. Also the average airof 48 miles per hour is much slower than that of cumilitary aircraft.Water as an internal coolant is of interest as a measuppressing knock in short bursts of high power outhat is, during take-off or during combat maneuvers.these cases it probably would be necessary to use a walcohol mixture to prevent freezing. Such a procedurepermit high powers during take-off with a fuel of low onumber.

59

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60 REPORT NO.7 56-NATIONAL ADVISORYCOMMITl'EE FORAERONAUTICSThe use of water injection as an internal coolant may haveimmediate application in types of aircraft in which, whereweight limitations are not severe, the water necessary forcontinuous operation can be carried in addition to. the fuelor can be recovered from the exhaust gases.In view of the possibilities offered by the use of internalcoolants, a series of investigations on a full-scale air-cooledaircraft-engine cylinder were undertaken using water as thecoolant, The investigations were made at Langley MemorialAeronautical Laboratory during the perio.d from December1941 to March 1942.

APPARATUS AND PROCEDUREThe determination of the effect of water inj ection on theincrease in permissible indicated mean effective temperatureas limited by engine knock over a range of fuel-air ratiosfrom 0.05 to 0.12 are reported herein. The equipment con-sisted of a full-scale air-cooled aircraft-engine cylinder of202-cubic-inch displacement mounted on a CUE crankcase."The following conditions were held constant:

E n g i n e s p e e d , r p m ~ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2 0 0 08 p a r k a d v a n c e , d ~ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2 0C o m pr e s s i o n r a t i o _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 7 . 0Inlet-air temperature, 0F 2 5 0The results have been separated into two. groups. GroupA includes investigations made with .AFD-28 fuel and aconstant cooling-air pressure- drop of 8.5 inches of wateracross the engine. Group B includes investigations madewith the fuel of 80-octane number and a constant cooling-airpressure drop of 14 inches of water.In both series of investigations, the term "maximumpermissible" as applied to power, indicated mean effectivepressure, or inlet pressure refers to the maximum permissible

value as limited by fuel knock or detonation and was takenas 93 percent of the value of the audible knock or detonation,Subsequent investigations with knock detectors of varioustypes showed that such procedure agreed very closely withincipient knock as determined by the detectors. The pro-cedure for establishing the maximum permissible values isgiven in reference 6.The data recorded include the maximum permissibleindicated mean effective pressure, the indicated specific fuelconsumption, the maximum permissible inlet pressure, andthe temperature of the cylinder and the head at differentpositions.The program was started with a CFR fuel designatedAFD-28 having a knock rating equal to isooctane plus LOBml TEL by the CFR Aviation (1-0) Method. Owing to

the increase of permissible power allowed by water intion, the capacity of the testequipment was reached beflarge water-fuel ratios (by weight) were tried.Investigations over a large range of water-fuel ratwere made with another fuel of lower octane ratinglower initial power output than those of the CFRAFD-28. This fuel, a commercial automobile gasoline,rated 80-octane number by the CFR Aviation Methodaccordance with specification AN-VV-F-74B.The water for the investigations made under Group A winjected through a suitable nozzle into the inlet pipe ab15 inches upstream of the inlet port of the engine and. inches upstream of the fuel-injection valve. The coolwas continuously injected downstream whereas the fspray was directed upstream and was injected only durthe inlet stroke. The maximum permissible inlet-air prsure was limited to 60 inches of mercury absolute bycapacity of the coils for heating the inlet air for the Groupinvestigations, The large water quantities used inGroup B investigations caused erroneous readings in inair temperature because surging of the air mass insideinlet pipe carried water into contact with the inlet-air thmometer, The water injection nozzle was moved 5 incfarther downsteam to remedy the condition before any dwere taken.Determinations of the value and the position of the cyder peak pressures for a fuel-air ratio. near 0.07, the fu80-octane and &-1 plus 6 ml TEL per gallon, and variowater-fuel ratios were made with 0. Farnsboro indicator.

RESULTSGRo.UP A

Ma.x imum. permissible engine performa.noe.-Figurepresents the relation between the fuel-air ratio. andmaximum permissible performance for different water-furatios." The data in figure 1 show a marked increase in pmissible indicated mean effective pressure with water injtion.The percentage increase in the maximum permissible incated mean effective pressure with water injection at eachthe three water-fuel ratios investigated is as follows:

~~~W8ter-ruelmtiO 0.2 0.4 0.6Fuel-air mtlo0.067 . __ Zl ~6 711176 _ _ __ 33 62.000................................. 13

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INDUCTION OF WATER TO INLET AIR AS MEANS OF INTERNAL COOLING

If the percentages of increase in indicated mean effectivepressure are assumed to be independent of the octane num-er of the fuel, it is estimated that for a water-fuel ratio of0.6, an engine requiring a fuel of 100-octane number couldperate satisfactorily on a fuel of 80-octane number. The

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62 REPORT NO. 756-NATIONAL ADVISORYCOMMITTEE FORAERONAUTICS

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INDUCTION OFWATER 'TO INLET AIR AS MEANS OF IN'l'ERNAL COOLINGs r : r -- - - - _ 1 ".-~ 1 " ' -If" 7 1 \ \V i \ 1\IrtV -, \

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cA/V " 0 "'I'-..t- f " - -7 (b ) irq I~ Water/ fuelo 0 - t--/ \ I lc ~ .20 .4- r-e V vn . 0 .6/ 0 / " " -s: I'-.Ii y o - . . . , 1 " ' \/ 1 \-j 1 7 . . . . . . _D \u r-,

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641600

REPORTNO. 756-NATIONAL ADVISORYCOMMITTEE FORAERONAUTICS

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2INDUCTION OF WATERTO INLET AIRAS MEANS OF INTERNAL COOLING

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.05 .06 .07 .08 .09 .10Fuel-air ralio . 1 1 .12(11) Maximum )}eI"IlI1ssIbJeindIcated mean effective pressure.(b) IndIcated specIJIc fuel consumption and maximnm pcrmlssIbJe Inl et-air pressure.

FIOURE 8.-R~Jation be tween Iue l-al r mt lo and maximum permissible euglne performanceCor dIfferent water-mel mUos. Cylinder displacement, 202 cubIc Inches; engine speed,2000rpm; spark advance, 20"; compression mtfo, 7.0; Inlet-alr temperature, 250" F; coolingpressure drop, B.O Inches water; fuel, s o - o C t a n e number.

From the standpoint of engine cooling, however, winjection can be used to an advantage. .All temperatuexcept the exhaust, decreased when the water was indu(figs. 7 (b) to 7 (f)). The exhaust temperatures shno change with increased water-fuel ratio (fig. 7 (a)).The exhaust temperatures as recorded in these cons

pressure tests were probably affected by radiation withresult that true gas temperatures were not indicated.

CROUP BMaximum permissible engine performanoe.-Figure

shows the relation between fuel-air ratio and maximum

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FIOURE D.-Relation between Inlet-alr pressure and air mass Indncted into oyllndltIerent water.fuel ratios, Cylinder displacement, 202 cubic inches; engine sperpm; spark advance, 20"; compres sion mtfo, 7.0; Inle t-alr temperature, 2 l i O " F;pressure drop, B.O inches water; Iuel, 80-0ctane nnmber

missible performance for different water-fuel ratios.data in figure 8 (a) show the maximum increase in pesible indicated mean effective pressure that was obtafrom the fuel of 80-0ctane number with the use of winjection. At a water-fuel ratio of 1.5 and fuel-air ratio0.06 to 0.08, the operation of the engine was rough. F8 (b) shows an increase in indicated specific fuel consumas the water-fuel ratio was increased at constant furatio. For a given power output, the specificfuel constion is seen to be less with water mixtmeso

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66 REPORT NO. 756-NATIONAL ADVISORYCOMMI'ITEE FORAERONAUTICSThe percentages of increase in maximum permissibleindicated mean effective pressure resulting from the waterinduction are as follows for the fuel of SO-octane number:

Water.fucl rat io I.5 LO 1.60.067 - : ; ; t 189 ~1

.07 6_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 100 175 2I2. 0 0 0 . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 6 2 1 2 1 1 3 8I . . .~I /.4~~ 1 .3~ 1 .2,gg /.I0) 1.03 . 9~ .8J, g - .7~'ij .6% .5" .4I3'"260

240

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C IJQ.140.S>(~ 120

100

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INDUCTION OF WATER TO INLET AIR AS MEANS OF INTERNAL COOLING

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68 REPORTNO.7 56-NATIONAL ADVISORYCOMMITTEE FORAERONAUTICS

.05 08 07 .08 09 .I0 /I 12 .05 DB 07 .08 .09 .10 .11 .IEFuel-air ratio, (a) Rear sparkplng boshlng.(b) Exhaost-valve guide.

(oj Above cyl inde r flange, rear.(d) Center orbead between va lves ,

FIG'OBE3.-Relation between Iuel-alr ratio, maximum permIsg!ble indicated mean effective pressure, e ngine temperatures, a nd water-foel mUos oi 0, 0.5, 1.0, and 1.5. CylIn dcrment, 202 cubIc Inches; engine speed. 2000 rpm; spark advance, 20"; oompressioo ratio, 7.0; 1nlet-alr temperature, JI5l)0 F; coo ling pre ssure drop, 14.0 Inc hes wat er; fue l,number.

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2BOINDUCTION OF WATER TO INLET AIR AS MEANS OF INTERNAL COOLING

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70 REPORTNO. 756-NATIONAL ADVISORYCOMMI'ITEE FORAERONAUTIC8

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JNDUGrION OF WATER TO INLET AIR AS MEANS OF INTERNAL COOLING

faired curves drawn from the indicator diagrams are pre-sented in figures 14 (a) to 14 (d). The data show that themaximum cylinder pressure was lower for a given indicatedmean effective pressure with water injection than with fuelalone. At a water-fuel ratio of 1.5, a maximum cylinderpressure of 1030 pounds per square inch at 23 A. T. C. wasrecorded by the Farnsboro indicator. The correspondingmaximum permissible indicated mean effective pressure was263.4 pounds per square inch. A similar power output with-out water injection was obtained with 8--1 plus 6 ml TELper gallon. The resulting peak pressure, as may be seen intable I and figure 14 (e) was 1080 pounds per square inchand occurred 20 A. T. C. The action of water injection inthis case showed a slight tendency to retard the combustion.The maximum permissible inlet pressure for the 8--1 plus6 'ml TEL per gallon under these conditions was notdetermined.Additional indicator cards were taken at a constant inlet-ail' pressure corresponding to the maximum permissible

inlet-ail' pressure for the fuel of 80-octane number withoutwater. The relative indicator diagrams and the data forwater-fuel ratios of 0.5, 1.0, and 1.5 are shown in figures14 (f), 14 (g), 14 (h), and table 1. In these cases the effectof the water in retarding combustion was very noticeable ..A water-fuel ratio of 1.5 caused the peak cylinder pressureto occur 42 A. T. C. or 22 later in the cycle than with fuelalone.Dilution of crankcase oil.-Considerable dilution of crank-case oil with water occurred during operation at high water-fuel ratios. After these runs, the volume of oil in the supplytank had increased and after it cooled a heavy gray sludgehad formed at the bottom. A sample of the sludge, when putthrough a centrifuge, was found to contain 30-percent water

by weight. In these investigations the oil-in temperaturewas maintained at 150 F and the oil-out temperature wasusually between. 190 and 200 F. The temperatures areprobably lower than those used with most multicylinder. engines and an increase in the oil temperature would be oneway to eliminate some of the dilution. When the engine wasoperated with the diluted oil and without water injection,much of the water came out of the oil.With high water-fuel ratios the cooling of the engine wascarried to an e ..xtrome in the rich fuel-air range. Average

head, barrel, and flange temperatures recorded were 240,200, and 180 F, respectively. The maintenance of these

temperatures above. the boiling point of water at atmosphepressure should further decrease dilution..CONCLUSIONSInvestigation of water induction in a single-cylinder enover a range of fuel-air ratios from 0.05 to 0.12 indicatedfollowing conclusions:1. Water injection allowed a fuel to be operated abovenormal maximum permissible performance limits.2. Water injection allowed a fuel to be operated ahigher indicated mean effective pressure, with a lowerdicated specific fuel consumption, or with both, thanpermitted without an internal coolant.3. Water injection had a marked cooling effect on

engine head and cylinder. The exhaust-valve guide wasonly point on the head at which the temperature showetendency to increase with indicated mean effective pressThe temperature was less, however, than that obtaiwith a straight fuel permitting equivalent power.4. Water injection showed no advantage in fuel econo

when the fuel was operated well below its maximum permsible performance limits.5. Water injection might be a disadvantage if the encooling effects are carried to an extreme and cause crankcaoil dilution. Operation at normal engine and crankcasetemperatures should minimize crankcase-oil dilution.

LANGLEY MEMORIAL AEij.ONAUTICAL LABORATORYNATIONAL ADVISORY COMMITTEE FOR AERONAUTICSLANGLEY F IELD , VA., August 15,194.

REFERENCES1. Prescott, Ford L.: Military Aircraft Engines of the Future. MEng., voL 58, no. 3, March 1936, pp. 157-161.2. Kuhring, M. S.: Water and Water-Alcohol Injection in a Su

charged Jaguar Airoraft Engine. Canadian Jour. Res., sevol. 16, Aug. 1938, pp. 149-176 .

3. Heron, S. E., and Beatty, Harold A.: Airoraft Fuels. Jour. AScI., voL 5, no. 12, Oct. 1938, pp. 463-479.

4. Hives, E. W., and Smith, F. Ll.: High Output Aircraft EngSAE Jour., vol. 46, no. 3, March 1940, pp. 106-117.

5. Kohr, Robert F.: Condensation of Water from Engine ExhaustAirship Ballasting. A. S. 1. C., voL 1, no. 44, May 1, 1924

6. Rothrock, Addison M., Biermann, Arnold E., and CorringLester C.: Maximum Permissible Engine Performance of ERepresentative Fuels of 100-0ctane Number. NACA AJan. 1942. .

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