MR No. E5D24

NA’T16NAL ADVISQltYC@thA!TTEE RX? AERC)NAUJTK’S “-

ORIGINALLY ISSUED

April 1945 asMemorandum Report E5D24

EFFECT OF FUEL VOLATILITY AND MIXTURE TEMPERATURE ON THE

KNOCKtNG CHARACTERISTICS OF A LIQUID-COOLED SINGLE -CYLINDER

TEST ENGINE

By Max J. Tauschek and A. F. Lietzke

Aircraft Engine Research LaboratoryCleveland, Ohio

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‘:: NACA “’~~‘WASHINGTON

NACA WARTIME REPORTS are reprints of papers originally issued to provide rapid distribution ofadvance 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.

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EAcABm Ho. E5D24

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EmMARY

An imestl~tioa was ccmducted to determine .%heeffect of fuel. .volatility on the relation between mixtkre temperature md bock-Mmited perfomanc e of a liquld-cooled eing.le-cylinder test 19ngine.“Wok-limited. mi.xture-responeetests were run at inlet-air temper-atures ranging frcm 150° to 380° F with.AN-F-28 fuel andwith tech-nical grade of butane. For these two sertes of tests; the fuelwas in~ected before a vaporization tank connected into the.ccmbustion-air system just befare the sngine. A similar series of tests wasalso run with 28-R fuel which was injected both before and afterthe vaporization tank.

. .The results of the tests shuq: “ ..

1. The mixture temperature at which the owve of .indicatedmean effective pressure plotted ~inst mixture temperature becauesnonlinear is independent of the fuel volatili*.

2. !J9aeknock-limited power output Is sli@tly higher when thefuel has been reasonably well vaporized prior to induction intothe engine than when the fuel is inJected dire@ly into the engineinlet pipe.

. . . .. . ImRcmclmxv

,.At the request of the ~ Air IKmces, a qeri4m at’tests Is

being conducted to determine the effect of engine-operatingvari-ables ti the knock-limited pover output of a liquid-moled engine.

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(See refereme 1.) m the a8t0zmi@@m of * “J@@t of ~creas-the Met -mixture temperature on the”Mock--lhited power output ofthe engine, the following characteristic.z%latiionswere obeemed:(1) the increase in the Jmcck-llmltd power was eater at leannwrtwes thm at rich -.wP; (2} We. *lU*” rat10 at ~~ch henuxxlm.mknock-llmlte~”pchr was observes aecreased frcm a @ch to a ,a Mm value; and (3) a value .0?the Inletmixtu?.% imuperataidewmreached beyond which further ‘decrfmms ~ ~1~ t~lWrat~. ca-.d “-I ..’.‘ “little or no further @cream in we lmock=liml~d pouw. Theseeffects am i~u+fited “in-fl~ 1 J *ich tS plot~d ~ ~wb -lished data.

.... .

These &me relatlons l~d..to.the..hypdtigsis~that Inccmpletivaporization of the fuel at low Inletmixture twnpera~s affectaathe knock Mmlts and that these relations wer# thmef%re dependentupon the fuel v~latIlity. The teats repcrttiqXerein were conductqdat the NACA Cleveland lalmratory dur~ th9 lsttal’ sM% of L944 ti .ordsr to detemmine whether f@l volatll~ty was responsible for theserelatsone. .

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Three fiela were28-R, and a t@xnlcalAmsndmsnt-2, and 28-Racteriatics:

r.. . g’. ‘. , . ..; . .. . .

.“ 1Umd in the teptq AN-F~28, Amendmerit?2,grad.bW. ‘g-butane(.butme); Ths MV-~-28z. .mh hti’the,fOliO* amdntion char-

.“,

lflper- 50 per- W pm-mmt c=mt . cent.point(OF)

P:g; .‘w””. - - ‘.

.“

& . 270 .137

140 : 208 ‘“”. 278 .“ ‘.

AN-F-28, “Amendment-2

28-R!.. ... . “,“.. .

The A. S. T. M. MstlD&im .c&v@m for these‘t+ i’uils& pre- “sentea in figures 2 ed”3. ” me butane had a nomel boiling pointof 31° T. The relatlcm betwwm the boiling temperature and mes-sure fcrobtalnea

butane is shown h f@ure 4, whic~ is.~ottad fmm ‘titsfrcm reference 2.

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IW3AMRI?0. 3S)24 3

APPARAmJB. . ,..: J

The teats were ruu in one cyllnd& of a liquid-coded cyl-IMsr block mounted on a CUE crankcase, ae deecrihed In refer-ence 3. Rhock was detected with a magoetic-vlbratlon-t~e pickwooupled through an smplifier to an osoiJJ.oscope.

The In@ction wstem ueed with the engine 1s d~ticd.uillustrated In figures 5 end 6. The mibuetion air, With wassupplled by the” central laboratory system, passed through a pl%MeUre-regulatlng valve and an electric heater before entering the surgetank. A thin’plate orifice was used to measure the air-flow rate.

I!&csuthe surge tank the ccunbustionalr passed through thevaporization tank ma the ln19t elbow of the ergine (flg. 5) . Thevaporlzation tank had a capacity of approximately 1 cublo foot.Seversl inclined baffles wers mounted In the vaporization tank *provide additional surface for tie evaporation of the fuel end tom~ ~oro@ ** of the *1 with the air. Iron-constantanthsmnocuuple Junctions were ~t~a at the Inlet (upstream frcantheinJectlon nozzle) and at the outlet of the vaporization tank todetemlne the Inlet-a& and the mixture tempsz%dmres, respectively.The mixture Wmm.ocoupla was mounted h such a position that anyunvaporized fuel leaving the vaporizatIon tmk would tend to passunderneath the thermocouple and aid in preventing Mquld fuel fraureaching the Junction.

For the tests with AN-F-28 and 28-R fuels, the fuel was meteredto the snglne by a v~lable -displacementfuel-irq)ectionpump drivenby the engti and the flow rate was detezmindl with a calibratedrotemeter. Two fuel-in~ectlonnozzles were pmtia, one at theinlet to the vaporization tank and one Just before the inlet elbowat the eng~.

For the tests.with buta&, a. special fuel system (fig. 6) waslnsteJJ.ed. Pressure uas matntalned In this sgstem by immersing thefuel tank in a hot-water bath malntaind at about 120° F. When thebutane left the tank, it passed through a coolQg coil, whichreduced the fuel temperature @’ficlently that It remained In theliquld state until it reached the fuel-lnJectionnozzle.

TmT PIu)clpcJRE

For the first and second series of tests, ~k-limlted ~-response tests wzw run with M-F-28 fuel and with butane. FiveInlet-alr temperatures, ranglmg frczn145° to 3S5° F, were used inobtaining the data for both fuels. The third series of tests was

—.. .—., —I

..,. . . ...

., .. .: ,: -. .

4. . “.-l” NACA MR NO. E5D24

run with 28-R .faelat a constant fuel-air “&tlo of 0.10 and withfuel-lnJectlon both before the vapmlzatlon tank and at the inletelbow of the engine; in thisthe independent variable.

&e followlng .operatlngthe tests:

wine, the Inlet-alr tempe~tme was

conditions were held constant for all

IMginespeed, ran . . . . . . . . . . . . . . . . . . . ...3000Ccmpreseion zatlo m.. . . . . . . . . . . . . . . . . ...6065llllet-oi ltempemture,~, . . . . . . . . . . . . . . . . . 1*Outlet-coolant temperature, OF . . . . . . . . . . . . . . . 25CICoolant flow, ~llons per minute 120Spark advance, deg B.T.C.:

In~et. OoOo . . ..oc@ .0.0.0G.000.0C~8

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RESULTS MD DISCUSSION

ComparIson of AN-F-28 fuel and butane. - In general; thehock-limited curves obtained In series 1 and 2 for the M-F-28 fueland the butane (figs. 7 and 8) show the same general trends. Atthe highest Inlet-air temperature tested, the knock-limited lndl-cated mean effective pressur9 continued to increase as the fuel-airratio was enriched from the stolcbiometricmixture to the richestmixture at which data were taken. As the Inlet-air tempel%ture wasdecreased, however, the performance curve developed a reverse bendand ~eaked at a fuel-air ratio that became leaner 88 the temperaturewas decreased. This characteristicwas more pronounced for AN-F-28fuel than for butane.

The cross plots of hock-limited indicated mean effectivepressure against mltiure temperature for AN-F-28 fuel and butane(fig. 9) show the same general trends. These curves are approx-imately linear over the higher range of mixture tementures butbend and level off at lowsr mixture temperatures. The mixture tem-perature at which these curves become nonllnear is the same forbet@ fuels at a c~mparable fuel-air ratio and therefore p~t beconsidered to be a function of the fuel volatility.

“The most pronounced difference in the cross piots for the twofuels Ues In the difference in slopes. This difference 3sbrought out more clearly by figure 10, in which Is plotted the ratioof the indicated mean effective pressure at a given mixture temper-ature to the Indicated mean effective pressure at a mixt-ue temper-ature of 275° F. This plot was made to ellmi.natedifferences in

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the power levels of the two fuels and *US ftiilitate a c-son.“At ocaupamble fuel-alrratios,.the-butane.shows.a proporti-tely .~er inchease In Indicated mean effective pressure than theAH-F-28 flujlfor a given decrease in mixture temperature. As thefuel-alr ratio is enriched, the difference in elopes Is further . .accentuated.

~ order to Illustrate sane effects on vaporization resultlng* t$.edifferences In the volatilitles,ofthe two fuels, deU-polnt curves are presented in fignw U. !l?heeecurves were obtained- equations ~bllehed in references 4 and 5 and frcaudata In mf-ez?ence6; the methods of calculation ere preeent&d In the appendix.The curves for the AH-F-28 fuel (fig. U.(a)) show that at the low-est mixtum temperature and at rich fuel-alr ratios saw liquldfuel is probably inducted into the engine. Because the de~pointtem~=tures of butane are Ve~ low (fig. U(b)), it IS ~wunlikely that any Mquld can exist at the be@nnlng of the cc#qpres-slon stroke with this fuel.

$ff@ct of fuel vaporization on km ck-llmited DarfomsmceThe z%eults of tests conducted with 26-R fuel to detezmine th~effect of fuel vaporization on the knock-limlted power of the engineare shown In fl@re 12. For these tests, the degree of vaporizationof the fuel was varied by changing the point of fuel InJection(figs. 5 and 6).

The results show that the difference between the curves ofknock-limited Indicated mean effective pressure against Inlet-air

&%~~&O~sFa M- in the range of temperatures betweenAs the Inlet-air temperature is decreaaed below

this range, thi~ difference beccmes less, indicating that the inlet-temp&ature Is too low to vaporize the fuel wi~ lnJectlon beforevaporization tank. At Inlet-air tempemt~s above this rangesdecrease In the difference between the two curves Indicates thattemperature of the inlet air is sufficiently hi@ to vaporhe

fuel mom canpletely with fuel InJectlon at the Inlet elbow.

.

SUMMARYOF RIWIJJB

The results of tests run on a single cylinder frcm a liquld-cooled engine block with f’uds of Mffemnt volatilltles, butaneand AN-F-26, and W* different‘degreesof fuel vaporization using “26-R show that:

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.

HACA m No, E5n24

1. The mlrture tempemture at which the ourve of Indioatedmean effective pressure plotted against mixtui% temperature beconmsnonlinear is independent of the fuel volatility. ,..

. .. . . .

2. “~ knock-llmlted power output of.the engine Is sll&lyhigher when the fuel has bsen reammably’ wqll vaporized prior toInduction Into the engine than when the fuel Is injected directlyinto the engine inlet pipe.

Aircraft Euglne “ResearchLaboratory,Hatlonal Advisory Comnlttee for Aeronautics, “”

Cleveland, Ohio, April 24, 1945.

.

.

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NACA m lb. E5D24,

APJ%NDn”. ”

-%. , .-Dti-POIibTtitiIOIJS ““’

—---

7

Calculation of ~-point curves for AN”-I’-28,Amendment-2, fuel. -No experimental data have beqp published on the dew ~ints of our-rent aircdaft fuels at &Lfferent fuel-air ntios and total preeaurea. .Refereno~ 4 outllnes a method whereby such.b Points maybe ~lcu-lated for-total preseures up to one atnxmphere. For the purpose ofthis.report, the equatiams of reference 4 were assumed to hold truefor total pressures up to 80 Inohes of mercury absolute and for therange of fuel-air ratios from 0.05 to 0.125.

When equations (31), (35), (38), and (42) in reference 4 arecombined, the followlng oquatlon is obtained:

. .

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1tdp = 0.132 + 0.109 10810 F A 0.0348 P - 00C4jr (tgo~+ 460)

( #

+$ t90$- 8.95 @ 106.5 (1)

where

‘dp

s

dew-point twmperat.uraat a given fuel-air ratio and at agiven total pressure, OF

fuel-air ratio

total preesurez in. I@ absolute

temperature of 90 percent point on A.S.T.M. distillationcurve, OF

slope of A.S.T.M. distillation curve at 90 percent point,% per percent distilled

Erom the distillation curve presented In figure 2, values of

t90% and S were determined to be a~ follows:

t90$= ~OQF

s = 3,9° F per percent “distilled

Substitution & these values in equation (1).yields the result:

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8 ivAcAm Ho.

‘dp = 79=6 ~610 [/ (~ A 0.0348 P - 0.04”)] + 152.4

Equation (2) was then used to oaloulate the curves of figure

E5D24

(2)

ll[a).

Calculation of dew-polnt curves for butane. - Because thebutane was a nearly pure hydrocarbon, it was coneidored more fea-sible to calculate the partial pressure of the fuel In the fuel-air mixture and then determine the saturation temperature from the “iapor-pressure curve than to use the method of reference 4.

The partial pressures c& the butane wero detezmlned by meansof Dalton’s law:

vhere

P pressure

M molecular weight, moles

For use in the tests reported herein,the form:

Pf=35?!%

where ..

P pressure, In. Hg absolute

M molecular wolght, lb-moles

f fuel

m mixture

(3)

the equation was written in

(4)

When the molecular weight of 56 for butane and 28.95 for air aresubstituted, the equation becomes:

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NACA~ HO ● -4 9

Pf = 0.01724 % (F/A).- ... . .,... (5).0.0539+0.01~24 (F/A). ..: ,.. .. .. ,

. .

From this equation the ~ial pressures of the fuel were calculated.. .

in order to titermlne.the tituratlon temperatures corre- ~spending to the ~lal pressures, tbe boiling-point curve (fIg. 4)was extrapolated by means of a D&ring line Plot. A deacriptlon oftme of c&.etructi& till be found in->-the D&rlng line

where

h

tf

DataWltll

1.

2.

3.

4.

Waa detemlined to

+ = 1$84 tf’ +

ref~ce 5., The equation”be:

178.7 (6)

satumtion temperature of reference liquld (water) at a givenpressure, W

eaturation temperatw-e of fuel at same pressures W

on the thermodynamic properties of water used in connectionthe ~lng line plot were obtained from reference 6..

..-REFERENCE

Harrleg, Myron L., Nelson, R. Lee, and Berguson, Howard E.:Effect of Wa+&r filjcctionon Knock-Ltiited Performance ofa V-me 12-Cyllnder Liquid-Cooled Engine. NACA Memo.rep.$ Sept. 9, 1944.

Anon.: Hendbook of Chemistry and ~SiCS s Chemical RubberPubllehing Co. (Clevelend), 24th ed., 1940, pp. 1836-1837.

Waldron, C. D., and Blemam , A. E“.: Method of Mounting Cyl-inder Blocks of b-Line Engines on CUE Cmnlccaees. MICA RBNO ● E4G27, 1944.

Bridgemah, Oscar C.: Equlllbrim Volatility of Motor Fuels fhcmthe Strmdpoint of Theti Use in IntQrnal Combustion Engines.Res. Paper 694, list.Bur. S~ .Jour.~s., VO1O 13,no. 12 Ju@ 1934, pp. 53-109.

..—

-1

10

5. -W 0. A., d Watson, K. M.: Mauatrlal Chauical Cl?lloulationa ●

John Wiley & SonEI,~., 2d cd.,,1956s pp. 74-76.

Keenan, Joeem H., and Keyes, Rederlck (3.: Themmlymmio Proper-ties of Steam. John Wiley & Sons, ho., 1936.

I

NACA MR No. E5D2UNATIONAL ADVISORY

COM41TTEE FOR AERONAUTICS

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.06 .07 . 0/3 .09 .10 .11 .12 .1>Fuel-air ratio

Fuel-air ratio, 0.095

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Figure 1. - Effect of mixture temperature on knock-lim

of liquid-cooled multicylinder engine at 3000 rpm.

ubl ished data. )

II

350

ted performance

Plotted from un-

NACA MR No. E5D211

,NATIONAL ADVISORY

COMMITTEE FOR AERONAUTICS

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Figure 2. - A.S.T.M. distillatlbn curve for AN-F-2t3,Amendment-2,fuel used in the first series of tests. Recovery, 9g.O percent;residue, 0.t3 percent.

1-—

NACA MR No. E5D24

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NACA MR MO, E5D24

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Pressure, In. HK abs.Figure l+.- Variation of boiling ~emperature of butane with

prescure. (Data from reference. )

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NACA MR No. E5D2%

~lnlet-air thermocouple

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-[Sur9e tank (used with injection at

~$A

otop of vaporization tank only) ~ ,

\ -(Fuel-injection nozzle-<

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NATIONAL AOVISORYCOhUITTEE FOR AERONAUTICS

Figure 5. - Diagram of induction system used with single-cylinder

liquid-cooled test engine.

MACA hiR NO. E502Q

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Low-volatility fuel system

FuelConsFuelFuel.VentFuelFuel

line from barrel pUISpant head tankline to flowmeterinjection nozzleng valveflowmeterline to engine

Vaporization tankPressure gageShut-off valveVariable displacementfuel-injection pumpfngine-inlet pipe

—G

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NATIONAL ADVISORY

9

Butane system

M Fuel line toinjection nozzle

N Throttling valveO Butane tankP Hot-water bathQ Cooling coilR Ice container

Figure 6. - Diagram of fuel systems used with single–cylinder liquid-

cooled test engine.

MACA MR HO, E5D2U

111111._All”ll

Fuel-air ratio

Figure 7. - Effect of inlet-ai r temperature on knock-limited performance

of single cylinder from liquid-cooled engine with AN-F-28, Amendment-

fuel . Engine speed, 3000 rpm; compression ratio, 6.65; inlet-oil terf

perature, 185° F; outlet-coolant temperature, 250° F; spark advance:

inlet, 28° B.T.C.; exhaust,34° B.T.C.

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HACA MR NO. E5D2~

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Fuel, AN-F-2g 1~~ -4s , t , & ,, t t , 1, , t , , , s , , , 1, 1, cI II 11 , , 1~ I 1 , , 11 t11~

.05 .0 6 .07 .(W .09 .10 .11 .12 .l-jFuel-air ratio

Figure 7. - Concluded.

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NACA MR NO. E5D2U

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NATIONAL ADVISORYCOMMITTEE FOR AERONAUTICS

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Inlet-airtemperature

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R-id~&3.J

Ill 1-111111 I-1-l-l

. .m

.* .06 .07 .a As .10 .11 lx!l?uel-alr ratio

Figure Et. - Effect of inlet-ai r temperature on knock-limited performanceof single cylinder from liquid-cooled engine using butane as a fuel.

Engine speed, 3000 rpm; compression ratio, 6.65; inlet-oil temperature,

165° F; outlet-coolant temperature, 250° F; spark advance: inlet, 28°

B.T.c.; exhaust, 34° B.T.C.,, ,, . . . ,. , ... -, .,, - , . .,., ------------ . .. . ..—. . . .

tiACA MR NO. E5D2U

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HACA MR NO. E5D211

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50 100 150 200 250 300 350

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137-8d“’’’”l’”l ’ >, ,1,,,,1,,,,1,,,,

Mixture temperature,OF

J’lgure 9. . Variationof knock-limitedlndloatedmean eff’ectlvepressure withmixture temperature for MI-F-2g, Amendment-2, fuel and butane.

I

NACA MR HO. E5D2~

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NATIONAL ADVISORYCOMMITTEE FOR AERONAUTICS

2.6

b \oIr-‘2.2 \$.!o

g4=Id

;.@ — AN-F-2~, Amendment-2

t

dE~

g~ 1.6

0wf#q

~ 1.40

sv!%

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1.0 150 100 150 200 250 300

Mixture temperature, %(a) Fuel-air ratio, 0.07.Figure 10. - Variation of relative knock-limited power output withmixture temperature for AN-F-2g, Amendment 2, and butane. (Datafrom figs. 7 and g.)

NACA MR No. E5D24

* 1 1 1 1 1+

N.ATIONAL ADVISORY

* COMMITTEE FOR AERONAUTICS

bllw 1 , , * ,

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Fuel

50 100 l~o 200 250 300Mixture temperature, ‘F’

(b) Fuel-air ratio, O.Og,Figure 10. - Continued.

NACA Mli No, E5C)2U

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NATIONAL ADVISORYCOMMITTEE FOR AERONAUTICS

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~ 1.85d~Q4g

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aj

$&l.2:

%o0d

GMixture temperature, W

(c) Fuel-air ratio, 0.09.Figure 10. - Continued.

NACA MR No. E5D2U

. . . . . . . . . . . . I . 1 , , # , , , , , , w , JNATIONAL ADVISORY

CWITTEE FOR AERONAUTICS,

Fuel

—AN-F-28, Amendment-2-‘–— Butane

--‘. .A

1.6:\

\\\

\\

. . . . . ~ . . . . —“\

1.

50 100 150 200 250 ~ooMixture temperature, OF

(d) Fuel-air ratio, 0.10.Figure 10. - Concluded.

,. . . .—-—— ..—

1

1

l“’’”’’’’’’’’’!’’’’’”””’ I , , r“” 1 1 1 ,1’”

, , 1 1 t I 1 1 I 1 u 1 1 v 1 , , ,

NATIONAL ADVISORYCOMMITTEE FOR AERONAUTICS

1

Total I

,20 “ in.

—

.00 L

~

40 :

uel, AN-F -2g

20““”’.05 .06 .07 .0?! .09 .10 ● 11 .12

Fuel-alr ratio

t-l s ,

●essurer .

~o

70;0.70

+0

$0

20

137-13

.13

(a) Fuel, AN-F-28.Figure 11. - Dew-point temperatures for AN-F-2$, Amendment-2, and butane at various

total pressures.

ma9

NATIONAL ADVISORYCOW.41TTEE FOR AERONAUTICS

-40 “ ~ ‘

P

~ — 60

8-60“, / ~ — ~ ~ 50

Q“k2dL1@ ,CL

*.w5

~-looa

Fuel, butane137-14

-120~’””~ ““a’ a“” ‘“” ““ ““ ““ ‘“” t,,, ** , s,,, a,,, afl.,,1.* .... ..,.-.05 .06 .07 ● Oi? ,09 .10 .11 .12 *

Fuel-alrratio(b) Fuel, butane.Figure 11. - Concluded,

—-....—- ,.,.,-. , , . . .. . .. ,.......-— --- -..—.——-------- .——-—. ——,———- .-,.. —,.., ,-,,,,,,,,- , . ..........—- ,,. ,,,.,—. !.!!.! !.!

.

NACA MR No. E5D2q

1 , # 1 1 I , , v , v , , ,

NATIONAL ADVISORYCOMMITTEE FOR AERONAUTICS

70 :

50 ~

Fuel injection at top of

Fuel Injection at inlet

r 1L

240

Fuel, 28-Fi 137-ii,

200 1 , , ,1 , ,, a a1 , 1 11 ,aa , ,, 1. a1, , ,1 ,

150 200 259 y20 350 400 45Inlet-air temperature, ‘F

0

Figure 12. - Effect of fuel vaporization on knock-limited performance of

single cylinder frem liquid-cooled engine. Engine speed, 3000 rpm;

fuel-air ratio, O.IO; compression ratio, 6.65; iniet-o”il temperature,

185° F; outlet-coolant temperature, 250° F; sparkadvance: inlet,280

B.T.C.; exhaust, 34° B.T.C.

..—. . ... .

Illllllll[[l[[lllfllmlllll:3 117601354 1934 —

— I