Tests made on a Curtiss D-12 engine in the Altitude Laboratory at the Bureau of Standards show the following effects on engine performance of change in jacket-water outlet temperature: 1) Friction at all altitudes is a linear function of the jacket-water temperature, decreasing with increasing temperature. 2) The brake horsepower below an altitude of about 9,000 feet decreases, and at higher altitudes increases, with jacket-water temperature. 3) The brake specific fuel consumption tends to decrease, at all altitudes, with increasing jacket-water temperature. 4) The percentage change in brake power output is roughly equal to the algebraic sum of the percentage change in volumetric efficiency and mechanical efficiency

Ellis, Greer

Garlock, E A

English

NASA Technical Reports Server

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NOTE S
NATIONAL ADVISORY COMMITTEE FOR AXRONAUTICS
NO. 4’76
THE EFF-ECT ON ENGINE PERFORMANCE! OF CHANGE
IN JACKET-’.YAZ!EROUTLET TEMP~R~T’JR3
By E. A. Garlock and Greer Ellis
~Lreau of Standards
Washington
November 1933
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https://ntrs.nasa.gov/search.jsp?R=19930081314 2020-06-17T22:27:02+00:00Z
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NAT IOHAL A3VISC)RY COMMITTEE FOR AERONAUTICS
TECHNICAL NOTE NO. 476
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-
. —
THE EI’.FECTON EITGINE PERFORMANCE OF CHANGE
IN JACKET-WATER OUTL3T TEMPERATURE
By E. A. Garlock and Greer Ellis
SUMMARY
Tests inde on a Curtiss D-12 engine in the Altitude_
Laboratory at the Bureau of Standards show the following
effects on engine performance of change in jacket-water
outlet teraperature:
1) Friction at all altitudes is a linear function
of jacket-water temperature, decreasing with
increasing temperature.
2) The brake horsepower below an altitude of about
9,000 feet decreases, and at higher altitudes
increases, with increasing Jacket-water tem-
perature.
.
3) The brake specific fuel consumption tends to de-
crease, at all altitudes, with increasing
jacket-water temperature.
4) The percentage change in br~._e power output is
roughly equal to the algebraic >um of the per-
centage change in volumetric efficiency and
..-.
—.
.—
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mechanical efficiency.
INTRODUCTION
Valuable information has been
vestigations of the performance of
...—— ___ .——
obtained by several in-
liquid-cooled aircraft
engines, with high coolant temperatures. All the”dyna-
mometer data, however, have been obtained with engines
operating at sea level.
.-
..
Because of the interest in this subject a brief.ex-
perimental program has been conducted in the Altitude
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,.-N.A.C,A, Technical l?otg NQt 476
.. .. .
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Laboratory (references 1 and 2)”’to determine the eff~cts
of change df jacket-coolant .teh~erature at altitudes of
10,000 and 20,000 feet as yell as at sea level. This iS
the only Ialoratory in this country where it i.spossible
to conductdynarnometer tests. of aircraft’ engines under
contrcllled conditions which precisely reproduce those
actually encount”efied in flight at various “altitudes.
—
~!he only coolabt” used was water )and the range of a-
vailable temperatures was therefore limited to that be-
tween the coldest obtainable from the city water mains
and a maximum of 100o C. The tests were made at but one
speed and one compression ratio. Altitudesof 10,000 and
20,00C’ fe6t”%&re selected becafi]e-previoug_te8~s with a
Libert~-6Ti@.tib s6me y+atis&.g6 ha~ indfcated th~t-the.power
output ”-~&Invariarit wl+h. jacket-wa~er ~~perature at an-”
altitude slightly below 10,OOO feet; .Since the power OUt-
put atsoa level decreased with increqsiqg jacket-water
tempar~tur~ , it ~.ppear?d t~at ~th~ghe,r Slfitudes the pow-
er output might increase with incre-asin~ ttynp6~attire.
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The-engine used was a Curtiss D-12 twelve-cylinder,
V-type with a compression ratio of 5.3 : 1, loaned by the
Bure-au--of Aeron~,ut$~-s,–Navy Depar:rnent. !l&e displacement
is 1;1’6’0“CU-. ”-in-i ;- and. t-he”~n~~ne .is rated 435 bra&e “horse-
power at 2,300 r.p.m. a“t sea lev’el, A1l.t~st runs were
made at an engine speed of.2,000 r.p.m: at which speed the
normal s~a-lev~l”power was 401 br+e horsppgtier at y70 ~.
jacket””t~mp-er%,~ur~.” : - ..“ ~~” . . .. ..
!*.. .. .,
The carbuiettir intake” air”was hei~&ii 156 C,, being
first li~humidifledby cooling to about -400 C, I By means of
an extlsrnal oil reservoir the oil inlet temperature was
held c,)nst~nt at.600 C. ‘The temperature of the jacket.
water was controlled by circulating it through a tank to
which Bteam or gold wqter could be added. The. $oldest ‘
runs W13TG-rna~e )y passjng ‘Gatbr frog the ~ity gai.ps di-
rectl”y~’~kToug~j the”:6fi#in6 w~tfiout”~~circul~tiln~~
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Sayb,o.lt,universal visqsity of 697 seconds at 130° T. .“
-. ‘f54~;4~C.), and 98 se.co~ds.at 2100 F. (98.9° C.) .
. =--- .~
All results are based on maximum power values obtained
from. mixture ratio rnn,s in which the mixture ratio was va-
ried Ori qach side..of the gptirn-mn..ti-tila definite reduction
in$powbr was obs8rvqd. ~uel.consumption w&.s”&etermined by
‘ tirnin&-”the flow from a calibrated measur~ng”t=nii =fid-a ven-
.tqri which had been calibrated -a~ains~”a Thomas me-r was —
used to, mea~ure the air flow to the carburetor. Friction
“power 1?ss was determined by motoring the engine with the
dynamometer.
. ., ., . RESULTS
—
.-. .-— —
-.
.,
—
For the purposes of this report, indicated horsepower
.is defined as the sum of ‘the measured b~ake horsepower ~~
the friction horsepower, the latter being the power re-
quired to drive ‘the engi~e when motoring with the dynamom-
eter. Volumetric $’fficiency is defined as the ratio of”
the volume of air received per cycle, measured at the temp-
erature and pressure existing at the carburetor entranc”e, .
to the piston displacement. Because less heat was a~sorbed
by the jacket water in the friction runs, lower jacket tem-
peratures were possible than when operat$ng under..power,
—
Referring to fig~~re 1, the friction horsepower at all
three altitudes deg’res,ses approximately linearly w~th”,ifi-
creasing jacket temperature. At an altitude-of 20-,000
feet the friction horsepower decreases 0.52 pbrcen~ for
each degree increase in jacket-water temperature. At “an
altitude of 10,000 feet the decrease is 0.50 percent for
each degree increase in jacket-water temperature and at
sea level 0.39 percent. Frank (reference 3) found that
the friction of a Curtiss conqueror engine operating at
sea level was’ approximately linearly variant with jacket-
coolant outlet temperature, th~:averag~ decret!iSe”Being.0333
par-cent for each degree”increase in tgmperafvre., .. - ,
This change in friction horsepower is primarily due
to change in the viscosity of the oil. Oils vary widel,y
in their viscosity-temperature relation. Accordingly other
oils would affect frictioti and consequently brake horse-
power differently. It seems probable that an oil with a A
different viscosity-temperature coefficient would give’s
friction curve of different slope, while “an oil of sj.mflar
.
.-
4 N,A. C.A.’ Technical Not-e No.’ 476
--- -.. ,. .... ..
vi sco~it~.-te,mpek~ture -c”oe$ficient ~?lt,of.diff@.ent .Saybolt
Vi scosity at a ~iveq””temperature would shi”ft‘“the curve p&r-
allel to Itself.
.. . . .. . . . :.
“’T’h6“brake’ ~ower. decreases with increasing jacket-water
temperature at sea ~etiel, “is nearly constant a? 10,000 feet
and increases at 20; 000 f~et. The decrease In brake horse-
power at sea level 3S $.n accor.d’with” lh.~.fiDcii.n.s of l?yknk
(refer.8hce”3) and~utt,’ (refqrencp 4) fo~.~hg range coverqd
ly the present’ tests. Figure 2 indicat~s that jacket tqm-
peratuze has no.’effect on Irake horsepower at an altitude
of a-Dcjut9,000 feet.
‘Ihe indicated horsepower’ at. all altitudes decreases
with increasing jacket water outlet temperature, the per-
centage dscreaso for an increase i.n jacket water tempera-
ture from 35° C, to 950 0; being 5.7p ercent at sea level,
4..5 pe*cen%, ”at.T.0~000-3ee= Arid 5.5 “peicent tit 2XS~(30G.fisi,
The change of volrimetric efficiency and mecha~ical
efficiency “with jackefi-water “temperature at se-a-16v61 and
at altitudes of 10JOQO ‘“and20,000 f-eet is ‘shown in ‘figure
3. Vol”umetria efficiency decreases with increa$fng jacket-
water temperature b~cavse the increased warming in tha
jacketed intake mqnif~lds and cylinders decrga~es .thq
charge” fiolght. iidu”cted. The increase :in mechanical Qffl-.
ciency”r-eimlts from the mo~6 rapid decrease of “fr~ction”
than of i.ndi,catedpaw~r with indreasitig jacket temperature.
The perceti~-age change in brake horsepower is titipiQ”X~m”ately
equal to ,the net change in the. volum.qtr$q ud rn.8Ch&ni”CaL
eff.icienc.i~s,- “.This is in accord with Ricardois view (ref.-
erence-6,e,pag’e 86) that the change in power is due to the
varlati.on..in vo~umetric. efficiency and friction, and “only
negligibly, tv-~hange in heat ,1OS.Sfrom the .ignitod,charge
to the-.Jecket with variation in jacket temperature,
.. .
.R”5fe..r~ingto fY.,gure3~ at ,sea levelz the, fncreq~e in
rnechani,c,al.ef.ficlency .~s,l.3 “percent four the range ‘of -
J’acket-coo.lan”t“tGmperature~9.5~ ~~ (1570 F.) to 100° C~--
(2120T.); whereas Frank (reference 3) with a Curtlss Con-
quer~r ‘engine noted, an.increase ‘of only 0.5.percent~.
IF. .+,.-2:..1~.~
,...,””-““
.. ,.
. . . The tende~cy ,at,&ll altitudes is for the brake specif=
ic .fu91 .c~nsu.mptaon to. decrease with increasing jacket=
water temperature.. This: tendency is due largely to the in-
cr,pa~sein rneehani.cal eff~,ciency .wi,$h,ingre.asing”jacket-..
.W.a:t.er. tetipeTatune, :tid- t,o, bet,~er vapo.rizti-tion.of, the fuel
.
._
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0N. A. C.A. Technical Note No. 476 5
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due to the warming up of the intake manifolds (figure 3).
Nutt (reference 4) u.si,nga Cumtj..s~c:o~qu~r~~ 6n~~n6~tiar’f~d
the jacket -coolmt te~perature from .86° C. to 149° C. He
found that ti~e brake specific fuel: con$tipt~~~ ‘K&icr~Is:ed“
gradually until the temperatur,e reached 121° C. an-~ ~hen “
.—
increase d,.. For a given engine, the temperature at which -
this reversal occurred would doubtless be “a funct~o~.”~f ‘-
the oil characteristics. Frank (reference 3) found for
the “same engine. an .,average.:decrease i-n.brakq ~pecific fubl
consumption of, 0.,22-percent p,er‘degree ‘~eni~gr.a~<~nc rease.—.
in jac.’cet-coQ1.ant .t,emperature. This is “t-he‘.saiieperce-ntage
c-nanqe as shown in figure 3. However, the-plo.~fid results
——
were obtatnad with the Curtiss D-12 engino under maximum
power conditions at 2,000 r.p. m., whereas Frankts results
were obtained with the Curtiss CQnqueror engine operating
at 99~- percent of maximum power and a speed of 2,100 r.p. m. .
With a Curtise D-12 engj.nez Frank (reference 3) reported
an increase in bra~ke specifie fuel consfipt.i.on_w~_~-incr_?ak--
——
.ing j,~cket-coolant temperat~re wh,e-n.runq~.ri~.fu.11~~ch at
.2,000 r.p.m~, and a decrease”-when-operatiqg on. the ~“”~~~.~
side. of maxiinum power. The .mechani.cal effici,e”ncy decr~ases
with altitude, accounting -for the increase i-n sp6c.I~ic-fuel
consumption with increase i,n.altitude.
.*.
.-
,.
At sca leve~ the. falling off in brake horsepower with
increasing jacket temperature, partly offsets .–the-.advan-
,tage gained due to the decrease in specific--fuel ‘cons@ii
tion. For the range covered, the decrease in brake specif-
ic fuel consumption is 13.7 percent, whe”reas tle decrease
in brake powor is only 3,4 percent. In the cad”~ of aircraft
engines this decrease in specific fuel. consum~t>on .~ay-bti
a great advantage and more--than off-set the d~sad+antage of
tho decrease in powor output,
In analyzing the distribution of the available heat in
the fuel and in computing thermal efficiency, a value of
19,600 B.%.u. per pound was as-sumed. Since the exhaust
gases were cooled by injecting water into them, (reference .
1) the higher heating value of the fuel has hoen chosen. - ‘“
In figuro 4 the percentage of fuel” heat appearing as us6f”u1
work iS seen to increase Iiqearly with “increasing jackef-
water temperature at all altitudes. The percentage of.fuel
h#at carried away by the jacket water decreaseti.with increas-
ing:;temperature at all altitudes because of increasing radi-
ation and convection from the 6ngine. ..,-.
Friction horsepower has been plotted as percentage of
heat in the fuel. While a part of the friction no doubt
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N,A,C,A, Technical Note l?’o”~’476
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,.,.IS,i.-->.’-,.+:+.,.+>-- -.-.-=—=.=-—= ..—---—-.:~ .-------------- -, --- --
a.pp’eaI:~ as: he~t:‘i~~’tti’ej&c”ket ~af”er, no difference_ veas de--
tedt,ett~in }i’t,~ke“ti~.outle”t .j~’ctidt~water:tatiper.atures ?@on.__... __
tek.i.n~fricti,o~ ~~owe.r~r~adlngs-,
L—.——— —----—
The amotifl:tof water c~rcu.
Iated. through ..t.helj&c~et was’‘about 200 kilograms per minute
and tlte““tempera~ti~~ ~~adi”n~s”:are”“p:ro.ba~lyaccurate to wi th-
in +CLC. .’ ““.~:’”‘ - ‘~’ ‘ .... ..:________
:-.-.-:; ...- “.. - ,’ —
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.3.t.i s e;i~e~;fi.tha$;the”’~reat-%” part of the friction
‘is acc.o~ted for.~as.heat .1os% in” rh?liati,oa ~nd .cohyectfgn,
Ptimpir.gtiloss,e@,afid.~ower ‘required” to drive the. ge&rs, pump 0
and. ac:ce. ssor.i-e”s. ‘ : .,. .— . .. . . —. .. . ..’-..:!r- ,. ..”. .,, ..
..:. ..—=:F,
,“ “ CON CL”U510ilS- ..
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.
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.. In .,view of “the l,~,g~’::change~ iti sp-eti~ficfuel” ~“onsump-- ‘-
tion..aad .,fricti-oriw~.”~hchan~d ‘of‘Jacke”t-”wat’e:rtemperature,
“-it wou,ld seem .th~t ‘$~@..su”bj%”ct““’de”ser”vesfurther attenti,o,n..
The questions .o”fsp$ed,:,independent ,oont~ol. -of inte,ke-mani-
fold temperature, fid ..c,orn~ree$ionrati”d should be studied ,
#he range of altitude ‘pressures and $aeket=cwolant tempera-
tures should. b.e.increased and tests should be conducted va-
rying., the car%:~jet~x intake.-air temperature with- altitude
according. to the s$aniard atmosphere. “It might also be
well to conduct. the tests with vtkfious lubricating oils and
jacket coolants. .. .,.,.. . . .._
..
.-.
,- ..
,,,
Bureau of st&daTds’,” - ; , s . . .. ,
Wash.ington, .D. C. , “OCt. ~8, 1933.
,,
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-----
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..
N. A. C.A, Technical Note No. 476
REl?iZRENCES
1. Dickinson, H, C. and Boutell, E. G. : The Altitude
Laboratory for the Testing of Aircraft Engines.
T.R. NO. 44, N.A.C.A. , 1918.
2. Cummings, H, K. and. Garlock, E. A.: A~tftude Labor~-’
tory Tests of Aircraft Engines. Aeronautical Engi-
neering, vol. 4, no. 2, April-June 1932, pp. 53-60.
3. Frank, Gerhardt W,: High-Temperature Liquid-Cooling.
S.A,E. Journal, vol. 25, no. 4, October 1929, pp.
3:9_343m
4. Nutt, Arthur: High Temperature Liquid-Cooled Aircraft
Engines, Aero Digest, Uarch .1932$ p. 35.
5. Ricardo, Harry R.: The High-Speed Internal-Combustion
Zngine. Chapter 111, p. 73. ~1.ackie & Son,: Ltd.,
London and Glasgow. 1931. ..-—
6. Standard Atmosphere Chart. Miscellaneous Publication
of the Z+lureauof Standards, No. 82.
.
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The effect on engine performance of change in jacket-water outlet temperature

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