Hensley, Reece V

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NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS ~ ti-
WN’’’’’IMII Iuwolrr
ORIGINALLY ISSUED
Ociober 19.44as
Restricted Bulletin E4JI-3
RELATIVE EFFECTS OF CYLINDER-HEADAND INLET-MIXTURE
TEMPERATURES UPON KNCCK LIMITS OF FUELS
l& Newell D. Sanders, Jerrold D. Wear
and Reece V. Hensley
Aircraft Engine Research Laboratory
Cleveland, Ohio
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LABORATORY
WASHINGTON LzulgkyMM.j Vq ~ -.
NACA WARTIME REPORTS arereprintsofpapersorigimllyissuedtoproviderapidistributionof
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E-37
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https://ntrs.nasa.gov/search.jsp?R=19930093468 2020-06-17T01:45:49+00:00Z
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lJACARB l’?~. E4J13
W4TIO?AL ADVISORY COMMITTEE
Illllllll!lllllflmfllfll!l
31176014033022 -
___ —.
FOR AERONAUTICS
RESTRICTED EHJLL?YTIN
RELATIVE EFFECTS OF CYLIit)ER-HENd)A.NDINLET-MIXTURE
TEXPER!4TURESUPON KNOCK LIVITS OF FUELS
By IlewellD. Sanders, Jerrold D. Wear
and Reece V. Hensley
Object. - To investigate the relation between the effects of
cylinder-headtemperature and inlet-mhture temperature upon the
knock limits of Iuels.
Scope. - Tests were r~ at a constant fuel-air ratio in which
the decrease in cylinder-head temperature r~quired to offset the
effect of increasing the inkt-mixture temperature on knock-limited
power was determined. The position of the knocking zone in the cyl-
inder was varied by cutting out one or the other of the two spark
plugsl All tests ware conducted on a Pratt &Whitney R-2800 single
cylinder.
Summary of results. - The follomtingresults were observed in
these tests:
1. The decrease in cylinder-hsadtemperature required to main-,
tain incipient knock.at constant power when the inlet-mixture temper-
ature was incrzased was directly proportional to the increase in
ifl~t-mixtme tempmaturs. The data are not sufficient to draw the
conclusion that such a lin~ar relation always exists.
2. The temperatures of portions of the innar cylinder wall
adjacent to the knocking zone had a predominant effect upon knock.
INTRODUCTION
The relative eff:cts of cylinder-head temperature and inlet-
mixtu.ru, or chargs, temperature on the knock-limited power of a fuel
is important from two considerations:
—
--.--—---- —-----—- -—---- -.-.--—.—--.———..—.-— —-...— —.. .- .-_ — —_________ .. . .. ___
-. ——-...—.-.-. .. ._ —._ — . — ——... ~— . _ —~ –..—... ——.—.— . .. .. .— . . —.-
2 NACA.F@ NO l E4J13
(1) Engine-temperature control required to obtain the same
results in knock tests of a series of fuels on the same engine model
in different laboratories
(2) The relative value of decreasing the inlet-mixture temper-
ature in relation to decreasing the cylinder temperature as a means
of increasing knock-limited power
A complete knowledge of the effect of cylinder-head temperature on
knock includes heat transfer during the intake stroke, during the
compression stroke, and during the combustion period~ as well as
localized heat transfer betn~en the knocking zone and the cylinder
wallsl In addition to cylinder-kleadtemperatures, piston and valve
temperatures influence knock. Reference 2 presents data showing the
effects of piston temperatuw on the knock limit of a fuel.
Tests were made of the effect of inlet-mixture temperature and
cylinder displacement on the charge temperature at the end of the
induction strcke by the NACA and were reported in reference 2. Data
on th-eeffects of cylinder temperature on knock-limited power have
been recently re~orted by Fratt & Vhitney Aircraft and lyi~the
Standard Oil Development Company in reports to the Coordinating
B.esearcllCouncil. The relations of cylinder temperatures to various
methods of increasing knock-limited power have been investigated at
the IJAC4.Clevelaiidlaboratory and the results are presented in
reference ~.
The purpose of the investi~ationreported herein was to deter-
mine the relative effects of cyiinder-head temperature and inlet-
mixture temperature upon knock at constant knock-limited power in an
alir-cooledcylinder and to obtain data showing the extent to which
the distribution of cylinder-head.temperatures controls knock. No
effort has been made toward evaluating heat transfer, but a direct
comparison of the effects of cylinder-head and inlet-,mixturetemper-
atures upon knock has been made and the results are compared with
the results presented in reference 2. The data were obtained at the
Aircraft Engine Research Laboratory of the NMM, Cleveland, Ohio,
during February 19M.
APPARATUS
Tests were conducted on a Pratt & ‘,%itneyR-2800 cylinder. In
an effort to sirmlate the cylinder temperature distribution expected
in fli@tj the cylinder was mounted with its standard baffles on a
CUE crankcase and ~,tithcoolin~-air directing vanes in front of the
cowling.
.__._.— .— . ..—
.. ..... . .. . . __
NACA R13NO. ~4J13 3
Combustion-air flow to the engine was measured by a thin-plate
orifice. The air passed tkrough a vaporization tank where fuel and
air were mixed and vaporized. The vaporization tank has a volume of
approximately 30 times the cylinder displacement (155.6 cm in.) and
was connected to the cylinder by an intake pipe, the inside diameter
of which was 2-5 inches and the length 24 inches. The inl.et-mtiture
16
tempcratu.rewas mcasurecl.by a thermocouple located in the intake
pipe a.ta point 15 j.nchesfrom the intake port of the cylinder. Fuel
was delivered from a Bosch injection pump to a fuel-spray nozzle
located at the upstrean end of the vaporization tank. lhel flowwas
measured by a calibrated rotametcr.
The fuel used in the tests was a blend consisting of Y2 percent
of AN-F-28,Amendmmt-2, fuel (130 grade) and @3 percent of
AN-F-22 fuel (62-oct~~~ grade),. It was impossible to use AN-F-28,
Amendment-2, fuel alone because the available cooling-air piiessure
drop was im.ufficicnt to lower the cylinder-head temperatures t.othe
desjred values du37inf,opsration at the high powsr levels permitted
by AY-F-28, Amendmcmt-2, fuel. The method of tests used in this
investigation,however, gives results that are independent of the
fuel inawnuch as the inlet-ml~ture density and the fwl-air ratio
WWQ maintained constant.
Knock was detected with a magnctostriction pickup unit and a
cathodti-rayoscilloscop~.
*
A first seriss of tests was run to determine the relative
effects of variations of inlet-mixture and rear spark-plug-bushing
temperatures upon knock for normal operating conditions. In order
to find the decrease in cylinder-head tcmparatum rcqutied to offset
the effect of increasing the inlet-mixture temperature on knock
intensity, the tests were run at constant fuel-air ratio and con-
stant weight of aI& inducted.
The followin< conditions were fixed for all tests:
Compression ratio. . . . . . . . . . . . . . . . . . . . . . ,6.7
Spark aclvz.nce(both plu[w), degrees B.T.C.. . . . . . . . . . . 20
Enginespeedjrpm. . . . . . . . . . . . . . . . . . . . . . 2000
Fuel-airratio . . . . . . . . . . . . . . . . . . . . . . 0.075
‘Theinitial conditions of the primary variables were as follows:
OF. , . . , , . , . 6 l l l l “ “ “Inlet-mtituretemperature. 125
Rear
.
spark-plug-bushingtemperature, OF*. l *.*.. . . . . 456
. .—.— .———... .. ._.-—_ ______ ___ _______ __+>
———...——...—..- _____
--L- — -— ..-..—-...— .-—-—-.. .—. —— .-.—.. — -.-—— .— ..— —.. .
4 IJACAF@ IJo.E4J15
J!tthe initial conditions, the engine WM adjusted to give inC@hIt
knock and the rate of air consumption of the engine was observed.
The inlet+nfiture temperature was then increased in successive incre-
ments of about 20° F over a range from 125° F to 190° F and the head
temperaturewas reduced to the point of incipient knock at each
increment by increasing the cooling-air flow. The inlet-air pressure
was adjusted to give th-esame rate of air consumption as was observed
at the initial condit-ion.
A second series of tests was run to find the effect of the dis-
tribution of cylinder temperatures on knock. Tests similar to the
ones just.described were run with only the front or the rear spark
plugs firing. This procedure shifted the l.oca.tionof the knocking
zone and
zone was
.;~enthe
permitted comparison of’results obtained when the knocking
near the hot Nortions of the cylinder with results obtained
knocking zone was near the cool portions of the cyl;inder.
R~~~~~s
Figure 1 shows the required rear spark-plug-bushingtemperature
at different inlet-mixture temperatures for constant knock-limited
cylinder-chargedensity or approximately constant indicated mean
effective pressure. The relation under the given conditions is
linear.
Fib-e 2, as well as showing the data presented in figure 1,
shows similar results for the front and the rear spark-plug bushing
with only the front or the rear spark plug firing. Again, straight
lines represent the data reasonably well. The correspondin~ cooling-
air pressyme drops across the cowling are presented in figure 3.
The indicated horsepower was 71 *3 for all tests.
ANALYSIS
IiIthe analysis of the results it is assumed that, if the knock-
ltiited cha.rgcdensity were held constant, an increase in the inlet-
air temperatm~e would raise the temperature of the gases in the
knocki?lgzone but the decrease in cylinder-head temperature would
lower the temperature of the gases iiithe knockiiigzone to its initial.
value. ~~o~e~ c~:an.:ein the temperature
therefore result.
Reference L gives a siz@e equation
perature and cylinder-chargetemperature
valve closur~. This equation can be put
of the k;ock.ingzone would
relatim inlet-.mixhxretem-
at the instant of inlet-
into the form
N4.CARB i’?O. E@3
where
Tc temperature of
Ta tenpcrature of
Tc=Ta B+~#-13)
5
(1)
cylinder char~e
inlet mMmre
at instant of inlet-valve closure
Tw mean temperature of cylinder walls
B constant, involving heat transfer, which is related to cylinder
displacement
Equation (1) will be applied to temperatures of the knocking zore
instead of to temperatures of the charge at the instant of inlet-
valve closure.
If the knocking-zone temperature I’c is assumed to be constant,
then
Equa,tion(2) gives a linear
(2)
relation between cylinder-we.1].tempera-
tvxe and inlet-mixture temperature that agrees well vriththe data in
figures 1 and 2. In figure 1, a change in temperature of the rear
spark-plug bushing of 100° F is equivalent to a change in inlet-
m.ixturetemperature of 42° F and the value of B is therefore 0.70.
This value is somevhat hi~er than the value of 0.65 predicted in
reference 2 for cylinders of 1~.$-cubic-inchdisplacement, The
disagreement is probably caused in part by the fact that the temper-
atur~ of the rear s;x.rk-plu~bushing is not a representative temper-
ature:of tkleinner cylinder wall.
The variation in the inlet-air pressure requtied to maintain a
constant rate of air consumption b,ythe engine is an indication of
the degree to which the charge temperature was maintained constant
at th= instant of inyst-valve closure. The inlet-air pressure rose
about ~ percent over the range of inlet-mixture temperatures tested,
which indicated that the cylinder head cooled the gases in the
knocking zone more effectively than it cooled the entire charge.
This result is to be expected because tineend zone was in contact
with the cylinder walls in all cases,
The variation in knock-limited in~et-mixtwe temperature at a
given cylind.er-headtempsratmre was less when the point of measure-
m~nt of the cylinder-head control temperature was located near the
.- — _ . . . . .. . . ______- ._ _ .- .. —.. ——.—.. -—.—.— .. ,.+
. ..-— —__________________ ._._
—-..—— .. ..-. .. —- . .. __.. .
6 IJACARB No. 134J13
knocking zcno (curves if.and B, fig. 2) than when the point of measure-
ment .o.t%b.ccylinder-bead control temperature was located a-wayfrom
the knocking zone (curves C andD, fig. 2). It is concluded that the
reproducibility of the knock-test data between different setups for
the same cylinder will be less affcctcd by differences in external
cooling of the cylinder if the control point of the cylinder-h>ad
temperature is located at or near the knocking zone.
DISCUSSION OF?2ESULTS
The effect of changes in cylinder-head temperature upon the
knock limit of-any fuel can be found with the aid of a curve of the
tygw shown in figure 1 if the variation of the knock limit with
inlet-air or inlet-r.ixturetemperature.is known. The variation of
cylinder-headtemperature can bc converted to an equivalent variation
of inlet-air temperature and the.variation of the knock limit can be
read frofith.~c~urvesshowin~ the effzct of inlet-ah tempsrat.ureon
knock iimit.. The relation shown in figure 1 applies, of course,
only to tests with the ~ngine and under the conditions that were used
in getting the data for this figure.
From the tests run at a constant fuel-air ratio to determine
the relative e&fects of cylinder-head temperature and inlet-mixture
temperature,.upon=theknock limits of fuels, the following results
were obtained:
1. The decrease in cylinder-head temperature required to main-
tain incipient knock at constant power when the inlet-mixture tem-
perature was increased was directiy proportional to the increase in
inlei-mixture temperature. The data are not sufficient to Chair the
conclusion that such a linear relation always exists.
2. The temperatures of portions of the inner cylinder wall
adjacent to the knocking zone had a predominant effect upon knock.
If it is desired to compare knock-test data from two engine cyl-
inders of the same model, the data will.not be directly comparable
unless:
(a) Rear spark-plug-bushingtemperatures are the same and both
cylinders have cooling-air supply systems and cylinder baffles to
give the s~~e temperature distributions over the cylinder heads; or
—.—-
--——-————- ---- -- —-.-——– —.—— .- ————..- .–_ —. _ __ _____
(b) The temperatures of the inner cylinder-headwalls near the
knockins zone are the same for both cylinders and the mean value of
all cylirder temperatures for both cylinders is equal.
Aircraft Engine Research Laboratory,
National Advisory Cormwitt,eefor Aeronautics,
Cleveland, Ohio.
1.
2.
3.
4.
R13Fl%lENCES
LmLing, Harry S.: The Effect of Piston-Head Temperate on’Knock-
LirritedPower. ~U~CA~RR No. ~4G~3,19440 “
Sanders, Newell D., Barnett, Henry C., and T30Lz,Ray E.: Effect
of Inlet-Air Temperature and Cylinder Displacement on Charge” “
Temperature of Internal-Com?mstionEngines. M-CA FW 4M7, 194h.
Cook, Harvey A., Van.demanjJack E., and Brown, Kenneth D.:
Effect of Several Methods of Increasing Knock-Limited PcIweron
Cylinder Temperatures. N}.CAARR No. E!lIIS,194bs
Taylor, C. Fayette, and ‘laylorjEdward S.: The Mternal Combus-
tion Engine. InternationalTextbook Co. (Scr~nton,Pa.), 1938,
P. 236.
.
. . .
—-.—. . -. ——. .. ...—— —--
— ..-. —..--—----- .....
.—— —. ——
NACA RB MO. E~J13 Fig. I
Figure 1. - Required variation of rear spa;k-plug-bushing temperature
with inlet-air temperature to maintain incipient knock when the
cylinder-charge densityand fuel-air ratto are held constant. “Pratt
& Whitney R-2800 cylinder; compression ratio, 6.7; spark advance,
20° B.T.C.; engine speed, 2000 rpm; fuel-air ratio, 0.075.
... —. . . . . —..- . ...-— . —...—...—.——-——-.—. .Z ..-—z —_.._.- __ _._.
—————.— ——. ———————— .--—
NACA RB NO. E4J13 Fig. 2
NATIONAL ADVISORY
g COMMITTEE FOR AERONAUTICS
s .
&l
*
~
Inlet-air temperature, ‘F
Figure 2. -’Required variation of cylinder-head temperatures with
Inlet-air temperature to maintain incipient knock when the cylinde
charge densityand fuel-air ratio are held constant. Pratt &
Whitney R-2800’cylinder; compression ratfo, 6.7; sp=k advance>
200 B.T.C.; engine speed, 2000 rpm; fuel-air ratio, 0.075.
r-
— ——— —--- ——. -— .— -—.—
NACA RB ~00 EUJ13 Fig. 3
NATIONAL ADVISORY
COMMITTEE FOR AERONAUTICS
10
Q
o
l\l I I
w I I \l I I
cd
~30 I v I I
v
Q I I M I
I IN I
o
0 Rear spark plug firing
g 20 I I h I I I I I I I I I
01 I Iia I\Ill I I I Ill
:1 I II N I
? ‘OhH+++w—
I I
v I
UJ 1 1 I 1
280
Ill’=&
lo$-~
I I 1 1’ 0I OH9 , .,
320 360 400 440 480 520
Ra9W =nawk.nl.>~bush~ng temperature, oF
r pressure drop with rear spark-plug-
? density when
inder;
ante. 20” B.T.C.: enzine sneed.
..-s.
-r-- --F-W
Figure 3. . Varlatlon of cooling-al:
bushing temperature at constant knock-limited charge
inlet-air temperature 1s changed. Pratt & Whitney R-2800 cyl:
compression ratio, 6.7; spark adv:- -
2000 rpm; fuel-air ratio$ 0.075. .W ----
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31176014033022
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.. —____ .— —. ..-. –—
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Relative effects of cylinder-head and inlet-mixture temperatures upon knock limits of fuels

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