Document
RB No. 4A25 . .
f NATIONAL ADVISORY COMMJTIEE FOR AERONAUTICS
wm’mm IUIPOW”
ORIGINALLYISSUED January 1944 as Restricted Bulletin 4A25 USE OF INTERNAL COOLANT AS A MEANS OF PERMITTING INCREASE IN ENGINE TAKE -OFF POWER By Addison M. Rothrock Aircraft Engine Research Laboratory Cleveland, Ohio
II!4ACA
N A C A LISTdJ<Y
‘~G~EY M15?IAo~ AERONAUTIC WASHINGTON LYFK)RATORY —.
J,~ley Fle@ v& 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.
L
— .— .-.
-.— . .._ ._ 31176 013(34 8051 a r NATIONAL ADVISORY COMHITTEE FOR AERONAUTICS RE!SYJXtTCTE31 BULLETIN ...... . . -.
..
USE OF INTEMWL COQLANT AS A YEANS (IFPERMITTING INCREASE TN ENGTNTZTMHI-QFF PCR’ER By Addison M, Rothrock Engine tests, together with estimates made at Langley Memorial Aeronautical Laboratory, indicate that a 2$percent increase in take- off puwer can be obtained with present-day aircr~rt en2ties without Increasing either the knock limit of the fuel or the external cooling This increase in power with present requirements of t?]eengine.
fuels and present extw’nal cooling is made possible through the use Estimates of an internal coolant.inducted through the inlet mani~old.
on aircraft indicate that this 2~-percent increase in power w1ll per- mit an anprox.imte usable incr~ase of 13.~percent in the take-o;f load of existing military airplanes. This increase in load is equivalent to an increase in the miEht of gasoline norm.1~ carried of bntween 30 and 65 percent.
IN!!XOLUCTICT!
Internal coolin~ thrcu~h the introduction of water or water- alcchol mixtures inta the inlet charge has been tested ;h vmlau~ labcratcr~es. Pertinent references to this work are ccntained in reference 1.
It is generally recognized that, if the take-off power of current enginss can be increased, the performance of the ,airplane, with par- ticular mphasls on range, can be increased.
Increase in take-off pmr with present engines is IimLted by three factors: (1) hock characteristics of th:?fuel, (2) engin”sstrength, and (3) engine cooling.
The knock characteristics of the fuel canbe improved only at the expense of fuel suppQ.
Because of limitations of supplies, this procedure can only b.?used for sm-il quantities of fuel, such as might be used during tam-off.
The engine strer@h Is limited by both the loads imposed within the engine and the temperatures that the engine parts can withstand.
Ftiernal coolinE of the engir~ with higher take-off powers does not provide so effective a means of relieving the thermal stresses within the cylinder as does internsl cooling, — — — _ _ —.
,— I fiterml cylinder cooling by means of introducing an inert liquid the incominc charge permits much higher powers to be taken from a to given fuel witiout k;oc~ and without ficreasing the external cooling.
D~ta obtained at Langley ?JemorialAeronautical kboratory during 1942 si~cwedthat the ~wrtissible indicated mean effective pressure can be This vzlue is increesed 100 percent by meal;sof internal cooling.
not mcmt tc reprrs=ent a practical goal b’ltto emphasize the fact that tilwou~hMternal cooling the kmock limit of present fuels can be placed well ahovs present demnds. Internal cooling removes engine cc~ling as a Fr~blsm for incregsed t~ke-off powers. ‘he lower tmperanres ohtaiccd with internal cooling also reduce the prcbabilitj- of engine f~ihlre thrGdgh incressed loads.
It Lsn@ey Memorial Aeronautical Labora- the sprtig of 1942.
Z!WINE THTS t,est.s recorded in reference 1, Dr. R, F.
Selden af the NACA st~ff sugflested the use OL”a ~ixture of a’rmania dissolved in rater (amcmirm hy~rcxide) for the internal coolant as a msms of ov-wcoming the difficulties re.sultinq from the hi6h freez- + of w?ter. iry pcti..
Axmonia is lJn~quein i%t cn a Vieiqktbasis it perilits~ mru~ter percentage cf’water in the c,oolqr,t. for a given freezin~ temperature than dcss any other knov.mliquid.
For exmple, ~CJp~rc=at ammonia by wei~ht and 70 ~ercent a m~;tura of =pproxime+.ely , .
r40 j’,
wxter h-s 3 f.re~>zin~ pdint of -1 A 2?-72 rqtio cf wmncr,i~ar.d
water ‘a:Ls used in t.~le ir.iernal-coclant tc!itsdescribed in this report.
qy t~ia11:=of +’~i~mqt.eriala given freeztir-temperatlll.e requirement is net with the l~r~est possible percentage of water in the internal Cocll%lt.
Ttlc~::ou~t of JYe=zinp.poict depressant requir~~ in the internal roolzn+-ic dekencent m the p~rti~ll~r in~tallatior. usej.
The fr~ezinz-prjjnt rnrpirem~nts of tne intr.rnalcoolcn+. are not necessarily the same 3s fcr the g~sol.ine.
Tne consid=rat.lon in tnis report of amwnium hydrcxide for the that,it givss better Coolinq and internal conlmt d~ec not imp& ketter knock suppression thml other internal ccol?qts, S-.lcn as water- qicgllcl.
The :!ecision~s to wwich internal coolant is best mst be considered on the basis of availability ard ease of handling as well ~ason the basis of engine performar.ce.
Preliminary tests conducted on the C.FRen~ine gave results suf- ficiently encouraF”lnE to warrant transferring.; the work to a single- cylinder Wrisht G2ClCJ engine mounted on a WE crankcase.
Figure 1 shows t.!!at a“mmfiiu.m hydroxide actually was a better knock suppressor .
—— ---- .
—.- ..
than was pure water. These data represent the prelimdmu’y tests, which show that as far as knock is concerned engines with present fuels can be taken-to much higher power outputs than are now permitted.
-.
The tests were conttiued on ammonium hydroxide rather than on water or water-alcohol mixtures in order to find out what deleterious (Ammonium effects ammonium hydroxide might have on the engtie.
hydroxide Is quite corrosive to any materials containing copper.)
In addition to fuel limitations, engine temperature was considered as a limiting factor, and a maximum allowable temperature of 32@ F M the at the middle rear of the cylinder barrel was decided upon.
test,sat eaoh fuel-air ratio for different quantities of internal coolmt,the inlet pressure was increased until (1) the engine knocked, (2) preignition or afterfiring occurred, or (3) the temperature at the middle rear of the cylinder barrel exceeded 32fi F.
The followinq engine conditions were maintained constant: Enginespeed, rpm. . . . . . . . . . . . . . . . . . . . . . 2~00 Spark advance, degB.T.C. . . . . . . . . . . . . . . . . . . . 20 . . . . . . . . . . . . . . . . . . . . . 7.0 ~i~~~s~~$e~~~.~r~; ‘F .< MO ., Inlet-air temperature b ~ore introduction ;fOcltlM Ml” 8F ”””””””” or internal coolant, . . . . . . . . . . . . . . . . . 250 Coolirip-ai.r pressure drop,’ir!. water . . . . . . . . . . . . . 10 Hr=re 2 presents the experimental ‘i~,t~. Hcept for the lean and rich ends of the curves, t,~elimitation was en@ne tem~erature rather t.fian fuel knock. The fnct thlt the specific fuel consumption in the rich reflionsincreased as the amount of ammonium hydroxide was increa~sd indic~t.es that the effect of ammoni:mn hydroxide in sup-press- in~ knock war twofold: (1) It provided internal cooling of combustion Rases; and (2) it retarded the combustion, giving the same effect as a retarded spark.
Cross plots from the data in fiwre 2 are shown in fi~res 3 and E@ne temperatures arc skwn h fi!wre s. A reference value h.
of 245 pounds per square inch indicated mean effective pressure, which corresponds to 210 pounls per zquare inch brake.mean effective pres- sure at a mechanical efficiency of !36 percent, approximates current take-off conditions. The dnt= h the upper half of figure 3 are based on this value of 245 pounds per square inch indicated mean effective pressure (reproduced in fig. ~) for comparing the increase in power recorded with the different quantities of the internal coolent.
With a 2~-percent ticrense in power, the reight of the internal .
coolant required is ~ percent of the fuel weight at a fuel-air ratio “1 of O.og. Other values given in figures 3, h, and ~ are as follows: ,.. j- , —.—.
.— .- —..— . . .—
I
COY?.’R@CN OF EI!51NTP~.~RBfANCE WITHOUT AFD WITH INTERNAL COOLANT tiithouttitem.al “Withinternal coolant (take- Coolant (1.25 off hp ) X take-6ff hp ) R A O*C9 .72 .
32CI 3?9 ~J.g I.ne . .
.
11433 R-1H30 .“ 8:98 41,!300 ll,~7fJ 210 1?6(2 K-28@d
II
3(11 1~,364
1?06 R-26C0
I
R-2800 -— .— ——— -..—— . ..—.
Completlecalculati.tms for estimating the total weight of the internal coolant end the titernal-coolant qystem are given h the . . . .
The followlng table present,sthe estimated incrcasee in appendix.
usable load for the four airplanes under consideration with a 2~-percent incresse in take-off power. The estimates of percentage total-load Increase were made by Mr. J. T. .#etmore of the Flip~t Research Division of kgley Memorial Aeronautical Laboratory.
h the calculations of the table an allowance of 0.78 pound of coolant per pound of fuel was used instead of the value of 0.S4 shown on the curve at point A of fi~re 3. This increase is introduced as ‘a factor of ssfetya All estktes are based on sufficient titernal propeller weight coolant for a s-minute operation. e ~ required for the =dciitional power output is estimated to be 100 pounds, and the weight of the systm-for introfluctig the coolsnt, exclusive These weights are of the tank weight, is esthated to be 75 pounds.
considered to be the name for each engine of the four airplanes listed.
lWTIX.ATEDINCI:FASE IN ‘TIXE-OFFLOAD FOR 2S-PERCEYT TNCWSR IN TAFIZ-@FF FOWER Percentage Load Airplane ‘Usqble load “Load Usable increase load incrense (gal of Rqs- ~:;e~:e (percent) (lb) inm;yse oline) (a) g;soline) A 11.5 ~ 11710 427 30 3631 ~
I
B 12.0 ‘ lh~ I 1~97 129 65 c m.~ 1300 153 51 II lo. ~ 1..32o 1037 122 36
I I I
aAssume1 E.91 ~lsoline wei hs 6.o lb; qanoline tank weighs 2.5 lblgal~ therefore, & = h27 g31.
..
The dntn show tinat. a 2$percsnt increase in take-off horsepower results in a marked increase in either the usable load or in this usable load hr,~slate~ into gallons of gasollne. The increase for airplanes 1?nnd.D 1P particularly noteworthy.
Increased rate of climb. - It is estimated that a 2$percent increase take-of in f power for airplane B will permit the rats of clhb up to 12,000 fe9t to he increased from 31b0 to 4100 feet per minute. Corresponding values for airplane C are from 1600 to .
2200 feet per minute.
— ..- . . . .. .. .... . . . . . . . . . . . .... .. .. ...------ . . . . ... .- .. . . .
I ,.
Decresned teke-off run. - In regard to take-off run, for the tne airplanes, it is estimated that a 2~p~rcent essum~~ofi~of increase in power till decrease the take-off runs of the fcmr air- . .
planes as follom: Airplane Present t*e-off Taks-off distance dist~nce 2~-percent ~ncrease (ft) in take-off power (ft) 17yJ A 1330 l~~@ E 1300 30(!
c 200 35~ D 25C I 1-,, At 8$percent mechanical efficiency, 2340 ihp = 2000 bhp, ihp3~ = 2920, and bhp = 25W0 . ..- . .
.. ----- ‘ ‘As”s&e suffici&t ammonium-hydroxide solution (NH40ii) for ~ minutes at 2s00 bhp: 0.96 bslc = — = 1.13 lb/bhp-hr 0.85 At 2000 bhp 0.72 bsfc - — - 0.85 lb/bhp-hr 0.85 At 2SOO bhp total liquid = 2500 x ax 1.13 = 235 lb .
TJlis 235 lb liquid is 1s2 lb of gasolti.eand 63 lb of ammonium- hydroxide solution.
At 2C?@0bhp 5 X ().fl~ = I-42 lb total Lqscline = 2000 X ~ It is noted that increased weight of gasoline is negligible- ~ensity of NH40!l= 7.5 lb/gal
70 lb rrr40FA = 9.4 gal
Allow for 15 ga~or 113 ~NH40H Assume tank for NH40H weighs 35 lb Total weifiht= 113 + 3S + 10 (for extra gasoline) Assume this weight requirement is proportional to bhp of engine.
Iet increased propeller weight = 100 lh Let weight of coolant- induction system = 75113 — . — — — —.
J.swme W2 const~at for engines considered.
‘Ivl + W2 R2 W1 Engine 1,2$.x take-off I horsepower (lb) (lb) (lb) HEF’%51?CE 1. l{othrosk, Addi:on N., Krsek, I.lois,Jr., nnd Jones, Anthcriy W.: Smmwy Report on the Induciion of ‘Yqtsrto tilefilet Air as a Uems of Intermal CocUnC in Aircrai’t Ehgina Cylinders.
T:.1-H. :.R7,A:;;’. 1s42. ‘ I ,,,, -!! . . . . . . . . . . . . . . . . . ,.,. —-, ----—-,. ,.., ,.. __, ________ . . . ., ,., . . . . . . . . . _. . .
.+ -,, ‘.J NACA Fig. I i I All 2 + nl~ -~aml M& / ex :ept ?%5 t, s lowed arte- knot c.
fl ?lng is we .1 as X)’ f / .
/ A F :300 / / w > / .
0.
?? 260 v L z E .-l : z 141 .152. 153.14 ~ ~ 4P 100.
L..
.05 .06 .07 .08 .09 .10 .11 .12 ,13 .14 .15 .16 Fuel-alp ratio F18ure 1. - Bffact of acldltlon of tetraatbxl land< writer, or a mfxturo of 20 percent monl~ + 72 percent mater on tlm knock-lhited lndlcatad man affective pressuro d 2-Z reforenoe fuel.
Wright 1820 G200 cylinder; compresalon rmtlo, 7.O& englae apoed, 2000 r= m~rk l dvance, 200 B.T.C.; inlet-slr tamparature. 2S0° F.
I
Fig. 2 NACA, z ‘-- - .-4 polr ts n ~ temp emit % we m a cm of 28 percent ammonia + 72 percent FIw.we 2. - 2ngine perforrnnce permitted by use of a mixture water l s an lnternml coolant at a cooling-air pressure drop acmes cowling of 10 inches of Lne speed, 2500 rpm: spark water. Wrl t 1820 G=O cylitiepi cowre~~lon ~atlo, 7.% e ?
250 F; coollng-a r upstream temperature, 125° F.
adv.nce, 2L#’B.T.C.\ inlet-alr tewerature,
I
NACA Fig. 3 ,- / .11
/ ‘ /
/ / /
/
.10
/ ‘
o a .10 I . 0s3 I , / I / ,+ ~ [ / I l Q- ,- .08 / / / / .11 ,/ / / / / / / .= / / B ~ / :urve are Croe,s-plo tted from pe rmi ssibl e ime p aga hat : ue 1- Bir tio iata, pnd limi t# tioqs d r epree ent lm~sed - / ‘ no wer / y el Ither knock or ermi~ati+ of pury r I -b o 10 20 30 40 50 60 70 Percentage coolant Figure 3.
- Permissible power as determined by percentage Internal coolant (referred to fuel weight supplled) at varlou~ fuel-air ratios and at a cooling-air preseure drop acros8 cowll~ of 10 inches of water.
Virlght 1820 0200 cylinder~ compression ratio, 7.0$ e~ine speed, z5Q0 rpm) spark advance, 20° B.T.C.~ Inlet-alr temperature, 250° F> coollng-air upstream temper- ature, 1250 FJ Army aviation gasoll~ (100 octane number)} coolant 28 percent NR3 + 72 PePC9tIt II#Y.
Fig. 4 NACA w
d — — — — — —
30 i MJ. //.26-73 ,,,, 1n m , # , , a 1 1 , m a I # 1 I1I II11- u,, o 10 20 30 40 50 60 Percantqja coolant - Permlsaible inlet pressure and total liquid conaumptlon 88 determined by paroentago Fl@ro 4.
internal coolant at various fuel-air ratioa and at l COO1lIWWIP pressure drop l croea cowling Wright 1820 13200c~llndor$ compression ratio, 7.0~ engine speed, 2500 of 10 Inches of wster.
spark advance, 200 B.T.C.~ lnht-alr temperature, 250° F* coolhg-alr upstream temperature, rpm l viation gasoline (100 ootane number)} cOOlant, 28 Percsnt N% + 72 peroent EZO, 125& F* fuel, Army I Fig. 5 NACA & Percentage ooolant Figure 5. - Representative en lne temperature and-percentage power lncre~se (as determined by percentage internal coolant! at various fuel-air ratios and at .ecooling-sir preaaure drop l crosm cowling of 10 inches of water. Wright 1820 U200 cylinder} compression ratio, 7.0; engine speed, 0 F} coollng-alr upstream tempera- 2500 r m spark advance, 20° B.T.C.; Inlet-air temperature, 250 ture, f2bo F} fuel, Army avlatlm gaaollne (100 octane number).
II
IIllllllllflull[[lnlllul
3 1176013648051