F\LE COpy NO. I-W "

TECHNICAL NOTES

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

No. 577

FRICTION OF COMPRESSION-IGNITION ENGINES

By Charles S. oore and John H. Collins, Jr. Langley Memorial Aeronautical Laboratory ILE COpy T. be returned to the iii 3 of the National Ad.laory Cormittll for Aeronauta WuhiIpln, 0. C.

Washington Augus t 1936

" NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

TECHNICAL NOTE NO. 577

FRICTION OF CO~PRESSION-IGNITION ENGINES

By Charles S. Moore and John H. Collins, Jr.

SUMMARY

The cost in mean effective pressure of generating air flow in the combustion chambers of single-cylinder compres­ sion-ignition engines was determined for the prechamber and the displacer-p iston typas of combustion chamber. For each type a wide runge of air-flow quantities, speeds, and boost pressur e s was investigated. Supp lementary tests were made to determine the effect of lubricating-oil tem­ perature, cooling-water temperature, and compression ratio on the friction mean effective pressure of the single-cyl­ inder test eng ines. Friction curves are included for two 9-cylinder, radial, compression-ignition aircraft enginos.

The results ind.icate that generating the optimum forced a ir flow increased the motoring losses approximate­ ly 5 pounds p~ r square inch mean effective pressure re­ gardless of chamber type or engin e speed. With a given type of cha m~e r, the rate of increase in friction mean ef­ fective pressu re with engine speed is independent of the air-flow speed. The effect of boost pressure on the fric­ tion cannot be predicted because the friction was de­ c ~ eased, u n c h ang ed, or increased depending on the combus­ tion-chamber typ e and design details. Hi g h compression ratio accoun t s for approximately 5 pounds per square inch mean effective pressure of the friction of these single­ cylinder comp ression-ignition engines. The single-cylin­ der test eng ines usod in this investigation had a much higher friction mean effective pressure than conventional aircraft eng ines or than the 9-cylinder, radial, compres­ sion-ignition engi n es tested so that performance should be compared on an indicated basis.

I NTRODUCTION

The importance of air flow in mixing fuel and air in the combustion chamber of a compression-ignition engine 2 N.A.C.A. Technical Note No: 577

has been recognized by i~vestigators for a number of years and various means have been used to generate high-speed air flow in the combustion chamber.

Of the several types of combustion chamber for com­ pression·-ignition eng-ines (reference 1), two distinct types are used in producing high-speed forced air flow. One type has a divided combustion space in which the air flow is generated by the flow of air through a fixed re­ striction from the cylinder into the prechamber. The other type uses a displacer that comes into operation at a predetermined point in the compression stroke and forces an orderly movement of the air from the cylinder into the combustion space .

In the study of forced and controlled air flow in the combustion chamber of an engine, most investigations (references' 2 and 3) have been directed toward the de­ termination of the optimum air-flow speed and direction and have ignored the cost of air flow in terms 6f fric­ ti on mean ef~ective pressure due ·to increased pumping losses . Int'he present investigation this condition ha.s been reversed; no attempt has been made to measure the actual air speeds but the cost of generating the air flow in t~rms of increased friction losses has been investi­ gated. Friction characteristics of the prechamber and displacer-type chambers have been investigated for a wide range of air-flow quantities and velocities as influenced by chamber shapes and passage sizes. The scope of the work was further broadened by determining the basic fric­ tion of the test unit with no air flow in the chamber and at a series of compression ratios covering the compres­ sion-ignition and the spark- ignition ranges.

APPARATUS AND METHODS

Two single-cylinder, 5- by 7-inch test engines were used in this work, both being water-cooled 4-stroke-cycle units identical in construction but with a small differ­ ence in crankcase bearing friction. Figure 1 shows the general arrangement of equipment for the tests. The en­ gine bases and cylinders , of regular universal test-en­ gine design (reference 4), were so constructed that the compression ratio could be varied at will by raising or lowering the cylinder and head . Two cylinder heads were used in .this investigation, N.A.C.A. no. 7 head (fig. 2) N.A.C.A. Technical Note No. 577 3

, ' used with and without a prechamber and N.A.C.A. no. 4 head (fig. 3) used with both a displacer piston and a conven­ tional piston. Each had its oVI'n valve gear a nd each was timed for 6ptimum 4-stroke-cycle operation. The same tim­ ing as was used in· previous work on these heads .(refer­ ences 5 ·and 6) was used in the present tests. No chang~ in valve timing was made for either head when c hanging from one type of co mbustion chamber to the other.

In all air-flow tests the procedure was the same. The ·ciombus tion chamber was assembled to give t he variabl~ to be studied and the .engine was motored by the dynamom­ eter at the predetermined test speed. When all conditions had become stabilized, the dynamometer scn le w~s read, fir s t , after externally app l ying an additional ~cad and, . second, after dpcreasing the load . In each case the scale arm was allowed t o come to rest before reading . Re adings obtained in thi s manner varied by only 0.3 pound (0.43 pound per s quar e inch mean effective pressure) and an av­ erage of the two readings was recorded . .

Both the prechamber head and the displacer h ead were used in determining the e ff ect of mass of ·air in motion. For the test with the p rechamber head , the air-flow speed for a gi ven e~gine speed Was kept c onstant and the volume of air displ a ~ed was changed by varying the size of the chamber fron 0 to 70 percent of the to tal clearance volume by using four different d e tachab13 auxi liary c hamb ers. For each chamber size the total f r i ction loai was observed a t 1,200 , 1,500, and 1,800 r. p . m. for a · co mpr es sion ratio o f 13.5. With the displacer piston head , the volume and speed of air displaced were c hanged by varying the height o f the displacer tha t changes t h e cra nk ang le at which the displ ac e r came into a ction . Tests were mad e at 1,200 , 1, 500 , and 1,700 r . p . m. with the di s p lacer height v aried from 7/1 6 inch to 1-1 / 2 i nches.

Both cylinder he~ds were used in d etermining the ef­ fect of air-fl ow spee d . ith each head the air-flow spee d was varied by changing the area of the res tri cting passage and keeping al l other co ndi tions constant. Wit h air-flow speed as the variab18 r u ns wero ma de only with both heads at 1,500 r.p. m.

In order to obtain a comparison between t he opt imum prec ha mber and the optimum dispiacer, the friction load of the optimum displacer was observod at 900 , 1,200 , 1, 500 , 4 N .A. C.A. Technical Note No·, 577 and 1,800 r.p.m. The displacer was next removed from the p iston; the bolt holes in the piston crown were pluggod; and, with the sarno compression ratio, tests were made at the same speeds. The"n the prechamber head was mounted on the "engine, first, with tneoptimum auxiliary chamber and second, with the head convert ed into an integral chamber: by clo~ing the connecting passage, and the te~ts were re~ p eated for e a ch assembly .

The prechamber head was again used first as an inte­ gral "and then as an auxiliary-chamber type of combustion chamber, and the effect on the friction mean effective p ressure of boosting the inlet pressure was determined. The inlet pressure was varie d from 0 to 10 inches of mer­ cury in four steps by means of an independentlj driven supercharger, and the friction mean effective pressure at each pressure was determined at 1,500 r.p . m.

Several supplementary tests were mad e to obtain com­ plete information on f ric tion losses . The effect of oil and water temperature, over a temperature range from 1200 F . to 200 0 F . , on the friction mean effective pressure was detDr~ined . By the use of a n integral chamber and the adjustment of the compression ratio of the universal t est :30 gin e ( ref ere n c e 4) t h El e f f e c t 0 f co mp res s ion rat i 0 on friction laean effective pressu re was investigated for a range of ~ompres sion ratios fr 0 m 6 to 20, all other conditions being constant. So t h at an idea of the magni­ tude of tho air - fl ow losses compar od to the mechanical losses might be obtained, a "breakdown ll test was made whi ch consisted of progressively removing the various op­ erating parts cf the Angine and obtaining the friction of the stripped unit . The friction of the part removed was obtained by differences .

RESULTS AND DISCUSSION

When noting the reported results, consideration ' should be giv e n the fact t hat an increase in friction mean effective pressure due to air flow was observed as an increase in the total friction of the engine . The breakdown tests, to be discussed later, show that the pumping loss at 1, 500 r.p.m. was about 33 percent of the t otal friction; as all the in c rease in friction mean ef­ fectiv e pressure should be charged to the pumping loss, an increase of 10 percen t in the total friction mean ef- N.A.C.A. Technical Note No. 577 5

fective pressure would be a 30 percent increase in the pumping loss.

Figure 4 shows that, as the proportion of the air charge forced into the prechamber was increased, the to­ tal friction mean effective pressure was increased even though the speed of the air movement was kept constant. The - increase in friction mean effective pressure was pro­ portional to the increase in the mass of air moved. These data were obtained from the motoring tests of the prechamber in which tho maximum speed of the air flow was held constant by properly proportioning the area of the connecting passag e to the volume of the prechamber.

I nth e f ric i ion t est s 0 f the dis pIa c e r c h e.. mb e r ( fig. 5) the displacer height is shown plotted against friction mean effective pressure. For the three test speeds, the friction mean effective pressure incr~ases at an increas­ ing rate as the displacer height is increased, showing the effect o f the co mbination .of the two variables: vol­ ume and speed.

The effect of forced air-flow speed on the friction mean effectiv e pressure is shown in figures 6 and 7. In g e neral, t h e friction mean effective pressure increas e s with i ncrease in air-flow speed. This increase is a straight-line function for both the p rechamber and the displacer. 'll he speeds are comput ed as shown in refer­ ence 6 and no attempt has been ma de actually to measure them or to investigate the nature of the flow.

A comp a r ison of t h e displac e r chamber and the pre­ chamber is s h own in fi gure 8. At the h i gher speeds the displacer has more friction than the prechamber because of the induction throttling action of the under-sized throat. Later tests have shown that enlarging the throat area of the displacer chamber but keeping the passage area the same ca used t he slope of the friction curve to decrease. I n either type of chamter the cost of generat­ ing the requi red air flow is approximately 5 pounds per square inch f riction mean effective pressure.

The prechamber head was used first as an auxiliary chamber type of combustion chamber and next as an inte­ gral type- of combusti o n chamber; t he effect of boost pressure on both types of combustion chamber was deter­ mlned. (See fig. 9.) As the inlet pressure was increas~d. a small increase in friction due to the .greater density 6 N.A.CiA. Technical Note No. 577

of the air forced through the connecting passag e was noted for the prechamber. With the i nte g ral chamber the fric­ tion mean effecti ve p ressure i s practically constant over the rang e of pressures tested . Lat er tests, using a dis­ p lacer piston at 15 .3 compressidn ratio and at 2, 000 r.p.m., have shown that the friction decr ease s from 44 to 38 pounds per squar e inch mean effective pressur e when the boost pressure is raised from a to 20 inch es of mercury. Enlarging the throat area was found t o decrease the fri c­ tion mean effective pressure at a ll speeds and boos t pres­ sures tested . In every case , the supercharger was 'driven independently of the eng ine and the friction me a n effective p res s u re measured for the engine alone.

The e ff ect of lubricating oil and coolan t temperatur e on friction is well known; however, in order to show the magnitude of these variables compared with changes in the pumping loss, curve-s' are presented tha t show the chang e in friction mean effective pressure with change in lubricat­ ing oi l and coola nt temperature (fig. 1 0) . These data, like a ll other data presented herein, are f or motoring conditions ; in this ca s e, however, the trend under p ower wa s checked against t hat under motoring condi tions , and the trends were found to be the same.

The ef f~ ct of compress ion ratio on friction is not so un iversally accepted as the effeo t on friction of the two v a riables d is cussed in the prec e a ing paragraph . In fa ct, compression ratio has been roportod by other investigators (reference 7) as having no eff ect on the friction mean ef­ fe ctive pressure . In the p resent paper, curves are pre­ sent ed (fl.'!: . 1 1) showing the effect cf compression rati o over a wid e ran e a nd at t h ree s peeds . The results are easily reproducible for motoring conditions and should be comparable with the other results presented in this report. The shape of the curves is s ignificant in that they flat­ ten out at the high comp ression ratios; ~onsequently, in­ creasing the compr e ssi on ratio of a compression-ignition engine incr eases the fricti on mean effective pressure less than a corr e spon1ing incre~se in the compression ratio of a gasoline engine be c ause the l atter engine op erates at the lower compression ratio where the rate of increase is high.

The a pparently inh erent and unavoidable loss due to compression-ratio increas e is caused by p rassure leakage and h eat lo~s, wh ich decrease the energy returned to the flywheel on the expans ion stroke. The curves indi~ate that a compression-ignition engine op erat ing at a compres- N.A.C.A. Technical Note No. 577 7

sion ratio of 15 would have a friction mean effective pressure greater by approximately 6 pounds per square inch than a carburetor engine at a compression r~tio of 7.

Table I is presented to givD an idea of the friction of the difforent parts of the test engine used in this work. No attempt will be made to justify the method used to obtain these data and the results may be subj ect to minor errors: however, the authors believe the results to be indicative of the friction caused by the different parts itemized in the table. Attention is called to the high fric~ion of this test engine. In the analysis of t h e o t h er results presented this fact must be borne in mind. It should also be r em emberod that all powe r tests made with single-cylinder engines by the N .A.C.A. at Langley Field are made on this same type of test unit and, owing to its high frictioni"the reported brake performance is correspondingly low, therefore performance should be compared on tho basis of indicated performance .

Friction characteristics of two 9-cylinder compres­ sion-ignition aircraft eng ines are s h own in figure 12. These data have been supplied b y the Bureau of Aeronau­ tics, Navy Department . The engi ne s are both air-cooled radial of tb8 sing le poppet-valve type. Because of the low friction values and slight s lop e of the curves, t h e lower curve has been completely rechecked by test. Dur­ ing these tests there was no inai cation that combustion of the lubricating oil was aecreasing the friction read­ ing. Tho low friction values ma y be attributed in part to the use of the sinb le large poppet valve, instead of t wo s ma ller valvas , aad to the co mple te a bsence of induc­ tion piping an d b lower. The test results are presented as the only available information reg~rdin g the friction characteris tics of aircraft compression-ignition engines.

CONCL USIONS

1. The increase in friction mean effective pressure due to forced air flow is directl y proportional to the increase in volume and speed of the displaced air.

2. With a given type of chamoe r, the rate of increase in friction mean effective pressure with engine speed is independent of the air-flow speed. J 8 N.A.C.A. Technical Note No. 577

3 . The effect of boost pressure on friction cannot be predicted because the friction was decreased, unchanged, or increased with incroase in boost pressure. depending on the combustion-chamber type and design dotails.

4 . For optimum conditions, the forced air-flow fric­ tion amounteq to approximatoly 5 pounds per square inch mean effective pressure regardless of the engine speed or the type of combustion chamber .

5 . High compression ratio accounts for approximately 5 pounds per square inch mean effective pressure of the friction of these single-cylinder compression-ignition en­ gines .

6 . The friction mean effective pressure of this type of single- cylinder en g ine, even without air flow and at a compression ratio of 5 . 5, is much hi gher than that of con­ ventional aircraft engines or the 9-cylinder radial com­ pression-ignition enginGs tested and performance should therefore be compared on an indicated basis.

Langley Memorial Aeronautical Laboratory, Nat iona l Advisory Co mmittee for Aeronautics, Langley Field, Va., July 9, 1 936.

------~- N.A.C.A. Technical Note No. 577 9

REFERENCES

1. Wild, J. E.: Combustion-Chambers, Injection Pumps and Spray Valves of Solid-Injection Oil-Engines. S.A.E. Jour., May 1930, pp. 587-600. 627.

2. Alcock, J. F.: Air Swirl in Oil Engines. Engineering, December 21, 1934, pp. 694- 695; December 28, 1934, pp.720-721.

3. Spanogle, J. A., and Moore, C. S.: Considerations of Air Flow in Combustion Chambers of High-Speed Com­ prossion-Ignition Engines. T.N. No. 414, N .A.C.A., 1932.

4. Ware, Marsden : Description of the N.A.C.A. Universal Test Engine and Some Test Results. T.R. No . 250, N . A.C.A., 1927.

5. Moore , C. S., and Foster, H. H. : Performance Tests of a Single-Cylinder Compression-Ignition Engine with a Displacer Piston. T .N. No . 518, N.A.C.A., 1935.

6. Moore, C. S., and Collins, J. H., Jr.: Effect of Com­ bustion -Chamber Shape on the Performance of a Pre­ chamber Compression-Ignition Engine. T.N. No. 514, N.A. C.A., 1934.

7. Sparrow, S. W., and Thorne, M. A.: Friction of Avia­ tion Engines. T . R . No . 262, N.A.C.A., 1927. N.A . C. A . Technical No t e No . 577 10

TAELE r

Breakdown Tests o f Test Unit 1

(Prechamber cylinder head a s integral chamber ; c om­ pression ratio, 13 . 5 ; oil temperature - out, 1800 F.; water temperature - out 1700 F.; engine speed, 1,500 r.p . m. ) Percentage Engine par t f . m. e . p . o f total losses

Ib . !sq.in . Pump ing losses 12 . 1 32 . 8

Pis t on, rings and rod 11 . 1 30 . 0

Main bearin g s 8 . 0 21 . 7

Valves and valve gear 2.7 7 . 3

Water pump 1.5 4 . 0

Oil pump .5 1.4

Fue l pUlI'}) 0 0 (Throt tle closed) I !, -- Fuel pump 1.0 2 . 8 (Injecting full load) I I Total losses, integral chamber 36.9 100 . 0

(Total losses ) ,I 70 percent prechamb e r I ( 4 1.0) N.A.C.A. Technical Note No. 577 Fig.l .2: 50 percent spherical chamber ------20 percent spherical ohamber >- .a ~ Chamber c ~ (II o g .... o PI ~ o~ ri­ (I) oIi:!:

01 -..J $ -..J

-,- -,I _1_ cro,m- ~ Piston -~ ... ______I posl tiona - < YL1

Cylinder head ------

'zJ Figure 2.- Prechamber combustion chamber. .... ~

£\) Fig.S N.A.C.A . Technical Jote No. 577

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N. A.C.A. Technical Note No. 577 Fig. 4

50

d 40 ---(fJ

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o 20 40 60 80 100 Clearance vol um e in chamb er. pe rc ~ nt of t otal cl earance

Figure 4.- Effect of prechamber size on f .m .e.p . Te st unit 1; prechamber cylinder head; co mp r e ssi o~ r a tio. 13. 5; oil temper a ture - out, 1800 F.; wa t er t empe r a tur e - out, 1700 F. N.A.e.A. Technical Note No. 5?? Fig. 5

50 . -- ' ~-'-+I- ' T Ti I I ' I r p .m. I -i-- --l I· ~ - - ____ L_ I I I ! 1100 I i 1.3 ! 40 ------I o , c .-I-o- I~oo I ; I I I or(1 '1 , . ,'--U='-=--I_~ --j-'---Yro' P rl I I, {:, I1 £, It>_ __ --r-. --n / I ~ 30 --l-'--=r~ -'-~r--: T '-- p., '--r- - T -- Iii I I ! 1-----+-1 --+-----+--11 I I ._, .. -L_. ______20 o 1 1 ~ 1 11.. 11.. 4 '2 4 4 2 Displ acer hei ght , in.

Figure 5.- Effect of displacer height on f. m.e .p. Te st unit 2; displacer combustion chamber; comp r ession r atio, 13 to 15,7; oil temper­ ature - out, 1650 F., wat er t empe r ature - out. 1700 F. N.A. C. A. Technical No t e No. 577 Fig. 6

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~ I- -I----+! ---+-1 ! 1 -t-j--+1-1- , 20 __l---,--- --'------'--.!.--'--I__ _L __ ._J 200 400 600 800 1000 1200 Maximum air-flow velocity , ft./sec.

Figure 6.- Effect of maxi mum air- flow speod on f .m . e.p . Test uni t Ii prechrunber cylinder h ead; 50 percent clear ance in pr echamber; comp ression r atio , 13 . 5; oil t empe rature - out, 1400 F.; wat er tempera­ ture - out, 1700 F.; engine speed, 1,500 r . p.m. N.A. C. A. Techn i ca l No te No . 577 Fi g . 7 r--, ---r- 1- ----,------I I I \ - 1------_. . -- . 8 ~ - --+- \

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Figur e 7 .- Effect of i:axi mul:l a i r-f l ow speed on f . m.e .p. Te st uni t 2 ; J di spla c er combusti on chan be r ; c O!:lp r essioll r a tio , 1 5 . 3 ; oil temp e r a ture - out, 1650 F .; wa t er t empe r a ture - out, 1700 F. : engi ne speed, 1, 500 r.p .m.

~ N.A. C.A. Te chni cal No t e No . 577 Fi g . 8

I , ------I _ I----I-----=--f--­ I /0

--j/<~ I ~ )~---+.----'-, ""--t,1 0' -::; 30 ~--.. .L'~f- --t----~ ~ I • 1 ~ r------+-----+-- --+-, ; I tri 20 I 4-----0 ~1WJtnw:uWs "9"---+-----1--- 1 x Eq - va l en in te r al

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Fi gure 8 .- Compar ison of prechrunoe r and integral chamoer with di sp1a c cr comoustion charnoer and integra l cbe. :iloer _ Te s t uni t 1; com­ pressi on r a t io, 15 .3; oil temper a ture - out , 1800 F .; water temp er ature­ out, 1700 F . • N.A .C.A. Technical No te No.5?? Fig . 9 . ~ .,-t, 0< (fJ '1'00 ---- r------r------,---n­ ---+-----r----~----t_

Q) H ;j (fJ (fJ Q) 600 I-­ H I P, I ~ I. __ I o ---- .,-t I (fJ +~~-+---+-----+----+------t- (fJ , , / Q) I pi H ~< /' .-- 500 off I k/·/ o f?~ 1-----i--f--- 'J-l i-~ - - I I I i 50 l, I I ++-+--r--+-----+----+-----t---l I I I I I , I __ ~~~~_I . I I I I I t ~ .,4 ' --I----i'--+----?-t-----t---- 0< 40 1-----+--+-1-'--I I I 1--+-----1-- (fJ F }'--r ---or -4--t--=r=--I'r-; ----1-- Pi. S 30 ----+-----L I .------Q) 1° '1'0 percent prechamb er ~~ Equivalent integral ~ I I 1----1- ! '-n--I----+----l 20 L_ _-1_ I I ~ ___L.._~_-'- _ _--'- __~_ o 2. 5 5 .0 '1' . 5 10 . 0 Boost pr essure , i n . Hg Figure 9.- Effect of hoost pressure on f.m . e .p . using bo th i ntegr a l and ?O- percent chamber. Test unit 1, ~re chamber cylinder head; compression r ati o , 13.5, oil t e~perature - out, 1800 F., water tempera­ ture - out, 170 0 F., engine speod , 1, 500 r. p .m. N.A .C.A. Technical Note No. 577 Fig. 10

50 ---r-i--'---l-ll .- -t---+---I I I I 0-__ Lubri I at i ~g O il~_ 40 .0-___ I . LI... ___ --- -...l!L_ --J-~-I s:: f-o--~ _ -- _ _ _ I .r! izs------h --· --~;--:- -I c- r ----- r ------_._- I Cooli pg T~~ --p ,--130 war-- -1 J . PI I I (j) -- t------~- --+- -+-- --f i I I 20 ------1-- --1------_~__ ~ . r--- --e-- 10 I i. I I J_I 1 20 140 160 180 200 Temperature (out), of.

Figure 10.- Effect of lubrlca ting oil and cooling-water temperature on f . lli •.a.p. Test uni t 1; prechamber cylinder h ead, integral chamber; compression r atio, 13.5; standa rd oil t emp er ature- out, 1800 F.; standard water tempe r atur e - out, 1700 F., engine speed, 1, 500 r .p.m. N. A. C. A. Techni cal Nota No. 5 7 7 Fig . 11 , , 800 ~----~ I - I . I I I I I 1 I . 700 ---/--. - 1---- - r--- f..----1---- - /'1 ~ ---{--- 'M 1 0' en 1 600 I i -- p/ A ---p ~ - Q) 500 -- I-tg lI - --~_+7lL~ en I Q) t:/ I-t p., 400

~ AT-----1-- 0 'M / ' en en 300 G) I I-t '0'/ ~ I I 0 200 / t--. 0 I I I V -r I j ! 100 I .-f.-- I I 1 i r .p .m ()1 800--)- -_....:.---J i I 40 i -- l---,----T-- --+-- I! .-

10 I o 4 8 12 16 20 Comp r e s si on r ati o Figur e 11.- Effect of c omp r e ssion r ati o on f .m. e.p. and comp r e s sion p reSiOurtS . TE:s t uni t 1, pr echamber cylinder h ead, integr a l ch amb er·, oil t emp er ature - out , 1800 F .; wa t e r t emp er a t u r e - out , 1800 F . _ _-...J n .A.C.A. Techni ca l Not e No . 5?? Fi g . 12

40 ----.--1 I 1 ·-1--1-1- --- '[' o Di spla cement 980 cu. in. i f--- -I---/ C.R· - 13 ' f -1'--1·- 1 I , ' o Di spl acemen t 918 cu. i ~ . I I 30 - -+----1CR _ - 16-r-TT---1 1 __+- __ ---+ .-.. _~ . ------L---i.-_; I--.J 0' i I I ' ! I I 1 I I rJl I I : i " I' I' ,i .---,i..------?-' I I ' ---- 20 ::h _-~~..::.. --+-- - - ~- .-1 ,D rl ! _ -+-- .- . ~ --- I iii f------I------,G-l~-i I -+-±o +-1 9--- --0j --- ~- . --~'\r' - I I I 10 ._----,---r-t--- -J[- --1--i-- ] .---, -i---+- l ------t-l- I I I. I ' 0 1 I ! I .J 1000 1400 1800 2200 Engi ne speed, r .p .m.

Figur e 12 .- Effect of speed on f. m. e .p. f or 9-cylinder, r adial, a ir­ cool ed, 4-st r oke cycle , singl e- valvo o ~ g i n e s. Lubr i ca t i ng o oil t emp ~ r a tur e - out, 150 F.