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Distribution authorized to DoD only;Administrative/Operational Use; 19 JAN 1948.Other requests shall be referred to NationalAeronautics and Space Administration,Washington, DC.

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21 JAN 1q18 Ina~

RESEARCH MEMORANDUM

SUBSONIC FLIGHT INVESTIGATION OF RECTANGULAR

I F\J\M JET OVER RANGE OF ALTITUDES

By Wesley E. Messing, and Dugald 0. Black

Flight Propulsion Research Laboratory . Cleveland, Ohio

OJ.ASStFtCATION CANCELLED

~ ---------- ----- ------ ----

j 1

By_~~- _!L/Itj~A-~ ___ sca -----------...

---·------------------------

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

WASHINGTON January 19, 1948

...

N.ACA RM No. E7B26

" .11\llill~li:Wlimiii\\IIU\11 IIIII'I..T 3 1176_~~-425 -~~~2' " !XlJI'PPfiA.L :.. .... -- -

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

RESEARCH MEMORANllJM

SOBSONIC FLIGm' INVESTIGATION OF RECTANGULAR RAM ~

OVER RANGE OF ALTITUDES

By wesley E. Messing, and Dugald 0. Black

L

A flight investigation was conducted on a rectangular ram jet incorporating a V-shaped gutter-type flame holder over a range of fuel-air ratios from O.Ol9 to 0.122, combustion-chamber-inlet veloc­ities from 39 to lOl feet per second, and ~~~ssure altitudes from l500 to 291 200 feet.

The maximum combustion efficiency obtained was approximately 84 percent at a fuel-air ratio of 0.069 and a pressure altitude of l500 feet. An increase in altitude resul.ted in a pronounced decrease in combustion efficiency. The highest pressure altitude at which ~ition was possible with the spark plug and ignition cone was 22,500 feet. Above 12,000 feet, an increase in altitude increased the value of fuel-air ratio at which lean blow-out occurred. Rough engine operation was encountered only at altitudes above 20,000 feet as the fuel-air ratio approached the lean or rich blow-out limits.

INTROilJCTION

As part of a research program for the study of' ram jets, a flight investigation is being conducted at the NACA Cleveland laboratory on a rectangular ram jet installed in a short-span wing mounted beneath the fuselage of a twin-engine, f~ter-type air­plane. This type of power plant was designed for installation within the wings of a high-speed airplane or missile.

The purpose of the investigation is to determine the perform­ance and operational characteristics of a rectangular ram jet over a range of altitudes at subsonic velocities. During a test-stand in:vestigation (reference l}, a similar engine operated satisfacto­rily over a range of fuel-air ratios from 0.025 to 0.083. Owing to the comparatively low in.J..et-air velocities available, only a limited amount of data could be obtained on ignition, blow~t, and combus­tion efficiency. The flight investigation reported herein was made

2 .... NACA RM No. E7H26

at pressure altitudes f'rom 1500 to 29,200 f'eet in order to determine the ef'f'eot of' altitude on ignition, lean arid rich blow-out limits, and combustion ef'f'iciency.

The results obtained over a range of' f'uel-air ratios f'rom 0.019 to O.ll2, combustion-chamber-inlet velocities f'rom 39 to 101 f'eet per second, and pressure altitudes f'rom 1500 to 29,200 f'eet are presented.

APPARA'IUS AND PROCEIXJRE

Bam-Jet Installation

The rectangular ram jet investigated was installed in a short­span wing supported beneath the fuselage of' a twin-engine, :righter­type airpl.a.ne, as shown in f'igu.res 1 and 2 . Ducts :f'or cooling air were provided to ventilate the space between the combustion chamber and the outer shell in order to avoid possible accumulation of' explosive vapors; these ducts, however, had no aff'ect on the operation of' the ram-jet engine. The entrances and exits of these ducts are located in the wing-tip sections, as shown in figure 2. Inasmuch as DD provisions were xga.de to vary the angle of attack o:t' the ram jet, it varied with a change in indicated airspeed. The variation ranged from 1° at an indicated airspeed o:t' 240 miles per hour to 6° at 160 miles per hour. Figure 3 shows the disassembled components o:t' the engine and the wing installation.

The rectangular ram jet (fig. 4) consists of an inlet diffuser, a combustion chamber, and an exhaust nozzle. The dif'fuser is of rectangular cross section with parallel sides and has a total dif'­fuser angle of 12° between the top and bottom walls . The maximum combustion-chamber area is twice and the exhaust-nozzle area 1.3 times the diffuser-inlet area. The combustion chamber was cooled by circul.a.ting fuel through a corrugated manifold seam-welded to the surface of the combustion-chamber wall. The fuel was introduced under pressure at the rear of' the_ combustion chamber, circulated in separate parallel paths the entire length of' the combustion chamber, and discharged into a common fUel-spray bar located along the hori­zontal center line of the di:t'fuser. In addition to cooling the combustion chamber, this system preheated the fuel. The fuel­pressure loss in the corrugated manifold was kept to a minimum by using a number of separate :t'low paths instead o:f one continuous path. The fuel-spray bar consisted of six evenly spaced nozzles. The nozzles discharged downstream in a 60° cone. Each nozzle was rated at a ~el flow of 40 gallons par hour at a fuel pressure of 100 pounds per square inch gaga. The i'lial U:Sed :t'or these testa was AN-F":'2:3A (73-octane gasoline).

NACA RM No. E7.B26 ;a•w> 3

The flame holder consisted of' 4 horizontal and 17 vertical v-shaped gutters and was fabricated from 0 .064-inch Inconal. . The measured static-pressure drop without combustion f'or this flame holder was 3.1 times the dynamic pressure in front of' the flame holder. The flame holder was mounted in such a manner (f'ig. 4) that no direct connection existed between the flame holder and the combustion-chamber walls, which could advance the flame to the walls and result in uneven wall temperatures. Burning was initi­ated by a spark :plug installed in a shielding cone mounted in f'ront of' the flame holder. No auxiliary fuel ~s introduced in the cone.

Instrumentation

The total and static pressures were IDdasured at the d1.f'f'user inlet by 3 total- and static-pressure rakes and 18 static-pressure wall orif'ices. A total-pressure rake in f'ront of' the flame holder measured the pressure at the inlet to the combustion chamber. At the exit of' the ram jet, the static pressure was measured by two static-pressure wall orif'ices and the total pressure was measured by a water-cooled rake. All pressure tubes were connected to a multiple-tube liquid-manometer board. Sensitive indicators were used to obtain the indicated airspeed and altitude as measured by a swiveling static-pressure tube and a shrouded total-pressure tube installed on a boom l chord length ahead of' the leading edge of the right wing tip. Pressure gages indicated the fuel pressure at the pump outlet and at the inlet to the ram-jet manif'old. The fuel flow was indica ted on a gage and was measured by a vane -type flow­meter. All indicators were mounted on the manometer board, which was photographed during flight.

An automatic potentiometer recorded temperatures obtained from chromel-alumel thermocouples located throughout the ram-jet unit. These measurements consisted of' 24 combustion-chamber-wall temperatures, 8 fuel temperatures at the inlet to the fuel-spray bar, 2 fuel temperatures at the inlet to the combustion-chamber manifold, and 8 ventilating-air temperatures between the combustion chamber and the top and bottom wing sections. The free-air tem­perature was measured by a flight-calibrated iron-constantan ther­mocouple installed under the left wing of' the airpl.e.ne.

Flight Program

The starting characteristics and blow-out limits for the rec­tangular ram jet were determined over a pressure-altitude range

42ii2 ELliE iii

4 -. NACA RM No. E7H26

from 1500 to 29,200 feet and for indicated airspeeds from 150 to 240 miles per hour.

The effect of altitude on combustion efficiency was determined for the following ranges of indicated airspeed and fuel-air ratio:

Pressure Indicated altitude airspeed Fu.el-air ratio

(ft) (mph)

1,500 160 0.025 - 0.076 200 .029 - .090 240 .066 - .090

6,000 160 .028 - .112 200 .023 - .096

16,000 160 .028 - .l.08 200 .040 - ,094 ~40 .062 - .098

26,000 l.60 .079 - .l.06 200 .068 - .082

METHOD OF CALCULATIONS

Engine air flow was calculated from the total and the static pressures measured at the inlet to the diffuser.

The exhaust-gas temperature at the exit of the ram jet was cal.­cul.ated from the measured gas flow and pressure measurements at the exit of the combustion-chamber nozzle in accordance with the method outl.ined in reference 2. The combustion efficiency was determined by the following equation:

where

Hs-Ha Tlb = f/a (hf) 100

combustion efficiency, percent

enthalpy of burned gases at exit gas temperature, Btu per pound of' original air

oma a r:-

NACA BM No. E7H26 a iK=' 5

entha.l.py of' air and fuel before combustion, Btu per pound of origina.l. air

f/a fuel-air ratio

ht- lower heating value of' fuel, 18,500 Btu per ];lound.

For the purpose of these calculations, :sg was assumed equal to the enthalpy of air at the exhaust-gas temperature plus the sum of the • enthalpies of the carbon dioxide and water tba.t result from complete combustion minus the enthalpy of oxygen required for complete com­bustion. Entha.l.py values were obtained from reference 3.

RESlJLTS AND DISCUSSION

At low altitudes {below 6000 f't), the exhaust flame was l~t blue in color at fuel-air ratios from 0.05 to 0.07 and extended approximately l foot beyond the exit of' the engine. As the fuel-air ratio was increased, the flame became longer and yellow in color owing to the afterburnirlg of' the excess fuel. The exhaust flame became less visible as the altitude was increased and was no longer visible even at h~ fuel-air ratios above an altitude of 16,000 feet. F~ 5 shows the ram jet operating at a pressure altitude of 6000 feet, an indicated airspeed of 160 miles per hour, and a fuel­air ratio of' 0.140. The .flame was very yellow and extended approx­imately 6 .feet beyond the engine.

Air-flow sepa.ra.t.ion occurred at the top leading edge of the dii'fuser section of the engine at indicated airspeeds in excess of' 240 miles per hour. This separation resulted in extremely rough O];leration of' the engine and erroneous air-flow measurements. As a result, the infestigation was 111n1ted and no data are given for indicated airspeeds in excess of 240 miles per hour.

Rough engine operation was also encountered at altitudes above 20,000 .feet as thA f"..:.a~-~ir ratio approached the lean or rich blow­out limits. Rapid acceleration o.f :fuel .flow at high altitudes resulted in extremely rough OIJeration;which was accompanied by a loud rumbling noise and soiDEftimes resul.ted in blow-out.

The ram jet cooled IJ:roperly at all altitudes and operating conditions over which the investigation was conducted. The :ma.:x:imum combustion-chamber-wall temperature was 350° F at an altitude of 1500 feet. An increase in altitude resulted in a decrease in combustion-chamber-wall temperatures.

1 QJitl>

6 NACA RM No. E7H26

The minimum fUel-air ratio at which ignition was :possible vas determined for a given altitude by maintaining a constant indicated airspeed, turning on the spark, and increasing the fuel flow 1mtil ignition occurred. This minimum fuel-air ratio is defined as the ratio of the fuel flow (lb/hr) at which ignition occurred to the air flow (lb/hr) as measured at the given altitude and airspeed with­out combustion. Figure 6 illustrates the e:f:fect of altitude on the minimuiD :fuel-air ratio at which ignition occurred. The indicated

• airspeeds are given for each test :point. At an altitude of 11,000 feet and above, the indica ted airspeeds are the maximum airspeeds at which ignition was :possible with the S]ark-plug cone. The lowest value of minimum :fuel-air ratio is 0.028 and occurs at an altitude of 1500 feet. Increasing the altitude increased the minimum :fuel-air ratio to 0.078 at an altitude of 22 1 500 f'eet. The ram jet would not start above this altitude with the s:park-plug cone and flame holder used.

The effect of' altitude and indicated airspeed on the fuel-air ratio at which blow~ut occurred is shown in :figure 7. This fuel­air ratio was determined as the ratio of the fUel f'low at which blow­out occurred and combustion ceased to the air flow :!.lmnediately pre­ceding blow-out. At altitudes below u,ooo· feet, a variation in altitude had little eff'ect on the fuel-air ratio at lean blow-out conditions for a given indicated airspeed. An increase in altitude above 11,000 feet, however, resul~ed in the occurrence of' lean blow­out at increasing values of fuel-air ratio. Inasmuch as no data were taken at f'uel-air ratios above 0 .ll2, rich blow-out was only noted at altitudes abo-ve 21,000 feet. An increase in indicated airspeed at a given altitude resulted in an increase in the fuel-air ratio at lean blow-out and a decrease in fuel-air ratio at rich blow-out f'or the altitudes at which rich blow-out occurred. In general, f'igure 7 shows the operating f'uel-air-ratio range for a given altitude and indicated airspeed.

The ef'fects of fuel-air ratio on gas total-temperature rise (defined as exhaust-gas temperature minus inlet-air tem:perature) for altitudes of' 1500, 6000 1 16,0001 and 26,000 feet are shown in figure 8 and compared in figure 9. The maximum gas total-tem:perature rise occurred at an altitude of 1500 feet and an increase in altitude resulted in a decrease in gas total-temperature rise for a given fuel-air ratio.

The effects of fuel-air ratio on combustion efficiency for alti­tudes of 1500, 6000 1 161 000 1 and 26,000 feet are shown in. figure 10 and compared in figure 11. An increase in altitude resulted in a pronounced decrease ip. combustion efficiency. No attempt was made to isolate the factors contributing to this decrease; however, the

I l

,

·-NACA RM No. E7H2.6 ~;annsw. 7

decrease· in efficiency may be .attributed to .. the combined effects of. a decrease in air pressure, .air temperature, 8.nd fuel pressure, which. resu:Lted in a decrease in atomization of the fuel and penetration of the fuel :Particles in the air stremn·. · The Iqa.Ximtiln combustion effi­ciency was approximately 84 percent at a.fuel-air ratto of 0.069 and an altitude of 1500 feet ·(fig. 11); as compared with ma.ximuzl efficien­cies of approximately 75.5 percent at 0.071 and 6000 feet, 53 percent at 0.085 and 16,000 feet, and 32 percent at '0.090 and. 26,000 feet. In general_, an increase in a:Ltitude resulted in the'~ combustion efficiency occrurring at h~r values of fuei-air ratio.

S01&!ABY OF RI!:SOLTS

From a flight investigatio~ of a ·rectangular ram jet incorpo­rating a V-shaped gutter-type f~ holder over a range of fuel-air ~tios from O.Ol9'to 0.112, combustion-chamber-inlet velocities from 39 tp lOl: feet per secoDd, a.:hd pressure a.J..titudes f'rom 1500 to 29,200 feet, the foliowing,resulta were obtained:

l. The ma.ximtun combuatio'n efficiency obtained wa,e approx1llla.tely 84 percent at a fuel-air_ratio of 0.069 and a pressure altitude of 1500 feet. An increase in altitude resulted in a pronounced decrease in combustion efficiency.

2. An. increase in a'.l.titude increased the value of' min.imum fuel­air ratio at which ignit~onwas·possible with the present spark-plug coria .and f'ia:me- holder. The highest altitude at which ignition was possible was 22,500 feet.

10 3 .. Above 11,000 feet, an increase in altitude increased the

value of ·fuel-air ratio at which ~an blow-out occurred.

4. Rough engine _operation was encountered onl:y at altitudes above 20,000 feet as the fuel-air ratio approached the lean or rich blow-o-q.t limits~

Flight Propulsion Research Laboratory_, National Advisory Committee for Aeronautics,

Cleveland, Ohio.

8

l.

N.ACA BM No. E7H2 6

REFERENCES

Black, Dugald 0., and Messing, Wesley E.: Test-stand Investiga­tion of a Recta.ngula.r Ram-Jet Engine. NACA BM No. E7Dll, 194 7.

2. Perchonok, Eugene, Wilcox, Fred A., and Sterbentz, William H.: Preliminary Development and Performance Investigation of a 20-Inch Steady-Flow Ram Jet. NACA ACR No. E6D05, 1.946.

3. Turner, L. Richard, and Lord, Albert M.: Thermodynamic Charts for the Computation of Combustion and Mixture Temperatures at Constant Pressure • NACA TN No • 1.086, 1.946.

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NACA RM N.o. E7H26

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NAT ION~L ADVI SOR• CO~ III TTEE FOR AERONAUTICS

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Figure 4.- Schematic drawing of rectangular ram jet Incorporating four-V gutter-type flame holder.

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miles per hour; fuel .. alr ratio, 0.140.

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NATIONAL ADVISORY COMMITTEE F~R AERO~AUTICS

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Figure 6. -Minimum fuel-air ratio at which ignition occurred for var­ious pressure altitudes and indicated airspeeds.

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22 NACA RM No. E7H26

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

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.02 .04 .06 .os .10 .12 Fuel-air ratio

Figure 7. - Effect of pressure altitude and indicated airspeed on blow­out limits.

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~ P(ATIONAL ADVISORY

COMMITTEE FOR AERONAUTICS

.02 .04 .06 .oa .10 Fuel-air ratio

Pressure altitude~ 1500 feet; ave~age inlet-air temperature. :sao F.

Figure 8. - Effect of fuel-air ratio on gas total-temperature rise.

23

24

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NATIONAL ADVISORY C01o41o41TTEE FOR AERONAUTICS

• )2 .c 4 0 • 5 .oa .10 .12 Fuel-air ratio

(b) Pressure altitude, 6000 reet; average inlet-air temperature, 520 F.

Figure a. -Continued. Effect of fuel-air ratio on gas total-tempera­ture rl se.

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NACA RM No. E7H26

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25

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Figure 8. -Continued. Effect of fuel-air ratio on gas total-tempera­ture rise.

26 •.. ~--·:c:::_ -----...-

1 56 f[li) NACA RM No. E7H26

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NATIONAL ADVISORY CO~MITTEE FOR AERONAUTICS

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NACA RM No. E7H26 ., -·WC-!E 2'"• 27

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NATIONAL AL'VlSORY COMI.II TTEE FOR AERONAUT! CS

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Comparison of effects of fuel-air ratio ature rise at various altitudes.

on gas total-temper-

28 • f(&¢U NACA RM No. E7H26

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

~· Indicated airspeed

(mph)

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29

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Figure 10. - Continued. Effect of fuel-air ratio on combustion effl-ciency.

30

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NATIONAL AOVI$0RY COiolMI TTEE FOR AERONAUTICS

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(c) Pressure altitude, 16,000 feet; average inlet-air temperature, 70 F.

40

Comb ... stio -chaJ rb;~-eloc .t:'l. P't se

9~~ iJl c 72~ 6g

gJT v I). '9~

81 696~ 62 20

0 • >2 .04 .06 .08 .10

Fuel-air ratio

(d) ~essure altitude, 26,000 feet; average inlet-air temperature, -30° F.

-51

.l2

nlet

.1 2

Figure 10. - Concluded. Effect of fuel-air ratio on combustion effi­ciency •

.. -!!~-· .-.~-f!M·

_ __.... ---

NACA RM No. E7H26 JiSt's ' ne• • Pft 31

100

80 ~ Gl 0 J'.< II) p.. ..

60 I» 0 t:: CD ..... 0 ..... ~ ~ CD 40 t:: 0 ..... +:1 co :j

~ 0 20 0

Figure ~I.

NATIONAL ADVISORY CO~~ITTEE FOR AERONAUTICS

Pr ~ssur a al.t tude,. . .rt

v- ..l500 -..........

/ 6000 ~ / - ....

I / ..........

"' !; 16, oo "' --- ---1/ I / / ..............

lj / 26,< 00 -1;. v , v I

.02 .04 .06 .08 .10 .12 Fuel-air ra tic

- Comparison of effects of fuel-air ratio ciency at various altitudes.

on combustion effi-

ll;DI:J Rli)lCJ o (ro .._, ~ l!essing, VI. E. Elack, Dugald 0.

~@~~0:§l[l[)ii1J0Cll). C-5-16-1 DIVISION, Pouer Plants, Jet and Turbine (5) SECTION, Performance (16) CROSS REFERENCES, Engines, Ram jet - Performance (;4o65)

AMER. TITLEo Subsonic flight investigation of rectangular ram jet over range of altitudes

FOI!G'N. TITLEo

On!GINATING AGENCYo National Advisory Committee for Aeronautics, Washington, D. C. TRANSLA TIONo

COUNTnY T I.ANGUAGElfORG'N.CI.ASSJ u. S.CI.ASS. I DATE 'PAGES l!lLUS.I fEATURES U.S. Eng. I I Confd'l 1Jan•4S 27 I 11 I photos, graphs, drwgs

Cl0~1J[l[l~1J A flight investigation "'as made on a rectangular ramjet incorporating a V-shaped

gutter-type flame holder over a range of fuel/ai.r ratios from 0.019 to 0.112, combustion chambsr-inlet velocities from 39 to 101 ft/sec, and pressure altitudes from 1500 to 29,200 ft. The maximum combustion efficiency obtained was approximately S4% at a fuel/ air ratio of O.o69 and a pressure altitude of 1500 ft. An increase in altitude resulted in pronounced decrease in combustion efficiency. Rough engine operation l'las encountered only above 20,000 ft as the fuel/air ratio approached the lean or rich blowout limits.

NOTE: llequosto for ~opioa of thio report muot. be llddrooood to N.A.C.A., ~llhington, D. Co

T·2. HQ., AIR MATERIEL COMMAND WaJGHT FIELD, OH:O, USAAF w;..o.21 f.\A0471~