N A S A TECHNICAL
ME M O R A N D U iVI
NASA TM X-2630
FACTORS AFFECTING * *ALTITUDE RELIGHT PERFORMANCEOF A DOUBLE-ANNULAR s
by Donald F, Schultz and Edward J. Midarz
Lewis Research Center
U.S. Army Air Mobility R&D Laboratory
Cleveland, Ohio 44135
N A T I O N A L A E R O N A U T I C S AND SPACE ADMINISTRATION WASHINGTON, D. C. SEPTEMBER 1972
1. Report No.
NASA TM X-26304. Title and Subtitle .FACTORS AFFEC
PERFORMANCE OF A DOUBL
RAM- INDUCTION COMBUSTOI
2. Government Accession No.
:TING ALTITUDE RELIGHTE- ANNULARI
Donald F. Schultz and Edward J. Mularz
9. Performing Organization Name and Address
NASA Lewis Research Center and
U.S. Army Air Mobility R&D Laboratory
Cleveland, Ohio 44135
12. Sponsoring Agency Name and Address
National Aeronautics and Space Administration
Washington, D. C. 20546
3. Recipient's Catalog No.
5. Report Date
September 19726. Performing Organization Code
8. Performing Organization Report No.
10. Work Unit No.
11. Contract or Grant No.
13. Type of Report and Period Covered
14. Sponsoring Agency Code
15. Supplementary Notes
A test program was conducted to evaluate the altitude relight capabilities of a short- length,double-annular, ram-induction combustor which was designed for Mach 3 cruise operation.The use of distorted inlet-air flow profiles was tried to evaluate their effect on the relightperformance. No significant improvement in altitude relight performance was obtainedwith this approach. A study was also made to determine the effects of the reference Machnumber, the fuel temperature, and the fuel volatility (ASTM-A1 against JP-4) on the altituderelight performance. Decreasing the reference Mach number, increasing the fuel temper-ature, and using more volatile fuel all decrease the combustor pressure necessary forrelight.
17. Key Words (Suggested by Author(s) )
Jet engine;' Combustor s (annular); Combus-tors (double annular); Hydrocarbon combus-tion; Altitude relight; Diffuser radial profile
19. Security Classif. (of this report)
18. Distribution Statement
Unclassified - unlimited
20. Security Classif. (of this page) 21. No. o
Unclassified 2f Pages 22. Price"
* For sale by the National Technical Information Service, Springfield, Virginia 22151
TEST FACILITY 2
CALCULATIONS 5Reference Mach Number 5Units 6
TEST COMBUSTOR 6
Combustor Design 6Combustor Configurations 9
TESTING PROCEDURE 12
RESULTS AND DISCUSSION 12Preliminary Investigation 13Performance Evaluation 14
Effect of variation in combustor reference Mach number 14Effect of variation of inlet-fuel temperature 15Comparison of ASTM-A1 and JP-4 fuels 16
SUMMARY OF RESULTS 16
CONCLUDING REMARKS 17
FACTORS AFFECTING ALTITUDE RELIGHT PERFORMANCE OF
A DOUBLE-ANNULAR RAM-INDUCTION COMBUSTOR
by Donald F. Schultz and Edward J. Mularz*
Lewis Research Center
A test program was conducted to evaluate the altitude relight capabilities of a short-length, double-annular, ram-induction combustor which was designed for Mach 3 cruiseoperation. The combustor was modified by the placing of airflow distortion plates in thediffuser inlet to redirect the inlet airflow as well as removing air swirlers on the innerannulus while adding blockage to the swirlers in the outer annulus. The intent of thesemodifications was to reduce the airflow through the outer annulus by diverting the air-flow toward the inner annulus. The resultant lower velocity in the outer annulus shouldfacilitate altitude relight since decreasing velocity increases flame stabilization. Inaddition, two sets of fuel nozzles were used to improve relight performance by providingbetter atomization at low fuel flow. However, no significant improvement in altituderelight performance was obtainable with any of these modifications. The relatively highpressure loss of this combustor redistributed the distorted inlet-air profile in such away that very little decrease in reference Mach number occurred in the outer annulus.
A study was also made relating the reference Mach number, the fuel temperature,and the fuel volatility with altitude-relight performance. Significant improvements inaltitude relight performance were obtained by reducing the reference Mach number, byincreasing the fuel temperature from 251 to 425 K (-8 to 305 F), and by using a morevolatile fuel, JP-4 instead of ASTM-A1.
This report presents the results of two efforts. One was an attempt to improve thealtitude relight capability of a double-annular, ram-induction combustor by using distor-ted inlet-air flow profiles. The other shows the effects of reference Mach number, fuel
*U.S. Army Air Mobility R&D Laboratory.
temperature, and fuel volatility on altitude relight performance.Previous testing of a short-length, double-annular, ram-induction combustor
(ref. 1) indicated a serious altitude relight problem. Relight could not be obtained atinlet-air pressures and temperatures below ambient with reference Mach numbers above0. 05. In an effort to improve altitude-relight capability, several modifications to thiscombustor were undertaken in light of its otherwise fine performance.
The previous testing indicated that the altitude-re light performance was very sensi-tive to reference Mach number. Decreasing the reference Mach number improved re-light performance. Because the double-annular combustor has the unique feature thatcombustion can be maintained in either annulus independent of the other, several meth-ods were proposed to improve relight performance by reducing the reference Mach num-ber in the outer annulus while maintaining the same diffuser inlet Mach number. Reduc-tion of velocity in the outer annulus was chosen because the igniters are located there.Hence, the combustor modifications all involved attempts to lower the airflow (i.e., thereference Mach number) in the outer annulus by directing part of the airflow that wouldnormally go to the outer annulus to the inner annulus while holding diffuser inlet condi-tions constant. In application, diffuser bleed (ref. 2) or variable combustor geometryhave been proposed for use on engines to redirect the airflow during altitude relight. Todetermine if airflow redistribution would enhance relight capability, a flow distortiondevice was used to redirect the airflow.
Other factors that may affect relight performance are fuel temperature, fuel vola-tility, and ignitor location. Fuel temperature was varied from 251 to 425 K (-8 to305 F) to evaluate its effect. A few tests using the more volatile JP-4 fuel were madeto compare its performance with ASTM-A1 fuel. Igniter location and energy were notvaried during the test program.
Combustor blowout and relight limits were obtained for several configurations. Inaddition, using the best relight configuration, maximum combustor average temperaturerise was determined as a function of inlet-air temperature, total pressure, and com-bustor reference Mach number. These average temperature rise data are useful indetermining how well the combustor could accelerate an engine.
The altitude-re light capabilities of the combustor were studied in a closed-duct testfacility. A flow path of this facility is shown in figure 1. Airflow rates for combustionfrom 2.3 to 136 kilograms per second (5 to 300 Ibm/sec) at pressures from 1. 7 to103 newtons per square centimeters (2.5 to 150 psia), could be cooled to 260 K (8 F)or heated to 922 K (1200 F) without vitiation before entering the combustor.
Inlet flowcontrol valve
;' temperature ri/ when used. 13
/ 333 K( 250 tot
1.430 or 0.968(0.563) or (0.381)
Support backing plate
Punched plate: 29 percent openarea; 0.061 cm (0.024 in.) thick;0.0838 cm (0.033 in.) holes''
Mr Exit probe shields
r Exit probe,
Figure 2. - Axial location of combustor instrumentation. (All dimensions are in cm (in.).)
Typical scoop(End view)
OuterCenter^ \Inner -v\ \
80.8 71.1(31.8) (28.0)diam diam
69.9 89.9(27.5) (35.4)diam diam
Figure 3. - Cross section of double-annular ram induction combustor. (All dimensions are in cm (in.).)
alumel thermocouples, five near the outer wall, were used to determine when ignition orblowout had occurred.
Reference Mach Number
The reference Mach number was computed from the total airflow, air density at thediffuser inlet, and reference area. The actual combustor reference area is 0. 428
osquare meter (662.8 in. ), the minimum cross-sectional area into which the combustorwill fit. However, this combustor was designed to operate in an engine that had a com-
9bustor reference area of 0. 448 square meter (695 in. ). The reference Mach numberwas computed-using the larger area. Therefore, all pressures, temperatures, andairflows were consistent with the altitude windmill operation of that engine.
The U.S. Customary system of units was used for primary measurements and cal-culations. Conversion to SI units (System International dfUnites)