T he Effects of Nozzle Geometry on the Specific Impulse of a Pulse Detonation Engine

1. The Effects of Nozzle Geometry on the Specific Impulse of a Pulse Detonation Engine -Final Project Report- 12/04/01 Madeline Close and Christopher Johnson Prof. Edward Greitzer, Advisor

2. Overview • Background and Motivation • Objective • Technical Approach • Experimental Results • Conclusions • Acknowledgements • Questions

3. Background-Motivation • Interest in pulse detonation engines (PDEs) has renewed in the past decade. • PDEs are a structurally lightweight form of propulsion with high specific impulse (Isp) CFD calculations have been done to estimate the effects of varying nozzle geometries; however, few experimental results exist to substantiate the theoretical conclusions

4. Objective To determine the effects of nozzle geometry on the specific impulse of pulse detonation engines

5. Technical Approach • Six nozzles were designed and manufactured for testing conditions at Air Force Research Laboratory (AFRL)

6. Nozzle Geometry Matrix All nozzles were manufactured on-campus in the Gelb Laboratory with the exception of the plug (Central Machine Shop).

7. Nozzle Design • Converging contour derived from the MIT supersonic wind tunnel design and scaled for specific area ratios • Diverging contours calculated using Method of Characteristics • Plug nozzle contour based on a previous geometry

8. Nozzle Contours Converging-Diverging Contour (CD3) Converging Contour (C10) Plug Nozzle Contour

9. Testing facility at AFRL • Multi-cycle pulse detonation engine • Sensors

10. PDE Schematic Spark Detonation tube Inlet Air flow Detonation Fuel injection

11. PDE Testing

12. Start/end PDE Terms • Cycle: 3-part process Frequency: engine cycles per second (Hz) • Ignition delay time: time between engine fill and ignition (ms) • Fill fraction: fraction of tube the gases would fill at STP Fill Purge Fire

13. Test Matrices (Complete)

14. Comparative Data Source: Aircraft Engines and Gas Turbines, Jack L. Kerrerbrock

15. Data Reduction Isp value for each test taken at steady state

16. Absolute Nozzle Performance

17. Relative Nozzle Performance

18. Absolute Nozzle Performance

19. Relative Nozzle Performance Frequency=30 Hz

20. Optimal Operating Conditions

21. Summary of Nozzle Performance • Straight nozzle gave slight improvement in performance over baseline at same dimensional frequencies [predicted by Eidelmann and Yang in AIAA paper 98-3877] • Smaller converging nozzle (C10) and small converging-diverging nozzle (CD10) backfired at higher frequencies.

22. Summary of Nozzle Performance • Larger converging nozzle (C3) performed well: maximum Isp of 4500 sec. at 40Hz • Larger converging-diverging nozzle (CD3) was consistently below baseline performance. • Plug nozzle (PG) was consistently 10%-20% above baseline performance

23. Conclusions • Shock reflections should be considered in choosing the Atube/A*. • Converging nozzles and plug nozzle performed best relative to baseline. • Converging-diverging nozzles performed poorly in the test conditions.

24. Future work • More families of nozzles need to be tested. CFD analysis of diverging nozzles shows they improve Isp. • Higher frequency tests should be performed. • Develop design method for making nozzles to maximize Isp.

25. Acknowledgements • Professor Ed Greitzer, Project Advisor • Don Weiner, Carl Dietrich, and Jerry Wentworth for machine shop help • Dr. Fred Schauer and Dr. Royce Bradley for help at WPAFB-APRL • Professors Ian Waitz and Mark Drela for technical assistance in nozzle design • Dr. David Tew (UTRC) and Dr. Doug Talley (AFRL) for project advice

26. Questions