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
Nozzle Designation
Tube to Throat Area Ratio
Exit to Throat Area Ratio
Straight 1
Converging 1 3
Converging 2 10
Converging-Diverging 1 2
Converging-Diverging 2
Plug
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 Converging Contour (CD3) Contour
Plug Nozzle
Contour

9. Testing facility at AFRL
Multi-cycle pulse detonation engine
Sensors
Variable
Instrument
Error Margin
Quantity
Temperature
Thermocouple
3–5% 4
Pressure, Velocity
Transducer
3-5%
Thrust
Thrust stand
5-10% 1

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

11. PDE Testing

12. PDE Terms
Start/end
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)
Tests
Nozzles
Test 1:
Ignition delay Impact
Test 2: Frequency Impact
Test 3:
Fill fraction Impact
Test 4:
Cold flow
Baseline
Small Converging (C10)
Large Converging (C3)
Small Converging-Diverging (CD10)
Large Converging Diverging (C3)
Plug
Bare Tube

14. Comparative Data Air-Breather H2 fuel
Typical Specific Impulse (Mo=2.2)
Turbojet
3800
Turbofan
5500
Ramjet
3900
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
Frequency
Fill Fraction
Baseline
steady
Straight
Converging 3
higher
Converging 10
middle*
C-D 3
lower
C-D 10
Plug
middle

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 ]
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