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

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

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

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

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

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).

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

Nozzle Contours Converging-Diverging Converging Contour (CD3) Contour Plug Nozzle Contour

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

PDE Schematic Spark Detonation tube Inlet Air flow Detonation Fuel injection

PDE Testing

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

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

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

Data Reduction Isp value for each test taken at steady state

Absolute Nozzle Performance

Relative Nozzle Performance

Absolute Nozzle Performance

Relative Nozzle Performance Frequency=30 Hz

Optimal Operating Conditions Frequency Fill Fraction Baseline steady Straight Converging 3 higher Converging 10 middle* C-D 3 lower C-D 10 Plug middle

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.

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

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.

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.

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

Questions