Performance characterization of a valveless pulse detonation engine
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A valveless pulse detonation engine geometry has been partially evaluated on a direct-connect test stand at simulated inlet flight conditions to the combustor. The geometry utilizes a enriched air initiator to initiate detonations in the main combustor and has been operated on ethylene, propane, and JP-10. The initiator has been operated at frequencies up to 100 Hz. The main combustor of the engine has only been evaluated up to 30 Hz operation due to a current design constraint which will be modified to allow higher frequencies in subsequent tests. The use of an initiator required the evaluation of the diffraction limits between the initiator exit and the main combustor. The successful use of an initiator to detonate a mixture in a larger main combustor has been demonstrated. Furthermore, experimental data corroborated that tailoring the initiator to produce an overdriven detonation condition at its exit plane, enhanced the detonation transition into the larger combustor. Using imaging optical diagnostics, Mach reflections were observed at the combustor’s wall just a few centimeters downstream of the initiator’s plane. These appear to be the primary re-initiation mechanism for the re-establishment of fuel-air detonations for this geometry. Results show that a diameter ratio between the combustor and the initiator of at least will allow successful operation for ethylene and propane. Single-shot diffraction tests evaluated combustor to initiator diameter ratios up to 1.58. The specific impulse was computed from experimental measurements using both ethylene and propane fuels at various equivalent ratios from 1.0 to1.5. the results showed Isp values ranging from 850 to almost 1200 seconds, but these relative low values were anticipated due to the oversize initiator used in this study. Such a large initiator was required in order to characterize the aforementioned diameter ratios. Future tests will incorporate an optimally sized initiator, and extrapolation of the current data indicates possible Isp values as high as 1800 seconds with a stoichiometric propane - air mixture. This would indicate similar performance values to more conventionally valved PDE systems.
The article of record as published may be found at http://dx.doi.org/10.2514/6.2013-1344
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