Initiator Diffraction Limits for Pulse Detonation Engine Operation

Operational characteristics of a valveless pulse detonation engine system are being characterized by both experimental and computational efforts. The detonation diffraction process from a small “initiator” combustor to a larger diameter main combustor in a continuous airflow configuration was evaluated during multi-cycle operation of a pulse detonation engine. The multi-cycle detonation experiments were performed on an axisymetric engine geometry operating on both ethylene and propane fuel/air mixtures. The new design explored the effect of forward relief area on performance and its ability to isolate the detonation products from the incoming air flow during cyclic operation. The use of a small fuel-oxygen initiator to initiate a fuel/air detonation in a larger main combustor has been achieved and has demonstrated the benefit of generating an overdriven detonation condition near the diffraction plane for enhanced transmission to a larger combustor. Mach reflections have been observed on the outer wall downstream of the diffraction plane for the two-dimensional geometry and appear to be the primary re-initiation mechanisms for the re-established fuel-air detonations for this geometry. Multi-cycle tests have successfully evaluated initiator/main combustor diameter ratios of up to 1.58 and are expected to continue through 2.0.