Cavity Ignition in Supersonic Flow by Spark Discharge and Pulse Detonation
U.S. Air Force Research Laboratory Wright-Patterson Air Force Base United States
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Ignition of an ethylene fueled cavity in a supersonic flow was achieved through the application of two energy deposition techniques a spark discharge and pulse detonator PD. High-frequency shadow graph and chemiluminescence imaging showed that the spark discharge ignition was passive with the ignition kernel and ensuing flame propagation following the cavity flow field. The PD produced a high-pressure and temperature exhaust that allowed for ignition at lower tunnel temperatures and pressures than the spark discharge, but also caused significant disruption to the cavity flow field dynamics. Under certain cavity fueling conditions a multiple regime ignition process occurred with the PD that led to decreased cavity burning and at times cavity extinction. Simulations were performed of the PD ignition process, capturing the decreased cavity burning observed in the experiments. The PD exhaust initially ignited and burned the fuel within the cavity rapidly. Simultaneously, the momentary elevated pressure from the detonation caused a blockage of the cavity fuel, starving the cavity until the PD completely exhausted and the flow field could recover. With sufficiently high cavity fueling, the decrease in burning during the PD ignition process could be mitigated. Cavity fuel injection and entrainment of fuel through the shear layer from upstream injection allowed for the spark discharge ignition process to exhibit similar behavior with peaks and valleys of heat release but to a lesser extent. The results of using the two energy deposition techniques emphasized the importance of cavity fueling and flow field dynamics for successful ignition. Published by Elsevier Inc. on behalf of The Combustion Institute.