Performance Studies of Pulse Detonation Engine Ejectors

Abstract

An experimental study on the performance of pulse detonation engine ejectors was performed. Time-averaged thrust augmentation produced by straight and diverging pulse detonation engine ejectors was measured using a damped thrust stand. The ejector length-to-diameter ratio was varied from 1.25 to 5.62 by changing the length of the ejector and maintaining a nominal ejector diameter ratio of 2.75. In general, the level of thrust augmentation was found to increase with ejector length. Also, the ejector performance was observed to be strongly dependent on the operating fill fraction. A new nondimensional parameter incorporating the fill fraction was proposed. When the pulse detonation engine ejector data were represented as a function of this new parameter, the ejector data were reduced to one representative thrust augmentation curve for ejectors of similar internal geometry. Straight pulse detonation engine ejectors compared well with the available data on straight steady-flow ejectors. Diverging pulse detonation engine ejectors produced nearly twice the thrust augmentation as their straight-ejector counterparts due to the additional thrust surface area the divergence provided. All pulse detonation engine ejectors tested were seen to be sensitive to the axial position of the ejector as well. The optimum ejector axial placement was found to be a function of fill fraction due to a tradeoff between the detonation wave induced drag and increased mass entrainment. Downstream ejector placements performed the best at the low fill-fraction operating conditions.