Effect of Porous Thrust Surfaces on Detonation Transition and Detonation Tube Impulse

As pulse detonation engine development matures, it becomes increasingly important to consider how practical details such as the implementation of valves and nozzles will affect performance. Inlet valve timing and valveless inlet designs may result in flow of products back upstream and, consequently, reduction in impulse over the ideal case. Although proper inlet design or operation under flowing conditions may minimize these losses, our study addresses the worst-case effect that a porous thrust surface may have on the measured impulse. A series of single-cycle tests have been carried out to measure the impulse in stoichiometric ethylene–oxygen mixtures, initially between 20 and 100 kPa, in a detonation tube with a porous thrust surface. The tested thrust surfaces had blockage ratios ranging from completely solid (100 % blockage ratio) to completely open (0 % blockage ratio). A 76 % loss in impulse was observed with a thrust surface blockage ratio of 52 % at an initial pressure of 100 kPa. The time to detonation transition was found to be more dependent on the mixture’s initial pressure than on the thrust surface blockage ratio. A model of the impulse in detonation tubes with porous thrust surfaces was developed. Nomenclature A = cross-sectional area A f = free area of holes in thrust surface A ∗ = cross-sectional area at sonic condition