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Pulse detonation engines (PDEs) with three different types of nozzle–straight ejector combinational structures at three different ejector positions were simulated by the unsteady 2-D axisymmetric method to understand the influence of nozzle–ejector combinational structures on the performance of PDEs. Three types of nozzles included the straight nozzle, convergent nozzle, and convergent–divergent (CD) nozzle. Three ejector positions were considered according to the ratio of the distance between the nozzle outlet and the ejector inlet to the diameter of PDEs (Δx/d). Propane was used as the fuel and air as the oxidizer. The simulation results indicated that for the PDE with the straight nozzle, it took the shortest time for high-temperature burnt gas to exhaust from the detonation tube. For the PDE with the CD nozzle, the time at which the ejector was filled with external air was the fastest. Within the time range of t = 0–10 ms, the ejected air was less than the original air in the ejector among all the nine combinational structures. The maximum ejected air was obtained with the convergent nozzle, followed by the CD nozzle, and the minimum with the straight nozzle. For certain nozzles, the maximum air was ejected at the ejector position of Δx/d = +1, followed by the ejector position of Δx/d = 0, and the minimum at the ejector position of Δx/d = −1. For the convergent nozzle–ejector combinational structure, the air ejection speed was the fastest. Oxygen concentration distribution in the PDE with the CD nozzle was more uniform along the axial direction than the other nozzles.

In order to investigate the influence of two successive ignitions on the detonation initiation characteristics, the processes of detonation initiation by one ignition and two successive ignitions with different ignition energy and ignition time interval were simulated numerically. Stoichiometric propane-air mixture was used as the fuel-oxidizer. The simulation and analysis results indicated that a detonation wave could not be initiated in the smooth tube by single ignition with the current ignition energy range of no more than 10000J, while a detonation wave was initiated successfully by two successive ignitions with a certain range of ignition time interval, even when the ignition energy of each ignition decreased to 100J. As the ignition energy decreased, the range of ignition time interval in which the detonation wave could be initiated successfully decreased, while the time and distance of detonation initiation increased.

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