The oblique detonation wave (ODW) triggered by a semi-infinite cowl or wedge has been widely studied, but the effects of finite-length cowls require further clarification to enhance their applicability. Based on two-dimensional inviscid Euler equations and a two-step induction–reaction model, two structures with smooth and abrupt transitions are simulated, and their interactions with the cowl-induced expansion wave are investigated. The expansion waves located downstream and far away from the initiation zone do not affect the macroscopic structures of the ODW. However, when the expansion waves move upstream, the structures evolve into a decoupled shock and a reactive front. Alongside findings from previous studies, these results indicate that the initiation mechanism, rather than the transition type, determines the near-quenching evolution of the structure. Moreover, given the same parameter settings for the chemical and inflow gas dynamics, these numerical results show that the abrupt transition evolves into a smooth transition under an expansion wave disturbance. This demonstrates that the local wave interaction plays a key role in the ODW structures.

Oblique detonation engines attract more and more attention due to their potential use in hypersonic propulsion, but the initiation of detonation still requires comprehensive study concerning the complicated interaction of wedge, supersonic flow, and heat release. In this study, the effects of the wedge angle on the initiation mode of oblique detonation have been investigated theoretically and with numerical simulation. Detailed chemical reaction models are used, and constant-volume combustion theory that considers the vibration excitation of the gas molecules is applied to study the characteristic length of the induction zone. It is found that the theoretical and numerical characteristic lengths in induction regions are in good agreement. Two initiation modes—kinetics-controlled and wave-controlled—are analyzed in depth at different Mach numbers and wedge angles. The results show that reducing the wedge angle can cause the initiation mode to change from kinetics-controlled to wave-controlled at different Mach numbers. The detailed induction zone length and the transit wedge angles between two initiation modes of wedge-induced oblique detonation have also been found.