Effects of inert gas addition on detonation initiation in a modeled rotating detonation engine

Due to the unresolved complexity of detonation initiation, which hinders a complete understanding of wave modes, this study investigates inert gas addition in a modeled rotating detonation engine configuration to quantify how the chemical sensitivity of the mixture governs initiation dynamics. High-resolution two-dimensional simulations of hydrogen/air mixtures with inert gas addition are conducted by solving the reactive Navier–Stokes equations with a detailed chemical mechanism. This work shows that forward- and backward-propagating detonation waves originate through different mechanisms, and clarifies how inert gas dilution modifies the hot-spot-driven backward initiation process and thereby controls the initial detonation mode. The results show that with increasing dilution, hot-spot formation near the inner wall is suppressed, causing the propagation mode to transition sequentially from two counter-rotating waves to a single wave and finally to a state without detonation. Two failure routes of the backward-propagating detonation wave are identified. At moderate dilution, a small detonation wave forms from the wall-induced hot spot but decouples into a leading shock and a deflagration wave. At stronger dilution, the hot spot itself is suppressed, so the backward-propagating wave is not initiated. Analysis shows that maximum thermicity is more strongly associated with the observed initiation-mode transitions than induction time within a certain range. The critical mixture exothermicity can therefore serve as a preliminary criterion for determining the existence of the backward-propagating detonation wave under the present conditions. These findings provide a physical basis for using inert gas addition to regulate the initial detonation propagation mode in rotating detonation engines.