Product Recirculation and Incipient Autoignition in a Rotating Detonation Engine

Abstract

In a rotating detonation engine, some amount of products from a previous detonation wave mix with the incoming reactants. Depending on the amount of mixing that occurs between the products and reactants, the overall mixture may exceed the autoignition temperature. If the time between detonations is sufficient, this mixture may begin to deflagrate. A simple reactor model was developed to include time-dependent expansion, mixing, and chemistry effects as a continuation of previous efforts. The model identified two operating modes affecting wavespeed in an RDE. A strong mode characterized by speeds approximately 85-100% Chapman-Jouguet and a marginal mode with speeds approximately 60-70% CJ. The change in operating modes is due to the autoignition of the pre-detonation mixture as the mass fraction of products circulated back into the reactants increases. It was found that even though the mixture had begun to deflagrate, there is still enough residual reactants to support a weakly propagating detonation wave. This marginal detonation regime was found to predict the experimentally measured wavespeeds observed in the premixed RDE at AFRL.