Distinctive features of galloping detonation in a supersonic combustible-mixture flow under an inert gas layer

Abstract

The problem of detonation initiation in a supersonic flow of a stoichiometric propane-air mixture occupying partially or completely the cross-section of a plane channel is considered. The initiation in the flow is produced by a step or a wall completely cutting off the flow. The study is conducted within the framework of one-stage combustion kinetics. A numerical method based on the Godunov scheme is employed. The critical conditions for detonation formation are determined in terms of the oncoming flow velocity. A previously unknown mechanism of detonation propagation is found; it is related with the presence of the combustible mixture in the wall layer under an inert gas layer. It is due to the formation of a complicated wave structure of the flow characterized by the penetration of a shock wave formed in the inert gas layer into a combustible mixture layer ahead of the detonation wave with the result that the latter layer is heated and ignited. The process as a whole is periodic in nature, as distinct from the conventional cellular detonation in a homogeneous fluid. Many problems arise in connection with the use of detonation in engines and other power plants. The most important among them are detonation excitation and stabilization in combustion chambers. The detonation initiation within a layer under conditions of unbounded space and a fluid at rest was experimentally investigated in [1]. In the case of a combustion chamber bounded in the transverse direction, some new effects accompanying the detonation might be expected.