Investigation of Combustion Structure and Flame Stabilization in an Axisymmetric Scramjet

The combustion characteristics and flame stabilization mechanisms in an axisymmetric scramjet with a high-enthalpy inflow are investigated numerically in this paper. To consider the strong compressibility induced by the high Mach number, a pressure-related flamelet/progress variable model is proposed, examined, and applied, which can efficiently relate the database to the local pressure and thus more accurately consider the effect of pressure changes on chemical reaction rates. On this basis, the cold flow and combustion flowfields are analyzed; it is found that the mixing process is mainly dominated by a large-scale flow structure, and the prominent shock waves further enhance the mixing and combustion intensity. The whole combustion process exhibits multiscale characteristics in time and space, and the intermediate's oxidation process determines the subsequent generation of end products and the primary heat release. The diffusion combustion and the scramjet mode dominate the main reactive zone: most of which satisfies the basic assumption of flamelet. The upstream recirculation zone acts as a hot reactive tank, which is a self-sustaining ignition source to shorten the ignition delay time and maintain flame stability.