Investigation on flame characteristics approaching thermal chocking in a cavity-based supersonic combustor

Abstract

This study experimentally investigated the combustion process in a cavity-based supersonic combustor at the inflow condition of Mach 2.92 with stagnation pressure 2.6 MPa and stagnation temperature 1530 K. Time-averaged flame distribution and oscillation characteristics were revealed by post-processing CH* chemiluminescence images. Wall pressures along the combustor bottom wall were also measured to provide quantitative information. Representative cascaded injection set-ups upstreaming the cavity were selected to compare ethylene flame characteristics. It is found that the combustion process is approaching thermal chocking when increasing the equivalence ratio to 0.8 according to the one-dimensional analysis of the Mach number distribution. At the same equivalence ratio, increasing the number of the cascaded injectors by lowering the injection pressure is not beneficial for the combustion enhancement, indicating that the injection pressure is also a key factor affecting the combustion heat release. However, increasing the injection pressure can cause obvious flame oscillations above the cavity as well as increasing the axis distance of the injectors. As a result, the injection scheme with two cascaded injectors which have the injection distance of 0.1 and 0.4 time the length of the cavity floor, respectively, upstreaming the cavity is suggested as a favorable scheme for scramjet applications.