Experimental study on the flame stabilization mode in the rear-wall-expansion cavity

Abstract

The present study experimentally investigates the transition of flame stabilization mode at Ma = 2.92 using a model scramjet combustor. The combustion mode is analyzed by pressure measurement and quasi-one-dimensional analysis. The effects of both equivalence ratio and aft wall offset on flame behaviors are further characterized by CH* chemiluminescence. The results show that the transition from cavity stabilized combustion mode to jet-wake stabilized combustion mode is realized by increasing the equivalence ratio. And the quasi-one-dimensional analysis reveals that all cases work in the Early Scram mode and approach thermal chocking after increasing equivalence ratio. As the equivalence ratio increases, the amplitudes of the flamebase and heat release gradually increase, and their distributions gradually migrate downstream. The amplitude of flamebase and heat transfer remains prominent with the consistent rise in equivalence ratio. At the same time, the spatial distribution of heat release tends to spread out upstream and occasionally appear upstream of the leading edge of the cavity, indicating that the flame stabilization mode transforms from cavity stabilized combustion mode to jet-wake stabilized combustion mode. The spatial variation of local heat release rate is responsible for the transition of flame stabilization mode. A slight aft wall offset promotes the transition from cavity stabilized combustion mode to jet-wake stabilized combustion mode at a higher equivalence ratio.