Experimental Study on the Combustion Process in a Scramjet Combustor with a Rear-Wall-Expansion Geometry

In this study, experiments were conducted in a Mach 2.92 supersonic flow to investigate the combustion process in an ethylene-fueled model scramjet combustor with a rear-wall-expansion geometry. It is concluded that at low equivalence ratios, successful ignitions would become rather hard in the cavity with a low rear wall height. Increasing the equivalence ratio could improve the ignition environment within such cavity geometry. During a stable combustion process, the rear-wall-expansion cavity with a higher rear wall height would always achieve an improvement in combustion performance in the combustor. At a relatively high equivalence ratio, when increasing the cavity rear wall height, the flame stabilization mode would vary from cavity shear layer-stabilized mode to cavity-assisted jet wake-stabilized mode, and finally to the thermal choking state. Besides, reaction zones flashback phenomenon is obviously observed during the flame propagation process at such equivalence ratio. It has been demonstrated that the cavity with a lower rear wall height is more able to prevent thermal choking in the combustor.