Characterization of Dual-Mode Scramjet With Distributed Fuel Injection

This study aims to characterize the behavior of a dual-mode scramjet combustor with distributed ethylene fuel injection. Experiments were performed in a cavity-stabilized model featuring upstream and downstream injectors, with the downstream fuel fraction varied between 0% and 37%. Pressure measurements, high-speed CH* chemiluminescence imaging, and high-speed shadowgraph imaging were used to examine how the fuel-injection distribution influences flame stabilization modes, thermal choking, and shock train dynamics. For sufficiently high equivalence ratios, injecting 37% of the fuel downstream yielded a stable jet wake flame, whereas upstream-only injection at the same conditions resulted in an oscillating flame between the cavity and the fuel injector. A thermal choking regime was established as a function of equivalence ratio and downstream injection fraction. Shock train locations for the thermally choked cases, obtained using a pressure standard-deviation criterion, shifted upstream with increasing equivalence ratio or decreasing downstream fuel fraction. These results provide new insight into the impact of fuel injection distribution on flame stability and shock train positioning in a dual-mode scramjet combustor.