Experimental investigation of mode transition process in a cavity-based scramjet

Abstract

A directly connected transient scramjet simulator was developed for supersonic combustion experiments to gain a deeper understanding of the process and mechanism of mode transitions in dual-mode scramjet engines. This study presents experimental simulations of flame development under constant combustor inlet conditions with increasing equivalence ratios, utilizing advanced high-speed measurement techniques such as high-frequency static pressure, schlieren imaging, and methylene radical chemiluminescence. The results demonstrated that abrupt changes occurred during the mode transition as the equivalence ratio increased. Specifically, lower equivalence ratios correspond to the shear layer mode, whereas higher equivalence ratios correspond to the jet-wake and jet-front modes. The stable position of the precombustion shock wave is determined by the heat released during combustion, whereas both the precombustion shock wave and the fuel-injection depth determine the combustion mode and flame-anchoring position. Finally, the dynamic variation of shock waves inside the combustor is significant in contributing to abrupt mode transitions.