Abstract: Experiments are designed to investigate the transient fluid-combustion phenomenon during simulated transient acceleration and deceleration between flight Ma5.0~6.0. Flow induced ram-scram mode transition and thrust abruption were observed. The transient fluid-combustion evolutions were characterized with high speed Schlieren imaging and summarized into four phases. The fluid phenomena were discussed based on the impulse function analysis. The accumulated heat release from the thermodynamic cycle analysis dominates the mode transition and thrust abruption process. The isolator pseudo-combustion shock train system is the dominating flow feature during the mode transition. The backpressure induced by the supersonic crossflow contributes to maintain thrust. In addition, the heat transfer and boundary layer disturbance could shift the combustion mode transition limits.