Flame Propagation and Oscillation Characteristics in a Liquid-Kerosene-Fueled Dual-Cavity Scramjet Model Combustor

Combustion oscillations pose considerable threats to scramjets; however, they have rarely been investigated by high-fidelity transient simulations using practical liquid hydrocarbon fuel. Here, flame dynamic evolutions and relevant flow mechanisms in a liquid-kerosene-fueled dual-cavity scramjet combustor are numerically investigated by the improved delayed detached-eddy simulations using the Eulerian–Lagrangian method, with particular emphasis given to the effects of the interaction between fuel spray dynamics and combustion. Results suggest that the flame evolution can be divided into two key processes, namely, the flame flashback from the ignition position and the subsequent low-frequency flame oscillation near the fuel injector. During the flame flashback, combustion-induced backpressure rise promotes flow separation of the upstream boundary layer with the formation of a separation shock wave, which creates favorable conditions for ignition and serves as the dominant factor of flame flashback. During the low-frequency flame oscillation, when the flame and the separation region are at downstream positions, the intensified heat release induces a higher backpressure, which drives the flame to propagate forward. Afterward, a weaker diffusion flame is formed because fuel droplets and fuel vapor are confined in the subsonic region, and consequently, the reduced heat release and backpressure make the flame unable to withstand the high-momentum airflow and force flame recession.