Effects of injection on flame flashback in supersonic crossflow

Abstract An approach that combines numerical, experimental, and theoretical analyses has been implemented to investigate the effects of the injection parameters on the flame flashback phenomenon of supersonic crossflow with a cavity flame holder. In the simulations, a hybrid large eddy simulation (LES)/flamelet progress variable (FPV) combustion model was implemented. The simulations showed a good level of agreement with experimental observations and measurements in terms of the instantaneous and time-averaged results. Higher global fuel equivalence ratios, sharper injection degrees, longer premixing distances, and the presence of multiple injectors promoted the interactions between fuel and incoming flow, resulting in increases in the mixing efficiency and fuel penetration height. Thus, the intense combustion in cavity and downstream enhanced the downstream backpressure and boundary layer separation. The low-speed zone in the interior of the boundary layer is also conducive to combustion enhancement and creates positive feedback. The gradually separated boundary layer forms a thermally choked flow, prompting the flame front to accelerate forward until it reaches the fuel injection position. The theoretical analyses demonstrated that the above factors can effectively influence the balance of heat release and dissipation for the system, reducing the temperature fluctuation thresholds. Thus, the system easily became unstable under the same temperature fluctuation range conditions, once certain temperature fluctuation thresholds in sensitive areas were exceeded. Finally, exhibiting an intense combustion in separation boundary layer and violent flame flashback phenomenon.