Influence of hydrogen equivalence ratios on supersonic combustion based on large eddy simulations

Scramjet engines are propulsion systems with high specific impulse performances, which are widely implemented for the realization of hypersonic flight. In this study, the influence of global hydrogen equivalence ratios on supersonic combustion under hypersonic flow was evaluated by conducting a large eddy simulation. First, numerical simulation results revealed a good agreement between the experimentally determined wall pressure and shockwave signal, which verified the accuracy of the numerical method. Moreover, the influence of the equivalence ratio on the characteristics of supersonic combustion was investigated. The results revealed that the complexity of the waveform increased with an increase in the equivalence ratio, owing to the higher combustor pressure and significant interactions between the flames and boundary layer. In particular, the combustion expanded to the center of the flow field, and the average Mach number of the flow field decreased. In addition, the size of the auto-ignition region decreased; however, it was under supersonic flow. The influence of the equivalence ratio on the heat release rate (HRR) under different combustion modes was investigated. The results revealed that the total HRR increased with an increase in the equivalence ratio. Moreover, the majority HRR was in the auto-ignition region, and supersonic combustion was pre-dominant. This study was based on the scramjet model engine without flameholders under hypersonic conditions; therefore, the findings cannot be applied to scramjet combustors under other conditions.