Numerical investigation of the auto-ignition of transient hydrogen injection in supersonic airflow

The auto-ignition process in high Mach number airflow is performed by Large Eddy Simulation. The predictions are in good agreement with experiment. The temporal and spatial analysis of the auto-ignition process are carried out. The results show that the auto-ignition process can be divided into five stages in terms of time sequence, and there are three regions in space at the steady state. It is also found that the maximum mass fraction of HO₂ is one of the best indicators to see whether the scramjet working on high Mach number reaches steady state, and the flame stabilization is dominated by auto-ignition. The heat release rate of different combustion modes is calculated. It reveals that the supersonic combustion mode dominates in all stages and regions, but premixed combustion mode dominates only in transient auto-ignition stage and the auto-ignition region.