Numerical study on cavity ignition process in a supersonic combustor

Large eddy simulations (LESs) of cavity ignition processes were performed in a 2D ethylene-fueled supersonic combustor with a single rear-wall-expansion cavity based on OpenFOAM. The ethylene combustion was modelled using a 35-step with 20-specie ethylene chemical mechanism, which had been validated by CHEMKIN calculations. The effect on the ignition process of different ignition sites inside the cavity was then studied. It was found that the rear region of the cavity floor is an optimized ignition site where successful ignitions will be achieved. According to different ignition behaviors, two flame extinguishing modes could be identified: blown-off extinguishing mode and flow dissipation extinguishing mode. Blown-off extinguishing mode mainly occurred after ignition near the cavity shear layer, in which the initial flame was blown off directly due to the high speed of the supersonic core flow. Flow dissipation extinguishing mode is likely to occur after ignition near the front and middle cavity floor as a result of severe turbulent dissipations and limited chemical reactions. The study indicates that the movement routine of the initial flame is important for the ignition process, including both moving towards a favorable flow field and forming a large heat release region along the movement.