Combustion modes of hydrogen jet combustion in a cavity-based supersonic combustor

Optical diagnosis-based combustion experiments were conducted to investigate the characteristics of cavity assisted hydrogen jet combustion in a supersonic flow with a total pressure of 1.6 MPa, a total temperature of 1486 K, and a Mach number of 2.52, simulating flight Mach 6 conditions. A supersonic combustor with a constant cross-sectional area was employed with several cavity configurations, fueling schemes and equivalence ratios. It was found that stable combustion could not be obtained without a cavity, indicating that pure jet-wake stabilized combustion could not be achieved and the cavity acted as a flameholder. Three combustion modes were observed for the cavity assisted hydrogen jet combustion: cavity assisted jet-wake stabilized combustion, cavity shear-layer stabilized combustion, and combined cavity shear-layer/recirculation stabilized combustion. The cavity assisted jet-wake stabilized combustion was observed to be the most unstable mode, accompanied by intermittent blowoff under the present conditions, while the combined cavity shear-layer/recirculation stabilized combustion mode seemed to be the most robust one.