Enhanced ignition with oxygen addition into cavity in expanding combustor of scramjet was conducted experimentally. The effects of different methods of oxygen addition on the characteristic of flame distribution and intensity of combustion in cavity were investigated with high speed camera. For combustor with double cavities installed in parallel, the process of flame spread from the side of cavity with oxygen addition to the opposite one was observed. Results confirm that the performance of cold-start in combustor can be improved with oxygen addition which can intensify the combustion within cavity due to modulation of the fuel concentration distribution. Once stable combustion obtained, two types of flame existing in cavity can be distinguished, namely trapped flame within cavity due to local feedback of heat release in recirculation zone and flame surrounding the shear layer because of full feedback of pressure response in the whole combustor. For double-cavity-combustor, the first step of fully pressure established circumstance in single cavity is necessary for flame propagation to the other side.
