Combustion characteristics in a supersonic combustor with ethylene injection upstream of dual parallel cavities

Combustion characteristics in a supersonic combustor with ethylene injection upstream of dual parallel cavities were investigated experimentally in a direct-connected test rig with inflow conditions of Ma=3.46, P-o=3.60 Mpa and T-o=1430K. The combustor has a two-dimensional rectangular configuration with single-side expansion. Two open cavities with the same size were mounted on the expanded and horizontal walls, respectively. Static pressure distribution in the axial direction was measured along the centerline of the expanded wall. High-speed flame luminosity and schlieren were used to capture the combustion and flow structures at different equivalence ratios. Two clusters of separated and asymmetric flames were found to be stabilized near the dual parallel cavities in all tests. The flame and flow characteristics changed with the combustion modes. For scramjet mode, no obvious flow separation occurred near the walls and the two flames were both stabilized in the cavity shear layer and recirculation zone. For ramjet mode, the high back pressure resulting from intense heat release induced a large-scale recirculation zone upstream of the cavity mounted on the expanded wall, which supplied a favorable combustion condition and the flame was stabilized in the jet-wake. Meanwhile, there was no obvious separation near the horizontal wall, with the local flame stabilized in the cavity shear layer. It is suggested that the combustion near the horizontal wall should be enhanced to improve the combustion performance and avoid a non-uniform flow field at the combustor exit.