Combustion characteristics of a cavity flameholder with a burned-gas injector at the cavity bottom wall in a scramjet model combustor

The combustion characteristics of the cavity flameholder with a burned-gas injector at the cavity bottom wall in the scramjet model combustor was investigated experimentally. The flame structure in the cavity was investigated by direct imaging and OH-PLIF measurement. As the result, four combustion modes were identified: jet-plume mode, jet-wake mode, one-sided cavity mode, and two-sided cavity mode. In response to the experimental results, the effects of the air-stream boundary layer thickness were additionally investigated numerically. Numerical results showed that an increase in the airstream boundary layer thickness adversely affected supported flameholding under conditions of a supersonic air-stream with low total temperature. When the airstream boundary layer becomes thicker, interaction between airstream and burned-gas jet creates a wider boundary layer separation upstream of the cavity leading edge. If the width of the separation region is greater than the width of the jet-plume, additional air entrainment path from separation region decreases static temperature inside the cavity flameholder, which makes supported flameholding difficult. It was concluded that the scramjet combustor needs suppression of the interaction between the supersonic airstream and burned-gas jet or avoidance of the boundary layer separation to avoid supported flameholding failure in a supersonic airstream with a thick boundary layer.