Effect of shock position on supersonic combustion in a Mach number 8 scramjet combustor

This study delves into the influence of shock position on supersonic combustion characteristics in a Mach number 8 scramjet combustor through direct-connect experiments. An 8° wedge was employed to generate controlled shock waves with various positions while maintaining induced flow loss below 5%. The excited methylidyne radical (CH*) chemiluminescence imaging, schlieren visualization, and wall pressure measurement were utilized to examine combustion intensity and flame stabilization under different shock positions and equivalent ratios. Flame intensity and wall pressure displayed significant increase with the assistance of shock waves. When the primary shock interacted with fuel jets on the windward side, the flame intensity increased by over 23% across all equivalence ratios. Shock waves also demonstrated a measurable regulatory effect on flame stabilization. Shifting shock waves upstream effectively shortened the duration of unstable combustion transition. While flame position oscillation could be suppressed by shock waves, fluctuation in flame intensity persisted. Proper orthogonal decomposition analyses reveal that optimally positioned shock waves remarkably amplified high-frequency turbulence in flow field, thereby accelerating fuel mixing and flame propagation. Considering both combustion intensification and oscillation mitigation, shock wave impinging on the windward side of fuel jets is recommended for application in high Mach number scramjet combustor to achieve excellent performance.