Flame stabilization modes in a cavity-based scramjet combustor with different fuel injection ratios

The impact of the upstream and downstream fuel injection ratio on the flame stabilization combustion modes in a cavity-based scramjet was investigated. Three different injection schemes with global equivalence ratio of 0.73 were comparatively researched. The kerosene injection ratios in upstream and downstream regions were 3:1, 1:1, and 1:4. Three typical flame stabilization modes and a transition combustion mode were identified by using multispectral imaging, high-speed framing of CH* chemiluminescence, and wall pressure measurement. The experimental results showed that the cavity shear layer stabilization mode occurred in a combustor with 75% fuel upstream injection ratio. When the fuel upstream and downstream injection ratio was 1:1, the cavity-jet-wake stabilization mode and cavity-assisted shear layer-jet-wake stabilization mode occurred alternately. The proportion of stable combustion area increased by 43.36% and 35.87% compared with the fuel upstream injection ratio of 75% and 20%, respectively. The peak CH* signal region with cavity-jet-wake stabilization mode occurred at the slope of the back edge of cavity and the downstream platform of the cavity. The peak CH* signal region with the cavity-assisted shear layer-jet-wake stabilization mode occurred simultaneously at the shear layer and the slope of the back edge of cavity. With decrease in the fuel upstream injection ratio to 20%, the flame stabilized in the jet-wake. The time-resolved flame temperatures in the case when fuel was injected equally in the upstream and downstream regions were 45 and 221 K higher than those in the cases with ratios of 3:1 and 1:4. The cavity-jet-wake stabilization mode was more beneficial to the operation of the scramjet engine.