Combustion enhancement in rearward step based scramjet combustor by air injection at step base

Numerical simulations were performed to model the non-reacting and reacting flow behind a rearward step flameholder in Mach 1.6 supersonic flow with fuel injection at the step base. The combustor geometry was based on the University of Florida scramjet experimental facility. Turbulence was modeled using k-ω shear stress transport (SST), laminar flamelet was used for combustion modeling. Wall static pressure showed good agreement with experimental data for non-reacting and reacting flow. For non-reacting flow, dummy fuel helium mole fraction distribution in the recirculation region behind the step was validated with planar laser induced fluorescence (PLIF) images in experiments. To improve the combustion characteristics, air was injected in tandem with hydrogen at step base using various configurations. With all fuel injection as baseline, the case with 2 air jets around each fuel jet and air injected at 2 times the stagnation pressure of fuel showed the most improvement compared to other cases. It was most effective in reducing the local fuel richness, shortening the flame length and increasing combustion efficiency