OH PLIF Imaging of Supersonic Combustion Using Cavity Injection

Abstract

Planar laser-induced fluorescence of the hydroxyl radical is used to investigate a cavitybased fuel injection system for scramjet operation at a flight Mach number of 11.5. Hydrogen and ethylene fuels are compared over a range of fuel-lean global equivalence ratios. Both fuels show evidence of combustion at each fuel injection pressure. Hydrogen burns diffusively in the shear layer and further downstream, with penetration distance increasing linearly with injection pressure. The combustion in the cavity shear layer sheds regular vortices. Ethylene behaves similarly to hydrogen at the lower equivalence ratios but shows evidence of intense, localized combustion at the highest equivalence ratio. In all cases combustion occurs in the shear layer above the cavity rather than in the recirculating cavity flow.