Supersonic combustion experiments have been performed using three different hydrogen-fuel-injection configurations in a cavity-based combustor with various global fuel-air equivalence ratios. The configurations tested were angled injection at 15° to the flow direction upstream of the cavity, parallel injection from the front step, and upstream injection from the rear ramp. Planar laser-induced fluorescence of the hydroxyl radical and time-resolved pressure measurements are used to investigate the flow characteristics. Angled injection generates a weak bow shock in front of the injector and recirculation zone to maintain the combustion as the equivalence ratio increases. Parallel and upstream injections both show similar flame structure over the cavity at low equivalence ratio. Upstream injection enhances the fuel diffusion and enables ignition with a shorter delay length than with parallel injection. The presence of a flame near the cavity is determined while varying the fuel injection location, the equivalence ratio and total enthalpy of the air flow. The flame characteristics agree with the correlation plot for the stable flame limit of non-premixed conditions. The pressure increase in the cavity for reacting flow compared to non-reacting flow is almost identical for all three configurations. More than 300 mm downstream of the duct entrance, averaged pressure ratios at low global equivalence ratio are similar for all three injection configurations.
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