Evaluation of Oblique and Traverse Fuel Injection in a Supersonic Combustor

The oblique and traverse configurations of injecting gaseous fuel in a low-aspect-ratio supersonic combustor are characterized and compared numerically using a validated code. Non-reacting conditions are considered, where fuel is simulated by helium. The combustor, which has a rectangular cross-section of constant span, is attached to a Mach 2 nozzle and expands along the top and bottom walls. A choked wall port is used for both injection configurations. Different sets of operating conditions have been simulated. It was found that injecting fuel obliquely results in higher efficiency as well as effectiveness. Unlike the traverse configuration, oblique injection makes use of the beneficial interaction of the injection-induced shock waves with the air/fuel shear layer. This interaction was proven in previous research to be effective for mixing enhancement in supersonic flows. However, in contrast with the results of previous research, normal or oblique injection at large angles (30° or 60°) is not necessary for the achievement of sufficient mixing in supersonic flows. Substantial mixing improvement was found at angles as small as 5°. Fuel injection at such small angles improves the fuel-air mixing while minimizing the injection-induced pressure losses, which leads to increased thrust. Our results on mixing under non-reacting conditions provide good preliminary insights on a more favorable fuel injection configuration that provides better mixing with lower losses and higher thrust.