Use of Fuel Injection to Attenuate Scramjet Inlet Recirculations

In this work, we propose a novel approach to reduce the size of the shock-induced recirculation regions in scramjet inlets through the use of ramp fuel injectors. The study is performed using UArizona’s CFDWARP code solving the Favre-averaged Navier-Stokes equations closed by the revised Wilcox kω model with dilatational dissipation and rapid compression corrections. The results obtained are representative of hydrogen fuel injected after the first shock of a 2-shock scramjet inlet at a flight Mach number of 7 and an altitude of 27 km. Injecting fuel in the inlet leads to particularly high values of the cross-stream velocities which reduce the size of the recirculation bubbles. This is attributed to the fuel having a lower density than the air and thus being accelerated more strongly by the pressure gradients. As opposed to previous methods which achieved partial reduction of the separation length, fuel injection can lead to a complete elimination of the recirculation bubbles in scramjet inlets. To eliminate recirculations, only one-third of the fuel needs to be injected in the inlet with the rest injected in the combustor as usual.