Fuel pre-injection in hypersonic inlet can greatly elongate the mixing length of the fuel in hypersonic inlets, and hence enhcance the mixing efficiency. It can further be utilized for the flow-control in hypersonic inlets. However, different to the supersonic inflow condition in scramjet combustors, pre-injected fuel must mix directly with high speed incoming flow at Mach number over 4 or maybe even hypersonic. The fuel mixing characteristics will hence be significant different. The shock-fuel multi-interaction phenomena is also noticeable. By adjusting the injector pressure, fuel pre-injection can control the oblique shock to get "shock on lip" for a better inlet performance. In the present work, four different injectors were used to investigate their influences on mixing efficiency and shock control. A basic 2-dimensional hypersonic inlet which was designed at Mach 5 at 26km was applied. The results indicated that "shock on lip" can be obtained for the inlet at Mach 6 for all injector configurations, whereas the mixing efficiency varied significnatly. Five parallel injectors achieved the fastest fully-mixing at a relatively low injector pressure.
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