Application of Inlet Injection to a Three-Dimensional Scramjet at Mach 8

An investigation of inlet injection in a scramjet having a three-dimensional inlet and an elliptical combustion was undertaken. Experiments were conducted using a test flow simulating a Mach 8.1 flight condition with an altitude of 32 km. The objective was to determine the feasibility of reducing the combustion-chamber length by injection of hydrogen fuel in the inlet. The study involved a self-starting three-dimensional inlet with an overall geometric contraction ratio of 5.80, of which 2.08 was internal. The fuel was injected through multiple portholes in the forward portion of the inlet to allow significant mixing upstream of the combustion chamber. The divergent elliptical combustion chamber had a length sized for fuel ignition and combustion only and used a fluid-dynamic ignition scheme requiring no physical obstructions to the flowpath. Results indicated that inlet injection produced robust combustion at good combustion efficiency over a large fueling range up to an equivalence ratio of 0.92. A further key result was that no evidence of combustion was observed in the inlet. These experiments suggest that fuel injection in the inlet is a promising concept for higher-speed scramjet applications.