Experimental Testing of an Airframe-Integrated Three-Dimensional Scramjet at Mach 10

Freejet experiments have been conducted in a shock tunnel with a small airframe-integrated three-dimensional scramjet engine. The goal of the investigation was to examine the influence of airframe integration on the engine operation. The tests were conducted at a condition replicating flight at Mach 10.4 and a dynamic pressure of 48 kPa. The internal flowpath featured a rectangular-to-elliptical shape transition inlet designed for flight at Mach 12, an elliptical combustor with a constant area and diverging section, and a three-dimensional thrust nozzle. This flowpath was integrated with a forebody and streamlined external geometry similar to what would be expected on a flight vehicle. Gaseous hydrogen fuel was injected either through portholes on the inlet or a combination of inlet injection with a series of portholes behind a rearward-facing step at the combustor entrance. Experiments at a range of fuel equivalence ratios indicated that both fuel-injection schemes produced robust combustion without the use of ignition aids. Comparison with semifreejet tests of a three-times scale engine with a truncated forebody showed a slight reduction in the overall combustion generated pressure rise in the current experiments. These results indicate that airframe integration does not lead to significant degradation in the performance of this engine.