Freejet testing of the 75%-scale HIFiRE 7 REST scramjet engine

This paper presents results from shock-tunnel experiments of a 75%-scale replica of the HIFiRE 7 scramjet engine. The engine was fuelled with gaseous hydrogen and tested in a freejet mode at a ight Mach number of 7.6 and an altitude of 29 km. The engine was tested at -2 , 0 and +2 angle-of-attack. In these experiments, static pressure and surface heattransfer measurements were taken along the owpath of the engine. The experimental results showed that robust combustion can be sustained in the scramjet engine, hence indicating that the full-scale engines on the HIFiRE 7 payload can operate robustly at the ight conditions with gaseous hydrogen as the fuel. The results also revealed that when the fuel-air mixtures ignite and burn, the surface heat-transfer levels in the combustor and nozzle of the engines can increase by up to three times that of the fuel-o levels. Lastly, the results showed that when hydrogen mass ow rates are kept constant, the absolute pressure levels through the engine for both fuel-o and fuel-on tests increases with the angle-of-attack of the engine, while the surface heat-transfer levels remain approximately constant with increasing engine angles-of-attack.