Altitude testing of the hypersonic turbojet engine at Mach 2 flight condition

Research on hypersonic turbojet engine with air-precooling system is under development in JAXA for the propulsion system of hypersonic transport. A notable feature of this engine is to use an air pre-cooling device using liquid hydrogen fuel as a coolant in order to protect the turbo-machinery from aerodynamic heating under hypersonic flight conditions. JAXA's recent model of the hypersonic turbojet engine is developed for a Mach 2 flight test with a balloon-launched missile-like vehicle. This paper reports pre-flight verification test results of the engine in altitude test facility. High altitude environment was formed in a combustion wind tunnel facility in JAXA's Akiruno Research Center. The wind tunnel consists of a vacuum chamber and a water ejector exhausting air including air-hydrogen combustion gas. Air flow rate and pressure was regulated properly with flow control valves connected in front of the engine. It was found that acceleration of rotational speed in flight conditions is larger than that in sea level condition. In the sea level static condition, turbine pressure ratio gradually increases with compressor rotational speed and pressure ratio, therefore the power for accelerating rotational speed is little at low rotational speed, while the wind-milling engine has plenty of turbine power independently from the compressor status. Turbine inlet temperature was found to be reduced by 200 K due to that the turbine power is enough.