Experimental study on restart control of a supersonic air-breathing engine

To study the dynamic response of a supersonic airbreathing engine and establish control logic for intake unstart, restart control tests were conducted at Mach 3 using a subscale engine model consisting of an axisymmetric intake (inlet) and a turbojet. Assuming that the combustion flame is blown out by intake unstart, restart control follows a sequence. First, after a flow is started the turbojet engine is ignited. Second, the intake is started while the rotational speed and the combustion gas temperature of the core engine are controlled. Third, the intake spike position and the terminal shock position are controlled, and the intake total pressure recovery achieves the design value (60%). The tests were successful, and engine thrust was recovered at approximately 30-40 s after engine start-up. A sudden increase in combustion gas temperature and rotational speed occurred after intake unstart. To reduce the sudden increase in the gas temperature, a new sequence that involved closing a fuel control valve after detection of intake unstart was implemented, and the increase in gas temperature was reduced. To avoid intake buzz, buzz margin control using a bypass door was successfully implemented.