Dual-mode scramjet engines must operate over a wide range of flight Mach numbers
(Mach~ 3.5 to 8+). For relatively low-speed operation, such engines operate in the thermally
choked ramjet mode. A pre-combustion shock train in the isolator slows the flow to a
subsonic Mach number before the start of the combustor. Unstart occurs when the pre-
combustion shock train moves outside of the isolator into the inlet. This causes an abrupt
mass flow change to the engine which can be catastrophic to the vehicle. Optimal engine …