re: Controlled Flame Speed Limited to Mach 5
Faster explosions have been recorded in coal mines, but the high temperatures would destroy engine parts, so there is no practical application. Mach 5 is pretty fast, but the expansion nozzle gets long. But flame speed isn't what limits aircraft speed. Remember, exhaust velocity is relative to the aircraft. Inlet flow velocity and temperature limits the speed of an aircraft. Mass-injection at the inlet has been use to cool the inflowing air at speed exceeding Mach 4, but the exhaust speed is relatively unaffected. Therefore it is common for an airbreathing engine exhaust to exceed Mach 5, but the aircraft engine inlets have greater and greater difficulty in this regime.