The afterburner on the SR-71's engine is being fed super-compressed bypass air from the intake. It can ignite the exhaust with comparatively minuscule amounts o

The afterburner on the SR-71's engine is being fed super-compressed bypass air from the intake. It can ignite the exhaust with comparatively minuscule amounts of fuel when compared to a regular turbojet. At speeds beyond Mach 3, you don't even need fuel to ignite the oxygen. The simple friction and drag of the airframe is enough to ignite the oxygen around it and surround the aircraft with superheated plasma.