Scramjet (supersonic combustion ramjet).

A scramjet (supersonic combustion ramjet) is an air-breathing jet engine that relies on the compression of air taken in at supersonic speeds for propulsion. Scramjets are a variant of the standard ramjet air-breathing engine. The key difference between the two is that while the ramjet engine decelerates the air to subsonic velocities prior to combustion, the scramjet relies on the speed of the aircraft itself to forcefully compress the air it takes in before combustion. This means that the airflow within the engine in a scramjet is supersonic at all times. The unique nature of the scramjet is reflected in the term scramjet itself, which is an abbreviation of “supersonic combustion ramjet.” Supersonic refers to speeds greater than that of sound.