A
scramjet (
supersonic combusting ramjet) is a variant of a
ramjet airbreathing jet engine in which combustion takes place in
supersonic airflow. As in ramjets, a scramjet relies on high vehicle speed to forcefully compress the incoming air before combustion (hence
ramjet), but a ramjet decelerates the air to
subsonic velocities before combustion, while airflow in a scramjet is supersonic throughout the entire engine. This allows the scramjet to operate efficiently at extremely high speeds: theoretical projections place the top speed of a scramjet between and .