Jet Engines (Part 3) Scramjet Engine The Scramjet (Supersonic Combustion Ramjet) has evolved out of the ramjet engine and extends the operational velocity of the ramjet into that of hypersonic velocities ( speeds in excess of Mach 5).  As the name says, the key difference in the scramjet to that of the ramjet is that the air passing through it is not slowed to subsonic speeds prior to entering the combustion chamber.  The operating velocities and altitudes of the various engines are clearly shown in the following chart.