As in ramjets, a scramjet relies on high vehicle speed to compress the incoming air forcefully before combustion (hence ram jet), but whereas a ramjet decelerates the air to subsonic velocities before combustion using shock cones, a scramjet has no shock cone and slows the airflow using shockwaves produced by its ignition source in place of a shock cone.

In summary, the key difference between ramjets and scramjets is that scramjets can operate at higher speeds due to their ability to handle supersonic air velocities during the combustion process, while ramjets must slow the air down to subsonic velocities before combustion.

A key difference is that the Ramjet has a clear distinction between the compression, combustion, and exhaust sections of the engine. Scramjet, due to its design and the speed at which it operates, blends these sections together, making for a more integrated flow.

Ramjets are very helpful in applications featuring a small, focused, and straightforward mechanism for high-speed operation, such as missiles. The acronym Scramjet stands for Supersonic Combustion Ramjet. It is distinguished from the ramjet by the fact that combustion occurs at supersonic air velocity inside the engine.