A scramjet is an engine that operates from Mach 6 to Mach 12, i.e. at hypersonic speeds.

Like a ramjet , it compresses the air simply by slowing it down in the air intake, but the speed remains supersonic at the combustor inlet and throughout the engine, which is why this type of engine is called scramjet (for supersonic combustion ramjet).

Research is essentially focused on the fuel injection system (usually hydrogen) and the combustor. It is mainly aimed at optimising mixing and combustion, which must be completed within a very short time, around one millisecond.