Really High Speed Propulsion by Scramjets

A quiet revolution is currently taking place in the field of propulsion, as engineers begin to appreciate the remarkable capability of the scramjet. The scramjet, or supersonic combustion ramjet, is a very simple device consisting only of an intake, combustion chamber and nozzle. It differs from the ramjet in that, at hypersonic speeds, the air velocity is only decreased by a few per cent in the inlet and the combustion heat release occurs at supersonic velocity. Although its efficiency is small at low supersonic speeds, FIG. 1 shows that it can achieve high efficiency over a very wide velocity spectrum. Furthermore, for much of this range, a fixed geometry (Ref. 2) can be used with little loss in efficiency (as indicated by the dashed line on FIG. 1), thus presenting unparalleled capability for a simple engine unit.