The simplest of jet engines, the ramjet compresses air to subsonic speed by the ram-effect of its forward motion. The compressed air is mixed with fuel within the engine, and ejected through a supersonic nozzle. The ramjet has no significant moving parts.


A supersonic-combustion ramjet (scramjet) is a ramjet in which combustion of the fuel/air mixture occurs at supersonic speeds. The scramjet can therefore achieve greater speeds than a ramjet that slows the incoming air to subsonic speeds before entering the combustion chamber. The scramjet, however, requires acceleration to supersonic speed before it will operate.

Dual-mode scramjet

This refers to an engine that can operate in both subsonic- combustion and supersonic combustion modes – usually as part of a turbine-based combined cycle or a rocket-based combined-cycle concept.

Turbine-based combined cycle

A propulsion system in which a gas turbine engine and a ramjet/scramjet are integrated in a dual-flowpath configuration. The turbine-based combined cycle is aimed at Mach 5 to 8.

Rocket-based combined cycle

A propulsion system in which rocket thrusters are integrated in the ramjet/scramjet flowpath. Aimed at speeds of Mach 5 and beyond.

Two-dimensional engine inlet

Rectangular inlet with straight sidewalls and upper and lower inlet walls.

Three-dimensional engine inlet

An asymmetric, or round inlet that produces lower skin friction, but higher-pressure rise.

Inward-turning inlet

Wedge-shaped inlet structure with reduced surface area, and lower cooling requirement.

Source: Flight International