A scramjet (supersonic combustion ramjet) is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow. As in ramjets, a scramjet relies on high vehicle speed to forcefully compress and decelerate the incoming air before combustion (hence ramjet), but whereas a ramjet decelerates the air to subsonic velocities before combustion, airflow in a scramjet is supersonic throughout the entire engine. This allows the scramjet to operate efficiently at extremely high speeds: theoretical projections place the top speed of a scramjet between Mach 12 (9,100 mph; 15,000 km/h) and Mach 24 (18,000 mph; 29,000 km/h). The fastest air-breathing aircraft is a SCRAM jet design, the NASA X-43A which reached Mach 9.6. For comparison, the second fastest air-breathing aircraft, the manned SR-71 Blackbird, has a cruising speed of Mach 3.2 (2,100 mph).

The scramjet is composed of three basic components: a converging inlet, where incoming air is compressed and decelerated; a combustor, where gaseous fuel is burned with atmospheric oxygen to produce heat; and a diverging nozzle, where the heated air is accelerated to produce thrust. Unlike a typical jet engine, such as a turbojet or turbofan engine, a scramjet does not use rotating, fan-like components to compress the air; rather, the achievable speed of the aircraft moving through the atmosphere causes the air to compress within the inlet. As such, no moving parts are needed in a scramjet. In comparison, typical turbojet engines require inlet fans, multiple stages of rotating compressor fans, and multiple rotating turbine stages, all of which add weight, complexity, and a greater number of failure points to the engine.

Due to the nature of their design, scramjet operation is limited to near-hypersonic velocities. As they lack mechanical compressors, scramjets require the high kinetic energy of a hypersonic flow to compress the incoming air to operational conditions. Thus, a scramjet-powered vehicle must be accelerated to the required velocity by some other means of propulsion, such as turbojet, railgun, or rocket engines. In the flight of the experimental scramjet-powered Boeing X-51A, the test craft was lifted to flight altitude by a Boeing B-52 Stratofortress before being released and accelerated by a detachable rocket to near Mach 4.5.

While scramjets are conceptually simple, actual implementation is limited by extreme technical challenges. Hypersonic flight within the atmosphere generates immense drag, and temperatures found on the aircraft and within the engine can be much greater than that of the surrounding air. Maintaining combustion in the supersonic flow presents additional challenges, as the fuel must be injected, mixed, ignited, and burned within milliseconds. While scramjet technology has been under development since the 1950s, only very recently have scramjets successfully achieved powered flight.

Read more about Scramjet:  History, Design Principles, Theory, Applications

Other articles related to "scramjet":

Scramjet Programs - Programs - X-15
... Among other things, one of the changes was provisions for a dummy scramjet to test if wind tunnel testing was correct ... flight of the X-15-A2 (flight 188), the shock waves sent out by the scramjet at Mach 6.7 caused extremely intense heating of over 2,700 °F (1,480 °C) ... limited due to the limited flights of the scramjet before the X-15-A2 and the X-15 project on the whole were cancelled.1 ...
The Hy-V Scramjet Flight Experiment
... The Hy-V Scramjet Flight Experiment is a research project being led by the University of Virginia whose goal is to better understand dual-mode scramjet combustion by analyzing and comparing wind ...
Scramjet Programs - Programs - Russia
... First working scramjet "GLL Holod" in world flies on 28 November 1991 reaching speed mach 5.8 ... French support successfully launched a scramjet engine "Holod" in Kazakhstan6 ... Russian Central Institute of Aviation Motors (CIAM) to test a dual-mode scramjet engine and transfer technology and experience to the West ...
Scramjet - Applications
... Scramjet vehicle has been proposed for a single stage to tether vehicle, where a Mach 12 spinning orbital tether would pick up a payload from a vehicle at around 100 km and carry it to orbit ...
Hy Shot - Overview
... The project has involved one launch of the scramjet designed by the British company QinetiQ, and the successful launch of one engine designed by the University of ... The first successful launch (Hyshot II) was of a University of Queensland scramjet on 30 July 2002 ... It is believed by many to be the first successful flight of a scramjet engine, although some dispute this and point primarily to earlier tests by Russian scientists ...