scramjet

SCRAMJET:

A scramjet (supersonic combustion ramjet) is a variation of a ramjet distinguished by supersonic combustion. A scramjet, like a ramjet, essentially consists of a constricted tube through which inlet air is compressed by the high speed of the vehicle, a combustion chamber where fuel is combusted, and a nozzle through which the exhaust jet leaves at higher speed than the inlet air. Commercial jet engines use a turbine to squeeze air into the engine then spray fuel into the compressed air and ignite it to produce thrust by funneling it through the back. A scramjet uses the speed of the aircraft to compress the air, so very few moving parts are needed to operate it.

 All scramjet engines have fuel injectors, a combustion chamber, a thrust nozzle and an intake, which compresses the incoming air. Sometimes engines also include a region which acts as a flame holder, although the high stagnation temperatures mean that an area of focused waves may be used, rather than a discrete engine part as seen in turbine engines. Other engines use pyrophoric fuel additives, such as silane, to avoid such issues. An isolator between the inlet and combustion chamber is often included to improve the homogeneity of the flow in the combustor and to extend the operating range of the engine.

ADVANTAGE & DISADVANTAGE:

Unlike a rocket that quickly passes mostly vertically through the atmosphere or a turbojet or ramjet that flies at much lower speeds, a hypersonic airbreathing vehicle optimally flies a "depressed trajectory", staying within the atmosphere at hypersonic speeds. Because scramjets have only mediocre thrust-to-weight ratios, acceleration would be limited. Therefore time in the atmosphere at hypersonic speed would be considerable, possibly 15–30 minutes. Similar to a reentering space vehicle, heat insulation would be a formidable task. The time in the atmosphere would be greater than that for a typical space capsule, but less than that of the space shuttle.

Lack of stealth:

There is no published way to make a scramjet powered vehicle (or any other hypersonic vehicle) have any sort of stealth. This is because the vehicle would be very hot due to its high speed within the atmosphere and it would be easy to detect with infrared sensors. Any[citation needed] aggressive act against a scramjet vehicle during flight would be nearly impossible, however, because of the high speed at which it operates. If the aircraft was covered with RADAR absorbent material (RAM) the scramjet vehicle would be slightly more stealthy at lower speeds and altitudes

APPLICATIONS;

Seeing its potential, organizations around the world are researching scramjet technology. Scramjets will likely propel missiles first, since that application requires only cruise operation instead of net thrust production. Much of the money for the current research comes from governmental defense research contracts.

Space launch vehicles may or may not benefit from having a scramjet stage. A scramjet stage of a launch vehicle theoretically provides a specific impulse of 1000 to 4000 s whereas a rocket provides less than 450 s while in the atmosphere,potentially permitting much cheaper access to space. A scramjet's specific impulse decreases rapidly with speed, however, and the vehicle would suffer from a relatively low lift to drag ratio.