Scramjets - Hypersonic Jet Engines

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The SCRAMJET, simply abbreviated from Supersonic Combustion Ramjet, is the latest evolution of the jet engine family. NASA made the news with each test of the X-43A scramjet craft, so I set about to discover why this type of jet engine should garner so much scientific attention.

Turbojet

The most basic jet engine is the turbojet. As soon as the air enters the front of the engine, the blades of the compressor, compresses the air before funneling it into the combustion chamber. During the compression, not only is the density of the air increased by compressing it in a confined chamber, but the temperature of the air also increases as the air molecules of squeezed closer together.

The resulting air that emerges into the combustion chamber is thereby preheated, and the amount of oxygen per volume is increased to facilitate combustion. This becomes an important factor at increased altitudes, where the air density (and thus also oxygen density) decreases. In the combustion chamber, fuel mixes with the air before being ignited.

As the air-fuel mixture is burned, the gases expand so that the pressure is increased further. Part of this energy is captured by the turbine blades and translated into the rotation of the compressor shaft, and thereby supplying the energy the compressor needs to function.

The rest of the hot gases are forced through the necked-down exhaust nozzle, thus accelerating them further. The force of the hot gases expelled in the exhaust, provides all of the planes thrust.

Turbofan

This a modified turbojet engine in which part of the air compressed in the compressor completely bypasses inner engine core housing the combustion chamber and turbine. Since the bypassed air is compressed and...

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...e the use of scramjets in missiles and satellite rockets is much more realistic than in aircraft. A missile can be fairly easily accelerated by a gun system, but it would be highly difficult to accelerate an aircraft to hypersonic speeds so that the scramjet can take over. Even if a way could be found to accelerate an aircraft, the design shape necessary to handle hypersonic speeds is not suited for subsonic speeds necessary for landings. The craft could be slowed by a system of parachutes, but seems highly uneconomical and impractical for a craft subject to regular use. The other alternative is the development of a hybrid engine that could be switched between subsonic jet operation, to ramjet, and finally scramjet configurations. In the future this may become a viable possibility, but first it will require years of research and testing of scramjet behavior.

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