Re: How does jet propulsion work?

How jet and rocket engines work

Jet engines and rocket engines both work using Sir Isaac Newton's Third Law. For every action there is an equal and opposite reaction. In this case, a volume of gas is heated and accelerated out the nozzle of an engine. The gas stream accelerates the craft in the opposite direction. This produces the thrust to drive the aircraft forward or a space shuttle into orbit.

The fundamental difference between jet engines and rocket engines is jet engines use atmospheric oxygen to burn the fuel while rocket engines carry an oxidizer, typically liquid oxygen.

Would a jet engine work in space?

As you may have guessed from the last paragraph, a jet engine, if oxygen was supplied to it, would work and produce thrust in space. It would become a type of rocket engine, though. The currently used method of burning a fuel in a chamber and using a large volume of superheated gas to provide thrust is more efficient for space travel, though.

Different types of jet engines

• Ramjet - In a ramjet, air is compressed by the body of the plane and the inlets as it flows over the plane. Fuel is added and ignited. Hot gasses expelled from the nozzle provide propulsion. The scramjet uses supersonic combustion. Sc/ramjets require another propulsion system to accelerate them to the point where air can be sufficiently compressed. They are, in principle, the simplest of the jet engines and closest to a rocket engine. They require no moving parts. An example of a ramjet was the BOMARC missile.
• Turbojet - In a turbojet, the compressor at the front of the engine is driven by a turbine section located in the middle of the engine. Fuel is added to the compressed air and burned in the combustor section. The hot, rapidly expanding gasses power the turbine and provide thrust when they exit at the back of the engine through the nozzle.
• Turboprop - Turboprop is short for turbo-propellor. The design is almost identical to a turbojet except the compressor section is much larger. Most of the air is directed out the nozzle rather than into the engine. This air provides thrust in a manner similar to a propellor on a WWI era plane but at much higher efficiency.

Related Web sites

• Principles of jet engine operation
• Rolls- Royce Trent Engine
• How a jet engine works
• How a linear aerospike engine works - also covers basics of rocket propulsion

Some suggested reading

• Constant, Edward W., II, The Origins of the Turbojet Revolution (1981)
• Cumpsty, Nicholas, Jet Propulsion: A Simple Guide to the Aerodynamic and Thermodynamic Design of Jet Engines (1997)
• Gunston, Bill, The Development of Jet and Turbo Aero Engines (1995)
• Hosny, A. N., Propulsion Systems, rev. ed. (1974)
• Rolls-Royce, Ltd., The Jet Engine, 4th ed. (1986)
• G.P. Sutton, Rocket Propulsion Elements, Fifth Ed., (1986)