Ramjets are used to provide propulsion on a number of high speed aircraft. Since they do not contain moving parts, ramjets have a distinct advantage over turbojets. They are lighter and much simpler in construction.
How Do Ramjets Work?
A typical ramjet consists on an inlet, a combustor, a flame holder, and an outlet nozzle. When an aircraft travels at high speeds, its forward motion forces air into a specially shaped inlet. This compresses the air to a high pressure and reduces it to a subsonic speed. Since air is compressed to a high pressure by the inlet, ramjets do not need the compressor stages used in a turbojet.
In the combustor, fuel is injected into the compressed air. This is ignited using a flame holder that localises the combustion process. This ensures that combustion occurs sub-sonically and the flame does not get "blown out" by the high air speeds.
The combustion of fuel causes rapid expansion of the gases leaving the flame holder. They are accelerated through the outlet nozzle at a high velocity. This provides the aircraft with a forward thrust and pushes it forward through the air.
Conclusion
The main disadvantage of ramjets is that they are not able to work at low flight speeds. This is because they rely purely on the forward motion of the aircraft to compress the air entering them. However, as aircraft velocity increases, ramjets continue to increase in efficiency. This makes them an ideal propulsion device for aircraft missiles.
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Cut and pasted. The clever bit of ramjets (I think) is if you can get them moving at a sufficient velocity, then they work without the moving parts you would normally find in a jet engine.
adam
