The Deceptively Simple Ramjets
What is a Jet engine and how is it different from a Rocket engine?
Both a jet engine and a rocket engine function by expelling hot gases that generate thrust. The main difference between the engines is that a rocket carries its own oxygen whereas jet engine gets the oxygen from the atmosphere, hence known as “Air-Breather”.
How does a jet engine work?
A traditional Jet Engine used in aeroplanes, also known as Turbojet, takes in air with the help of a fan. This air is then passed through a number of turbines which compress the gas and are let into the combustion chamber. It is very important for this air to be compressed for the engine to work efficiently. In combustion chamber, fuel is ignited and the air expands. These hot exhaust gases escape at a very high speed imparting a high amount of momentum to the engine.
Jet engines can operate around 0-3.5 Mach.
Ramjets…
In a Jet engine, it was the job of the compressors to compress the air. But at a high speed, we don’t need the compressor. Reducing the speed of the air from Supersonic to Subsonic would give us the Temperature and Pressure where we can do good combustion. So after removing the compressor and turbines, we are left with something that looks like this…
This is called a Ramjet. The air enters the inlet at supersonic speed and is reduced to subsonic by an obstacle and the gases are compressed.
You may have noted that there is no movable part in a Ramjet. Also, it is important to observe that the engine requires the air to pass in the inlet at Supersonic speed. This makes it unable to work at low velocities. This is one of the drawbacks of the engine. The engine has to attain a minimum velocity to be operable. This engine works at speed of 3 Mach – 6 Mach. Ramjet has been more efficient with fuel than a Jet Engine.
Mostly this engine is used in Missiles but it is also seen in Aircrafts and with some variations, in Helicopters.
Wait, there is more…
At even high speeds, the pressure and temperature created by lowering the velocity in a Ramjet give rise to Shockwaves which itself reduces the efficiency of Combustion.
Scramjet (Supersonic-Combustion Ramjet)
So, a Scramjet is just like a Ramjet. The only difference is that in Scramjet the air enters the combustion chamber at only slightly reduced velocity, yet supersonic.
Scramjets are a new development, not many engines work on this principle yet. A Scramjet works over 6 Mach of velocity. Its upper limit is not yet found.
An Article By: Piyush Bhujbal
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