A ramjet engine is a propulsion machine in which the fuel is burned in a tube, or duct, together with the compressed air generated by the forward speed of the aircraft. It lacks the compressor and turbine that are essential parts of the turbojet engine. Thus, the ramjet engine is a simple design, which is composed of an inlet, a combustion zone, and a nozzle.
How does it works?
The air enters the inlet, where it is compressed. Then it flows into the combustion zone where it gets mixed with fuel and burned. Next, the hot gases are expelled through the nozzle, generating a thrust. The operation of the ramjet depends on the inlet to decelerate the incoming air to raise the pressure in the combustion zone. Therefore, the pressure rise makes it possible for the ramjet to operate. The higher the velocity of the incoming air, the greater the pressure rise. It is for this reason that the ramjet works best at high supersonic speeds. At subsonic velocity, it is inefficient, and to start the ramjet, air must enter the inlet at a relatively higher velocity.
At high supersonic flight velocities, a very large pressure rise is generated, which is more than enough to support the operation of the ramjet. If the inlet must decelerate a supersonic high velocity airstream to a subsonic velocity, large pressure losses will result. This deceleration process also causes a rise in temperature. At some limiting flight speed, the temperature will approach the limit set by the wall materials and cooling methods. Therefore, when the rise in temperature reaches the limit, it may not be possible to burn fuel in the airstream.
Below, a basic diagram of a ramjet engine.
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