Working principle of jet engine

For understanding the working prince of jet engine, first we have to know about the propulsion of a jet engine.



Propulsion:- propulsion means to push forward or drive an object forward.A propulsion system is a machine that produces thrust to push an object forword .On airplane, thrust is usually generated through some application of Newton 's third law of action and reaction.A gas, or working fluid, is accelerated by the engine ,and the reaction to this acceleration produces a force on the engine.
The term jet propulsion refer to the action produced by a reactor to the ejection of matter.For example, , when the matter in a typical rocket (like gunpowder in fireworks) is ignited, the resulting chemical reaction produce heat and gases, which escape from the rocket and cause it to move forward. The oxygen necessary for combustion is carried(in tanks or in a combined from) in the rocket itself on the air inducted into the engine to supply the necessary oxygen.After heat is released by the combination, the hot gases are accelerated through the engine so that the exit velocity is greater than the airstream velocity.

Turbojet:-


  • It consists of diffuser at entrance which slows down the air (entering at velocity equal to the plane speed)and part of the kinetic energy of the air stream is converted into pressure:this type of compression is called as ram compression. 
  • The air is further compressed to a pressure of 3 to bar in a rotary compressor(usually of axial flow type. 
  • The compressed air then enters the combustion chamber (C.C) where fuel is added.The combustor fuel place at sensible constant pressure and subsequently temperature rises rapidly.
  • The hot gases than enter the gas turbine where partial experience take place. The power produced is just sufficient to drive the compressor, fuel pump and other auxiliaries. 
  • The exhaust gases from the gas turbine which are at a higher provides a forward motion to the aircraft by the jet reaction (Newtons third law of motion) 
At higher speeds the turbojet gives higher propulsion efficiency. The turbojet are most suited to the rcrafts travelling above 800 km/h.
     The overall efficiency of a turbo jet          is the product of the thermal                      efficiency of the gas turbojet plant            and the opulsive efficiency of the              jet(nozzle).
  • Ramjet Engine:-Ramjet produce thrust by ejecting a smaller mass of material at higher velocity than do turbofan engines.

     Fuels contain a large quantity of              protential energy, which is rapidly          released during combustion. A portion of this heat energy is converted into useful work, moving the vehicle through the atmosphere or into the atmosphere. The very fuel efficient turbofan engines used in modern commercial aircraft engines attempt to minimize the latter portion.To do so, impart a moderate increase in the mass velocity to the combustion products for the large mass of air drawn through the engine in a given time. But turbojet and  ramjet engine, which meet more demanding supersonic flight requirements, are less fuel efficient.
A pulse jet engine (or pulse jet)is a type of jet engine in which combustion occurs in pulses.A pulse jet engine an be made with few or on moving parts ,and is capable of running statically(ie.it does not need to have air forced into its inlet typically by forward motion).
 Pulse jet engines are a lightweight from of jet propulsion, but usually have a poor compression ratio, and hence give a low specific impulse. 
One notable line of research of pulse jet engines includes the pulse detonation engine which involves repeated detonations in the engine, and which can potentially give high compression and good efficiency.

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