JET ENGINE - CONSTRUCTION, WORKING, OPERATION

MECHANICAL TIPS AND STUDY MATERIAL

In 1905, when first plane was invented used SI engine which used piston- cylinder arrangement. The fuel was compressed to develop large pressure and then burned which helped to run turbine and subsequently develop thrust to lift the plane. This is old story and today we are highly advanced and succeeded in attaining supersonic speed with help of jet engines. Today we will look at the outline, construction and working of such jet engines. Today most of the fighter planes, Boeing and airbus uses such engines to generate thrust.

Principle of operation

Newtons third law of motion says "every action has equal and opposite reaction". This law is completely applicable on jet engines as in case of such engines the exhaust coming out from back side pushes the body in forward direction.

You might have noticed a skeeter, who drags his feet in backward direction and generates motion in forward direction. This same principle works for jet engines.

Explain the working of jet engine.

A jet engine is made up of mainly five major component

• Inlet fan
• Compressor
• Combustion chamber
• Turbines
• Exhaust nozzle

The working of jet engine is very simple and easy to understand.

• There is a fan at front section which rotates at high speed and sucks air into the compressor. The air sucked is relatively cold.
• The compressor chamber helps to compress the air and it may be up to 6-9 times of its initial state.

• The compressed air is then passed to combustion chamber (next to compressor) where fuel (kerosene) is sprinkled and it is mixed with compressed air in proper ratio. This mixture is allowed to burn. The burning of fuel-air mixture generates temperature above 950°c and then directed to turbine blades.
• The turbines has set of blades which rotates as the hot exhaust passes over the. The turbine is mounted on the same shaft on which fan and compressor is mounted. When blades of turbine rotates, the shaft also rotates hence the fan and compressor rotates. This helps to save engine power to rotate compressor and fan individually.
• The exhaust is then forced through exhaust nozzle. This is  tapered section which helps to speed up the exhaust gases as the area of cross section keeps reducing. The speed of the exhaust is almost double of that at inlet. This generates thrust required to accelerate object in forward direction.
• Further in cases of military fighters some times extra speed and thrust is required during operation and war. To meet such demand fuel (kerosene) is sprinkled at the exit of the exhaust nozzle that burns and generate extra thrust. Though it consumes large fuel but can accelerate the machine at high rate.