Each of the jet engine parts performs a specific function, serving the overall purpose of the machine, which is to provide thrust to propel an aircraft, or to drive an AC generator in a power plant. Therefore, the essential parts that make it work are: the shafts, the fan/propeller, low-pressure compressor, high-pressure compressor, combustion chamber (burner), high-pressure turbine, low-pressure turbine, nozzle, the stator vanes/blades, and an accessory gearbox. You have to understand that the fan, low-pressure compressor, and low pressure turbine rotates around the same shaft/axle, while the high-pressure compressor and the high-pressure turbine turns around another shaft.
The fan can only be seen in a turbofan engine, supplying it with extra thrust. The function of the low-pressure compressor is to suck in air through the air intake. Then the high-pressure compressor pressurizes this flow of air, which get mixed with fuel and the hot gas in the combustion chamber. Then the high-pressure turbine converts the highly-pressurized hot gas into rotatory mechanical shaft power or torque, while the low-pressure turbine contributes to the hot gas expansion. Meanwhile the fixed blades of the stator (casing) provide guidance and direction to the pressurized air and hot gas. The accessory gear box is usually located right below the low-pressure compressor and serves to start the engine, containing the hydraulic, air, and fuel pumps.
These working parts are about the same for every type of jet engines. The different lies between a turbojet and a turbofan engine, where the latter is fitted with a larger diameter fan located in front of the low-pressure compressor and sharing the same shaft. This fan not only sucks in air but it also generates a bypass air which provides the engine with an extra thrust, with the portion of the turbine work being employed to turn the fan.
Below, a schematic diagram/drawing showing the different parts of a turbofan jet engine used in commercial aircraft.
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