Main Parts of a Jet Engine

Compressor
Situated at the front of the engine, the compressor draws air in, pressurises it, then delivers it into the combustion chamber. There are two types of compressor design, centrifugal and axial flow.

The centrifugal flow compressor consists of an impeller supported in a casing which houses a ring of diffuser vanes. The impeller is driven at high speed, by the turbine, and air is drawn in through its center. Centrifugal action forces the air radially outwards and accelerates it into the diverging diffuser outlet, which further increases the pressure. The pressurised air then passes into the combustion system.

The axial flow compressor consists of a number of stages of alternate rotating and stationary aerofoil-section blades which force the incoming air through a convergent angular duct. The rotating blades are carried on discs or a drum and driven by a turbine via a connecting shaft. As the air passes through each stage it is accelerated by the rotating blades and forced rearwards through the static blades, known as vanes, which reduce the velocity and increase the pressure. The pressure is gradually built up as the air passes through the compressor stages until it reaches the combustion system.

Gas turbines often have more than one compressor. This is because many stages of compression are required to achieve a high overall pressure and, since each compressor stage has an ideal rotational speed for best efficiency, if all the stages are on the same shaft only some will run efficiently. To overcome this, the compressor can be divided into two or three parts, each driven by a seperate turbine and rotating at its most efficient speed. This method enables compression ratios up to 30:1 to be achieved, resulting in extremely high efficiency and very low specific fuel consumption.

Combustion chamber
This is an annular tube, or ring of tubes, made from heat resistant steel, in which the fuel and air are mixed and ignited. It is designed to achieve the most efficient combustion of the mixture so that the maximum possible heat energy is extracted from the fuel to give the greatest rise in temperature and hence expansion of gases.

The air from the compressor, at pressures up to 450 pounds per square inch (3.1 MPa), passes into the combustion chamber where it is mixed with the vaporised fuel sprayed from burners located in the head of the chamber. The mixture is ignited, during the engine starting cycle, by igniter plugs located in the combustor. Once ignition has taken place, the igniters are isolated and combustion is continuous.

Turbine
The turbine consists of one or more stages of alternate stationary and rotating aerofoil-section blades. The rotating blades are carried on discs, in a similar way to the compressor, and the discs are connected by a shaft to the compressor rotating assembly. The stationary blades, known as nozzle guide vanes, are housed in the turbine casing. The function of the turbine is to absorb sufficient energy from the hot expanding gases leaving the combustor to keep the compressor rotating at its most efficient speed.