Published by Milon Hossain Department of EEE Mymensingh Engineering College

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Gas Turbine
Milon

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A Gas Turbine is a rotating engine that receives energy from the flow of combustible
gas.
For example, a jet aircraft whose engine is much larger. This engine is basically
powered by turbofan. Turbofan is an example of gas turbine.
Gas turbine engines use high pressure gas to rotate the blades.
Jet Turbofan

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Structure and Operation of Gas Turbines
In the image above we can see the axial flow gas turbines that are commonly used in
helicopter rotors. Let's talk briefly about how they work.

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Compressor
The compressor compresses the incoming air at high pressure. It is an angled cylinder with small fan blades
to it. In this engine the compressor receives air. When air enters the compressor, its pressure will be much lower and
after compressing the air through the compressor, its pressure will increase by about 30 times.

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Combustion chamber
It basically burns fuel and produces high pressure and high speed gases. High pressure air enters the combustion
chamber. The fuel is then injected steadily from the belt of the fuel injector. Kerosene, jet-fuel, propane or other
natural gas is used as fuel. High pressure air inside the combustion chamber travels at a speed of about 100 miles /
hour and combustion has to be completed in this environment which is almost impossible to do. To solve this
problem, flame holders or cans are used in the combustion chamber. The cans are usually hollow, with heavy metal
parts perforated.
The injector is on the right side of the can and compressed air enters through the hole. The discarded gas is
from the left side of the can.

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Turbines
Receive energy from much higher pressure and much higher speed gases flowing from the combustion chamber.
The figure below shows two sets of turbines
The first part of which runs directly to the compressor. The turbine and compressor are connected by shafts so the
three will rotate at the same time. The end of the turbine is directly connected to the output shaft. They are separate
from the rest of the engine and can rotate freely. This part is also called the free rotating part. The hot gas produced
after combustion in the combustion chamber rotates the free rotating part and can generate energy up to about
1500 horsepower.

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Advantages and Disadvantages of Gas Turbines
Advantages:
 They can generate much more energy than its weight.
 The power and weight ratio of gas turbine engines is much higher than other engines.
 Lower operational cost
 High operational speed and low lubrication cost.
Disadvantages:
 It is very expensive
 Temperature of combustion chamber is too high thus resulting in a lower life.
 They are incompatible with solid fuels.
 Most of power is used to drive the compressor so it gives less output.