Author Topic: Merits and Demerits of Gas Turbines - Interview Questions  (Read 506 times)

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Merits and Demerits of Gas Turbines - Interview Questions
« on: October 08, 2016, 02:41:43 AM »
Merits and Demerits of Gas Turbines
Merits over I.C. engines :


1. The mechanical efficiency of a gas turbine (95%) is quite high as compared with I.C.
engine (85%) since the I.C. engine has a large many sliding parts.
2. A gas turbine does not require a flywheel as the torque on the shaft is continuous and
uniform. Whereas a flywheel is a must in case of an I.C. engine.
3. The weight of gas turbine per H.P. developed is less than that of an I.C. engine.
4. The gas turbine can be driven at a very high speeds (40,000 r.p.m.) whereas this is not
possible with I.C. engines.
5. The work developed by a gas turbine per kg of air is more as compared to an I.C. engine.
This is due to the fact that gases can be expanded upto atmospheric pressure in case of
a gas turbine whereas in an I.C. engine expansion upto atmospheric pressure is not
possible.
6. The components of the gas turbine can be made lighter since the pressures used in it are
very low, say 5 bar compared with I.C. engine, say 60 bar.
7. In the gas turbine the ignition and lubrication systems are much simpler as compared
with I.C. engines.
8. Cheaper fuels such as paraffine type, residue oils or powdered coal can be used whereas
special grade fuels are employed in petrol engine to check knocking or pinking.
9. The exhaust from gas turbine is less polluting comparatively since excess air is used for
combustion.
10. Because of low specific weight the gas turbines are particularly suitable for use in aircrafts.

Demerits of gas turbines

1. The thermal efficiency of a simple turbine cycle is low (15 to 20%) as compared with I.C.
engines (25 to 30%).
2. With wide operating speeds the fuel control is comparatively difficult.
3. Due to higher operating speeds of the turbine, it is imperative to have a speed reduction
device.
4. It is difficult to start a gas turbine as compared to an I.C. engine.
5. The gas turbine blades need a special cooling system.