Merits and Demerits of Gas Turbines

Merits of Gas Turbines 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 over I.C. engines

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.

Simple gas turbine plant