COMPARISON BETWEEN GAS TURBINE AND IC ENGINE

Following are the merits of gas turbine compared to reciprocating I.C engine.

• Gas turbine has no reciprocating parts. It is free from vibrations since it develops uniform torque.

• Its weight per kW power is less.

• The installation and running cost is less. Lubrication is simpler.

• No flywheel is required.

• It has much simplified cooling system.

• It has higher mechanical efficiency. Its exhaust is free from smoke.

• The working pressure is relatively lower (5 bar)

• It can be driven at a very high speed and is suitable for air crafts.

• Absence of valves render continuous combustion and there is no problem of ignition timings.

• But starting of a gas turbine is not simpler.

COMPARISON OF CLOSED CYCLE WITH OPEN CYCLE GAS TURBINE

CLOSED CYCLE GAS TURBINE

1. Compressed air is heated in a heating chamber by an external source; the amount of gas remains the same.

2. The exhaust gases from the turbine pass into cooling chamber.

3. The working fluid (air) is confined within the plant and is circulated continuously.

4. Any fluid with better thermo- dynamic properties can be used as it will not mix with the products of combustion.

5. Turbine blades do not suffer corrosion and no carbon deposits form on them ; no internal cleaning of the plant is required.

6. The weight of turbine per kW power is high.

7. Thermal efficiency of the plant is higher.

OPEN CYCLE GAS TURBINE

1. Compressed air is heated in a combustion chamber and gets mixed up with hot gases ; the mass of gases and air increases.

2. The exhaust gases from turbine are let out into atmosphere.

3. The working fluid is replaced after each cycle of operations.

4. Only air is used as the working fluid.

5. Frequent cleaning of the plant is necessary ; turbine blades wear away earlier.

6. The weight of turbine per kW is less.

7. Thermal efficiency is lower.

CONSTANT PRESSURE GAS TURBINE VS CONSTANT VOLUME GAS TURBINE

CONSTANT PRESSURE GAS TURBINE

1. Combustion of fuel and heating of air is at constant pressure

2. Combustion of fuel is continuous, so the rotation of turbine is smoother.

3. High combustion temperature is reduced by supplying excess amount of air.

4. The unit is relatively simple.

5. There is no need of condenser.

6. Cycle of operations follows reversed Joule's cycle or Brayton Cycle.

7. Most commonly built type of turbine.

CONSTANT VOLUME GAS TURBINE

1. Combustion of fuel and heating of air is at constant volume

2. Combustion is not continuous but it is intermittent; rotation of turbine shaft is not so smooth.

3. High combustion temperature is reduced by providing water jacket around combustion chamber.

4. The unit is not simpler because of steam generator etc.

5. Condenser may be employed to condense steam.

6. Cycle of operations follows Atkinson's cycle.

7. It is rarely built.