The gas turbine can be classified as follows:
1) According to types of combustion process
I.
Constant volume or explosion type gas turbine:
This type of Gas turbine works on Atkinson cycle in which combustion of air
fuel mixture is takes place at constant volume, hence air and fuel mixture
should be isolated from compressor. This is possible by valves in the
combustion chamber, resulting in an intermittent combustion which inherently
impairs smooth running of machine. This type of turbine has better thermal
efficiency than a constant pressure cycle gas turbine. The main disadvantages
of this type of gas turbine is that complexity in mechanical system and
pressure difference and velocity of hot gases are not constant, so turbine
speed fluctuates. The constant volume combustion type gas turbine is not
popular in practical use. The constant volume gas turbines are absolute in use.
II.
Constant pressure or continuous combustion type
gas turbine: This type of gas turbine works on Brayton cycle in which
combustion of air fuel mixture is takes place at constant pressure.
2) According to direction of flow
I.
Axial flow gas turbine
II.
Radial flow gas turbine.
3) According to action of expanding gases
I.
Impulse gas turbine
II.
Impulse- Reaction gas turbine
4) According to path of working substance
I.
Open cycle gas turbine plants: In the open cycle
gas turbine, ambient air enters at the compressor and after the compression of
air, fuel is burned in the air itself to raise it to a high temperature and
then product of combustion is passed on to the turbine for expansion and which
after delivering the work are finally ejected to atmosphere. In the open cycle
the working medium is continuously replaced by fresh air and fuel.
II.
Closed cycle gas turbine plants: In the closed
cycle gas turbine power plant, the same air or the working fluid is circulated
over and over again. The working medium is not mixed with fuel, but it is
heated by the burning of fuel in separate supply of air in the combustion
chamber and transferring this heat to the working fluid which passes through
tubes fitted in the combustion chamber. The working fluid does not come into
direct constant with product of combustion.
III.
Semi-closed cycle gas turbine plants:
Semi-closed cycle gas turbine plant is combination of open and closed cycle, in
which some part of working fluid is recirculated to the plant and another part
of working fluid flows into and from the atmospheric air.
5) According to thermodynamic cycle
I.
Simple cycle
II.
Simple cycle with intercooling: in which the air
is cooled between stages of compression.
III.
Simple cycle with regeneration: in which the air
after compression is heated with help of exhaust gases coming from turbine.
IV.
Simple cycle with reheating: in which combustion
products (gases) after part of expansion in high pressure turbine is reheated
in second combustion chamber and then it is expanded in the low pressure turbine.
V.
Simple cycle with intercooling, regeneration and
reheating.
6) According to shaft configuration
I.
Single shaft engine: - Examples: Turbojet
engine, Turboshaft engine.
II.
Multi-shaft engine: - Example: Two shaft engine
with power turbine, Turbojet engine, industrial slit shaft engine, Twin-spool
engine.
7) According to applications
I.
Power or industrial gas turbines
II.
Aviation or aircraft turbines
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