OCTOBER 19-20, 2012 - YMCA University of Science & Technology

Proceedings of the National Conference on
Trends and Advances in Mechanical Engineering,
YMCA University of Science & Technology, Faridabad, Haryana, Oct 19-20, 2012
Compression ratio of compressor also affects the mass of fuel to be injected in combustion chamber but in an
irregular fashion. Upto a pressure ratio of 15 there is decrease in fuel consumption and after that it starts
increasing. Similar pattern is observed for the exergy destruction in combustion chamber.
Mass of fuel injected in combustion
chamber (g/Kg of air)
1.8
1.75
1.7
1.65
1.6
1.55
1.5
5 10 15 20 25 26
Cycle pressure ratio
Figure: 4. Fuel consumption in combustion chamber with change in CR
As the turbine inlet temperature increases, exergy destruction in combustion chamber decreases (figure.5). It is
due to the reason that, increase in temperature inside the combustion chamber increases the fuel utilization
efficiency. Due to increased fuel utilization efficiency, exergy destruction in combustion chamber is decreased.
With increase in TIT from 900°C to 1300°C, exergy destruction is decreased by 6.22%.
Exergy destruction in combustion
chamber
27000
26500
26000
25500
25000
24500
24000
900 950 1000 1050 1100 1150 1200 1250 1300
Turbine inlet temperature (°C)
Figure: 5. Exergy destruction in combustion chamber with change in turbine inlet temperature (°C)
If heat is transferred from a high temperature to lower temperature then its quality goes down and exergy
destruction takes place. Exergy (or available energy, or availability) is the maximum useful work that can be
extracted from a quantity of energy and refers to the quality of energy. Thus, though the energy is conserved in
the process of conversion, its quality deteriorates and less work can be obtained with each conversion. The
various irreversible processes encountered within the combustor leads to certain degree of exergy loss. It is
observed that the second-law efficiency is the maximum for the stoichiometric supply of air. The lower product
gas temperature at the exit for a lean mixture as a result of the excess air supply reduces the second-law
efficiency of the combustor. This is despite the fact that all the energy stored in the fuel is contained in the
product gas with the complete combustion of the fuel in case of a lean fuel–air mixture in the adiabatic
combustor. Therefore, it is clear that neither the completeness of combustion nor the energy content of the
product gas determines the exergy-based performance of the combustor. As the product gas temperature at the
combustor exit decreases with the increase in the excess supply of air, the maximum ability of it to perform
useful work decreases. Therefore, the second-law efficiency decreases. The same decrease in exergetic efficiency
is also observed with the insufficient supply of air, when the exit temperature decreases because of the
incomplete release of fuel’s stored energy. The maximum efficiency, which is obtained with the stoichiometric
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