BRAYTON CYCLE: THE IDEAL CYCLE FOR GASTURBINE ENGINES
The combustion process is replaced by a constant-pressure heat-addition process
from an external source, and the exhaust process is replaced by a constant-pressure
heat-rejection process to the ambient air.
1-2 Isentropic compression (in a compressor)
2-3 Constant-pressure heat addition
3-4 Isentropic expansion (in a turbine)
4-1 Constant-pressure heat rejection
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The two major application areas of gasturbine engines are aircraft propulsion and
electric power generation.
The highest temperature in the cycle is
limited by the maximum temperature that
the turbine blades can withstand. This also
limits the pressure ratios that can be used in
the cycle.
The air in gas turbines supplies the necessary
oxidant for the combustion of the fuel, and it
serves as a coolant to keep the temperature
of various components within safe limits. An
air–fuel ratio of 50 or above is not
uncommon.
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Development of Gas Turbines
1. Increasing the turbine inlet (or firing) temperatures
2. Increasing the efficiencies of turbomachinery components (turbines,
compressors):
3. Adding modifications to the basic cycle (intercooling, regeneration or
recuperation, and reheating).
Deviation of Actual Gas-Turbine
Cycles from Idealized Ones
Reasons: Irreversibilities in turbine and
compressors, pressure drops, heat losses
Isentropic efficiencies of the compressor
and turbine