1BRAYTON CYCLE: THE IDEAL CYCLE FOR GAS-TURBINE ENGINESAn
open-cycle gas-turbine engine. A closed-cycle gas-turbine
engine.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 compressor2-!
"onstant-pressure heat addition!-# Isentropic expansion (in a
turbine#-1 "onstant-pressure heat rejection2T-s and P-v diagrams
for the ideal $rayton cycle.%ressure ratioThermal e&ciency of
the ideal $rayton cycle as a function of the pressure ratio.!The
fraction of the turbine 'or( used to dri)e the compressor is called
the bac( 'or( ratio.The t'o major application areas of gas-turbine
engines are aircraft propulsion and electric power generation.The
highest temperature in the cycle is limited by the maximum
temperature that the turbine blades can 'ithstand. This also limits
the pressure ratios that can be used in the cycle.The air in gas
turbines supplies the necessary oxidant for the combustion of the
fuel, and it ser)es as a coolant to (eep the temperature of )arious
components 'ithin safe limits. An air*fuel ratio of +, or abo)e is
not uncommon.#Development of Gas T!"#nes1. Increasing the turbine
inlet (or -ring temperatures2. Increasing the e&ciencies of
turbomachinery components (turbines, compressors.!. Adding
modi-cations to the basic cycle (intercooling, regeneration or
recuperation, and reheating.Dev#at#on of A$tal Gas-T!"#ne C%$les
f!om I&eal#'e& OnesThe de)iation of an actual gas-turbine
cycle from the ideal $rayton cycle as a result of
irre)ersibilities.Reasons: Irre)ersibilities in turbine and
compressors, pressure drops, heat lossesIsentropic e&ciencies
of the compressor and turbine+THE BRAYTON CYCLE (ITH REGENERATIONIn
gas-turbine engines, the temperature of the exhaust gas lea)ing the
turbine is often considerably higher than the temperature of the
air lea)ing the compressor. Therefore, the high-pressure air
lea)ing the compressor can be heated by the hot exhaust gases in a
counter-/o' heat exchanger (a regenerator or a recuperator. The
thermal e&ciency of the $rayton cycle increases as a result of
regeneration since less fuel is used for the same 'or( output. T-s
diagram of a $rayton cycle 'ith regeneration.A gas-turbine engine
'ith regenerator.0T-s diagram of a $rayton cycle 'ith
regeneration.12ecti)eness of regenerator12ecti)eness under cold-air
standard assumptions3nder cold-air standard assumptionsThermal
e&ciency of the ideal $rayton cycle 'ith and 'ithout
regeneration.The thermal e&ciency depends on the ratio of the
minimum to maximum temperatures as 'ell as the pressure ratio.
4egeneration is most e2ecti)e at lo'er pressure ratios and lo'
minimum-to-maximum temperature ratios."an regeneration be used at
high pressure ratios5 6THE BRAYTON CYCLE (ITH INTERCOOLING)
REHEATING) AND REGENERATIONA gas-turbine engine 'ith t'o-stage
compression 'ith intercooling, t'o-stage expansion 'ith reheating,
and regeneration and its T-s diagram.7or minimi8ing 'or( input to
compressor and maximi8ing 'or( output from turbine.9"omparison of
'or( inputs to a single-stage compressor (1AC and a t'o-stage
compressor 'ith intercooling (1ABD.*lt#sta+e $omp!ess#on ,#t-
#nte!$ool#n+: The 'or( re:uired to compress a gas bet'een t'o
speci-ed pressures can be decreased by carrying out the compression
process in stages and cooling the gas in bet'een. This (eeps the
speci-c )olume as lo' as possible.*lt#sta+e e.pans#on ,#t-
!e-eat#n+ (eeps the speci-c )olume of the 'or(ing /uid as high as
possible during an expansion process, thus maximi8ing 'or(
output.Inte!$ool#n+ an& !e-eat#n+ al'ays decreases the thermal
e&ciency unless they are accompanied by regeneration. (-%/As
the number of compression and expansion stages increases, the
gas-turbine cycle 'ith intercooling, reheating, and regeneration
approaches the 1ricsson cycle.;IDEAL 0ET-1RO1ULSION CYCLESIn jet
engines, the high-temperature and high-pressure gases lea)ing the
turbine are accelerated in a no88le to pro)ide thrust.tto cycle.
The ideal cycle for spar(-ignition engines?iesel cycle. The ideal
cycle for compression-ignition engines=tirling and 1ricsson
cycles$rayton cycle. The ideal cycle for gas-turbine enginesThe
$rayton cycle 'ith regenerationThe $rayton cycle 'ith intercooling,
reheating, and regenerationIdeal jet-propulsion cycles=econd-la'
analysis of gas po'er cycles