2. IntroductionIntroduction
Gas-turbine engine:Gas-turbine engine: Any internal combustion Any internal combustion
engine, employing aengine, employing a gasgas as the working fluid whichas the working fluid which
is used to turn a is used to turn a turbineturbine..
The term also is conventionally used to describe aThe term also is conventionally used to describe a
complete internal combustion engine consisting ofcomplete internal combustion engine consisting of
at leastat least
• A compressor,A compressor,
• A combustion chamber, andA combustion chamber, and
• A turbine. A turbine.
In the gas turbine, there is a continuous flow of
the working fluid.
3. ApplicationsApplications
The outgoing gaseous fluid (exhaust) can be used
to generate thrust. Useful work or propulsive thrustUseful work or propulsive thrust
can be obtained from a gas-turbine engine.can be obtained from a gas-turbine engine.
It may drive aIt may drive a generator, pump, or propellergenerator, pump, or propeller or, inor, in
the case of a purethe case of a pure jet aircraft enginejet aircraft engine, develop thrust, develop thrust
by accelerating the by accelerating the turbine exhaust flow through a exhaust flow through a
nozzle (e.g. after-burner).nozzle (e.g. after-burner).
7. Working PrincipleWorking Principle
This working fluid is initially compressed in the
compressor.
It is then heated in the combustion chamber.
Finally, it goes through the turbine.
The turbine converts the energy of the gas into
mechanical work.
Part of this work is used to drive the compressor.
The remaining part is known as the net work of the
gas turbine.
8. Cont…
When examining the gas turbine cycle, we
make a few assumptions.
The working fluid is a perfect gas .
The kinetic/potential energy of the
working fluid does not vary along the gas
turbine.
Finally, pressure losses, mechanical
losses and other kinds of losses are
ignored.
9. Variant:Variant:
Closed Brayton CycleClosed Brayton Cycle
A closed Brayton cycle re-circulates the A closed Brayton cycle re-circulates the
working fluidworking fluid, the air expelled from the, the air expelled from the
turbine isturbine is reintroducedreintroduced into the compressor.into the compressor.
This cycle uses a This cycle uses a heat exchangerheat exchanger to heat to heat
the working fluid instead of an internalthe working fluid instead of an internal
combustion chambercombustion chamber..
The closed Brayton cycle is used forThe closed Brayton cycle is used for
example in example in closed-cycle gas turbineclosed-cycle gas turbine and and
space power generation.space power generation.
12. The Ideal Gas Turbine Cycle
(Closed Brayton Cycle)
Turbine
gives drive
to run the
compressor
13. Work done by Turbine per kg of air,Work done by Turbine per kg of air,
WWTT = c= cpp (T(T33-T-T44))
Note: For Isentropic expansion,Note: For Isentropic expansion,
Work Done = Mass (m) X Specific heat at constantWork Done = Mass (m) X Specific heat at constant
Pressure (cPressure (cpp) X Change in Temperature) X Change in Temperature
or,or, W= m. cW= m. cpp(T(T33-T-T44))
14. Work required by Compressor per kg of air,Work required by Compressor per kg of air,
WW cc = c= cpp (T(T22-T-T11))
Note: For Isentropic compression,Note: For Isentropic compression,
Work Done = Mass (m) X Specific heat at constantWork Done = Mass (m) X Specific heat at constant
Pressure (cPressure (cpp) X Change in Temperature) X Change in Temperature
or,or, W= m. cW= m. cpp(T(T22-T-T11))
15. Net Work available in a Gas Turbine,Net Work available in a Gas Turbine,
W= WW= WT-T- WWcc
or,or, WW = c= cpp (T(T33-T-T44) - c) - cpp (T(T22-T-T11))
or,or, WW = c= cpp {(T{(T33-T-T44) - (T) - (T22-T-T11)})}
For Isentropic process,For Isentropic process,
TTSS/T/TLL = (p= (p SS / p/ p LL)^ ()^ (γγ-1-1)/)/γγ
18. Basic ComponentsBasic Components
CompressorCompressor
– Draws in air & compresses itDraws in air & compresses it
Combustion ChamberCombustion Chamber
– Fuel pumped in and ignited to burn withFuel pumped in and ignited to burn with
compressed aircompressed air
TurbineTurbine
– Hot gases converted to workHot gases converted to work
– Can drive compressor & external loadCan drive compressor & external load
19. Basic ComponentsBasic Components
CompressorCompressor
– Draws in air & compresses itDraws in air & compresses it
Combustion ChamberCombustion Chamber
– Fuel pumped in and ignited to burn withFuel pumped in and ignited to burn with
compressed aircompressed air
TurbineTurbine
– Hot gases converted to workHot gases converted to work
– Can drive compressor & external loadCan drive compressor & external load
20. Basic ComponentsBasic Components
CompressorCompressor
– Draws in air & compresses itDraws in air & compresses it
Combustion ChamberCombustion Chamber
– Fuel pumped in and ignited to burn withFuel pumped in and ignited to burn with
compressed aircompressed air
TurbineTurbine
– Hot gases converted to workHot gases converted to work
– Can drive compressor & external loadCan drive compressor & external load
21. CompressorCompressor
Supplies high pressure air forSupplies high pressure air for
combustion processcombustion process
Compressor typesCompressor types
– Radial/centrifugal flow compressorRadial/centrifugal flow compressor
– Axial flow compressorAxial flow compressor
22. CompressorCompressor
Radial/centrifugal flowRadial/centrifugal flow
– Advantages: simpleAdvantages: simple
design, good for lowdesign, good for low
compression ratioscompression ratios
(5:1)(5:1)
– Disadvantages: DifficultDisadvantages: Difficult
to stage,less efficientto stage,less efficient
Axial flowAxial flow
– Good for highGood for high
compression ratioscompression ratios
(20:1)(20:1)
– Most commonly usedMost commonly used
23. Use of Compressed AirUse of Compressed Air
Primary Air (30%)Primary Air (30%)
– Passes directly to combustor forPasses directly to combustor for
combustion processcombustion process
Secondary Air (65%)Secondary Air (65%)
– Passes through holes in perforated innerPasses through holes in perforated inner
shell & mixes with combustion gasesshell & mixes with combustion gases
Film Cooling Air (5%)Film Cooling Air (5%)
– Insulates/cools turbine bladesInsulates/cools turbine blades
25. Combustion ChambersCombustion Chambers
Where air & fuel are mixed, ignited,Where air & fuel are mixed, ignited,
and burnedand burned
Spark plugs used to ignite fuelSpark plugs used to ignite fuel
TypesTypes
– Can: for small, centrifugal compressorsCan: for small, centrifugal compressors
– Annular: for larger, axial compressorsAnnular: for larger, axial compressors
(LM 2500)(LM 2500)
– Can-annular: rarely usedCan-annular: rarely used
26. TurbinesTurbines
Consists of one or more stagesConsists of one or more stages
Designed to develop rotational energyDesigned to develop rotational energy
Uses sets of nozzles & bladesUses sets of nozzles & blades
Single shaftSingle shaft
– Power coupling on same shaft as turbinePower coupling on same shaft as turbine
– Same shaft drives rotor of compressorSame shaft drives rotor of compressor
and power componentsand power components
27. TurbinesTurbines
Split ShaftSplit Shaft
– Gas generator turbine drives compressorGas generator turbine drives compressor
– Power turbine separate from gas generator turbinePower turbine separate from gas generator turbine
– Power turbine driven by exhaust from gas generatorPower turbine driven by exhaust from gas generator
turbineturbine
– Power turbine drives power couplingPower turbine drives power coupling
29. Improving Turbine EfficiencyImproving Turbine Efficiency
IntercoolerIntercooler
– Compressing the air in two stages andCompressing the air in two stages and
using an intercooler between the two.using an intercooler between the two.
30. Improving Turbine EfficiencyImproving Turbine Efficiency
ReheatingReheating
– Expanding the air in two stages and usingExpanding the air in two stages and using
a re-heater between the two.a re-heater between the two.
31. Other TypesOther Types
Semi-Closed Cycle Gas TurbinesSemi-Closed Cycle Gas Turbines
– Combination of an open and a closedCombination of an open and a closed
cycle gas turbinescycle gas turbines
Constant Pressure Gas TurbinesConstant Pressure Gas Turbines
– Air heated in combustion chamber atAir heated in combustion chamber at
constant pressureconstant pressure
Constant Volume Gas TurbinesConstant Volume Gas Turbines
– Air heated in combustion chamber atAir heated in combustion chamber at
constant volumeconstant volume
32. Gas Turbine SystemsGas Turbine Systems
Air SystemAir System
– Air intakes are located high up & multipleAir intakes are located high up & multiple
filtersfilters
– Exhaust discharged out stacksExhaust discharged out stacks
Fuel SystemFuel System
– Uses either DFM or JP-5Uses either DFM or JP-5
Lubrication SystemLubrication System
– Supply bearings and gears with oilSupply bearings and gears with oil
33. Advantages of gasAdvantages of gas
turbine enginesturbine engines
Very high power-to-weight ratioVery high power-to-weight ratio
More size efficientMore size efficient
Moves in one direction only, with fewerMoves in one direction only, with fewer
moving partsmoving parts
Low operating pressuresLow operating pressures
High operation speedsHigh operation speeds
Low lubricating oil cost andLow lubricating oil cost and
consumptionconsumption
34. Disadvantages of gasDisadvantages of gas
turbine enginesturbine engines
More expensive compared to aMore expensive compared to a
similar-sized reciprocating enginesimilar-sized reciprocating engine
More complex machining operationsMore complex machining operations
Usually less efficient thanUsually less efficient than
reciprocating engines, especially atreciprocating engines, especially at
idleidle
Delayed response to changes inDelayed response to changes in
power settingspower settings
35. ComparisonComparison
Gas Turbines vs Steam TurbinesGas Turbines vs Steam Turbines
Gas Turbines vs IC EnginesGas Turbines vs IC Engines
Closed Cycle Gas Turbines vs OpenClosed Cycle Gas Turbines vs Open
Cycle Gas TurbinesCycle Gas Turbines