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Gas Turbine TheoryGas Turbine Theoryand Constructionand Construction
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Introduction
Introduction
Comprehend the thermodynamicprocesses occurring in a gas turbineComprehend the basic components of gasturbine engines and their basic operationComprehend the support systemsassociated with gas turbine engines
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Background
BackgroundAircraft turbojet/turbofan engines are precursors
to gas turbinesInstalled for propulsion in:
FFGsDDsDDGsCGs
M-1 tanksAlso used for electrical generation & auxiliaryapplications
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Advantages of GTEsAdvantages of GTEsWeight reduction of 70%SimplicityReduced manning requirements
Quicker response timeFaster Acceleration/decelerationModular replacementLess vibrationsMore economical
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Disadvantages of GTEs
Disadvantages of GTEs
Many parts under high stressHigh pitched noiseNeeds large quantities of airLarge quantities of hot exhaust (target)
Cannot be repaired in place
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Brayton CycleBrayton CycleUnlike diesels, operate on STEADY-FLOW cycleOpen cycle, unheated engine
1-2: Compression
2-3: Combustion
3-4: Expansion throughTurbine and Exhaust
Nozzle
(4-1: Atmospheric
Pressure)
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Basic ComponentsBasic Components
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Basic ComponentsBasic Components
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Basic ComponentsBasic ComponentsCompressorCompressor
Draws in air & compresses itCombustion Chamber
Fuel pumped in and ignited to burn with compressed
airTurbineHot gases converted to workCan drive compressor & external load
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Basic ComponentsBasic ComponentsCompressor
Draws in air & compresses itCombustion ChamberCombustion Chamber
Fuel pumped in and ignited to burn with compressed
airTurbineHot gases converted to workCan drive compressor & external load
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Basic ComponentsBasic ComponentsCompressor
Draws in air & compresses itCombustion Chamber
Fuel pumped in and ignited to burn with compressed
airTurbineTurbineHot gases converted to workCan drive compressor & external load
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CompressorCompressorSupplies high pressure air for combustionprocessCompressor types
Radial/centrifugal flow compressorAxial flow compressor
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CompressorCompressorRadial/centrifugal flow
Adv: simple design, good for low compression
ratios (5:1)Disadv: Difficult to stage,less efficient
Axial flowGood for highcompression ratios (20:1)Most commonly used
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CompressorCompressor
Controlling Load on CompressorTo ensure maximum efficiency and allow forflexibility, compressor can be split into HP &LP sectionsVane control: inlet vanes/nozzle angles can be
varied to control air flowCompressor StallInterruption of air flow due to turbulence
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Use of Compressed AirUse of Compressed Air
Primary Air (30%)Passes directly to combustor for combustionprocess
Secondary Air (65%)Passes through holes in perforated inner shell& mixes with combustion gases
Film Cooling Air (5%)Insulates/cools turbine blades
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Combustion ChambersCombustion Chambers
Where air & fuel are mixed, ignited, and burned Spark plugs used to ignite fuelTypes
Can: for small, centrifugal compressors
Annular: for larger, axial compressors (LM2500)Can-annular: for really large turbines
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TurbinesTurbinesConsists of one or more stages designed todevelop rotational energy
Uses sets of nozzles & blades
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TurbinesTurbinesSplit Shaft
Gas generator turbine drives compressorPower turbine separate from gas generator turbinePower turbine driven by exhaust from gas generator
turbinePower turbine drives power coupling
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Single ShaftSingle Shaft
Efficiently operates at constant speedsUsed in GTGS (gas turbine generator systems)Single shaft
Power coupling on same shaft as turbineSame shaft drives rotor of compressor and powercomponents
*Primarily used for electric power because of constant speed, regardless of load.
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Split ShaftSplit Shaft
Best where speeds and loads varyUsed in LM-2500
Power shaft is decoupled from compressorAllows both to operate at efficient speeds (notthe same)
*More suitable for main propulsion applicationsdue to the fact that the gas generator turbine and power turbine operate near their most efficientspeeds throughout a RANGE of load demands.
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Accessory
Drive
Assembly
Accessory
Drive
Assembly
Purpose - Provides motive force for driving
the accessories required for operation and control of engineAttached Accessory Equipment
Fuel oil pumpLube oil pumpStarter (pneumatic, electric, hydraulic)
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Gas Turbine SystemsGas Turbine Systems
Air SystemAir intakes are located high up & multiplefiltersExhaust discharged out stacks
Fuel SystemUses either DFM or JP-5
Lubrication SystemSupply bearings and gears with oil
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Q uestions?Q uestions?
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