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Gas Turbine Gas Turbine Theory and Theory and
ConstructionConstruction
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IntroductionIntroduction
• Comprehend the thermodynamic processes occurring in a gas turbine
• Comprehend the basic components of gas turbine engines and their basic operation
• Comprehend the support systems associated with gas turbine engines
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BackgroundBackground• Aircraft turbojet/turbofan engines are
precursors to gas turbines• Installed for propulsion in:
• FFG’s• DD’s• DDG’s• CG’s• M-1 tanks
• Also used for electrical generation & auxiliary applications
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Advantages of GTE’sAdvantages of GTE’s• Weight reduction of 70%• Simplicity• Reduced manning requirements• Quicker response time• Faster Acceleration/deceleration• Modular replacement• Less vibrations• More economical
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Disadvantages of Disadvantages of GTE’sGTE’s
• Many parts under high stress• High pitched noise• Needs large quantities of air• Large quantities of hot exhaust
(target)• Cannot be repaired in place
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Brayton CycleBrayton Cycle• Unlike diesels, operate on STEADY-FLOW cycle• Open cycle, unheated engine
1-2: Compression
2-3: Combustion
3-4: Expansion through Turbine 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 Components• CompressorCompressor
• Draws in air & compresses it• Combustion Chamber
• Fuel pumped in and ignited to burn with compressed air
• Turbine• Hot gases converted to work• Can drive compressor & external load
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Basic ComponentsBasic Components• Compressor
• Draws in air & compresses it• Combustion ChamberCombustion Chamber
• Fuel pumped in and ignited to burn with compressed air
• Turbine• Hot gases converted to work• Can drive compressor & external load
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Basic ComponentsBasic Components• Compressor
• Draws in air & compresses it• Combustion Chamber
• Fuel pumped in and ignited to burn with compressed air
• TurbineTurbine• Hot gases converted to work• Can drive compressor & external load
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CompressorCompressor
• Supplies high pressure air for combustion process
• Compressor types• Radial/centrifugal flow compressor• Axial flow compressor
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CompressorCompressor• Radial/centrifugal flow
• Adv: simple design, good for low compression ratios (5:1)
• Disadv: Difficult to stage, less efficient
• Axial flow • Good for high
compression ratios (20:1)
• Most commonly used
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CompressorCompressor
• Controlling Load on Compressor• To ensure maximum efficiency and
allow for flexibility, compressor can be split into HP & LP sections
• Vane control: inlet vanes/nozzle angles can be varied to control air flow
• Compressor Stall• Interruption 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
combustion process• 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 fuel• Types
• Can: for small, centrifugal compressors
• Annular: for larger, axial compressors (LM 2500)
• Can-annular: for really large turbines
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TurbinesTurbines• Consists of one or more stages
designed to develop rotational energy
• Uses sets of nozzles & blades
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TurbinesTurbines• Split Shaft
• Gas generator turbine drives compressor• Power turbine separate from gas generator
turbine• Power turbine driven by exhaust from gas
generator turbine• Power turbine drives power coupling
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Single ShaftSingle Shaft
• Efficiently operates at constant speeds• Used in GTGS (gas turbine generator
systems)• Single shaft
• Power coupling on same shaft as turbine• Same shaft drives rotor of compressor and
power components
*Primarily used for electric power because of constant speed, regardless of load.
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Split ShaftSplit Shaft
• Best where speeds and loads vary• Used in LM-2500• Power shaft is decoupled from compressor• Allows both to operate at efficient speeds
(not the same)*More suitable for main propulsion
applications due to the fact that the gas generator turbine and power turbine operate near their most efficient speeds throughout a RANGE of load demands.
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Accessory Drive Accessory Drive AssemblyAssembly
• Purpose - Provides motive force for driving the accessories required for operation and control of engine
• Attached Accessory Equipment• Fuel oil pump• Lube oil pump• Starter (pneumatic, electric, hydraulic)
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Gas Turbine SystemsGas Turbine Systems
• Air System• Air intakes are located high up &
multiple filters• Exhaust discharged out stacks
• Fuel System• Uses either DFM or JP-5
• Lubrication System• Supply bearings and gears with oil
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Gas Turbine SystemsGas Turbine Systems
• Starting System• To get compressor initially rotated, HP
air used (can use electrical also)• Once at certain RPM, fuel injected and
spark ignited• Power Transmission System
• Reduction gears used to transfer torque• With split shaft, turbines can run @
different speeds
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QuestionQuestions?s?