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Gas Turbine TheoryGas Turbine TheoryGas Turbine TheoryGas Turbine Theory
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GAS TURBINE ENGINESLM 2500
GAS TURBINE GENERATORSALLISON 501-k 17
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USES OF GAS TURBINE
ENGINES Aircraft Engines
Main Propulsion
Arleigh Burke, Tichonderoga, Spruance, OliverHazard Perry LCACS, Pegasus
Auxiliary Applications
Electric generators
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ADVANTAGES OF GTEs
Weight reduction of 70%
Simplicity
Reduced manning requirements
Quicker response time
Faster Acceleration/deceleration
Modular replacement
Cleaner and safer fuels
Less vibrations
More economical
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DISADVANTAGES OF GTEs
Many parts under high stress
High pitched noise
Needs large quantities of air
Large heat source
Must be in-port for major repairs
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Operating Principles
Shipboard GTEs can be thought of in terms ofthermodynamic processes:
Steady flowOpen cycle
Unheated engine
Working fluid = air that is compressed in the
compressor and combustion chamber Unlike the steam plants and reciprocating engines,
the gas turbines operate on the Brayton Cycle.
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Operating Principles contd
Air is drawn into the compressor where it is
compressed and sent to the combustion
chamber. Fuel is injected into the
combustion chamber where it is ignited by
the compression (spark on startup). The
gases are directed into the turbine where thethermal energy is converted into work
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BRAYTON CYCLE
P
R
E
S
S
U
R
E
VOLUME
SUCK
SQUEEZE
BURN
BLOW
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BRAYTON CYCLE
P
R
E
S
S
U
R
E
VOLUME
COMPRESSOR
COMBUSTOR
TURBINE
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Thermodynamic Relationships
P1 = Pr1
P2 Pr2
P1= Inlet Pressure
P2=Outlet Pressure
Pr1= Inlet reduced PressurePr2= Outlet reduced Pressure
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Thermodynamic Relationships
Example:
T1 = 80 F
P1 = atmosphere =14.7 PSIA
Compression ration = 17:1
Efficiency = 92.5%
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4 COMPONENTS OF A GAS
TURBINE ENGINE
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(1) COMPRESSORS
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Radial Flow
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Axial Flow
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Axial vs. Radial
Axial
Adv:
simple andinexpensive
light weight
Dis:
less efficient large frontal area
limitedcompression
ratio (4:1 ratio)
Radial
Adv:
efficient high
compression
ratios (20:1)
Dis:
complex
expensive
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LM 2500 COMPRESSOR
Compressor - 16 stage Axial flow 17:1
compression ratio
Inlet Guide Vanes
1st 6 Stages of Stator Vanes variable
Provides proper air flow for Rotor Vanes
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COMPRESSOR STALL
Occurs if for some reason air velocity
decreases without a commensurate decrease
in RPM or if RPM increases without thenecessary air velocity increase.
Similar to wing stall
Can result in blade failure
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GTE AIRCompressed Air Distribution:
Primary Air- 30% of
the compressed air is
supplied directly to thecombustion chamber
Secondary Air- 65% of
the air provides cooling
for the combustion
chamber
Film Cooling Air- 5%
of the air provides
cooling directly to the
turbine blades
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(2) COMBUSTORS
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LM 2500 COMBUSTOR
Annular = RING OF FIRE
30 Fuel Nozzles
2 Ignitors
Allison 501-K17 (Gas Turbine Generator) CAN ANNULAR - 6 Cans/6 Fuel Nozzles-Ingitors
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(3) TURBINES
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LM 2500 Turbine Section
High Pressure Turbine
Maintains Compressor Rotation
Power Turbine (Low Pressure)
6 sets of nozzles/Blades
NOT Attached to Compressor Shaft
Directly Attached to Power Drive Shaft
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ACCESSORY DRIVE
ASSEMBLY Provides the motive force for driving the
accessories required for the operation and control
of the engine Accessory equipment attached at the assembly:
fuel oil pump
lube oil pump
starter (pneumatic, electric, hydraulic)
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Gas Turbine Module
A LM2500 engine is encased in a module to
provide cooling, noise reduction, shock
mounting, and safety CO2 flooding.
Modular in design facilitates easy
replacement
Inlet Duct has louvers and demisters
Outlet duct has coolers and silencers
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Why Dont We Use GTEs on all
Ships? Some Disadvantages are:
inefficient at low speeds
large inlet and outlet ducting
CBR warfare problems
complex shafting (clutches and CRPs)
large fuel storage requirements
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Summary
Advantages and disadvantages of GTEs and
some of their components
The parts and operation of GTEs
The different types of GTEs
Air distribution
Support systems
Platforms that use GTEs