Gas Turbine Engine

1
Gas Turbine Engine Theory
2
Course Objectives

• 1. Introduction to Gas Turbine Engine Theory
• 2. Gas Turbine Engine Construction
• 3. Engine Variations and Applications
• 4. Gas Turbine Engine Accessory Systems

3
Learning Outcomes

• On successful completion of this training the
  learner will
• be able to explain the following
• Basic operating principles and engine
  construction
• Variations and applications of Gas Turbine
  Engines
• Accessory systems required to operate a Gas
  Turbine Engine

4
Objectives

• 1. Introduction to Gas Turbine Engine Theory
• Principles of Operation
• History of Gas Turbine Engine Development
• Basic Laws of Physics
• Terms and Definitions

5
Principles of Operation

• Jet propulsion
• As it applies to Gas Turbine Engines
• A confined substance (air) is heated, allowed to
  expand, and then forced to escape in a
  controlled manner through an orifice or nozzle.
• The force produced by the substance will be equal
  to the mass multiplied by the acceleration.

6
Principles of Operation

• Newton's Laws of Motion
• Newtons 1st Law
• A body in motion will tend to stay in motion
  unless acted upon by an external force.
• Newtons 2nd Law
• The acceleration of an object is directly
  proportional to the force applied and inversely
  proportional to its mass.
• Newtons 3rd Law
• For every action there is an equal and opposite
  reaction

7
History of Development
Examples of Jet Propulsion
8
Jet Engines

• All jet engines operate based on the principles
  of jet
• propulsion and the Newtons 3rd Law.
• Jet Engine Types
• Ramjet, Scramjet
• Pulsejet
• Rockets
• Liquid gas
• Solid gas
• Gas Turbine Engines
• Turbojet
• Turboprop/shaft
• Turbofan

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Jet Engines
10
Jet Engines

• Compressor (impeller) is used to
• compress air.
• Compressed air is mixed with fuel
• and combusted.
• Turbine extracts power from airflow
• to turn compressor.
• Remaining airflow used to produce
• thrust or drive a propeller, fan, generator.

11
Terms Definitions

• Energy
• Two forms of energy discussed in gas turbine
  engine theory
• Potential energy static pressure (pressure)
• Eg. Airflow at the engine inlet duct or inlet to
  combustor
• Kinetic energy dynamic pressure (velocity)
• Eg. Combustion gases striking turbine blades

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Airflow Characteristics
Bernoullis Principle
http//home.earthlink.net/mmc1919/venturi.html
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Airflow Characteristics
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Airflow Characteristics

• Mass
• The amount of matter in an object.
• M W
• g
• Weight
• Considers the effect of gravity on mass.
• W M x g
• Density
• Measures the mass in a unit volume. Eg. Cubic
  inch or in3
• The denser the air the greater its weight will be
  given the same mass.

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Airflow Characteristics

• Temperature
• Heat energy added to an object will increase its
  molecular activity. The opposite is true if heat
  energy is removed.
• Temperature (heat) as it effects engine mass
  airflow
• Hotter air is less dense as fewer molecules are
  contained in a given volume.
• Colder air is more dense as more molecules are
  contained in a given volume

16
Airflow Characteristics
Standard Day Conditions Engine
Performance Used to evaluate an engines
performance based on known conditions. Gas
Turbine Engines operate in constantly changing
air conditions related to pressure, temperature,
airspeed, and altitude. Standard Day Conditions
are used to evaluate the engines performance
against the manufacturers established
criteria. Atmospheric pressure 29.92 in Hg 100
kA Atmospheric temperature 59o
F 15oC Altitude 0 feet 0 meters Humidity 0
0 Airspeed 0 knots 0 km/hr
17
Airflow Characteristics

• Speed of Sound / Mach number
• The rate at which a disturbance in the air will
  move through it.
• Air temperature will cause the speed of sound to
  vary.
• This is due to the effect temperature has on air
  density.
• The MACH number is used to express an objects
  speed compared to the local speed of sound (air
  temperature factored in)
• M V, V velocity.
• C
  C local speed of sound

http//www.grc.nasa.gov/WWW/K-12/airplane/shock.ht
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http//www.grc.nasa.gov/WWW/K-12/airplane/atmosi.h
tml
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Airflow Characteristics
Note A nozzle may be used to increase subsonic
airflow to M 1.0 (turbine) or it may be used to
decrease supersonic airflow to M 1.0 (engine
inlet)
19
Objectives

• 2. Gas Turbine Engine Construction
• Engine Modules/Sections
• Inlet
• Compressor
• Combustion
• Turbine
• Exhaust
• Accessory Gearbox
• Principles of Operation
• Materials of Construction

20
Introduction

• Most Gas Turbine Engines are designed to reflect
  what is called Modular Design. The purpose of
  this is to assist the ease of maintenance by
  allowing certain sections or modules to be
  replaced with a new or overhauled one instead of
  replacing the entire engine. The following
  examples are the basic modules that make up a
• Turbojet engine. All other engines are derived
  from this basic
• engine design. A turbojet engine typically
  consists of 6 modules
• each of which is designed to suit the end use of
  the engine.
• Airframe or Package inlet / engine inlet
• Compressor / Diffuser
• Combustor
• Turbine
• Exhaust
• Accessory Drive

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Introduction
22
Introduction
Engine Station Numbering
23
Link to NASA
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Airframe or Package Inlet Module

• Provides supply of air to the engine under all
  conditions
• May have provisions for anti-icing
• Categories Subsonic or Supersonic

(turbulence, takeoff, idle, engine rpm,
temperature, altitude)
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Airframe or Package Inlet Module
Subsonic
26
Airframe or Package Inlet Module
Subsonic
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Airframe or Package Inlet Module
Supersonic Ducts
http//www.grc.nasa.gov/WWW/K-12/airplane/mshock.h
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Engine Inlet Module
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Compressor Module
Airfoil An airfoil is a specially designed body
used to create a reaction to the air that flows
around it. Typical airfoil Higher (static)
pressure air on the bottom and lower (static)
pressure air on the top. Total pressure will
remain the same Angle of Attack
Is the angle between the airfoil chord line
and the relative wind.
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Compressor Module

• Primary Purpose
• To increase pressure of air received from the
  inlet to provide
• sufficient volume of air at the proper
  pressure for combustion.
• Minimal rise in temperature
• Secondary Purpose
• Provide bleed air for engine cooling, de-icing,
  cabin heating,
• engine start
• Typical compressor ratios of 15-1, 300-400 lbs/s
• 3 types
• Centrifugal, Axial, and Axial/Centrifugal Flow

31
Compressor Module
Centrifugal Flow

• Impeller, diffuser, compressor manifold
• Impeller increases air velocity and pressure
• Diffuser is a series of divergent passages
• Manifold is use to direct high pressure air to
  combustor

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Compressor Module
Centrifugal Flow
33
Compressor Module
Centrifugal Flow
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Compressor Module
Axial Flow

• Compressor rotor, compressor rotor wheels/disks,
  
• compressor stator vanes, compressor cases.
• Compressor rotor blades - increases velocity and
  pressure
• Compressor wheels/disks control air flow and
  provide
• a means of attaching the rotors blades
• Compressor stator vanes - divergent passages
  increase pressure
• Compressor cases control air flow and provide a
  means of attaching the stators vanes

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Compressor Module
Axial Flow - Airflow
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Compressor Module
Axial Flow - Airflow
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Compressor Module
Axial Flow - Multi-spool

• A coaxial shaft allows for different engine
  designs
• Maximizes engine efficiency
• Responds quickly to changes in power setting

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Compressor Module
Axial Flow - Multi-spool
1 compressor driven by 1 turbine
2 compressors driven by 2 turbines (Free Turbine)
3 compressors driven by 3 turbines
40
Compressor Module
Axial-Centrifugal Flow

• Combines both axial and centrifugal styles
• Uses best features of both
• Used on many small engines, helicopter, business

41
Compressor Module
Rotor Blade Design/Construction

• Designed with a twist or stagger angle
• Ensures constant airspeed over length of blade
• Attached to the disk or wheel using solid, fir
  tree,
• dovetail methods

42
Compressor Module
Stator Vane Design/Construction

• Shrouds help eliminate air leakage and smooth
  airflow
• Variable vanes may be used to improve
  performance

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Mass Airflow vs Engine RPM
Mass Airflow / Engine RPM
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Mass Airflow / Engine RPM
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Mass Airflow / Engine RPM
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Compressor Module
Stall Avoidance Techniques
1. Bleed valves to dump excess air 2. Split
compressor into spools 3. Variable inlet guide
vanes 4. Radical blade design

• Stall consequences, load bangs, flames,
• smoke, possible damage to engine

47
Compressor Module
Diffuser

• Divergent to allow air to expand and slow before
  entering combustor
• Exit guide vanes will straighten and smooth
  airflow
• Point of highest air pressure
• May utilize bleed air ports to dump excess air,
  heating, anti-icing

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Compressor Module
Diffuser
49
Compressor Module
Diffuser
50
Combustion Module

• Function is to add heat energy to compressed air
• Combustor allows air to expand / accelerate into
  turbine
• Temperatures may reach 3500F
• 4 types
• Can
• Can annular
• Annular
• Annular reverse flow

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Combustion Module
Combustor Air Flow

• 2 air flows
• Primary/combustion air,
• secondary/dilution air
• Dilution air mixes with combustion air to
  protect turbine

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Combustion Module
Can Type

• Individual combustors in their own chambers/cans
• Results in a large diameter engine
• Ease of maintenance
• Convergent in shape

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Combustion Module
Can Annular Type

• Individual liners contained in a single outer
  chamber
• Maintenance friendly
• Transition or convergent shape to increase
  velocity

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Combustion Module
Annular Combustor

• Inner and outer wall construction
• Uses best practices from can and
• can annular designs
• Most efficient of all designs

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Combustion Module
Annular Reverse Flow
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Turbine Module

• Turbine is used to drive the compressor, and/or
  other devices ex.Fan, Gear Box
• A turbine extracts energy by converting kinetic
  energy into
• mechanical work or shaft horsepower
  (windmill).
• Turbines may also provide torque for rotors,
  props, generators.
• 2 types of turbines radial inflow, axial flow

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Turbine Module
Radial Inflow

• Inexpensive and simple in design.
• Almost 100 efficient at extracting
• SHP from gas path airflow.
• Stationary nozzle and rotating turbine wheel.

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Turbine Module
Axial Flow

• Turbine nozzles or stator vanes form convergent
  passages to
• increase air velocity
• The turbine rotor converts kinetic energy to
  rotational or
• mechanical energy to drive the compressor

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Turbine Module
Axial Flow - Fixed Turbine (Single Shaft)
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Turbine Module
Axial Flow - Fixed Turbine (Single Shaft)
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Turbine Module
Axial Flow - Fixed Turbine (Single Shaft)
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Turbine Module
Axial Flow - Free Turbine (Coaxial Shaft)
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Turbine Module
Axial Flow - Free Turbine (Coaxial Shaft)
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Turbine Module
Axial Flow Turbine Blades

• Blade Types
• Impulse
• Reaction
• Combination impulse / reaction

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Turbine Module
Impulse vs. Impulse - Reaction
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Turbine Module
Turbine Cooling

• Most common way to cool internal engine
  components is to use
• bleed air
• Convection and film cooling

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Turbine Module
68
Exhaust Module

• Used to collect hot gases and discharge to
  atmosphere
• Convergent and divergent passages may be used to
  extract
• energy
• Struts are used to reduce swirl in the escaping
  gases

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Exhaust Module
Thrust Producing Engine Flight Application
Torque Producing Engine Marine Application
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Exhaust Module
Afterburners
Thrust Reversers
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Accessory Module
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Accessory Module
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Accessory Module
Accessory Gearbox - Geartrain
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Accessory Module
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GTE Variations Applications

• 1. Thrust Producers
• Turbojet
• Turbofan
• 2. Torque Producers
• Turboprop/shaft
• 3. Fixed and Free Turbine

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GTE Variations Applications
Thrust Producer - Turbojet
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GTE Variations Applications
Thrust Producer - Turbofan
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GTE Variations Applications
Thrust Producer - Turbofan

• Bypass ratio refers to the ratio of incoming air
  that bypasses the core to the amount of air that
  passes through the engine core
• Low (1-1)
• Medium (2-1 or 3-1)
• High (4-1 or greater)

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GTE Variations Applications
Thrust Producer - Turbofan
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GTE Variations Applications
Torque Producers - Turboprop/shaft
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GTE Variations Applications
Torque Producers - Turboprop
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GTE Variations Applications
Torque Producers - Turboshaft
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GTE Variations Applications
Fixed Turbine

• Turbine and compressor are on same shaft

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GTE Variations Applications
Free Turbine

• No connection between 1st and 2nd turbine (air
  coupling)

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GTE Accessory Systems
1. Lubrication 2. Fuel 3. Starting systems 4.
Ignition 5. Monitoring
86
GTE Accessory Systems
Lubrication System

• Decrease friction
• Provide a cushion
• Dissipate heat
• Carry away debris
• Synthetic oils are used in GTEs
• Resists oxidation
• Resists coking
• low viscosity
• High viscosity range

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GTE Accessory Systems
Lubrication System
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GTE Accessory Systems
Lubrication System - Wet vs Dry Sump Systems

• Wet sump - oil is contained in oil sump under
  engine, relies on gravity to return to sump
• Dry sump - oil supply is carried in an oil tank,
  oil flows under pressure to and from engine and
  bearings

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GTE Accessory Systems
Lubrication System - Dry Sump System

• System Components
• Oil tank
• Oil pumps (pressure and scavenge)
• Filters
• Coolers
• Oil jets
• Chip detectors
• Breathers and pressurization
• Seals (labyrinth or wind back)

90
GTE Accessory Systems
Dry Sump System Components - Oil Tank

• May be mounted on engine or
• airframe
• May be under 3 -6 psi to ensure
• positive flow of oil to pressure pump
• Components
• Tank pressurizing venting systems
• Oil level indicator
• Oil temperature indicator
• De-aerator
• Filler cap
• Chip Detector

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GTE Accessory Systems
Dry Sump System Components - Oil Pumps
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GTE Accessory Systems
Dry Sump System Components - Oil Filters

• Used to remove contaminants (typically 25
  microns)
• Bypass valve may provide cockpit indication

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GTE Accessory Systems
Dry Sump System Components - Oil Cooler
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GTE Accessory Systems
Dry Sump System Components - Oil Nozzles/Jets
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GTE Accessory Systems
Dry Sump System Components - Chip Detector
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GTE Accessory Systems
Dry Sump System Components - Seals

• Labyrinth Seal
• Non rubbing seal
• Series of rotating
• knife edge seals

• Air pressure decreases as
• it passes through each
• cavity
• This pressure differential
• prevents oil from leaking
• past seal

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GTE Accessory Systems
Dry Sump System - Seals

• Classified as rubbing or non-rubbing
• May use air as the main sealing
• media or a combination of a seal
• element (carbon) and air.

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GTE Accessory Systems
Dry Sump System Components - Seals
Carbon Radial Seals

• Carbon Seal
• Rubbing seal
• Series of carbon seal
• segments
• May use air pressure to
• provide additional sealing

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GTE Accessory Systems
Dry Sump System Components - Seals
Carbon Axial Face Seals
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GTE Accessory Systems
Dry Sump System Components - Vent/Breather System

• System of breathers (vents) will allow excess
  air to escape
• Pressure differentials between sumps, oil tank,
  and oil pumps keep oil flowing in correct
  direction

• Allows for pressure equalization (internal
  -external)
• Bearing sumps are pressurized to ensure oil flow
• Prevents large amounts of air from being trapped
  in the oil

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GTE Accessory Systems
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GTE Accessory Systems
Engine Fuel System

• Supply a precise amount of fuel for all
  operating conditions
• Fuel system will store, transfer, and meter fuel
  to the engine
• Fuel may contain additives for anti-icing, as
  well as, anti-microbial to kill fungus and
  bacteria which tend to form slime in tanks
• Typical fuel used is a high grade kerosene which
  has more heat energy per gallon than other fuels

103
GTE Accessory Systems
Engine Fuel System
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GTE Accessory Systems
Engine Fuel System

• Fuel System Components
• Main engine driven fuel pump
• Fuel filter(s)
• Fuel control unit
• Fuel Manifold(s)
• Fuel nozzles
• Combustor drain valve(s)

105
GTE Accessory Systems
Engine Fuel System Components - Fuel Pump

• Positive displacement pump
• Designed to deliver an excess amount of fuel to
  Fuel Control Unit
• May use shear sections to allow operation if one
  pump element fails
• Typical pumps may develop 750-1500 psi

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GTE Accessory Systems
Engine Fuel System Components - Fuel Heater
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GTE Accessory Systems
Engine Fuel System Components - Fuel Filter

• Common practice to filter fuel
• Incorporate a by-pass
• Relief valve
• Protect the system
• components from contamination

108
GTE Accessory Systems
Engine Fuel System Components - Fuel Control Unit

• Engine driven accessory
• Schedules the fuel going to the fuel nozzles
• Maintains an ideal mixture of fuel and air 151
  by
• weight (stoichometric)
• Typically receives signals/inputs from the
  following
• Throttle or Power Lever position
• Engine RPM
• Compressor inlet pressure or Compressor
  discharge pressure
• Compressor inlet temperature or Compressor
  discharge temperature

109
GTE Accessory Systems
Engine Fuel System Components - Fuel Control Unit
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GTE Accessory Systems
Engine Fuel System Components - Combustor Drain
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GTE Accessory Systems
Engine Fuel System Components - Fuel Manifolds
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There are two types of fuel nozzles on Gas
Turbine engines -- simplex and duplex. With
simplex fuel nozzles, you have two different
nozzles -- primary and secondary. Each nozzle has
a single orifice. Simplex nozzles are typically
set up as either all primary (in some engines) or
in a ratio of 7 to 7 or 10 to 4 primary to
secondary. The configuration depends on the
engine model and the configuration status of the
engine. Upon startup, fuel is distributed to the
primary nozzles only. At a given N1, the
secondary nozzles kick in. With duplex nozzles,
fuel is introduced in a similar way as with a
simplex nozzle system -- in two stages with
primary spray upon startup and secondary kicking
in as the engine spools up. The difference is
that in a duplex nozzle system, all of the
nozzles are identical. Each one has two passages
and two concentric ports in the tip that spray
fuel. The primary and secondary are, in effect,
within each nozzle.
113
Module 4 - GTE Accessory Systems
Engine Fuel System Components - Fuel Nozzles

• Used to create a highly atomized, accurately
  shaped, spray pattern of fuel
• Must operate under all operating conditions

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Duplex
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Simplex
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GTE Accessory Systems
Starting Systems

• Used to accelerate engine to a speed at which the
  turbine is powering the compressor in order to
  allow engine operation
• High pressure air (APU, GTE)
• Electrically driven (starter-generator)

Pneumatic Starter
Starter/Generator
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GTE Accessory Systems
Starting Systems
Pneumatic Starter
119
GTE Accessory Systems
Ignition Systems

• Used to ignite fuel/air in combustor
• Low or high tension (voltage) systems
• Intermittent or continuous duty cycle
• Power supply - AC (115 vac) or DC (28 vdc)

120
GTE Accessory Systems
Engine Monitoring

• Fuel Fuel pressure
• Fuel Flow
• Oil Quantity
• Oil pressure
• Oil temperature
• Turbine Temperature
• RPM
• Vibration
• Torque (turboprop/shaft)

121
GTE Accessory Systems
Engine Monitoring - Turbine Temperature

• Temperature has impact on engine performance
• Alumel and chromel thermocouples
• Turbine Inlet Temperature
• Inter Turbine Temperature
• Turbine Outlet Temperature
• Exhaust Gas Temperature

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GTE Accessory Systems
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GTE Accessory Systems
Engine Monitoring - Vibration

• As engine wears, vibration levels will change,
  indicator of engine condition
• Help to predict engine life and maintenance
  required
• Transducer converters vibration to electrical
  current

124
GTE Accessory Systems
Engine Monitoring - Torque Measurement

• Hydro-Mechanical

• Electronic Phase Shift

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QUESTIONS