Turbine engine 1

TURBINE ENGINESTURBINE ENGINES Design of a working gas turbine engine had been Design of a working gas turbine engine had been

under way for years prior to WWII.under way for years prior to WWII. The war effort had brought about many advances in The war effort had brought about many advances in

gas turbine technology.gas turbine technology. Advantages over reciprocating engines:Advantages over reciprocating engines:

1- Increased reliability.1- Increased reliability.2- longer mean times between overhaul.2- longer mean times between overhaul.3- higher airspeeds.3- higher airspeeds.4- Ease of operation at high altitudes.4- Ease of operation at high altitudes.5- high power to engine weight ratio5- high power to engine weight ratio..

DESIGN AND CONSTRUCTIONDESIGN AND CONSTRUCTION NewtonNewton’’s third law of motion s third law of motion

states that states that for every action there is for every action there is an equal and opposite reaction.an equal and opposite reaction.

A squidA squid takes sea water into its takes sea water into its body and uses its muscles to add body and uses its muscles to add energy to the water, then expels energy to the water, then expels the water in the form of a jet. This the water in the form of a jet. This action produces a reaction that action produces a reaction that propels the squid forward.propels the squid forward.

Jet propulsion take a quantity of Jet propulsion take a quantity of air and accelerating it through an air and accelerating it through an orifice or nozzle.orifice or nozzle.

DESIGN AND CONSTRUCTIONDESIGN AND CONSTRUCTION Hero devised a toy called aeolipile used the reaction principle.Hero devised a toy called aeolipile used the reaction principle. Inflated balloon is anther example of NewtonInflated balloon is anther example of Newton’’s reaction principle.s reaction principle. Dr. Sanford Moss submitted his master thesis on gas turbine in Dr. Sanford Moss submitted his master thesis on gas turbine in

1900.1900. He uses his concepts to develop turbo-supercharger.He uses his concepts to develop turbo-supercharger. Frank Whittle of England uses Dr. Moss research to develop the Frank Whittle of England uses Dr. Moss research to develop the

first successful turbojet in 1930.first successful turbojet in 1930. The engine completed its first flight in 1941, producing about The engine completed its first flight in 1941, producing about

1000 lb at a speed over 400 miles/hr. 1000 lb at a speed over 400 miles/hr. Hans Von Ohain, German engineer design and built a jet engine Hans Von Ohain, German engineer design and built a jet engine

that produced 1100 lb and made its first flight in 1939.that produced 1100 lb and made its first flight in 1939. United states build its first jet engine which produces 1600 lb and United states build its first jet engine which produces 1600 lb and

made its first flight in 1942. made its first flight in 1942.

DESIGN AND CONSTRUCTIONDESIGN AND CONSTRUCTION

JET PROPULSION TODAYJET PROPULSION TODAY The majority of commercial aircraft utilize some The majority of commercial aircraft utilize some

form of jet propulsion.form of jet propulsion. Development of military and commercial aircraft Development of military and commercial aircraft

that moves faster than the speed of sound.that moves faster than the speed of sound. Extremely popular for use on business jets.Extremely popular for use on business jets.

TYPES OF JET PROPULSIONTYPES OF JET PROPULSION

1- ROCKET.1- ROCKET.

2- RAMJET.2- RAMJET.

3- PULSEJET.3- PULSEJET.

4- GAS TURBINE ENGINE.4- GAS TURBINE ENGINE.

ROCKETROCKET Non air breathing engine that carries its own fuel as well Non air breathing engine that carries its own fuel as well

as the oxygen needed for the fuel burn.as the oxygen needed for the fuel burn. Types of rockets:Types of rockets:

1- solid-propellant rockets.1- solid-propellant rockets.2- liquid-propellant rockets.2- liquid-propellant rockets.

Solid- propellant rockets use a solid fuel that is mixed Solid- propellant rockets use a solid fuel that is mixed with an oxidizer and shaped into a specific shape that with an oxidizer and shaped into a specific shape that promotes an optimum burning rate.promotes an optimum burning rate.

Produce extremely high velocity, and used to propel some Produce extremely high velocity, and used to propel some weapons and to provide additional thrust for take off of weapons and to provide additional thrust for take off of heavy loaded aircraft.heavy loaded aircraft.

Liquid-fuel rocket uses fuel and oxidizing agent such as Liquid-fuel rocket uses fuel and oxidizing agent such as liquid oxygen carried in tanks aboard the rocket.liquid oxygen carried in tanks aboard the rocket.

When mixed the reaction is so violent that produce a When mixed the reaction is so violent that produce a tremendous amount of heat.tremendous amount of heat.

ROCKETROCKET

RAMJETRAMJET Ramjet engine is an athodyd, or Ramjet engine is an athodyd, or

aero-thermodynamic-duct.aero-thermodynamic-duct. Air breathing engine with no Air breathing engine with no

moving parts.moving parts. Must be moved forward at a high Must be moved forward at a high

velocity before it can produce velocity before it can produce thrust.thrust.

Limited in there use, military Limited in there use, military weapons delivery systems.weapons delivery systems.

PULSEJETPULSEJET Similar to ramjet except that the Similar to ramjet except that the

air intake duct is equipped with a air intake duct is equipped with a series of shutter valves.series of shutter valves.

Shutter valves are spring loaded Shutter valves are spring loaded to the open position.to the open position.

Air is drawn and mixed with fuel Air is drawn and mixed with fuel in the combustion chamber, as in the combustion chamber, as pressure build up the shutter pressure build up the shutter valves closes causing the air to valves closes causing the air to expand backward.expand backward.

More useful than ramjet because More useful than ramjet because it will produce thrust prior to it will produce thrust prior to being accelerated to a high speed.being accelerated to a high speed.

GAS TURBINE ENGINEGAS TURBINE ENGINE The most practical form of jet engine in use today.The most practical form of jet engine in use today. The standard on nearly all transport and military The standard on nearly all transport and military

aircraft.aircraft. Types of gas turbine engines:Types of gas turbine engines:

1- Turbojet.1- Turbojet.2- Turboprop.2- Turboprop.3- Turboshaft.3- Turboshaft.44- Turbofan.- Turbofan.

TURBOJET ENGINESTURBOJET ENGINES Straight forward operating principle.Straight forward operating principle. Air enters through the air intake, compressed by the Air enters through the air intake, compressed by the

compressor, fuel is added and burned in the compressor, fuel is added and burned in the combustion chamber, heat causes the compressed combustion chamber, heat causes the compressed air to expand rearward, passes through the turbine air to expand rearward, passes through the turbine and spins it, which drives the compressor, and the and spins it, which drives the compressor, and the air then exit the engine at a much higher velocity air then exit the engine at a much higher velocity than the incoming air.than the incoming air.

The difference between the entering air and the The difference between the entering air and the exiting gases that produces the thrust.exiting gases that produces the thrust.

EPR is the ratio of the turbine discharge pressure to EPR is the ratio of the turbine discharge pressure to engine inlet air pressure.( EPR probes)engine inlet air pressure.( EPR probes)

TURBOJET ENGINESTURBOJET ENGINES

TURBOPROP ENGINESTURBOPROP ENGINES Turboprop engine is a gas turbine engine that Turboprop engine is a gas turbine engine that

delivers power to a propeller.delivers power to a propeller. Power produced by a turboprop is delivered to a Power produced by a turboprop is delivered to a

reduction gear system that spins a propeller.reduction gear system that spins a propeller. Used in business and commuter type aircraft Used in business and commuter type aircraft

because of the combination of jet power and because of the combination of jet power and propeller efficiency at speeds between 300 and 400 propeller efficiency at speeds between 300 and 400 mph.mph.

Provide the best specific fuel consumption of any Provide the best specific fuel consumption of any gas turbine engine.gas turbine engine.

TURBOPROP ENGINESTURBOPROP ENGINES

TURBOSHAFT ENGINESTURBOSHAFT ENGINES Turboshaft engine is a gas turbine Turboshaft engine is a gas turbine

engine that delivers power to a shaft engine that delivers power to a shaft that can drive something else.that can drive something else.

Most of the energy produced by the Most of the energy produced by the expanding gases is used to drive a expanding gases is used to drive a turbine.turbine.

Helicopters, auxiliary power units, Helicopters, auxiliary power units, electric generators, and surface electric generators, and surface transportation systems use turboshaft transportation systems use turboshaft engines.engines.

Turboshaft engine power is measured Turboshaft engine power is measured in shaft horsepower. in shaft horsepower.

TURBOSHAFT ENGINESTURBOSHAFT ENGINES

TURBOFAN ENGINESTURBOFAN ENGINES Consist of a multi-bladed ducted propeller Consist of a multi-bladed ducted propeller

driven by a gas turbine engine.driven by a gas turbine engine. Provide a compromise between the best Provide a compromise between the best

features of the turbojet and the turboprop.features of the turbojet and the turboprop. Have turbojet-type cruise speed capability, yet Have turbojet-type cruise speed capability, yet

retain some of the short-field takeoff capability retain some of the short-field takeoff capability of a turboprop.of a turboprop.

TURBOFAN ENGINESTURBOFAN ENGINES

TURBOFAN ENGINESTURBOFAN ENGINES Forward-fan engines have the fan mounted in Forward-fan engines have the fan mounted in

the front of the compressor.the front of the compressor. Aft-fan mounted engines have the fan Aft-fan mounted engines have the fan

mounted to the turbine section.mounted to the turbine section. Inlet air is divided into two separate streams.Inlet air is divided into two separate streams.

( engine core air, bypass air).( engine core air, bypass air).

TURBOFAN ENGINESTURBOFAN ENGINES Thrust ratioThrust ratio, , bypass ratiobypass ratio, and , and fan pressurefan pressure ratio ratio are are

the terms you should be familiar with.the terms you should be familiar with. Thrust ratioThrust ratio is the comparison of the thrust produced is the comparison of the thrust produced

by the fan to the thrust produced by the engine core by the fan to the thrust produced by the engine core exhaust.exhaust.

Bypass ratioBypass ratio is the ratio of incoming air to that is the ratio of incoming air to that bypasses the core to the amount of air that passes bypasses the core to the amount of air that passes through the engine core.through the engine core.

Fan pressure ratioFan pressure ratio is the ratio of air pressure leaving is the ratio of air pressure leaving the fan to the air pressure entering the fan.the fan to the air pressure entering the fan.

TURBOFAN ENGINESTURBOFAN ENGINES Turbofan engines are divided into three classification Turbofan engines are divided into three classification

based on bypass ratio:based on bypass ratio:1- low bypass (1:1).1- low bypass (1:1).2- medium bypass (2:1 or 3:1).2- medium bypass (2:1 or 3:1).3- high bypass (4:1 or greater).3- high bypass (4:1 or greater).

Low bypass engine, bypass air could be ducted directly Low bypass engine, bypass air could be ducted directly overboard through a short fan duct or in a ducted fan overboard through a short fan duct or in a ducted fan where the bypass air is ducted along the entire length of where the bypass air is ducted along the entire length of the engine.the engine.

Full fan ducts reduce aerodynamic drag and noise Full fan ducts reduce aerodynamic drag and noise emissions.emissions.

Both use a converging discharge nozzle that increases Both use a converging discharge nozzle that increases velocity and produce thrust. velocity and produce thrust.

TURBOFAN ENGINESTURBOFAN ENGINES Medium bypass engines have thrust ratio similar Medium bypass engines have thrust ratio similar

to their bypass ratios.to their bypass ratios. Fan diameter determines a fanFan diameter determines a fan ’’s bypass ratio and s bypass ratio and

thrust ratio.thrust ratio. High bypass ratio engines use the largest High bypass ratio engines use the largest

diameter fan of any of the bypass engines.diameter fan of any of the bypass engines. Offer higher propulsive efficiencies and better Offer higher propulsive efficiencies and better

fuel economy of low and medium bypass fuel economy of low and medium bypass engines.engines.

TURBOFAN ENGINESTURBOFAN ENGINES Fan pressure ratioFan pressure ratio is the ratio of air pressure leaving the is the ratio of air pressure leaving the

fan to the air pressure entering the fan.fan to the air pressure entering the fan. Ranging from 1.5:1 on a low bypass engines up to 7:1 on Ranging from 1.5:1 on a low bypass engines up to 7:1 on

some high bypass engines.some high bypass engines. Most high bypass ratio engines use high aspect ratio Most high bypass ratio engines use high aspect ratio

blades.blades. Aspect ratio is the ratio of a bladeAspect ratio is the ratio of a blade’’s length to its width, s length to its width,

or cord.or cord. Low aspect ratio blades are desirable because of their Low aspect ratio blades are desirable because of their

resistance to foreign object damage, especially bird resistance to foreign object damage, especially bird strikes.strikes.

UNDUCTED FAN ENGINESUNDUCTED FAN ENGINES Ultra high bypass (UHB) propfan and unducted Ultra high bypass (UHB) propfan and unducted

fan engine (UDF) are recently developed engines fan engine (UDF) are recently developed engines with higher efficiencies than any engine in use.with higher efficiencies than any engine in use.

Better fuel economy than high bypass turbofan Better fuel economy than high bypass turbofan engines.engines.

Achieve 30:1 bypass ratio by using single or dual Achieve 30:1 bypass ratio by using single or dual propellers made of composite blades that are 12 propellers made of composite blades that are 12 to 15 feet in diameter. to 15 feet in diameter.

UNDUCTED FAN ENGINESUNDUCTED FAN ENGINES

ENGINE COMPONENTSENGINE COMPONENTS Basic section of gas turbine engine:Basic section of gas turbine engine:

1- Air inlet.1- Air inlet.2- Compressor section.2- Compressor section.3- Combustion section.3- Combustion section.4- Turbine section.4- Turbine section.5- Exhaust section.5- Exhaust section.6- Accessory section.6- Accessory section.7- Necessary auxiliary systems.7- Necessary auxiliary systems.

ENGINE COMPONENTSENGINE COMPONENTS

AIR INLET DUCTSAIR INLET DUCTS Normally considered to be a part of the airframe rather Normally considered to be a part of the airframe rather

than the engine.than the engine. Functions of air inlet duct:Functions of air inlet duct:

1- (ram or pressure recovery) to recover as much of the 1- (ram or pressure recovery) to recover as much of the total pressure of the free airstream as possible and total pressure of the free airstream as possible and deliver it to the compressor.deliver it to the compressor.2- Shaped to raise the air pressure above atmospheric 2- Shaped to raise the air pressure above atmospheric pressure .pressure .3- Provide a uniform supply of air to the compressor so 3- Provide a uniform supply of air to the compressor so it can operate efficiently.it can operate efficiently.4- Must cause as little drag as possible.4- Must cause as little drag as possible.

Ram effect results from forward movement which Ram effect results from forward movement which causes the air to pile up in the air inlet.causes the air to pile up in the air inlet.

AIR INLET DUCTSAIR INLET DUCTS

AIR INLET DUCTSAIR INLET DUCTS Inlet ducts are mounted :Inlet ducts are mounted :

1- On the engine.1- On the engine.2- In the wing.2- In the wing.3- On the fuselage.3- On the fuselage.

Engine mounted inlets:Engine mounted inlets: Used on several large commercial and military Used on several large commercial and military

aircraft.aircraft. The air inlet is located directly in front of the The air inlet is located directly in front of the

compressor and is mounted to the engine.compressor and is mounted to the engine.

AIR INLET DUCTSAIR INLET DUCTSWing mounted inlets:Wing mounted inlets:

On some aircraft where the engines are mounted inside the On some aircraft where the engines are mounted inside the wings.wings.

Typically wing mounted inlets are positioned near the wing root.Typically wing mounted inlets are positioned near the wing root.

AIR INLET DUCTSAIR INLET DUCTSFuselage-mounted inlets:Fuselage-mounted inlets:

Engines mounted inside a fuselage typically use air Engines mounted inside a fuselage typically use air inlet ducts located near the front of the fuselage.inlet ducts located near the front of the fuselage.

Used on many old military and modern supersonic Used on many old military and modern supersonic aircraft. aircraft.

Using this type allow the manufacturer to build more Using this type allow the manufacturer to build more aerodynamic aircraft.aerodynamic aircraft.

Some military aircraft use air inlet ducts mounted on Some military aircraft use air inlet ducts mounted on the sides of the fuselage.the sides of the fuselage.


Types of air inlet ducts:Types of air inlet ducts:1- Subsonic inlets.1- Subsonic inlets.2- Supersonic inlets.2- Supersonic inlets.3- Bellmouth inlets.3- Bellmouth inlets.

Subsonic inletsSubsonic inlets Fixed geometry duct whose diameter progressively Fixed geometry duct whose diameter progressively

increases from front to back. increases from front to back. In a divergent duct as the intake air spreads out, In a divergent duct as the intake air spreads out,

the velocity of the air decreases and the pressure the velocity of the air decreases and the pressure increases.increases.

The increased pressure increase the engine The increased pressure increase the engine efficiency when it reach its designed cruise speed. efficiency when it reach its designed cruise speed. ( optimum aerodynamic efficiency, best fuel ( optimum aerodynamic efficiency, best fuel economy).economy).

Inlet, compressor, combustor, turbine, and exhaust Inlet, compressor, combustor, turbine, and exhaust duct are designed to match each other at this speed duct are designed to match each other at this speed as a unit. as a unit.

Subsonic inletsSubsonic inlets

Supersonic inletsSupersonic inlets Fixed or variable geometry whose diameter Fixed or variable geometry whose diameter

progressively decreases, then increases from progressively decreases, then increases from front to back.front to back.

Convergent-divergent duct used to slow the Convergent-divergent duct used to slow the incoming air to subsonic speed before it reaches incoming air to subsonic speed before it reaches the compressor.the compressor.

Movable plug or throat changes the duct Movable plug or throat changes the duct geometry to accommodate a wide range of geometry to accommodate a wide range of flight speeds.flight speeds.

Supersonic inletsSupersonic inlets

Bellmouth inletsBellmouth inlets Convergent profile that is designed for Convergent profile that is designed for

obtaining very high aerodynamic efficiency obtaining very high aerodynamic efficiency when stationary or in slow flight.when stationary or in slow flight.

Used on helicopters, some slow moving Used on helicopters, some slow moving aircraft, and ground run stands.aircraft, and ground run stands.

Short in length and has rounded shoulders Short in length and has rounded shoulders offering very little air resistance.offering very little air resistance.

Bellmouth inletsBellmouth inlets

FOREIGN OBJECT DAMAGEFOREIGN OBJECT DAMAGE(F.O.D)(F.O.D)

Prevention of F.O.D. is a top priority among Prevention of F.O.D. is a top priority among turbine engine operators.turbine engine operators.

Methods of FOD prevention:Methods of FOD prevention:1- Inlet screen over an engine inlet duct.1- Inlet screen over an engine inlet duct.2- Sand or ice separators.2- Sand or ice separators.3- Vortex dissipater, vortex destroyer, blow-3- Vortex dissipater, vortex destroyer, blow-away jet. away jet.

FOREIGN OBJECT DAMAGEFOREIGN OBJECT DAMAGE(F.O.D)(F.O.D)

The use of inlet screen is common on many The use of inlet screen is common on many rotorcraft and turboprop engines and on engine rotorcraft and turboprop engines and on engine installed in test stand.installed in test stand.

Inlet screen is not used on high mass airflow Inlet screen is not used on high mass airflow engines.engines.

Sand or ice separator consists of an air intake Sand or ice separator consists of an air intake with at least one venturi and a series of sharp with at least one venturi and a series of sharp bends.bends.

Sand or ice separatorsSand or ice separators

VORTEX DISSIPATERVORTEX DISSIPATER Some engines form a vortex between the Some engines form a vortex between the

ground and the ground and the inlet during ground and the ground and the inlet during ground operations.ground operations.

This vortex can lift water and debris or small This vortex can lift water and debris or small hardware and direct it to the engine.hardware and direct it to the engine.

Vortex dissipater routes high pressure bleed air Vortex dissipater routes high pressure bleed air to a discharge nozzle between the ground the to a discharge nozzle between the ground the air inlet to prevent vortex from developing.air inlet to prevent vortex from developing.

Landing gear switch arms the dissipater when Landing gear switch arms the dissipater when ever the aircraft is on ground. ever the aircraft is on ground.

VORTEX DISSIPATERVORTEX DISSIPATER

COMPRESSOR SECTIONCOMPRESSOR SECTION The more air that is forced into an engine, the The more air that is forced into an engine, the

more thrust the engine can produce.more thrust the engine can produce. Modern compressors must increase the intake Modern compressors must increase the intake

air pressure 20 to 30 times above the ambient air pressure 20 to 30 times above the ambient air pressure and move the air at a velocity of air pressure and move the air at a velocity of 400 to 500 feet per second.400 to 500 feet per second.

Compressor pressure ratio is the ratio of the Compressor pressure ratio is the ratio of the compressor discharge static pressure to the inlet compressor discharge static pressure to the inlet air static pressure. air static pressure.

COMPRESSOR SECTIONCOMPRESSOR SECTION Functions of compressors:Functions of compressors:

1- Support the combustion and provide the air 1- Support the combustion and provide the air necessary to produce thrust.necessary to produce thrust.2- Supplies bleed air :2- Supplies bleed air :a- to cool the hot section.a- to cool the hot section.b- heated air for anti-icing.b- heated air for anti-icing.c- cabin pressurization and air conditioning.c- cabin pressurization and air conditioning.d- fuel system deicing.d- fuel system deicing.e- pneumatic engine starting.e- pneumatic engine starting.

COMPRESSOR SECTIONCOMPRESSOR SECTION

TYPES OF COMPRESSORSTYPES OF COMPRESSORS1- 1- CENTRIFUGAL FLOW COMPRESSOR.CENTRIFUGAL FLOW COMPRESSOR.

2- AXIAL FLOW COMPRESSOR.2- AXIAL FLOW COMPRESSOR. Each is named according to the direction the air Each is named according to the direction the air

flows through the compressor.flows through the compressor.

CENTRIFUGAL FLOW CENTRIFUGAL FLOW COMPRESSORCOMPRESSOR

Some times called radial outflow compressor.Some times called radial outflow compressor. Earliest compressor design and still in use in Earliest compressor design and still in use in

some small engines and APUsome small engines and APU’’s.s. Consist of :Consist of :

1- impeller or rotor.1- impeller or rotor.2- diffuser.2- diffuser.3- manifold.3- manifold.


Impeller or rotor:Impeller or rotor: Consist of forged disc with integral blades, fastened by Consist of forged disc with integral blades, fastened by

a splined coupling to a common power shaft.a splined coupling to a common power shaft. The function of the impeller is to take the air in and The function of the impeller is to take the air in and

accelerate it outward by centrifugal force.accelerate it outward by centrifugal force. Single stage compressors have only one impeller.Single stage compressors have only one impeller. Two stage compressors have two impellers.Two stage compressors have two impellers. Double-sided or double entry compressors have two Double-sided or double entry compressors have two

impellers mounted back to back.impellers mounted back to back.

SINGLE STAGE COMPRESSORSINGLE STAGE COMPRESSOR

DOUBLE-STAGE COMPRESSORDOUBLE-STAGE COMPRESSOR

DOUBLE-SIDED COMPRESSORDOUBLE-SIDED COMPRESSOR


The use of more than two stages in a compressor is The use of more than two stages in a compressor is impractical:impractical:1- Energy lost when the air flow slows down as it 1- Energy lost when the air flow slows down as it passes from one impeller to the next.passes from one impeller to the next.2- The added weight from each impeller requires more 2- The added weight from each impeller requires more energy from the engine to drive the compressor.energy from the engine to drive the compressor.

Double sided impeller allows a higher mass air flow Double sided impeller allows a higher mass air flow than single impeller compressor. But the ducting to get than single impeller compressor. But the ducting to get the air from one side of the impeller to the other is the air from one side of the impeller to the other is complicated.complicated.


Diffuser, a divergent Diffuser, a divergent duct where the air duct where the air loses its velocity and loses its velocity and increases its increases its pressure.pressure.

In a divergent duct, In a divergent duct, air spreads out, air spreads out, slows down and slows down and increases in static increases in static pressure.pressure.


Compressor manifold distributes the air in a smooth Compressor manifold distributes the air in a smooth flow to the combustion section.flow to the combustion section.

The manifold has one outlet for each combustion The manifold has one outlet for each combustion chamber so the air is evenly divided.chamber so the air is evenly divided.

Outlet ducts is an elbow mounted to the outlet ports to Outlet ducts is an elbow mounted to the outlet ports to act as air duct.act as air duct.

Outlet ducts change the radial direction of the air to an Outlet ducts change the radial direction of the air to an axial direction.axial direction.

Turning vanes or cascade vanes help changing the Turning vanes or cascade vanes help changing the direction of the air with minimum energy loses. direction of the air with minimum energy loses.


Advantages of centrifugal compressor:Advantages of centrifugal compressor:1- Simplicity of manufacture.1- Simplicity of manufacture.2- Relatively low cost, low weight, low starting power 2- Relatively low cost, low weight, low starting power requirements.requirements.3- Operating efficiency over a wide range of rotational 3- Operating efficiency over a wide range of rotational speeds.speeds.4- Accelerate air rapidly and immediately deliver it to 4- Accelerate air rapidly and immediately deliver it to the diffuser.the diffuser.5- Tip distance may reach 1.3 mach with out air flow 5- Tip distance may reach 1.3 mach with out air flow separation.separation.6- High pressure rise per stage.6- High pressure rise per stage.


Disadvantages of centrifugal compressor:Disadvantages of centrifugal compressor:1- large frontal area, which mean increased 1- large frontal area, which mean increased aerodynamic drag.aerodynamic drag.2- limited number of stages restrict its uses to 2- limited number of stages restrict its uses to smaller and less powerful engines.smaller and less powerful engines.

Principles of operation

The impeller is rotated at high speed by the turbine and air is continuously induced into the centre of the impeller.

Centrifugal action causes it to flow radially outwards along the vanes to the impeller tip, thus accelerating the air and also causing a rise in pressure to occur.

The engine intake duct may contain vanes that provide an initial swirl to the air entering the compressor .

The air, on leaving the impeller, passes into the diffuser section where the passages form divergent nozzles that convert most of the kinetic energy into pressure energy.


To maximize the airflow and pressure rise through the compressor requires the impeller to be rotated at high speed, therefore impellers are designed to operate at tip speeds of up to 1,600 ft. per sec.

By operating at such high tip speeds the air velocity from the impeller is increased so that greater energy is available for conversion to pressure.

To maintain the efficiency of the compressor, it is necessary to prevent excessive air leakage between the impeller and the casing; this is achieved by keeping their clearances as small as possible

AXIAL FLOW COMPRESSORAXIAL FLOW COMPRESSOR Consist of :

1- ROTOR.2- STATOR.

The rotor consist of rows of blades fixed on a rotating spindle. The angle and airfoil contour forces the air backward as a

propeller. The stator vanes are arranged infixed rows between the rows of

rotor blades and act as a diffuser at each stage. Stators decrease the air velocity and raise the pressure. Each pressure stage consist of one row of blades and one row of

vanes.

AXIAL FLOW COMPRESSORAXIAL FLOW COMPRESSOR

AXIAL FLOW COMPRESSORAXIAL FLOW COMPRESSOR Single stage in an Axial compressor is capable of

rising the pressure ratio of only 1.25 : 1. High compressor pressure ratio is obtained by adding

more stages. Unlike centrifugal compressors, axial flow

compressors raise the air pressure rather than the velocity.

The rotor of each stage rise the velocity of the air while the stator vanes diffuse the air, slowing it and increase the pressure.

The overall result is increased air pressure and relatively constant velocity.


The space between the rotor shaft and the stator casing gradually decreases from front to back.

This shape is necessary to maintain a constant air velocity as air density increases.

The case of most axial compressors is horizontally divided into two halves.

Bleed air ports are provided on the comp. case for ancillary functions.

AXIAL FLOW COMPRESSORAXIAL FLOW COMPRESSOR Disadvantage of axial compressor:

1- High weight 2- High starting power requirements.3- Low pressure rise per stage.4- Expensive and difficult to manufacture.

Advantages over radial flow compressors:1- High ram efficiency.2- The ability to obtain higher compressor pressure ratio.3- Reduced aerodynamic drag because of small frontal area.

COMPRESSOR ROTOR BLADESCOMPRESSOR ROTOR BLADES Aerofoil cross-section

with a varying angle of incidence or twist blades.

The twist compensates for the blade velocity variation between the tip and the root.

Axial flow compressors typically have 10 to 18 compression stages.

COMPRESSOR ROTOR BLADESCOMPRESSOR ROTOR BLADES

The roots of the blades often fits loosely into the rotor, to The roots of the blades often fits loosely into the rotor, to allow for easy assembly and vibration damping.allow for easy assembly and vibration damping.

As the blades rotate the centrifugal force keeps the blades in As the blades rotate the centrifugal force keeps the blades in their correct position.their correct position.

Bulb, Fir tree, or dovetail are the design of rotor blades roots.Bulb, Fir tree, or dovetail are the design of rotor blades roots. The blades is secured in their position by using a pin and lock The blades is secured in their position by using a pin and lock

tab or locker.tab or locker. Some long fan blades have a mid-span shroud that helps Some long fan blades have a mid-span shroud that helps

support the blades, making them more resistant to the bending support the blades, making them more resistant to the bending force created by airstream.force created by airstream.

Shingling happen when the mating surfaces on a mid-span Shingling happen when the mating surfaces on a mid-span shroud become excessively worn and the shrouds overlap.shroud become excessively worn and the shrouds overlap.

COMPRESSOR ROTOR BLADESCOMPRESSOR ROTOR BLADES Flat machine tip blade is cut off square at the tip.Flat machine tip blade is cut off square at the tip. Profile tip blade have a reduced thickness at the tips.Profile tip blade have a reduced thickness at the tips. Profiling a compressor blade increases its natural vibration Profiling a compressor blade increases its natural vibration

frequency, which reduce the blade vibration tendency.frequency, which reduce the blade vibration tendency. Thin trailing edge of profile tipped blades causes a vortex Thin trailing edge of profile tipped blades causes a vortex

which increases air velocity and prevent air from spilling back which increases air velocity and prevent air from spilling back over the blade tip.over the blade tip.

Tight clearance around the blade tips of some newer engine is Tight clearance around the blade tips of some newer engine is accomplished by using a shroud strip of abradable material.accomplished by using a shroud strip of abradable material.

Localized increase in blade camber, both at blade tip and root Localized increase in blade camber, both at blade tip and root increases compressor efficiency.increases compressor efficiency.

The increased blade camber overcome the friction caused by The increased blade camber overcome the friction caused by the boundary layer of air near the compressor case. (end bend). the boundary layer of air near the compressor case. (end bend).

COMPRESSOR STATOR VANESCOMPRESSOR STATOR VANES

Stator vanes is stationary blades located between Stator vanes is stationary blades located between rows of rotating blades.rows of rotating blades.

Act as diffusers for the air coming off the rotor Act as diffusers for the air coming off the rotor decreasing its velocity, increasing pressure, prevent decreasing its velocity, increasing pressure, prevent swirling, and direct the flow of air to the next stage.swirling, and direct the flow of air to the next stage.

Stator vanes are made of steel, nickel, and titanium.Stator vanes are made of steel, nickel, and titanium. Secured directly to the compressor casing or to a Secured directly to the compressor casing or to a

stator vane retaining ring.stator vane retaining ring. Stator vanes are often shrouded at their tips to Stator vanes are often shrouded at their tips to

minimize vibration.minimize vibration.


Inlet guide vanes are a set of stator vanes Inlet guide vanes are a set of stator vanes immediately in front of the first stage rotor blades.immediately in front of the first stage rotor blades.

Inlet guide vanes direct the airflow into the first stage Inlet guide vanes direct the airflow into the first stage rotor blades at the best angle, to improve the rotor blades at the best angle, to improve the aerodynamics of the compressor by reducing the drag aerodynamics of the compressor by reducing the drag on the 1on the 1stst rotor blades. rotor blades.

To maintain proper airflow through the engine, To maintain proper airflow through the engine, variable IGVvariable IGV’’s and several stator vanes are used on s and several stator vanes are used on some high compressor pressure ratio engines.some high compressor pressure ratio engines.

The outlet vane assembly is the last set of vanes that The outlet vane assembly is the last set of vanes that straighten the air flow and eliminate any swirling straighten the air flow and eliminate any swirling motion or turbulence. motion or turbulence.

MULTIPLE-SPOOL COMPRESSORSMULTIPLE-SPOOL COMPRESSORS

Single spool compressor has only one Single spool compressor has only one compressor unit connected to the turbine.compressor unit connected to the turbine.

Drawback of single spool compressors:Drawback of single spool compressors:1- rear stages operate at a fraction of their capacity, 1- rear stages operate at a fraction of their capacity,

while the forward stages are overloaded.while the forward stages are overloaded.2- does not respond quickly to sudden control input 2- does not respond quickly to sudden control input

changes.changes. Single-spool compressors are relatively Single-spool compressors are relatively

simple and inexpensive.simple and inexpensive.

MULTIPLE-SPOOL COMPRESSORSMULTIPLE-SPOOL COMPRESSORS Single spool compressor Drawbacks were overcome by Single spool compressor Drawbacks were overcome by

splitting the compressor into two or three sections.splitting the compressor into two or three sections. Each compressor is connected to its turbine by shafts that run Each compressor is connected to its turbine by shafts that run

coaxially, one within the other.coaxially, one within the other. Dual-spool, twin-spool compressors has two compressors Dual-spool, twin-spool compressors has two compressors

connected to two turbines.connected to two turbines. Front section is called low pressure, low speed, or N1 Front section is called low pressure, low speed, or N1

compressor. Driven by 2 stage low pressure turbine (rear compressor. Driven by 2 stage low pressure turbine (rear turbine).turbine).

Second compressor is called high pressure, high speed, or N2 Second compressor is called high pressure, high speed, or N2 compressor. Driven by single stage high pressure turbine compressor. Driven by single stage high pressure turbine (front turbine). (front turbine).

The low pressure compressor is driven by the high pressure The low pressure compressor is driven by the high pressure turbine by a shaft that rotate inside the high pressure turbine by a shaft that rotate inside the high pressure compressor shaft.compressor shaft.

MULTIPLE-SPOOL COMPRESSORSMULTIPLE-SPOOL COMPRESSORS Since the spools are not connected together, each is free to Since the spools are not connected together, each is free to

seek its own best operating speed.seek its own best operating speed. High pressure compressor speed is relatively constant.High pressure compressor speed is relatively constant. Low pressure compressor speeds up or slows down with Low pressure compressor speeds up or slows down with

changes in the inlet sir flow caused by flight condition.changes in the inlet sir flow caused by flight condition. N1 increases at high altitude and decreases at low altitude to N1 increases at high altitude and decreases at low altitude to

supply the high pressure compressor with constant air supply the high pressure compressor with constant air pressure and mass flow for each power setting. pressure and mass flow for each power setting.

Triple-spool compressor turbo-fan engine has three Triple-spool compressor turbo-fan engine has three compressors connected to three turbines.compressors connected to three turbines.

The fan, low pressure, or N1 compressor, the next in line is The fan, low pressure, or N1 compressor, the next in line is called intermediate or N2 compressor, and the inner most is called intermediate or N2 compressor, and the inner most is called high pressure or N3 compressor.called high pressure or N3 compressor.

COMPRESSOR STALLCOMPRESSOR STALL Compressor blades are airfoils, so its subjected to the Compressor blades are airfoils, so its subjected to the

same aerodynamic principles as aircraft wings.same aerodynamic principles as aircraft wings. Compressor blade has an angle of attack which is : an Compressor blade has an angle of attack which is : an

acute angle between the chord line and the relative acute angle between the chord line and the relative wind.wind.

The angle of attack of a compressor blade is the The angle of attack of a compressor blade is the result of inlet air velocity and the compressorresult of inlet air velocity and the compressor’’s s rotational velocity.( vector ) Quantity to the rotational velocity.( vector ) Quantity to the approaching inlet air. approaching inlet air.

Compressor stall is an imbalance between the two Compressor stall is an imbalance between the two vector quantities, inlet velocity and compressor vector quantities, inlet velocity and compressor rotational speed. rotational speed.

COMPRESSOR STALLCOMPRESSOR STALL Compressor stall occur when the compressor Compressor stall occur when the compressor

bladeblade’’s angle of attack exceeds the critical s angle of attack exceeds the critical angle of attack.angle of attack.

Smooth airflow is interrupted and turbulence Smooth airflow is interrupted and turbulence is created with pressure fluctuations.is created with pressure fluctuations.

During stall airflow in the compressor slow During stall airflow in the compressor slow down and stagnate sometimes reverse down and stagnate sometimes reverse direction.direction.

Heard as pulsating or fluttering sound in its Heard as pulsating or fluttering sound in its mildest form to a loud explosion in its most mildest form to a loud explosion in its most developed state.developed state.

COMPRESSOR STALLCOMPRESSOR STALL Cockpit indications for compressor stall:Cockpit indications for compressor stall:

1- fluctuations in rpm.1- fluctuations in rpm.2- increase in exhaust gas temperature.2- increase in exhaust gas temperature.

Transient stall are mild and not harmful to the Transient stall are mild and not harmful to the engine, and often correct themselves easily.engine, and often correct themselves easily.

Sever or hung stall can significantly impair engine Sever or hung stall can significantly impair engine performance, cause loss of power and can damage performance, cause loss of power and can damage the engine.the engine.

Reducing the angle of attack on the rotor blades is Reducing the angle of attack on the rotor blades is the only way to overcome a stalled condition.the only way to overcome a stalled condition.

COMPRESSOR STALLCOMPRESSOR STALL Methods of preventing compressor stall:Methods of preventing compressor stall:

1- Variable inlet guide vanes and stator vanes.1- Variable inlet guide vanes and stator vanes.2- Air-bleed valves.2- Air-bleed valves.

Reasons of compressor stall:Reasons of compressor stall:1-When A/C flies in sever turbulence or performs 1-When A/C flies in sever turbulence or performs abrupt flight maneuvers.abrupt flight maneuvers.2- Excessive fuel flow caused by sudden engine 2- Excessive fuel flow caused by sudden engine acceleration.acceleration.3- Contamination or damaged compressor blades, 3- Contamination or damaged compressor blades, stator vanes or turbine components. (FOD) stator vanes or turbine components. (FOD)

AIR-BLEED VALVEAIR-BLEED VALVE

COMBINATION COMPRESSORSCOMBINATION COMPRESSORS Axial flow-centrifugal flow compressors were developed to Axial flow-centrifugal flow compressors were developed to

combine the best features of centrifugal and axial compressors.combine the best features of centrifugal and axial compressors. Currently used in some smaller engines installed on business Currently used in some smaller engines installed on business

jets and helicopters.jets and helicopters.

COMPRESSOR AIR BLEEDCOMPRESSOR AIR BLEEDCompressor supplies high pressure, high Compressor supplies high pressure, high temperature air for various secondary functions temperature air for various secondary functions such as:such as:1.1. Cabin pressurization.Cabin pressurization.2.2. Heating.Heating.3.3. Cooling.Cooling.4.4. Deicing.Deicing.5.5. Anti-icing.Anti-icing.6.6. Pneumatic engine starting.Pneumatic engine starting.

COMPRESSOR AIR BLEEDCOMPRESSOR AIR BLEED Bleed air or customer bleed air is tapped from the Bleed air or customer bleed air is tapped from the compressor through bleed ports at various stages.compressor through bleed ports at various stages.

Bleed port is a small opening adjacent to the Bleed port is a small opening adjacent to the compressor stage selected for bleed air supply. compressor stage selected for bleed air supply.

The required air pressure and temperature determine The required air pressure and temperature determine the compressor stage to bleed air from.the compressor stage to bleed air from.

The air bled from the last stage often need cooling The air bled from the last stage often need cooling because the air temperature would be very high because the air temperature would be very high because of compression. (650because of compression. (650 ْْ F).F).

Bleeding air dose cause a small drop in engine Bleeding air dose cause a small drop in engine power, power loss can be detected by observing EPR, power, power loss can be detected by observing EPR, and EGT.and EGT.

COMPRESSOR AIR BLEEDCOMPRESSOR AIR BLEED

DIFFUSERDIFFUSER The divergent shape of a The divergent shape of a

diffuser slows compressor diffuser slows compressor discharge while at the same discharge while at the same time increase its pressure to time increase its pressure to the highest value in the the highest value in the engine.engine.

Air speed must be slowed Air speed must be slowed to support combustion.to support combustion.

Diffuser is a separate Diffuser is a separate section bolted to the rear of section bolted to the rear of the compressor ahead of the the compressor ahead of the combustion section.combustion section.

COMBUSTION SECTIONCOMBUSTION SECTION Located directly between the compressor diffuser Located directly between the compressor diffuser

and turbine section.and turbine section. Basic components of combustion section:Basic components of combustion section:

1- one or more combustion chambers (combustors).1- one or more combustion chambers (combustors).2- fuel injection system.2- fuel injection system.3- ignition source.3- ignition source.4- fuel drainage system.4- fuel drainage system.

COMBUSTION SECTIONCOMBUSTION SECTION Combustion chamber or combustors is where Combustion chamber or combustors is where

the fuel and air are mixed and burned.the fuel and air are mixed and burned. Consist of an outer casing with a perforated Consist of an outer casing with a perforated

inner liner.inner liner. Perforation are various shapes and sizes that Perforation are various shapes and sizes that

effect the flame propagation within the liner.effect the flame propagation within the liner.

COMBUSTION SECTIONCOMBUSTION SECTION Fuel injection system meters the right amount Fuel injection system meters the right amount

of fuel through the fuel nozzles.of fuel through the fuel nozzles. Fuel nozzles are located in the combustion Fuel nozzles are located in the combustion

chamber case or compressor outlet elbow.chamber case or compressor outlet elbow. Fuel is sprayed in a finely atomized spray into Fuel is sprayed in a finely atomized spray into

the liner.the liner. The finer the spray the more rapid and The finer the spray the more rapid and

efficient the combustion process.efficient the combustion process.

COMBUSTION SECTIONCOMBUSTION SECTION High energy capacitor discharge system is High energy capacitor discharge system is

typically used as ignition source for turbine typically used as ignition source for turbine engine.engine.

Ignition system produces 60 to 100 sparks per Ignition system produces 60 to 100 sparks per minute.minute.

A ball of fire results at the igniter electrodes.A ball of fire results at the igniter electrodes. Some systems can shoot sparks several inches.Some systems can shoot sparks several inches. Care must be taken to avoid lethal shock Care must be taken to avoid lethal shock

during maintenance.during maintenance.

COMBUSTION SECTIONCOMBUSTION SECTION Unburned fuel is drained out after engine shut Unburned fuel is drained out after engine shut

down.down. Draining the unburned fuel eliminates engine Draining the unburned fuel eliminates engine

fire after shutdown, and reduces the possibility fire after shutdown, and reduces the possibility of exceeding tail pipe or turbine inlet of exceeding tail pipe or turbine inlet temperature.temperature.

Helps to prevent gum deposits in the fuel Helps to prevent gum deposits in the fuel manifold and the combustion chamber.manifold and the combustion chamber.

COMBUSTION SECTIONCOMBUSTION SECTION To accomplish the task of burning the fuel air To accomplish the task of burning the fuel air

mixture efficiently the C.C must:mixture efficiently the C.C must:1- Mix fuel and air effectively in the best ratio 1- Mix fuel and air effectively in the best ratio

for good combustion.for good combustion.2- Burn the mixture as efficiently as possible.2- Burn the mixture as efficiently as possible.3- Cool the hot combustion gases to a 3- Cool the hot combustion gases to a temperature the turbine blades can tolerate.temperature the turbine blades can tolerate.4- Distribute hot gases evenly to the turbine 4- Distribute hot gases evenly to the turbine section.section.

COMBUSTION SECTIONCOMBUSTION SECTION Air flow through the combustor is divided into Air flow through the combustor is divided into

primary and secondary paths.primary and secondary paths. 25 to 35 % of the incoming air is primary.25 to 35 % of the incoming air is primary. 65 to 75 % of the incoming air is secondary.65 to 75 % of the incoming air is secondary. Primary or combustion air is directed inside the liner, Primary or combustion air is directed inside the liner,

passing through a set of swirl vanes which give the passing through a set of swirl vanes which give the air a radial motion.air a radial motion.

As air is swirled the speed is reduced to about five to As air is swirled the speed is reduced to about five to six feet per second.six feet per second.

Its important to slow the air to prevent flameout.Its important to slow the air to prevent flameout.

COMBUSTION SECTIONCOMBUSTION SECTION Radial motion generate a vortex in the flame area which Radial motion generate a vortex in the flame area which

properly mix the fuel and air.properly mix the fuel and air. The combustion process is completed in the first third of The combustion process is completed in the first third of

a combustor.a combustor. The secondary air flow at high speed (several hundred The secondary air flow at high speed (several hundred

feet per sec.) around the combustorfeet per sec.) around the combustor’’s periphery.s periphery. Secondary air forms a cooling blanket on both sides of Secondary air forms a cooling blanket on both sides of

the liner and centers the combustion flames.the liner and centers the combustion flames. Some air enters the combustors through the perforations Some air enters the combustors through the perforations

to ensure the burning of any remaining fuel.to ensure the burning of any remaining fuel. Secondary air mix with the combustion gases to provide Secondary air mix with the combustion gases to provide

an even distribution of energy to the turbine nozzle.an even distribution of energy to the turbine nozzle.

COMBUSTION SECTIONCOMBUSTION SECTION

COMBUSTION SECTIONCOMBUSTION SECTION Types of combustion chambers:Types of combustion chambers:

1- Multiple-can type.1- Multiple-can type.2- Annular type and reverse flow annular type.2- Annular type and reverse flow annular type.3- Can-annular type3- Can-annular type

MULTIPLE-CAN TYPEMULTIPLE-CAN TYPE Consist of a series of individual combustor cans which Consist of a series of individual combustor cans which

acts as individual burner units.acts as individual burner units. Well suited to centrifugal compressor engines.Well suited to centrifugal compressor engines. Each Can has a case and a perforated stainless steel liner.Each Can has a case and a perforated stainless steel liner. Inner liner is heat resistant and easily removed for Inner liner is heat resistant and easily removed for

inspection.inspection. Each Can has a large curvature to provide high resistance Each Can has a large curvature to provide high resistance

to warpage.to warpage. Tow igniter plugs in two cans start the combustion, then Tow igniter plugs in two cans start the combustion, then

the flame is traveled to the other cans by flame the flame is traveled to the other cans by flame propagation tubes (interconnectors).propagation tubes (interconnectors).

Each flame propagation tubes is a small tube surrounded Each flame propagation tubes is a small tube surrounded with larger tube or jacket.with larger tube or jacket.

MULTIPLE-CAN TYPEMULTIPLE-CAN TYPE

ANNULAR TYPEANNULAR TYPE Commonly used on small and large engines.Commonly used on small and large engines. The most efficient for thermal efficiency, weight, and The most efficient for thermal efficiency, weight, and

physical size.physical size. Consist of a housing and a perforated inner liner or Consist of a housing and a perforated inner liner or

basket.basket. The liner is single unit that encircle the turbine shaft.The liner is single unit that encircle the turbine shaft. An annular combustor with two baskets is known as a An annular combustor with two baskets is known as a

double annular combustion chamber.double annular combustion chamber. Two igniters are used to ignite the fuel/air mixture.Two igniters are used to ignite the fuel/air mixture.

ANNULAR TYPEANNULAR TYPE

ANNULAR TYPEANNULAR TYPE Air flow enters at the front and is discharged at the rear Air flow enters at the front and is discharged at the rear

with primary and secondary airflow.with primary and secondary airflow. Must be removed as one unit for repair or replacement.Must be removed as one unit for repair or replacement. Reverse flow combustors are designed so the airflow can Reverse flow combustors are designed so the airflow can

reverse direction.reverse direction. The combustion gases enters from the rear and flowing in The combustion gases enters from the rear and flowing in

the opposite direction of the normal airflow through the the opposite direction of the normal airflow through the engine.engine.

The turbine wheels are inside the combustor area, which The turbine wheels are inside the combustor area, which allow for a shorter and lighter engine.allow for a shorter and lighter engine.

Compressor discharge air is preheated as it passes around Compressor discharge air is preheated as it passes around the combustion chamber.the combustion chamber.

Lighter weight and air preheat make up for the losses Lighter weight and air preheat make up for the losses caused by the reversing of the direction of the air. caused by the reversing of the direction of the air.

ANNULAR TYPEANNULAR TYPE

CAN-ANNULAR TYPECAN-ANNULAR TYPE Combination of the multiple-can and annular type Combination of the multiple-can and annular type

combustors.combustors. Consist of a casing that encircles multiple cans (liners) Consist of a casing that encircles multiple cans (liners)

assembled radially around the engine axis.assembled radially around the engine axis. A fuel nozzle cluster is attached at the forward end of A fuel nozzle cluster is attached at the forward end of

each burner can.each burner can. Pre-swirl vanes are placed around each fuel nozzle. Pre-swirl vanes are placed around each fuel nozzle.

(through fuel mixing and slow the air).(through fuel mixing and slow the air). Tow igniter plugs initiate the combustion and Tow igniter plugs initiate the combustion and

propagation tubes connect the liners.propagation tubes connect the liners. Each can and its liner removed individually for Each can and its liner removed individually for

maintenance.maintenance. Combine the ease of overhaul and testing of multiple-can Combine the ease of overhaul and testing of multiple-can

combustors with the compactness of annular combustors. combustors with the compactness of annular combustors.

CAN-ANNULAR TYPECAN-ANNULAR TYPE

FLAME OUTFLAME OUT High air flow rate or excessively slow airflow can High air flow rate or excessively slow airflow can

extinguish the combustion flame.extinguish the combustion flame. Flameout is uncommon in modern engine but if the Flameout is uncommon in modern engine but if the

correct set of circumstances can cause engine die out.correct set of circumstances can cause engine die out. Turbulent weather, high altitude, slow acceleration, and Turbulent weather, high altitude, slow acceleration, and

high speed maneuvers can induce a flameout.high speed maneuvers can induce a flameout. Lean die-out occurs at high altitude where low engine Lean die-out occurs at high altitude where low engine

speeds and low fuel pressure form a weak flame that can speeds and low fuel pressure form a weak flame that can die out in normal airflow.die out in normal airflow.

Rich blow-out occurs during rapid engine acceleration Rich blow-out occurs during rapid engine acceleration when an overly rich mixture causes the fuel temperature when an overly rich mixture causes the fuel temperature to drop below the combustion temperature or when there to drop below the combustion temperature or when there is insufficient airflow to support combustion.is insufficient airflow to support combustion.

TURBINE SECTIONTURBINE SECTION Transforms a portion of the kinetic energy in Transforms a portion of the kinetic energy in

the hot exhaust gases into mechanical energy the hot exhaust gases into mechanical energy to drive the compressor and accessories.to drive the compressor and accessories.

In a turbojet engine the turbine absorbs In a turbojet engine the turbine absorbs approximately 60 to 80 % of the total pressure approximately 60 to 80 % of the total pressure energy from exhaust gases.energy from exhaust gases.

Consist of:Consist of:1- case. 2- stator. 3- shroud. 4- rotor. 1- case. 2- stator. 3- shroud. 4- rotor.

TURBINE SECTIONTURBINE SECTION


TURBINE CASINGTURBINE CASING Encloses the turbine rotor and stator assembly, Encloses the turbine rotor and stator assembly,

support the stator elements.support the stator elements. Has flanges on both ends that provide a means Has flanges on both ends that provide a means

of attaching the turbine section to the of attaching the turbine section to the combustion section and the exhaust assembly.combustion section and the exhaust assembly.

TURBINE SECTIONTURBINE SECTIONTURBINE STATORTURBINE STATOR

Stator element, turbine nozzle, turbine guide vanes, and nozzle Stator element, turbine nozzle, turbine guide vanes, and nozzle diaphragm.diaphragm.

Located directly aft of the combustion section and Located directly aft of the combustion section and immediately forward of the turbine wheel.immediately forward of the turbine wheel.

Exposed to the highest temperatures in a gas turbine engine.Exposed to the highest temperatures in a gas turbine engine. Function: To collect the high energy airflow from the Function: To collect the high energy airflow from the

combustors and direct the flow to strike the turbine rotor at the combustors and direct the flow to strike the turbine rotor at the appropriate angle.appropriate angle.

The stator vanes form a converging nozzles which convert The stator vanes form a converging nozzles which convert some of the pressure energy to velocity energy.some of the pressure energy to velocity energy.

The velocity energy of the exhaust gases is converted to The velocity energy of the exhaust gases is converted to mechanical energy by the rotor blades.mechanical energy by the rotor blades.

TURBINE SECTIONTURBINE SECTIONTURBINE SHROUDTURBINE SHROUD

Turbine nozzle assembly consist of an inner and outer shroud Turbine nozzle assembly consist of an inner and outer shroud that retains and surround the nozzle vanes.that retains and surround the nozzle vanes.

The vanes are assembled between the inner and outer shroud The vanes are assembled between the inner and outer shroud in deferent methods.in deferent methods.

The nozzle vanes must be constructed to allow for thermal The nozzle vanes must be constructed to allow for thermal expansion, to prevent distortion or warping of the nozzle expansion, to prevent distortion or warping of the nozzle assembly.assembly.

Installing the vanes loosely in the inner and outer shrouds and Installing the vanes loosely in the inner and outer shrouds and encase them in an inner and outer support rings allow thermal encase them in an inner and outer support rings allow thermal expansion of the vanes.expansion of the vanes.

Rigidly weld or rivet the vanes into the inner and outer Rigidly weld or rivet the vanes into the inner and outer shrouds which are cut into segments that have gaps between shrouds which are cut into segments that have gaps between them allow for expansion.them allow for expansion.


TURBINE ROTORTURBINE ROTOR Consist of a shaft and a turbine rotor, or wheel.Consist of a shaft and a turbine rotor, or wheel. Turbine wheel is a dynamically balanced unit Turbine wheel is a dynamically balanced unit

consisting of blades attached to a rotating disk.consisting of blades attached to a rotating disk. The disk is the anchoring component for the turbine The disk is the anchoring component for the turbine

blades and bolted or welded to the shaft.blades and bolted or welded to the shaft. The shaft rotates in bearing that are lubricated by oil The shaft rotates in bearing that are lubricated by oil

between the outer race and the housing to reduce between the outer race and the housing to reduce vibration and allows for a slight misalignment in the vibration and allows for a slight misalignment in the shaft.shaft.


TURBINE ROTORTURBINE ROTOR The high velocity gases pass through the The high velocity gases pass through the

turbine nozzle to rotate the turbine wheel.turbine nozzle to rotate the turbine wheel. Many engines use multiple turbine stages to Many engines use multiple turbine stages to

absorb sufficient energy to drive the absorb sufficient energy to drive the compressor.compressor.

The turbine is exposed to high rotational speed The turbine is exposed to high rotational speed and elevated operating temperature stress.and elevated operating temperature stress.

This stress could lead to turbine bleed growth This stress could lead to turbine bleed growth or creep. or creep.

TURBINE SECTIONTURBINE SECTIONTURBINE BLADESTURBINE BLADES

Airfoil shaped designed to extract the maximum Airfoil shaped designed to extract the maximum amount of energy from the hot gases.amount of energy from the hot gases.

Blades are either forged or cast.Blades are either forged or cast. Steel forged or cast nickel-based alloys.Steel forged or cast nickel-based alloys. Development of reinforced ceramic holds promise.Development of reinforced ceramic holds promise. Blades fit loosely into turbine disk when cold, and Blades fit loosely into turbine disk when cold, and

expand to fit tightly when hot.expand to fit tightly when hot. Fir tree slots is the most commonly used method for Fir tree slots is the most commonly used method for

attaching turbine blades.attaching turbine blades. The blade may be retained in its groove by peening, The blade may be retained in its groove by peening,

welding, rivets, or lock tabs.welding, rivets, or lock tabs.


TURBINE BLADESTURBINE BLADES Classification of turbine blades:Classification of turbine blades:

1- Impulse.1- Impulse.2- Reaction.2- Reaction.3- Impulse-Reaction.3- Impulse-Reaction.


IMPULSE TURBINE BLADESIMPULSE TURBINE BLADES The total pressure drop across each stage

occurs in the fixed nozzle guide vanes which, because of their convergent shape, increase the gas velocity whilst reducing the pressure.

Turbine blades absorb the force required to Turbine blades absorb the force required to change the direction of airflow and change it change the direction of airflow and change it to rotary motion.to rotary motion.

IMPULSE TURBINE BLADESIMPULSE TURBINE BLADES


REACTION TURBINE BLADESREACTION TURBINE BLADES Turning force is produced based on an Turning force is produced based on an

aerodynamic action.aerodynamic action. The turbine blades form a series of converging The turbine blades form a series of converging

duct that increase gas velocity and reduce duct that increase gas velocity and reduce pressure.pressure.

Reduced pressure produces a lifting force that Reduced pressure produces a lifting force that rotate the turbine wheel.rotate the turbine wheel.

REACTION TURBINE BLADESREACTION TURBINE BLADES


IMPULSE REACTION TURBINE BLADESIMPULSE REACTION TURBINE BLADES Most modern engines uses impulse-reaction Most modern engines uses impulse-reaction

turbine blades.turbine blades. Evenly distribute the workload along the Evenly distribute the workload along the

length of the blade.length of the blade. The blade base is impulse shaped while the The blade base is impulse shaped while the

blade tip is reaction shaped.blade tip is reaction shaped. Creates a uniform velocity and pressure drop Creates a uniform velocity and pressure drop

across the entire blade length.across the entire blade length.

TURBINE SECTIONTURBINE SECTIONTURBINE BLADESTURBINE BLADES

Can be open or shrouded at their tips.Can be open or shrouded at their tips. Open ended are used on high speed turbines, shrouded ended Open ended are used on high speed turbines, shrouded ended

are used on slower rotational speed turbines.are used on slower rotational speed turbines. The end of each blade has a shroud attached to its end, once The end of each blade has a shroud attached to its end, once

installed the shrouds contact each other and provide support.installed the shrouds contact each other and provide support. The shroud reduces the vibration and prevent the air from The shroud reduces the vibration and prevent the air from

escaping over the blades tips.escaping over the blades tips. The added weight cause the turbine blades to be more The added weight cause the turbine blades to be more

susceptible to blade growth.susceptible to blade growth. A knife edge seal is machined around the outside of the shroud A knife edge seal is machined around the outside of the shroud

which reduces air losses at the blade tip.which reduces air losses at the blade tip.

TURBINE SECTIONTURBINE SECTIONCOOLINGCOOLING

The most limiting factor in running a gas turbine The most limiting factor in running a gas turbine engine is the temperature.engine is the temperature.

The higher the temperature raises, the more power or The higher the temperature raises, the more power or thrust an engine can produce.thrust an engine can produce.

The effectiveness of a turbine engineThe effectiveness of a turbine engine’’s cooling s cooling system plays a big role in engine performance.system plays a big role in engine performance.

Cooling systems allow the turbine to operate 600 to Cooling systems allow the turbine to operate 600 to 800800 ْْ F above the temperature limits of their metal F above the temperature limits of their metal alloys.alloys.

Engine bleed air is used to cool the components in the Engine bleed air is used to cool the components in the turbine section.turbine section.

TURBINE SECTIONTURBINE SECTIONCOOLINGCOOLING

Turbine disk absorb heat from the hot gases passing around Turbine disk absorb heat from the hot gases passing around their rim and the heat conducted from the turbine blades.their rim and the heat conducted from the turbine blades.

Cooling air is directed over each side of the disk.Cooling air is directed over each side of the disk. Convection cooling or film cooling is the type of cooling used Convection cooling or film cooling is the type of cooling used

to cool turbine blades and vane by directing compressor bleed to cool turbine blades and vane by directing compressor bleed air through the hollow blades and out through holes in the tip, air through the hollow blades and out through holes in the tip, leading edge, and trailing edge.leading edge, and trailing edge.

Some vanes are constructed of a porous high temp material, Some vanes are constructed of a porous high temp material, bleed air is ducted into the vane and exits through the porous bleed air is ducted into the vane and exits through the porous material (transpiration cooling).material (transpiration cooling).

The turbine vane shrouds may also be perforated with cooling The turbine vane shrouds may also be perforated with cooling holes. holes.

COUNTER-ROTATING TURBINECOUNTER-ROTATING TURBINE Not common on large engine.Not common on large engine. Effective in damping gyroscopic effects and reduce Effective in damping gyroscopic effects and reduce

engine vibration.engine vibration.

EXHAUST SECTIONEXHAUST SECTION Exhaust section determine to some extent the Exhaust section determine to some extent the

amount of thrust developed.amount of thrust developed. The size and shape of exhaust section affect:The size and shape of exhaust section affect:

1- Turbine inlet temperature.1- Turbine inlet temperature.2- the mass air flow through the engine.2- the mass air flow through the engine.3- The velocity and pressure of the exhaust jet.3- The velocity and pressure of the exhaust jet.

Exhaust section extend from the rear of the Exhaust section extend from the rear of the turbine section to the point where the exhaust turbine section to the point where the exhaust gases leave the engine. gases leave the engine.

EXHAUST SECTIONEXHAUST SECTION The exhaust section consist of:The exhaust section consist of:

1- Exhaust cone.1- Exhaust cone.2- Exhaust duct or tail pipe.2- Exhaust duct or tail pipe.3- Exhaust nozzle.3- Exhaust nozzle.

EXHAUST SECTIONEXHAUST SECTIONEXHAUST CONEEXHAUST CONE

Consist of:Consist of:1- Outer duct or shell. 2- Inner cone or tail cone.1- Outer duct or shell. 2- Inner cone or tail cone.3- Hollow struts. 4- Tie rods.3- Hollow struts. 4- Tie rods.

The outer duct is made of stainless steel and attached to the The outer duct is made of stainless steel and attached to the rear flange of turbine section.rear flange of turbine section.

Purpose of the tail cone is to channel and collect turbine Purpose of the tail cone is to channel and collect turbine discharge gases into a single jet.discharge gases into a single jet.

The outer duct and the inner cone form a divergent duct, so the The outer duct and the inner cone form a divergent duct, so the air pressure increases and velocity decreases.air pressure increases and velocity decreases.

Hollow struts support the inner cone and help straighten the Hollow struts support the inner cone and help straighten the swirling exhaust gases.swirling exhaust gases.

The tie rods assist the struts in centering the inner cone within The tie rods assist the struts in centering the inner cone within the outer duct.the outer duct.

EXHAUST SECTIONEXHAUST SECTION

EXHAUST SECTIONEXHAUST SECTIONTAIL PIPETAIL PIPE

An extension of the exhaust section that directs An extension of the exhaust section that directs exhaust gases safely from the exhaust cone to the exhaust gases safely from the exhaust cone to the nozzle.nozzle.

Tail pipe cause heat and friction losses that causes Tail pipe cause heat and friction losses that causes drop in exhaust gas velocity and thrust.drop in exhaust gas velocity and thrust.

Used with engines that are installed within the Used with engines that are installed within the fuselage to protect the surrounding airframe.fuselage to protect the surrounding airframe.

On engine that require no tailpipe, the nozzle is On engine that require no tailpipe, the nozzle is mounted directly to the exhaust cone assembly.mounted directly to the exhaust cone assembly.

EXHAUST SECTIONEXHAUST SECTIONEXHAUST NOZZLEEXHAUST NOZZLE

Provides the exhaust gases with the final boost in Provides the exhaust gases with the final boost in velocity.velocity.

Converging design and the converging-diverging Converging design and the converging-diverging design used on aircraft.design used on aircraft.

Converging design produces a venturi that accelerates Converging design produces a venturi that accelerates the exhaust gases and increases engine thrust.the exhaust gases and increases engine thrust.

Converging-diverging diameter decrease then Converging-diverging diameter decrease then increase from front to back which increase the increase from front to back which increase the velocity of exhaust gases above the speed of sound.velocity of exhaust gases above the speed of sound.

EXHAUST SECTIONEXHAUST SECTION The flow of cool and hot gases in a ducted low The flow of cool and hot gases in a ducted low

by pass turbofan engine combined in a mixer by pass turbofan engine combined in a mixer unit.unit.

High bypass turbofan engines exhaust the two High bypass turbofan engines exhaust the two streams separately through two sets of nozzles streams separately through two sets of nozzles arranged coaxially around the exhaust nozzle.arranged coaxially around the exhaust nozzle.

On some high pass engines a common or On some high pass engines a common or integrated nozzle is used to mix the hot and integrated nozzle is used to mix the hot and cold gases prior to their ejection.cold gases prior to their ejection.

Exhaust nozzle opening can be fixed or Exhaust nozzle opening can be fixed or variable geometry.variable geometry.

EXHAUST SECTIONEXHAUST SECTION

AFTERBURNERSAFTERBURNERS Used to accelerate the exhaust gases to increase Used to accelerate the exhaust gases to increase

thrust.thrust. Installed after the turbine and in front of exhaust Installed after the turbine and in front of exhaust

nozzle.nozzle. Consist of fuel manifold, ignition source and flame Consist of fuel manifold, ignition source and flame

holder.holder. The gases in the tailpipe sill contain a large quantity The gases in the tailpipe sill contain a large quantity

of oxygen.of oxygen. Fuel manifold consist of fuel nozzle or spray bars Fuel manifold consist of fuel nozzle or spray bars

inject fuel into the tailpipe.inject fuel into the tailpipe.

AFTERBURNERSAFTERBURNERS

THRUST REVERSERSTHRUST REVERSERS The brakes are unable to slow the A/C The brakes are unable to slow the A/C

adequately during landing.adequately during landing. Brake wear would be prohibitive and heat Brake wear would be prohibitive and heat

buildup could lead to brake fire.buildup could lead to brake fire. Most turbojet and turbofan powered A/C are Most turbojet and turbofan powered A/C are

fitted with thrust reversers to assist in braking.fitted with thrust reversers to assist in braking. Thrust reversers redirect the flow of gases to Thrust reversers redirect the flow of gases to

provide thrust in the opposite direction.provide thrust in the opposite direction.

THRUST REVERSERSTHRUST REVERSERS

ACCESSORY SECTIONACCESSORY SECTION Functions of accessory drive sectionFunctions of accessory drive section

1- Used to power both engine and aircraft accessories.1- Used to power both engine and aircraft accessories.2- Act as an oil reservoir or sump and housing the accessory 2- Act as an oil reservoir or sump and housing the accessory drive gears and reduction gears.drive gears and reduction gears.

Accessory drive could located at engineAccessory drive could located at engine’’s midsection or front s midsection or front or rear of the engine.or rear of the engine.

Rear mounted gear boxes allow the narrowest engine diameter Rear mounted gear boxes allow the narrowest engine diameter and lowest drag configuration.and lowest drag configuration.

Bevel gear drive the gear box using engine main power shaft.Bevel gear drive the gear box using engine main power shaft. The gear box distributes power to each accessory drive pad.The gear box distributes power to each accessory drive pad. Reduction gear is necessary to provide the appropriate drive Reduction gear is necessary to provide the appropriate drive

speed for the accessories.speed for the accessories. Intermediate or transfer gearbox is used on some engines to Intermediate or transfer gearbox is used on some engines to

obtain the needed reduction gearing.obtain the needed reduction gearing. The more accessories an engine has the more power is needed The more accessories an engine has the more power is needed

to drive the gearbox. to drive the gearbox.

ACCESSORY SECTIONACCESSORY SECTION

ENGINE STATION NUMBERINGENGINE STATION NUMBERING Engine manufacturers assign station number to Engine manufacturers assign station number to

several points along a turbine engineseveral points along a turbine engine’’s gas path.s gas path. Station number provide a mean of rapidly locating Station number provide a mean of rapidly locating

certain engine areas during maintenance.certain engine areas during maintenance. Establish locations for taking pressure and Establish locations for taking pressure and

temperature readings.temperature readings. Engine inlet pressure station is pt2 while turbine Engine inlet pressure station is pt2 while turbine

discharge pressure station is pt7.discharge pressure station is pt7. Engine pressure ratio is pt7 : pt2.Engine pressure ratio is pt7 : pt2. Pt2 is total pressure at station 2 and Tt2 is total Pt2 is total pressure at station 2 and Tt2 is total

temperature at station 2.temperature at station 2.

ENGINE STATION NUMBERINGENGINE STATION NUMBERING

NOISE SUPPRESSIONNOISE SUPPRESSION Noise produced by a turbine engine results when hot, Noise produced by a turbine engine results when hot,

high velocity gases mix with cold, low velocity air high velocity gases mix with cold, low velocity air surrounding the engine.surrounding the engine.

Turbofan engines reduce the noise levels both inside Turbofan engines reduce the noise levels both inside the cabin and on ground .the cabin and on ground .

Turbofan engines seldom require noise suppressors Turbofan engines seldom require noise suppressors because the hot gases mix with cold gas prior to their because the hot gases mix with cold gas prior to their release to atmosphere.release to atmosphere.

Turbojet engine require additional noise suppression Turbojet engine require additional noise suppression equipment.equipment.

NOISE SUPPRESSIONNOISE SUPPRESSION A device that breaks up the airflow behind the A device that breaks up the airflow behind the

tail cone and sound insulating material are tail cone and sound insulating material are used as noise suppressors.used as noise suppressors.

The sound intensity is measured in decibels.The sound intensity is measured in decibels. Decibel is the ratio of one sound to another.Decibel is the ratio of one sound to another. One decibel is the smallest change in sound One decibel is the smallest change in sound

intensity that the human ear can detect.intensity that the human ear can detect. FAA establish rules for aircraft operators that FAA establish rules for aircraft operators that

specify maximum noise levels.specify maximum noise levels.

NOISE SUPPRESSIONNOISE SUPPRESSION

ENGINE MOUNTSENGINE MOUNTS Gas turbine engine relatively produce little torque so Gas turbine engine relatively produce little torque so

they do not need heavily constructed mounts.they do not need heavily constructed mounts. The mounts support the engine weight and allow for The mounts support the engine weight and allow for

transfer of stresses created by the engine to the transfer of stresses created by the engine to the aircraft structure.aircraft structure.

Wing mounted turbofan engine, the engine is attached Wing mounted turbofan engine, the engine is attached to the A/C by two to four mounting brackets.to the A/C by two to four mounting brackets.

Turboprop and turboshaft engines use heaver mounts Turboprop and turboshaft engines use heaver mounts because of the torque developed.because of the torque developed.

ENGINE MOUNTSENGINE MOUNTS

BEARINGSBEARINGS Engine main bearing support the compressor and Engine main bearing support the compressor and

turbine rotor, and located along the length of the rotor turbine rotor, and located along the length of the rotor shaft.shaft.

The number of bearing is determined by the length The number of bearing is determined by the length and weight of the rotor shaft.and weight of the rotor shaft.

Spilt spool axial compressor require more main Spilt spool axial compressor require more main bearing than a centrifugal compressor.bearing than a centrifugal compressor.

Ball and roller bearing are used to support an engineBall and roller bearing are used to support an engine’’s s main rotor shaft.main rotor shaft.

Consist of inner and outer races that provide support Consist of inner and outer races that provide support and hold lubricating oil.and hold lubricating oil.

BEARINGSBEARINGS Advantages of ball and roller bearings:Advantages of ball and roller bearings:

1.1.Offer little rotational resistance.Offer little rotational resistance.2.2.Enable precision alignment of rotating elements.Enable precision alignment of rotating elements.3.3.Tolerate high momentary overloads.Tolerate high momentary overloads.4.4.Are easily replaced.Are easily replaced.5.5.Are relatively inexpensive.Are relatively inexpensive.6.6.Are simple to cool, lubricate, and maintain.Are simple to cool, lubricate, and maintain.7.7.Accommodate both radial and axial loads.Accommodate both radial and axial loads.8.8.Are relatively resistant to elevated temperatures.Are relatively resistant to elevated temperatures.

BEARINGSBEARINGS

Disadvantages of ball and roller Disadvantages of ball and roller bearings:bearings:

1.1.Vulnerability to damage caused by foreign Vulnerability to damage caused by foreign matter.matter.

2.2.Tendency to fail without appreciable warning.Tendency to fail without appreciable warning.Proper lubrication and sealing against entry of Proper lubrication and sealing against entry of

foreign matter is essential.foreign matter is essential.Labyrinth, helical thread, and carbon seal are Labyrinth, helical thread, and carbon seal are

used to seal the bearings from foreign matter.used to seal the bearings from foreign matter.

BEARINGSBEARINGSLabyrinth seal does not rub against an outer Labyrinth seal does not rub against an outer

surface, instead each seal consist of a series of surface, instead each seal consist of a series of rotating fins that come very close but do not touch a rotating fins that come very close but do not touch a fixed abradable race.fixed abradable race.

Air pressure on one side prevent the oil from Air pressure on one side prevent the oil from coming out of the bearing.coming out of the bearing.

Helical seals depend on reverse threading to stop Helical seals depend on reverse threading to stop oil leakage.oil leakage.

Carbon seals are spring loaded to hold the carbon Carbon seals are spring loaded to hold the carbon ring against the rotating shaft.ring against the rotating shaft.

BEARINGSBEARINGS

TURBOPROP ENGINESTURBOPROP ENGINES Gas turbine engine that drives a propeller to produce Gas turbine engine that drives a propeller to produce

thrust.thrust. The turbine of a turboprop engine extract up to 85% The turbine of a turboprop engine extract up to 85%

of the engineof the engine’’s total power output to drive the s total power output to drive the propeller.propeller.

Multiple stages turbine and special design blades to Multiple stages turbine and special design blades to extract more energy from the exhaust gases.extract more energy from the exhaust gases.

Most turboprop engines use a free turbine to drive the Most turboprop engines use a free turbine to drive the propeller.propeller.

TURBOPROP ENGINESTURBOPROP ENGINES Free turbine is an independent turbine that is not Free turbine is an independent turbine that is not

mechanically connected to the main turbine.mechanically connected to the main turbine. Power turbine is placed in the exhaust stream after the Power turbine is placed in the exhaust stream after the

main turbine and dedicated to drive the propeller.main turbine and dedicated to drive the propeller. Fixed shaft engines is used to extract the gas energy to Fixed shaft engines is used to extract the gas energy to

drive the propeller by adding more turbine stages to drive the propeller by adding more turbine stages to the main shaft.the main shaft.

High speed low torque turbine output is converted to High speed low torque turbine output is converted to low speed high torque by a reduction gear to drive the low speed high torque by a reduction gear to drive the propeller.propeller.

Constant speed propellers are used to maintain a Constant speed propellers are used to maintain a constant engine rpm.constant engine rpm.

TURBOPROP ENGINESTURBOPROP ENGINES

TURBOSHAFT ENGINESTURBOSHAFT ENGINES Gas turbine engine that operate something Gas turbine engine that operate something

other than a propeller.other than a propeller. Use almost all the energy in the exhaust gases Use almost all the energy in the exhaust gases

to drive an output shaft.to drive an output shaft. Power may be taken from the engine turbine Power may be taken from the engine turbine

or from a free turbine.or from a free turbine. Free turbine is not mechanically coupled to the Free turbine is not mechanically coupled to the

main turbine and may operate at its own speed.main turbine and may operate at its own speed. Used to power helicopters and APUs.Used to power helicopters and APUs.

AUXILIARY POWER UNITSAUXILIARY POWER UNITS Turbine powered aircraft require large amounts of Turbine powered aircraft require large amounts of

power for starting and operation.power for starting and operation. Electrical power is needed for passenger amenities Electrical power is needed for passenger amenities

such as lighting, entertainment, and food preparation.such as lighting, entertainment, and food preparation. High pressure, high volume pneumatic air source is High pressure, high volume pneumatic air source is

needed to start the engine and ground air needed to start the engine and ground air conditioning.conditioning.

Auxiliary power units meet these demands for ground Auxiliary power units meet these demands for ground power when the engines are not running.power when the engines are not running.

AUXILIARY POWER UNITSAUXILIARY POWER UNITS Consist of a small turbine powerplant driving an electric Consist of a small turbine powerplant driving an electric

generator identical to aircraft generators.generator identical to aircraft generators. APU compressor supplies bleed air for heating cooling, anti-APU compressor supplies bleed air for heating cooling, anti-

icing and engine starting.icing and engine starting. APU is started using its own electric starter motor and aircraft APU is started using its own electric starter motor and aircraft

battery power using the fuel of the aircraft.battery power using the fuel of the aircraft. APU fuel control unit automatically adjust the fuel flow to APU fuel control unit automatically adjust the fuel flow to

operate the APU at its rated speed.operate the APU at its rated speed. Load control valve protect the APU from overheating by Load control valve protect the APU from overheating by

modulate the pneumatic load automatically.modulate the pneumatic load automatically. Cool down period is specified by the manufacturer to keep the Cool down period is specified by the manufacturer to keep the

APU from being damaged because of thermal shock.APU from being damaged because of thermal shock.

AUXILIARY POWER UNITSAUXILIARY POWER UNITS

OPERATING PRINCIPLESOPERATING PRINCIPLES Gas turbine engine is a heat engine that Gas turbine engine is a heat engine that

converts the chemical energy of fuel into heat converts the chemical energy of fuel into heat energy.energy.

Heat energy is converted into kinetic energy in Heat energy is converted into kinetic energy in the form of a high velocity stream of air.the form of a high velocity stream of air.

The kinetic energy is converted into The kinetic energy is converted into mechanical energy by the turbine that drive the mechanical energy by the turbine that drive the compressor and the accessories and/or the compressor and the accessories and/or the propeller or gearbox.propeller or gearbox.

ENERGY TRANSFORMATION CYCLEENERGY TRANSFORMATION CYCLE

Energy transformation cycle in a gas turbine engine is Energy transformation cycle in a gas turbine engine is known as the Brayton or constant pressure cycle.known as the Brayton or constant pressure cycle.

Intake, compression, combustion, and exhaust event Intake, compression, combustion, and exhaust event occur in both piston and turbine cycle.occur in both piston and turbine cycle.

In turbine engine all four events happen In turbine engine all four events happen simultaneously and continuously.simultaneously and continuously.

Gas turbine engine produce power continuously.Gas turbine engine produce power continuously. Gas turbine engine must burn a great deal of fuel to Gas turbine engine must burn a great deal of fuel to

support the continuous production of power.support the continuous production of power.

ENERGY TRANSFORMATION CYCLEENERGY TRANSFORMATION CYCLE

ENERGY TRANSFORMATION CYCLEENERGY TRANSFORMATION CYCLE The air is continuously drawn into the engine thorough the The air is continuously drawn into the engine thorough the

inlet to the first compressor stage.inlet to the first compressor stage. The compressor increase the static air pressure of the air.The compressor increase the static air pressure of the air. Fuel is sprayed in the combustion chamber and ignited Fuel is sprayed in the combustion chamber and ignited

resulting in continuous combustion.resulting in continuous combustion. The heat increase the airThe heat increase the air’’s volume while maintaining a s volume while maintaining a

relatively constant pressure.relatively constant pressure. Exhaust gases leave the combustion gases through the turbine Exhaust gases leave the combustion gases through the turbine

where pressure decreases and the velocity increases where pressure decreases and the velocity increases dramatically.dramatically.

Gas turbine engine produces thrust based on NewtonGas turbine engine produces thrust based on Newton’’s third s third law of motion.law of motion.

The acceleration of a mass of air by the engine is the action The acceleration of a mass of air by the engine is the action while forward movement is the reaction.while forward movement is the reaction.

ENERGY TRANSFORMATION CYCLEENERGY TRANSFORMATION CYCLE The working cycle upon which the gas

turbine engine functions is represented by the cycle shown on the pressure volume diagram

Point A represents air at atmospheric pressure that is compressed along the line AB. From B to C heat is added to the air by introducing and burning fuel at constant pressure, thereby considerably increasing the volume of air. Pressure losses in the combustion chambers are indicated by the drop between B and C. From C to D the gases resulting from combustion expand through the turbine and jet pipe back to atmosphere. During this part of the cycle, some of the energy in the expanding gases is turned into mechanical power by the turbine.

VELOCITY AND PRESSUREVELOCITY AND PRESSURE Velocity and pressure of the air passing through a gas turbine

engine must change to produce thrust. Pressure is increased in the compressor while velocity remains

relatively constant. Gas velocity must be increased after combustion to rotate the

turbine. Bernoulli’s principle stats that; when a fluid or gas is supplied

at a constant flow rate through a duct, the sum of the potential, or pressure energy, and kinetic, or velocity energy is constant.

The pressure and velocity of a mass of air flowing in a divergent or convergent duct must increase or decrease accordingly. (energy can not be created or destroyed)

The temperature of the air will change too.

VELOCITY AND PRESSUREVELOCITY AND PRESSURE

THRUST CALCULATIONSTHRUST CALCULATIONS Jet engine produces thrust by accelerating an

air mass to a velocity higher than that of the incoming air.

Newton’s 2nd law of motion stats that force is proportional to the product of mass and acceleration or acceleration is directly proportional to force and inversely proportional to mass.

F = M X A F = force. M = mass. A = acceleration.

THRUST CALCULATIONSTHRUST CALCULATIONS The acceleration of air mass through a gas turbine

engine is the difference between the exiting jet exhaust and the intake air.

The acceleration must be compared to a constant. (gravitational constant = 32.2 f/sec²)

Applying this to the formulaF = Ms (V2 – V1)/g

F =force. Ms = mass airflow through the engineV2 =air velocity at the exhaust.V1 = forward velocity of the engine.g = acceleration of gravity which is 32.2 ft./sec².

THRUST CALCULATIONSTHRUST CALCULATIONS Example: GivenMs = 50 pounds per sec. V1 = 0 feet per sec.V2 = 1,300 feet per sec. g = 32.2 ft./sec².

F gross = Ms x (V2 – V1 )/g= 50 lb./sec x (1300 ft/sec. – 0 )/ 32.2 ft./sec².

=65,000 lb ft./sec²/ 32.2 ft./sec².= 2,018.6 pounds

THRUST CALCULATIONSTHRUST CALCULATIONS Example 2: GivenMs = 50 pounds per sec. V1 = 734 feet per sec.V2 = 1,300 feet per sec. g = 32.2 ft./sec².

F net = Ms x (V2 – V1 )/g= 50 lb./sec x (1300 – 734)/ 32.2 ft./sec².

=50 x 566 / 32.2.= 878.9 pounds net thrust.

Thrust can be increased by increasing mass flow of air or by increasing the exhaust velocity.

As the aircraft speed increase more air enters the engine resulting in an increase in exhaust velocity.

THERMAL EFFICIENCYTHERMAL EFFICIENCY Thermal efficiency is the ratio of the actual power

an engine produces divided by the thermal energy in the fuel consumed.

Gas turbine engine can operate with thermal efficiency as high as 50 % while the thermal efficiency of reciprocating engine is between 30 to 40 %.

Factors which determine thermal efficiency:1. Turbine inlet temperature.2. Compression ratio.3. Component efficiency of the compressor and the

turbine.

THERMAL EFFICIENCYTHERMAL EFFICIENCY The higher a gas turbine engine raises the temperature

of the incoming air, the more thrust the engine can produce,.

The limiting factor to increasing the temperature of the air is the amount of heat the turbine section can withstand.

The more a gas turbine engine compresses the incoming air, the more thrust the engine can produce.

Engine with high compression ratio force more air into the engine, so more heat energy transferred to internal airflow thus increasing the thermal efficiency.

Compressor and turbine efficiency directly impact the compression ratio of the engine which has a direct impact on the thermal efficiency.

THERMAL EFFICIENCYTHERMAL EFFICIENCY

FACTORS AFFECTING THRUSTFACTORS AFFECTING THRUST

FACTORS AFFECTING THRUST:1. TEMPERATURE.2. ALTITUDE.3. AIRSPEED.4. ENGINE RPM.5. FAN EFFICIENCY.

FACTORS AFFECTING THRUSTFACTORS AFFECTING THRUSTTEMPERATURE

The more dense the air passing through an engine is, the more thrust the engine can produce.

Air density is inversely proportional to temperature, as outside temperature increases (OAT), air density decreases.

As the density of the air entering a gas turbine engine decreases, engine thrust also decreases.

Thrust augmentation system is used to compensate for the effect of hot weather on the amount of thrust.

Water injection system inject water, or a mixture of water and alcohol into the compressor inlet or in the combustion chamber.

Water will cool the air mass, allow more fuel to be burned, and increase the air mass to maintain air pressure in the engine.

FACTORS AFFECTING THRUSTFACTORS AFFECTING THRUSTALTITUDE

As altitude increases the air pressure drops. The pressure at 18,000 feet is about 7.34 psi. The pressure at 20,000 feet is about 6.75 psi. The pressure at 30,000 feet is about 4.36 psi. As altitude increases the temp. also decreases. The decrease in the temp. increases the air density which

increase the thrust. But the drop in pressure has a greater effect on decreasing

the thrust. At 36,000 the temp. stabilizes at -69.7 deg. F, so the density

of air stop increasing. Long range jet aircraft find 36,000 feet an optimum altitude

to fly.

FACTORS AFFECTING THRUSTFACTORS AFFECTING THRUSTAIRSPEED

As forward airspeed increases, the air mass acceleration in the engine decreases, so less thrust is produced.

As the aircraft speeds up, more air is forced into the engine (ram effect), results in an increase in air pressure within the engine, which produces more thrust.

The result of the thrust reduced by increasing the airspeed and the thrust increased by ram effect is known as ram recovery.

FACTORS AFFECTING THRUSTFACTORS AFFECTING THRUSTENGINE RPM

Early engines had a linear relationship between compressor rpm and engine thrust.

Engine power output could be set using an rpm gauge. Modern turbofan engines have a non-linear relationship

between compressor rpm and thrust produced. Power is set using an engine pressure ratio EPR since thrust

and EPR have more proportional relationship than thrust and rpm.

At low engine speeds, large increases in rpm produce relatively small increase in thrust and vise versa.

FACTORS AFFECTING THRUSTFACTORS AFFECTING THRUSTENGINE RPM

Compressor aerodynamics limits engine rpm because the efficiency begins to drop when the blade tip speed reach the speed of sound.

The longer the blade is, the higher the tip rotational speed.

Large diameter compressors turn at a relatively slow rotational speed, while small diameter compressors could reach 50,000 rpm.

FACTORS AFFECTING THRUSTFACTORS AFFECTING THRUSTFAN EFFICIENCY

The more efficient the fan is, the more thrust the engine can produce.

Turbofan replaced turbojet engines on most transport and business jet aircraft.

Turbofan is quieter and much more fuel economic.

QUESTIONSQUESTIONS

Turbine engine 1

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