1

IINNTTRROODDUUCCTTIIOONN TTOO AAEERROO EENNGGIINNEESS

SSoommee ddeeffiinniittiioonnss rreellaatteedd ttoo jjeett eennggiinnee

11.. EEnnggiinnee:: EEnnggiinnee iiss aa mmaacchhiinnee wwhhiicchh ccoonnvveerrttss cchheemmiiccaall eenneerrggyy ooff ffuueell iinnttoo hheeaatt eenneerrggyy

ttoo ddoo wwoorrkk..

22.. AAeerroo eennggiinnee:: AAeerroo eennggiinnee iiss aa mmaacchhiinnee wwhhiicchh ttrraannssffoorrmmss ppootteennttiiaall eenneerrggyy ccoonnttaaiinneedd iinn

tthhee ffuueell aanndd aaiirr iinnttoo kkiinneettiicc aanndd // oorr mmeecchhaanniiccaall eenneerrggyy..

33.. GGaass TTuurrbbiinnee EEnnggiinnee:: AA ttyyppee ooff eennggiinnee wwhhiicchh ttrraannssffoorrmmss eenneerrggyy bbyy mmeeaannss ooff aa

ccoommpprreessssoorr,, ccoommbbuussttiioonn cchhaammbbeerr aanndd ttuurrbbiinnee..

44.. TTuurrbbiinnee:: TTuurrbbiinnee iiss aa wwhheeeell wwhhiicchh ddeerriivveess iittss ppoowweerr ffrroomm tthhee mmoottiioonn ooff aa fflluuiidd..

55.. PPrrooppuullssiioonn:: IImmppaarrttiinngg aacccceelleerraattiioonn ttoo aa cceerrttaaiinn mmaassss..

66.. TThhrruusstt:: AA ggaass jjeett eexxhhaauussttiinngg aatt hhiigghh vveelloocciittyy ffrroomm aa nnoozzzzllee ggeenneerraattiinngg aa ffoorrccee iinn tthhee

ooppppoossiittee ddiirreeccttiioonn iiss tteerrmmeedd aass tthhrruusstt..

77.. TTuurrbboo jjeett:: AAllll aaiirr ffllooww ggooeess tthhrroouugghh aa ggaass ggeenneerraattoorr ii..ee.. ccoommpprreessssoorr,, ccoommbbuussttiioonn

cchhaammbbeerr aanndd ttuurrbbiinnee..

88.. BByyppaassss TTuurrbboo jjeett:: IItt aaddmmiittss mmoorree aaiirr tthhaann nneecceessssaarryy ffoorr GGaass GGeenneerraattoorr,, aaddddiittiioonnaall ffllooww

bbyy--ppaassssiinngg tthhee GGaass GGeenneerraattoorr..

99.. TTwwiinn ssppooooll bbyyppaassss TTuurrbboo jjeett:: AA ggeenneerraattoorr iinnccoorrppoorraatteess ttwwoo iinnddeeppeennddeenntt rroottaattiinngg

aasssseemmbblliieess.. AA llooww pprreessssuurree ttuurrbbiinnee aanndd hhiigghh pprreessssuurree ttuurrbbiinnee sshhaafftt rruunnss ccooaaxxiiaallllyy ee..gg..

AALL--3311FFPP,, RRDD--3333 eennggiinnee..

1100.. TTuurrbboo pprroopp:: AA ggaass ttuurrbbiinnee eennggiinnee ddrriivviinngg aa pprrooppeelllleerr ee..gg.. AAVVRROO,, AANN--3322 aaiirrccrraafftt..

1111.. TTuurrbboo SShhaafftt:: AA ggaass ttuurrbbiinnee eennggiinnee ssuuppppllyyiinngg mmeecchhaanniiccaall eenneerrggyy oonn aa sshhaafftt ffoorr

vvaarriioouuss aapppplliiccaattiioonnss,, ee..gg.. HHeelliiccoopptteerr rroottoorrss,, eelleeccttrriicc ggeenneerraattoorrss..

1122.. FFrreeee ttuurrbbiinnee ttuurrbboo sshhaafftt:: PPoowweerr ttuurrbbiinnee iiss mmeecchhaanniiccaallllyy iinnddeeppeennddeenntt ooff GGaass

GGeenneerraattoorr,, ee..gg.. TTuurrbboo ssttaarrtteerr GGTTDDEE 111177--11MMOO..

1133.. MMoodduullee:: AAnn iinnddeeppeennddeenntt ssuubb aasssseemmbbllyy wwhhiicchh ccaann bbee eeaassiillyy rreemmoovveedd ffrroomm ootthheerr

aasssseemmbbllyy.. MMoodduullaarr ddeessiiggnn ppeerrmmiittss rreeppllaacceemmeenntt ooff aa mmoodduullee bbyy uusseerr wwiitthhoouutt rreettuurrnniinngg

ccoommpplleettee aasssseemmbbllyy ttoo ffaaccttoorryy..

2

DESCRIPTION OF AERO-ENGINE:

TThhee aavviiaattiioonn ggaass ttuurrbbiinnee eennggiinnee iiss ccaatteeggoorriizzeedd aass aa hheeaatt eennggiinnee.. IItt uusseess ggaass aass iittss wwoorrkkiinngg

fflluuiidd aanndd pprroodduucceess ((mmeecchhaanniiccaall)) sshhaafftt ppoowweerr aanndd tthhrruusstt.. GGeenneerraattiinngg tthhrruusstt,, iinn ppaarrttiiccuullaarr,,

iiss ppoossssiibbllee oonnllyy iiff tthhee eexxhhaauusstt vveelloocciittyy ooff ggaass iiss hhiigghheerr tthhaann tthhee vveelloocciittyy aatt wwhhiicchh aaiirr

eenntteerrss tthhee eennggiinnee.. IInn oorrddeerr ttoo aacccceelleerraattee tthhee ggaass,, eenneerrggyy mmuusstt bbee aaddddeedd ttoo tthhee aaiirrffllooww

wwiitthhiinn tthhee eennggiinnee wwhhiicchh ccaann tthheenn bbee ccoonnvveerrtteedd iinnttoo kkiinneettiicc eenneerrggyy..

IInn aa ggaass ttuurrbbiinnee eennggiinnee,, tthhee iinnccrreeaassee ooff eenneerrggyy iiss aaccccoommpplliisshheedd iinn ttwwoo ccoonnsseeccuuttiivvee

sstteeppss,, aanndd bbyy ttwwoo ddiiffffeerreenntt,, tthhoouugghh aaddjjaacceenntt,, eennggiinnee ccoommppoonneennttss.. FFiirrsstt,, pprreessssuurree ooff tthhee

aaiirrffllooww iiss rraaiisseedd bbyy aaccttiioonn ooff mmeecchhaanniiccaall sshhaafftt ppoowweerr.. TThhiiss iiss ddoonnee iinn tthhee ccoommpprreessssoorr

sseeccttiioonn.. AAfftteerr iittss ddiisscchhaarrggee ffrroomm tthhee ccoommpprreessssoorr,, tthhee pprreessssuurriizzeedd aaiirr eenntteerrss iinn tthhee

ccoommbbuussttiioonn cchhaammbbeerr,, wwhheerree tthhee ffuueell aanndd pprreessssuurriizzeedd aaiirr bbuurrnnss,, tthheerreebbyy tteemmppeerraattuurree ooff tthhee

ggaass iiss sstteeeeppllyy rraaiisseedd ((dduuee ttoo cchheemmiiccaall rreeaaccttiioonn ooff aaiirr aanndd ffuueell mmiixxttuurree))..

TThhee ggaass iiss nnooww ssuuffffiicciieennttllyy pprroocceesssseedd ttoo pprroovviiddee pphhyyssiiccaall wwoorrkk ffoorr tthhee ttuurrbbiinnee,, tthhee

ffiirrsstt ssttaattiioonn wwiitthhiinn tthhee eennggiinnee wwhheerree wwoorrkk eexxttrraacctteedd ffrroomm tthhee hhoott ggaass iiss ttuurrbbiinnee.. AAss tthhee

ggaass eexxppaannddss aanndd aacccceelleerraatteess,, iitt rroottaatteess tthhee ttuurrbbiinnee wwhhiicchh iinn ttuurrnn rroottaatteess tthhee ccoommpprreessssoorr aass

ttuurrbbiinnee iiss ddiirreeccttllyy ccoouupplleedd ttoo tthhee ccoommpprreessssoorr bbyy aa sshhaafftt ((ssppooooll)).. AAfftteerr ddiisscchhaarrggiinngg ffrroomm

tthhee ttuurrbbiinnee,, tthhee ggaass iiss ffuurrtthheerr aacccceelleerraatteedd iinn tthhee eexxhhaauusstt nnoozzzzllee,, wwhheerree aallll rreemmaaiinniinngg

uussaabbllee hheeaatt eenneerrggyy iiss ccoonnvveerrtteedd iinnttoo kkiinneettiicc eenneerrggyy wwhhiicchh pprroodduucceess tthhrruusstt ffoorr mmoovviinngg tthhee

aaiirrccrraafftt ffoorrwwaarrdd ((NNeewwttoonn TThhiirrdd LLaaww))..

3

Types of aero engines

There are mainly three types of aero gas turbine engines. Those are:

Turbojet: A turbojet engine is a gas turbine engine that works by compressing airwith an inlet and a

compressor (axial, centrifugal or both), mixing the fuel with compressed air, burning the

mixture in the combustor, and then passing the hot, high pressure air through a turbine,

which extracts energy from the expanding gas passing through it. The engine converts

internal energy in the fuel to kinetic energy in the exhaust, producing thrust.

Turbofan: A turbofan engine is a gas turbine engine that is very similar to the turbojet. Like a

turbojet it uses the gas generator core (compressor, combustor, turbine) to convert

internal energy in fuel to kinetic energy in the exhaust. Turbofans differ from turbojets in

that they have an additional component, a fan. Like the compressor the fan is powered by

the turbine section of the engine. Unlike the turbojet some of the flow accelerated by fan

bypasses the gas generated core and is exhausted through a nozzle making the thrust

produced by the fan more efficient than that produced by the core.

4

Turboprop: It is a type of gas turbine engine. In turboprop engines, a portion of the engine’s thrust is

produced by spinning a propeller, rather than relying solely on high speed jet exhaust. As

their jet thrust is augmented by a propeller, turboprops are occasionally referred to as a

type of hybrid jet engine.

AAiimm ooff jjeett eennggiinnee

AAiimm ooff jjeett eennggiinnee iiss ttoo ggeenneerraattee hhoott ggaasseess aatt aa pprreessssuurree mmuucchh hhiigghheerr tthhaann aammbbiieenntt

pprreessssuurree ffoorr eexxppaannssiioonn iinn aa nnoozzzzllee ttoo pprroodduuccee tthhrruusstt.. CCeennttrraall eelleemmeenntt ooff jjeett eennggiinnee iiss ggaass

ggeenneerraattoorr wwhhiicchh ccoommpprriisseess ooff ccoommpprreessssoorr,, ccoommbbuussttiioonn cchhaammbbeerr aanndd ttuurrbbiinnee.. BByy aaddddiinngg

aann iinnlleett aanndd aa nnoozzzzllee,, aa ttuurrbboojjeett rreessuullttss..

5

Major parts and their functions of Aero gas turbine engine: AIR IN TAKE SYSTEM

Air intake of any turbojet powered aircraft has to carry out the very

important function of converting type kinetic energy of air flow to pressure energy

by compressing the air to a sufficiently high degree before it reaches the

compressor face. The engine performance i.e. thrust and specific fuel consumption

will depend upon the affiant conversion of this energy. At subsonic flight speeds,

the compression takes place mainly on the compressor. However, with the increase

in flight speeds more and more compression takes place in the air intake duct. At

Mach 2 the degree of compression in the air intake and the compressor is almost

equal.

Operation of air intake is quit complex for a supersonic aircraft due to

the wide range of the operating flight spectrum. As a component in the engine

aircraft system, the intake must satisfy a number of requirements such as:

a. Delivering the correct amount of air to the engine face as correct

speed with minimum loss of total energy contents.

b. Operating with a uniform discharge velocity profile as the

compressor surface.

c. Maintaining surge free steady flow in the air intake.

d. Creating maximum external drag due to airflow.

PRESSURE RECOVERY

In order to obtain high thrust, it is necessary to recover the full energy

of free system with minimum of pressure loss. The pressure losses occur due to

friction, eddy loss and shows. At the supersonic speed pressure loss due to friction

and eddies is less compared to the loss across the shock system. Pressure loss

across the shock system is highest if declaration of flow is achieving by normal

shock and is reduce if it is achieved through series of oblique shocks. A shock

system for minimum pressure loss as a particular Mach no. can always be design.

Reducing the slow speed and channel length reduces the frictional losses.

Adequate lip contouring reduces Eddy losses.

6

MASS FLOW

The mass flow coefficient is the ratio of actual mass flow captured by

the intake to the maximum mass flow corresponding to check operation. The

operation of the air intake is said to be subcritical if the ratio is less than one and is

said to be super critical if the ratio is one or more. If the air supply is less than

engine requirement, then auxiliary profile must be provided so that engine does not

flame out. Such condition occurs during takeoff. The air is inducted through the

take of shutter which opens automatically during takeoff due to the difference in

the pressure between the outside air and air inside the channel. If supply is more

this extra air is must bypass to atmosphere before it reaches as the engine speed

increases the air requirement increases. In order to provide the correct amount of

air, it is necessary to contend the lip area.

DRAG OF INTAKE

Drag of intake consists of frictional drag. Low pressure drags additive

drag due to spillage of flow and shock drag. Additive drag is zero if mass flow co-

efficient is unity skin friction drag and pressure drag are generated due to the air

flow over the internal and external surface of the air channel. These drag forces

reduce the net thrust available on the aircraft.

To reduce the drag, it is necessary to reduce the fontal size of air

intake to minimum. The air spillage reduce the shock strength contour the lip

geometry properly avoid sudden turning of flow in the channel and use adequate

boundary air bleed.

ACCESSORY DRIVE

LP compressor shaft provides the drive for following accessories through

suitable gear train and quill shaft.

a) Front scavenging oil pump.

b) Up compressor rotor with techno meter generator.

c) Centrifugal governor of main fuel regulating pumps.

HP turbine shaft provides the drive to the accessory gearbox through a

bevel gear train and coupling shaft from where the drive from the following

accessories is taken through and work of gear train and shafting.

Starter generator

Fuel regulating pump

7

Hydraulic pump

Fuel booster pump

Oil unit

De­aestor

Breather

Air craft generator

HP rotor tachometer generator

COMPRESSOR

Axial flow compressor is used in aero engine because in centrifugal

compressor the compression ratio is fixed. But in axial flow compressor C.R is

very high. There are two types

1. Single spool (Only one shaft is used)

2. Double spool (Two shafts are used)

Compressor has basically –

(i) Rotor blades (ii) Stator blades

Rotor blades add kinetic energy to the suction air, stator blades

converts the kinetic energy into pressure energy.

COMPRESSOR CASING

It consists of a distance ring, front casing, middle casing, split casings

(IVth, Vth, Vith, stage rotor) and rear casing (VIth stage stator).

DISTANCE RING

Distance ring provides smooth entry of air into the compressor and

also helps to couple the engine to the aircraft intake through the air radiator of

intake. The rear flange of the casing is bolted to the front casing.

FRONT CASING

The front casing houses the 1st stage rotor blades, which are in, turn

bolted to the front bearing housing. The IInd stage casing comprises of the outer

and inner rings and IInd stage stator blades spot-welded to the rings.

MIDDLE CASING

Middle casing houses IIIrd stage stator blades, which are welded as

the outer radius. At the inner radius, a flange ring is welded to the stator blades. Air

is tapper from inter space between the inner ring of the middle casing and IVth

stage rotor assembly for various purposes such as pressurization of HP compressor

8

lubricating oil seals, cooling and seal pressurization for the turbine assembled and

thrust balancing of the HPCR.

SPLIT CASING

Split casings accommodate IVth and Vth stage stator blades, which

are welded to them. The casings are bolted to the middle casing at one end to the

load ring of the rear casing at the other end.

REAR CASING

The rear compressor casing houses the VIth stage stator blades, which

are bolted to the outer casing which at the inner radius. They are bolted to the rear

casing diaphragm flange.

COMPRESSOR ROTOR

The rotor assembly consists of individual discs with each set of HP

and LP spools forming ad room type construction except the 1st stage compressor

disc. The 1st stage disc is mounted as a cantilever on the LP compressor shaft with

the help of involute splined joint. The disc is located on the shaft by a splined lock

bolt. The nose bullet is of double construction and is given hydro phobic enamel

coating to prevent ice formation and erosion.

The rotor blades of 1st, 2nd and 3rd stages are secured in the

respective discs by dove tailed locks. The axial movement is restricted either by

retaining dowels or by blades retaining rings or by both. HP compressor assembly

is built as an integral unit with the journal. The journal in the main torque

transmitting member and is fitted in the center bearing housing in two radial thrust

half bearings.

COMBUSTION CHAMBER

The combustion chamber is can annular type with ten straight flame

tubes, which are arranged between the combustion chamber outer casing and the

surround of the rear casing. Each flame tube consists of a conical section followed

by five cylindrical liners followed by one rear transition liner which are seem

welded to each other. The conical section has a vanned swirler and a deflector and

is spot-welded to the liner.

The combustion liners are provided with 12 slots in welded zone to

reduce thermal stresses and for a closer fit of the welded surfaces. The outer wall

9

of conical section has holes for providing air for cooling the deflector. The

deflector itself has two rows of holes. Holes on 3rd, 4th, 5th liners are suitably at

the shoulders of the liners (near welded section) for cooling liner walls. The air

form these holes are made to flow along the circumference by the extension of

liners. Flame tubes are inter connected by the inter connector tubes located in the

conical section. The inter connectors between flame tubes I, II, IX and X are

provided with fuel connection to receive the two ignitor connections. Flame

propulsion and pressure equalization among the flame tube is effected by the inter

connectors. The ignition assembly is mounted on the compressor chamber outer

casing and has three connections, one for supply of starting fuel to the inner cavity

of ignitors another for location of spare plug and the other for oxygen supply

required for flight relighting. The extended steam of ignitor has four holes to

provided P2 air supply to inner cavity. A deflector provides in the cavity gives P2

air and upward motion.

The front end of flame tube rest on burners to spherical to incorporate

in the swirlers and at the rear end the flange of the flame tube is redidity secured to

the common ring. Combustion chamber outer casing is fabricated from the sheet

metal sections and is provided with three flanges, front flange for securing the

C.C.O.C to the stator none of six stage compressor, middle and front flanges serve

for mounting the bracket of accessory drive gearbox assembly and rear flange is

connected to turbine nozzle diaphragm assembly. For inflight relighting oxygen at

7-9 kg/cm2 at the rate of 0.95 to 1.2 gm/sec/ignitor, which is taken from oxygen

bottles in aircraft. Flame tubes are made up of Ni base alloy and coated with

spherical enamel to improve heat and corrosion properties. The C.C.O.C and

C.C.I.C are made up of S.S

TURBINE

The function of the turbine is to drive the compressor and accessories

by extracting pressure and kinetic energy from high temperature gases coming

from C.C. Based on the flow of gases on the gas turbine it is classified into

1. Axial flow turbines

2. Radial flow turbines

In axial flow turbine gas enters and leaves axially where in radial flow

turbine gas enters radially and leaves axially and vice-versa. The axial flow turbine

consists of two main elements consisting of a set of stationary vanes and one or

more turbine rotors. In stationary vanes the pressure energy is converted to K.E

and the same is converted into mechanical energy with rotary blades. Nozzle vanes

either cast or forged. Some vanes are made hollow to allow cooling using pump,

bleed air. The blades of turbine are two basic types.

10

1. Impulse turbine

2. Reaction turbine

The turbine is of axial flow reaction type T3 maximum is limited to 936°c.

Turbine needed cool to avoid over heating of components. A rotor assembly are

supported by radial thrust ball bearings and cylindrical roller bearing as the

compressor and turbine and respectively. Fixed vanes are arranged radially

between concentric rings.

1st stage NGVS are made of hollow for cooling air in investment

casting. These are sliding fit over the spokes arrange radially between the internal

and external rings.

ROTORS

Discs of L.P.T and H.P.T are presses fitted into the shaft are fastened

together by means of radial pins, which ensures concentricity of disc and shaft.

Blades are fixed in broached fire-tree slots in the disc and are lock by plate locks.

Blades are cropped at the tip in order to eliminate occurrence of cracks due to

unfavorable resonance vibration at the railing edge. LP blades are placed together

at about 2/3 of the blade height to avoid resonance vibration. Where the lace passes

extra material is provided and this locally thickened area blends itself with aerofoil

to minimize aerodynamic losses. No hairline cracks and under cuts is permitted at

this place. Natural frequency limits of H.P.T.R blades are 1130 ­ 1190 LPS.

Frequencies of higher order should not be less than 9200 cps.

Delta turbine temperature = 278°c

Turbine efficiency = 0.9

Pressure ratio at turbine = 3.43

AFTER BURNER AND JET NOZZLE

To provide higher thrust for short durations such as during take-off,

acceleration, climb and combat after burner are made use of a higher thrust engine

without thrust augmentation would mean a higher of the basic engine large fontal

area and high A/F ratio in gas turbines. Levels sufficient amount of unburnt

oxygen is made use of for burning consist of introduction and burning of fuel

between turbine and jet nozzle. The engine after burner system comprises of the

following.

1. DIFFUSER

A diffuser serves to reduce the velocity of gases from the turbine to a

level suitable the flame. It consists of outer shell and an inner shell or truncated

cone, supported by five aerofoil shaped fairings.

11

2. REHEAT PILOT COMBUSTION CHAMBER

Installed in the truncated cone of the diffuser, this provided the hot

stream of the pilot flame to light of the after burner fuel. This comprises of an

ignitor head with ignitor plug and ignitor case with nozzle. Electric current is fed to

the ignitor housing is coated with heat resistant enamel. Also cooling is provided

by air at P2.

3. AFTER BURNER MAIN FOLDS

It consists of an outer manifold with 60 burners (40 shaped on ring

and 20 shaped on pipes burning offering) and an inner manifold with 40 burners

(30 on ring and 10 on pipes along with two starting burners). The burners are of

simplex type and all supply atomized fuel against the direction of gas flow except

the starting burners, the starter burners supply fuel into the proposating the pilot

flame.

4. FLAME STABILIZER

Flame stabilizers are of radial type, which serves as flame holder and

are mounted near the out let of the diffuser.

5. VARIABLE AREA JET NOZZLE

It is a convergent nozzle, which increases the velocity of gases leaving

the after burner, thereby increasing thrust. The high mass flow and temperature of

exhaust gases during reheat requires the nozzle to be opened up, which is not done

result in unstable operation of the engine. This explains the need for variable area

jet nozzle. Nozzle flaps 18 in number are provided for this purpose with the flap

control ring being actuated by the cylinders.

SOME MORE TERMS RELATED IN VARIOUS SYSTEMS TO AN

AEROENGINE:

GAS TURBINE ENGINE: ­ An engine in which the working fluid is heated by

internal combustion be expanded through a turbine.

AERO ENGINE: An engine used to provide the main propulsive or lifting power

for aircraft.

CONSUMPTION: The total quantity of fuel consumed per hour.

SPECIFIC CONSUMPTION: - The weight propellant or fuel consumed per Kg of

thrust per hour.

12

ACCESSORY GEARBOX: - An engine drives the gearbox driving accessories.

ENGINE RATING: - A statement of the guaranteed minor alternately the average

performances of the engine, including output r.p.m specific fuel consumption, gas

temp, time limit and other relevant data specified conditions.

HEIGHT POWER FACTOR: - The ratio of power or thrust developed at a

specified attitude to that which would be developed at standard sec level it applied

to maximum power or thrust conditions of fuel throttle.

POWER UNIT: - An engine or two more engines complete with all components

and accessories used as fitted into an aircraft.

DRY WEIGHT: - The weight of an aero engine without liquid but including all

accessories essential to its running and any drives incorporated it for non-essential

accessories.

WEIGHT PER KG THRUST: - The dry weight of an engine divided by the

maximum permissible thrust under standard sec level conditions.

13

PRINCIPLE OF FLIGHT

Four forces come into action in an aero engine while flying.

1) Lift

2) Gravity

3) Thrust

4) Drag

1) LIFT

It is produced by a lower pressure created on the upper surface of an

airplane’s wings compared to the pressure on the wing’s lower surface, causing the

wing to be lifted upwards. Lift depends upon: -

i) Shape of the airfoil.

ii) The angle of attack.

iii) The area of the surface exposed to airstream.

iv) The square of the air speed.

v) The air density.

2) GRAVITY

It is due to weight of the plane itself that acts vertically downwards

from the center of gravity of the airplane.

3) THRUST

It is the forward direction pushing or pulling force created by the air

passing through the adjustable nozzle. This includes reciprocating engines, turbojet

engines and turboprop engines.

4) DRAG

Drag is the force which opposes the forward motion of airplane. It is a

retarding force acting upon a body in motion through a fluid, parallel to the

direction of motion of a body. It is created by air impact force, skin friction and

displacement of air.

14

PRINCIPLE OF JET ENGINE/GAS TURBINE ENGINE

Modern gas turbine engines follow the Brayton Cycle. An engine cycle is named after

George Brayton (1830-1892), the American Engineer who developed it originally for use

in piston engines, although it was originally proposed and patented by Englishman John

Barber in 1791.

The ideal Brayton cycle in gas turbine engine consists of three components:

1. A gas compressor

2. A burner (or combustion chamber)

3. An expansion turbine

The processes involved in Ideal Brayton cycle are:

Isentropic process- ambient air is drawn into the compressor where it is pressurized.

Isobaric process- the compressed air then runs through a combustion chamber, where

fuel is burned, heating the air- a constant pressure process, since the chamber is open to

flow in and out.

Isentropic process- the heated, pressurized air then gives up energy, expanding through a

turbine. Some of the work extracted by the turbine is used to drive the compressor

Isobaric process- heat rejection (in the atmosphere).

The processes involved in Actual Brayton cycle are:

Adiabatic process- compression

Isobaric process-heat addition

Adiabatic process-expansion

Isobaric process-heat rejection

Brayton Cycle

15

WWoorrkkiinngg ooff aa jjeett eennggiinnee // ggaass ttuurrbbiinnee eennggiinnee TThhee aavviiaattiioonn ggaass ttuurrbbiinnee eennggiinnee iiss ccaatteeggoorriizzeedd aass aa hheeaatt eennggiinnee.. IItt uusseess ggaass aass iittss

wwoorrkkiinngg fflluuiidd aanndd pprroodduucceess ((mmeecchhaanniiccaall)) sshhaafftt ppoowweerr aanndd tthhrruusstt.. GGeenneerraattiinngg tthhrruusstt,, iinn

ppaarrttiiccuullaarr,, iiss ppoossssiibbllee oonnllyy iiff tthhee eexxhhaauusstt vveelloocciittyy ooff ggaass iiss hhiigghheerr tthhaann tthhee vveelloocciittyy aatt

wwhhiicchh aaiirr eenntteerrss tthhee eennggiinnee.. IInn oorrddeerr ttoo aacccceelleerraattee tthhee ggaass,, eenneerrggyy mmuusstt bbee aaddddeedd ttoo tthhee

aaiirrffllooww wwiitthhiinn tthhee eennggiinnee wwhhiicchh ccaann tthheenn bbee ccoonnvveerrtteedd iinnttoo kkiinneettiicc eenneerrggyy..

IInn aa ggaass ttuurrbbiinnee eennggiinnee,, tthhee iinnccrreeaassee ooff eenneerrggyy iiss aaccccoommpplliisshheedd iinn ttwwoo ccoonnsseeccuuttiivvee

sstteeppss,, aanndd bbyy ttwwoo ddiiffffeerreenntt,, tthhoouugghh aaddjjaacceenntt,, eennggiinnee ccoommppoonneennttss.. FFiirrsstt,, pprreessssuurree ooff tthhee

aaiirrffllooww iiss rraaiisseedd bbyy aaccttiioonn ooff mmeecchhaanniiccaall sshhaafftt ppoowweerr.. TThhiiss iiss ddoonnee iinn tthhee ccoommpprreessssoorr

sseeccttiioonn.. AAfftteerr iittss ddiisscchhaarrggee ffrroomm tthhee ccoommpprreessssoorr,, tthhee pprreessssuurriizzeedd aaiirr eenntteerrss iinn tthhee

ccoommbbuussttiioonn cchhaammbbeerr,, wwhheerree tthhee ffuueell aanndd pprreessssuurriizzeedd aaiirr bbuurrnnss,, tthheerreebbyy tteemmppeerraattuurree ooff tthhee

ggaass iiss sstteeeeppllyy rraaiisseedd ((dduuee ttoo cchheemmiiccaall rreeaaccttiioonn ooff aaiirr aanndd ffuueell mmiixxttuurree))..

TThhee ggaass iiss nnooww ssuuffffiicciieennttllyy pprroocceesssseedd ttoo pprroovviiddee pphhyyssiiccaall wwoorrkk ffoorr tthhee ttuurrbbiinnee,, tthhee

ffiirrsstt ssttaattiioonn wwiitthhiinn tthhee eennggiinnee wwhheerree wwoorrkk eexxttrraacctteedd ffrroomm tthhee hhoott ggaass iiss ttuurrbbiinnee.. AAss tthhee

ggaass eexxppaannddss aanndd aacccceelleerraatteess,, iitt rroottaatteess tthhee ttuurrbbiinnee wwhhiicchh iinn ttuurrnn rroottaatteess tthhee ccoommpprreessssoorr aass

ttuurrbbiinnee iiss ddiirreeccttllyy ccoouupplleedd ttoo tthhee ccoommpprreessssoorr bbyy aa sshhaafftt ((ssppooooll)).. AAfftteerr ddiisscchhaarrggiinngg ffrroomm

tthhee ttuurrbbiinnee,, tthhee ggaass iiss ffuurrtthheerr aacccceelleerraatteedd iinn tthhee eexxhhaauusstt nnoozzzzllee,, wwhheerree aallll rreemmaaiinniinngg

uussaabbllee hheeaatt eenneerrggyy iiss ccoonnvveerrtteedd iinnttoo kkiinneettiicc eenneerrggyy wwhhiicchh pprroodduucceess tthhrruusstt ffoorr mmoovviinngg tthhee

aaiirrccrraafftt ffoorrwwaarrdd ((NNeewwttoonn TThhiirrdd LLaaww))..

EExxppllaannaattiioonn ooff wwoorrkkiinngg pprriinncciippllee..

AA.. TThhee aaiirr ffrroomm aattmmoosspphheerree iiss

ttaakkeenn iinn tthhrroouugghh aa ssiimmppllee oorr

ccoommpplleexx aaiirr iinnttaakkee ddeeppeennddiinngg oonn

tthhee fflliigghhtt ssppeeeedd aanndd ggeeoommeettrryy ooff

tthhee aaiirrccrraafftt aaiirr iinnttaakkee..

BB.. AAiirr iiss ccoommpprreesssseedd iinn aa cceennttrriiffuuggaall

oorr aaxxiiaall ffllooww ccoommpprreessssoorr ttoo iinnccrreeaassee

tthhee pprreessssuurree aanndd tteemmppeerraattuurree ooff aaiirr..

CC.. CCoommpprreesssseedd aaiirr eenntteerrss iinn

ccoommbbuussttiioonn cchhaammbbeerr wwhheerree ffuueell

iiss iinnjjeecctteedd aanndd bbuurrnneedd,, tthhuuss aaddddiinngg

mmoorree eenneerrggyy ttoo aaiirrffllooww.. TTeemmppeerraattuurree ooff ggaass

iinnccrreeaasseess wwhheerree aass pprreessssuurree rreemmaaiinnss

ccoonnssttaanntt..

16

DD.. PPaarrtt ooff tthhee eenneerrggyy ggeenneerraatteedd

iiss uusseedd ttoo rruunn aa ttuurrbbiinnee wwhhiicchh

pprroovviiddeess ppoowweerr ffoorr rruunnnniinngg tthhee

ccoommpprreessssoorr aanndd aallssoo ssoommee

aacccceessssoorriieess nneecceessssaarryy ffoorr eennggiinnee

ooppeerraattiioonn..

EE.. TThhee rreemmaaiinniinngg eenneerrggyy ooff ggaass

ssttrreeaamm iiss ccoonnvveerrtteedd iinnttoo kkiinneettiicc

eenneerrggyy bbyy eexxhhaauusstt nnoozzzzllee ttoo pprroodduuccee

tthhrruusstt.. HHiigghh eexxhhaauusstt vveelloocciittyy iiss

pprreerreeqquuiissiittee ttoo ggeenneerraattiioonn ooff tthhrruusstt..

Thank You