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Jet Propulsion

Lecture-7

Ujjwal K Saha, Ph. D.Department of Mechanical Engineering

Indian Institute of Technology Guwahati

Prepared underQIP-CD Cell Project

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Thrust AugmentationWater Injection Afterburning

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Thrust from an existing engine

Raising FPR: Additional Fan Stage, Addl. Weight.Addl. turbine stage with further power extraction

Raising CPR : High RPM of compressor or additional compressor stage.

Raising BPR : Diameter increases, weight increasesAddl. power extraction in turbine.Ground clearance decreases.

Raising TIT : Redesign of blades especially at the inlet.Improved cooling method.

TIT

CPRF

BPR

CPRF

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Thrust Augmentation: (increase of F )

Two alternatives :TIT (TO3)

Increase of Redesignam

Temporal increase of Thrust:

Take-off

Climb

Acceleration (From M<1 to M>1)

Combat maneuvers

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Schemes:1) Liquid injection2) Afterburning

Liquid Injection: Used to raise the take-off thrust.* water is sprayed into the compressor inlet. * compressor inlet temperature reduced.

Evaporation of water dropletsExtraction of heat from the airflow.Cooling of the airflow density

mass flow

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General Practice :

Water + Methanol

Lowers the freezing point of water

Burns as it reaches the Combustor

Turbine inlet temperature is restored

Power is restored

(without fuel flow adjustment)

∴

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Penalty :1) System makes the engine very heavy2) Compressor blade erosion (when the system is

activated), Compressor stall.3) Methanol and jet fuel have different burning

characteristics.

( ) ( )0.5B Balcohol jet fuelη η=

Water/ Air Ratio:1 lb - 100 lb (0.454 kg to 45 kg)5 lb - 100 lb (2.25 kg to 45 kg)

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Attractive features :

* Power can be Restored (at high H)* Power can be Boosted (10 to 30%)

On a hot day

Power Rating :Wet Thrust (injection ON)Dry Thrust (injection OFF)

. Compressor inletWater injection

Compressor diffuser case

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ALLISON J33 TURBOJET ENGINE

SPECIFICATIONS

Compressor: Single-stage centrifugal Turbine: Single axial Weight: 1,795 lbs. Thrust: 4,600 lbs. (5,400 lbs. with water/alcohol injection) Maximum RPM: 11,750 Maximum Operating Altitude: 47,000 ft.

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Afterburning :

to augment thrust during

take-off

climb

combat performance

Increased power

From a larger engine

Frontal areaWeightSFC

High

Reheat

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Method :

Burning of fuel in jet pipe Turbine and

propelling nozzle

Effected by unburnt O2 of exhaust gas

Temperature increase

Velocity of jetincreases

F increases

2000 KJP

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F 110 129

F 100 229

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Design : Flame concentration along the axis

Turbine discharges gas along the wall.Typically, the Mach number at the Turbine exit, M = 0.50Diffuser to reduce the Mach No. from M = 0.25 to M=0.30

Nozzle : Variable Area Two Position Large to suit change in

density resulting from large change in temperature

Due to high Tdensity

Area increase to suit the increase in volume of gas stream

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Comparison :

Engine 1: AB OFF

Engine 2: Without AB

Less efficiency

Pressure loss due to presence of burner & stabilizing devices

Added restriction in the jet pipe

Also high overall weight

AB Increases high SFCLimited for short period

Additional Fuel added for required temp. ratioNoisy exhaust (objectionable)

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AB also used in Turbofan engines

The exact increase in thrust depends uponMaximum AB Temperature Bypass Ratio Type of Stream/Streams

Mixed Type Non-Mixed Type

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Applications: PW 100 (Mixed Flow Turbofan)

GE J79 Turbojet Engine (Variable Area Nozzle)

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Applications: Olympus engine (Concorde) M= 0.9 to 1.4

15-20% increase in take-off FDry Thrust = 139.4 kN; Afterburning = 169.2 kN

Objectionable :Noisy Exhaust

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AB incurs an increase of SFCOperated for short duration

Time saved

Time

Alti

tude

with A

B w/o AB

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0

1

2

3

4

5

6

7Reheat

before N

before N

S

T

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SummarySummary

oo Thrust from an existing engineThrust from an existing engine

oo Increase of Thrust for short durationIncrease of Thrust for short durationWater Injection, AfterburningWater Injection, Afterburning

oo Afterburning (Turbojet, Turbofan) Afterburning (Turbojet, Turbofan)

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References1. Hill, P.G., and Peterson, C.R., (1992), Mechanics and

Thermodynamics of Propulsion, Addison Wesley.2. Saravanamuttoo, H.I.H, Rogers, G.F.C, and. Cohen, H, (2001), Gas

Turbine Theory, Pearson Education.3. Oates, G.C., (1988), Aerothermodynamics of Gas Turbine and Rocket

Propulsion, AIAA, New York.4. Mattingly, J.D., (1996), Elements of Gas Turbine Propulsion, McGraw

Hill.5. Cumpsty, N.A., (2000), Jet Propulsion, Cambridge University Press.6. Bathie, W.W., (1996), Fundamentals of Gas Turbines, John Wiley.7. Treager, I.E., (1997), Aircraft Gas Turbine Engine Technology, Tata

McGraw Hill. 8. Anderson, J. D. Jr., (2000), Introduction to Flight, 4th Edition, McGraw

Hill. 9. M.J.L.Turner, (2000), Rocket and Spacecraft Propulsion, Springer.10. Sutton, G.P. and Biblarz, O., (2001), Rocket Propulsion Elements,

John Wiley & Sons.11. Zucrow, M.J., (1958), Aircraft and Missile Propulsion, Vol. II, John

Wiley.12. Barrere, M., Jaumotte, A., Veubeke, B., and Vandenkerckhove, J.,

(1960), Rocket Propulsion, Elsevier.

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1. http://www.soton.ac.uk/~genesis2. http://www.howstuffworks.co3. http://www.pwc.ca/4. http://rolls-royce.com5. http://www.ge.com/aircraftengines/6. http://www.ae.gatech.edu7. http://www.ueet.nasa.gov/Engines101.html8. http://www.aero.hq.nasa.gov/edu/index.html9. http://home.swipnet.se/~w65189/transport_aircraft10. http://howthingswork.virginia.edu/11. http://www2.janes.com/WW/www_results.jsp12. http://www.allison.com/13. http://wings.ucdavis.edu/Book/Propulsion14. http://www.pilotfriend.com/15. http://www.aerospaceweb.org/design/aerospike16. http://www.grc.nasa.gov17. http://www.hq.nasa.gov/office/pao/History18. http://membres.lycos.fr/bailliez/aerospace/engine19. http://people.bath.ac.uk/en2jyhs/types.htm20. http://roger.ecn.purdue.edu/~propulsi/propulsion/rockets21. http://www.waynesthisandthat.com/ep2.htm22. http://www.answers.com/main23. http://www.astronautix.com

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