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Jet Propulsion

Lecture-13

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

Indian Institute of Technology Guwahati

Prepared underQIP-CD Cell Project

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GE J79 Turbojet

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Features

• Highly used engine for Military aircrafts specially in Supersonic Fighters.

• Developed in early 1955 during the initial cold war period by General Electric for McDonnell Douglas, Lockheed Martin and North American.

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SpecificationsNumber of Compressor Stages 17Number of Turbine Stages 3Number of Combustors 10Maximum Diameter 0.99 mMaximum Length 5.28 mMaximum Dry Weight 1634 KgSFC at maximum power 203.9 g/N/hMaximum Power 80,143 NCompression Ratio at maximum RPM 13.5:1

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Engine Assembly

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Engine Airflow

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Compressor Assembly

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Compressor Assembly

1. Compressor Front Frame : The Compressor Front Frame forms the air inlet passage for the engine and supports the front of the compressor rotor. Frame is made of Stainless Steel and has eight evenly placed hollow struts and also 20 inlet guide vanes for the first compressor stage.

2. Compressor Casing Assembly : Compressor casing Assemblies consist of two cylindrical, stainless steel casing, split along the horizontal line for removal.

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Compressor Assembly3. Compressor Rotor : The Compressor rotor consists of a front stub shaft , 17

disks, spacers and sets of blades as shown below

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Compressor Assembly4 . Compressor Rear Frame : The

compressor rear frame absorbs the thrust loading of the rotors and radial forces of the compressor turbine coupling.

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Combustion SectionThe Combustion chamber is and Can type Combustion chamber and the parts are shown below.

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Turbine Assembly

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Turbine Assembly

• Turbine Stator Assembly : The turbine stator assembly is split on a horizontal line for easy removal and includes the second and third stage nozzles assembled into the turbine casing.

• Turbine Rotor: The turbine rotor provides the rotary power to the compressor. The rotor is equipped with three sets of rotor blades and two torque rings. It also consists of the hollow conical shaft. The shaft has an external spline that engages with the compressor rotor rear stub shaft.

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Afterburner Assembly

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Afterburner Assembly• Forward Exhaust Duct Assembly : The forward exhaust is

bolted to the rear flange of the turbine frame.• After Burner Manifold and Multijet Fuel Nozzle : The four after

burner manifolds encircles the forward exhaust duct. Each manifold has 21 outlets ports. Holes in the side of the tubes spray the fuel at right angles to the exhaust flow.

• Pilot Burner : The pilot burner, or the torch igniter, ignite the afterburner fuel in the exhaust section. The pilot burner attaches to the forward exhaust duct at the bottom and extends into the innner and the middle flame holder.

• Flame Holder : The flame holder consists of three concentric, V gutter rings connected by seven, equally spaced radial links. The rings are staggered to ensure efficient burning.

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Tailpipe AssemblyThe tailpipe assembly consists of rear exhaust duct, liners and the exhaust nozzle. The liners are ceramic coated to withstand high after the high after burner temperature. The exhaust nozzle assembly consists of 24 flaps and seals interconnected by flap actuators and bellcranks to provide variable opening area of the exhaust nozzle.

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Applications of GE J79 Engines

B-58 BomberMc Donnell Douglas F-4

Lockheed Martin F-104 F-16

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Teledyne CAE J69-T-25Turbojet Engine

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Specifications

Number of compressor stages: 1Number of turbine stages: 1Number of combustors: 1Maximum power at sea level: 4.559 kNSFC at maximum power: 0.1162 kg/N/hCompressor ratio at max rpm: 4:1Maximum diameter: 0.632 mMaximum length: 1.27 mMaximum dry weight: 165 kg

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Specifications cont…J69 engine consists of…• Accessory case• Compressor housing• Turbine housing

External accessories…• Starter generator (airframe supplied)• Starting-fuel system• Ignition system• Fuel pump• Fuel control• Oil pump• Oil filterFuel, air and oil lines

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CUTAWAY

VIEW

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ConstructionCentrifugal compressor blades – integral with hub metal

Turbine blade – removable & replaceable

Combustion chamber (side-entry annular, L shaped) – sheet-metal construction of high-temp.-resistant alloy

Turbine-shaft-assembly part – machined

Turbine housing, turbine inlet nozzle, radial and exhaust diffuser –welded, build up construction

Compressor housing, accessory case, its cover, oil pump, drive adaptor, starter-generator adaptor, axial diffuser, rear bearing housing, front bearing cage etc. – machined item

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SECTIONAL

VIEW

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Air flow

Primary air (Part B & Part C)• Forms air-fuel mixture in cc• Part C cools the vanes of turbine inlet nozzle

Secondary air (Part D)• Dilute the combustion product and hence holds down

peak temperatures

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Operation, some statistics

Flame established – 3500 rpmStarter-generator cutout – 5000 rpmStarting combustion occurs – 1500 to 2000 rpm

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Continental J69-T-25, Application

Cessna T-37A Tweet, Trainer aircraft USAF

Cessna T-37C, Trainer aircraft USAF

Other application – target drones, special purpose aircraft

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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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