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JET PROPULSION Part 3 The Jet Engine. The jet engine used in this section is the Rolls-Royce Avon. It is a relatively simple engine known as a ‘Turbo-jet’.

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Presentation on theme: "JET PROPULSION Part 3 The Jet Engine. The jet engine used in this section is the Rolls-Royce Avon. It is a relatively simple engine known as a ‘Turbo-jet’."— Presentation transcript:

1 JET PROPULSION Part 3 The Jet Engine

2 The jet engine used in this section is the Rolls-Royce Avon. It is a relatively simple engine known as a ‘Turbo-jet’.

3 The Jet Engine Intake Anti-Icing Tube Rear Compressor Case Combustion Chambers (Cans) Jet Pipe (Exhaust) Front Compressor Casing Accessory Gearbox Fuel, Oil & Hydraulic Pumps, Electrical Generators, RPM Governor. Oil Tank Turbine Section External Features Carries hot air from the rear of the compressor, to the outer casing, front vanes bullet, as ice can build up and restrict airflow to the engine, reducing efficiency and thrust.

4 The Jet Engine Intake Anti-Icing Tube Rear Compressor Case Compressor Handling Bleed Valve Combustion Chambers (Cans) Jet Pipe (Exhaust) Front Compressor Casing Accessory Gearbox Fuel, Oil & Hydraulic Pumps, Electrical Generators, RPM Governor. Oil Tank Turbine Section External Features Allows compressor air to bleed overboard. This prevents engine surging in what is known as the Off Design Condition ‘Off Design Condition’

5 The Jet Engine Intake Anti-Icing Tube Front Engine Mount Rear Compressor Case Compressor Handling Bleed Valve Combustion Chambers (Cans) Jet Pipe (Exhaust) Front Compressor Casing Accessory Gearbox Fuel, Oil & Hydraulic Pumps, Electrical Generators, RPM Governor. Oil Tank Turbine Section Rear Engine Mount External Features Used to fix the engine into the aircraft, the front mount is flexible to allow expansion and contraction due to temperature changes.

6 The Jet Engine The Static Assembly

7 The Jet Engine The Static Assembly COMPRESSOR OUTER CASINGS COMBUSTION INNER CASING COMBUSTION OUTER CASINGS REAR CONE AND SUPPORT VANES COMBUSTION FLAME TUBES The casing is the structural frame work of the engine. It has to be strong enough to carry the weight of all the external fitments and accessories and to withstand the internal temperatures and pressures (‘hoop-stress’). FRONT BULLET & SUPPORT VANES

8 The Jet Engine The Static Assembly STATOR VANES NOZZLE GUIDE VANES (NGV’S) SUPPORT BEARINGS The power to weight ratio is very important, the heavier the engine, the less payload the aircraft can carry. Designers strive to get he most power out of the lightest engine design.

9 The Jet Engine The Rotating Assembly Compressor Blades Turbine Blades Shaft Assembly The rotating assembly - compressor, shaft and turbine – is carried on bearings and is known as a ‘spool’. Located in the casings via the three bearing assemblies, the shaft rotates at whatever rpm the combustion gases drive it. Compressor blades generally use a ‘Dove-tail’ root fixing, and turbine blades generally use a ‘Fir-Tree’ root fixing.

10 The Jet Engine The Rotating Assembly Compressor Blades Turbine Blades Shaft Assembly The compressor and turbine ‘drums’ are a series of discs fixed together at the rims by bolting or welding together. The turbine absorbs just sufficient energy from the gas stream to drive the compressor, leaving the remainder to provide the thrust.

11 The Gas Path and Temperatures The Jet Engine The shaded area is called the ‘ GAS PATH ’. As the air passes through the engine, its temperature is changed, its temperature is changed, first by compression, then by adding and burning fuel, the burnt gasses then pass through the turbine section, and finally through the exhaust to the atmosphere.

12 The Gas Path and Temperatures The Jet Engine Temperature changes cause the shaft Temperature changes cause the shaft and casings to expand and contract. But by different amounts ! But by different amounts ! When the engine is started, the casings expand before the rotor does. Ambient temp 450 Deg C 2,500 Deg C 1,000 Deg C Above ambient Problem !

13 The Gas Path and Temperatures The Jet Engine Ambient temp 450 Deg C 2,500 Deg C 1,000 Deg C Above ambient These sections expand first And this could put tremendous unwanted forces on the casings, shaft and rotor, leading to failures.

14 The Gas Path and Temperatures The Jet Engine The solution is in the bearings Front Bearing Chamber Centre Bearing Chamber Rear Bearing Chamber Roller Bearing Ball Bearing (Location Bearing) Roller Bearing

15 The Engine Bearings The Jet Engine Shaft CasingCasing Front Bearing Chamber Centre Bearing Chamber Rear Bearing Chamber Front Bearing Chamber Centre Bearing Chamber Rear Bearing Chamber Remember the Problem Temperature changes cause the shaft and casings to expand and contract. The solution is in the bearings

16 The Engine Bearings The Jet Engine Shaft CasingCasing The bearings are selected to allow expansion (and contraction on cool down) without causing undue stresses. Ball Bearings provide positive Axial Location and don’t allow lateral movement between the casings and the rotor

17 The Engine Bearings The Jet Engine Shaft CasingCasing The bearings are selected to allow expansion (and contraction on cool down) without causing undue stresses. These bearings use Rollers instead of ball bearings. The outer track prevents the rollers from moving laterally. The inner track allows lateral movement without undue stress.

18 The Engine Bearings The Jet Engine Shaft CasingCasing Hot section Shaft and Casing have no differential movement at this point The casing expands first, pushing the rear outer bearing with it Then, with ‘heat soak’ the shaft expands

19 The Engine Bearings The Jet Engine Shaft CasingCasing Hot section Shaft and Casing have no differential movement at this point The casing expands first, pushing the rear outer bearing with it Then, with ‘heat soak’ the shaft expands The same happens at the front with pressured air and heat sink from the combustor heating the hardware The engine is actually designed to dimensions based on normal operating temperatures

20 Check of Understanding The compressor handling bleed valve allows compressor air to bleed overboard and so prevent engine surging. What is this surging known as? Induced Flow Condition Hoop Stress Root Fix Condition Off Design Condition

21 What are the front and rear engine mounts used for? To stop ice build-up in the engine To fix the engine into the aircraft To allow expansion without stress To hold the shaft assembly in place Check of Understanding

22 Where would you expect the fuel, oil & hydraulic pumps, electrical generators and RPM governor to be situated on a jet engine? In the turbine section In the front bullet In the rear compressor case In the accessory gearbox Check of Understanding

23 Which of these does not form part of the static assembly? Stator vanes Rear support vanes Compressor blades Combustion flame tubes Check of Understanding

24 The casing the engine has to be strong enough to withstand the internal pressures. What are these pressures known as? What are these pressures known as? Hoop Stress Ambient Pressure Root Fix Stress Fir Tree Pressure Check of Understanding

25 The shaft assembly and turbine blades are part of which engine assembly? Bearing Assembly Rotating Assembly Static Assembly Outer Casing Assembly Check of Understanding

26 Which of these statements applies to the centre bearing chamber? Use rollers instead of ball bearings Allows lateral movement without undue stress Ball Bearings provide positive axial location Prevents rollers from moving laterally Check of Understanding

27 Questions?

28 JET PROPULSION End of Presentation


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