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ME 151 Course > Prime Movers > Flashcards

Prime Movers Flashcards

1
Q

What is the definition of a Gas Turbine?

A

A self-contained heat engine, using a continuous flow of gas as the working fluid. Its state is changed through a compressor. It is combined with an energy source and then expanded through one or more turbines, producing a net energy output in a useable form.

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2
Q

What two things may the energy output be used for?

A

1) Jet thrust as a reaction force to drive the body forward.

2) Power Turbine to turn a rotary shaft and transfer this energy.

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3
Q

What is the purpose of the inlet guide vanes?

A

Guides the inlet air at an angle to the direction of flow towards the first rotor stage.

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4
Q

What is the rotor assembly?

A

A rotating assembly of discs that carry the rotor blade spools sequentially in between the stator assemblies. The spools also progressively follow the casing in an opposite direction to contribute to the compression effect of the air.

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5
Q

Describe what makes up a compression stage?

A

Each pairing of one stator and one rotor comprises a compression stage. Most axial compressors have multiple stages.

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6
Q

Describe the purpose of the injector / burner?

A

Used to introduce high pressure, atomised fuel into the compressed air flow so it will efficiently combust and produce energy.

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7
Q

What is the purpose of the high energy igniter?

A

Produces a high voltage spark, causing the initial fuel/air mixture to ignite on engine startup.

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8
Q

What are nozzle guide vanes?

A

Stator vanes situated on the outlet side of the combustion chambers, which direct the path of the outlet, high energy, high temperature gas onto the turbine.

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9
Q

What is the turbine?

A

A rotating disc of turbine blades, utilising the high energy gas emitted from the nozzle guide vanes.

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10
Q

What is the Turbine Driveshaft?

A

The shaft connecting the turbine to the compressor. The drive energy captured by the turbine drives the compressor directly and facilitates the self-sustaning motion of the gas turbine.

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11
Q

What is the Turbine Casing?

A

A high temperature resistant alloy casing designed to contain the turbine gasses and direct energy onto the turbine blades.

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12
Q

List 5 advantages of gas turbines:

A

1) Good power to weight ratio.

2) Quick start-up capability available.

3) Rapid / flexible response to changes in power demand and operational requirement.

4) Comparatively low development cost.

5) Low on-board maintenance requirements.

6) Ease of upkeep by exchange of critical parts.

7) Reduced watchkeeping manpower. Automation means unmanned spaces.

8) Good fuel consumption at higher power ranges. Engines designed to be run at top speed.

9) Reduced noise signature - high frequency.

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13
Q

List 5 disadvantages of Gas Turbines:

A

1) Unidirectional turbine output.

2) High quality fuel requires complex fuel cleaning systems.

3) Good air quality required - complex air filter needed.

4) Installation - large intake and exhaust ducting needed.

5) High infrared signature - cooling arrangements required to determine infrared seeking missiles.

6) High spares and maintenance costs.

7) Poor fuel consumption and combustion at part load conditions.

8) Increased number of prime movers on gas turbine warship.

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14
Q

What are the two main operational considerations of Gas Turbines?

A

Economy of fuel and economy of engine hours.

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15
Q

Name the configuration of propulsion on type 23’s and the types of gas turbines on-board.

A

Combination of Diesel, Electric, and Gas.

Spey SM1A or SM1C gas turbines.

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16
Q

Name the configuration of propulsion on Type 45’s and the types of gas turbines on-board.

A

Integrated Electrical Propulsion.

Two WR21 gas turbines.

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17
Q

Name the configuration of propulsion on QE class ships and the types of gas turbines on-board.

A

Integrated Electrical Propulsion.

Two MT30 Gas turbines.

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18
Q

List 5 compressor design requirements:

A

1) Production of a large mass flow of air.

2) Production of a substantial pressure rise.

3) The compression process must be as efficient as possible.

4) The compressor operation should be stable over as large a range of mass flow as possible.

5) Ideally, it should be compact and to be modularity, with components as light as possible.

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19
Q

On an axial compressor, what passes through the feed tubes?

A

Lubricating oil and cooling / sealing air.

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20
Q

On an axial compressor, what is bolted to the drive shaft?

A

Three diaphragm assemblies to which five rotor disc assemblies are bolted.

21
Q

On an axial compressor, what is the purpose of the interstage spacing rings?

A

Provide rigidity and designed spacing between the rotor discs. Forms the inner labyrinth of inter stage seals and assists the axial flow of air.

22
Q

Describe the three types of compressor blade attachments.

A

Solid root - blade root drilled and fitted into channel, held in place by retaining pin and locking rings.

Fir tree root - Blade root slotted axially into profiled channelling and secured with locking plate.

Dovetail root - blade root inserted into single profiled channel and secured by a grub screw.

23
Q

Describe pressure and velocity change through an axial compressor.

A

Overall, on average, the velocity remains constant, and the pressure and temperature increase as the volume decreases.

Each rotor stage increases velocity and pressure.

Each stator stage decreases velocity but increases pressure.

24
Q

What are the properties of gas turbine lub oil?

A

Anti foaming.
High viscosity, low pour point.
High flash point.
Good film strength.
Wide operating temperature range.

25
Q

What is the purpose of the lub oil scavenge system?

A

Each scavenge pump draws oil away from the bearings. Each pump is fitted with an in-line magnetic chip detector and filter.

26
Q

What components are fitted in the lub oil return line?

A

A SW cooled oil cooler, a set of duplex filters, and a conical air oil separator.

27
Q

Describe the purpose of the high speed gearbox.

A

The gearbox provides drives to the oil pump, hydraulic pump, fuel pump, and centrifugal air/oil sep.

28
Q

Where is the high speed gearbox located?

A

Slung beneath the engine, in the region between the HP and LP compressor, called the intermediate casing.

29
Q

What type of engine would have an air starter motor, and where is the air discharged.

A

Spey gas turbines.
Air discharged into the atmosphere of the module.

30
Q

Where are the hydraulic starter motors located?

A

The hydraulic equipment is mounted on hydraulic skids separate to the module.

31
Q

How are starter motors disengaged?

A

When the engine reaches a self-sustaining speed, the starter motors are disengaged by a combination of centrifugal clutches and control systems.

32
Q

What facility is unique to the WR21 hydraulic start system?

A

Fwd/Aft hydraulic systems can be cross connected.

33
Q

Where is air extracted from in the engine?

A

From air bleeds at the comparatively colder end of the engine.

34
Q

What is the purpose of air bleeds?

A

Extracts air to cool and improve the performance of the hot end components and prevent them from overheating. In addition, it prevents the cross contamination of:
1) Air to Oil
2) Air to Gas
3) Gas to Oil

35
Q

What are the three uses of air bleeds?

A

Cooling
Sealing
Bearing air mist lubrication.

36
Q

How is air transferred from origin to service?

A

Air is tapped from various parts of the compressors. The air is extracted through drillings in the stator blade roots or casing outlets. The air can be transferred through either internal or external piping. Internally, it is transported through drillings, the engine support struts, and turbine stator manifolds.

37
Q

Why are different air extraction points necessary?

A

Each tapping point is dependant on the service its needed for. Hence, the pressure, temperature, flow rate/direction must be correct.

38
Q

What are the requirements of sealing air?

A

Prevent external gas leaks.
Prevent internal gas leaks.
Prevent oil leaks.

39
Q

What components can be affected by poor quality fuel?

A

Carbon build up in combustion Chambers and nozzle guide vanes leading to hot end corrosion.

Sensitive components like filters and LPAs can become blocked.

Fuel pumps can sustain bearing damage.

40
Q

How is fuel supplied to the gas turbine.

A

By the ships low pressure (1 - 1.5 bar) fuel supply system via a filtration and coalescing process to rid the fuel of particulates and water contamination down to 5 microns.

41
Q

What are the 6 fundamental requirements for fuel control system?

A

To supply fuel to the burners for starting.

To supply fuel to the burners and a controlled rate over has turbine operating rpm ranges and temperatures.

To shut off fuel supply to the burners under normal and emergency conditions.

Prevent surge rich flameout during acceleration.

Prevent overtemperature of components.

Prevent stall and rich flame-out during deceleration.

42
Q

What are the two main functions of the high pressure shut off cock?

A

To provide a positive fuel shut off to the burners for normal and emergency shut down.

When closed, it recirculates the fuel back to the suction side of the fuel pump.

43
Q

What are the three types of combustion Chambers in gas turbines, and on what engines are they used?

A

Can-annular - spey 1a and 1c

Annular - MT30 and LM2500

Radial - WR21

44
Q

What are the requirements for a combustion chamber to ensure good performance?

A

High combustion efficiency.
Good combustion stability.
Ease of ignition.
Clean exhaust, minimal pollution.
Uniform outlet temperature profile.
Wide operating range.

45
Q

Describe can-annular combustion Chambers.

A

A series of axially mounted combustion Chambers that sit in the direct air flow path from the delivery outlet from the HP compressor

46
Q

Describe annular combustion Chambers.

A

Consists of a single flame tube, completely annular in form, contained in an inner and outer casing.

47
Q

Describe the HP/LP turbine casing.

A

Made from a high strength titanium alloy material. Where the stator blades are contained.

48
Q

Describe the inter turbine duct.

A

Provides an interface between the GTCU turbines and the power turbine fitted to the ship.

49
Q

What fire detectors are fitted to the different types of gas turbines?

A

Speys - three infrared detectors.

WR21 - eight heat / flame detectors (IR and near visible light)

MT30 - five infrared and two heat detectors.

ME 151 Course (10 decks)

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