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151/23/005 > Gas turbines- prime movers > Flashcards

Gas turbines- 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 it is expanded through the turbines, producing a energy output of a useable form.

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2
Q

What can energy output of a turbine be used for?

A

1) jet thrust as a reaction force to drive a body forward
2) Power turbine to turn a rotary shaft and transfer this energy

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3
Q

what are inlet guide vanes?

A

The first stator stage which guides the inlet air at an angle to the direction of flow toward the first stage

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4
Q

what are compressor stages?

A

Each pairing of one stator and one rotor compressor stage. Most axial compressors have multiple stages.

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5
Q

What are Injector/burners?

A

Device situated within the combustion and used to introduce high pressure, atomised fuel into the compressed air flow so it will efficiently combust and produce energy.

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6
Q

what is a high energy igniter?

A

High voltage spark ignition device for causing the initial fuel/air mixture to ignite on engine start up

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7
Q

What are nozzle guide vanes?

A

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

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8
Q

what is a turbine?

A

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

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9
Q

What are the advantages of a gas turbine?

A
  • good power to weight ratio.
  • quick start up capacity
  • rapid response to change in power/operational requirement
  • low development cost
    -low maintenance
  • ease of up keep
  • reduced noise
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10
Q

Disadvantages of gas turbines?

A
  • may need CPP/gear box
  • requires high standard fuel cleaning systems
  • good air quality required
  • poor fuel consumption
  • increased number of prime movers
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11
Q

what is the configuration of a type 23, what gas turbines are used?

A

CODLAG
SM1A or SM1C

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12
Q

what is the configuration of a type 45, what gas turbines are used?

A

IEP
WR 21

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13
Q

what is the configuration of a QE class, what gas turbines are used?

A

IEP
MT30

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14
Q

what is the configuration of a type 26, what gas turbines are used?

A

CODLOG
MT30

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15
Q

What are the requirements of a compressor design?

A
  • production of a large mass flow of air
  • production of a substantial pressure rise
  • efficient as possible
  • stable over as large range of mass flows as possible
  • modularised and designed as light in mass as possible
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16
Q

Describe the central drive shaft

A

The central drive shaft connects the LP turbine to the LP compressor as one assembly

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17
Q

What passes through the feed tubes?

A

They pass lubricating oil and cooling and sealing air.

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18
Q

What is bolted to the drive shaft?

A

Bolted to the shaft are three diaphragm assemblies to which five rotor disc assemblies are bolted.

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19
Q

What is the purpose of inter stage spacer rings?

A

They provide rigidity and designed spacing between the rotor discs, forms the inner labyrinth of inter stage seals and assists the axial flow of air.

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20
Q

What blade attachments can you get on a gas turbine?

A
  • solid root, blade root drilled and fitted into channel, then pinned and retained by circlip.
  • firtree root, blade root slotted axially into profiled channelling and secured by sectioned retaining plate.
  • dovetail root- blade root inserted into single profiled channel in disc periphery and secured by grub screw.
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21
Q

What happens in each rotor stage?

A

increased velocity and pressure

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22
Q

what happens in each stator stage?

A

decreases velocity but increases pressure.

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23
Q

what happens overall inside the axial compressor?

A

velocity remains constant
pressure, temp increase
volume decreases

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24
Q

what is the formula for combined gas law?

A

p1v1/t1=p2v2/t2

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25
Q

what is the purpose of a scavenger system?

A

oil collects and is drawn away from the bearings by the scavenger pumps

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26
Q

what is fitted in the scavenger line?

A

in-line magnetic chip detectors
filters

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27
Q

what is fitted in the return line?

A

seawater cooled oil
duplex filters
conical air oil separator

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28
Q

where is the high speed gear box positioned?

A

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

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29
Q

give a brief description of a highspeed gear box

A

provides drives to the oil pump, hydraulics pump, fuel pump and centrifugal air/oil separator. The starter motor is attached to the rear, with its drive shaft engaged in the gear train, to rotate the HP compressor rotor. This allows the spur gears to also drive engaging other systems.

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30
Q

what do starter motors WR21, MT30 and LM2500 gas turbines have in common?

A

They have hydraulically operated gas turbines, the hydraulic equipment powers the motors is mounted on hydraulic skids on the exterior of the modules.

31
Q

what type pf engine would have a air start and what type of exhaust?

A

Spey
discharge atmosphere

32
Q

other engines have a hydraulic start, how is this achieved?

A

hydraulic reservoir are on a skid

33
Q

how are starter motors disengaged?

A

when the engine reaches self sustaining speed, the starter motors are disengaged by a combination of centrifugal clutches and controls

34
Q

what facility is unique to the WR21 hydraulic start system?

A

FWD and AFT systems can be connected.

35
Q

where in the engine is air extracted from?

A

air bleed from the compressors at the comparatively colder end of the engine.

36
Q

what is the purpose of air bleeds in an engine?

A

to stop cross contamination of the following:
- air to oil
- air to gas
- gas to oil

37
Q

Briefly describe how air is transferred from origin to service?

A

through internal piping or external piping, internally it is transferred through drillings, support struts and stator manifolds

38
Q

explain why we have to choose the correct temp and pressure of air bleed

A

avoids wastage of compressor work

39
Q

explain why we have controlled flow direction

A

it is important that there is no back flow

40
Q

explain why we have controlled flow rates

A

adequate cooling, to make sure it is not over cooled. this is controlled by restrictors but can not be shut off.

41
Q

explain how air is extracted and how different extraction points are necessary?

A

The air extracted through drilling roots or casing outlets. Each tapping is dependent on the service it is needed for hence the pressure temp, flow rate need to be accurate

42
Q

what are the requirements of seals?

A
  • prevent external gas leaks, reduced to min for economy, comfort and CBRNDC requirements
  • prevent internal gas leaks, prevent wasted compressor and turbine work
  • prevent oil leaks, prevents carbon build build up which prevents overheating
43
Q

what components on a gas turbine can be affected by poor quality fuel?

A

combustion chambers
nozzle guide vanes
filters and lpas can be blocked
bearing damage

44
Q

list the fundamental requirements of the control system

A
  • to supply fuel to the burners to start
  • supply fuel to burners at a controlled rate over the gas turbine operating range of rpm and temps
  • to shut off fuel supply to the burners under emergency and normal shut down conditions
  • prevent surge rich flame out during acceleration
  • prevent over temperature of components
  • prevent stall and rich flame-out during engine deceleration.
45
Q

state the function of HPSOC

A
  • to provide a positive fuel shut off to the burners for normal and emergency shut downs.
  • when closed, it recirculates the fuel back to the suction side of the fuel pump
46
Q

what combustion cans are used, on what turbines ?

A

can-annular - spey 1A/1C
annular - MT30/LM25000
radial - WR21

47
Q

what are the requirements of combustion chambers?

A
  • high combustion
  • good combustion stability
  • ease of ignition
  • clean exhaust
  • uniform outlet temp profile
  • wide operating range
48
Q

what is a can-annular?

A

a series of axially mounted combustion chambers which sit in the direct air flow paths from the delivery outlet from the high pressure computer

49
Q

what are the advantages of can-annular combustion chambers?

A
  • it is fairly easily developed
  • easy to maintain
  • good mixing is achieved in primary zone
  • low engine diameter
50
Q

what are the disadvantages of annular combustion chambers?

A
  • heavier than annular
  • possibility of difficulties in lighting adjacent chambers on start
51
Q

what is an annular combustion chamber?

A

it consists of a single flame tube, completely annular form, which is contained in an inner and outer casing

52
Q

what are the advantages of an annular combustion chamber?

A
  • low pressure loss
  • min overall weight
  • no problem of ‘light round’ when starting
53
Q

what are the disadvantages of an annular combustion chamber?

A
  • it is difficult to develop
  • mixing is less uniform in primary zone
  • it is difficult to ensure even temperature distribution outlet
54
Q

what are the advantages of radical combustion chambers?

A
  • easy to maintain
  • easy to monitor
  • excellent combustion efficiency
55
Q

what are the disadvantages of radical combustion chambers?

A
  • complex design
  • increased turbulence
  • overall efficiency loss
  • burners
56
Q

Describe the HP and LP turbine casing

A

the HP and LP casings are made from high strength titanium alloy material. This is where the stator blades of the turbine are contained.

57
Q

explain what nozzle guide vanes are

A

they direct high temp gas flow from the combustion system onto the HP turbine. They are kept cool relative to the gas flow by internal cooling ports and nozzles.

58
Q

what is the purpose of LP/HP turbines, how are they connected ?

A

the HP turbine is used to drive the HP compressor they are connected by the HP compressor drive shaft, this runs over the outside of the LP compressor shaft. This is vice verser for the LP compressor and LP turbine.

59
Q

describe the inter-turbine duct

A

it provides an interface between the GTCU turbines ad the power turbines fitted to the ship.

60
Q

describe the power turbine output shaft.

A

to provide mechanical movement for gearing or drive for an alternator transmitted by the power turbine output shaft

61
Q

explain the intake filtration system

A

a three stage air cleaning system,
first, water droplets are trapped and drained away.
secondly, it passes through knit mesh to remove debris
thirdly, and residual water is removed.

62
Q

what are splitter/silencers used for?

A

They are to ensure there is laminar flow and reduce noise.

63
Q

what dire detection systems to gas turbines have?

A

SMIC- 3 infra-red detectors
WR21- 8 heat/flame detectors
MT30 - 5 infra-red and 2 heat detectors

64
Q

how do suppressant systems work?

A

They deny oxygen, oxygen feeds fire. Water and mist offer cooling functions. The systems realise the suppressant, operate the inlet and outlet emergency cooling flap trips and vent flaps. this minimizes the oxygen to the fire.

65
Q

what type of suppressant is used for diesels and speys?

A

Halon 1211

66
Q

what is the most commonly used suppressant used in the fleet?

A

CO2

67
Q

what suppressant is used for MT30?

A

water mist and nitrogen

68
Q

how are suppressant systems operated?

A

first manually/auto shot is under the control of MEOOW1
second shot requires MEO’s permission

69
Q

where can the suppressant system be activated?

A

locally, adjacent to the module door with a key switch box
some ships have a second position that works in conjunction with the local box

70
Q

what is the purpose of cleaning a gas turbine?

A
  • removal of corrosive deposits from compressor blading
  • maintain engine performance and extend component life
71
Q

when should a gas turbine be cleaned?

A
  • limits set:
    - spey- 48 running hours
    - WR21- 150 running hours
    - MT30- 100 running hours
    - 1 month
    - by local orders
  • before inhibiting an engine
  • return an engine to a running condition from an inhibited condition
  • before a performance assessment or trail
  • when the GTCU is t be shut down for up to 20 days.
72
Q

what is a borescope?

A

a ridged optical inspection scope that allows inspections to access remote areas in straight lines.

73
Q

What is a flexible borescope?

A

these are more versatile compared to the ridged version, they are ideal for gas turbine inspections as they can access hard to reach areas.

151/23/005 (13 decks)

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