Gas turbines- prime movers Flashcards
What is the definition of a gas turbine?
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.
What can energy output of a turbine be used for?
1) jet thrust as a reaction force to drive a body forward
2) Power turbine to turn a rotary shaft and transfer this energy
what are inlet guide vanes?
The first stator stage which guides the inlet air at an angle to the direction of flow toward the first stage
what are compressor stages?
Each pairing of one stator and one rotor compressor stage. Most axial compressors have multiple stages.
What are Injector/burners?
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.
what is a high energy igniter?
High voltage spark ignition device for causing the initial fuel/air mixture to ignite on engine start up
What are nozzle guide vanes?
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.
what is a turbine?
rotating disk of turbine blades, utilising the high energy gas emitted from the nozzle guide vanes.
What are the advantages of a gas turbine?
- 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
Disadvantages of gas turbines?
- may need CPP/gear box
- requires high standard fuel cleaning systems
- good air quality required
- poor fuel consumption
- increased number of prime movers
what is the configuration of a type 23, what gas turbines are used?
CODLAG
SM1A or SM1C
what is the configuration of a type 45, what gas turbines are used?
IEP
WR 21
what is the configuration of a QE class, what gas turbines are used?
IEP
MT30
what is the configuration of a type 26, what gas turbines are used?
CODLOG
MT30
What are the requirements of a compressor design?
- 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
Describe the central drive shaft
The central drive shaft connects the LP turbine to the LP compressor as one assembly
What passes through the feed tubes?
They pass lubricating oil and cooling and sealing air.
What is bolted to the drive shaft?
Bolted to the shaft are three diaphragm assemblies to which five rotor disc assemblies are bolted.
What is the purpose of inter stage spacer rings?
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.
What blade attachments can you get on a gas turbine?
- 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.
What happens in each rotor stage?
increased velocity and pressure
what happens in each stator stage?
decreases velocity but increases pressure.
what happens overall inside the axial compressor?
velocity remains constant
pressure, temp increase
volume decreases
what is the formula for combined gas law?
p1v1/t1=p2v2/t2
what is the purpose of a scavenger system?
oil collects and is drawn away from the bearings by the scavenger pumps
what is fitted in the scavenger line?
in-line magnetic chip detectors
filters
what is fitted in the return line?
seawater cooled oil
duplex filters
conical air oil separator
where is the high speed gear box positioned?
beneath the engine, in the region between HP and LP compressor called intermediate casing.
give a brief description of a highspeed gear box
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.