Theory2 Flashcards
Advantages of gas turbines
An ability to underway quickly Ease of operation with the emphasis on remote control High power / weight ratio Minimum shipboard maintenance Low manpower required
What does IEP stand for
Integrated Electric Propulsion
What does CODLAG stand for
Combination of Diesel Electric and Gas
Gas turbine system components
Air intake 3 stage filter system Silencer Stone guard Transition duct Cascade bend Module ventilation Engine intake flare Gas turbine Power tribute Exhaust trunking
What is the purpose of the air intake filters
to remove water, dirt and debris form the air entering the intake trunking
Describe the first stage of filter system
1st stage: Air enters the filter system (called spray eliminators), where the air changes direction due to the baffle plates. The change of direction causes the water held in suspension to drop out. The water will now fall to the water trough. Dry air will continue through to the next stag.
Describe the second stage of the filter system
After the first stage spray eliminator the air passes through a knitmesh filter where any particulate matter is removed.
Describe the final stage in the filter system
A final stage of water separation ensures any residual water in also removed. Air to the engine is now completely water and particulate free
What is the purpose of a Splitter-Silencer
The filtered air passes through the intake trunking to the splitter/silencer.
The filtered air passes over vanes which split up and smooth out the ait flow removing any turbulence, air noise and buffeting.
Turbulence in the air flow massively effects the engines performance.
What is the purpose of the stone guard
The stone guard prevents large particles of debris from entering the gas turbine when maintenance is being carried out.
What is the four strike cycle for a gas turbine
Induction Compression Combustion Power Exhaust
Describe the induction phase in the gas turbine
Induction:
Air from intake system is drawn into the engine
Describe the Low Pressure compression phase
The compression state is divided into Low pressure and High pressure.
Air is drawn in from the intake at atmospheric pressure and enters the LP compressor.
The low Pressure section then increases the pressure of the air using a series pf rotating blades, that have divergent passages within them, that continually moves and compresses the air as it passes the vanes.
Describe the High Pressure compression stroke in the four strike cycle
Air leaves the LP Compressor passes through to a second set of rotating blades known as the High Pressure compressor, which increases the pressure even more, using the same principle of squeezing the air through divergent passages.
By slowing down the air divergent passage we will raise its pressure.
Describe the Combustion phase during the four section phase
The Gas Turbines combustion system is designed to release the max amount of chemical energy from our fuel in the smallest possible space, with the min of losses.
The combustion chambers of the GT mixes the compressed air with atomised fuel, For initial starting of the engine an ignitor housed within the combustion chamber provides a High Tension spark to ignite the air/fuel mixture
What are the three parts of combustion
Primary air: 15% of the air providing air for initial combustion
Secondary air: Makes up 10% of the total air flow. it is used to ensure complete combustion of the fuel and provides a layer of air between the fuel and the flame tube.
Tertiary air: accounts for the remaining 75% of the air flow.
What drives the HP and LP turbines
The hot expanded gasses leaving the combustion chamber
What is the purpose of the HP and LP turbines
To drive the HP and LP compressors respectively. meaning the gas turbine uses hot gasses to produce its own compressed air
What causes the power turbine to move
The remaining energy within the hot gases after it passes through the HP and LP Turbines, will pass through the power turbines causing it to turn
What’s the lubrication used for the Gas turbine
OX22
What’s the name of the gas turbine used on a type 23
Spey
Why are safety devices and trips fitted on a Gas Turbine
They are fitted to protect the engines and personnel from damage or injury should the engine fail to perform
What does the hand trip device do
Activates the HP fuel shut off cock
Command approval must be met before operating this trip
What does the fire detector do
They are fitted to provide indication of high temp/ fire inside the engine module
What are the two types of Power Turbines Entry Temperature Devices and explain them
Governor- Monitors the PTET and controls the amount of fuel to the engine if these set levels exceeded
Trip- This will stop the engine should the engine exhaust gas temperature exceed the safety parameters
What’s the purpose of the Partial Overspeed Safety Device
If the engine over speeds, this device will reduce the quantity of fuel supplied to reduce the engines speed
what’s the purpose of the LP and HP compressor governor
Monitors and controls the speed of the compressor
Purpose of vibration monitors
this safety device monitors the vibration levels of the engine. It activates and alarm if the levels exceed the safety parameters. Vibration often gives an early indication there is a fault developing within the engine
What do igniters do
They produce powerful sparks using voltages in excess of 2000 Volts
What are to be worn when entering an engine that is running
Ear defenders
Running Checks are carried hourly on a running engine and include amongst others…
Pressure and temperatures
Oil levels
Noise and Vibration
Leaks
Reasons why a dry motor routine is generally carried out….
To purge the combustion chamber of unburnt fuel and explosive gases after an aborted start or fail start.
To turn over the compressors to enable the washing and inhibiting routines to be carried out
After wet motoring
Water washing is carried out on the following occasions…
WR21 150 running hours.
Spey- 100 hours or 2 months.
When engine performance deteriorates.
What are the warning for PX24
Warning: PX24 IS HIGHLY FLAMMABLE NO SMOKING ENSURE THE ENGINE ROOM VENT FAN ARE RUNNING ENSURE THE ENGINE IGNITERS ARE ISOLATED
What PPE is to be worn when working with PX24 or CCF
thick rubber gloves up to the elbow
plastic aprint over overalls
Face protection
Whats the purpose of a gearbox
Transmit power form the prime mover to the shaft
Allow for variations in speed and power
Allow for changes between ahead and astern thrust
uses of gears
The gear box reduces the speed of the gas turbine to a more manageable speed
Change speed
Change direction
Types of gear teeth Forms/Drives used in the RN…
STRAIGHT SPUR
HELICAL GEAR
DOUBLE HELICAL GEAR
WORM WHEEL
Straight spur disadvantages and advantages…
STRAIGHT SPUR- Known as straight cut or spur.
Easy to manufacture, not good for high speed, generally used for low speed. Wont find these on ships on gearbox.
Helical gear disadvantages and advantages…..
HELICAL GEAR- Cut at an angle and slightly curved ( helix ), which allows a gradual smoother meshing of gears, which eliminates the noise. Due to them being at an angle it doesn’t allow a straight push which causes axial thrust.
Double helical gear disadvantages and advantages…
DOUBLE HELICAL GEAR- Negate the problem of axial thrust which is a problem in the Helical gears. Each gear wheel have opposing angled teeth in a “V” that produces thrust in both directions.
Worm wheel advantages and disadvantages….
WORM WHEEL- Resembles a screw with a continues tooth forming parallel helical teeth. The worm is always the driving gear and can achieve a higher gear ratio than Spurs gears in a comparable space. WILL SELF LOCK IF DRIVE IS TAKEN AWAY
Whats the max ratio for a single pair of gears
15:1
The ancillary components on the gearbox
Shaft Brake
Thrust Block
Turning Gear
Bulkhead glands do what…
seal to keep compartments watertight lubricated with grease
purpose of the plummer block
Support shaft btwn bulkheads
Lubricated oil
“Dynamic” lubrication
There are two types of propellers…
Fixed blade
controllable pitch propeller
Shaft break checks on application of brake
Ensure no fire risks
All Brake Pads are APPLIED
The shaft is stationary
Shaft break checks on removal of brake
All pads are clear/released
No fire danger exists
The shaft is turning
