G.T Theory Flashcards
What is the function of a Gas Turbine on board?
To turn heat energy into rotary motion to provide propulsion.
What is IEP?
Integrated electrical propulsion
What is CODLAG?
Combination of diesel electric and gas
What type of Gas Turbine is fitted to a T23 and how many?
Type 23’s use 2 spey turbines
What are the advantages of Gas Turbines?
- Allow the ship to get underway quickly
- Ease of operation and emphasis on remote control
- High Power to Weight Ratio
- Minimum ship-borne maintenance
- Lower Man-Power requirement
What is the purpose of the 3 stage air intake system?
To provide clean debris free and water free air to the system
What is step 1 of the 3 step air intake system?
SPRAY ELIMINATOR (encourages the air to let go of the water) Aluminium fins change direction of air, catching the spray and causing the majority to drop off and mainly dry air passes through.
What is step 2 of the 3 step air intake system?
KNITMESH FILTER (Aluminium frame supporting woven material) Removes particulate matter.
What is step 3 of the 3 step air intake system?
The same as step 1 to ensure all water particles are gone
What is the purpose of the Splitter/Silencer?
To smother out the air an disperse turbulence
What is the purpose of the stone guard?
To catch any large debris
What is the purpose of the transition duct?
To change the shape of the duct from square to circle
What is the purpose of the cascade bend?
Directs the air smoothly and turns at 90 degrees without causing any turbulence
What is the purpose of the engine intake flare?
Seals the engine intake from the rest of the module and houses the water wash ring used for maintenance
Describe the Module Ventilation system.
- The module ventilation system is a section of ducting around the turbine that cools it. The air is pulled through the ventilation system by Bernoulli’s principle acting on the exhaust side of the system creating a depression in the ducting on the exhaust side that draws air through the module to cool it.
- There are valves on the ventilation system the position of the valves must always be known.
What principle is used in module ventilation?
Bernoulli’s principle
What component provides drive into the gearbox?
Power turbine both high pressure and low pressure
Explain how the compressors are driven.
The exhaust gases from combustion expand rapidly which acts on the high and low pressure turbine blades. The force on the blades causes the respective shafts to spin and will turn through the whole turbine up to the respective compressor. The low pressure turbine shaft sits inside and the high pressure shaft and are allowed to spin separately.
Explain the air flow through a gas turbine system.
The air is drawn into the engine by a depression crated by the spinning compressor blades. The air is then worked on and compressed into a smaller volume preparing it for the high-pressure compression phase.
The air is then compressed further by the high-pressure compressor phase preparing the air for the combustion phase.
In the combustion phase 15% of the air is used as primary air in the initial combustion. Then 10% of the air is used in secondary combustion area which allows the flame to develop further. The remaining 75% of the air is used in the final stage of combustion when the flame has had time to fully develop and is allowed to expand greatly.
The air then passes through the high- and low-pressure turbines which are attached to the high- and low-pressure compressors. The rapidly expanding gases does work on the blades of the turbine causing it to turn and the shafts with them.
The air then uses its leftover energy to do work on the power turbine which is attached to the gearbox.
What oil is used to lubricate a gas turbine?
OX22
Why are Mag Chips fitted and how often are they checked?
Mag chips are fitted to attract ferrous material which indicates how worn the turbine is. They are checked once every 24 hours of running time
List safety devices fitted to a Gas Turbine.
- Fire detector – to detect fires
- Vibration accelerometer – to detect vibrations that may be a sign of engine wear
- Thermometers – for the lubricant and exhaust temperature on the power turbine
- Pressure gauges – so that lube oil pressure doesn’t drop
- Hand trip – stops the fuel from flowing to the engine when a problem is developing
- Tachometer – so stop over speeding of the engine, high- and low-pressure turbines
Describe Partial Over Speed.
This is where the load is suddenly reduced on the engine and causes it to overspeed. EG the propeller comes out of the water, there is reduce load on an electricity generator
Describe Power Turbine Over speed.
This is where the engine begins to overseed above 110% normal speed the high pressure shut off cock will be closed and shut off all fuel to the engine
What hazards are associated with Igniters?
High voltage – above 2000V
What hazards are associated with Gas Turbines?
- Heat
- High pitch noise
- Fire
- High voltage
Whose permission is needed to enter a gas turbine module?
MEO’s Permission (MEOOW)
What firefighting systems are fitted to a gas turbine module?
BCF or BTM suppression system which starves the fire of oxygen
What are the dangers of module fire suppression systems?
The chemicals used are toxic
High pressure systems which may be harmful
What running checks are carried out on a gas turbine?
- Pressures and temperatures
- Oil levels
- Noise and vibration
- leaks
What is a wet motor and when would it be performed?
- Wet motoring is where you use the started motor to turn over the engine and supply fuel to the engine but the ignitors have been removed
- It is done after maintenance of the fuel system has been done
What is a dry motor and when would it be performed?
- This is where you turn the engine over with the fuel and ignitors isolated so the engine cannot be run.
- This is done after a wet motor to remove any explosive gases from the system or when inhibiting the turbine
How often is water washing performed?
- 150 hours on WR21
- 100 hours on Spey
- Or when the engine performance deteriorates
What is gas turbine inhibiting and when would it be performed?
- This is where you coat all the internal surfaces with a coating that prevents corrosion
- The inhibitor also removes moisture from the turbine to prevent corrosion
- It is done when the turbine is going to be shut down for a long time
Diagrams to learn
Draw and Label a Gas Turbine Intake System.
Draw and Label a Module Ventilation System.
Draw and Label a Gas Turbine engine.
Draw and Label a Combustion Can.
Who is Gay?
Harley
