GT construction Flashcards
Definition of CODLOG?
Combination of diesel electric or gas, type 26
Definition of CODLAG?
Combination of diesel electric and gas, type 23
Description of CODLAG?
Each shaft has its own direct drive SM1A or SM1C and electric motor. They can be run either both or a mixed combination driving twin shafts in any configuration the command desires. Astern power is not available when the gas turbines are clutched into the transmission system
GT on each class of ship?
Spey - type 23
MT30 - carrier
WR21 - type 45
Creep is a combination of which stresses?
Heat and centrifugal
Definition of IEP?
Integrated electric propulsion - type 45
How can we minimise blade creep?
Hot starts
Over temperature running
Long periods at high power
Over load the engine
Description of IEP?
The system uses 2 x WR21 complex cycle gas turbine alternators and 2 x Wartsila diesel generators. These produce 4160 volts to power the advanced induction motors. Configuration is decided by command depending on fuel remaining and speed required
Maximum output of GTs?
Spey SM1A 12.75 MW
Spey SM1C 18.75 MW
WR21 21 MW
MT30 36 MW
Definition of blade creep?
The phenomena where a piece of material will lengthen over time
What are the benefits of a single crystal turbine blade?
High resistance to creep and fatigue
Very high strength
Excellent mechanical properties
Improved heat resistance
No crystalline grain boundaries
What are the requirements for a turbine blade?
Withstand high temperatures
Creep resistance
Low coefficient of expansion
Workable
Corrosion and erosion resistance
Thermal shock resistance
Low cost
Maintain high tensile strength at high temperatures
Oxidation resistant
Compact and light
How do we minimise the possibility of surge and stall?
Compressor air bleed valves
Multi-spool engines
Variable inlet guide vanes
What is the function of the LP accumulator?
Smooths out fluctuations in the fuel supply pressure
What is the function of the pressurising valve?
Meters fuel through the locating pin atomisers on start up and then to main burners
What are the functions of a gas turbine fuel control system?
Supply fuel to the burners for starting to running and over its full operating range
Acceleration and deceleration control
Shut off fuel supply under normal and emergency conditions
Definition of surge?
A complete breakdown of airflow leading to the reverse of flow. This will result in a violent expulsion of previously compressed air back through the intake
Contributing factors that lead to surge and stall?
Obstruction of air intake system
Rapid acceleration of the compressor
Compressor blade fouling
Malfunction of the compressor bleed valves
What are the functions of the HPSOC?
Recirculates fuel back to the section side of the pump when closed
Provides positive fuel shut off when engine shutting down
Provides a safe method of tripping the engine manually
Definition of stall?
A breakdown of laminar airflow over the compressor blades
Start operation of a Spey?
The air turbine start motor engages via a centrifugal clutch inside the accessory gearbox. Air is supplied from HP air ring main at 275 bar and reduced to 24 bar to the GT inlet valve, it is then reduced further by a dome reducer to a cranking pressure of 3.5 bar. The air start solenoid is energised during the start sequence allowing air to crank the engine up to speed. Once the engine is self sustaining air is shut off by the engine control system which deenergises the air start solenoid valve. The clutch now disengages allowing the air start motor to reduce to idle
What fire detection system does the WR21 use?
Two shot CO2
What fire detection system does the MT30 use?
Two shot HI FOG fine water mist and nitrogen system
Spey infrared detection system?
The system comprises of 3 infrared detectors which are designed to measure radiation heat levels within 2 narrow bands within the module. If any sensor senses a fire condition it will send a signal to the control unit within 25 milliseconds.
When the control unit is set to auto mode the first shot is released due to the operation of metron pyrotechnic cartridges
