Gas Turbines Flashcards
What are gas turbines used for?
They are used to convert heat energy into rotary motion for ships propulsion.
What does CODLAG stand for?
Combination of diesel, electric and gas.
What does IEP stand for?
Integrated electric propulsion.
Name 5 advantages of using gas turbines.
Ability to get underway quickly Ease of operation with the emphasis on remote control High power/weight ratio Minimum shipboard maintenance Low manpower requirement
What brand turbines are found on type 23’s and where?
2 X Spey gas turbines, one port, one starboard
What is the purpose of a splitter/silencer
Smooth out turbulent air flow and quieten it down.
What is the purpose of a stone guard?
One inch wire mesh which catches debris, mainly that which has been accidentally dropped.
What is the purpose of a transition duct?
Changes air flow from square to circular without creating turbulence.
What is the purpose of a cascade bend?
Metal plates inside the bend in the tube which direct air round the 90 degree bend without causing turbulence.
What is the purpose of the engine intake flare?
Guides air into compressors and seals engine intake from the module that its in. Also houses the water wash ring.
What is the purpose of the three stage filter?
Removes water, dirt and debris from the air entering the intake trunking.
What is the purpose of the water wash ring?
Glass reinforced plastic flare that has a series of holes that allow water and CCF (compressor cleaning fluid) to be sprayed into engine intake for cleaning and maintenance.
Explain the three stages of the air intake filter.
1 - Spray eliminator. Baffle plates cause air to change direction and therefore change speed. This causes water droplets to fall out of the air as they are heavier than it.
2 - Knitmesh filter. This removes particles from the air. It can be removed and replaced.
3 - Water separation. Water removed from air drains down into troughs. Manometric leg maintains water level and allows excess to drain. Water trough ensures water seal across bottom of filters, preventing unfiltered air from bypassing filter system.
What is the purpose of the module vent flaps?
To isolate the module in the event of an emergency e.g. a fire. When the engine is running the module vent flaps are to be open to allow airflow to cool the module and remove any exhaust fumes.
Explain module ventilation.
A depression of air is formed by the rushing exhaust gasses (Bernoulli’s theorem). Air is drawn into the module at the other end because of the depression formed. This air circulates around the module keeping it cool. Vent flaps are fitted to seal the module in case of fire. When the engine is running the flaps must be open.
What are the five ‘strokes’ of a gas turbine?
Induction Compression Combustion Power Exhaust
Explain the induction stage.
Air from the intake system is drawn into the engine.
Explain the compression stage.
Air enters from the intake at atmospheric pressure. The low pressure section increases the pressure of the air using rotating blades. Air then goes to high pressure section which increases pressure even more using faster spinning rotating blades.
Explain the combustion stage.
Combustion chambers mix compressed air with atomised fuel. For initial start up, an igniter provides a high tension spark to ignite air/fuel.
Not all the air is used initially for combustion. The majority of the air from the compressors cools the combustion can.
Primary Air – 15% - helps to atomise the fuel and provides air for the initial combustion.
Secondary Air – 10% - is used to ensure complete combustion of the fuel and provides a layer of air between the fuel and the flame tube preventing flame impingement.
Tertiary air – 75% - after cooling the combustion can the tertiary air is heated by the combustion process causing it rise in pressure and becomes the “working fluid” to drive the turbines.
