15.5 Flashcards
Important requirement of combustion
It must be complete , no unburnt fuel leaves the combustion chamber
What important about combustion chamber outlet
Equal temperature distribution, especially at first turbine stage
3 requirements of combustion chamber
Small and light
Dependable cooling system
High operating lifetime
Why do we need a small and light chamber
To save weight
What’s the problem with replacing engine components in the combustion chamber
It’s very time consuming
2 parts of combustion chamber
Casing (can be inner and outer)
Flame tube
What does the casing do
Outer shield that takes air pressure loads and protects external engine parts
What does the housing support
Flame tube and other combustion chamber components (fuel nozzle and igniter plugs)
What does the flame tube do
Control and guides the flame
Made of segments and had lots of holes and slots
Conditions for correct and safe combustion
Correct fuel to air ratio
Air velocity slow enough to make sure combustion is completed inside the chamber
Kerosene air fuel mix ratio
15 parts air 1 part fuel
15:1
What air is used for combustion process
Primary
What % of air is primary from the compressor
20-30%
What part of the chamber does the flame stabilise
Primary zone
3 types of combustion chambers
Can-type
Can-annular
Annular
Where are can-type combustion chambers used
Old gas turbines with centrifugal compressors
Advantage of can-type
Simple and goodstructural strength
Removed and replaced individually
Disadvantage of can-type
Difficult ignition from one chamber to another
Advantage on can-annular
Smaller and lighter than a similar multiple can-type combustion chamber
Disadvantage of can-annular
Poor ignition from flame tubes and aerodynamic loses are high
What’s the most used combustion chamber construction
Annular
How does annular combustion chamber work
One annular flame tubes supported by inner and outer chamber casing
3 parts of annular construction
Dome
Inner liner
Outer liner
Why is annular a reverse flow combustion chamber
Airflow direction in the flame tube
Disadvantage of annular
Expensive to make and removal is very difficult and time consuming
Annular construction
Combustion case
Flame tube
External components fitted to the outer wall
Annular combustion case construction
Outer wall
Inner wall
Diffuser
Why is the inner wall removable and what does it attach
Removable so the flame tube can be installed
Attaches the nozzle guide vanes HPT and support flame tube
What are stator vanes also known as
Exit guide vanes
How many igniter plugs are installed
2
Flame tube components
Outer and inner liner
Outer and inner cowl
Dome
How does primary air enter the flame tube
Swirl vanes
How does secondary air enter the flame tube
Passed the cowl and enters through liners
What is film cooling
Secondary airflow forms a film to protect the liner from intense heat of combustion gases
What is transpiration cooling
Inner surface of flame tubes liner covered with detachable tiles
How does secondary air get into the liner
Radial holes
What does excessive fuel cause a build up of
Carbon monoxide
What does an increase in combustion temperature have an effect on
Decrease carbon monoxide and hydrocarbon emissions
Increase nitrogen oxide emissions and vice versa
What’s a benefit of dual dome combustion chambers
Shorter then standard chambers
What’s the advantage of shorter combustion chambers
Reduces time the exhaust gas is in the hot area and build up of nitrogen oxides
What’s a rich mix
Too much fuel for primary air in the combustion chamber
What’s a lean mix
Not enough fuel for the combustion chamber
What does the dome do
Connect the inner and outer liner
What is the outer liner and dome made in
One piece
How is the dome centred
By mounting pins
Where is the inner liner bolted to
Inner flange of HPT nozzle guide vanes
