M15.5 Flashcards
What’s the purpose of the combustion chamber?
To produce a hot stream of gas for the turbines and jet nozzle
The combustion chamber must be…
Small and light
Have a cooling system
A high operating lifetime
Combustion must have a minimum amount of what?
Pressure loss
What components comprise the combustion section?
Casing
Flame tube
What does the combustion chamber casing do?
Take air pressure loads
Protects internal and external parts from hot combustion gasses
What does the combustion chamber housing do?
Give support to:
Flame tube
Fuel nozzles
Igniter plugs
What’s the purpose of the flame tube?
It controls and guides the flame
How is the flame tube protected from the extreme temps of combustion
By using secondary airflow
What will hot spots in the flame tube indicate?
Cooling airflow is not correct or the ceramic lining is damaged
What do fuel nozzles do in the combustion chamber?
Spray fuel into the centre of the airflow
How is the fuel and air mixture ignited?
Electrically with a igniter plug
After combustion has started what happens with ignition?
Turned off
What are the 2 primary conditions for safe combustion?
The ratio of fuel to air must be kept correct
The airs velocity must be slowed down enough to ensure combustion is completed
What percentage of air from the compressor is used for combustion?
20 - 30%
What percentage of air from the compressor is used for cooling?
70 - 80%
What is the required fuel to air ratio for combustion?
1:15
Fuel:air
What is the primary zone in the combustion chamber?
Where the flame stabilises
What is the secondary air used for in the combustion chamber?
Keep the flame away from the flame tube walls
What is the secondary zone also known as?
The dilution zone
What cooling methods are used on combustion liners?
Film cooling and transpiration cooling
What are the 3 types of combustion chambers?
Can- type
Can-annular
Annular
Where are can-type combustion chambers usually found?
Old GTE’s with centrifugal compressors
What are the advantages of a can-type combustion chamber?
Individually removable
Good structural strength
Simple design
What are the disadvantages of a can-type combustion chamber?
Ignition difficulties
Aerodynamic loss
Large and heavy
What are the advantages of a can-annular combination chamber?
Structural strength
Simple air supply
Dimension and weight
What are the disadvantages of a can-annular combustion chamber?
Ignition difficulties
Aerodynamic loss
What are the advantages of a annular combustion chamber?
Thermal load distribution
Flame propagation
Complete combustion
Efficient
Dimension and weight
What are the disadvantages of a annular combustion chamber?
Maintenance costs
Manufacturing costs
What type of combustion chamber is most common on modern a/c?
Annular type
The annular combustion chamber case carries structural loads between what?
Compressor case
Turbine case
What does the flame tube do?
Stabilises and controls the flame
Why is a flame tube only secured at one end?
To allow for thermal expansion
What is the purpose of the diffuser?
To reduce velocity of airflow coming from the compressor
The combustion case assembly is made up of what?
Outer wall
Inner wall
Diffuser
Why is the rear part of the inner wall on the combustion case removable?
To allow for access to the flame tube
What’s the purpose of the combustion case?
Part of the load carrying structure of the engine, protects engine parts from excess heat and provides mounts for the combustion chambers components
How many igniter plugs are there usually in the combustion case?
2
What’s fitted to the combustion case for Maintenance?
Borescope ports
What does the compressor rear frame house?
Bearings for high pressure rotor
What does the dome section of the flame tube do?
Connects inner and outer liners
Also houses swillers and swill vanes
What is the outer liner of the flame tube attached to?
Inner surface of the outer wall in a axial direction only by a recess
How is the inner liner support for the flame tube attached?
Bolted to inner wall of combustion case
How is the dome centred in the combustion case?
By mounting pins
How does primary airflow enter the flame tube?
Through swill vanes
How does secondary airflow enter the flame tube?
Passes the cowl and enters via liners
What are the 3 types of film cooling?
Machined cooling
Corrugated strip cooling
Splash cooling strip
What’s the advantage and disadvantage of transpiration cooling?
Requires less air but is Sophisticated
What is the inner surface of the flame tube covered with in the transpiration cooling method?
Detachable tiles called liner segments
How do liner segments allow for cooling?
By allowing air to flow between the segments and liner
