15.5 Combustion Section Flashcards
What is the primary function of the combustion process in an aircraft engine?
To raise the temperature of the air passing through the engine and release energy from the air/fuel mixture
This energy is primarily needed at the turbine stages to drive the compressor.
List the requirements for safe and efficient operation of a combustion chamber in an aircraft engine.
- Safe ignition of the fuel-air mixture
- Stable combustion in all operating conditions
- Complete combustion with no unburnt fuel
- Equal temperature distribution at the combustion chamber outlet
- Minimum pressure loss in the combustion chamber
- Small and light design
- Dependable cooling system
- High operating lifetime
What are the two main components of a combustion chamber?
- Combustion chamber casing
- Flame tube
What is the role of the flame tube in the combustion chamber?
To control and guide the flame
The flame tube is composed of many segments with holes and slots.
What is the purpose of the primary airflow in the combustion process?
To be used for the combustion process, approximately 20% to 30% of the airflow from the compressor.
True or False: The secondary airflow in the combustion chamber is primarily used for combustion.
False
The secondary airflow is mainly used for cooling.
What is the required air-to-fuel ratio for complete combustion of a kerosene-air mixture?
15 parts of air for 1 part of fuel.
Fill in the blank: The airflow from the compressor has a velocity of approximately _______ m/s.
150
What are the three types of combustion chambers used in gas turbine engines?
- Can-type combustion chamber
- Can-annular combustion chamber
- Annular combustion chamber
What are the advantages of can-type combustion chambers?
- Simple design
- Good structural strength
- Can be removed and replaced individually
What is a disadvantage of can-annular combustion chambers?
High aerodynamic losses and difficult ignition from one flame tube to another.
Describe the major components of an annular combustion chamber.
- Dome
- Inner liner
- Outer liner
What is the purpose of the cooling air holes in the flame tube?
To cool down the combustion gases.
How does transpiration cooling work in the flame tube?
Secondary airflow enters through radial holes in the liner and flows through gaps to create a cooling film on the inner surface.
What is a rich air-fuel mixture?
A mixture with too much fuel for the primary air, leading to unburnt fuel in the exhaust.
What is the effect of low combustion temperatures on emissions?
Decreases nitrogen oxide emissions but increases carbon monoxide emissions.
What is a dual dome combustion chamber?
A chamber with two sets of combustion areas, allowing better control of air-fuel ratios and reduced emissions.
What is the purpose of the diffuser in the combustion chamber?
To decrease the velocity of airflow to stabilize flame and ensure combustion completion.
