What is the purpose of the combustion section?
It produces a hot stream of gas for the turbines and jet nozzle by continuous combustion of a fuel-air mixture
What are the requirements for safe and efficient combustion?
- safe ignition
- stable combustion
- complete combustion
- equal temperature distribution
- combustion with minimum pressure loss
What properties must the combustion chamber have?
- lightweight and small
- have a cooling system
- high operating lifetime
What is the purpose of the combustion chamber casing?
It protects the internal and external engine parts from the hot gases and also takes air pressure loads
When are the igniters turned off?
After the engine has been started and is self-sustaining
What are the two primary conditions for safe combustion?
- the ratio of air to fuel must be correct
- the air velocity must be slow enough for complete combustion
What happens to the airflow from the compressor?
It splits into the primary airflow and secondary airflow
What is the primary airflow from the compressor?
It is approximately 20% to 30% of the air which is used for the combustion process
What ratio of kerosene to air mixture is required for complete combustion?
15 parts air to 1 part fuel
What is the secondary airflow from the compressor?
- bypasses the primary combustion zone and mixes with hot gas in dilution zone
- used for cooling (as temperature 2000°C in centre of flame)
How does the secondary airflow bypass the primary combustion zone?
It enters the dilution zone of the flame tube via dilution air holes
What are the three types of combustion chamber?
- the can-type combustion chamber
- the can-annular combustion chamber
- the annular combustion chamber
Where would you find a single-chamber combustion chamber?
Small gas turbine engines such as APU
What is the purpose of the interconnector tubes in a multiple-can type combustion chamber?
They connect all chambers together and ensure equal pressure throughout and also ignition from the two chambers with the igniter plugs
What are the advantages of a can-type combustion chambers?
- simple design
- very good structural strength
- can be installed and removed individually
What are the disadvantages of a can-type combustion chambers?
- difficult ignition from one chamber to another
- heavy and require a lot of space
- complicated air supply ducts
What type of combustion chamber has flame tubes surrounding it?
The “can-annular” combustion chamber
What are the advantages of can-annular combustion chambers?
- simple air supply ducts
- good structural strength
- smaller and lighter than the simple multiple can-type
What are the disadvantages of using the can-annular combustion chambers?
- Aerodynamic losses are high
- ignition from one flame tube to another is difficult
What type of combustion chamber is the most commonly used one on modern gas tubing engines?
The annular combustion chamber
What is important about the annular combustion chamber’s outer casings?
They are part of the load carrying engine structure
What are annular combustion chambers also known as because of their special design?
Reverse flow combustion chamber
What are the advantages of annular combustion chambers?
- better thermal load distribution
- smaller and lighter
- larger combustion area = better efficiency and smokeless combustion
- flame is easier to spread over the flame tube
What are the disadvantages of annular combustion chambers?
- expensive to make
- removal is difficult and time consuming
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15.1 Fundamentals47
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15.3 Inlet49
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15.11 Fuel Systems48
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15.7 Exhausts & Thrust Reversers39
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15.12 Air Systems30
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15.13 Starting and Ignition Systems43
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15.14 Engine Indication Systems52
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15.18 APU99
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15:20 Fire Protection Systems66
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15:10 Basic Lubrication Systems39
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15.19 Powerplant Installation65
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15:09 Lubricants And Fuels55
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15.17 Turbo-shaft Engines11
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15.16 Turbo-Prop Engines23
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15.05 Combustion Section40
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15.06 Turbine Section55
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15.04 Compressors91
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15.21 Engine Monitoring and Ground Operation55
