15.5 COMBUSTION SECTION👌🏼 Flashcards
Simply explain combustion process
- raises temperature of air
- releases energy contained in air/fuel mixture
- which drives turbine and compressor
What are the 2 main components in a combustion chamber
- combustion chamber casing
- flame tube found inside casing
What is the fuel-air mixture electrically ignited by
- igniter plug
After the combustion has been started what occurs to the ignition
It is switched off
What 2 primary conditions are necessary for correct and safe combustion
- ratio of air and fuel must be correct
- air velocity must be slow to ensure complete combustion inside combustion chamber
What is the complete ratio for complete combustion
- 15 parts of air, 1 part of fuel
Airflow are split into 2 parts
- primary airflow
- secondary airflow
20% to 30% of the airflow from the compressor
- primary airflow
What are the 3 types of combustion chambers used on gas turbine engines
- can-type combustion chamber
- can-annular combustion chamber
- annular combustion chamber
Explain Can-type combustion chambers
- found on old gas turbine engines with centrifugal compressors
Advantage of can-type combustion chambers
- simple in design
- very good structural strength
Disadvantage of can-type combustion chambers
- heavy
- require a lot of space
-need complicating air supply ducts from compressor
Explain can-annular combustion chambers
- set of flame tubes installed around combuster section
- all flame tubes have common outer casing and inner casing
Advantages of can-annular combustion chamber
- smaller, lighter than multiple can-type combustion chamber
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Disadvantage of can-annular combustion chamber
- high aerodynamic losses
- ignition from one flame tube to another is difficult
Which combustion chamber is used on modern gas turbine engines
- annular combustion chamber
How many flame tubes does the annular combustion chamber have
1
In a annular combustion chamber what is the flame tube supported by
- inner and outer combustion chamber casing
What are the 3 major parts of a combustion chamber casing
- dome
- inner liner
- outer liner
Advantages of annular combustion chamber
- Smaller, lighter
- better efficiency
- combustion is smokeless
Disadvantage of annular combustion
- expensive to make
- removal is difficult and time consuming
What does the dome have openings for
- fuel nozzles
What are the fuel nozzles surrounded by
Swirl vanes
Annular combustion chamber construction
- combustion case
- flame tube
- external components (fitted on outer wall)
What is included in the combustion case assembly
- outer wall
- inner wall
- diffuser
Explain Flame tube cooling
Done by secondary airflow, forms a cooling film
What is a more sophisticated method of film cooling
- transpiration cooling (requires less air for cooling the flame tube liners)
How is secondary airflow entered in the flame tube
- radial holes in the liner
Explain rich mixture
-too much fuel for primary air in combustion chamber
- some fuel therefore cannot be burnt and released into the exhaust
When does lean mixture occurs
If insufficient fuel is available in the combustion chamber
What occurs to the remaining airflow from compressor (secondary airflow)
- bypasses and mixes with hot gas in the dilution zone
Where is the flame stabilised. PRIMARY ZONE OR SECONDARY ZONE
primary zone
