15.5 - Combustion Section Flashcards
Name the hot section components of a gas turbine engine.
Combustors, Turbine and Exhaust
Where is a reverse flow combustion chamber used?
Annular Reverse-flow combustion chambers are commonly used in turbo-prop and some business jet engines.
What is the function of a primary airflow and what airflow is used for cooling?
Primary air is the portion of the air which mixes with the fuel for combustion processes.
Tertiary air is the air which is used as a cooling agent. It is metered towards the outlet end of the combustion chamber to cool the hot gases as they leave the chamber to pass to the turbine. This air takes no part in combustion.
(Note: Could be secondary air possible as it is metered into the combustion chamber to lower the temperature of the primary air so as it doesnt damage the turbine inlet)
Explain an Annular combustion chamber
The annular combustion chamber consists of an inner and outer liner assembly with the area between these liners forming an ‘’annular’’ tunnel in which the fuel and air is burnt. Holes are drilled into the annular chamber for various functions such as igniter plug receptacles, cooling and fuel nozzles. This assembly takes air in the front and discharges it at the rear.
What happens the velocity of the air as it enters the combustion chamber?
The velocity of the air entering the combustion chamber is slowed down by the nose or ‘’snout’’ shape of the combustion chamber which acts as a diffuser
Name the section between the compressor and combustion section
Diffuser
Explain the purpose of the 3 types of airflow in a Combustion Chamber?
Primary Air is that portion of the air, which mixes with the fuel for combustion purposes
Secondary Air is that part of the air, which is metered into the combustion chamber to complete combustion
Tertiary Air is that air that acts as a cooling agent. It is metered towards the outlet end of the combustion chamber to cool the hot gases as they leave the chamber to pass the turbine. This air takes no part in combustion
The ‘‘Stoichiometric Ratio’’ refers to what?
The ideal proportion of air and jet fuels is 15:1
This is called the stoichiometric ratio.
What is the purpose of a snout on a combustion chamber?
The nose or ‘‘snout’’ of the combustion chamber is so shaped, that is also acts as a diffuser to slow the airflow down and create an area of still lower velocity air within the combustor.
Describe mutliple combustion chambers?
(igniters?)
Older design - multiple combustion cans which are interconnected
(multiple can combustors)
Igniters are normally installed in only two of the cans to provide the spark for starting the engine. The cans are connected by small flame propagation tubes, also called crossover tubes 2
Describe Can-annular combustion chambers?
A number of chambers are placed inside a common outer air casing to form a combination of the annular and the multiple chamber design.
more efficienct and reduced length advantages over mutliple chamber design
cans can be removed individually easily for service
What is the purpose of interconnectors?
Found in Mutliple Chamber/Cannular design
'’Combustion takes place in these cans and spreads to the other cans via interconnector tubes.
The interconnectors also allow the pressures in the various chambers to balance out’’
Describe an annular combustion chamber?
Area between the inner and outer liners forms an annular tunnel in which the fuel and air is burnt.
Holes drilled in for cooling purposes, igniter plug receptacles and fuel nozzle attachment
commonly used today as most efficient design in terms of thermal efficiency
Disadvantage - not easy to access
Describe a Reverse flow combustion chamber ( What is its advantage)?
Flow enters from the rear - opposite direction to the general flow of the engine
revered 180 degrees onto turbine
Main advantage = compact
used of turbo-prop and some business jet engines
