Module 15.5 Combustion Section Flashcards
What does the combustion section do to the temperature of air?
It raises it.
Where is a large part of the energy released required?
At the turbine or turbine stages to drive the compressor.
What does the combustion process release?
Energy contained in the air/fuel mixture.
Combustion should happen with…
Minimum pressure loss in the combustion chamber.
What are the two main components of the combustion chamber?
The combustion chamber casing.
The flame tube found inside the casing.
The casing can be split into what?
Inner and an outer casing.
What is the combustion chamber casing?
The outer shield of the combustion section.
What does the combustion chamber casing do?
Takes the air pressure loads and protects the internal and external engine parts from the hot combustion gases.
What does the flame tube do?
Controls and guides the flame.
Describe the combustion chamber process?
Compressed air enters the combustion chamber. Fuel nozzles/injectors spray the fuel into the centre of this airflow.
The fuel vaporises and mixes with the airflow and the mix is electrically ignited by an igniter plug.
When is the ignition switched off?
After the combustion has been started.
For complete combustion of a kerosene-air mixture, what air:fuel ratio is required?
15 parts of air for 1 part of fuel.
Airflow coming from the compressor is split into what two parts?
The primary airflow
The secondary airflow
What is the primary air flow used for?
For the combustion process.
What percentage of the airflow from the compressor is primary?
20% to 30%
What is done with the secondary airflow?
It bypasses the primary combustion zone and mixes with the hot gas in the dilution zone
List the three combustion chamber types?
Can-type
Can-annular
Annular
What engines can can-type combustion changes be found on?
Old gas turbine engines with centrifugal compressors.
What is a can-type combustion chamber?
One with multiple-can combustion chambers that are installed around the engine combustion section.
What is a can-annular combustion chamber?
A set of flame tubes installed around the combustor section. All the flame tubes have a common outer casing and inner casing.
What type of combustion chamber is most commonly used on modern jet gas turbine engines?
Annular combustion chamber
How many flame tubes does an annular combustion chamber have?
One
What are the three major parts of the annular combustion chamber?
Dome
Inner liner
Outer liner
What are the fuel nozzles surrounded by?
Swirl vanes
Why is the annular combustion chamber called the reverse flow combustion chamber?
Because of the airflow direction in the flame tube.
How many igniter plugs are installed in the combustor case of an engine?
Two
A typical annular combustion chamber consist of what three things?
Combustion case
Flame tube
External components
What does the combustion case consist of?
Outer wall
Inner wall
A diffuser
What does the dome section of the flame tube do?
Connects the inner liner with the outer liner.
What does the dome section of the flame tube house?
The swirlers with swirl vanes.
What does the secondary airflow do?
Forms a cooling film on the inner surface of the liners, which helps to protect the liner from the intense heat (film cooling).
The secondary airflow enters the flame tube through what?
Holes in the liner.
What is a rich mixture?
A mixture where there is too much fuel for the primary air in the combustion chamber.
In this condition, some of the fuel cannot be burned and is released into the exhaust.
What is a lean mixture?
Where there is insufficient fuel available in the combustion chamber. This causes the flame to go out?
What does a lean mixture cause in terms of emissions?
Less pollution
What does a rich mixture cause in terms of emissions?
A build-up of carbon monoxide.
What compressor type would a can-type compressor be used with?
Centrifugal compressor
Where in the combustion case are the igniters found?
Behind the nozzles on the lower half.
What kind of combustion chamber is used to decrease emissions?
Dual dome combustion chambers.
