Turbine Engine Combustion Section Flashcards
Describe the purpose of the combustion chamber
Has the job of providing suitable and stable conditions for combustion of the air and fuel.
Needs to be done with minimum loss of pressure and provide the most amount of heat, and do so within a small a space as possible.
Describe the uses of primary flow through a combustion chamber
airflow used to provide the necessary high temperature for rapid combustion. Only around 20% of the air leaving the diffuser of the compressor flows axially through the front of the combustion chamber.
Around 12% of the 20 flows over the swirl vanes and mixes with atomised fuel, remaining % flows through a perforated flare and stabilises the flame by creating a turbulent, slow moving zone of air in the primary zone of the combustion chamber.
Describe use and reasoning of secondary air.
air Introduced through holes in the flame tube in the secondary zone to complete the combustion. Approx 10% of the non-bypass airflow.
Air must be introduced into the combustion chamber in stages, if not the flame would be too cold and reduce efficiency. Also it would otherwise be moving faster then the flame burns which has the risk of extinguishing the flame.
Describe use of tertiary airflow.
Used for cooling and is approx 70% of the non-bypass airflow.
Remaining air is mixed with products of combustion to cool them down to the temp required at inlet to the turbine.
Sufficient turbulence must be promoted so hot and cold streams are mixed to get desired temp.
Describe multiple can combustion chamber.
Consist of a number of individual chambers (cans) placed around the engine.
consist of an air casing and a flame tube with air flowing between the two, to equalise the pressures in each individual can, and so that each can doesn’t require its own ignition system inter connectors are used.
Advantages of multiple can (3)
- Simple in design
- individual cans can be replaced or removed for maintenance
- strong structural strength
Describe a can-annular combustion chamber.
Evolution of can type. A number of flame tubes are fitted inside a common air casing.
This arrangement combines the ease of overhaul and testing of the multiple system with the compactness of the annular system.
Advantages of can-annular system (2)
- Straightforward construction
- individual cans can be replaced or accessed easily.
Describe the annular combustion chamber.
Uses a single flame tube. Is very efficient as for the same power output, the annular chamber length is 75% of a can-annular chamber of similar diameter.
Meaning the flame tube wall area is considerably less, and the amount of cooling air required to prevent burning of the flame tube wall is reduced by 15%.
Combustion efficiency is increased and air pollution reduced.
Advantages of annular combustion systems (4)
- Even gas distribution
- less surface area than can-annular and multiple can type chambers, therefore less pressure loss, so more efficient
- lighter then other combustion systems
- easy to manufacture
Describe reverse flow annular
- to shorten length of combustion chamber some turbines feature one of these.
- used extensively in turbo shaft engines.
Advantages of reverse flow annular
Shorter overall length, thus lighter, and able to be used in helis.
Purpose of swirl chambers
Used to atomise fuel, has holes or slots imparted swirl to the fuel by converting its pressure energy to kinetic energy
Describe use of air shroud
Helps in dismissing excess heat from the engine.
What are interconnectors
Tubes that connect each can to the adjacent can.
