Combustor Flashcards
What is the purpose of the combustor?
Increase thermal energy of the air-fuel mix flowing through the engine
How is the thermal energy increased in the combustor?
An electric spark ignites the fuel, causing a flame that must be selfsustained after the ignition
Explain the “can type”-combustor
- A number of separate chamber spaced around the compressor-turbine-shaft
- Each has their own jet fuel feed
- Airflow is separated into streams that each supply their own chamber
Explain the “cannular type”-combustor
Individual flame tubes are uniformly spaced around a annular casing
Explaing the “annular type”-combustor
- Single flame tube
- Completely annular
- Contained in an inner and outer casing
Gives some advantages and drawbacks for the “can type”-combustor
+ Development can be carried out on a single can using a fraction of the overall airflow and fuel
- Undesirable in aircraft due to weight, volume and frontal area
Gives some advantages and drawbacks for the “cannular type”-combustor
+ Combines ease of overhaul and testing of multiple systems
+ Reverse flow arrangement allows reduction in shaft length
+ Easy access for maintenance
- Connection to first turbine stage favours uniform temperature distribution at the turbine inlet
Gives some advantages and drawbacks for the “annular type”-combustor
+ Maximum use of space for a given diameter
+ Good relightning capability in case of engine flameout
- Difficult to have even fuel/air distribution
- Structurally weak, prone to buckling
- Development work must be carried out on whole chamber
- Uneven outlet temperature distribution
Explaing the principles of a non-premixed combustor
- Fuel is injected directly into the combustion chamber
- Fuel is injected in a swirling flow (achieve stable operation)
- Air enters the chamber through larger holes or cooling liner
- Common in aero-engines
Advantages: Good flame stability
Disadvantages: High NOx-emissions
Explain the principles of a premixed combustor
- Introduces as much air as possible through the burner (can be as much as 90%)
Advantages: Flame temp can be kept low, even thermal loads, low NOx-emissions
Explain cooling in combustors: principles, serial and parallell
The flame tube
- Gets energy by convection of hot gases and flame raditation
- Loses energy by convection to cooler airflow over outer casing and radiation to outer casing
Serial cooling: Common in premixed systems, air is used for cooling flame tube and then the same air is used for combustion
Parallell cooling: Common in non-premixed systems, air is divided from the compressor into cooling air and combustion air
Name some types of industrial gas turbine fuels
Name an ideal type of fuel
Diesel
Ethane
Biogas
Syngas
Rapeseed oil
Hydrogen
Ideal: Natural gas. Expensive but does not require atomization or vaporization as liquid fuels do
Name some aviation fuels and their properties
Jet A and Jet A1. Similar to diesel fuel. They have higher flash points, are less flammable and safer to transport and handle
Why must aviation be free from water contamination?
Low temperatures on high altitudes can cause precipitation of the dissolved water in the fuel. This drops to the bottom of the tank and freezes. Can cause blocked fuel supply.
Name some primary emissions (exhaust gases/pollutants)
Exhaust gas: CO2, H2O, O2, N2
Pollutant: NOx, CO, SOx, UHC
