Combustion is the act or process of burning. For combustion to occur, fuel, oxygen (air), and heat must be present together. Per definition combustion is the chemical reaction of a particular substance with oxygen. The combustion process is started by heating the fuel above its ignition temperature in the presence of oxygen. Under the influence of heat, the chemical bonds of the fuel are split. If complete combustion takes place, the elements carbon (C), hydrogen (H) and sulphur (S) react with the oxygen content of the air to form carbon dioxide CO2, water vapour H2O and sulphur dioxide SO2 and, to a lesser degree, sulphur trioxide SO3. If not enough oxygen is present or the fuel / air mixture is insufficient then the burning gases are partially cooled below the ignition temperature (too much air or cold burner walls), and the combustion process stays incomplete. The flue gases then still contain burnable components, mainly carbon monoxide CO, carbon C (soot) and various hydrocarbons CxHy. Since these components are, along with NOx, pollutants which harm our environment, measures have to be taken to prevent the formation of them. To ensure complete combustion, it is essential to provide a certain amount of excess air. Combustion optimization saves money! The quality of a combustion system is determined by a maximum percentage of complete combustion, along with a minimum of excess air (commonly 5 to 20% above the necessary level for ideal combustion )


AIR
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FUEL
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FLUE GAS
Oxygen (O2)
Carbon (C)
Carbon dioxide (CO2)
Hydrogen (H2)
Carbon monoxide (CO)
Nitrogen (N2)
Sulphur (S)
Sulphur dioxide (SO2)
Oxygen (O2)
excess O2
Water vapour
Nitrogen (N2)
Nitrogen oxides (NOx )
Water (H2O)
Nitrogen (N2)
Water vapour
Soot