Fuels release heat on burning: Heat of combustion is total amount of heat released when a fuel is burnt when there is complete combustion with oxygen. It is a chemical reaction in which hydrocarbon is burnt and it produces carbon dioxide, heat and water. The heat of combustion can be expressed as follows: energy/mole of fuel, energy/volume of the fuel.
The amount of heat produced by a fuel is measured by calorimeter. Different amount of carbon dioxide is produced by different fuels; it is in relation with the energy produced on burning. Here is a list of some fuels and the amount of CO2 released in per million British thermal units (Btu).
The carbon content in a fuel decides the amount of CO2 that will be produced from that fuel. This content is decided by carbon and hydrogen content in the fuel. When carbon and hydrogen combines with oxygen during combustion then heat is released. Methane which is a natural gas has higher energy content as compared to other fuels and has lower CO2 release level
When coal is burnt it produces carbon dioxide and pollutants are released into air. There are many fuels that contains small amount of sulphur compounds and small amount of sulphur dioxide is released. If enough amount of oxygen is present and the fuel is incompletely burnt then it is called incomplete combustion and carbon monoxide is produces which is very poisonous.
Incomplete combustion produces many particulate matters which are very injurious for health and also makes the building dirty.
At high temperatures nitrogen and oxygen combine to form nitrogen oxides. These are very harmful for health and when it combines with rain it caused acid rain.