A fuel is a material that is burned in order to get heat and light, and also to generate power. The process of burning, or combustion, is a chemical reaction. A material combines with oxygen from the air and gives off energy. The energy is given off in the form of heat and light.
The energy in fuels came originally from the sun. the plants from which fuels come trap energy from the sun’s rays and use it to build their tissues. Burning wood and charcoal releases energy that has been stored up by plants in this way. When we burn coal or oil, we use energy stored up by plants that lived millions of years ago.
There are many different types of fuels, and actually anything that burns can be called a fuel. But most common fuels are wood, coal, natural gas, and petrol.
Fuels can also be classified as solid, liquid, or gaseous. Or they can be classified according to their origin-natural, chemical, or metal based.
Wood was one of the first fuels used by man, and was his most important one for many centuries. It was the easiest to get, and the cheapest. But during the sixteenth century, wood started to become scarce in Europe, and coal began to replace it.
Coal contains a high percentage of carbon. Carbon is the most important part of most fuels. Fuels with a high percentage of carbon burn evenly and with a hot flame. Hard coal, or anthracite, has a higher percentage of carbon than other types of coal, and so makes less smoke and ash.
The most important liquid fuels come from petroleum. They include kerosene, petrol, and heating oils.