A fuel may be defined as a substance, which on burning with oxygen produces a large amount of heat. A fuel is mainly composed of carbon and hydrogen. The energy produced by burning of fuel in the form of heat is known as chemical energy.
Fuels may be classified as follows:
Natural fuels occur in nature and they are also called primary fuels, whereas artificial fuels are prepared by further processing of primary fuels and they are also called secondary fuels.
A detailed classification ...