The process of burning fuels. Traditionally biomass was used as fuel, but now fossil fuels are the major source of energy for human activities. Combustion is essentially an oxidation process that yields heat and light. Most fuels are carbon and hydrogen which use oxygen in the air as an oxidant. More exotic fuels are used in some combustion processes, particularly in rockets where metals such as aluminum or beryllium or hydrazine (a nitrogen containing compound) are well known as effective fuels. As rockets operate beyond the atmosphere they carry their own oxidants, which may also be quite exotic.

Combustion involves a mixture of fuel and air, which is thermodynamically unstable. The fuel is then converted to stable products, usually water and carbon dioxide, with the release of a large amount of energy as heat. At normal temperatures fuels such as coal and oil are quite stable and have...