FUEL: A GENERAL SURVEY. Fuel is a term applied to materials used to produce heat by combustion in air. Man alone among living creatures has discovered ways of creating heat and power by the use of fuel. He has thereby improved his means of procuring food, has adapted himself to live and flourish on almost the entire area of the globe and has secured an immeasurably increased standard of comfort. Modern civilization could no longer exist if fuel supplies failed or became exhausted. Generally speaking, the bulk of natural fuels such as coal, wood, peat, oil and natural gas, are made up of compounds of carbon, hydrogen and oxygen in association with small proportions of nitrogen and sulphur, in addition to moisture and mineral ash; but in special circumstances such elements as phosphorus, and the more readily oxidizable metals such as magnesium and aluminium may be utilized as fuel.
When the constituent elements of a fuel burn, or unite with oxygen, heat is evolved ; and a fuel is completely burned only when the whole of its combustible components are oxidized to the highest possible degree. In the process a definite quantity of heat is produced which can be calculated approximately from the chemical composition of a fuel. Thus one pound of carbon in complete combustion to carbon dioxide produces 14,650 B.Th.U.; but only 4,410 B.Th.U. are produced in burning to the lower oxide, carbon monoxide, (CO). If however, this is subse quently burned to the balance of 10,240 B.Th.U. is liberated. Hydrogen burns to water vapour, 53,000 B.Th.U. being produced per lb. of hydrogen burned. The value of a fuel depends primarily upon its potential heat producing capacity per unit mass or "calorific value"; but the calorific intensity, or the temperature to which this amount of heat can raise the products of combustion without excess air, is also of importance. The impurities in a fuel affect both its calorific value and calorific intensity.