Fuel

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For other uses, see Fuel (disambiguation).

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Fuel is any material that is capable of releasing energy when its chemical or physical structure is altered. Fuel releases its energy either through chemical means, such as burning, or nuclear means, such as nuclear fission or nuclear fusion. An important property of a useful fuel is that its energy can be stored to be released only when needed, and that the release is controlled in such a way that the energy can be harnessed to produce work.

All carbon-based life forms—from microorganisms to animals and humans—depend on and use fuels as their source of energy. Their cells engage in an enzyme-mediated chemical process called metabolism that converts energy from food or solar power into a form that can be used to sustain life. ^[1] Additionally, humans employ a variety of techniques to convert one form of energy into another, producing usable energy for purposes that go far beyond the energy needs of a human body. The application of energy released from fuels ranges from heat to cooking and from powering weapons to combustion and generation of electricity.

1 Extraction of energy from fuel and oxygen
2 See also
3 Notes
4 Further reading

[edit] Extraction of energy from fuel and oxygen

Fuels do not store energy in their chemical structure, but rather the energy is stored in the fuel/oxygen system. It is during respiration of food or combustion of fuel that the fuel/food joins with the reactive gas oxygen. Oxygen has weakly bonded molecules, which can be broken apart with relatively small energy input. When the resultant atoms bond with the atoms from the fuel (mostly hydrogen and oxygen) more energy is released than was needed to break up the original molecules. This chemical energy is released and available to drive our technology or life itself. There are many ways to express and compare the amounts of energy stored in fuel/oxygen systems. For example, a fuel value is used to quantify fuel's potential energy. Because oxygen is freely available for respiration and combustion we carelessly think that the energy is stored in the fuel, and talk of food and fuels 'containing' energy. This is so commonplace that most scientists have come to believe that food and fuels 'contain' energy. We need to think of combustion and (aerobic) respiration as constructive processes that build up oxides. One of these, carbon dioxide, is released by the burning of fossil fuels and is being released into the atmosphere causing climate change. We need to keep separate accounts of the matter and energy when considering fuels: the matter in fuels joins with oxygen forming oxides; the energy, stored as chemical energy as the fuel and oxygen are kept apart, is released, usually as heat, but in respiration, as chemical energy again as the respiration process drives metabolism.

The method of conversion used for a particular type of fuel depends on the molecular structure of the fuel. For example, the most efficient method for obtaining energy from fossil fuels is by burning them in oxygen. In this process known as combustion, fuel reacts with oxygen and releases energy as heat. In chemistry and the field of fire safety, anything that is capable of burning is called fuel. Humans have also been able to extract energy from an atom by subjecting fissile materials to nuclear reaction.