Fuel

A lump of coal.

Fuel is any material that is capable of releasing energy when its chemical or physical structure is altered. The release of energy takes place either by chemical means, such as by burning the fuel, or nuclear means, such as nuclear fission or nuclear fusion of the fuel. For a fuel to be useful, it should be possible to store its energy and to release it when needed. Moreover, one should be able to control the release such 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 enzyme-mediated chemical processes collectively called metabolism that converts energy from food or the Sun into a form that can be used to sustain life. Furthermore, people employ a variety of techniques to convert energy from one form into another, thereby producing energy that can be used for purposes that go well beyond the energy needs of the human body. The energy released from fuels can serve a wide range of purposes, such as heating, cooking, transportation, powering weapons, and generating electricity.

Extraction of energy from fuel

Chemical energy is stored in the chemical structure of a fuel. When the chemical structure of the fuel is altered, this chemical energy is converted into other forms of energy and released. The amount of energy stored in a fuel can be expressed in various ways. For example, "fuel value" is used to quantify the potential energy of a fuel.

The most efficient method for releasing energy from fossil fuels is by burning them in oxygen. In this process, known as combustion, the fuel reacts with oxygen and releases energy as heat. In the fields of chemistry and fire safety, anything that is capable of burning is called fuel. In the case of nuclear energy, certain materials (called fissile materials) are subjected to nuclear reaction.

Types of fuel

Theoretically any fuel can be used as a source of energy. Natural uses of fuel by organisms focus on conversion of food into energy. Other natural fuel use includes the nuclear fusion that occurs in stars. For use by humans it is economically practical to use only those fuels that contain large amounts of easily extractable energy. Different types of fuel are utilized, many of which can be obtained and prepared for consumption relatively inexpensively. Some types of fuels are focused on their ability to be transported easily from where they are produced to where they are used.

Fuels storing chemical energy

Food

Carbohydrates, fats, and proteins, derived from food, are the fuels for biological systems. For instance, glucose (a simple carbohydrate) combines with oxygen to produce water, carbon-dioxide, and energy. In the bodies of most animals, the released energy is used by the muscles.

Fossil fuel

Solid fossil fuels include coal and perhaps peat. All these types of fuel are combustible (they create fire and heat). Coal was burnt by steam trains to heat water into steam to move parts and provide power. Peat and wood are mainly used for domestic and industrial heating, though peat has been used for power generation, and wood-burning steam locomotives were common in times past.

Non-solid fossil fuels include alkanes such as petroleum and gas (both fuel types have myriad varieties including petrol (gasoline) and natural gas). The former is widely used in the internal combustion engine while both are used in power generation.

Other types of fuel

Hydrogen also features as an upcoming fuel in the proposed hydrogen economy. In this case the hydrogen fuel does not occur naturally in usable amounts, and it must be made using other fuels or energy sources. Hydrogen can react with oxygen in a fuel cell, producing water (H₂O) and electrical energy, which then can drive an electric motor to run a car (or a variety of other uses). In this reaction the chemical energy of the chemicals is converted into electrical energy via a redox reaction.

Biofuels such as alcohol fuel and biodiesel are made from various kinds of biomass. The biomass is plant matter from plants such as hemp, maize, sugarcane, etc, and byproducts from animals such as lard.

Nuclear fuel

In a nuclear reaction a radioactive fuel will undergo fission. This provides a useful source of energy without combustion. Also, in stars (and our sun), hydrogen (a gas) is the fuel for the nuclear fusion.

See also

• Energy density
• List of energy topics
• Alternative fuels
• Solid fuel
• Liquid fuels
• Gas fuel
• Alcohol fuel
• Biomass
• Biofuel
• Fuel oil
• Fuel poverty
• Fossil fuel
• Propellant
• Combustion
• Hydrocarbon
• Oxidation

Further reading

• Biofuel news and information, Southern Grease, retrieved August 17, 2006.
• DIRECTIVE 1999/94/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 13 December 1999, relating to the availability of consumer information on fuel economy and CO2 emissions in respect of the marketing of new passenger cars.

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