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Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. In other words, it is a substance that contains energy that can be released and then manipulated, mostly heat. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air. Other processes used to convert fuel into energy include various other exothermic chemical reactions and nuclear reactions, such as nuclear fission or nuclear fusion. Fuels are also used in the cells of organisms in a process known as cellular respiration, where organic molecules are oxidized to release usable energy. Hydrocarbons are by far the most common source of fuel used by humans, but many other substances, such as radioactive metals, are currently used as well.

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Nuclear

Nuclear fuel is any material that is consumed to derive nuclear energy. Technically speaking this definition includes all matter because any element will under the right conditions release nuclear energy, the only materials that are commonly referred to as nuclear fuels though are those that will produce energy without being placed under extreme duress.

Fission

The most common type of nuclear fuel used by humans is heavy fissile elements that can be made to undergo nuclear fission chain reactions in a nuclear fission reactor; nuclear fuel can refer to the material or to physical objects (for example fuel bundles composed of fuel rods) composed of the fuel material, perhaps mixed with structural, neutron moderating, or neutron reflecting materials. The most common fissile nuclear fuels are ²³⁵U and ²³⁹Pu, and the actions of mining, refining, purifying, using, and ultimately disposing of these elements together make up the nuclear fuel cycle, which is important for its relevance to nuclear power generation and nuclear weapons.

Fusion

Fuels that produce energy by the process of nuclear fusion are currently not utilized by man but are the main source of fuel for stars, the most powerful energy sources in nature. Fusion fuels tend to be light elements such as hydrogen which will combine easily.

In stars that undergo nuclear fusion, fuel consists of atomic nuclei that can release energy by the absorption of a proton or neutron. In most stars the fuel is provided by hydrogen, which can combine together to form helium through the proton-proton chain reaction or by the CNO cycle. When the hydrogen fuel is exhausted, nuclear fusion can continue with progressively heavier elements, although the net energy released is lower because of the smaller difference in nuclear binding energy. Once iron-56 or nickel-56 nuclei are produced, no further energy can be obtained by nuclear fusion as these have the highest nuclear binding energies.^[1]

World trade

World Bank reported that the USA was the top fuel importer in 2005 followed by the EU and Japan.^{[citation needed]}

Use over time

The first use of fuel was the combustion of wood or sticks by Homo erectus near 2 million years ago.^[2]^{[page needed]} Throughout the majority of human history fuels derived from plants or animal fat were the only ones available for human use. Charcoal, a wood derivative, has been used since at least 6,000 BCE for smelting metals. It was only supplanted by coke, derived from coal, as the forests started to become depleted around the 18th century. Charcoal briquettes are now commonly used as a fuel for barbecue cooking.^[3]

Coal was first used as a fuel around 1000 BCE in China. With the development of the steam engine in 1769, coal came into more common use as a power source. Coal was later used to drive ships and locomotives. By the 19th century, gas extracted from coal was being used for street lighting in London. In the 20th century, the primary use of coal is for the generation of electricity, providing 40% of the world's electrical power supply in 2005.^[4]

Humans have been consuming fossil fuels since the industrial revolution, because they were more readily available then the existing standards such as whale oils, and they were much cheaper to produce.

Currently the trend has been towards renewable fuels, such as biofuels like alcohols.

Footnotes

^ Fewell, M. P. (1995). "The atomic nuclide with the highest mean binding energy". American Journal of Physics. 63 (7): 653–658. doi:10.1119/1.17828.
^ Leakey, Richard (1994). Origin of Humankind. Basic Books. ISBN 0465031358.
^ Hall, Loretta (2007). "Charcoal Briquette". How Products Are Made. Retrieved 1 October 2007.
^ "History of Coal Use". World Coal Institute. Retrieved 10 August 2006.

References

Ratcliff, Brian; et al. (2000). Chemistry 1. Cambridge University press. ISBN 0-521-78778-5. {{cite book}}: Explicit use of et al. in: |author= (help)

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 '''Fuel''' is any material that stores [[energy]] that can later be extracted to perform [[mechanical work]] in a controlled manner. In other words, it is a substance that contains energy that can be released and then manipulated, mostly heat. Most fuels used by humans undergo [[combustion]], a [[redox reaction]] in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air. Other processes used to convert fuel into energy include various other [[exothermic reaction|exothermic chemical reactions]] and nuclear reactions, such as [[nuclear fission]] or [[nuclear fusion]]. Fuels are also used in the [[Cell (biology)|cells]] of [[organisms]] in a process known as [[cellular respiration]], where organic molecules are oxidized to release usable energy. [[Hydrocarbons]] are by far the most common source of fuel used by humans, but many other substances, such as radioactive metals, are currently used as well.
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-==Chemical==
-Chemical fuels are substances that release energy by reacting with substances around them, most notably by the process of [[oxidation]].
-===Biofuels===
-{{Main|Biofuel}}
-[[Biofuel]] can be broadly defined as solid, liquid, or gas fuel consisting of, or derived from [[biomass]]. Biomass can also be used directly for heating or power—known as ''biomass fuel''. Biofuel can be produced from any carbon source that can be replenished rapidly e.g. plants. Many different plants and plant-derived materials are used for biofuel manufacture.
-Perhaps the earliest fuel  employed by humans is wood. Evidence shows controlled fire was used up to 1.5 million years ago at [[Swartkrans]], [[South Africa]]. It is unknown which hominid species first used fire, as both ''[[Australopithecus]]'' and an early species of ''[[Homo (genus)|Homo]]'' were present at the sites.<ref>{{Cite news
- | last=Rincon | first=Paul | date=2004-03-22
- | title=Bones hint at first use of fire | publisher=BBC News
- | url=http://news.bbc.co.uk/1/hi/sci/tech/3557077.stm
- | accessdate=2007-09-11 }}</ref> As a fuel, wood has remained in use up until the present day, although it has been superseded for many purposes by other sources. Wood has an [[energy density]] of 10&ndash;20 [[Joule|MJ]]/[[Kilogram|kg]].<ref>{{Cite web
- | last=Elert | first=Glenn | year=2007
- | url=http://hypertextbook.com/physics/matter/energy-chemical/
- | title=Chemical Potential Energy
- | publisher=The Physics Hypertextbook
- | accessdate=2007-09-11 }}</ref>
-Recently biofuels have been developed for use in automotive transport (for example [[Bioethanol]] and [[Biodiesel]]), but there is widespread public debate about how carbon efficient these fuels are.
-===Fossil fuels===
-{{Main|Fossil fuel}}
-Fossil fuels are [[hydrocarbon]]s, primarily [[coal]] and [[petroleum]] ([[liquid petroleum]] or [[natural gas]]), formed from the [[fossil|fossilized remains]] of ancient plants and animals<ref>{{Cite web|author=Dr. Irene Novaczek|title=Canada's Fossil Fuel Dependency|url=http://www.elements.nb.ca/theme/fuels/irene/novaczek.htm|publisher=Elements|accessdate =2007-01-18}}</ref> by exposure to high heat and pressure in the absence of oxygen in the [[Earth]]'s [[Crust (geology)|crust]] over hundreds of millions of years.<ref>{{Cite web|title=Fossil fuel|url=http://oaspub.epa.gov/trs/trs_proc_qry.navigate_term?p_term_id=7068&p_term_cd=TERM|publisher=EPA|accessdate=2007-01-18 |archiveurl = http://web.archive.org/web/20070312054557/http://oaspub.epa.gov/trs/trs_proc_qry.navigate_term?p_term_id=7068&p_term_cd=TERM <!-- Bot retrieved archive --> |archivedate = 12 March 2007}}</ref> Commonly, the term fossil fuel also includes hydrocarbon-containing [[natural resource]]s that are not derived entirely from biological sources, such as [[tar sands]].  These latter sources are properly known as ''mineral fuels''.
 ==Nuclear==