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From Wikipedia, the free encyclopedia

Firewood was one of the first fuels used by humans.[1]

A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy but has since also been applied to other sources of heat energy, such as nuclear energy (via nuclear fission and nuclear fusion).

The heat energy released by reactions of fuels can be converted into mechanical energy via a heat engine. Other times, the heat itself is valued for warmth, cooking, or industrial processes, as well as the illumination that accompanies combustion. 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 and related organic molecules are by far the most common source of fuel used by humans, but other substances, including radioactive metals, are also utilized.

Fuels are contrasted with other substances or devices storing potential energy, such as those that directly release electrical energy (such as batteries and capacitors) or mechanical energy (such as flywheels, springs, compressed air, or water in a reservoir).

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  • How Uranium Becomes Nuclear Fuel
  • Nuclear fuel and Energy | Understanding them Logically
  • Nuclear Reactor - Understanding how it works | Physics Elearnin
  • Nuclear Energy Explained: How does it work? 1/3


There's a lot of talk about nuclear technology, what with Iran and Fukushima and Green Energy being thrown around every day. But how do we even MAKE nuclear fuel? Howdy atomic children, Trace here for DNews… Despite the controversy they often raise, nuclear power plants are a huge source of energy. The Environmental Protection Agency says nuclear power accounts for about 20% of electricity production in the U.S. One of the reasons why is because it’s the most efficient means of extracting energy from a fuel source - about 8,000 times more efficient than coal or oil. According to the Nuclear Energy Institute, a fingertip-sized pellet of nuclear fuel contains as much energy as "17,000 cubic feet of natural gas, 1,780 pounds of coal, or 149 gallons of oil." Nuclear energy comes in two flavors, fusion or fission. Fusion is when two hydrogen atoms fuse -- this happens in stars; and fission is when large "heavy" atoms are broken apart. Both release energy, and both have pros and cons, but so far, we've only figured out nuclear fission; so when I say fuel, I'm talking about fuel for nuclear fission. Nuclear fuel is commonly referred to in the news, as "highly-enriched Uranium," but getting it to that point requires a LOT of effort. In 1941, Enrico Fermi, created the first controlled nuclear chain reaction using a small amount of uranium-235; and since then we've gotten much better at taking uranium and creating usable fuel from it. Uranium ore is most commonly mined in Canada, Australia, Niger, Kazakhstan, Russia, and Namibia; though it's not THAT rare -- it's 40 times more prevalent than silver in the Earth's crust. Once drilled or dug out of the ground, the uranium atoms are mixed in with the surrounding minerals -- so it has to be processed -- this involves some pretty intense chemistry. First, the ore is crushed, and then heated, to dry out carbon content (like clay) so it can be washed away. That slurry of ore and water is leached with sulfuric acid. These processes cause the uranium atoms to bond with the sulfur and oxygen forming uranium oxide liquid. To get it to that yellow powder we recognize from movies, the uranium is pulled out of solution using ammonia. This "yellow cake" uranium is put in barrels and shipped off to be purified even MORE. At this point the uranium isn't super radioactive, yet… If you stood one meter from a barrel full of U three O eight, you'd get no more radiation than from the cosmic rays hitting passengers on a commercial airplane. This uranium still needs to then be enriched before it can be used in power generation. That yellow cake uranium is 99.3 percent Uranium 238 and only 0.7 percent of uranium-235. To make the fuel, scientists need that U235 isotope -- this is where the now-famous nuclear centrifuges come in. If you watch the news, you know Iran is developing a nuclear program -- whether for energy or weaponry, I'll leave that to the experts; but they use centrifuges to enrich that uranium. As things go forward from here, it gets more dangerous, and more radioactive, so the engineering has to be VERY precise or people can die. First, they take the yellowcake uranium and they turn it into a gas by creating a reaction with fluorine -- the resulting uranium hexafluoride gas is even MORE pure than yellowcake and ready to go in a centrifuge. A centrifuge is a giant spinning container designed to use physics in order to separate materials. When you donate plasma, doctors draw blood and spin it in a centrifuge. During the spinning, centrifugal -- or center fleeing -- forces cause the heavier red blood cells to come out of solution and collect as far from the center as possible; lighter plasma stays nearer the inside! In the case of uranium, it's the same. The heavier U238 isotopes get thrown outward, allowing the lighter U235 to stay closer to the middle. It's not as good as blood, because there's only a 1 percent difference in mass; so it has to be spun again and again in centrifuge after centrifuge THOUSANDS of times. Eventually, the gas in the middle of the centrifuge gets more and more concentrated -- or ENRICHED! The gas is MORE U235! Once the fuel is 5 percent U235 (95 percent U238) it's suitable for some nuclear reactors. Others require as high as 20 percent. But that's nowhere NEAR enriched enough for nuclear weapons, which can require as high at 90 percent U235. Once it's reached the desired enrichment for the type of power plant you want to run, the enriched uranium hexafluoride has to be turned into a solid by adding calcium. The calcium and fluoride react, creating a salt, leaving behind only uranium oxide, which is heated to 1400C and extruded into tiny ceramic pellets. Those uranium pellets are, in turn, put into rods, and then hundreds or thousands of those rods can be placed in various configurations inside a nuclear power plant. When we talk about nuclear energy programs in other countries, world leaders get nervous. And now that you know the process, can you see why? The massive centrifuges used make nuclear fuel, are the same ones that could create weapons grade uranium. It requires a lot of technical and chemical knowledge to GET to that point, but in the end it's dig uranium out, clean it up, and then spin it! Nuclear energy continues to be a controversial choice for powering the future, and it's connection to nuclear weapons is clear, but how do you feel about nuclear energy?


Wood as fuel for combustion

The first known use of fuel was the combustion of firewood by Homo erectus nearly two million years ago.[citation needed] Throughout most of human history only fuels derived from plants or animal fat were used by humans. Charcoal, a wood derivative, has been used since at least 6,000 BCE for melting metals. It was only supplanted by coke, derived from coal, as European forests started to become depleted around the 18th century. Charcoal briquettes are now commonly used as a fuel for barbecue cooking.[citation needed]

Crude oil was distilled by Persian chemists, with clear descriptions given in Arabic handbooks such as those of Muhammad ibn Zakarīya Rāzi.[2] He described the process of distilling crude oil/petroleum into kerosene, as well as other hydrocarbon compounds, in his Kitab al-Asrar (Book of Secrets). Kerosene was also produced during the same period from oil shale and bitumen by heating the rock to extract the oil, which was then distilled. Rāzi also gave the first description of a kerosene lamp using crude mineral oil, referring to it as the "naffatah".[3]

The streets of Baghdad were paved with tar, derived from petroleum that became accessible from natural fields in the region. In the 9th century, oil fields were exploited in the area around modern Baku, Azerbaijan. These fields were described by the Arab geographer Abu al-Hasan 'Alī al-Mas'ūdī in the 10th century, and by Marco Polo in the 13th century, who described the output of those wells as hundreds of shiploads.[4]

With the development of the steam engine in the United Kingdom in 1769, coal came into more common use, the combustion of which releases chemical energy that can be used to turn water into steam.[5] 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 and 21st centuries, the primary use of coal is to generate electricity, providing 40% of the world's electrical power supply in 2005.[6]

Fossil fuels were rapidly adopted during the Industrial Revolution, because they were more concentrated and flexible than traditional energy sources, such as water power. They have become a pivotal part of our contemporary society, with most countries in the world burning fossil fuels in order to produce power, but are falling out of favor due to the global warming and related effects that are caused by burning them.[7]

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


Chemical fuels are substances that release energy by reacting with substances around them, most notably by the process of combustion.

Chemical fuels are divided in two ways. First, by their physical properties, as a solid, liquid or gas. Secondly, on the basis of their occurrence: primary (natural fuel) and secondary (artificial fuel). Thus, a general classification of chemical fuels is:

General types of chemical fuels
Primary (natural) Secondary (artificial)
Solid fuels wood, coal, peat, dung, etc. coke, charcoal
Liquid fuels petroleum diesel, gasoline, kerosene, LPG, coal tar, naphtha, ethanol
Gaseous fuels natural gas hydrogen, propane, methane, coal gas, water gas, blast furnace gas, coke oven gas, CNG

Solid fuel

Coal is a solid fuel

Solid fuel refers to various types of solid material that are used as fuel to produce energy and provide heating, usually released through combustion. Solid fuels include wood, charcoal, peat, coal, hexamine fuel tablets, and pellets made from wood (see wood pellets), corn, wheat, rye and other grains. Solid-fuel rocket technology also uses solid fuel (see solid propellants). Solid fuels have been used by humanity for many years to create fire. Coal was the fuel source which enabled the industrial revolution, from firing furnaces, to running steam engines. Wood was also extensively used to run steam locomotives. Both peat and coal are still used in electricity generation today. The use of some solid fuels (e.g. coal) is restricted or prohibited in some urban areas, due to unsafe levels of toxic emissions. The use of other solid fuels as wood is decreasing as heating technology and the availability of good quality fuel improves. In some areas, smokeless coal is often the only solid fuel used. In Ireland, peat briquettes are used as smokeless fuel. They are also used to start a coal fire.

Liquid fuels

A filling station

Liquid fuels are combustible or energy-generating molecules that can be harnessed to create mechanical energy, usually producing kinetic energy. They must also take the shape of their container; the fumes of liquid fuels are flammable, not the fluids.

Most liquid fuels in widespread use are derived from the fossilized remains of dead plants and animals by exposure to heat and pressure inside the Earth's crust. However, there are several types, such as hydrogen fuel (for automotive uses), ethanol, jet fuel and bio-diesel, which are all categorized as liquid fuels. Emulsified fuels of oil in water, such as orimulsion, have been developed as a way to make heavy oil fractions usable as liquid fuels. Many liquid fuels play a primary role in transportation and the economy.

Some common properties of liquid fuels are that they are easy to transport and can be handled easily. They are also relatively easy to use for all engineering applications and in home use. Fuels like kerosene are rationed in some countries, for example in government-subsidized shops in India for home use.

Conventional diesel is similar to gasoline in that it is a mixture of aliphatic hydrocarbons extracted from petroleum. Kerosene is used in kerosene lamps and as a fuel for cooking, heating, and small engines. Natural gas, composed chiefly of methane, can only exist as a liquid at very low temperatures (regardless of pressure), which limits its direct use as a liquid fuel in most applications. LP gas is a mixture of propane and butane, both of which are easily compressible gases under standard atmospheric conditions. It offers many of the advantages of compressed natural gas (CNG) but is denser than air, does not burn as cleanly, and is much more easily compressed. Commonly used for cooking and space heating, LP gas and compressed propane are seeing increased use in motorized vehicles. Propane is the third most commonly used motor fuel globally.

Fuel gas

A 20-pound (9.1 kg) propane cylinder

Fuel gas is any one of a number of fuels that are gaseous under ordinary conditions. Many fuel gases are composed of hydrocarbons (such as methane or propane), hydrogen, carbon monoxide, or mixtures thereof. Such gases are sources of potential heat energy or light energy that can be readily transmitted and distributed through pipes from the point of origin directly to the place of consumption. Fuel gas is contrasted with liquid fuels and from solid fuels, though some fuel gases are liquefied for storage or transport. While their gaseous nature can be advantageous, avoiding the difficulty of transporting solid fuel and the dangers of spillage inherent in liquid fuels, it can also be dangerous. It is possible for a fuel gas to be undetected and collect in certain areas, leading to the risk of a gas explosion. For this reason, odorizers are added to most fuel gases so that they may be detected by a distinct smell. The most common type of fuel gas in current use is natural gas.


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 were present at the sites.[8] 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 10–20 MJ/kg.[9]

Recently biofuels have been developed for use in automotive transport (for example bioethanol and biodiesel), but there is widespread public debate about how carbon neutral these fuels are.[citation needed]

Fossil fuels

Extraction of petroleum

Fossil fuels are hydrocarbons, primarily coal and petroleum (liquid petroleum or natural gas), formed from the fossilized remains of ancient plants and animals[10] by exposure to high heat and pressure in the absence of oxygen in the Earth's crust over hundreds of millions of years.[11] Commonly, the term fossil fuel also includes hydrocarbon-containing natural resources that are not derived entirely from biological sources, such as tar sands. These latter sources are properly known as mineral fuels.

Fossil fuels contain high percentages of carbon and include coal, petroleum, and natural gas.[12] They range from volatile materials with low carbon:hydrogen ratios like methane, to liquid petroleum to nonvolatile materials composed of almost pure carbon, like anthracite coal. Methane can be found in hydrocarbon fields, alone, associated with oil, or in the form of methane clathrates. Fossil fuels formed from the fossilized remains of dead plants[10] by exposure to heat and pressure in the Earth's crust over millions of years.[13] This biogenic theory was first introduced by German scholar Georg Agricola in 1556 and later by Mikhail Lomonosov in the 18th century.

It was estimated by the Energy Information Administration that in 2007 primary sources of energy consisted of petroleum 36.0%, coal 27.4%, natural gas 23.0%, amounting to an 86.4% share for fossil fuels in primary energy consumption in the world.[14] Non-fossil sources in 2006 included hydroelectric 6.3%, nuclear 8.5%, and others (geothermal, solar, tidal, wind, wood, waste) amounting to 0.9%.[15] World energy consumption was growing about 2.3% per year.

Fossil fuels are non-renewable resources because they take millions of years to form, and reserves are being depleted much faster than new ones are being made. So we must conserve these fuels and use them judiciously. The production and use of fossil fuels raise environmental concerns. A global movement toward the generation of renewable energy is therefore under way to help meet increased energy needs. The burning of fossil fuels produces around 21.3 billion tonnes (21.3 gigatonnes) of carbon dioxide (CO2) per year, but it is estimated that natural processes can only absorb about half of that amount, so there is a net increase of 10.65 billion tonnes of atmospheric carbon dioxide per year (one tonne of atmospheric carbon is equivalent to 4412 (this is the ratio of the molecular/atomic weights) or 3.7 tonnes of CO2.[16] Carbon dioxide is one of the greenhouse gases that enhances radiative forcing and contributes to global warming, causing the average surface temperature of the Earth to rise in response, which the vast majority of climate scientists agree will cause major adverse effects. Fuels are a source of energy.


The amount of energy from different types of fuel depends on the stoichiometric ratio, the chemically correct air and fuel ratio to ensure complete combustion of fuel, and its specific energy, the energy per unit mass.

Energy capacities of common types of fuel
Fuel type Specific energy
Air–fuel ratio
Energy @ λ=1
Diesel 48 14.5 : 1 3.310
Ethanol 26.4 9 : 1 2.933
Gasoline 46.4 14.7 : 1 3.156
Hydrogen 142 34.3 : 1 4.140
Kerosene 46 15.6 : 1 2.949
LPG 46.4 17.2 : 1 2.698
Methanol 19.7 6.47 : 1 3.045
Methane 55.5 17.2 : 1 3.219
Nitromethane 11.63 1.7 : 1 6.841

MJ ≈ 0.28 kWh ≈ 0.37 HPh.

(The fuel-air ratio (FAR) is the reciprocal of the air-fuel ratio (AFR).)

λ is the air-fuel equivalence ratio, and λ=1 means that it is assumed that the fuel and the oxidising agent (oxygen in air) are present in exactly the correct proportions so that they are both fully consumed in the reaction.


Two CANDU ("CANada Deuterium Uranium") fuel bundles, each about 50 cm long and 10 cm in diameter

Nuclear fuel is any material that is consumed to derive nuclear energy. In theory, a wide variety of substances could be a nuclear fuel, as they can be made to release nuclear energy under the right conditions. However, the materials commonly referred to as nuclear fuels are those that will produce energy without being placed under extreme duress. Nuclear fuel can be "burned" by nuclear fission (splitting nuclei apart) or fusion (combining nuclei together) to derive nuclear energy. "Nuclear fuel" can refer to the fuel itself, or to physical objects (for example bundles composed of fuel rods) composed of the fuel material, mixed with structural, neutron moderating, or neutron-reflecting materials.

Nuclear fuel has the highest energy density of all practical fuel sources.


Nuclear fuel pellets are used to release nuclear energy.

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.

When some of these fuels are struck by neutrons, they are in turn capable of emitting neutrons when they break apart. This makes possible a self-sustaining chain reaction that releases energy at a controlled rate in a nuclear reactor, or at a very rapid uncontrolled rate in a nuclear weapon.

The most common fissile nuclear fuels are uranium-235 (235U) and plutonium-239 (239Pu). The actions of mining, refining, purifying, using, and ultimately disposing of nuclear fuel together make up the nuclear fuel cycle. Not all types of nuclear fuels create energy from nuclear fission. Plutonium-238 and some other elements are used to produce small amounts of nuclear energy by radioactive decay in radioisotope thermoelectric generators and other types of atomic batteries.


In contrast to fission, some light nuclides such as tritium (3H) can be used as fuel for nuclear fusion. This involves two or more nuclei combining into larger nuclei. Fuels that produce energy by this method are currently not utilized by humans, but they are the main source of fuel for stars. Fusion fuels are light elements such as hydrogen whose nucleii will combine easily. Energy is required to start fusion by raising the temperature so high that nuclei can collide together with enough energy that they stick together before repelling due to electric charge. This process is called fusion and it can give out energy.

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 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.[17] Any nucleii heavier than 56Fe and 56Ni would thus absorb energy instead of giving it off when fused. Therefore, fusion stops and the star dies. In attempts by humans, fusion is only carried out with hydrogen (2H (deuterium) or 3H (tritium)) to form helium-4 as this reaction gives out the most net energy. Electric confinement (ITER), inertial confinement (heating by laser) and heating by strong electric currents are the popular methods.

Liquid fuels for transportation

Most transportation fuels are liquids, because vehicles usually require high energy density. This occurs naturally in liquids and solids. High energy density can also be provided by an internal combustion engine. These engines require clean-burning fuels. The fuels that are easiest to burn cleanly are typically liquids and gases. Thus, liquids meet the requirements of being both energy-dense and clean-burning. In addition, liquids (and gases) can be pumped, which means handling is easily mechanized, and thus less laborious. As there is a general movement towards a low carbon economy, the use of liquid fuels such as hydrocarbons is coming under scrutiny.

See also


  1. ^ Schobert, Harold (17 January 2013). Chemistry of Fossil Fuels and Biofuels. Cambridge University Press. ISBN 978-0521114004. OCLC 1113751780.
  2. ^ Forbes, Robert James (1958). Studies in Early Petroleum History. Brill Publishers. p. 149.
  3. ^ Bilkadi, Zayn. "The Oil Weapons". Saudi Aramco World. 46 (1): 20–27.
  4. ^ Salim Al-Hassani (2008). "1000 Years of Missing Industrial History". In Emilia Calvo Labarta; Mercè Comes Maymo; Roser Puig Aguilar; Mònica Rius Pinies (eds.). A shared legacy: Islamic science East and West. Edicions Universitat Barcelona. pp. 57–82 [63]. ISBN 978-84-475-3285-8.
  5. ^  One or more of the preceding sentences incorporates text from a publication now in the public domainChisholm, Hugh, ed. (1911). "Fuel". Encyclopædia Britannica. Vol. 11 (11th ed.). Cambridge University Press. pp. 274–286.
  6. ^ "History of Coal Use". World Coal Institute. Archived from the original on 7 October 2006. Retrieved 10 August 2006.
  7. ^ IPCC AR5 WG1 Summary for Policymakers 2013, p. 4: Warming of the climate system is unequivocal, and since the 1950s many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased; IPCC SR15 Ch1 2018, p. 54: Abundant empirical evidence of the unprecedented rate and global scale of impact of human influence on the Earth System (Steffen et al., 2016; Waters et al., 2016) has led many scientists to call for an acknowledgment that the Earth has entered a new geological epoch: the Anthropocene.
  8. ^ Rincon, Paul (22 March 2004). "Bones hint at first use of fire". BBC News. Retrieved 11 September 2007.
  9. ^ Elert, Glenn (2007). "Chemical Potential Energy". The Physics Hypertextbook. Retrieved 11 September 2007.
  10. ^ a b Dr. Irene Novaczek. "Canada's Fossil Fuel Dependency". Elements. Retrieved 18 January 2007.
  11. ^ "Fossil fuel". EPA. Archived from the original on 12 March 2007. Retrieved 18 January 2007.
  12. ^ "Fossil fuel". Archived from the original on 10 May 2012.
  13. ^ "Fossil fuel". EPA. Archived from the original on 12 March 2007. Retrieved 18 January 2007.
  14. ^ "U.S. EIA International Energy Statistics". Archived from the original on 27 May 2013. Retrieved 12 January 2010.
  15. ^ "International Energy Annual 2006". Archived from the original on 5 February 2009. Retrieved 8 February 2009.
  16. ^ "US Department of Energy on greenhouse gases". Retrieved 9 September 2007.
  17. ^ Fewell, M. P. (1995). "The atomic nuclide with the highest mean binding energy". American Journal of Physics. 63 (7): 653–658. Bibcode:1995AmJPh..63..653F. doi:10.1119/1.17828.

Works cited


Further reading

This page was last edited on 9 February 2024, at 19:31
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