gas, fuel, gaseous substance that burns in air and releases enough heat to be useful as a fuel, while also remaining sufficiently stable at ordinary temperatures to permit long-term storage without deterioration or undue hazard. It is advantageous if a fuel gas is readily transportable through pipes and is easily liquefied. Practically all fuel gases meet the first condition, and some meet the second as well. Natural gas, which occurs alone and in conjunction with petroleum deposits, is an excellent fuel gas in wide commercial use. Liquefied petroleum gas is a manufactured mixture of flammable gases that is easily stored in its liquefied condition. Oil gas is a type of gas made by applying heat to various petroleum distillates. Its principal use is as a supplement to natural gas during periods of heavy demand. Coal gas may be any of a variety of gases produced by heating coal in the absence of air and driving off the volatile constituents. It is not as high in fuel value as other gases and often contains tars, light oils, ammonia, and hydrogen sulfide. Producer gas is made by forcing a mixture of air and steam through burning coal or coke. Water gas, or blue gas, which burns with a bright blue flame, is made by passing steam over glowing coke.
fuel, material that can be burned or otherwise consumed to produce heat. The common fuels used in industry, transportation, and the home are burned in air. The carbon and hydrogen in fuel rapidly combine with oxygen in the air in an exothermal reaction—one that liberates heat. Most of the fuels used by industrialized nations are in the form of incompletely oxidized and decayed animal and vegetable materials, or fossil fuels, specifically coal, peat, lignite, petroleum, and natural gas. From these natural fuels other artificial ones can be derived. Coal gas, coke, water gas, and producer gas can be made using coal as the principal ingredient. Gasoline, kerosene, and fuel oil are made from petroleum. For most transportation, fuel must be in a liquid form.

There is a growing concern about the environmental contamination caused by the burning of great amounts of fossil fuels and about the increasing expense of finding them and processing them into easily usable forms (see energy, sources of). During the last 100 years the amount of carbon dioxide in the atmosphere has increased, and there is evidence that this phenomenon may be due to the burning of fossil fuel. Use of biomass, which consists of plants or plant waste, would not produce excess carbon dioxide because the plants absorb the gas for their growth. Wood is not as concentrated a form of energy as fossil fuels, but it can be converted into a more energy-rich fuel called charcoal. Burning fossil fuel also releases acidic oxides of sulfur and nitrogen, which are deposited on the earth in rainwater (see acid rain). The clearing of forests, particularly in the tropical regions, also threatens to increase the amount of carbon dioxide in the atmosphere because the forests utilize carbon dioxide for growth.

The amount of fossil fuel available is limited and new methods of recovery are being developed. One proposed alternative fuel is hydrogen, which is now employed as a fuel only for a few special purposes because of its high cost. Hydrogen can be produced by electrolysis of water for which nonfossil fuels would supply the energy. Solar energy could be utilized either by direct conversion to electricity using photovoltaic cells or by trapping solar heat. Fuels are rated according to the amount of heat (in calories or Btu) they can produce. Nuclear fuels are also possible substitutes for fossil fuels. Nuclear fuels are not burned; they undergo reactions in which the nuclei of their atoms either split apart, i.e., undergo fission, or combine with other nuclei, i.e., undergo fusion. In either case, a small part of the nuclear mass is converted to heat energy. All nuclear fuels currently employed in practical, nonweapons applications react by fission.

High-energy fuels for jet engines and rockets are rated by their specific impulse in thrust per pound of propellant per second. Hydrogen, which is the lightest element, is usually used in the form of compounds, because the density of liquid hydrogen is low and therefore a large volume is required. Addition of aluminum powder or lithium increases the efficiency. Rockets usually have a self-contained supply of oxygen or some other oxidizer, such as ammonium, lithium, or potassium perchlorate. Fuels such as turpentine, alcohol, aniline, and ammonia use nitric acid, hydrogen peroxide, and liquid oxygen as oxidizers. More power can be obtained by oxidizing hydrazine, diborane, or hydrogen with oxygen, ozone, or fluorine.

See oil gas; liquefied petroleum gas; gas, fuel; nuclear energy.

Fuel is any material that is burned or altered in order to obtain energy. Fuel releases its energy either through a chemical reaction means, such as combustion, 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 light into a form that can be used to sustain life. 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.

Energy sources

A large majority of currently-known fuels ultimately derive their energy from a small number of sources. Much of the chemical energy produced by life forms, such as fossil fuels, is derived from the utilization of solar energy through photosynthesis. Solar energy in turn is generated by the thermonuclear fusion process at the core of the Sun. The radioactive isotopes used as fuel to power nuclear plants were formed in supernova explosions.


Chemical fuels are substances that generate energy by reacting with substances around them, most notably by the process of oxidization. These substances were the first fuels to be known and used by humans and are still the primary type of fuel used today.


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 that was 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. 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.

Recently biofuels have been developed for use in automotive transport (for example E10 fuel), but there is widespread public debate about how carbon efficient these fuels are.

Fossil fuels

Fossil fuels are hydrocarbons, primarily coal and petroleum (liquid petroleum or natural gas), formed from the fossilized remains of dead plants and animals by exposure to heat and pressure in the Earth's crust over hundreds of millions of years. In common parlance, 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.

Modern large-scale industrial development is based on fossil fuel use, which has largely supplanted water-driven mills, as well as the combustion of wood or peat for heat. With global modernization in the 20th and 21st centuries, the growth in energy production from fossil fuels, especially gasoline derived from oil, is one of the causes of major regional and global conflicts and environmental issues. A global movement toward the generation of renewable energy is therefore under way to help meet the increased global energy needs.

The burning of fossil fuels by humans is the largest source of emissions of carbon dioxide, which is one of the greenhouse gases that enhances radiative forcing and contributes to global warming. The atmospheric concentration of CO2, a greenhouse gas, is increasing, raising concerns that solar heat will be trapped and the average surface temperature of the Earth will rise in response.


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.


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.


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.

World trade

World Bank reported that the USA was the top fuel importer in 2005 followed by the EU and Japan.

Use over time

The first use of fuel was the combustion of wood or sticks by Homo erectus near 2 million years ago. 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 became depleted around the 18th century. Charcoal briquettes are now commonly used as a fuel for barbecue cooking.

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.

See also



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