Fuels are any materials that store
potential energy in forms that can be practicably released and used for work or
as heat energy. The concept originally applied solely to those materials
storing energy in the form of chemical energy that could be released through
combustion but the concept has since been also applied to other sources of heat
energy such as nuclear energy (via nuclear fission or
The heat energy released by many
fuels is harnessed into mechanical energy via an engine. Other times the heat
itself is valued for warmth, cooking, or industrial processes, as well as the
illumination that comes with combustion. Fuels are also used in the cells of
organisms in a process known as cellular respiration, where organic molecules
are oxidized to release un-usable energy. Hydrocarbons 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
methods of storing potential energy, such as those that directly release
electrical energy (such as batteries and c apacitors) or mechanical energy
(such as flywheels, springs, compressed air, or water in a reservoir).
History
The first known use of fuel was the combustion of wood or
sticks by Homo erectus near 2,000,000 (two million) years ago.[page needed]
Throughout most of human history fuels derived from plants or animal fat were
the only ones humans used. 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.
Coal was first used as a fuel around 1000 BCE in China. With
the development of the steam engine in the United Kingdom 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 and 21st centuries, the primary use of
coal is to generate electricity, providing 40% of the world's electrical power
supply in 2005.
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.
Currently the trend has been towards renewable fuels, such
as biofuels like alcohols.
Chemical
Chemical fuels are substances that release energy by
reacting with substances around them, most notably by the process of oxidation.
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, naptha, ethanol
Gaseous fuels natural
gas hydrogen, propane, coal gas,
water gas, blast furnace gas, coke oven gas, CNG
Solid fuel
Main article: Solid fuel
Coal is an important 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 (see wood fuel), 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 such 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 fuel
Main article:
A gasoline station.
Liquid fuels are combustible or energy-generating molecules
that can be harnessed to create mechanical energy, usually producing kinetic
energy; they also must take the shape of their container. It is the fumes of
liquid fuels that are flammable instead of the fluid. Most liquid fuels in
widespread use are derived from fossil fuels; however, there are several types,
such as hydrogen fuel (for automotive uses), ethanol, and biodiesel, which are
also categorized as a liquid fuel. 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 with relative ease. Also they are
relatively easy to use for all engineering applications, and home use. (Fuels
like Kerosene are rationed and available in government subsidized shops in
India for home use.) Liquid fuels are also used most popularly in Internal
combustion engines. Most liquid fuels used currently are produced from
petroleum. The most notable of these is gasoline. Scientists generally accept
that petroleum formed from the fossilized remains of dead plants and animals by
exposure to heat and pressure in the Earth's crust.
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 be compressed to a liquid and used as a
substitute for other traditional liquid fuels. 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.
Gaseous fuels
A 20 pound (9.1 kg) propane cylinder.
Fuel gas is any one of a number of fuels that under ordinary
conditions are gaseous. 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.
Biofuels
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. 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 Bioethanol and Biodiesel), but there is widespread
public debate about how carbon efficient these fuels are.
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 by exposure to high heat and pressure in the absence
of oxygen in the Earth's crust over hundreds of millions of years. 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.[9] 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 by exposure to heat and pressure in the Earth's crust over millions of
years. 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.[11] Non-fossil sources in 2006
included hydroelectric 6.3%, nuclear 8.5%, and others (geothermal, solar,
tidal, wind, wood, waste) amounting to 0.9%. 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 it 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 44/12 or 3.7
tonnes of carbon dioxide). 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.
Nuclear
CANDU fuel bundles Two CANDU ("CANada Deuterium Uranium")
fuel bundles, each about 50 cm long, 10 cm in diameter. Photo courtesy of
Atomic Energy of Canada Ltd.
Nuclear fuel is any material that is consumed to derive
nuclear energy. Technically speaking this definition includes all matter
because any element under the right conditions will 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. Nuclear
fuel is a material that can be 'burned' by nuclear fission or fusion 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.
Most nuclear fuels contain heavy fissile elements that are
capable of nuclear fission. When 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 with a controlled rate in
a nuclear reactor or with 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 power from nuclear fission.
Plutonium-238 and some other elements are used to produce small amounts of
nuclear power by radioactive decay in radioisotope thermoelectric generators
and other types of atomic batteries. Also, light nuclides such as tritium (3H)
can be used as fuel for nuclear fusion. Nuclear fuel has the highest energy
density of all practical fuel sources.
Fission
Nuclear fuel pellets are used to create 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. 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.
Fusion fuels tend to be light elements such as hydrogen which will combine
easily. Energy is required to start fusion by raising temperature so high all
materials would turn into plasma, and allow nuclei to collide and stick
together with each other 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 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. The elements then on use up energy
instead of giving out when fused, and therefore fusion stops and the stars die.
In attempts by humans, fusion is only carried out with hydrogen (isotope of 2
and 3) 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 used. .
World trade
Fuel imports in 2005
World Bank reported that the USA was the top fuel importer
in 2005 followed by the EU and Japan.
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