Alternative fuel sources
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. alternative fuel sources
1 Energy sources
2.2 Fossil fuels
4 World trade
5 Use over time
6 See also
9 Further reading
fuel 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.
fuel Biofuels alternative fuel sources
Main article: 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 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.
fuel Fossil fuels
Main article: Fossil fuel
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.
Main article: Nuclear fuel
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.
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.
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.
fuel World trade alternative fuel sources
Fuel imports in 2005World Bank reported that the USA was the top fuel importer
in 2005 followed by the EU and Japan.