Fuel

Fuels are any materials that store potential energy in forms that can be practicably released and used as heat energy. The substances classified as fuel must necessarily contain one or several of the combustible elements: carbon, hydrogen, sulphur, etc. The concept originally applied solely to those materials storing energy in the form of chemical energy that could be released through combustion. To utilize the energy of fuel in most usable form, it is required to transform the fuel from its one state to another, i.e. from solid to liquid or gaseous state, liquid to gaseous state, or from its chemical energy to some other form of energy via single or many stages. In this way, the energy of fuels can be utilized more effectively and efficiently for various purposes. 

The concept has been also applied to other sources of heat energy such as nuclear energy (via nuclear fission or nuclear fusion), as well as releases of chemical energy released through non-combustion oxidation ( such as in cellular biology or in fuel cells). 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 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 capacitors) or mechanical energy (such as flywheels, springs, compressed air, or water in a reservoir).



History

A reconstruction of Homo erectus

The first known use of fuel was the combustion of wood or sticks by Homo erectus near 2,000,000 (two million) years ago. 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. Coal became a more popular power source after the development of the steam engine in the United Kingdom in 1769. 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 to generate electricity. In year 2005, 40% of the world's electrical power supply was provided by using coal. 

Fossil fuels were rapidly adopted during the industrial revolution, because they were more concentrated and flexible than traditional energy sources, such as water power.  



Classification of Fuels
Chemical fuels are classified in many ways such as by their physical properties (solid, liquid or gas), on the basis of their occurrence: primary (natural fuel) and secondary (artificial fuel) or by their nature (what it is derived from).



Solid Fuels

 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, corn, wheat, rye and other grains. Solid-fuel rocket technology also uses solid fuel. The most commonly used and easily obtainable solid fuel is wood. It is the oldest type of fuel which man had used for centuries after the discovery of the fire itself.

Liquid Fuels
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.

Gaseous Fuels

Gaseous fuels occur in nature, besides being manufactured from solid and liquid fuels. Gaseous fuel is any one of a number of fuels that under ordinary conditions are gaseous. Many gaseous fuels are composed of hydrocarbons (such as methane or propane), hydrogen, carbon monoxide, or mixtures thereof in different ratio and this means that different amounts of oxygen are needed to burn the fuel gas efficiently. This ratio of fuel to oxidant affects the temperature of the flame, the flammability and explosive limits. 

Primary fuel
Primary fuel is an energy carrier found in nature that has not been subjected to any conversion or transformation process. Primary fuel can be used directly, as they appear in the natural environment: coal, oil, peat, dung, natural gas and wood, nuclear fuels (uranium), the sun, the wind, tides, mountain lakes, the rivers (from which hydroelectric energy can be obtained) and the Earth heat that supplies geothermal energy.


Secondary Fuels
Secondary fuel refers to the more convenient forms of energy carrier which are transformed from other, primary, energy sources through energy conversion processes. Examples are electricity, which is transformed from primary sources such as coal, raw oil, fuel oil, natural gas, wind, sun, streaming water, nuclear power, gasoline etc., but also refined fuels such as gasoline or synthetic fuels such as hydrogen fuels. Another example is petrol that derives from the treatment or crude oil and electric energy, obtained from the conversion of mechanical energy (hydroelectric plants, Aeolian plants), chemical plants (thermoelectric), or nuclear (nuclear plants).

Fossil Fuels

Fossil fuels are natural resources such as coal, oil (including gasoline and diesel fuel) and natural gas. They are formed from the remains of ancient plant and animal life by exposure to high heat and pressure in the absence of oxygen in the Earth's crust over hundreds of millions of years. In common dialogue, the term fossil fuel also includes hydrocarbon-containing natural resources that are not derived from animal or plant sources such as tar sands. These latter sources are sometimes known instead as mineral fuels. 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. 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.

Bio Fuels

Biofuels are produced from living organisms or from metabolic by-products (organic or food waste products). In order to be considered a biofuel the fuel must contain over 80 percent renewable materials. It is originally derived from the photosynthesis process and can therefore often be referred to as a solar energy source. Many different plants and plant-derived materials are used for biofuel manufacture. 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.

Nuclear Fuels

Nuclear pellets

Nuclear fuel is any material that is consumed to derive nuclear energy. Technically speaking this definition includes all matter because any element under 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. The main nuclear fuels are uranium and plutonium. These are radioactive metals. Nuclear fuels are not burnt to release energy. Instead, the nuclear fission reactions (where the nuclei in atoms are split) in the fuels release heat energy. 

Example of Fuels

Gasoline

Gasoline, also spelled gasolene, also called gas or petrol, mixture of volatile, flammable liquid hydrocarbons derived from petroleum and used as fuel for internal-combustion engines. It is also used as a solvent for oils and fats. Originally a by-product of the petroleum industry (kerosene being the principal product), gasoline became the preferred automobile fuel because of its high energy of combustion and capacity to mix readily with air in a carburetor. Gasoline is primarily consumed as a fuel for transportation. It is produced by refining crude oil in an oil refinery. Today, gasoline is the fuel used by most passenger vehicles in the world. Nearly two-thirds of fuel used for transportation is in the form of gasoline. While other forms of fuel are being sought, and being worked on, gasoline is still the primary method by which we fuel our cars. The problem is that gasoline prices keep climbing higher and higher, making it more difficult to

get. The demand for gasoline has actually decreased, and we are still struggling to meet the rising gasoline prices. Gasoline is also used to power many other devices, such as generators, tractors, and construction vehicles.

Coal

Coal is usually occurring in rock strata in layers or veins called coal beds or coal seams. Coal is the largest source of energy for the generation of electricity worldwide, as well as one of the largest worldwide anthropogenic sources of carbon dioxide releases. In 1999 world gross carbon dioxide emissions from coal usage were 8,666 million tons of carbon dioxide. Coal is extracted from the ground by coal mining, either underground by shaft mining, or at ground level by open pit mining extraction. Coal is very important because it is burnt to create electricity. It is also considered an important ingredient in the manufacturing industry. It is widely used because it is abundant and inexpensive and it is also renewable. However, it also affects the environment as it generates hundreds of millions of tons of waste products, including fly ash, bottom ash, and flue-gas desulfurization sludge, that contain mercury, uranium, thorium, arsenic, and other heavy metals. It causes premature deaths, lung cancer, acid rain, and interference with groundwater and water table levels due to mining.

Coal-fired Power Station

Diesel

Diesel fuel in general is any liquid fuel used in diesel engine. The most common is a specific fractional distillate of petroleum fuel oil. Diesel fuel contains more energy and greater power density than other fuels such as gasoline and is the fuel of choice for tough jobs. Efforts are underway to reduce the amount of harmful emission caused by burning diesel fuel. Therefore it is more common used in heavy vehicles such as bus, trucks and some aircrafts because diesel is 15 percent more energy dense than gasoline. Another major user of diesel fuel is the construction industry. Equipment such as forklifts, cranes, excavators and loader backhoes depend on diesel's power to fuel their work. Diesel is also an alternative of gasoline in transportation. In same unit volume, diesel releases less carbon dioxide into the air because it is more fuel efficient. Diesel fuel does not evaporate as easily as gasoline, so it is much safer in accidents.

Biofuels

Biofuels are liquid fuels which have been derived from other materials such as waste plant and animal matter. There are two main types of biofuels - bioethanol and biodiesel. Bioethanol is used as a replacement for gasoline and biodiesel is used as a replacement for diesel. Nowadays, transportations are dependent on finite fossil fuels such as oil and petroleum for its energy needs so it is important that we move towards more renewable and sustainable fuels. Added to this, transport is the third largest emitter of greenhouse gases and biofuels can significantly reduce transport’s carbon footprint. Bio-fuels burn more cleanly than gasoline and diesel. Using biofuels means producing fewer emissions of carbon monoxide, particulates, and toxic chemicals that cause smog, aggravate respiratory and heart disease, and contribute to thousands of premature death each year.

Natural gas

Natural gas is a fossil fuel formed when layers of buried plants and animals are exposed to intense heat and pressure over thousands of years. The energy that the plants originally obtained from the sun is stored in the form of chemical bonds in natural gas. Natural gas is an environmentally friendly and efficient energy source, natural gas is the cleanest-burning conventional fuel, producing lower levels of greenhouse gas emissions per unit of energy released than heavier hydrocarbon fuels such as coal and oil. Natural gas is also a major source of electricity generation through the use of gas turbines and steam turbines. Most grid peaking power plants and some off-grid engine-generators use natural gas. Natural gas dispensed from a simple stovetop can generate heat in excess of 2000°F (1093°C) making it a powerful domestic cooking and heating fuel. 

Uranium

Uranium is a very heavy metal which can be used as an abundant source of concentrated energy. In nature, uranium is found as uranium-238 (99.2739 - 99.2752%), uranium-235 (0.7198 - 0.7202%), and a very small amount of uranium-234 (0.0050 - 0.0059%). The main use of uranium in the civilian sector is to fuel nuclear power plants. One kilogram of uranium-235 can theoretically produce about 20 terajoules of energy (2×10¹³ joules), assuming compleate fission; as much energy as 1500 tons of coal. Commercial nuclear power plants use fuel that is typically enriched to around 3% uranium-235. U-235 is ideal for producing nuclear power is that unlike most materials, U-235 can undergo induced fission. When a free neutron collides with a U-235 nucleus, the nucleus will usually capture the neutron and split extremely quickly. The splitting of a single U-235 can release roughly 200 MeV (million electron volts). However, the uranium has great impacts to the environment. Normal functioning of the kidney, brain, liver, heart and other systems can be affected by uranium exposure, because, besides being weakly radioactive, uranium is a toxic metal. Uranyl ions, such as from uranium trioxide or uranyl nitrate and other hexavalent uranium compounds, have been shown to cause birth defects and immune system damage in laboratory animals.

Uranium-235

Nuclear fission