Alternative fuel

Typical Brazilian filling station with four alternative fuels for sale: biodiesel (B3), gasohol (E25), neat ethanol (E100), and compressed natural gas (CNG). Piracicaba, São Paulo, Brazil.

Alternative fuels, also known as non-conventional fuels, are any materials or substances that can be used as fuels, other than conventional fuels. Conventional fuels include: fossil fuels (petroleum (oil), coal, propane, and natural gas), and nuclear materials such as uranium.

Some well known alternative fuels include biodiesel, bioalcohol (methanol, ethanol, butanol), chemically stored electricity (batteries and fuel cells), hydrogen, non-fossil methane, non-fossil natural gas, vegetable oil and other biomass sources.

Background

The main purpose of fuel is to store energy in a form that is stable and can be easily transported from the place of production to the end user. Almost all fuels are chemical fuels, which store chemical potential energy. The end user may consume the fuel at will and release energy, usually in the form of heat, for a variety of applications, such as powering an engine or heating a building.

Factors increasing demand for alternative fuels

In 2007, there were 1.8 million alternative fuel vehicles sold in the United States, indicating an increasing popularity of alternative fuels. There is growing perceived economic and political need for the development of alternative fuel sources. This is due to general environmental, economic, and geopolitical concerns of sustainability.

The major environmental concern, according to an IPCC report, is that "Most of the observed increase in globally averaged temperatures since the mid-20th century is due to the observed increase in anthropogenic greenhouse gas concentrations" . Since burning fossil fuels is known to increase greenhouse gas concentrations in the atmosphere, they are a likely contributor to global warming.

Other concerns which have fueled demand revolve around the concept of peak oil, which predicts rising fuel costs as production rates of petroleum enter a terminal decline. According to the Hubbert peak theory, when the production levels peak, demand for oil will exceed supply and without proper mitigation this gap will continue to grow as production drops, which could cause a major energy crisis.

Lastly, the majority of the known petroleum reserves are located in the Middle East. There is general concern that worldwide fuel shortages could intensify the unrest that exists in the region, leading to further conflict and war. (See future energy development for a general discussion)

In an attempt to increase demand for alternative fuels in the US, the IRS began allowing taxpayers to claim a special tax credit for using alternative fuels, known as the Alternative Fuel Vehicle Refueling Property Credit. The definition used for alternative fuel under this credit is: Any fuel containing at least 85 percent of one or more of ethanol, natural gas, compressed natural gas, liquefied natural gas, liquefied petroleum gas, or hydrogen; or any mixture which consists of two or more of biodiesel, diesel fuel, or kerosene, and at least 20% of which consists of biodiesel.

The production of alternative fuels can have widespread effects. For example, the production of corn-based ethanol has created an increased demand for the feed stock, causing rising prices in almost everything made from corn. However, in a competitive free market, an increased supply of ethanol reduces the demand for conventional fuels, and thus lowers fuel prices. The ethanol industry enables agricultural surpluses to be used to mitigate fuel shortages.

Biofuel

Main article: Biofuel

Biofuels are also considered renewable if their source is sustainable. Although renewable energy is used mostly to generate electricity, it is often assumed that some form of renewable energy or at least sustainable energy is used to create alternative fuels. Several alternative fuels, however, such as nuclear fuel and alternative fossil fuels, are made from non-sustainable sources, and fuels for Hydrogen fuel cells and air engines can be created by non-sustainable means as well. Such non-sustainable fuels are offered as alternatives usually because they cause less pollution at the point of use.

Biomass

Main article: Biomass

Switchgrass, a hardy plant used in the biofuel industry in the United States

Main article: Biomass

Biomass in the energy production industry is living and recently dead biological material which can be used as fuel or for industrial production. Biomass is grown from several plants, including miscanthus, switchgrass, hemp, corn, poplar, willow, sugarcane, oil palm (palm oil), and algae oil.

Most commonly, biomass is plant matter grown for use as biofuel, but it also includes plant or animal matter used for production of fibres, chemicals or heat. Biomass may also include biodegradable wastes that can be burnt as fuel. It excludes organic material which has been transformed by geological processes into substances such as coal or petroleum.

Alcohol fuels

Main articles: Alcohol fuel, Ethanol fuel, and Methanol fuel

Methanol and ethanol are typically not primary sources of energy; however, they are convenient fuels for storing and transporting energy. These alcohols can be used in internal combustion engines such as flexible fuel vehicles with minor modifications.

Methanol can be produced from a wide variety of sources including fossil fuels, but also agricultural products and municipal waste, wood and varied biomass. More importantly, it can also be made from chemical recycling of carbon dioxide (such as from the CO₂ rich flue gases of fossil fuel burning power plants or exhaust of cement and other factories, of even atmospheric CO₂). Ethanol can be mass-produced by fermentation of the starch or sugar in a wide variety of crops (bio-ethanol), or by hydration of ethylene from petroleum and other sources.

There has been considerable debate about how useful bio-ethanol will be in replacing fossil fuels in vehicles. Concerns relate to the large amount of arable land required for crops, as well as the energy and pollution balance from the ethanol production cycle . Recent developments with cellulosic ethanol production and commercialization may allay some of these concerns.

Methanol as a fuel also has several disadvantages.

Hydrogen

Main article: Hydrogen economy

An algae bioreactor for hydrogen production.

Hydrogen as a fuel has been suggested to have the capability to create a hydrogen economy. However, there is no accessible natural reserve of uncombined hydrogen, since what little there is resides in Earth's outer atmosphere. Therefore, hydrogen for use as fuel must first be produced using another energy source, making it a means to transport energy, rather than an energy source, similar to a rechargeable battery. One existing method of hydrogen production is steam methane reformation; however, this method requires methane (most commonly available as natural gas), which raises sustainability concerns. Another method of hydrogen production is through electrolysis of water, in which electricity generated from any source can be used. Photoelectrolysis, biohydrogen, and biomass or coal gasification have also been proposed as means to produce hydrogen.

According to the majority of energy experts and researchers, hydrogen is currently impractical as an alternative to fossil-based liquid fuels. While hydrogen has a very high energy content by weight, it has a very low energy content by volume, making it very challenging to store in average-sized vehicles. Hydrogen can be stored as compressed hydrogen, as cryogenic liquid hydrogen, or in compounds containing hydrogen which must undergo a chemical change to release the gas such as metal hydrides. However, because of the lower volumetric energy, hydrogen gas tanks would need to be two to three times as large for compressed hydrogen storage as conventional gasoline tanks.

The production of fuel cells for hydrogen cars is often expensive as most designs require large amounts of platinum as a catalyst. Other concerns involve the fragility of fuel cells and their tendency to freeze, the flammability of hydrogen, and vehicle and infrastructure production costs. Currently, due to efficiencies of scale, it is more efficient to burn fossil fuels to produce hydrogen than to burn oil directly in car engines.

Oxyhydrogen, HCNG

Main article: Hydrogen fuel enhancement

Besides hydrogen, oxyhydrogen and HCNG are also commonly used as alternative fuels.

Liquid nitrogen

Liquid nitrogen is another type of emissionless fuel.

Compressed air

Main article: Air engine

The air engine is an emission-free piston engine using compressed air as fuel. Unlike hydrogen, compressed air is about one-tenth as expensive as fossil oil, making it an economically attractive alternative (hydrogen is about 10 times more expensive than oil or 100 times more expensive than compressed air). The air engine has also broken most barriers (storage of the energy, range, ....). Models exist which can achieve speeds over 35 mph with air alone, but at least one company claims it will produce an "Air Car" hybrid by 2010 which will be able to achieve over 100 mpg with a top speed of 96 mph.

Alternative fossil fuels

See also: Coal liquefaction and Coal gasification

Compressed natural gas (CNG) is a cleaner burning alternative to conventional petroleum automobile fuels. The energy efficiency is generally equal to that of gasoline engines, but lower compared with modern diesel engines. CNG vehicles require a greater amount of space for fuel storage than conventional gasoline power vehicles because CNG takes up more space for each GGE (Gallon of Gas Equivalent). Almost any existing gasoline car can be turned into a bi-fuel (gasoline/CNG) car. However, natural gas is a finite resource like all fossil fuels, and production is expected to peak soon after oil does.

There are large but finite coal reserves which may increasingly be used as a fuel source during oil depletion. The Fischer-Tropsch process converts carbon dioxide and carbon monoxide into heavier hydrocarbons, including synthetic oil. It is used today in South Africa to produce most of that country's diesel from coal. The Karrick process is an improved methodology for coal liquefaction, with higher efficiency. Since there are large but finite coal reserves in the world, this technology could be used as an interim transportation fuel if conventional oil were to become scarce. There are several companies developing the process to enable practical exploitation of so-called stranded gas reserves, those reserves which are impractical to exploit with conventional gas pipelines and LNG technology.

Methane hydrate is a form of natural gas. This substance consists of methane molecules trapped within the crystalline structure of water ice and is found in deposits under ocean sediments or within continental sedimentary rock formations. It is estimated that the global inventory of methane hydrate may equal as much as ten times the amount of natural gas. With current technology, most gas hydrate deposits are unlikely to be commercially exploited as an energy source. In addition, the combustion of methane releases the greenhouse gas carbon dioxide into the atmosphere. Methane is also a greenhouse gas. In other respects methane hydrate has the same problems of fossil fuel.

Nuclear power

Nuclear power is any nuclear technology designed to extract usable energy from atomic nuclei via controlled nuclear reactions. The most common method today is through nuclear fission, though other methods include nuclear fusion and radioactive decay. All current methods involve heating a working fluid such as water, which is then converted into mechanical work for the purpose of generating electricity or propulsion. Today, more than 15% of the world's electricity comes from nuclear power, over 150 nuclear-powered naval vessels have been built, and a few radioisotope rockets have been produced.

Fission reactors use the U-235 isotope of uranium for fuel. While uranium is a fairly common element, the U-235 isotope is relatively rare. Using current reactor technology and current usage levels, and assuming an economical price of extraction, there is approximately 50 years of viable uranium available. Alternative reactor technologies exist which can use the much more common U-238 isotope, but these breeder reactors have technical issues (resulting from the higher levels of heat and radiation produced) to overcome before they can be employed economically.

Since automobiles and trucks consume a great deal of the total energy budget of developed countries, widespread electric vehicles technology would be required to convert the energy generated from nuclear power to transportation.

The long-term radioactive waste storage problems of nuclear power have not been solved, although on-site spent fuel storage in casks has allowed power plants to make room in their spent fuel pools. Today, the only industrial solution lies with storage in underground repositories. There are widespread public concerns about the health risks, security risks and radioactive waste disposal problems of nuclear materials.

See also

• Alternative fuel cars
• Alternative propulsion
• Comparisation of alternative ICE fuels
• Greasestock - An alternative fuel festival in New York
• List of 2007 Hybrid Vehicles
• Alcohol fuel
• Algae fuel
• Biodiesel
• Biogas
• NGH - A possible future alternative to LNG for transporting natural gas
• Vegetable oil used as fuel
• Swiftfuel -- A potential lead-free alternative to 100LL aviation gasoline.
• Energy development
• List of energy topics
• Heating value

External links

• Alternative Fuels Data Center (U.S. DOE)
• Alternative Fuels Information Centre (Victorian Government)
• Alternative Fuel Vehicle Training: National Alternative Fuels Training Consortium, West Virginia University U.S.
• Clean Cities Program: U.S. DOE program encouraging alternative fuel use
• International Air Transport Associationoverview of alternative aviation fuels
• ScienceDaily - Research in Alternative Fuels: Latest research news on alternative fuels
• Student's Guide to Alternative Fuel (California Energy Commission)
• Sustainable Green Fleets: EU-sponsored dissemination project for alternatively propelled cars and alternative fuels
• Pop. Mechanics: Crunching the numbers on alternative fuels
• Alternative fuel station and price map for the US