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Alcohol fuel
Although fossil fuels have become the dominant energy resource for the modern world, Alcohol has been used as a fuel throughout history. The first four aliphatic alcohols (methanol, ethanol, propanol, and butanol) are of interest as fuels because they can be synthesized biologically, and they have characteristics which allow them to be used in current engines. One advantage shared by all four alcohols is octane rating. Biobutanol has the advantage that its energy density is closer to gasoline than the other alcohols (while still retaining over 25% higher octane rating) - however, these advantages are outweighed by disadvantages (compared to ethanol and methanol) concerning production, for instance. Generally speaking, the chemical formula for alcohol fuel is CnH2n+1OH. The larger n is, the higher the energy density. Alcohol fuels are usually of biological rather than petroleum sources. When obtained from biological sources, they are known as bioalcohols (e.g. bioethanol). It is important to note that there is no chemical difference between biologically produced alcohols and those obtained from other sources. However, ethanol that is derived from petroleum should not be considered safe for consumption as this alcohol contains about 5% methanol and may cause blindness or death. This mixture may also not be purified by simple distillation, as it forms an azeotropic mixture. Bioalcohols are still in developmental and research stages. Use of optimized crops with higher yields of energy, elimination of pesticides and fertilizers based on petroleum, and a more rigorous accounting process will help improve the feasibility of bioalcohols as fuels. Additional recommended knowledge
Methanol and Ethanol
Methanol and Ethanol both have advantages and disadvantages over fossil fuels, such as petrol and diesel. For instance, both alcohols can run at a much higher compression ratio without octane-boosting additives (ethanol's octane rating is 129 (RON), 102 (MON), which equates to 116 (AKI). Methanol is 129 (RON), 103 (MON), which equates to 113 (AKI) as opposed to ordinary European petrol which is approximately 91 (RON), 81 (MON), equal to 86 (AKI); Note that (AKI) refers to the U.S. rating which stands for 'Anti-Knock Index' which averages the RON and MON ratings,(Ron+Mon)/2 or (R+M)/2. Alcohols burn more completely because their molecules contain oxygen; carbon monoxide emissions are 100% lower than fossil-fueled engines because the only products of an alcohol combustion reaction are carbon dioxide, water, and heat. Despite this reduction in carbon monoxide, alcohol releases as much or more carbon dioxide than its gasoline counterpart (though this carbon dioxide has previously been drawn from the air in biologically-produced ethanol, so if any petroleum burned to produced the ethanol is ignored (see below), there is no net modern release, as there is for fossil fuels). There are also lower NOx emissions, as ethanol needs more energy to vaporise than petrol - so it draws more heat out of the air in a cylinder than petrol, having a greater cooling effect, which reduces the opportunity for nitrogen and oxygen in the cylinder (as air) to fuse into poisonous nitrogen oxides. For the past few decades automotive fuel system plastics and rubber have been designed to tolerate up to 10% ethanol (Regular gas/E10) without problem. In very old engines Ethanol may degrade some compositions of plastic or rubber fuel delivery components designed for conventional petrol. U.S. "FlexFuel" vehicles have upgraded fuel system components which are designed for long life using E85. The cost of this E85 upgrade to a modern engine is inexpensive and is less than $100. "Total Flex" Autos destined for the Brazilian market can burn E100 (100% Ethanol). Ethanol has 27% less energy per litre than petrol. Methanol is even more corrosive and its energy per liter is 55% lower than that of petrol. Higher compression ratios and corrosion-resistant materials easily overcome these issues, and require modest engine modifications with known technologies/metals such as stainless steel. Given the higher octane rating of Ethanol, forced induction engine architectures (Turbocharging or Supercharging) with modern sensors, actuators, and computer controls are capable of generating equivalent or higher horsepower and torque burning ethanol than conventional gasoline despite the lower energy density of Ethanol. Methanol has also been proposed as a fuel of the future. There has been extensive use of methanol fuel in Funny Cars for years, and it has been used as a fuel for open wheel car racing in North America since 1965. Unfortunately, although its octane rating is comparable to ethanol and it has similar emissions, it is also toxic (producing some toxic emissions, formaldehyde and formic acid), and has a lower (-38%) energy content than ethanol (-55% compared to petrol.) Ethanol is already being used extensively as a fuel additive, and the use of ethanol fuel alone or as part of a mix with gasoline is increasing. From 2007, the Indy Racing League will use ethanol as its exclusive fuel, after 40 years of using methanol.[1]. Since September 2007 petrol stations in NSW, Australia are mandated to supply all their petrol with 2% Ethanol content[2] Methanol combustion is: 2CH3OH + 3O2 → 2CO2 + 4H2O + heat Ethanol combustion is: C2H5OH + 3O2 → 2CO2 + 3H2O + heat Butanol
Propanol and butanol are considerably less toxic and less volatile than methanol. In particular, butanol has a high flashpoint of 35 °C, which is a benefit for fire safety, but may be a difficulty for starting engines in cold weather. The concept of flash point is however not directly applicable to engines as the compression of the air in the cylinder means that the temperature is several hundred degrees Celsius before ignition takes place. The fermentation processes to produce propanol and butanol from cellulose are fairly tricky to execute, and the Weizmann organism (Clostridium acetobutylicum) currently used to perform these conversions produces an extremely unpleasant smell, and this must be taken into consideration when designing and locating a fermentation plant. This organism also dies when the butanol content of whatever it is fermenting rises to 7%. For comparison, yeast dies when the ethanol content of its feedstock hits 14%. Specialized strains can tolerate even greater ethanol concentrations - so-called turbo yeast can withstand up to 16% ethanol [3]. However, if ordinary Saccharomyces yeast can be modified to improve its ethanol resistance, scientists may yet one day produce a strain of the Weizmann organism with a butanol resistance higher than the natural boundary of 7%. This would be useful because butanol has a higher energy density than ethanol, and because waste fibre left over from sugar crops used to make ethanol could be made into butanol, raising the alcohol yield of fuel crops without there being a need for more crops to be planted. Despite these drawbacks, DuPont and British Petroleum have recently announced that they are jointly to build a small scale butanol fuel demonstration plant [4] alongside the large bioethanol plant they are jointly developing with Associated British Foods. Enerey Environment International developed a method for producing butanol from biomass, which involves the use of two separate micro-organisms in sequence to minimize production of acetone and ethanol byproducts.[5] The Swiss company Butalco GmbH uses a special technology to modify yeasts in order to produce butanol instead of ethanol. Yeasts as production organisms for butanol have decisive advantages compared to bacteria[6]. Butanol combustion is: 2C4H9OH + 12O2 → 8CO2 + 10H2O + heat The 3-carbon alcohol, propanol (C3H7OH), is not used as a direct fuel source for petrol engines that often (unlike ethanol, methanol and butanol), with most being directed into use as a solvent. However, it is used as a source of hydrogen in some types of fuel cell; it can generate a higher voltage than methanol, which is the fuel of choice for most alcohol-based fuel cells. However, since propanol is harder to produce than methanol (biologically OR from oil), methanol fuel cells are still used a lot more often than those that utilise propanol. By countryAlcohol in BrazilBrazil is the largest producer of alcohol fuel in the world, typically fermenting ethanol from sugarcane. The country produces a total of 18 billion liters annually, of which 3.5 billion are exported, 2 billion of them to the US [7]. Alcohol cars debuted in the Brazilian market in 1978 and became quite popular because of heavy subsidy, but in the 80's prices rose and gasoline regained the leading market share. But from 2004 on, alcohol is rapidly rising its market share once again because of new technologies involving hybrid fuel car engines [8], called "Flex" by all major car manufacturers (Volkswagen, General Motors, Fiat, etc.). "Flex" engines work with gasoline, alcohol or any mixture of both fuels. As of February 2007, approx. 80% of new vehicles sold in Brazil are hybrid fuel [9] Because of the Brazilian leading production and technology, many countries became very interested in importing alcohol fuel and adopting the "Flex" vehicle concept.[8] In March 7th of 2007, US president George W. Bush visited the city of São Paulo to sign agreements with Brazilian president Lula on importing alcohol and its technology as an alternative fuel. Alcohol in RussiaOther than Brazil, the only other country with an extensive programme for supplying alcohol fuel to supplement petroleum use is Russia, which has reduced its dependency on oil by using methanol made from the destructive pyrolysis of eucalyptus wood and fibre. However, this system is less likely to be emulated elsewhere, due to the disadvantages of methanol fuel, as compared to ethanol fuel Energy density, toxicity, and corrosiveness are the main concerns; methanol contains 40% less energy than ethanol, is more corrosive, and is also 4 times as toxic, with an average lethal dose of as little as 100-125ml (10 to 12.5 units), compared to 400-500ml, 40 to 50 units, for ethanol. Alcohol in the United States
E10 or Gasohol is commonly marketed in Delaware and E85 is found in many states, particularly in the Mid West where ethanol from corn is produced locally. Due to government subsidies, many new vehicles are sold each year that can use E85, although the majority are run solely on gasoline due to the limited availability of E85. Many states and municipalities have mandated that all gasoline fuel be blended with 10 percent alcohol (usually ethanol) during some or all of the year. This is to reduce pollution and allows these areas to comply with federal pollution limits. Because alcohol is partially oxygenated, it produces less overall pollution, including ozone. In some areas (California in particular) the regulations may also require other formulations or added chemicals that reduce pollution, but add complexity to the fuel distribution and increase the cost of the fuel. See also
References
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| This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Alcohol_fuel". A list of authors is available in Wikipedia. |
