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Ethanol (ethyl alcohol) and methanol (methyl alcohol) are two types of alcohol fuels. In their anhydrous or pure forms, they can be mixed with gasoline (petrol) if running either pure or 190 proof alcohol is not practical. Typically, only ethanol is used widely in this manner, particularly since methanol is toxic.
E5, E7, E10
E10, also frequently called gasohol, is a fuel mixture of 10% ethanol and 90% gasoline that can be used in the internal combustion engines of most modern automobiles.
It has been introduced nationwide in Denmark. It is also commonly available in the Midwestern United States and is the only type of gasoline allowed to be sold in the state of Minnesota, along with E85. As of spring of 2006, due to the phasing out of MTBE as a gasoline additive, E10 has become very common throughout the United States.
Similar blends include E5 and E7. These concentrations are generally safe for recent engines that run on pure gasoline. Some regions and municipalities mandate that the locally-sold fuels contain limited amounts of ethanol. One way to measure alternative fuels in the US is the "gasoline-equivalent gallons" (GEG). In 2002, the U.S. used as fuel an amount of ethanol equal to 137 petajoules (PJ), the energy of 1.13 billion US gallons (4,280,000 m³) of gasoline. This was less than 1% of the total fuel used that year.*
The Tesco chain of supermarkets in the UK have started selling an E5 brand of gasoline marketed as 99 RON super-unleaded. Price-wise it is cheaper than the other two forms of high-octane unleaded on the market, Shell's Optimax (98 RON) and BP's Ultimate (97 RON).
E15
E15 contains 15% ethanol and 85% gasoline. This is generally the greatest ratio of ethanol to gas that is recommended by auto manufacturers that sell vehicles in the United States, though it is possible that many vehicles can handle the higher mixtures E20 or E25 without trouble. Flexible-fuel vehicles are designed to take even higher concentrations, up to 96% v/v ethanol (and no gasoline, E100).
E20 & E25
E20 contains 20% ethanol and 80% gasoline. This fuel is not yet widely used in the United States, but will be mandated by the U.S. state of Minnesota for all gasoline sold by 2013. Since February 2006, E20 is required for all gasoline sold in Brazil. Concerns with the alcohol supply in Brazil resulted in a drop in the ethanol percentage, previously at 25% (E25) for all gasoline. Most modern vehicles, even if not flexible fuel, usually can run well using E20 or E25.
E85
E85 is a mixture of 85% ethanol and 15% gasoline, and is generally the highest ethanol fuel mixture found in the United States. It is common in Sweden, and there are more than 400 public E85 fuel pumps in the U.S. as of 2005, mostly concentrated in the Midwest, with over half of those in Minnesota.
] This mixture has an octane rating of about 105. This is down significantly from pure ethanol but still much higher than normal gasoline. The addition of a small amount of gasoline helps a conventional engine start when using this fuel under cold conditions. E85 does not always contain exactly 85% ethanol. In winter, especially in colder climates, additional gasoline is added (to facilitate cold start). E85 has traditionally been similar in cost to gasoline, but with the large oil price rises of 2005 it has become common to see E85 sold for as much as $0.70 less per gallon than gasoline, making it highly attractive to the small but growing number of motorists with cars capable of burning it.
E95
E95 contains just 5% gasoline and is used in some diesel engines where high compression is used to ignite the fuel, as opposed to the operation of gasoline engines where spark plugs are used.
E100
E100 is straight ethanol, which is most widely used in Brazil and Argentina. Operation in ambient temperatures below 15 °C (59 °F) causes problems with pure, or so-called neat, ethanol for starting engines. The most common cold weather solution is to add an additional small gasoline reservoir to increase the gasoline content momentarily to permit starting the engine. Once started, the engine is then switched back to neat ethanol. Ethanol used as a fuel in Brazil is hydrated ethyl alcohol, which is a mixture of 96% of ethanol and 4% of water (this is the purest form of ethanol that can be achieved via distillation). However, since the E nomenclature is not adopted in the country, one can tag hydrated ethanol as E100 so as to say that it doesn't have gasoline. Gasoline itself is sold as E20 up to E25, in accordance with current legislation (since February 2006, the concentration ranges from 19% to 21%), but since the value is not typically disclosed by gas stations, adulterations to lower gas costs could rise the ethanol concentration up to 40% in extreme cases .
See also
"Common ethanol fuel mixtures"