Throughout history, alcohols have been used as a fuel. The first four aliphatic alcohols (methanol, ethanol, propanol, and butanol)are of interest as fuels because they can be synthesized chemically or biologically, and they have characteristics which allow them to be used in internal combustion engines. The general chemical formula for alcohol fuel is CnH2n+1OH. Most methanol is produced from natural gas, although it canbe produced from biomass using very similar chemical processes. Ethanol is commonly produced from biological material through fermentationprocesses. However, ethanol that is derived from petroleum should notbe considered safe for consumption as the mixture contains about 5% methanol and may cause blindness or death. Biobutanol has the advantage in combustion engines in that its energy densityis closer to gasoline than the simpler alcohols (while still retaining over 25% higher octane rating); however, biobutanol is currently more difficult to produce than ethanol or methanol. When obtained from biological materials and/or biological processes, they are known as bioalcohols (e.g. "bioethanol"). There is no chemical difference between biologically produced and chemically produced alcohols. One advantage shared by the four major alcohol fuels is their high octane rating.This tends to increase their fuel efficiency and largely offsets the lower energy density of vehicular alcohol fuels (as compared to petrol/gasoline and diesel fuels), thus resulting in comparable "fuel economy" in terms of distance per volume metrics, such as kilometers perliter, or miles per gallon.

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