Oxygenated chemical compounds contain oxygen as a part of their chemical structure. The term usually refers to oxygenated fuels. Oxygenates are usually employed as gasoline additives to reduce carbon monoxide and soot that is created during the burning of the fuel. Compounds related to soot, like polyaromatic hydrocarbons (PAHs) and nitrated PAHs, are reduced also.
In the United States, the Environmental Protection Agency had authority to mandate that minimum proportions of oxygenates be added to automotive gasoline on regional and seasonal basis from 1992 until 2006 in an attempt to reduce air pollution, in particular ground-level ozone and smog. In addition to this North American automakers have in 2006 and 2007 promoted a blend of 85% ethanol and 15% gasoline, marketed as E85, and their flex-fuel vehicles, e.g. GM's "Live Green, Go Yellow" campaign. U.S. Corporate Average Fuel Economy (CAFE) standards give an artificial 54% fuel efficiency bonus to vehicles capable of running on 85% alcohol blends over vehicles not adapted to run on 85% alcohol blends. There is also alcohols' intrinsically cleaner combustion, however due to its lower energy density it is not capable of producing as much energy per gallon as gasoline. Much gasoline sold in the United States is blended with up to 10% of an oxygenating agent. This is known as oxygenated fuel and often (but not entirely correctly, as there are reformulated gasolines without oxygenate) as reformulated gasoline. Methyl tert(iary)-butyl ether (MTBE) was the most popular fuel additive in the US, prior to government mandated use of ethanol.
Alcohols' (particularly methanol's) solvent properties cause swelling damage to fuel system materials not designed for alcohols, corrosion of metal, increase water contamination, loosening of deposits causing clogging and destruction of fuel system components. This property was demonstrated with methanol in the 1970's and has reappeared to a slightly lesser degree with ethanol. Most forms of automobile racing that require the use of gasoline as fuel (as opposed to higher-energy blended fuels or straight alcohols) prohibit the use of oxygenate compounds in fuels, as they can allow higher fuel burn than the engine intake restrictions are designed to permit. Prior to the 2007 Daytona 500, for example, NASCAR driver Michael Waltrip and his team were heavily penalized when evidence of an unspecified oxygenate compound was found in the car's intake manifold during inspections.
- "Code of Federal Regulations, title 40, part 600, section 600.510-93". United States Government Printing Office. 1 August 2005.