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Because alcohols have limited solubility in diesel, a stable emulsion must be formed that will allow it to be injected before separation occurs. Numerous techniques have been evaluated to allow for the concurrent use of diesel and ethanol in compression ignition engines. Some of these techniques include alcohol fumigation, dual injection, alcohol-diesel fuel emulsions, and alcohol-diesel fuel blends. Among these approaches, only alcohol-diesel emulsions and blends are compatible with most commercial diesel engines. Since emulsions are difficult to achieve and tend to be unstable, blends—either as micro-emulsions or using co-solvents—are the most common approach as they are stable and can be used in engines with relatively no modifications.

Blends of ethanol with diesel fuel are often referred to as E-Diesel or eDiesel or oxygenated diesel – a term that is not particularly precise since diesel blends containing methyl ester (biodiesel) or any other additive that includes oxygen can be also described as oxygenated diesel. In e-diesel blends, standard diesel fuel (such as US No. 2) is typically blended with up to 15% v/v of ethanol using an additive package that helps maintain blend stability and other properties such as the cetane number and the lubricity. The additive package may comprise from 0.2% to 5.0% v/v of the blend.

The use of e-diesel can bring some reductions in diesel PM emissions, while contradictory reports exist on its effect on nitrogen oxides, carbon monoxide, and emissions of hydrocarbon derivatives. Perhaps the biggest advantage of e-diesel is its partially renewable character, especially if renewable ethanol is used as the blending stock.

See also: Alcohols, Biodiesel, Butanol, Diesel Fuel, Ethanol, Hydroshear Emulsification, Methanol, Propanol.