Alcohols have an interesting potential as blending components for diesel fuels because of their capacity to reduce soot formation. Because they have increasing routes for their production from renewable sources, they could contribute toward increasing the renewable fraction of these fuels and, therefore, toward reducing the impact of diesel transportation on the global warming effect. To increase the knowledge about the implications of the use of short- and long-chain alcohols/diesel fuel blends in diesel engines, the stability, lubricity, viscosity, and cold filter plugging point (CFPP) have been tested. Blends of methanol, ethanol, propanol, butanol, and pentanol with diesel fuel have been analyzed at 1, 2.5, 7.7, 17, 50, 75, and 90% in volume [including 95% (v/v) in the case of CFPP]. Results have shown that short-chain alcohols depict poor blending stability and low viscosity (mainly for concentrations of ethanol and propanol in diesel fuel blends beyond 22 and 45%, respectively). A synergistic effect was observed in viscosity when moderate concentrations of butanol and pentanol were mixed with diesel fuel. The lubricity of the blends decreases with the alcohol content, but this effect is partially compensated by the alcohol volatility. The blends with the highest restriction of use are those containing pentanol, which should be limited to concentrations below 10% (v/v), because its volatility does not compensate for its lubricating capacity. The use of alcohol/winter diesel fuel blends provides a substantial benefit only when high alcohol concentrations are used. It can be concluded that alcohols can be blended with diesel fuel under low and high concentrations, although to improve the blending stability of short-chain alcohols in medium concentrations, the use of additives or fatty acid esters would be necessary.

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The stability diagrams of ethanol (e)-biodiesel (b)-diesel blends were studied at different temperatures. It was found that biodiesel acts as a stabilizer component in e-diesel blends, except at low temperatures, where it favors the formation of a gelatinous phase. Three blends (two e-diesel and an e-b-diesel) were selected to be tested in a diesel engine, and their performance and emissions were compared to those of a reference diesel fuel. The results show that, with increasing ethanol content in the blends, hydrocarbon emissions increase significantly because of the high heat of vaporization of alcohol, thus promoting the appearance of a nuclei mode. With all of the blends tested, reductions in smoke opacity and particulate matter emissions with respect to diesel fuel are obtained, but these decreases were not lineal with the oxygen content. The oxygen provided by ethanol resulted in more efficiency in the opacity reduction than the oxygen provided by methyl ester (e-b-diesel blend), but in the case of particulate matter emissions, the opposite trend was observed.

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