Effect of alcohol on the properties of water-in-diesel microemulsion fuels

Microemulsions are thermodynamically stable alternatives to diesel, which could be directly used in the engine, without any modification. Surfactant-free water-in-diesel microemulsions with 60.0-70.0% (vol/vol) diesel, 29.0-39.5% (vol/vol) butanol, and 0.5-2.0% (vol/vol) water were formulated, and their properties were compared against standard specifications of diesel fuel oil (ASTM D975). The calorific values of the microemulsion fuels (41.23-44.75 MJ/kg) were higher than the volume-fraction weighted averages (39.20-40.75 MJ/kg). The cloud points (-0.5 to -3.5 degrees C) were lower than expected (0 degrees C). The specific gravities (0.825-0.831), viscosities (2.16-2.39 mm(2)/s), and sulfur contents (27-45 mg/kg) were also within the permissible limits. Some of the microemulsions showed improved cetane indices (cetane index up to 49.5), while the microemulsions with higher butanol percentages, for which cetane index reduced to 38, would require the use of cetane improvers. Since these microemulsions satisfied the ASTM specifications, they could be potentially used as a cleaner alternative to diesel.