Monohydric aliphatic alcohols as liquid fuels for using in internal combustion engines: A review

The environmental and air pollution brought about by the increasing energy consumption has increased the interest in the use of renewable energy sources in the transportation sector, where internal combustion engines are used, which is responsible for a large part of the exhaust emissions. Alcohol fuels have been evaluated as renewable energy sources for utilising in internal combustion engines and they are reported to have lowering exhaust emissions and costs. This study analyses four monohydric aliphatic alcohol fuels (methanol, ethanol, propanol and butanol) by reviewing the available literature to represent their applicability as an alternative fuel in internal combustion engines. In the study, researches on the directly use of acetone–butanol–ethanol and isopropanol–butanol–ethanol as alcohol fuel were also examined because the production of butanol by acetone–butanol–ethanol and isopropanol–butanol–ethanol distillation is costly, and isopropanol–butanol–ethanol is more preferred due to the corrosive feature of acetone. The higher fuel consumption of alcohol fuels than fossil fuels was the most common result, with reductions in NO_x and smoke emissions except for isopropanol–butanol–ethanol, which had higher NO_x emissions. It has been reported that less carbon and high oxygen content, low cetane number and high latent heat of alcohol fuels are responsible for the above results. The increase in thermal efficiency with the use of acetone–butanol–ethanol and isopropanol–butanol–ethanol in contrast to other alcohol fuels was a notable result. A comparison among the alcohol fuels showed that methanol was more effective than ethanol in reducing CO, unburned HC and smoke emissions while isopropanol–butanol–ethanol demonstrated high NO_x emissions. A simultaneous reduction of NO_x and Smoke emissions, which was commonly reported for most of alcohol fuels, makes a significant contribution to the development of internal combustion engines. This study gains importance in terms of comparing the individual effects of the use of alcohol fuels on exhaust emissions and better understanding the current status of these fuels.