The use of biofuel emulsions as fuel for diesel engines: A review

Abstract

Animal fats/vegetable oils (called biofuels) and their emulsions are quite promising alternative fuels for diesel engines. This article reports a comprehensive study on the use of animal fats/vegetable oils and their emulsions as fuel in compression ignition engines. Emulsions preparation method and their effects on engine performance, emission, and combustion characteristics have been studied in detail. Information indicates that biofuel emulsions in diesel engines enhanced the combustion efficiency with improved performance as compared to neat fuels. The maximum percentage of water addition to biofuel was found as 30 per cent by volume for maximum efficiency. They reduced NO x, smoke, and particulate emissions considerably. Emulsions resulted in higher ignition delay as a result of vaporization of water as compared to neat fuels. Peak pressure, rate of pressure rise, and premixed combustion rate in the heat release curve were found to be higher when compared to neat oils because of longer ignition delay. Further improvements could be achieved by adding oxygenated fuels like methanol, dimethyl carbonate, and cetane number improvers like diethyl ether with biofuels in small quantities. It has also been suggested that dual fuel operation can significantly reduce particulate and NO x emissions with biofuels. Exhaust gas recirculation can reduce ignition delay considerably with reduced NO x emissions. Finally, modelling techniques were presented because they can help in in-depth analysis of the combustion process of biofuel emulsions in diesel engines.