Evaluation of hydrous ethanol as a fuel for internal combustion engines: A review

Ethanol has been extensively used worldwide as a renewable biofuel to partly substitute fossil fuels, aiming to reduce pollutant and greenhouse gas emissions. However, due to the azeotropic points of water and ethanol, the production of anhydrous ethanol is energy intensive as significant energy is consumed in the distillation and dehydration processes. Therefore, the direct use of hydrous ethanol in engines can dramatically conserve energy and reduce costs. Under this background, this review focuses on the direct use of hydrous ethanol in internal combustion engines. This paper begins with a brief description of the fuel physicochemical properties relevant to engine applications. Furthermore, fundamental combustion characteristics, including the laminar burning velocity, ignition delay time and flame instability, are introduced. Then, the applications of hydrous ethanol or its blends with gasoline in spark ignition engines are summarized. Next, compression ignition engines running on hydrous ethanol in blended and dual-fuel modes are described. Subsequently, the use of hydrous ethanol in advanced combustion concepts, such as homogeneous charge compression ignition and thermally stratified compression ignition, is reviewed. Finally, the conclusions are presented and recommendations for future research are proposed.