Recent developments in utilizing hydrous ethanol for diverse engine technologies

•Various techniques to employ hydrous ethanol in engines is critically reviewed.•Hydrous ethanol showed the reasonable cost savings in engine fuel.•Complete combustion is achieved by using hydrous ethanol.•Hydrous ethanol reduces NOx and soot emissions significantly. This study presents the way to use renewable fuel like ethanol in its hydrous form. The higher cost required for anhydrous ethanol production beyond the azeotropic point is the need to use ethanol in the hydrous form. As ethanol can be produced from a renewable energy source using various bio-mass, many countries are targeting to increase ethanol usage as fuel. Specific methods for using hydrous ethanol in SI and CI engines are discussed. Blending hydrous ethanol with gasoline and diesel using various additives is a good alternative for using biofuel-like ethanol in its hydrous form. Combustion techniques like (GPI+EDI), HCCI, RCCI, and PCCI have incorporated hydrous ethanol, reducing harmful emissions like NOx and Soot with good energy conversion efficiency. Using hydrous ethanol as an engine fuel has shown reasonable cost savings in countries like the USA, India, and Brazil. [Display omitted]