Optimizing alcohol fumigation for sustainable combustion of waste plastic oil in common rail direct injection diesel engine

Growing environmental concerns have intensified the search for cleaner fuels and eco‐friendly combustion strategies for internal combustion engines. This study investigates the effects of ethanol and methanol fumigation on the performance, combustion, and emission characteristics on a multi‐cylinder DI diesel engine operating on blends of waste plastic oil (WPO). Tests were conducted with fumigation rates varying from 20 to 100 g/h to quantify brake thermal efficiency (BTE), in‐cylinder pressure, total heat release rate (THRR), and NO ₓ /smoke emissions. The maximum performance was achieved at a fumigation rate of 60 g/h at which BTE increased from 26.5% with WPO to 29.8% with methanol and 28.9% ethanol, respectively. The maximum cylinder pressure increased from 72.5 to 76.2 bar with methanol and to 74.8 bar with ethanol, relative to the D80WPO20 baseline. The maximum THRR increased from 70 J/°CA at baseline to 91 J/°CA with methanol and to 89 J/°CA with ethanol. Methanol fumigation decreased NO x emissions by about 15% compared to WPO alone and smoke opacity improved with methanol and ethanol fumigation, decreasing from 52% with WPO to 44% and 46%, respectively, at 80 g/h. In general, methanol showed higher performance because it has a higher oxygen content and vaporizes faster, leading to more complete combustion. Therefore, alcohol fumigation of WPO‐fueled engines is a viable path to improved performance and emission reductions, contributing to more sustainable energy use and environmental protection.