Optimization of Engine Efficiency and Emission Characteristics Using Waste Cooking Oil Biodiesel Blends

This study investigates the influence of alternative diesel fuels containing waste cooking oil (WCO) biodiesel on engine performance, combustion efficiency, and exhaust emissions under varying operating conditions. Experimental analysis was carried out for three fuel types – pure diesel, Diesel WCO20, and Diesel WCO40 – by systematically evaluating the effects of load, engine speed (RPM), and air–fuel ratio (λ). The results demonstrated that increasing the biodiesel share significantly improves the combustion quality and reduces harmful emissions. Compared with conventional diesel, WCO20 and WCO40 blends decreased carbon monoxide (CO) emissions by up to 70%, carbon dioxide (CO₂) by 10–15%, and particulate number (PN) by nearly six times. A moderate increase in nitrogen oxides (NOx) was observed for WCO20 due to higher in-cylinder temperatures; however, NOx levels decreased again for WCO40 because of slower combustion and lower temperature peaks. Brake thermal efficiency (BTE) increased by approximately 10%, while brake-specific fuel consumption (BSFC) exhibited a non-linear dependence on biodiesel concentration—initially increasing for WCO20 and later decreasing for WCO40, reaching 254 g/kWh. Statistical tests (Kruskal–Wallis, p < 0.05) confirmed significant differences among fuel types, especially for CO, NO, and PN emissions. Regression and artificial neural network (ANN) modeling (R² up to 0.99) accurately described the relationships between engine parameters and emission behavior. Overall, the 40% WCO blend (WCO40) provided the optimal balance between engine efficiency and emission reduction, proving its potential as a sustainable and environmentally friendly diesel substitute without requiring engine modifications.