Optimizing waste cooking biodiesel production using ultrasonic-assisted and studying its combustion characteristics blended with diesel in diesel engine

This study aimed to optimize biodiesel production from waste cooking oil using ultrasonic-assisted transesterification and evaluate the combustion characteristics of a diesel engine powered by various biodiesel blends. The effects of transesterification parameters, including reaction time, alcohol-to-oil molar ratio, catalyst concentration, and ultrasonic amplitude, were experimentally investigated. The optimal conditions for achieving a biodiesel yield of 96.65% were found to be a reaction time of 6 min, an alcohol-to-oil molar ratio of 6:1, a catalyst concentration of 1.0 wt.%, and an ultrasonic amplitude of 75% with a duty cycle of 0.7. In the subsequent phase, engine performance and emissions were evaluated for biodiesel–diesel blends at volume ratios of 0:100 (B0), 10:90 (B10), 20:80 (B20), 30:70 (B30), 40:60 (B40), and 100:0 (B100) under varying load conditions at a constant speed of 1500 rpm. The results indicated that biodiesel blends exhibited similar engine performance to diesel, with a slight increase in brake-specific fuel consumption and a minor decrease in brake thermal efficiency. Emission analysis revealed significant improvements, with B100 reducing carbon monoxide (CO), unburned hydrocarbons (HC), and smoke opacity by 42.9%, 29.9%, and 42.1%, respectively, compared to B0. Notably, B40 showed the highest reduction in nitrogen oxide (NO_x) emissions, achieving a 4.94% decrease. These findings suggested that B40 can serve as a viable diesel substitute without requiring fuel system modifications, offering comparable mechanical performance and enhanced emission characteristics.