Optimizing combustion and emission characteristics of waste cooking oil biodiesel blended with dimethyl isosorbide and 1-nitrooctane using tabu search optimization

South Africa relies on imported fossil fuels, and the unregulated disposal of waste cooking oil presents major sustainability challenges. The current study explores the use of waste cooking oil biodiesel with Dimethyl Isosorbide and 1-Nitrooctane in diesel engine applications to enhance combustion, performance, and emission characteristics. Experiments were conducted on a Yanmar L48N6CF1T1AA diesel engine over a speed range of 1200-3000 rpm. Combustion behavior, engine performance, and emissions were analyzed, and the Tabu Search optimization method was employed to determine the optimal blend-speed combination. Gas chromatography mass spectroscopy analysis revealed the biodiesel contains a complex mix of methyl esters, saturated and unsaturated fatty acids, and oxygenated compounds. Results showed a peak in-cylinder pressure of 107.27 bar for biodiesel, 5.86 % higher than diesel. 20 % (v/v) of biodiesel and 4 % (v/v) of 1-Nitrooctane demonstrated the highest brake thermal efficiency (35.86 %) and the lowest brake specific fuel consumption (0.306 kg kWh -1 ). Emission reductions included 48.4 % carbon monoxide with 20 % (v/v) of biodiesel and 8 % (v/v) of Dimethyl Isosorbide, 35.54 % hydrocarbon and 7.9 % oxides of nitrogen with 20 % (v/v) of biodiesel and 4 % (v/v) of 1-Nitrooctane. Smoke opacity decreased by 36.36 % for 20 % (v/v) of biodiesel and 4 % (v/v) of 1-Nitrooctane, though it recorded the highest carbon dioxide emissions (11.71 %). Based on a multi criteria evaluation, 20 % (v/v) of biodiesel and 4 % (v/v) of 1-Nitrooctane at 2400 rpm was identified as the optimal biodiesel-based fuel blend. The study highlights the potential of waste cooking oil biodiesel with performance enhancing additives as a localized, cleaner energy alternative for developing regions.