A comprehensive CFD study of the spray combustion, soot formation and emissions of ternary mixtures of diesel, biodiesel and gasoline under compression ignition engine-relevant conditions

In this research, the spray combustion, soot formation and exhaust emissions of diesel, biodiesel, gasoline fuels and their mixtures are analysed in a constant volume chamber. A multicomponent kinetic mechanism (CDBG) suitable for diesel-biodiesel-gasoline mixtures developed by our research group is utilised, and the associated physicochemical properties are thoroughly calculated. Adaptive mesh refinement scheme with appropriate mesh independency analysis are applied. Liquid penetration length, lift-off length, ignition delay and soot formation have been benchmarked against experimental data in the literature. A hybrid RANS-LES model, known as DES model, is used to simulate the turbulent condition. The effects of different ambient temperature/oxygen levels on the flame structure, soot formation and emissions of different ternary mixtures of D75|BD20|G5, D70|BD20|G10 and D65|BD20|G15 were analysed. D65|BD20|G15 resulted in a lower soot mass yield than that of BD100 (pure biodiesel) and D100 (pure diesel) for about 35% and 27%, respectively, at T = 900 K | O₂ = 15%. Greater soot mass reductions for the tested fuels were captured by the decrease in ambient temperature from 900 K to 800 K by a factor of ∼1/3 (same ambient O₂ concentration). Lower nitrogen oxides (NO_x) emissions were obtained for D100 by factors of ∼1/2 at T = 900 K | O₂ = 15% compared to BD100. Gasoline-added mixtures revealed lower NO_x compared to BD100 (∼20%) yet still higher than D100. Lower carbon dioxide (CO₂) and carbon monoxide (CO) emissions were captured for D65|BD20|G15 compared to BD100 and D100.