Numerical Simulation to Study the Effect of Oxygenated Fuels on the Combustion and Emission Characteristics of Engines

Oxygenated fuels, as a potential alternative energy source, are of great significance in promoting the sustainable transition of the energy structure. Through an in-depth analysis of the combustion characteristics of <i>n</i>-butanol and its derivatives, this study not only reveals the potential of these fuels in improving combustion efficiency and reducing pollutant emissions but also provides a scientific basis for promoting the sustainable development of clean energy. <i>n</i>-Butanol is a clean alternative fuel because of its good impermissibility with diesel, volatility, and oxygenation. In this paper, the effects of different blending ratios of <i>n</i>-butanol/diesel fuel on engine combustion and emission were investigated using chemical reaction kinetics combined with three-dimensional simulation, and the chemical mechanism of fuel oxygen in the combustion system on combustion and pollutant generation was revealed. The results show that the addition of <i>n</i>-butanol fuel has a significant effect on both combustion and emission. Since <i>n</i>-butanol has good volatility and low cetane number (CN), the ignition delay time (ID) is gradually prolonged with the increase in the <i>n</i>-butanol blending ratio. The mixture is more homogeneous, the proportion of premixed combustion increases, and the soot emission decreases, while the NO _<i>x</i> emission is not much different. From the chemical kinetics point of view, the ignition of the blended fuel is mainly triggered by the low-temperature active diesel component <i>n</i>-heptane. During the low-temperature reaction before ignition, the OH group produced by <i>n</i>-heptane is occupied by <i>n</i>-butanol, which inhibits the low-temperature dehydrogenation reaction of <i>n</i>-heptane itself. Thus, the ignition of the blended fuel is delayed. At the same time, the addition of <i>n</i>-butanol provided more OH, HO₂, and other oxidizing radicals for the combustion system, which enhanced the in-cylinder oxidation activity and promoted the oxidation of carbon smoke precursors and soot. Moreover, the O atoms in <i>n</i>-butanol combined with C to form a more stable CO, which reduced the amount of C atoms that could form carbon smoke precursors and led to a reduction in soot generation.