All-round inhibition of soot generation during diesel combustion by oxygenated biomass fuels: A numerical simulation and experimental study

Soot generated from diesel combustion is an important pollutant source in the atmosphere. Meanwhile, oxygenated biomass fuels are potential green alternatives to diesel that suppress soot formation. The purpose of this study is to evaluate the effect of oxygenated biomass fuels (biodiesel and ethanol) on all soot precursors (polycyclic aromatic hydrocarbons (PAHs)) and soot particles during diesel combustion. Kinetic modeling results showed that both biodiesel and ethanol monotonically reduced the concentration of PAHs mainly by inhibiting their production and facilitating their oxidation. Specifically, the C2-C4 content reduced and the O, H, and OH concentrations increased. Ethanol has a more profound inhibitory effect on pyrene than biodiesel, mainly due to the reduction of C2-C4 species and increased production of CO2 and CO. Soot particles generated from the combustion of diesel (D100) and its blends (D0.8B0.2/B0.1D0.8E0.1/D0.8E0.2; D and E represent the volume fractions of biodiesel and ethanol in diesel, respectively) were collected on an in-house premix burner. Soot particles were further characterized using thermogravimetric analysis (TGA), elemental analysis (EA), fourier infrared spectroscopy (FTIR), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM). The activation energy of D100 was found to be significantly higher than that of other soot particle samples. After blending oxygenated biomass fuels, there is an increase in O elements, oxygen-containing functional groups, layer spacing and streak distance inside PAH crystals, and streak curvature in soot particles; however, there is a decrease in C elements, aliphatic functional groups, crystal size and crystal stacking thickness of PAHs, and average stripe length. These changes indicate that oxygenated biomass fuels allow soot particles to exhibit a higher oxidation activity, which reduces the amount of soot generated by diesel combustion.