The role of surface functional groups and nanostructure on the oxidation rate of soot derived from an oxygenated fuel

This study addresses the effect of n-butanol as an oxygenated compound on soot oxidation rate of diesel surrogate. Soot oxidation rates of different n-butanol/n-dodecane mixtures were studied experimentally in a two-stage burner, where soot was produced in a first-stage premixed burner, while in a second stage the soot was oxidized under slightly-rich conditions. Particle size distributions (PSDs), were measured on the second burner to evaluate the soot oxidation rate. A detailed kinetic model was used to predict OH concentration in the secondary flame. Gas-phase compounds, O₂, CO, CO₂, H₂, were measured to validate the result of detailed kinetic model. The concentrations for O₂and OH were used to determine the contribution of each oxidizer during the oxidation process. OH was found to be the principle oxidizer and the role of O₂was not significant in the oxidation process. Further analysis showed that OH reacting with a radical site (oxy-radical) on the surface of the soot particle turned out to be the primary mechanism for soot oxidation. Surface chemistry analysis by X-ray photoelectron spectroscopy (XPS) revealed comparable surface functional groups for soot samples derived from different n-butanol/n-dodecane mixtures. This observation suggested that the fuelbound oxygen in the n-butanol did not contribute in the soot particle surface.