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The purpose of the present study is to better understand the reaction kinetics of diesel exhaust soot during oxidation process. A thermogravimetric analyzer was used to oxidize real diesel exhaust soot generated from a Euro VI diesel engine under non-isothermal conditions. The Friedman-Reich-Levi method and the Sestak-Berggren model were used to determine the oxidation kinetics. Raman spectroscopy and high-resolution transmission electron microscopy were employed to follow the changes of the soot structure during oxidation. The activation energy gradually increased with increasing conversion level during soot oxidation. The oxidation process of diesel exhaust soot could be described as three-step kinetics, and the calculated conversions fitted the experimental results very well. The kinetic predictions of diesel soot oxidation that were obtained using the proposed kinetic models were more accurate and precise than those with the common first-order model. The structural order increased as oxidation progressed, which was responsible for the increased activation energy. The structural ordering was principally caused by the preferential oxidation of the disordered fraction in the diesel soot, especially for the amorphous carbon, which was oxidized in the initial stage of the oxidation reaction. [Display omitted] • The oxidation reaction kinetics of diesel exhaust soot were studied. • The activation energy of soot gradually increases with conversion during oxidation. • The oxidation process of diesel soot can be described as three-step kinetics. • The developed kinetic models can reflect the soot oxidation process accurately. • The structural ordering of diesel soot causes the increase in activation energy. [ABSTRACT FROM AUTHOR]

Experiments were performed on a CH 4 lean premixed flame to better understand the effect of the oxidation-induced fragmentation of primary particles on soot oxidation reactivity. An aerosol generator was used to homogeneously disperse diesel soot into the flame. Because minimal soot was formed in this flame itself, the information about diesel soot fragmentation was readily obtained. The thermophoretic and probe sampling techniques were used to obtain soot particles at various heights above the burner. The particle size distribution, oxidation reactivity, nanostructure and carbon chemical state of each sample were characterized. The soot reactivity was evaluated in terms of activation energy. The results indicate a higher extent of aggregate fragmentation occurs at moderate soot burnout percentages and that the internal structure in soot is not destroyed during aggregate fragmentation. At higher soot burnout percentages, the internal burning produces more primary particle fragmentation, so that the soot particles exhibit an increase in fringe tortuosity and decreases in fringe length and sp2/sp3 hybridization ratio. These variations in physicochemical properties increase the oxidation reactivity of the soot particles. [ABSTRACT FROM AUTHOR]