Effects of thermal aging atmospheres on oxidation activity, element composition and microstructure of diesel soot particles

Abstract

As an emission control device for diesel engines, DPF plays an important role in reducing particulate matter emissions. The research work on soot thermal aging will help optimize DPF regeneration strategies, improve regeneration efficiency, and promote the progress of engine emission control technology. In order to explore the influence of thermal aging under different atmospheres on particle physicochemical characteristics from diesel engines, the oxidation activity of soot particles after different thermal aging were evaluated by thermogravimetric analysis (TGA) and pyrolysis kinetics calculation, and the distribution of functional groups and elemental composition on the soot surface were investigated by FT-IR and XPS analysis. Additionally, the microstructure and graphitization degree of basic carbon with O₂/NO₂ aging were analyzed by HRTEM technology. The results show that the ignition temperature and activation energy of soot significantly increase after thermal aging, and their lowest values are 569 °C and 165.29 kJ mol⁻¹ in O₂/NO₂/N₂ atmosphere, respectively. The branching degree and content of hydrocarbon functional groups on the soot surface decrease after thermal aging, and the relative content of hydrocarbon functional groups with NO₂ participating in thermal aging is the highest. The content of O element on the soot surface decreases after thermal aging, and the maximum O/C molar ratio of soot particles after thermal aging in O₂/NO₂/N₂ atmosphere is 0.15. After thermal aging, the hybridization degree of carbon atoms and the content of –C–OH and –CO functional groups on the soot surface decrease. The content of –C–OH functional group decreases to 0.21% and 0.53% respectively after the addition of O₂ and NO₂ in the thermal aging atmosphere, while the content of –CO functional group increases to 4.98% and 5.98% respectively. In addition, the layer spacing and microcrystalline curvature of basic carbon particles decrease after thermal aging, however, the microcrystalline size and the graphitization degree increase.