Oxidation-induced variations in the physical and fragmentation characteristics of exhaust soot from DMC-diesel blend: Effect of NO presence in the air atmosphere

Abstract

This study investigated the changes in physical properties (including morphology, primary particle diameter, fractal dimension, and nanostructure) and fragmentation characteristics of exhaust soot from a modern direct injection diesel engine fueled with diesel (D100) and its blend with 7 vol% of dimethyl carbonate (DMC7) during oxidation processes in air and air-NO atmospheres. Soot particles (D100 soot and DMC7 soot) with specific oxidation degrees (0%, 20%, 50%, and 80%) were produced using a thermogravimetric analyzer, then applied to a high-resolution transmission electron microscopy to generate images. The results exhibited that the morphology for D100 soot and DMC7 soot transformed similarly through oxidation, experiencing an increase in fractal dimension, and a decrease in primary particle diameter, while the introduction of NO to the air accelerated these transformations. Additionally, the nanostructure of both soot particles was gradually ordered through oxidation, as evidenced by longer fringe length, narrower separation distance, and lower tortuosity, while DMC7 soot showed lower order degree compared to D100 soot. Interestingly, the ordering processes of soot nanostructure were decelerated as NO was involved in the oxidation process. Furthermore, the aggregate fragmentation rate for both soot particles declined over the oxidation process, while the possibility for primary particle fragmentation increased overall. Moreover, DMC7 soot exhibited significantly lower aggregate fragmentation rate and higher possibility for primary particle fragmentation than D100 soot at the same oxidation stage. This suggests that DMC7 soot is more susceptible to internal oxidation compared to D100 soot. Furthermore, the presence of NO in the air promoted aggregate fragmentation, while reducing the possibility of primary particle fragmentation.