Probing the oxidation reactivity of ultra-low-sulfur diesel soot with controlled particle size and organic mass fraction

Abstract

The oxidation reactivity of soot plays a key role in the regeneration of diesel particulate filters, which are used to prevent atmospheric soot emissions. Thus, discovering correlations between this reactivity and the characteristics of soot is essential. The present study investigated the effects of pyrolysis temperature (1200–1400 °C), fuel mole fraction (0.0007–0.0058), and pyrolysis time (0.15–0.46 s) on the physical and chemical properties of synthesized soot. Ultra-low-sulfur diesel (ULSD) and nitrogen carrier gas were used to synthesize soot under oxygen-free conditions. The particle size and composition were controlled, and the soot nanostructure was modified by adjusting the pyrolysis conditions. The characteristics of soot were analyzed using a transmission electron microscope (TEM), particle sizers, combustion type PM analyzer, and thermogravimetric analyzer (TGA). According to the analysis results, when fuel mole fraction and pyrolysis time were insufficient, high pyrolysis temperature contributed to soot growth and development of a highly ordered graphitic structure. However, with relatively sufficient fuel mole fraction and pyrolysis time, the best soot growth was observed at an intermediate pyrolysis temperature (1300 °C). The synthesized soot had an organic mass fraction (OMF) range of 0.05–0.62, while mass reduction due to oxidation during thermogravimetric analysis appeared at a temperature range of 406–670 °C. In conclusion, the oxidation temperature could be correlated to the primary particle size and OMF, and the pyrolysis conditions played a role in the formation and growth of soot, while the carbonization level attributable to such process affect soot oxidation reactivity.