Understanding the role of exhaust gas recirculation in gasoline/diesel dual-fuel combustion soot features

Exhaust gas recirculation (EGR) can not only mitigate the pressure rise rate but also reduce the NOx emissions in dual-fuel combustion, especially at high loads. With the introduction of EGR, the thermal, chemical, and dilution effects may alter the soot oxidation reactivity and related features. However, little research has been conducted on the effect of EGR on dual-fuel combustion soot features. The paper targets this gap by assessing the oxidation reactivity, morphology and nanostructure, and oxygenated surface functional groups of particulates from dual-fuel combustion with various EGR ratios. The results from thermogravimetric analysis showed that increasing EGR ratios decreased the mass distribution of volatile organic fraction and soot oxidation reactivity under the operating point. This indicated that introducing EGR in dual-fuel combustion would increase the regeneration temperature of diesel particulate filters. Owing to the dilution and thermal effects, mean primary particle diameter gradually increased with the increasing EGR ratio. Soot particulates produced by higher EGR ratios tended to a more graphitic structure, characterized by longer fringe length but smaller tortuosity from high resolution transmission electron micrograph (HRTEM) images. The Raman results also verified the observations from HRTEM. In addition, the concentration of C-OH slightly reduced with increasing EGR ratio, while that of C=O showed no clear trend.