Oxidation and nanostructural characterization of exhaust particulates from gasoline/diesel dual-fuel combustion

It is commonly accepted that gasoline/diesel dual-fuel combustion is an effective path to simultaneously reduce particulate matter and nitrogen oxides. However, how such a combustion mode affects soot oxidation reactivity and related features is not well known. This work focused on physicochemical characteristics of carbonaceous particulates emitted by a gasoline/diesel dual-fuel engine with 20% and 40% gasoline premixed substitutions (G20 and G40, respectively), under different engine speeds. Thermogravimetric (TG) results showed that under both engine speeds, particles from dual-fuel combustion were easier to be oxidized and had higher volatile organic fraction (VOF) than diesel particles, following the order G40 > G20 > diesel. Also, particles at lower engine speed exhibited higher oxidation reactivity and VOF. Samples from dual-fuel combustion exhibited a disordered nanostructure, characterized by shorter fringe length but larger tortuosity from high-resolution transmission electron micrograph images and higher I_D1/I_G and A_D1/A_G values from Raman spectroscopy. The structure–property relationship showed that more amorphous nature in the nanostructure of dual-fuel soot brought about the increase in oxidative reactivity. However, surface oxygen content obtained by X-ray photoelectron spectroscopy was not a significant indicator affecting soot oxidation reactivity in this work.