Study on Nanostructure and Oxidation Reactivity of Diesel Engine Exhaust Particulates Burning Methanol/F-T Diesel

In this study, the exhaust particulates of a diesel engine burning methanol/F-T diesel blends were collected. The nanostructure and oxidation reactivity of the particulates were explored using the Brunauer–Emmett–Teller (BET) method, high-resolution transmission electron microscope (HRTEM), and thermogravimetric analysis (TGA), and the relationship between them was assessed via the partial least squares (PLS) and variable importance in the projection (PLS-VIP). The results showed that particulates from methanol/F-T diesel combustion were aggregates composed of several primary particles, and the distribution range of particulate half pore width (R) was 8~76 nm. As the methanol mixture ratio increased, the mean R of particulates decreased, and the particulates′ total pore volume (Vp), specific surface area (SBET), and the fractal dimension (Df) increased. Compared with F-T diesel, methanol/F-T diesel blends particulates showed more disordered structure with a smaller diameter (dp) of primary particles, a shorter fringe length (La), a wider separation distance (d), and a larger tortuosity (Tf). With increasing the methanol mixture ratio, it was also found that the amount of soluble organic fraction (SOF) of particulates increased, while oxidation characteristic temperature and the apparent activation energy (Ea) reduced. The correlation coefficients of Ea with Tf and Df were 0.99 and 0.98, respectively, by the linear fitting, illustrating that they showed the strongest linear relationship with the reactivity among the discussed nanostructure parameters. The VIP values of Df, Tf, Vp, and d, with Ea obtained by the PLS and PLS-VIP, were greater than 1, indicating that they were the chief factors influencing particulate reactivity.