Experimental investigation into the pore structure and oxidation activity of biodiesel soot

To investigate the effect of diesel fuel and different fatty acid methyl esters (FAMEs) biodiesels on the pore structure and oxidation activity of exhaust soot, an experiment was performed on a 4-cylinder high-pressure common-rail diesel engine fueled with commercial diesel fuel and three types of biodiesels (used soybean oil methyl eater (SME), palm oil methyl eater (PME), and waste cooking oil methyl eater (WME) as the main resources, respectively). Results showed that four kinds of exhaust soot had similar porous morphology, while the C/O ratio of biodiesel soot was lower than diesel soot. The N2 adsorption of four kinds of soot belonged to the multi-layer adsorption of mesopore or macropore media, and the N2 adsorption capacity of biodiesel soot was more substantial than that of diesel soot. The specific surface area, the pore volume, and the fractal dimension of three biodiesel soot were larger than that of diesel soot, and the mean pore size was smaller, which meant that the porosity of biodiesel soot was higher than that of diesel soot, and it had a rougher surface. Biodiesel particles contained more aliphatic C-H surface functional groups (SFGs), which may be related to the adsorption of more soluble organic fractions (SOF) by soot surface. A larger surface area and a higher porosity of biodiesel soot also improved the reactivity of soot. The iodine number and oxygen content of biodiesel had a significant effect on the pore structure and oxidation activity of soot. The low iodine number and high oxygen content of biodiesel (mainly consist of WME) helps to reduce PM emissions and improve the porosity and oxidation activity of biodiesel soot.