Effects of surface functional groups on the wettability of biodiesel combustion particulate matter

This paper investigates the impact of particle surface functional groups on the wettability of particulate matter (PM) emitted from biodiesel engines. Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectrometry (XPS), and Contact Angle Measurement techniques were employed to detect and analyze PM generated from combustion of diesel, soybean oil methyl ester (SME), palm oil methyl ester (PME), and waste edible oil methyl ester (WME) biodiesels. The results showed that PM derived from biodiesel exhibited a higher content of aromatic nuclei compared to that from diesel. The surface of the PM displayed significantly elevated levels of C–OH functional groups in comparison to CO functional groups, and the relative proportion of C–OH and CO functional groups on the biodiesel-derived PM surface decreased with an increase in biodiesel iodine value. The contact angles of the PM to the diesel droplets were less than 20°, and the PM is highly lipophilic. The wettability of the PM with both water and diesel droplets increased as the relative content of C–OH and CO functional groups rose. Moreover, it was observed that biodiesel-derived PM exhibited superior wettability towards water and diesel droplets when compared to its diesel counterpart, thereby enhancing its susceptibility to wetting by diesel droplets. •Biodiesel particulate matter has a large number of oxygen-containing functional groups on its surface.•Biodiesel particulate matter is hydrophilic and lipophilic.•The wettability of particulate matter increases with the increase of oxygen-containing functional groups on the surface.