Evaluation of the Oxidation Reactivity and Behavior of Exhaust Soot Particles from Diesel Engines with Different Emission Levels

The aim of this study was to investigate the oxidation reactivity and behavior of exhaust particulate matter (PM) from diesel engines. PM samples from two diesel engines (1K, CY4102) with different emission levels were collected by a thermophoretic system and a quartz filter. The oxidation reactivity, oxidation behaviors, and physicochemical properties of the PM samples were analyzed using thermogravimetric analysis (TGA), high-resolution transmission electron microscopy (HRTEM), Fourier-transform infrared spectrometry (FTIR), and Raman spectroscopy. The results showed that there was a great difference in the oxidation reactivity of soot particles emitted by the two different diesel engines. A qualitative analysis of the factors influencing oxidation reactivity showed that the nanostructure, degree of graphitization, and relative concentration of aliphatic C-H functional groups were the most important factors, whereas no significant correlation was found between the primary particle size and activation energy of the diesel soot. Based on the oxidation behavior analysis, the diesel soot particles exhibited both internal and surface oxidation modes during the oxidation process. Surface oxidation was dominant during the initial stage, and as oxidation progressed, the mode gradually changed to internal oxidation. Internal oxidation mode of soot particles from the 1K engine was significantly higher than that of CY4102.