Insight into the mechanism of solution organic fractions on soot oxidation activity enhancement

The particulate matter and soluble organic fraction emitted by diesel engine are hazardous to environment and human health. Exploring the effect mechanism of soluble organic fraction on soot oxidation is beneficial for reducing the emissions. In this study, the effects of four different types of soluble organic fractions on the soot oxidation activity and physicochemical properties are investigated. The results show that the attachment of oxygen-containing soluble organic fractions enhances the soot oxidation and reduces the peak characteristic temperature. However, the low volatility soluble organic fractions without oxygen element inhibit soot oxidation. Additionally, the high volatility soluble organic fractions without oxygen element elicit limited effects on soot oxidation. the contents of aliphatic C-H functional groups, carbonyl CO functional groups, and carboxylic acid O-CO functional groups significantly increase after adding oxygen-containing soluble organic fractions, while the limited increase in functional groups is observed in soluble organic fractions without oxygen element. Solid soluble organic fractions adhere to soot particles in the form of small particles, leading a reduction in the initial particle size distribution, while liquid soluble organic fractions exhibit block and chain shapes around the soot particles, which makes the initial particle size distribution increasing. Moreover, the attachment of all soluble organic fractions disrupts the surface order of soot particle, leading to a decrease in soot graphitization. This study is beneficial for revealing the interaction mechanism between soot and soluble organic fractions.