Abstract: This study aims to analyze the influence of the polycyclic aromatic hydrocarbon (PAH) content in diesel on the physical and chemical properties of diesel soot particles. Four diesel fuels with different PAH content were tested on a 11.6 L direct- injection diesel engine. The raw particulate matter (PM) before the after-treatment devices was collected using the thermophoresis sampling system and the filter sampling system. A transmission electron microscope and Raman spectrometer are used to analyze the physical properties of the soot particles, including morphology, primary particle size distribution, and graphitization degree. A Fourier transform infrared spectrometer and thermogravimetric analyzer are
used to characterize the surface chemical composition and oxidation reactivity of soot particles, respectively. The results show that as the PAH content in the fuel decreases, the size of the primary soot particles decreases from 29.58 to 26.70 nm. The graphitization degree of soot particles first increases and then decreases, and the relative content of the aliphatic hydrocarbon functional groups of soot particles first decreases and then increases. The T10, T50, and T90 of soot from high-PAH fuel are 505.3, 589.3, and 623.5 °C, while those from low-PAH fuel are 480.1, 557.5, and 599.2 °C, respectively. This indicates that exhaust PM generated by the low-PAH fuel has poor oxidation reactivity. However, as the PAH content in fuel is further decreased, the excessively high cetane number may cause uneven mixing and incomplete combustion, leading to enhanced oxidation reactivity.

Key words: Aromatics, Morphology, Nanostructure, Oxidation reactivity