Comparative Study of the Physical and Chemical Characteristics of Particulates from Diesel and Gasoline Direct Injection Engines

Particulate matter (PM) from internal combustion engines poses substantial environmental and mechanical risks, yet systematic comparisons of PM properties across Stage VI engine types and existing forms remain limited. Herein, three typical PM samplesdiesel exhaust PM (DS), gasoline direct injection (GDI) exhaust PM (GS), and diesel lubricant-derived PM (LS)were comprehensively characterized using high-resolution transmission electron microscopy (HR-TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA), coupled with statistical validation via one-way ANOVA. All PM samples exhibited a core-shell nanostructure, but their structural parameters differed significantly: DS (57.8 ± 2.17 nm) had the thickest graphitic shell (14.39 nm) and lowest fractal dimension (1.71 ± 0.044); GS (45.5 ± 2.05 nm) showed the smallest size, thinnest shell (11.65 nm), and highest fractal dimension (1.79 ± 0.022); and LS (51.2 ± 2.92 nm) displayed friction/additive-modulated compactness (1.76 ± 0.036). Elementally, DS/GS were dominated by C/O, while LS uniquely contained lubricant-derived Ca (1.07 wt %), S, P, and Zn (primarily as CaSO(4)/CaO) with higher O content (15.43 wt %). GS had the highest surface CO proportion (7.7%). Raman analysis revealed that LS had the highest graphitization degree (lowest A_D(1)/A_G ratio), followed by DS and GS. Oxidation reactivity (assessed via apparent activation energy, E) was synergistically regulated by graphitization and surface/structural properties: GS exhibited the lowest E (197.01 ± 2.19 kJ·mol(-1), highest reactivity) due to low graphitization and abundant active sites; DS had the highest E (205.46 ± 2.09 kJ·mol(-1), lowest reactivity); and LS (201.94 ± 2.08 kJ·mol(-1)) showed lower E than DS, as additive adsorption and small size offset high graphitization's inhibitory effect. These findings provide critical insights for optimizing GDI engine aftertreatment systems (e.g., low-temperature diesel particulate filters) and antipollution lubricant formulations, aligning with sustainable development goals for clean energy and public health.