An experimental study on particle number, micromorphology and nanostructure characteristics of particulate matter from a China Ⅵ gasoline direct injection engine

This study investigated the variation of particle number (PN), morphological features and nano structural parameters of particulate matter (PM) from a China Ⅵ GDI engine under different working conditions, oxidation temperatures, and aerodynamic diameters. The results showed that, particles with a diameter less than 10 nm or 23 nm accounted for 40–65% and 68–94% of total PN respectively. Engine speed has a larger effect on PN emissions with the diameter less than 10 nm. PM emitted from the GDI engine were mainly consisted of primary particles with a diameter of 12–72 nm. Primary particles were composed of numerous graphite fringes with a length of 0.1–1.8 nm, tortuosity of 1.10–2.65, and separation distance of 0.2–1.6 nm. The boundaries of primary particles became vague, the fringe tortuosity and separation distance decreased with the progress of oxidation. Particles in larger aerodynamic diameters were more likely to form cluster-like PM in micromorphology. PM accumulated by particles with an aerodynamic diameter of 52.1 nm had larger fractal dimension, smaller fringe length, higher fringe tortuosity, and greater fringe separation distance, and was more easily be oxidized.