Study on the restructuring of soot particles from diesel engine exhaust gas discharged into a simulated atmospheric environment

Abstract

This paper investigates the restructuring of soot particles from a diesel engine (operated at low and high (30% and 90%) loads of 1200 rpm) exhaust gas discharged into a simulated atmospheric environment. The morphological characteristics of soot particles during the aging times of 0 min, 30 min, 60 min, 120 min, and 180 min were observed by transmission electron microscopy (TEM) to analyze the changes of primary particle diameter (dp), the radius of gyration (Rg), aggregation parameters (aspect ratio, roundness, and root form factor) and fractal dimension (Df) of soot. The results indicate that the dp of the low-load soot tends to increase in the 0–30 min aging period and then it behaves smoothly till to 180 min, while the dp of the high-load soot tends to decrease and then increase, with the minimum value of dp occurring at 60 min of aging. In terms of Rg, the low-load soot appears to age more quickly than the high-load soot, owing to the shorter branch chains for the low-load soot than that for the high-load soot. The trends in the aspect ratio (AR), roundness (RN), and root form factor (RFF), of soot during aging indicate that soot is developing towards a more compact aggregation, especially for the low-load soot. In addition, the Df value tends to increase during the aging process for the low- and high-load soot, but compared to the high-load soot, the low-load soot shows a higher aging degree and faster aging speed during the aging process.