Degradation mechanism of diesel particulate emissions induced by non-thermal plasma

Particulate matter (PM) has serious hazards to the ecological environment and human health. The development of green and sustainable technologies for efficient removal of PM has become an urgent need in the field of environmental engineering. In this study, a non-thermal plasma (NTP) online oxidation decomposition experimental system for PM was established to explore the effects of NTP on the microstructure, oxidation characteristics and carbon and oxygen element composition of PM under different loads (25 %, 50 %, 75 %, and 100 %), and to clarify the effect of exhaust temperature that changes with load on the oxidation and decomposition of PM. The results show that NTP significantly weakened the aggregation degree of PM particles, the proportion of short crystallites (<1 nm) at each load increased significantly, the proportion of small crystallite spacing (<1 nm) increased significantly, and the crystallite curvature decreased significantly at low load. NTP treatment improves the PM graphitization degree, increases crystallite defects, and produces more amorphous carbon. The ignition temperature Ts, burnout temperature Te and maximum oxidation rate temperature Tmax of element carbon (EC) tend to shift to lower temperatures, the oxidation temperature of PM decreases, and the oxidation activity increases. The carbon particle microcrystals contain a large amount of C element. After the microcrystals are cracked, O atoms are continuously typed into the carbon particles, C-C transforms into C-O, the relative content of C element decreases, and C-O is transformed into CO after NTP oxidation. The treatment process of NTP oxidation of PM is fastest at 75 % load due to the moderate treatment temperature range. The research results can provide an online and efficient PM degradation solution for diesel engine exhaust treatment, which has important theoretical value and engineering significance for the purification of atmospheric PM.