Analysis of the microstructure and elemental occurrence state of residual ash-PM following DPF regeneration by injecting oxygen into non-thermal plasma

Particulate matter (PM) capture tests were carried out on clean diesel particulate filters (DPFs) under different loads (25%, 50%, 75% and 100%). DPFs were regenerated by a non-thermal plasma (NTP) injection device. Raman spectroscopy and x-ray photoelectron spectroscopy were used to investigate changes in the microstructure and element occurrence state of the sediment in DPF channel before and after regeneration. The order of the PM samples decreased before NTP treatment as the load increased; the amorphous carbon content was high, and the oxidation activity was higher. After NTP treatment, the carbon atoms at the edge of the microcrystalline structure in the ash-PM samples were oxidized, and the structure was reorganized; in addition, the amorphous carbon content decreased, and the structure was more diversified. Before NTP, the C element of PM samples was the main component, and the content of the O element was relatively low. The C element occurred in the form of C–C, C–OH, and O–C=O functional groups, and O atoms were mainly combined with C–O. After NTP, the content of Na, P, S, Ca, and other inorganic elements in ash-PM samples was prominent because C atoms were removed by NTP active substances. There were two forms of S element occurrence (SO₄²⁻ and SO₃²⁻); the proportion of SO₄²⁻ was approximately 40%, and the proportion of SO₃²⁻ was approximately 60%. Study of the microstructure and element occurrence of the residues in the DPF channels improved our understanding of the mechanism of the low-temperature regeneration of DPF from NTP.