Investigation on the evolution in physiochemical properties of soot from ammonia/diesel engines along the after-treatment devices in the exhaust process

Exploring the changes of soot emissions from ammonia/diesel engines in the exhaust process is essential for developing specialized emission control strategies. This study investigates the evolution pattern in physiochemical properties of soot from ammonia/diesel engines along the after-treatment devices. The results show that the C-H and C-N functional groups are formed after soot passing through diesel oxidation catalyst (DOC), while the catalytic diesel particulate filter (CDPF) facilitates the decomposition of C-H groups and the conversion of C-N to C=N functional groups. The degree of soot graphitization gradually increases in the exhaust process, with DOC exhibiting the significant effects on the D1 carbon component, while the CDPF mainly acts on the D3 and D4 carbon components. DOC reduces the degree of soot agglomeration, causing a slight shift in the particle size distribution towards small diameter. In contrast, diesel particulate filter (DPF) or CDPF enhances the soot agglomeration. The orderliness of soot nanostructure increases in the exhaust process, and the length of microcrystals shifts towards large microcrystalline size, accompanied by soot edge oxidation affected by CDPF. The DOC and DPF reduce the content of C=O functional groups, while the CDPF promotes the generation of oxygen-containing groups. In addition, the nitrogen-containing groups such as pyridine structure compounds (N-6), pyrrole structure compounds (N-5) and nitrogen oxides (N-O_x) gradually decrease during the exhaust.