Soot particles undergo in-cylinder oxidation again via EGR recirculated gas: Analysis of exhaust soot particle characteristics

Exhaust gas recirculation (EGR) is one of the effective methods to control NOx emission from diesel engine. The present study focused on the amount of soot particles that are back into the engine cylinder via EGR recirculated gas, to explore its influence mechanism on exhaust soot particle characteristics. A DPF (diesel particulate filter) was integrated in EGR loop, which was employed to remove recirculated soot particles and reduce PM emissions. A comprehensive set of experimental techniques were used to characterize the morphology, nanostructure, surface functional groups and oxidation behaviors of soot particles. Results revealed that when soot particles underwent in-cylinder oxidation again via EGR recirculated gas, exhaust soot particles had smaller primary particle size (dp), longer fringe length (La), smaller separation distance (Ds) and tortuosity (Tf), as well as lower relative amount of aliphatic C-H group and oxidation reactivity. Due to higher graphitization degree of recirculated soot particles, the internal burning was conducted earlier during oxidation processes, which resulted in hollow structure at 50% and 75% burn-off stages.