Modeling of soot fragmentation that proceeds in a catalyzed diesel particulate filter of a diesel engine

Abstract

Catalyzed diesel particulate filters (CDPFs) are crucial technologies to control the particulate emissions from diesel engines. While obvious drops in filtration efficiencies (FEs) for particle number (PN) occur during the passive regeneration of CDPFs, which can lead to the deterioration of transient emissions. Therefore, in this study, a quasi-2-D model, including a fluid dynamic model, a back-diffusion model, a global kinetic model and a basic filtration model, was established for describing the PN-filtration-behavior of a CDPF. An extended filtration model was developed based on the soot fragmentation hypothesis, considering the effects of the particle diameter, soot load, exhaust gas temperature and flow velocity. An 8.8L, heavy duty diesel engine equipped with a commercial DOC and a CDPF was employed. The particle number and size distributions before and after the CDPF were determined with an engine exhaust particle sizer (EEPS) under eight operating conditions. The extended filtration model was calibrated with the test data, and the model results aligned with those of experiments with a maximal error less than 5% and an average error less than 1%. Then, the undetermined parameters in the extended filtration model were evaluated under the eight working conditions, and distinct regularities were observed among these parameters. The time-dependent PN-filtration-behavior of the tested CDPF was also explored based on the model. According to the model predictions, it was found that the PN-filtration-behavior of a CDPF was different from that of a DPF, and the PN-FE of a CDPF might be still unsatisfactory under the high-soot-load conditions.