Abstract: In connection with the fact that the diesel engine exhaust particulate is characterized by the fractal feature, a mathematical model was built for the trapping efficiency of the fibrous diesel particulate filter (DPF) based on fractal theory, and its correctness was proved. The filtering mechanism, the trapping efficiency, and the pressure drop across the filtering element were analyzed using the fibrous material as DPF element material, and the effect of the particulate fractal dimension on the trapping efficiency was studied. The calculation results showed that the main filtration mechanism of the fibrous DPF are diffusion trapping and direct interception, the role of the inertial trapping is very small. The fibrous filter material appears least efficient in trapping the diesel particulate with size of 200~400 nm. To improve the trapping efficiency in this size range, the filter flow velocity should be reduced, and the filter temperature should be raised to enhance the diffusion trapping mechanism, and the filtering fiber diameter should be reduced, the fiber filling density should be raised to enhance the interception trapping mechanism. Comprehensive considering the trapping efficiency and the pressure drop, it can be concluded that the fiber filling density should be reduced to reduce the pressure drop and the filtering fiber diameter should be reduced to raise the trapping efficiency.

Key words: environment engineering, filtration theory, diesel particulate filter, fibrous filter material, diesel exhaust particles, fractal theory