基于分形理论的纤维材料微粒捕集器捕集效率模型

针对柴油机尾气微粒的分形特性,基于分形理论建立了纤维材料对尾气微粒的过滤效率数学模型,并证明了模型的正确性。应用该模型分析了纤维材料作为微粒捕集器过滤材料时的过滤机理、过滤效率和压降特性,研究了微粒分维数对过滤效率的影响。计算结果表明,柴油机尾气微粒的主要捕集机理为扩散和直接拦截,惯性机理的作用很小。纤维过滤材料对粒径为200～400nm的尾气微粒的捕集效率最低,为了提高这一尺寸范围微粒的过滤效率,应降低过滤流速、提高过滤温度以提高扩散机理的作用,并且减小过滤材料纤维直径、提高填充密度以提高直接拦截机理的作用。综合考虑材料捕集效率和压降,应尽量减小填充密度以降低压降,缩小材料纤维直径以提高捕集效率。

Trapping efficiency model of fibrous DPF based on fractal theory

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.