Diesel Particulate Filters: Trends and Implications of Particle Size Distribution Measurement

In order to comply with tightening environmental standards, diesel particulate filters will be used for engine particle emission control. A well-defined testing method is needed to characterize and evaluate the diesel particulate filters. A previously developed testing method yielded unexpected results which were believed to be caused by dilution air contamination and particle formation downstream of the filters. In this study, the testing method has been modified in order to address these issues. Various wall-flow diesel particulate filters of fibrous and porous materials were tested using the modified method in this study. The results were compared with the previous data to evaluate the level of improvement. The results were also analyzed using particle size distributions and filtration mechanisms described by various theories.

Particle size distributions demonstrated significant improvement of the modified testing method. The fractional efficiency data were consistent with theoretical predictions. This paper describes the modified method developed for measuring particle emissions on a mass and number basis. The paper also reports and discusses the fractional efficiencies and the particle size distributions downstream of various diesel particulate filters.