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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.

To meet stringent emission regulations, particulate filters will be required for diesel engines. Effective filters should reduce both the mass and number concentrations of particulate matter. For this reason, the performance of diesel particulate filters (DPFs) should be evaluated by measuring both gravimetric and fractional efficiency. This paper reports on a method developed for measuring particulate emissions on a mass and number basis. A two-stage dilution process was used in which the entire engine exhaust gas is directed into a primary dilution tunnel with a critical flow venturi. This constant volume system maintains proportional sampling throughout temperature excursions. A portion of the diluted exhaust gas is directed to a secondary dilution tunnel, for further dilution and determination of particle size distribution using a scanning mobility particle sizer. The engine was run at ISO 8178 modes.