Exhaust non-volatile particle filtration characteristics of three-way catalyst and influencing factors in a gasoline direct injection engine compared to gasoline particulate filter

Abstract

Three-way catalyst (TWC) integrated gasoline particulate filter (GPF) has become a standard configuration for the aftertreatment of a gasoline direct injection (GDI) engine. Although filtration effects on particulate emissions of GPFs have been widely investigated, effects of TWCs on non-volatile particulate emissions are still ambiguous. In the present work, particle size distributions were measured by DMS500 with hot sampling at three locations: before TWC, after TWC and after GPF. The particle filtration characteristics of the TWC and GPF are compared, and the influencing factors and filtration mechanism are analyzed. The results show that the TWC have obvious filtration effects on exhaust particles, and the total filtration efficiency is 20–35% for the TWC compared to 70–85% for the GPF. The TWC exhibits high efficiency in the small and large particle size ends, indicating the particle collection process in the TWC may resemble the collection process in the GPF. Regarding the influencing factors, the filtration efficiency of the TWC is related to both the exhaust temperature and exhaust flow rate, while that of the GPF mainly depends on the exhaust flow rate. With high engine-out PN concentrations, the filtration efficiency of the TWC on AM particles largely decreases, while the filtration efficiency of the GPF on AM particles increases to >95%. It is believed that in TWCs firstly the small particles are collected by diffusion and the large particles by inertia or gravity collection on the washcoat, and then the collected particles get oxidized with the help of the catalyst.