Using Artificial Ash to Improve GPF Performance at Zero Mileage

Gasoline particulate filters (GPF) with high filtration efficiency (>80%) at zero mileage are in growing demand to meet increasingly tight vehicle emission standards for particulate matter being implemented in US, EU, China and elsewhere. Current efforts to achieve high filter performance mainly focus on fine-tuning the filter structure, such as the pore size distribution and porosity of the bare substrate, or the washcoat loading and location of catalyzed substrates. However, high filtration efficiency may have a cost in high backpressure that negatively affects engine power. On the other hand, it has been recognized in a few reports that very low amounts of ash deposits (from non-combustible residue in the exhaust) can significantly increase filtration efficiency with only a mild backpressure increase. This observation suggests a potential alternative approach to increase zero mileage particulate filtration efficiency by coating the filter with a small amount of very fine, thermally stable particles. In the present study, this new approach is investigated by loading a bare filter substrate with submicron alumina particles generated by an atomizer to fabricate an “artificial ash” coating. The substrate backpressure showed only a mild increase after loading with artificial ash. The FTP weighted average filtration efficiency increased from ~75% for a blank substrate to ~90% after loading with 1.5 g/L of artificial ash. Tests over the WLTC with the ash coated filter showed much reduced soot emission during the cold start and nearly negligible emissions thereafter. The PN emissions were as low as 2×10¹¹ #/km. The study demonstrates the effectiveness of using an ash-like porous fine structure to improve filtration efficiency while minimizing additional backpressure.