Experimental Investigation of Soot Accumulation and Regeneration in a Catalyzed Gasoline Particulate Filter Utilizing Particulate Quantification and Gas Speciation Measurements

Abstract

Recent particulate regulations for gasoline passenger cars have prompted the utilization of Gasoline Particulate Filters (GPF’s) to mitigate particulate emissions. This study overviews a comprehensive experimental methodology for examination of essential GPF parameters: spatial exothermic temperature rise, particulate trapping efficiency, and the pressure rise versus particulate loading. A GDI vehicle equipped with a subfloor catalytically washcoated GPF downstream of the three-way catalyst was operated on a chassis dynamometer for data collection. Accelerated soot accumulation procedures were developed to expedite the testing while avoiding passive particulate regeneration based on both particulate concentration and size distributions. Soot concentrations pre and post GPF were used to measure the soot trapping efficiency and total soot accumulation. Fuel-cut coast events, common in real-world driving, were utilized to initiate worst case GPF regenerations, namely regenerations which produce maximum temperature rise due to the limited exhaust flow through the GPF. CO2 measurements simultaneously measured before and after the GPF were examined to calculate the quantity of soot burned during each regeneration event. Thermocouples located inside the GPF were implemented to obtain the spatially disparate, transient temperature traces and analyzed to obtain insights on the soot distribution inside the GPF. The maximum exothermic temperature rise within the GPF was tracked for different soot loadings and regeneration temperatures to ensure GPF substrate and catalytic washcoat health. Most initial soot loadings required multiple ‘fuel-cut coast’ regenerations for complete soot oxidation of all trapped particulate mass. Additionally, externally supplied oxygen was utilized to obtain complete GPF regeneration in a single event. This purpose built system created O2 availability while maintaining constant GPF temperatures, similar to actively commanding lean A/F ratios during vehicle operation. Emissions measurements indicated that this system successfully regenerated all GPF soot. However, due to magnitude disparity between exhaust flow and total exothermic heat released, the thermocouples inside the GPF recorded only minimal exothermic temperature rises, providing confidence that lean active regeneration strategies pose little threat to GPF health.