With the increased use of engines utilizing direct fuel injection and the upcoming introduction of more stringent emissions legislation that regulates not only particulate mass (PM) but also particulate number (PN), the emissions from Direct Injection Spark Ignition Engines (DISI) are an increasing concern. Gasoline Particle Filters (GPF) represent a potential way to reduce particle number emissions from DISI engines and are particularly effective considering the tough performance requirements during cold start and over RDE operation. Even though some learning from the development and application of particulate filters to diesel engines can be transferred to gasoline engines, the particle composition, mass to number ratio as well as the exhaust gas temperature and composition from gasoline engines are significantly different to diesel engines. Therefore, there is the need to study the application of particulate filters to gasoline engines in more depth. Of particular concern, is the understanding of the ash accumulation mechanism within the GPF and its negative impact on the backpressure over lifetime.
This paper presents the results from a fundamental study of an uncoated ceramic GPF in the exhaust after-treatment system of a 1.6 litre turbo DISI engine. Soot and ash accumulation data are reported comparing two aggressive driving cycles (Artemis Urban vs. Artemis Motorway). Each cycle was operated for 20k km on a dynamic engine bench. PN emissions were then measured over WLTC and NEDC test cycles after 20k km. The results are discussed with respect to the differences from each cycle for the ash formation and backpressure increase; it also considers the possibility of extrapolating the results to a more balanced driving pattern over 160k km. Results from the engine bench investigation are compared to a vehicle durability run, using the same engine and type of GPF in the under-floor (UF) location.
Results show PN filtration efficiency of the GPF, above 70% in fresh condition and above 90% with increasing mileage. Further, low soot accumulation and low ash amounts were detected after the durability run was completed. Ash is mainly related to the oil consumption of the engine and small differences were observed between the two Artemis cycles. In particular the Artemis Urban cycle shows higher ash amount over 20k km (1.26 g/l) compared to the Artemis Motorway (0.4 g/l). These ash values from the engine bench correlate well with the findings of the vehicle durability run. Post mortem analysis (PMA) of the GPF after both engine bench and vehicle durability tests are also reported.