With Post Euro 6 emission standards in discussion, stricter particulate number (PN) targets as well as a decreased PN cut-off size from 23 to 10 nm are expected. Sub-23 nm particulates are considered particularly harmful to human health, but are not yet taken into account in the current vehicle certification process. Not considering sub-23 nm particulates during the development process could lead to significant additional efforts for Original Equipment Manufacturers (OEM) to comply with future Post Euro 6 PN emission limits. It is therefore essential to increase knowledge about the formation and filtration of particulates below 23 nm.
In the present study, a holistic Gasoline Particulate Filter (GPF) characterization has been carried out on an engine test bench under varying boundary conditions and on a burner bench with a novel ash loading methodology. PN emissions upstream GPF as well as at the tailpipe are measured to determine the GPF filtration efficiency and the impact on the final PN emission results.
Complete engine map measurements on a Gasoline Direct Injection (GDI) engine show that for a simultaneous increase of engine speed and load, the filtration efficiency increases for sub-23 nm particulates. On the contrary, the filtration efficiency decreases significantly for larger particulates with sizes up to 200 nm. An increasing GPF efficiency can be observed for increasing soot and increasing initial ash load. The share of sub-23 nm PN downstream GPF varies between 7 % and 36 % of the total PN concentration during steady-state operating conditions.