Sub-23 nm Particulate Emissions from a Highly Boosted GDI Engine

The European Particle Measurement Program (PMP) defines the current standard for measurement of Particle Number (PN) emissions from vehicles in Europe. This specifies a 50% count efficiency (D50) at 23 nm and a 90% count efficiency (D90) at 41 nm. Particulate emissions from Gasoline Direct Injection (GDI) engines have been widely studied, but usually only in the context of PMP or similar sampling procedures. There is increasing interest in the smallest particles - i.e. smaller than 23 nm - which can be emitted from vehicles. The literature suggest that by moving D50 to 10 nm, PN emissions from GDI engines might increase by between 35 and 50% but there remains a lot of uncertainty. In this work, an existing data set from the Ultraboost engine - a highly boosted engine running at up to 32 bar BMEP - has been evaluated using two filtering methodologies, one with a 50% count efficiency (D50) at 10 nm and a 90% count efficiency (D90) at 23 nm (Filter 1) and the other with a D50 at 10 nm and a D90 at 15 nm (Filter 2) and the results have been compared to PMP equivalent filtering. The effect of engine parameters relevant to highly boosted engines such as exhaust back pressure, EGR, spark and injection timing is analysed, as well as the effect of fuel composition. The results show that an increase in PN emissions of 36% with Filter 1 and 45% with Filter 2 is on average observed with the two different count efficiencies with the baseline fuel.