For many years, the health impacts of particulate matter have been known. Monitoring of particulates in urban areas is widespread and alerts are given when levels are high. When it comes to vehicle tailpipe emissions of particulates, limits have been applied to particles larger than 23 nanometers (nm - one nanometer is a millionth of a millimeter). However, increasing evidence of serious health issues from even smaller particles and developments in particulate measurement technology, has led to the inclusion of particulate number (PN) down to 10 nm (PN10) for the forthcoming Euro 7 legislation. The challenge is increased by the widening of real driving emissions (RDE) test conditions.
Tight PN10 limits mean implications for both engine and aftertreatment hardware. Reducing particulates at source (engine out PN10) is always preferable, so improvements in engine combustion technology will be a priority. Higher injection pressures and finer orifices will be used, and these will be more sensitive to deposits. Inlet valves also need to be kept clean to ensure good airflow into cylinders.
The most significant implications of tight PN10 limits are for aftertreatment, namely particulate filters. Particulate filters are currently widely used on diesel and gasoline direct injection (GDI) engines. They will be universally used on all Euro 7 engines, including more basic port fuel injected (PFI) gasoline engines. The next generation of filters will be capable of controlling particulates right down to 10 nm.
Euro 7 will take into account particulates during filter regeneration—the period during which the soot accumulated within the filter is burned off, preventing filter blockage. Control of when and how the filters regenerate will be important for Euro 7 vehicles.
Fuel and Lubricant Implications
Studies have shown that trace amounts of engine oil burned in the cylinders can impact PN levels, especially around the 10 nm size. However, these can be minimized by using high quality engine oils developed for low emission engines. The engine oil also needs to be compatible with the aftertreatment used. As Euro 7 particulate filters will be designed to filter much finer particulates, the choice of engine oil will be even more critical in order to prevent filter blockage due to ash and to ensure catalytic coatings remain in good condition.
For more information on Euro 7, contact your Lubrizol representative.