Controlling Nanoparticle Emissions

May 16, 2023

Topics: Euro 7, Passenger Cars, Transportation, On-Highway Trucks, Fuels

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.

Hardware Implications

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

Lower engine out PN₁₀ is impacted by both fuel and lubricant technology. Fuel injector deposit control will be critical in this area. There can be very large increases in particulate emissions when injector deposits build up, especially in more modern direct injection engines. These deposits may be inside the injector or outside on the tip. High performance fuel additives are very effective at minimizing the PN increase and can also be used at higher concentrations to clean up fouled injectors.

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.

Our View

The tight PN₁₀ limits included in Euro 7, will be one of the most significant changes in terms of the impact on both hardware, fuels and lubricants. Improvements in fuel injection systems, combustion chambers and aftertreatment will enable vehicles to meet the tight limits. Maintaining this level of performance for the extended emissions durability periods included in the legislation, will require high performance fuel and lubricant technology.

For more information on Euro 7, contact your Lubrizol representative.