26 April 2007
The European Commission has added a particle number limit to its Euro 5/6 proposed emission standards for light-duty vehicles. Particle number emissions from diesel cars would be measured according to the procedure developed by the Particle Measurement Programme (PMP). It is the first introduction of a particle number emission limit in any diesel emission regulation for new engines or vehicles in the world. The revisions were introduced last month to the technical part of the proposed regulation.
The proposed number emission limit of 5 × 1011 particles per km would be applicable to all categories of light-duty diesel vehicles at the Euro 5 (2009.09) and Euro 6 (2014.09) stage. Only solid particles are counted, as volatile material is removed from the sample, according to the PMP procedure. The proposed numerical limit reflects the technical capabilities of diesel engines fitted with wall-flow particulate filters. The limit is very stringent—it is believed that wall-flow filter materials with larger pore sizes, such as those being developed for coating with complex catalyst systems for simultaneous NOx and PM emission reduction, may actually fail the proposed standard.
The PMP procedures have also been adopted for mass-based PM measurements at the Euro 5/6 stage. To account for the difference between the PMP and the existing methods, the proposed Euro 5/6 mass-based PM limit has been changed to 3 mg/km (from the previous 5 mg/km). The PMP procedure—which is similar to the US 2007 method—produces lower PM mass results than the currently used methods.
The Euro 5/6 legislation is being developed under a rather complex “split-level” regulatory approach which involves two Directives: (1) a main, political Euro 5/6 directive and (2) a technical (“implementing legislation”, also referred to as “comitology”) Directive. The political Euro 5/6 Directive (adopted through the European parliamentary law-making process) is expected to be finalized within a few months. The time frame for the adoption of the technical Euro 5/6 Directive (developed in a simplified process by the European Commission, without the involvement of the Parliament) remains unclear. The PMP procedures to be referenced, developed under the auspices of the UN ECE GRPE group, have not yet been finalized by the UN ECE.
The introduction of the number-based PM emission limit seems to be an “insurance policy” that particulate filters—the best available technology to control PM emissions—continue to be used on new diesel engines in the future. The European regulators intended to force the use of particulate filters by legislating increasingly more stringent mass-based PM emission limits at the previous stages, but they underestimated the potential of in-cylinder emission controls. The usage of particulate filters on Euro 4 cars, common in France, Germany, and some other countries, is voluntary, and in most cases not needed to meet the Euro 4 PM standard of 25 mg/km.
Source: European Commission