In Europe, the average amount of NOx present in exhaust emissions from modern diesel passenger cars under real-world conditions is more than double the levels from modern trucks and buses, according to a new briefing paper released by the independent research organization International Council on Clean Transportation (ICCT).
The ICCT paper shows data for 24 Euro VI buses and trucks, some tested on a chassis dynamometer by the Technical Research Centre of Finland (VTT), and others tested on-road using portable emissions testing equipment by the German type-approval agency KBA. On average, NOx emissions of the heavy-duty vehicles tested were approximately 210 mg/km. Currently, NOx emissions of Euro 6 diesel passenger cars under real-world driving conditions are approximately 500 mg/km, as determined by testing carried out by KBA and other European type-approval agencies. In addition, the average conformity factor—the ratio of the test result to the regulatory limit—for the heavy-duty engines was less than 1, meaning that on-road emissions stayed below the Euro VI engine type-approval test limits.
Further, CO2 emissions—which are proportional to fuel consumption—for heavy-duty vehicles are roughly five times those of cars. In other words, on an engine-load basis, heavy-duty vehicles are about 10 times better than light-duty diesels at reducing NOx.
The differences are attributable in large part to differences in how light-duty and heavy-duty vehicle emissions are regulated, according to Rachel Muncrief, ICCT researcher and author of the paper. Significant real-world emissions and conformity-factor reductions were accomplished in the transition from Euro V to Euro VI heavy-duty vehicle standards.
Among the significant changes between Euro IV/V and Euro VI that likely contributed to that improvement were:
Addition of an off-cycle test during type approval.
Improved type-approval test cycle that includes cold start and lower load conditions as well as transient and high-load conditions.
PEMS test for in-service conformity testing, with limited restrictions on the boundary conditions used during the test and subsequent data processing.
In its current form, the Euro 6 regulation for diesel passenger cars makes none of the three changes (aside from cold-start and lower-load conditions), which is likely contributing to the high in-use emissions of these cars. The current Euro 6 regulation does not include transient or high-load test, does not include an off-cycle test, and does not include a PEMS in-service conformity test.—“NOx emissions from heavy-duty and light-duty diesel vehicles in the EU”
The contrasting performance highlights the importance of an upcoming decision on strengthening the real-driving emissions (RDE) test for passenger cars in the EU.
The significantly lower NOx emission levels of trucks and buses are most likely a result of differences in regulation. Official testing requirements of light-duty vehicles remain limited to laboratory measurements of carefully prepared prototype vehicles.
In contrast, for measurement of NOx emissions from trucks and buses, mobile testing devices became mandatory in 2013. As a consequence, randomly selected vehicles can be tested under real-world driving .— Dr. Peter Mock, Managing Director of ICCT in Europe
Similar tests with portable emissions measurement systems (PEMS) will be introduced for passenger cars beginning in September 2017, as part of the European Real-Driving Emissions (RDE) regulation. That should bring about a significant improvement in the NOx emission levels of diesel cars, the ICCT said. But further improvements in the light-duty vehicle testing protocols will be needed to truly measure and control NOx emissions.
According to the current status of the RDE regulation, vehicle manufacturers will still be allowed to carefully select special prototype cars for emissions testing. Instead, it would be much better to measure the emissions of ordinary mass-production vehicles, obtained from customers who have had been driving them in an ordinary way, and not from the manufacturers.—Peter Mock
The European Commission, despite resistance from some vehicle manufacturers and EU member states, plans to bring forward for discussion a package of possible revisions to the existing RDE regulation as part of a working group meeting on 17 January in Brussels. The package would include, among other changes, provisions for testing in-use, privately owned cars by independent third parties.