Comparison between limit values for NOx, PM and CO2 from EU type approval regulations (black clouds) to emissions in “real life” city traffic from the average Euro 6 diesel passenger car on the Helsinki city cycle. Measured at +23 °C (red clouds) and -7 °C (blue clouds). The size of the red and blue clouds indicate the difference in emissions from the emissions in the type approval test (NEDC). Figure credit: Institute of Transport Economics. Click to enlarge.

Based on the measurements of the 12 heavy vehicles with new Euro VI approved engines and seven Euro 6 approved cars with diesel engines, they drew two clear conclusions when it comes to exhaust emissions:

• All the tested heavy vehicles with Euro VI engines have very low emissions of NO_x and PM in real traffic. The tested NO_x and PM emissions were less than 1/10 of that from previous generations of city buses and other heavy vehicles with Euro VI engines, more or less regardless of the driving cycle used when testing.

• Euro 6 type-approved private cars with diesel engines have 4-20 times higher emission of NO_x in city traffic and during cold weather than the type approval limit value (0.08 g/km). The average emission of NO_x from the tested Euro 6 private cars with diesel engines was also about four times higher than the average emission from the tested city buses and heavy vehicles with Euro VI engines.

One caveat is that no heavy vehicles have yet been tested in cold weather conditions. Although the researchers believe that heavy vehicles with Euro VI engine will have low emissions of NO_x even in cold test conditions, they will test this during the winter 2015/2016.

We notice that new private cars with diesel engines generally have trouble complying with the limit values for NO_x from the type approval, when used in real life city traffic. The type approval of light vehicles is conducted by driving the NEDC driving cycle (New European Driving Cycle). The NEDC driving cycle has low acceleration levels and provide emission values of NO_x and NO₂ which is lower than emissions when driving in real city traffic, and often significantly lower than emissions when starting and driving in cold weather conditions (-7 °C).

—TØI Report 1407/2015

In real traffic, Euro 5 diesel cars and the seven tested Euro 6 passenger cars with diesel engines generally have low emissions of particulate matter (PM). The PM limit value for Euro 6 approval is significantly higher than what the researchers measured from new Euro 6-approved diesel vehicles under all driving conditions. In other words, new diesel cars have efficient and well-functioning particulate filters.

Modern heavy vehicles—including city buses with Euro VI engines—also have low emissions of NO_xand exhaust particles (PM) for all types of test cycles. The reductions are more than 90% compared to the emissions from previous Euro V generations. Indeed, the researchers found that NO_x emissions from the light duty vehicles exceeded those from the city buses.

New heavy vehicles with Euro VI approved diesel engines have very low emission of all types of local emissions. NOx emissions from new passenger cars with Euro 6 diesel engines under demanding city driving conditions is still a challenge for urban air quality. The emissions shown are typical for demanding city-driving for passenger cars and city-buses, respectively. Figure credit: Institute of Transport Economics. Click to enlarge.

For fuel consumption and exhaust emissions of CO₂, the values from all kinds of new light vehicles are higher than what is measured in the NEDC cycle type approval testing. A car that has low CO₂ emissions in type approval will have, as a rule, emissions ranging from 20-95% higher in real traffic. A car that has high CO₂ emissions in type approval will have even higher emissions in real traffic. The low emission values from the type approval may give the impression that the cars are more environmentally friendly than they actually are, the researchers said.

The problem of harmful local emissions has more aspects than the discussion about fuel consumption, and petrol versus diesel. The real challenge is the emission of PM and NO_x from older vehicles, as well as NO_x and NO₂ emissions from new Euro 6 diesel cars in real traffic and during cold weather conditions.

—TØI Report 1407/2015

The study was funded by the Norwegian Public Roads Administration, as part of the “EMIROAD” program.

Resources

• TØI Report 1407/2015. Emissions from new vehicles - trustworthy? Authors: Rolf Hagman, Christian Weber and Astrid H. Amundsen

• TØI Report 1405/2015. Emission from vehicles with Euro 6/VI-technology. Authors: Christian Weber, Rolf Hagman, Astrid H. Amundsen

• TØI Report 1259/2013. Exhaust emissions from vehicles with Euro 6/VI technology. Authors: Rolf Hagman and Astrid H. Amundsen