Comparing real-world off-cycle NOx emissions control in Euro IV, V, and VI

Published: 2015.03.02

Heavy-duty vehicles built and certified in conformity to Euro IV and V emissions standards frequently do not achieve the real-world NOx emissions expected under those standards. Now data is becoming available to show whether new certification protocols in the Euro VI regulation resolve this problem. The evidence thus far indicates that under Euro VI NOx emissions are indeed meeting expectations, even in the most difficult operating conditions. As a result, Euro VI standards may achieve a much greater reduction in NOx emissions from Euro IV/V levels than the emissions limits alone would indicate.

Euro IV and V vehicles tend to produce a wide range of real world emissions. In tests conducted recently at VTT Technical Research Centre of Finland, the Euro IV emissions ranged from just under 2.8 to 11.3 gNOx/kWh, with an average of 6.5 g/kWh, and the Euro V emissions ranged from 0.9 to 9.7 gNOx/kWh, with an average of 4.4 g/kWh. The Euro VI vehicles showed a much smaller range, 0.01 to 0.50 gNOx/kWh, with an average of 0.13 g/kWh.

The results of this recent round of tests indicate that going directly from Euro IV to Euro VI will achieve a larger NOx reduction than the 88% reduction in certification level would indicate. In practice, the reducdtion is likely closer to 98%, and could be even higher due to the fact that real-world Euro IV/V emissions are much higher than the emissions limits would indicate. Euro VI standards not only ensure lower NOx emissions but can also give regulators confidence that off-cycle NOx emissions should no longer be an issue even for low-speed urban vehicles.

Although it is possible to adopt supplemental or improved test procedures for Euro IV/V vehicles (as is being done in China ), the best solution is to implement Euro VI. In addition to lowered real-world NOx emissions, the stricter standard brings additional benefits — e.g., a significant reduction in particulate matter emissions. Although these results clearly show that Euro VI standards are working effectively, in-use compliance and enforcement programs will help ensure a successful and well-rounded approach to HDV emissions control.