In-use NOx emissions from Euro V trucks higher than anticipated
24 March 2010
Under real-life driving conditions, NOx emissions from Euro V trucks fitted with urea-SCR systems are only marginally better than emissions from Euro III trucks, even though the Euro V NOx standard is 60% lower than the Euro III standard, according to a recent Dutch study conducted by TNO. Real life truck emissions from Euro V trucks during urban driving were found to be about 3 times higher than the regulatory levels. The emissions approached the regulated levels only during highway driving, at speeds of about 80 km/h and above.
The TNO study, which did not include regulatory ESC/ETC emission testing, fell short of implying that the Euro V trucks were out of compliance with emission standards. However, the results of the study “brought to light possible emission control failure and tampering”.
The study has prompted an action by the Dutch government, who warned the European Council that “inadequate engine calibration software” in Euro V trucks may prevent the Netherlands and other Member States from meeting their emission ceilings and air quality limits. The Dutch government suggested that the European Commission negotiates an agreement with the industry to modify the calibration software of existing and new Euro V vehicles and requested that PEMS (portable emission measurement system) measurements be included in the Euro VI comitology regulation currently being prepared by the European Commission.
The issue was considered at the European Council on March 15, 2010. It remains uncertain if the Commission will act on the Dutch requests.
The higher NOx emissions at slower driving conditions are due, at least in part, to high engine-out NOx engine calibration in Euro V trucks with SCR systems. The engines are calibrated for high fuel economy, with engine-out NOx emissions believed to be as high as 8-10 g/kWh. The NOx emissions are then reduced over the SCR catalyst. However, SCR systems are not effective under low exhaust gas temperatures, resulting in relatively high NOx levels under slow driving conditions.
Increased in-use NOx emissions were found in the past in older generations of European trucks, such as by the German UBA, but no regulatory actions followed those reports.