Experimental assessment of the potential to decrease diesel NOx emissions beyond minimum requirements for Euro 6 Real Drive Emissions (RDE) compliance

Highlights: • Study confirms high on-road NO_x levels of a typical diesel Euro 6 car. • New regulations have potential to significantly control on-road NO_x. • SCR based emission control achieved conformity factor of 0.53. • Limited side effects of new technology observed for CO₂ and NH₃ emissions. The objective of this study was to test the potential for NO_x emissions improvements on a typical Euro 6 diesel vehicle, following modifications to its emissions control system, under Real Drive Emissions (RDE) testing conditions. A commercially available car was selected and was first measured in its original configuration according to RDE on the road and an initial conformity factor (CF) of 5.4 was determined. Subsequent engine calibration and installation of a Selective Catalytic Reduction (SCR) device were conducted and tested on a fully transient engine dyno setup, which precisely reproduced the engine operation under the on-road RDE test. The NO_x reduction achieved with those upgrades was 90%, leading to a CF of 0.53, with no CO₂ or fuel consumption penalty. These findings demonstrate that diesel vehicles can reach low NO_x levels under real world driving conditions, when well-designed modern exhaust aftertreatment components are installed and properly calibrated.