Monitoring Euro 6 diesel passenger cars NO_x emissions for one year in various ambient conditions with PEMS and NO_x sensors

In this study, the NO_x emissions of four Euro 6 diesel passenger cars ranging from Euro 6 b to Euro 6 d-TEMP in different ambient conditions and driving routes were investigated with a Portable Emissions Measurement System (PEMS) and continuous NO_x concentration monitoring device. A model was also generated for translating NO_x concentration values into a gram basis. The results suggest that there is a marked difference in NO_x emissions based on the Euro 6 step for the car is type approved. The study showed that the conformity factor for NO_x emissions on a route in a city environment (“City route”) changed from 0.65 to 5.2 depending on the Euro 6 step and car. Surprisingly, a Euro 6 b car equipped with Selective Catalytic Reduction SCR system and updated engine control unit (ECU) software for lower tailpipe NO_x emissions provided lower average NO_x emissions than a Euro 6 d-TEMP diesel car equipped with dual lean-NO_x traps. Results for the City route also showed that the road infrastructure (crossroads and speed limitations) can have a noticeable effect on promoting driving that leads to higher NO_x emissions even with a Euro 6 d-TEMP car. Estimations of NO_x emissions with modelling based on continuous NO_x concentration monitoring suggested that Euro 6 b diesel cars can provide NO_x emissions close to the current RDE legislation. In addition, the modelling suggested that the Euro 6 b car with updated ECU software and the Euro 6 d-TEMP diesel car are capable of extremely low daily average NO_x emissions, even close to 20 mg/km, in normal daily usage. Nevertheless, the monitoring results and model also suggest that cold ambient temperature has a high effect on the NO_x emissions reduction performance of these vehicles, occasionally increasing their daily average emissions to as high as 900 mg/km.