Exhaust gas temperature and NOₓ after-treatment performance of euro 6 passenger cars

Pollution affect air quality of cities around the world. With the objective to constrain this problem, new homologation procedures have been introduced for a long time. In Europe, the real driving emissions (RDE) tests by means of portable emissions measurement systems (PEMS) has the potential to assess emissions in amore realistic driving with a more robust framework (Hooftman et al., 2018). They also could be used to find gaps in emission models and to increase knowledge of transportation pollution phenomena. Operating temperatures of aftertreatment systems are relevant to their performance, which is crucial for urban air quality. During cold start, which mainly occurs in urban (Weiss et al., 2017), cool combustion conditions of internal combustion engine (ICE) limit exhaust gas temperatures, sothermal heat transfer to aftertreatment systems is reduced (Chan and Hoang, 2000; Roberts et al., 2014). Aftertreatments need an initial stage of warming-up until reach the optimal operating temperatures, and they also could be affected by conditions of cooling down. Engine gas recirculation (EGR) has been widespread used to control NOₓ emissions. Depending on the application, it could be complemented with after-treatment technologies as: three-way catalyst (TWC), lean-NOₓ trap (LNT) or selective catalytic reduction (SCR). Although SCR has shown high efficiency reducing NOₓ emissions in diesel vehicles, it is affected by low operating temperatures produced by stop periods (v< 1 km h⁻1) and low engine loads (Weiss et al., 2011). In the same way, long engine-off periods (engine speed < 50rpm) of hybrid vehicles could affect to the performance of their TWC systems (Koltsakis et al., 2011). In light of these considerations, this study aims to show the association between the exhaust gas temperature at tailpipe and the NOₓ reduction performance of aftertreatment systems installed indifferent Euro 6 passenger cars. For this objective, cold start emissions were analysed from real driving tests during engine warming-up in a unique close loop urban route. In addition, RDE tests were performed to correlate the exhaust gas temperatures with the performance of NOₓ aftertreatments. The tested fleet represent the most common fuel / powertrain / aftertreatment architectures in the market.