On-road emissions of passenger cars beyond the boundary conditions of the real-driving emissions test

Abstract

Passenger cars are an important source of air pollution, especially in urban areas. Recently, real-driving emissions (RDE) test procedures have been introduced in the EU aiming to evaluate nitrogen oxides (NOx) and particulate number (PN) emissions from passenger cars during on-road operation. Although RDE accounts for a large variety of real-world driving, it excludes certain driving situations by setting boundary conditions (e.g., in relation to altitude, temperature or dynamic driving). The present work investigates the on-road emissions of NOx, NO 2 , CO, particle number (PN) and CO 2 from a fleet of 19 Euro 6b, 6c and 6d-TEMP vehicles, including diesel, gasoline (GDI and PFI) and compressed natural gas (CNG) vehicles. The vehicles were tested under different on-road driving conditions outside boundaries. These included ‘baseline’ tests, but also testing conditions beyond the RDE boundary conditions to investigate the performance of the emissions control devices in demanding situations. Consistently low average emission rates of PN and CO were measured from all diesel vehicles tested under most conditions. Moreover, the tested Euro 6d-TEMP and Euro 6c diesel vehicles met the NOx emission limits applicable to Euro 6d-TEMP diesel vehicles during RDE tests (168 mg/km). The Euro 6b GDI vehicle equipped with a gasoline particulate filter (GPF) presented PN emissions < 6 × 10 11 #/km. These results, in contrast with previous on-road measurements from earlier Euro 6 vehicles, indicate more efficient emission control technologies are currently being used in diesel and gasoline vehicles. At the same time, the results suggest that particular attention should be given to CO and PN emissions of certain types of vehicles when driven under dynamic conditions, and possibly additional work is necessary. In particular, the emissions of CO (measured in this study during the regulated RDE test, but without an emission limit associated to it) or PN from PFI vehicles (presently not covered by the Euro 6 standard) showed elevated results in some occasions. Emissions of CO were up to 7.5 times higher when the more dynamic tests were conducted and the highest PN emissions were measured from a PFI gasoline vehicle during dynamic driving. Although based on a limited sample of cars, our work points to the relevance of a technology- and fuel-neutral approach to vehicle emission standards, whereby all vehicles must comply with the same emission limits for all pollutants.

On-road gaseous and particulate emissions from GDI vehicles with and without gasoline particulate filters (GPFs) using portable emissions measurement systems (PEMS)

“…CO emissions were found to be higher for the more dynamic Downtown SD route compared to the Downtown LA route, due to more transition engine operating conditions and higher loads that favor rich air-fuel mixtures. Similarly, Demuynck et al (2017) and Suarez-Bertoa et al (2019) reported higher real-world CO emissions over more dynamic routes. Results reported here indicate the effects from rich engine operation during uphill/downhill and high-speed driving conditions for the Downtown SD route compared to the flat road Downtown LA route.…”

Regulated and Non-Regulated Emissions from Euro 6 Diesel, Gasoline and CNG Vehicles under Real-World Driving Conditions

“…This suggests that gasoline vehicles equipped with TWC can result in high emissions of CO not only during cold start but also after catalyst light-off. High CO emissions from gasoline vehicles during dynamic driving have recently been reported during on-road and on-dyno RDE tests [52,53]. Moreover, Kelly and Groblicki already reported this operation in the U.S. in 1993 [54].…”

Exhaust emission factors of greenhouse gases (GHGs) from European road vehicles

“…Diesel L-category as well as dual fuel heavy-duty vehicles are excluded. As a help to the eyes, 1% is represented with a red circle system (higher urea injection flow, more frequent LNT/ NSC regeneration) so that diesel light-duty vehicles will be able to comply with the more stringent NOx standards [52,55,65]. In such context and without setting a standard on the tailpipe N 2 O emissions from diesel LDV and HDV vehicles, the regulation defined to reduce GHG emissions from on-road transportation will have lower impact on climate change mitigation.…”