An Analysis of Emissions at Low Ambient Temperature from Diesel Passenger Cars Using the WLTP Test Procedure 2020-01-2186

The aim of this paper is to analyse the results of regulated and unregulated emissions and carbon dioxide (CO₂) emissions of passenger cars equipped with compression-ignition engines that meet the emission Euro 6d standards. Both test vehicles featured selective catalytic reduction (SCR) systems for control of oxides of nitrogen (NO_x) and one vehicle also featured a passive NO_x absorber (PNA). Research was performed using the current European Union exhaust emission test methods for passenger cars (Worldwide harmonized Light vehicles Test Procedures (WLTP)). Emission testing was performed on a chassis dynamometer, within a climatic chamber, at two different ambient temperatures: 23°C (i.e. Type I test) and -7°C (known as a Type VI test - currently not required for this engine type according to EU legislative requirements). Gaseous and particulate emissions limited in the Euro 6 standard were measured using the applicable legislative procedures and the additional components CO₂, NH₃ (ammonia), NO (nitrogen oxide), NO₂ (nitrogen dioxide) and N₂O (nitrous oxide) were also measured. The results revealed variable emissions behaviour in response to ambient temperature, for both regulated and unregulated emissions. NO_x emissions were subjected to additional analyses, which indicated high performance of the PNA for NO_x control. The ratio of NO to NO₂ in the exhaust was found to differ for the first phase following cold start at -7°C compared to other periods of engine operation. Some considerations of the powertrain’s warmup behaviour over the 30-minute, 23-km test cycle and the impact on exhaust emissions are briefly discussed.