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

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.