In Europe, the development and implementation of new regulatory test procedures including the chassis dynamometer (CD) based World Harmonised Light Duty Test Procedure (WLTP) and the Real Driving Emissions (RDE) procedure, has been driven by the close scrutiny that real driving emissions and fuel consumption from passenger cars have come under in recent times. This is due to a divergence between stated certification performance and measured on-road performance, and has been most pointed in the case of NO_x (oxides of nitrogen) emissions from diesel cars. The RDE test is certainly more relevant than CD test cycles, but currently certification RDE cycles will not necessarily include the most extreme low speed congested or low temperature conditions which are likely to be more challenging for NO_x after-treatment systems. To build understanding of the emissions and fuel consumption performance of the latest available diesel passenger cars, Concawe has conducted a study of the performance of three vehicle types. Two of the vehicles featured urea-dosed Selective Catalytic Reduction (SCR) after-treatment, whilst the third was fitted with a Lean NO_x Trap (LNT) and a downstream passive SCR catalyst (pSCR). For each vehicle, triplicate tests were conducted over a moderate RDE on-road cycle, as well as CD testing of the Transport for London (TfL) Urban Inter Peak (UIP) cycle, developed directly from real-driving trips in the City of London, UK. The TfL UIP is considered a severe urban cycle and was run over ambient temperatures ranging from -15 °C to 23 °C. After the initial 2-3 minute warm up period, the SCR-equipped vehicles were effective at controlling NO_x, while the LNT-equipped vehicle was more effective in the initial minutes of running. The data generated provides insights into the emissions performance of Euro 6 diesel passenger cars, and their after-treatment systems, in extreme congested cold urban conditions including, and beyond, the most demanding likely to be encountered under regulatory RDE testing.
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