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Due to the need to properly quantify vehicle emissions in real world operation, Real Driving Emissions (RDE) test procedures will be used for measuring gaseous emissions on new EURO 6 vehicles.at the RDE 1 & 2: Commission Regulation (EU) 2016/427 of 10 March 2016 amending Regulation (EC) No 692/2008 as regards emissions from light passenger and commercial vehicles. Updated regulations have been enhanced to define RDE tests boundaries and data analysis procedures, in order to provide an accurate way to obtain representative results. The boundary conditions defined for vehicle testing include external atmospheric temperature, which can range from 0°C to around 30°C, for moderate conditions and -7°C up to 35°C for extended conditions in RDE tests. As a result of this range of possible test ambient temperature, pollutant emissions and energy consumption can vary considerably.

The gap between regulated emissions from vehicle certification procedures and real-world driving has become increasingly wider, particularly for nitrogen oxides (NOx). Even though stricter emission regulations have been implemented, NOx emissions are dependent on specific, short-duration driving events which are difficult to control, therefore high concentrations of these pollutants are still being measured in European cities. Under certification procedures, vehicle emissions compliance is evaluated through standards, recurring to driving cycles performed on chassis dynamometer under controlled laboratory conditions. Different countries use different standard cycles, with the US basing their certification cycle on FTP-75 and Europe using NEDC (Euro 5/6c)/WLTP (Euro 6d).

Internal combustion engine (ICE) cold-start is an issue that occurs either in conventional and hybrid powertrains before the ICE reaches its normal operation temperature, affecting both fuel consumption due to higher heat losses, and pollutant emissions due to low catalytic converter temperatures. The study of cold start emissions on conventional powertrains has been extensively addressed, although typically under laboratorial conditions, however studies addressing the impact of this phenomenon on hybrid powertrains is still reduced. Hybrid electric (HEV) and plug-in hybrid electric (PHEV) vehicles usually incorporate technologies to manage the battery and ICE power supply leading to ICE on/off operation under regular driving, which can result in a decrease on catalytic converter efficiency (due to cooling).