The Real-Driving Emissions (RDE) legislation is important to reduce the gap between type-approval vehicle emissions results and those in the real-world so that vehicles driving on the European roads deliver low emissions as is meant by the EU emissions legislation. RDE provisions have the possibility of positively influencing air quality for European citizens by ensuring that vehicle manufacturers integrate emissions control technologies with engine measures to achieve optimal emissions reduction under driving conditions encountered in use.
The RDE legislation, introduced within the Euro 6 regulation, has been developed in 4 packages. The first RDE package, adopted in May 2015, defines the RDE test procedure. The second RDE package, adopted in October 2015, defines the NOx Conformity Factors and the introduction dates. The third package, adopted in December 2016, adds a Particle Number (PN) Conformity Factor and inclusion of RDE cold-start emissions (i.e. at engine start). The fourth package adopted in May 2018 deals with In-Service Conformity RDE testing and market surveillance and lowers the error margin of the 2020 NOx Conformity Factor from 0.5 to 0.43.
All four RDE acts have been published in the Official Journal and requirements entered into force from 1 September 2017 for new car types.
The agreed stepwise and realistic approach on NOx Conformity Factors, to be introduced from 2017 and 2020, will allow best-available technologies to be used and to spread across the fleet over time.
From April 2016 onwards new Euro 6 passenger car models have to be tested not only on the regulatory test cycle at type-approval but also on the road where emissions are measured with a Portable Emissions Measurement System (PEMS). During this monitoring phase, RDE are measured but no Not-To-Exceed (NTE) limit applies.
As of September 2017 a Not-To-Exceed (NTE) emissions limit is set for RDE emissions of new car models with a Conformity Factor (i.e. NTE/Euro 6 limit ratio) of 2.1 for NOx. It will apply to all new cars in September 2019. A CF for Particle Number (PN) of 1.5 (1.0 + 0.5 error margin to be reviewed) was also introduced. It is referred to as the Euro 6d-temp standard.
From January 2020/21 for new models and all new cars respectively, the NOx CF will be lowered to 1.0 + an error margin of 0.43 (and the error margin is to be reviewed annually). It is the Euro 6d standard.
Catalysts, traps and filters are used on new vehicles as part of an integrated approach to emissions control which includes the combustion system, fuel and reductant quality and electronic control systems. Catalysts, traps and filters are extremely durable and effective means of controlling emissions from engines and vehicles to ensure that modern vehicles contribute to improving air quality and are able to meet legislative limits on emissions.
PEMS trips validity criteria have been developed to avoid that tests are conducted in an unrealistic manner. For instance PEMS trips have to last between 1h30 and 2h; they have to include specified shares of urban, rural, and motorway driving.
NTE emissions (or Conformity Factors) then apply to a range of ambient and driving conditions. For example moderate ambient conditions are temperatures between 0 and 30°C and altitudes up to 700 m; extended ambient conditions are temperatures between -7 and 0°C and between 30 and 35°C, and altitudes between 700 and 1300 m.
A Moving Average Window-based methodology (EMROAD, originally developed by the Joint Research Centre – JRC – of the European Commission) is used to check the trip validity.
Also, for a PEMS trip to be valid, the driving cannot be either too aggressive or too soft (this is checked via the “95th percentile of the vehicle speed x positive acceleration” and via the Relative Positive Acceleration both in each of the urban, rural, and motorway phases. Another criteria is the positive altitude gain during the PEMS trip which is limited to 1200 m /100 km.
Once the trip validity has been confirmed, PEMS data are post-processed, using the raw emissions for a good percentage of RDE trips, while balancing the raw emissions against CO2 for the more demanding trips (compared to WLTP). A specific evaluation factor is used in the case of plug-in hybrid vehicles; it compares CO2 emissions during the RDE test and CO2 emitted over the WLTP test in Charge Sustaining mode. The PEMS data evaluation methodology will be reviewed against technological progress.
The output emission value has to be below the NTE limit.