Real Driving Emissions
The Real-Driving Emissions (RDE) legislation is important to reduce the gap between type-approval vehicle emissions (procedure for showing the compliance of a vehicle with the prescribed emissions limits to be able to be put on the market) results and those in the real-world. The aim is for vehicles driving on the European roads to 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.
LATEST UPDATE (September 2020)
On 13 December 2018, the EU’s General Court delivered a judgment on the case that Brussels, Madrid and Paris withhold against the European Commission Regulation (EU) 2016/646 amending Commission Regulation (EC) No 692/2008 as regards emissions from light passenger and commercial vehicles (Euro 6). Regulation (EU) 2016/646 set out the conformity factors used to assess compliance of the vehicle with the emission limits while performing a Real Driving Emissions (RDE) test.
The contested conformity factors were used to progressively reduce the discrepancy between emissions measured in real driving and those measured in a laboratory. The Court did not rule on the technical necessity of the conformity factors. It finds that the Regulation (EU) 2016/646 ‘de facto’ modifies the limit of 80mg/km set by Regulation (EU) 715/2007 by allowing for a higher level of emissions in real-driving emission tests than when measuring emissions under laboratory conditions.
In order to address the General Court’s concerns, the European Commission presented an amendment proposal that is currently being discussed between the European Parliament and the European Council.
The original proposal can be found here
HISTORY OF REAL DRIVING EMISSIONS IN LIGHT-DUTY STANDARDS
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.
- 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 applies to all new cars from 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 is lowered to 1.0 + an error margin of 0.43 (with the error margin to be reviewed annually). This is the Euro 6d standard
NEW EMISSIONS MEASUREMENT AND ANALYSIS, THE RDE METHODOLOGY
Catalysts, adsorbers 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, adsorbers 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.
Portable Emission Measurement Systems (PEMS) on-road trips validity criteria have been developed to avoid tests being 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 limits, in other words Conformity Factors to be applied to the emission limit value, then apply to a range of ambient and driving conditions. For example, moderate conditions are temperatures between 0 and 30°C and altitudes up to 700 m; extended 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.
For a PEMS trip to be valid, the driving can be neither too aggressive nor 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 criterium is the cumulative positive altitude gain during the PEMS trip which is limited to 1200m over 100km.
Once the trip validity has been confirmed, PEMS data are post-processed, the output emission value has to be below the NTE limit.. 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.