JRC provides initial results and qualitative trends of study of regulated gaseous emissions under NEDC and new WLTP; data from 21 vehicles
A team from the European Commission-Joint Research Centre (JRC) reports initial results of regulated gaseous emissions (CO2, NOx, CO, and THC) from Euro 4, 5, and 6 vehicles measured at JRC under the existing New European Driving Cycle (NEDC) and newly developed Worldwide Harmonized Light Duty Test Procedure (WLTP) in a paper published in the ACS journal Environmental Science & Technology. Based on their testing, the team also provides some analysis of initial qualitative trends.
In 2009, the World Forum for the Harmonization of Vehicle Regulations of the United Nations Economic Commission for Europe (UNECE) launched a project with the aim to develop a worldwide harmonized light duty test cycle (WLTC) and test procedure (WLTP) more representative of real-world driving conditions and emissions that other existing driving cycles used for vehicle testing and certification.
|Average speed (km/h)||33.6||46.5|
|Max speed (km/h)||120.0||131.3|
|Stop duration (%)||23.7||12.6|
|Constant driving (%)||40.3||3.7|
|Average positive acceleration (m/s2)||0.59||0.41|
|Maximum positive acceleration (m/s2)||1.04||1.67|
|Average positive “speed·acceleration” (m2/s3)||1.04||1.99|
|Maximum positive “speed·acceleration” (m2/s3)||9.22||21.01|
|Average deceleration (m/s2)||−0.82||−0.45|
|Minimum deceleration (m/s2)||−1.39||−1.50|
|Speed profiles of NEDC and WLTP. Click to enlarge.|
During the period from 2010 to 2015, JRC—involved in the process from the beginning—tested the various versions of the new test cycle and test procedure on a number of vehicles that were also tested under NEDC conditions. The result is a compendium of experimental data regarding the regulated gaseous pollutants and fuel consumption on 21 vehicles.
The vehicles were chosen to be representative of the different segments of the European market; 12 were gasoline-fueled, and 9 were diesel-fueled. Two vehicles were type approved for the Euro 6 standard, three vehicles for Euro 4, and the rest for Euro 5.
The average NEDC inertia mass was 1,522 kg, the average engine capacity 1847 cc, and the average engine maximum power 106.5 kW (143 hp).
(As an aside, the researchers noted that PM mass measurements were routinely carried out; however nothing worth mentioning was found, as most of the diesel vehicles were Euro 5 and thus equipped with diesel particulate filter (DPF).)
While cautioning that the results in no way constitute a complete and exhaustive comparison between NEDC and WLTP, the JRC team said, the data show some interesting trend—in line with other similar studies—in particular for CO2 emission and fuel consumption. Broadly:
The results showed minimal average differences between CO2 emissions over the NEDC and WLTP; the average ratio between CO2 emissions over NEDC and over WLTP is around 1 (1.00 ± 0.06).On the other hand, CO2 emissions measured at JRC on the NEDC were on average 9% higher than the respective type-approval values. For the tested vehicles, CO2 emissions over WLTP were almost 10% higher than the respective NEDC type-approval values. That difference is likely to increase with application of the full WLTP test procedure, the researchers said.
Measured THC emissions from most vehicles stayed below the legal emission limits and in general were lower under the WLTP compared to NEDC.
Moving from NEDC to WLTP did not have much impact on NOx from gasoline vehicles and CO from diesel vehicles. By contrast, NOx from diesel vehicles and CO from low-powered gasoline vehicles were significantly higher over the more dynamic WLTP and in several cases exceeded the emission limits.
This seems to suggest a general trend: for those pollutants whose emissions are mainly due to the cold start phase of the cycle (ex. THC on all vehicles, CO on diesel vehicles), moving from NEDC to WLTP brings an improvement due to the lower weight of the cold start emissions on the whole cycle and this has also been seen in previous research. On the other hand, for pollutants that are emitted also during high engine load conditions (ex. NOx on diesel vehicles and CO on gasoline vehicles) the change from NEDC to WLTP can lead to substantial emission increase.
…Results from this study can be considered indicative of emission patterns of modern technology vehicles and useful to both policy makers and vehicle manufacturers in developing future emission policy/technology strategies.—Marotta et al.
Alessandro Marotta, Jelica Pavlovic, Biagio Ciuffo, Simone Serra, and Georgios Fontaras (2015) “Gaseous Emissions from Light-Duty Vehicles: Moving from NEDC to the New WLTP Test Procedure” Environmental Science & Technology doi: 10.1021/acs.est.5b01364