Understandably, the differences between laboratory and on-the-road measurements of diesel pollutant emissions have given rise to many questions.
In addition, on September 1, 2017, the Worldwide Harmonised Light Vehicles Test Procedure (WLTP) and Real Driving Emissions (RDE) introduced new procedures for the certification of all newly produced model series and model variants, for the first time including measurements during on-road operation. Road tests were quite simply not envisaged for certification prior to that. We not only welcome their introduction – we have called for it for years.
This is because we need both: measurements under laboratory conditions that are internationally comparable and reproducible. And measurements on the road to give our customers more realistic values.
Mercedes-Benz has already had diesel vehicles on the market since 2016 that meet the more stringent EU emission limits forming part of the RDE requirements (Stage 1).
The decision to develop this new engine family was made at the beginning of the decade. The innovative technologies implemented in the process ensure low NOx emissions. With the complete changeover to the new engine generation in the first half of 2019, all new cars available for order from Mercedes-Benz meet the Euro 6 d-TEMP or Euro 6d emissions standard.
The limits for NOx in emissions measurements are so-called "not to exceed" limits, and must be complied with in every valid RDE drive. This means that a vehicle may also not exceed the limit under the worst conceivable combinations of RDE conditions – for example, with a heavy load, in hilly topography, and in unfavourable temperature and traffic conditions. The limit applies not only to new vehicles, but also to vehicles with more than 100,000 kilometers on the clock. Results of real-world tests on the road often stay significantly below the limit of 80 milligrams per kilometer, which is confirmed by independent measurements.
In its 13/19 issue, German auto specialist magazine "auto motor und sport" reported that¹ emission measurements on twelve test vehicles of different brands resulted in the tested Mercedes C 300 d Estate emitting "almost no NOx". In the article, the measurement result for the Mercedes-Benz C 300 d Estate (combined fuel consumption 5.6-5.0 l/100 km, combined CO₂ emissions 147-133 g/km)² were described more pithily: "With a measly 13 milligrams of NOx, it goes to the top of our ‘Mr Clean’ hit list. […] However, the new two-litre diesel engine known as the OM 654 was systematically trimmed for reduced emissions. The NOx problem of many cities is therefore bound to be resolved as soon as more new cars are registered".³
In February 2019, the German automobile club ADAC reported on its extensive in-house measurements: "The NOx emissions of current cars are far below the test bench limits in real-world driving on the road". The result was particularly positive for the Mercedes-Benz C 220 d (combined fuel consumption 4.8 l/100 km, combined CO₂ emissions 126-117 g/km)², with a scarcely measurable NOx value between 0 and 1 mg/km“.
Such individual measurements illustrate that the NOx challenge can be solved technically also for diesel-powered vehicles with the new engine generation. However, the average emissions of a vehicle over many thousands of kilometers are much more meaningful in this regard: Mercedes-Benz passenger cars equipped with the latest diesel technology achieve average figures of 20 to 30 mg of NOx per kilometer under RDE conditions.
¹Issue 13, 6 June 2019
²The stated figures are the measured "NEDC CO₂ figures" in accordance with Article 2 No. 1 Implementing Regulation (EU) 2017/1153. The fuel consumption figures were calculated based on these figures. A higher value may apply as the basis for calculating the motor vehicle tax.
³auto, motor und sport, Issue 13, 6 June 2019
