Mercedes-Benz discusses the aftertreatment technology serving its new generation diesel engines

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As regulations continue to tighten, Mercedes-Benz vehicles now achieve average NOx emissions of between 40mg/km and 60mg/km under the RDE measuring method. The German OEM details how its aftertreatment tech makes this possible.

Diesel engines from Mercedes-Benz are now available from the compact class to the large, luxury class. As is already the case with the OM 654 and OM 656, the OM 608 engine features a compact exhaust-gas aftertreatment system close to the engine as well as high- and low-pressure exhaust gas recirculation (EGR), ensuring that average NOx emissions are below the current limits of the new RDE test method. For the first time, this model series also features an SCR catalyst with AdBlue exhaust fluid.

In the coming months, the German auto maker will launch more models that are certified in accordance with Euro 6d-TEMP. By September 2018, more than 30 of the currently available models and more than 200 variants are to be changed over to Euro 6d-TEMP Norm – a full year before this is mandatory for all vehicles.

“Mercedes-Benz’s new generation of engines already demonstrated two years ago, how the NOx-challenge in diesel cars can be solved technically,” said Ola Källenius, board member at Daimler, responsible for group research and Mercedes-Benz Cars development. “We are fully committed to modern diesel engines as part of the drive mix for the future.”

Current Mercedes-Benz vehicles equipped with the latest diesel technology can achieve NOx emissions in a very low double-digit and sometimes even single-digit range in some RDE-measurements on the road.

This was highlighted when the technical inspection company TÜV Hessen tested a new C-Class with a new 1.6-liter four-cylinder OM 654 engine according to the currently applicable RDE regulations, and measured nitrogen-oxide emissions below 10mg/km in the overall cycle, both with and without cold starts.

When a sedan version of the new C-Class with the same engine was tested in accordance with the RDE method, NOx emissions of approximately 10mg/km were measured.

At low levels of engine load, the effectiveness of exhaust-gas aftertreatment can be enhanced due to the close proximity of the system to the engine and further developed exhaust-gas temperature management.

The low levels of NOx emissions in real driving operation of vehicles with the new diesel engines explains why the market penetration of new generations of vehicles is an effective means of further reducing NOx emissions from traffic in urban areas.

But, according to Källenius, the new engines still have the potential for technical improvements: “We have already achieved enormous progress, but our engineers are of course developing the technology even further. Our goal is to arrive at average NOx emissions of around 30mg/km in RDE Stage 2 tests by 2020.

“And we are determined to achieve averages approaching 20mg in the following years. We are targeting these figures in particular for our vehicles on RDE driving tests in cities.”


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Sam joined the UKi Media & Events automotive team in 2017. Having started out as assistant editor for a number of titles including Automotive Powertrain Technology International, Automotive Testing Technology International and Professional Motorsport World, he was appointed editor of PTI in 2020. Sam produces content for both the magazine and website.

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