Ist der Diesel etwa doch gar nicht so schlecht?

12.01.21 Diesel cars are better than their reputation, yet still have no future in Germany Hans-Joachim Ziegler • 7 min.

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In 2015 news broke that Volkswagen had illegally manipulated its diesel engines’ exhaust in order to comply with emission thresholds. That, for many people in Germany, sealed diesel’s fate. Even the latest advances – diesel engines whose exhaust supposedly contains less particulate matter than the ambient air – probably won’t give diesel a viable future.

Few technologies have had their reputation so swiftly and permanently tarnished as the diesel engine. Today, many people in Germany associate diesel with air pollution, corporate malfeasance, and class-action lawsuits. According to the executive director of German Environmental Action (DUH), however, this costly chapter of German industrial history may actually have accelerated the trend toward green transportation: diesel hardly plays any role in future urban scenarios, VW itself is increasingly focusing on electric engines, and only 22% of 18 to 23 year-olds in Germany consider diesel a forward-looking technology.

Not everyone agrees. The German Automobile Association (ADAC), for example, continues to promote diesel, whose ill repute it believes is unjustified. Others point to noteworthy technological progress: Daimler-Benz has developed a new ignition system that boosts diesel engines’ efficiency and environmental performance, while VW has added two selective catalytic reduction devices that cut nitrous oxide emissions by 80%. In April 2020 Markus Köhne, head of diesel development at VW, told a German weekly news magazine that the “diesel engine is in Volkswagen’s DNA. It makes an important contribution toward achieving fleet carbon emission targets and the EU’s climate objectives.” That doesn’t exactly sound like a declaration of surrender.

Can diesels clean the air?

Diesel engines breathe: they inhale air for combustion and exhale exhaust fumes. Can the latter, as the auto industry claims, actually be cleaner than the former? In late 2020 a German automotive magazine tested this assertion. It first measured particulate matter levels in Stuttgart and then compared these with the latest diesel engines’ emissions. The results are somewhat astounding: “On days with low particulate matter levels, a diesel only acts as an air scrubber in extremely favorable operating conditions. On particularly smoggy days, however, the air almost always benefits from diesels.”

Admittedly, these findings apply only to the latest generation of diesels, not older models. Also, an advanced diesel engine’s cleansing potential varies. For instance, its exhaust is cleanest while the engine is still cold. When the engine heats up, by contrast, its particulate matter emissions rise (yet still remain below the levels near Stuttgart's main traffic arteries). Although the test focused exclusively on particulate matter emissions, not on nitrous oxides and other emissions, advanced diesels emit the latter in fairly small quantities. In sum, the latest diesel engines are cleaner than many people think.

A new dawn for diesel?

Despite diesel’s laudable advances, carmakers know its future isn’t bright. BMW, Jaguar, and Range Rover are discontinuing their biggest models. Mercedes and Opel are gradually limiting their offerings too. One reason is development costs. These, according to one expert, are too high for the latest diesels to be profitable. Moreover, there are other more sustainable alternatives. Despite diesels’ tax advantages (particularly in Germany), the same expert predicts that diesels only have a viable future in the commercial-vehicle segment.

But even in this segment things look bleak. An industry alliance formed by Daimler, Scania, MAN, and four other truck manufacturers is currently considering not producing diesel trucks after 2040. Henrik Henrikson, Scania CEO and Chairman of the European Automobile Industry Association’s Commercial Vehicles Division, believes that the internal combustion engine needs to become obsolete “as quickly as possible.”

The diesel engine is likely about to sing its swansong. That's probably a good thing. After all, even the cleanest diesel is dirtier than an electric motor.

Diesel’s demise isn’t a panacea

Yet even with diesel-free roads, there will still be particulate matter. The Baden-Württemberg Environmental Institute found that, in a city like Stuttgart, cars are only responsible for 7% of particulate matter emissions. Fully 45% results from tire abrasion, brake abrasion, and road dirt. In other words, even the cleanest diesels – and, indeed, electric cars – will still emit particular matter. In the long term, therefore, only one thing will significantly reduce ambient particulate matter: far fewer cars on Germany’s roads.


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