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too late to save it?

Bosch might just have solved the problem of diesel NOx emissions

The solution involves combining a number of existing technologies.

Jonathan M. Gitlin – | 302
A VW Golf fitted with an emissions monitoring system
Credit: Bosch
Credit: Bosch

Is there still a future for the diesel engine? According to Bosch, the answer is yes—this week the German company announced it had made a breakthrough by combining a number of existing technologies, which means that modern turbodiesel engines can still make good power and deliver excellent fuel efficiencies. At the same time, Bosch says this combo will emit very low levels of dangerous nitrogen oxides (NOx)—in fact, the company says it can beat future European emissions regulations by 90 percent.

Diesel is a dirty word

For a while, it looked like the turbodiesel engine was an easy way to boost fuel efficiency and cut carbon emissions without sacrificing power or torque. But its dirty secret was that the modern turbodiesels that gained so much marketshare in Europe and were starting to gain popularity here in the US came with some serious baggage. Although they appeared to satisfy EPA and European emissions regulations, it turned out that in many cases that was only because of chicanery. So-called "defeat devices" could tell when a car was being tested, switching engine mapping to beat the test. Out on the open road, a different engine management map would be in charge, resulting in high levels of nitrogen oxide (NOx) pollutants coming out in the exhaust.

Volkswagen Group was the highest-profile offender, and Bosch itself had to cough up $328 million for its part in the scandal. But Fiat Chrysler has been in trouble with US regulators, and, in Europe, Renault, PSA Peugeot-Citroen, Daimler, and BMW have all received unscheduled visits from law enforcement over dodgy engines. The fallout has been far-reaching. In the US, diesel has once again fallen from grace. Volkswagen's reputation suffered a beating, and the company was ordered to pay massive fines and spend even more money building a network of electric car charging stations. The EU even revised its emissions test procedures in an attempt to prevent them from being gamed. And some automakers have even decided to end development of diesel engines.

13mg/km NOx?

Bosch's solution to the NOx problem involves optimizing a number of different steps in the process. Engine displacement is reduced from 2.0L down to 1.7L. The turbocharger has been tweaked to be more responsive, thereby improving transient and low-end torque behavior. Exhaust gas treatment has been enhanced to increase the temperature of the catalyst as quickly as possible upon startup.

The engine also has to maintain those high temperatures (above 392° Fahrenheit/200°Celsius) while driving, otherwise the exhaust gases themselves can cool the catalyst below the point at which it's most effective. New engine management software is optimized for low fuel consumption at a lower NOx level. High- and low-pressure exhaust gas recirculation means the engine's air flow management is more finely controlled, coupled with revised fuel injection to reduce transient NOx peaks.

The result is an engine that can emit as little as 13mg/km NOx and just 40mg/km even under the worst conditions. Last year, I actually got to try an earlier version of these systems in one of Bosch's test Volkswagen Golf GTDs fitted with a portable emissions measurement system. My lead-footed co-driver (a European journalist) and I averaged 54mg/km, so the advancements the company has made since then represent a 25-percent improvement over that system.

A graph of diesel emissions from a Bosch test vehicle
This graph shows the results of journalists' test drives in a previous iteration of Bosch's cleaner diesel engines.
This graph shows the results of journalists' test drives in a previous iteration of Bosch's cleaner diesel engines.
A VW Golf equipped with a portable emissions monitoring system
A look at the Portable Emissions Measurement System fitted to the back of the diesel Golf. The bit that's mounted to the side of the car measures things like air temperature and pressure.
Jonathan Gitlin
A look at the Portable Emissions Measurement System fitted to the back of the diesel Golf. The bit that's mounted to the side of the car measures things like air temperature and pressure. Jonathan Gitlin

Even at 40mg/km, that's half the 2020 European NOx limit, which sets the limit for diesel engined passenger cars at 80mg/km. (Although technically I should point out that the regulations actually allow cars to emit 1.5x that amount in 2020, compared to 2.1x that amount today.) Meanwhile, here in the US under a different testing cycle, the federal limit is just 40mg/km.

Bosch says no more cheating

Given Bosch's role in the Volkswagen scandal, it's natural if you've read all of this and are still skeptical. But Volkmar Denner, Bosch's CEO, says the company's principles for development have been changed to prevent a future occurrence. For one thing, it will no longer allow any of its products to include functions that can detect when they're undergoing testing as opposed to real-world use, nor will it allow Bosch engineers to optimize products for tests rather than the real world.

Whether any of this can save diesel engines is unknown, but I am a little doubtful. The fuel's reputation is as bad as it ever was here in the US, and it never achieved that much market penetration anyway. And while diesel was extremely popular in Europe thanks to government subsidies, those same governments are now putting in place measures to ban all new internal combustion engine sales between 2030 and 2040. Meanwhile, car makers—and suppliers like Bosch itself—are throwing their resources into developing electric powertrains instead.

Listing image: Bosch

Photo of Jonathan M. Gitlin
Jonathan M. Gitlin Automotive Editor
Jonathan is the Automotive Editor at Ars Technica. He has a BSc and PhD in Pharmacology. In 2014 he decided to indulge his lifelong passion for the car by leaving the National Human Genome Research Institute and launching Ars Technica's automotive coverage. He lives in Washington, DC.
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