Diesel have had to be clean since the beginning of September. Hardly any new car can do without special catalysts. However, exhaust gas cleaning does not always work as it should. In the United States, this could finally break the neck of the German diesel engine: The authorities caught VW manipulating emission values. But why is there so much trickery with diesel?
Nitrogen oxide emissions are currently the biggest problem with diesel engines - apparently also the stumbling block for VW in the USA. After ten years of regulatory calm, new limit values have also been applicable in Europe since September. The Euro 6 emissions standard limits the emission of harmful gases by a further 100 milligrams to only 80 milligrams per kilometer. In the US, only 31 milligrams of the NOx abbreviated substance can be emitted. This is a serious hurdle for diesel in North America. And a problem for the German manufacturers who have wanted to establish it there for years. Currently with a manageable but stable success. After all, just under a percent of the market share has been conquered, which makes up almost 140.000 cars and light commercial vehicles. VW puts the greatest energy into technology - with 56 percent of the market for diesel cars, Wolfsburg is by far the strongest provider before BMW and Audi. But all brands have a problem: nitrogen oxide. The gases can damage and irritate respiratory organs, are involved in the formation of ozone and smog and increase global warming.
The gasoline engine no longer has the NOx problem, because the three-way catalytic converter effectively filters the gases from the burned fuel-air mixture. However, this catalyst does not work with diesel because of the higher proportion of air. In addition, turbo diesel engines generally generate significantly more NOx than gasoline engines because they work with higher combustion temperatures. Car manufacturers have therefore been relying on new technologies to reduce nitrogen oxide emissions for several years.
VW has apparently largely relied on NOx storage catalysts for the cars affected by the impending recall. A relatively inexpensive measure compared to the approaches of the competition. Group sister Audi, for example, mainly sells vehicles with the mostly more expensive SCR catalytic converters, while BMW takes the silver bullet and combines NOx storage catalysts with SCR technology. The latter works with the injection of urea, the so-called Ad Blue, and is almost indispensable in Germany from the middle class upwards if you want to comply with the limit values. In comparison with the premium manufacturers Audi and BMW, VW naturally has smaller vehicles on offer on the US market - but the NOx storage catalysts may also have reached their limits in models such as Jetta or Beetle. The US Environmental Protection Agency (EPA) has registered emissions that are up to 40 times higher.
Even in this country, where the limit values are much more lax than in the USA, diesel has come into disrepute. The environmental organization ICCT recently published a study according to which numerous models in practice were far removed from the NOx emissions generated in the laboratory. In the current NEDC test, which is decisive for the approval of new vehicle types, the 32 diesel cars checked still performed well and were below the limit value for NOx emissions. In the more realistic WLTP test, however, 22 models failed. The new procedure is to be gradually introduced in Europe from 2017 and replace the NEDC test. This does not change the limit values for pollutants, only the way in which emissions are determined is different - but not fundamental.
The strong deviations in the test are therefore surprising: Volvo cars exceeded the limit 15 times, Renault models exceeded it nine times and Hyundai cars seven times. Audi models achieved three times the limit, Opel vehicles were hardly better. Mercedes cars just barely missed the limit, BMW achieved the targets with all models tested.
According to the study, the suspicion was obvious in some cases that the exhaust gas purification technology of the vehicles had been optimized for the approval test. Like apparently now also at VW in the USA. And that it reduces nitrogen oxide emissions far less under more realistic conditions. Politicians are aware of this, and from 2017 they will also require exhaust gas measurement in real driving conditions. The determination of the so-called Real Driving Emissions (RDE) would help to sort out problem diesel. However, this may mean a further surcharge for diesel cars. Because exhaust gas cleaning not only costs more consumption, but also a lot of money. But you will hardly be able to do without the diesel - because without the economical engines, the future CO2 limit values can hardly be reached.
