Volkswagen's ongoing diesel emissions scandal has brought nearly every automaker's diesel offerings under increased scrutiny. While no other automaker has been caught cheating on emissions testing via a system as elaborate as VW's, investigators are on the lookout for diesel-powered cars that pollute more than their manufacturers claim. And the deeper they look, the more cheating they find.

A sweeping study by Transport & Environment (T&E)–a non-governmental group promoting sustainable transportation in Europe–accuses nearly every European automaker of employing some form of emissions cheat on diesel-powered vehicles. T&E's testing confirms once again that real-world diesel emissions are much higher than what's measured in government testing.

The report says that Volkswagen diesel-powered vehicles run the cleanest of any European automaker, at least when it comes to vehicles built to the new Euro 6 standards. That might come as a surprise given Volkswagen's cheating past, but the automaker seems to have engineered its newest crop of diesel engines to run far cleaner than the slightly older TDIs at the heart of the scandal.

VW's Euro 6-compliant engines only emit two times the legal limit in real-world driving, while Renualt and Nissan products were found to emit more than 14 times the limit. Compare that to cars built to meet the previous Euro 5 standards, in effect from September 2011 to August 2014. Volkswagen diesels built during that period were among the dirtiest of 20 automakers tested by T&E. (In the U.S., which holds diesel vehicle emissions to a much stricter standard than Europe, Volkswagen TDIs produced during this period emitted up to 40 times the legal limit of certain pollutants.)

The organization claims nearly every European-market producer of diesel automobiles uses one of three types of strategies to shut off emissions controls during real-world driving. Most use so-called "thermal window" defeat devices that shut off exhaust treatment systems at ambient temperatures warmer or colder those used in laboratory tests. There's also "hot restart" devices, which switch off emission controls when a car is restarted with a warm engine, and "cycle detection" devices, which shut off emission controls after 22 minutes. Alarmingly, these defeat devices may actually be legal in Europe, thanks to a loophole that allows automakers to program their vehicles to shut off emissions controls under the claim that doing so will prevent harm to the engine. To learn more about this loophole, and the strategies automakers use to skirt emissions laws, see here.

For decades, European law favored diesel-powered vehicles as a way to reduce fuel consumption—diesel fuel was taxed less than gasoline, and emissions regulations were tweaked to encourage automakers to build more diesel-powered vehicles. Now that the car industry's widespread diesel emissions cheating is being uncovered, it's hard to say what the future of diesel will be in Europe, and worldwide.

via Green Car Reports

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