Friday, October 30, 2015

Dieselgate: a technical analysis

I never bothered to write a post about Volkswagen's dieselgate. But I found some conflicting stories about what this meant for people driving a Volkswagen. Will Volkswagen's fix lead to reduced torque and fuel economy?

So far Volkswagen has released few details of what they did technically, but the EPA's Notification of Violation to Volkswagen gives us an insight into what Volkswagen did and from this we can deduct what the consequences will be of fixing it.

Many media have written already that Volkswagen used a 'cheat device'. According to the EPA Volkswagen "installed software in the electronics control module (ECM) that sensed when the vehicle was being tested for compliance with EPA emission standards." "During EPA emission testing, the vehicles' ECM ran software which produced compliant emission results". "At all other times during normal operation" ... "software" ... "reduced the effectiveness of the emission control system (specifically the selective catalytic reduction or the lean NOx trap). As a result, emissions of NOx increased by a factor of 10 to 40 times above the EPA compliant levels".

So what does this mean for your Volkswagen? Both in vehicles equipped with selective catalytic reduction (SCR) and a lean NOx trap (LNT), Volkswagen can fix the problem by updating the ECM software.
As a result if your car has SCR then your car will start to consume a lot more reducer (Adblue). There will be no noticeable consequences for performance. Increased Adblue consumption of course will mean that the Adblue reservoir will have to be refilled more frequently.
On a car with a lean NOx trap (LNT), the car will have to burn off the trapped NOx more frequently, which is done using diesel fuel. As a consequence diesel fuel consumption will increase significantly without other consequences for performance. Volkswagen had trouble meeting emission standards when using their LNT technology. Most likely increased fuel consumption led to Volkswagen's decision to cheat the test.

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