How did Volkswagen's diesel defeat device work?


Every media outlet in the world covered Volkswagen's tangled web of lies and deceit as "Dieselgate" opened up and spewed the truth nearly three years ago. Its consequences are ongoing today, and VW's future trajectory has been changed forever. But, how exactly did VW's "defeat device" work?

Jason Fenske, host of Engineering Explained, breaks it all down, and in the simplest ways, shows how VW was able to fool regulatory bodies for so long. 

First, Jason gives us an explanation of how VW's exhaust system operates. Following the intake path, air enters through the intake, passes through the turbocharger's compressor, heads to the intake manifold and then into the cylinder. From there, it enters the exhaust manifold and it can route one of two ways: a high-pressure exhaust gas recirculation or to the exhaust turbine. From there, if it heads to the exhaust turbine, it flows through a catalytic converter and diesel particulate filter. A low-pressure EGR can route exhaust back to intake, but if it doesn't, the byproduct heads to a nitrogen-oxide trap, and finally a hydrogen sulfide to sulfur dioxide converter.

Where VW got mischevious is with the EGR valves. The "defeat device" understood if the car was on a dyno for, say, emission testing, or if a human was driving it on the road. How did it know this? If the car received steering input, like a driver handling the car in real life, the EGR systems performed minimal work and the engine used a leaner air-to-fuel mixture. This improved performance and fuel economy significantly, but produced much more nitrous oxide (NOx). The NOx trap was also ineffective, which uses fuel to clean it. With more fuel available, efficiency also increased, but NOx levels did as well.

If the car was on a dyno and no steering input was detected, the car performed as it should and used the EGR systems normally to keep NOx levels down and at required levels. While operating as intended, performance and fuel economy worsened as fuel was used to clean the NOx trap and the high- and low-pressure EGR curbed NOx production.

It's all very intricate, but Jason does an excellent job to break it all down. Check out the entire explanation up above.

 
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