I don't mean this to sound like a rhetorical question. I own Volkswagen Passat TDI (which is part of VW scandal) and currently awaiting approved modification for my car. What I'm trying to do is to understand why it is claimed that VW produces a higher level of NOx than other cars, when most diesel pick-up trucks (unsure on actual percentage) do not have a system for utilizing DEF to clean exhaust gasses to reduce NOx emissions. My car is equipped secondary tank for DEF fluid which resides in the trunk and I have to refill it with AdBlue (VW specific DEF fluid) every 10,000 miles or significantly less depending on driving condition.
My understanding on DEF system is very limited, same goes for my chemistry knowledge, but upon reading documentation about Cummins Filtration system in commercial vehicles which seems to be very similar to the technology employed by Volkswagen in later models, I'm confused why I'm buying and refilling DEF fluid that is supposed to do exactly what EPA says my car does NOT do.
Lastly, what is exactly causing diesel engines to produce black smoke which my car never produced?