If you go back and read through Diesel innovation and technology development....there’s some peak that occurred in the late 1990s. As much as people want to suggest that there’s some great clean method to develop and utilize for the Diesel engine....it’s been twenty years and nothing has really occurred.
These two charming engineers probably reached a point where they admitted....you can have performance, durability and gas mileage....or you can have great emissions success. You can’t have all four. So, they cheated the system. It’s kinda like Captain Kirk in that silly scenario game at Star Fleet HQ’s....the only way to win....is to cheat.
The urea injection system seems to work well.
http://www.scientificamerican.com/article/what-s-behind-vw-s-downfall-and-secretive-emissions-deals/