Volkswagen has suffered environmental backlash in the past several years for producing the "meanest" (or worst polluting) car on the road several years in a row (that would be the Touareg). According to an ACEEE report, it beats out both the Hummer and the Bugatti sportscar for its horrendous fuel efficiency, and dirty exhaust. But being green in the 21st century certainly has its paradoxes.
Volkswagen won the 2008 award from Green Car Journal for its spectacularly impressive Jetta TDI ultra-clean diesel vehicle. Despite the fact that Volkswagen was test driving the Touareg right next to the Jetta TDI when I went to sign up (I thought that was a bit brazen), you still have to give it to VW for getting to market so quickly a car that delivers 50 MPG while adhering to the world's most stringent emission control standards, California’s Tier II, Bin 5.
But real thanks must be shared with Mercedes who pioneered the BlueTec technology back in 2006 and licensed the technology to VW under a cooperative agreement that would make the technology legal in 50 states.
Diesel is a powerful and efficient fuel, but one that comes with some pretty heavy environmental impacts, owing to its higher burn temperatures. A higher burn temperature means more efficiency but along with that comes more soot and more NOx (Nitrogen Oxides). But Mercedes discovered a solution, and it involves Urea.
The particulate matter from a diesel engine can be easily trapped to eliminate smoke and soot in the engine block. But the NOx is trickier. Nitrogen Oxides are heavily regulated in Europe and now (just barely) in the US. Why? Fuel combustion doesn’t create very much NOx, but Nitrogen Oxides are notoriously potent as a greenhouse gas. 1 lb of N20, for example has approximately 310 times the effect in terms of global warming as 1 lb of CO2.
The US now has a Tier 2 emissions regulation of .05 grams per mile. But in Europe the regulation is 8x higher! So leave it to the Germans to figure out an innovative solution. In the BlueTEC engine, there are 2 catalytic converters. One traps the NOx gas, then another injects urea NH3 which Mercedes calls “Adblue” which then turns the separated Nitrogen Oxides into nitrogen and oxygen. It’s a pretty amazing innovation that ends up creating a waste product that is in fact an environmental nutrient. And, as Mercedes claims, no sacrifices on performance.
Here's a video explaining how it works: