VW TDI engines either combust the nitrogen oxide or mix it with urea to reduce emissions: http://thinkblue.vw.com/tdi-academy-clean-diesel-vs-gasoline/ http://t

VW TDI engines either combust the nitrogen oxide or mix it with urea to reduce emissions: http://thinkblue.vw.com/tdi-academy-clean-diesel-vs-gasoline/ http://thinkblue.vw.com/tdi-academy-clean-diesel-vs-gasoline...