BMW, not content to let rival Mercedes-Benz bask in the diesel spotlight, is bringing a twin-turbo, diesel-powered 3 Series sedan to all 50 of these United States late in 2008. Like its Teutonic rival, BMW uses urea injection to turn nitric oxides into nitrogen and water vapor, thereby meeting emissions regulations. BMW’s diesel is a 3.0-liter, inline-six cylinder, twin-turbo engine that is already sold in other parts of the world. The 335d goes on sale in the fall.