With the release of the 2013 Cayenne Diesel, manufactured by Porsche, the U.S. will get its first taste of the popular European car that runs on diesel fuel. The Cayenne Diesel, which has been sold in Europe since 2009, has undergone an upgrade in order to pass U.S. emissions standards. It may sound strange that a diesel car has passed emissions standards, but this is yet another strand in the web of bringing more fuel-efficient cars to the fore. The emission-reducing feature in the Cayenne is known as SCR, or selective catalytic reduction. SCR uses the car’s catalytic converter and diesel exhaust fluid to reduce the vehicle’s emissions.