Exhaust Gas Aftertreatment of Volkswagen FSI Fuel Stratified Injection Engines

For substantial reduction of fuel consumption of their vehicle fleet, Volkswagen AG has decided to develop spark-ignition engines with direct fuel injection. To launch this new engine concept with stratified lean operation mode while at the same time meeting the stringent EU IV emission standards, it was necessary to develop a suitable exhaust gas aftertreatment system. This was achieved as part of an intensive co-operation between Volkswagen AG and OMG, formerly dmc² Degussa Metals Catalysts Cerdec AG.

The paper describes the demands for exhaust gas aftertreatment due to lean burn operation. In addition the main development steps of the exhaust gas aftertreatment system for Volkswagen FSI engines and catalyst durability over vehicle lifetime are discussed. Focus is laid on the catalyst system design and coating variations. Volkswagen developed a new closed-loop emission control management system which uses NOx-sensor signals for the first time worldwide.

European fuel quality standards required the development of a new active and lambda-controlled desulfation process. Although the Volkswagen FSI exhaust gas aftertreatment concept can withstand high fuel sulfur contents, sulfur-free fuel is required for best fuel economy. With widespread available sulfur-free fuel, advanced NOx storing components with a wider NOx activity window can be used, which leads to more frequent use of fuel-saving lean operation mode.