Since 2018, only SCR exhaust gas treatment systems have been used in Volkswagen models with diesel engines. SCR (selective catalytic reduction) technology significantly reduces nitrogen oxides in the exhaust gas. Volkswagen has now developed the next evolutionary stage of the SCR system which is called twin dosing. 

Adblue is injected selectively upstream of two SCR catalytic converters which are arranged in series. The system is used in the new Passat 2.0 TDI Evo with 110 kW (150 PS), which already meets the technical requirements of the future Euro 6d emission standard as a result. The second model which will use this system will be the upcoming Volkswagen Golf 8, the model being scheduled to be unveiled later this year. 

The twin dosing process requires a second SCR catalytic converter which is located in the underbody of the vehicle. Since the distance to the engine is greater, the exhaust temperature upstream of the second catalytic converter can be as much as 100°C lower and this means it can reduce the NOX levels by around 80% compared to the previous generation of the engines.