The active tank is connected to a second reservoir, the so-called passive tank. With its additional capacity of approximately 4.5 gallons, this passive tank offers a plentiful supply of the urea solution required within the car. The average range provided on this supply capacity is indeed sufficient to have the tank system replenished as part of normal scheduled maintenance.
From the active tank AdBlue is delivered to the dosing valve and atomized into the exhaust emissions. Consistent distribution of AdBlue within the flow of exhaust emissions is ensured by the SCR mixer. The ammonia generated in this way in the hot emission gas subsequently acts in the SCR catalyst as a reduction agent and converts environmentally harmful nitric oxides into nitrogen and water vapor in a process referred to as selective catalytic reduction.
This process gives the special SCR catalyst its name with the SCR system as such being masterminded by highly efficient engine management. A nitric oxide sensor, finally, provides information on the concentration of NOX in the exhaust emissions.