SCR-System filter

The SCR-System works in the following way: An aqueous urea dilution according to DIN 70040 is sprayed to the exhaust gases and provides a reduction of NOx up to 80%.  This dilution is also well-known under the brand name "AdBlue. This HWL acts as a reducing agent and is transformed with the help of a catalytic converter into ammonia (NH3). The ammonia is then reacting with the NOx gases into harmless water and nitrogen. This special system has to be created, because a normal three-way catalytic converter can only be used in petrol engines due to the oxygen overplus in the exhaust gases of a diesel engine. The urea dilution is located in a separate tank, which is heated electrically or through the waste heat of the en-gine. A pump-/ dosing unit conditions the dilution and sprays it into the exhaust gases during the operation mode. The quantity depends on load and engine revolutions. 
This aerosol meets afterwards a special coated SCR-catalytic converter. The converter is enabling the chemical reduction which reduces the NOx gases by 80%. The entire process is supervised by the SCR-Control Unit.