SCR system - Diesel engine: Notes

The introduction will initially involve only the M57TU2TOP engine with DDE 73 in BMW X5 and BMW 3-Series vehicles and vehicles derived from these. In order to meet the stricter exhaust-emission regulations for a sustained period, this engine will be equipped for the first time with an SCR system that sprays the urea/water mixture into the exhaust tract. As can be seen in the following graphics, this mixture is metered into the exhaust tract after the diesel particulate filter in the form of a fine spray. The metered mixture reacts there with the hot exhaust particles that arise in the course of combustion inside the engine, reducing the overall content of harmful NOx emissions (nitrogen oxide) in the exhaust gas. The chemical reaction takes place in the SCR catalytic converter downstream of the microfilter. This chemical reaction can only take place when the SCR catalytic converter has reach a required minimum temperature. Before this temperature (around 200 °C in SCR catalytic converter) is reached, the metering is inactive.