What is 'SCR' technology?

SCR stands for selective catalytic reduction, which is a technology used for reducing nitrogen oxides (NOx) from the exhaust gas of diesel engines. It's based on AdBlue® - also called diesel exhaust fluid - a 32.5% urea solution in purified water, which is injected into the exhaust pipe.

The urea in the AdBlue® releases ammonia (NH3) with the exhaust gas's high temperatures. This ammonia reacts with nitrogen oxides (NO and NO2) in the catalytic converter to form harmless nitrogen (N2) and water (H2O) vapour.