BlueTec refers to a filter and scrubbing system designed to stop particulates from spewing out the tailpipe and to neutralize oxides of nitrogen.
The particulate filter piece of the emissions controlling system is not complicated or new. However, the tricky part of BlueTec is the injection of a urea-based fluid called AdBlue that is designed to reduce nitrogen oxide emissions by 80 per cent.
The urea - AdBlue - is sprayed into the stream of exhaust gases as they head out the tailpipe. But before exiting emissions are treated by a fourth catalytic converter known as the Selective Catalytic Reduction (SCR) filter.
The urea solution is held in a separate on-board tank (28-litre capacity for the ML and R models; 32 litres for the GL). So little is used, a fill-up will usually be required only every 20,000 km at a Mercedes dealer during regular service.
In the Mercedes' case, if the tank runs empty, there is no impact on performance. A signal in the instrument cluster indicates to the driver that the tank is empty. After 10 starts of a vehicle with an empty tank, the engine control system is designed to prevent ignition until the tank is refilled.