Many modern diesel cars come with AdBlue installed. This system has a range of names - Mercedes calls it, for example, "BlueTEC", Peugeot - "BlueHDI", VW cars have it included in Bluemotion, and so on. AdBlue helps to reduce the amount of NOx (Nitrous oxide) in the diesel exhaust gases. The system usually consists of the following components: AdBlue tank, heating system, pump, agent spray nozzle, NOx sensor, an additional catalytic convertor, and AdBlue system control unit. .
Principle of operation. AdBlue reagent is fed into the exhaust gases after they are cleaned in the diesel particulate filter. A nozzle sprays the required amount of the agent into the exhaust gases, then they enter the catalytic converter. There, thanks to the added chemical agent, the purification process is accelerated, and the exhaust gases contain minimum amount of NOx at the exhaust pipe. Please note that the AdBlue system has nothing to do with the DPF regeneration procedure. It is a separate component of the exhaust system and does not affect the performance of the DPF. Confusion arises due to the fact that some cars feature a separate injection system for other agents (EOLS, for example) to reduce the DPF regeneration (burn-off) temperature. Again, AdBlue has nothing to do with this process.
Despite the fact that the principle of the system looks quite simple, it is not very reliable. Due to a large number of components the system is very "capricious" and easily malfunctions even due to weather conditions. Most common problems are: heating failure, freezing of AdBlue and the resulting expansion damage to the system, nozzle failure, NOx sensor failure, pump failure, and failure of AdBlue system control unit. Especially fragile iteration of this system is found on Mercedes cars (BLUETEC). The most unpleasant thing about it - even if one component of the system fails, the whole AdBlue system stops functioning and a light appears on the dashboard to inform the driver about the limit of times the engine can be started or mileage left to travel until driving is prohibited altogether.