How does AdBlue work in an SCR system? – If your diesel vehicle requires you to top up AdBlue periodically, it is equipped with an SCR catalyst. If this system fails, the consequences can be more serious than just an illuminated check engine light or a basic vehicle inspection (MOT) fault. After a certain distance countdown, the engine will not start unless the AdBlue reservoir is refilled.
Why is SCR exhaust gas treatment system necessary?
Many people recognise the importance of Euro VI emissions compliance as the standard that vehicles must achieve to enter urban low emission zones without paying a toll.
One of the main pollutants associated with NOx emissions from car exhaust pipes, is formed by a group of gases that can cause respiratory problems when inhaled.
Manufacturers use a number of methods to reduce NOx, one of which is exhaust gas recirculation (EGR). However, EGR alone often cannot reduce NOx enough to meet Euro VI limits. The solution is a system. The solution is Selective Catalytic Reduction (SCR).
How does AdBlue work in an SCR system?
Unlike EGR, the SCR system treats NOx emissions after they are formed. As the exhaust gases leave the engine, they enter the exhaust system into an oxidation catalytic converter, where some of the gases are converted.
They then enter the diesel particulate filter (DPF), which removes soot particles (fine particulate matter (PM). Finally, they enter the SCR catalytic converter, which converts NOx into harmless nitrogen gas and water vapor.
This order can vary. For example, on some Citroën/Peugeot BlueHDi vehicles, the exhaust gases pass through the SCR catalyst before entering the DPF, not after.
Unlike oxidation catalytic converters, SCR catalysts require urea, also known as AdBlue exhaust gas treatment solution, to function, which is consumed during the chemical reaction. Madin AdBlue, known as the quality AdBlue brand in Vietnam, provides highly pure urea in a safe, water-soluble form.
AdBlue is stored in a separate tank and is injected into the exhaust system under certain conditions, when the gas reaches a temperature of 150-200 degrees Celsius. The system takes into account the driving style and the amount of urea retained by the SCR catalyst.
The engine’s electronic management system determines when and how much AdBlue is needed, using NOx and gas temperature sensors installed in the exhaust system.
After passing through the injector, AdBlue passes through a mixer in the exhaust system, where its water evaporates, causing the urea to deposit on the SCR catalyst, where it is consumed in a chemical reaction.
Things to know
AdBlue consumption needs to be replenished periodically, the frequency of refilling will vary between makes and models. Faster driving styles also increase consumption. AdBlue is harmless to health and can be washed off with water, however it is corrosive to some metals. Therefore, avoid spilling it.
Overfilling the AdBlue tank can also cause a system failure, as air space is needed at the top of the tank to accommodate the expansion of the fluid, should the AdBlue freeze.
In addition to a faulty SCR catalyst, the system’s sensors can also malfunction. Of course, other related components can also fail, such as wiring.
The AdBlue injector has a number of nozzles that atomize the liquid chemical before it enters the mixing plate and SCR catalyst. In addition to electrical failure, these can leak, causing white urea crystals to build up on the injector. This affects the spray pattern and can over-saturate the SCR catalyst with AdBlue, causing blockage.
The advice is “Do not ignore dashboard warnings about the SCR system” and take any engine start countdown warnings seriously, by consulting a garage as soon as possible.
For all details about the system and products, please contact hotline 0886 634 634 for the fastest support and advice!
