An SCR system is used to reduce the amount of exhaust emissions from vehicles. It breaks down the various chemicals within the exhaust fumes into mostly water and nitrogen, which are much better suited for the environment. To operate properly, the SCR system needs to be supplied with AdBlue, which is a simple, non-toxic solution made with about 32.5% synthetic urea and 67.5% deionised water.
How does it work?
The process is simple to understand and does not require extensive knowledge to have a basic understanding.
The main components of the SCR system are the catalytic converter and the injection pump/doser.
- The vehicle outputs noxious emissions, including NOx.
- The emissions are filtered at the DPF (Diesel Particulate Filter) to remove a large amount of soot.
- When reached a certain point, the gases are then sprayed by the pump/doser with AdBlue, which separates NOx into ammonia (NH3) and carbon oxide (CO2).
- The resulting mix then goes into the catalytic converter, which helps to create a chemical reaction, where the emissions are separated into nitrogen (N2) and water (H2O).
Components like the SCR control unit, NOx sensor, AdBlue pressure sensor and temperature sensor are there to control and monitor the system, ensuring that every component is operational.
- The SCR system does not work until the fluid temperature is at least at 220C, power consumption is 20% and the RPM is at at least 1000.
- NOx sensors constantly monitor the amount of noxious emissions from the vehicle to identify if the SCR system is doing its job.
- The SCR control unit is the brain behind the whole system. It monitors all of the sensors to calculate the AdBlue injections amount and type. It also controls the heating unit that brings the gases to an acceptable temperature for the chemical process to take place.
- The AdBlue pressure sensor makes sure to record the pressure of the AdBlue fluid, which will affect the injection.
- The temperature sensor monitors the temperature of the AdBlue and emission gasses, bringing it up if it is not warm enough. If the temperature is off, the fluid will be heated beforehand.
There are differences in the SCR systems between the last 3 Euro-standards:
- Euro 4: no NOx sensors
- Euro 5: typically 1 NOx sensor after catalyst (DAF trucks being an exception, with two)
- Euro 6: DPF, 2 NOx sensors (before and after catalyst
How is the SCR system emulated?
Our CanSmart emulators send specific signals that indicate that the SCR system is fully functioning. This includes the following components:
- SCR control unit
- AdBlue pump/doser
- AdBlue level sensor
- AdBlue tank with heating system
- NOx sensor
The values are well balanced and imitate the SCR system very well, making it an ideal choice when the SCR system is not working or is not needed.
Cheaper emulators have workarounds or sloppy implementation which means that the SCR system will be emulated improperly. For example, some emulators rather than emulating a working SCR system will only emulate the temperature sensors around it.
This makes it easier to emulate the AdBlue system since you do not need to have dynamic values on the various components, but it can be harmful to your vehicle if the temperature values are not adjusted properly. The reason for that is the heating system tries to heat the AdBlue tank whenever the temperature of the exhaust is too low, which might lead to significant damage to the tank and also uses extra fuel to heat it up. This method of emulation is especially prevalent in Euro 5 AdBlue emulators (cheap copies and chineese units).