SCR System

What is the SCR (DEF / AdBlue) system?

SCR is a Selective Catalytic Reduction system, the purpose of which is to minimize emissions of particulate matter (PM) and nitrogen oxides (NOx) in diesel engines.

The entire process takes place in a catalytic converter installed in the exhaust system. Nitrogen oxides are converted to nitrogen and water vapor (H2O + N) by combining the exhaust gas with a urea solution, which is injected into it under high pressure. The process is monitored by a NOx sensor responsible for monitoring the correct concentration of nitrogen oxides (NOx) in the exhaust gas.

SCR system – its role and construction

The system consists of the following elements:

  • urea solution tank (AdBlue / NOXy)
  • heater to prevent freezing of the fluid during sub-zero temperatures
  • pumps
  • injector located in the catalytic converter
  • the NOx sensor at the end of the SCR system

In the event of any malfunction in the system, the controller (ECU) restricts engine operation. In the case of trucks, there is a torque restriction, and this is done to reduce emissions despite a faulty DEF system. On the other hand, in the case of agricultural and construction machinery, quite often the machine is completely disabled. The most commonly broken components of the SCR system are the urea pump and the NOx sensor. Unfortunately, service costs are not cheap. An SCR emulator avoids these costs.

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