Maintenance and Misuse of Commercial Vehicle SCR Tail Gas Aftertreatment System

Composition of SCR tail gas post-treatment system

SCR system can be divided into three parts: urea injection system for urea injection, SCR catalyst assembly for catalytic noise reduction, sensor and other parts. It mainly includes urea supply unit (urea pump), urea injection unit (urea nozzle), urea tank, urea pipeline and injection control unit (DCU)

Urea pump
The urea pump is responsible for pressurizing the urea solution in the urea tank and sending it to the urea nozzle, while pumping the excess urea solution back to the urea tank to maintain the system pressure at about 9bar. After the engine shuts down, the urea pump pumps the urea solution in the system back to the urea tank to avoid system failure caused by residual urea solution. There is a replaceable filter in the urea pump to prevent the fine dust particles (diameter>30 um) in the urea solution from entering the injection valve. The filter element and its auxiliary balance elements need to be replaced regularly

Urea nozzle
The function of the urea nozzle is to inject the urea solution at a certain pressure provided by the urea pump into the tail gas of the exhaust pipe. The urea nozzle has 1 urea pipe connector and 2 cooling water connectors. The two cooling water connectors are the water inlet and return ports for the engine coolant to cool the urea nozzle to prevent the urea nozzle from failure due to high temperature