Nowadays, many card friends, especially those of Guo 4 and Guo 5 cars, often hear such problems as blockage of urea pipeline and urea nozzle during vehicle maintenance. In fact, these problems all come from SCR. Then the urea minor edition of Guangdong Bao Di Vehicle gives some introductions to you from several aspects:

I. What is SCR

The principle of selective Catalytic Reduction (SCR) is to selectively reduce NO and NO2 to N2 under the catalytic action of NH3 at 290-400 ~C without the oxidation reaction between NH3 and O2, thus improving the selectivity of N2 and reducing the consumption of NH3.

SCR system is composed of ammonia supply system, ammonia/air injection system, catalytic reaction system and control system. In order to avoid energy consumption by flue gas reheating, SCR reactor is usually placed behind economizer and before air preheater, i.e. high dust section. Ammonia is added to the horizontal pipe in front of the air preheater and mixed with the flue gas.

Selective Catalytic Reduction (SCR) technology has been used in Europe since 2003. As a mature technology, SCR technology has become the mainstream of diesel vehicle exhaust treatment technology. It is also the exhaust treatment technology developed and popularized by our country. It is stipulated that the fifth and sixth national vehicles must be equipped with SCR system when they leave the factory.

2. What are the common problems of SCR system?

During the operation of SCR vehicles, due to the special properties of urea solution, urea crystallization will occur in urea pipelines and urea nozzles; when the crystallization is serious, it will cause the blockage of urea pipelines or urea nozzles, resulting in excessive emissions, OBD lights on, engine power limitations and other phenomena.

3. Cleaning of urea nozzles

Remove urea nozzle

Note: When disassembling the nozzle, the urea pipe should be disassembled first, then the cooling pipe, and finally the solenoid valve connector.

(2) Put urea nozzle in hot water and shake it from side to side.

The purpose of this method is to dissolve urea crystals quickly. If the conditions permit, the urea pipeline and cooling pipeline of urea nozzle can also be cleaned on the car without removing them. The cleaning method is the same.

Note: When cleaning, who should not splash into the plug-in plug;

The nozzle is mounted with three M6 bolts with a minimum installation torque of 6N? M and a maximum of 10N? M.

The bolt length is minimum 25 mm and maximum 30 mm.

Note: After each removal of urea nozzle: when assembling, the gasket of urea nozzle should be replaced; after installing urea nozzle, first install solenoid valve connector, then install cooling water pipe, and finally install urea pipe.

IV. Cleaning of Urea Pipeline

Remove the urea pipe and fill it with hot water.

Note: When removing the urea pipe, press the snaps on both sides of the urea pipe joint and pull out the urea pipe joint.

(2) Shake the urea tube left and right to dissolve the crystals in the urea tube quickly.

3. Pour out the hot water in the urea tube

Note: When cleaning the urea tube, be careful not to splash water into the heating joint of the urea tube.

5. Cleaning of Urea Crystallization in Exhaust Pipeline

Remove the crystallized exhaust pipe

Note: Urea crystallization at the joint of urea nozzle on the exhaust pipe (crystallization in the exhaust pipe)

(2) Wash one end of the exhaust pipe with hot water until the urea crystals in the exhaust pipe dissolve completely.

(3) Install exhaust pipelines as required to ensure the sealing of exhaust pipelines.

Note: In the process of cleaning urea nozzle, urea pipeline and exhaust pipeline, the hot water temperature should not be too high to avoid scalding.