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Truck SCR catalyst clogging problem analysis and overcomes


SCR catalyst blockage is a common problem. Due to the harsh working environment of the SCR catalyst itself and its chemical conversion and reduction characteristics, various faults can occur during use.


For example, due to the engine power drop caused by the blockage of the SCR catalyst, the difficulty of starting, and the exhaust gas exceeding the standard, it may interfere with our fault judgment. The severe blockage of the SCR catalyst will cause the exhaust pipe to burn red and even cause the vehicle to spontaneously ignite.

Today, I will analyze the eight reasons leading to blockage of the SCR catalyst:

High temperature inactivation

The SCR catalyst will cause high temperature deactivation under high temperature conditions for a long time. Under high temperature environment, the oxygen storage capacity of the oxidation aid in the SCR catalyst will be reduced, and the oxygen absorption capacity of the catalyst will also decrease rapidly, so that the activity of the catalyst is greatly reduced.

Even when the engine is in good condition and debugging is in place, improper use of it can result in excessive SCR catalyst temperatures.

Reasons for high temperature in SCR catalysts

A. Engine misfire causes the unburned mixture to burn in the catalyst to cause a severe oxidative exothermic reaction;

B. Continuous high speed and large load operation;

C, sudden braking, slowdown;

D, too long idle speed, never more than 10 minutes;

E. Turn off the ignition switch during driving;

F, the mixture is too rich.

Chemical poisoning

The noble metal catalyst on the SCR catalyst carrier has strong adsorption to sulfur, phosphorus, carbon monoxide, incomplete combustion, lead, manganese, etc., and the noble metal catalyst strongly oxidizes and catalyzes, so that the incomplete combustion of the adsorbed diesel is more easily oxidized and polycondensed. Polymerization forms a colloidal carbon deposit, causing clogging of the SCR catalyst.

These reasons can cause SCR catalyst blockage poisoning failure. The so-called "poisoning" refers to the surface of the catalytic carrier layer being covered by other substances, preventing the harmful components in the exhaust gas from coming into contact with it and losing the catalytic effect. This is commonly referred to as SCR catalysis. The device is "poisoned".


Causes of poisoning of SCR catalyst

1 Manganese and lead in fuel oil and engine oil;

2 carbon monoxide produced by incomplete combustion of fuel;

3 The high sulfur content of diesel fuel easily forms a chemical complex in the SCR catalyst.

"Poison" is mainly adsorbed on the active surface of the catalyst and forms a chemisorbed complex. Lead and manganese poisoning is often irreversible. When the catalyst is operated in a lead-containing atmosphere for several tens of hours, it will completely lose its activity. For sulfur, phosphorus and carbon monoxide poisoning, the activity of the catalyst can be recovered under certain conditions.


Carbon blockage inactivation

The carbon blockage of the SCR catalyst is gradually formed, and the formation of the plug is reversible. The blockage can be reduced by chemical processes such as oxidation and gasification, or by physical processes such as desorption and volatilization components, and vapor phase component evaporation.


The carbon deposition on the surface of the SCR catalyst is caused by carbon deposition on the SCR catalyst and the surface of the coating. The carbon deposit on the surface of the layer is often a mixture of various elements including carbon, hydrogen, sulfur, nitrogen, oxygen, and heavy metals. Carbon inactivation is one of the main causes of the failure of SCR catalysts.


Common form of carbon deposit blockage in SCR catalyst

A, the gelatinous carbon deposit is blocked.

B, sulfur phosphorus chemical complex sintering blockage.

C. Lead manganese metal deposits are sintered and clogged.

D. The ignition of the engine causes the catalytic carrier to be dissolved and blocked.

E. Engine misfire causes high temperature aging of the sealing layer between the catalytic carrier and the metal casing of the SCR catalyst, which becomes the catalytic carrier of the latter half of the powder.

Road congestion

Since the vehicle generates the most incomplete combustion under acceleration and deceleration conditions, it is easy to cause the SCR catalyst to clog on the road section where the road is crowded.

No cleaning and maintenance

Since a large amount of colloidal carbon is washed out during the cleaning process, it is easy to cause the SCR catalyst to clog, which is also the reason for the increase in fuel consumption of some vehicles after the maintenance cleaning.

Slamming or dragging


The catalytic carrier of the catalyst is a ceramic or metal device. After the vehicle with the SCR catalyst ceramic catalytic carrier is dragged, a severe bump may cause the catalyst ceramic core to be broken and scrapped.

When the engine is decelerating rapidly, the broken ceramic powder will be sucked into the cylinder with the fluctuation of the exhaust pressure, causing serious wear of the engine, and even the engine may be scrapped.

Fuel supply system failure

Diesel vehicle oil circuit is a part with more faults. Although many advanced engine control systems now have self-protection function, once a cylinder fails, the computer will automatically cut off the fuel injector of the cylinder and prevent it from being supplied. Oil to protect the engine and catalyst, but there are still very few such advanced features, many machines do not currently have this feature.

Moreover, the engine must not be started in a stroller, which would result in excessive fuel being discharged into the SCR catalyst.

Post-processing system failure

When there is a problem with the urea pump in the post-treatment; the nozzle on the urea system has a blockage or its own quality problem; the quality of the urea itself is unqualified; the tail pipe has a leak;

It will cause the urea spray atomization effect is poor, the urea solution is sprayed directly onto the exhaust pipe wall, and at the same time, because the exhaust pipe is always at 500 ° high temperature, the water is easily evaporated, and then the phenomenon of crystallization occurs;

After a long time, the phenomenon of crystallization will be severe, resulting in low catalytic efficiency of the SCR catalyst, resulting in insufficient power.

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