How to deal with urea crystallization in automotive SCR after treatment system

“The Crystal has crystallized again in the exhaust pipe!” The customer is very annoyed about this. Urea crystals will block the exhaust pipe tightly, not only causing emissions to not meet standards, but also causing engine torque restrictions, feeling sluggish and fuel consumption will increase.

Why does it cause this problem? Some people may say, “You’re not afraid to add high-quality urea.” But is the problem really that simple? Today, let’s take a closer look at the causes and solutions that lead to urea crystallization.

The following fault code is reported:

P246385 Particle Trap (DPF) adsorption particle overload
P24A409 engine forced torque limit indication, due to detection of particle trap (DPF) adsorbing particle overload to prevent DPF burning.

Disassemble the DPF for inspection as shown in the following picture:

Cause of urea crystallization: Excessive urea solution sprayed out or urea not atomized, resulting in urea reaching the catalyst carrier before gasification. When in contact with the pipe wall, the solution continues to accumulate and forms crystals as its moisture evaporates. The crystals continue to grow and become white block like objects, which can be hydrolyzed by boiling water.

2.Check the atomization situation of the urea nozzle: raise the exhaust temperature to allow the urea pump to build pressure and spray. The urea nozzle flows urea like urination, indicating a malfunction of the urea nozzle.

Fault handling:

Replacing the new urea nozzle, blowing back DPF soot, tapping to clean the white crystals of urea, and performing driving regeneration can burn off residual soot in DPF and urea crystals in SCR, restoring the vehicle to normal operation.

Case Summary:

Severe urea crystallization can also lead to DPF blockage faults, and crystallization problems are highly correlated with urea nozzle atomization.