1. SCR system does not work for a long time
The urea nozzle is located in the exhaust pipe and has been in the high temperature environment for a long time. When it works, it is cooled through the cycle of the vehicle urea equipment. If the cooling effect of urea solution is not available, the urea nozzle will be damaged. If SCR system does not work for a long time, the residual urea solution in SCR system will crystallize and block the pipeline and nozzle. Moreover, due to the lack of liquid immersion for a long time, the service life of SCR system components will be reduced or even damaged.
2. Objective factors
The physical and chemical reactions in SCR system are disordered, including atomization, breaking, transpiration of urea solution, energy and momentum exchange between droplet and exhaust, particle wall collision process, liquid film composition, NOx catalytic reduction reaction, etc. the atomization field and temperature field formed after urea eruption change with the change of engine operating conditions. When urea droplet decomposes into ammonia, the time of atomization and temperature field changes It also forms cyanic acid, biuret, cyanuric acid and other central products, which simply forms urea crystal stone and other deposits. The deposit will accumulate continuously, which will also cause nozzle blockage.
3. The quality of vehicle urea solution is unqualified
Too many impermeable substances and impurities in the low-cost defective vehicle urea solution in the market will cause nozzle blockage and damage.
4. Residual solution after spraying of urea solution nozzle
After the engine is shut down, the residual urea liquid in the nozzle pipe will crystallize and form the blockage of the pipe and nozzle.