In the cases of urea crystallization, the temperature is the main factor for controlling the shelf life and the crystallization of urea. Therefore, should pay much attention to the temperature. Today introduce the methods of how to prevent the crystallization of SCR urea, hope that could be able to help you, and welcome to complement by experts.
The crystallization of SCR ures is easy to soluble in water, that’s way the SCR urea should be avoided to contact with the dry air, especially in the vehicle urea injection valve and exhaust pipe where need pays attention. At the ambient temperature of 100~130℃, the water around it evaporates very quickly, so it is necessary to avoid storing urea at this temperature. Urea crystallization is a white powder, the melting point is 190℃, can be dissolved into water to use as the solution at this high temperature.
And the problem of flameout and power failure, flameout and switch at 1 gear, do not immediately cut off the power, the urea solution will be returned to the tank from the line when flameout, but if you pull off immediately which will not return the tank, it is easy to block the pipeline.
Also, how can we prevent the accessory substance of urea from crystallizing? The crystallization of accessory substance of urea is formed by lots of reaction. It is hard to dissolve into water and formed a solid surface. Therefore, the product begins to decompose when the temperature reaches to 400℃. After 800℃, the product is decomposed.
If urea is crystallized at the vehicle exhaust pipeline, it will cause the economic problems such as exhaust gas consumption of the engine, so we should pay attention to it at ordinary times.
To avoid the crystallization of using urea which could cuase so many disadvantageous affection, the best way is to install the evaluate devices or adopt measures to provent the urea crystallization.
Handling methods of the crystallization of SCR urea
Urea crystallization is a normal phenomenon, the best urea will crystallize. Daily maintenance is to clear a urea tank per six month, and then use boiling water cleaning urea tank of about 80 degrees, the nozzle is the same, clean with boiling water if there is crystallization. But do not use the cleaning agent, which sold in the market will damage the key element catalyst in SCR system.
1. The quality of automotive urea solution cannot reach the standard
The undissolved substance and impurities in the cheap urea solution of market could cause block and damage the nozzle.
2. Residual solution after injection of urea solution nozzle
After the ignition of the engine is closed, the residual urea liquid in the nozzle pipe will crystallize, which will result in the blockage of the pipe and nozzle.
3. The SCR system does not work for a long time
Injection nozzle is located inside exhaust pipe at high temperature for a long time. During working it is cooled by the circulation of urea solution. It will be damaged if cannot obtain the cooling effect from urea solution. SCR system does not work for a long time will lead the residual urea solution crystallize in SCR system to block the pipeline and nozzle, and because of the lack of liquid immersion for a long time, the life of each component of the SCR system is reduced or even damaged.
4. Objective factors
Complex physical and chemical reactions occur in the SCR system, including atomization, fragmentation, evaporation of the urea solution, energy and momentum exchange between droplets and exhaust gases, particle impingement processes, liquid film formation, Nox catalytic reduction reactions and so on. Moreover, the atomization field and temperature field formed by the urea injection always change with the change of engine operating conditions. When the urea liquid drops are decomposed into ammonia, they also produce cyanuric acid, biuret, cyanuric acid and other intermediate products, which are easy to form urea crystal and other sediments etc. The accumulation of sediments can also cause blocking of the nozzle.
In addition, urea crystallization is a normal phenomenon, the best urea will crystallize. Daily maintenance is to clear a urea tank per six month, and then use boiling water cleaning urea tank of about 80 degrees, the nozzle is the same, clean with boiling water if there is crystallization. And the problem of flameout and power failure, flameout and switch at 1 gear, do not immediately cut off the power, the urea solution will be returned to the tank from the line when flameout, but if you pull off immediately which will not return the tank, it is easy to block the pipeline.