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Urea Crystallization

The reason of urea crystallization is the natural deposition of the Adblue solution which was not pyrolyzed by the high-temperature exhaust.

There are two kinds of urea crystallization. The first one is the water of the Adblue is evaporated, the urea appeared to crystallize. The second one is the adhesive urea by-product while the reaction happens. The crystallization can be easily found at the end of the Adblue injection unit and exhaust pipe.

What’s the adverse effects of urea crystallization?

When urea crystallization appears, part of or even the complete exhaust pipe of the engine will be blocked. The waste flow will be changed, conversion rate will be reduced, and the exhaust will be affected.

There is a big waste of Adblue solution with the result of crystallization. The distribution of Adblue solution spray will not be In-homogeneous and finally, lead to blockage of the injection nozzle. Under high temperature, the decomposition of urea also produces ammonia gas causing the pollution to the surroundings.

How to prevent the urea crystallization?

The temperature is the main factor to control the warranty and crystallization. So more attention should be paid to this.

The urea crystals are easy to dissolve in water, so the automotive urea needs to avoid the contact with dry air, especially at the Adblue injection valve and exhaust pipe. At 100~130 degrees centigrade, the water of the Adblue solution evaporates very quickly. So it is necessary to avoid storing Adblue solution at this temperature. Urea crystal is a white powder, with a melting point at 190 degrees. At this high temperature, the urea crystal can be dissolved in water, changed into the Adblue solution.


One thing should be noticed when stall and cut out the engine. When the engine is stalled, do not cut out it immediately. The Adblue solution will be returned to the jar from the line. But if you cut out immediately, The solution is easy to block the pipeline.

Also mentioned is how to prevent the crystallization of urea by-products. The urea crystallization of the by-product of urea is mainly formed after the reaction. They are difficult to dissolve into the water, forming a solid surface. While the temperature reaches 400 degrees, the by-product begins to decompose. At the temperature of 800 degrees, a total of the by-products will be decomposed.

If there is urea crystallization on the exhaust pipe of the automobile, the engine’s fuel consumption will be more, so we should pay attention to it at ordinary times.

Therefore, avoiding the urea crystallization, it is better to install an evaluate equipment, or take measures to avoid the urea crystallization.

Method for solving the urea crystallization

Urea crystallization is a normal phenomenon. Daily maintenance of the Adblue tank is as follows: clearing the Adblue tank every half year, cleaning the Adblue tank with 80 degrees boiled water. The solving of the problem for the nozzle is the same. Immersing the nozzle into the boiled water when urea crystallization appeared, problems will be solved. Cleaning agents cannot be used while cleaning The commercially marketed cleaning agents will damage the key ingredients in the SCR system.

The reason of blocking the nozzles.

1.The quality of Adblue is not up to standard.
In the market, the low quality and inferior urea or urea are sold. Too much insoluble matter and impurity in the Adblue solution may cause the block and damage to the nozzles.

2. Residual Adblue solution after injection from the urea solution nozzle.
After the ignition of the engine is closed, the residual Adblue solution in the nozzle pipe will crystallize, resulting in the blockage of the pipes and nozzles.

3. SCR system does not work for a long time.
Urea nozzle is arranged in the exhaust pipe. In the high-temperature environment, it is cooled by the Adblue solution circulation. Without the cooling effect of the solution, the urea nozzle is also prone to damage. SCR system without working for a long time will lead the residual Adblue solution in the SCR system crystal and block the pipes and nozzles. Lacking enough liquid immersion, the life of components of the SCR system will be reduced or even damaged.

4. Objective factors
Occurrence of complex physical and chemical reaction in the SCR system, including the atomization, broken, and evaporation of Adblue solution, the energy and momentum exchange between the droplet and exhaust, particle impingement, film formation, and Nox catalytic reduction reaction. The atomization field and temperature field after the injection change according to the engine operating conditions, During the time of decomposition of ammonia, the Adblue solution droplets also generate acid and shrink two urea, cyanuric acid and other intermediate products, easy to form urea crystal stone sediment. The accumulation of sediment can also cause blocking of the nozzle.