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Industry News

   The important application of refractometer products in the measurement of quality   of urea for vehicles

In the hot summer weather, in order to ensure driving safety, please keep the following six points in mind:

1、Prevent drowsy driving;

2、Prevent road rage;

3、Prevent engine overheating;

4、Prevent brake failure;

5、Prevent vehicle puncture;

6、High temperature fire prevention;

In addition, diesel drivers should also pay attention to the choice and use of urea for vehicles. Today, we take automotive urea as the topic, about the application and quality testing of automotive urea.

Application of Urea for Vehicles

Automotive urea, the scientific name is diesel exhaust treatment fluid, used in diesel engines. It is a liquid used in SCR technology to reduce nitrogen oxide pollution from diesel vehicle exhaust. Its composition is 32.5% high-purity urea and 67.5% deionized water.

SCR  Technology:(Selective Catalytic Reduction Technology)SCR system includes urea tank (loaded diesel exhaust treatment fluid), SCR catalytic reaction tank. The operation process of SCR system is: when nitrogen oxides are found in the exhaust pipe, the urea tank automatically ejected diesel exhaust treatment liquid, and the diesel exhaust treatment liquid and nitrogen oxides occur the REDOX reaction in the SCR catalytic reaction tank, generating pollution-free nitrogen and water vapor discharge.

Urea Solution for Vehicles

It is an aqueous solution with a urea concentration of 31.8%~33.2%, and one ton of automotive urea particles makes about three tons of automotive urea solution. Automotive urea is a special exhaust gas purification reducing agent for diesel engines, it is an odorless and non-toxic solution, stored in a special storage container on diesel vehicles.When the exhaust gas is discharged from the engine, it goes with the exhaust gas to the SCR catalytic converter, which then converts the nitrogen oxides into harmless nitrogen and water, thus greatly reducing the exhaust gas emissions.

Environmental Protection Background

From January 1, 2015, domestic diesel vehicles will implement national IV emission standards, and national III standard diesel vehicles will not be sold and registered from now on.At present, SCR (selective catalytic reduction technology) technology has become the preferred technology for diesel engine national Ⅳ standard. Domestic engine manufacturers are beginning to use SCR technology to meet environmental requirements.

If the diesel exhaust treatment liquid is not loaded, or the purity is not enough, or the quality is shoddy, the vehicle engine will automatically slow down. At the same time, the inferior quality of diesel exhaust treatment liquid will pollute the catalyst in the SCR catalytic reaction tank, causing serious consequences.

The Importance of Automotive Urea

Unlike ordinary industrial and agricultural urea, automotive urea has a higher purity.For this stage, environmental protection is is getting more and more attention, in the vehicle is also the case.In the vehicle exhaust treatment, vehicle urea solution can convert nitrogen oxides into harmless nitrogen and water into the atmosphere, energy saving and environmental protection.

In order to enable the car to start normally, we should also ensure the adequacy of the car urea solution in the storage tank. The selection of different vehicle urea solutions for vehicle maintenance effects are not the same.

If the concentration of urea solution is too low, and the proportion of heavy metals and other chemical components is high, then these substances will react with the catalyst to reduce the tail gas conversion effect, or even lose its effect; If the solution contains particles, heavy metal ions and other impurities, it will cause serious damage to the nozzle, filter and other parts of the vehicle SCR system, bringing unnecessary economic losses.

Storage Requirements for Automotive Urea

According to the above, temperature will affect the urea content and stability of vehicles.

The storage temperature of urea is -5℃-25℃, too high or too low will affect the use of urea solution. At high temperature, urea solution is easy to decompose, ≤10℃ shelf life is greater than 36 months, ≤30℃ shelf life is greater than 12 months, ≤35℃ shelf life is about 6 months.

In the summer, due to the significantly shortened shelf life, it should be tested before each use. The initial crystallization point of urea solution is -11 ℃, and too low a temperature will crystallize the urea solution and change the concentration of urea solution.

Because the urea solution is easy to be polluted by impurities after opening or to breed algae after being exposed to sunlight, and the urea itself decomposes to produce ammonia loss, which causes the solution to volatilize and causes urea deterioration. According to the recommendations of domestic urea solution manufacturers, if the packaging is opened, it should be stored as required and used within 30 days.

Technical Index of Urea for Vehicle

Urea Content

In SCR reduction system, the concentration of urea solution is one of the key factors, too high or too low concentration not only can not improve the conversion efficiency of NOx, but will cause ammonia leakage, forming the secondary pollution.

Most European diesel vehicle manufacturers prefer to use a urea solution with a urea concentration of 32.5% as a reducing agent, because this concentration of automotive urea solution has the lowest crystallization point.


The density of vehicle urea solution is closely related to the concentration. At a certain temperature, the concentration of urea solution has a one-to-one correspondence with the density, and it increases with the increase of the concentration (as shown in the figure). The density measurement helps to verify the concentration and quality of urea solution for vehicles.

Refractive Index

The density of vehicle urea solution is also closely related to the refractive index. Similar to the density, the refractive index of urea solution at a certain temperature also has a one-to-one correspondence with the concentration, and increases with the concentration increasing (as shown in the figure). The measurement of refractive index can further assist in verifying the concentration and quality of urea solution for automotive use. The concentration of urea solution can be calculated by using the refractive index of standard urea solution and sample.


Urea can be hydrolyzed to produce ammonia under the action of acids, alkalis and enzymes (acids and alkalis need to be heated). Too high alkalinity indicates that some urea is not pure or has been decomposed. This index controls the content of ammonia in urea.

Other Impurities

Biuret: It is a byproduct of urea in the production process, and the urea solution is improperly stored then easily condensed into biuret. As an impurity, it should be strictly controlled.

Other impurities, as well as aldehydes, phosphates, metal ions and insoluble matter, all should be strictly controlled.

Determination of Urea for Vehicles

From the above technical indicators of automotive urea, we find that in order to ensure the quality of automotive urea, concentration measurement has become an important indicator of the quality detection of automotive urea. How to find qualified suppliers of automotive urea solution and rapid measurement, these two problems have become an important issue that domestic automobile manufacturers urgently need to solve in the short term.

The concentration of urea solution is one of the key factors in SCR reduction system. Domestic and foreign standards generally specify that the concentration of urea solution is 31.8-33.3/33.2%. At present, the main detection methods at home and abroad are:

Chemical Reagent Method

The chemical reagent method is to convert the sample into hexamethyltetramine salt and ammonium ion and then titrate with a base.GB/T696 and the local standards of Beijing and Shenzhen all use this method, this method has a small investment, but the operation is cumbersome and with the long time, the user needs to have a certain chemical test operation experience, and will use formaldehyde, sulfuric acid and other solvents, which is harmful to the operator and not environmentally friendly.

Kjeldahl Method for Nitrogen Determination

Kjeldahl nitrogen determination method is a general nitrogen content determination method to determine nitrogen content through Kjeldahl nitrogen analyzer, and then converted into urea content.This method takes a long time, and it cannot determine where the measured nitrogen is coming from, for example, if melamine is added to the urea solution, the nitrogen content will also increase.

Refractive Index Method

The concentration of urea solution was calculated by measuring the refractive index of standard urea solution and sample solution.The refractive index itself is also an indicator of automotive urea solution, domestic and foreign standards generally specify the refractive index of 1.3814-1.3843, similar to density, at a certain temperature of urea solution refractive index and concentration has a corresponding relationship, measurement of refractive index is helpful to judge and verify the concentration and quality of automotive urea solution.

It can be seen that it is the most convenient and accurate method to measure and judge the quality of automobile urea by measuring the refractive index of automobile urea solution.

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