With the implementation of the IV emission policy of diesel vehicles, our company will use more and more diesel vehicles for vehicle urea. However, the use of vehicle urea is new after all, and many people still lack of understanding and even some use Misunderstanding, in this car on the working principle of urea and the use of some of the considerations on some simple introduction, hoping to give the use of vehicle urea unit to provide useful reference.

 

First, the diesel vehicle emission control SCR technology line works

 

       The main pollutant emissions from diesel engines are NOx (NO x) and PM (particulate), and the working conditions required to reduce these two emissions are exactly the opposite and as a result EGR (exhaust gas recirculation) and SCR Sex Catalytic Reduction) two technical solutions to meet the country's four emission requirements. In the combustion process, the engine adopting the SCR technology has already achieved the goal of effectively controlling the PM emission through technical means of fully burning the diesel while NOx needs to be reduced to nitrogen (N2) and water during the exhaust gas discharge (H2O), the process of reducing agent is car urea solution. Exhaust gas from the turbocharger into the exhaust pipe, the exhaust pipe is equipped with urea measurement and injection device, when the temperature reaches 300 ℃ -500 ℃ into the urea solution, the catalyst under the action of urea (NH2CONH2) hydrolysis of NH3 And CO2, NH3 and NOx react to generate nitrogen and water discharge. Vehicle urea solution in the catalytic reduction reaction control is a very fine process, the injection of urea must be consistent with the concentration of NOx, urea injection is too small, you can not reach the appropriate level of treatment , The amount of urea injection too much, it will make excess ammonia into the atmosphere, resulting in new pollution.

 

Second, the car with urea solution requirements

 

       Vehicle urea solution is called Adblue in Europe, DEF (Diesel Exhaust Fluid) in North America and vehicle urea solution or "Tim Blue" in China. Automotive urea solution purity and cleanliness requirements higher relative to the industrial urea, biuret, insolubles, iron, sulfide, chloride and other content has strict requirements. As the SCR catalyst carrier prone to poisoning of metal ions and thus lose the catalytic effect, therefore, car urea solution must use the electronics industry-level ultra-pure water. The current vehicle urea solution generally consists of 32.5% of high purity urea and 67.5% of ultrapure water, because the concentration of urea solution crystallization lowest point, below -11 degrees when crystallization. In order to prevent crystallization and solidification of the solution at low temperatures, it is currently prevented by adding a modifier to lower the freezing point of the solution and applying a heating device.

 

Third, the use of low-grade car urea solution or do not use car urea solution hazards

 

       In order to reduce expenses, the use of low-cost urea or cut off the OBD detection signal without the use of urea, these practices not only cost savings, but also because of damage caused by the SCR system will increase the cost, but also increase the atmospheric Pollution affects the health of humanity as a whole.

 

1, the use of poor quality urea solution

 

       Why can not the general urea solution instead of car urea solution? Because when the purity of the urea solution is not enough, there are particles, heavy metal ions, minerals and other impurities exist, it will cause serious damage to the vehicle SCR system nozzles, filters and other parts, resulting in unnecessary economic losses. Such as biuret, aldehydes and insoluble impurities, may lead to the SCR system, urea pump, infusion tube and nozzle plug; urea contained in the metal ions is not only impurities, while the SCR system catalyst has the poison effect, the impact The efficiency of catalytic reduction; combustion of the resulting deposits, will block the catalyst skeleton, thereby reducing the efficiency of the catalyst, reducing the life of the catalyst. If the concentration of urea solution deviates from the standard concentration, it will not only affect the conversion efficiency of NOX, but also increase the crystallization point of urea solution and unexpectedly block the pipeline, nozzle and urea pump.

 

2, the harm of water instead of urea

 

       One common practice of cheating in the country is to circumvent the OBD monitoring and replace the urea solution with water. This method is more subtle, but the water can not restore the exhaust gas, resulting in the higher NOx emission than the third-country car. Nitric acid generated by the combination of NOx and water in the air is a major cause of acid rain. At the same time, NOx can cause photochemical smog pollution with other pollutants under the action of ultraviolet light, which is harmful to the atmosphere. Therefore, as a responsible enterprise, there should be no replacement of urea with water. At the same time, if ordinary water is added instead of pure water, the metal ions contained in ordinary water will cause poisonous effect on the catalyst. Impurities, insolubles and sediments in normal water will block the nozzle and the catalyst support.

 

3, do not use the dangers of urea

 

   Some units in order to reduce costs, cut off the detection of OBD, in the use of urea solution does not appear to be added, but it will cost savings, but the entire SCR system will have irreparable damage. Such as automotive urea nozzle is an important component, located in the exhaust pipe, long-term high temperature environment, and it is working through the cycle of urea solution cooling, urea solution can not be cooling effect, urea nozzle is also prone to In other words, if the urea solution is not added, the post-processor does not work and is easily oxidized at a high temperature. Therefore, this method not only increases the environmental damage but also increases the overall cost.

 

Fourth, the use of car urea solution considerations

 

1, pay attention to prevent car urea solution to human damage

 

       Car urea solution under normal circumstances, the human body is not harmful, such as contact with the skin just use plenty of soap and water or rinse; such as unfortunate splash in the eyes: open the upper and lower eyelids, rinse with water; if swallowed by a large number, You need medical treatment. Just pay attention to the above matters, basically you can safely use car urea solution. Under high temperature urea solution may free ammonia, ammonia on the skin contact have corrosion and irritation, long-term exposure to ammonia, some people may appear skin pigmentation or finger ulcers and other symptoms, this happens, then Need to go to the hospital for medical treatment.

 

2, car urea how to store

 

       Automotive urea is a less stable and pure chemical, therefore, should pay attention to the following points during storage:

 

(1) pay attention to the impact of storage temperature on the vehicle urea solution

 

Automotive urea requirements storage temperature is about -5 ~ 25 °, to avoid light and heat, and different storage temperature, the shelf life is not the same, the corresponding shelf life of different temperatures as shown in the following table:

 

           Relationship between shelf life and temperature of automotive urea solution

 

Storage temperature (0C)

 

Shelf life (months)

 

≦ 10

 

36

 

11-25

 

18

 

26-30

 

12

 

31-35

 

6

 

> 35

 

Pre-use testing

 

As can be seen from the table, in southern China, product performance is generally guaranteed within six months is stable, it is recommended to use the factory within six months of the product, at most not more than a year. In the summer, be sure to cool down the car urea storage solution. If you find that there is a very exciting ammonia smell when opening the tank sealing cap, it should be sealed immediately and can not be used any more. Immediately through the relevant instruments, the qualified rear be usable.

 

(2) Note the vehicle urea storage tank and filling equipment

 

   Urea will react with some materials, such as copper, iron, aluminum, etc., if it is loaded into a jars of this kind of material, or filled with such material filling facilities, it will cause car urea deterioration, Thus affecting the performance of SCR. Therefore, when using the car urea do not pour the urea solution installed in other jars, filling also use special filling equipment. Also note that vehicle urea will crystallize at low temperatures, the volume will expand about 7%, so do not overfill the urea solution, to maintain the storage capacity of about 90% up and down.

 

(3) Note car urea solution storage and use of the environment to be clean

 

Storage car urea solution environment should be clean and dust-free, if the car urea solution stored in dust everywhere, it will certainly pollute the car with urea, so that it reduces the concentration, but also produce insoluble. Therefore, the tank, filling equipment, etc. must be well sealed, and breathing port must be installed filter device. Urea solution to open in order to avoid contamination or exposure to algae breed algae, ammonia decomposition caused by the deterioration of urea, open the vehicle after the car urea solution in addition to the required storage, but also should be used within 30 days.

 

3, pay attention to use and carry anti-pollution and leak-proof

 

   Urea solution in the course of the need to avoid impurities into the solution and urea tank. General urea solution when filling a dedicated tube, just open the urea tank, plug in the filler tube just fine. But there are also some people usually pay little attention to the impurities into the tank, plug the urea tank urea pump. Some people also do not pay attention to, in the cleaning of SCR systems, storage tanks or filling equipment, the use of ordinary water, due to ordinary water, the metal elements of calcium, magnesium, potassium, sodium ion content is relatively high, once these sources of pollution, will lead to exhaust emissions System catalyst poisoning, increasing SCR operating costs, it should be eradicated using ordinary water rinse. In addition, urea is alkaline, copper, iron, aluminum corrosion, urea overflow inappropriate overflow, will corrode the vehicle, the other in the usual car with urea, we must do a good job in earthquake-resistant measures to avoid the car urea tank Vibration damage and leakage of corrosion caused by vehicles.

 

In short, the use of vehicle urea solution, seemingly simple, in fact, there are many places to pay attention, I hope through this article, so that users can correctly understand and use a good car urea solution, on the one hand to keep the car good Technical status, on the other hand can reduce air pollution. What is not clear you can call us.