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The Back Door Is Blocked And The Car Is Boring. You Need To Know About Scr

  • Since entering the Fourth National Congress of the people’s Republic of China, SCR (selective catalytic reduction) post-treatment technology has come into everyone’s attention. It can reduce NOx emission by spraying urea solution into the post-treatment unit. Intuitively speaking, our trucks need to “drink urine” in addition to “drink oil”. Since there is such a post-processing device, sometimes some problems will be encountered.
SCR
  • A few days ago, a card friend complained that he had just bought the national five emission light truck, which had just run more than 60000 kilometers. Recently, the power has decreased sharply, and the fuel consumption has also increased. After checking the engine, he found no problem. Since the vehicle is a national five emission vehicle, SCR selective reduction post-treatment device is added to the post-treatment, so it is suspected that this series of problems are caused by the blockage of the post-treatment device.
SCR
  • After inquiring about kayou, we learned that kayou purchased urea solution produced by regular manufacturers at regular Sinopec gas stations. There should be no problem of using inferior urea. There may be another reason for this failure.

1. Add urea saving screw of SCR

SCR
  • Due to the high sulfur content of domestic diesel, in order to adapt to this situation, the domestic SCR post-treatment system mostly adopts vanadium based which is insensitive to sulfur. However, this vanadium based post-treatment carrier has a disadvantage. The catalytic effect is not ideal when the temperature is low, so the system does not inject urea when the exhaust temperature does not reach 200 ℃.
  • The principle of SCR this screw is that after the sensor is raised, it will cause the sensor to be inaccurate. During normal driving, let the sensor think that the exhaust temperature does not meet the standard, so as to achieve the effect of less or no urea injection. Because the sensor is out of alignment, the system does not spray when it should be sprayed, but it becomes normal to spray hard when it should not be sprayed. In this way, it is easy to cause crystals of urea solution to block the post-treatment device.

2.Deliberately driving with SCR low throttle for a long time

SCR
  • We have learned that the catalyst needs a proper working temperature. In order to save fuel, many card friends deliberately run with a low speed and small throttle when cruising on the flat road. At this time, the exhaust temperature and carrier will not reach the working temperature. In addition, the misinjection caused by the urea saving screw mentioned in Article 1 will not be able to continuously decompose and catalyze the urea solution, The product that fails to fully participate in the catalytic reaction, that is, the crystal, is attached to the catalyst surface, resulting in blocking the catalyst channel.

3. SCR system failure

SCR
  • In addition to the above two cases, the SCR system itself has design defects or faults, such as the front section of the exhaust pipe is too long and the thermal insulation measures are not in place; The urea injection pressure is abnormal, the atomization is not good, or the nozzle is not tightly closed; The emptying pipeline of urea pump after flameout is not complete; The damage of urea filter element leads to impurities blocking the nozzle and so on, which may lead to the crystallization blockage of the post-treatment system.
  • To sum up, the blockage of SCR system is not just the problem of urea. If it is not used properly, even if you buy the best urea, it will cause the failure of crystallization blocking the catalyst. If only the urea crystal is blocked, the catalyst can be regenerated and reduced by cleaning, but the whole post-treatment unit can only be scrapped due to heavy metal poisoning caused by the use of inferior urea, which is a loss that our ordinary card friends can’t afford.
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