Urea crystal formation analysis

1970 - 01 - Five truck 01 new countries, to run thirty thousand kilometers feel the so-called 270 horsepower car speed run up, also special oil. To the repair shop to check, the result is the post-processing catalysts the front end of the SCR system, has been a big gray solid blockage, apparently caused by urea crystallization. This is because the urea solution is unqualified. The other reasons besides urea solution was found to be of poor quality will lead to urea crystallization? The following for urea crystallization cause analysis: 1 distribution, structural design flaws early production vehicles often appear urea the distance between the nozzle to the SCR catalysts are too short, as the urea is jet had not a moment after gasification is reach the catalyst carrier, thus forming the crystallization; Distribution and urea and the Angle of nozzle installation pedestal welding encapsulation does not conform to the requirement. 2, the effect of the spray nozzle and nozzle failure models chosen post-processing SCR system can be divided into common type airless help and have spirit to help type two kinds. There is no work of urea injection pressure of the gas is relatively high, so often appear nozzle needle valve closed lax, resulting in low temperature stage still work, shouldn't work urea can't high temperature hydrolysis so that rapid crystallization, such as: Bosch, tenneco systems, etc. ; Have spirit to urea type nozzle is normally open, the atomization is assisted by pressure, such as urea pump pressure piping malfunction or nozzle at high temperature cracking can cause bad jet atomization, as a result causes crystallization jam. 3, remove from urea pump to empty the incomplete due to the vehicle to stop working after urea pump and piping in the presence of residual liquid, so the vehicle off after the ignition switch must be clean, prevent crystallization or freeze. 4, shielding the urea system caused by the vicious circle when you blocked the urea system will make the nozzle in the isolated situation, only doing nothing in high temperature environment. Long time did not run urea pump and pipeline for liquid evaporation residue in internal will be chocked up with crystallization. 5, urea pump filter urea pump has no change regularly all the filter or filter element, the technical requirements for regular cleaning or replacement, or over time will result in blocked or damaged so that lose filtering effect, cause the system work disorder. If you accidentally when adding urea dust into irrigation, if after filtering function failure is easy to cause clogging nozzle, generally there are 3 - nozzle 4 holes, if blocked one or two hole will appear the atomization caused by poor crystallization. 6, sensor and actuator components failure, for example: when in the exhaust gas temperature sensor fault, may actually exhaust temperature is 100 degrees Celsius, and sensor feedback to computer if is 200 degrees Celsius, will cause the system to advance the injection of urea, urea injection hydrolysis gasification, cannot be obtained in low temperature exhaust will naturally form crystals on the catalyst carrier, gradually form a solid urea crystal compounds. 7, use inferior diesel vehicles, and poor working conditions cause the catalyst failure of SCR system is to improve urea solution hydrolysis gasification breaks down into ammonia at high temperature and the NOx in waste chemical reaction, sulfur content in diesel oil has a high technical requirements, high temperature formed sulfide has irreversible damage to the catalysts, all once the failure will cause excessive exhaust catalysts by limiting the engine power output. To sum up, in order to save the cost of driving, to avoid system damage cause computer limit torque output, regular cleaning maintenance to SCR system and selection of washing powder is very important! A: liquid detergent white sediment is what?