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EURO 4 IV With UREA How To Maintain The Posttoprocessing System

- Jun 06, 2018 -

Only care about adding urea and not maintaining the posttoprocessing system is a problem!

Under normal circumstances, if the car does not burn urea, the SCR system will report a fault exceeding 5g/kw.h and a fault exceeding 7g/kw.h, and the car will be limited to twisting (usually the engine will be limited to 60% of the power output). The consumption of 100L of diesel in the State V vehicle corresponds to the consumption of urea in the range of 3L to 5L. If it exceeds this range, no matter whether it is more or less an abnormal working condition, it needs to be overhauled. Urea consumption of longtodistance transport vehicles on the trunk line is relatively shorter than on shorttoduty roads or on urban roads. In addition, summer is more than winter, because urea injection conditions require exhaust temperatures above 200 degrees Celsius.

Then let the technician analyze some of the reasons for the urea crystal blockage.

01 defects in the structural design of catalytic converters

Early production vehicles often have short distances between the urea nozzle and the SCR catalyst. When the urea is sprayed, it does not reach the catalyst carrier before it reaches the catalyst carrier. This results in the formation of crystals; there is also the urea nozzle installation base welding angle and catalysis. The device package does not meet the requirements.

02 nozzle atomization effect or nozzle failure

The posttoprocessing SCR systems used in common models can be classified into two types: airless and airtoassisted. The pressure of urea injection is generally relatively high without gas assistance. Therefore, the frequent closure of the nozzle valve needle leads to the failure of the low temperature stage of the work. The urea cannot be hydrolyzed at a high temperature, resulting in rapid crystallization. For example, the Bosch system is heavy. Steam generation system, Tenneco system, etc.; airtoassisted urea nozzle is normally open type, its atomization is assisted by air pressure, such as urea pump pressure pipeline failure or the nozzle burst at high temperatures will cause spray mist Poorly chemicalized, resulting in crystallization blockages, such as: Imitaike, Cummins Ecofit, Pageli, Weifu Lida, heavy truck second generation and so on.

03 The urea pump is empty after the vehicle is extinguished

Since the residual liquid exists in the urea pump and the pipeline after the vehicle stops working, the emptying work must be performed after the vehicle is turned off to prevent crystallization or freezing.

At present, most urea pumps are more or less defective in the emptying design. Take the Bosch 6.5 system, using a diaphragm motor to operate at a frequency of 9 Hz to conduct evacuation. When the rubber ring at the bottom of the motor core is damaged, suction and reciprocation will occur. In addition, onetoway diaphragm seals often appear. Causes the motor to have no suction, etc., which can cause emptiness due to incomplete evacuation.

04 The vicious cycle caused by shielding urea system

In terms of the Tenneco system, Tenneco's urea pump fluid circuit is a ring, and the urea pump starts running immediately after the start of the urea fluid to disperse the nozzles, so when you shield the urea system, the nozzles will stand alone. The situation can only sit still in the high temperature environment. Urea pumps and pipelines that do not operate for a long time will crystallize and block due to the evaporation of the water that remains in the interior.

05 Urea pump filter is not replaced regularly

All urea pumps have filters or filter elements. The technical requirements must be cleaned or replaced on a regular basis. Otherwise, it will cause plugging or breakage and loss of filtration during a long period of time. This will inevitably cause system misalignment.

If you inadvertently add dust to the urea when you add urea, you can easily block the nozzle if the filtration function fails. Generally, the nozzle has 3to4 holes. If you block one or two holes, it will inevitably result in poor atomization and cause crystallization. .

06 Failure or damage of other external sensor and actuator components

Example: When the exhaust temperature sensor has a performance failure, the actual exhaust temperature may be 100 degrees Celsius. If the sensor feeds back to the computer at 200 degrees Celsius, it will cause the system to inject urea ahead of time. Urea injection cannot be performed at low temperature exhaust. Hydrolysis and gasification will naturally result in the formation of crystals at the catalyst support, which will form hard urea crystal compounds over time.

07 Vehicles use poor quality diesel and poor working conditions cause catalyst failure

The catalyst of the SCR system is to promote the chemical reaction of ammonia formed by hydrolysis and gasification of urea solution at high temperature and NOx in the waste. It has high technical requirements for the sulfur content in diesel fuel, and the sulfide formed at high temperature is irreversible to the catalyst. The destructive effect of all catalytic converter failure will cause the exhaust gas to exceed the limit and limit the engine power output.

To sum up, in order to save running costs and avoid system damage caused by the computer to limit torque output, regular cleaning and maintenance of the SCR system and use of reliable car urea is particularly important!

Technician recommends:

Change the urea pump filter every 3 to 5 million kilometers, and clean the urea tanks and pipes and nozzles;

Replace the oil separator every 50 to 80,000 kilometers (some models do not have this device), check the nitrogen oxide sensor and exhaust temperature sensor probe to remove carbon deposits or crystals;

The brand urea solution produced by the regular manufacturers is used to ensure that the quality meets the national standard requirements (a total of 18 indicators of the national standard, 32.5% of the concentration is only one of them, other indicators need to pass the laboratory inspection)


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