Diesel engine post-treatment urea crystallization rapid test method

Abstract

The invention relates to the technical field of aftertreatment performance testing, in particular to a diesel engine aftertreatment urea crystallization rapid testing method which comprises the steps that on an engine pedestal, a high crystallization risk cycle test is carried out according to a calibration program of a target engine, the single high crystallization risk cycle is the first 1200 s of a WHTC standard cycle test, and the single high crystallization risk cycle is the second 1200 s of the WHTC standard cycle test; urea with the biuret mass concentration of 0.35%-0.50% is adopted as a post-treatment agent in the post-treatment system of the WHTC standard cycle test. According to the method, the original urea crystallization evaluation performance test cycle can be continued, the test time can be greatly shortened only by obtaining a proper high biuret urea product, the operation is simple, and the feasibility is high.

Description

Technical Field

[0001] The present invention relates to the technical field of post-treatment performance testing, and particularly relates to a rapid test method for urea crystallization in diesel engine post-treatment. Background Art

[0002] Under the background of increasingly stringent environmental protection requirements, heavy-duty diesel vehicles, as one of the important sources of air pollutant emissions, have attracted much attention in their exhaust gas treatment. With the widespread use of the SCR (Selective Catalytic Reduction) technology route in heavy-duty diesel vehicles to control nitrogen oxide emissions in diesel engine exhaust gas, the SCR technology has become a key technology in the field of heavy-duty diesel vehicle exhaust gas purification.

[0003] The core of the SCR technology lies in the catalytic conversion reaction. In this reaction process, ammonia is required as a reducing agent to reduce nitrogen oxides in the exhaust gas to harmless nitrogen and water, thereby effectively reducing nitrogen oxide emissions. However, in actual use, due to the certain danger and inconvenience in the storage and transportation of ammonia, urea is usually added to provide ammonia for the SCR system. When the aqueous urea solution is sprayed into the exhaust pipe, under the action of high-temperature exhaust gas, urea will undergo a series of chemical reactions and finally decompose to produce ammonia. Although the urea injection module in the current SCR system has undergone a large number of optimizations and improvements to maximize the urea decomposition efficiency. But in the actual operation process, when the diesel engine is in a low-speed and low-load condition for a long time, the exhaust gas temperature will significantly decrease. And the decomposition of urea requires certain temperature conditions, and the lower exhaust gas temperature will cause the urea to not decompose sufficiently, resulting in a relatively large risk of urea crystallization.

[0004] The generation of the urea crystallization problem has a complex chemical mechanism. Urea crystallization mainly comes from incompletely decomposed urea and by-products in the urea hydrolysis process, mainly biuret and triuret. The formation route of biuret is relatively diverse. In addition to being formed during the use of urea due to insufficient urea decomposition or inappropriate reaction conditions, a certain amount of biuret will also be inevitably generated in the qualified urea production process. Triuret is formed by the further condensation of urea under specific reaction conditions. These crystalline substances will gradually accumulate in parts such as the pipelines, mixers, and catalyst surfaces of the SCR system.

[0005] Urea crystallization can cause many serious hazards. On the one hand, it can lead to pipeline blockage, increase the exhaust resistance, affect the normal operation of the engine, and reduce the power performance and fuel economy of the engine. On the other hand, the crystalline substances covering the catalyst surface will reduce the contact area between the catalyst and the exhaust gas, lower the catalytic conversion efficiency, and make the emission of nitrogen oxides unable to achieve the expected control effect, thus affecting the performance and reliability of the entire SCR system. Since the occurrence of urea crystallization problems involves multiple complex factors such as the urea decomposition process, chemical reaction conditions, and the operating conditions of the engine, and these factors interact and restrict each other, currently, urea crystallization problems can only be alleviated through design and calibration, rather than completely solved.

[0006] During the SCR system design and selection process, the urea crystallization performance, as an important evaluation index, needs to be strictly and systematically verified through a large number of simulation calculations and bench tests. Simulation calculations can use advanced computer simulation technology to conduct detailed simulations and analyses of the fluid flow, chemical reactions, and urea decomposition process within the SCR system. By establishing an accurate mathematical model, the decomposition situation and crystallization risk of urea under different operating conditions can be predicted, providing a theoretical basis for the design and optimization of the system.

[0007] Bench tests, on the other hand, simulate the actual engine operating conditions in a laboratory environment to comprehensively test and evaluate the SCR system. Bench tests mostly adopt the method of running high-crystallization-risk cycle conditions for a long time, and the single test time usually exceeds 100 hours. This is because only within a sufficient long time can various situations that may occur in actual operation be fully simulated, enabling the urea crystallization phenomenon to fully emerge. Moreover, to ensure the reliability of the results, multiple repeated tests need to be carried out for each design. Different test conditions, equipment states, and the operating habits of operators and other factors may all have a certain impact on the test results. Through multiple repeated tests, the interference of these factors can be reduced, and the accuracy and reliability of the test results can be improved. However, this strict verification process also results in a long test cycle, requiring a large amount of test resources and time, including the use of test equipment, the input of test personnel, and the consumption of test materials, etc. This undoubtedly increases the R & D cost and time cost of the SCR system, posing relatively high requirements for the enterprise's R & D capabilities and financial strength.

[0008] The existing test method technical solutions have the following defects: The existing technical solutions mostly focus on designing different types of high-crystallization-risk cycles, such as the first 1200s of the WHTC standard cycle in GB17691, or the road spectra extracted from actual vehicle driving by each company, or special cycles researched and designed by each company, etc., only improving and optimizing in terms of test conditions.

[0009] CN 115165953 A discloses a non-road forklift post-treatment crystallization test method, including the following steps: Step P1: Select the engine and post-treatment before the test; Step P2: Run-in the engine and pre-treat the post-treatment; Step P3: Confirm the engine performance; Step P4: Confirm the post-treatment urea injection system to ensure that the injection accuracy meets the design index value; Step P5: Conduct a catalytic efficiency test to confirm that the engine and post-treatment system are working properly; Step P6: Confirm the bench responsiveness; Step P7: Conduct a post-treatment SCR urea crystallization verification test; Step P8: Evaluate the urea crystallization situation of the engine SCR system and calculate the weight of the urea crystallization; Step P9: Determine whether the SCR urea crystallization test is passed. The present invention has the advantages of early identification of potential crystallization risks, reduction of after-sales claim risks after market launch, and cost reduction, etc.

[0010] CN 105547707 A discloses a method for verifying urea crystallization on an engine bench of an SCR post-treatment system, including the following steps: S1: Complete the emission performance calibration of the diesel engine and the SCR post-treatment system; S2: Select the test engine; S3: Confirm that the state of the test engine is stable; S4: Method for verifying urea crystallization on the SCR post-treatment system for transport vehicles: The verification time is 60 hours, divided into a 30-hour WHTC suburban and highway condition cycle and a 30-hour ETC cycle, and check the urea mixing chamber of the SCR catalytic muffler every 10 hours; S5: Method for verifying urea crystallization on the SCR post-treatment system for urban road vehicles: The verification time is 60 hours, divided into a 30-hour WHTC urban condition cycle and a 30-hour ETC cycle, and check the urea mixing chamber of the SCR catalytic muffler every 10 hours; S6: Determine whether the engine passes the verification.

[0011] The above methods are used to determine the time and location of urea crystallization, and are verified through transient conditions that can reflect actual road conditions. Their test times are all relatively long. Summary of the Invention

[0012] Aiming at the technical problem of long test time in the existing diesel engine post-treatment urea crystallization test, the present invention provides a rapid test method for diesel engine post-treatment urea crystallization. It can follow the original urea crystallization evaluation performance test cycle. Only by obtaining a suitable high-biuret urea product can the test time be significantly reduced. The operation is simple and the feasibility is high.

[0013] The technical method adopted by the present invention is as follows: A rapid test method for urea crystallization in diesel engine aftertreatment, comprising: on an engine test bench, performing a high-crystallization-risk cycle test according to the calibration procedure of the target engine. A single high-crystallization-risk cycle is the first 1200 s of the WHTC standard cycle test, and in the aftertreatment system of the WHTC standard cycle test, the aftertreatment agent is urea with a biuret mass concentration of 0.35% - 0.50%.

[0014] It should be further noted that the number of high-crystallization-risk cycle tests is at least one.

[0015] It should be further noted that the number of high-crystallization-risk cycle tests is 100 times.

[0016] It should be further noted that the high-crystallization-risk cycle test time is determined according to the biuret mass concentration in urea, or the biuret mass concentration in urea is determined according to the high-crystallization-risk cycle test time. The present invention can perform urea crystallization tests in the above two ways, so as to accurately determine the test time suitable for the to-be-tested aftertreatment system and the urea product to be used.

[0017] It should be further noted that the method for determining the high-crystallization-risk cycle test time includes the following steps: (1) On an engine test bench, according to the calibration procedure of the target engine, run 300 high-crystallization-risk cycles, record the total weight of urea crystallization W0 in the aftertreatment system, and the aftertreatment agent in the aftertreatment system is urea with a biuret mass concentration ≤ 0.3%; (2) Remove the crystallization in the aftertreatment system in step (1), and replace the aftertreatment agent in the aftertreatment system with urea with a biuret mass concentration of 0.35% - 0.50%; (3) On an engine test bench, according to the calibration procedure of the target engine, continuously run high-crystallization-risk cycles, and record the urea crystallization weight at each node in the aftertreatment system at the node of the unit cycle number or the unit cycle time, denoted as W i , i = 1, 2, 3, ……, when W i = W0, record the running cycle duration at this time, which is the test time.

[0018] It should be further noted that the unit cycle number is three times, and the unit cycle time is one hour.

[0019] It should be further noted that the method for determining the biuret mass concentration in urea includes the following steps: (1) On an engine test bench, according to the calibration procedure of the target engine, run 300 high-crystallization-risk cycles, and record the total weight of urea crystallization W0 in the aftertreatment system; (2)Clear the crystallization in the post-treatment system after step (1), and successively replace the post-treatment agent in the post-treatment system in step (1) with urea having a gradient biuret mass concentration; (3)On the engine test bench, respectively run the high-crystallization-risk cycles for the same time according to the calibration procedure of the target engine, and respectively record the urea crystallization weight W corresponding to the urea with different biuret mass concentrations. Select the urea with the biuret mass concentration corresponding to the W that is less than and closest to W0.

[0020] It should be further noted that in step (2), the biuret mass concentrations in the urea are 0.35%, 0.40%, 0.45%, and 0.50% respectively.

[0021] It should be further noted that in step (3), the operation time of the high-crystallization-risk cycles is 10 hours.

[0022] It should be further noted that in the post-treatment system of the WHTC standard cycle test, the post-treatment agent uses urea with a biuret mass concentration of 0.40%.

[0023] The beneficial effects of the present invention are as follows: The present invention has a minimal impact on the current test bench configuration and test process, and the original urea crystallization evaluation performance test cycle can be used. Only by obtaining a suitable high-biuret urea product can the test time be significantly reduced, the urea crystallization performance evaluation test be accelerated, and the test resources and time costs be saved. The operation is simple and the feasibility is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

[0025] Figure 1 It is a flowchart of determining the high-crystallization-risk cycle test time according to the biuret mass concentration in urea in Embodiment 1 of the specific implementation manner of the present invention.

[0026] Figure 2 It is a flowchart of determining the biuret mass concentration in urea according to the high-crystallization-risk cycle test time in Embodiment 2 of the specific implementation manner of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] To enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0028] The present invention provides a rapid test method for urea crystallization in diesel engine aftertreatment. Based on the long-term operation of high-crystallization-risk cycle conditions commonly used in bench tests (the first 1200 s of the WHTC standard cycle in GB17691, or the road spectrum extracted from actual vehicle driving by each company, or the special cycle designed by each company), a high biuret urea product is selected to increase the urea crystallization tendency and accelerate the crystallization test.

[0029] The key of the present invention lies in that the concentration of biuret, a non-major component in urea, plays a key role in urea crystallization. When the biuret concentration is high, the crystallization risk of urea during normal use increases significantly. Therefore, the crystallization process can be accelerated by increasing the biuret concentration of the test urea to achieve the purpose of rapid testing. At the same time, in order to more reasonably design the test time and quantitatively equivalent to the previous test time, it is necessary to first conduct a comparative test to determine the appropriate test duration or number of cycles.

[0030] Specifically, the present invention provides a rapid test method for urea crystallization in diesel engine aftertreatment, including: on an engine bench, performing a high-crystallization-risk cycle test according to the calibration procedure of the target engine. A single high-crystallization-risk cycle is the first 1200 s of the WHTC standard cycle test, and the aftertreatment agent in the aftertreatment system of the WHTC standard cycle test uses urea with a biuret mass concentration of 0.35% - 0.50%.

[0031] In some specific embodiments, the number of high-crystallization-risk cycle tests is at least one. More preferably, the number of high-crystallization-risk cycle tests is 100 times.

[0032] In some specific embodiments, the high-crystallization-risk cycle test time is determined according to the biuret mass concentration in urea, or the biuret mass concentration in urea is determined according to the high-crystallization-risk cycle test time. The present invention can perform urea crystallization tests according to the above two methods, so as to accurately determine the test time suitable for the to-be-tested aftertreatment system and the urea product used.

[0033] In some specific embodiments, the method for determining the high-crystallization-risk cycle test time includes the following steps: (1) On the engine test bench, run 300 high-crystallization-risk cycles according to the calibration procedure of the target engine, record the total weight W0 of urea crystallization in the aftertreatment system, and use urea with a biuret mass concentration ≤ 0.3% as the aftertreatment agent in the aftertreatment system; (2) Remove the crystallization in the aftertreatment system in step (1), and replace the aftertreatment agent in the aftertreatment system with urea with a concentration of 0.35% - 0.50%; (3) On the engine test bench, run high-crystallization-risk cycles continuously according to the calibration procedure of the target engine. Take the number of cycles per unit or the time per unit as the node, and record the urea crystallization weight at each node in the aftertreatment system, denoted as W i (i = 1, 2, 3,...). When W i = W0, record the running cycle duration at this time, which is the test time.

[0034] In some specific embodiments, the number of cycles per unit is three, and the time per unit is one hour. That is, the number of cycles per unit time is three. In some specific embodiments, the cycle time or the number of cycles can be selected according to the specific test conditions.

[0035] In some specific embodiments, the method for determining the biuret mass concentration in urea includes the following steps: (1) On the engine test bench, run 300 high-crystallization-risk cycles according to the calibration procedure of the target engine, and record the total weight W0 of urea crystallization in the aftertreatment system; (2) Remove the crystallization in the aftertreatment system in step (1), and sequentially replace the aftertreatment agent in the aftertreatment system in step (1) with urea having a gradient biuret mass concentration; (3) On the engine test bench, run high-crystallization-risk cycles for the same time according to the calibration procedure of the target engine respectively, record the urea crystallization weights W corresponding to urea with different biuret mass concentrations respectively, and select the urea with the biuret mass concentration corresponding to the W that is less than W0 and closest to W0.

[0036] In some specific embodiments, in step (2), the biuret mass concentrations in urea are 0.35%, 0.40%, 0.45%, and 0.50% respectively. More specifically, the biuret mass concentration in this urea can be any value within the range of 0.35% - 0.50% of the biuret mass concentration in urea.

[0037] In some specific embodiments, in step (3), the running time of the high-crystallization-risk cycles is 10 hours for all.

[0038] In some specific embodiments, the aftertreatment agent in the aftertreatment system of the WHTC standard cycle test uses urea with a biuret mass concentration of 0.40%.

[0039] Example 1 Combined with Figure 1 , in the urea crystallization test for the post-treatment of a diesel engine in Example 1, the high-crystallization-risk cycle test time was determined according to the mass concentration of biuret in urea.

[0040] A rapid test method for urea crystallization in the post-treatment of a diesel engine includes: (1) Purchase urea products with a biuret concentration of 0.4%. The national standard requires that the biuret concentration in industrial urea products should not be higher than 0.3%. Urea products with a biuret concentration of 0.4% need to be negotiated with urea suppliers. The production of this concentration of products has no technical difficulties and can be provided by normal urea suppliers.

[0041] (2) Test steps (a) Use urea products with a normal biuret concentration that meets the national standard and run 300 high-crystallization-risk cycles (corresponding to 100 h) on the target engine and exhaust system according to the normal type-approval calibration procedure, and record the total weight of urea crystallization W0 = 20 g.

[0042] (b) Remove the crystallization in the above-mentioned post-treatment system and replace the urea product with a urea product with a biuret concentration of 0.4%.

[0043] (c) Continuously run high-crystallization-risk cycles on the target engine and exhaust system according to the normal type-approval calibration procedure, and record the urea crystallization weight every 3 cycles or 1 hour, denoted as W i (i = 1, 2, 3,...). When W i = W0, record the number of cycles or duration of operation at this time. The number of cycles and duration recorded here are the rapid test durations equivalent to the ordinary crystallization test. Table 1 shows the corresponding relationship between the number of operating cycles and the urea crystallization amount in Example 1.

[0044] Table 1 Corresponding relationship between the number of operating cycles and the urea crystallization amount

[0045] It can be seen from Table 1 that when the number of operating cycles in Example 1 is 120 (corresponding to a cycle duration of 40 h), compared with 300 cycles (corresponding to 100 h) of the original method, 60 h is saved.

[0046] Based on the cycle test time obtained in Example 1, the present invention can use 120 cycles (corresponding to a cycle duration of 40 h) in Example 1 as the time standard, and use urea with the same biuret concentration as in Example 1 as the catalyst for the post-treatment system to compare the urea crystallization capabilities of different post-treatment system designs: Specifically, on the engine test bench, a high-crystallization-risk cycle test is carried out according to the calibration procedure of the target engine. The number of cycles is 120 (corresponding to a cycle duration of 40 h). A single high-crystallization-risk cycle is the first 1200 s of the WHTC standard cycle test. In the aftertreatment system of the WHTC standard cycle test, the post-treatment agent is urea with a biuret mass concentration of 0.4%.

[0047] When the designed urea crystallization amount of a certain aftertreatment system after the experiment is less than 20 g, it is determined that the design of this aftertreatment system meets the standard.

[0048] Example 2 Combined with Figure 2 , in the diesel engine aftertreatment urea crystallization test of Example 2, the biuret mass concentration in urea is determined according to the high-crystallization-risk cycle test time.

[0049] A rapid test method for diesel engine aftertreatment urea crystallization includes: (1) Prepare a series of high-biuret urea products with different concentrations, namely 0.35%, 0.4%, 0.45%, and 0.5%.

[0050] (2) Use a urea product with a normal biuret concentration that meets the national standard. Run 300 high-crystallization-risk cycles on the target engine and exhaust system according to the normal type-approval calibration procedure, and record the total urea crystallization weight W0 = 20 g.

[0051] (3) Remove the crystallization, and sequentially replace the urea product with the product in the above step (1). Run 10-hour high-crystallization-risk cycles on the target engine and exhaust system according to the normal type-approval calibration procedure, and record the crystallization weights W corresponding to different concentration products respectively. Select the product concentration with W closest to W0. Table 2 shows the urea crystallization weights corresponding to urea with different biuret concentrations.

[0052] Table 2 Corresponding relationship between urea with biuret concentration and urea crystallization weight

[0053] As shown in Table 2, when the biuret concentration is 0.45%, the corresponding urea crystallization weight is 12 g, which is closest to W0 = 20 g. Therefore, it is determined that the urea with a biuret concentration of 0.45% is used in the diesel engine aftertreatment urea crystallization test. Use the urea product with this concentration and run 10-hour high-crystallization-risk cycles on several different designed aftertreatment systems that need to test the crystallization performance. When the crystallization weight is 12 ± 2 g (the 2 g here is the recommended weight, and this error range can be adjusted according to the design target), the crystallization performance of this design is close to that of the initial design; when it is less than 2 g, the urea crystallization performance of this design is better than that of the initial design; when it is greater than 12 g, the urea crystallization performance of this design is inferior to that of the initial design.

[0054] That is, in Example 2, urea with a biuret concentration of 0.45% was used for the urea crystallization test of diesel engine aftertreatment, and the technical effect of testing the urea crystallization ability of diesel engine aftertreatment within the target experimental time of 10 h was achieved.

[0055] Based on Example 2, the performance of different engine aftertreatment systems can be further tested. For example, to ensure the consistency of product performance, urea products with a biuret concentration of 0.45% were used for three aftertreatment system designs (labeled as Ⅰ, Ⅱ, and Ⅲ respectively), and a high-crystallization-risk cycle was run on the engine bench for 10 h. Each design was repeated 3 times, denoted as T1, T2, and T3 respectively. After each test, the urea crystallization weight was recorded and the crystallization was removed. The results are recorded in Table 3.

[0056] Table 3 Urea Crystallization Weight in Tests of Different Aftertreatment System Designs

[0057] For Design Ⅰ, the results of its three repeated tests were close, and the average value was taken as the final result; for Design Ⅱ, there were relatively large differences among the three repeated test values, but the differences were small (compared with the normal test error) and were all less than the standard value of 12 g, so the average value was also taken as the final result; for Design Ⅲ, the three results had large differences, and there were situations where they were greater than, equal to, and less than the standard value of 12 g at the same time. It is recommended to conduct 2 additional tests and select the average value of three similar groups of results as the final result. By comparing the final results of the three designs, the product with the smallest urea crystallization weight value is the product with the best anti-crystallization performance; the product with a final result less than the standard value of 12 g is the product whose crystallization performance meets the design requirements.

[0058] Although the present invention has been described in detail by referring to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, those of ordinary skill in the art can make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions should all be within the scope of the present invention. / Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention.

Claims

1. A rapid test method for urea crystallization in diesel engine aftertreatment, characterized in that Including: On an engine test bench, perform a high crystallization risk cycle test according to the calibration procedure of the target engine. A single high crystallization risk cycle is the first 1200 s of the WHTC standard cycle test. In the aftertreatment system of the WHTC standard cycle test, the aftertreatment agent is urea with a biuret mass concentration of 0.35% - 0.50%.

2. The rapid test method for urea crystallization in diesel engine aftertreatment according to claim 1, characterized in that, The number of high crystallization risk cycle tests is at least one time.

3. The rapid test method for urea crystallization in diesel engine aftertreatment according to claim 2, characterized in that, The number of high crystallization risk cycle tests is 100 times.

4. The rapid test method for urea crystallization in the post-treatment of diesel engines according to claim 1, characterized in that Determine the high crystallization risk cycle test time according to the biuret mass concentration in urea, or determine the biuret mass concentration in urea according to the high crystallization risk cycle test time.

5. The rapid test method for urea crystallization in diesel engine aftertreatment according to claim 4, wherein, The method for determining the high crystallization risk cycle test time includes the following steps: (1) On an engine test bench, according to the calibration procedure of the target engine, run 300 high crystallization risk cycles, record the total weight of urea crystallization W0 in the aftertreatment system. The aftertreatment agent in the aftertreatment system is urea with a biuret mass concentration ≤ 0.3%; (2) Remove the crystallization in the aftertreatment system in step (1), and replace the aftertreatment agent in the aftertreatment system with urea with a biuret mass concentration of 0.35% - 0.50%; (3) On the engine test bench, according to the calibration procedure of the target engine, continuously run the high-crystallization-risk cycle. Taking the number of cycles per unit or the time per unit cycle as a node, record the urea crystallization weight at each node in the after-treatment system, denoted as W i , i = 1, 2, 3, ……, when W i = W0, record the running cycle duration at this time, which is the test time.

6. The rapid test method for urea crystallization in diesel engine aftertreatment according to claim 5, characterized in that, The number of unit cycles is three times, and the unit cycle time is one hour.

7. The rapid test method for urea crystallization in diesel engine aftertreatment according to claim 4, characterized in that The method for determining the biuret mass concentration in urea includes the following steps: (1) On an engine test bench, according to the calibration procedure of the target engine, run 300 high crystallization risk cycles, and record the total weight of urea crystallization W0 in the aftertreatment system; (2) Remove the crystallization in the aftertreatment system in step (1), and sequentially replace the aftertreatment agent in the aftertreatment system in step (1) with urea with a gradient biuret mass concentration; (3) On an engine test bench, respectively according to the calibration procedure of the target engine, run high crystallization risk cycles for the same time, respectively record the urea crystallization weights W corresponding to the urea with different biuret mass concentrations, and select the urea with the biuret mass concentration corresponding to the W that is less than W0 and closest to W0.

8. The rapid test method for urea crystallization in diesel engine aftertreatment according to claim 7, wherein In step (2), the biuret mass concentrations in urea are 0.35%, 0.40%, 0.45%, and 0.50% respectively.

9. The rapid test method for urea crystallization in diesel engine aftertreatment according to claim 7, characterized in that In step (3), the running time of the high crystallization risk cycle is 10 hours for all.

10. The rapid test method for urea crystallization in diesel engine aftertreatment according to claim 1, wherein, In the aftertreatment system of the WHTC standard cycle test, the aftertreatment agent is urea with a biuret mass concentration of 0.40%.

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