Development evaluation method for automobile urea mixer

Abstract

According to the automobile urea mixer development evaluation method provided by the invention, CAE analysis, rack verification and whole vehicle verification are combined, whether the design scheme of the urea mixer meets the design requirements is judged, the risk is recognized in advance, and the situation that the project development progress is affected due to the fact that the structure of the urea mixer is repeatedly changed in the design development process is avoided.

Description

Technical Field

[0001] The invention relates to the field of automobile emissions, and in particular to a development and evaluation method for an automobile urea mixer. Background Art

[0002] With the gradual implementation of my country's sixth-stage light-duty vehicle emission pollutant regulations, the limit requirements for emission pollutants NOx are becoming increasingly stringent, especially the increase in RDE requirements in the National VIb stage, which poses great challenges to light-duty diesel vehicle engines and after-treatment. The technical route for light-duty diesel vehicle after-treatment is DOC+SDPF+SCR. DOC oxidizes CO and HC in engine exhaust pollutants, and NOx undergoes redox reaction with the reducing agent NH3 inside the SDPF and SCR catalysts to generate NO2 and H2O.

[0003] like Figure 1 As shown, the exhaust aftertreatment device in the prior art mainly includes a diesel oxidation catalyst (DOC) 10, a diesel urea mixer 20, a diesel particulate filter (SDPF) 30, a selective reduction catalyst (SCR) 40, a muffler 50 and a tail pipe 60, which are arranged in sequence, and a urea nozzle 70 is arranged on the diesel urea mixer 20. By adding a cylindrical diesel urea mixer 20 in front of the diesel particulate filter (SDPF) 30, NOx and the reducing agent NH3 can be fully mixed and evenly improved to improve the NOx conversion efficiency. Among them, the urea mixer has a relatively complex structure, and the structure has high requirements on the uniformity of urea mixing and urea crystallization. The urea mixer is often prone to uneven urea mixing and urea crystallization problems during the development process and after-sales, thereby affecting the performance of the catalyst and causing the vehicle emissions to fail to meet regulatory requirements. Its design is a difficult point in the entire industry, and there is currently no effective design method or specification. Most manufacturers design urea mixers based on experience and then verify the performance of the urea mixers on a test bench, which results in a long development cycle for urea mixers and is prone to problems that do not meet design requirements. Summary of the invention

[0004] In view of the defects in the prior art, the purpose of the present invention is to provide an automobile urea mixer development evaluation method, which combines CAE analysis, bench verification and vehicle verification to determine whether the urea mixer design meets the design requirements, identify risks in advance, and avoid repeated changes to the urea mixer structure during the design and development process, thereby affecting the project development progress.

[0005] In order to achieve the above technical effects, the present invention adopts the following technical solutions:

[0006] A method for developing and evaluating an automobile urea mixer comprises the following steps:

[0007] Step S1: the software collects the power, torque, exhaust flow rate after vortex, exhaust temperature and urea injection amount parameters of all operating points under the WLTC emission cycle of the whole vehicle, extracts the maximum operating point and the minimum operating point of urea injection amount, and then selects several representative operating points by clustering method, and determines the whole vehicle layout boundary and post-processing parameters of the urea mixer; the maximum operating point, the minimum operating point and several representative operating points of urea injection amount are the test points of this operating condition;

[0008] Step S2: designing a urea mixer structure according to the vehicle layout and catalyst size;

[0009] Step S3: constructing a CFD model of a urea mixer in the CFD software, inputting urea nozzle parameters in the software, performing simulation calculation and analysis of the operating test points extracted in step S1, optimizing the design of the urea mixer, and ensuring that the urea mixing uniformity, liquid film thickness and minimum liquid film temperature at each operating point meet the standard requirements;

[0010] Step S4: after the CFD analysis of the urea mixer meets the requirements, a sample of the exhaust aftertreatment system with the urea mixer is manufactured to conduct bench and vehicle experimental verification;

[0011] Step S5: verifying the ammonia mixing uniformity of the urea mixer through a bench test to ensure that the test results meet the set standards;

[0012] Step S6: Verify urea crystallization through a SDPF regeneration interval mileage bench test, and conduct multiple rounds of repeatability tests to ensure that the bench urea crystallization test meets the standards;

[0013] Step S7: Performing a WLTC emission test and RDE road verification on the vehicle in a rotary test laboratory to ensure that the emission indicators meet the standards;

[0014] Step S8: verifying the urea crystallization of the whole vehicle by simulating the actual driving of the whole vehicle under different working conditions to ensure that the crystallization amount is within the specified range within different regeneration mileage intervals;

[0015] Step S9: If there are no problems in the verification of steps S5 to S8, the design and development of the urea mixer is finally completed.

[0016] Preferably, in step S2, the outer diameter of the urea mixer is consistent with the diameter of the catalyst carrier, a double-partition multi-swirl mixing structure or a layered broken mixing structure is adopted inside the urea mixer, a urea nozzle is arranged at the inlet end of the urea mixer, and the angle between the injection axis of the urea nozzle and the horizontal plane is in the range of 15° to 45°; 8 to 10 mm thermal insulation cotton is wrapped on the surface of the urea mixer to reduce temperature loss.

[0017] Preferably, in step S3, the urea nozzle parameters include the number of spray holes, the diameter of the spray holes, the diameter of the spray hole arrangement circle, the spray hole arrangement angle, the average spray particle size, the spray frequency, the static mass flow rate, the spray visible cone angle, the spray beam cone angle, the spray beam angle and the initial droplet velocity.

[0018] Preferably, in step S3, ensuring that the urea mixing uniformity, liquid film thickness and liquid film minimum temperature at each operating point meet standard requirements means that the urea mixing uniformity UI at each operating test point is ≥0.95, the maximum liquid film thickness is ≤1 μm, and the minimum liquid film temperature is ≥160°C.

[0019] Preferably, in the step S4 of making the urea mixer sample, the internal components of the urea mixer are made of soft modules, and then the assembly sample is manually welded.

[0020] Preferably, the test of the uniformity of urea mixing on the test bench in step S5 specifically includes the following steps:

[0021] (1) Check the hardware used for the test and take photos to record the status before the test;

[0022] (2) Install the engine, exhaust aftertreatment system sample with urea mixer, multi-probe position sampler and sensor on the engine stand, and connect the gas analyzer;

[0023] (3) Starting and adjusting the engine operating conditions to the operating parameters designed for the urea mixer;

[0024] (4) Monitor and record the concentrations of NOx, NH3, N2O, and HNCO at each operating test point after the SCR;

[0025] (5) Re-measure the working condition test points to ensure that the error is less than 10% compared with the initial measurement value, otherwise re-measure;

[0026] (6) Convert the data measured at each operating test point at the rear end of the SCR into the NH3 concentration value of the corresponding measurement point at the front end of the SCR, and calculate the ammonia mixing uniformity UI value;

[0027] (7) Calculating NH3 peak to average value and NH3 min to average value; the NH3 peak to average value refers to the ratio of the peak value to the average value of the ammonia concentration; the NH3 min to average value refers to the ratio of the minimum value to the average value of the ammonia concentration;

[0028] (8) Determine whether the ammonia mixing uniformity NH3-UI at the test operating point meets the following requirements: ammonia mixing uniformity UI ≥ 0.95; NH3 Peak to average < 1.5; NH3 min to average < 1.5.

[0029] Preferably, verifying whether crystallization occurs in the urea mixer in step S6 specifically comprises the following steps:

[0030] (1) Confirm that the hardware used in the test meets the test requirements, weigh the urea mixer and urea nozzle before the test, and take photos of the main parts to record the status before the test;

[0031] (2) Confirm that the calibration program used in the experiment is the latest calibration program. If the post-processing includes SDPF hardware, the calibration program needs to include a carbon particle active regeneration program; the urea injection amount in the calibration program is continuously injected at a ratio of 1.1 times the ammonia nitrogen;

[0032] (3) Start bench testing and complete an SDPF regeneration interval mileage test according to WLTC conditions;

[0033] (4) After completing the first SDPF regeneration interval mileage test, stop the test, remove the urea mixer and urea nozzle within 30 minutes, weigh them, record the weight, observe whether there is crystallization inside the mixer and urea nozzle, and take photos for record;

[0034] (5) Reassemble the mixer back to the test bench, restart the test bench, start the SDPF carbon particle active regeneration program, and verify the effect of SDPF carbon particle active regeneration on urea crystallization;

[0035] (6) After the SDPF carbon particles are actively regenerated, the test is stopped, and the urea mixer and urea nozzle are removed and weighed within 30 minutes. The parts are checked for crystallization, and the crystallization status of each part is recorded by taking photos;

[0036] (7) Verify repeatability and conduct a second round of tests; if the amount of crystals inside the urea mixer does not exceed 1g within the SDPF regeneration interval mileage test, the urea nozzle hole and nozzle base are not blocked by crystals, and the crystals inside the mixer can be burned off after SDPF regeneration, then the bench urea crystallization verification meets the requirements.

[0037] Preferably, the vehicle urea crystallization verification test in step S8 specifically includes the following steps:

[0038] (1) Prepare a sample vehicle in good condition and confirm that the calibration procedure used in the test is the latest calibration procedure;

[0039] (2) Confirm that the hardware used in the test meets the test requirements, weigh the urea mixer and urea nozzle before the test, and take photos of the main parts to record the status before the test;

[0040] (3) Under simulated urban conditions (vehicle speed ≤ 40 km / h), after the sample vehicle has traveled once for the SDPF regeneration mileage interval (> 500 km), the test is stopped, the urea mixer is removed within 30 minutes, the urea nozzle is weighed, the weight is recorded, and the inside of the mixer, the urea nozzle hole, and the nozzle base are observed for crystallization and photographed for record;

[0041] (4) Reassemble the urea mixer to the prototype vehicle, and start the SDPF carbon particle active regeneration program on the prototype vehicle. Stop the test after SDPF regeneration. Remove the urea mixer within 30 minutes and weigh the urea mixer and urea nozzle. Check whether there is crystallization inside each part, and take photos to record the crystallization status of each part.

[0042] (5) Repeat the above steps (3) and (4) to verify the crystallization of the urea mixer under two working conditions: suburban working condition (vehicle speed 55-70 km / h), SDPF regeneration mileage interval (>600 km) and high-speed working condition (vehicle speed >75 km / h), SDPF regeneration mileage interval (>700 km); if the amount of crystallization inside the mixer does not exceed 1g during the SDPF regeneration interval mileage test, the urea nozzle hole and the nozzle base are not blocked by crystallization, and the crystallization inside the mixer can be burned after SDPF regeneration, then the vehicle urea crystallization verification meets the requirements.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] The automobile urea mixer development evaluation method provided by the present invention can quickly and comprehensively evaluate whether a new urea mixer meets the design requirements by combining CAE analysis, bench test and whole vehicle verification, identify risks in advance, avoid repeated changes to the urea mixer structure during the design and development process, thereby affecting the project development progress, and at the same time reduce after-sales quality problems caused by unqualified urea mixers in whole vehicle mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0046] Figure 1 It is a schematic diagram of the structure of an exhaust gas after-treatment device in the prior art;

[0047] Figure 2 A schematic block diagram of the automotive urea mixer development and evaluation method described in the embodiments;

[0048] Figure 3 Schematic diagram of the steps of the automotive urea mixer development and evaluation method described in the examples.

[0049] The figure shows:

[0050] 10-Diesel Oxidation Catalyst DOC

[0051] 20-Diesel Urea Mixer

[0052] 30-Diesel Particulate Filter SDPF

[0053] 40-Selective reduction catalyst SCR

[0054] 50-Muffler

[0055] 60-Tail pipe

[0056] 70-Urea Nozzle DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0058] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0059] It should be noted that similar numbers and letters represent similar items in the following figures. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in the subsequent figures. In addition, all directional indications in this application (such as up, down, left, right, front, back, bottom...) are only used to explain the relative position relationship, movement, etc. between the components under a certain specific posture (as shown in the figures). If the specific posture changes, the directional indication will also change accordingly. Furthermore, the descriptions involving "first", "second", etc. in the application are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated.

[0060] like Figure 2 , 3 As shown, this embodiment provides a development evaluation method for an automobile urea mixer, which combines CAE analysis, bench verification and vehicle verification to determine whether the urea mixer design meets the design requirements, identify risks in advance, and avoid repeated changes to the urea mixer structure during the design and development process, thereby affecting the project development progress. Specifically, the following steps are included:

[0061] Step S1: Design input, obtaining the basic data and parameters required in the design process of the urea mixer, including the following steps:

[0062] Data collection: Use the calibrated Inca software to collect data from all operating points in the WLTC (World Light Vehicle Test Cycle) emission cycle of the whole vehicle, including: power, torque, exhaust flow after the turbine, exhaust temperature, and urea injection amount.

[0063] Extract operating test points: Extract the maximum and minimum operating points of urea injection, and use the "clustering method" to select 3-4 representative operating points from all operating points. The extracted maximum and minimum operating points of urea injection and 3-4 representative operating points will replace all operating points in the vehicle's WLTC emission cycle as test operating points for subsequent simulation analysis.

[0064] Vehicle layout boundary of urea mixer: Determine the layout position of urea mixer in the vehicle and ensure its coordination with the layout of the entire exhaust system.

[0065] After-treatment system parameters: Consider the role and effect of the urea mixer in the after-treatment system, including how it cooperates with other after-treatment components (such as catalysts, filters, etc.).

[0066] Step S2: structural design of the urea mixer;

[0067] The urea mixer structure is designed according to the layout position of the vehicle and the diameter of the catalyst carrier. The outer diameter of the urea mixer is consistent with the diameter of the catalyst carrier. The interior of the urea mixer generally adopts a double-diaphragm multi-swirl mixing structure or a layered broken mixing structure. The urea nozzle is arranged at the inlet end of the urea mixer, and the angle between the urea nozzle injection axis and the horizontal plane is within the range of 15° to 45°. Wrap 8-10mm insulation cotton on the surface of the urea mixer to reduce temperature loss.

[0068] Step S3: CFD analysis;

[0069] The CFD analysis condition is to use the maximum operating point of urea injection amount extracted in step S1, the minimum operating point and 3 to 4 operating points selected by the "clustering method" as test operating points. The main parameters of each test operating point are exhaust mass flow, exhaust temperature, urea injection amount and mixer pressure difference target. At the same time, enter the urea nozzle parameters in the CDF software: number of spray holes, spray hole diameter, spray hole arrangement circle diameter, spray hole arrangement angle, average spray particle size, injection frequency, static mass flow rate, spray visible cone angle, spray beam cone angle, spray beam angle and droplet initial velocity. Build a urea mixer CFD model in the CFD software to perform simulation calculation and analysis of each test operating point. After the analysis is completed, check the urea mixing uniformity, liquid film thickness and liquid film minimum temperature data at each test operating point, requiring urea mixing uniformity UI ≥ 0.95, maximum liquid film thickness ≤ 1E-6m, and liquid film minimum temperature ≥ 160℃. If CFD does not meet the above requirements, the internal structure of the urea mixer needs to be redesigned until CFD meets the requirements.

[0070] Step 4: Sample production;

[0071] After the urea mixer meets the target through CFD analysis, a post-treatment system sample with a urea mixer is made to conduct bench and vehicle urea crystallization and ammonia mixing uniformity experiments. In order to ensure the quality of the sample, the components inside the urea mixer are usually soft modules, and then the assembly sample is manually welded.

[0072] Step 5: Verification of urea mixing uniformity on the bench;

[0073] 1. Choose a suitable engine performance test bench;

[0074] 2. Confirm that the hardware used in the test meets the test requirements, and take photos of the main parts to record the status before the test;

[0075] 3. Install the engine and the post-treatment system sample with urea mixer on the engine stand. Install NOx sensor, temperature sensor and flow meter at the outlet of the engine turbocharger. Install NOx sensor and temperature sensor at the inlet section of the front-stage SDPF carrier. Install a multi-probe position sampler 10mm away from the outlet of the front-stage SDPF. Generally, 30 to 50 measuring points are arranged on the SCR outlet. The multi-probe position sampler is connected to the sampling pipeline switch box SWITCH BOX, and the SWITCH BOX transmits signals with the FTIR gas analyzer.

[0076] 4. Start the engine and adjust the engine operating conditions to the operating conditions input by the urea mixer design in step S1, including speed, torque, and original exhaust NOx;

[0077] 5. Move the sampler probe to the center of the carrier for data monitoring. After the speed, torque, temperature before SCR, flow, urea injection and other data are stable, move the sampler probe to test operating point 1. After re-stabilization for 2 minutes, measure the NOx, NH3, N2O, and HNCO concentrations. The measurement time is 30 seconds, and the average value is taken as the concentration value of each component at this point; then measure the subsequent test operating points in turn.

[0078] 6. After testing all test conditions, retest all test conditions and compare them with the initial measurement value. If the error is less than 10%, it is considered that the tested experimental data meets the requirements; if the error is greater than 10%, retest again until the requirements are met.

[0079] 7. Convert the concentration values ​​of NOx, NH3, N2O and HNCO at each measuring point measured at the rear end of the SCR into the NH3 concentration values ​​at the corresponding measuring points at the front end of the SCR, and then use the ammonia mixing uniformity calculation formula to calculate the value of the ammonia mixing uniformity NH3_UI.

[0080] The conversion equation is:

[0081] NO+NO2+2NH3=2N2+3H2O

[0082] NO+NH3=N2+3 / 2H2O

[0083] NO2+4 / 3NH3=7 / 6N2+2H2O

[0084] (NH2)2CO=NH3+HNCO

[0085] HNCO+H2O=NH3+CO2

[0086] 8. Calculate the NH3 peak to average value and the NH3 min to average value; the NH3 peak to average value refers to the ratio of the peak value to the average value of the ammonia concentration; the NH3 min to average value refers to the ratio of the minimum value to the average value of the ammonia concentration.

[0087] 9. Test Assessment Judgment Criteria

[0088] Determine whether the ammonia mixing uniformity NH3-UI at the test operating point meets the following requirements: NH3_UI≥0.95, NH3Peak to average<1.5, NH3 min to average<1.5. If so, the bench urea mixing uniformity verification meets the standards.

[0089] Step 6: bench urea crystallization test;

[0090] 1. Choose a suitable engine performance test bench;

[0091] 2. Confirm that the hardware used in the test meets the test requirements, weigh the urea mixer and urea nozzle before the test, and take photos of the main parts to record the status before the test;

[0092] 3. Confirmation of the calibration procedure before the experiment. It is necessary to confirm that the calibration procedure used in the experiment is the latest calibration procedure. The closer the calibration procedure is to the final calibration procedure, the better. If the post-treatment system has SDPF hardware, the calibration data needs to contain the carbon particle active regeneration procedure. The urea injection amount in the calibration data is continuously injected at a ratio of 1.1 times ammonia nitrogen;

[0093] 4. Build the test bench and conduct trial operation to confirm that all indicators meet the above requirements;

[0094] 5. Start the bench test and complete a bench test corresponding to the SDPF regeneration interval mileage according to the WLTC working condition;

[0095] 6. After completing the first SDPF regeneration interval mileage test, stop the test, remove the mixer and urea nozzle within 30 minutes, weigh them, record the weight, observe whether there is crystallization inside the mixer, nozzle, and nozzle seat, and take photos for record.

[0096] 7. To verify the effect of active regeneration of SDPF carbon particles on urea crystallization, reassemble the mixer back to the test bench, restart the test bench, and start the SDPF carbon particle active regeneration program. The test time is carried out according to the time required by each project, generally controlled at about 30 minutes.

[0097] 8. After SDPF regeneration, weigh and photograph each part. Remove the urea mixer and urea nozzle within 30 minutes, weigh them, check whether there is crystallization inside each part, and take photos to record the crystallization status of each part.

[0098] 9. Verify repeatability and conduct a second round of tests until the test is completed. If the test results meet the following conditions: the amount of crystals inside the mixer during the SDPF regeneration interval mileage test does not exceed 1g, the urea nozzle hole and base are not blocked by crystals, and the crystals inside the mixer can be burned off after SDPF regeneration, then the bench urea crystallization test meets the standards.

[0099] Step S7: vehicle emission verification;

[0100] After the bench urea mixing uniformity and crystallization tests are verified to be no problem, the vehicle emission verification is carried out; the exhaust after-treatment system with urea mixer is assembled on the vehicle, and the WLTC emission test and RDE actual road emission verification test are carried out in the vehicle rotary hub test room. The test results need to meet the emission target requirements.

[0101] Step S8: vehicle urea crystallization verification;

[0102] 1. Prepare a sample vehicle in good condition and confirm that the calibration procedure used in the experiment is the latest calibration procedure, which should be as close to the final calibration procedure as possible;

[0103] 2. Confirm that the hardware used in the test meets the test requirements, weigh the urea mixer and urea nozzle before the test, and take photos of the main parts to record the status before the test;

[0104] 3. The test condition of the prototype vehicle is to simulate the urban condition (vehicle speed ≤ 40km / h). After the vehicle has traveled once for the SDPF regeneration mileage interval (generally > 500km), the test is stopped, the urea mixer is removed within 30 minutes, the urea nozzle is weighed, the weight is recorded, and the inside of the mixer, urea nozzle and nozzle base are observed for crystallization and photographed for record.

[0105] 4. Reassemble the mixer to the prototype vehicle, and start the active regeneration of SDPF carbon particles on the prototype vehicle. The test time shall be carried out in accordance with the requirements of each project, generally controlled at about 30 minutes. Stop the test after SDPF regeneration, remove the urea mixer within 30 minutes, weigh the urea mixer and urea nozzle, check whether there is crystallization inside each part, and take photos to record the crystallization status of each part.

[0106] 5. Repeat the above steps 3 and 4 to verify the crystallization of urea mixer under two working conditions: suburban working condition (vehicle speed 55-70km / h), SDPF regeneration mileage interval (>600km) and high-speed working condition (vehicle speed>75km / h), SDPF regeneration mileage interval (>700km).

[0107] 6. The test assessment judgment standard is that the amount of crystallization inside the mixer does not exceed 1g during the SDPF regeneration interval mileage test, and the urea nozzle hole and base are not blocked by crystallization; the crystallization inside the mixer can be burned after SDPF regeneration. If the crystallization of the urea mixer under the above-mentioned urban working conditions, suburban working conditions and high-speed working conditions meets the above judgment standards, the vehicle urea crystallization verification meets the standards.

[0108] Step S9: After the above verification is completed without any problem, the design and development of the urea mixer is completed.

[0109] like Figure 2 As shown in the figure, during the development and evaluation process of the entire urea mixer, if the CFD analysis, bench test of urea mixing uniformity and urea crystallization, vehicle urea crystallization experimental test or vehicle emission test do not meet the standards (i.e. NOK in the figure), the structural design of the urea mixer must be redone.

[0110] The above describes the specific embodiments of the present invention. Based on the above description, relevant personnel can make various changes and modifications without departing from the technical concept of the present invention.

Claims

1. A method for developing and evaluating an automobile urea mixer, characterized in that: The following steps are involved: Step S1: the software collects the power, torque, exhaust flow rate after vortex, exhaust temperature and urea injection amount parameters of all operating points under the WLTC emission cycle of the whole vehicle, extracts the maximum operating point and the minimum operating point of urea injection amount, and then selects several representative operating points by clustering method, and determines the whole vehicle layout boundary and post-processing parameters of the urea mixer; the maximum operating point, the minimum operating point and several representative operating points of urea injection amount are the test points of this operating condition; Step S2: designing a urea mixer structure according to the vehicle layout and catalyst size; Step S3: constructing a CFD model of a urea mixer in the CFD software, inputting urea nozzle parameters in the software, performing simulation calculation and analysis of the operating test points extracted in step S1, optimizing the design of the urea mixer, and ensuring that the urea mixing uniformity, liquid film thickness and minimum liquid film temperature at each operating point meet the standard requirements; Step S4: after the CFD analysis of the urea mixer meets the requirements, a sample of the exhaust aftertreatment system with the urea mixer is manufactured to conduct bench and vehicle experimental verification; Step S5: verifying the ammonia mixing uniformity of the urea mixer through a bench test to ensure that the test results meet the set standards; Step S6: Verify urea crystallization through a SDPF regeneration interval mileage bench test, and conduct multiple rounds of repeatability tests to ensure that the bench urea crystallization test meets the standards; Step S7: Performing a WLTC emission test and RDE road verification on the vehicle in a rotary test laboratory to ensure that the emission indicators meet the standards; Step S8: verifying the urea crystallization of the whole vehicle by simulating the actual driving of the whole vehicle under different working conditions to ensure that the crystallization amount is within the specified range within different regeneration mileage intervals; Step S9: If there are no problems in the verification of steps S5 to S8, the design and development of the urea mixer is finally completed.

2. The automotive urea mixer development and evaluation method according to claim 1, characterized in that: In step S2, the outer diameter of the urea mixer is consistent with the diameter of the catalyst carrier, a double-partition multi-swirl mixing structure or a layered broken mixing structure is adopted inside the urea mixer, a urea nozzle is arranged at the inlet end of the urea mixer, and the angle between the injection axis of the urea nozzle and the horizontal plane is in the range of 15° to 45°; 8 to 10 mm thermal insulation cotton is wrapped on the surface of the urea mixer to reduce temperature loss.

3. The automotive urea mixer development and evaluation method according to claim 1, characterized in that: In step S3, the urea nozzle parameters include the number of spray holes, the diameter of the spray holes, the diameter of the spray hole arrangement circle, the spray hole arrangement angle, the average spray particle size, the spray frequency, the static mass flow rate, the spray visible cone angle, the spray beam cone angle, the spray beam angle and the initial droplet velocity.

4. The method for developing and evaluating an automotive urea mixer according to claim 1, characterized in that: In step S3, ensuring that the urea mixing uniformity, liquid film thickness and liquid film minimum temperature at each operating point meet standard requirements means that the urea mixing uniformity UI at each operating test point is ≥0.95, the maximum liquid film thickness is ≤1 μm, and the minimum liquid film temperature is ≥160°C.

5. The automotive urea mixer development and evaluation method according to claim 1, characterized in that: In step S4 of making a urea mixer sample, the internal components of the urea mixer are made of soft modules, and then the assembly sample is manually welded.

6. The method for developing and evaluating an automotive urea mixer according to claim 1, characterized in that: The test of the uniformity of urea mixing on the test bench in step S5 specifically includes the following steps: (1) Check the hardware used for the test and take photos to record the status before the test; (2) Install the engine, exhaust aftertreatment system sample with urea mixer, multi-probe position sampler and sensor on the engine stand, and connect the gas analyzer; (3) Starting and adjusting the engine operating conditions to the operating parameters designed for the urea mixer; (4) Monitor and record the concentrations of NOx, NH3, N2O, and HNCO at each operating test point after the SCR; (5) Re-measure the working condition test points to ensure that the error is less than 10% compared with the initial measurement value, otherwise re-measure; (6) Convert the data measured at each operating test point at the rear end of the SCR into the NH3 concentration value of the corresponding measurement point at the front end of the SCR, and calculate the ammonia mixing uniformity UI value; (7) Calculating NH3 peak to average value and NH3 min to average value; the NH3 peak to average value refers to the ratio of the peak value to the average value of the ammonia concentration; the NH3 min to average value refers to the ratio of the minimum value to the average value of the ammonia concentration; (8) Determine whether the ammonia mixing uniformity NH3-UI at the test operating point meets the following requirements: ammonia mixing uniformity UI ≥ 0.95; NH3 Peak to average < 1.5; NH3 min to average < 1.

5.

7. The method for developing and evaluating an automotive urea mixer according to claim 1, characterized in that: Verifying whether crystallization occurs in the urea mixer in step S6 specifically includes the following steps: (1) Confirm that the hardware used in the test meets the test requirements, weigh the urea mixer and urea nozzle before the test, and take photos of the main parts to record the status before the test; (2) Confirm that the calibration program used in the experiment is the latest calibration program. If the post-processing includes SDPF hardware, the calibration program needs to include a carbon particle active regeneration program; the urea injection amount in the calibration program is continuously injected at a ratio of 1.1 times the ammonia nitrogen; (3) Start bench testing and complete an SDPF regeneration interval mileage test according to WLTC conditions; (4) After completing the first SDPF regeneration interval mileage test, stop the test, remove the urea mixer and urea nozzle within 30 minutes, weigh them, record the weight, observe whether there is crystallization inside the mixer and urea nozzle, and take photos for record; (5) Reassemble the mixer back to the test bench, restart the test bench, start the SDPF carbon particle active regeneration program, and verify the effect of SDPF carbon particle active regeneration on urea crystallization; (6) After the SDPF carbon particles are actively regenerated, the test is stopped, and the urea mixer and urea nozzle are removed and weighed within 30 minutes. The parts are checked for crystallization, and the crystallization status of each part is recorded by taking photos; (7) Verify repeatability and conduct a second round of tests; if the amount of crystals inside the urea mixer does not exceed 1g within the SDPF regeneration interval mileage test, the urea nozzle hole and nozzle base are not blocked by crystals, and the crystals inside the mixer can be burned off after SDPF regeneration, then the bench urea crystallization verification meets the requirements.

8. The method for developing and evaluating an automotive urea mixer according to claim 1, characterized in that: The vehicle urea crystallization verification test in step S8 specifically includes the following steps: (1) Prepare a sample vehicle in good condition and confirm that the calibration procedure used in the test is the latest calibration procedure; (2) Confirm that the hardware used in the test meets the test requirements, weigh the urea mixer and urea nozzle before the test, and take photos of the main parts to record the status before the test; (3) Under simulated urban conditions (vehicle speed ≤ 40 km / h), after the sample vehicle has traveled once for the SDPF regeneration mileage interval (> 500 km), the test is stopped, the urea mixer is removed within 30 minutes, the urea nozzle is weighed, the weight is recorded, and the inside of the mixer, the urea nozzle hole, and the nozzle base are observed for crystallization and photographed for record; (4) Reassemble the urea mixer to the prototype vehicle, and start the SDPF carbon particle active regeneration program on the prototype vehicle. Stop the test after SDPF regeneration. Remove the urea mixer within 30 minutes and weigh the urea mixer and urea nozzle. Check whether there is crystallization inside each part, and take photos to record the crystallization status of each part. (5) Repeat the above steps (3) and (4) to verify the crystallization of the urea mixer under two working conditions: suburban working condition (vehicle speed 55-70 km / h), SDPF regeneration mileage interval (>600 km) and high-speed working condition (vehicle speed >75 km / h), SDPF regeneration mileage interval (>700 km); if the amount of crystallization inside the mixer does not exceed 1g during the SDPF regeneration interval mileage test, the urea nozzle hole and the nozzle base are not blocked by crystallization, and the crystallization inside the mixer can be burned after SDPF regeneration, then the vehicle urea crystallization verification meets the requirements.

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