A Development and Evaluation Method for Automobile Urea Mixers

Abstract

The present invention provides a development and evaluation method for an automotive urea mixer. By combining CAE analysis, bench verification, and vehicle verification, the method determines whether the design of the urea mixer meets the design requirements, identifies risks in advance, and avoids repeated changes to the urea mixer structure during the design and development process, which in turn affects the project development progress.

Description

Technical Field

[0001] The present 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] The after-treatment technology route for light-duty diesel vehicles is DOC+SDPF+SCR. CO and HC in the engine exhaust pollutants are oxidized by DOC, and NOx undergoes redox reaction with the reducing agent NH3 inside the SDPF and SCR catalysts to produce NO2 and H2O.

[0003] like Figure 1 As shown, the exhaust after-treatment 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. At the same time, a urea nozzle 70 is provided 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 structure is relatively complex, and the structure has very high requirements for urea mixing uniformity and urea crystallization. Urea mixers are 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 the urea mixers and is prone to problems that do not meet the design requirements. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the purpose of the present invention is to provide a development and evaluation method for automotive urea mixers. The method 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, which in turn affects the project development progress.

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

[0006] A development and evaluation method for an automotive urea mixer comprises the following steps:

[0007] Step S1: The software collects power, torque, exhaust flow after vortex, exhaust temperature, and urea injection amount parameters at all operating points under the vehicle's WLTC emission cycle, extracts the maximum and minimum urea injection operating points, then selects several representative operating points using a clustering method, and determines the vehicle layout boundary and post-processing parameters of the urea mixer; the maximum and minimum urea injection operating points and several representative operating points serve as the test points for this operating condition;

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

[0009] Step S3: Build a CFD model of the urea mixer in the CFD software, input the urea nozzle parameters into the software, perform simulation calculation and analysis on the operating test points extracted in step S1, optimize the urea mixer design, and ensure 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 after-treatment system with the urea mixer is manufactured for bench and vehicle test verification;

[0011] Step S5: Verify 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 full vehicle WLTC emission test and RDE road verification in a rotary drum test chamber to ensure that emission indicators meet the standards;

[0014] Step S8: Verify the urea crystallization of the vehicle by simulating the actual driving of the vehicle under different operating 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 with 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, the 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°; the surface of the urea mixer is wrapped with 8-10 mm thermal insulation cotton to reduce temperature loss.

[0017] Preferably, in step S3, the urea nozzle parameters include the number of nozzles, nozzle diameter, nozzle arrangement circle diameter, nozzle 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.

[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 assembled sample is manually welded.

[0020] Preferably, the test of the urea mixing uniformity 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 experiment;

[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) Start and adjust 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 on the SCR back end;

[0025] (5) Re-measure the working condition test point 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 point at the SCR rear end into the NH3 concentration value at the corresponding measurement point at the SCR front end, and calculate the ammonia mixing uniformity UI value;

[0027] (7) 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;

[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 volume in the calibration program is continuously injected at a ratio of 1.1 times the ammonia nitrogen;

[0032] (3) Start the bench test and complete an SDPF regeneration interval mileage test according to the WLTC operating 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 inside of each part is checked for crystallization, and the crystallization status of each part is recorded by taking photos;

[0036] (7) Verify the repeatability and conduct a second round of tests; if the amount of crystallization 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 crystallization, and the crystallization 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 prototype vehicle in good condition and confirm that the calibration procedure used in the test is the latest one;

[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. Within 30 minutes, the urea mixer is removed and the urea nozzle is weighed and recorded. 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 urea mixer crystallization conditions 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 1 g 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 automotive urea mixer development and evaluation method provided by the present invention, by combining CAE analysis, bench testing, and vehicle verification, can quickly and comprehensively evaluate whether a new urea mixer meets design requirements, identify risks in advance, and avoid repeated changes to the urea mixer structure during the design and development process, which in turn affects the project development progress. At the same time, it can reduce after-sales quality problems caused by unqualified urea mixers in mass-produced vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments 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 development and evaluation method for an automotive urea mixer as described in the examples;

[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-Tailpipe

[0056] 70-Urea nozzle DETAILED DESCRIPTION

[0057] To make the objectives, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Generally, the components of the embodiments of the present application described and shown in the drawings herein 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 protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application 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 or explained in 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 specific posture (as shown in the figures). If the specific posture changes, the directional indication will also change accordingly. Furthermore, the descriptions of "first", "second", etc. in the application are for descriptive purposes only and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features.

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

[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: Calibrated Inca software is used to collect data from all operating points of the vehicle's WLTC (World Light Vehicle Test Cycle) emissions cycle, including: power, torque, exhaust gas flow after the turbine, exhaust temperature, and urea injection rate.

[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 the urea mixer in the vehicle and ensure that it is coordinated 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 based on the vehicle's layout and the diameter of the catalyst carrier. The outer diameter of the urea mixer matches the diameter of the catalyst carrier. The mixer typically utilizes a double-baffle, multi-swirl mixing structure or a layered, broken mixing structure. The urea nozzle is located at the mixer's inlet, with the nozzle's injection axis angled between 15° and 45° to the horizontal. The urea mixer surface is wrapped with 8-10mm thick insulation to minimize temperature loss.

[0068] Step S3: CFD analysis;

[0069] The CFD analysis conditions used the maximum and minimum urea injection points extracted in step S1, along with three to four other points selected using the clustering method, as test points. The key parameters for each test point were exhaust mass flow rate, exhaust temperature, urea injection rate, and target mixer differential pressure. Urea nozzle parameters were also entered into the CDF software: number of nozzles, nozzle diameter, nozzle arrangement circle diameter, nozzle arrangement angle, average spray droplet size, injection frequency, static mass flow rate, spray visible cone angle, spray beam angle, spray beam angle, and initial droplet velocity. A urea mixer CFD model was constructed in the CFD software, and simulation analysis was performed for each test point. After the analysis, the urea mixing uniformity, liquid film thickness, and minimum liquid film temperature data were reviewed for each test point. The requirements were that the urea mixing uniformity UI should be ≥ 0.95, the maximum liquid film thickness should be ≤ 1E-6 μm, and the minimum liquid film temperature should be ≥ 160°C. If the CFD does not meet the above requirements, the internal structure of the urea mixer needs to be redesigned until the CFD meets the requirements.

[0070] Step 4: Sample production;

[0071] After CFD analysis confirmed that the urea mixer met the requirements, a prototype post-treatment system with the urea mixer was fabricated for bench and vehicle-based urea crystallization and ammonia mixing uniformity testing. To ensure prototype quality, the internal components of the urea mixer were typically constructed from soft modules, which were then assembled by hand welding.

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

[0073] 1. Select 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 after-treatment system samples with a urea mixer on the engine test bench. Install a NOx sensor, temperature sensor, and flow meter at the engine turbocharger outlet. Install a NOx sensor and temperature sensor at the inlet of the pre-stage SDPF carrier. Install a multi-probe position sampler 10 mm from the pre-stage SDPF outlet. Generally, 30 to 50 measurement points are arranged at the SCR outlet. The multi-probe position sampler is connected to the sampling line switch box, which then transmits signals to 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 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 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 operating points, retest all test operating points 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 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. Select 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. Confirm 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 after-treatment system has SDPF hardware, the calibration data must include the carbon particle active regeneration program. 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 operating conditions;

[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 shall be 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 photograph and 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 crystallization inside the mixer during the SDPF regeneration interval mileage test does not exceed 1g, the urea nozzle hole and base are not blocked by crystallization, and the crystallization 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 normal, 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 drum test room. The test results must meet the emission target requirements.

[0101] Step S8: Verification of urea crystallization on the entire vehicle;

[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 conditions of the prototype vehicle are to simulate urban conditions (vehicle speed ≤ 40km / h). After the vehicle has traveled once for the SDPF regeneration mileage interval (generally > 500km), the test is stopped. Within 30 minutes, the urea mixer is removed and the urea nozzle is weighed and the weight is recorded. 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 SDPF carbon particle active regeneration on the prototype vehicle. The test time shall be carried out in accordance with the requirements of each project and 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 steps 3 and 4 to verify the urea mixer crystallization conditions 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).

[0107] 6. The test assessment criteria are 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. After SDPF regeneration, the crystallization inside the mixer can be burned off. If the urea mixer crystallization meets the above criteria under the above-mentioned urban operating conditions, suburban operating conditions, and highway operating conditions, the vehicle's urea crystallization verification meets the standards.

[0108] Step S9: After the above verification is completed and no problems are found, 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 structure of the urea mixer needs to be redesigned.

[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 scope of the technical concept of this invention.

Claims

1. A method for developing and evaluating an automotive urea mixer, characterized in that: The following steps are involved: Step S1: The software collects power, torque, exhaust flow after vortex, exhaust temperature, and urea injection amount parameters at all operating points under the vehicle's WLTC emission cycle, extracts the maximum and minimum urea injection operating points, then selects several representative operating points using a clustering method, and determines the vehicle layout boundary and post-processing parameters of the urea mixer; the maximum and minimum urea injection operating points and several representative operating points serve as the test points for this operating condition; Step S2: designing a urea mixer structure according to the vehicle layout and catalyst size; Step S3: Build a CFD model of the urea mixer in the CFD software, input the urea nozzle parameters into the software, perform simulation calculation and analysis on the operating test points extracted in step S1, optimize the urea mixer design, and ensure 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 after-treatment system with the urea mixer is manufactured for bench and vehicle test verification; Step S5: Verify 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 full vehicle WLTC emission test and RDE road verification in a rotary drum test chamber to ensure that emission indicators meet the standards; Step S8: Verify the urea crystallization of the vehicle by simulating the actual driving of the vehicle under different operating conditions to ensure that the crystallization amount is within the specified range within different regeneration mileage intervals; Step S9: If there are no problems with the verification of steps S5 to S8, the design and development of the urea mixer is finally completed.

2. The method for developing and evaluating an automotive urea mixer according to claim 1, wherein: In step S2, the outer diameter of the urea mixer is consistent with the diameter of the catalyst carrier, the interior of the urea mixer adopts a double-partition 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 injection axis of the urea nozzle and the horizontal plane is in the range of 15° to 45°; the surface of the urea mixer is wrapped with 8-10 mm thermal insulation cotton to reduce temperature loss.

3. The method for developing and evaluating an automotive urea mixer according to claim 1, wherein: In step S3, the urea nozzle parameters include the number of nozzles, nozzle diameter, nozzle arrangement circle diameter, nozzle 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.

4. The method for developing and evaluating an automotive urea mixer according to claim 1, wherein: In step S3, ensuring that the urea mixing uniformity, liquid film thickness and liquid film minimum temperature at each operating point meet the 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 method for developing and evaluating an automotive urea mixer according to claim 1, wherein: 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, wherein: The test of the urea mixing uniformity 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 experiment; (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) Start and adjust 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 on the SCR back end; (5) Re-measure the working condition test point 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 point at the SCR rear end into the NH3 concentration value at the corresponding measurement point at the SCR front end, and calculate the ammonia mixing uniformity UI value; (7) Calculating 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; (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, wherein: 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 volume in the calibration program is continuously injected at a ratio of 1.1 times the ammonia nitrogen; (3) Start the bench test and complete an SDPF regeneration interval mileage test according to the WLTC operating 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 inside of each part is checked for crystallization, and the crystallization status of each part is recorded by taking photos; (7) Verify the repeatability and conduct a second round of tests; if the amount of crystallization 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 crystallization, and the crystallization 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, wherein: The vehicle urea crystallization verification test in step S8 specifically includes the following steps: (1) Prepare a prototype vehicle in good condition and confirm that the calibration procedure used in the test is the latest one; (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. Within 30 minutes, the urea mixer is removed and the urea nozzle is weighed and recorded. 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 urea mixer crystallization conditions 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 1 g 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.

Images