Airflow collection device, SCR ammonia and post-treatment airflow velocity uniformity test method

Abstract

The present invention discloses an airflow collection device, an SCR ammonia and post-processing airflow velocity uniformity test method, which collects airflow data simultaneously through a collection tube. When performing an ammonia uniformity test or an airflow velocity uniformity test, the airflow data of each position of the entire cross section can be obtained by only one test, which greatly reduces the time of the entire test process. A plurality of air collection pipes are supported at a fixed position by a support plate. During the test, the air collection pipes only pick up the airflow data of the fixed position, and no movement occurs. The data has low volatility and high accuracy and reliability.

Description

Technical Field

[0001] The present invention relates to the technical field of airflow collection and testing of an engine post-processing system, in particular to an airflow collection device, an SCR ammonia uniformity testing method and a post-processing airflow velocity uniformity testing method. Background Art

[0002] Automobile exhaust aftertreatment device belongs to the engine exhaust system. Its main function is to remove nitrogen oxides (NO X ), hydrocarbons (CH), carbon monoxide (CO) and other harmful gases into nitrogen (N2) and water (H2O) that are harmless to the environment. At present, the post-treatment device of diesel engine often adopts DOC (oxidation catalyst) + DPF (particulate filter) + SCR (selective catalytic reduction) technology to post-treat the exhaust emissions. DOC, DPF and SCR are all equipped with corresponding carriers, and the distribution uniformity of air flow velocity in each carrier has a great influence on the conversion efficiency of the carrier, the aging of the catalyst, the service life, etc. In SCR, the distribution uniformity of ammonia has a great influence on NO X The conversion rate has a great impact; therefore, in the design and development stage of the post-processing device, it is necessary to evaluate the uniformity of the flow rate of each carrier of the post-processing device and the uniformity of the ammonia of the SCR carrier, so as to evaluate the structural rationality of the post-processing device. In the prior art, CFD (Computational Fluid Dynamics) simulation technology is generally used to calculate the uniformity of the flow rate of each carrier and the uniformity of the ammonia of the SCR carrier through fluid dynamics theory, but the analysis result of CFD is only a simulation result, which is different from the actual situation after actual use and cannot accurately reflect the actual situation of the post-processing device.

[0003] The Chinese invention patent application "202010024911.3--Ammonia concentration uniformity test method for exhaust aftertreatment system" discloses an ammonia concentration uniformity test method, which samples the gas at several detection positions of the detection end face downstream of the SCR through a sampling probe, and obtains the ammonia concentration value of the detection position; the ammonia concentration uniformity value is calculated using a formula. This test method has the following problems: (1) This method uses a single sampling probe to move within the detection end face to obtain the concentration values ​​of multiple detection positions, and each detection position is tested in sequence. During the test, the sampling probe needs to be moved and tested multiple times according to different detection positions. Each movement and test takes time, so the entire test process takes a long time; moreover, the sampling probe collects data while moving, and the collected data fluctuates greatly, which reduces the accuracy of the data; further, in order to ensure that the sampling probe can be moved at will, it is necessary to set up corresponding auxiliary structures and devices to control the probe. The overall structure of the test device is relatively complex, and the cost required will also be relatively high. (2) The detection end face of this method is set downstream of the SCR. The ammonia retrieved is only the ammonia concentration remaining after the SCR carrier undergoes a reduction reaction, not all the ammonia entering the SCR carrier. It cannot accurately reflect the actual situation of the uniformity of the ammonia entering the SCR carrier. The accuracy and reliability of the test are relatively low. Summary of the invention

[0004] In view of the shortcomings of the above-mentioned existing ammonia uniformity test methods, such as long test time, large data volatility, and low accuracy and precision of test results, the applicant provides a rationally structured airflow collection device, an SCR ammonia uniformity test method and a post-treatment airflow velocity uniformity test method, which have short test time, small data fluctuation, and high test accuracy and reliability.

[0005] The technical solution adopted by the present invention is as follows:

[0006] An airflow collection device comprises a cylinder, in which a plurality of air extraction pipes are arranged axially, and the plurality of air extraction pipes are distributed at different positions of the cross section of the cylinder; a plurality of support plates are arranged in the cylinder, and the plurality of support plates have gaps between each other, so as to divide the cross section of the cylinder into a plurality of airflow areas, and each airflow area contains a plurality of air extraction pipes; the corresponding ends of the support plates are fixed on the inner wall surface of the cylinder, and the air extraction pipes are fixed to the surfaces of the corresponding support plates; a collection pipe is arranged on each air extraction pipe, and the collection pipes pass through the cylinder and are divergently distributed on the circumferential wall surface of the cylinder, and one end of the collection pipe is vertically connected to the air extraction pipe.

[0007] As a further improvement of the above technical solution:

[0008] The support plate is a straight plate or an approximately V-shaped plate; one end of the straight plate support plate is fixed on the inner wall surface of the cylinder, and the other end is fixedly connected to the outer wall surface of the central air intake pipe; the two ends of the V-shaped plate support plate are respectively fixed on the inner wall surface of the cylinder.

[0009] A plurality of collecting tubes are distributed on the same circumference of the cylinder; or a plurality of collecting tubes are staggeredly arranged on the circumferential wall of different cross sections of the cylinder and distributed on circumferences of different circles of the cylinder.

[0010] The air extraction pipes at various positions in the collection device of the present invention extract air at the same time, and the airflow data is collected simultaneously through the collection pipes. When performing an ammonia uniformity test or an airflow velocity uniformity test, the airflow data at various positions of the entire cross section can be obtained through only one test, which greatly reduces the time of the entire test process. Several air extraction pipes are supported in fixed positions by support plates. During the test, the air extraction pipes only pick up the airflow data at the fixed positions, and will not move. The data has low volatility, high accuracy and reliability. On the other hand, the support plate can also play a role in diversion and guidance, guiding the airflow in the corresponding airflow area into the air extraction pipe, which is more conducive to the collection of airflow data; moreover, the positions of the air extraction pipe and the collection pipe are fixed, and there is no need to set up auxiliary structures and devices for control. The overall structure of the test device is simpler and the required cost is low.

[0011] A method for testing the uniformity of SCR ammonia. The ammonia uniformity test bench comprises a gas source, a post-processing device, a collection device, and an ammonia analyzer. One end of the post-processing device is connected to the gas source through an air inlet pipe, and the other end of the collection device is arranged on the post-processing device and connected to the ammonia analyzer.

[0012] The post-treatment device includes a mixer, an SCR white carrier part, and an SCR carrier part;

[0013] The collecting device is arranged at the downstream end of the SCR white carrier part of the post-processing device and between the SCR white carrier part and the SCR carrier part; the inner end of the collecting pipe extends into the gas intake pipe to form an extending part, and a plurality of collecting holes are opened on the wall surface of the extending part;

[0014] The test method comprises the following steps:

[0015] S1: The gas source provides exhaust gas, which enters the post-treatment device and reacts chemically with the injected urea liquid in the mixer to produce ammonia and form a mixed gas. The mixed gas flows through the SCR white carrier part, the collection device, and the SCR carrier part in sequence;

[0016] S2: The collection device collects gas components from the gas extraction pipes at various locations in the cylinder at the same time and inputs them into the ammonia analyzer to obtain the ammonia concentration values ​​in several gas extraction pipes. φ n; Add up several ammonia concentration values ​​and divide by the number of sampling pipes to get the average ammonia concentration of all sampling pipes φ f ;

[0017] S3: Calculate the SCR ammonia uniformity value according to the ammonia uniformity index formula U NH3 :

[0018] ,

[0019] In the formula, n is the number of air intake pipes, φ i is the ammonia concentration value of the i-th gas extraction pipe, φ f is the average ammonia concentration of all gas sampling pipes, A i is the cross-sectional area of ​​the ith air extraction pipe.

[0020] As a further improvement of the above technical solution:

[0021] The extending portion of the collecting tube is directly opposite to the center of the air extraction tube and extends radially into the air extraction tube, and the extending end thereof abuts against the inner wall surface of the air extraction tube.

[0022] The SCR white carrier part has the same structure as the SCR carrier part. The carrier of the SCR white carrier part is a white carrier, and the carrier of the SCR carrier part has a catalyst.

[0023] When conducting an ammonia uniformity test, the collection device of the present invention is arranged downstream of the SCR white carrier part. All the ammonia generated from the mixer flows into the collection device from the downstream of the SCR white carrier part. The collected data can more accurately and reliably reflect the actual situation of the ammonia uniformity, and the accuracy and reliability of the test are higher.

[0024] A post-processing airflow velocity uniformity test method, the velocity uniformity test bench comprises an air source, a carrier, and a collection device connected in sequence, and the collection device is connected to a velocity meter;

[0025] The inner end of the collecting tube of the collecting device is inserted into the inner surface of the gas extraction tube to connect the gas extraction tube;

[0026] The test method comprises the following steps:

[0027] S1: The gas source provides exhaust gas, which enters the post-processing device and flows through the carrier and the collection device in sequence;

[0028] S2: The collection device collects the air flow pressure of the air intake pipes at various positions in the cylinder at the same time and inputs it into the flow meter to obtain the air flow velocity values ​​in several air intake pipes. v n; Add several flow rate values ​​and divide by the number of air sampling pipes to get the average flow rate of all air sampling pipes v f ;

[0029] S3: Calculate the velocity uniformity value according to the air flow velocity uniformity index formula U flow :

[0030] ,

[0031] In the formula, n is the number of air intake pipes, v i is the flow rate value of the i-th air extraction pipe, v f is the average flow rate of all air intake pipes, A i is the cross-sectional area of ​​the ith air extraction pipe.

[0032] As a further improvement of the above technical solution:

[0033] The inner end of the collection tube is directly opposite to the center of the gas extraction tube and is inserted into the wall surface of the gas extraction tube in the radial direction.

[0034] Collecting devices are separately arranged downstream of the DOC part, downstream of the DPF part, downstream of the mixer, and downstream of the SCR carrier part of the post-processing device.

[0035] An empty cylinder is also connected downstream of the collecting device.

[0036] The beneficial effects of the present invention are as follows:

[0037] The air extraction pipes at various positions in the collection device of the present invention extract air at the same time, and the airflow data is collected simultaneously through the collection pipes. When performing an ammonia uniformity test or an airflow velocity uniformity test, the airflow data at various positions of the entire cross section can be obtained through only one test, which greatly reduces the time of the entire test process. Several air extraction pipes are supported in fixed positions by support plates. During the test, the air extraction pipes only pick up the airflow data at the fixed positions, and will not move. The data has low volatility, high accuracy and reliability. On the other hand, the support plate can also play a role in diversion and guidance, guiding the airflow in the corresponding airflow area into the air extraction pipe, which is more conducive to the collection of airflow data; moreover, the positions of the air extraction pipe and the collection pipe are fixed, and there is no need to set up auxiliary structures and devices for control. The overall structure of the test device is simpler and the required cost is low.

[0038] When conducting an ammonia uniformity test, the collection device of the present invention is arranged downstream of the SCR white carrier part. All the ammonia generated from the mixer flows into the collection device from the downstream of the SCR white carrier part. The collected data can more accurately and reliably reflect the actual situation of the ammonia uniformity, and the accuracy and reliability of the test are higher.

[0039] The collection tube of the present invention is directly opposite to the center of the air extraction pipe and extends radially into the air extraction pipe. The extended end thereof basically abuts against the inner wall surface of the air extraction pipe. The collection area of ​​the collection hole is located on the diameter of the largest cross-sectional length of the air extraction pipe. The collection range is larger, which is more conducive to improving the precision and accuracy of data collection, thereby improving the precision and accuracy of the test results.

[0040] The present invention can select the airflow conditions at various axial positions in the cylinder, which is more conducive to improving the accuracy and precision of data collection, and further improving the precision and accuracy of the test results. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a stereoscopic diagram of the airflow collecting device of the present invention.

[0042] Figure 2 This is the front view of the collection device when it is used for ammonia uniformity test. At this time, the collection device is used to collect gas components.

[0043] Figure 3 This is a schematic diagram of the structure of the ammonia uniformity test bench.

[0044] Figure 4 This is the main view of the collection device when it is used for flow rate uniformity test. At this time, the collection device is used to collect air pressure.

[0045] Figure 5 This is a schematic diagram of the structure of a flow rate uniformity test bench, in which a collection device is set behind a carrier.

[0046] Figure 6 same Figure 5 In this case, a collection device is set behind each carrier.

[0047] In the figure: 1, collection device; 11, cylinder; 12, flange; 13, support plate; 14, air extraction pipe; 15, collection pipe; 151, insertion part; 152, collection hole;

[0048] 2. Post-treatment device; 21. DOC unit; 22. DPF unit; 23. Mixer; 24. SCR white carrier unit; 25. SCR carrier unit;

[0049] 3. Gas source; 4. Air inlet pipe; 5. Exhaust pipe; 6. Ammonia analyzer;

[0050] 7. Carrier; 8. Empty cylinder; 9. Flow meter;

[0051] 100. Ammonia uniformity test bench; 200. Flow rate uniformity test bench. DETAILED DESCRIPTION

[0052] The specific implementation of the present invention will be described below in conjunction with the accompanying drawings.

[0053] like Figure 1 As shown, the cylindrical body 11 of the collecting device 1 of the present invention is provided with flanges 12 at both ends for docking and fixing with the post-processing device 2; a plurality of air extraction pipes 14 are arranged axially in the body 11, and the plurality of air extraction pipes 14 are distributed at different positions of the cross section of the body 11, and the inner diameter of each air extraction pipe 14 is the same to ensure uniform and reasonable air extraction; a collecting pipe 15 is provided on each air extraction pipe 14, and one end of the collecting pipe 15 is vertically connected to the circumferential wall of the air extraction pipe 14, as shown in FIG. Figure 2 , Figure 4 As shown, a part of the collecting tubes 15 is a straight tube, and its inner end is directly and vertically connected to the gas extraction tube 14, and the inner end of the other part of the collecting tubes 15 is bent at a certain angle to form a curved portion, and the curved portion is vertically connected to the gas extraction tube 14; the other end of the collecting tube 15 passes through the wall of the cylinder 11, and a plurality of collecting tubes 15 are distributed radially on the circumferential wall of the cylinder 11. The plurality of collecting tubes 15 can be distributed on the same circumferential part of the cylinder 11, or can be staggered on the circumferential wall of different cross sections of the cylinder 11, or distributed on the cylinder 11. The circumferential parts of different circles on the cylinder 11 can select the airflow conditions of various axial parts in the cylinder 11, which is more conducive to improving the accuracy and precision of data collection, and thus improving the accuracy and precision of the test results; when the airflow passes through, the air intake pipes 14 at various positions take air at the same time, and the airflow data is collected simultaneously through the collection pipe 15. When performing ammonia uniformity test or airflow velocity uniformity test, only one test is needed to obtain the airflow data of various positions in the entire cross section, which greatly reduces the time of the entire test process. Figure 3 , Figure 5 , Figure 6As shown, the end of the collection tube 15 passing through the cylinder 11 is connected to the ammonia analyzer 6 or the flow meter 9 through the corresponding pipeline, and the collected air flow data is input into the ammonia analyzer 6 or the flow meter 9. A plurality of support plates 13 are also provided in the cylinder 11, including a plurality of straight plate-type support plates 13 and a plurality of approximately V-shaped plate-type support plates 13. One end of the straight plate-type support plate 13 is fixed to the inner wall surface of the cylinder 11, and the other end is fixedly connected to the outer wall surface of the central air intake pipe 14. The two ends of the V-shaped plate-type support plate 13 are respectively fixed to the inner wall surface of the cylinder 11; the plurality of support plates 13 have gaps between each other, and the cross section of the cylinder 11 is divided into a plurality of air flow areas, each of which includes a plurality of air intake pipes 14, and the outer wall surface of the air intake pipe 14 in each air flow area is fixed to the surface of the corresponding support plate 13. On the one hand, the air intake pipe 14 is supported at a fixed position in the cylinder 11 by the support plate 13. During the test, the air intake pipe 14 only picks up the airflow data at the fixed position without any movement. The data has small volatility and high accuracy and reliability. On the other hand, the support plate 13 can also play a role in diversion and guidance, guiding the airflow in the corresponding airflow area into the air intake pipe 14, which is more conducive to the collection of airflow data. Moreover, the positions of the air intake pipe 14 and the collection pipe 15 are fixed, and there is no need to set up auxiliary structures and devices for control. The overall structure of the test device is simpler and the required cost is low.

[0054] I. Such as Figure 2 , Figure 3 As shown, the collection device 1 can be applied to an ammonia uniformity test bench 100 to collect ammonia concentration data.

[0055] like Figure 2 As shown, at this time, the inner end of the collection tube 15 extends into the air intake pipe 14 to form an extension portion 151, and a plurality of through collection holes 152 are opened on the wall surface of the extension portion 151 facing the air inlet side, which are used to collect the gas components flowing through the air intake pipe 14; the extension portion 151 is directly opposite to the center of the air intake pipe 14 and extends radially into the air intake pipe 14, and its extended end basically rests on the inner wall surface of the air intake pipe 14, and the collection area of ​​the collection hole 152 is located on the diameter of the largest cross-sectional length of the air intake pipe 14, so the collection range is larger, which is more conducive to improving the precision and accuracy of data collection, thereby improving the precision and accuracy of the test results.

[0056] like Figure 3As shown, the ammonia uniformity test bench 100 includes a gas source 3, a post-processing device 2, a collection device 1 and an ammonia analyzer 6. The air inlet end of the post-processing device 2 is connected to the gas source 3 through an air inlet pipe 4, and the air outlet end is connected to the exhaust pipe 5. The collection device 1 is arranged on the post-processing device 2 and is connected to the ammonia analyzer 6 through a pipeline; the gas source 3 can be an engine bench to simulate the engine working condition and provide engine exhaust gas; the ammonia analyzer 6 is used to collect the gas composition data of each collection pipe 15 of the collection device 1 to obtain the ammonia concentration value of each gas extraction pipe 14. The post-treatment device 2 includes a DOC unit 21, a DPF unit 22, a mixer 23, an SCR white carrier unit 24 (white carrier means that there is no catalyst on the carrier, and no reduction reaction occurs when the gas passes through the white carrier) and an SCR carrier unit 25. The DOC unit 21, the DPF unit 22, the mixer 23, and the SCR white carrier unit 24 are connected in sequence, and the collection device 1 is arranged between the SCR white carrier unit 24 and the SCR carrier unit 25; the SCR white carrier unit 24 and the SCR carrier unit 25 have the same structure, and the difference between the two is that there is no catalyst on the carrier of the SCR white carrier unit 24, and there is a catalyst on the carrier of the SCR carrier unit 25. agent, so the distribution of the ammonia generated in the mixer 23 that flows directly into the SCR white carrier part 24 is the same as the distribution that flows directly into the SCR carrier part 25. The ammonia distribution collected by the collection device 1 at the downstream end of the SCR white carrier part 24 can accurately reflect the distribution of the ammonia after entering the SCR carrier part 25; since no reduction reaction occurs when ammonia flows through the SCR white carrier part 24, all the ammonia generated in the mixer 23 flows into the collection device 1 from the downstream of the SCR white carrier part 24. The collected data can more accurately and reliably reflect the actual situation of the uniformity of the ammonia, and the accuracy and reliability of the test are higher.

[0057] The specific steps of using the ammonia uniformity test bench 100 to perform the SCR ammonia uniformity test are as follows:

[0058] S1: The gas source 3 simulates the engine working condition and provides exhaust gas; the exhaust gas enters the post-treatment device 2 from the intake pipe 4, flows through the DOC part 21, the DPF part 22, and the mixer 23 in sequence, reacts chemically with the injected urea liquid in the mixer 23 to produce ammonia and form a mixed gas, and the mixed gas containing ammonia flows through the SCR white carrier part 24 and the collection device 1 in sequence, and finally flows into the SCR carrier part 25 for reduction reaction, and then is discharged from the exhaust pipe 5;

[0059] S2: The collection device 1 collects gas components from the gas extraction pipes 14 at various positions of the cross section of the cylinder 11 through the collection pipe 15, and inputs the gas composition data into the ammonia analyzer 6 to obtain the ammonia concentration value in each gas extraction pipe 14. φ , corresponding to the plurality of gas extraction pipes 14 in the collection device 1, a plurality of ammonia concentration values ​​are obtained: φ1 , φ 2 ,…… φ i ,…… φ n ; Add a number (n) of ammonia concentration values ​​and divide by the number of gas extraction pipes 14 to obtain the average ammonia concentration of all gas extraction pipes 14 φ f ;

[0060] S3: Calculate the SCR ammonia uniformity value according to the following ammonia uniformity index formula U NH3 :

[0061] ,

[0062] Wherein, n is the number of the air intake pipes 14, φ i is the ammonia concentration value of the i-th air extraction pipe 14, φ f is the average ammonia concentration of all gas extraction pipes 14, A i is the cross-sectional area of ​​the i-th air extraction pipe 14.

[0063] S4: According to the uniformity value of ammonia U NH3 Determine the uniformity of ammonia distribution within the SCR carrier.

[0064] II. Figure 4 , Figure 5 , Figure 6 As shown, the collection device 1 can be applied to a flow rate uniformity test bench 200 to collect airflow pressure data.

[0065] like Figure 4 As shown, at this time, the inner end of the collection tube 15 is inserted into the inner surface of the air extraction tube 14, does not extend into the interior of the air extraction tube 14, is communicated with the air extraction tube 14, and collects the air flow pressure data flowing through the air extraction tube 14; the inner end of the collection tube 15 is opposite to the center of the air extraction tube 14 and is radially inserted into the wall of the air extraction tube 14, which is convenient for manufacturing.

[0066] like Figure 5 As shown, the flow rate uniformity test bench 200 includes an air source 3, a carrier 7, a collection device 1, an empty cylinder 8 and a flow meter 9 connected in sequence. The air inlet end of the carrier 7 is connected to the air source 3 through an air inlet pipe 4. The empty cylinder 8 is used to provide support and is connected to an exhaust pipe 5. The air source 3 can be an engine bench or a burner to provide airflow. The flow meter 9 is used to collect the airflow pressure data of each collection pipe 15 of the collection device 1 to obtain the flow rate value of each air extraction pipe 14. Figure 6As shown, collection devices 1 are separately arranged downstream of the DOC section 21, downstream of the DPF section 22, downstream of the mixer 23, and downstream of the SCR carrier section 25 of the post-treatment device 2, respectively, to collect the air pressure value of the airflow passing through each part, and obtain the flow velocity value of each part, so as to more comprehensively evaluate the uniformity of the flow velocity of the airflow passing through each carrier in the post-treatment device 2.

[0067] The specific steps of using the flow rate uniformity test bench 200 to test the flow rate uniformity of the post-processing airflow are as follows:

[0068] S1: The gas source 3 provides exhaust gas; the exhaust gas enters the post-processing device 2 from the intake pipe 4, flows through the carrier 7, the collection device 1, and the empty cylinder 8 in sequence, and is discharged from the exhaust pipe 5;

[0069] S2: The collecting device 1 collects the air flow pressure of the air intake pipes 14 at various positions of the cross section of the cylinder 11 through the collecting pipe 15, and inputs the air flow pressure data into the velocity meter 9 to obtain the air flow velocity value in each air intake pipe 14. v , corresponding to a plurality of air extraction pipes 14 in the collection device 1, a plurality of flow rate values ​​are obtained: v 1 , v 2 ,…… v i ,…… v n ; After adding a number (n) of flow rate values, divide it by the number of air intake pipes 14 to obtain the average flow rate of all air intake pipes 14 v f ;

[0070] S3: Calculate the velocity uniformity value according to the following air flow velocity uniformity index formula: U flow :

[0071] ,

[0072] Wherein, n is the number of the air intake pipes 14, v i is the flow rate value of the i-th air intake pipe 14, v f is the average flow rate of all air intake pipes 14, A i is the cross-sectional area of ​​the i-th air extraction pipe 14.

[0073] S4: According to the flow rate uniformity value U flow Determine the uniformity of the airflow velocity distribution in the post-processing device 2.

[0074] The above description is an explanation of the present invention, not a limitation of the present invention. The present invention may be modified in any form without violating the spirit of the present invention.

Claims

1. A method for testing the uniformity of ammonia in an SCR system. The ammonia uniformity testing bench (100) comprises a gas source (3), a post-processing device (2), a collection device (1), and an ammonia analyzer (6). One end of the post-processing device (2) is connected to the gas source (3) through an air intake pipe (4), and the other end of the collection device (1) is arranged on the post-processing device (2) and connected to the ammonia analyzer (6). The method is characterized in that: The collection device (1) is an airflow collection device for collecting gas composition data; the airflow collection device comprises a cylinder (11), a plurality of air extraction pipes (14) are arranged in the cylinder (11) along the axial direction, and the plurality of air extraction pipes (14) are distributed at different positions of the cross section of the cylinder (11); a plurality of support plates (13) are arranged in the cylinder (11), and the plurality of support plates (13) have gaps between each other, so as to divide the cross section of the cylinder (11) into a plurality of airflow areas, and each airflow area contains a plurality of air extraction pipes (14); the corresponding ends of the support plates (13) are fixed to the inner wall surface of the cylinder (11), and the air extraction pipes (14) are fixed to the surface of the corresponding support plates (13); each air extraction pipe (14) is provided with a collection pipe (15), the collection pipes (15) pass through the cylinder (11) and are distributed divergently on the circumferential wall surface of the cylinder (11), and one end of the collection pipe (15) is vertically connected to the air extraction pipe (14); The post-treatment device (2) comprises a mixer (23), an SCR white carrier part (24), and an SCR carrier part (25); The collection device (1) is arranged at the downstream end of the SCR white carrier part (24) of the post-treatment device (2) and is located between the SCR white carrier part (24) and the SCR carrier part (25); the inner end of the collection pipe (15) extends into the gas intake pipe (14) to form an extension part (151), and a plurality of collection holes (152) are opened on the wall surface of the extension part (151); The testing method comprises the following steps: S1: the gas source (3) provides exhaust gas, which enters the post-treatment device (2), undergoes a chemical reaction with the injected urea liquid in the mixer (23) to generate ammonia gas and form a mixed gas, which flows through the SCR white carrier part (24), the collection device (1), and the SCR carrier part (25) in sequence; S2: The collection device (1) collects gas components from the gas collection pipes (14) at various positions in the cylinder (11) at the same time and inputs the gas components into the ammonia analyzer (6) to obtain ammonia concentration values ​​in the gas collection pipes (14). φ n ; Add up several ammonia concentration values ​​and divide by the number of gas sampling pipes (14) to obtain the average ammonia concentration of all gas sampling pipes (14) φ f ; S3: Calculate the SCR ammonia uniformity value according to the ammonia uniformity index formula U NH3 : ， Where n is the number of air intake pipes (14), φ i is the ammonia concentration value of the i-th gas extraction pipe (14), φ f is the average ammonia concentration of all gas extraction pipes (14), A i is the cross-sectional area of ​​the i-th air extraction pipe (14).

2. The SCR ammonia uniformity testing method according to claim 1, characterized in that: The extending portion (151) of the collection tube (15) faces the center of the air extraction tube (14) and extends radially into the air extraction tube (14), with the extending end portion abutting against the inner wall surface of the air extraction tube (14).

3. The SCR ammonia uniformity testing method according to claim 1, characterized in that: The SCR white carrier part (24) and the SCR carrier part (25) have the same structure. The carrier of the SCR white carrier part (24) is a white carrier, and the carrier of the SCR carrier part (25) has a catalyst.

4. The SCR ammonia uniformity testing method according to claim 1, characterized in that: The support plate (13) is a straight plate type or a V-shaped plate type; one end of the straight plate type support plate (13) is fixed to the inner wall surface of the cylinder (11), and the other end is fixedly connected to the outer wall surface of the central air intake pipe (14); the two ends of the V-shaped plate type support plate (13) are respectively fixed to the inner wall surface of the cylinder (11).

5. The SCR ammonia uniformity testing method according to claim 1, characterized in that: The plurality of collecting tubes (15) are distributed at the same circumferential position on the cylinder (11); or the plurality of collecting tubes (15) are staggeredly arranged on the circumferential wall surface of the cylinder (11) with different cross sections and distributed at circumferential positions of different circles on the cylinder (11).

6. A method for testing the uniformity of a post-processing airflow velocity, wherein a velocity uniformity testing bench (200) comprises an air source (3), a carrier (7), and a collection device (1) connected in sequence, wherein the collection device (1) is connected to a velocity meter (9), and wherein: The collection device (1) is an airflow collection device for collecting airflow pressure data; the airflow collection device comprises a cylinder (11), a plurality of air extraction pipes (14) are arranged in the cylinder (11) along the axial direction, and the plurality of air extraction pipes (14) are distributed at different positions of the cross section of the cylinder (11); a plurality of support plates (13) are arranged in the cylinder (11), and the plurality of support plates (13) have gaps between each other, so as to divide the cross section of the cylinder (11) into a plurality of airflow areas, and each airflow area contains a plurality of air extraction pipes (14); the corresponding ends of the support plates (13) are fixed to the inner wall surface of the cylinder (11), and the air extraction pipes (14) are fixed to the surface of the corresponding support plates (13); each air extraction pipe (14) is provided with a collection pipe (15), the collection pipes (15) pass through the cylinder (11) and are distributed divergently on the circumferential wall surface of the cylinder (11), and one end of the collection pipe (15) is vertically connected to the air extraction pipe (14); The inner end of the collection tube (15) of the collection device (1) is inserted into the inner surface of the gas extraction tube (14), thereby connecting the gas extraction tube (14); The testing method comprises the following steps: S1: The gas source (3) provides exhaust gas, which enters the post-processing device (2) and flows through the carrier (7) and the collection device (1) in sequence; S2: The collecting device (1) collects the air flow pressure of the air intake pipes (14) at various positions in the cylinder (11) at the same time and inputs the pressure into the flow meter (9), thereby obtaining the air flow velocity values ​​in the air intake pipes (14). v n ; Add several flow rate values ​​and divide them by the number of air intake pipes (14) to obtain the average flow rate of all air intake pipes (14) v f ; S3: Calculate the velocity uniformity value according to the air flow velocity uniformity index formula U flow : ， Where n is the number of air intake pipes (14), v i is the flow rate value of the i-th air intake pipe (14), v f is the average flow rate of all air intake pipes (14), A i is the cross-sectional area of ​​the i-th air intake pipe (14).

7. The method for testing the uniformity of the post-processing airflow velocity according to claim 6, characterized in that: The inner end of the collection tube (15) faces the center of the air extraction tube (14) and is inserted into the wall of the air extraction tube (14) in the radial direction.

8. The method for testing the uniformity of the post-processing airflow velocity according to claim 6, characterized in that: A collection device (1) is separately provided downstream of the DOC section (21), downstream of the DPF section (22), downstream of the mixer (23), and downstream of the SCR carrier section (25) of the post-treatment device (2).

9. The method for testing the uniformity of the post-processing airflow velocity according to claim 6, characterized in that: An empty cylinder (8) is also connected downstream of the collecting device (1).

10. The method for testing the uniformity of the post-processing airflow velocity according to claim 6, characterized in that: The support plate (13) is a straight plate type or a V-shaped plate type; one end of the straight plate type support plate (13) is fixed to the inner wall surface of the cylinder (11), and the other end is fixedly connected to the outer wall surface of the central air intake pipe (14); the two ends of the V-shaped plate type support plate (13) are respectively fixed to the inner wall surface of the cylinder (11).

11. The method for testing the uniformity of the post-processing airflow velocity according to claim 6, characterized in that: The plurality of collecting tubes (15) are distributed at the same circumferential position on the cylinder (11); or the plurality of collecting tubes (15) are staggeredly arranged on the circumferential wall surface of the cylinder (11) with different cross sections and distributed at circumferential positions of different circles on the cylinder (11).

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