Low-back-pressure sixth-generation aftertreatment urea mixer

Abstract

The utility model discloses a kind of low back pressure national six aftertreatment device urea mixers, including inner end cap, outer end cap, inner mixing pipe, outer mixing pipe, support plate, partition plate and rear spoiler etc..Inner end cap and cover plate cooperate to form flow guide cavity, and into gas cavity and outlet gas cavity are divided by partition plate. Inner, outer mixing pipe coaxially set, pipe wall is respectively set up blade window, long circle hole, rectangular slot and mesh, support plate is set up vent hole, and four-way air inlet passage are formed jointly. The utility model greatly reduces back pressure and exhaust resistance by double-tube cyclone mixing and porous pressure relief structure, improves mixing efficiency;Avoid metal mesh structure, significantly reduce PN emission;And by airflow purging and intermittent tank design effectively prevent urea crystallization, with compact structure, low in cost, high reliability advantage, applicable to national six emission standard diesel vehicle SCR system.

Description

Technical Field

[0001] This utility model relates to the technical field of motor vehicle catalytic reduction, and in particular to a low back pressure China VI emission standard after-processor urea mixer. Background Technology

[0002] With increasing global emphasis on environmental protection, the automotive industry faces increasingly stringent emission and energy consumption regulations. In my country, to effectively control emissions of pollutants such as nitrogen oxides (NOx) from vehicle exhaust, the China VI emission standard has been fully implemented. This standard sets significantly higher limits for NOx emissions than previous standards, forcing vehicle after-treatment systems to have more efficient pollutant purification capabilities. Simultaneously, the implementation of Stage IV fuel consumption regulations requires vehicles to not only meet emission compliance but also further improve power economy and reduce fuel consumption. This makes energy consumption and drag control of various vehicle systems a core focus for OEMs' R&D.

[0003] In automotive exhaust aftertreatment systems, the SCR (Selective Catalytic Reduction) system is a key technological path for achieving efficient reduction of nitrogen oxides (NOx). The urea mixer, a core component of the China VI emission standard aftertreatment system, directly determines the NOx purification efficiency and the vehicle's overall fuel economy. Specifically, the core function of the urea mixer is to thoroughly mix a urea solution with the high-temperature exhaust gas from the engine, causing the urea solution to rapidly hydrolyze and evaporate at high temperatures to produce ammonia. Simultaneously, it ensures that the ammonia is evenly distributed in the exhaust gas. Then, under the action of a catalyst, the ammonia reacts with NOx to produce harmless nitrogen and water, ultimately ensuring that exhaust emissions meet the China VI emission standards.

[0004] However, the current development of urea mixers faces a key technical dilemma: on the one hand, to ensure thorough mixing of urea and exhaust gas, prevent urea crystallization, and ensure uniform ammonia distribution, a specific structural design is needed to enhance the mixing effect; on the other hand, such enhanced mixing designs often lead to an increase in the overall back pressure of the aftertreatment system. This increased back pressure directly increases engine exhaust resistance, causing engine power loss and reducing overall vehicle performance and fuel economy, which contradicts the requirements of the Stage IV fuel consumption regulations. Therefore, developing a urea mixer for a China VI aftertreatment system that can achieve efficient mixing of urea and exhaust gas while minimizing back pressure has become a pressing technical problem in the automotive aftertreatment field.

[0005] To address these needs, various urea mixer designs have emerged in the existing technology, but all have significant drawbacks and cannot simultaneously meet the comprehensive requirements of low back pressure, high mixing efficiency, low emission risk, and low cost, as detailed below:

[0006] 1. Metal wire mesh fragmentation structure;

[0007] This solution is a common design in existing China VI emission standard after-processor urea mixers. Its core principle is: after the urea aqueous solution is initially mixed with the high-speed flowing exhaust gas, they flow together through a densely wound metal mesh. The high temperature environment of the metal mesh promotes the hydrolysis and evaporation of urea, and the physical barrier effect of the mesh breaks up the urea droplets to enhance the mixing effect.

[0008] However, this structure has the following significant drawbacks:

[0009] Excessive back pressure: The densely wrapped metal mesh creates significant resistance to airflow, resulting in a significant increase in the overall back pressure of the after-treatment system. This severely increases the engine exhaust load, which is detrimental to the improvement of the vehicle's power economy and conflicts with the requirements of the Stage IV fuel consumption regulations.

[0010] High risk of crystallization accumulation: The dense structure of the metal mesh makes it easy for urea crystals to accumulate quickly in the gaps between the mesh once they are formed. The accumulated crystals are difficult to remove through the conventional regeneration process of the after-processor (such as high-temperature combustion). Long-term use will lead to blockage of the exhaust passage, further aggravating the problem of increased back pressure, and ultimately causing a decrease in the power of the whole vehicle.

[0011] High risk of PN emissions exceeding standards: When the exhaust gas passes through the dense metal wire mesh, wear on the surface of the wire mesh or airflow impact may generate additional particulate matter, resulting in a significant increase in the PN (number of particulate matter) concentration in the exhaust gas. This not only increases the requirements for the particulate capture performance of the DPF (particulate filter), increases the risk of DPF blockage and regeneration frequency, but may also cause PN emissions to exceed the limits of the China VI regulations.

[0012] High cost: The processing, winding and assembly of metal wire mesh are complex, and the requirements for the high temperature resistance and corrosion resistance of the wire mesh material are high, resulting in high production and maintenance costs for this structure.

[0013] 2. Side-mixed double-layer pipe structure;

[0014] To improve some of the defects of the metal wire mesh structure, the existing technology has also proposed a urea mixer with a side-mixing double-layer tube structure. It adopts an inner and outer double-layer tube design: the airflow first passes through the swirl blades on the outer mixing tube to form a high-speed rotating vortex, and then enters the inner tube through the mesh on the inner tube to mix with the urea aqueous solution sprayed in the inner tube; the bottom of the inner tube adopts a sealing design, and the urea droplets need to pass through the mesh of the inner tube and the outer tube in turn for secondary breakage to reduce the risk of crystallization.

[0015] While this structure offers a slight improvement in crystallization control, it still suffers from the following key shortcomings:

[0016] Complex structure and process: Multiple components such as inner and outer double-layer tubes and swirl blades need to be processed separately, and the assembly precision requirements between components are high, resulting in a complex overall structure and slightly poorer manufacturing process.

[0017] Poor back pressure control: The gap between the inner and outer pipes is too small and the number of openings on the pipe body is too small. The airflow resistance in the pipe is large, which cannot effectively reduce the back pressure of the after-treatment system and still has an adverse effect on the power economy of the whole vehicle.

[0018] High cost: The design of multiple components and the requirement for high-precision assembly result in high material and processing costs for this structure, making it difficult to meet the cost control requirements of OEMs.

[0019] In summary, existing urea mixers for China VI emission standard aftertreatment systems have significant shortcomings in both structural design and performance balance. They cannot simultaneously meet the requirements of China VI emission regulations regarding nitrogen oxide purification efficiency and particulate matter (PN) emission limits, as well as the requirements of Stage IV fuel consumption regulations for low back pressure and high power economy. Furthermore, they struggle to balance low crystallization risk with low-cost industrialization. Therefore, developing a China VI emission standard aftertreatment urea mixer with a reasonable structure, low back pressure, high mixing efficiency, low PN emissions, and controllable cost has become an urgent need in the field of automotive aftertreatment technology. Summary of the Invention

[0020] This utility model aims to address the technical deficiencies of existing China VI after-treatment urea mixers, and to provide a low back pressure China VI after-treatment urea mixer that meets the requirements of the China VI motor vehicle pollutant emission standards for exhaust gas purification efficiency and the requirements of the fourth-stage fuel consumption regulations for vehicle power economy.

[0021] The technical solution adopted in this utility model is: a low back pressure China VI emission standard after-processor urea mixer, including an inner end cover, an outer end cover, an inner mixing pipe, a support plate, an outer mixing pipe, a cover plate, a partition plate, a rear spoiler, a temperature base, a low-pressure gas intake base, a nozzle, and a nozzle seat.

[0022] The inner end cap and the cover plate cooperate to form a flow guiding cavity. The partition plate is fixed in the flow guiding cavity and divides the flow guiding cavity into an independent air inlet cavity and an air outlet cavity.

[0023] The cover plate is fitted onto the inner end cover; the cover plate has two large circular holes, which correspond to the air inlet chamber and the air outlet chamber, respectively;

[0024] The rear spoiler is fixed to the outlet of the cover plate on one side of the air outlet cavity;

[0025] The outer mixing pipe passes through the partition plate and the support plate is provided on the top of the outer mixing pipe; the support plate is located in the air intake cavity; the inner mixing pipe is coaxially arranged inside the outer mixing pipe and is fixed to the outer mixing pipe by the support plate;

[0026] The inner mixing pipe has openings and blade windows for airflow, the outer mixing pipe has blade windows, and the support plate has openings for airflow, so as to form four air intakes that respectively enter the inner mixing pipe and the outer mixing pipe.

[0027] The nozzle seat is located on the top of the inner end cover, and the nozzle is mounted on the nozzle seat; the temperature base and the low-pressure gas intake base are respectively fixed to the inner end cover.

[0028] Furthermore, the diameter of the inner mixing tube is 20-40 mm smaller than the diameter of the outer mixing tube.

[0029] Furthermore, the length of the inner mixing tube is shorter than the length of the outer mixing tube.

[0030] Furthermore, the top of the inner mixing tube is provided with two positioning bosses, which are used for welding positioning and circumferential positioning of the inner mixing tube; the inner mixing tube has elongated holes evenly distributed circumferentially near the top; the middle part of the inner mixing tube has a blade window with a preset angle, which is used to guide the airflow to form a high-speed rotating airflow; the lower part of the inner mixing tube has rectangular grooves evenly distributed circumferentially; the rectangular grooves are intermittently arranged at the bottom of the inner mixing tube.

[0031] Furthermore, the upper side of the outer mixing pipe is provided with a blade window with a preset angle, which is used to guide the airflow to form a high-speed rotating airflow; the lower part of the outer mixing pipe is provided with a mesh arranged in a preset manner, which is used to relieve pressure and break urea droplets.

[0032] Furthermore, a nozzle seat mounting platform is stamped on the upper part of the inner end cap, and a positioning groove is provided on the nozzle seat mounting platform; the positioning boss at the upper end of the inner mixing tube is inserted into the positioning groove to ensure the coaxiality of the nozzle center and the inner mixing tube center.

[0033] The beneficial effects of this utility model are:

[0034] 1. This utility model adopts a four-way air intake structure, which significantly reduces intake resistance by separating the airflow. Simultaneously, both the inner and outer mixing pipes are equipped with numerous mesh holes, oblong holes, and rectangular grooves, and the inner pipe diameter is 20-40mm smaller than the outer pipe, greatly enhancing the airflow exchange and pressure relief capacity between the inner and outer mixing pipes, effectively reducing airflow resistance. Compared to existing metal wire mesh breaking structures and side-mixing double-layer pipe structures, this utility model can significantly reduce the overall back pressure of the aftertreatment system, reduce engine exhaust load, and thus improve the vehicle's power performance and fuel economy, fully meeting the requirements of the Stage IV fuel consumption regulations for low energy consumption and high power economy.

[0035] 2. This invention abandons the metal mesh structure that easily generates particulate matter in existing technologies. By incorporating angled blade windows in both the inner and outer mixing pipes, a high-speed rotating airflow is formed, optimizing the airflow swirling mixing and urea crushing method. The lower mesh of the outer mixing pipe is depressurized and crushed, and the airflows from the inner and outer pipes collide and mix, thus avoiding the increase in particulate matter (PN) caused by the metal mesh from the source. Based on actual results, compared to the metal mesh crushing structure, the exhaust gas PN emissions treated by this invention can be reduced by 90%. It not only eliminates the need for the high-load capture performance of the DPF but also reduces the risk of DPF clogging and regeneration frequency, lowering DPF usage and maintenance costs, and ensuring that exhaust gas PN emissions easily meet the China VI emission standards.

[0036] 3. In this invention, urea is mixed in the inner mixing tube by airflow purging and swirling, and then diffused to the outer mixing tube to further interweave and collide with the high-speed rotating airflow. The mixing effect is far superior to the single mixing mode of the existing side-mixing double-layer tube structure. At the same time, the exhaust chamber is equipped with a rear baffle, which can further improve the uniformity of ammonia concentration distribution, ensure that ammonia and nitrogen oxides react fully, and ensure the SCR system's efficient reduction capability of nitrogen oxides.

[0037] With four air intakes, the first airflow directly blows urea near the nozzle seat, while the other three airflows heat and blow urea off the outer wall of the inner mixing tube, effectively removing urea residue from easily crystallizing areas in real time. The bottom of the inner mixing tube is intermittently arranged to avoid airflow turbulence and crystal accumulation caused by sudden pressure changes. The rear baffle can also change the airflow direction in the outlet chamber, further reducing the possibility of localized crystallization. Compared to existing metal mesh structures and side-mixing double-layer tube structures, this invention can prevent urea crystallization and blockage for a long time, ensuring the stable operation of the SCR system.

[0038] 4. The core components of this utility model only include an inner end cap, an outer end cap, an inner / outer mixing tube, and a support plate. The number of parts is far fewer than that of a side-mixing double-layer tube structure that requires additional complex components such as swirl blades. Furthermore, the inner end cap uses a stamped, one-piece formed nozzle seat mounting platform with a positioning groove, achieving coaxial positioning of the inner tube and nozzle without the need for additional positioning components, thus simplifying the assembly process. The overall structural design is simple, the processing difficulty is low, and the assembly accuracy is easy to control, effectively reducing material and manufacturing costs, improving mass production efficiency, and possessing extremely high industrial application value. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the overall structure of this utility model;

[0040] Figure 2 This is an exploded view of the structure of this utility model;

[0041] Figure 3 This is a schematic diagram of the four air intake flow paths of the air intake chamber and the air outlet chamber in this utility model;

[0042] Figure 4 This is a schematic diagram showing the structural details of the inner mixing tube in this utility model;

[0043] Figure 5 This is a schematic diagram showing the detailed structure of the blade window and mesh of the hybrid pipe in this utility model.

[0044] Figure 6 This is a schematic diagram of the structure of the nozzle seat mounting platform on the outer end cap in this utility model;

[0045] In the diagram: 1-Inner end cap, 2-Outer end cap, 3-Inner mixing pipe, 4-Support plate, 5-Outer mixing pipe, 6-Cover plate, 7-Divider plate, 8-Rear spoiler, 9-Temperature base, 10-Low-pressure air intake base, 11-Nozzle, 12-Nozzle seat, 13-Inlet chamber, 14-Outlet chamber, 15-Positioning boss, 16-Oblong hole, 17-Blade window, 18-Rectangular groove, 19-Mesh, 20-Nozzle seat mounting platform, 21-Positioning groove. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this utility model and are not intended to limit this utility model.

[0047] like Figure 1 and Figure 2As shown, this utility model is a low back pressure China VI emission standard after-processor urea mixer, including an inner end cover 1, an outer end cover 2, an inner mixing pipe 3, a support plate 4, an outer mixing pipe 5, a cover plate 6, a partition plate 7, a rear spoiler 8, a temperature base 9, a low-pressure air intake base 10, a nozzle 11, and a nozzle seat 12. The outer end cover 2 and the inner end cover 1 are fixedly connected by welding or bolts, and the inner end cover 1 and the cover plate 6 together form a closed flow guiding cavity. The partition plate 7 is fixedly installed in the flow guiding cavity, preferably connected to the inner end cover by welding, and divides the flow guiding cavity into two independent and airtightly isolated air intake cavities 13 and 14.

[0048] The cover plate 6 is fixed to the inner end cover by welding. The cover plate 6 has two round holes, which are respectively located in the intake chamber 13 and the exhaust chamber 14 below, serving as the total inlet of engine exhaust gas and the total outlet of the mixed gas.

[0049] The rear spoiler 8 is fixed to the cover plate 6 at the circular hole corresponding to the outlet cavity 14. The rear spoiler 8 can improve the uniformity of ammonia concentration distribution and change the airflow direction of the outlet cavity, further reducing the risk of urea crystallization.

[0050] The external mixing pipe 5 is vertically inserted into the pre-reserved through hole in the partition plate 7, and its top end extends into the air intake chamber 13. A support plate 4 is fixedly installed at the top end of the external mixing pipe 5. The support plate 4 is preferably an annular plate, and its outer edge is fixed to the top end of the external mixing pipe 5.

[0051] The lower part of the inner mixing tube 3 is coaxially sleeved inside the outer mixing tube 5. The inner mixing tube 3 is positioned and fixed by the support plate 4, specifically by welding the middle part of the inner mixing tube 3 to the inner edge of the support plate 4. The bottom end of the inner mixing tube 3 is suspended and located in the upper part inside the outer mixing tube 5.

[0052] The inner mixing pipe 3 has various openings on its wall for airflow and mixing. Specifically, such as... Figure 4 As shown, multiple elongated holes 16 are evenly distributed circumferentially near the top of the tube. In the middle of the tube wall, blade windows 17 with a preset tilt angle are provided to guide the airflow into a high-speed swirling flow. At the lower part of the tube wall, multiple rectangular grooves 18 are evenly distributed circumferentially, and these rectangular grooves 18 are intermittently arranged at the bottom of the tube wall, i.e., not continuous annular grooves, to avoid crystal accumulation caused by turbulent airflow due to sudden pressure changes.

[0053] The outer mixing pipe 5 also has perforated structures on its wall for airflow, pressure relief, and urea breakup. Specifically, for example... Figure 5As shown, a blade window 17 with a preset angle is provided on the upper part of its pipe wall to guide the external airflow to form a rotation. On the lower part of its pipe wall, a large number of mesh holes 19 are provided. These mesh holes 19 and the rectangular grooves 18 on the inner mixing pipe 3 enhance the airflow exchange between the inner and outer mixing pipes, while greatly reducing the product back pressure.

[0054] Multiple ventilation holes are also provided on the support plate 4 to allow airflow.

[0055] The four air intake channels are formed by the openings in the inner mixing pipe 3, the outer mixing pipe 5, and the support plate 4. Figure 3 As shown, after the airflow enters the intake chamber:

[0056] The first airflow enters the inner mixing tube 3 through the elongated hole 16 above the inner mixing tube 3, directly blowing the area of ​​the nozzle 11 and nozzle seat 12 to prevent urea crystallization caused by low temperature in that area.

[0057] The second airflow enters the inner mixing pipe 3 through the blade window 17 with a certain angle, forming a high-speed rotating airflow;

[0058] The third airflow enters the outer mixing tube 5 through the opening on the support plate 4, heating and blowing away the urea on the outer wall of the inner mixing tube 3.

[0059] The fourth airflow enters the outer mixing pipe 5 through the blade window 17 with a certain angle, forming a high-speed rotating airflow. Part of it enters the inner mixing pipe 3 and collides with the airflow inside the inner mixing pipe 3 to further increase urea mixing; the other part is in the cavity between the inner and outer pipes, which completely surrounds the inner mixing pipe 3 and rotates downwards, playing the role of heating the inner mixing pipe 3.

[0060] After the airflow enters the outlet chamber 14, the airflow in the inner mixing pipe 3 is completely released to the outer mixing pipe 5 at the outlet of the inner mixing pipe 3. It intertwines with the rotating airflow in the outer mixing pipe 5, further enhancing the mixing of urea. After mixing, part of it is released through the mesh 19 on the outer mixing pipe 5, and part of it flows out from the bottom of the outer mixing pipe 5. Finally, after passing through the rear baffle 8, the urea is completely hydrolyzed and fully mixed.

[0061] The four-way air intake structure can divide the airflow, reducing the air intake resistance. At the same time, the airflow rotates relatively independently in the inner and outer mixing pipes, increasing the swirling intensity and improving urea mixing. In addition, each air intake can blow to the nozzle position and the inner pipe wall position, which can effectively reduce the risk of crystallization.

[0062] The nozzle seat 12 is welded to the top center of the inner end cap 1. The nozzle 11 is fixedly mounted on the nozzle seat 12, with its spray direction aligned below the central axis of the inner mixing pipe 3.

[0063] Temperature sensor base 9 and low-pressure gas intake base 10 are welded and fixed to the side wall of inner end cover 1, respectively, for installing temperature sensor and connecting gas intake pipeline to monitor the internal temperature and gas pressure of mixer.

[0064] As a preferred embodiment, the diameter of the inner mixing tube 3 is designed to be 20-40 mm smaller than that of the outer mixing tube 5. This size range ensures that there is a sufficient annular airflow channel between the inner and outer tubes, effectively reducing flow resistance while ensuring good airflow interaction and mixing effect.

[0065] The inner mixing tube 3 is shorter than the outer mixing tube 5. After the urea is mixed for the first time in the inner mixing tube 3, it diffuses to the outer mixing tube 5 for a second mixing, which enhances the airflow collision and improves the mixing effect.

[0066] To ensure assembly accuracy, the top of the inner mixing tube 3 is provided with two symmetrical positioning bosses 15. Correspondingly, above the inner end cap 1, a nozzle seat mounting platform 20 is integrally formed by stamping. This nozzle seat mounting platform 20 is provided with positioning grooves 21 that match the positioning bosses 15, such as... Figure 6 As shown. During assembly, the positioning boss 15 at the top of the inner mixing tube 3 is inserted into the positioning groove 21 of the nozzle seat mounting platform 20, which can quickly and accurately achieve the coaxial positioning of the inner mixing tube 3 and the center of the nozzle 11. Then, the support plate 4 is welded and fixed, which simplifies the assembly process and ensures the alignment of the spray center and the center of the mixing tube.

[0067] The working principle of this utility model is as follows: High-temperature exhaust gas from the engine enters the intake chamber 13 through the inlet hole of the cover plate 6 and is guided by the partition plate 7, flowing into the core area of ​​the mixer in four directions. Urea aqueous solution is atomized through the nozzle 11 and sprayed into the inner mixing pipe 3. The first airflow first purges and heats the nozzle area. The second and fourth airflows enter the interior of the inner mixing pipe 3, initially mix with the atomized urea droplets, and form a swirling flow through the vane window 17 on the inner pipe, enhancing the first mixing and breaking. The third airflow enters the annular space tangentially through the vane window 17 of the outer mixing pipe 5, forming a high-speed rotating airflow. The initially mixed airflow carrying urea droplets flows out from the rectangular groove 18 and outlet at the lower end of the inner mixing pipe 3, and violently collides, shears, and intertwines with the third high-speed swirling flow from the annular space, achieving secondary breaking and efficient mixing of urea. After the mixed airflow is depressurized and finally broken up through the mesh 19 at the bottom of the outer mixing pipe 5, it enters the outlet chamber 14. After the flow equalization effect of the rear baffle 8, it is discharged from the outlet of the cover plate 6 and enters the downstream SCR catalytic unit.

[0068] The above are merely preferred embodiments of this utility model, but the scope of protection of this utility model is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in this utility model, based on the technical solution and inventive concept of this utility model, should be included within the scope of protection of this utility model.

Claims

1. A low back pressure China VI emission standard after-processor urea mixer, characterized in that, Includes inner end cap (1), outer end cap (2), inner mixing pipe (3), support plate (4), outer mixing pipe (5), cover plate (6), partition plate (7), rear spoiler (8), temperature base (9), low-pressure gas intake base (10), nozzle (11) and nozzle seat (12). The inner end cap (1) and the cover plate (6) cooperate to form a flow guide cavity. The partition plate (7) is fixed in the flow guide cavity and divides the flow guide cavity into an independent air inlet cavity (13) and an air outlet cavity (14). The cover plate (6) covers the inner end cover (1); the cover plate (6) has two large round holes, which correspond to the air inlet chamber (13) and the air outlet chamber (14) respectively. The rear spoiler (8) is fixed to the outlet of the cover plate (6) on one side of the air outlet cavity (14); The outer mixing pipe (5) passes through the partition plate (7) and the support plate (4) is provided on the top of the outer mixing pipe (5); the support plate (4) is located on one side of the air intake cavity (13); the inner mixing pipe (3) is coaxially arranged inside the outer mixing pipe (5) and is fixed to the outer mixing pipe (5) by the support plate (4); The inner mixing pipe (3) is provided with an opening and a blade window for airflow, the outer mixing pipe (5) is provided with a blade window for airflow, and the support plate (4) is provided with an opening for airflow, so as to form four air intakes that pass into the inner mixing pipe (3) and the outer mixing pipe (5) respectively. The nozzle seat (12) is located on the top of the inner end cover (1), and the nozzle (11) is located on the nozzle seat (12); the temperature base (9) and the low-pressure gas intake base (10) are respectively fixed on the inner end cover (1).

2. The low back pressure China VI emission standard after-processor urea mixer according to claim 1, characterized in that, The diameter of the inner mixing tube (3) is 20-40 mm smaller than the diameter of the outer mixing tube (5).

3. The low back pressure urea mixer for a China VI emission standard aftertreatment system according to claim 1, characterized in that, The length of the inner mixing tube (3) is shorter than the length of the outer mixing tube (5).

4. A low back pressure urea mixer for a China VI emission standard aftertreatment system according to claim 1, characterized in that, The top of the inner mixing tube (3) is provided with two positioning bosses (15), which are used for welding positioning and circumferential positioning of the inner mixing tube (3); the inner mixing tube (3) is provided with elongated holes (16) evenly distributed along the circumference near the top; the middle part of the inner mixing tube (3) is provided with a blade window (17) with a preset angle, which is used to guide the airflow to form a high-speed rotating airflow; the lower part of the inner mixing tube (3) is provided with rectangular grooves (18) evenly distributed along the circumference; the rectangular grooves (18) are intermittently arranged at the bottom of the inner mixing tube (3).

5. A low back pressure urea mixer for a China VI emission standard aftertreatment system according to claim 1, characterized in that, The upper side of the outer mixing pipe (5) is provided with a blade window (17) with a preset angle. The blade window (17) is used to guide the airflow to form a high-speed rotating airflow. The lower part of the outer mixing pipe (5) is provided with a mesh (19) arranged in a preset manner. The mesh (19) is used to depressurize and break urea droplets.

6. A low back pressure China VI emission standard after-processor urea mixer according to claim 1, characterized in that, A nozzle seat mounting platform (20) is formed by stamping on the upper part of the inner end cap (1), and a positioning groove (21) is provided on the nozzle seat mounting platform (20); the positioning boss (15) at the upper end of the inner mixing tube (3) is inserted into the positioning groove (21) to ensure the coaxiality of the center of the nozzle (11) and the center of the inner mixing tube (3).

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