Exhaust gas aftertreatment device and its sandwich-type mixing pipe

Abstract

An exhaust gas aftertreatment device includes a mixing pipe for realizing the mixing of a reducing agent for exhaust gas treatment in the exhaust gas. The mixing pipe includes an inner pipe and an outer pipe. Among them, the upstream end of the outer pipe surrounds and is connected to the upstream end of the inner pipe, and the downstream end of the outer pipe surrounds and is connected to a part of the inner pipe. A cylindrical surrounding space is formed between the outer pipe and the part of the inner pipe that faces the outer pipe radially. Axially of the mixing pipe, the surrounding space at least covers the installation position of a mixer in the mixing pipe for promoting the mixing of the reducing agent and the exhaust gas and generating a swirl flow.

Description

Technical Field

[0001] This application relates to a mixing tube for an exhaust gas aftertreatment device, and an exhaust gas aftertreatment device including such a mixing tube. Background Art

[0002] Engine exhaust gas contains harmful components. In order to reduce the emissions of harmful components in the exhaust gas, various aftertreatment technologies have been developed. A typical exhaust gas aftertreatment device for a diesel engine includes a diesel oxidation catalyst, a selective catalytic reduction device, and a particulate filter.

[0003] The exhaust gas aftertreatment device further includes a reductant injector for injecting reductant into the mixing tube in a metered manner, so that the reductant is mixed with the exhaust gas in the mixing tube, so as to carry out a catalytic reduction reaction in the selective catalytic reduction device to reduce the content of NOx in the exhaust gas.

[0004] After the particulate filter has been used for a period of time, the particulate matter captured therein will increase to a certain extent, affecting the performance of the particulate filter. At this time, the particulate filter needs to be regenerated. The regeneration of the particulate filter usually requires heating the exhaust gas flowing through the particulate filter to burn the particulate matter in the particulate filter, thereby reducing the amount of particulate matter in the particulate filter.

[0005] During the regeneration of the particulate filter, the temperature of the exhaust gas is increased. At high temperatures, the reductant has a tendency to corrode the mixing tube, and the corrosion of the mixing tube will shorten its life. Summary of the Invention

[0006] An object of this application is to improve the corrosion resistance of the mixing tube.

[0007] To this end, in one aspect of this application, there is provided a mixing tube for an exhaust gas aftertreatment device for realizing the mixing of a reductant for exhaust gas treatment in the exhaust gas. The mixing tube includes an inner tube and an outer tube; wherein, the upstream end of the outer tube surrounds and is connected to the upstream end of the inner tube, the downstream end of the outer tube surrounds and is connected to a part of the inner tube, and a cylindrical surrounding space, preferably a closed space, is formed between the outer tube and the part of the inner tube facing the outer tube radially; in the axial direction of the mixing tube, the surrounding space at least covers the installation position of a mixer in the mixing tube for promoting the mixing of the reductant and the exhaust gas and generating a swirl.

[0008] Optionally, the outer tube includes a main body part, and the diameter of the main body part is greater than the diameter of the downstream end of the outer tube and greater than or equal to the diameter of the upstream end of the outer tube.

[0009] Optionally, the diameter of the upstream end of the outer tube is greater than or equal to the diameter of the downstream end of the outer tube.

[0010] Optionally, the diameter of the inner tube portion facing the outer tube radially is smaller than the diameter of the upstream portion of the inner tube located upstream of this inner tube portion and the diameter of the downstream portion of the inner tube located downstream of this inner tube portion; the diameter of the upstream portion of the inner tube is equal to or greater than the diameter of the downstream portion of the inner tube.

[0011] Optionally, the inner tube has a constant diameter.

[0012] Optionally, the inner tube is a single pipe fitting.

[0013] Optionally, the inner tube includes a first tube and a second tube axially connected to each other, and the diameter of the connection portion between the first tube and the second tube is smaller than the diameters of other portions of the first tube and the second tube.

[0014] Optionally, the downstream end of the inner tube constitutes the downstream support portion of the mixing tube in the box body of the exhaust gas aftertreatment device, and the upstream end of the inner tube or the outer tube constitutes the upstream support portion of the mixing tube in the box body of the exhaust gas aftertreatment device.

[0015] Optionally, a flange for installation in the box body is formed near the upstream end of the outer tube; at least one notch is formed on the end face of the upstream support portion for positioning the mixing tube relative to the box body.

[0016] The present application provides an exhaust gas aftertreatment device in one of its aspects, which includes:

[0017] An oxidation catalyst, a particulate trap, the aforementioned mixing tube, and a selective catalytic reduction device, which are arranged in the box body to be successively flowed through by the exhaust gas;

[0018] A reducing agent injector, which is arranged facing the mixing tube; and

[0019] A mixer located in the mixing tube for promoting the mixing of the reducing agent and the exhaust gas and generating a swirl.

[0020] According to the present application, the mixing tube has a sandwich structure in the reducing agent injection area, thereby improving the corrosion resistance of the mixing tube, which can extend the service life of the mixing tube and improve the durability and reliability of the exhaust gas aftertreatment device.

[0021] In addition, the sandwich-type mixing tube can also suppress the loss of exhaust gas temperature in the exhaust gas aftertreatment device during low-speed operation of the engine, improve the catalyst conversion efficiency under low-temperature conditions of the engine, and reduce the crystallization of the reducing agent caused by low-temperature exhaust gas. Description of the Drawings

[0022] The foregoing and other aspects of the present application will be more fully understood from the following detailed description with reference to the accompanying drawings, in which:

[0023] Figure 1is a schematic cross-sectional view of an exhaust gas aftertreatment device according to a feasible embodiment of the present application;

[0024] Figure 2 is a perspective view of a feasible structure of a mixer in the exhaust gas aftertreatment device;

[0025] Figure 3 is a cross-sectional view of a feasible structure of a mixing pipe (equipped with a mixer therein) in the exhaust gas aftertreatment device;

[0026] Figures 4 - 6 is Figure 3 a cross-sectional view of a component part of the mixing pipe in

[0027] Figure 7 is a cross-sectional view of another feasible structure of the mixing pipe in the exhaust gas aftertreatment device. Detailed Embodiment

[0028] The present application generally relates to an exhaust gas aftertreatment device and a mixing pipe used therein. The exhaust gas aftertreatment device is used to treat engine exhaust gas, especially the exhaust gas of a diesel engine; however, the exhaust gas aftertreatment device can also be applicable to engines consuming other types of fuels (some components in the exhaust gas aftertreatment device may need to be modified accordingly). The mixing pipe is used to uniformly mix a reducing agent with the exhaust gas therein, so as to improve the degree of NOx reduction in a subsequent selective catalytic reduction device.

[0029] The exhaust gas aftertreatment device and its mixing pipe according to a feasible embodiment of the present application will be described below with reference to the accompanying drawings. It should be noted that the relative position terms "upstream" and "downstream" used in the following description are defined relative to the flow direction of the exhaust gas.

[0030] Figure 1 The exhaust gas aftertreatment device shown in

[0031] includes a box body 1, and the box body 1 is provided with an inlet 2, which is configured to be connected to an upstream exhaust pipe section, for example, connected to the outlet end of a supercharger turbine in an exhaust gas recirculation (EGR) system, so as to receive the exhaust gas discharged from the engine. As shown by the arrows in the figure, the vehicle exhaust gas enters the box body 1 through the inlet 2 and flows through the oxidation catalytic converter 3 and the particulate trap 4 axially downstream thereof. The exhaust gas undergoes an oxidation catalytic reaction in the oxidation catalytic converter 3 to convert carbon monoxide and hydrocarbons into water and carbon dioxide, and then the particulate matter in the exhaust gas is trapped by the particulate trap 4.

[0032] A mixer 7 is arranged in the mixing pipe 6, and a reductant injector 8 is installed on the first housing 5 for injecting reductant, such as an aqueous solution of urea, usually AdBlue, into the mixing pipe 6 in a metered manner. The reductant injector 8 is installed in a recess on the first housing 5, and its injection port faces the inlet of the mixing pipe 6. Preferably, the central axis of the injection port of the reductant injector 8 is substantially collinear (coaxial) with the central axis of the mixing pipe 6. The mixer 7 is arranged in the mixing pipe 6 at such an axial position that substantially all of the reductant ejected by the reductant injector 8 is sprayed onto the mixer 7, and substantially no reductant is sprayed onto the inner wall of the mixing pipe 6. The mixer 7 is used to cause the reductant flowing through it and the exhaust gas to generate a swirl to promote the mixing of the reductant in the exhaust gas.

[0033] The reductant is sprayed into the mixing pipe 6 by the reductant injector 8 and moves axially towards the mixer 7 while being mixed with the exhaust gas. The reductant impinges on the mixer 7 and is guided by the mixer 7 to rotate, while the exhaust gas is also guided by the mixer 7 to rotate. In this way, a swirl of the mixture of the reductant and the exhaust gas is formed in the mixing pipe 6.

[0034] The mixture of the reductant and the exhaust gas flows into the second housing 9 installed on the other side of the box body 1 after being discharged from the mixing pipe, and then enters one or more (for example, two) selective catalytic reduction reactors ( Figure 1 not shown in the figure) arranged side by side with the oxidation catalytic converter 3, the particulate trap 4 and the mixing pipe 6. The exhaust gas undergoes a selective catalytic reduction reaction with the reductant in the selective catalytic reduction reactor, so that nitrogen oxides are converted into nitrogen and other non-toxic components (such as water). Then, the relatively clean exhaust gas after undergoing the above various treatments is discharged from the box body 1.

[0035] As described above, the mixer 7 is configured to generate a swirl in the mixing pipe 6 in order to improve the mixing degree of the reductant in the exhaust gas.

[0036] The mixer 7 can be designed to have any structure suitable for causing the air flow flowing through it to form a swirl, that is, the mixer 7 constitutes a swirl guide. According to a feasible embodiment, as Figure 2 shown, the mixer 7 includes a cylindrical wall 71 and a plurality of evenly distributed fins 72 and 73 respectively extending radially inward from the axial front and rear edges of the cylindrical wall 71. The surfaces of the fins 72 and 73 are inclined relative to the plane perpendicular to the central axis of the cylindrical wall, and the inclination angles can be the same. In this way, the mixed air flow of the reductant and the exhaust gas impinging on the fins 72 and 73 will be deflected circumferentially by these fins. Under the deflection action of all the fins 72 and 73, a swirl will be formed. It can be understood that if sufficient swirl can be formed, only the fins 72 or 73 are provided on one axial side edge of the cylindrical wall 71. The mixer 7 can be made by stamping a single metal plate.

[0037] The mixing tube 6 of the present application has a sandwich structure, which has a two-layer or multi-layer structure at least in the upstream part (the part close to the reducing agent injector 8). The two-layer or multi-layer structure is formed by nesting different tubes together, and each tube can be made of stainless steel.

[0038] Figure 3 A feasible structure of the mixing tube 6 is shown in Figures 4 - 6 The components of the mixing tube 6 are shown in

[0039] As Figure 3 shown, the mixing tube 6 includes an axially connected first tube 10 and second tube 20, which together form an inner tube. The second tube 20 is located upstream of the first tube 10, that is, the second tube 20 will be installed in the box 1 close to the reducing agent injector 8. The downstream end of the second tube 20 is inserted into and connected to the upstream end of the first tube 10. In addition, an outer tube 30 surrounds at least a part of the first tube 10 and the entire second tube 20. The upstream end of the outer tube 30 extends beyond the upstream end of the second tube 20 in the upstream direction, and the upstream end of the outer tube 30 surrounds and is connected to the upstream end of the second tube 20. The downstream end of the outer tube 30 surrounds and is connected to the first tube 10, for example, connected to the axial middle part of the first tube 10.

[0040] The above connections of the first tube 10, the second tube 20 and the outer tube 30 can be achieved by welding.

[0041] As Figure 4 shown, the first tube 10 includes a downstream large-diameter part 11 and an upstream small-diameter part 12 that are axially continuous with each other. The diameter of the small-diameter part 12 is smaller than that of the large-diameter part 11, and there is a smooth transition between them. The mixer 7 is adapted to be installed in the small-diameter part 12. The length of the large-diameter part 11 is equal to or greater than that of the small-diameter part 12. The first tube 10 can be formed by reducing or expanding the diameter of a pipe (such as spinning).

[0042] As Figure 5 shown, the second tube 20 includes a downstream small-diameter part 21 and an upstream large-diameter part 22 that are axially continuous with each other. The diameter of the large-diameter part 22 is larger than that of the small-diameter part 21, and there is a smooth transition between them. The outer diameter of the small-diameter part 21 is equal to the inner diameter of the small-diameter part 12 of the first tube 10, and the outer diameter of the large-diameter part 22 is greater than or equal to the large-diameter part 11 of the first tube 10. The second tube 20 can also be formed by reducing or expanding the diameter of a pipe (such as spinning).

[0043] As Figure 6As shown, the outer tube 30 includes a main body portion 31, a downstream connection portion 32 connected to the downstream of the main body portion 31 (constituting the downstream end of the outer tube 30), and an upstream connection portion 33 connected to the upstream of the main body portion 31 (constituting the upstream end of the outer tube 30). The diameter of the main body portion 31 is greater than that of the downstream connection portion 32 and greater than or equal to that of the upstream connection portion 33, and the transitions between the three are smooth. The diameter of the main body portion 31 is greater than the large-diameter portion 11 of the first tube 10 and the large-diameter portion 22 of the second tube 20. The inner diameter of the downstream connection portion 32 is equal to the outer diameter of the large-diameter portion 11 of the first tube 10, and the inner diameter of the upstream connection portion 33 is equal to the outer diameter of the large-diameter portion 22 of the second tube 20. In addition, a circumferential flange 34 protruding outward may be formed between the main body portion 31 and the upstream connection portion 33, and this flange 34 is used for installation in the box 1. A transition portion 35 with a diameter slightly larger than that of the main body portion 31 may be formed between the flange 34 and the main body portion 31. The outer tube 30 may also be formed by processing a pipe through diameter reduction and / or diameter expansion (such as spinning).

[0044] In addition, at least one notch 36 is formed on the end face of the upstream connection portion 33 for positioning the mixing tube 6 relative to the box 1.

[0045] Due to the above relationships between the respective parts of the first tube 10, the second tube 20, and the outer tube 30, they can be assembled together as Figure 3 shown. In the assembled state, the outer tube 30 surrounds the upstream portion of the inner tube (a part of the first tube 10 and the second tube 20), thereby forming a cylindrical surrounding space between the outer tube 30 and the inner tube, and this surrounding space is preferably airtight. Axially, the surrounding space at least covers the installation position of the mixer 7 in the mixing tube 6.

[0046] The mixing tube 6 is supported by the corresponding structure (such as a wall portion) in the box 1 through the downstream end of its first tube 10 (i.e., the downstream end of the inner tube) and the upstream end of the outer tube 30.

[0047] Those skilled in the art can make various modifications to Figure 3 the specific structure of the mixing tube 6 shown.

[0048] According to a modification, the downstream end of the outer tube 30 can surround and connect to the small-diameter portion 12 of the first tube 10.

[0049] According to another modification, the entire first tube 10 can have a constant diameter.

[0050] According to yet another modification, the upstream end of the second tube 20 (i.e., the upstream end of the large-diameter portion 22) axially extends beyond the upstream end of the outer tube 30, so that the upstream end of the second tube 20 (i.e., the upstream end of the inner tube) rather than the upstream end of the outer tube 30 is supported by the corresponding structure in the housing 1. In this case, at least one notch may be formed in the end face of the large-diameter portion 22 for positioning the mixing tube 6 relative to the housing 1.

[0051] According to yet another modification, the axial length of the large-diameter portion 11 of the first tube 10 is much smaller than that of the small-diameter portion 12, and the large-diameter portion 11 is completely or almost completely surrounded by the downstream end of the outer tube 30. In this way, almost the entire inner tube is surrounded by the outer tube 30.

[0052] According to yet another modification, as Figure 7 shown, the entire inner tube 80 is a single pipe fitting, rather than being composed of two tubes as Figure 3 in the previous case. The inner tube 80 includes a first part 81, a second part 82, and a third part 83 that are circumferentially joined. The diameter of the first part 81 is larger than that of the second part 82 and is equal to or smaller than that of the third part 83. The second part 82 actually corresponds to Figure 4 the combination of the small-diameter portion 12 of the first tube 10 and the small-diameter portion 21 of the second tube 20 in the embodiment shown. The small-diameter portion 32 (downstream end) of the outer tube 30 surrounds and connects to the first part 81. The inner tube 80 can be formed from a single pipe material through necking and / or expanding processes (such as spinning).

[0053] Figure 7 Other aspects of the embodiment shown are the same as those in the embodiment shown in Figure 3 . In addition, the various modifications described above for the embodiment shown in Figure 3 also apply to the embodiment shown in Figure 7 .

[0054] Other feasible structures of the mixing tube 6 can also be conceived.

[0055] Generally speaking, the mixing tube 6 of the present application includes a sandwich structure composed of an inner tube and an outer tube. The outer tube at least sleeves outside the upstream portion of the inner tube (or even the outer tube can sleeve outside almost the entire inner tube), so as to generate a surrounding space between the outer tube and the upstream portion of the inner tube. The mixer is arranged in the upstream portion of the inner tube.

[0056] When regenerating a particulate filter, it is necessary to increase the temperature of the exhaust gas flowing through the particulate filter so that the particulate matter captured in the particulate filter burns, thereby reducing the amount of particulate matter in the particulate filter. During the regeneration of the particulate filter, the exhaust gas temperature may reach above 700 °C. When the high-temperature exhaust gas flows through the mixing tube and mixes with the reducing agent, the temperature of the reducing agent increases, and the high-temperature reducing agent tends to corrode the mixing tube. Since the mixing tube of the present application has a sandwich structure, the corrosion resistance of the mixing tube can be improved. Specifically, even if the upstream part of the inner tube is corroded, the outer tube can still maintain the performance of the entire mixing tube. Therefore, the service life of the mixing tube can be extended, and the durability and reliability of the exhaust gas aftertreatment device are improved.

[0057] In addition, the surrounding space between the outer tube and the inner tube constitutes a heat insulation space, which improves the heat preservation ability of the mixing tube. When the engine is running at low speed, the exhaust gas temperature is low. If the exhaust gas heat preservation ability of the mixing tube is insufficient, it is not conducive to the evaporation and uniform mixing of the reducing agent in the exhaust gas, thereby affecting the NOx conversion efficiency. Sometimes, it may cause the reducing agent to deposit on the inner wall of the mixing tube and form reducing agent crystals after the engine stops running. According to the present application, through the sandwich-type mixing tube structure, compared with the single-layer mixing tube structure, the heat preservation ability of the mixing tube can be improved, heat loss can be inhibited, especially the exhaust gas temperature loss can be inhibited when the engine is running at low speed, the evaporation and uniform mixing of the reducing agent in the exhaust gas can be ensured, thereby improving the NOx conversion efficiency. At the same time, it can also avoid or reduce the reducing agent crystallization caused by the low-temperature exhaust gas condition.

[0058] Although the present application has been described here with reference to specific embodiments, the scope of the present application is not limited to the details shown. Various modifications can be made to these details without departing from the basic principles of the present application.

Claims

1. An exhaust gas aftertreatment device, comprising: a housing (1); an oxidation catalyst (3), a particulate trap (4), a mixing pipe (6) and a selective catalytic reducer which are arranged in the housing and are successively flowed through by the exhaust gas; a reductant injector (8) which is arranged facing the mixing pipe; and a mixer (7) located in the mixing pipe for promoting the mixing of the reductant and the exhaust gas and generating a swirl; the mixing pipe includes an inner pipe (10, 20; 80) and an outer pipe (30); wherein, the outer pipe includes a main body part (31), a downstream end, and an upstream end. The upstream end of the outer pipe surrounds and is connected to the upstream end of the inner pipe. The downstream end of the outer pipe surrounds and is connected to a part of the inner pipe. A cylindrical closed surrounding space is formed between the outer pipe and the inner pipe part facing the outer pipe radially. Axially of the mixing pipe, the surrounding space at least covers the installation position of the mixer (7) in the mixing pipe. A protruding flange (34) is formed between the main body part and the upstream end of the outer pipe. The downstream end of the inner pipe constitutes the downstream support part of the mixing pipe in the housing, and the upstream end of the inner pipe or the outer pipe constitutes the upstream support part of the mixing pipe in the housing. The flange (34) is used for installation in the housing (1), and a transition part (35) with a diameter larger than that of the main body part (31) is formed between the flange (34) and the main body part (31).

2. The exhaust gas after-treatment device according to claim 1, wherein, The diameter of the small-diameter part of the inner pipe facing the outer pipe radially is smaller than the diameters of the upstream part of the inner pipe located upstream of the small-diameter part of the inner pipe and the downstream part of the inner pipe located downstream of the small-diameter part of the inner pipe. The mixer (7) is suitably installed in the small-diameter part of the inner pipe.

3. The exhaust gas post-treatment device according to claim 1, wherein, The diameter of the main body part of the outer pipe is larger than the diameter of the downstream end of the outer pipe and is larger than or equal to the diameter of the upstream end of the outer pipe.

4. The exhaust gas post-treatment device according to claim 3, wherein, The diameter of the upstream end of the outer pipe is larger than or equal to the diameter of the downstream end of the outer pipe.

5. The exhaust gas aftertreatment device according to any one of claims 1 to 4, wherein, The diameter of the upstream part of the inner pipe is equal to or larger than the diameter of the downstream part of the inner pipe.

6. The tail gas post-treatment device according to any one of claims 1 to 4, wherein, The inner pipe has a constant diameter.

7. The tail gas post-treatment device according to any one of claims 1 to 4, wherein, The inner pipe is a single pipe fitting.

8. The exhaust gas aftertreatment device according to any one of claims 1 to 4, wherein, The inner pipe includes a first pipe (10) and a second pipe (20) which are axially connected to each other. The diameter of the connection part between the first pipe and the second pipe is smaller than the diameters of other parts of the first pipe and the second pipe.

9. The exhaust gas post-treatment device according to any one of claims 1 to 4, wherein, At least one notch is formed on the end face of the upstream support part for positioning the mixing pipe relative to the housing.

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