Exhaust mixing device

Abstract

To provide an exhaust gas mixing device capable of preventing retention and deposition of urea water even if the urea water not hydrolyzed in a cylindrical fin is discharged.SOLUTION: In the exhaust mixing device interposed upstream of an exhaust emission control device in an exhaust flow passage of an engine, a first partition wall and a second partition wall are arranged in a cylindrical casing, one end part of a cylindrical mixing pipe having a plurality of slits and fins formed on a peripheral wall is fixed to the casing, and the other end part is arranged in a cutout part of the first partition wall. An injection device configured to inject a reducing agent into the mixing pipe is provided at one end portion of the mixing pipe, the first partition wall has a communication port near an inner surface of the casing facing the mixing pipe, the second partition wall is provided with multiple holes, a cylindrical inner cylinder provided with multiple holes is sandwiched between the first partition wall and the second partition wall, and the inflow port communicates with a gap between the inner cylinder and the casing.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an exhaust gas mixing device that is installed in an exhaust pipe of an internal combustion engine. [Background technology]

[0002] The exhaust gas emitted from internal combustion engines such as diesel engines contains nitrogen oxides (NO x ) are included. Exhaust gas purification devices equipped with a selective catalytic reduction (SCR) catalyst are well known as devices for purifying such exhaust gases. In order to improve the purification performance of the SCR catalyst, this type of exhaust gas purification device is often equipped with a reducing agent addition device that sprays and mixes urea water as a reducing agent into the exhaust gas flowing through the exhaust passage upstream of the SCR catalyst. The urea water sprayed into the exhaust gas is hydrolyzed by the heat of the exhaust gas, and the ammonia (NH3) produced by the hydrolysis is supplied to the SCR catalyst along with the exhaust gas. Nitrogen oxides in the exhaust gas react with the ammonia in the SCR catalyst and are reduced and purified.

[0003] This type of reducing agent mixing device is often combined with an exhaust gas mixing device in order to promote the hydrolysis of urea water and supply ammonia evenly to the front surface of the downstream SCR catalyst. In particular, for exhaust gas mixing devices that are installed between a DPF (diesel particulate filter), which is an exhaust gas purification device installed coaxially in the exhaust pipe, and a selective reduction SCR catalyst, a configuration like the exhaust gas mixing device disclosed in Patent Document 1 is common.

[0004] As shown in FIG. 8, the exhaust gas mixer of Patent Document 1 is a portion of a casing 122 serving as an exhaust pipe, sandwiched between an upstream DPF 128 and a downstream SCR catalyst 129. A crank-shaped partition wall 124 is fixed inside the casing 122, separating the exhaust gas mixer into a front chamber and a rear chamber. One end of a cylindrical fin 138 (also referred to as a mixing pipe) is opened and fixed to a central surface 124a of the partition wall 124. The other end of the cylindrical fin 138 is fixed and passes through the casing 122, and an injection nozzle 136 is fixed thereto so as to be able to inject a reducing agent into the cylindrical fin 138. Slits and fins extend axially along the peripheral wall of the cylindrical fin 138.

[0005] The exhaust gas discharged from the upstream DPF 128 into the front chamber flows into the cylindrical fins 138, and at that time, the radially arranged fins and slits create a swirling flow inside the cylindrical fins 138. The reducing agent is injected into this swirling flow and is discharged into the rear chamber while being mixed with the exhaust gas, so that the urea aqueous solution is well diffused in the exhaust gas and the ammonia produced by hydrolysis is evenly supplied to the front surface of the SCR catalyst 129 downstream. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-150338 Summary of the Invention [Problem to be solved by the invention]

[0007] However, with the configuration described in Patent Document 1, there is a concern that the urea aqueous solution that is not hydrolyzed while being mixed with the exhaust gas and discharged into the rear chamber may adhere to and precipitate on the low-temperature inner wall surface of the casing 122. In particular, the corners of the rear chamber at the lower side when mounted are prone to becoming low-temperature areas where the exhaust gas flow stagnates, and precipitation is a concern in these areas.

[0008] In view of the above-mentioned problems, an object of the present invention is to provide an exhaust gas mixing device that can prevent urea water from accumulating and precipitating even if urea water that has not been completely hydrolyzed in the cylindrical fins is discharged into the mixing chamber. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides an exhaust gas mixing device that is disposed upstream of an exhaust gas purification device in an exhaust flow path of an engine, the device comprising: a cylindrical casing having a first partition wall and a second partition wall; a cylindrical mixing pipe having a plurality of slits and fins formed in a peripheral wall, one end of which is fixed to the casing and the other end of which is disposed in a notch in the first partition wall; and an injection device that injects a reducing agent into the mixing pipe, provided at one end of the mixing pipe; The first partition has a communication port near the inner surface of the casing facing the mixing pipe, the second partition has multiple holes, a cylindrical inner tube having multiple holes is sandwiched between the first partition and the second partition, and the inlet is connected to the gap between the inner tube and the casing. [Effects of the Invention]

[0010] According to the present invention, even if urea water that has not been completely hydrolyzed in the cylindrical fin is discharged into the mixing chamber, it is possible to prevent the urea water from accumulating and thus preventing precipitation. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view of an exhaust gas mixer according to a first embodiment of the present invention. [Figure 2] 1 is a front view of an exhaust gas mixing device according to a first embodiment of the present invention. [Figure 3] 1 is a schematic diagram illustrating the configuration of an exhaust gas mixing device according to a first embodiment of the present invention. [Figure 4] 1 is a schematic diagram showing the flow of exhaust gas in an exhaust gas mixing device according to a first embodiment of the present invention. [Figure 5] FIG. 4 is a cross-sectional view of an exhaust mixer according to a second embodiment of the present invention. [Figure 6] FIG. 4 is a front view of an exhaust mixer according to a second embodiment of the present invention. [Figure 7] FIG. 6 is a rear view of an exhaust mixer according to a second embodiment of the present invention. [Figure 8] FIG. 1 is a cross-sectional view of an exhaust gas mixing device according to an embodiment of Patent Document 1. DETAILED DESCRIPTION OF THE INVENTION

[0012] A preferred embodiment of the present invention will be described below with reference to Figures 1 to 7. In this embodiment, taking into consideration the mounting position of the exhaust purification device on a vehicle, the left side of Figure 1 is the vehicle travel direction and the exhaust upstream side, and the upper side of Figures 1 to 3 is the upper side of the vehicle. Exhaust gas flows downward from left to right in Figure 1.

[0013] (First embodiment) A first embodiment of the present invention will be described with reference to Figures 1, 2, and 3. Figure 1 is a cross-sectional view showing an exhaust gas mixing device 1 according to the first embodiment of the present invention, taken along a vertical plane passing through the axis of a casing 2. Figure 2 is a front view of the exhaust gas mixing device 1 as seen from the upstream side (left side of the page). The exhaust gas mixing device 1 is disposed upstream of an exhaust gas purification device in the exhaust flow path of an engine.

[0014] The exhaust gas mixer 1 is used in a form interposed between an upstream DPF (not shown) and a downstream SCR catalyst (not shown), and is airtightly connected to the DPF by screwing together flanges 3 and to the SCR catalyst by fitting the rear end of the casing 2. In this embodiment, the DPF, exhaust gas mixer 1, and SCR catalyst are separate entities, but they may also be housed in a common casing. For the positional and joint relationships of the components of the exhaust gas mixer 1, please refer to the perspective schematic diagram in Figure 3.

[0015] The casing 2, which is the housing of the exhaust gas mixer 1, is approximately cylindrical and houses a first partition wall 7, which is an upstream partition wall, and a second partition wall 8, which is a downstream partition wall. A small-diameter inner cylinder 9, which is coaxial with the casing 2, is sandwiched between the first partition wall 7 and the second partition wall 8 and fixed to both partition walls 7, 8. Therefore, an annular gap C is formed between the casing 2 and the inner cylinder 9. As a result, an upstream chamber A is formed upstream of the first partition wall 7, a downstream chamber D is formed downstream of the second partition wall 8, and an intermediate chamber B is formed between the first partition wall 7 and the second partition wall 8.

[0016] A mount member 6 is fitted into the upper opening of the casing 2 when it is mounted on the vehicle (in operation), and the outer surface of the mount member 6 is closed by a cover member 4. A base 5, shown in imaginary lines, for mounting an injection device 28 is tightly fixed above the cover member 4. A coaxial opening is formed in the center of the base 5 and the mount member 6, and the tip of the injection device 28 is inserted into the opening. The upper opening of the mixing pipe 10 is attached to the underside of the mount member 6. A portion of the downstream side of the mixing pipe 10 is supported by a support member 27, which is also attached to the inner surface of the casing 2, although the support member 27 is not essential.

[0017] The mixing pipe 10 is substantially cylindrical, and an opening 13 on the opposite side to the mount member 6 faces downward and opens into the intermediate chamber B. A plurality of axially extending slits 11 that connect the inside and outside of the wall are formed on the circumferential surface of the mixing pipe 10, and fins 12 extend radially from the sides of each slit 11.

[0018] The mixing pipe 10 is housed in a notch 25 provided in the upper part of the first partition wall 7, and the opening 13 faces closely to a communication port 17 at the upper end of a bulge 14 formed in the center of the first partition wall and oriented toward the upstream side. More specifically, the semicircular communication port 17 and a part of the opening 13 face closely to each other, and a gap 29 is formed in the facing part, connecting the upstream chamber A and the intermediate chamber B. The bulge 14 of the first partition wall 7 also has a porous portion 21. Specifically, a group of multiple small holes formed in the bulge 14 constitutes the porous portion 21, and the upstream chamber A and the intermediate chamber B are also connected through the porous portion 21.

[0019] The second partition wall 8 has a first louver 15 that bulges forward and a communication opening 18, and a second louver 16 that bulges rearward and a communication opening 19. The communication openings 18 and 19 connect the intermediate chamber B and the downstream chamber D. The first louver 15 is provided with a perforated portion 22, and the second louver 16 is provided with a perforated portion 23, and the perforated portions 22 and 23 also connect the intermediate chamber B and the downstream chamber D.

[0020] Next, the flow and reaction of exhaust gas and urea water in the first embodiment will be described with reference to FIG. 4 . Exhaust gas that flows from the upstream DPF into the upstream chamber A travels downstream via four paths. The first path is the main flow, which becomes a spiral flow as it passes through the fins 12 and slits 11 and enters the mixing pipe 10. The spiral flow agitates the reducing agent spray 26 as it flows into the intermediate chamber B through the opening 13. The second path is a path from the gap 29 into the intermediate chamber B, but the amount is small. The third path is a path from the porous portion 20 formed in the bulge portion 14 into the intermediate chamber B, but the amount is also small. Although the flow rates of gas from the second and third paths are small, they contribute to maintaining a high temperature inside the intermediate chamber B by appropriately flowing high-temperature exhaust gas into the intermediate chamber B. The fourth path is a path in which the fluid flows into the annular gap C from a communication port 24 formed in the lower part (bottom in the figure) of the first partition wall 7, and then passes through the porous portion 20 and flows into the intermediate chamber B.

[0021] The exhaust gas that has flowed into intermediate chamber B via these four routes is agitated within intermediate chamber B together with the sprayed reducing agent, and then diffuses as it flows into downstream chamber D through communication ports 18, 19 and porous sections 22, 23 of second partition wall 8, and reaches the front surface of the downstream SCR catalyst in a further agitated state evenly.

[0022] At this time, the intermediate chamber B is maintained at a high temperature by the annular gap C surrounding its outer periphery, and is also maintained at a high temperature by the exhaust gas flowing in through the gap 29 and the porous portions 20 and 21. Therefore, even if the reducing agent that was not completely hydrolyzed in the mixing pipe 10 above drips downward, it is reliably hydrolyzed in the intermediate chamber maintained at a high temperature. Even if the reducing agent that was not hydrolyzed drips downward and adheres to the lower inner surface of the inner cylinder 9, the inner surface itself is maintained at a high temperature, so it does not remain there and precipitate, but is instead subjected to hydrolysis.

[0023] In this way, even if there is reducing agent that has not been completely hydrolyzed in the mixing pipe 10, it is reliably hydrolyzed in the intermediate chamber B, and is then stirred and homogenized before being transferred to the downstream chamber D, thereby preventing the reducing agent from remaining in the exhaust gas mixing device 1 and precipitating.

[0024] (Second embodiment) Next, a second embodiment of the present invention will be described using Figures 5, 6, and 7. Numbers are omitted for parts that are the same as those in the first embodiment. In the exhaust gas mixer 30 according to the second embodiment, the mixing pipe 35 is extended downward compared to the first embodiment, and accordingly, the bulging portion 32 of the first partition wall 31 is formed downward, and no perforations are formed in the bulging portion 32. A communication port 36 that communicates with the annular gap C is provided in the lower part of the first partition wall 31. Furthermore, a bulging portion 34 toward the upstream side is formed in the center of the second partition wall 33 instead of a louver.

[0025] By extending the mixing pipe 35, the stirring area created by the swirling flow is expanded, promoting stirring, and the bulging portion 34 also creates a swirling flow around the pipe axis in the intermediate chamber B, further promoting hydrolysis in the intermediate chamber B. In this way, by changing the dimensions and shapes of each component, it is possible to appropriately adapt to the exhaust gas flow and the amount of reducing agent injected.

[0026] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and even if there are modifications within the scope of the present invention that deviate from the spirit of the present invention, they are still included within the present invention. [Explanation of symbols]

[0027] 1, 30 Exhaust gas mixing device 2 Casing 7, 31 First bulkhead 8, 33 Second bulkhead 9 Inner cylinder 10, 35 Mixing pipe 11 Slit 12 Finn 13 Aperture 14, 32, 34 bulge 15 First louver 16 Second louver 17, 18, 19 Connection ports 20, 21, 22, 23 Porous section 24, 36 Connection port 25 Notch 26 Spraying 28 Spraying device 29 void A Upstream room B Intermediate room C annular cavity D downstream chamber

Claims

[Claim 1] An exhaust gas mixing device that is interposed upstream of an exhaust gas purification device in an exhaust flow path of an engine, A first partition wall and a second partition wall are disposed in a cylindrical casing; a cylindrical mixing pipe having a plurality of slits and fins on a peripheral wall, one end of which is fixed to the casing, and the other end of which is disposed within the notch of the first partition wall; an injection device for injecting a reducing agent into the mixing pipe is provided at one end of the mixing pipe; the first partition wall has a communication port near the inner surface of the casing facing the mixing pipe, The second partition wall has holes formed therein, An exhaust mixing device characterized in that a cylindrical inner cylinder having multiple holes is sandwiched between the first partition wall and the second partition wall, and the communication port is connected to the gap between the inner cylinder and the casing.

Images