JPH09158720A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an exhaust gas flow passage from being clogged due to deposition of carbon on an exhaust emission control catalyst. SOLUTION: A foam catalyst 5 and a honeycomb catalyst 30 are arranged in a casing 3 connected to an exhaust gas passage 1 through a straightening device 10. The straightening device 10 is provided with a plurality of latticeshaped exhaust gas flow passages formed by a plurality of plates arranged parallel to the flow. The turbulent exhaust gas flowing out of the foam catalyst on the upstream side is damped in passing through the straightening device, and flows into the honeycomb catalyst in the less turbulent condition. Deposition of carbon in the exhaust gas due to the turbulent flow in the vicinity of an outlet of the upstream side foam catalyst and in the vicinity of an inlet of the downstream side honeycomb catalyst is suppressed to prevent the exhaust gas flow passage from being clogged by the catalysts.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust purification device, and more particularly to an exhaust purification device that uses an exhaust purification catalyst that uses a carrier having a large number of small-diameter exhaust passages such as ceramic foam.

[0002]

2. Description of the Related Art Generally, a catalyst carrier used for an exhaust gas purification catalyst has a large number of small-diameter exhaust flow passages. It has a structure that raises. As the catalyst carrier having a small-diameter exhaust passage, for example, a honeycomb carrier or a ceramic foam carrier is used.

[0003] For example, as an example of an exhaust gas purification apparatus using this type of exhaust gas purification, there is one described in Japanese Utility Model Laid-Open No. 62-97213. In the apparatus of the publication, a catalyst using a foam carrier (hereinafter referred to as "foam catalyst") is arranged in an exhaust passage of an internal combustion engine, and a catalyst using a honeycomb carrier is provided downstream of the foam catalyst (hereinafter referred to as "honeycomb catalyst"). That is) is arranged in series. As will be described later, the foam catalyst has a large number of bent small-diameter exhaust passages formed in a carrier, and a catalyst component such as an oxidation catalyst is carried on the wall surface of the exhaust passage. In addition, a large number of linear small-diameter exhaust passages (hereinafter referred to as "cells") are formed in parallel with each other in the carrier of the honeycomb catalyst.

Unburned H is present in the combustion exhaust gas, especially in the exhaust gas of an internal combustion engine.
In addition to gaseous pollutants such as C, CO and NO _x , soot and S
It contains fine particles such as OF (SOLUBLE ORGANIC FRACTION). When only the honeycomb catalyst is used to purify such exhaust gas, gaseous HC, CO, NO _x components and the like can be purified without any problem, but exhaust particulates such as SOF are not purified and the honeycomb catalyst can be directly used. It tends to pass through.

This is because the exhaust passage in the honeycomb catalyst has a small diameter, the exhaust flow in the passage is laminar, and the exhaust passage in the honeycomb catalyst is linear. Therefore, the exhaust particulates that have flowed into the flow path flow along with the laminar exhaust flow with little turbulence, and many particulates pass through the flow path inside the honeycomb catalyst without contacting the catalyst components on the wall surface. is there.

In order to prevent this problem, the above-mentioned actual exploitation 62
The apparatus disclosed in Japanese Laid-Open Patent Publication No. 97213 has a structure in which a foam catalyst is arranged on the upstream side of an exhaust passage, and a honeycomb catalyst is arranged close to the downstream side of the foam catalyst. The carrier of the foam catalyst is formed by absorbing a liquid ceramic material (cordierite, alumina, etc.) in a foam material such as urethane, and firing the ceramic together with urethane. Since the urethane is burned by the firing, a large number of foam-like cavities communicating with each other corresponding to the urethane portion remain in the carrier after firing, and a bent exhaust passage having a small diameter is formed. A catalyst component is supported on the wall surface of the exhaust passage by impregnation or the like.

Since the foam catalyst has a large number of bent exhaust passages, the exhaust gas flowing into the foam catalyst changes its direction many times along the bent passages in the foam catalyst. However, the specific particles in the exhaust cannot change the traveling direction rapidly due to inertia, and collide with the wall surface of the flow path at the point where the flow direction of the exhaust changes. On the other hand, since fine particles such as SOF contained in the exhaust gas have an adhesive property, they adhere to the wall surface at the time of collision with the wall surface, are oxidized by the catalyst component carried on the wall surface, and are removed from the exhaust gas.

In the device of the above publication, the SOF in the exhaust gas is first provided by disposing the foam catalyst on the upstream side of the exhaust passage.
Of the SOF-free exhaust gas that has passed through the foam catalyst and is passed through the honeycomb catalyst to remove H
It purifies gaseous pollutants such as C, CO, and NO _x .

[0009]

However, when the honeycomb catalyst is arranged in the vicinity of the downstream side of the foam catalyst as in the device of Japanese Utility Model Laid-Open No. 62-97213, carbon is formed at the cell inlet portion of the honeycomb catalyst on the downstream side. It has been found that there is a problem that the soot is likely to be accumulated and the cell is clogged.

As described above, SO among the fine particles in the exhaust gas
Since F has an adhesive property, it adheres to the wall surface of the flow path while passing through the foam catalyst and does not flow out much to the downstream side of the foam catalyst.
However, since carbon particles (soot) in the exhaust gas have almost no adhesiveness as compared with SOF, even if they collide with the wall surface of the flow channel in the foam catalyst, they do not adhere to the wall surface, and after repeated collisions, the exhaust gas is exhausted. Along with this, it flows out from the foam catalyst. On the other hand, at the foam catalyst outlet, the exhaust gas flows out of the small-diameter flow passage in the foam catalyst, and the flow passage sharply expands, so that the flow velocity sharply decreases. Further, the exhaust flow is significantly disturbed due to the rapid expansion of the flow path.

Therefore, when the honeycomb catalyst is arranged close to the foam catalyst outlet, carbon particles in the exhaust gas flowing out from the foam catalyst collide with the inner wall surface of the cell near the honeycomb catalyst inlet due to the turbulence of the flow and are deposited. Come to do. Therefore, when the catalyst is used for a long period of time, in the honeycomb catalyst on the downstream side of the foam catalyst, the cells at the inlet portion are clogged due to the accumulation of carbon, which causes a problem that the pressure loss of the exhaust gas flowing through the honeycomb catalyst increases.

On the other hand, in order to prevent this problem, a honeycomb catalyst is arranged at a sufficient distance from the foam catalyst so that the turbulence of the flow near the foam catalyst outlet does not directly reach the honeycomb catalyst inlet. It is also possible to do so. However, in this case, although the honeycomb catalyst cells can be reduced in clogging, carbon is deposited on the exhaust passage wall surface on the downstream side of the foam catalyst due to the stagnation of the flow at the peripheral edge of the foam catalyst outlet. That is, at the catalyst peripheral edge, the exhaust flow velocity is lower than that at the center of the exhaust passage due to the effect of the exhaust passage wall surface, and eddies are generated near the exhaust passage pipe wall at the catalyst peripheral edge due to the difference in exhaust velocity. The stagnation of the flow is easy to occur. For this reason, carbon particles in the exhaust gas are deposited on the exhaust passage wall surface at the peripheral edge of the foam catalyst, and the catalyst exhaust flow path outlet portion is blocked by the deposited carbon, which causes a problem of increasing the pressure loss of the foam catalyst. Will occur.

Further, not only the foam catalyst but also a catalyst using a carrier having an exhaust passage of a small diameter such as a honeycomb catalyst,
Similarly, since the turbulence of the exhaust gas occurs due to the expansion of the flow path in the vicinity of the catalyst outlet, the problem of carbon deposition is likely to occur similarly.
The present invention provides an exhaust gas purification device that solves the above problems, reduces turbulence in the exhaust flow near the outlet of a catalyst carrier having a large number of small-diameter exhaust passages, and can prevent the problem of carbon deposition near the outlet of the catalyst. Is intended.

[0014]

According to the invention as set forth in claim 1, a catalyst carrier having a large number of small-diameter exhaust passages arranged in an exhaust passage through which combustion exhaust flows, and an exhaust outlet of the catalyst carrier. Disposed on the exhaust passage proximate to the side portion,
An exhaust gas purification device is provided, which comprises: a laminar flow forming means for rectifying an exhaust flow flowing out from the catalyst carrier into a flow along an exhaust passage axial direction.

According to the invention described in claim 2, according to claim 1
In the exhaust gas purifying apparatus, the laminar flow forming means includes a plurality of exhaust passages extending in the exhaust passage axial direction, and the cross-sectional area of each exhaust passage is exhausted from the exhaust passage on the exhaust passage center side. The exhaust passage on the outer side in the radial direction of the passage is set to be smaller. According to the invention described in claim 3, in claim 1, in the exhaust passage on the downstream side of the laminar flow forming means,
An exhaust gas purification device is further provided in which a second catalyst carrier having a large number of small-diameter exhaust gas channels is further arranged.

According to the invention set forth in claim 4, according to claim 3,
In the exhaust gas purification device, the cross-sectional area of the exhaust flow passage of the laminar flow generating means is larger than the cross-sectional area of the exhaust flow passage of the second catalyst carrier. According to the invention of claim 5, in the exhaust emission control device of claim 3, the laminar flow forming means includes a plurality of plate bodies arranged in parallel with each other along the exhaust passage axial direction, The exhaust passage of the forming means is defined by the plate body, and each downstream end surface of the plate body coincides with the exhaust passage wall surface upstream end portion of the second catalyst carrier when viewed from the exhaust passage axial direction. An exhaust emission control device according to claim 3 arranged as described above is provided.

According to the invention of claim 6, claim 5
In the exhaust gas purifying apparatus, the thickness of the downstream end of the plate body is set to be substantially the same as the thickness of the exhaust passage wall surface upstream end of the second catalyst carrier. Next, the operation of the invention of each of the above claims will be described. In the exhaust gas purifying apparatus of claim 1, the exhaust flow flowing out from the catalyst carrier outlet is rectified by the laminar flow forming means into a flow along the exhaust passage axial direction, so that the turbulence of the exhaust flow near the catalyst carrier outlet is reduced. To be done. Therefore, carbon deposition due to the stagnation of the flow near the carrier outlet is suppressed.

In the exhaust gas purifying apparatus according to claim 2, the laminar flow forming means according to claim 1 has a plurality of exhaust passages in the exhaust passage axial direction, and the exhaust passage located closer to the outer side in the exhaust passage radial direction flows. The cross-sectional area of the road is reduced. In the vicinity of the catalyst carrier outlet, the exhaust flow velocity decreases toward the outer side in the exhaust passage radial direction (peripheral portion), so that stagnation of the flow easily occurs and carbon deposition easily occurs, but in the present invention, the exhaust flow passage cross-sectional area of the laminar flow forming means Since the value is set to be smaller toward the outer peripheral portion, a decrease in the exhaust flow velocity at the outer peripheral portion is suppressed, and carbon is less likely to be deposited.

In the exhaust gas purifying apparatus of the third aspect, since the second catalyst carrier having the small-diameter flow passage is arranged on the downstream side of the laminar flow forming means of the first aspect, the second catalyst carrier has a less disturbed state. Exhaust flows in. Therefore, in addition to the effect of the first aspect, carbon deposition on the inner wall of the exhaust passage of the second catalyst carrier on the downstream side is suppressed, and clogging of the exhaust passage of the second catalyst carrier is prevented.

In the exhaust gas purifying apparatus according to claim 4, the laminar flow forming means according to claim 3 has an exhaust passage cross-sectional area larger than that of the downstream second catalyst carrier. For this reason,
In addition to the effect of the third aspect, even when carbon is deposited on the wall surface of the exhaust passage of the laminar flow forming means, the exhaust passage of the laminar flow forming means is prevented from being blocked by the carbon. In the exhaust gas purification device according to claim 5, the outlet side end portion of the exhaust passage wall surface of the laminar flow forming means according to claim 3 is arranged so as to match the exhaust passage wall surface inlet side end portion of the second catalyst carrier. It Therefore, in addition to the function of claim 3, the plate of the laminar flow forming means does not cover the exhaust passage opening of the second catalyst carrier,
The reduction of the total area of the exhaust passage of the second catalyst carrier is prevented.

According to a sixth aspect of the present invention, there is provided the exhaust gas purifying apparatus according to the fifth aspect, wherein the downstream end wall thickness of the plate forming the laminar flow forming means is the second.
The thickness of the carrier is substantially the same as the wall thickness at the upstream end of the exhaust passage wall surface.
Therefore, in addition to the effect of the fifth aspect, there is no step between the wall surface of the exhaust flow passage of the laminar flow forming means and the wall surface of the exhaust flow passage of the second catalyst carrier, and the disturbance of the exhaust flow does not occur.

[0022]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration of an embodiment of an exhaust emission control device of the present invention. In FIG. 1, 1 is an exhaust passage connected to, for example, an exhaust manifold of an internal combustion engine, 3 is a casing containing an exhaust purification catalyst 5, and 7 is an outlet exhaust passage opened to the atmosphere via a muffler (not shown). .

In the present embodiment, a rectifier 10 is arranged as a laminar flow forming means on the outlet side of the exhaust purification 5 inside the casing 3. In the present embodiment, the rectifier 10 is formed by a plurality of rectifying plates 11 arranged in parallel in the vertical and horizontal directions, and has a plurality of lattice-shaped exhaust passages 13 surrounded by the rectifying plates 11. . FIG. 2 shows an enlarged cross-sectional view of a portion surrounded by a circle A in FIG.

In this embodiment, a foam catalyst having a ceramic foam carrier such as cordierite or alumina is used as the exhaust purification catalyst 5. As shown in FIG. 3, the foam catalyst 5 is attached to the inner wall of the casing 3 via a cushioning cushioning material 23, a sealing material 25, and a holding material 27. Inside the carrier of the foam catalyst 5, a large number of cavities formed by incineration of urethane foam etc. and communicating with each other (one of which is shown at 21 in FIG. 1)
Has occurred. This cavity functions as a large number of bent small-diameter exhaust passages that connect the inlet side end surface and the outlet side end surface of the catalyst 5. A porous washcoat layer of alumina or the like is formed on the wall surface of the cavity (exhaust passage) 21, and the washcoat layer is loaded with a catalyst component such as platinum Pt, palladium Pd, or rhodium Rh by impregnation. There is. The exhaust gas that has flowed into the carrier of the catalyst 5 from the exhaust passage 1 flows through the bent exhaust flow path formed by the cavity 21, and flows out from the outlet side of the catalyst 5. At this time, S contained in the exhaust gas
Fine particles of OF, carbon, etc. go straight due to inertia and collide with the wall surface of the exhaust passage at the bent portion of the exhaust passage. SO
Since the F fine particles have adhesiveness, they adhere to the wall surface of the flow channel when they collide with the wall surface, and are oxidized and removed by the catalyst component carried on the wall surface.

On the other hand, since the carbon particles in the exhaust gas are not sticky, they hardly adhere even when they collide with the wall surface, pass through the exhaust gas passage 21 while repeatedly colliding with the wall surface, and reach the outlet side of the catalyst 5. It flows out from the end surface 5a. By the way, in the vicinity of the end surface of the catalyst 5 on the outlet side, the exhaust gas is discharged from the small-diameter exhaust flow passage 21 into the wide space in the casing 3, and the flow passage is suddenly expanded and the exhaust flow is greatly disturbed. In the present embodiment, by disposing the rectifier 10 close to the end surface on the outlet side of the catalyst 5, it is possible to prevent large disturbance of the exhaust flow.

Before describing the rectifier 10 of this embodiment, first, the problem in the case where the rectifier 10 is not provided on the outlet side of the catalyst 5 will be described with reference to FIG. FIG.
FIG. 3 is an enlarged cross-sectional view similar to FIG. 2, showing a case where no rectifier is provided on the outlet side of the catalyst 5. As shown in FIG. 3, the exhaust gas passing through each flow path of the foam catalyst 5 and flowing out from the outlet side end portion of the catalyst 5 is greatly disturbed due to the rapid expansion of the flow path at the time of outflow, and Not only the velocity component in the main flow direction (catalyst 5 axis direction) but also the variation velocity component in random directions. Further, the velocity of the exhaust gas in the mainstream direction drops sharply due to the rapid expansion of the flow passage, and the mainstream velocity of the exhaust gas becomes smaller due to the influence of the casing wall surface from the central part of the catalyst to the peripheral part. Therefore, as shown by the dotted line in FIG. 3, vortexes of the exhaust gas are generated in the region 28 near the periphery of the outlet end face of the catalyst 5, and stagnation of the exhaust gas flow occurs, so that carbon particles in the exhaust gas accumulate in this region, Accumulation on the end surface of the catalyst 5 and the wall surface of the casing 3 is easy. As the usage time increases,
The amount of carbon deposited on the peripheral portion of the catalyst 5 and the wall surface of the casing 3 gradually increases, and the outlet of the exhaust passage 21 after the catalyst is blocked from the peripheral portion to increase the pressure loss of the exhaust gas passing through the catalyst 5. Become.

On the other hand, in this embodiment, the rectifier 10 as shown in FIG. 2 is provided close to the end face of the catalyst 5 outlet.
FIG. 4 is a sectional view taken along the line IV-IV in FIG. 1, showing the shape of the rectifier 10 of this embodiment. As shown in FIG. 4, the rectifier 10 of the present embodiment includes rectifying plates 11 arranged in a lattice shape in parallel with the axial direction of the casing 3, and the exhaust passages 13 defined by the rectifying plates 11 in the casing axial direction. have. In addition, the distance between the straightening vanes 10 becomes smaller from the central portion of the casing 3 (catalyst 5) toward the peripheral portion, and the area of the lattice forming each exhaust passage 13, that is, the cross-sectional area of the exhaust passage 13 is It is smaller from the center toward the periphery.

Next, the carbon deposition suppressing effect of providing the rectifier 10 will be described with reference to FIG. As shown in FIG. 2, in the present embodiment, the exhaust gas flowing out from each exhaust flow path 21 of the catalyst 5 directly flows into the exhaust flow path 13 of the rectifier 10. Exhaust gas that has flowed into the exhaust flow path 13 is turbulent as the speed decreases due to the expansion of the flow path.
In the exhaust passages 0 of 0, the velocity of the exhaust gas flowing out of the exhaust passages 21 of the catalyst 5 in the mainstream direction is substantially uniform, so that no stagnation of the flow occurs in the exhaust passages 21. Therefore, carbon deposition due to the stagnation of the flow is suppressed. The exhaust passage 13 of the rectifier 10 is set so that the cross-sectional area becomes smaller toward the peripheral portion. For this reason, a large decrease in the speed of the exhaust gas flowing out from the exhaust passage 21 in the peripheral portion of the catalyst is suppressed, and stagnation of the flow does not occur even in the exhaust passage 13 in the peripheral portion of the rectifier 10.

Further, as described above, the exhaust passage 21 of the catalyst 5
Exhaust gas flowing out of has a fluctuation velocity component other than the main flow direction due to turbulence of the flow. Therefore, in the vicinity of the inlet of each exhaust flow path 13 of the rectifier 10, the exhaust gas collides with the flow path wall surface, so that carbon is likely to be deposited. However, since the carbon deposition occurs in a distributed manner on the wall surface of each flow passage 13 of the rectifier 10, the amount of carbon deposited in each flow passage 13 decreases. Moreover, since the cross-sectional area of the exhaust flow path 13 of the rectifier 10 is relatively large (for example, in the central portion, one side 3 to 4).
The exhaust channel 13 is not blocked by the deposited carbon. Further, the rectifier 10
The turbulence of the exhaust gas that has flowed into the exhaust gas flow path 13 is attenuated in a short distance after flowing into the flow path 13, so that carbon is less likely to be deposited on the wall surface in the flow path 13 except the inlet portion.

As described above, in the present embodiment, by providing the rectifier 10 on the end face of the catalyst 5 on the outlet side, it is possible to effectively prevent carbon deposition on the peripheral portion of the end face of the catalyst on the outlet side. Next, another embodiment of the present invention will be described with reference to FIG. FIG. 5 is a view similar to FIG. 1, showing the exhaust emission control device of the present embodiment. Also in the present embodiment, the foam catalyst 5 in the casing 3 as in FIG.
A rectifier 10 similar to that in FIG. 1 is arranged on the end face on the outlet side. However, the present embodiment is different from the embodiment of FIG. 1 in that the honeycomb catalyst 30 is arranged close to the downstream side of the rectifier 10.

FIG. 6 shows an enlarged cross section of a portion surrounded by a circle B in FIG. The honeycomb catalyst 30 uses a ceramic carrier such as cordierite, and a large number of linear small-diameter exhaust passages (cells) 31 are formed in the carrier in the axial direction. The diameter of the exhaust passage 21 of the honeycomb catalyst 30 is set to be considerably smaller than the diameter of the exhaust passage of the foam catalyst 5, for example, 200 to 400 per square inch.
Some number of cells are formed.

7 and 8 show the downstream side of the foam catalyst 5,
[Fig. 7] Fig. 7 is a diagram showing a problem when the honeycomb catalyst 30 is provided without the rectifier 10, Fig. 7 shows a case where the honeycomb catalyst 30 is directly arranged so as to be in contact with a downstream end face of the foam catalyst 5, and Fig. 8 shows a foam catalyst. 5 shows the case where the honeycomb catalyst 30 is arranged with a certain gap from the downstream end face.

As shown in FIG. 7, when the honeycomb catalyst 30 is provided in contact with the downstream end surface of the foam catalyst 5, the exhaust gas flow flowing out from the exhaust passage 21 of the foam catalyst 5 is directly disturbed by the honeycomb catalyst 30. Since it flows into the cell 31, collision occurs between the flow passage wall surface 32 and the exhaust gas near the inlet of the cell 31, and carbon is deposited near the inlet of the cell 31 as indicated by 35 in FIG. . For this reason, there arises a problem that the inlet portion of the cell 31 is blocked due to carbon deposition. As described with reference to FIG. 2, even when the rectifier 10 is provided, carbon is likely to deposit at the inlet portion of the exhaust passage 13 of the rectifier 10, but the cross-sectional area of the exhaust passage 13 is relatively large. Even if carbon is deposited, the problem of blocking the exhaust passage 13 does not occur. On the other hand, since the cross-sectional area of the cell 31 is extremely small, there arises a problem that the cell is blocked even with a slight amount of carbon deposited.

A similar problem occurs when the honeycomb catalyst 30 is arranged at a distance from the foam catalyst 5 as shown in FIG. In this case, the exhaust gas flowing out of the exhaust gas passage 21 of the foam catalyst 5 reaches the cell inlet of the honeycomb catalyst 30 in a largely disturbed state due to the rapid expansion of the flow passage. Since the turbulence of this exhaust gas is further amplified when flowing into the cell 31, the carbon deposition 35 in the vicinity of the cell 31 is further increased as compared with FIG. 7.

On the other hand, in this embodiment, as shown in FIG. 6, the exhaust gas flowing out from the foam catalyst 5 is attenuated in turbulence when passing through the exhaust passage 13 of the rectifier 10, so that the honeycomb catalyst is exhausted. The exhaust gas reaching 30 is in a state of extremely little turbulence. For this reason, even when flowing into the cells 31 of the honeycomb catalyst 30, a large disturbance does not occur, and carbon deposition at the cell 31 inlet portion is suppressed.

By providing the rectifier 10 between the foam catalyst 5 and the honeycomb catalyst 30 in this way,
In this embodiment, the effect of reducing the amount of sulfate (SO ₃ ) generated in the honeycomb catalyst 30 is obtained. In general, the exhaust gas of an internal combustion engine contains SO ₂ produced by the combustion of sulfur components contained in fuel. This SO
₂ is catalytically oxidized to produce SO ₃ . Since SO ₃ is detected as exhaust particulates, there is a problem that if the amount of SO ₃ produced is large, the amount of exhaust particulates released to the atmosphere will increase.
It is also known that the amount of SO ₃ produced increases as the exhaust gas temperature rises.

In the present embodiment, the rectifier 10 is provided between the foam catalyst 5 and the honeycomb catalyst 30, and when the exhaust gas passes through the exhaust passage 13 of the rectifier 10, the rectifier plate 11 is provided.
Contacted and cooled. That is, in the present embodiment, each of the flow straightening plates 11 that define the flow path 13 of the flow straightener 10 also functions as a cooler that removes the heat of the exhaust gas and radiates the heat from the casing 3 to the atmosphere. Therefore, the honeycomb catalyst 30
The temperature of the exhaust gas flowing into the chamber is lower than that in the case where the rectifier 30 is not provided, and the amount of SO ₃ generated in the honeycomb catalyst 30 is reduced.

As shown in FIG. 6, the cross-sectional area of the exhaust passage of the rectifier 10 must be set as large as possible without losing the damping effect of the turbulence of the exhaust flow. As described above, carbon is likely to be deposited at the inlet portion of the exhaust flow passage 13 of the rectifier 10, so that when the cross-sectional area of the exhaust flow passage 13 is small (for example, the cross-sectional area of the cell 31 is the same), This is because, as in the case where the honeycomb catalyst 30 is directly arranged on the downstream side of the foam catalyst 5, the flow path 13 may be blocked due to carbon deposition.

Further, as shown in FIG. 6, the downstream end of each rectifying plate 11 of the rectifier 10 coincides with the upstream end face of the wall surface 32 that separates each cell 31 of the honeycomb catalyst 30 when viewed from the main exhaust flow direction. It is preferable to place it in a position. By aligning the end face of the cell wall surface 32 and the downstream end of each rectifying plate 11, the inlet of the cell 31 of the honeycomb catalyst 30 is not blocked by the rectifying plate 11, so that the exhaust pressure loss passing through the honeycomb catalyst 30 is reduced. It is possible to keep it low.

Further, in this case, as shown in FIG. 6, it is preferable that the wall thickness of the flow regulating plate 11 is substantially the same as the wall thickness of the wall surface 32 separating the cells 31. If the difference between the wall thickness of the cell wall and the wall thickness of the straightening vane 11 is large, a step will be formed between the straightening vane 11 and the wall of the cell 31 as shown in FIG. 9, for example. This is because when a step is generated in this way, a vortex of the exhaust flow is generated in the step portion, and the stagnation 36 is likely to occur, so that carbon is likely to be deposited in the stagnation portion.

In each of the above-described embodiments, the case where the rectifier 10 is arranged on the downstream side of the foam catalyst 5 has been described as an example. However, in addition to the foam catalyst, a catalyst using a carrier having an exhaust passage with a small diameter is used. Then, the same problem may occur.
Therefore, the present invention can be applied, for example, to the case where a catalyst carrier having another small-diameter exhaust passage such as a honeycomb catalyst is arranged instead of the foam catalyst 5 in each of the above-described embodiments.

[0042]

According to the invention described in each claim, when a catalyst having a carrier having an exhaust passage of a small diameter is used for purification of combustion exhaust, the exhaust passage of the carrier is blocked by carbon deposition. There is a common effect that it is possible to effectively prevent the above.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an embodiment of an exhaust emission control device of the present invention.

FIG. 2 is an enlarged sectional view of a portion A in FIG.

FIG. 3 is a diagram illustrating a problem of a conventional exhaust emission control device.

FIG. 4 is a diagram showing a cross section taken along line IV-IV of the rectifier of FIG.

FIG. 5 is a diagram showing a schematic configuration of an embodiment of an exhaust emission control device of the present invention different from that of FIG.

FIG. 6 is an enlarged sectional view of a portion B in FIG. 5;

FIG. 7 is a diagram illustrating a problem of a conventional exhaust emission control device.

FIG. 8 is a diagram illustrating a problem of a conventional exhaust emission control device.

FIG. 9 is a diagram for explaining the influence of a step caused by the difference between the current plate and the cell wall thickness.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Exhaust passage 3 ... Casing 5 ... Exhaust purification catalyst (foam catalyst) 7 ... Outlet exhaust passage 10 ... Rectifier 11 ... Rectifier plate 13 ... Exhaust flow passage 21 ... Cavity (small diameter exhaust flow passage) 30 ... Honeycomb catalyst 31 ... Cell

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display area F01N 3/28 301 B01D 53/36 ZABC

Claims (6)

[Claims] 1. A catalyst carrier having a large number of small-diameter exhaust passages arranged on an exhaust passage through which combustion exhaust flows, and arranged on the exhaust passage in the vicinity of an exhaust outlet side portion of the catalyst carrier, An exhaust gas purification device, comprising: a laminar flow forming means for rectifying an exhaust flow flowing out from the catalyst carrier into a flow along an exhaust passage axial direction. 2. The laminar flow forming means includes a plurality of exhaust passages extending in the exhaust passage axial direction, and the cross-sectional area of each exhaust passage is larger than that of the exhaust passage on the center side of the exhaust passage. The exhaust emission control device according to claim 1, wherein the exhaust gas passage on the outer side in the radial direction is set to be smaller. 3. The exhaust emission control device according to claim 1, further comprising a second catalyst carrier having a large number of small-diameter exhaust passages arranged on the exhaust passage downstream of the laminar flow forming means. 4. The exhaust emission control device according to claim 3, wherein the cross-sectional area of the exhaust flow passage of the laminar flow generating means is larger than the cross-sectional area of the exhaust flow passage of the second catalyst carrier. 5. The laminar flow forming means comprises a plurality of plate bodies arranged in parallel with each other along the exhaust passage axial direction, and the exhaust flow passage of the laminar flow forming means is defined by the plate bodies. The exhaust emission control device according to claim 3, wherein each downstream end surface of the plate body is arranged so as to match an upstream end portion of the exhaust passage wall surface of the second catalyst carrier when viewed from the exhaust passage axial direction. 6. The exhaust emission control device according to claim 5, wherein the thickness of the downstream end of the plate body is substantially the same as the thickness of the exhaust passage wall surface upstream end of the second catalyst carrier. .