JP2009013862A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology capable of further diffusing a reducing agent, in an exhaust emission control device of an internal combustion engine. <P>SOLUTION: This exhaust emission control device has a catalyst arranged in an exhaust passage of the internal combustion engine, and a reducing agent supply device 5 arranged in the exhaust passage on the upstream side of the catalyst and supplying the reducing agent in exhaust gas. The exhaust passage is constituted of a double structure 20 of an inside passage 21 and an outside passage 22 surrounding the inside passage 21 in at least a part of the exhaust passage on the upstream side of the catalyst. The exhaust gas respectively flows to the inside passage 21 and the outside passage 22, and at least a part of the outside passage 22 is a passage for spirally turning around the inside passage 21, and the reducing agent supply device 5 supplies the reducing agent in the outside passage 22. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

A technique is known in which an NOx storage reduction catalyst (hereinafter simply referred to as a NOx catalyst) is disposed in an exhaust passage of an internal combustion engine. This NOx catalyst occludes NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reduces the NOx occluded when the oxygen concentration of the inflowing exhaust gas decreases and a reducing agent is present.

  Also known is a technique for collecting particulate matter (hereinafter referred to as PM) in exhaust gas, which includes a particulate filter (hereinafter simply referred to as filter) carrying or having a catalyst having oxidation ability. Yes. When the amount of PM collected in the filter reaches a certain amount, the reducing agent is supplied to the catalyst having oxidation ability, and the temperature of the filter is raised to oxidize and remove PM. This removal of PM is referred to as filter regeneration.

And the technique which gives centrifugal force to PM contained in exhaust_gas | exhaustion by letting exhaust_gas | exhaustion pass spirally, and collects dust inside the outer wall of an exhaust gas purification apparatus is known (for example, refer patent document 1). .
JP 2000-170519 A Special table 2003-503172

In order to reduce NOx and regenerate the filter in this way, the air-fuel ratio of the exhaust gas flowing into the catalyst by, for example, fuel injection or the like is set to a rich air-fuel ratio. However, when the fuel is injected into the exhaust gas, there is a possibility that the diffusion of the fuel becomes insufficient. If the fuel does not diffuse in this way, there are places where the air-fuel ratio of the exhaust gas flowing into the catalyst is too high or too low. In such a case, NOx is not sufficiently reduced in the NOx catalyst. In addition, since the temperature of the filter does not rise sufficiently, it is difficult to regenerate the filter. Furthermore, if the injection hole of the fuel injection valve faces exhaust, deposits may adhere to the injection hole and the fuel addition valve may be clogged.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique capable of further diffusing a reducing agent in an exhaust purification device of an internal combustion engine.

In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention employs the following means. That is, the exhaust gas purification apparatus for an internal combustion engine according to the present invention is
A catalyst provided in the exhaust passage of the internal combustion engine;
A reducing agent supply device that is provided in an exhaust passage upstream of the catalyst and supplies a reducing agent into the exhaust;
With
In at least a part of the exhaust passage upstream of the catalyst, the exhaust passage has a double structure of an inner passage and an outer passage surrounding the inner passage, and each of the inner passage and the outer passage. Exhaust gas circulates, and at least a part of the outer passage is a passage that spirals around the inner passage, and the reducing agent supply device supplies the reducing agent into the outer passage. And

  If the exhaust passage has a double structure, the temperature drop of the exhaust gas flowing through the inner passage can be suppressed. When the reducing agent is supplied from the reducing agent supply device in the outer passage, the reducing agent diffuses due to the flow of the spiral exhaust. Further, the outer passage spirally surrounds the inner passage so that when the exhaust gas flowing through the outer passage flows into the inner passage, the exhaust gas flows spirally through the inner passage. This spiral flow also promotes diffusion of the reducing agent. Further, since the reducing agent is diffused by the flow of the spiral exhaust gas, the reducing agent injection pressure can be lowered, and therefore, the reducing agent supply device can be simplified.

  Here, the temperature of the outer passage is lower than that of the inner passage. By supplying the reducing agent to the outer passage, deterioration and clogging of the reducing agent supply device can be suppressed.

  According to the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the reducing agent can be further diffused.

  Hereinafter, specific embodiments of an exhaust emission control device for an internal combustion engine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 and its exhaust system according to the present embodiment. The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine.

  An exhaust passage 2 leading to the combustion chamber is connected to the internal combustion engine 1. This exhaust passage 2 communicates with the atmosphere downstream.

  In the middle of the exhaust passage 2, a particulate filter 4 (hereinafter referred to as filter 4) carrying an NOx storage reduction catalyst 3 (hereinafter referred to as NOx catalyst 3) is provided.

The NOx catalyst 3 has a function of storing NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reducing the stored NOx when the oxygen concentration of the inflowing exhaust gas is low and a reducing agent is present. . Further, the filter 4 collects PM contained in the exhaust gas.

  A double structure 20 is provided upstream of the filter 4 to separate a part of the exhaust passage 2 into the central axis A side and the outer wall 24 side of the exhaust passage 2. Here, FIG. 2 is an enlarged view of the double structure portion 20. In addition, the arrow in FIG. 2 has shown the flow direction of exhaust_gas | exhaustion.

  The double structure portion 20 includes a partition wall 23 between the central axis A side of the exhaust passage 2 and the outer wall 24 side. The partition wall 23 has a cylindrical shape having a central axis that overlaps the central axis A of the exhaust passage 2, and is accommodated closer to the central axis A than the outer wall 24 of the exhaust passage 2. The partition wall 23 is provided without contacting the outer wall 24 of the exhaust passage 2.

  That is, a passage closer to the central axis A than the partition wall 23 (hereinafter referred to as the inner passage 21) and a passage closer to the outer wall 24 than the partition wall 23 (hereinafter referred to as the outer passage 22) are formed, and the exhaust gas is exhausted. Flows. The upstream end 231 of the partition wall 23 is bent toward the center side and the upstream side of the exhaust passage 2 so that the exhaust gas can easily flow into the outer passage 22. Further, the downstream end 232 of the partition wall 23 is bent toward the center side and the downstream side of the exhaust passage 2 so that the exhaust gas easily flows out from the outer passage 22.

Further, in the outer passage 22, a spiral plate 233 having a spiral shape around the central axis A of the exhaust passage 2 is provided.
Is provided. The inside of the spiral plate 233 is welded to the partition wall 23 and the outside is welded to the outer wall 24. Accordingly, the outer passage 22 becomes a spiral passage surrounded by the spiral plate 233, the partition wall 23, and the outer wall 24, and the exhaust gas flows spirally around the inner passage 21.

  A fuel addition valve 5 for adding fuel (light oil) as a reducing agent to exhaust gas flowing through the outer passage 22 is attached to the inlet of the outer passage 22. The injection hole of the fuel addition valve 5 is in the outer passage 22 and faces the downstream side in the exhaust flow direction. That is, the fuel addition valve 5 is attached so as not to be directly exposed to the high-temperature exhaust gas flowing through the inner passage 21. In this embodiment, the fuel addition valve 5 corresponds to the reducing agent supply device in the present invention.

  The fuel addition valve 5 is opened to inject fuel into the exhaust. The fuel injected from the fuel addition valve 5 into the outer passage 22 reduces the air-fuel ratio of the exhaust gas flowing through the outer passage 22. The fuel injection from the fuel addition valve 5 is performed when NOx stored in the NOx catalyst 3 is reduced and when sulfur poisoning is recovered. Further, fuel injection from the fuel addition valve 5 is also performed when the filter 4 is regenerated.

  It should be noted that the exhaust passage 2 has a double structure on the downstream side of the downstream end 232 of the partition wall 23. Here, the upstream end and the downstream end of the partition wall are bent toward the outer wall 24 of the exhaust passage 2 and are welded to the outer wall 24. Thereby, since the location corresponding to the outer passage 22 is sealed, the exhaust does not flow. Hereinafter, this sealed portion is referred to as a sealed portion 234. The sealing portion 234 is filled with a heat insulating material.

  With such a configuration, the temperature drop of the exhaust is suppressed. That is, the provision of the outer passage 22 is limited to the upstream side of the double structure portion 20, so that a decrease in exhaust gas temperature can be suppressed. Thereby, the temperature fall of the NOx catalyst 3 and the filter 4 can be suppressed. Further, the temperature of the NOx catalyst 3 can be quickly raised to the activation temperature.

  Further, since the nozzle hole of the fuel addition valve 5 is in the outer passage 22, the fuel addition valve 5 is attached at a location where the temperature of the exhaust is low. Therefore, it is possible to suppress clogging of the injection hole of the fuel addition valve 5.

  Further, since the fuel injected from the fuel addition valve 5 flows in the outer passage 22 together with the exhaust gas, the fuel can be diffused in the outer passage 22. Further, since the outer passage 22 has a spiral shape, the flow of exhaust gas flowing from the outer passage 22 into the inner passage 21 vortexes in the inner passage 21, and fuel diffusion is further promoted.

  Note that the length of the outer passage 22 can be determined based on a decrease in the temperature of the exhaust or the degree of fuel diffusion. That is, if the outer passage 22 is long, the degree of fuel diffusion increases, but the temperature drop of the exhaust gas increases. On the other hand, if the outer passage 22 is short, the degree of fuel diffusion is reduced, but the temperature drop of the exhaust gas is reduced. These may be compared by experiment or the like to determine the optimum length of the outer passage 22. In addition, the bending angle and length at the end of the partition wall 23 can be determined to be optimum values through experiments or the like.

  Since the fuel diffuses into the exhaust gas in this way, the pressure of the fuel injected from the fuel addition valve 5 can be lowered, so that the fuel addition valve 5 and the fuel supply pipe can be simplified.

  In addition, although the sealing part 234 is provided in a present Example, when the area which can make the exhaust passage 2 into a double structure is short, it is not necessary to have the sealing part 234.

Further, the downstream end 232 may be shaped as follows. FIG. 3 is a view of another shape of the downstream end 232 of the partition wall 23 as viewed from the downstream side of the exhaust passage 2. The end of the partition wall 23 is bent and extended toward the center side and the downstream side of the exhaust passage 2, and a plurality of holes 235 are formed in the extended portion. By doing so, the exhaust gas flowing through the inner passage 21 can pass through the plurality of holes 235. Further, when exhaust flows from the outer passage 22 into the inner passage 21, a part of the exhaust travels along the end of the partition wall 23 to the vicinity of the center of the inner passage 21, so that fuel can be diffused in a wider range. it can. Here, the optimum values of the bending angle, the length, the number of the holes 235, and the like at the end of the partition wall 23 can be obtained by experiments. The upstream end 231 of the partition wall 23 may have the same shape.

It is a figure which shows schematic structure of the internal combustion engine which concerns on an Example, and its exhaust system. It is an enlarged view of a double structure part. It is the figure which looked at the other shape of the downstream edge part of the partition from the downstream of the exhaust passage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Exhaust passage 3 NOx storage reduction catalyst 4 Particulate filter 5 Fuel addition valve 20 Double structure part 21 Inner passage 22 Outer passage 23 Partition 24 Outer wall 231 Upstream end 232 Downstream end 233 Spiral plate 234 Sealed Part 235 hole

Claims (1)

A catalyst provided in the exhaust passage of the internal combustion engine;
A reducing agent supply device that is provided in an exhaust passage upstream of the catalyst and supplies a reducing agent into the exhaust;
With
In at least a part of the exhaust passage upstream of the catalyst, the exhaust passage has a double structure of an inner passage and an outer passage surrounding the inner passage, and each of the inner passage and the outer passage. Exhaust gas circulates, and at least a part of the outer passage is a passage that spirals around the inner passage, and the reducing agent supply device supplies the reducing agent into the outer passage. An exhaust purification device for an internal combustion engine.

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