JP2010127125A - Exhaust emission control device of diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of melting damage of a filter, by reducing a quantity of supported noble metal to an oxidation catalyst. <P>SOLUTION: The oxidation catalyst 16 arranged in an exhaust passage 12 of a diesel engine 11 raises the exhaust gas temperature by oxidizing fuel mist supplied in exhaust gas of the engine 11. A particulate filter 17 arranged in the exhaust passage on the exhaust gas downstream side of the oxidation catalyst 16, collects a particulate in the exhaust gas passing through the exhaust passage, and this collected particulate is burnt and removed by heat of the exhaust gas being raised in the temperature by the oxidation catalyst. The cylindrical oxidation catalyst 16 having the length of 75 mm or more is arranged by four or more. Assuming the cross-sectional area in an orthogonal surface to the flowing direction of the exhaust gas of the filter 17 as S<SB>1</SB>, the total cross-sectional area S<SB>2</SB>of totalling the respective cross-sectional areas in the orthogonal surface to the flowing direction of the exhaust gas of the four or more of oxidation catalysts 16 is 0.5S<SB>1</SB>≤S<SB>2</SB><0.8S<SB>1</SB>. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus that collects particulates contained in exhaust gas of a diesel engine and burns and removes the collected particulates.

  Conventionally, as this type of exhaust gas purification device, a particulate collector is provided in an exhaust pipe connected to an exhaust manifold of an engine, and a particulate filter is accommodated in the exhaust gas downstream side of the collector, and the collector Among them, an oxidation catalyst is accommodated on the exhaust gas upstream side, and an electronically controlled accumulator that is installed in each cylinder of the engine adjusts an injection amount and an injection timing by a solenoid valve so that fuel is injected into each cylinder. An exhaust gas purification device for an engine configured in (1) is disclosed (for example, see Patent Document 1). In this exhaust gas purification device, the pressure sensor detects that a predetermined amount or more of particulates has been collected in the filter, and the controller injects fuel into the cylinder immediately before closing the exhaust valve of the cylinder based on the detection output of the pressure sensor. Configured to control the solenoid valve.

In the engine exhaust gas purification apparatus configured as described above, the oxidation catalyst and the particulate filter are sequentially accommodated in the particulate collector from the exhaust gas upstream side, and the controller controls the exhaust valve of the cylinder based on the detection output of the pressure sensor. Since the electromagnetic valve of the electronically controlled accumulator injector is controlled so that fuel is injected into the cylinder immediately before closing, the fuel flows into the collector without being burned, and is oxidized and burned by the oxidation catalyst. As a result, the exhaust gas that has reached a high temperature flows into the filter, so that the particulates collected by the filter burn and the filter is regenerated.
JP-A-8-42326 (Claim 1, paragraph [0019], FIG. 1)

However, the conventional exhaust gas purification apparatus for an engine disclosed in Patent Document 1 normally uses one oxidation catalyst for regenerating a filter for one particulate filter, and the diameter of the oxidation catalyst is equal to that of the filter. Since it was formed almost the same as the diameter, there was a problem that the amount of noble metal supported on the oxidation catalyst was increased and the production cost of the oxidation catalyst was increased. In addition, the price fluctuations of precious metals are severe, and precious metals are now becoming expensive, raising the problem of further raising the production cost of the oxidation catalyst. Therefore, the cross-sectional area in an orthogonal plane to the flow direction of the exhaust gas filter and S _1, the sectional area S ₂ of an orthogonal plane to the flow direction of the exhaust gas of the oxidation catalyst, cross sectional area S ₂ of the oxidation catalyst of the filter As the area S _{1 was} reduced, it was found that the minimum cross-sectional area S ₂ of the oxidation catalyst capable of burning all the particulates deposited on the filter was 0.8S ₁ . That is, it was found that even if the cross-sectional area S ₂ of the oxidation catalyst is made 20% smaller than the cross-sectional area S _{1 of} the filter, all the particulates deposited on the filter can be burned. However, if the cross-sectional area S ₂ of the oxidation catalyst is further reduced by more than 20% with respect to the cross-sectional area S ₁ of the filter, the exhaust gas heated by the oxidation catalyst does not flow in the vicinity of the outer periphery of the filter, and particulates are present in this portion. If too much is accumulated, the particulates burn at a time when the filter is regenerated, and the filter becomes extremely hot, and there is a possibility that the filter may be melted or cracked. Even if the cross-sectional area S ₂ of the oxidation catalyst is 20% smaller than the cross-sectional area S _{1 of} the filter, when one oxidation catalyst is used for one filter, the center of the exhaust gas downstream end of the filter is regenerated. However, since this temperature becomes extremely high, there is also a problem that this portion becomes a starting point for the occurrence of melting damage and cracks in the filter.

  A first object of the present invention is to provide an exhaust gas purifying apparatus for a diesel engine that can reduce the amount of noble metal supported on an oxidation catalyst. A second object of the present invention is to provide an exhaust gas purifying apparatus for a diesel engine that can prevent the center of the exhaust gas downstream side end of the filter from becoming a starting point for occurrence of melting damage and cracks in the filter.

As shown in FIGS. 1 and 2, the invention according to claim 1 oxidizes fuel mist provided in the exhaust passage 12 of the diesel engine 11 and supplied to the exhaust gas of the engine 11 to raise the temperature of the exhaust gas. The catalyst 16 is provided in the exhaust passage 12 on the downstream side of the exhaust gas from the oxidation catalyst to collect particulates in the exhaust gas, and the collected particulates are burned and removed by the heat of the exhaust gas heated by the oxidation catalyst 16. This is an improvement of the exhaust gas purification device for a diesel engine provided with the particulate filter 17. Its characteristic configuration is provided a cylindrical oxidation catalyst 16 than the length 75mm of 4 or more, when the cross-sectional area of a plane perpendicular to the flow direction of the exhaust gas filter 17 and S _1, four The total cross-sectional area S _{2 obtained} by summing the cross-sectional areas of the oxidation catalyst 16 in the plane perpendicular to the flow direction of the exhaust gas is 0.5S ₁ ≦ S ₂ <0.8S ₁ .
The invention according to claim 2 is the invention according to claim 1, and further, as shown in FIGS. 1 and 2, four or more oxidation catalysts 16 are point-symmetric with respect to the center of the cylindrical catalyst case 13. It is characterized by being arranged in.

In the invention according to claim 1, by reducing the cross-sectional area of the oxidation catalyst by the diffusion phenomenon of the high-temperature exhaust gas at the oxidation catalyst outlet, the total cross-sectional area S ₂ of four or more oxidation catalysts is reduced to the cross-sectional area S of the filter. _Since it is reduced within the range of 0.5S ₁ ≦ S ₂ <0.8S ₁ with respect to ₁ , it is possible to reduce the amount of noble metal supported on the oxidation catalyst, and to prevent melting or cracking of the particulate filter. Occurrence can be prevented. In the invention according to claim 2, since four or more oxidation catalysts are arranged point-symmetrically with respect to the center of the cylindrical catalyst case, the center of the exhaust gas downstream end of the filter becomes extremely hot during regeneration of the filter. You can avoid that. As a result, the center of the exhaust gas downstream side end of the filter can be prevented from becoming a starting point for the occurrence of melting damage or cracks in the filter.

Next, the best mode for carrying out the present invention will be described with reference to the drawings.
<First Embodiment>
As shown in FIG. 1, an exhaust pipe 12b is connected to an exhaust port of a cylinder of a diesel engine 11 mounted on a vehicle via an exhaust passage 12, that is, an exhaust manifold 12a. The exhaust pipe 12b is provided with a catalyst case 13 and a filter case 14 in order from the exhaust gas upstream side. An oxidation catalyst 16 is accommodated in the catalyst case 13, and a particulate filter 17 is accommodated in the filter case 14. The oxidation catalyst 16 is a honeycomb-shaped monolith catalyst in this embodiment, and has a plurality of holes (cell paths) having regular cross-sectional shapes (squares, triangles, hexagons, etc.) in the exhaust gas flow direction and open at both ends. A cordierite-made honeycomb carrier having noble metal such as Pt is supported. The filter 17 is a honeycomb filter in this embodiment. The filter 17 has a circular cross section partitioned by a porous partition wall 17a made of cordierite, through which exhaust gas can pass and particulates cannot pass. Adjacent inlet portions 17c and outlet portions 17d of through holes 17b formed in parallel with each other by these partition walls 17a are alternately sealed by sealing walls 17e through which both exhaust gas and particulates cannot pass. The The filter 17 is configured such that the particulates contained when the exhaust gas of the engine 11 introduced from the inlet side of the filter 17 passes through the porous partition wall 17a is filtered and then discharged from the outlet side. Further, the cross-sectional area of the catalyst case 13 is formed to be about 20% smaller than the cross-sectional area of the filter case 14. The rear end of the catalyst case 14 is connected to the front end of the filter case 14 via a cone-shaped connection case 18.

  Here, the movement of the fuel mist and the oxidation reaction in the cell path of the honeycomb-shaped oxidation catalyst 16 will be described. Since the particle size (micron order) of the light oil fuel mist is larger than the particle size of the gas, the fuel mist has a larger mass than the gas. For this reason, according to the Brownian motion theory that the fine particles are a phenomenon caused by irregular collisions with molecules of a thermally moving medium (air, water, etc.), the probability that the fuel mist contacts the cell wall of the oxidation catalyst 16. Is extremely low. Further, when the fuel mist comes into contact with the cell wall of the oxidation catalyst 16, the fuel gas is oxidized by reacting with oxygen on the noble metal particles supported on the oxidation catalyst 16. Therefore, the oxidation reaction of the fuel mist in the cell path of the oxidation catalyst 16 is different from the normal space velocity (SV) chemical reaction. According to experiments, the oxidation reaction of the fuel mist increases in proportion to the length of the cell path of the oxidation catalyst 16, but the reaction of the fuel mist is small when the inner diameter of the cell path is large and the length of the cell path is short. Tend to be. For this reason, if measures are taken to increase the chance that the fuel mist contacts the cell wall, it is considered that the oxidation reaction of the fuel mist proceeds. Further, since the particle size of the fuel mist is relatively large on the order of microns, it is considered that the fuel mist reacts while repeating collision with the cell wall and diffusion.

  Consider the flow of fuel mist in the cell path of the oxidation catalyst 16. When the cell path is short, the flow of fuel mist in the cell path becomes turbulent inside the cell path and in the vicinity of the inlet of the cell path, but thereafter becomes laminar. On the other hand, when the cell path is long, the flow of fuel mist in the cell path becomes turbulent inside the cell path and in the vicinity of the entrance of the cell path, but then becomes laminar and swirl at a predetermined pitch ( Spiral flow) occurs. The swirl flow (spiral flow) is generated based on the following reason. Even if the flow containing fuel mist becomes a laminar flow in the cell path, near the wall surface of the cell path, this flow is in contact with the wall surface to generate vortices, and these vortices are synchronized with standing waves. A vortex remains. Further, since the cell path is long, the tuning vortex gradually increases. Therefore, a tuning vortex is generated by setting the length and inner diameter of the cell path. Specifically, it is found that if the inner diameter of the cell path is d, a swirling flow (spiral flow) is generated in the fuel mist if the length of the cell path is 20d to 30d or more.

  From the above, the following can be understood. The fuel mist becomes a turbulent flow at the inlet of the cell path of the oxidation catalyst 16 and collides with the cell wall, and then once becomes a laminar flow. The fuel mist advances and collides with the cell wall. A part of the colliding fuel mist reacts, the remaining part diffuses and collides with the cell wall again by centrifugal force. By repeating this collision, diffusion, and collision, the fuel mist undergoes an oxidation reaction in a form proportional to the length of the cell path of the oxidation catalyst 16. Even if the space velocity (SV) increases, if the flow velocity in the cell path increases, the centrifugal force also increases by the square of the flow velocity, so the number of collisions of the fuel mist with the cell wall does not decrease much.

  On the other hand, post injection is performed on the cylinder of the engine 11. The post-injection is to inject fuel (light oil) into the cylinder of the engine 11 later than the main injection, and the fuel is injected at the moment when the exhaust valve is opened. This post-injected fuel has a very short time in the cylinder, and when the high-temperature and high-pressure exhaust gas in the cylinder flows out of the cylinder, it becomes a fuel mist and rides on the exhaust gas flow, so it burns in the cylinder. The amount discharged from the cylinder without burning is larger than the amount. Therefore, the fuel mist flows into the exhaust pipe 12b through the exhaust manifold 12a. The oxidation catalyst 16 has a function of oxidizing the fuel mist supplied in the exhaust gas to raise the temperature of the exhaust gas, and the filter 17 has a function of collecting particulates in the exhaust gas. The particulates collected by the filter 17 and deposited on the filter 17 are configured to be burned and removed by the heat of the exhaust gas at a predetermined temperature or higher (250 ° C. or higher). In the post-injection, a controller (not shown) accumulates the accumulated amount of particulates on the filter 17 based on the detection outputs of the engine rotation sensor and the engine load sensor, and indicates that this accumulated amount is equal to or greater than a predetermined amount. It is configured to be performed when detected.

Four or more cylindrical oxidation catalysts 16 having a length of 75 mm or more, preferably 90 to 110 mm are provided. Further, when the cross-sectional area of the filter 17 in the plane orthogonal to the exhaust gas flow direction is S ₁ , the total cross-sectional areas of the four or more oxidation catalysts 16 in the plane orthogonal to the exhaust gas flow direction are totaled. The total cross-sectional area S ₂ is 0.5S ₁ ≦ S ₂ <0.8S ₁ , preferably 0.7S ₁ ≦ S ₂ <0.8S ₁ . Further, in this embodiment, four oxidation catalysts 16 are accommodated in a cylindrical catalyst case 13 (FIG. 2). These oxidation catalysts 16 are arranged point-symmetrically with respect to the center of the catalyst case 13, that is, the four oxidation catalysts 16 are arranged at equal intervals by being shifted by 90 degrees with respect to the center of the catalyst case 13. Here, the reason why the length of the oxidation catalyst 16 is limited to 75 mm or more is that if it is less than 75 mm, there is a high probability that the fuel mist will pass through without contacting the wall experimentally, and the fuel mist (HC) due to insufficient oxidation reaction time. This is because oxidation is insufficient. The upper limit value of the preferable range of the length of the oxidation catalyst 16 is limited to 110 mm. If the length exceeds 110 mm, the oxidation catalyst 16 becomes larger and difficult to mount on the vehicle, and the oxidation reaction time becomes relatively long, so that fuel mist (including HC mist) is included. Because most of it has already been oxidized and no further oxidation can be expected. Further, the number of oxidation catalysts 16 is limited to four or more. If the number is three or less, a portion where the exhaust gas heated by the oxidation catalyst 16 does not flow is generated near the outer periphery of the filter 17, and the particulates accumulated in this portion are accumulated. This is because the curate cannot be removed by combustion. Further, The reason for limiting the total cross-sectional area S ₂ of the oxidation catalyst 16 in the range of 0.5S ₁ ≦ S ₂ <0.8S ₁ is larger combustion remaining particulates experimentally less than 0.5S ₁ with the outer periphery near the portion exhaust gas heated by the oxidation catalyst 16 does not flow in the filter 17 would occur, can not burn off particulates deposited on this portion, at 0.8 S ₁ or more noble metals to the oxidation catalyst 16 This is because the carrying amount increases from the conventional level.

  The number of oxidation catalysts 16 is preferably 9 or less. Here, the number of oxidation catalysts 16 is limited to nine or less. If the number exceeds nine, the amount of noble metal supported on the oxidation catalyst 16 becomes the same as the conventional amount, and the production cost of the oxidation catalyst 16 is reduced. This is because the merit is lost. Further, reference numerals 19 and 19 in FIG. 1 denote SUS (stainless steel) in which four through holes 19a and 19a for positioning the four oxidation catalysts 16 at point-symmetric positions with respect to the center of the catalyst case 13 are formed. A pair of separators made of (steel), and a reference numeral 20 is a cylindrical body that can accommodate the oxidation catalyst 16 one by one. One end of the cylindrical body 20 is inserted into the through hole 19 a of one separator 19, and the other end of the cylindrical body 20 is inserted into the through hole 19 a of the other separator 19. Thereby, the cylinder 20 is spanned between the pair of separators 19 and 19. The inner diameter of the cylinder is formed larger than the outer diameter of the oxidation catalyst, and the space between the inner peripheral surface of the cylinder 20 and the outer peripheral surface of the oxidation catalyst 16 is filled with the catalyst sealing material 21. The catalyst sealing material 21 is formed of ceramic fibers (for example, alumina fibers). Further, reference numeral 22 is a filter sealing material made of SUS (stainless steel) knit filled in a space between the outer peripheral surface of the filter 17 and the inner peripheral surface of the filter case 14.

Operation | movement of the exhaust gas purification apparatus of the diesel engine 11 comprised in this way is demonstrated. When the engine 11 is started, the particulates in the exhaust gas of the engine 11 are collected by the particulate filter 17 and accumulated on the filter 17. When the controller accumulates the accumulated amount of particulates on the filter 17 based on the detection outputs of the engine rotation sensor and the engine load sensor and detects that the accumulated amount exceeds a predetermined amount, the controller detects the fuel injection device. (Not shown) is controlled to post-inject fuel into the cylinder of the engine 11. As a result, the fuel mist flows into the oxidation catalyst 16 through the exhaust manifold 12a and the exhaust pipe 12b, so that the fuel mist is oxidized by the oxidation catalyst 16 and the temperature of the exhaust gas rises. This high-temperature exhaust gas whose temperature has risen is diffused and discharged by the diffusion phenomenon at the outlet of the oxidation catalyst 16. Therefore, even if the total cross-sectional area S ₂ of the four oxidation catalysts 16 is smaller than the cross-sectional area S ₁ of the filter 17 within the range of 0.5S ₁ ≦ S ₂ <0.8S ₁ , the entire filter 17 is reduced. Since it can be heated substantially uniformly above a predetermined temperature, the particulates deposited on the filter 17 are quickly burned and removed. As a result, it is possible to reduce the amount of noble metal supported on the oxidation catalyst 16 as compared with the conventional oxidation catalyst, and to prevent the filter 17 from being melted or cracked.

  In this embodiment, since the four oxidation catalysts 16 are arranged symmetrically with respect to the center of the catalyst case 13, the exhaust gas downstream end center of the filter 17 becomes extremely hot when the filter 17 is regenerated. It can be avoided. As a result, it is possible to prevent the center of the exhaust gas downstream side end of the filter 17 from becoming the starting point for the occurrence of melting damage or cracks in the filter 17. Further, as the catalyst sealing material 21 filled in the space between the inner peripheral surface of the cylindrical body 20 and the outer peripheral surface of the oxidation catalyst 16 in the catalyst case 13, an expensive scrubbing shape that has elasticity and follows the thermal deformation of the catalyst case 13. Even if an inexpensive ceramic fiber (for example, alumina fiber) that has little elasticity and hardly follows the thermal deformation of the catalyst case 13 is used instead of the metal wire rod, each oxidation catalyst 16 has a smaller diameter than the conventional oxidation catalyst. The sealing performance of the catalyst sealing material 21 is hardly impaired.

<Second Embodiment>
FIG. 3 shows a second embodiment of the present invention. 3, the same reference numerals as those in FIG. 2 denote the same components. In this embodiment, seven oxidation catalysts 56 having the same cross-sectional area are accommodated in a cylindrical catalyst case 13. These oxidation catalysts 56 are arranged point-symmetrically with respect to the center of the catalyst case 13. Specifically, one oxidation catalyst 56 is installed so as to coincide with the center of the catalyst case 13, and the remaining six oxidation catalysts 56 are shifted from the center of the catalyst case 13 by 60 degrees at equal intervals. Be placed. 3 is a cylinder for accommodating the oxidation catalysts 56 one by one, and 59a is a through hole formed in the separator 59 for inserting the cylinder 50 therein. The configuration other than the above is the same as that of the first embodiment.

In the exhaust gas purification apparatus for a diesel engine configured in this way, the total cross-sectional area S ₂ of the seven oxidation catalysts 56 can be made slightly smaller than the total cross-sectional area of the four oxidation catalysts of the first embodiment. At the same time, heating the filter with the oxidation catalyst 56 of this embodiment can heat the filter more uniformly than heating the filter with the oxidation catalyst of the first embodiment. Since operations other than those described above are substantially the same as those in the first embodiment, repeated description will be omitted.

<Third Embodiment>
FIG. 4 shows a third embodiment of the present invention. 4, the same reference numerals as those in FIG. 2 denote the same components. In this embodiment, four main oxidation catalysts 76a having a slightly smaller cross-sectional area than the oxidation catalyst of the first embodiment and five sub-areas significantly smaller in cross-sectional area than the oxidation catalyst of the first embodiment. The oxidation catalyst 76 b is accommodated in the cylindrical catalyst case 13. That is, the four main oxidation catalysts 76a and the five sub oxidation catalysts 76b constitute the oxidation catalyst 76 of the present embodiment. The four main oxidation catalysts 76 a are arranged point-symmetrically with respect to the center of the catalyst case 13, and the five sub-oxidation catalysts 76 b are also arranged point-symmetrically with respect to the center of the catalyst case 13. Specifically, the four main oxidation catalysts 76 a are arranged at equal intervals by being shifted by 90 degrees with respect to the center of the catalyst case 13. Of the five sub-oxidation catalysts 76b, one sub-oxidation catalyst 76b is installed so as to coincide with the center of the catalyst case 13, and the remaining four sub-oxidation catalysts 76b are 90 degrees with respect to the center of the catalyst case 13. They are arranged at regular intervals so as to be shifted and positioned between the four main oxidation catalysts 76a. In FIG. 4, reference numeral 70a denotes a main cylinder for accommodating the main oxidation catalysts 76a one by one, and reference numeral 70b denotes a sub cylinder for accommodating the sub oxidation catalysts 76b one by one. Further, 79a in FIG. 4 is a main through hole formed in the separator 79 for inserting the main cylinder 70a, and reference numeral 79b is a sub-hole formed in the separator 79 for inserting the sub cylinder 70b. It is a through hole. The configuration other than the above is the same as that of the first embodiment.

In the exhaust gas purification apparatus for a diesel engine configured in this way, the total cross-sectional area S ₂ of the four main oxidation catalysts 76a and the five sub-oxidation catalysts 76b is the total of the four oxidation catalysts of the first embodiment. The cross-sectional area can be substantially the same, and the filter is heated more uniformly when the filter is heated by the oxidation catalyst 76 of this embodiment than when the filter is heated by the oxidation catalyst of the first embodiment. can do. Since operations other than those described above are substantially the same as those in the first embodiment, repeated description will be omitted.

  In the first to third embodiments, the engine mounted on the vehicle is described as the diesel engine. However, a diesel engine mounted on an industrial machine, a ship, or the like may be used. In the first to third embodiments, the fuel mist is supplied to the oxidation catalyst by post-injection into the engine cylinder. However, a fuel injection nozzle is inserted into the exhaust passage, and a pump and a fuel tank are connected to the nozzle. You may connect and inject a fuel from this nozzle.

Next, examples of the present invention will be described in detail together with comparative examples.
<Example 1>
As shown in FIGS. 1 and 2, the exhaust pipe 12b is provided with a cylindrical catalyst case 13 and a cylindrical filter case 14 in order from the exhaust gas upstream side, and four oxidation catalysts 16 are accommodated in the catalyst case 13, A particulate filter 17 was accommodated in the filter case 14. The four oxidation catalysts 16 are arranged symmetrically with respect to the center of the catalyst case 13. The length of each of the four oxidation catalysts was 90 mm. Also when the cross-sectional area in plane perpendicular to the flow direction of the exhaust gas filter 17 and S _1, the sum of the cross-sectional area in plane perpendicular to the four flow direction of the exhaust gas of the oxidation catalyst 16 The total cross-sectional area S ₂ was 0.6S ₁ (0.15S ₁ × 4). This exhaust gas purification apparatus was designated as Example 1.

<Comparative Example 1>
Instead of the four oxidation catalysts of Example 1, the same configuration as that of Example 1 was adopted except that a single oxidation catalyst having a cross-sectional area S ₂ of 0.8S ₁ was accommodated in the catalyst case. This exhaust gas purification apparatus was designated as Comparative Example 1.

<Comparative test 1 and evaluation>
The temperature distribution inside the filter when exhaust gas at a predetermined temperature was discharged from the oxidation catalyst of the exhaust gas purifying apparatus of Example 1 and Comparative Example 1 was calculated by simulation using a computer. The results are shown in FIGS. As apparent from FIGS. 5 and 6, the filter of Comparative Example 1 was extremely high at 690 ° C. at the center of the rear end of the filter (FIG. 6), whereas the filter of Example 1 From the central part of the rear end of the filter to the periphery, it became as low as 670 ° C. (FIG. 5). As a result, it was found that the inside of the filter can be heated more uniformly by using four small-diameter oxidation catalysts than by using a single large-diameter oxidation catalyst.

It is a block diagram which shows the exhaust gas purification apparatus of the diesel engine of 1st Embodiment of this invention and Example 1. FIG. It is the sectional view on the AA line of FIG. It is sectional drawing corresponding to FIG. 2 which shows the exhaust gas purification apparatus of 2nd Embodiment of this invention. It is sectional drawing corresponding to FIG. 2 which shows the exhaust gas purification apparatus of 3rd Embodiment of this invention. FIG. 3 is a diagram illustrating a temperature distribution in the particulate filter according to the first embodiment. 6 is a diagram showing a temperature distribution in a particulate filter of Comparative Example 1. FIG.

Explanation of symbols

11 Diesel Engine 12 Exhaust Passage 13 Catalyst Case 16, 56, 76 Oxidation Catalyst 17 Particulate Filter

Claims (2)

An oxidation catalyst (16, 56, 76) provided in the exhaust passage (12) of the diesel engine (11) and oxidizing the fuel mist supplied into the exhaust gas of the engine (11) to increase the temperature of the exhaust gas; Provided in the exhaust passage (12) on the exhaust gas downstream side of the oxidation catalyst (16, 56, 76) to collect the particulates in the exhaust gas, and the collected particulates are the oxidation catalyst (16, 56 , 76), a diesel engine exhaust gas purification device comprising a particulate filter (17) that is combusted and removed by the heat of the exhaust gas heated at
Four or more cylindrical oxidation catalysts (16, 56, 76) with a length of 75 mm or more are provided,
When the cross-sectional area in plane perpendicular to the flow direction of exhaust gas of the filter (17) and S _1, perpendicular to the flow direction of exhaust gas of the four or more oxidation catalysts (16,56,76) An exhaust gas purifying apparatus for a diesel engine, characterized in that a total cross-sectional area S ₂ obtained by summing up the respective cross-sectional areas on the surface to be operated is 0.5S ₁ ≦ S ₂ <0.8S ₁ .   The exhaust gas purification apparatus for a diesel engine according to claim 1, wherein four or more oxidation catalysts (16, 56, 76) are arranged symmetrically with respect to the center of the cylindrical catalyst case (13).

Images