JP2008128045A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of introducing a reducing agent, which is injected toward a honeycomb catalyst, into the entire catalyst uniformly. <P>SOLUTION: The exhaust emission control device 10 comprises the honeycomb type exhaust purifying catalyst 31 interposed in an exhaust passage communicating with the exhaust port of an engine, and an injector 35 provided upstream of the honeycomb type exhaust emission control catalyst 31 for injecting an additive agent toward the upstream end surface of the honeycomb type exhaust purifying catalyst 31. The honeycomb type exhaust purifying catalyst 31 has a front stage carrier 43 situated on an upstream side for receiving the additive agent injected from the injector 35, a rear stage carrier 41 situated on a downstream side of the front stage carrier 43 and having a larger dimension than the front stage carrier 43 along the flow direction of exhaust gas, and a diffusion part 42 which comprises a gap provided between them and functions so that the exhaust gas discharged from the front stage 43 is diffused and introduced into the rear stage carrier 41. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device that purifies exhaust gas discharged from an engine, that is, removes (reduces) harmful substances from the exhaust gas.

  There is a risk of adverse effects on the environment such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) in exhaust gas discharged from engines mounted on automobiles, especially diesel engines. It contains a lot of pollutants and particulate matter (PM). For this reason, in general, for example, a three-way catalyst for decomposing (reducing, etc.) the pollutants and a particulate filter for capturing PM in an exhaust passage through which exhaust gas discharged from the engine passes. Etc., so that the exhaust gas is discharged into the atmosphere as harmless as possible.

  In such a particulate filter, since PM accumulates in the filter and the passage resistance increases with use, it is necessary to perform a regeneration process as necessary. As such regeneration processing, a heating device is provided in the particulate filter, and PM is burned and removed by heating. However, fuel (light oil) is added to the oxidation catalyst provided upstream of the particulate filter. A method is also proposed in which an exothermic reaction is caused by flowing a hydrocarbon-based liquid such as) and the particulate filter is regenerated by this heat (see, for example, Patent Document 1).

  In diesel engines, nitrogen oxides (NOx) are particularly likely to be generated. For this reason, in order to efficiently decompose NOx in exhaust gas, for example, many so-called NOx storage catalysts that decompose and reduce (reduce) NOx by repeatedly adsorbing and reducing NOx are often employed in diesel engines. ing.

  Such a NOx occlusion catalyst decomposes (reduces) adsorbed NOx, and therefore it is necessary to appropriately supply a reducing agent from the outside to the NOx occlusion catalyst. For this reason, in general, fuel (light oil) or the like is injected into the exhaust passage as a reducing agent so as to be supplied to the NOx storage catalyst. As an example thereof, for example, there is an injector in which a NOx reducing agent is injected toward a NOx storage catalyst by an injector provided in an exhaust passage (see, for example, Patent Document 2).

JP 2002-89237 A JP-A-2005-214100

  Here, as described in Patent Document 1 and Patent Document 2, a reducing agent such as fuel is applied from upstream toward a honeycomb-type catalyst having a shape in which a plurality of flow paths are bundled, such as an oxidation catalyst and a NOx storage catalyst. When injected, the reducing agent is not sufficiently atomized and diffused until it reaches the end face of the honeycomb type catalyst, and adheres only to a partial region of the end face in the form of droplets. There is a possibility that only a part of the catalytic function of the oxidation catalyst is used or only a part of the NOx adsorbed on the NOx storage catalyst is decomposed (reduced). is there. That is, there is a problem that atomization and diffusion of the injected reducing agent is insufficient and the reducing agent reaches only a part of the honeycomb catalyst.

  In addition, when the reducing agent injected in this manner is sprayed onto a partial region of the end face of the honeycomb type catalyst in a droplet state, the catalyst temperature locally decreases due to the vaporization heat of the reducing agent, and the exhaust gas temperature May decrease.

  In this case, if the heat capacity of the honeycomb type catalyst is reduced, the local temperature drop of the catalyst can be reduced, and since there is no local temperature drop, the control by the exhaust gas temperature detected in real time downstream of the honeycomb catalyst is adversely affected. However, since the catalyst is easily cooled by stopping the engine, there is a problem that an exhaust gas deterioration phenomenon is likely to occur at the start of operation.

  This invention is made | formed in view of such a situation, and it aims at providing the exhaust gas purification apparatus which can introduce | transduce the reducing agent injected toward a honeycomb type catalyst equally to the whole catalyst.

  A first aspect of the present invention that solves the above problems is a honeycomb type exhaust purification catalyst interposed in an exhaust passage communicating with an exhaust port of an engine, and provided upstream of the honeycomb type exhaust purification catalyst. An exhaust gas purification apparatus comprising an injector that injects an additive toward an upstream end face of a honeycomb type exhaust gas purification catalyst, wherein the honeycomb type exhaust gas purification catalyst is upstream and injected from the injector A front carrier for receiving the additive, a rear carrier downstream of the front carrier and having a size in the exhaust flow direction larger than that of the front carrier, and a gap provided therebetween, from the front carrier. The exhaust gas purification apparatus includes a diffusion unit that functions to diffuse the exhaust gas that is discharged and introduce the exhaust gas into the rear carrier.

  In such a first aspect, even if the additive sprayed toward the front carrier is introduced into only a part of the front carrier, it diffuses after passing through the diffusion section and is introduced uniformly throughout the rear carrier. It will be.

  According to a second aspect of the present invention, there is provided the exhaust gas purification apparatus according to the first aspect, wherein the upstream carrier is a honeycomb structure having no catalyst layer.

  In the second aspect, the honeycomb structure having no catalyst layer has a small heat capacity corresponding to the catalyst layer, and is easily heated at the start of operation. In addition, the cost can be reduced by the amount of omitting the catalyst layer.

  According to a third aspect of the present invention, there is provided the exhaust gas purification apparatus according to the first or second aspect, wherein the front carrier is a metal honeycomb structure.

  In the third aspect, since the metal honeycomb structure has a small heat capacity and a high thermal conductivity, the metal honeycomb structure is easily heated at the start of operation, and the temperature of the portion is lowered even when the droplet-like additive adheres directly. Therefore, it is difficult to vaporize the additive and it is difficult to lower the temperature of the exhaust gas.

  According to a fourth aspect of the present invention, in the exhaust gas purification apparatus according to any one of the first to third aspects, the rear carrier is a ceramic honeycomb structure.

  In the fourth aspect, the catalyst performance of the post-stage carrier can be maintained at a high level.

  In the present invention, since the additive injected from the injector toward the honeycomb type exhaust gas purification catalyst passes through the upstream carrier and enters the diffusion portion, it is diffused, so that the additive is substantially evenly distributed over the entire exhaust gas purification catalyst. The catalyst efficiency can be improved.

  Hereinafter, the present invention will be described based on embodiments. FIG. 1 is a diagram showing a schematic configuration of the exhaust gas purification apparatus according to the first embodiment, and FIG. 2 is a longitudinal sectional view of an essential part thereof.

  As shown in FIG. 1, an exhaust purification device 10 according to the present embodiment has a plurality of exhaust purification catalysts and exhaust purification filters, and the plurality of exhaust purification catalysts and exhaust purification filters are vehicles. Is installed in an exhaust pipe (exhaust passage) 12 of a multi-cylinder diesel engine (hereinafter simply referred to as an engine) 11.

  The engine 11 includes a cylinder head 13 and a cylinder block 14, and a piston 16 is accommodated in each cylinder bore 15 of the cylinder block 14 so as to be reciprocally movable. A combustion chamber 17 is formed by the piston 16, the cylinder bore 15, and the cylinder head 13. The piston 16 is connected to a crankshaft 19 via a connecting rod 18, and the crankshaft 19 is rotated by the reciprocating motion of the piston 16.

  An intake port 20 is formed in the cylinder head 13, and an intake pipe (intake passage) 22 including an intake manifold 21 is connected to the intake port 20. The intake port 20 is provided with an intake valve 23, and the intake port 20 is opened and closed by the intake valve 23. An exhaust port 24 is formed in the cylinder head 13, and an exhaust pipe (exhaust passage) 12 including an exhaust manifold 25 is connected to the exhaust port 24. The exhaust port 24 is provided with an exhaust valve 26. Like the intake port 20, the exhaust port 24 is opened and closed by the exhaust valve 26. A turbocharger 27 is provided in the middle of the intake pipe 22 and the exhaust pipe 12, and an exhaust gas purification device constituting the exhaust gas purification apparatus 10 according to the present embodiment is provided downstream of the turbocharger 27 of the exhaust pipe 12. A catalyst and an exhaust purification filter are interposed.

  The turbocharger 27 has a turbine (not shown) and a compressor connected to the turbine. When exhaust gas flows from the engine 11 into the turbocharger 27, the turbine is rotated by the flow of the exhaust gas, and the rotation of the turbine. Along with this, the compressor rotates to suck air from the intake pipe 22a into the turbocharger 27 and pressurize it. The air pressurized by the turbocharger 27 is supplied to each intake port 20 of the engine 11 through the intake pipe 22b.

  The cylinder head 13 is provided with an electronically controlled fuel injection valve 28 that directly injects fuel into the combustion chamber 17 of each cylinder. The fuel injection valve 28 has a predetermined fuel pressure from a common rail (not shown). Controlled high pressure fuel is supplied.

  Here, in the present embodiment, a diesel oxidation catalyst (hereinafter simply referred to as an oxidation catalyst) 31 and an NOx storage catalyst 32 that are exhaust purification catalysts, an exhaust purification filter, and an exhaust pipe 12 downstream of the turbocharger 27. A diesel particulate filter (DPF: Diesel Particulate Filter: hereinafter referred to as DPF) 33 is arranged in order from the upstream side. As will be described in detail later, an injector 35 that injects fuel (light oil) as a reducing agent toward the oxidation catalyst 31 as an additive is provided in the exhaust pipe 12a between the turbocharger 27 and the oxidation catalyst 31. It has been.

  The oxidation catalyst 31 includes a post-stage carrier 41 having a catalyst layer in which a noble metal such as platinum (Pt) or palladium (Pd) is supported on a honeycomb structure carrier made of a ceramic material, for example. Further, the oxidation catalyst 31 includes a front carrier 43 that is shorter in the flow direction of the exhaust gas than the rear carrier 41 via a diffusion portion 42 that is a gap having a predetermined length on the upstream side of the rear carrier 41. To do. That is, the rear carrier 41 and the front carrier 43 are held in the exhaust pipe 12a via the catalyst holding mat 44 in a state where a predetermined interval is formed as the diffusion portion 42, and the exhaust gas flowing through the exhaust pipe 12a is Then, it passes through the front carrier 43, passes through the diffusion part 42, and is introduced into the rear carrier 41. Here, the catalyst holding mat 44 serves as a buffer material to protect the ceramic carrier. Details of the configuration of the oxidation catalyst 31 will be described later.

In such an oxidation catalyst 31, when exhaust gas flows in, carbon monoxide (NO) in the exhaust gas is oxidized and nitrogen dioxide (NO ₂ ) is generated. Further, in order for the oxidation reaction in the oxidation catalyst 31 to occur, the oxidation catalyst 31 needs to be heated to a predetermined temperature or higher, and therefore the oxidation catalyst 31 may be arranged as close to the engine 11 as possible. preferable. By being arranged at a position close to the engine 11, the oxidation catalyst 31 is heated by the heat of the engine 11, and the oxidation catalyst 31 can be heated to a predetermined temperature or higher in a relatively short time even when the engine is started. it can.

For example, the NOx storage catalyst 32 supports a noble metal such as platinum (Pt) and palladium (Pd) on a honeycomb structure carrier made of aluminum oxide (Al ₂ O ₃ ), and barium (Ba) as a storage agent. An alkali metal or alkaline earth metal is supported. The NOx occlusion catalyst 32 temporarily occludes NO _x in the oxidizing atmosphere, that is, NO ₂ produced by the oxidation catalyst 31 and NO remaining in the exhaust gas without being oxidized by the oxidation catalyst 31. In a reducing atmosphere containing carbon oxide (CO), hydrocarbon (HC) and the like, NO _x is released and reduced to nitrogen (N ₂ ) and the like.

Most of the NO ₂ produced by the oxidation catalyst 31 is adsorbed / decomposed (reduced) by the NOx storage catalyst 32, and the remaining NO _{2 that} has not been adsorbed / decomposed is purified by the reaction in the DPF 33. Yes.

Usually, very little amount of HC majority of the exhaust gas discharged from the engine 11 occupies is NO, only the NOx storage catalyst 32 becomes an oxidizing atmosphere, the NOx storage catalyst 32 in NO _x is adsorbed The adsorbed NO _x is not decomposed (reduced). For this reason, when a predetermined amount of NO _x is adsorbed on the NO _x storage catalyst 32, fuel (light oil) as a reducing agent is injected from the injector 35 fixed to the exhaust pipe 12 a between the turbocharger 27 and the oxidation catalyst 31. It has come to be. Thus, the exhaust gas fuel is mixed through the oxidation catalyst 31 is supplied to the NOx storage catalyst 32, the NOx storage catalyst 32 becomes a reducing atmosphere, the adsorbed NO _x is decomposed (reduced).

  Here, in the present invention, as shown in FIG. 2, the injector 35 is provided on the upstream side that is not so far away from the oxidation catalyst 31, and the injection direction of the nozzle 36 at the front end is the upstream end surface 43 a of the front carrier 43. It fixes to the exhaust pipe 12a so that it may go to the center part vicinity. Therefore, the fuel (reducing agent) injected from the nozzle 36 of the injector 35 is atomized while flying in a droplet state toward the center of the front carrier 43, but most of the fuel in the front carrier 43 remains in a droplet state. It adheres to the central part of the upstream end face 43a. Thus, the fuel injected from the injector 35 adheres to the front carrier 43 and then flows through the central flow path while reaching the diffusion section 42 while being vaporized. Each flow path of the front carrier 43 communicates with the diffusion part 42 and spreads in the direction intersecting the flow, that is, in the radial direction, so that the reducing agent discharged from the flow path in the central region of the front carrier 43 Is diffused in the radial direction in a vaporized state in the diffusion portion 42 (mixed with the exhaust gas discharged from other flow paths) and is introduced to the entire upstream end face of the rear carrier 41 before being introduced into the rear carrier 41. It diffuses evenly and is introduced almost uniformly into the entire flow path of the rear carrier 41. In addition, the reducing agent diffused evenly in this way is evenly mixed in the exhaust gas even after leaving the post-stage carrier 41, and evenly in the NOx storage catalyst 32, DPF 33, etc. disposed downstream. Supplied.

  In general, the injector is provided at a considerable distance from the exhaust purification catalyst so that the injected reducing agent is sufficiently diffused and atomized before reaching the exhaust purification catalyst. Therefore, there are cases where such an arrangement cannot be obtained. For example, in the present embodiment, the oxidation catalyst 31 is provided in the vicinity immediately below the turbocharger 27, and the exhaust pipe 12a between the turbocharger 27 and the oxidation catalyst 31 is curved in a substantially L shape. Since it is constituted by a tube, the injector 35 cannot be provided at a position separated from the oxidation catalyst 31 by a considerable distance. In this embodiment, the reducing agent injected from the injector 35 is in the state of droplets in the oxidation catalyst 31. It adheres to only a part of the region on the upstream end face. However, as described above, the pre-stage carrier 43 is provided on the upstream side of the post-stage carrier 41 via the diffusion portion 42, so that the reducing agent adhering to a partial region of the pre-stage carrier 43 is sufficiently transmitted via the diffusion portion 42. In this state, it is uniformly introduced into the entire rear carrier 41.

  In this embodiment, as shown in FIG. 2, the injector 35 is provided at a position substantially opposite to the upstream end face 43a of the front carrier 43. However, the injector 35 is provided in a direction inclined toward the upstream end face 43a. May be. Further, in order to diffuse the fuel satisfactorily in the diffusing portion 42, the fuel is injected from the nozzle 36 toward the central portion (partial region) of the upstream end surface 43a of the front carrier 43. Is preferable, but it may be sprayed only to other parts, not the central part.

  Here, it is preferable that the diffusion part 42 has a length in the flow direction so that the reducing agent from the upstream carrier 43 can sufficiently diffuse in the radial direction. In other words, the exhaust gas substantially rectified by the front carrier 43 may be diffused as a turbulent flow in the diffusion portion 42 and introduced into the rear carrier 41.

  Further, the length (thickness) of the upstream carrier 43 in the flow direction is not particularly limited, but it is preferable that the length can be sufficiently vaporized while the reducing agent attached in the droplet state passes. Needless to say, the front carrier 43 is not preferable because only a part of the entire carrier 43 is used in relation to the reducing agent injected from the injector 35, and the longer the longer the carrier, the more unused parts.

  Further, in the present embodiment, the former carrier 43 is provided with a catalyst layer on a honeycomb structure carrier formed of a ceramic material, as with the latter carrier 41. However, if the honeycomb carrier is a honeycomb structure, the catalyst layer is not necessarily provided. It is not necessary to have.

  When the honeycomb structure is provided with no catalyst layer, the cost can be reduced and the heat capacity can be reduced by the amount of the catalyst layer using the noble metal. When the heat capacity is small as described above, for example, since it is easily heated at the start of operation, there is an advantage that it is easy to vaporize even if a droplet-like reducing agent is directly attached.

  Further, the post-stage carrier 41 and the pre-stage carrier 43 do not necessarily need to use a ceramic carrier, and may use a metal honeycomb carrier. Since such a metal honeycomb structure has a small heat capacity and a high thermal conductivity, it is easy to be heated at the start of operation and has an advantage that the catalyst is activated when the temperature of the exhaust gas is relatively low. In particular, when the pre-stage carrier 43 is made of metal, even if a droplet-like reducing agent adheres directly, heat conduction from the surroundings is fast, so that the temperature of the part is not easily lowered, and the attached reducing agent is easily vaporized. Also, there is an advantage that the temperature of the exhaust gas is difficult to decrease. Even in the case of a metal honeycomb structure, the above-described effects can be obtained by omitting the catalyst layer of the front carrier 43.

  Here, the metal honeycomb structure generally has a structure in which a corrugated plate and a thin plate are wound in a cylindrical shape, but the cross-sectional shape of the flow path is close to a triangle, and when a catalyst layer is provided, the corner portion is provided. In general, it is said that the effective volume is smaller than when a ceramic carrier is used. Therefore, from the viewpoint of catalyst efficiency, it is preferable to use a ceramic carrier for the post-stage carrier 41. However, if importance is attached to the heat capacity as described above, it is preferable to use a metal carrier for the pre-stage carrier 43.

  An example of such a configuration is shown in FIG. The oxidation catalyst 31A shown in this figure has a diffusion part 42 having a predetermined gap on the upstream side of a rear carrier 41 using a ceramic carrier as described above, and a front carrier 43A using a metal carrier. It is provided.

  The effect of such an oxidation catalyst 31A is as described above, but the front carrier 43A using a metal carrier is directly connected to the exhaust pipe 12a without providing the catalyst holding mat 44 for holding the rear carrier 41. It is fixed by attaching. The catalyst holding mat 44 is generally made of a material that absorbs and holds the reducing agent when directly attached, and in some cases, the reducing agent such as the absorbed and held fuel may burn and disappear. However, such a problem does not occur in the configuration of FIG. For example, even when the injector 35 is provided on the side of the front carrier 43A and the reducing agent is injected from the direction inclined toward the upstream end face, all the reducing agent is introduced into the metal front carrier 43A. .

  Further, since the metal carrier has a sufficiently large mechanical strength compared to the ceramic carrier, the length (thickness) of the upstream carrier 43 in the flow direction can be reduced. That is, when a ceramic carrier is used, it needs to have a certain length (thickness) in consideration of the strength when held in the exhaust pipe 12a, but a metal carrier is used. If so, there is no such restriction.

In any case, by providing the upstream carrier 43 (43A) via the diffusion part 42 on the upstream side of the downstream carrier 41, the downstream carrier 41 as a whole in a state where the reducing agent attached to the upstream carrier 43 (43A) is sufficiently diffused. Will be introduced equally. If the exhaust gas passes through the oxidation catalyst 31 in a state where the fuel is not evenly mixed, the amount of NO ₂ produced decreases at the portion where the fuel concentration is high, and the desired amount of NO ₂ may not be produced as a whole. There is. The exhaust gas fuel is not mixed uniformly, for example, if it is supplied to the NOx storage catalyst 32, in the lower portion of the concentration of the fuel, there is a fear that the adsorbed NO _x is not sufficiently reduced.

  The DPF 33 is a filter having a honeycomb structure formed of, for example, a ceramic material. In the DPF 33, an exhaust gas passage 33a in which an upstream end is opened and a downstream end is closed and a downstream end are opened. The exhaust gas passages 33b whose upstream end portions are closed are alternately arranged. The exhaust gas first flows into the exhaust gas passage 33a with the upstream end opened, and the exhaust with the downstream end opened from the porous wall surface provided between the adjacent exhaust gas passages 33b. The gas flows into the gas passage 33b and flows downstream. In this process, the particulate matter (PM) in the exhaust gas collides with the wall surface or is adsorbed and captured.

The trapped PM is oxidized (combusted) by NO ₂ in the exhaust gas and discharged as CO ₂ , and NO ₂ remaining in the DPF 33 is decomposed into N ₂ and discharged. That is, in the DPF 33, to purify the exhaust gas, so that the can be greatly reduced emissions of PM and NO _x. Moreover, the performance of the DPF 33 is regenerated to some extent by burning PM.

Here, normally, as described above, since NO _x is adsorbed by the NO _x storage catalyst 32, the amount of NO _{2 in} the exhaust gas supplied to the DPF 33 is small, and PM is gradually deposited on the DPF 33. . When a predetermined amount of PM accumulates on the DPF 33, a predetermined amount of fuel is injected from the injector 35 fixed to the exhaust pipe 12a. When the fuel is mixed in exhaust gas as described above, because the NOx storage catalyst 32 in the adsorbed NO _x is reduced, _NO x _{(NO 2)} contained in the exhaust gas is adsorbed by the NOx storage catalyst 32 Without being supplied to the DPF 33. As a result, PM combustion in the DPF 33 is promoted.

  An exhaust gas temperature sensor 38 is provided in the vicinity of the upstream side of the oxidation catalyst 31, the NOx storage catalyst 32 and the DPF 33, and the downstream side of the DPF 33, and the oxidation catalyst 31, The temperature of the exhaust gas flowing into the NOx storage catalyst 32 and the DPF 33 and the temperature of the exhaust gas discharged from the oxidation catalyst 31, the NOx storage catalyst 32 and the DPF 33 are detected. Further, an oxygen concentration sensor 39 for detecting the oxygen concentration in the exhaust gas is provided in the vicinity of the upstream side of the oxidation catalyst 31 and the DPF 33. The vehicle is provided with an electronic control unit (ECU) (not shown). The ECU includes an input / output device, a storage device for storing a control program and a control map, a central processing unit, a timer and a counter. There is a kind. The ECU performs comprehensive control of the engine 11 and the exhaust purification device 10 based on information from the sensors.

  Although one embodiment of the present invention has been described above, the present invention is not limited to this embodiment. For example, in the above-described embodiment, as the exhaust purification device 10, the exhaust pipe (exhaust passage) 12 includes the oxidation catalyst 31 and the NOx storage catalyst 32 that are exhaust purification catalysts, and the DPF 33 that is an exhaust purification filter upstream. Although the example which has arrange | positioned in order of the oxidation catalyst 31, the NOx storage catalyst 32, and DPF33 from the side was given, arrangement | positioning and kind of these exhaust gas purification catalysts and exhaust gas purification filters are not specifically limited.

  For example, as shown in FIG. 4A, the NOx storage catalyst 32, the oxidation catalyst 31, and the DPF 33 may be arranged in this order in the exhaust pipe 12 on the downstream side of the turbocharger 27. Further, for example, as shown in FIG. 4B, the oxidation catalyst 31 and the DPF 33 may be sequentially arranged in the exhaust pipe 12 on the downstream side of the turbocharger 27 without providing the NOx storage catalyst 32. .

  In the above-described embodiment, the configuration in which the upstream carrier 43 is provided upstream of the downstream carrier 41 via the diffusion portion 42 is applied to the oxidation catalyst 31. However, the exhaust purification catalyst having the injector that injects the reducing agent upstream is provided. As long as it is applicable to any catalyst. For example, in the above-described embodiment, the structure applied to the oxidation catalyst 31 may be applied to the NOx storage catalyst 32 instead, and the same structure may be applied to both.

  FIG. 5 shows another example of arrangement when the configuration of the present invention is applied to a NOx storage catalyst.

  FIGS. 5A and 5B have NOx storage catalysts 32A and 32B to which the structure of the present invention is applied. In the example of FIG. 5A, an injector 35A for injecting a reducing agent toward the upstream end face of the NOx storage catalyst 32A is provided upstream of the NOx storage catalyst 32A, and the NOx storage catalyst 32A is disposed upstream of the rear carrier 51. In this configuration, the upstream carrier 53 is provided via the diffusion portion 52. Further, a DPF 33 is interposed on the downstream side of the NOx storage catalyst 32A. In the example of FIG. 5B, a NOx storage catalyst 32B and an oxidation catalyst 31A having the same configuration are arranged on the downstream side of the same NOx storage catalyst 32A as in FIG. 5A, and further a DPF 33 is interposed downstream thereof. It is a disguise.

Thus, even if the reducing agent injected toward the NOx storage catalysts 32A and 32B adheres to a partial region of the upstream end face of the upstream carrier 53, it is diffused when it is vaporized and introduced into the diffusion section 52. Thus, the latter carrier 51 is evenly supplied. Then, in the configuration of FIG. 5 (a), the reducing agent injected from the injector 35A is subjected to the reduction of NO _x adsorbed in the NOx storage catalyst 32A, also, the reducing agent to the NOx storage catalyst 32A The DPF 33 can be regenerated by increasing the exhaust gas temperature due to the supply. On the other hand, in the configuration of FIG. 5 (b), the supply of the reducing agent from the injector 35A or 35B, the NO _x adsorbed on the NOx storage catalyst 32A or 32B can be reduced, also, the NOx storage catalyst 32A or When the reducing agent is introduced into the oxidation catalyst 31A through 32B, the exhaust gas temperature rises and the DPF 33 is regenerated.

Further, in the above embodiment, as an exhaust purification catalyst for decomposition (reduction) of NO _x, is exemplified NOx storage catalyst for fuel decompose NO _x a (light oil) as a reducing agent (reduction), are limited to not, for example, the NO _x in the exhaust gas selectively adsorbed to the catalyst, decomposing the ammonia or urea is injected from the injector NO _x as a reducing agent (reduction), a so-called SCR (selective catalytic reduction), etc. May be.

  An example of a configuration using this SCR is shown in FIG. In the configuration of this figure, an oxidation catalyst 31A, a DPF 33, and an SCR 34 are arranged in order in the exhaust pipe 12. An injector 35C for injecting urea liquid as a reducing agent is disposed upstream of the SCR 34. The SCR 34 is configured to include a front carrier 63 via a diffusion portion 62 on the upstream side of the rear carrier 61. As a result, even if the urea liquid injected from the injector 35C adheres to a partial region of the front carrier 63, it is vaporized and diffused by the diffusion part 62, and is supplied uniformly to the entire rear carrier 61. Become.

  In the above-described embodiment, the reducing agent is used as the additive. However, the present invention is not limited to the purpose of reducing action, and the same may be used as an additive for burning the injected fuel to raise the temperature of the catalyst. An effect is obtained.

  Furthermore, in the above-described embodiment, an example of the configuration of an intake / exhaust system including a turbocharger as a supercharger is shown. However, the present invention is not particularly limited thereto. For example, the supercharger is not necessarily provided. Further, a cooling exhaust gas recirculation device having a cooling exhaust gas recirculation passage between the exhaust passage and the intake passage, that is, a so-called EGR device may be provided.

1 is a schematic configuration diagram of an exhaust emission control device according to an embodiment of the present invention. It is a longitudinal cross-sectional view of the principal part of the exhaust gas purification apparatus which concerns on one Embodiment of this invention. It is a longitudinal cross-sectional view of the principal part which shows the modification of the exhaust gas purification apparatus which concerns on one Embodiment of this invention. It is a schematic block diagram which shows the modification of the exhaust gas purification apparatus which concerns on one Embodiment of this invention. It is a schematic block diagram which shows the modification of the exhaust gas purification apparatus which concerns on one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Exhaust purification device 11 Engine 12 Exhaust pipe 27 Turbocharger 31, 31A Oxidation catalyst 32, 32A, 32B NOx occlusion catalyst 33 DPF
34 SCR
35, 35A, 35B, 35C Injector 36 Nozzle 41, 51, 61 Rear carrier 42, 52, 62 Diffusion part 43, 53, 63 Front carrier

Claims (4)

A honeycomb type exhaust purification catalyst interposed in an exhaust passage communicating with an exhaust port of the engine, and added toward the upstream end face of the honeycomb type exhaust purification catalyst provided upstream of the honeycomb type exhaust purification catalyst An exhaust purification device comprising an injector for injecting an agent,
The honeycomb-type exhaust purification catalyst is upstream of the front carrier that receives the additive injected from the injector, and the downstream side of the front carrier has a dimension in the exhaust flow direction that is larger than that of the front carrier. Exhaust gas having a large rear carrier and a diffusion portion that functions as a gap provided between them and the exhaust gas discharged from the front carrier diffuses and is introduced into the rear carrier. Purification equipment.   2. The exhaust emission control device according to claim 1, wherein the upstream carrier is a honeycomb structure having no catalyst layer.   The exhaust emission control device according to claim 1 or 2, wherein the front carrier is a metal honeycomb structure.   The exhaust emission control device according to any one of claims 1 to 3, wherein the rear carrier is a ceramic honeycomb structure.

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