WO2013017943A1

WO2013017943A1 - Exhaust gas purification system and exhaust gas purification method for internal combustion engine

Info

Publication number: WO2013017943A1
Application number: PCT/IB2012/001616
Authority: WO
Inventors: Kazuhiro Itoh; Shinya Hirota; Masanori Hatta; Toru Sasatani; Schoichi MAEDA; Shintaro Kawasaki
Original assignee: Toyota Jidosha Kabushiki Kaisha; Kabushiki Kaisha Toyota Jidoshokki
Priority date: 2011-08-03
Filing date: 2012-08-03
Publication date: 2013-02-07
Also published as: JP2013036332A

Abstract

In an exhaust gas purification system for an internal combustion engine that includes an exhaust gas purification catalyst disposed in an exhaust passage in the internal combustion engine and a reducing agent addition valve disposed upstream the exhaust gas purification catalyst in the exhaust passage for injecting a reducing agent in a direction across an exhaust gas flow, the reducing agent addition valve supplies a reducing agent in such a manner that makes a diameter of an agent particle away from the reducing agent addition valve larger than a diameter of an agent particle in the vicinity of the reducing agent addition valve.

Description

EXHAUST GAS PURIFICATION SYSTEM AND EXHAUST GAS PURIFICATION

METHOD FOR INTERNAL COMBUSTION ENGINE

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates to an exhaust gas purification system and an exhaust gas purification method that provide a reducing agent to an exhaust passage in an internal combustion engine.

2. Description of Related Art

[0002] An exhaust gas purification system in which a selective reduction catalyst is provided in an exhaust passage in an internal combustion engine and a urea addition valve is provided upstream of the selective reduction catalyst in the exhaust passage is known. In such an exhaust gas purification system, a construction in which a dispersion plate disperses a urea solution supplied through a urea addition valve is known (see Japanese Patent Application Publication No. 2007-032472 (JP 2007-032472 A), for example).

[0003] When such an exhaust gas purification system is utilized in a passenger car and like, there is possibility that the distance between the urea addition valve and the selective reduction catalyst becomes short due to limited installation space. In such a case, there is possibility that a reducing component (such as urea solution or ammonia (NH₃) which is produced by hydrolysis of the urea solution) reaches (flows into) the selective reduction catalyst before being mixed with an exhaust gas due to limited arrangement of the urea addition valve.

[0004] As a result, there is possibility that the reducing component is not distributed evenly throughout the selective reduction catalyst. If a dispersion plate is provided for the solution as in the related art described above, exhaust pressure loss may increase. SUMMARY OF THE INVENTION

[0005] An object of the present invention is to evenly distribute a reducing agent, which is supplied through a reducing agent addition valve, throughout an exhaust gas purification catalyst.

[0006] A first aspect of the invention is directed to an exhaust gas purification system for an internal combustion engine that includes an exhaust gas purification catalyst disposed in an exhaust passage in an internal combustion engine and a reducing agent addition valve disposed upstream the exhaust gas purification catalyst in the exhaust passage for injecting a reducing agent in a direction across an exhaust gas flow, in which the reducing agent addition valve supplies a reducing agent in such a manner that makes a diameter of an agent particle away from the valve larger than a diameter of an agent particle in the vicinity of the valve. In other words, the reducing agent addition valve of this aspect injects a reducing agent such that a part of the reducing agent injected from the reducing agent addition valve forms coarse particles with a larger diameter compared to the rest of the reducing agent.

[0007] Specifically, the exhaust gas purification system for an internal combustion engine of this aspect includes an exhaust gas purification catalyst disposed in an exhaust passage in an internal combustion engine and a reducing agent addition valve disposed upstream the exhaust gas purification catalyst in the exhaust passage for injecting a reducing agent in a direction across an exhaust gas flow, in which the reducing agent addition valve injects a part of the reducing agent in a larger particle compared to the rest of the reducing agent- in the exhaust passage.

[0008] With this construction, the reducing agent supplied (injected) through the reducing agent addition valve to the exhaust passage includes a reducing agent with small particle diameter (hereinafter referred to as "fine-particle reducing agent") and a reducing agent with larger particle diameter than the fine-particle reducing agent (hereinafter referred to as "coarse-particle reducing agent").

[0009] The fine-particle reducing agent has low penetration (short flying distance) in the exhaust gas due to small inertial mass. In contrast, the coarse-particle reducing agent has high penetration (long flying distance) in the exhaust gas due to large inertial mass. Accordingly, the fine-particle reducing agent tends to gather in the vicinity of the reducing agent addition valve and the coarse-particle reducing agent tends to gather away from the reducing agent addition valve.

[0010] In the case where the distance between the reducing agent addition valve and the exhaust gas purification catalyst is short, in other words, in such a case where an installation space of the reducing agent addition valve is , the reducing agent addition valve is likely to be disposed to inject a reducing agent across an exhaust gas flow.

[0011] In the case where an arrangement as described above, is adopted, when only the fine-particle reducing agent (or a mixture of a large amount of the fme-particle reducing agent and a very small amount of the coarse-particle reducing agent) is supplied through the reducing agent addition valve, a large amount of the reducing agent is supplied to a region near the reducing agent addition valve in an radial direction of the exhaust gas purification catalyst while a small amount of reducing agent is supplied to a region away from the reducing agent addition valve. As a result, concentration distribution of the reducing agent in the radial direction of the exhaust gas purification catalyst becomes uneven. In other words, the reducing agent supplied through the reducing agent addition valve is not distributed throughout the exhaust gas purification -catalyst. If the reducing agent is not distributed throughout the exhaust gas purification catalyst, the exhaust gas purification catalyst may not provide sufficient purification performance appropriate to the supplied amount of the reducing agent.

[0012] In contrast, when the fine-particle reducing agent and the coarse-particle reducing agent are supplied through the reducing agent addition valve to the exhaust passage, the fme-particle reducing agent is supplied to a region near the reducing agent addition valve in the radial direction of the exhaust gas purification catalyst and the coarse-particle reducing agent is supplied to a region away from the coarse-particle reducing agent. Accordingly, it is possible to allow the concentration distribution of the reducing agent in the radial direction of the exhaust gas purification catalyst to be evener. As a result, it is possible to evenly distribute the reducing agent supplied through the reducing agent addition valve throughout the exhaust gas purification catalyst.

[0013] However, since the coarse-particle reducing agent is harder to be . vaporized than the fine-particle reducing agent, there is concern that the coarse-particle reducing agent reaches the exhaust gas purification catalyst while remaining in a liquid phase. Specifically, in the case where a reducing agent derived from ammonia (such as urea or solution of ammonium carbamate., for example) is used as a reducing agent, there is concern that the coarse-particle reducing agent reaches the exhaust gas purification catalyst without being hydrolyzed. However, as the flying distance of the coarse-particle reducing agent becomes long, the period of exposure of the coarse-particle reducing agent to exhaust gas heat becomes long. As a result, it is possible to avoid the situation i which the coarse-particle reducing agent reaches the exhaust gas purification catalyst while remaining in a liquid phase.

[0014] Thus, if the reducing agent is evenly distributed throughout the exhaust gas purification catalyst by means of the method described above, the exhaust gas purification catalyst can achieve purification performance appropriate to the amount of supplied reducing agent.

[0015] In such a case where the flow rate of exhaust gas is low, there is possibility that the flying distance of the fine-particle reducing agent becomes long. In such a case, there is possibility that an amount of the reducing agent supplied to a region in the vicinity of the reducing agent addition valve in the radial direction of the exhaust gas purification catalyst becomes too small. Therefore, it is necessary to hold the fine-particle reducing- agent in the vicinity of the reducing agent addition valve even if the flow rate of exhaust gas is low.

[0016] In this regard, the reducing agent addition valve according to this aspect may inject a reducing agent in a radial direction of the exhaust passage at a wide angle (wide angle injection).

[0017] If the reducing agent is injected at a wide angle, the flying distance of the reducing agent in the radial direction of the exhaust passage can be made short. Therefore, it is possible for the fine-particle reducing agent to remain in the vicinity of the reducing agent addition valve even if the flow rate of exhaust gas is low.

[0018] Also, when the reducing agent is injected at a wide angle, particles exfoliated from an injected mist easily bind with each other in the center of the injected mist to increase in size. Therefore, when the reducing agent addition valve injects a reducing agent at a wide angle, the amount of the coarse-particle reducing agent increases. Accordingly, it is possible to supply the fine-particle reducing agent and the coarse-particle reducing agent through the reducing agent addition valve.

[0019] As the other method for supplying the fine-particle reducing agent and the coarse-particle reducing agent through the reducing agent addition valve, in other words as the other method for increasing the amount of the coarse-particle reducing agent injected from the reducing agent addition valve, a method- may be used in which the valve opening speed (transferring speed of the reducing agent addition valve from a closed state to a fully open state) of the reducing agent addition valve is relatively decreased compared with the case where the amount of the coarse-particle reducing agent injected from the reducing agent addition valve is not increased.

[0020] In this case, the exhaust gas purification system for an internal combustion engine of this aspect may further include a control section that decreases the valve opening speed of the reducing agent addition valve in the case where a part of the reducing agent injected from the reducing agent addition valve is made to have particles coarser than those in the rest of the reducing agent compared with the case where no coarse particle is produced.

[0021] Injection pressure (pressure of the reducing agent) applied on an injection hole tends to be lower during the period of valve opening operation of the reducing agent addition valve compared with the period after the valve opening operation has been completed (fully open period). Especially in the case of a reducing agent addition valve which is opened or closed by moving a needle, injection pressure applied on an injection hole decreases during the period while the needle moves from a fully closed position to a fully opened position compared to the period after the needle has been moved to the fully opened position. The particle diameter of the reducing agent when injection pressure applied on an injection hole is low tends to be larger than that when injection pressure applied on an injection hole is high. In this regard, although the period of valve opening operation is adapted to be shortened by, for example, increasing a drive current (inrush current) when opening the valve (starting to open from a fully closed state) in the related art, the period of valve opening operation may be lengthened in this aspect. In this case, the amount of the coarse-particle reducing agent and the amount of the fine-particle reducing agent supplied through the reducing agent addition valve can be generally equalized, because the amount of the coarse-particle reducing agent injected from the reducing agent addition valve is increased.

[0022] As the other method for increasing the amount of the coarse-particle reducing agent injected from the reducing agent addition valve, a method in which an injection period of the reducing agent each time (a period that the reducing agent is continuously injected by the reducing agent addition valve) is shortened may be used.

[0023] In this case, the exhaust gas purification system for an internal combustion engine of this aspect may further include a control section that shortens the injection period of the reducing agent each time in the case where a part of the reducing agent injected from the reducing agent addition valve is made to have particles coarser than those in the rest of the reducing agent compared with the case where no coarse particle is produced.

[0024] When the injection period of the reducing agent each time of the reducing agent addition valve is shortened, the proportion of the period of valve opening operation to the injection period of the reducing agent becomes large. As described above, the amount of the coarse-particle reducing agent tends to increase during the period of valve opening operation of the reducing agent addition valve compared with during the fully open period. In other words, the amount of the fine-particle reducing agent tends to decrease during the period of valve opening operation of the reducing agent addition valve compared with during the fully open period. Accordingly, when the proportion of the period of valve opening operation to the injection period of the reducing agent is increased, the amount of the coarse-particle reducing agent and the amount of the fine-particle reducing agent injected from the reducing agent addition valve during the injection period of the reducing agent can be generally equalized.

[0025] Incidentally, when the injection period of the reducing agent each time is shortened, it may cause the shortage of the amount of supplied reducing agent to the exhaust gas purification catalyst. In such a case, the control section may secure the amount of supplied reducing agent to the exhaust gas purification catalyst by adding the reducing agent through the reducing agent addition valve in multiple times while shortening the injection period of the reducing agent each time.

[0026] In the case where a target supplied amount that is a supplied amount of the reducing agent to be supplied through the reducing agent addition valve exceeds a predetermined amount, the target supplied amount of the reducing agent may be continuously injected from the reducing agent addition valve without shortening the injection period of the reducing agent. That is, in the case where the target supplied amount of the reducing agent exceeds the predetermined amount, the target supplied amount of the reducing agent may be continuously injected from the reducing agent addition valve by increasing the injection period of the reducing agent each time.

[0027] At this time, if the injection period of the reducing agent each time is lengthened, particles of the fine-particle reducing agent bind with each other to form a reducing agent with large particle diameter from the midstream of the injection period of the reducing agent. Therefore, when the injection period of the reducing agent each time is lengthened, the amount of the coarse-particle reducing agent can be increased. At this time, the "predetermined amount" used here corresponds to a minimum target supplied amount for which the injection period of the reducing agent is adjusted to the extent in which the amount of the coarse-particle reducing agent and the amount of the fine -particle reducing agent injected from the reducing agent addition valve are equalized in the injection period of the reducing agent each time.

[0028] That is, the exhaust gas purification system for an internal combustion engine of this aspect may further include a control section that lengthens the injection period of the reducing agent each time in the case where a part of the reducing agent injected from the reducing agent addition valve is made to have particles coarser than those in the rest of the reducing agent compared with the case where no coarse particle is produced when the target supplied amount of the reducing agent exceeds the predetermined amount.

[0029] If the injection period of the reducing agent each time of the reducing agent addition valve is lengthened, particles of the reducing agent tend to bind with each other to form a reducing agent with large particle diameter from the midstream of the injection period of the reducing agent. Accordingly, if the injection period of the reducing agent each time of the reducing agent addition valve is lengthened, the amount of the coarse-particle reducing agent injected from the reducing agent addition valve can be increased. _As a result, the amount of the coarse-particle reducing agent and the amount of the fine-particle reducing agent injected from the reducing agent addition valve can be generally equalized.

[0030] As the other method for increasing the amount of the coarse-particle reducing agent injected from the reducing agent addition valve, a method that decreases injection pressure of the reducing agent addition valve my be used.

[0031] In this case, the exhaust gas purification system for an internal combustion engine of this aspect may further include a control section that decreases injection pressure of the reducing agent addition valve in the case where a part of the reducing agent injected from the reducing agent addition valve is made to have particles coarser than those in the rest of the reducing agent compared with the case where no coarse particle is produced.

[0032] When the injection pressure of the reducing agent addition valve is low, the diameter of a reducing agent particle injected from the reducing agent addition valve becomes large compared to when the injection pressure of the reducing agent addition valve is high. Thus, if the injection pressure of the reducing agent addition valve is decreased, the amount of the coarse-particle reducing agent injected from the reducing agent addition valve can be increased. As a result, the amount of the coarse-particle reducing agent and the amount of the fine-particle reducing agent injected from the reducing agent addition valve can be generally equalized.

[0033] Also, the exhaust gas purification system for an internal combustion engine of this aspect may further include an impinging plate that is disposed in a flight path of the reducing agent injected from the reducing agent addition valve, on which the fine-particle reducing agent injected from the reducing agent addition valve impinges, and through which the coarse-particle reducing agent passes.

[0034] According to the impinging plate described above, since the fine-particle reducing agent injected from the reducing agent addition valve impinges on the impinging plate, the fine-particle reducing agent can surely remain in the vicinity of the reducing agent addition valve. In contrast, the coarse-particle reducing agent injected from the reducing agent addition valve does not impinge on the impinging plate and therefore the coarse-particle reducing agent can surely reach far from the reducing agent addition valve. As a result, the fine-particle reducing agent is supplied to a region near the reducing agent addition valve in the radial direction of the exhaust gas purification catalyst and the coarse-particle reducing agent is supplied to a region away from the reducing agent addition valve.

[0035] At this time, the exhaust gas purification system for an internal combustion engine of this aspect may further include a dispersion plate on which the coarse-particle reducing agent impinges after passing through the impinging plate.

[0036] According to the dispersion plate described above, after reaching far from the reducing agent addition valve,, the coarse-particle reducing agent impinges on the dispersion plate to be -atomized. The atomized reducing agent is subjected to exhaust gas heat to be easily vaporized. Accordingly, in such a case where a reducing agent derived from ammonia is used as a reducing agent, the coarse-particle reducing agent can surely be hydrolyzed.

[0037] According to each of aspects of the invention, it is possible to evenly distribute the reducing agent supplied through the reducing agent addition valve throughout the exhaust gas purification catalyst.

[0038] A second aspect of the invention is directed to an exhaust gas purification method for an internal combustion engine that includes an exhaust gas purification catalyst disposed in an exhaust passage in the internal combustion engine and a reducing agent addition valve disposed upstream the exhaust gas purification catalyst in the exhaust passage for injecting a reducing agent. in a direction across an exhaust gas flow. The exhaust gas purification method comprises a step of injecting a reducing agent such that a part of the reducing agent injected from the reducing agent addition valve forms coarse particles with a larger diameter compared to the rest of the reducing agent.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 illustrates a schematic diagram of an exhaust system of an internal combustion engine to which the present invention is applied;

FIG. 2 schematically shows the concentration distribution of reducing agent in a radial direction of a selective reduction catalyst when a fine-particle reducing agent is injected from a reducing agent addition valve;

FIG. 3 A is a horizontal cross-sectional view of a tip of the reducing agent addition valve and FIG. 3B is a vertical cross-sectional view thereof;

FIG. 4 schematically shows a resulting injected mist immediately after the injection of the reducing agent has been started;

FIG. 5 schematically shows an injected mist immediately before the injection of the reducing agent has been completed;

FIG. 6 chronologically shows a relationship between a needle position of the reducing agent addition valve and the distribution of particle diameter of the reducing agent;

FIG. 7 shows variation of a drive current applied to the reducing agent addition valve;

FIG. 8 chronologically shows a relationship between the needle position of the reducing agent addition valve and the amount of a coarse-particle reducing agent; FIG. 9 is a graph that shows a relationship between injection pressure of the reducing agent addition valve and the particle diameter of the reducing agent;

FIG. 10 shows a construction of an exhaust passage in the vicinity of the reducing agent addition valve;

FIG. 11 schematically shows a flow of the reducing agent toward an impinging plate; FIG. 12 shows another exemplary construction of the impinging plate;

FIG. 13 shows an exemplary construction including two pieces of impinging plate; FIG. 14 shows another exemplary construction including two pieces of impinging plate;

FIG. 15 shows still another exemplary construction including two pieces of impinging plate;

FIG. 16 shows an exemplary construction in which the reducing agent addition valve and the impinging plate are provided in a first catalyst casing;

FIG. 17 shows an exemplary construction in which the reducing agent addition valve and the impinging plate are provided in a second catalyst casing;

FIG. 18 shows an example in which a particulate filter and a selective reduction catalyst are housed in the same catalyst casing; and

FIG. 19 shows an exemplary construction of an adhesion prevention plate;

DETAILED DESCRIPTION OF EMBODIMENTS

[0040] Specific embodiments according to the present invention will be described hereinafter with reference to the attached drawings. Dimensions, materials, shapes, and relative arrangement of components described in this embodiment are not intended to limit technical scope of the present invention therein unless otherwise specified.

[0041] [First Embodiment]

First, a first embodiment of the invention is described based on FIG. 1 through FIG. 5. FIG. 1 illustrates a schematic diagram of an exhaust system of an internal combustion engine to which the present invention is applied. An internal combustion engine 1 shown in FIG 1 is a compression ignition type internal combustion^' engine (diesel engine). A spark ignition type internal combustion engine (gasoline engine) capable of operating in lean burn (lean burn operation) may also be used.

[0042] In FIG. 1 , an exhaust passage 2 is connected to the internal combustion engine 1. The exhaust passage 2 is a passage through which a burned gas (exhaust gas) discharged from a cylinder of the internal combustion engine 1 is flowed. In the midstream of the exhaust passage 2, a first catalyst casing 3 and a second catalyst casing 4 are disposed serially from upstream side.

[0043] The first catalyst casing 3 incorporates an oxidation catalyst and a particulate filter in a tubular casing. At this time, the oxidation- catalyst may be supported by a catalyst carrier disposed upstream the particulate filter or supported by the particulate filter.

[0044] The second catalyst casing. 4 houses a catalyst carrier that supports a selective reduction catalyst in a tubular casing. The catalyst carrier, for example, includes a monolith type base having a honeycomb cross-section made of cordierite or Fe-Cr-Al heat-resistant steel and coated with an alumina-based or zeolite-based active component (carrier). The catalyst carrier further supports a precious metal catalyst (such as platinum (Pt) and palladium (Pd) for example) capable of oxidizing. Further, a catalyst carrier that supports an oxidation catalyst may be disposed downstream the selective reduction catalyst inside the second catalyst casing 4. The oxidation catalyst in this case is dedicated to oxidize a reducing agent having slipped from the selective reduction catalyst among reducing agents that are supplied- to the selective reduction catalyst from a reducing agent addition valve 5 which is described later.

[0045] In the exhaust passage 2 between the first catalyst casing 3 and the second catalyst casing 4, the reducing agent addition valve 5 for adding (injecting) a reducing agent derived from ammonia into the exhaust gas is installed. The reducing agent addition valve 5 is a valve device having an injection hole which is opened or closed by moving a needle. The reducing agent addition valve 5 is connected to a reducing agent tank 51 via a pump 50. The pump 50 sucks in the reducing agent reserved in the reducing agent tank 51 and feeds the sucked reducing agent to the reducing agent addition valve 5 by pressure. The reducing agent addition valve 5 injects the reducing agent fed from the pump 50 by pressure into the exhaust passage 2. Open/close timing of the reducing agent addition valve 5 and the discharge pressure of the pump 50 are electrically controlled by an electronic control unit (ECU) 6.

[0046] At this time, the reducing agent reserved in the reducing agent tank 51 is a reducing agent derived from ammonia. As a reducing agent derived from ammonia, urea solution or ammonium carbamate solution may be used. In this embodiment, urea solution is used as a reducing agent derived from ammonia.

[0047] When a urea solution is injected from the reducing agent addition valve 5, the urea solution together with the exhaust gas flow in the second catalyst casing 4. At this time, the urea solution is subjected to exhaust gas heat to be pyrolyzed or hydrolyzed. When the urea solution is pyrolyzed or hydrolyzed, ammonia (NH₃) is formed. The ammonia (NH₃) produced in this way is absorbed or stored by the selective reduction catalyst. The ammonia (NH₃) absorbed or stored by the selective reduction catalyst reacts with nitrogen oxides (ΝΟχ) to form nitrogen (N₂) or water (H₂0). That is, ammonia (NH₃) functions as a reducing agent for nitrogen oxides (ΝΟχ). In this case, if ammonia. (NH₃) is absorbed in a large region of the selective reduction catalyst, nitrogen oxides (ΝΟχ) conversion efficiency at the selective reduction catalyst can be enhanced.

[0048] Incidentally, when the spacing between the first catalyst casing 3 and the second catalyst casing 4 is narrow, in other words, when the spacing between the particulate filter and the selective reduction catalyst is narrow, there is possibility that the reducing agent addition valve 5 is disposed along a radial direction of the exhaust passage 2 (direction perpendicular to an axial direction of the exhaust passage 2). Further, recently, a reducing agent that is injected from the reducing agent addition valve 5 tends to be atomized so as to evenly mix a reducing agent with the exhaust gas.

[0049] However, if the atomized reducing agent is injected from the reducing agent addition valve 5 in the radial direction of the exhaust passage 2, there is possibility that the concentration distribution of the reducing agent in the radial direction when flowing into the selective reduction catalyst becomes uneven. For example, as shown in FIG. 2, a large amount of the reducing agent is supplied to a region near the reducing agent addition valve 5 in a radial direction of the second catalyst casing 4 (region A in FIG. 2) and a very small amount of the reducing agent is supplied to a region away from the reducing agent addition valve 5 (region B in FIG. 2). This is because the atomized reducing agent (fine-particle reducing agent) has a small inertial mass and has low penetration (flying distance) in the exhaust gas.

[0050] As shown in FIG. 2, if the supplied amount of the reducing agent in the radial direction of the selective reduction catalyst becomes uneven, there is possibility that an ammonia slip in which ammonia (NH₃) slips from the selective reduction catalyst in a region of excessive supplied amount of the reducing agent occurs or sufficient ΝΟχ conversion is not achieved in a region of short supplied amount of the reducing agent. That is, there is possibility that the selective reduction catalyst cannot achieve sufficient ΝΟχ conversion efficiency appropriate to the supplied amount of the reducing agent.

[0051] To cope with this concern, it is possible to provide a mixer between the reducing agent addition valve 5 and the selective reduction catalyst for promoting to mix -the reducing agent with the exhaust gas. However, in the case where the reducing agent addition valve 5 is disposed just upstream the selective reduction catalyst as in an example of FIG. 1 , it is difficult to arrange a mixer there.

[0052] In this regard, in the exhaust gas purification system for an internal combustion engine of this embodiment, a coarse-particle reducing agent whose particle diameter is larger than the particle fine-particle reducing agent is injected from the reducing agent addition valve 5 besides the fine -particle reducing agent. In other words, in the exhaust gas purification system for an internal combustion engine of this embodiment, the amount of the coarse -particle reducing agent injected from the reducing agent addition valve 5 is increased.

[0053] Specifically, as shown in FIG. 3A and FIG. 3B, an injection valve that has a tip formed in a hemisphere or a conical shape and is formed with a slit injection hole 5a having a rectangular cross-section at the tip is employed as the reducing agent addition valve 5. Here, length L of the injection hole 5a is adapted to widen the spread of injected mist (spray angle a) with respect to the axis of the reducing agent addition valve 5 as much as possible.

[0054] According to the reducing agent addition valve 5 constructed in this way, as shown in FIG. 4, fine particles of the reducing agent positioned near the center of the injected mist (in the vicinity of an imaginary line passing through the axis of the reducing agent addition valve 5) bind with each other to form a coarse particle immediately after the injection of the reducing agent has been started. That is, the coarse-particle reducing agent is formed near the center of the injected mist while the fine-particle reducing agent is formed near the outer edge of the inj ected mist.

[0055] At this time, since the fine-particle reducing agent has a small inertial mass and travels obliquely with respect to the radial direction of the exhaust passage 2 (axial direction of the reducing agent addition valve 5), the flying distance of the fine-particle reducing agent in the radial direction becomes short. In contrast, since the coarse-particle reducing agent has a large inertial mass and travels generally in parallel with the radial direction of the exhaust passage 2, the flying distance of the coarse-particle reducing agent in the radial direction becomes long.

[0056] Therefore, when a certain time elapses after the injection of the reducing agent has been started, the fine -particle reducing agent remains in a region in the vicinity of the reducing agent addition valve 5 while the coarse-particle reducing agent reaches a region far from the reducing agent addition valve 5 in the radial direction of the exhaust passage 2 as shown in FIG. 5. As a result, the fine-particle reducing agent is supplied to a region in the vicinity of the reducing agent addition valve 5 (region A in FIG. 2) in the radial direction of the second catalyst casing 4 while the coarse-particle reducing agent is supplied to a region away from the reducing agent addition valve 5 (region B in FIG. 2). In other words, the concentration distribution of the reducing agent in the radial direction when flowing into the selective reduction catalyst can be made close to even. Incidentally, the coarse-particle reducing agent is harder to be vaporized and hydrolyzed than the fine-particle reducing agent. However, since the flying distance of the coarse-particle reducing agent is longer than that of the fine-particle reducing agent, the period of exposure of the coarse-particle reducing agent to the exhaust gas heat becomes longer than the period of exposure of the fine-particle reducing agent to the exhaust gas. Accordingly, it is possible to avoid the situation in which the coarse-particle reducing agent flows into the exhaust gas purification catalyst while remaining in a liquid phase.

[0057] As the concentration distribution of the reducing agent in the radial direction when flowing into the selective reduction catalyst comes close to even, occurrences of ammonia slip in the region A can be decreased and ΝΟχ conversion efficiency in the region B can be enhanced. Further, since the reducing agent is allowed to evenly distribute throughout the selective reduction catalyst, the selective reduction catalyst can achieve sufficient ΝΟχ conversion efficiency appropriate to the supplied amount of the reducing agent.

[0058] In this embodiment, an example in which the particulate filter and the selective reduction catalyst are independently housed is described. However, the particulate filter and the selective reduction catalyst may be housed in a single catalyst casing. In this case, the reducing agent addition valve 5 may be installed in a catalyst casing positioned between the particulate filter and the selective reduction catalyst.

[0059] [Second Embodiment]

Next, a second embodiment of the invention is described based on FIG. 6 and FIG. 7. Here, a construction other than the aforementioned first embodiment is described and no description is made on the similar construction.

[0060] In the first embodiment, an example in which the amount of the coarse-particle reducing agent is increased by allowing the reducing agent addition valve 5 having a slit injection hole to inject the reducing agent at a wide angle is described. In the second embodiment, an example in which the amount of the coarse-particle reducing agent is increased by decreasing the valve opening speed of the reducing agent addition valve 5 is described.

. [0061] An injection valve having an injection hole which is opened or closed by moving a needle injects a coarse-particle reducing agent easily during the period of valve opening operation of the reducing agent addition valve 5 (the period while the needle moves from a fully closed position to a fully opened position). Thus, in the related art, injected amount of the coarse-particle reducing agent is decreased by increasing the valve opening speed of the reducing agent addition valve 5 (needle moving speed). In contrast, in the exhaust gas purification system for an internal combustion engine of this embodiment, the amount of the coarse-particle reducing agent is increased by decreasing the valve opening speed of the reducing agent addition valve 5.

[0062] FIG. 6 chronologically shows a relationship between a needle position and the distribution of particle diameter of the reducing agent. In an upper diagram of FIG. 6, a region enclosed by solid lines shows the distribution of particle diameter of the reducing agent when the needle moving speed is slow (corresponds to the needle position shown by solid lines in a lower diagram of FIG. 6), while a region enclosed by dot-and-dash lines shows the distribution of particle diameter of the reducing agent when the needle moving speed is fast (corresponds to the needle position shown by dot-and-dash lines in the lower diagram of FIG. 6).

[0063] In the lower diagram of FIG. 6, the period of valve opening operation Tl when the needle moving speed is fast (the dot-and-dash lines in the lower diagram of FIG. 6) is shorter than the period of valve opening operation T2 when the needle moving speed is slow (the solid lines in the lower diagram of FIG. 6). Accordingly, the amount of a reducing agent with a small particle diameter increases and the amount of a reducing agent with a large particle diameter decreases in Tl . That is, when the needle moving speed is fast, the amount of the coarse-particle reducing agent is smaller than the amount of the fine-particle reducing agent.

[0064] In contrast, the period of valve opening operation T2 when the needle moving speed is slow (the solid lines in the lower diagram of FIG. 6) is longer than the period of valve opening operation Tl when the needle moving speed is fast (the dot-and-dash lines in the lower diagram of FIG. 6). Accordingly, the amount of a reducing agent with the large particle diameter increases and the amount of a reducing agent with the small particle diameter decreases in T2. - That is, when the needle moving speed is slow, the amount of the coarse-particle reducing agent comes close to the amount of the fine-particle reducing agent.

[0065] Therefore, as compared to the case where the needle moving speed is fast, in the case where the needle moving speed is slow, the amount of the coarse-particle reducing agent increases and the amount of the fine-particle reducing agent decreases.

[0066] In this regard, the ECU 6 controls the reducing agent addition valve 5 such that the needle moving speed is set slower m the case where the amount of the coarse-particle reducing agent is increased compared to the case where the amount of the coarse-particle reducing agent is not increased. Specifically, the ECU 6 may gradually increase a drive current applied on the reducing agent addition valve 5 when starting valve opening of the reducing agent addition valve 5. At this time, increasing speed of the drive current when valve opening of the reducing agent addition valve 5 is started is preferably set so that the amount of the coarse-particle reducing agent comes close to the amount of the fine-particle reducing agent. Thus, such the increasing speed of the drive current is preferably acquired in advance by conformance evaluation utilizing experiments. A control section according to the invention is achieved by controlling the valve opening speed of the reducing agent- addition valve 5 with the ECU 6.

[0067] Further, the ECU 6 may decrease the needle moving speed by stopping application of an inrush current (dot-and-dash lines in FIG. 7) or decreasing the inrush current when starting valve opening of the reducing agent addition valve 5 as shown in FIG. 7.

[0068] By controlling the drive current of the reducing agent addition valve 5 in the aforementioned method, the amount of the fine-particle reducing agent and the amount of the coarse-particle reducing agent injected from the reducing agent addition valve 5 can be generally equalized. As a result, it is possible to uniform the concentration distribution of the reducing agent in the radial direction when flowing into the selective reduction catalyst. Accordingly, it is possible to evenly distribute the reducing agent throughout the selective reduction catalyst. [0069] Any type of reducing agent addition valve may be used as the reducing agent addition valve 5 according to this embodiment as long as it has an injection hole which is opened or closed by moving a needle. However, a reducing agent addition valve having a slit injection hole as described in the first embodiment may be used to decrease the valve opening speed. In this case, it is likely that the fine-particle reducing agent surely remains in the vicinity of the reducing agent addition valve 5 while the coarse-particle reducing agent surely reaches far from the reducing agent addition valve 5.

[0070] [Third Embodiment] .

Next, a third embodiment of the invention is described based on FIG. 8. Here, a construction other than the aforementioned second embodiment is described and no description is made on the similar construction.

[0071] In the second embodiment, an example in which the amount of the coarse-particle reducing agent is increased by decreasing the valve opening speed of the reducing agent addition valve 5 is described. In the third embodiment, an injection period of the reducing agent each time (the period while the reducing agent is continuously added by the reducing agent addition valve 5) of the reducing agent addition valve 5 is shortened.

[0072] The diameter of a reducing agent particle injected from the reducing agent addition valve 5 tends to become larger during the period of valve opening operation of the reducing agent addition valve 5. For example, as shown in FIG. 8, the amount of the coarse-particle reducing agent injected from the reducing agent addition valve 5 in the injection period of the reducing agent each time tends to be increased during the period of valve opening operation T. Therefore, when the injection period of the reducing agent each time is shortened, the proportion of the period of valve opening operation to the injection period of the reducing agent becomes large. As a result, the amount of the coarse-particle reducing agent injected from the reducing agent addition valve 5 in the injection period of the reducing agent each time can be increased.

[0073] Thus, the ECU 6 shortens the injection period of the reducing agent each time when the reducing agent is supplied to the selective reduction- catalyst. More specifically, the ECU 6 shortens the period while the drive current is continuously applied to the reducing agent addition valve 5. In this regard, the length of application period of the drive current is preferably set so that the amount of the coarse-particle reducing agent and the amount of the fine-particle reducing agent injected from the reducing agent addition valve 5 in the injection period of the reducing agent each time are equalized. Thus, such the application period of the drive current is preferably acquired in advance by conformance evaluation utilizing experiments.

[0074] By the way, when the injection period of the reducing agent each time is shortened, the amount of the reducing agent supplied to the selective reduction catalyst in each injection period of the reducing agent is decreased. This may cause the case where the amount of the reducing agent supplied to the selective reduction catalyst is smaller than the target supplied amount. To cope with this concern, the ECU 6 may control the reducing agent addition valve 5 to inject the target supplied amount of the reducing agent in multiple times in the case where the amount of the reducing agent that can be supplied to the selective reduction catalyst in the injection period of the reducing agent each time is smaller than the target supplied amount. In this case, it is possible to shorten the injection period of the reducing agent each time and at the same time to supply the target supplied amount of the reducing agent to the selective reduction catalyst.

[0075] Further, when the target supplied amount of the reducing agent exceeds the predetermined amount, the ECU 6 may control the reducing agent addition valve 5 to continuously inject the target supplied amount of the reducing agent without shortening the injection period of the reducing agent. In other words, in the case where the target supplied amount of the reducing agent exceeds the predetermined amount, the ECU 6 may control the reducing agent addition valve 5 to continuously inject the target supplied amount of the reducing agent by increasing the injection period of the reducing agent each time.

[0076] At this time, if the injection period of the reducing agent is lengthened, particles of the fine-particle reducing agent bind with each other to form a reducing agent with large particle diameter from the midstream of the injection period of the reducing - agent. Therefore, when the injection period of the reducing agent each time is lengthened, the amount of the coarse-particle reducing agent can be increased. At this time, the aforementioned predetermined amount is a minimum target supplied amount for which the injection period of the reducing agent is adjusted to the extent in which the amount of the coarse-particle reducing agent and the amount of the fine-particle reducing agent injected from the reducing agent addition valve are equalized in the injection period of the reducing agent each time. .

[0077] According to the embodiment as described above, the similar effects to the aforementioned second embodiment can be obtained. Any type of reducing agent addition valve may be used as the reducing agent addition valve 5 according to this embodiment as long as it has an injection hole which is opened or closed by moving a needle. However, a reducing agent addition valve having a slit injection hole as described in the first embodiment may be used to shorten the injection period of the reducing agent each time. In this case, it is likely that the fine-particle reducing agent surely remains in the vicinity of the reducing agent addition valve 5 while the coarse-particle reducing agent surely reaches far from the reducing agent addition valve 5.

[0078] [Fourth Embodiment]

Next, a fourth embodiment of the exhaust gas purification system for an internal combustion engine according to the invention is described based on FIG. 9. Here, a construction other than the aforementioned second embodiment is described and no description is made on the similar construction.

[0079] In the second embodiment, an example in which the amount of the coarse-particle reducing agent is increased by decreasing the valve opening speed of the reducing agent addition valve 5 is described. In the fourth embodiment, injection pressure (discharge pressure of the pump 50) of the reducing agent addition valve 5 is decreased.

[0080] As shown in FIG. 9, the diameter of a reducing agent particle injected from the reducing agent addition valve 5 tends to become larger when the injection pressure of the reducing agent addition valve 5 is low as compared to when the injection pressure of the reducing agent addition valve 5 is high. Therefore, the ECU 6 controls to decrease the injection pressure of the reducing agent addition valve 5 by decreasing the discharge pressure of the pump 50 when the reducing agent is injected from the reducing agent addition valve 5. The discharge pressure of the pump 50 in this case is preferably set so that the amount of the coarse-particle reducing agent and the amount of the fine-particle reducing agent injected from the reducing agent addition valve 5 are equalized. Such the discharge pressure may be acquired in advance by conformance evaluation utilizing experiments.

[0081] According to the embodiment as described above, the similar effects to the aforementioned second embodiment can be obtained. Any type of reducing agent addition valve may be used as the reducing agent addition valve 5 according to this embodiment as long as it has an injection hole which is opened or closed by moving a needle. However, a reducing agent addition valve having a slit injection hole as described in the first embodiment may be used to decrease the injection pressure of the reducing agent addition valve 5. In this case, it is likely that the fine-particle reducing agent surely remains in the vicinity of the reducing agent addition valve 5 while the coarse-particle reducing agent surely reaches far from the reducing agent addition valve 5.

[0082] [Fifth Embodiment].

Next, a fifth embodiment of the exhaust gas purification- system for an internal combustion engine according to the invention is described based on FIG. 10 through FIG. 19. Here, a construction other than the aforementioned first embodiment is described and no description is made on the similar construction.

[0083] The difference between the aforementioned first embodiment and the fifth embodiment is that an impinging plate is disposed in the exhaust passage 2 so as to interfere not with the coarse-particle reducing agent but with the fine-particle reducing agent among the reducing agents injected from the reducing agent addition valve 5. [0084] FIG. 10 shows a construction of the exhaust passage in the vicinity of the reducing agent addition valve. In FIG. 10, identical components are given identical reference numerals and symbols in the aforementioned first embodiment.

[0085] In the exhaust passage 2 between the first catalyst casing 3 and the second catalyst casing 4, a plate-like impinging plate 7 that extends in the axial direction of the exhaust passage 2 is provided. The impinging plate 7 is arranged so that its surface faces the reducing agent addition valve 5. At this time, the position of the impinging plate 7 in the radial direction of the exhaust passage 2 is set near the center of the exhaust passage 2. The position of the impinging plate 7 in the axial direction of the exhaust passage 2 is displaced downstream with respect to the reducing agent addition valve 5.

[0086] At this time, the fine-particle reducing agent injected from the reducing agent addition valve 5 has small penetration in the exhaust gas and therefore travels in the radial direction of the exhaust passage 2 while flowing downstream. Accordingly, the fine-particle reducing agent impinges on the impinging plate 7 as shown in FIG. 11 by a solid arrow and remains in the vicinity of the reducing agent addition valve 5. In contrast, the coarse-particle reducing agent injected from the reducing agent addition valve 5 has large penetration and therefore travels generally straight in a direction to which the injection hole of the reducing agent addition valve 5 points. Accordingly, the coarse-particle reducing agent does not impinge on the impinging plate 7 and reaches far from the reducing agent addition valve 5 as shown in FIG. 11 by a dot-and-dash arrow.

[0087] Thus, according to the aforementioned impinging plate 7, among the reducing agents injected from the reducing agent addition valve 5, the fine-particle reducing agent can be kept to surely remain in the vicinity of the reducing agent addition valve 5 while the coarse-particle reducing agent can be allowed to surely reach far from the reducing agent addition valve 5. As a result, the fine-particle reducing agent is supplied to a region (region A in FIG. 2 described above) near the reducing agent addition valve 5 in the radial direction of the second catalyst casing 4 and the coarse-particle reducing agent is supplied to a region (region B in FIG. 2 described above) away from the reducing agent addition valve 5. In other words, the concentration distribution of the reducing agent in the radial direction when flowing into the selective reduction catalyst can be made close to even.

[0088] It would be understood that the construction and arrangement of the impinging plate 7 are not limited to the examples shown in FIG. 10 and FIG. 11. Any construction and arrangement may be used as long as they include an impinging plate on which the fine-particle reducing agent impinges and through which the coarse-particle reducing agent passes.

[0089] For example, as shown in FIG. 12, an impinging plate 9 provided with a plurality of through-holes 8 may be arranged at a position facing the reducing agent addition valve 5. In this case, the through-holes 8 shall be arranged in a flight path of the coarse-particle reducing agent injected from the reducing agent addition valve 5. According to such the impinging plate 9, the fine-particle reducing agent impinges on the impinging plate 9 while the coarse-particle reducing agent passes through the through-holes 8. As a result, the fine-particle reducing agent remains in the vicinity of the reducing agent addition valve 5 in the radial direction of the exhaust passage 2 while the coarse-particle reducing agent reaches far from the reducing agent addition valve 5.

[0090] When the diameter of the exhaust passage 2 is large, two pieces of impinging plate 10, 11 may be provided in FIG. 13. In this case, among the two impinging plates 10, 11 , the impinging plate 10 which is near the reducing agent addition valve 5 may be provided with through-holes 100 through which the coarse-particle reducing agent passes. Among the two impinging plates 10, 11, the impinging plate 11 which is away the reducing agent addition valve 5 may be provided with through-holes 110 through which only a part of the coarse-particle reducing agent having passed through the through-holes 100 of the impinging plate 10 passes. With these two impinging plates 10, 11 , the fine-particle reducing agent can be kept in a region between the reducing agent addition valve 5 and the impinging plate 10 and a part of the coarse-particle reducing agent can be kept in a region between the impinging plate 10 and the impinging plate 11. As a result, the concentration distribution of the reducing agent in the radial direction of the exhaust passage 2 can be even. It would be understood that the impinging plate 11 corresponds to a dispersion plate according to the invention. -

[0091] When two pieces of impinging plate are provided in the exhaust passage 2, either one of the impinging plates may have no through-hole and may be set shorter in length in the axial direction of the exhaust passage 2 than the other one. For example, as shown in FIG. 14, among the two impinging plates 10, 1 1 , the impinging plate 11 which is away from the reducing agent addition valve 5 may have no through-hole and a shorter length than the impinging plate 10. Also, as shown in FIG. 15, among the two impinging plates 10, 11 , the impinging plate 10 which is near the reducing agent addition valve 5 may have no through-hole and a shorter length than the impinging plate 1 1.

[0092] In the aforementioned FIG. 13 through FIG. 15, examples having two impinging plates are described. However, the number of the impinging plate is not limited to two. Three or more impinging plates may be provided in the exhaust passage 2 as long as they contribute to uniform the concentration distribution of the reducing agent in the radial direction of the exhaust passage 2.

[0093] When the reducing agent addition valve 5 is installed in the first catalyst casing 3, the tip of the reducing agent addition valve 5 may be inclined upstream at a region upstream a particulate filter 30 as shown in FIG. 16. Further, in the first catalyst casing 3 between the particulate filter 30 and the reducing -agent addition valve 5, a disk-like impinging plate 12 which has a diameter generally identical to the inner diameter of the first catalyst casing 3 and a number of through-holes 120 may be provided. With such a construction, since the flying distance of the reducing agent injected from the reducing agent addition valve 5 to flow into the selective reduction catalyst becomes long, hydrolysis of the reducing agent (especially hydrolysis of the coarse-particle reducing agent) can be promoted.

[0094] When the reducing agent addition valve 5 is installed in the second catalyst casing 4, the tip of the reducing agent addition valve 5 may be inclined upstream at a region upstream a selective reduction catalyst 40 as shown in FIG. 17. Further, in the second catalyst casing 4 in a region upstream the reducing agent addition valve 5, a disk-like impinging plate 13 which has a diameter generally identical to the outer diameter of the first catalyst casing 4 and a number of through-holes 130 may be provided. With such a construction, even if the reducing agent addition valve 5 is arranged just upstream the selective reduction catalyst 40, the flying distance of the reducing agent injected from the reducing agent addition valve 5 to flow into the selective reduction catalyst 40 can be made long. As a result, hydrolyzation of the reducing agent (especially hydrolyzation of the coarse-particle reducing agent) can be promoted.

[0095] When the reducing agent is injected into the second catalyst casing 4 as shown in the aforementioned FIG. 17 or when the particulate filter 30 and the selective reduction catalyst 40 are housed in a single catalyst casing 400 as shown in FIG. 18, a part of the reducing agent (coarse-particle reducing agent, for example) injected from the reducing agent addition valve 5 may adhere to an inner wall of catalyst casing 4, 400. Also, the particulate filter 30 and the selective reduction catalyst 40 are retained in the catalyst casing 4, 400 via a retaining member 401 such as an alumina mat and therefore have a smaller diameter than the inner diameter of the catalyst casing 4, 400. As a result, a reducing agent adhered to an inner wall of the catalyst casing 4, 400 hardly flows into the selective reduction catalyst 40.

(0096] Therefore, when the reducing agent addition valve 5 is installed in the catalyst casing 4, 400 in which the selective reduction catalyst 40 is housed, an adhesion prevention plate for preventing the reducing agent injected from the reducing agent addition valve 5 from adhering to an inner wall of the catalyst casing 4, 400 may be arranged in the catalyst casing 4, 400. For example, as shown in FIG. 19, a tubular adhesion prevention plate 14 having an outer diameter smaller than the inner diameter of the catalyst casing 4, 400 may be installed in the catalyst casing 4, 400. The adhesion prevention plate 14 may preferably be formed so that the inner diameter thereof is within the outer diameter of the selective reduction catalyst 40. In this case, it is possible to prevent the coarse-particle reducing agent from adhering to an inner wall of the catalyst casing 4, 400. Therefore, substantially all the reducing agent injected from the reducing

agent addition valve 5 can be flown into the selective reduction catalyst 40.

Claims

1. An exhaust gas purification system for an internal combustion engine, comprising: an exhaust gas purification catalyst disposed in an exhaust passage of the internal combustion engine; and

a reducing agent addition valve that is disposed upstream the exhaust gas purification catalyst in the exhaust passage and injects a reducing agent in a direction across an exhaust gas flow,

wherein the reducing agent addition valve injects a part of the reducing agent to the exhaust passage, the part of the reducing agent being made to include particles coarser than particles included in rest of the reducing agent.

2. The exhaust gas purification system according to claim 1 , wherein the reducing agent addition valve injects the reducing agent at a wide angle in a radial direction of the exhaust passage.

3. The exhaust gas purification system according to claim 1 or 2, further comprising: a control section that decreases the valve opening speed of the reducing agent addition valve in the case where a part of the reducing agent injected from the reducing agent addition valve is made to have particles coarser than those in the rest of the reducing agent compared with the case where no coarse particle is produced.

4. The exhaust gas purification system according to claim 1 or 2, further comprising: a control section that shortens the injection period of the reducing agent each time of the reducing agent addition valve in the case where a part of the reducing agent injected from the reducing agent addition valve is made to have particles coarser than those in the rest of the reducing agent compared with the case where no coarse particle is produced.

5. The exhaust gas purification system according to claim 1 or 2, further comprising: a control section that lengthens the injection period of the reducing agent each time in the case where a part of the reducing agent injected from the reducing agent addition valve is made to have particles coarser than those in the rest of the reducing agent compared with the case where no coarse particle is produced when a target supplied amount that is a target amount of the reducing agent to be supplied through the reducing agent addition valve exceeds a predetermined amount.

6. The exhaust gas purification system according to claim 1 or 2, further comprising: a control section that decreases injection pressure of the reducing agent addition valve in the case where a part of the reducing agent injected from the reducing agent addition valve is made to have particles coarser than those in the rest of the reducing agent compared with the case where no coarse particle is produced.

7. The exhaust gas purification system according to any one of claims 1 to 6, further comprising:

an impinging plate that is disposed in a flight path of the reducing agent injected from the reducing agent addition valve, on which a fine-particle reducing agent injected from the reducing agent addition valve impinges, and through which a coarse-particle reducing agent passes.

8. The exhaust gas purification system according to claim 7, further comprising:

a dispersion plate on which the coarse-particle reducing agent having passed through the impinging plate impinges.

9. An exhaust gas purification method for an internal combustion engine includes an exhaust gas purification catalyst disposed in an exhaust passage of the internal combustion engine, and a reducing agent addition valve that is disposed upstream the exhaust gas purification catalyst in the exhaust passage and injects a reducing agent in a direction across an exhaust gas flow, the method comprising: injecting a part of the reducing agent to the exhaust passage, the part of the reducing agent being made to include particles coarser than particles included in rest of the reducing agent.