JP2020029777A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

To evaporate a droplet of a reductant supplied into an exhaust gas which flows in an exhaust emission control catalyst before flowing in the exhaust emission control catalyst as far as possible.SOLUTION: An exhaust emission control device 40 of an internal combustion engine 1 for cleaning an exhaust gas of the internal combustion engine comprises: an exhaust emission control catalyst 46 arranged in an exhaust passage of the internal combustion engine; an electric heating member 45 arranged at an upstream side of the exhaust emission purification catalyst in an exhaust emission flow direction, and having a honeycomb body which is at least partially heated by being supplied with electric power; and a reductant supply device 44 for supplying a liquid reductant toward the electric heating member. The electric heating member is constituted so that a surface of a partition wall constituting the honeycomb body has an irregular shape. The irregular shape of the partition wall is formed so that at least a part of a droplet of the reductant is dispersed by colliding with a heated wall face of the electric heating member, and at least a part of the dispersed droplet repeatedly collides with the wall face which defines recesses.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine.

  2. Description of the Related Art Conventionally, exhaust gas purification of an internal combustion engine includes a NOx selective reduction catalyst that purifies NOx in exhaust gas using ammonia as a reducing agent, and a reducing agent supply device that supplies liquid urea to the NOx selective reducing catalyst as a reducing agent. An apparatus is known (for example, Patent Document 1). In particular, in the exhaust gas purification device described in Patent Document 1, a mixer is provided between a reducing agent supply device and a NOx selective reduction catalyst in order to sufficiently mix liquid urea and exhaust gas to increase NOx purification efficiency. It has been proposed to provide

  On the other hand, in order to promote the evaporation of the fuel droplets, the heating surface of the electric heating member is raised to the Leidenfrost temperature or higher, and an electric field is generated around the heating surface to reduce the force in the direction toward the heating surface. It has been proposed to act on droplets (for example, Patent Document 2). Thus, even if the heating surface is raised to a temperature equal to or higher than the Leidenfrost temperature, it is possible to suppress the liquid droplets from rising from the heating surface, and it is possible to increase the evaporation rate.

JP 2018-044528 A JP-A-8-200168

  An electric heating member is used for evaporating a liquid reducing agent such as urea or fuel supplied to the exhaust gas on the upstream side in the exhaust gas flow direction of the exhaust purification catalyst such as the NOx selective reduction catalyst and supplying the same to the exhaust purification catalyst. Can be considered.

  However, when an electric field is generated around the heating surface as described in Patent Document 2 when using the electric heating member, when a relatively large droplet of the reducing agent comes into contact with the heating surface, the droplet contacts the droplet. In the region, the heated surface is locally cooled by the latent heat of vaporization. As a result, in this region, the droplet cannot be temporarily evaporated, and proper evaporation of the droplet is prevented.

  The present invention has been made in view of the above problems, and an object of the present invention is to evaporate droplets of a reducing agent supplied in exhaust gas flowing into an exhaust purification catalyst as much as possible before flowing into the exhaust purification catalyst. An object of the present invention is to provide an exhaust gas purification catalyst for an internal combustion engine that can be made to work.

  The present invention has been made to solve the above problems, and the gist thereof is as follows.

  (1) An exhaust gas purification device for an internal combustion engine that purifies exhaust gas of an internal combustion engine, wherein an exhaust purification catalyst provided in an exhaust passage of the internal combustion engine and an exhaust gas upstream of the exhaust purification catalyst in an exhaust flow direction. An electric heating member provided with a honeycomb body that is provided and is at least partially heated by supplying electric power; and a reducing agent supply device that supplies a liquid reducing agent toward the electric heating member; The heating member is configured such that the surface of the partition wall constituting the honeycomb body has an uneven shape, and the uneven shape of the partition wall is such that at least a part of the droplet of the reducing agent is a heated wall surface of the electric heating member. An exhaust gas purification device for an internal combustion engine, wherein the exhaust gas purification device is formed such that at least a part of the dispersed droplets repeatedly collides with a wall surface that defines a concave portion.

  According to the present invention, there is provided an exhaust gas purification catalyst for an internal combustion engine which can evaporate droplets of a reducing agent supplied in exhaust gas flowing into the exhaust gas purification catalyst as much as possible before flowing into the exhaust gas purification catalyst. .

FIG. 1 is a schematic configuration diagram of the internal combustion engine. FIG. 2 is a sectional view schematically showing the vicinity of a casing of the exhaust gas purification device according to the first embodiment. FIG. 3 is a sectional view schematically showing the surface of the partition wall of the honeycomb body. FIG. 4 is a conceptual diagram showing a state where a large droplet collides with a wall surface defining a concave portion. FIG. 5 is a conceptual diagram showing the movement of the atomized droplet in the concave portion. FIG. 6 is a diagram for explaining the recess angle α. FIG. 7 is a diagram showing the relationship between the angle of the recess and the time required for the aqueous urea solution to pass through the honeycomb body. FIG. 8 is a cross-sectional view schematically showing the vicinity of a casing of the exhaust gas purification device according to the second embodiment. FIG. 9 is a conceptual diagram illustrating a state where a large droplet collides with the surface of the flat partition wall 60b of the heating honeycomb body 60. FIG. 10 is a conceptual diagram showing the movement of the atomized droplet in the concave portion.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, similar components are denoted by the same reference numerals.

<First embodiment>
≫Explanation of the entire internal combustion engine≫
First, with reference to FIG. 1, a configuration of an internal combustion engine 1 equipped with the exhaust gas purification device according to the first embodiment will be described. FIG. 1 is a schematic configuration diagram of the internal combustion engine 1. As shown in FIG. 1, the internal combustion engine 1 includes an engine main body 10, a fuel supply device 20, an intake system 30, an exhaust gas purification device 40, and a control device 50.

  The engine body 10 includes a cylinder block in which a plurality of cylinders 11 are formed, a cylinder head in which intake ports and exhaust ports are formed, and a crankcase. A piston is arranged in each cylinder 11, and each cylinder 11 communicates with an intake port and an exhaust port.

  The fuel supply device 20 includes a fuel injection valve 21, a delivery pipe 22, a fuel supply pipe 23, a fuel pump 24, and a fuel tank 25. The fuel injection valve 21 is arranged on the cylinder head so as to directly inject fuel into each cylinder 11. The fuel pumped by the fuel pump 24 is supplied to the delivery pipe 22 through the fuel supply pipe 23 and is injected from the fuel injection valve 21 into each cylinder 11.

  The intake system 30 includes an intake manifold 31, an intake pipe 32, an air cleaner 33, a compressor 34 of the supercharger 5, an intercooler 35, and a throttle valve 36. An intake port of each cylinder 11 communicates with an air cleaner 33 via an intake manifold 31 and an intake pipe 32. A compressor 34 of the supercharger 5 for compressing and discharging the intake air and an intercooler 35 for cooling the air compressed by the compressor 34 are provided in the intake pipe 32. The throttle valve 36 is driven to open and close by a throttle valve drive actuator 37.

  The exhaust gas purification device 40 includes an exhaust manifold 41, an exhaust pipe 42, a turbine 43 of the supercharger 5, a reducing agent supply device 44, and a casing 47 containing an electric heating member 45 and a NOx selective reduction catalyst 46. An exhaust port of each cylinder 11 communicates with an electric heating member 45 and a NOx selective reduction catalyst 46 via an exhaust manifold 41 and an exhaust pipe 42. In the exhaust pipe 42, a turbine 43 of the supercharger 5 driven to rotate by the energy of the exhaust gas is provided. The reducing agent supply device 44 supplies a liquid reducing agent toward the electric heating member 45 built in the casing 47. The electric heating member 45 is provided with a power control device 48 for controlling electric power supplied to the electric heating member 45. The exhaust manifold 41, the exhaust pipe 42, and the casing 47 form an exhaust passage through which exhaust gas discharged from the engine body 10 flows.

  The exhaust purification device 40 may include an exhaust purification device different from the electric heating member 45 and the NOx selective reduction catalyst 46, such as a three-way catalyst, in addition to the electric heating member 45 and the NOx selective reduction catalyst 46.

  The control device 50 includes an electronic control unit (ECU) 51 and various sensors. Examples of the various sensors include a flow rate sensor 52 for detecting the flow rate of the intake gas flowing through the intake pipe 32 and a temperature sensor 53 for detecting the temperature of the electric heating member 45. These sensors are connected to the ECU 51. The various sensors also include a load sensor 55 that detects the load of the internal combustion engine 1 and a crank angle sensor 56 that is used to detect the engine speed. These sensors are also connected to the ECU 51. The ECU 51 is connected to each actuator that controls the operation of the internal combustion engine 1. In the example shown in FIG. 1, the ECU 51 is connected to the fuel injection valve 21, the fuel pump 24, the throttle valve drive actuator 37, and the power control device 48, and controls these actuators.

具体 Specific configuration of exhaust gas purification device≫
Next, with reference to FIG. 2, an exhaust gas purification device 40 according to the present embodiment will be described. FIG. 2 is a sectional view schematically showing the vicinity of the casing 47 of the exhaust gas purification device 40. FIG. 2 shows an exhaust pipe 42, a reducing agent supply device 44, and a casing 47 containing an electric heating member 45 and a NOx selective reduction catalyst 46.

  The reducing agent supply device 44 is attached to the exhaust pipe 42 on the upstream side of the casing 47 and supplies a liquid reducing agent toward the electric heating member 45. As a result, the reducing agent injected from the reducing agent supply device 44 is directly supplied to the upstream end surface of the electric heating member 45. In the present embodiment, the liquid reducing agent is an aqueous urea solution. Note that the reducing agent supply device 44 may have any configuration as long as the reducing agent can be supplied to the upstream end surface of the electric heating member 45. For example, in the exhaust flow direction (the direction indicated by the arrow in FIG. 2). It may be attached to the casing 47 on the upstream side of the electric heating member 45.

The NOx selective reduction catalyst 46 is a catalyst that selectively reduces NOx in exhaust gas, and reduces and purifies NOx by absorbing ammonia and reacting the NOx in the inflowing exhaust gas with ammonia. As the NOx selective reduction catalyst 46, for example, a catalyst V ₂ O ₅ / TiO ₂ (vanadium-titania catalyst) in which titania is supported on a carrier and vanadium oxide is supported on the carrier, or a zeolite is used as a carrier and copper is Used is Cu / ZSM5 (copper zeolite catalyst).

In thus constructed has been NOx selective reduction catalyst 46, using ammonia NH _3, to reduce and purify NOx in the exhaust gas containing excess oxygen. NO in the exhaust gas is reduced by, for example, a reaction represented by the following formula (1), and NO ₂ in the exhaust gas is reduced by, for example, a reaction represented by the following formula (2).
4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O (1)
8NH ₃ + 6NO ₂ → 7N ₂ + 12H ₂ O (2)

Further, the NOx selective reduction catalyst 46 has an adsorption ability to adsorb ammonia. In addition, the urea aqueous solution supplied from the reducing agent supply device 44 on the upstream side of the NOx selective reduction catalyst 46 is hydrolyzed by a reaction represented by the following formula (3) to produce ammonia. The ammonia thus generated is adsorbed on the NOx selective reduction catalyst 46. The adsorbed ammonia reduces and purifies NOx in the exhaust gas as described above.
(NH ₂ ) 2CO + H ₂ O → 2NH ₃ + CO ₂ (3)
When ammonia is supplied from the reducing agent supply device 44 instead of the urea aqueous solution, the ammonia is directly adsorbed on the NOx selective reduction catalyst 46.

  The electric heating member 45 is provided in the exhaust passage, downstream of the reducing agent supply device 44 and upstream of the NOx selective reduction catalyst 46 in the flow direction of the exhaust gas. The electric heating member 45 includes a honeycomb body 60 formed of a conductor such as a metal into a honeycomb shape. Specifically, the honeycomb body 60 of the electric heating member 45 includes a plurality of partition walls 60b that define a plurality of cells 60a. Each cell 60a extends parallel to each other in the axial direction of the electric heating member 45, that is, in the axial direction of the casing 47 (therefore, in the flow direction of the exhaust gas flowing through the casing 47), and has a polygonal cross section. It is formed to have.

  The electric heating member 45 includes a center electrode (not shown) at the center in a cross section perpendicular to the axial direction, and a cylindrical outer peripheral electrode (not shown) arranged to cover the outer periphery of the electric heating member 45. ). Both the center electrode and the outer peripheral electrode are electrically connected to the power control device 48. When a voltage is applied between the center electrode and the outer peripheral electrode by the power control device 48, the honeycomb body 60 of the electric heating member 45 is heated. That is, it can be said that the honeycomb body of the electric heating member 45 is a member that is entirely heated when electric power is supplied.

  FIG. 3 is a cross-sectional view schematically showing the surface of the partition wall 60b of the honeycomb body 60. As can be seen from FIG. 3, the surface of the partition wall 60b has an uneven shape. Therefore, many concave portions 61 are formed on the surface of the partition wall 60b. The concave portion 61 is formed, for example, so that the average diameter of the opening is about 20 μm and the average depth is about 100 μm.

≫Phenomenon that occurs in the recess≪
Next, a phenomenon that occurs in the concave portion 61 of the partition wall 60b of the electric heating member 45 will be described with reference to FIGS. FIG. 4 is a conceptual diagram showing a state in which a large droplet collides with a wall surface defining the concave portion 61, and FIG. 5 is a conceptual diagram showing a movement of the atomized droplet in the concave portion 61. .

  As described above, the reducing agent supply device 44 is provided upstream of the electric heating member 45 in the exhaust gas flow direction. The reducing agent supply device 44 supplies the urea aqueous solution to the exhaust gas toward the electric heating member 45. The aqueous urea solution supplied to the exhaust gas flows into the electric heating member 45 in a state of being dispersed in the form of droplets, and enters each cell 60 a of the honeycomb body 60.

  When a droplet of the urea aqueous solution enters each cell 60a of the honeycomb body 60, the droplet D passes over the partition wall 60b as shown in FIG. Collides with a wall surface 62 defining a concave portion 61. When the droplet D collides with the wall surface 62 defining the concave portion 61, the droplet D is crushed so as to spread on the wall surface 62 as shown in FIG. 4B.

  Here, it is assumed that the honeycomb body 60 is heated and the surface temperature of the partition wall 60b is higher than a temperature at which the Leidenfrost phenomenon starts (hereinafter, referred to as “Leidenfrost temperature”). In this case, a portion of the droplet D spread on the wall surface 62 and in contact with the wall surface 62 is vaporized, and a thin film of vapor is formed between the droplet D and the wall surface 62 as shown in FIG. The droplet D rises from the wall surface 62. As the droplet D rises from the wall surface 62, the large droplet D is atomized into many small droplets as shown in FIG. That is, in the present embodiment, at least a part of the droplet of the urea aqueous solution that has entered the electric heating member 45 is dispersed by colliding with the heated wall surface 62 of the electric heating member.

  The atomized small droplets rebound on the wall surface 62 in accordance with the collision angle of the large droplet D shown in FIG. Therefore, as shown by the arrow in FIG. 4D, the atomized small liquid droplets generally travel in a direction away from the wall surface 62 that has collided toward the depth of the concave portion 61. The droplet D that has been atomized and rebounded on the wall surface 62 in this way collides with the opposite wall surface that defines the concave portion 61, as shown in FIG. After that, in the recess 61, the body advances toward the depth of the recess 61 while repeatedly bouncing between the facing wall surfaces. That is, according to the present embodiment, at least a portion of the dispersed droplet repeatedly collides with the wall surface defining the concave portion 61 a plurality of times.

  In other words, in the present embodiment, in the present embodiment, the unevenness of the partition wall 60b is dispersed by the fact that at least a part of the droplet of the urea aqueous solution collides with the heated wall surface of the electric heating member 45. It can be said that at least a part of the droplet is formed so as to repeatedly collide with the wall surface defining the concave portion 61. As described above, in the concave portion 61 formed so that the average diameter of the opening is about 20 μm and the average depth is about 100 μm, the droplets are dispersed as described above, and a part of the droplets repeatedly strikes the wall surface. become.

  In this way, the liquid droplets that have entered the concave portion 61 repeatedly collide, and may be atomized at the time of the collision. For this reason, the residence time of the droplet in the concave portion 61 becomes longer, and the droplet becomes smaller in the concave portion 61, so that the droplet is easily evaporated. In addition, since the droplets are reduced and dispersed in the concave portion 61, the locations where the droplets evaporate are dispersed, and local cooling of a part of the partition wall 60b is suppressed.

  Here, the relationship between the angle α of the wall surface defining the recess 61 with respect to the surface of the partition wall 60b and the residence time of the droplet will be described with reference to FIGS. FIG. 6 is a diagram for explaining the concave portion angle α, and FIG. 7 is a diagram showing a relationship between the concave portion angle α and the time required for the urea aqueous solution to pass through the honeycomb body 60.

As shown in FIG. 6, in the following description, the angle of the wall surface defining the recess 61 with respect to the surface of the partition wall 60b is referred to as a recess angle α. When the recess angle α is defined in this manner, as shown in FIG. 7, if the recess angle α is less than α ₁ (for example, 45 °), the residence time of the droplet in the recess 61 is short, and the honeycomb body The time it takes to pass through 60 is relatively short. On the other hand, when the recess angle alpha becomes ₁ or more alpha, time taken to pass through the honeycomb body 60 with in the recess angle alpha increases abruptly becomes longer. Therefore, if it is concave angle alpha is alpha ₁ or more, it can be seen that easily evaporate droplets of the aqueous urea solution. For this reason, in the present embodiment, it is preferable that the recess 61 is formed such that the recess angle α is equal to or larger than a predetermined angle.

≪Modified example≫
In the above embodiment, the NOx selective reduction catalyst is used as an exhaust purification catalyst that purifies NOx in exhaust gas. However, as long as NOx in the exhaust gas can be purified, an exhaust purification catalyst other than the NOx selective reduction catalyst may be used. Examples of such an exhaust purification catalyst include a three-way catalyst, a NOx storage reduction catalyst, and the like.

  Further, in the above embodiment, an aqueous urea solution is used as the reducing agent. However, other reducing agents may be used as long as NOx can be reduced. Examples of such a reducing agent include ammonia and fuel (hydrocarbon).

  In addition, in the above embodiment, the electric heating member 45 includes the heating honeycomb body 60 that functions as a heating member. However, the electric heating member 45 may be formed of a heating honeycomb body 60 and another holding honeycomb body provided for holding the honeycomb structure of the heating honeycomb body 60. In this case, the holding honeycomb body is configured so as not to be supplied with electric power, and thus not to generate heat.

<Second embodiment>
Next, an exhaust emission control device according to a second embodiment will be described with reference to FIGS. The configuration of the exhaust gas purification device according to the second embodiment is basically the same as the configuration of the exhaust gas purification device according to the first embodiment. Hereinafter, a description will be given focusing on a portion different from the exhaust gas purification device according to the first embodiment.

  FIG. 8 is a cross-sectional view schematically showing the vicinity of a casing 47 of the exhaust emission control device according to the second embodiment. As shown in FIG. 8, the electric heating member 45 ′ of the present embodiment holds a heating honeycomb body 60 formed of a conductor such as a metal in a honeycomb shape, and a honeycomb structure of the heating honeycomb body 60. And a holding honeycomb body 65 provided in the main body. The holding honeycomb body 65 is formed of, for example, a metal. Similarly to the heating honeycomb body 60, the holding honeycomb body 65 includes a plurality of partition walls 65b defining a plurality of cells 65a. Each cell 65a extends parallel to each other in the axial direction of the electric heating member 45, that is, in the axial direction of the casing 47 (therefore, in the flow direction of the exhaust gas flowing through the casing 47), and has a polygonal cross section. It is formed to have. In particular, the holding honeycomb body 65 has the same honeycomb structure as the heating honeycomb body 60 (that is, the size and the position of the cells and the partition walls are the same).

  As shown in FIG. 8, the holding honeycomb body 65 is disposed downstream of the heating honeycomb body 60 in the exhaust gas flow direction. Part of the partition wall 65b of the holding honeycomb body 65 is connected to a corresponding part of the partition wall 60b of the heating honeycomb body 60 by a holding member 66. The honeycomb structure of the heating honeycomb body 60 is held by the holding honeycomb body 65 via the holding member 66.

  In the present embodiment, the surface of the partition wall 60b of the heating honeycomb body 60 is formed flat without any irregularities. On the other hand, the surface of the partition wall 65b of the holding honeycomb body 65 has an uneven shape like the partition wall 60b of the honeycomb body 60 of the first embodiment shown in FIG. Therefore, a large number of recesses 67 are formed in the partition wall 65b of the holding honeycomb body 65.

  In the electric heating member 45 'thus configured, as shown in FIG. 9, on the surface of the partition wall 60b of the heating honeycomb body 60, the droplets of the urea aqueous solution are finely divided into many small droplets by the Leidenfrost phenomenon. Be transformed into FIG. 9 is a conceptual diagram illustrating a state where a large droplet collides with the surface of the flat partition wall 60b of the heating honeycomb body 60.

  When a droplet of the urea aqueous solution enters each cell 60a of the heating honeycomb body 60, the droplet D collides with the surface of the partition wall 60b as shown in FIG. 9A. When the droplet D collides with the surface of the partition wall 60b, it crushes so as to spread on the surface of the partition wall 60b as shown in FIG. 9B.

  Here, when the heating honeycomb body 60 is heated and the surface temperature of the partition wall 60b is heated to the Leidenfrost temperature or higher, a portion of the droplet D that is in contact with the partition wall 60b is vaporized. As a result, as shown in FIG. 9C, a thin film of vapor is formed between the droplet D and the surface of the partition 60b, and the droplet D rises from the surface of the partition 60b. Along with this, the large droplet D is atomized into many small droplets as shown in FIG.

  The droplets atomized by the heating honeycomb body 60 then enter the holding honeycomb body 65. The surface of the partition wall 65b of the holding honeycomb body 65 has an uneven shape. For this reason, the atomized droplet enters the concave portion 67 formed in the partition wall 65b as shown in FIG.

  The small droplet D that has entered the concave portion 67 collides with the wall surface 68 that defines the concave portion 67 and rebounds. The droplet bounced in this manner proceeds in a direction away from the collided wall surface 68 toward the depth of the concave portion 67 according to the collision angle with the wall surface 68, and eventually collide with the opposite wall surface 68 defining the concave portion 67. I do. After that, in the concave portion 67, the body advances toward the depth of the concave portion 67 while repeatedly bouncing between the facing wall surfaces 68.

  Since the holding honeycomb body 65 also receives heat from the heating honeycomb body 60 via the holding member 66, the temperature becomes a certain high temperature. Therefore, the droplets repeatedly collide in the concave portion 67 and the residence time in the concave portion 67 is prolonged, so that the droplet is easily evaporated.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 10 Engine main body 20 Fuel supply device 30 Intake system 40 Exhaust purification device 44 Reducing agent supply device 45 Electric heating member 46 NOx selective reduction catalyst 48 Power control device 50 Control device 60 Honeycomb body 60a Cell 60b Partition wall 61 Depression 62 Wall surface

Claims (1)

An exhaust gas purification device for an internal combustion engine, which purifies exhaust gas of an internal combustion engine,
An exhaust purification catalyst provided in an exhaust passage of the internal combustion engine;
An electric heating member including a honeycomb body that is provided at an upstream side in the exhaust gas flow direction with respect to the exhaust gas purification catalyst and is at least partially heated by supplying electric power;
A reducing agent supply device that supplies a liquid reducing agent toward the electric heating member,
The electric heating member is configured such that the surface of the partition wall constituting the honeycomb body has an uneven shape,
The concavo-convex shape of the partition wall is such that at least a part of the droplet of the reducing agent is dispersed by colliding with a heated wall surface of the electric heating member, and at least a part of the dispersed droplet defines a concave portion. An exhaust purification device for an internal combustion engine, which is formed so as to repeatedly collide with a wall surface.

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