JP2018071455A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control system for an internal combustion engine that can increase temperature of an outer periphery of a fine particle collecting device.SOLUTION: In an exhaust emission control system for an internal combustion engine, an oxidation catalyst device 11 includes: a central part 11B extending in a flow direction at an axial center of an exhaust pipe 10; and an annular outer periphery 11A extending in the flow direction on an axial outer side, where the outer periphery 11A has an amount of supporting an oxidation catalyst that is larger than that of the central part 11B.SELECTED DRAWING: Figure 4

Description

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

  While exhaust is intensively flowed into the central cell of the catalyst arranged upstream of the particulate collection device, PM is collected by the particulate matter collection section formed on the outer periphery of the catalyst. There has been proposed an exhaust purification device that reduces the amount of PM flowing into the outer peripheral portion of the collection device and suppresses unburned PM in the particulate collection device (see, for example, Patent Document 1).

JP 2014-134122 A

  By the way, the exhaust gas discharged from the engine and flowing through the exhaust pipe generates a velocity distribution between the central portion and the outer peripheral portion, and further generates a temperature distribution due to heat radiation from the outer peripheral portion. This temperature distribution is also generated inside the particulate collection device through which the exhaust gas passes, and the temperature of the outer peripheral portion of the particulate collection device becomes low.

  Therefore, in the conventional technology as described above, even if the gas component such as HC is increased during forced PM regeneration, the temperature of the exhaust gas radially outside the exhaust pipe passing through the oxidation catalyst is low, and the outer peripheral portion of the particulate collection device Temperature does not rise. Therefore, PM collected at the outer periphery of the particulate collection device cannot be removed.

  An object of the present invention is to provide an exhaust gas purification system for an internal combustion engine that can increase the temperature of the outer peripheral portion of a particulate collection device.

  In order to achieve the above object, an exhaust gas purification system for an internal combustion engine of the present invention comprises an oxidation catalyst device and a particulate collection device in order from the upstream side in an exhaust pipe of the internal combustion engine, and forms a honeycomb structure of the oxidation catalyst device In an exhaust gas purification system of an internal combustion engine in which an oxidation catalyst that oxidizes a gas component of exhaust gas is supported on a base material that performs the oxidation catalyst device, a central portion that extends in a flow direction at a radial center of the exhaust pipe; And an annular outer peripheral portion extending in the flow direction on the outer side in the radial direction, and the carrying amount of the oxidation catalyst in the outer peripheral portion is larger than that in the central portion.

  According to the exhaust gas purification system for an internal combustion engine of the present invention, since the amount of catalyst supported on the outer peripheral portion is increased, the amount of heat generated on the outer peripheral portion of the oxidation catalyst device can be increased. This is advantageous in increasing the temperature outside the radial direction of the exhaust gas that has passed through the oxidation catalyst device, and can increase the temperature outside the radial direction of the downstream particulate collection device. In connection with this, PM which flows in the radial direction outer side of particulate collection device can be removed reliably.

It is a figure showing composition of an exhaust-gas purification system of an internal-combustion engine of a 1st embodiment of the present invention. It is a figure which shows the structure of the oxidation catalyst apparatus of FIG. It is a figure which shows the carrying | support state of the oxidation catalyst inside the oxidation catalyst apparatus of FIG. It is a figure which shows the structure of the particulate collection apparatus of FIG. It is a figure which shows the radial direction temperature distribution line which is the relationship between the distance to the radial direction from the center of the inlet cross section of a particulate collection device, and the temperature of the exhaust gas which flows into a particulate collection device. It is a figure which shows the accumulation state of the ash inside the particulate collection apparatus of this invention. It is a figure which shows the accumulation state of the ash inside the particulate collection device of a prior art. It is a figure which shows the carrying | support state of the oxidation catalyst inside the oxidation catalyst apparatus of the exhaust gas purification system of the internal combustion engine of 2nd Embodiment. It is a figure which shows the carrying | support state of the oxidation catalyst inside the oxidation catalyst apparatus of the exhaust gas purification system of the internal combustion engine of 3rd Embodiment.

  Hereinafter, an exhaust gas purification system for an internal combustion engine according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the exhaust gas purification system 1 of the first embodiment is provided with an oxidation catalyst device 11 and a particulate collection device 12 that are sequentially provided in the exhaust pipe 10 of the engine 2 from the upstream side.

  The oxidation catalyst device 11 is configured by supporting a noble metal catalyst (oxidation catalyst) that oxidizes hydrocarbons (HC), carbon monoxide (CO), and the like of the exhaust gas G on a base material that forms a honeycomb structure. The noble metal catalyst is preferably a platinum (Pt) catalyst that oxidizes hydrocarbons to water and carbon dioxide and carbon monoxide to carbon dioxide.

  Since the oxidation reaction of hydrocarbon and carbon monoxide by the noble metal catalyst is an exothermic reaction, the temperature of the exhaust gas G rises due to this exotherm. Utilizing this, when high temperature exhaust gas G is required, such as during forced PM regeneration control of the particulate collection device 12, it is included in the exhaust gas G passing through the exhaust passage 10 upstream of the oxidation catalyst device 11. The exhaust gas G is heated to a high temperature by temporarily increasing the amount of hydrocarbons and oxidizing the increased amount of hydrocarbons in the oxidation catalyst device 11.

  As a method of temporarily increasing the amount of hydrocarbons, for example, a method of performing post-injection of fuel in a cylinder (cylinder) 2a of the engine 2 or a fuel in the exhaust passage 10 upstream of the oxidation catalyst device 11 is used. There is a method of injecting fuel from the fuel injection device provided with an injection device (not shown).

  As shown in FIG. 2, the oxidation catalyst device 11 has a central portion 11B and an outer peripheral portion 11A. In the central portion 11B, the base material is formed in a columnar shape, and extends in the flow direction at the radial center of the exhaust pipe 10. 11 A of outer peripheral parts are formed in the torus in the base material, and are extended in the flow direction on the radial direction outer side. The temperature of the exhaust gas Ga flowing into the outer peripheral portion 11A is lower than the temperature of the exhaust gas Gb passing through the central portion 11B. The exhaust gas G flowing through the exhaust pipe 10 decreases in speed from the center of the cross section of the exhaust pipe 10 (the center of the inlet cross section is 11M in FIG. 2) toward the radially outer side (outer wall 11P side) (a speed distribution is generated). This is because there is heat radiation from the outer periphery of the exhaust pipe 10 to the outside.

  As shown in FIG. 3, the oxidation catalyst device 11 provided in the exhaust gas purification system 1 of the first embodiment is characterized in that the amount of the noble metal catalyst supported on the outer peripheral portion 11A is larger than the amount of the noble metal catalyst supported on the central portion 11B. And In FIG. 3, the difference in the amount of the noble metal catalyst is shown by the difference in the hatching interval (short hatching interval: a large amount of the noble metal catalyst (peripheral portion), and a long hatching interval: the amount of the noble metal catalyst. There are few (central part).

  With this configuration, the amount of heat generated at the outer peripheral portion 11A of the oxidation catalyst device 11 can be increased, so that the temperature of the exhaust gas Ga flowing through the outer peripheral portion 11A and flowing into the downstream particulate collection device 12 is increased. Can be made.

  Here, the particulate collection device 12 (see FIG. 4) will be described. The particulate collection device 12 includes a filter therein. This filter is a monolith honeycomb wall flow type filter in which the inlets and outlets of cells (channels) of a porous ceramic honeycomb are alternately plugged.

  In the first embodiment of the present invention, the diameter of the oxidation catalyst device 11 and the diameter of the particulate collection device 12 are made equal, and the oxidation catalyst device 11 and the particulate collection device 12 arranged on the same axis are single exhausted. It is stored in the tube 10. The exhaust pipe 10 in which the oxidation catalyst device 11 and the particulate collection device 12 are housed is a circular tube that does not shrink or expand at a position in the middle of the flow direction. The inner diameter of the exhaust pipe 10 is equal to the outer diameter of the oxidation catalyst device 11 and the particulate collection device 12.

  As shown in FIG. 4, the particulate collection device 12 includes a low temperature part 12A and a high temperature part 12B. A method for classifying the low temperature portion 12A and the high temperature portion 12B will be described later.

  The central portion 11B of the oxidation catalyst device 11 is a region facing the high temperature portion 12B of the particulate collection device 12, and the outer peripheral portion 11A of the oxidation catalyst device 11 is a region facing the low temperature portion 12A of the particulate collection device 12. . With this configuration, the temperature of the downstream low-temperature portion 12A can be raised by the exhaust gas Ga that has been heated by the increase in the amount of heat generated at the upstream outer peripheral portion 11A. It is possible to prevent defective combustion of PM in the portion 12A, and to promote ash (ash-like substance) form transition (wall ash → plug ash) described later.

  A method of classifying the low temperature part 12A and the high temperature part 12B of the particulate collection device 12 will be described. In this exhaust gas purification system for an internal combustion engine, when the oxidation catalyst device in which the supported amount of the noble metal catalyst is made uniform without using the oxidation catalyst device 11 is used, The radial temperature distribution is measured, and the measurement result is based on the inflection point IP of the radial temperature distribution TL of the particulate collection device 12 shown in FIG. The radial temperature distribution TL is a distance d from the cross-sectional center (for example, the inlet cross-sectional center 12M) of the fine particle collecting device 12 to the radial outer side (the outer wall 12P side), and the exhaust passing through the fine particle collecting device 12. It is a distribution line with the temperature T of the gas G as the vertical axis. Further, at the inflection point IP (coordinates (d1, T1) shown in FIG. 5), the temperature of the exhaust gas G decreases from the center of the cross section of the particulate collection device 12 toward the outside in the radial direction. It is a point where it suddenly increases (decreases in temperature rapidly).

  In the first embodiment of the present invention, the region radially outward from the inflection point IP (region on the right side from the inflection point IP shown in FIG. 5) is the low temperature portion 12A, and the region in the radial direction (shown in FIG. 5). A region on the left side from the inflection point IP is defined as a high temperature portion 12B.

  By doing in this way, since the exhaust gas Ga heated by the calorific value increase in the outer peripheral portion 11A of the oxidation catalyst device 11 passes through the low temperature portion 12A, which is a particularly low temperature region, inside the particulate collection device 12. Thus, the temperature of the low temperature part 12A can be reliably raised, and the expansion of the temperature difference between the low temperature part 12A and the high temperature part 12B of the particulate collection device 12 can be suppressed with high efficiency and low cost.

  Here, the ash deposited inside the particulate collection device 12 will be described. In addition to the PM contained in the exhaust gas G, ash is deposited on the particulate collection device 12. There are two types of ash, plug ash PA and wall ash WA. The plug ash PA is an ash that accumulates in the form of plugging the plugged portion on the downstream side of the particulate collection device 12. The wall ash WA is an ash that is uniformly deposited on the surface of the wall for collecting PM.

  As shown in FIG. 7, when the exhaust gas G passes through the particulate collection device 12, PM (particulate matter: not shown) contained in the exhaust gas G is placed on the PM collection wall 12c (12ca, 12cb, 12cc). ) And ash (ash-like substance) accumulate. The ash is initially deposited in a form that uniformly accumulates on the surface of the wall 12c for collecting PM (wall ash WA: shaded portion).

  When the exhaust gas Gb passes through the high temperature portion 12B of the particulate collection device 12 during forced PM regeneration control of the particulate collection device 12, the ash particles constituting the wall ash WA are aggregated by the heated exhaust gas Gb. Thus, the wall ash particles having a larger particle diameter are formed, and the increased wall ash WA is flowed downstream of the fine particle collecting device 12 to plug the plugged portion 12aa (plug ash PA: cross) Hatch (DX) part). In FIG. 7, the cell sealing the outlet side is 12Ba, and the cell sealing the inlet side (sealing portion 12bb) is 12Bb.

  On the other hand, when the oxidation catalyst device in which the supported amount of the noble metal catalyst is made uniform without using the oxidation catalyst device 11 described above, the exhaust gas Ga is fine particles during the forced PM regeneration control of the fine particle collecting device 12. When passing through the low temperature part 12A of the collection device 12, the temperature of the exhaust gas Ga is lower than the temperature of the exhaust gas G passing through the high temperature part 12B, so that the aggregation of ash particles constituting the wall ash WA does not proceed and partly Changes to plug ash PA, but most remains as wall ash WA, hindering the flow of exhaust gas Ga. In FIG. 7, the cell sealing the outlet side is 12Aa, and the cell sealing the inlet side is 12Ab.

  As a result, the amount of exhaust gas G flowing from the low temperature portion 12A to the high temperature portion 12B increases every time the forced PM regeneration control of the particulate collection device 12 is performed, so the temperature difference between the high temperature portion 12B and the low temperature portion 12A increases. I will do it. Therefore, in the low temperature part 12A, the wall ash WA remains more and more.

  On the other hand, in the present invention, the temperature of the low-temperature part 12A of the downstream particulate collection device 12 is raised by the increase in the amount of heat generated at the outer peripheral part 11A of the oxidation catalyst device 11, so that the low-temperature part as shown in FIG. Wall ash WA remaining in 12A also changes to plug ash PA (ΔDX portion in FIG. 6). As a result, the difference between the amount of the exhaust gas Ga flowing through the low temperature part 12A and the amount of the exhaust gas Gb flowing through the high temperature part 12B hardly changes, so that the expansion of the temperature difference between the low temperature part 12A and the high temperature part 12B can be suppressed. .

  Next, an exhaust gas purification system 1A according to a second embodiment of the present invention will be described with reference to FIG. The exhaust gas purification system 1A has the same configuration as the exhaust gas purification system 1 shown in FIGS. 1 and 2 except for the distribution of the amount of the noble metal catalyst supported on the outer peripheral portion 11A of the oxidation catalyst device 11.

  More specifically, in the exhaust gas purification system 1A, the amount of the noble metal catalyst supported on the outer peripheral portion 11A of the oxidation catalyst device 11 is changed according to the radial temperature distribution TL. The amount of the catalyst is increased as the distance d from the center of the inlet cross section of the oxidation catalyst device 11 to the radially outer side increases. In FIG. 8, as in FIG. 3, the difference in the amount of the noble metal catalyst is indicated by the difference in the hatching interval (short hatching interval: large amount of noble metal catalyst, long hatching interval: noble metal catalyst. Less).

  According to this configuration, as in the exhaust gas purification system 1 for the internal combustion engine of the first embodiment, the temperature difference inside the particulate collection device 12 can be reduced, and further, as follows. It is possible to achieve various effects.

  That is, since the calorific value of each cell of the outer peripheral portion 11A of the oxidation catalyst device 11 is gradually increased as the distance d from the center of the inlet cross section of the particulate collection device 12 to the radially outer side is increased, the oxidation catalyst device 11 is increased. While optimizing the amount of the noble metal catalyst supported on the outer peripheral portion 11A, the calorific value of the cell near the outer peripheral end portion (the outer wall of the exhaust pipe 10) of the oxidation catalyst device 11 can be secured.

  As a result, a sufficient amount of heat can be supplied to the cell that is close to the outer peripheral end of the particle collecting device 12 and has a large amount of heat released to the outside of the particle collecting device 12, so that the outer edge of the particle collecting device 12 The temperature drop in the vicinity can be suppressed.

  Next, an exhaust gas purification system 1B according to a third embodiment of the present invention will be described with reference to FIG. The exhaust gas purification system 1B has the same configuration as the exhaust gas purification system 1 shown in FIGS. 1 and 2 except for the distribution of the amount of the noble metal catalyst supported on the outer peripheral portion 11A of the oxidation catalyst device 11.

  More specifically, in the exhaust gas purification system 1B, the amount of the noble metal catalyst supported on each cell of the outer peripheral portion 11A of the oxidation catalyst device 11 is changed in the flow direction. The amount of the catalyst is reduced as it goes from the inlet to the outlet of the oxidation catalyst device 11. 9, as in FIG. 3, the difference in the amount of the noble metal catalyst is shown by the difference in the hatching interval (short hatching interval: large amount of noble metal catalyst, long hatching interval: noble metal catalyst. Less).

  According to this configuration, as in the exhaust gas purification system 1 for the internal combustion engine of the first embodiment, the temperature difference inside the particulate collection device 12 can be reduced, and further, as follows. It is possible to achieve various effects.

  That is, the noble metal catalyst to be supported in order from the position near the inlet of the oxidation catalyst device 11 where the oxidation reaction of hydrocarbons and carbon monoxide contained in the exhaust gas Ga by the noble metal catalyst supported on the oxidation catalyst device 11 is frequently performed. Since the amount is reduced, the amount of the noble metal catalyst supported on the outer peripheral portion 11A of the oxidation catalyst device 11 can be optimized while maintaining the heat generation efficiency of the oxidation catalyst device 11.

  In addition, the oxidation catalyst device 11 is manufactured by separately manufacturing a donut-shaped member constituting the outer peripheral portion 11A and a cylindrical member constituting the central portion 11B, and then adding the cylindrical member to the donut-shaped member 11A. It is preferable to assemble and manufacture 11B because process management becomes easy.

  According to the exhaust gas purification systems 1, 1 </ b> A, and 1 </ b> B of the internal combustion engine of the present invention, the amount of catalyst supported on the outer peripheral portion 11 </ b> A is increased, so that the amount of heat generated at the outer peripheral portion 11 </ b> A of the oxidation catalyst device 11 can be increased. This is advantageous in increasing the temperature on the radially outer side of the exhaust gas G that has passed through the oxidation catalyst device 11, and can increase the temperature on the radially outer side of the downstream particulate collection device 12. That is, PM collected on the radially outer side of the particulate collection device 12 can be reliably removed.

  Note that the ratio of the amount of the precious metal catalyst supported on the outer peripheral portion 11A to the amount of the precious metal catalyst supported on the central portion 11B is such that the temperature difference between the high temperature portion 11B and the low temperature portion 11A approaches zero or zero during forced PM regeneration control. The ratio is preferred.

  Further, the amount of the precious metal catalyst supported on the outer peripheral portion 11A is preferably such that the low temperature portion 11A is below the endurance temperature during forced PM regeneration control.

  As described above, compared to the case where the amount of the noble metal catalyst is increased over the entire region of the oxidation catalyst device 11, PM can be removed in the entire region of the particle collecting device 12 while suppressing the cost, and the durability of the particle collecting device 12. It becomes advantageous for improvement.

DESCRIPTION OF SYMBOLS 1, 1A, 1B Exhaust gas purification system 2 of internal combustion engine 2 Engine 10 Exhaust pipe 11 Oxidation catalyst device 11A Outer peripheral part of oxidation catalyst device 11B Central part of oxidation catalyst device 12 Fine particle collecting device 12A Low temperature part (outer periphery) Part)
12B High temperature part (center part) of particulate collection device
d Distance from the center of the inlet cross section of the particulate collection device to the radially outer side T Temperature of the exhaust gas flowing into the particulate collection device TL Radial temperature distribution IP Inflection point G Exhaust gas Ga Peripheral portion of the oxidation catalyst device and particulates Exhaust gas Gb passing through the low temperature part of the collection device Exhaust gas passing through the central part of the oxidation catalyst device and the high temperature part of the particulate collection device

Claims (2)

An internal combustion engine in which an exhaust catalyst of an internal combustion engine is provided with an oxidation catalyst device and a particulate collection device in order from the upstream side, and an oxidation catalyst for oxidizing a gas component of exhaust gas is supported on a base material forming a honeycomb structure of the oxidation catalyst device In the exhaust gas purification system of
The oxidation catalyst device has a central portion extending in the flow direction at the radial center of the exhaust pipe, and an annular outer peripheral portion extending in the flow direction on the radial outer side;
An exhaust gas purification system for an internal combustion engine, wherein the amount of the oxidation catalyst supported on the outer peripheral portion is larger than that of the central portion. In the exhaust gas purification system of the internal combustion engine, when using an oxidation catalyst device in which the supported amount of the noble metal catalyst is uniform without using the oxidation catalyst, the radial temperature distribution of the particulate collection device is measured, When the region outside the radial direction from the inflection point of the radial temperature distribution is the low temperature portion of the particulate collection device, and the region in the radial center is the high temperature portion of the particulate collection device,
The central portion of the oxidation catalyst device is a region facing the high temperature portion of the particulate collection device, and the outer peripheral portion of the oxidation catalyst device is a region facing the low temperature portion of the particulate collection device. The exhaust gas purification system for an internal combustion engine according to claim 1.

Images