JP2018071454A - 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 improve durability of a fine particle collecting device and improve fuel economy with a decline in frequency of forcible regeneration.SOLUTION: In an exhaust emission control system for an internal combustion engine, a boundary between a central part 12B and an outer periphery 12A of a fine particle collecting device 12 is set based on flow velocity distribution of an exhaust gas G flowing through an exhaust pipe 10 and is set so as to equalize flow velocities of the exhaust gas G flowing into the fine particle collecting device 12 at the boundary. A plugging member 20 is disposed in each end part of a cell of the outer periphery 12A.SELECTED DRAWING: Figure 3

Description

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

  In the exhaust pipe of the diesel engine, a particulate collection device constituted by a filter is arranged. As this filter, a ceramic honeycomb in which the inlet of the outermost channel (outermost cell) in the circumferential direction of the porous ceramic honeycomb is plugged and the inlet and outlet are alternately plugged in the other channels. A filter has been proposed (see, for example, Patent Document 1).

  In this ceramic honeycomb filter, exhaust gas does not flow in the outermost cell in contact with the exhaust pipe, and an air layer exists in this cell, so that heat radiation from the outermost cell is suppressed and the entire filter is Keep warm.

WO2005-045207 Patent

  By the way, the inside flow rate of the exhaust pipe is slower than the central part. In this particulate collection device, the temperature is lowered at a portion where the flow velocity becomes slow due to the influence of the velocity distribution of the exhaust gas in the exhaust pipe. Therefore, in the above ceramic honeycomb filter, there is a problem in that the durability decreases due to a large temperature distribution width during forced regeneration and the frequency of forced regeneration increases due to the high residual rate of PM outside the exhaust pipe radial direction. It was.

  An object of the present invention is to provide an exhaust gas purification system for an internal combustion engine that can improve the durability of a particulate collection device and improve the fuel consumption associated with a decrease in the frequency of forced regeneration.

  In order to achieve the above object, an exhaust gas purification system for an internal combustion engine according to the present invention is an exhaust gas purification system for an internal combustion engine provided with a particulate collection device comprising a wall flow type filter in an exhaust pipe of the internal combustion engine. The particulate collection device has a central portion in the radial center of the exhaust pipe and an annular outer peripheral portion on the outer side in the radial direction, and a boundary between the central portion and the outer peripheral portion of the exhaust gas flowing through the exhaust pipe. This boundary is set based on the flow velocity distribution, and this boundary is set so that the flow velocity of the exhaust gas flowing into the particulate collection device at this boundary becomes the same flow velocity. A sealing member is disposed.

  Here, the cell is a minute space formed in the exhaust gas flow direction by dividing the filter of the particulate collection device into a plurality of particulate collection walls.

  According to the exhaust gas purification system for an internal combustion engine of the present invention, the flow rate of the exhaust gas becomes slow, and an air layer is provided without circulating the exhaust gas through the outer peripheral portion that is particularly low temperature inside the particulate collection device. Therefore, the heat insulation effect by heat insulation can be improved as compared with the prior art. This is advantageous for reducing the temperature distribution width during forced regeneration and improving the PM removal rate, improving the durability of the particulate collection device, and improving fuel efficiency as the frequency of forced regeneration decreases. .

  In particular, by sealing the both end portions on the inlet side and outlet side of the cell in the outer peripheral portion, the inflow of exhaust gas to the outer peripheral portion can be further suppressed.

  In addition, the flow rate of the exhaust gas flowing into the particulate collection device and the internal temperature of the particulate collection device through which the exhaust gas at that flow rate is closely related, the boundary between the outer peripheral portion and the central portion is defined as this boundary. By setting so that the flow rate of the exhaust gas flowing into the gas flow rate becomes the same flow rate, it is possible to reliably partition only the region where the temperature is particularly low inside the particulate collection device as the outer peripheral portion.

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 particulate collection apparatus of FIG. It is a figure which shows the state of each cell inside the particulate collection apparatus of FIG. The distance from the center of the inlet cross section of the particulate collection device to the radially outer side and the temperature of the exhaust gas flowing into the particulate collection device when no sealing member is disposed at both ends of the cell of the particle collection device It is a figure which shows the temperature distribution line which is the relationship. It is a figure which shows the temperature condition of the center part at the time of forced PM regeneration control of the particulate collection device of embodiment of this invention. It is a figure which shows the temperature condition of the center part at the time of forced PM regeneration control of the particulate collection device of the comparative example which has not arrange | positioned the sealing member in the both ends of the cell of a particle collection device. It is a figure which shows the state of each cell inside the particulate collection apparatus of the exhaust gas purification system of the internal combustion engine of 2nd Embodiment. It is a figure which shows the state of each cell inside the particulate collection 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, an exhaust gas purification system 1 for an internal combustion engine according to the first embodiment includes an oxidation catalyst device 11 and a particulate collection device 12 that are sequentially provided in an exhaust pipe 10 of an engine 2 from the upstream side. The

  The oxidation catalyst device 11 is a noble metal catalyst (platinum (Pt) system or the like) that oxidizes gas components (hydrocarbon (HC), carbon monoxide (CO), etc.) of the exhaust gas G on a substrate forming a honeycomb structure ( An oxidation catalyst is supported.

  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 illustrated in FIG. 2, 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.

  The particulate collection device 12 has a central portion 12B and an outer peripheral portion 12A. In the central portion 12B, the base material is formed in a columnar shape, and extends in the flow direction at the radial center of the exhaust pipe 10. 12 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 passing through the outer peripheral portion 12A is lower than the temperature of the exhaust gas Gb passing through the central portion 12B. 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 12M in FIG. 2) toward the outside in the radial direction (on the outer wall 12P side). This is because there is heat radiation from 12A to the outside.

  As shown in FIG. 3, the particulate collection device 12 included in the exhaust gas purification system 1 of the first embodiment has a flow velocity distribution of the exhaust gas G flowing through the exhaust pipe 10 at the boundary between the central portion 12B and the outer peripheral portion 12A. And the flow rate of the exhaust gas G flowing into the particulate collection device 12 at this boundary is set to be the same flow rate, and the sealing members 20 are disposed at both ends of the cell of the outer peripheral portion 12A. It is arranged.

  The material of the sealing member 20 is not particularly limited as long as it has heat resistance sufficient to withstand high heat during the forced PM regeneration control of the particulate collection device 12. Moreover, the both ends of the cell of outer peripheral part 12A are the inlet end part and outlet end part of a cell. The cell inlet (exit) end portion is a region from one end of the cell inlet (exit) to a point separated by a distance set in advance on the outlet (inlet) side.

  According to this configuration, since the sealing members 20 are provided at both ends of the outer peripheral portion 12A set in a wider range in consideration of the influence of the flow velocity distribution of the exhaust gas G as compared with the prior art, the particulate collection device The temperature unevenness inside 12 can be reduced, and the durability of the particulate collection device 12 can be improved.

  Moreover, since the particulate matter (PM) residual rate after forced PM regeneration control can be reduced, the wall flow in the particulate collection device 12 can be effectively utilized. As a result, the frequency | count of reproduction | regeneration of the particulate collection apparatus 12 can be reduced, and a fuel consumption can be improved.

  Further, in the first embodiment of the present invention, as illustrated in FIG. 4, the boundary between the central portion 12B and the outer peripheral portion 12A is in the radial direction of the particulate collection device 12 accompanying the flow velocity distribution of the exhaust gas G. It is set based on the temperature distribution TL that changes concentrically from the center.

  A method for creating the temperature distribution TL of the particulate collection device 12 will be described. First, in the particulate collection device 12X in which no sealing member is disposed at both ends of the cell, the center of the inlet cross section of the particulate collection device 12X with respect to the cross section of the particulate collection device 12X orthogonal to the inflow direction of the exhaust gas G A temperature distribution line TL configured by previously measuring the temperature T of the exhaust gas G flowing into the particulate collection device 12X by an experiment or the like is created according to the distance d from 12M to the radially outer side.

  Next, as shown in FIG. 4, the maximum value αmax at which the absolute value α (= | ΔT / Δd |) of the change amount of the temperature T of the exhaust gas G with respect to the change amount of the distance d is the largest value. Is set to the inflection point IP (point (d1, T1) shown in FIG. 4). In other words, at the inflection point IP, the temperature of the exhaust gas G decreases as it goes radially outward from the center of the cross section of the particulate collection device 12, but the amount of temperature change increases rapidly (decreases rapidly). ) Point.

  A region radially outside from the inflection point IP (a region on the right side from the inflection point IP shown in FIG. 4) is defined as the outer peripheral portion 12A, and a region in the radial direction (a region on the left side from the inflection point IP shown in FIG. 4). Region) is defined as the central portion 12B.

  That is, in the case where no sealing member is arranged at both ends of the cell, in other words, with the particle collection device 12X, the temperature distribution TL in the radial direction of the particle collection device 12X in the above flow velocity distribution is measured, and the center The boundary between the part and the outer peripheral part is set based on the temperature distribution in the radial direction. More specifically, the boundary is set so that the temperature of the particulate collection device 12X at this boundary becomes the same temperature. This boundary is defined as a boundary between the central portion 12b and the outer peripheral portion 12A of the particulate collection device 12.

  According to this configuration, the air layer A (cross-hatched portion in FIG. 3) is present without circulating the exhaust gas Ga in the outer peripheral portion 12A in the region that has been particularly low temperature inside the particulate collection device 12, Compared to technology, heat insulation effect by heat insulation can be improved. This is advantageous for reducing the temperature distribution width during forced regeneration and improving the PM removal rate, improving the durability of the particulate collection device 12, and improving fuel efficiency as the frequency of forced regeneration decreases. it can.

  As described above, in the first embodiment of the present invention, as shown in FIG. 5, the temperature Ta of the cell in the central portion 12B near the outer peripheral portion 12A exceeds the reference temperature Tp during forced PM regeneration control, and the outer peripheral portion 12A. Since the temperature Tb of the cell in the central portion 12B far from the center can be approached, temperature unevenness inside the particulate collection device 12 can be reduced.

  The temperatures Ta and Tb are provided with temperature sensors at positions facing the respective cells in the exhaust pipe 10 at the front stage of the particulate collection device 12, and values detected by these temperature sensors are used. Compared with the comparative example of the particulate collecting device 12X in which both ends of the outer peripheral cell in FIG. 6 are not sealed, in FIG. 5, the temperature Ta of the cell in the central portion 12B near the outer peripheral portion 12A is the regeneration time. It can be seen that the reference temperature Tp is reached in a short time. The reference temperature Tp is a temperature (target temperature) at which most of the PM accumulated in the particulate collection device 12 can be burned and removed during forced PM regeneration control of the particulate collection device 12.

  Next, an exhaust gas purification system 1A for an internal combustion engine according to a second embodiment of the present invention will be described with reference to FIG. This exhaust gas purification system 1A for an internal combustion engine includes a plug member 20 on the inlet side of a part or all of the outer peripheral portion 12A that is spaced from the inlet to the outlet side, and the outer peripheral portion 12A. 1 to 2, except that an oxidation catalyst (noble metal catalyst) (not shown) is carried on the cell from the inlet to the sealing member 20 on the inlet side. 1 is the same configuration.

  More specifically, in the exhaust gas purification system 1A for an internal combustion engine, the plugging member 20 at the inlet end of a part or all of the outer peripheral portion 12A is set in advance from the inlet end to the outlet side. While being arranged at a position separated by one distance L1, an oxidation catalyst is supported between one end of the inlet of the cell where the sealing member 20 is arranged and the sealing member 20. The first distance L1 is set in advance by experiments or the like, while ensuring the heat retaining performance of the particulate collection device 12, the exhaust gas can be reliably turbulent and retained at the inlet of the cell, and More preferably, the exhaust gas turbulent at the cell inlet can pass through the wall flow.

  According to this configuration, as in the exhaust gas purification system 1 for the internal combustion engine of the first embodiment, the durability and fuel consumption of the particulate collection device 12 can be improved. It is possible to achieve various effects.

  That is, since the exhaust gas G can be temporarily retained in the region between the one end of the cell inlet of the outer peripheral portion 12A of the particulate collection device 12 and the sealing member 20, the exhaust gas G is retained in the retention region. The contained hydrocarbons, carbon monoxide and the like can be purified with high efficiency by the oxidation catalyst.

  Note that the oxidation catalyst may be supported in the region (other region) of the particulate collection device 12 other than the retention region of the exhaust gas G. In this case, the amount of the oxidation catalyst supported in the retention region It is more preferable to increase the amount of the oxidation catalyst supported on the region.

  Next, an exhaust gas purification system 1B according to a third embodiment of the present invention will be described with reference to FIG. In the exhaust gas purification system 1B of the internal combustion engine, the sealing member 20 on the outlet side of a part or all of the outer peripheral portion 12A of the particulate collection device 12 is arranged away from the outlet toward the inlet side. Except for this point, the configuration is the same as that of the exhaust gas purification system 1A for the internal combustion engine of the second embodiment shown in FIG.

More specifically, in the exhaust gas purification system 1B of the internal combustion engine, the sealing member 20 at the outlet of the cell adjacent to the central portion 12B among the cells of the outer peripheral portion 12A is set in advance to the inlet side from one end of the outlet. The second catalyst is disposed at a position spaced apart from the second distance l2, and an oxidation catalyst (not shown) is supported between one end of the outlet of the cell in which the sealing member 20 is disposed and the sealing member 20 on the outlet side. The second distance l2 is set in advance by experiments or the like.
According to this configuration, as in the exhaust gas purification systems 1 and 1A for the internal combustion engine of the first and second embodiments, the durability and fuel consumption of the particulate collection device 12 can be improved, Furthermore, the following operational effects can be achieved.

  That is, the exhaust gas G is passed through the region between the end of the outlet of the cell adjacent to the central portion 12B and the sealing member 20 in the cell of the outer peripheral portion 12A of the particulate collection device 12, and in this region. By supporting the oxidation catalyst, hydrocarbons and carbon monoxide contained in the exhaust gas G can be oxidized and removed by the oxidation catalyst.

  As described above, according to the exhaust gas purification system 1 for an internal combustion engine of the present invention, the flow rate of the exhaust gas G is slow, and the exhaust gas Ga is circulated through the outer peripheral portion 12 </ b> A that was particularly low in the particulate collection device 12. Without providing the air layer, the heat insulation effect by heat insulation can be improved as compared with the prior art.

  As a result, it is possible to reduce the possibility of breakage of the particulate collection device 12, and the durability of the particulate collection device 12 can be improved. In addition, since the particulate (PM) remaining rate after forced PM regeneration control can be reduced, the PM collection wall in the particulate collection device 12 can be used effectively, and the forced PM regeneration of the particulate collection device 12 can be performed. This can contribute to a reduction in fuel consumption due to a longer control interval. Furthermore, the method of disposing the sealing member 20 on the outer peripheral portion 12A of the particulate collection device 12 can be performed at low cost.

  The outer peripheral portion 12A provided with the sealing members 20 at both ends of the cell is configured as two or more rows of cells radially inward from the outer periphery of the particulate collection device 12 adjacent to the exhaust pipe wall. It is preferable from the viewpoint of effect.

  Moreover, if the detection part of the sensor which acquires the state of the particulate collection device 12 is arranged in the central portion 12B, the state of the particulate collection device 12 can be reliably ensured even if both ends of the outer peripheral portion 12A are plugged. It is preferable because it can be grasped. Examples of the sensor include a temperature sensor and a front / rear differential pressure sensor.

DESCRIPTION OF SYMBOLS 1, 1A, 1B Exhaust gas purification system 2 of internal combustion engine 2 Engine 10 Exhaust pipe 12 Particulate collection device 12X Particulate collection device 12A in which sealing members are not disposed at both ends of the cell Center part of collector 12M Center of inlet cross section of particulate collector 20 Sealing member TL Radial temperature distribution IP Inflection point G Exhaust gas Ga Exhaust gas Gb passing through outer periphery of particulate collector Particulate collector Exhaust gas passing through the center of the

Claims (3)

In an exhaust gas purification system for an internal combustion engine provided with a particulate collection device composed of a wall flow type filter in an exhaust pipe of the internal combustion engine,
The particulate collection device has a central portion in the radial center of the exhaust pipe and an annular outer peripheral portion on the outer side in the radial direction, and the boundary between the central portion and the outer peripheral portion is a flow velocity of exhaust gas flowing through the exhaust pipe. Is set based on the distribution, is set so that the flow rate of the exhaust gas flowing into the particulate collection device at this boundary is the same flow rate,
An exhaust gas purification system for an internal combustion engine, wherein sealing members are disposed at both ends of the outer peripheral cell.   In the case where no sealing member is disposed at both ends of the cell, the temperature distribution in the radial direction of the particulate collection device in the flow velocity distribution is measured, and the boundary between the central portion and the outer peripheral portion is in the radial direction. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the exhaust gas purification system is set based on a temperature distribution and set so that the temperature of the particulate collection device at the boundary is the same.   The sealing member on the inlet side of a part or all of the outer peripheral portion is arranged away from the inlet to the outlet side, and between the inlet of the outer peripheral portion and the sealing member on the inlet side. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein an oxidation catalyst is supported on the cell.

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