JP2009074438A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sufficiently remove particulate matter in exhaust gas while improving maintenance property and reducing electric power consumption in an exhaust emission control device. <P>SOLUTION: An upstream side DPF 14 and a downstream side DPF 18 are disposed at different positions in exhaust gas flow. A charge device 16 is connected between the upstream side DPF 14 and the downstream side DPF 18. The charge device 16 is provided with a charge electrode charging particulate matter and a collecting part provided at an exhaust gas downstream side and grounded. The collecting part can collect at least part of particulate matter sent to the charge device 16 from the upstream side DPF 14 under a condition where the same is concentrated in an electrostatically large lump. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for removing particulate matter contained in exhaust gas from an internal combustion engine such as a diesel engine.

  The exhaust gas discharged from an internal combustion engine, for example, a diesel engine, includes particulate matter (PM) such as soot, fuel and engine oil. For this reason, conventionally, for example, in an exhaust device of a diesel engine, it has been considered to provide a diesel particulate matter removal filter, that is, a DPF, to remove particulate matter.

  Patent Document 1 discloses a device for removing smoke from diesel engine exhaust gas, which includes a diesel dust filter that houses a honeycomb-shaped porous element and a pair of electrodes. When soot accumulates in the filter, an electrical discharge occurs and the soot is removed.

  Patent Document 2 describes a gas purification device in which a CF denitration device and a low-voltage air purification device on the downstream side thereof are installed in an exhaust system of a diesel engine. The low-voltage air cleaning device includes a charging member connected to a negative electrode of a DC power source, and a collecting member connected to the positive electrode on the downstream side of the charging member. Thus, exhaust gas is passed through the charging member and the collecting member in this order, whereby dust in the gas can be charged and adsorbed on the collecting member.

Special table 2003-535255 gazette JP 2000-130273 A JP 2003-269134 A

  In the removal apparatus described in Patent Document 1, a collection part for collecting PM such as conductive soot is not provided on the exhaust upstream side of a diesel dust filter having an electrode for discharging. For this reason, in the removal device, PM such as soot discharged from the internal combustion engine is not removed or reduced before being sent to the diesel dust filter, and soot is applied to the non-conductive electrode support in the diesel dust filter. In some cases, the insulation of the electrode support portion cannot be secured. If insulation of the electrode support portion cannot be ensured, the discharge performance by the electrode may be reduced, and the power consumption required to remove PM may increase. In this case, maintenance such as removing the conductor attached to the electrode support portion may occur and maintenance may be deteriorated. In addition, a special removal device may be required to remove the conductor attached to the electrode support portion.

  In the case of the gas purification device described in Patent Document 2, a coarse filter made of a metal or a polymer resin material is installed on the exhaust upstream side of the low-voltage air purification device, and the charging member of the low-voltage air purification device is used. It cannot be said that there is no possibility that a part of the PM is collected by the coarse filter before the PM is sent. However, in the case of this gas purification device, it is not considered to collect PM that has not been collected by the collecting member connected to the positive electrode after being charged by the charging member. For example, when the exhaust flow rate increases due to acceleration of a vehicle provided with a gas purification device, etc., when the collected PM is peeled off from the collection unit and collected, the gas purification device directly enters the atmosphere. There is a possibility of being discharged. For this reason, there is room for improvement in terms of sufficiently removing PM.

  On the other hand, Patent Document 3 describes an exhaust emission control device having a reaction case including a charging electrode, a ground electrode, and a diesel particulate filter inside. Exhaust gas discharged from the engine is supplied to the reaction case through the exhaust pipe. In the reaction case, PM charged from the charging electrode and then flowing from the installation electrode is collected by a diesel particulate filter. However, in the case of such an exhaust purification device, there is not provided a collection unit that collects a conductor such as soot in PM in the exhaust discharged from the engine before being sent into the reaction case. For this reason, similarly to the removing device described in the above-mentioned Patent Document 1, a non-conductive electrode supporting portion that supports the charging electrode, for example, a conductor such as soot adheres to an insulator or the like, and PM is removed. Therefore, there is a possibility that the power consumption required for this will increase, and the maintenance performance may decrease.

  SUMMARY OF THE INVENTION An object of the present invention is to improve the maintainability of an exhaust emission control device and to sufficiently remove particulate matter in exhaust gas while reducing power consumption.

  An exhaust emission control device according to the present invention is an exhaust emission control device for removing particulate matter contained in exhaust gas of an internal combustion engine, and includes a plurality of particulate matter removal filters arranged at different positions with respect to an exhaust flow, and charging And a charging device is connected between the upstream particulate matter removal filter on the exhaust upstream side and the downstream particulate matter removal filter on the exhaust downstream side among the plurality of particulate matter removal filters. The charging device includes a charging unit that charges the particulate matter, and a collection unit that is provided on the exhaust downstream side of the charging unit and is grounded, and the collection unit includes at least the charged particulate matter. Capable of collecting in a state where a part is electrostatically collected in a large lump, and the downstream particulate matter removal filter is capable of collecting at least a part of the particulate matter collected by the collection part. Exhaust gas purification characterized by It is a device.

  Preferably, the charging unit charges the particulate matter with a negative high voltage.

  More preferably, the upstream particulate matter removal filter and the downstream particulate matter removal filter have the same structure.

  More preferably, the collection part is made of a porous or mesh-like conductor, and the downstream particulate matter removing filter has a porous wall part, and the received particulate substance is passed through the wall. The micropores provided in the wall portion are discharged through the micropores provided in the portion, and the passage width of the micropores provided in the wall portion is made smaller than the minimum passage width of the particulate matter passage hole provided in the collection portion.

  According to the exhaust emission control device of the present invention, in the charging device, the particulate matter is charged by the charging unit, and the charged particulate matter can be electrostatically collected by the collecting unit. Moreover, a particulate matter can be made into the big lump shape electrostatically collected by the collection part. Further, even when the massive particulate matter flows from the collecting portion to the exhaust downstream side, the flowing particulate matter can be sufficiently collected by the downstream particulate matter removing filter. In addition, since the upstream particulate matter removal filter is provided on the exhaust upstream side of the charging device, particulate matter sent to the charging device after being discharged from the internal combustion engine can be reduced, and the charging device has non-conductivity. Particulate matter adhering to the charging portion supporting portion can be sufficiently reduced. For this reason, it is possible to suppress the trouble of removing the particulate matter adhering to the charging portion support portion, and to improve the maintenance property, coupled with being able to reduce the amount of the particulate matter to be charged by the charging device, The power consumption required for removing the particulate matter can be reduced. As a result, the maintenance property can be improved, and the particulate matter in the exhaust gas can be sufficiently removed while reducing the power consumption.

  On the other hand, in the case of a structure that excludes the charging device from the exhaust purification device according to the present invention and deviates from the present invention, the particulate matter having a size in the range downstream from the particulate matter removing filter is collected. It will be easy to leak without being. For example, as a certain range, the particle size is in the vicinity of 100 nm, and this range is related to the structure of the particulate matter removal filter, particularly when an exhaust purification device is used, in order to ensure practicality. It turns out that there is almost no change. In contrast, according to the present invention, since the charging device is provided on the exhaust downstream side of the upstream particulate matter removing filter, a large amount of particulate matter having a size of around 100 nm, that is, a particle diameter, is sent to the charging device. Even in such a case, the particulate matter can be greatly changed into a lump by electrification collection, and the size of the particulate matter flowing out from the charging device can be greatly shifted from the particle size around 100 nm. Particulate matter having a particle size greatly deviated from around 100 nm can be sufficiently collected by the downstream particulate matter removal filter. As a result, according to the present invention, the particulate matter discharged from the exhaust purification device can be suppressed to a sufficiently small amount.

  In addition, according to the configuration in which the upstream particulate matter removal filter and the downstream particulate matter removal filter have the same structure, it is possible to reduce the particulate matter discharged from the exhaust emission control device while reducing the particulate matter in common. The cost can be reduced by making it easier.

  The collection part is made of a porous or mesh-like conductor, and the downstream particulate matter removal filter has a porous wall part, and the received particulate substance is provided on the wall part. According to the configuration in which the passage width of the micropore provided in the wall portion is made smaller than the minimum passage width of the particulate matter passage hole provided in the collection portion. It becomes easy to collect the particulate matter flowing from the collection part more effectively by the downstream particulate matter removal filter.

  Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of an example of an exhaust emission control device according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a charging device provided in the exhaust purification device of FIG. FIG. 3 is a schematic diagram for explaining a state in which the size of the particulate matter is increased at the collection unit of the charging device.

  As shown in FIG. 1, the exhaust purification device 10 is more upstream than an upstream DPF 14 and an upstream DPF 14 that are upstream diesel particulate matter removal filters that are supplied with exhaust discharged from a diesel engine 12 that is an internal combustion engine. A charging device 16 provided on the exhaust downstream side (right side in FIG. 1) and a downstream DPF 18 that is a downstream diesel particulate matter removal filter provided on the exhaust downstream side of the charging device 16 are provided. The diesel engine 12, the upstream DPF 14, the charging device 16, and the downstream DPF 18 are connected by an exhaust pipe 20. The exhaust purification device 10 is intended to purify exhaust gas by removing particulate matter, that is, PM, contained in the exhaust of the diesel engine 12.

  The upstream DPF 14 and the downstream DPF 18 have the same structure and the same performance, and are disposed at different positions with respect to the exhaust flow. Each of the DPFs 14 and 18 holds, in the case, a filter main body that mainly collects soot among PMs in exhaust gas. For example, the filter body is composed of a porous honeycomb sintered body. For example, the honeycomb sintered body is a cordierite sintered body which is a kind of ceramic sintered body. The honeycomb sintered body has a honeycomb-shaped wall portion, and the received PM is discharged after passing through the filter-side micropores provided in the wall portion. The filter-side micropore has a very small passage width on the order of μm.

  As shown in detail in FIG. 2, the charging device 16 includes a charging electrode 24 that is a charging unit and a collecting unit 26 inside a case 22 having conductivity. The case 22 has an exhaust inlet 28 for receiving exhaust gas and an exhaust outlet 30 for sending exhaust gas. The charging electrode 24 has a rod shape and charges the PM passing therearound. A plurality of protrusions are provided on the exhaust gas downstream side of the charging electrode 24 (on the right side in FIG. 2). Both ends of the charging electrode 24 are supported by the case 22 in an insulated state via insulators 32 as electrode support portions. The charging electrode 24 is disposed in a direction orthogonal to the exhaust flow direction (the direction of arrow A in FIG. 2). The charging electrode 24 is connected to the negative electrode side of the power supply device 34 so that a constant negative high voltage of, for example, −10 kV is applied.

  Further, the collection unit 26 is supported by the grounded case 22 and is electrically connected to serve as a ground electrode. The collection unit 26 serves as a counter electrode for the charging electrode 24. The collection part 26 is made of a conductor such as a porous or mesh metal. For example, the collection part 26 is comprised with a metal foam or a stainless net | network. As will be described in detail later, the collection unit 26 enables collection in a state where at least a part of the PM 36 sent into the case 22 is electrostatically collected into a large lump. Such a charging device 16 has a function similar to that of the structure excluding the diesel particulate filter in the reaction case described in Patent Document 3 described above. Further, the downstream DPF 18 is collected by the collection unit 26 and can collect at least a part of the PM 36 flowing from the collection unit 26.

  Note that a catalyst such as a PM oxidation catalyst or a NOx purification catalyst can be supported on the collection unit 26. Further, the minimum passage width D (FIG. 3) of the hole 35 (FIG. 3 to be described later), which is a particulate matter passage hole provided in the collection portion 26, is provided in each of the upstream DPF 14 and the downstream DPF 18. It is made larger than the passage width of the filter side micropore. Conversely, the passage width of the filter-side minute hole is made smaller than the minimum passage width D of the hole 35 provided in the collection part 26.

  With this configuration, when a negative high voltage is applied to the charging electrode 24 by the power supply device 34, a voltage gradient is generated between the charging electrode 24 and the collection unit 26, and the charging electrode 24 Plasma is generated around. The PM in the exhaust gas supplied to the charging device 16 is negatively charged by the plasma. The charged PM is collected in a state where it is electrostatically collected in a lump by the collection unit 26.

  FIG. 3 shows that in the exhaust gas purification apparatus described in Patent Document 3, PM36, which is a particulate material, is collected in a large lump in the collection unit 26 in the same manner as the particulate matter is collected at the ground electrode. A state in which they are gathered to form a massive PM38 is shown. As shown in FIG. 3, when the amount of PM 36 collected in the collection unit 26, that is, the amount of accumulation is increased in the case 22 (FIG. 2), a part of the bulk PM 38 is a large lump from the collection unit 26. Peel off. The peeled bulk PM38 is discharged from the case 22 (FIG. 2) to the exhaust downstream side and then sent to the downstream DPF 18 (FIG. 1). In the downstream DPF 18, a large amount of large PM 38 is sent, so that a large amount of PM 36 is collected by the downstream DPF 18. Exhaust gas discharged from the downstream DPF 18 is discharged into the atmosphere via a muffler (not shown). Thus, the charging device 16 (FIGS. 1 and 2) has a function of a particulate matter enlarging device that enlarges the size of the PM 36.

  Returning to FIG. 1, a controller (not shown) is provided in the exhaust gas purification apparatus 10, and control is performed to increase the exhaust temperature by increasing the rotational speed of the diesel engine 12 or changing the fuel injection timing by the controller. You can also.

  According to the exhaust purification apparatus 10 of this embodiment, in the charging device 16, the PM 36 is charged with a negative high voltage by the charging electrode 24, and the charged PM 36 is collected by the collection unit 26 on the exhaust downstream side. It can be collected electrostatically. Moreover, PM36 can be made into large lump PM38 electrostatically terminated by the collection part 26. FIG. Further, even when the massive PM 38 flows from the collection unit 26 to the exhaust downstream side, the massive PM 38 that has flowed can be sufficiently collected by the downstream DPF 18.

  Further, since the upstream DPF 14 is provided on the exhaust upstream side of the charging device 16, PM 36 sent to the charging device 16 after being discharged from the diesel engine 12 can be reduced. That is, most of the PM 36 discharged from the diesel engine 12 can be removed by the upstream DPF 14. By being sent to the charging device 16, the PM 36 adhering to the non-conductive insulator 32 that supports the charging electrode 24 of the charging device 16 can be sufficiently reduced. For this reason, the trouble of removing PM36 adhering to the insulator 32 can be suppressed, and maintenance can be improved. Further, coupled with the fact that the amount of PM 36 to be charged by the charging device 16 can be reduced, the power consumption required for removing the PM 36 can be reduced.

  For example, according to the experiment by the inventors of the present invention, the exhaust gas purifying apparatus having a configuration excluding the upstream DPF 14 in the configuration of the present embodiment and deviating from the present invention has a certain amount or less of PM contained in the exhaust gas discharged. The power required to reduce the power to 20 kV was 16 W when 0.8 mA at 20 kV, but according to the exhaust gas purification apparatus similar to the present embodiment, when the required power is 0.37 mA at 20 kV 7.4 W, and it was found that the power consumption can be sufficiently reduced by about 54% compared to the case without the upstream DPF 14, that is, the power can be saved. Moreover, according to this Embodiment, in order to remove PM36 adhering to the insulator 32, it becomes unnecessary to newly provide another removal apparatus. As a result, according to the present embodiment, the manufacturing cost can be reduced, the maintenance can be improved, and the PM in the exhaust gas can be sufficiently removed while reducing the power consumption.

  In addition, since the upstream DPF 14 and the downstream DPF 18 have the same structure, the cost can be reduced by sharing parts while suppressing the PM 36 discharged from the exhaust purification device 10 to a sufficiently small amount.

  The collection part 26 is made of a porous or mesh-like conductor, and the downstream DPF 18 has a porous wall part, and the received PM 36 is a filter-side micropore provided in the wall part. When the passage width of the filter-side microhole is made smaller than the minimum passage width D of the hole 35 that is a PM passage hole provided in the collection portion 26, the collection portion 26 PM 36 flowing from the downstream side DPF 18 can be collected more effectively.

  4 and 5 are diagrams for explaining the effect of the configuration of the present embodiment in more detail. FIG. 4 is a diagram illustrating an example of the collection rate distribution with respect to the particle size of the particulate matter (PM) in the upstream diesel particulate matter removal filter (upstream DPF). FIG. 5 shows the discharge rate distribution with respect to the particle size of the particulate matter (PM) immediately after being discharged from the diesel engine 12 or the charging device 16 in the experimental results performed to confirm the effect of the present embodiment. FIG. As shown by a solid line α in FIG. 4, the collection rate of PM36 of each particle size with respect to PM36 (FIG. 3) of all particle sizes in the upstream DPF 14 (FIG. 1) is within a certain range, for example, 100 nm. It has been found that it falls excessively in the vicinity of. In the description and drawings of the present embodiment, “PM particle size” includes not only the particle size of PM 36 but also the diameter of massive PM 38 in which PM 36 is aggregated in a massive shape.

  The reason why the PM36 collection rate decreases excessively within a certain range is as follows. That is, the one-dot chain line β in FIG. 4 indicates the collection rate generated only by the cause of PM36 being collected in the upstream DPF 14 by the intermolecular force of the PM36 and Brownian motion among the collection rate of PM36 in the upstream DPF 14. Represents. Also, the two-dot chain line γ in FIG. 4 is a collection that occurs only due to the fact that the size of PM36 in the upstream DPF 14 is larger than the size of the filter-side micropores in the upstream DPF 14. Represents the rate.

  When the particle size of the PM 36 is smaller than around 100 nm, the PM 36 is likely to adhere to the filter body due to the intermolecular force acting between the PM 36 and the filter body of the upstream DPF 14. Further, when the particle size of the PM 36 is smaller than 100 nm, the PM 36 easily moves in a Brownian motion, so that the PM 36 is liable to stay in the filter-side micropore provided in the wall portion of the filter body. As a result, as shown in FIG. 4, when the particle size of the PM 36 is smaller than a certain range, that is, near 100 nm, the PM 36 is easily collected by the upstream DPF 14.

  Further, when the particle size of PM36 becomes larger than around 100 nm, the particle size of PM36 becomes larger than the filter-side micropores of the upstream DPF 14, so that the PM 36 is easily collected by the upstream DPF 14. That is, as shown in FIG. 4, when the particle size of PM 36 is larger than a certain range, that is, near 100 nm, the particles are easily collected due to a dimensional difference from the portion through which PM 36 passes in upstream DPF 14.

  As a result, it is difficult for the upstream DPF to collect PM36 having a particle size near 100 nm, and therefore, a large amount of PM36 having a particle size near 100 nm flows out from the upstream DPF 14. In contrast, in the present embodiment, the charging device 16 is provided on the exhaust downstream side of the upstream DPF 14. As described above, in the charging device 16, the particle size can be increased by changing the PM 36 to the bulk PM 38 by charging with the charging electrode 24. For this reason, even when the PM 36 is peeled off from the collecting unit 26 and flows out of the charging device 16, the downstream DPF 18 having the same structure as that of the upstream DPF 14 captures a large amount of PM 36 having a large particle size deviating from around 100 nm. As a result, PM 36 discharged from the downstream DPF 18 can be sufficiently reduced.

  In FIG. 5, the discharge rate of PM 36 and massive PM 38 immediately after being discharged from the diesel engine 12 (FIG. 1) is represented by a one-dot chain line δ. The solid line η represents the discharge rate of PM 36 and bulk PM 38 immediately after being discharged from the diesel engine 12 and then discharged from the charging device 16 after charging. Note that FIG. 5 shows the distribution of the emission rate, and the actual PM 36 and massive PM 38 emissions are those immediately after being discharged from the charging device 16 (solid line η in FIG. 5) and those immediately after being discharged from the diesel engine 12. The total is smaller than (the one-dot chain line δ in FIG. 5). As is apparent from the experimental results shown in FIG. 5, according to the present embodiment, the particle size of PM 36 having the largest amount discharged is 1.5 μm, which is greatly deviated from 100 nm, through the charging device 16. I was able to confirm that it can be enlarged.

  Note that the present invention is not limited to the configuration of the present embodiment. For example, the structure of the collecting portion 26 of the charging device 16 is not limited to that of a metal foam or a stainless steel mesh, and is porous for plating. Various structures such as a body and a honeycomb structure filter coated with a conductive paint can be employed.

1 is a schematic configuration diagram of an example exhaust emission control device according to an embodiment of the present invention. It is a schematic sectional drawing which shows the charging device with which the exhaust gas purification device of FIG. 1 is provided. It is a schematic diagram for demonstrating the state where the magnitude | size of a particulate matter becomes large in the collection part of a charging device. It is a figure which shows one example of the collection rate distribution with respect to the particle size of the particulate matter (PM) in an upstream diesel particulate matter removal filter (upstream DPF). In the experimental result performed in order to confirm the effect by this Embodiment, it is a figure which shows the discharge rate distribution with respect to the particle size of the particulate matter (PM) immediately after discharging | emitting from a diesel engine or a charging device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Exhaust purification device, 12 Diesel engine, 14 Upstream DPF, 16 Charging device, 18 Downstream DPF, 20 Exhaust pipe, 22 Case, 24 Charging electrode, 26 Collection part, 28 Exhaust inlet, 30 Exhaust outlet, 32 Insulator , 34 power supply, 35 holes, 36 particulate matter (PM), 38 bulk PM.

Claims (4)

An exhaust emission control device for removing particulate matter contained in exhaust gas from an internal combustion engine,
A plurality of particulate matter removal filters arranged at different positions with respect to the exhaust flow;
A charging device;
Among the plurality of particulate matter removal filters, a charging device is connected between the upstream particulate matter removal filter on the exhaust upstream side and the downstream particulate matter removal filter on the exhaust downstream side,
The charging device includes a charging unit that charges the particulate matter, and a collection unit that is provided on the exhaust downstream side of the charging unit and is grounded.
The collection unit is capable of collecting in a state where at least a part of the charged particulate matter is electrostatically concentrated into a large lump.
An exhaust emission control device characterized in that the downstream particulate matter removal filter is capable of collecting at least a part of the particulate matter collected by the collection unit. The exhaust emission control device according to claim 1,
The charging unit is characterized in that the particulate matter is charged with a negative high voltage. The exhaust emission control device according to claim 1 or 2,
The exhaust gas purification apparatus, wherein the upstream particulate matter removal filter and the downstream particulate matter removal filter have the same structure. The exhaust emission control device according to any one of claims 1 to 3,
The collection part is made of a porous or network conductor,
The downstream particulate matter removal filter has a porous wall portion, and the received particulate matter is discharged through the micropores provided in the wall portion,
An exhaust emission control device characterized in that the passage width of the micropores provided in the wall portion is smaller than the minimum passage width of the particulate matter passage hole provided in the collection portion.

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