JP4736724B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to an exhaust gas purification apparatus that purifies particulate matter in exhaust gas discharged from a diesel engine by collecting and oxidizing the exhaust gas.

  In general, exhaust gas of a diesel engine contains particulate matter (hereinafter referred to as PM (Particulate Matter)) whose main component is carbon, and is known to cause air pollution. Therefore, various apparatuses or methods for capturing and removing these particulate substances from exhaust gas have been proposed.

For example, by forcibly supplying fuel, the temperature of a diesel particulate filter (DPF) is raised to oxidize and burn the collected PM. NO ₂ is generated from NO in exhaust gas, and NO ₂ The one that oxidizes PM by the above (for example, Patent Document 1), the one that attempts to oxidize PM using a catalyzed DPF (for example, Patent Document 2, Patent Document 3), and the like have been proposed. However, the one that forcibly inject and supply fuel, with deteriorated fuel efficiency, DPF corruption problem caused by the temperature rise of the results of the rapid combustion of PM, than those described in Patent Document 1, according to the NO ₂ PM The problem that it is difficult to completely oxidize and remove PM discharged from the engine because the oxidation rate of the catalyst is not sufficient, and those using the catalyzed DPF described in Patent Document 2 and Patent Document 3, Further, since both PMs are solid, there is a problem that they are not sufficiently in contact with each other and PM oxidation reaction is insufficient.

Therefore, recently, a technique for oxidizing and treating PM using ozone O ₃ having a stronger oxidizing power than NO ₂ has been disclosed (for example, Patent Document 4). In the method and apparatus for post-processing exhaust gas of a diesel engine described in Patent Document 4, ozone O ₃ or nitrogen dioxide NO ₂ as an oxidant is generated from the exhaust gas by plasma upstream of the particulate filter. According to the exhaust gas temperature, ozone and nitrogen dioxide are selectively used at low temperatures and nitrogen dioxide is selectively used at high temperatures to oxidize and remove the soot collected in the particulate filter.

Special Table 2002-53762 JP-A-6-272541 JP-A-9-125931 JP 2005-502823 A

By the way, in the method and apparatus for post-processing the exhaust gas of the diesel engine described in Patent Document 4, since ozone O ₃ having a stronger oxidizing power than NO ₂ is used, the improvement in PM oxidation removal capability is described. Can be evaluated. However, in the thing of patent document 4, sufficient ozone does not spread to the site | part of the downstream of a particulate filter, but there exists a problem that PM deposited on this site | part cannot fully be oxidized and removed.

  For example, when a wall flow type is used as the particulate filter, ozone that has flowed into the particulate filter from the upstream end of the particulate filter first removes the PM deposited on the upstream side of the particulate filter by oxidation. When this happens, the flow path resistance is reduced at the upstream site where the PM is removed, and ozone flows exclusively through that site. As a result, sufficient ozone does not reach the part downstream of the particulate filter, and PM oxidation removal by ozone cannot be sufficiently performed.

  Accordingly, an object of the present invention is to provide an internal combustion engine that can effectively oxidize and remove PM deposited at a downstream site of a particulate filter when oxidizing and removing PM deposited on the particulate filter using ozone. An object is to provide an exhaust emission control device.

  In order to achieve the above object, an embodiment of the present invention includes a particulate filter that collects particulate matter in exhaust gas in an exhaust passage, and an ozone supply that can supply ozone from the upstream side to the particulate filter. An exhaust gas purification apparatus for an internal combustion engine comprising means for supporting a catalyst for oxidizing and removing the particulate matter in a downstream portion of the particulate filter.

  According to this aspect of the present invention, the catalyst for oxidizing and removing the particulate matter is supported on the downstream side of the particulate filter where sufficient ozone does not spread. Particulate matter can be effectively oxidized and removed.

  Here, preferably, the particulate filter includes a large number of front-end open cells and rear-end open cells arranged alternately adjacent to each other with a partition wall as a boundary, and the front-end open cell includes the particulate filter. It opens at the front end position to form an exhaust gas inlet, the rear end is closed, and the rear end open cell opens at the rear end position of the particulate filter to form an exhaust gas outlet, and the front end is The partition is made of a porous material that allows the passage of exhaust gas from the front-end open cell to the rear-end open cell while collecting the particulate matter during the passage, and the catalyst is the partition It is not carried on the front side of the partition, but is carried on the rear side of the partition wall.

  As described above, when the particulate filter is a wall flow type having a large number of open front cells and open rear cells that are alternately adjacent to each other with a partition wall as a boundary, supply ozone is difficult to spread behind the open front cells. . According to this preferred embodiment, since the catalyst is supported on the rear side of the partition wall, the particulate matter deposited without being oxidized by ozone can be effectively removed by the catalyst.

  Preferably, the catalyst is supported on the front end open cell side behind the partition wall.

  Particulate matter that is not oxidized by ozone is deposited only on the front open cell side behind the partition wall. Therefore, by supporting the catalyst at this site, particulate matter deposited without being oxidized by ozone can be effectively removed by the catalyst.

  Preferably, the catalyst is also supported on the rear open cell side on the rear side of the partition wall.

  This simplifies the manufacture of the particulate filter.

  Preferably, the front end of the catalyst is positioned following the flow velocity distribution shape of the exhaust gas flowing into the particulate filter.

  Particulate matter that is not oxidized by ozone is deposited at the rear portion of the flow velocity distribution shape of the exhaust gas flowing into the particulate filter. Therefore, by positioning the front end of the catalyst following this shape, the particulate matter can be effectively removed by oxidation with the minimum necessary catalyst.

  Preferably, the front end of the catalyst is positioned forwardly toward the outer peripheral side of the particulate filter.

  According to the present invention, when the PM deposited on the particulate filter using ozone is oxidized and removed, the PM deposited on the downstream portion of the particulate filter can be effectively oxidized and removed. The effect is demonstrated.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a system diagram schematically showing an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention. In the figure, 10 is a compression ignition type internal combustion engine, that is, a diesel engine, 11 is an intake manifold communicated with an intake port, 12 is an exhaust manifold communicated with an exhaust port, and 13 is a combustion chamber. In the present embodiment, the fuel supplied from a fuel tank (not shown) to the high pressure pump 17 is pumped to the common rail 18 by the high pressure pump 17 and accumulated in a high pressure state. The fuel is directly injected into the combustion chamber 13. Exhaust gas from the diesel engine 10 flows from the exhaust manifold 12 through the turbocharger 19 and then flows into the exhaust passage 15 downstream thereof, and after being purified as described later, is discharged to the atmosphere. In addition, as a form of a diesel engine, it is not restricted to the thing provided with such a common rail type fuel injection device. It is also optional to include other exhaust purification devices such as EGR devices.

The exhaust passage 15 is provided with a particulate filter that collects particulate matter (PM) in the exhaust gas, that is, a diesel particulate filter (hereinafter referred to as DPF) 30. An ozone supply member 40 as an ozone supply means capable of supplying ozone (O ₃ ) to the DPF 30 is disposed in the exhaust passage 15 upstream of the DPF ₃₀ . An ozone generator 41 as an ozone generating means is connected to the ozone supply member 40, and ozone generated by the ozone generator 41 is supplied to the ozone supply member 40 via the ozone supply passage 42, and this ozone supply member Injected into the exhaust passage 15 from 40 toward the downstream DPF 30.

  The DPF 30 is supported via a support member (not shown) in a substantially cylindrical metal casing 20 that forms a part of the exhaust passage 15 and has both ends formed in a truncated cone shape. The support member has insulating properties, heat resistance, buffer properties, and the like, and is made of, for example, an alumina mat.

  2 and 3 show details of the DPF 30. FIG. The DPF 30 is formed in a monolithic shape as a whole, and is arranged such that its axis coincides with the axis of the exhaust passage 15, that is, the axis of the casing 20. Here, in the DPF 30, the direction toward the upstream side in the exhaust gas flow direction (shown by the white arrow in the drawing) in the exhaust passage 15 is “front”, and the direction toward the downstream side in the exhaust gas flow direction in the exhaust passage 15 is “ After.

  The DPF 30 includes a so-called wall flow type honeycomb structure 30a formed of a porous material made of ceramics or metal such as cordierite, silica, alumina, silicon carbide, and the like, and is divided into a number of cells partitioned by porous partition walls 31. 310, 320 are provided. These cells 310 and 320 form an exhaust gas passage, and both extend in the axial direction of the DPF 30 along the entire length of the DPF 30. These cells include a front end open cell 310 and a rear end open cell 320. The front end open cell 310 is opened at the position of the front end 32 of the DPF 30 to form the exhaust gas inlet 33 of the DPF 30, and the rear end is closed by a plug 311. The rear end open cell 320 is opened at the position of the rear end 34 of the DPF 30 to form the exhaust gas outlet 35 of the DPF 30, and the front end thereof is closed by a plug 321.

  The front end open cell 310 and the rear end open cell 320 are arranged so as to be alternately adjacent to each other with the partition wall 31 as a boundary and in parallel with each other. As shown in FIG. 3, the front end open cell 310 and the rear end open cell 320 are arranged in a checkered pattern when viewed from the front. The exhaust gas that has flowed into the front end open cell 310 from the exhaust gas inlet 33 flows in the axial direction along the front end open cell 310, and at the same time passes through the partition wall 31 (that is, flows in the radial direction). And then flows along the rear-end open cell 320 and is discharged from the exhaust gas outlet 35. When the exhaust gas passes through the partition wall 31, PM in the exhaust gas is filtered and collected by the partition wall 31 to prevent the release of PM into the atmosphere.

  As the ozone generator 41, the form which generate | occur | produces ozone, flowing the dry air or oxygen used as a raw material in the discharge tube which can apply a high voltage, and the other arbitrary forms can be used. The dry air or oxygen used as a raw material here is a gas taken from outside the exhaust passage 15, for example, a gas contained in the outside air, unlike the case of Patent Document 4, and the exhaust gas in the exhaust passage 15 as in Patent Document 4 is used. It is not a gas contained in gas. Moreover, the air or oxygen used here is not limited to a dry state. In the ozone generator 41, ozone generation efficiency is higher when a low temperature source gas is used than when a high temperature source gas is used. Therefore, by generating ozone using the gas outside the exhaust passage 15 in this way, it is possible to improve the ozone generation efficiency as compared with the case of Patent Document 4.

  Although the ozone supply member 40 will be described in detail later, the ozone supply member 40 is positioned immediately upstream of the DPF 30 so that the ozone that is injected and supplied from this reacts with NOx and unburned components (CO, HC, etc.) in the exhaust gas and is not consumed by anyone. The ozone is supplied to the DPF 30 from there. Moreover, it has the several ozone supply port 43 arrange | positioned so that the whole diameter of the front-end surface of DPF30 may be covered so that ozone can be supplied to the whole front-end surface of DPF30 uniformly. The ozone supply member 40 extends in the diameter direction of the DPF 30 and is fixed in the casing 20. The ozone supply port 43 is disposed on the back side of the ozone supply member 40 and is directed rearward. As a result, the exhaust gas coming from the upstream side is not directly received by the ozone supply port 43, and the ozone supply port 43 is prevented from being clogged. Various forms other than the ozone supply member 40 are possible as the form of the ozone supply means. For example, when there is only one ozone supply port, the ozone supply port and the front end surface of the DPF The distance should be separated by a distance that allows ozone to spread throughout the entire front end face.

Here, the reaction consumption of NOx and ozone will be described in detail. If ozone O ₃ reacts with NOx in exhaust gas, particularly NO, the reaction formula is expressed by the following formula.
NO + O ₃ → NO ₂ + O ₂ (1)

The NO ₂ produced by this reaction further reacts with ozone O ₃ as in the following formula.
NO ₂ + O ₃ → NO ₃ + O ₂ (2)

Further, NO ₃ produced by this reaction is decomposed into NO ₂ and O ₂ as shown in the following equation.
2NO ₃ → 2NO ₂ + O ₂ (3)

Here, when attention is paid to the equation (1), ozone O ₃ is consumed for the oxidation of NO, and when attention is paid to the equation (2), the ozone O ₃ is consumed for the oxidation of NO ₂ . When attention is paid to the equation (3), NO _{2 on} the right side becomes NO ₂ on the left side of the equation (2), and thus ozone O ₃ is consumed to oxidize NO ₂ on the left side of the equation (2).

  Thus, NOx and ozone repeat a chain reaction. Therefore, if ozone is supplied into the exhaust gas atmosphere containing NOx, ozone is consumed for oxidation and decomposition of NOx, and the amount of ozone that can be provided to the DPF 30 is reduced accordingly. Since generation of ozone by the ozone generator 41 requires electric power, such wasteful consumption of ozone leads to wasteful consumption of electric power, which may result in deterioration of fuel consumption. Therefore, it is preferable that ozone reaches the DPF 30 as soon as possible.

On the other hand, when ozone is supplied into an exhaust gas atmosphere in which HC exists, a reaction occurs in which ozone O ₃ partially oxidizes HC to generate CO, CO ₂ , and H ₂ O. This also causes the same problem as described above. Therefore, it is preferable that ozone reaches the DPF 30 as soon as possible.

  In the present embodiment, means for detecting the amount of PM collected or the degree of clogging in the DPF 30 is provided. That is, exhaust pressure sensors 51 and 52 for detecting exhaust pressure are provided in the exhaust passage 15 upstream and downstream of the DPF 30, respectively, and these exhaust pressure sensors 51 and 52 are connected to the ECU 100 as control means. The ECU 100 determines the PM in the DPF 30 based on the deviation (Pu−Pd) between the upstream exhaust pressure Pu detected by the upstream exhaust pressure sensor 51 and the downstream exhaust pressure Pd detected by the downstream exhaust pressure sensor 52. Judge the amount of clogged or clogged.

  More specifically, the ECU 100 determines that the PM collection amount in the DPF 30 has reached the maximum value when the deviation (Pu−Pd) exceeds a predetermined value, and turns on the ozone generator 41 to turn on the ozone generator. Ozone generation by 41 is executed. The generated ozone is jetted and supplied from the supply port 43 of the ozone supply member 40 to the DPF 30, whereby the PM deposited on the DPF 30 is removed by oxidation with ozone. In this way, the operation for removing the PM deposited on the DPF 30 by oxidation (combustion) to restore the original performance of the DPF 30 is called regeneration.

  Although the upstream exhaust pressure sensor 51 is disposed on the upstream side of the ozone supply member 40 in the present embodiment, it may be disposed on the downstream side of the ozone supply member 40. In this embodiment, the amount of PM trapped or clogged is detected by the differential pressure on the upstream and downstream sides of the DPF 30, but the amount of trapped or clogged is only detected by one exhaust pressure sensor arranged on the upstream side of the DPF 30. It may be detected. Furthermore, the degree of clogging can also be detected by obtaining the temporal integration of the soot signal of the soot sensor arranged upstream of the DPF. Similarly, engine characteristic map data stored in the ECU relating to soot generation can be evaluated and integrated over time. In the present embodiment, ozone generated by turning on the ozone generator 41 is supplied immediately when ozone is supplied. However, ozone may be generated and stored in advance, and ozone may be supplied by switching valves. Good. It is also possible to supply ozone by pressurizing it with a pump or a compressor.

  In the present embodiment, means for detecting the temperature of the exhaust gas flowing into the DPF 30 or the DPF floor temperature is provided. That is, a temperature sensor 53 is provided at a position immediately upstream of the DPF 30, and the ECU 100 calculates an exhaust temperature at a position immediately upstream of the DPF 30 based on a detection signal of the temperature sensor 53. The temperature sensor 53 detects the exhaust temperature at a position between the ozone supply member 40 and the DPF 30. In addition, it is preferable that the temperature detection part (the front-end | tip in the case of a thermocouple) of the temperature sensor 53 is located in the center vicinity of the front-end surface of DPF30. Since the temperature sensor 53 detects the bed temperature inside the DPF 30, the temperature detection unit may be embedded in the DPF 30.

  When oxidizing and removing PM by ozone, there is an optimum window showing high removal efficiency (PM oxidation rate) with respect to the temperature of exhaust gas flowing into the DPF 30 or the DPF bed temperature. That is, a remarkable removal efficiency is exhibited when the temperature is within a predetermined range (for example, 150 to 250 ° C.). Therefore, in the case of the present embodiment, even if the exhaust pressure deviation of the DPF 30 exceeds a predetermined value, the ECU 100 executes ozone supply only when the detected exhaust temperature is within the predetermined range, and is detected. If the exhaust temperature is not within the predetermined range, ozone supply is not executed. This makes it possible to use ozone efficiently.

  Referring to FIG. 2, in the case of the DPF 30, the exhaust gas flows from the exhaust gas inlet 33 of the front end 32 and flows through the front end open cell 310, and passes through the partition wall 31 in the process to the rear end open cell 320. Inflow. At this time, PM in the exhaust gas is collected by filtration by the partition wall 31 and is particularly deposited on the front end open cell 310 side that is the inflow side of the partition wall 31. On the other hand, ozone supplied to the DPF 30 flows along the same path as the exhaust gas, and oxidizes PM deposited on the front end open cell 310 side of the partition wall 31.

  At this time, since ozone flows into the DPF 30 from the front end side, PM is oxidized from the front end of the DPF 30. When the PM deposited on the front portion (upstream side) of the DPF 30 is oxidized and removed, the flow path resistance when ozone and exhaust gas pass through the partition wall 31 at that portion is reduced. Passes exclusively through the front. In this case, ozone is difficult to spread in the rear part (downstream side) of the DPF 30, and PM that is not oxidized remains and accumulates in that part. For example, when the exhaust temperature rises to about 500 to 600 ° C., the accumulated PM is self-ignited and burns at once. If this happens, there is a possibility that the DPF 30 may be damaged, such as cracking in the DPF 30 or melting of the DPF 30 due to the heat generation.

  Therefore, in the DPF 30 according to the present embodiment, as shown in FIG. 2, a catalyst for removing PM by oxidation, that is, a PM oxidation catalyst 37 is supported on the rear portion, that is, the downstream side portion of the DPF 30. By doing so, it becomes possible to oxidize and remove PM at the rear portion of the DPF that is not oxidized and removed by ozone by the PM oxidation catalyst 37. As a result, self-ignition of PM can be prevented and damage to the DPF 30 can be prevented.

  Here, as the PM oxidation catalyst 37, in addition to the Ce—Zr composite oxide, as a catalyst material for oxidizing PM, for example, noble metals such as platinum Pt, palladium Pd, rhodium Rh, and potassium K, sodium Na, lithium At least one selected from alkali metals such as Li and cesium Cs, alkaline earth metals such as barium Ba, calcium Ca, and strontium Sr, rare earths such as lanthanum La, yttrium Y, and cerium Ce, and transition metals such as iron Fe are active. Coated or supported as an oxygen generator.

  In the first form of the DPF 30 shown in FIG. 2, the PM oxidation catalyst 37 is not carried on the front side of the partition wall 31, in the present embodiment, on the front half, but on the rear side of the partition wall 31, in the present embodiment. The entire rear half is supported or coated. Here, the PM oxidation catalyst 37 is supported on both the front end open cell 310 side and the rear end open cell 320 side of the partition wall 31, that is, on both the inflow side and the outflow side of the partition wall 31.

  As a method of manufacturing the DPF 30, first, a DPF material (ceramic honeycomb structure 30a) having a plug 321 only provided at the front end of the rear end open cell 320 is prepared, and the rear end is directed downward. -It is immersed so that the latter half part of DPF30 may be immersed in the slurry containing Zr complex oxide. Next, the DPF material coated with this Ce—Zr composite oxide is immersed in, for example, a potassium acetate solution so that the latter half portion is immersed therein, water is loaded with potassium, dried, and then fired at a predetermined temperature for a predetermined time. In this way, in the DPF material carrying the PM oxidation catalyst 37, the plug 311 is applied to the rear end of the front end open cell 310 using a ceramic bond or the like to complete the DPF 30.

  When viewed microscopically, the PM oxidation catalyst 37 is only supported on the surface of countless ceramic structures forming the partition walls 31, and pores between the ceramic structures are still secured (that is, the PM oxidation catalyst 37). Therefore, the filter function of the partition wall 31 is not lost by the coating of the PM oxidation catalyst 37.

  Next, a second form of the DPF 30 is shown in FIG. In addition, about the structure similar to said 1st form, the same code | symbol is attached | subjected in a figure, and detailed description is abbreviate | omitted. In the second form of the DPF 30, the PM oxidation catalyst 37 is not carried on the first half part of the partition wall 31, but is carried on the second half part of the partition wall 31, similar to the first form. The PM oxidation catalyst 37 is different from the first embodiment in that the PM oxidation catalyst 37 is supported only on the front end open cell 310 side of the partition wall 31 and is not supported on the rear end open cell 320 side.

  In this case, as a method for manufacturing the DPF 30, a plug 321 is applied to the front end of the rear end open cell 320 of the DPF material, and a temporary plug that can be removed is also applied to the rear end of the rear end open cell 320. The same process as in the first embodiment is performed so that the solution does not enter the open cell 320 from the rear end. Finally, the temporary plug is removed to complete the DPF 30.

  When comparing the first form and the second form, the first form is disadvantageous than the second form in that a useless PM oxidation catalyst 37 that does not contribute to PM oxidation is carried. That is, PM in the exhaust gas is captured by the partition wall 31 and does not flow into the rear end open cell 320. Therefore, it is meaningless to support the PM oxidation catalyst 37 on the partition wall 31 defining the rear end open cell 320. That's why. On the other hand, the first form is advantageous over the second form in that the manufacturing is simplified. That is, in the second embodiment, a process of attaching / detaching temporary plugs one by one is added to the rear ends of many rear end open cells 320, and the number of processes and the process time increase.

  Next, a third form of the DPF 30 is shown in FIG. In addition, about the structure similar to said 1st form, the same code | symbol is attached | subjected in a figure, and detailed description is abbreviate | omitted. In the third form of the DPF 30, the PM oxidation catalyst 37 is not carried on the first half part of the partition wall 31 and is supported on the second half part of the partition wall 31 as in the first and second embodiments. It is. The PM oxidation catalyst 37 is supported only on the front end open cell 310 side of the partition wall 31 and is not supported on the rear end open cell 320 side, as in the second embodiment.

  The difference from the first and second embodiments is that the front end 38 of the PM oxidation catalyst 37 is positioned following the flow velocity distribution shape of the exhaust gas flowing into the DPF 30. That is, the PM oxidation catalyst 37 is supported on the partition wall 31 from the position of the front end 38 to the rear end of the front end open cell 310.

As shown in FIG. 5, the exhaust gas flow velocity distribution shape is a curved shape connecting points that are located rearward toward the center side of the DPF 30 in the present embodiment, and conversely, the outer periphery of the DPF 30. It is a curved shape connecting points that are located forward as it goes to the side. More specifically, in the case of this embodiment, in the side cross-section as shown, the center of the DPF 30 is the y axis, and a line perpendicular to the y axis is drawn at the front end position of the plug 311 on the y axis. When this is the x-axis, the shape is equal to or approximate to a quadratic curve represented by y = ax ² + b. Here, the intersection of the x-axis and the y-axis is the origin, the direction toward the front of the DPF 30 is the positive direction of the y-axis, and a and b are predetermined constants (provided that a> 0) obtained by experiments or the like. In this embodiment, b = 0. In the case of this embodiment, the front end 38 of the PM oxidation catalyst 37 is positioned in the middle of the partition wall 31 in the longitudinal direction in the outermost peripheral cell. Such a shape applies not only to the side cross section shown in the figure but also to the plane cross section. The same can be applied to a case where a DPF having an elliptical cross section is assumed as an embodiment. However, the exhaust gas flow velocity distribution shape can be changed according to the shape and structure of the DPF, the way of exhaust gas inflow, and the like, and is often obtained by experiments. The front end position and the carrying length of the PM oxidation catalyst 37 are appropriately changed according to the exhaust gas flow velocity distribution shape.

  According to experiments conducted by the present inventors using a DPF that does not carry a PM oxidation catalyst, it is clear that the flow velocity distribution of the exhaust gas in the DPF is as described above. Was deposited and remained without being oxidized by ozone. That is, as it goes from the center of the DPF to the outer peripheral side, the longitudinal length of PM deposited without being oxidized becomes longer, and the front end position thereof is shifted forward. This is because the amount of ozone flowing into the DPF is large on the center side according to the flow velocity distribution of the exhaust gas, decreases on the outer peripheral side, and PM is removed earlier on the center side. This is because the amount of ozone decreases and more ozone flows through the central side, and sufficient ozone does not reach the outer peripheral portion and the rear portion. Therefore, by supporting the PM oxidation catalyst 37 only on the part where the PM is not oxidized by such ozone, it becomes possible to remove the PM that cannot be oxidized and removed by the ozone with the minimum amount of the PM oxidation catalyst 37. Become.

  In the third embodiment, as in the first embodiment, the PM oxidation catalyst 37 can be supported on both the front end open cell 310 side and the rear end open cell 320 side of the partition wall 31.

Next, the results of an experiment using a simulated gas (model gas) performed with respect to the present embodiment are shown below.
(1) Experimental apparatus FIG. 6 shows the whole experimental apparatus, and FIG. 7 shows the details of the VII part of FIG. 61 is a plurality of gas cylinders, and each gas cylinder is filled with a raw material gas for making a simulated gas imitating the exhaust gas composition of a diesel engine. The source gas here is a gas such as N ₂ , O ₂ , and CO. A simulation gas generator 62 includes a mass flow controller, and generates a simulation gas MG by mixing each raw material gas by a predetermined amount. As shown in detail in FIG. 7, the simulated gas MG passes through the DPF 66 disposed in the quartz tube 65 and is discharged to the outside from an exhaust duct (not shown).

As shown in FIG. 6, the gaseous oxygen O ₂ supplied from the oxygen cylinder 67 is bifurcated. On the other hand, the flow rate is controlled by the flow rate control unit 68 and then supplied to the ozone generator 69. In the ozone generator 69, oxygen is selectively and partially converted into ozone O _3, and these oxygen and ozone (or only oxygen) reach the ozone analyzer 70. On the other side of the branch, the flow rate of oxygen is controlled by another flow rate control unit 71, and then mixed with the gas supplied from the ozone generator 69 to reach the ozone analyzer 70. The ozone analyzer 70 measures the ozone concentration of the gas flowing into the gas, that is, the supply gas supplied to the DPF 66, and then the flow rate of the supply gas is controlled by the flow rate control unit 71. Excess supply gas is discharged to the outside from an exhaust duct (not shown), and the supply gas whose flow rate is controlled is connected to the simulated gas MG at a three-way elbow 72 arranged upstream of the quartz tube 65 as shown in FIG. After being mixed, it is supplied to the DPF 66 together with the simulation gas MG.

  An electric heater 73 is provided on the outer periphery of the quartz tube 65 so that the temperature of the DPF 66 is controlled. Further, a temperature sensor 76 for measuring the temperature at the position immediately upstream of the DPF 66 is provided.

Downstream of the DPF 66, an exhaust gas analyzer 77 for measuring HC, CO, NOx concentration, an exhaust gas analyzer 78 for measuring CO ₂ concentration, and an ozone analyzer 79 for measuring ozone concentration are respectively provided from the upstream side. They are arranged in series.

(2) Experimental conditions The electric heater 74 was controlled so that the temperature detected by the temperature sensor 76 was 200 ° C or 400 ° C. The composition of the simulated gas is 5% by volume, O ₂ is 5%, H ₂ O is 3%, and the balance is N ₂ . The flow rate of the simulation gas is 9.5 L (liter) / min, and the pressure of the simulation gas is 0.4 MPa. The composition of the supply gas is 20000 ppm for ozone O ₃ and the balance for O ₂ . The flow rate of the supply gas is 0.5 L (liter) / min.

(3) Experimental method Until the temperature detected by the temperature sensor 76 becomes constant, N ₂ is allowed to flow as a simulation gas. After the temperature becomes constant, oxygen is introduced into the ozone generator 69 to generate ozone. The instrument 69 is turned on. The oxidation amount (oxidation rate) of PM in the DPF 66 was calculated based on the CO and CO ₂ concentrations detected by the exhaust gas analyzers 77 and 78, and the average oxidation rate for 5 minutes after the supply gas supply was started. In other words, by dividing the product of the simulated gas flow rate, the detected volume concentration, and the measurement time (5 minutes) by the volume of 1 mol (for example, 22.4 L), the number of moles in the measurement time can be obtained. Based on this mol number, the oxidation amount (oxidation rate) of PM is calculated.

(4) Examples and Comparative Examples / Examples The DPF according to the first embodiment is manufactured as follows. That is, 30 mm in diameter, 50 mm in length, cuff thickness of 12 mil (milli inch length, 1/1000 inch) (0.3 mm), and 300 cpsi (cells per square) inch) (about 50 pieces per square centimeter) cordierite-made DPF material (honeycomb structure) with the rear end facing down and dipped in a slurry containing Ce-Zr composite oxide, the latter half of the DPF material is Ce Coat with -Zr composite oxide. The coating amount is 50 g / L (however, the denominator L (liter) means per 1 DPF). To this, potassium was absorbed in the latter half of the DPF material using a potassium acetate solution, dried, and then fired at 450 ° C. for 1 hour. The supported amount of potassium is 0.1 mol / L. A plug was applied to the rear end of the open end cell of the DPF material using a ceramic bond. In the DPF 66 thus formed, the catalyst is supported on the entire rear half of the partition wall, that is, on the front end open cell side and the rear end open cell side of the rear partition part, and the catalyst is not supported on the front half of the partition wall.

  Next, PM is deposited on the DPF 66 by the following method. That is, a container capable of installing 12 D Cordierite DPFs with a diameter of 30 mm and a length of 50 mm in parallel is placed in the exhaust pipe of a 2 L diesel engine, and exhaust gas under operating conditions of 2000 rpm and 30 Nm is circulated through it for 1 hour. PM was collected and deposited in DPF66.

  The DPF 66 on which the PM was deposited was placed in the quartz tube 65 and an experiment was conducted.

Comparative example 1
For the DPF of the above example, a catalyst is also coated on the first half in the following manner. That is, a DPF material (honeycomb structure) similar to that of the above-described example, in which neither the front end nor the rear end is plugged, is first dipped in a slurry containing Ce—Zr composite oxide with the rear end facing down. The latter half of the material is coated with Ce—Zr composite oxide. Next, this DPF material is dipped in a slurry containing Ce—Zr composite oxide with the front end facing down, and the front half of the DPF material is coated with Ce—Zr composite oxide. The total coating amount is 50 g / L, and each of the latter half and the first half 25 g / L. A potassium acetate solution was used for this, and potassium was absorbed in the latter half and the first half of the DPF material in the same manner, dried, and then fired at 450 ° C. for 1 hour. The total supported amount of potassium is 0.1 mol / L. The DPF material was plugged with a ceramic bond at the rear end of the front end open cell and the front end of the rear end open cell. In the DPF 66 thus formed, the catalyst is supported on the entire partition wall.

  PM was deposited on the DPF 66 in the same manner as in the previous example, and the DPF 66 on which this PM was deposited was placed in the quartz tube 65, and an experiment was conducted.

Comparative example 2
The DPF material (honeycomb structure) similar to the above example was not coated with a catalyst, and only the front and rear ends were plugged to prepare DPF 66. PM was deposited on the DPF 66 in the same manner as in the previous example, and the DPF 66 on which this PM was deposited was placed in the quartz tube 65, and an experiment was conducted.

(5) Experimental Results FIG. 8 shows a comparison of the PM oxidation rates of the examples, comparative example 1 and comparative example 2. In the figure, the unit g / hL of the PM oxidation rate on the vertical axis represents the number of grams of PM oxidized per liter of DPF and per hour. In each pair of bar graphs, the left bar graph is at a temperature of 200 ° C., and the right side is at a temperature of 400 ° C.

  When the temperature is 200 ° C., the Example has a higher PM oxidation rate than that of Comparative Example 1, and the PM purification efficiency is higher. This is presumably because, in Comparative Example 1, ozone was decomposed by the catalyst coated on the first half of the DPF and was not effectively used for PM oxidation. In addition, the Example has a PM oxidation rate equivalent to that of Comparative Example 2, and it was confirmed that the PM oxidation ability by ozone was not reduced by the catalyst coated on the latter half of the DPF of the Example.

  When the temperature is 400 ° C., the overall PM oxidation rate is lower than when the temperature is 200 ° C. This is because ozone naturally decomposes at such a high temperature. In particular, in Comparative Example 2, the PM oxidation rate is extremely low. This is because Comparative Example 2 has no catalyst and there is almost no means for oxidizing PM. On the contrary, since Example and Comparative Example 1 have a catalyst, PM can be oxidized by the catalyst, and an approximately equivalent allowable PM oxidation rate can be obtained. In particular, the active temperature range of the catalyst is about 350 to 400 ° C., which is higher than the effective temperature range of ozone, and PM oxidation by the catalyst can be performed even in such a temperature range where ozone cannot be used substantially. From the above results, in the case of the DPF according to the present embodiment, PM oxidation removal by ozone can be performed in a low temperature range where ozone can be used, and PM oxidation by a PM oxidation catalyst can be performed in a high temperature region where ozone cannot be used. There is an advantage that PM oxidation can be performed over a temperature range.

  As mentioned above, although embodiment of this invention has been described, this invention can also take other embodiment. For example, in the above embodiment, the partition wall is divided into the first half part and the second half part, and the catalyst is supported on the second half part, but the boundary between the front part and the rear part is at an intermediate position in the longitudinal direction of the partition wall. Not limited. For example, it may be before or after the intermediate position. It is also possible to provide another catalyst such as a NOx catalyst or an oxidation catalyst in series with the particulate filter according to the present invention.

  The present invention can be applied to all internal combustion engines that may generate PM, in addition to a diesel engine as a compression ignition type internal combustion engine. For example, a direct-injection spark ignition internal combustion engine, more specifically, a direct-injection lean burn gasoline engine. In this engine, fuel is directly injected into the in-cylinder combustion chamber. However, in a high load region where the fuel injection amount is large, the fuel does not completely burn and PM may be generated. Even when the present invention is applied to such an engine, the same effect as described above can be sufficiently expected.

1 is a system diagram schematically showing an exhaust gas purification apparatus for an internal combustion engine according to a first embodiment of the present invention. It is side surface sectional drawing which shows the 1st form of DPF. It is a front view of DPF. It is side surface sectional drawing which shows the 2nd form of DPF. It is side surface sectional drawing which shows the 3rd form of DPF. It is a figure which shows the whole experimental apparatus of the experiment conducted in relation to this embodiment. It is the VII section detail of FIG. It is a graph which shows an experimental result.

Explanation of symbols

10 Engine 15 Exhaust passage 20 Casing 30, 66 Diesel particulate filter (DPF)
31 Bulkhead 310 Front end open cell 311 Plug end 320 Rear end open cell 321 Plug end 32 Front end 33 Exhaust gas inlet 34 Rear end 35 Exhaust gas outlet 37 PM oxidation catalyst 38 Front end 40 Ozone supply member 41 Ozone generator 43 Ozone supply port 100 Electron Control unit (ECU)

Claims (4)

An exhaust gas purification apparatus for an internal combustion engine, comprising: a particulate filter that collects particulate matter in exhaust gas in an exhaust passage; and ozone supply means that can supply ozone to the particulate filter from its upstream side. ,
A catalyst for oxidizing and removing the particulate matter is supported on the downstream side of the particulate filter ,
The particulate filter comprises a number of front end open cells and rear end open cells arranged alternately adjacent to each other with a partition wall as a boundary,
The front end open cell opens at the front end position of the particulate filter to form an exhaust gas inlet, and the rear end is closed,
The rear end open cell opens at the rear end position of the particulate filter to form an exhaust gas outlet, and its front end is closed,
The partition wall is made of a porous material that collects the particulate matter during passage while allowing passage of exhaust gas from the front end open cell to the rear end open cell,
The catalyst is not supported on the front side of the partition wall, and is supported on the rear side of the partition wall,
An exhaust purification device for an internal combustion engine, wherein the front end of the catalyst is positioned following the flow velocity distribution shape of the exhaust gas flowing into the particulate filter .   2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the front end of the catalyst is positioned forward toward the outer peripheral side of the particulate filter. The exhaust purification device for an internal combustion engine according to claim 1 or 2 , wherein the catalyst is supported on the front end open cell side behind the partition wall. The exhaust purification device for an internal combustion engine according to any one of claims 1 to 3 , wherein the catalyst is supported on the rear end open cell side on the rear side of the partition wall.

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