JP2011174383A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of largely improving a fuel efficiency by reducing the frequency of forced regenerations more than before. <P>SOLUTION: This exhaust emission control device includes a main filter 13 which is installed halfway in an exhaust pipe 11 and collects the soot contained in exhaust gas 9, a sub filter 17 which is disposed on the former stage of the main filter 13 and reduced more in collecting efficiency than the main filter 13 so that a part of the soot contained in the exhaust gas 9 can be pre-collected, and a forced regeneration means (fuel injection device 16, a fuel oxidation catalyst 14) for burning and removing the soot collected in the main filter 13 by increasing the exhaust gas temperature to a predetermined one or higher on the inlet side of the sub filter 17. The soot oxidation catalyst is carried by the sub filter 17 so that the collected soot can be oxidized in a temperature range lower than the exhaust gas temperature increased by the forced regeneration means. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device.

  Since exhaust gas exhausted from diesel engines contains a large amount of carbonaceous soot, it has been conventionally practiced to install a particulate filter in the middle of the exhaust pipe through which exhaust gas flows. . This type of particulate filter has a porous honeycomb structure made of a ceramic such as cordierite, and the inlets of the flow paths partitioned in a lattice pattern are alternately sealed, and the inlets are not sealed. About the flow path, the exit is sealed, and only the exhaust gas which permeate | transmitted the porous thin wall which divides each flow path is discharged | emitted downstream.

And since the apportioned gas in the exhaust gas is collected and deposited on the inner surface of the porous thin wall, the apportioned material is appropriately burned and removed before the exhaust resistance increases due to clogging. Although it is necessary to regenerate, in normal diesel engine operating conditions, there are few opportunities to obtain exhaust temperatures that are high enough to cause self-combustion, so an oxidation catalyst such as Pt / Al ₂ O ₃ is supported. It has become so. That is, if such a catalyst regeneration type particulate filter is adopted, the oxidation reaction of the collected soot is promoted, the ignition temperature is lowered, and soot can be burned and removed even at a lower exhaust temperature than before. It becomes.

  However, even when such a catalyst regeneration type particulate filter is used, the trapped amount exceeds the apportioned amount in the operation region where the exhaust gas temperature is low. If the operation state at the temperature continues, there is a possibility that the particulate filter will fall into an over trapped state without the regeneration of the particulate filter proceeding well.

  In view of this, a flow-through type fuel oxidation catalyst is separately arranged in the front stage of the particulate filter, and when the accumulated amount of soot has increased, fuel is added to the exhaust gas upstream of the fuel oxidation catalyst and the particulate filter is added. It is considered to perform forced regeneration of the curate filter.

  That is, the fuel (HC) added upstream from the particulate filter undergoes an oxidation reaction while passing through the preceding fuel oxidation catalyst, and the particulate filter catalyst immediately after the inflow of exhaust gas heated by the reaction heat. The bed temperature is raised and the apportionment is burned out, and the particulate filter is regenerated.

  As a specific means for executing this kind of fuel addition, post-injection is added at the timing of non-ignition later than the compression top dead center following the main injection of fuel performed near the compression top dead center. What is necessary is just to add a fuel in gas.

  As prior art document information related to the forced regeneration of such a particulate filter, there is the following Patent Document 1 by the same applicant as the present invention.

JP 2003-193824 A

  However, in such a conventional exhaust purification device, a large amount of fuel is consumed by post-injection or the like for increasing the exhaust temperature every time forced regeneration is performed on the particulate filter with a large amount of accumulated deposits. Therefore, there was a problem that the fuel consumption of the diesel engine deteriorated.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide an exhaust emission control device capable of significantly improving fuel efficiency by reducing the frequency of forced regeneration as compared with the prior art.

  The present invention is equipped with a main filter that is provided in the middle of an exhaust pipe and collects soot in exhaust gas, and is arranged in front of the main filter so that a part of soot in exhaust gas can be collected in advance. A sub-filter having a lower collection efficiency than that of the main filter, and a forced exhaust of the soot collected in the main filter by raising the exhaust temperature to a predetermined temperature or more on the inlet side of the sub-filter An exhaust gas comprising a regeneration means, and a soot oxidation catalyst supported on the sub-filter so as to oxidize the soot collected in a temperature range lower than an exhaust temperature raised by the forced regeneration means This relates to a purification device.

  Thus, since a part of the spillage in the exhaust gas is collected in advance by the sub-filter in the front stage, the amount of spillage that must be collected by the main filter in the rear stage is small. As a result, the pace of apportioning in the main filter is significantly slower than when a conventional particulate filter is used alone. As a result, the regeneration interval from immediately after the completion of forced regeneration by the forced regeneration means until the next forced regeneration becomes necessary becomes longer, and the frequency of forced regeneration is less than before.

  In addition, the sub-filter of the front stage has a coarse pore diameter with a relatively lower collection efficiency than the main filter of the rear stage, and only a part of the fraction in the exhaust gas is collected in advance. In addition, the collected soot is also oxidized in the temperature range lower than the exhaust temperature during forced regeneration due to the catalytic action of the soot oxidation catalyst. There is no risk of the sub-filter in the previous stage becoming clogged before the forced regeneration is required.

Furthermore, in the present invention, a sub-filter is supported on the sub-filter by using one or more of CeO ₂ , ZrO ₂ , and Pr ₆ O ₁₁ as active species. It is preferable to support a CO / HC oxidation catalyst having Pt as an active species, which can oxidize CO and HC without any loss. Further, the average pore diameter of the main filter is 5 to 25 μm, and the collection efficiency is 60 It is preferable that the average pore diameter of the sub-filter is 25 to 100 μm and the collection efficiency is 30 to 70%.

  Further, in the present invention, a fuel oxidation catalyst that is disposed upstream of the sub-filter and that oxidizes the unburned fuel in the exhaust gas and heats the exhaust gas by reaction heat, and an exhaust gas upstream from the fuel oxidation catalyst. The forced regeneration means can be constituted by the fuel addition means for adding the fuel therein, or the forced regeneration means can be constituted by a burner arranged in front of the sub-filter.

  According to the above-described exhaust gas purification apparatus of the present invention, a part of the spillage in the exhaust gas is preliminarily collected by the front sub-filter, thereby significantly reducing the pace of the spillage accumulated in the rear-stage main filter. Therefore, the frequency of forced regeneration of the main filter can be reduced as compared with the prior art, so that the fuel consumed to increase the exhaust temperature during forced regeneration can be remarkably suppressed, and the fuel efficiency can be greatly improved compared to the conventional case. An excellent effect that it can be achieved can be achieved.

It is the schematic which shows an example of the form which implements this invention. It is a graph which shows the result of the combustion characteristic test of a prominent oxidation catalyst. It is a schematic diagram which shows the state of depth filtration. It is the schematic which shows another form example of this invention.

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

  FIG. 1 shows an example of an embodiment of the present invention. In FIG. 1, 1 denotes a diesel engine equipped with a turbocharger 2, and intake air 4 guided through an air cleaner 3 is connected to an intake pipe 5. Through, the intake air 4 sent to the compressor 2 a of the turbocharger 2 and pressurized by the compressor 2 a is sent to the intercooler 6 to be cooled, and the intake air 4 is further guided from the intercooler 6 to the intake manifold 7. Accordingly, each cylinder 8 of the diesel engine 1 (only four cylinders are schematically shown in FIG. 1) is distributed. Further, the exhaust gas 9 discharged from each cylinder 8 of the diesel engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 10, and the exhaust gas 9 that has driven the turbine 2b passes through the exhaust pipe 11. It is designed to be discharged outside the vehicle.

  A filter case 12 is interposed in the middle of the exhaust pipe 11, and a main filter 13 similar to the conventional particulate filter is accommodated in a subsequent stage in the filter case 12. In the former stage, a flow-through type fuel oxidation catalyst 14 that oxidizes unburned fuel in the exhaust gas 9 and heats the exhaust gas 9 by reaction heat is accommodated.

  A fuel injection device 16 composed of an injector 15 for injecting fuel into each cylinder 8 of the diesel engine 1 also has a function as a fuel addition means. More specifically, the compression top dead center (crank) The fuel can be added to the exhaust gas 9 by adding post-injection at a non-ignition timing later than the compression top dead center following the main injection of the fuel near the angle 0 °.

  In other words, when post-injection is added by the fuel injection device 16 when the accumulation amount of soot in the main filter 13 increases and forced regeneration needs to be performed, the uninjected exhaust gas 9 added to the exhaust gas 9 by the post-injection is added. While the fuel fuel passes through the fuel oxidation catalyst 14, it undergoes an oxidation reaction. The flow of exhaust gas 9 heated by the reaction heat raises the catalyst bed temperature of the main filter 13 and burns out the soot. The filter 13 can be regenerated, and in the case of the example shown here, the forced regeneration means is constituted by the fuel injection device 16 as the fuel addition means and the fuel oxidation catalyst 14. It has become.

  The configuration described so far is substantially the same as the configuration in the existing exhaust purification device, but in the present embodiment, the main filter 13 is provided between the fuel oxidation catalyst 14 and the main filter 13. In addition, a sub-filter 17 having a relatively reduced collection efficiency is newly provided so that a part of the spillage in the exhaust gas 9 can be pre-collected by the sub-filter 17.

Here, the sub-filter 17 carries a prominent oxidation catalyst having one or more of CeO ₂ , ZrO ₂ , and Pr ₆ O ₁₁ as active species, and the fuel at the time of forced regeneration of the main filter 13 is supported. The collected soot can be oxidized in a temperature range lower than the exhaust temperature raised by the oxidation reaction of the added fuel in the oxidation catalyst 14.

For example, although the exhaust temperature is raised to about 600 ° C. or more by the oxidation reaction of the unburned fuel added to the exhaust gas 9 by the post injection of the fuel injection device 16, FIG. 2 shows the result of the combustion characteristic test by the present inventors. As shown in the graph, it has been confirmed that mixing CeO ₂ and carbon black (corresponding to apportionment) and heating the carbon black well in the temperature range of 300 to 600 ° C. (CO ₂ concentration) Combustion is judged by the rise).

Here, since it has been confirmed that CeO ₂ does not affect the combustion start temperature of carbon black even if Pt is supported, Pt is not particularly supported, but carbon is supported by supporting a large amount of Ag. Since it has been confirmed that the combustion start temperature of black decreases, Ag may be supported on CeO _{2 as} necessary.

On the other hand, the main filter 13 carries Pt / Al ₂ O ₃ similar to that carried on the particulate filter so far, but as indicated in the graph of FIG. In the case of / Al ₂ O ₃ , it is possible to burn carbon black satisfactorily in a temperature range of about 600 ° C. or higher which is increased during forced regeneration.

Note that the catalyzed oxidation catalyst that uses CeO ₂ , ZrO ₂ , and Pr ₆ O ₁₁ supported on the sub-filter 17 in the previous stage as an active species has little ability to oxidize CO and HC in the exhaust gas 9. Pt / Al ₂ O ₃ (CO / HC oxidation catalyst using Pt as an active species: Pt / Pd, etc.) capable of oxidizing CO and HC as well as the collected soot. In other words, it is possible to obtain a merit that it is not necessary to separately provide an oxidation catalyst for oxidizing CO and HC in the subsequent stage.

  Further, on the premise of the relationship between the subfilter 17 and the main filter 13 having a relatively low collection efficiency, the average pore diameter of the main filter 13 is 5 to 25 μm, and the collection efficiency is 60 to 100. %, The subpores 17 can have an average pore diameter of 25 to 100 μm and a collection efficiency of 30 to 70%. The average pore diameter is 20 μm, the collection efficiency is 95%, the average pore diameter of the sub-filter 17 is 50 μm, and the collection efficiency is 60%.

  Thus, if the exhaust gas purification device is configured in this way, a portion of the spillage in the exhaust gas 9 is collected in advance by the sub filter 17 at the front stage, and must be collected by the main filter 13 at the rear stage. The amount of spillage that needs to be reduced is small, and the pace of spillage that accumulates in the main filter 13 is significantly slower than when a conventional particulate filter is used alone. As a result, the regeneration interval from the completion of the forced regeneration until the next forced regeneration becomes necessary becomes longer (in the verification experiment by the present inventors, it was confirmed that the regeneration interval can be tripled). Therefore, the amount of fuel consumed to increase the exhaust temperature during forced regeneration is remarkably suppressed, and the fuel efficiency can be greatly improved as compared with the conventional case.

  In addition, the sub-filter 17 in the front stage has a coarse pore diameter with a relatively lower collection efficiency than the main filter 13 in the rear stage, and only a part of the spillage in the exhaust gas 9 is pre-captured. In addition, the collected soot is also oxidized at a temperature lower than the exhaust temperature during forced regeneration due to the catalytic action of the soot oxidation catalyst. There is no possibility that the sub-filter 17 in the previous stage will be clogged before the forced regeneration of the main filter 13 is required.

  In particular, when the average pore diameter of the sub-filter 17 is increased in the range of 25 to 100 μm and the collection efficiency is decreased in the range of 30 to 70%, as shown schematically in FIG. It becomes rough and becomes a state of deep layer filtration where the soot content is trapped inside the base material (a general low pore size filter is a surface layer filter deposited on the surface of the base material) and is coated on the base material. Since the contact property with the partial oxidation catalyst is improved and the performance of oxidizing the soot is greatly improved, the sub-filter 17 in the front stage is required to be forcibly regenerated after the main filter 13 in the rear stage is required. It is possible to more reliably avoid a situation that causes clogging.

  Therefore, according to the above-described embodiment, a part of the spillage in the exhaust gas 9 is preliminarily collected by the sub-filter 17 at the front stage, so that the pace of the spillage accumulated in the main filter 13 at the rear stage is greatly reduced. Therefore, the frequency of forced regeneration of the main filter 13 can be reduced as compared with the conventional case, so that the fuel consumed as post injection for increasing the exhaust temperature in the fuel injection device 16 can be remarkably suppressed, compared with the conventional case. The fuel consumption of the diesel engine 1 can be greatly improved.

  FIG. 4 shows another embodiment of the present invention. In the embodiment shown in FIG. 1, the forced regeneration means is composed of the fuel injection device 16 and the fuel oxidation catalyst 14. A burner 18 is arranged in front of the filter 17 to form a forced regeneration means. The burner 18 injects fuel toward the main filter 13 and is injected from the fuel injector 19. An igniter 20 that ignites the fuel and a combustion air introduction pipe 21 that supplies combustion air are provided.

  Even in an exhaust gas purification device that performs exhaustive regeneration of the main filter 13 by raising the exhaust gas temperature to a predetermined temperature or higher by combustion by such a burner 18, as in the case of the embodiment of FIG. A part of the spillage in the gas 9 is preliminarily collected by the sub-filter 17 in the front stage, so that the pace of the spillage accumulated in the main filter 13 in the back stage is greatly slowed down and the main filter 13 is forcibly regenerated. Since the frequency can be reduced as compared with the conventional frequency, the fuel consumed by the burner 18 can be remarkably suppressed, and the fuel consumption of the diesel engine 1 can be greatly improved as compared with the conventional frequency.

  Note that the exhaust emission control device of the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

9 Exhaust gas 11 Exhaust pipe 12 Filter case 13 Main filter 14 Fuel oxidation catalyst (forced regeneration means)
16 Fuel injection device (fuel addition means: forced regeneration means)
17 Sub-filter 18 Burner (Forced regeneration means)

Claims (5)

  A main filter that is installed in the middle of the exhaust pipe and collects a portion of the exhaust gas, and a main filter that is arranged in front of the main filter so that a portion of the portion of the exhaust gas can be collected in advance. And a sub-filter having a relatively low collection efficiency, and a forced regeneration means for raising the exhaust temperature to a predetermined temperature or more on the inlet side of the sub-filter to burn and remove the soot collected in the main filter. An exhaust emission control apparatus comprising: a substituting oxidation catalyst supported on the sub-filter so as to oxidize the collected soot in a temperature range lower than the exhaust temperature raised by the forced regeneration means. A sub-filter is supported by a sub-filter that contains one or more of CeO ₂ , ZrO ₂ , and Pr ₆ O ₁₁ as active species, and the main filter oxidizes not only the collected soot but also CO and HC. The exhaust emission control device according to claim 1, further comprising a CO / HC oxidation catalyst having Pt that can be activated as an active species.   The average pore diameter of the main filter is 5 to 25 μm and the collection efficiency is 60 to 100%, and the average pore diameter of the sub filter is 25 to 100 μm and the collection efficiency is 30 to 70%. The exhaust emission control device according to claim 1 or 2.   A fuel oxidation catalyst that is disposed upstream of the sub-filter and that oxidizes the unburned fuel in the exhaust gas and heats the exhaust gas by reaction heat, and a fuel that adds fuel to the exhaust gas upstream from the fuel oxidation catalyst The exhaust emission control device according to claim 1, 2 or 3, wherein a forced regeneration means is constituted by the addition means.   The exhaust emission control device according to claim 1, 2 or 3, wherein the forced regeneration means is constituted by a burner arranged in front of the sub-filter.

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