JP2007120346A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To forcibly regenerate the innermost plug type particulate filter of integrally constituting an oxidation catalyst in a front part without risk of clogging. <P>SOLUTION: This exhaust emission control device is constituted so that a plug body 13 of sealing a mesh on the inlet side of respective flow passages 12 is arranged in a position of entering by the required length into the flow passage innermost side from an inlet side end surface, and the innermost plug type particulate filter 11 of carrying the oxidation catalyst 11a on the front part up to the inlet side end surface from an arranging position of its inlet side plug body 13 is interposed in the middle of an exhaust pipe 9, and fuel is added in exhaust gas 7 by leaving the unburnt fuel content much by controlling fuel injection to respective cylinders of a diesel engine 1 (an engine), and the particulate filter 11 is forcibly regenerated by burning a collected particulate by reaction heat when its adding fuel reacts in oxidation by the oxidation catalyst 11a. In this case, a pre-oxidation catalyst 16 is arranged in the most upstream part of the exhaust pipe 9 near to an outlet of an exhaust manifold 8. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device.

  Particulate matter (particulate matter) discharged from a diesel engine is mainly composed of soot made of carbonaceous matter and SOF content (Soluble Organic Fraction) made of high-boiling hydrocarbon components. The composition contains a small amount of sulfate (mist-like sulfuric acid component). As a measure to reduce this type of particulates, a particulate filter is installed in the middle of the exhaust pipe through which the exhaust gas flows. It has been done conventionally.

  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. The outlet of the flow channel is sealed, and only the exhaust gas that has permeated through the porous thin wall that defines each flow channel is discharged downstream, and the particulates in the exhaust gas are porous. It is intended to be collected on the inner surface of the thin wall.

  Then, the particulates in the exhaust gas are collected and deposited on the inner surface of the porous thin wall, so that the particulates are appropriately burned and removed before the exhaust resistance increases due to clogging. It is necessary to regenerate, but in normal diesel engine operating conditions, there are few opportunities to obtain exhaust temperatures that are high enough for particulates to self-combust, so an oxidation catalyst that uses Pt, Pd, etc. as an active species is integrated. The catalyst regeneration type particulate filter supported on the surface is being put to practical use.

  That is, if such a catalyst regeneration type particulate filter is employed, the oxidation reaction of the collected particulates is promoted to lower the ignition temperature, and the particulates can be burned and removed even at an exhaust temperature lower than the conventional one. It becomes possible.

  However, even when such a catalyst regeneration type particulate filter is used, the trapped amount exceeds the particulate processing amount in the operation region where the exhaust temperature is low, so such a low exhaust gas. 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.

  Therefore, a flow-through type oxidation catalyst is separately installed in the previous stage of the particulate filter, and when the accumulated amount of particulates has increased, fuel is added to the exhaust gas by fuel injection control on the diesel engine side. It is considered to perform forced regeneration of the filter.

  That is, the HC gas generated by this fuel addition undergoes an oxidation reaction while passing through the preceding oxidation catalyst, and the catalyst bed temperature of the particulate filter immediately after is raised by the inflow of the exhaust gas heated by the reaction heat, and the particulates. The curate is burned out and the particulate filter is regenerated.

  As a specific means for performing this type of fuel addition, exhaust gas is obtained by performing post injection at a timing of non-ignition later than compression top dead center following main injection of fuel performed near compression top dead center. The fuel is generally added to the inside, but the fuel may be added to the exhaust gas by delaying the timing of the main injection into the cylinder.

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, separately installing an oxidation catalyst in the front stage of the particulate filter leads to an increase in arrangement space and a cost increase. The idea of using plug-type particulate filters has been invented, and the clogging problem described in detail below is one of the factors that hinders practical application in research and development for its practical application. I found.

  That is, in such a back plug type particulate filter, the plug body sealing the inlet side of each flow path is arranged at a position where it enters the flow path back side by a required length from the input side end face. The front part from the position of the plug on the inlet side to the end face on the inlet side carries an oxidation catalyst with an enhanced function to assist the oxidation reaction of HC gas, and the oxidation catalyst that should be separately arranged in the previous stage is particulate. In this case, the oxidation catalyst is supported on the same base material as the rear part (the part behind the plug on the inlet side) that functions as the original filter. In addition, the particulates are positively collected even in the front portion which only has a function of oxidizing the HC gas satisfactorily.

  On the other hand, the oxidation reaction of HC gas in the oxidation catalyst in the front part is activated by increasing the contact frequency with the catalyst surface toward the downstream side, so the temperature distribution in the front part where the oxidation catalyst is supported is The temperature gradually increases due to reaction heat from the temperature of the inlet side end surface substantially equal to the temperature toward the downstream side, and the inlet side end surface of the front portion on which the oxidation catalyst is supported always has a low catalytic activity.

  For this reason, in the case of a vehicle with an operation mode in which the operation state with a low exhaust temperature continues for a long time, such as an urban route bus that travels only on a congested road, the amount of fuel injected into the exhaust gas by the fuel injection control on the diesel engine side. Even if the particulate filter is forcibly regenerated with the addition of, it is easy for particulates to remain unburned around the inlet end surface of the particulate filter, and this particulate burning residue blocks the flow path. There was a risk of clogging.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to enable forced regeneration of a back plug type particulate filter in which an oxidation catalyst is integrally formed in a front portion without worrying about clogging. It is said.

  According to the present invention, the plug body sealing the inlet side of each flow path is arranged at a position where it enters the flow path back side by a required length from the inlet side end face, and is inserted from the arrangement position of the plug body on the inlet side. A plug-type particulate filter with an oxidation catalyst supported on the front part up to the side end face is inserted in the middle of the exhaust pipe, and fuel injection into each cylinder of the engine is controlled to leave a large amount of unburned fuel. In the exhaust emission control device, the fuel is added to the exhaust gas and the particulate filter is combusted by the reaction heat when the added fuel undergoes an oxidation reaction with the oxidation catalyst to forcibly regenerate the particulate filter. A pre-oxidation catalyst is disposed at the most upstream portion of the exhaust pipe close to the outlet of the exhaust manifold.

  In this way, since the high-temperature exhaust gas that has just been exhausted from the engine is introduced into the pre-oxidation catalyst, the catalyst bed of the pre-oxidation catalyst can be relatively easily obtained even when the exhaust temperature is low. Since the temperature rises and the activity increases, when fuel addition is performed by controlling the fuel injection to each cylinder of the engine in this state, a part of the HC gas generated by this fuel addition acts as a pre-oxidation catalyst. An oxidation reaction takes place during the passage, and the temperature of the exhaust gas is raised by the reaction heat.

  As a result, even if the exhaust temperature is lowered while the exhaust gas is led from the engine to the particulate filter, the particulate matter cannot be burned and removed satisfactorily by the oxidation catalyst in the front portion. The HC gas is oxidized by a pre-oxidation catalyst targeting high-temperature exhaust gas that has just been exhausted to raise the temperature of the exhaust gas, and the activity of the oxidation catalyst in the front part of the particulate filter is increased and captured. It is possible to promote combustion removal of the collected particulates, and to significantly reduce the unburned particulates in the front part of the particulate filter.

  According to the exhaust emission control device of the present invention described above, various excellent effects as described below can be obtained.

  (I) When forced regeneration is performed using a back-plug type particulate filter in which an oxidation catalyst is integrally formed in the front portion, the activity of the oxidation catalyst in the front portion of the particulate filter is increased even in an operation region where the exhaust temperature is low. It is possible to promote the burning and removal of collected particulates and greatly reduce the remaining unburned particulates in the front part of the particulate filter, which may cause clogging in the front part of the particulate filter. Can be avoided in advance.

  (II) Since the forcible regeneration of the back-plug type particulate filter in which the oxidation catalyst is integrally formed in the front portion can be performed without worrying about clogging, the oxidation catalyst is separately arranged in front of the conventional particulate filter. Compared to the case, the installation space can be reduced in the longitudinal direction of the exhaust pipe to greatly improve the mountability to the vehicle, and the number of parts related to the catalyst installation can be reduced to greatly reduce the cost. Furthermore, the reaction heat generated in the front part of the particulate filter can be directly transmitted to the rear part, and the regeneration time can be greatly shortened.

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

  1 to 4 show an example of an embodiment for carrying out the present invention. In FIG. 1, reference numeral 1 denotes a diesel engine equipped with a turbocharger 2, and air 4 guided from an air cleaner 3 is connected to an intake pipe 5. Is sent to the compressor 2a of the turbocharger 2, and the air 4 pressurized by the compressor 2a is further sent to the intercooler 6 to be cooled, and the air 4 is led from the intercooler 6 to an intake manifold (not shown). Thus, it is introduced into each cylinder of the diesel engine 1.

  The exhaust gas 7 discharged from each cylinder of the diesel engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 8, and the exhaust gas 7 driving the turbine 2b passes through the exhaust pipe 9 to the outside of the vehicle. To be discharged.

  And, in the filter case 10 interposed in the middle of the exhaust pipe 9 through which the exhaust gas 7 flows, a back-plug type particulate filter 11 integrally containing an oxidation catalyst 11a is housed in the front portion. Referring to FIG. 2 schematically showing the structure, the particulate filter 11 has a porous honeycomb structure made of ceramic, and the inlets of the respective flow paths 12 partitioned in a lattice shape are plug bodies. For the flow path 12 that is alternately sealed by 13 and the inlet is not sealed, the outlet is sealed by the plug 14, and the porous thin wall 15 that partitions each flow path 12. However, only the exhaust gas 7 that has collected particulates through the gas passage is discharged downstream, but the plug 13 on the inlet side enters the depth side of the flow path 12 by a required length from the inlet side end face. Is An oxidation catalyst 11a (see FIG. 3) having an enhanced function of assisting the oxidation reaction of HC gas is carried on the front part from the arrangement position of the plug 13 on the inlet side to the entry side end face. An oxidation catalyst 11b (see FIG. 3) having an enhanced function of assisting the oxidation reaction of the collected particulates is carried on the rear part from the arrangement position of the plug 13 on the inlet side to the outlet end face.

  In general, the oxidation catalyst 11a in the front portion is usually a larger amount of active species such as Pt and Pd than the oxidation catalyst 11b in the rear portion, but the particulate filter 11 A uniform oxidation catalyst may be supported on the whole, and the rear portion oxidation catalyst 11b may be replaced with a NOx storage reduction catalyst.

  Further, in the exhaust pipe 9 immediately after the turbine 2b of the turbocharger 2 (the most upstream part of the exhaust pipe 9 close to the outlet of the exhaust manifold 8), a catalyst raw material having Pt, Pd or the like as an active species is used as a stainless metal carrier. A pre-oxidation catalyst 16 that is supported is spaced apart from the particulate filter 11 at a required interval.

  As shown in an enlarged view in FIG. 4, the pre-oxidation catalyst 16 has a catalyst material supported on a cylindrical metal carrier in which a flat plate material 16a made of stainless steel and a corrugated plate material 16b are spirally wound. 5 is formed as a relatively small capacity flow-through type oxidation catalyst having a diameter substantially equal to the pipe diameter of the exhaust pipe 9, but as shown in FIG. 5, the catalyst raw material is supported on a ceramic honeycomb carrier. It is also possible to make it.

  Further, in this embodiment, the fuel injection control of the fuel injection device 17 (see FIG. 1) for injecting fuel into each cylinder of the diesel engine 1 is usually performed when the forced regeneration of the particulate filter 11 becomes necessary. The mode is switched from the regeneration mode to the non-ignition timing after the main injection of fuel performed near the compression top dead center (crank angle 0 °) (the start timing is 90 ° to 120 ° crank angle). (Range) post-injection is executed.

  That is, when post-injection is performed at a non-ignition timing later than the compression top dead center following main injection, unburned fuel (mainly HC: hydrocarbon) is added to the exhaust gas 7 by this post-injection. As a result, the exhaust gas 7 is discharged from the diesel engine 1 by the HC gas generated by the unburned fuel.

  Thus, the high-temperature exhaust gas 7 that has just been exhausted from the diesel engine 1 is introduced into the pre-oxidation catalyst 16 in this way, so that the pre-oxidation can be performed relatively easily even in an operation state at a low exhaust temperature. Since the catalyst bed temperature of the catalyst 16 rises and the activity increases, the fuel injection control of the fuel injection device 17 is switched from the normal mode to the regeneration mode in such a state, and the non-ignition which is slower than the compression top dead center following the main injection. When post-injection is executed at the timing, the fuel that has been added to the exhaust gas 7 without being burned by the post-injection becomes high-concentration HC gas, and a part of the HC gas passes through the pre-oxidation catalyst 16. In the meantime, an oxidation reaction occurs, and the temperature of the exhaust gas 7 is raised by the reaction heat.

  As a result, the exhaust gas temperature is lowered while the exhaust gas 7 is led from the diesel engine 1 to the particulate filter 11, and the particulates cannot be burned and removed well by the oxidation catalyst 11 a in the front portion. Even so, the HC gas is oxidized by the pre-oxidation catalyst 16 for the hot exhaust gas 7 that has just been exhausted from the diesel engine 1 to raise the temperature of the exhaust gas 7. It is possible to greatly reduce the unburned particulates in the front portion.

  Therefore, according to the above embodiment, when the forced regeneration is performed using the back plug type particulate filter 11 in which the oxidation catalyst 11a is integrally formed in the front portion, the particulate filter 11 is also used in the operation region where the exhaust temperature is low. It is possible to increase the activity of the oxidation catalyst 11a in the front part of the catalyst to promote the combustion removal of the collected particulates and to greatly reduce the unburned particulates in the front part of the particulate filter 11, so that the particulate filter The possibility that clogging may occur in the front portion of 11 can be avoided in advance.

  Further, the forced regeneration of the back-plug type particulate filter 11 in which the oxidation catalyst 11a is integrally formed in the front portion can be performed without worrying about clogging, so that the oxidation catalyst 11a is separately arranged in the front stage of the conventional particulate filter 11. Compared with the case where it has been done, the arrangement space can be reduced in the longitudinal direction of the exhaust pipe 9 to greatly improve the mountability to the vehicle, and the number of parts related to catalyst installation can be reduced and the cost can be greatly increased. In addition, the reaction heat generated in the front part of the particulate filter 11 can be directly transmitted to the rear part, and the regeneration time can be greatly shortened.

  The exhaust emission control device of the present invention is not limited to the above-described embodiment. In the previous embodiment, the main injection of fuel performed near the compression top dead center is followed by the compression top dead center. Fuel is added to the exhaust gas by performing post-injection at a slow non-ignition timing, but fuel is added to the exhaust gas by delaying the timing of main injection into the cylinder later than usual. Of course, various modifications can be made without departing from the scope of the present invention.

It is the schematic which shows an example of the form which implements this invention. It is sectional drawing which shows typically the structure of the particulate filter of FIG. It is a perspective view of the particulate filter of FIG. It is a perspective view which shows the detail of the pre-oxidation catalyst of FIG. It is a perspective view which shows another example of the pre-oxidation catalyst of FIG.

Explanation of symbols

1 Diesel engine (engine)
7 exhaust gas 8 exhaust manifold 9 exhaust pipe 11 particulate filter 11a oxidation catalyst 12 flow path 13 plug body 16 pre-oxidation catalyst

Claims (1)

  The plug body sealing the inlet side of each flow path is arranged at a position where it enters the flow path back side by a required length from the inlet side end face, and from the arrangement position of the inlet side plug body to the inlet side end face. A plug-type particulate filter with an oxidation catalyst supported in the front part is installed in the middle of the exhaust pipe, and fuel injection into each cylinder of the engine is controlled to leave a large amount of unburned fuel in the exhaust gas. In the exhaust emission control apparatus, the particulate filter is forcibly regenerated by burning the collected particulates by the reaction heat when the added fuel undergoes an oxidation reaction with the oxidation catalyst. An exhaust gas purification apparatus, wherein a pre-oxidation catalyst is disposed at the most upstream part of the exhaust pipe close to the exhaust pipe.

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