JP2009228611A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of inhibiting the sulfur poisoning of a NO<SB>X</SB>catalyst by a simple device constitution. <P>SOLUTION: This exhaust emission control device includes the NO<SB>X</SB>catalyst for removing NO<SB>X</SB>in exhaust gas discharged from an internal combustion engine, and a particulate matter filter disposed upstream of the NO<SB>X</SB>catalyst and collecting particulate matter in the exhaust gas. A sulfur oxide collecting material for collecting a sulfur oxide in the exhaust gas is carried by the particulate matter filter. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust emission control technology for an internal combustion engine.

Main components of exhaust gas discharged after fuel combustion of an internal combustion engine are carbon dioxide (CO ₂ ), water vapor (H ₂ O), nitrogen (N ₂ ), oxygen (O ₂ ), and particles mainly composed of carbon. Such as unburned fuel components such as particulate matter (PM), HC (hydrocarbon) and CO (carbon monoxide), nitrogen oxide (NO _x ), sulfur oxide (SO _x ) and the like.

As a device for purifying nitrogen oxides which are toxic components in exhaust gas, when the air-fuel ratio of the exhaust gas is leaner than a predetermined value (typically the theoretical air-fuel ratio), NO _X is occluded, and the stoichiometric air-fuel ratio or when rich There is known an exhaust emission control device provided with a NO _X catalyst that releases absorbed NO _X when the concentration is low and causes a reduction reaction with unburned fuel components (HC, CO) contained in the exhaust gas. Further, in a diesel engine, PM emission is required, and it is necessary to install a PM filter that collects PM simultaneously with the NO _X catalyst.

In this exhaust purification apparatus, SOx to sulfur contained in fuel or lubricating oil occurs caused is occluded into the NO _X catalyst with NOx, causing reduction of the NOx occlusion amount of the NO _X catalyst (sulfur poisoning) There's a problem. For example, Patent Document 1 and Non-Patent Document 1, the sulfur oxide trapping device arranged upstream of the NO _X catalyst, exhaust gas purification device to avoid sulfur poisoning of the NO _X catalyst is proposed.

Further, for example, Patent Document 2, when the amount of SOx occluded in the NO _X catalyst is estimated to exceed the limit value, the exhaust gas purification apparatus is proposed which performs reduction control for reducing the SOx ing. This reduction control, after raising the temperature of the NO _X catalyst through the supply of fuel to the exhaust gas (catalyst bed temperature) to a target temperature, by the rich air-fuel ratio of the exhaust gas through the supply of fuel to the exhaust gas The SOx of the catalyst device is reduced to restore the NOx storage capacity.

German Patent Invention No. 19753533 JP 2002-122019 A Nakatsuji et al., “Chemistry Letters”, Chemical Society of Japan, 1998, 10, p. 1029

However, Patent Document 1, the exhaust purification device of Non-Patent Document 1, NO _X catalyst, in addition to the PM filter, for providing an additional sulfur oxide trapping device, the exhaust purification apparatus is enlarged. With large-sized exhaust gas purifying apparatus to lower a diesel engine exhaust gas temperature is not elevated temperature of the NO _X catalyst, may not be obtained a high catalytic efficiency.

Also, in the exhaust purification device of Patent Document 2, for controlling so as to raise the temperature of the NO _X catalyst to the target temperature, there are cases where the consumption of fuel, the catalyst due to thermal deterioration problems.

An object of the present invention is to provide an exhaust purification device which can in a simple device configuration, suppressing the sulfur poisoning of the NO _X catalyst.

The exhaust purification apparatus of the present invention includes a NO _X catalyst that purifies NO _X in exhaust gas exhausted from an internal combustion engine, and particles that are disposed upstream of the NO _X catalyst and collect particulate matter in the exhaust gas. A particulate matter filter, and the particulate matter filter carries a sulfur oxide collecting material for collecting sulfur oxides in the exhaust gas.

  In the exhaust gas purification apparatus, the particulate matter filter includes an inflow port through which the exhaust gas flows in, an exhaust port through which the exhaust gas is discharged, an inflow passage communicating with the inflow port, and an exhaust communication with the exhaust port. It is preferable that a gas permeable partition wall partitioning the passage and the inflow passage and the discharge passage is provided, and the sulfur oxide trapping material is supported on the discharge passage side of the partition wall.

  In the exhaust purification apparatus, it is preferable that an oxidation catalyst for oxidizing particulate matter or unburned fuel components in the exhaust gas is supported on the inflow passage side of the partition wall.

  In the exhaust emission control device, the sulfur oxide trapping material is a basic substance selected from at least one of alkali metals, alkaline earth metals, and rare earth elements, or at least one of them. Is preferred.

  In the exhaust emission control device, the sulfur oxide trapping material is preferably an oxide selected from at least one of alkali metals, alkaline earth metals, and rare earth elements.

According to the present invention, a simple apparatus configuration, it is possible to suppress the sulfur poisoning of the NO _X catalyst.

  Embodiments of the present invention will be described below.

  FIG. 1 is a schematic diagram illustrating an example of a configuration of an internal combustion engine including an exhaust purification device according to the present embodiment. As shown in FIG. 1, the internal combustion engine 1 includes an internal combustion engine body 10, a turbocharger 12, an exhaust gas recirculation device 14, and an exhaust purification device 16. An example of the internal combustion engine 1 is a diesel engine that obtains output by repeating four cycles of an intake stroke, a compression stroke, an explosion stroke, and an exhaust stroke.

  The internal combustion engine main body 10 is provided with a plurality of cylinders 18, and a combustion chamber for burning a mixture of air and fuel is formed in the cylinders 18.

  In the internal combustion engine 1, the intake manifold 24 and the intake pipe 22 are provided with an intake passage 24 for circulating external air into the combustion chamber. In the internal combustion engine 1, an exhaust passage 30 through which the gas in the combustion chamber is circulated to the outside is provided by the exhaust manifold 26 and the exhaust pipe 28.

  In the intake passage 24, an air cleaner 32, a compressor wheel 34 of the turbocharger 12, and an intercooler 36 are installed in order from the upstream side in the air flow direction.

Installed in the exhaust passage 30, in order from the upstream side of the exhaust gas flow direction, the exhaust fuel injection valve 38, the turbine wheel 40 of the turbocharger 12, particulate matter (PM) filter 42 and NO _X catalyst 44 of the exhaust purification device 16 Has been.

  The turbocharger 12 includes a rotor shaft (not shown) that connects a compressor wheel 34 disposed in the intake passage 24 and a turbine wheel 40 disposed in the exhaust passage 30. By rotating the compressor wheel 34 together with the wheel 40, the air in the intake pipe 22 is compressed, and the amount of air supplied into the combustion chamber of the internal combustion engine body 10 is increased.

  Injection of fuel into each combustion chamber is performed by a fuel injection valve 46. Specifically, fuel in a fuel tank (not shown) is sucked by a fuel pump (not shown), the sucked fuel is supplied to the fuel injection valve 46, and each fuel chamber is opened by opening the fuel injection valve 46. Fuel is injected into

  The exhaust gas recirculation device 14 includes a communication pipe 48, an EGR cooler 50, and an EGR valve 52. The communication pipe 48 is connected to the exhaust passage 30 upstream from the turbine wheel 40 and the intake passage 24 downstream from the intercooler 36. The communication pipe 48 is provided with an EGR cooler 50 and an EGR valve 52 in order from the upstream side in the exhaust gas flow direction. The EGR cooler 50 cools the exhaust gas supplied to the intake pipe 22 via the communication pipe 48. The EGR valve 52 adjusts the flow rate of exhaust gas supplied to the intake pipe 22 through the communication pipe 48.

By the exhaust gas recirculation device 14 as described above, part of the exhaust gas flowing through the exhaust passage 30 flows into the communication pipe 48, and the gas that has flowed in is cooled by the EGR cooler 50, and the intake pipe 22 is passed through the EGR valve 52. Supplied in. As a result, it is possible to reduce the combustion temperature of the mixture to reduce the generation amount of NO _X.

The exhaust gas purification device 16, the NO _X catalyst 44 for purifying NO _X in the exhaust gas, the particulate matter filter 42 which traps particulate matter in exhaust gas (hereinafter, may be referred to as PM filter 42), the Have. The PM filter 42 is disposed on the upstream side of the NO _X catalyst 44.

As the NO _X catalyst 44, an occlusion reduction type NO _X catalyst, a selective reduction type NO _X catalyst, or the like is used. Storage reduction NO _X catalyst, the air-fuel ratio is a predetermined value of the exhaust gas occluding NO _X when the lean side (typically the stoichiometric air-fuel ratio is in), stoichiometric or the rich in the exhaust gas (when oxygen concentration is low) the occluded NO _X released in, that allowed to reduction reaction with unburned fuel component contained in the exhaust gas (HC, _CO), is to purify N _2, H 2 _O, the CO 2, CO ₂ . The selective reduction type NO _X catalyst purifies to N ₂ , H ₂ O and CO ₂ by reacting HC and NO _X in the exhaust gas constantly and simultaneously under the condition that the air-fuel ratio of the exhaust gas is lean It is.

The material constituting the occlusion reduction type NO _X catalyst, on a substrate surface made of oxide such as alumina (Al 2 _{O 3),} a noble metal such as platinum as a catalyst component, and a _the NO _X storage component is carried A thing etc. are used. The NO _X storage component is, for example, at least one selected from alkali metals, alkaline earth metals, and rare earth elements. The materials constituting the selective reduction type NO _X catalyst are those in which a noble metal such as Pt is supported on the surface of a base material such as zeolite or alumina, or in which a transition metal such as Cu is supported on the surface of the base material by ion exchange. In addition, a material in which a titania / vanadium catalyst (V ₂ O ₅ / WO ₃ / TiO ₂ ) is supported on the surface of the substrate is used.

Diesel engines are usually operating under lean conditions. So, to NO _X reduction or the like in NO _X catalyst 44, it is necessary to set the gas flowing into the NO _X catalyst 44 the stoichiometric air-fuel ratio or rich conditions. Therefore, in the purification or the like of the NO _X by the NO _X catalyst 44, the air-fuel ratio control to temporarily stoichiometric or rich condition the air-fuel ratio is performed. In the air-fuel ratio control, the fuel is supplied into the cylinder 18 before the exhaust stroke, or the fuel is supplied into the exhaust gas by the exhaust fuel injection valve 38, thereby reducing the air-fuel ratio in the exhaust. Specifically, fuel in a fuel tank (not shown) is sucked by a fuel pump (not shown), the sucked fuel is supplied to the exhaust fuel injection valve 38, and the fuel is opened by opening the exhaust fuel injection valve 38. Is injected. Then, the fuel injected from the exhaust fuel injection valve 38 is supplied to the PM filter 42 and NO _X catalyst 44 with exhaust gas. Thereby, the reduction reaction on the NO _X catalyst 44 is realized.

The likely catalyst affected sulfur poisoning, is known storage reduction NO _X catalyst. Storage reduction NO _X catalyst, when occluding NO _X, the property of SO _X also occluding generated from sulfur components derived from fuel and lubricating oil. On the other hand, since the storage amount of the storage reduction NO _X catalyst is limited, if many SO _X storage amount, so causing reduction of _the NO _X storage amount (sulfur poisoning). Therefore, storage reduction NO _X catalyst by adsorption of SO _X, before interfere with occlusion of NO _X, it is necessary to collect the SO _X. Therefore, in this embodiment, on the upstream side of the NO _X catalyst 44, disposed PM filter 42 with a sulfur oxide trapping material for trapping SO _X, suppress sulfur poisoning of the NO _X catalyst 44. In particular, when the NO _X catalyst 44 storage reduction NO _X catalyst is used, the exhaust gas purifying apparatus of the present embodiment is preferred.

The PM filter 42 is a porous structure in which the surface of a ceramic material such as cordierite is coated with a support layer such as alumina, and the sulfur oxide collection material that collects sulfur oxide is supported on the porous structure. It has been done. Although the function of the PM filter 42 will be described in detail later, PM in the exhaust gas is collected in a large number of pores in the PM filter 42 when passing through the PM filter 42. On the other hand, of the gas that passes through the pores, sulfur oxide is collected by the sulfur oxide collecting material. Thus, it is possible to suppress the sulfur poisoning of the NO _X catalyst 44.

  The structure of the PM filter 42 is not particularly limited as long as it is a porous structure on which a sulfur oxide collection material is supported. However, in terms of PM and sulfur oxide collection rates, the internal combustion engine is not limited. Gas that separates the inlet into which the exhaust gas discharged from the main body 10 flows, the outlet through which the exhaust gas is discharged, the inlet passage that communicates with the inlet, the outlet passage that communicates with the outlet, and the inlet passage and the outlet passage It is preferable to have a configuration in which a permeable partition wall is provided and a sulfur oxide trap is supported on the discharge passage side of the partition wall. Specific examples thereof will be described below.

  FIG. 2 is a schematic longitudinal sectional view showing an example of the configuration of the PM filter used in this embodiment. FIG. 3 is a schematic cross-sectional view showing an example of the configuration of the PM filter used in the present embodiment. As shown in FIGS. 2 and 3, the PM filter 42 includes an inflow passage 56 that communicates with an inflow port 54 through which exhaust gas flows and an exhaust passage 60 that communicates with an exhaust port 58 that exhausts exhaust gas. A plurality of gas permeable partition walls 62 partitioning the passage 60 are formed, and the inflow passages 56 and the discharge passages 60 are formed in a lattice shape. That is, in the PM filter 42, the inflow passages 56 and the discharge passages 60 are alternately arranged, the inlet of the discharge passage 60 is blocked at one end face of the PM filter 42, and the inflow passage 56 is closed at the other end face. The outlet is closed. The PM filter 42 carries a sulfur oxide trapping material at least on the discharge passage 60 side of the partition wall 62. Here, the side of the partition wall 62 facing the discharge passage 60 is the surface of the partition wall facing the discharge passage 60 or the inside of the partition wall. That is, the sulfur oxide trapping material is carried at least on the partition wall surface facing the discharge passage 60 or inside the partition wall.

As shown in FIGS. 2 and 3, with the above configuration, the exhaust gas flowing in from the inlet 54 passes through the inlet passage 56, and always passes through the partition wall 62, and is discharged from the outlet 58 through the discharge passage 60. Will be. FIG. 4 is a schematic diagram illustrating an example of a configuration inside the partition wall of the PM filter. As shown in FIG. 4, the partition wall 62 is formed of a ceramic material 64, and the sulfur oxide trapping material 66 is supported on the partition wall surface facing the discharge passage 60 and the ceramic material 64 inside. The partition wall 62 is formed with countless pores through which exhaust gas can pass but PM cannot pass. Therefore, when exhaust gas passes through the partition wall 62, PM in the exhaust gas is separated from the partition wall 62. It is collected in the pores and deposited mainly on the partition wall surface facing the inflow passage 56. When the exhaust gas from which PM has been removed passes through the discharge passage 60, sulfur oxides in the exhaust gas are collected by the partition wall surface facing the discharge passage 60 and the sulfur oxide collecting material 66 supported therein. The Thus, the exhaust gas purifying device 16 disposed on the upstream side of the NO _X catalyst 44 to the PM filter 42 having the above structure is to prevent the sulfur oxides from flowing to the NO _X catalyst 44, suppress the generation of sulfur poisoning be able to.

  The sulfur oxide collecting material 66 is not particularly limited as long as it is a substance capable of collecting sulfur oxide. For example, alkali metal such as potassium, sodium, lithium, cesium, barium, calcium A basic substance selected from at least one of rare earth elements such as alkaline earth metals, lanthanum and yttrium, or at least one of them, particularly an oxide selected from at least one of them Etc. Further, for example, known sulfur oxide trapping materials described in JP-A No. 2004-58054, German Patent No. 19753573 and the like may be used. From the viewpoint of the collection rate of sulfur oxides, the ease of carrying work, etc., a basic substance selected from at least one of alkali metals, alkaline earth metals, and rare earth elements, particularly from at least one of them. The selected oxide is preferred. Moreover, Ba oxide is more preferable at the point which the collection temperature range of sulfur oxide is wide. The method for supporting the sulfur oxide trapping material 66 is not particularly limited, and for example, the partition wall 62 may be coated with a paste obtained by dissolving an alkali metal or the like in a solvent, or the alkali metal or the like. May be supplied together with the gas into the PM filter 42 and carried on the partition wall 62.

  FIG. 5 is a schematic diagram illustrating an example of another configuration inside the partition wall of the PM filter. As shown in FIG. 5, the PM filter 42 of the present embodiment preferably supports an oxidation catalyst 68 that oxidizes PM or unburned fuel components at least on the inflow passage 56 side of the partition wall 62. Here, the inflow passage 56 side of the partition wall 62 is the surface of the partition wall facing the inflow passage 56 or the inside of the partition wall. That is, it is preferable that the oxidation catalyst 68 is supported at least on the partition wall surface facing the inflow passage 56 or inside the partition wall. Examples of the oxidation catalyst 68 include noble metal catalysts such as platinum that can oxidize PM and unburned fuel components.

As described above, the exhaust gas flowing in from the inlet 54 of the PM filter 42 passes through the partition wall 62 through the inflow passage 56. When the exhaust gas passes through the partition wall 62, PM in the exhaust gas is collected in the pores of the partition wall 62 and is mainly deposited on the surface of the partition wall 62 facing the inflow passage 56. As in the present embodiment, the PM deposited on the surface of the partition wall 62 facing the inflow passage 56 is mainly oxidized by supporting the oxidation catalyst 68 such as a noble metal catalyst on the surface of the partition wall facing the inflow passage 56 or inside thereof. Can do. In particular, at the time of PM regeneration control or the like, the temperature around the oxidation catalyst on which PM is deposited can be raised by the heat generated by the oxidation of the unburned fuel component on the catalyst, and the oxidation of the deposited PM can be promoted. Then, by oxidizing the PM, by discharged as carbon dioxide (CO ₂₎ or the like, it is possible to prevent clogging due PM in the PM filter 42 and NO _X catalyst 44.

In the exhaust purifying apparatus 16 of the present embodiment, although by arranging the PM filter 42 on the most upstream side, it is only necessary to place the PM filter 42 upstream of the NO _X catalyst 44, the upstream side of the PM filter 42 ( Alternatively, an oxidation catalyst that oxidizes NO in exhaust gas to NO ₂ may be provided on the downstream side.

The oxidation reaction of PM by the oxidation catalyst 68 provided in the PM filter 42 is mainly NO ₂ + C → NO + CO, 2NO ₂ + C → 2NO + CO ₂ , and 2NO ₂ + 2C → N ₂ + 2CO ₂ . Therefore, by disposing an oxidation catalyst that oxidizes NO upstream of the PM filter 42, NO _{2 in} the exhaust gas before being supplied to the PM filter 42 is increased, and the PM collected by the PM filter 42 is It is easily removed by the oxidation catalyst 68 provided in the PM filter 42. As a result, PM can be prevented from accumulating and clogging in the PM filter 42.

As the oxidation catalyst for oxidizing NO in the exhaust gas to NO ₂ , a catalyst support layer made of alumina or the like carrying a catalyst component such as platinum or palladium is used.

It is a mimetic diagram showing an example of composition of an internal-combustion engine provided with an exhaust-air-purification device concerning this embodiment. It is a longitudinal cross-sectional schematic diagram which shows an example of a structure of PM filter used for this embodiment. It is a cross-sectional schematic diagram which shows an example of a structure of PM filter used for this embodiment. It is a schematic diagram which shows an example of a structure inside the partition of PM filter. It is a schematic diagram which shows an example of the other structure inside the partition of PM filter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine, 10 Internal combustion engine main body, 12 Turbocharger, 14 Exhaust gas recirculation device, 16 Exhaust gas purification device, 18 Cylinder, 20 Intake manifold, 22 Intake pipe, 24 Intake passage, 26 Exhaust manifold, 28 Exhaust pipe, 30 Exhaust passage , 32 Air cleaner, 34 Compressor wheel, 36 Intercooler, 38 Exhaust fuel injection valve, 40 Turbine wheel, 42 Particulate matter filter, 44 NO _X catalyst, 46 Fuel injection valve, 48 Communication pipe, 50 EGR cooler, 52 EGR valve , 54 inlet, 56 inlet passage, 58 outlet, 60 outlet passage, 62 partition, 64 ceramic material, 66 sulfur oxide collector, 68 oxidation catalyst.

Claims (5)

NO _X catalyst for purifying NO _X in exhaust gas exhausted from the internal combustion engine;
Wherein arranged upstream of the NO _X catalyst, anda particulate filter for collecting particulate matter in the exhaust gas,
An exhaust emission control device, wherein the particulate matter filter carries a sulfur oxide collecting material for collecting sulfur oxide in the exhaust gas. 2. The exhaust gas purification apparatus according to claim 1, wherein the particulate matter filter includes an inflow port through which the exhaust gas flows in, an exhaust port through which the exhaust gas is exhausted, an inflow passage communicating with the inflow port, and the exhaust port. A discharge passage communicating with the gas, and a gas permeable partition wall that partitions the inflow passage and the discharge passage,
The exhaust gas purification apparatus, wherein the sulfur oxide trapping material is carried on the discharge passage side of the partition wall.   3. The exhaust gas purification apparatus according to claim 2, wherein an oxidation catalyst that oxidizes particulate matter or unburned fuel component in the exhaust gas is supported on the inflow passage side of the partition wall. .   The exhaust emission control device according to any one of claims 1 to 3, wherein the sulfur oxide trapping material is at least one of alkali metals, alkaline earth metals, rare earth elements, or at least one of them. An exhaust emission control device, which is a basic substance selected from one kind.   5. The exhaust emission control device according to claim 4, wherein the sulfur oxide trapping material is an oxide selected from at least one of alkali metals, alkaline earth metals, and rare earth elements. Exhaust purification device.

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