KR20050105604A - Catalytic filter for diesel engine - Google Patents

Abstract

The present invention comprises an upstream portion consisting of a plurality of upstream side open cells and a cell wall, a middle portion consisting of a plurality of intermediate side open cells and a cell wall coaxially arranged with the upstream side open cell, and a plurality of downstream coaxially arranged with the intermediate side open cell. A downstream portion consisting of a side open cell and a cell wall is formed in an integral cylinder, and relates to a filter catalyst structure for a diesel engine having different upstream, intermediate and downstream cell densities.

Description

Filter catalyst structure for diesel engine {Catalytic Filter for diesel engine}

The present invention relates to a filter catalyst structure for a diesel engine, and more particularly, to a filter catalyst structure for a diesel engine that can be molded into a ceramic sintered body, capable of simultaneously purifying HC, CO, and PM, and minimizing pressure loss. will be.

In recent years, the number of automobiles has increased rapidly, and the amount of exhaust gas emitted from the internal combustion engine of automobiles has increased rapidly in proportion to the number of automobiles. For gasoline engines, the strict regulation of the exhaust gas and the advancement of the technology that can cope with it are reducing the harmful components in the exhaust gas. However, for diesel engines, progress in regulation and technology is delayed compared to gasoline engines. In particular, various substances contained in the exhaust gas of diesel engines cause pollution, and have a very serious effect on the global environment. Furthermore, there have been reports that particulate matter (diesel particle) in the exhaust gas can cause allergic disorders or decrease in sperm count. Therefore, the problem of removing the microparticles | fine-particles in exhaust gas has emerged as an urgent research subject. The fine particles refer to carbon-containing fine particles, sulfur-containing fine particles such as sulfate, and particulate matter such as high molecular weight hydrocarbon fine particles (hereinafter collectively referred to as 'PM').

Various exhaust gas purification apparatuses have been proposed in the past. A general exhaust gas purifier includes a casing provided in the middle of an exhaust pipe connected to an exhaust manifold of an engine, and a filter having a fine cell mounted inside the casing. The material for forming the filter may be a metal, an alloy or a ceramic, and a honeycomb filter made of cordierite is known as a representative example of a filter made of ceramic. Recently, porous silicon carbide sintered bodies having advantages of high heat resistance, high mechanical strength and collection efficiency, chemical stability, and low pressure loss are often used as filter forming materials. Here, the term "pressure loss" means the pressure value at the outflow side minus the pressure value at the inflow side of the filter, and receiving the resistance when the exhaust gas passes through the filter is the biggest factor that brings about the pressure loss.

The filter of the exhaust gas purifier for diesel engines is divided into trap type (or wall flow) and open type (or straight flow), and the honeycomb structure (diesel PM filter, DPF) is one of the trap type exhaust gas filters.

Conventional honeycomb filters have a plurality of cells extending along their axial direction. As the exhaust gas passes through the filter, the particulates are trapped by the cell walls, which removes the particulates from the exhaust gas. However, in the honeycomb filter, the pressure loss due to PM deposition increases as the use time increases. Therefore, in the case of DPF, it is necessary to periodically remove the deposited PM. Therefore, when the pressure loss increases, PM has been recovered by burning PM deposited by a burner or a heater. However, as the deposition amount of PM increases, the combustion temperature of the deposited PM increases, and as a result, the DPF may be damaged due to thermal stress due to the temperature rise.

Korean Patent Publication No. 2003-96062 discloses a filter catalyst for purifying exhaust gas. According to this publication, the exhaust gas upstream straight flow honeycomb structure is placed on the upstream side of the exhaust gas with respect to the wall flow honeycomb structure, and is provided integrally with the wall flow honeycomb structure. However, the filter catalyst has a problem in that pressure loss is increased due to PM deposited on the wall flow honeycomb structure.

Hereinafter, the structure of the exhaust gas purification device 1 for diesel engines and the conventional honeycomb filter catalyst will be described in detail.

As shown in Fig. 1, the exhaust gas purification apparatus 1 is an apparatus for purifying exhaust gas discharged from the diesel engine 2 as an internal combustion engine. The diesel engine 2 is provided with many cylinders, and each cylinder is connected with the branch part 4 of the manifold 3 which consists of metal materials. Each branch 4 is connected to one manifold main body 5, respectively, and exhaust gas discharged from each cylinder is concentrated in one place. On the downstream side of the exhaust manifold 3, a first exhaust pipe 6 and a second exhaust pipe 7 made of a metal material are arranged. The upstream end of the first exhaust pipe 6 is connected to the manifold body 5. Between the 1st exhaust pipe 6 and the 2nd exhaust pipe 7, the cylindrical casing 8 which consists of metal materials is arrange | positioned. The upstream end of the casing 8 is connected with the downstream pipe of the first exhaust pipe 6, and the downstream end of the casing 8 communicates with the upstream end of the second exhaust pipe 7. Therefore, the casing 8 is arrange | positioned at the intermediate part of exhaust pipe 6,7. Then, the first exhaust pipe 6, the casing 8 and the second exhaust pipe 7 communicate with each other, and exhaust gas flows therein.

As shown in Fig. 1, the central portion of the casing 8 has a larger diameter than the exhaust pipes 6,7. Therefore, the inner region of the casing 8 is wider than the inner regions of the exhaust pipes 6, 7, and the ceramic filter catalyst structure 9 is accommodated in the casing 8. The heat insulating material 10 is normally inserted between the outer peripheral surface of the structure 9 and the inner peripheral surface of the casing 8. The heat insulating material 10 is a mat-shaped object including a ceramic fiber and is a member for minimizing energy loss during regeneration by preventing heat from being discharged from the outermost circumference of the filter catalyst structure 9.

Fig. 2 is an enlarged cross-sectional view of a honeycomb filter in which a conventional cylindrical ceramic filter catalyst structure is mounted on a casing. The ceramic filter catalyst structure is formed of a porous silicon carbide sintered body which is a kind of ceramic sintered body. The reason for employing the silicon carbide sintered body is that it is superior in heat resistance and thermal conductivity as compared to other ceramics. Sintered bodies, such as), can also be selected. In the honeycomb structure, a plurality of through cells 12 having a substantially square cross section are formed regularly along the axial direction, and each through cell 12 is partitioned from each other by a thin cell wall 13. On the outer surface of the cell wall 13, an oxidation catalyst made of platinum group element, other metal element, oxide thereof, or the like is supported. The opening part of each through cell 12 is sealed by the sealing material 14 at either end face 9a, 9b side. Therefore, the whole cross section of the conventional filter structure shows a checkerboard shape. The density of the cell is set at around 200 / inch ² and the thickness of the cell wall is set at around 0.3mm. Of the plurality of cells, about half are opened in the inlet end face 9a, and the remaining cells are opened in the outlet end face 9b.

However, the conventional honeycomb filter catalyst structure has a disadvantage in that the exhaust gas does not easily pass the honeycomb filter smoothly and thus the pressure loss is large. In other words, the difference between the upstream pressure value and the downstream pressure value is large, impeding the internal combustion engine, especially the mechanically controlled diesel engine, to impede the operating conditions or to deteriorate fuel efficiency, or to deteriorate or severely drive the engine. There was a problem such as stopping. The inventors have determined that the excess of the pressure loss is due to a part of the sealing structure of the conventional honeycomb filter catalyst structure, thereby completing a filter catalyst structure improved from the conventional honeycomb structure.

Accordingly, it is an object of the present invention to provide a filter catalyst structure that minimizes pressure loss.

Another object of the present invention is to provide a filter catalyst structure for improving the operating conditions of a mechanical control diesel engine.

Still another object of the present invention is to integrate the conventional wall flow honeycomb structure and the straight honeycomb structure to suppress PM deposition and at the same time improve the purification activity.

The filter catalyst structure according to the present invention can achieve the above object.

According to the present invention, an improved filter catalyst structure for a diesel engine includes an upstream portion composed of a plurality of upstream side open cells and cell walls, an intermediate portion composed of a plurality of intermediate side open cells and cell walls coaxially arranged with the upstream side open cells, A downstream portion consisting of a plurality of downstream open cells and cell walls coaxially arranged with the middle part open cell is formed as an integral cylinder, and the filter catalyst structure for the diesel engine in which the upstream part, the middle part and the downstream part cell density are differently formed. .

The filter catalyst structure is a structure in which each of the straight flow honeycomb structures having different cell densities is integrated in the coaxial direction in the conventional straight flow honeycomb structure. All of the upstream opening cells in the upstream cross section are opened, and all of the middle opening cells integrally coupled with the upstream section are opened, and all of the downstream opening cells formed integrally with the intermediate section are also opened. When the inside, middle and downstream cell densities are different and the inside of the cell is observed from the upstream cross section toward the downstream side, it is partially sealed by the cell wall formed between the open cells of each part at the inter-part coupling site due to the different cell density, In part, it consists of an open cell configuration. Specifically, the upstream cell wall bottom surface at the upstream lower end portion and the middle end upper surface connection portion is partially disposed on the middle open cell inflow end surface to partially close the middle open cell opening, thereby forming a portion of the opening. In addition, the cell cross section of each of the upstream portion, the intermediate portion, and the downstream portion may be generally square or hexagonal. In addition, the outer surface of the cell wall may be supported with an oxidation catalyst made of a platinum group element or other metal element, an oxide thereof, or the like. In the improved filter catalyst structure for diesel engine according to the present invention, the average pore diameter is preferably 1 μm to 50 μm, and when the average pore diameter is less than 1 μm, filter clogging due to accumulation of fine particles becomes remarkable, and the average If the pore diameter exceeds 50 µm, small fine particles cannot be collected, and the collection efficiency is lowered. The improved filter catalyst structure for diesel engines according to the present invention preferably has a porosity of 30-70%. If the porosity is less than 30%, the filter becomes too dense and it is impossible to distribute the exhaust gas therein. If the porosity exceeds 70%, the voids become excessively high, resulting in weakening of strength and deterioration of particulate collection efficiency. There is a problem that becomes.

3 is an enlarged cross-sectional view of the filter catalyst structure of the present invention mounted on a casing.

The exhaust gas upstream cell cross section of the integrated cylindrical filter catalyst structure is all opened, and the intermediate cell arranged coaxially with the upstream cell is denser than the upstream cell density, so that the upstream open cell and the cell wall The lower end is bonded to the middle open cell and the top of the cell wall to form a partially open or partially closed structure. On the other hand, the middle open cell and the cell wall bottom are combined with the downstream open cell and the downstream cell wall top to form a partial opening or partial sealing to form a trap structure for particulate collection. The cell structure of the partial opening or sealing formed between the upstream part and the intermediate part or between the middle part and the downstream part is derived from the coaxial coupling structure of the three-stage straight honeycomb filter having different densities. In addition, the cell cross section may be generally square or hexagonal cross section or circular, but is not limited thereto. As the filter catalyst structure according to the present invention, a sintered body such as silicon carbide sintered body, silicon nitride, sialon (SIALON), alumina, cordierite, mullite or the like may be selected. It is preferable that an oxidation catalyst layer is formed in the cell wall layers at the upstream, intermediate and downstream portions. By the oxidation catalyst layer, HC and CO contained in the exhaust gas can be oxidized and purified, and since the oxidation catalyst layer generates heat during oxidation and purification, the temperature of the filter catalyst structure according to the present invention is more easily increased. Meanwhile, the present invention is not limited to the filter catalyst structure for the diesel engine, in which the upstream part, the middle part, and the downstream part are integrally formed, as shown in FIG. Of course, the same can be applied to the catalyst system.

Next, the manufacturing process of a filter catalyst structure is demonstrated, taking the case of a silicon carbide sintered compact.

First, the ceramic raw material slurry used in an extrusion molding process is prepared beforehand.

Ceramic raw material slurry is produced by mix | blending and kneading an organic binder and water by predetermined amount with silicon carbide powder. Firstly, a ceramic raw material slurry is introduced into an extrusion molding machine, and then continuously extruded through a mold to produce a primary upstream extrusion molded body having a predetermined cross-sectional shape and having a density of 200 cells / inch ² cells opened in the upper and lower sections. . In the same manner, a primary intermediate extrusion molded product having a 300 cell / inch ² cell density was manufactured, and the same method was repeated to prepare a primary downstream molded product having a 400 cell / inch ² cell density. Each of the extruded bodies is bonded by applying a sealing material to each of the upper and lower circumferential portions in the coaxial direction. The sealing material is composed of at least an inorganic fiber, an inorganic binder, an organic binder, and an inorganic particle, and is preferably made of an elastic material formed by combining inorganic fibers and inorganic particles intersected three-dimensionally with each other through an inorganic binder and an organic binder. Do. As an inorganic fiber contained in a sealing material, at least 1 sort (s) of ceramic fiber selected from a silica alumina fiber, a mullite fiber, an alumina fiber, and a silica fiber can be illustrated. The integrally adhered upstream, middle and downstream extruded bodies are dry cured at 50 ° C. to 100 ° C. for 1 hour to complete the filter catalyst structure. The catalyst layer can be formed in the following manner. The oxide powder or composite oxide powder is slurried together with a binder component such as alumina sol and water. The slurry is deposited on the filter catalyst structure cell wall and then fired. When the slurry is deposited on the cell walls, conventional dipping methods can be used. As the catalyst component supported on the catalyst layer, a catalyst component capable of reducing NOx by catalytic reaction and promoting oxidation of PM can be used. Preferably, it is preferable to support at least one species selected from the group consisting of noble metals of platinum group such as Pt, Rh, Pd on the catalyst layer.

Hereinafter, the catalysis and the particulate trapping will be described briefly.

The exhaust gas is supplied to the filter catalyst structure 9 accommodated in the casing 8 to the upstream end surface side. The exhaust gas supplied through the first exhaust pipe 6 flows into all the upstream opening cells 20 opened in the cross section. This exhaust gas then passes through the upstream cell wall 21 to reach the interior of the joined intermediate open cell 30 or above the upstream cell wall 21 and above the middle cell wall 31. By the primary trap in the partially closed portion. Particulates and the like are again trapped by the sealing portion formed by passing through the middle opening cell 30 into the downstream opening cell 40 or by cell wall joining between the middle and downstream portions. Exhaust gas passing through the downstream open cell flows out. On the other hand, while passing through each of these cell walls, gas components such as HC and CO contained in the exhaust gas are oxidized and purified by the catalyst layer, and the trapped fine particles are Pt catalyst when the internal temperature of the filter reaches a predetermined temperature. It is ignited and combusted by the action of. As a result, the purified exhaust gas passes through the second exhaust pipe 7 and is finally discharged into the atmosphere. Therefore, the particulate trap structure formed by the three-stage filter catalyst structure having a different cell density allows the exhaust gas to pass through the filter catalyst without causing a pressure loss, and does not overwhelm the diesel engine, and enables efficient exhaust gas purification. .

The filter catalyst structure for the diesel engine according to the present invention is attached to the diesel engine to solve the conventional problems due to the pressure loss, to enable efficient exhaust gas purification, and impede the mechanical contron diesel engine to interfere with the operating conditions. This can solve problems such as worsening fuel economy, poor driving fill, or severe engine failure.

1 is a schematic diagram of an exhaust gas purification device.

FIG. 2 is an enlarged cross-sectional view of main parts of the exhaust gas purifying apparatus of FIG. 1. FIG.

3 is an enlarged cross-sectional view of a main portion of a purification apparatus equipped with a filter catalyst structure according to the present invention.

<Description of the symbols for the main parts of the drawings>

1: exhaust gas purification device 2: diesel engine

3: manifold 4: branch part

5 Manifold Body 6, 7 Exhaust Pipe

8 casing 9 filter catalyst structure

9a: Inflow section 9b: Outflow section

10: heat insulating material L1, L2, L3: upstream, middle, downstream

20: upstream open cell 21: upstream cell wall

30: middle part open cell 31: middle part cell wall

40: downstream open cell 41: downstream cell wall

Claims (4)

An upstream portion comprising a plurality of upstream open cells and cell walls, An intermediate portion consisting of a plurality of intermediate side open cells and cell walls coaxially arranged with the upstream side open cell, A downstream portion consisting of a plurality of downstream open cells and cell walls coaxially arranged with the intermediate side open cell is formed as an integral cylinder, A filter catalyst structure for a diesel engine, wherein the upstream, middle and downstream cell densities are formed differently. The filter catalyst structure for a diesel engine according to claim 1, wherein the upstream, middle and downstream cell densities are gradually increased. The filter catalyst structure for a diesel engine according to claim 1, wherein an oxidation catalyst layer is formed on the upstream, intermediate, and downstream cell walls. The diesel engine according to claim 1 or 2, wherein the upstream cell density is 200 cells / in ^{2, the} middle cell density is 300 cells / in ² , and the downstream cell density is 400 cells / in ² . Filter catalyst structure.