WO2005106218A1

WO2005106218A1 - Diesel particulate filter

Info

Publication number: WO2005106218A1
Application number: PCT/KR2004/001754
Authority: WO
Inventors: Hyun-Sik Han; Jae-Ho Bae; Tae-Woo Lee
Original assignee: Heesung Engelhard Corporation
Priority date: 2004-04-30
Filing date: 2004-07-14
Publication date: 2005-11-10
Also published as: KR20050105603A; KR100636051B1; CN100453774C; CN1853034A

Abstract

Disclosed is a particulate collecting filter structure for a diesel engine. The filter structure includes a plurality of through cells axially and regularly arranged therein. The through cells are partitioned by thin cell walls. Half of the through cells are sealed by a sealant at outflow ends thereof, and the remaining half of the through cells are opened at outflow ends thereof. The filter structure is provided in the diesel engine to solve conventional problems caused by pressure loss. It is possible to avoid the problems in which operating conditions and fuel consumption efficiency are worsened, convenience of operation is reduced, and, at worst, operation of the engine is stopped, because overstrain is applied to the mechanically controlled diesel engine.

Description

[DESCRIPTION]

[invention Title] DIESEL PARTICULATE FILTER

[Technical Field] The present invention relates, in general, to a particulate collecting filter structure for a diesel engine and, more particularly, to a particulate collecting filter structure for a diesel engine, which includes a ceramic sintered body to minimize a drop in pressure. [Background Art] Recently, in proportion to a rapid increase in the number of automobiles, the amount of exhaust which is discharged from internal combustion engines of the automobiles has abruptly increased. Particularly, various substances contained in exhaust from diesel engines act as a source of pollution, and very negatively affect the global environment. In addition, a study which found that particulates (diesel particulates) of exhaust may cause allergies or reduction of sperm count was reported. Accordingly, removing the particulates from exhaust has been considered an urgent research goal. The term ^articulates' (hereinafter, referred to as ^ΛPM' ) as used herein is the general term for carbon-containing particulates, sulfur-containing particulates, such as sulfate, and high molecular weight hydrocarbon particulates . Various conventional exhaust purifying devices have been suggested. The typical exhaust purifying device comprises a casing which is provided in the middle of an exhaust pipe connected to an exhaust manifold of an engine, and a filter which has fine cells contained in the casing. Material constituting the filter may be exemplified by metal, alloy, or ceramic, and a representative example of the filter made of ceramic is a honeycomb filter made of cordierite. Currently, a porous silicon carbide sintered body, which has advantages in that heat resistance, mechanical strength, collection efficiency, and chemical stability are high and pressure loss is low, has frequently been used as a material constituting the filter. The term ^pressure loss'^' means a value that is obtained by subtracting pressure of gas flowing out from the filter from pressure of gas flowing into the filter. Resistance occurring when exhaust passes through the filter is the biggest factor affecting pressure loss. The filter of the exhaust purifying device for the diesel engine is classified into a trap-type (or wall flow) and an open-type (or straight flow) . Of them, a honeycomb structure (diesel PM filter, DPF) is one of the trap-type exhaust filters . The conventional honeycomb filter has a plurality of axially arranged cells. When exhaust passes through the filter, particulates are trapped by cell walls, resulting in removal of the particulates from exhaust. However, in the honeycomb filter, the PM is deposited thereon, thus increasing pressure loss. Accordingly, when using the DPF, it is necessary to regularly remove the deposited PM. Therefore, when the pressure loss increases, the deposited PM is combusted using a burner or a heater, and thus, is removed. However, the combustion temperature of the deposited PM increases as the amount of PM deposited increases, thus the DFP may be damaged by heat stress due to an increase in temperature. Hereinafter, a detailed description will be given of structures of an exhaust purifying device 1 for a diesel engine and a conventional honeycomb filter. As shown in FIG. 1, the exhaust purifying device 1 is a device for purifying exhaust discharged from a diesel engine 2 as an internal combustion engine. The diesel engine 2 has a plurality of cylinders, and the cylinders are connected to branched parts 4 of a manifold 3 made of metal. The branched parts 4 communicate with one manifold main body 5 to collect exhaustes discharged from the cylinders in one place. A first exhaust pipe 6 and a second exhaust pipe 7 which are made of metal are connected to a downstream end of the exhaust manifold 3. An upstream end of the first exhaust pipe 6 communicates with the manifold main body 5. A tub-shaped casing 8 made of metal is interposed between the first exhaust pipe 6 and the second exhaust pipe 7. An upstream end of the casing 8 communicates with a downstream end of the first exhaust pipe 6, and a downstream end of the casing 8 communicates with an upstream end of the second exhaust pipe 7. Accordingly, the casing 8 is interposed between the exhaust pipes 6, 7. Furthermore, the first exhaust pipe 6, the casing 8, and the second exhaust pipe 7 communicate with each other to allow exhaust to flow therethrough. As shown in FIG. 1, a middle part of the casing 8 has a larger diameter than do the exhaust pipes 6, 7. Hence, the casing 8 has a larger internal space than do the exhaust pipes 6, 7, and a ceramic filter structure 9 is contained in the casing 8. An insulator 10 is usually interposed between an external surface of the structure 9 and an internal surface of the casing 8. The insulator 10, which includes ceramic fibers, has the shape of a mat, and is a member for preventing emission of heat from an outermost side of the filter structure 9 so as to minimize energy loss during purification. FIG. 2 is a sectional view of a honeycomb filter, in which a typical cylindrical ceramic filter structure is provided in a casing. Since the ceramic filter structure removes diesel particulates, generally, it is called a diesel particulate filter (DPF, DSF) . The ceramic filter structure is made of a porous silicon carbide sintered body which is a kind of ceramic sintered body. The reason why the silicon carbide sintered body is used is that heat resistance and heat conductivity are excellent in comparison with other ceramics. Silicon nitride, sialon, alumina, cordierite, or mullite may be selected for the sintered body, in addition to silicon carbide. In the honeycomb structure, a plurality of through cells 12 having a section of an almost square shape is axially and regularly arranged, and the through cells 12 are partitioned by thin cell walls 13. An oxidation catalyst which includes platinum-based elements or other metal I elements and oxides thereof is incorporated onto external surfaces of the cell walls 13. Each through cell 12 has an opening sealed by a sealant 14 at either of both ends 9a, 9b. Accordingly, a section of the conventional filter structure has the shape of a checkerboard pattern. The density of the cells is set to 200 cells/inch, and the thickness of the cell wall is set to 0.3 mm or so. Half of the cells are opened at inflow ends 9a thereof, and the remaining half are opened at outflow ends 9b thereof.

[Detailed Description of Invention] [Technical Problem] However, a conventional honeycomb filter structure is disadvantageous in that, since exhaust passes through a honeycomb filter with difficulty, pressure loss is high. That is to say, since the difference between the pressure of gas flowing into the filter and the pressure of gas flowing out of the filter is high, overstrain is applied to an internal combustion engine, particularly, a mechanically controlled diesel engine. Thus, its operating conditions and fuel consumption efficiency are worsened, convenience of operation is reduced, and, at worst, operation of the engine is stopped. The inventor of the present invention believes that the large pressure loss is partially caused by a sealing structure of the conventional honeycomb filter structure, and thus invented a filter structure obtained by improving on the conventional honeycomb filter structure. Therefore, an object of the present invention is to provide a filter structure which is capable of minimizing pressure loss. Another object of the present invention is to provide a filter structure which improves the operation conditions of a mechanically controlled diesel engine. A further object of the present invention is to integrate a conventional wall flow honeycomb structure with a straight honeycomb structure so as to prevent deposition of PM and improve purification efficiency. [Technical Solution] In order to accomplish the above objects, the present invention provides a particulate collecting filter structure. According to the present invention, the improved particulate collecting filter structure for the diesel engine includes a plurality of through cells axially and regularly arranged therein. The through cells are partitioned by thin cell walls, half of the through cells are sealed by a sealant at outflow ends thereof, and the remaining half of the through cells are opened at outflow ends thereof . In the filter structure, all of the through cells are opened at inflow ends thereof, and half of the through cells are sealed at outflow ends thereof. The sealed cells having the outflow ends sealed by the sealant may be arranged adjacent to the open cells so that they form a checkerboard pattern in a cross-section of the filter structure. Alternatively, the sealed cells may be arranged so that they form circles and the circles are concentrically arranged in the cross-section of the filter structure. Otherwise, the sealed cells may be arranged in any one of two portions which are divided by a central line in the cross-section of the filter structure. Furthermore, each of the through cells is square or hexagonal in cross- section. Additionally, an oxidation catalyst which includes platinum-based elements or other metal elements and oxides thereof may be incorporated onto external surfaces of cell walls . It is preferable that the improved particulate collecting filter structure for the diesel engine according to the present invention have an average pore diameter of 1 - 50 μm. When the average pore diameter is less than 1 μm, the filter easily becomes clogged due to accumulation of the particulates . When the average pore diameter is more than 50 μm, it is impossible to collect small particulates, thus reducing collection efficiency. It is preferable that the improved particulate collecting filter structure for the diesel engine according to the present invention have a porosity of 30 - 70 %. If the porosity is less than 30 %, the filter becomes very dense, thus it is impossible to pass exhaust through it. If the porosity is more than 70 %, a large number of pores are formed, thus, undesirably, strength and particulate collection efficiency are reduced.

[Advantageous Effects] A particulate collecting filter structure for a diesel engine according to the present invention, which is to be provided in diesel engines, can solve conventional problems caused by pressure loss . Accordingly, it is possible to avoid problems in which operating conditions and fuel consumption efficiency are worsened, convenience of operation is reduced, and, at worst, operation of the engine is stopped because overstrain is applied to the mechanically controlled diesel engine.

[Brief Description of Drawings] FIG. 1 schematically illustrates an exhaust purifying device; FIG. 2 is a sectional view of a main part of the exhaust purifying device of FIG. 1; and FIG. 3 is a sectional view of a main part of a purifying device which is equipped with a filter structure according to the present invention. <Description of reference numerals for main parts of the drawings> 1: exhaust purifying device 2: diesel engine 3: manifold 4: branched part 5: manifold main body 6, 7: exhaust pipe 8: casing 9: filter structure 9a: inflow end 9b: outflow end 10: insulator 12: through cell 13: cell wall 14: sealant 15: sealed cell 16: open cell [Mode for Carrying Out the Invention] FIG. 3 is a sectional view of a casing which is provided with a filter structure according to the present invention. In the cylindrical filter structure, an end of the cylindrical filter structure, into which exhaust flows, are fully opened, and the other end of the cylindrical filter structure, from which exhaust flows out, are partially sealed. A plurality of through cells 12 consists of sealed cells 15 and open cells 16. All of the through cells are opened at inflow ends thereof. Half of the through cells are sealed by a sealant 14 at outflow ends thereof, and the remaining half of the through cells are opened at outflow ends thereof. The open cells 16 and the sealed cells 15 are provided in almost identical numbers, and the open cells may be arranged adjacent to the sealed cells so that they form a checkerboard pattern in a cross-section of the filter structure. Alternatively, the open cells may be arranged so that they form circles around the center of the filter structure and so that the circles are concentrically arranged in a cross-section of the filter structure. Otherwise, the open cells may be asymmetrically arranged in the cross-section of the filter structure. Hence, when the

, filter structure is cylindrical, the open cells and the sealed cells may be arranged in different semicircles in the cross-section of the filter structure. Furthermore, each cell may be square or hexagonal in section. The filter structure of the present invention may include a sintered body, such as silicon carbide, silicon nitride, sialon, alumina, cordierite, or mullite. It is preferable that oxidation catalyst layers be formed on the cell wall layers. HC and CO contained in exhaust can be oxidized and purified by the oxidation catalyst layers . The oxidation catalyst layers generate heat during oxidation and purification, thereby easily increasing the temperature of the filter structure according to the present invention. FIG. 3 illustrates a single filter structure, but, needless to say, a plurality of particulate collecting filter structures may be arranged at 5 mm intervals in the direction of exhaust flow. Next, a description will be given of a process of producing the particulate collecting filter structure using a silicon carbide sintered body. First, ceramic slurry used as raw material in an extrusion process is prepared, and sealing paste used to form sealed cells in a sealing process is prepared. Predetermined amounts of organic binder and water are mixed and kneaded with the silicon carbide powder to produce the ceramic slurry. An organic binder, a lubricant, a plasticizer, and water are mixed and kneaded with silicon carbide powder to produce the sealing paste. The ceramic slurry is fed into an extruder, and continuously extruded using a mold to produce a first extrudate having a section of a predetermined shape, which includes a plurality of cells with open inflow and outflow ends. Half of the open outflow ends of the cells of an extruded first filter are sealed with the sealing paste. The sealed cells may be arranged adjacent to the open cells so that they form a checkerboard pattern in a cross-section of the filter structure. Alternatively, the sealed cells may be arranged so that they form circles and so that the circles are concentrically arranged in a cross-section of the filter structure, and the open cells may be arranged along a circumference of the filter structure. Otherwise, the sealed and open cells may be arranged in different semicircles in a cross-section of the filter structure. Temperature and time are set to predetermined values, and sintering is conducted, thereby creating the particulate collecting filter structure which is made of a porous silicon carbide sintered body. The catalyst layer may be formed through the following procedure. Oxide powder or complex oxide powder is mixed with a binder component, such as alumina sol, and water to produce slurry. The slurry is deposited on cell walls of the filter, and then sintered. The slurry may be deposited on the cell walls using a typical dipping method. A catalyst component which is capable of reducing NOx through a catalytic reaction and promoting oxidation of PM may be incorporated into the catalytic layer. It is preferable to incorporate one or more selected from the group consisting of platinum-based precious metals, such as Pt, Rh, and Pd, into the catalytic layer. Hereinafter, a brief description will be given of trapping of particulates. Exhaust is fed through an upstream end of a casing into a filter structure 9 contained in the casing 8. Exhaust fed through a first exhaust pipe 6 flows into all of the cells with open inflow ends . Subsequently, exhaust flows along cell walls 13, is stopped by sealed ends of sealed cells 15 and flows out through open ends of open cells 16. Particulates contained in exhaust are trapped in the sealed cells 15, and purified exhaust is discharged through a second exhaust pipe 7. Furthermore, the trapped particulates are ignited with the aid of a catalyst when the temperature of an internal part of the filter approaches a predetermined value, and thus combusted. Meanwhile, exhaust flowing into the open cells having a sectional area that is the same as that of the sealed cells passes through the filter without pressure loss, thereby preventing overstrain applied to a diesel engine.

Claims

[CLAIMS] [Claim l] A particulate collecting filter structure for a diesel engine, the filter structure including a plurality of through cells axially and regularly arranged therein, wherein, the through cells are partitioned by thin cell walls, half of the through cells are sealed by a sealant at outflow ends thereof, and the remaining half of the through cells are opened at outflow ends thereof.

[Claim 2] The particulate collecting filter structure as set forth in claim 1, wherein the open cells with the open outflow ends and the sealed cells with the sealed outflow ends are alternately arranged, so that the open and sealed cells form a checkerboard pattern in a cross-section of the filter structure.

[Claim 3] The particulate collecting filter structure as set forth in claim 1, wherein the sealed cells with the sealed outflow ends are arranged so that the sealed cells form circles concentrically arranged in a cross-section of the filter structure.

[Claim 4] The particulate collecting filter structure as set forth in claim 1, wherein the sealed cells with the sealed outflow ends are arranged in any one of two portions which are divided by a central line in a cross-section of the filter structure.

[Claim 5] The particulate collecting filter structure as set forth in any one of claims 1 to 4, wherein each of the through cells is square or hexagonal in cross-section.