JPH03258347A - Ceramic structure for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To eliminate cracking of the ceramic structure for purifying exhaust gas by providing one or more annular notches along the periphery inward at about the center of the structure in its axial direction and forming the structure. CONSTITUTION:Many cells 3 partitioned by cell walls 2 are provided in a columnar ceramic honeycomb 1, and a U-shaped groove 4 is formed along the periphery at about the center in the axial direction to form a ceramic structure for purifying exhaust gas. When the structure is used as a filter for removing the fine carbon particles exhausted from a diesel engine, the exhaust gas is introduced into the cell 3a opened to the engine end connection 8 and permeated through the cell wall 2 into the cell 3b opened to the muffler end connection 9. The particulates contained in the exhaust gas are not permeated through the cell wall 2 and deposited in the cell 3a.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to ceramic structures used in catalyst carriers and filters for purifying harmful exhaust gases emitted by internal combustion engines, etc. HC, CO or N in exhaust gas
In order to reduce harmful components such as O, etc., an integrated ceramic honeycomb supporting a three-way catalyst has come to be used.Also, as in diesel engines, fine particles such as carbon (hereinafter referred to as particulates) are contained in the exhaust gas. Attempts have been made to remove this by using an integrated ceramic honeycomb that forms a filter structure by alternately closing both ends of a large number of cells.

Furthermore, foamed ceramics, which have a sponge-like structure with countless communicating pores, have been researched to be used in catalysts and filters. When used in a filter, the internal part is exposed to high-temperature exhaust gas, and the internal temperature rises due to the heat of oxidation reaction of HC and CO.Also, when used in a filter, the internal temperature increases when the accumulated carbon burns. Even if the ceramic is heated to a high temperature, in either case, the inside of the ceramic will be at a high temperature. As a result, tensile stress in the axial direction is generated on the outer periphery of the ceramic.4 Ceramics can withstand this stress and often break with ring-shaped cracks on the outer periphery. The purpose of the present invention is to provide an exhaust gas purification structure that can perform an effective exhaust gas purification function by preventing the inside of the ceramic from being heated to a high temperature and causing L-ring-shaped cracks. A feature of the present invention is to provide a cut or groove along the outer periphery near the middle of the length of the integrated ceramic in the exhaust gas flow direction.This cut or groove goes around the structure and reaches a certain depth from the surface. When the ceramic is a honeycomb and is used as a filter, the above structure is used to close both ends of the cell corresponding to the depth of the cut or groove to prevent the leakage of particulates (i. The axial thermal stress that occurs on the outer periphery of the ceramic when heated by the combustion reaction heat is released by the notches or grooves. An embodiment of the ceramic structure for purifying exhaust gas according to the invention will be described based on the accompanying drawings. FIG. 1 is an external view of a cylindrical ceramic honeycomb 1. The ceramic honeycomb 1 is divided into cells by cell walls 2 inside. Although it has a large number of cells 3, it also has a U-shaped groove 4 carved around its outer circumference near the middle in the axial direction of the cylinder. This is an example in which the structure is applied as a filter to remove carbon particulates discharged from a diesel engine. In the figure, 1 is the ceramic honeycomb 1 described above, and rectangular cells 3a or 3b that serve as gas flow paths are formed inside the cell walls. There are many types divided by 2.
One ends of the cells 3a and 3b are alternately sealed with plugs 5 to prevent the exhaust gas from passing straight through.Also, the depth of the grooves 4 carved on the outer periphery of the ceramic honeycomb 1 corresponds to the depth of the cells 3a and 3b. Both ends are sealed with plugs 5.Furthermore, a sheet-like buffer material 6 made of thermally expandable vermiculite, ceramic fiber, and an organic binder is wrapped around the outer periphery of the ceramic honeycomb 1.The ceramic honeycomb 1 is then stored in a can case 7 made of heat-resistant stainless steel. Both ends of the can case 70 are cone-shaped, and one end is connected to the engine connection port 8.
, the other end is used as the muffler connection port 9. Inside the can case 7, stoppers 10a and 10b are welded to fix the front and rear cushioning material 6 of the ceramic honeycomb 1. The operation of the configuration will first be explained from the normal operation of the diesel engine.
When the engine is operated, exhaust gas containing particulates flows into the cell 3a that is open to the engine connection port 8, passes through the cell wall 2, and opens to the muffler connection port 9. At this time, the particulates 1 contained in the exhaust gas cannot pass through the cell wall 2 and remain in the cell 3a and accumulate.
- Person Exhaust gas from which particulates have been removed and purified (i.e. enters the muffler connection port 9, passes through the exhaust muffler, and is released into the atmosphere) Work 11 to accumulate particulates in the ceramic honeycomb 1 takes 1 to 2 hours. Even if this is done continuously, if enough particulates accumulate and it reaches the stage where continued operation will have a negative impact on the engine, regeneration (filter regeneration work) is performed to incinerate the particulates.

With regeneration, first throttle the intake port of the diesel engine and put it into an overload state.If you maintain this state for about 5 minutes, the exhaust gas temperature will rise to over 600℃.
The temperature inside the ceramic honeycomb 1 also rose to about 600°C, and the particulates that had accumulated inside started to burn.Then, the internal temperature of the ceramic honeycomb 1 rose to 800°C to 1000°C due to the heat of combustion. The inside of the ceramic honeycomb 1 expands thermally, but at the outer periphery, heat is radiated from the container 7 to the outside through the buffer material 6, and the temperature is kept relatively low, so it does not expand much.
Since a groove is provided in the middle part of the axial length of the L-shaped ceramic honeycomb 1 and goes around the outer periphery, the outer periphery can be freely displaced in the axial direction according to the internal thermal expansion. Even though the tensile thermal stress in the axial direction that originally occurs at the outer circumference is greatly alleviated, as a result, cracks no longer occur at the outer circumference of the ceramic honeycomb 1. The same holds true even under usage conditions where rapid heating is repeatedly applied. Therefore, this structure for purifying exhaust gas will not be destroyed (°C) Effect of the Invention According to the present invention, the structure for purifying exhaust gas will not be destroyed. By providing a groove along the outer periphery in the axially intermediate portion, the outer periphery is free to deform in response to the axial tensile stress that the outer periphery receives due to internal thermal expansion during use, and eliminates cracks that occur on the outer periphery. Therefore, the internal combustion engine purification system ζ that uses this has become extremely durable.

[Brief explanation of drawings]

FIG. 1 is an external view of an exhaust gas purifying structure according to an embodiment of the present invention. FIG. 2 is a longitudinal cross-sectional view of an application example of the same exhaust gas purifying structure. 1. To the ceramic structure 2. Cell folds 3.3a,
3b...C)L,, 4...Groove, 5...
Plaque", 6. Cushioning material, 7. Container

Claims (4)

[Claims] (1) In an elliptical or cylindrical ceramic structure through which gas flows in the axial direction, a ring-shaped cut is made inward along the outer periphery near the middle of the axial length of the ceramic structure. A ceramic structure for exhaust gas purification, characterized in that it is provided in at least one location. (2) The ceramic structure for exhaust gas purification according to claim 1, wherein the depth of the ring-shaped cut is 1/10 or less of the diameter (the minor axis in the case of an elliptical cylinder). (3) The ceramic structure for exhaust gas purification according to claim 1, wherein the ceramic structure is a honeycomb filter in which the ends of the internal cells are alternately closed, and both ends of the cells in the ring-shaped cut are closed. . (4) The ceramic structure for exhaust gas purification according to claim 1, wherein the ceramic structure is a foamed ceramic having a sponge structure.