JPS62149316A - Exhaust gas filter - Google Patents

Abstract

PURPOSE:To obtain the titled filter having high mechanical strength by making density of a material in a rear part of a closed part of an outlet for exhaust gas of a ceramic honeycomb-shaped filter higher density in comparison with the part excepted from this rear part. CONSTITUTION:The titled filter is constituted by closing alternately the end parts of the cells 5 of a porous ceramic honeycomb structural body in an inlet part and an outlet part. An outlet reinforced part 15 is formed by constituting the filter so that density of a material in a rear part of a closed part of an outlet for exhaust gas of the filter is made to higher density in comparison with the other part. Therefore when burning the collected grains, resistance to cracking properties sufficient in practical use is exhibited and also cracking properties sufficient in practical use is exhibited and also sufficient strength is obtained for shear fracture or the like due to the pressure of the exhaust gas. Also similarly breakage of the inlet part due to the collision of the fine grains contained in exhaust gas can be prevented by increasing density of the material of the inlet part of exhaust gas.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an exhaust gas filter that collects particulates emitted from, for example, a diesel engine and purifies exhaust gas by burning the collected particulates. be.

BACKGROUND OF THE INVENTION Particulates emitted by diesel engines consist of particulates and heavy hydrocarbon compounds (soluble organic substances).

In recent years, there has been increasing interest in controlling the emission of particulates in order to protect the atmosphere and the environment, and in the United States in particular, very strict regulations are scheduled to be implemented soon for diesel vehicles. −
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In this regulation, there is a trade-off relationship between the generation of NOx and the generation of fine particles during zero combustion, which requires reducing NOx as well as fine particles.
, reduction measures generally tend to increase particulate emissions. For this reason, it is considered extremely difficult to comply with this regulation by simply improving the engine itself, and fine particles are physically collected using a filter installed in the exhaust system, deposited in a certain amount, and then combusted. As one of the most promising methods, various studies are being conducted on the method of regenerating the filter by using SAE Paper.
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Problems to be Solved by the Invention Various types of filters have been proposed for collecting fine particles, but the most widely used is a ceramic monolith filter in the shape of a no-nicum made by extrusion using porous cordierite. It is being considered. This cordierite monolith filter has excellent properties such as high particle collection efficiency and low pressure loss, but when regenerating the filter by burning the captured particles within the filter, Exposure to localized high temperatures may cause cracks or melting of the component, resulting in damage.

In response to this problem, the present inventors have developed a filter using a sintered body of mullite fiber ceramics, which has better heat resistance than cordierite (Japanese Patent Application Laid-Open No. 174212/1982). However, even in this filter,
It was recognized that cracks may occur during this combustion. The object of the present invention is to solve this crack problem and provide a practically excellent filter for purifying diesel engine exhaust gas.

Means for Solving the Problems The present invention aims to improve crack resistance by using a sintered body of porous ceramics such as extremely low-density mullite fibers, and also improves the material at the rear of the exhaust gas outlet blocking part. By increasing the density of the material, the lack of mechanical strength is compensated for and the above-mentioned problem is effectively solved.

Working Mullite fiber ceramics have a very high porosity of about 70-80%. Therefore, under the temperature distribution conditions,
Even if a minute crack occurs due to excessive thermal stress being applied to one point, the crack is difficult to propagate because of the abundance of void space around the crack. It has been confirmed that this crack resistance improves as the porosity of the fiber ceramic increases, that is, as the density decreases. However, as the density decreases, the mechanical strength decreases. It has both practical crack resistance and sufficient mechanical strength. f, %: It is extremely difficult to find divisions of density. Therefore, as mentioned above, a configuration was devised in which a fiber ceramic sintered body with extremely low density was used to increase the density of the material at the rear of the exhaust gas outlet closing portion. In other words, since particulates in the diesel exhaust gas do not accumulate at the rear of the exhaust gas outlet blockage, this rear part is not directly exposed to high temperatures caused by combustion of the deposited particulates, and cracks occur even if the density is relatively high. Never. In addition, although the mechanical strength of the low-density part where fine particles accumulate is weak, shear failure due to exhaust gas pressure, which is a problem, is effectively prevented by the high-density part located at the rear.

EXAMPLE FIG. 1 shows an inlet end face and a part of a sectional view of the mullite fiber ceramic sintered filter of the present invention. This filter is created as follows.

First, a mixture of cut silica alumina fibers and ceramic raw material powder is suspended in water, and after adding a binder such as polyvinyl acetate to this mixed slurry, it is agglomerated with a flocculant, and then processed using a fourdrinier paper machine. Create a paper sheet. Sheet density is variable depending on the weight ratio of the mixture. Using the obtained sheet, a corrugated sheet 1 and a flat sheet 2 are bonded together in the same manner as in the production of corrugated board to create a corrugate, which is then bonded around the core and has the same components as the sheet. A pasty material is wound around the ends of the cells while providing closing parts 3 alternately to form a no-nikum shape. That is, the cell 6 is constituted by the filter wall 4 made up of the corrugated sheet 1 and the flat sheet 2. The shape of the filter can be circular or oval depending on the method of winding the sheet. After drying, it is fired at 1000° C. to 140° C. to obtain the desired filter. Figure 2 shows an overview of the circularly shaped filter.

The Murai H3lt fiber ceramic sintered body used in this filter has the following two characteristics.

First, it has a higher melting temperature compared to cordierite.

Therefore, the particulates deposited on the filter are burned and the filter is less likely to be melted and damaged, which is a problem when the filter is regenerated.

Secondly, the porosity is extremely small at 70-80%.

Generally, when the porosity of porous ceramics is increased, the filter efficiency decreases. However, since this material has a structure in which ceramic fibers are irregularly intertwined with each other, it has practically excellent filter efficiency and low ventilation resistance. Since mullite has a larger coefficient of thermal expansion than cordierite, it is more likely to crack if a temperature gradient occurs inside the member. However, the porosity of the material is 7
When the cracks become extremely large (from 0 to 80%), even if excessive thermal stress is applied to a single point and a minute crack occurs, this crack will not propagate because there are plenty of void spaces around that part. It's hard to do. Such crack resistance increases as the porosity of the fiber ceramic increases, that is, 1(
1; It was confirmed that the lower the density, the better the performance.

However, as shown in Figure 3, when the density of a material is reduced, its mechanical strength is reduced. It is extremely difficult to choose.

When using a fiber ceramic filter bursting from a material with low mechanical strength, the first fracture that occurs is as shown in Figure 4, the glabella joint of the filter is sheared and fractured by the pressure of the exhaust gas, causing the surrounding area to break. The only remaining part, including the central part, protrudes toward the rear. FIG. 6 is an enlarged view of the joint between the corrugated sheet and the flat sheet. When particulates accumulate in the filter and the flow rate of exhaust gas increases, and the pressure difference between the filter population and the outlet increases, the shear force applied to the filter increases, and as shown in FIG. 6, the corrugated sheet 1 and the joint part 1 of the flat sheet 2
A peeled portion 13 of the sheet is generated in the vicinity of 3. This peeling gradually spreads and finally leads to the protruding fracture shown in FIG. FIG. 6 is a perspective view showing the state of interlayer failure at this time.

In the exhaust gas filter of the present invention, the density of the material at the rear of the exhaust gas outlet side closing part in FIG. 1 is higher than that of the other parts.

FIG. 7 shows the state in which fine particles are deposited on the filter. As shown in the figure, since particulates do not accumulate at the rear of the exhaust gas outlet side blocking part, this part is not directly exposed to the high temperature caused by particulate combustion, and cracks can occur even if the density of the particles is relatively high. There isn't. Furthermore, although the mechanical strength of the low-density portion where the particles are deposited is low, shear failure due to the pressure of exhaust gas as described above is effectively prevented by the bulk-density portion with high mechanical strength located at the rear.

FIG. 8 shows the structure of an exhaust gas filter according to another embodiment of the present invention. In addition to the material 15 at the rear of the exhaust gas outlet side closing portion described above, the density of the material at the exhaust gas inlet portion 16 is also increased. By increasing the strength of the inlet in this way, it is possible to prevent problems such as parts of the inlet being broken due to repeated collisions of particulates contained in the exhaust gas with the inlet. This inlet part is a part where fine particles accumulate, but since the temperature reached during combustion remains relatively low, there is little concern that cracks will occur in this part.

In this way, the method of partially increasing the density of the exhaust gas filter material is (1) applying ceramic raw material powder to a part of the sheet made by a paper machine, and then forming a honeycomb shape using a corrugating machine. How to bake. (2)
A method in which after forming a honeycomb shape, the outlet end or inlet end is immersed in a liquid in which ceramic raw material powder is suspended, and then fired. (3) A method may be used in which the outlet end or inlet end of the filter after firing is impregnated with colloidal silica.

+11, f2! The method described above is a suitable method for obtaining high mechanical strength, but if the amount of ceramic raw material powder is too large, the propagation of combustion may be deteriorated when the collected fine particles are combusted. Therefore, it may be practically preferable to strengthen the outlet end by coating or impregnating it with ceramic raw material powder before firing, and to strengthen the inlet end by impregnating it with colloidal silica after firing.

Effects of the Invention As described above, according to the present invention, 1! '! : By partially reinforcing the outlet end, or the inlet and outlet ends of a filter made of low-density porous ceramic material, it has sufficient crack resistance for practical use when burning the collected particulates. , an excellent exhaust gas filter having practically sufficient mechanical strength against shear failure due to exhaust gas pressure can be obtained.

[Brief explanation of drawings]

Figures 1 α and b are cross-sectional views of an exhaust gas filter according to an embodiment of the present invention, and Figure 2 is an overview of the same exhaust gas filter.
Figure 3 is a characteristic diagram showing the relationship between ceramic density and mechanical strength of the exhaust gas filter, Figures 4, 5, and 6 are diagrams illustrating the state of destruction of the exhaust gas filter, and Figure 7
8 are cross-sectional views of the reinforced trap. DESCRIPTION OF SYMBOLS 1... Corrugated sheet, 2... Group/flat sorting, 3... Obstruction part, 4... Filter wall, 6... Cell, 6... Entrance end, 7...
River/outlet end, 8...mark/exhaust gas, 9...joint case, 1o...group/insulation material, 11...filter, 12...exhaust gas flow, 13...Joint part, 14...Peeling part, 16...Outlet reinforcement part, 16...Inlet reinforcement part. Name of agent: Patent attorney Toshio Nakao (1st person)
Figure 2 Figure 3 Figure 2 Figure 1, 7 Figure 4 Figure 5 Figure 7

Claims (5)

[Claims] (1) A filter is constructed by alternately closing the ends of the cell pores of the porous ceramic honeycomb structure at the inlet and outlet, and the bulk density of the material at the rear of the exhaust gas outlet closing section of this filter is adjusted to the area other than this rear. An exhaust gas filter characterized in that the exhaust gas filter is configured to have a higher density than the part of the exhaust gas filter. (2) The exhaust gas filter according to claim 1, wherein the porous ceramic is a sintered fiber ceramic. (3) The exhaust gas filter according to claim 2, wherein the material density at the exhaust gas inlet end as well as at the rear of the exhaust gas outlet closing portion of the filter is higher than that at other portions. (4) The exhaust gas filter according to claim 3, which uses a method of impregnating or coating fireclay or colloidal silica as a means of obtaining a locally high-density structure. (5) The exhaust gas inlet end is made denser by impregnating or coating colloidal silica, and the rear part of the exhaust gas outlet closing part is made denser by impregnating or coating fireclay. Exhaust gas filter as described in section.