JPH0523512A - Diesel particulate filter - Google Patents

Abstract

PURPOSE:To provide a particulate filter for a diesel engine reduced in pressure loss and enhanced in collection efficiency. CONSTITUTION:A particulate filter for a diesel engine reduced in pressure loss and enhanced in collection efficiency is characterized by that the average value m1 of a pore size measured by a mercury pressure introducing method is within the range of 1-15mum and the value SD1 of standard deviation in a pore size distribution obtained when the pore size is shown by general logarithms is 0.20 or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter for collecting particulates (black smoke, fine particles, SOF, etc.) contained in exhaust gas of a diesel engine.

[0002]

2. Description of the Related Art Particulates contained in the exhaust gas of a diesel engine have an average particle size of 0.1 μm to 0.3 μm and are extremely fine. Therefore, it is preferable that the filter for collecting the particles also has a small average pore diameter. However, in the wall-flow type monolith filter, if the pore diameter becomes smaller, the pressure loss when the exhaust gas passes through the inner wall of the filter becomes extremely large, and the engine may be stopped.

Further, in a commonly used honeycomb filter made of cordierite, a pore-forming agent is added in order to reduce the pressure loss, so that 20 μm is contained in the filter.
Large pores of about 100 μm are formed. However, in such a filter including large pores, the number of pores having a size suitable for collecting particulates is relatively small. Therefore, it is unavoidable that the collection efficiency of particulates is lowered.

The present invention has been made in view of the above circumstances and on the basis of the finding that the collection efficiency is improved if the pore diameters are distributed within a limited narrow range. An object of the present invention is to provide a diesel particulate filter with low loss and high collection efficiency.

[0005]

Means and Actions for Solving the Problems In order to solve the above problems, the present invention has an average pore diameter measured by mercury porosimetry in the range of 1 μm to 15 μm. The value of the standard deviation in the pore size distribution in the case of is defined as 0.20 or less.

It is known that the pore diameter of this level is suitable for collecting fine particulates,
Therefore, by setting the average pore diameter within the above range, it is possible to reliably collect the particulates. If the average pore diameter is less than 1 μm, the pressure loss when the exhaust gas passes through the inner wall becomes extremely large, which may cause the engine to stop. In addition, the average pore diameter is 15μ.
If it is m, it is not possible to efficiently collect fine particulates.

Further, when the standard deviation value in the pore size distribution is 0.20 or less, that is, when the pore size is distributed within a narrow and limited range, the number of pores in the suitable collection range is Relatively more. Therefore, the pressure loss is lower than the conventional one, and the collection efficiency can be increased.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is embodied in an exhaust gas purifying apparatus will be described in detail below with reference to FIGS.

As shown in FIG. 1, the exhaust gas purifying apparatus 1 comprises a casing 2 made of a metal pipe, and the casing 2
2a is connected to the exhaust pipe Ea of the diesel engine E. A diesel particulate filter 3 for purifying exhaust gas emitted from the diesel engine E is arranged in the casing 2. A burner 4 for regeneration processing is installed in the exhaust pipe Ea.

As shown in FIG. 2, the filter 3 is formed into a honeycomb shape by a porous sintered body such as a silicon carbide sintered body, and has a cylindrical shape as a whole (length 1 in this embodiment).
50 mm, outer diameter 140 mm). This filter 3
A plurality of hollow portions 5a and 5b are formed in the axial direction of, and the hollow portions 5a and 5b are open at both ends of the filter 3. An end opening on either the exhaust gas inflow side or the outflow side of each hollow portion 5a, 5b is closed by a sealing piece 6 made of a porous sintered body and having a thickness of 5 mm. By closing the sealing piece 6, a cell 7a opening to the inflow side and a cell 7b opening to the outflow side are formed. The cells 7a and 7b are adjacent to each other via an inner wall 8 (wall thickness 0.43 μm in this embodiment), and the outer surface of the inner wall 8 is oxidized by a platinum group element, another metal element, or an oxide thereof. A catalyst is supported. In the filter 3 of this example, the cell densities on both end surfaces were set to 170 cells / square inch.

As indicated by the curve C ₁ in the graph of FIG. 3, the filter 3 of this embodiment has an average pore diameter m ₁ of 7 μm measured by the mercury porosimetry method, and the pore diameter is commonly used. Manufacture is performed so that the standard deviation value SD ₁ in the pore size distribution expressed by logarithm is 0.12.

As a raw material for producing such a filter 3, for example, 20 parts by weight of α-type silicon carbide powder having an average particle size of 11 μm and 80 parts by weight of β-type silicon carbide powder having an average particle size of 0.3 μm are used. Parts, 6 parts by weight of methyl cellulose as a binder, 1 part by weight of lubricant and 20 parts by weight of water are used. After this mixture is kneaded, it is formed into a honeycomb shape by extrusion molding. Then, after the molded product is dried and degreased, it is calcined in a nitrogen atmosphere at 1700 ° C. for 4 hours. afterwards,
The hollow portions 5a and 5b are sealed. Further, after the main firing at 2000 ° C. for 4 hours in a nitrogen atmosphere, the desired filter 3
Is manufactured.

Next, the filter 3 constructed as described above.
The exhaust gas purifying action and the regeneration of the filter 3 will be described. When the filter 3 is arranged in the casing 2 and the exhaust gas is circulated, the exhaust gas first flows into each cell 7 a through each end opening on the inflow side, and is discharged to the outflow side via the inner wall 8. It is discharged from the adjacent cell 7b side that opens. Particulates in the exhaust gas are trapped when the exhaust gas passes through the inner wall 8, whereby the exhaust gas is purified. Further, when the amount of collected particulates in the filter 3 reaches a certain value, the burner 4 is ignited,
The heating of the filter 3 is started. Then, the particulate matter in the filter 3 is burned by the action of the catalyst carried by the filter 3, and the filter 3 is regenerated to the original state.

The fill film of this embodiment formed as described above
Collection of particulates to investigate the characteristics of data
The rate and pressure loss were investigated. About the former
Before and after mounting the filter 3
Particulates contained in the exhaust gas that has passed the mounting position
The filter paper is adsorbed on the filter paper, and the reflectance (%) of the filter paper is measured by JI
According to S-D1101, optical using smoke tester
Measured. For the latter, install the filter 3
The pressure of the exhaust gas inflow side and outflow side of the filter 3
The difference (mmHg) was measured 60 minutes after the start of collection. Furthermore, the book
As a comparative example to the example, it is made of cordierite.
And the same investigation using the same shape and size filter
I went. Incidentally, in FIG. 3, the curve C₂As indicated by
In addition, this cordierite filter uses the mercury injection method.
Therefore, the average value m of the pore diameters measured ₂Is 14 μm
And the pore diameter when the pore diameter is expressed in common logarithm
Standard deviation value SD for cloth₂Was 0.40. This
Table 1 shows the results of investigations on these filters.

[0015]

[Table 1]

As is clear from Table 1, the reflectance of the filter paper measured in a state where all the particulates in the exhaust gas are discharged without mounting the filter in the casing 2 is 40%. Met. Next, the reflectance with each filter attached was 0% in the example, while it was 10% in the comparative example. As is clear from this result, it was found that the filter of the example was able to completely remove the particulates and had a better collection ability than the filter of the comparative example.

The pressure difference between the exhaust gas inflow side and the outflow side of each filter was as low as 60 mmHg in the example, but was 120 mmHg in the comparative example, which was a double value. As described above, the superiority of the filter 3 of this example was also shown in that the pressure loss was smaller than that of the comparative example.

[0018]

As described above in detail, according to the diesel particulate filter of the present invention, the pressure loss is low and the trapping efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a partial front sectional view showing a mounted state of a diesel particulate filter according to an embodiment of the present invention.

FIG. 2 is a partially enlarged sectional view of the diesel particulate filter of FIG.

FIG. 3 is a graph showing a pore size distribution state of filters of Examples and Comparative Examples.

[Explanation of symbols]

m ₁ average pore size measured by mercury porosimetry,
SD ₁ Standard deviation value in the pore size distribution when the pore size is represented by a common logarithm.

Claims (1)

Claims: 1. The average pore diameter (m ₁ ) measured by mercury porosimetry is in the range of ₁ μm to 15 μm, and the pore diameter when expressed in common logarithm. A diesel particulate filter having a standard deviation value (SD ₁ ) in the distribution of 0.20 or less.