JPH0422012Y2 - - Google Patents

Description

[Detailed explanation of the idea]

(Industrial Application Field) The present invention relates to a filter for purifying exhaust gas emitted from an internal combustion engine, and particularly to a filter for collecting particulate matter emitted from a diesel engine. (Prior Art) Conventionally, ceramic structures have generally been used as filters for collecting particulate matter discharged from diesel engines due to their collection efficiency and heat resistance. This ceramic structure is formed into a honeycomb or foam shape.
For example, a honeycomb ceramic structure has a structure as shown in FIGS. 4 and 5. That is, a large number of cells 2 are formed by a partition wall 1 made of porous ceramic (usually cordierite).
, and the openings at both ends of the cell 2 are alternately plugged with plugs 3.
It is blocked. There is also a ceramic film 5 made of gamma alumina or the like on the partition wall 1, on which an oxidation catalyst is supported to increase the ability to collect fine particles other than soot (hydrocarbons, sulfates, metals, etc.). . When using such a filter, the openings of the cells 2 should be directed upstream and downstream.
It is attached to the exhaust system of the engine and captures particulate matter from the engine while the exhaust gases flow through the bulkhead 1 into the adjacent cell 2, as indicated by the arrow in FIG. By the way, as the filter is used repeatedly, the back pressure increases due to the accumulation of particulate matter and the exhaust efficiency decreases. Therefore, it is necessary to periodically incinerate the particulate matter and regenerate it. A method of external ignition using a heating means such as a burner is adopted. (Problem that the invention aims to solve) However, this external ignition method ignites the particulate on the upstream side of the filter and propagates combustion to the downstream side of the filter to perform regeneration, so it has poor thermal conductivity. In the above conventional ceramic filter, which is inferior in quality, it is difficult for the combustion heat of the particulate to be transmitted to the particulate on the downstream side, and combustion often stops midway. As a countermeasure against this problem, for example, attempts have been made to lower the combustion temperature of particulate by having the partition walls 1 carry platinum group elements such as platinum (Pt) and palladium (Pd) (Japanese Patent Application Laid-open No. 55-24597), or Attempts have been made to lower the combustion temperature of particulate by supporting base metal elements such as (Cu) and manganese (Mn) (Japanese Patent Application Laid-open Nos. 1983-109136 and 1983-109139). Even with this, the current situation is that a sufficiently satisfactory combustion propagation performance cannot be obtained. In this regard, the inventor of the present application
In No. 94868, a filter with improved combustion propagation performance was realized by forming a metal film with good thermal conductivity such as copper (Cu) or silver (Ag) on the particulate collection surface of the ceramic structure. . However, in this case, the metal coating is in the pores 1a of the partition wall 1.
(Fig. 5), pressure loss increases, or as the regeneration performance improves, the combustion rate of the particulate increases, so the amount of temperature rise of the filter during regeneration becomes large, causing damage to the ceramic structure. A new problem arose: cracks and melting damage were likely to occur. The present invention was devised in view of the above-mentioned conventional problems, and its purpose is to improve the combustion propagation performance while preventing an increase in pressure loss and damage to the ceramic structure. An object of the present invention is to provide a filter for collecting particulate matter that can improve reproducibility. (Means for Solving the Problems) The present invention is characterized in that a metal coating is formed on the particulate collection surface on the upstream side of the porous ceramic structure. The ceramic structure is formed in a honeycomb shape or a foam shape, and is usually made of cordierite, which has a high marketability. In the present invention, the range in which the metal film is provided is 5 to 50%, preferably 10 to 30%, of the total length of the ceramic structure.
%. The metal film is preferably a metal with good thermal conductivity, such as Cu or Ag.
In this case, the metal film is formed by immersing the ceramic structure in a palladium chloride solution, then reducing palladium in an aqueous sodium borohydride solution to form a plating nucleus, and then immersing it in an electroless plating solution to form a plating nucleus. It can be formed by performing the following steps. The filter according to the present invention also includes one in which a ceramic film, such as a γ-alumina film, which has the ability to collect many types of fine particles is formed under the metal film. (Function) In the particulate collection filter configured as described above, the presence of the metal film improves the thermal conductivity of the particulate collection surface and improves ignitability and combustion propagation performance. In addition, since the metal film is formed only on the particulate collection surface on the upstream side of the ceramic structure, the area where the pores of the ceramic structure are blocked is reduced, and an increase in pressure loss is suppressed. At this time, the combustion speed of the particulate on the downstream side slows down, and an excessive rise in combustion heat is suppressed. (Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 1 and 2 show a particulate collection filter according to the present invention. In addition,
This embodiment shows an example of application to a honeycomb filter, and its overall structure is the same as that shown in FIG. 4 above, so a description thereof will be omitted here. The feature of this embodiment is that a γ-alumina film 12 is formed on the entire particulate collection surface of a columnar porous ceramic structure (made of cordierite) 11, and further, on the γ-alumina film 12,
The point is that a copper plating layer 13 is formed over a predetermined range from the end face of the ceramic structure. However, such a filter 10 will be put into practical use by being attached to the exhaust system of an engine with the portion on which the copper plating layer 13 is formed facing upstream. Here, the filter 10 is manufactured by the following procedure, for example. That is, a commercially available columnar cordierite ceramic structure 11 is provided, immersed in a slurry consisting of γ alumina, alumina sol, an aqueous aluminum nitrate solution, and distilled water, and then pulled up.
Excess droplets were blown off with an air stream, dried at 120°C for 2 hours, and fired at 600°C for 3 hours, and the ceramic structure 11 (particulate collection surface) was dried.
A γ alumina film 12 is provided on the surface. Next, this ceramic structure 11 is immersed in distilled water to perform water absorption treatment, and after blowing off the excess distilled water, 0.2g/
It is immersed in a palladium chloride (PdCl ₂ ) aqueous solution a predetermined distance from the end face to adsorb palladium.
After that, palladium is reduced in a sodium borohydride solution to form an electroless plating nucleus, which is then immersed in a commercially available electroless copper plating solution for 30 minutes, pulled out, washed with water, dried, and then deposited on the γ alumina film. A copper plating layer 13 is formed. Hereinafter, the range in which the copper plating layer 13 was formed was varied and subjected to various tests to be described later. The sample filter has a ratio of the copper plating layer 13 to the total length of the filter 10: A: 10%, B: 25%, C: 50%.
% was used. For comparison, the ratio of the copper plating layer 13 was set to D: 0% (no copper plating) and E: 100% (copper plating over the entire length). Test example 1 The filters A to E above (however, the filter size is 100 mm in diameter and 100 mm in length) are installed in the exhaust system of a swirl chamber type diesel engine with a displacement of 2400 c.c., and the engine speed is 200 rpm.
It was operated for 3 hours at a torque of 6 kg/m, and the change in pressure loss was recorded. The results are shown in Table 1. Test Example 2 After completing Test Example 1, a regeneration test was performed on filters A to E under the following conditions: Regeneration gas (air): 650°C Gas flow rate: 300/min Regeneration time: 3 to 5 minutes. The temperature inside the filter
Measurements were taken at 12 points. A sheathed thermocouple (CA) with a diameter of 0.5 mm was used for measurement. Of the temperature measurement data obtained,
The maximum temperature is shown in Table 2 as the filter internal temperature during regeneration. In addition, the amount of particulate matter adhering to the filter was within the range of 9.8 to 10.5 g in all cases. Test example 3 Filters A to E (However, the filter size is 30 mm in diameter.
mm, length 50 mm) is attached to the exhaust system of a swirl chamber type diesel engine with a displacement of 2400 c.c., and the rotational speed is
The filter was operated for 2.5 hours at 2000 rpm and a torque of 3 kg/m, and 0.60 to 0.65 g of particulate was deposited on each filter.The filter was then assembled into the test equipment shown in Figure 3 and a combustion test was conducted to determine the regenerating temperature. I asked for

【table】

【table】

[Table] From the results shown in Tables 1 to 3, Filter D, which is not plated, has a small pressure loss and a low maximum temperature during regeneration, but the regeneration temperature is high and the regeneration performance is poor, making it unsuitable for practical use. It was confirmed that it was unsuitable. In addition, Filter E, which is entirely copper plated,
It was confirmed that although the regeneration temperature is low and the regeneration performance is excellent, the pressure loss is large and the combustion temperature is high, which poses a high risk of filter damage.
On the other hand, filters A~
It was confirmed that C satisfied the three characteristics of pressure drop, heating temperature, and reproducibility at a high level, and was extremely practical. (Effects of the invention) As explained in detail above, the present invention provides a metal coating on the particulate collection surface of the porous ceramic structure, which improves ignitability and combustion propagation performance and facilitates combustion of particulate. becomes easier,
Filter replayability has been improved. In addition, since the metal coating was formed only on the upstream side,
Not only is it possible to suppress the increase in pressure loss as much as possible by narrowing the range in which the pores of the ceramic structure are blocked, but also the excessive rise in combustion heat during regeneration is suppressed, making the ceramic structure This makes it possible to prevent damage to the filter, and the practicality of this filter as a whole has been significantly improved.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing the external appearance of a particulate collection filter according to the present invention, Fig. 2 is a sectional view showing its partition structure, Fig. 3 is a sectional view showing a filter regeneration test device, and Fig. 4 is a sectional view showing the filter for collecting particulate matter according to the present invention. The figure is a sectional view showing the structure of a conventional filter, and FIG. 5 is a detailed view of section A thereof. 11... Ceramic structure, 12... Ceramic film, 13... Metal film.

Claims (1)

[Scope of utility model registration request] On the particulate collecting surface on the upstream side of the porous ceramic structure,
A filter for collecting particulate matter, characterized in that a metal film is formed over a range of 50%, preferably 10 to 30%.