JPS6146413A - Diesel exhaust gas filter - Google Patents

Abstract

PURPOSE:To enable re-production of a filter by burning soot caught easily by providing electric resistant heat generators a Diesel exhaust gas filter in which cell ends of honeycomb construction made of porous ceramic are alternately closed. CONSTITUTION:A honeycomb type exhaust gas filter 1 is constructed a collected body of lots of honeycomb cells whose one ends made of porous ceramic such as fiber ceramic are closed, and arranged around a core 2. And on one end of the exhaust gas filter 1, closed portions of honeycomb cells and ports 4 are positions alternately. And electric resistant heat generators 5 are arranged in the exhaust gas filter and both the ends of the generation are drawn out. This time, the generators 5 are buried or attached to the exhaust gas flow-in side end, and the generators 5 themselves are coated by at least one of heat-resisting alloy and heat-resisting oxide. Then, soot caught by the exhaust gas filter 1 can easily be burned and re-production of the filter can be made.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention captures fine particles whose main component is carbon (hereinafter referred to as soot) emitted from diesel engines, and burns the captured soot to reduce exhaust gas. This invention relates to an exhaust gas filter for diesel engines that purifies gas.

Conventional structure and its problems As a filter to capture soot emitted from diesel engines, a 1-nicum-shaped ceramic monolith filter made by extrusion using cordierite, metal coated with alumina. Filters packed with wire mesh, ceramic foam filters with porous structures made using foaming agents, and ceramic fiber mats have been devised. All of these filters experience increased pressure drop through the filter as soot builds up, reducing engine performance. Therefore, to maintain engine performance, it is necessary to burn off the soot and regenerate the filter once a certain amount of soot has accumulated.

For this purpose, there is a method of increasing the exhaust gas temperature to 550 to 660'C, which is the ignition temperature of soot, by increasing the engine load υ, increasing the exhaust gas temperature with a burner, etc., but the equipment is complicated and is not suitable for practical use. Furthermore, since the heat generated by the combustion of soot is added to the heat generated by the burner, the temperature inside the filter rises at an accelerated rate as the combustion propagates, and as a result, the filter is melted.

The problems associated with filter regeneration are enumerated as follows.

(1) The method of heating soot to 500-600°C and igniting it is complicated.

(Rumor: After the soot is ignited, the combustion propagation is insufficient and it cannot be completely regenerated. (■ When the soot burns, the filter cannot withstand the heat.)

(4) The filter must not withstand severe thermal cycles due to repeated regeneration.

As mentioned above, this method has many problems.

Purpose of the Invention By providing an electrical resistance heating element to a diesel exhaust gas filter formed by alternately closing the cell ends of a honeycomb structure made of porous ceramic, captured soot can be easily burned and the filter can be regenerated. The purpose is to provide diesel exhaust gas filters.

Structure of the Invention Simply heat the electric resistance heating element attached to the porous ceramic filter to about 600'C and ignite the soot captured in the vicinity, and the combustion will propagate and spread, burning all the remaining soot. To provide a diesel exhaust gas filter that can perform filter regeneration.

Description of examples Examples according to the present invention will be described below.

[Example 1] After the surface of a nichrome-based heating wire was degreased and cleaned, sandblasting was performed using general abrasive particles such as alumina and silicon carbide. Wash off any abrasive particles or debris on the surface with water 1
It was dried at 00-150'Q. The thus pretreated heating wire was thermally sprayed with an alumina and silica mixture using a plasma spraying method to form a coating layer with a thickness of 10 to 100 μm.

As heat-resistant oxides other than alumina used here, metal oxides such as zirconia and spinel-type double oxides such as MqA1204 can also be used. By forming such a coating layer, the heating wire can be prevented from carburizing corrosion. Furthermore, a heat-resistant alloy of Ni--Cr was sprayed by the same plasma spraying method to form a coating layer of about 6 to 30 microns. Heat-resistant alloys other than Ni-Cr used here include N1-Cr-Al, Fe-Cr, Fe-C
r-A1 etc. can also be used. By using the coating layer made of this heat-resistant alloy, it becomes possible to use the diesel exhaust gas filter stably for a long period of time even under severe thermal cycles or as a heating element. However, since these coating layers essentially have 5 to 30% pores, the interface between the heating wire and the coating layer was sealed with a mixture of alumina sol and colloidal silica.

The heating element thus produced did not suffer any corrosion and did not lose its function as a heating wire even when heated up to 1400''C.

On the other hand, a mixed slurry of 30 parts by weight of cut silica alumina fibers and 16 parts by weight of ceramic raw powder was added with organic binders such as polyvinyl acetate and polyacrylic acid ester, and then coagulated with a flocculant, and then made into a paper using a fourdrinier paper machine. I created a sheet. A corrugated sheet was made by bonding a corrugated sheet and a flat sheet using the obtained sheet in the same manner as in the production of corrugated poles, and this was then bonded around the core and wound to form a honeycomb shape. At this time, the heating element described above was adhesively fixed to a part of the full gate sheet, and the corrugated sheet was rolled up so that both ends of the heating element were exposed outside the honeycomb. This heating element was placed so as to be embedded in the exhaust gas inlet side end of the exhaust gas filter of the diesel engine. When molding ceramics using the extrusion method, it has been impossible to insert such a heating element inside the molded body, but it is quite easy to insert it using the corrugation method. Next, the outlet and inlet sides of the honeycomb are alternately blocked using a material similar to a sheet so that the fluid that has entered one honeycomb cell passes through the cell wall, transfers to another cell, and is then discharged. did.

This molded product was fired at 1260° C. in the air to form ceramic fibers and ceramic raw material powder into a ceramic fiber lamic honeycomb structure exhaust gas filter.

The exhaust gas filter obtained in this example is shown in FIG. 1
is a honeycomb-shaped exhaust gas filter constructed around a fiber ceramic core 2, which is an assembly of a large number of honeycomb cells with one end closed. It is constructed so that the openings 4 and 4 are exposed alternately, and both ends of the buried heating element 60 are drawers. It is assumed that the exhaust gas flows in the direction of the arrow. FIG. 2 shows a partial sectional view showing the location where the heating element 5a is buried.

[Example 2] Using the same sheet as in Example 1, it was formed into a honeycomb by the same method, the cell ends were alternately closed, and then heated to 1250'C.
The heating element obtained in Example 1 was embedded in the exhaust gas inflow side end of the exhaust gas filter obtained by firing in a groove having a depth of about 10 mm. An adhesive made of commercially available ceramics such as colloidal silica, alumina sol, diherconia sol, etc. was used to fix the heating element. The state in which the heating element is buried in the exhaust gas filter obtained in this example is similar to that shown in FIG. 2.

[Example 3] As shown in FIG. 3, the heating element 5b obtained in Example 1 was attached to the end face of the exhaust gas inlet side of the exhaust gas filter obtained in the same manner as in Example 2 with the adhesive used in Example 2. It was fixed.

FIG. 4 shows the results when the filter thus obtained was run at a constant speed of 64 km/h in an actual diesel engine. A filter with an initial pressure of 1 o mm Hg,
As soot was captured by the filter, the pressure loss increased to 100+nmH (7 hours) in 3 hours and 10 minutes.By the way, the heating element was heated by electricity.

It was observed that the pressure drop due to the filter and the pressure drop decreased rapidly to almost the same value as the initial pressure.

This indicates that the soot trapped in the exhaust gas filter was burned out and the exhaust gas filter was successfully regenerated. Heated by a heating element installed on the exhaust gas inflow side,
Once the soot ignites and starts burning, the combustion quickly propagates and completes the regeneration of the exhaust gas filter. The exhaust gas filter of this example is made of fiber ceramic with a porosity of 7.
Since a material with a porosity of 0- or more is used, both the heat capacity and thermal conductivity are smaller than an exhaust gas filter made by extrusion molding such as cordierite, which is made of sintered powder and has a porosity of 35 to 55%. Therefore, the heat generated in the soot combustion part can be quickly removed by a large amount of exhaust gas, making it possible to prevent localized abnormal overheating of the filter material. On the other hand, the temperature required to maintain combustion is maintained only in the immediate vicinity of the burning part due to low thermal conductivity, and therefore rapid combustion or extinguishing due to cooling may occur, but at a gentle and highly desirable rate. It performs combustion. Therefore, stable regeneration processing can be performed without causing overheating caused by rapid combustion and melting and damaging the exhaust gas filter.

Effects of the Invention By attaching an electric resistance heating element to the end of the exhaust gas inlet side of a diesel exhaust gas filter made of porous ceramic, captured soot can be easily ignited, and the filter can be regenerated through stable combustion. This allows the diesel exhaust gas filter to withstand repeated treatments and have a long lifespan.

[Brief explanation of drawings]

Fig. 1 is an overall configuration diagram of an exhaust gas filter in which a heating element is embedded according to an embodiment of the present invention, Fig. 2 is a partial sectional view showing the state of the part in which the heating element of Fig. 1 is embedded, and Fig. 3 shows the heat generation Fig. 4 is a partial configuration diagram showing a state in which the body is attached and fixed to the exhaust gas inflow side end, and Fig. 4 is a graph showing the change in pressure loss of the exhaust gas filter over time when the diesel engine runs at a constant speed of 64 Krn/h. ...Exhaust gas filter, 5, 6a, 5b...
...heating element. Name of agent: Patent attorney Toshio Nakao and 1 other person @1
figure

Claims (5)

[Claims] (1) A diesel exhaust gas filter in which an electrical resistance heating element is provided within the diesel exhaust gas filter, which is formed by alternately closing the cell ends of a honeycomb structure made of porous ceramic. (2) The diesel exhaust gas filter according to claim 1, wherein the heating element is embedded in the exhaust gas inflow side end and is provided so as to be able to come into contact with the inflowing exhaust gas. (3) The diesel exhaust gas filter according to claim 1, wherein the heating element is attached and fixed to the exhaust gas inflow side end and is provided so as to be able to come into contact with the inflowing exhaust gas. (4) Claim 1, characterized in that the heating element is coated with at least one of a heat-resistant alloy and a heat-resistant oxide.
Diesel exhaust gas filter as described in section. (5) The diesel exhaust gas filter according to claim 1, wherein the porous ceramic is made of fiber ceramic.