JPH0621548B2 - Diesel exhaust gas filter - Google Patents

Description

Description: TECHNICAL FIELD The present invention captures particulates (hereinafter referred to as soot), which is mainly composed of carbon, emitted from a diesel engine, and exhausts the soot captured by burning the particulates. The present invention relates to an exhaust gas filter for a diesel engine that purifies gas.

Configuration of conventional example and its problems As a filter for capturing soot discharged from a diesel engine, a honeycomb-shaped ceramic monolith filter manufactured by an extrusion method using cordierite and a metal wire mesh coated with alumina were packed. A ceramic foam filter, a ceramic fiber mat, and the like, which have a porous structure using a filter and a foaming agent, have been devised. All of these filters have a high pressure loss through the filters as the soot accumulates, degrading engine performance. Therefore, in order to maintain the engine performance, when a certain amount of soot is deposited, it is necessary to burn the soot to regenerate the filter. Therefore, there is a method of increasing the exhaust gas temperature to 55 to 660 ° C. which is the ignition temperature of soot by increasing the engine load or increasing the gas temperature by a burner, but the device is complicated and cannot be put to practical use. In addition, since the heat quantity of soot combustion is added to the heat quantity of the burner, the temperature inside the filter is accelerated due to the propagation of combustion, and as a result, the filter is melted.

The following is a list of problems associated with performing filter regeneration.

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

(2) After soot is ignited, the propagation of combustion is insufficient and it cannot be completely regenerated.

(3) When soot burns, the filter must not withstand the heat.

(4) The filter must not withstand the severe thermal cycles of repeated regeneration.

As described above, there are many problems.

Object of the invention By providing an electric resistance heating element to a diesel exhaust gas filter in which cell ends of a honeycomb structure made of a porous ceramic are alternately closed, the trapped soot can be easily burned to regenerate the filter. An object is to provide a diesel exhaust gas filter.

Structure of the Invention An electric resistance heating element mounted on a porous ceramic filter is heated to about 600 ° C., and the soot trapped in the vicinity thereof is ignited, and the combustion propagates to spread and spread all the remaining soot. To provide a diesel exhaust gas filter capable of performing filter regeneration.

Description of Examples Examples of the present invention will be described below.

[Example 1] After degreasing and cleaning the surface of a nichrome heating wire, sandblasting was performed using general ground particles such as alumina and silicon carbide. Wash the surface grinding particles and debris with water 100
Dried at ~ 150 ° C. The heating wire pretreated in this manner was sprayed with a mixture of alumina and silica by using a plasma spraying method to form a coating layer having a thickness of 10 to 100 μm. As the heat-resistant oxide other than the alumina used here, a spinel type double oxide such as a metal oxide such as zirconia or MgAl ₂ O ₄ can be used. By forming such a coating layer, it is possible to prevent the heating wire from undergoing carburizing corrosion. On the other hand, Ni-C as a heat resistant alloy coating
A heat resistant alloy of r-Al was sprayed by the same plasma spraying method to form a coating layer of about 5 to 30 μm. As a heat-resistant alloy other than Ni-Cr-Al used here, Ni-Cr
-Ti etc. can also be used. By using the coating layer 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 heat cycles or as a heat cycle as a heating element.
However, since these coating layers essentially have pores of 5 to 30%, the interface between the heating wire and the coating forming layer was sealed with a mixture of alumina sol and colloidal silica. The heating element thus produced did not corrode at all even when heated to 1400 ° C. and did not lose its function as a heating wire.

On the other hand, a mixed slurry of 30 parts by weight of the cut silica-alumina fiber and 16 parts by weight of the ceramic raw material powder was added with an organic binder of polyvinyl acetate and polyacrylic acid ester and then agglomerated with an aggregating agent, followed by papermaking with a Fourdrinier paper machine. I made a sheet. A corrugated sheet was prepared by adhering the obtained sheet to a corrugated sheet and a flat sheet in the same manner as in corrugated board production, and then the corrugated sheet was adhered around the core to form a honeycomb shape. At this time, the above-mentioned heating element was adhered and fixed to a part of the corrugated 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 arranged so as to be embedded in the cell opened on the inflow side at the exhaust gas inlet side end of the exhaust gas filter of the diesel engine. In the molding of ceramics by the extrusion method, it was impossible to insert such a heating element inside the molded body, but it can be inserted quite easily by using the corrugated method. Next, the outlet and inlet sides of the honeycomb are alternated so that the fluid that has entered the cells of one honeycomb passes through the cell walls, moves to the other cells, and is then discharged. did. This molded product was fired in air at 1250 ° C. to ceramicize the ceramic fibers and the ceramic raw material powder to obtain an exhaust gas filter having a honeycomb structure of fiber ceramics. The exhaust gas filter obtained in this example is shown in FIG. Reference numeral 1 denotes a honeycomb-shaped exhaust gas filter formed around a core 2 by a fiber ceramic, which is composed of an aggregate of a large number of honeycomb cells whose one end is closed. The openings 4 are configured to appear alternately, and both ends of the embedded heating element 5 are drawn out. Exhaust gas shall flow in the direction of the arrow. FIG. 2 shows a partial cross-sectional view showing the buried portion of the heating element 5a.

[Example 2] The same sheet as in Example 1 was used to form a honeycomb by the same method, and the end portions of the exhaust gas inflow side of the exhaust gas filter obtained by alternately closing the cell end portions and then firing at 1250 ° C were used. The heating element obtained in Example 1 was embedded with a groove having a depth of about 10 mm. To fix the heating element, an adhesive made of colloidal silica or commercially available ceramics such as aliminasol and zirconia sol was used. The embedded state of the heating element of the exhaust gas filter obtained in this example is similar to that shown in FIG.

[Example 3] An exhaust gas filter obtained in the same manner as in Example 2 was attached and fixed to the end face on the exhaust gas inflow side with the heating element 5b obtained in Example 1 as shown in Fig. 3 with the adhesive used in Example 2. Let

FIG. 4 shows the results when the filter thus obtained was run at a constant speed of 64 km / h with an actual diesel engine. A filter with an initial pressure of 10 mmHg increases in pressure loss as the soot is captured by the filter, and the pressure loss increases for 3 hours.
When 100 mmHg was reached in 0 minutes, the heating element was energized and heated. Then, it was observed that the pressure loss due to the filter drastically decreased to almost the same value as the initial pressure. This indicates that the soot trapped in the exhaust gas filter burned out and the exhaust gas filter was regenerated properly. When heated by a heating element provided in the cell that opens on the exhaust gas inflow side, the soot ignites and begins to burn,
The combustion quickly propagates and completes the regeneration of the exhaust gas filter. Since the exhaust gas filter of the present embodiment uses a material made of fiber ceramics and having a porosity of 70% or more, compared with an exhaust gas filter formed by extrusion molding of cordierite or the like having a porosity of 35 to 55% made of sintered powder. Both heat capacity and thermal conductivity are small. Therefore, the heat generated in the burning portion of soot is easily removed rapidly by a large amount of exhaust gas, and it becomes possible to prevent local 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 combustion area due to its low thermal conductivity, so that rapid combustion or digestion by cooling cannot occur, and at a moderate and extremely desirable rate. It burns. Therefore, a stable regeneration process can be performed without causing overheating caused by rapid combustion and melting and damaging the exhaust gas filter.

Effects of the Invention A diesel exhaust gas filter made of a porous ceramic, by attaching an electric resistance heating element to the exhaust gas inflow side end portion, while easily igniting the captured soot,
It is possible to obtain a diesel exhaust gas filter having a long service life by performing stable combustion and enduring repeated filter regeneration processing.

[Brief description 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 a state of a portion in which the heating element of FIG. 1 is embedded, and FIG. 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 portion, and FIG. 4 is a graph showing a time change of the pressure loss of the exhaust gas filter in the diesel engine 64 Km / h constant speed running. 1 ... Exhaust gas filter, 5, 5a, 5b ... Heating element.

Front page continuation (72) Toshihiro Mihara Toshihiro Mihara 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. References JP-A-58-106115 (JP, A) JP-A-57-179317 (JP, A) Actual development JP-A-58-161116 (JP, U) US Patent 4276066 (US, A)

Claims (2)

[Claims] 1. A diesel exhaust gas filter in which corrugated honeycomb structure made of porous ceramic is alternately closed at cell ends, and the electric resistance heating element is coated with at least one of a heat resistant alloy and a heat resistant oxide. A diesel exhaust gas filter which is embedded in the exhaust gas inflow side end over a plurality of cells having an opening on the exhaust gas inflow side along the winding direction and is capable of contacting the cell end or the soot accumulated in the cell. 2. The diesel exhaust gas filter according to claim 1, wherein the porous ceramic is a fiber ceramic.