JPH06129229A - Particulate trap for diesel engine - Google Patents

Abstract

PURPOSE:To provide a particulate trap for a diesel engine which has a low pressure loss, a high degree of trapping efficiency, and which is shock-proof. CONSTITUTION:A filter element 10 is located in a container provided in an exhaust system. The filter element 10 is formed of a three-dimensional mesh-like porous metal member made of a heat-resistant metal frame having communication pores. A combination is made such that the more the difference among the bores of the pores, or the larger the same, the nearer to the exhaust inflow side, they are arranged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a particulate trap for collecting and removing fine particles (particulates) such as carbon in exhaust gas of a diesel engine.

[0002]

2. Description of the Related Art Exhaust gas from an automobile is one of the major causes of air pollution, and a technique for removing harmful components contained in the exhaust gas is extremely important.

Particularly in diesel engine vehicles, the removal of fine particles (particulates) mainly composed of NOx and carbon is an important issue.

In order to remove these harmful components, EG
Although R is applied, the fuel injection system is improved, and efforts are being made on the engine side, there is no fundamental deciding factor,
It has been proposed to install an exhaust trap in the exhaust passage, collect particulates by the trap, and remove them by post-treatment (Japanese Patent Laid-Open No. 58-51235, etc.).
To date, this post-treatment method is considered to be the most practical and is being studied.

By the way, as a particulate trap for collecting the particulates contained in the exhaust gas of a diesel engine, it is necessary to satisfy the following performance from the conditions of use.

Collection Performance First of all, it is necessary to have a collection efficiency of particulates sufficient to satisfy the cleanliness of exhaust gas. The particulate emission amount changes depending on the exhaust amount and load of the diesel engine, but it is said that it is necessary to collect an average of 60% or more of the emission amount from the diesel engine.

Pressure loss Secondly, the pressure loss with respect to the exhaust gas is small. As the particulates are collected, the pressure loss when the engine exhaust passes through the trap increases, and the back pressure is exerted on the engine, which causes an adverse effect. For this reason, it is said that it is usually necessary to suppress the pressure loss after collection to 30 KPa or less. Therefore, it is necessary that the particulate trap has a small initial pressure loss and that the pressure loss is unlikely to increase even if the exhaust gas is passed therethrough and the particulates are collected.

Conventionally, as a filter element material satisfying the above requirements, a wall-flow type honeycomb porous body of cordierite ceramics has been considered to be the most practical. However, in this method, particulates are likely to locally accumulate, and since cordierite ceramics have a low thermal conductivity, heat spots are likely to be formed during regeneration, and the filter may be melted or cracked due to thermal stress. In some cases, reliability could not be ensured.

Therefore, attention is now being paid to a highly reliable metal trap that does not cause cracks during reproduction and a ceramic fiber trap in which ceramic fibers are formed into a candle shape.

[0010]

However, due to the structure of the metallic trap and the ceramic fiber trap, the surface area (exhaust area) through which the exhaust gas can flow cannot be as large as that of the cordierite filter. Therefore, when a filter is designed so as to obtain high collection efficiency, particulates are only collected on the filter surface and cause clogging, resulting in a rapid increase in pressure loss and a short filter life.

[0011]

In order to solve the above problems, in the present invention, at least two kinds of three-dimensional network structure porous bodies having a large hole diameter and a small hole diameter are combined from the exhaust gas inflow side to the outflow side. Also another 1
As one means, a three-dimensional network structure porous body having a large pore size and a three-dimensional network structure porous body filled with ceramic or metal to substantially reduce the pore size are
The larger the pore size, the closer to the exhaust gas inflow side.

It is desirable that the difference in pore diameter between the porous bodies to be combined should satisfy the condition of a / b ≦ 15, where a is the average pore diameter of the porous body having the maximum pore diameter and b is the average pore diameter of the porous body having the minimum pore diameter. . The lower limit of a is preferably about 1.5b. When combining a porous body having a small pore size with a ceramic or metal filler, a substantial difference in pore size is provided. The filling here includes not only filling the pores with the granular material, but also forming a film or whiskers on the skeleton surface by chemical or physical vapor deposition.

The three-dimensional network structure porous body having a small pore size may be prepared by increasing the volume filling rate or increasing the skeleton size from the beginning, and a three-dimensional network structure porous body having a large pore size may be prepared. It may be created by compression by a method such as rolling.

The diesel engine particulate trap collects particulates and then heats them with an electric heater or the like to burn the particulates for regeneration. It is important to reduce the heat capacity to enable regeneration in a short time. Needless to say, in the present invention as well, the weight of the filter can be reduced to achieve regeneration in a short time.

[0015]

First, the state of particulate deposition will be described with reference to the schematic diagrams of FIGS. 1 shows a structure in which the volume filling rate is inclined from the exhaust gas inflow side to the outflow side to change the pore diameter, FIG. 2 is a structure in which the diameter of the skeleton 1 is inclined to change the pore diameter, and FIG. 3 is a volume in the filter thickness direction. The conventional metal filter and ceramic fiber filter structure in which the packing rate and the skeleton diameter are not inclined, that is, the pore diameter does not change is shown. Further, (a) of FIGS. 1 to 3 shows the case where the particulate collection amount is small (when the collection time is short), and (b) shows the case where the collection amount is large. Further, (c) shows a particulate collection amount distribution in the filter thickness direction in the state of (b).

In a structure in which the volume filling rate and the skeleton diameter are not inclined, as shown in FIG. 3B, the filter surface becomes clogged as the collection of particulates 2 progresses. On the other hand, in the structure in which the volume filling rate and the skeleton diameter are inclined, in the initial state (see FIG. 1A and FIG. 2A), the filter rear layer mainly collects the particulates, but after that, It comes to be collected in the front layer of the filter (see FIG. 1 (b) and FIG. 2 (b)). Therefore, clogging is less likely to occur on the surface and inside of the filter.

When the filter is clogged, the pressure loss starts to rise rapidly. Therefore, the structure of the present invention in which the volume filling rate and the skeleton diameter are tilted and the pore diameter is changed from the particulate deposition state described above is more preferable. It is considered that the pressure loss will be low when the same amount of particulates is collected. Moreover, in this inclined structure, a high collection efficiency can be secured by the action of the filter rear layer.

[0018]

Embodiments of the present invention will be described below.

Experimental Example 1 FIG. 4 shows an experimental apparatus. 34
00 cc shows the results of evaluations performed by an experimental apparatus including a chassis dynamo and a dilution tunnel of a 4-cylinder direct injection diesel engine vehicle. As the filter element 10, a cylinder of a Ni-based three-dimensional network structure porous body (trade name: Celmet) manufactured by Sumitomo Electric Industries, Ltd. was used, and seven trap containers 11 were mounted. The end face opposite to the gas inlet is sealed with a gasket and an iron plate so that the exhaust gas is introduced into the space outside the cylindrical body and flows through the wall of the filter element to the inside of the pipe.

FIG. 5 shows an evaluation sample. Sample A has no change in pore size in the thickness direction of the filter for comparison, Sample B
Indicates that the pore size is changed. In addition, the product number in FIG. 4 indicates the number of cells (the number of holes) per unit area,
# 7 is 50 to 70 per square inch, # 4 is 26 to 3
There are five. That is, sample B has a combination of # 4 with a large hole diameter on the exhaust gas inlet side and # 7 on the outlet side.

6 and 7 show changes in differential pressure and collection efficiency with respect to the amount of soot deposited. It can be seen that sample B has the same collection efficiency as sample A, but the increase in differential pressure is gentle and the filter life is extended.

[Experimental Example 2] An evaluation result obtained by the same experimental apparatus as in Experimental Example 1 will be shown. As the filter element 10, a Ni-based three-dimensional network structure porous body (trade name: Celmet) manufactured by Sumitomo Electric Industries, Ltd. was used as a Ni—Cr alloy cylinder, and seven cylinders were mounted in the trap container. The end face opposite to the gas inlet is sealed with a gasket and an iron plate so that the exhaust gas is introduced into the space outside the cylindrical body and flows through the wall of the filter element to the inside of the pipe.

FIG. 8 shows an evaluation sample. Sample C has no change in pore size in the thickness direction of the comparative filter, Sample D has 3 layers of # 4 on the exhaust gas inlet side, then 3 layers of # 7 porous material with a thickness of 1.8 mm, and exhaust gas. The thickness of # 7 on the exit side is 0.
Three layers of 9 mm porous material were layered to change the pore size. The # 7 0.9 mm thick product used here is a # 7 1.8 mm product compression molded.

The meanings of # 4 and # 7 are as described in the first embodiment.

9 and 10, the differential pressure with respect to the amount of soot deposited,
The change of collection efficiency is shown. It can be seen that sample B has the same collection efficiency as sample A, but the increase in differential pressure is gentle and the filter life is extended.

[0026]

As described above, according to the present invention,
Even if particulates are collected, the rise in differential pressure is small,
A particulate trap with a long life and high collection efficiency can be obtained.

The particulate trap is
It can sufficiently withstand the thermal stress at the time of combustion regeneration and can be expected to have a great effect for various diesel engines including diesel engine cars.

[Brief description of drawings]

FIG. 1 is a schematic diagram {(a), (b)} showing a particulate accumulation state of the product of the present invention, and a collection amount distribution diagram (c).

FIG. 2 is a schematic diagram {(a), (b)} showing a particulate deposition state of the product of the present invention, and a collection amount distribution diagram (c).

FIG. 3 is a schematic diagram {(a), (b)} showing a state of particulate accumulation of a conventional product of the present invention, and a collection amount distribution diagram (c).

FIG. 4 is a schematic diagram of an experimental device used for evaluation of collection performance.

FIG. 5 is a table showing details of evaluation samples used in Experimental Example 1.

FIG. 6 is a graph showing changes in the differential pressure with respect to the amount of accumulated soot.

FIG. 7 is a graph showing changes in collection efficiency with respect to the amount of accumulated soot.

FIG. 8 is a table showing details of evaluation samples used in Experimental Example 2.

FIG. 9 is a graph showing changes in differential pressure with respect to accumulated soot amount.

FIG. 10 is a graph showing changes in collection efficiency with respect to the amount of accumulated soot.

[Explanation of symbols]

 1 Filter skeleton 2 Particulate 10 Filter element 11 Trap container

Front page continuation (72) Inventor Takao Maeda 1-1-1 Kunyokita, Itami-shi Itami Works Ltd. Business Itami Manufacturing Co., Ltd.

Claims (5)

[Claims] 1. A particulate trap for a diesel engine configured by mounting a filter element in a container installed in the middle of an exhaust system, wherein the filter element is a three-dimensional heat-resistant metal skeleton having communicating pores. This filter element is composed of a net-structured porous body, and is characterized in that at least two types of three-dimensional network-structured porous bodies having different pore sizes are combined so that the larger the pore size, the closer to the exhaust gas inflow side. Particulate trap for diesel engine. 2. The pore size ratio of the three-dimensional network structure porous body having the maximum pore size and the three-dimensional network structure porous body having the minimum pore size in the filter element is 15: 1 or less. Particulate trap for diesel engine described. 3. The three-dimensional network structure porous body having a small pore size of the filter element is produced by compression molding of a three-dimensional network structure porous body having a large pore size. Particulate trap for diesel engines. 4. A particulate trap for a diesel engine, which is configured by mounting a filter element in a container installed in the middle of an exhaust system, wherein the filter element is made of a heat-resistant metal skeleton having communicating pores. A porous body having a three-dimensional network structure porous body and a three-dimensional network structure porous body filled with ceramics or metal to have a substantially small pore size are combined so that a porous body having a substantially larger pore size is closer to the exhaust gas inflow side. A particulate trap for diesel engines, which is characterized. 5. The pore size ratio of the three-dimensional network structure porous body having the maximum pore size in the filter element and the three-dimensional network structure porous body having a minimum substantial pore size filled with ceramics or metal is 15: 1 or less. Particulate trap for diesel engine characterized by