JPH07286510A - Diesel particulate filter - Google Patents

Abstract

PURPOSE:To improve particulate trapping efficiency and durability of a diesel particulate filter which traps particulates in exhaust gas by providing the filter with functions of cake filtration and deep layer filtration. CONSTITUTION:This diesel particulate filter traps particulates 12, 13 contained in exhaust gas which is exhausted from a diesel engine by a tubular filter 1 made of ceramics nonwoven fabric. The weight of METSUKE (weight/unit area) of the ceramics nonwoven fabric which constitutes the tubular filter 1 is set to a range of 200-350g/m<2>, and the filter l is provided with both functions of cake filtration and deep layer filtration. The length of fiber of the ceramics nonwoven fabric is adjusted to 35mm or more to reduce a spatter of fibers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel particulate filter incorporated in an exhaust system for purifying exhaust gas discharged from a diesel engine.

[0002]

2. Description of the Related Art Combustion of a diesel engine is based on so-called heterogeneous mixing, in which fuel is injected into high temperature, high pressure air. Unlike the homogeneous mixture, the heterogeneous mixture does not mix the air and the fuel uniformly, so the carbon component in the fuel changes to soot, HC, etc. due to the high temperature heat of combustion, and they aggregate to form particulates. It is released into the air. Then, the smoke becomes particulates in which finely divided carbon and hydrocarbons adhere to the outer periphery thereof, and the particulates float in the atmosphere, so that the pollution of the urban environment progresses and the transparency of the air extremely deteriorates. . By the way, it is said that the particulates or smoke such as carbon and HC contained in the exhaust gas discharged from the diesel engine have a diameter of about 200Å, but they are gradually aggregated to 10 μm to 2 μm.
It grows into soot with a diameter of 0 μm. These soots are usually burned to carbon dioxide gas in the presence of oxygen at a temperature of 600 ° C to 700 ° C.

Conventionally, as an exhaust gas purifying device for treating exhaust gas of a diesel engine, for example, a device using a filter made of cordierite is disclosed in JP-A-3-294614 and JP-A-3-85315. It is disclosed.

Japanese Utility Model Laid-Open No. 61-149715 discloses a diesel particulate exhaust treatment system. The diesel particulate exhaust treatment device is disposed in the exhaust gas flow passage in proximity to a filter member for collecting particulates in the exhaust gas and an end portion of the filter member in the exhaust gas inflow direction. A heater member for igniting and burning the particulates, and a cavity provided so as to penetrate through the filter member in the exhaust gas flow direction, and a particulate matter collecting the flow rate of the exhaust gas flowing into the cavity. And a flow rate control mechanism for increasing it when igniting and burning.

[0005]

However, in the above diesel particulate exhaust treatment device, the particulates such as carbon and smoke captured by the heater member disposed in the vicinity of the filter member are ignited and burned. However, the filter member is being regenerated. Therefore, the diesel particulate exhaust treatment device utilizes the propagation of flame to regenerate the region other than the tip of the filter member, and the non-combustion soot causes regeneration defects or abnormalities due to nonuniform soot adhesion to the filter member. There is a problem that the filter member is melted by combustion and the filter member is damaged by thermal stress caused by them. Further, in the regeneration process of the filter member, it is difficult to shorten the regeneration time because the flame propagation speed is rate-determining.

An object of the present invention is to solve the above-mentioned problems, and a filter for collecting particulates such as soot, carbon and smoke contained in exhaust gas is made of a ceramic non-woven fabric, and the cake by the filter ( cak
e) To provide a diesel particulate filter that enables both filtration and deep layer filtration to be compatible with each other to improve collection efficiency, reduce fiber scattering of a ceramic nonwoven fabric, and improve durability and corrosion resistance. .

[0007]

In order to achieve the above object, the present invention is configured as follows. That is,
This invention is a diesel particulate filter that collects particulates contained in exhaust gas discharged from a diesel engine by a ceramics filter, wherein the ceramics filter is made of a ceramics nonwoven fabric, and the weight of the ceramics nonwoven fabric is 200 to 350g. The present invention relates to a diesel particulate filter characterized by being set in a range of / m ² .

In this diesel particulate filter, the fiber length of the ceramic non-woven fabric is
It is adjusted to 35 mm or more.

Further, in this diesel particulate filter, a wire mesh heater is provided at least on the exhaust gas inflow side of the felt made of the ceramics non-woven fabric which constitutes the ceramics filter.

In this diesel particulate filter, the felt made of the ceramic non-woven fabric that constitutes the ceramic filter has its exhaust gas inflow side entirely surrounded by a wire mesh heater.

[0011]

The diesel particulate filter according to the present invention is constructed as described above and operates as follows. That is, in this diesel particulate filter, the basis weight of the ceramic non-woven fabric constituting the filter was set in the range of 200 to 350 g / m ² ,
Particulates in the exhaust gas are subjected to cake filtration on the surface of the filter, deep layer filtration is also performed inside the filter, and the trapping efficiency is improved by making both trapping functions compatible, and the filter is The pressure loss of itself can be kept small.

In this diesel particulate filter, the ceramic nonwoven fabric has a fiber length of 35 m.
Since it is adjusted to m or more, the fibers are properly entangled with each other, scattering of the fibers is reduced, collection efficiency is improved, and durability of the filter can be improved. Further, since the wire mesh heater is disposed on the exhaust gas inflow side of the ceramics nonwoven fabric, the filter can be heated by energizing the wire mesh heater, and the carbon collected by the filter,
Particulates such as smoke can be incinerated by heating.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the diesel particulate filter according to the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic view showing an embodiment incorporating a diesel particulate filter according to the present invention, and FIG. 2 is a sectional view taken along the line AA in FIG.

This embodiment is a diesel particulate filter (DPF) for purifying the exhaust gas used by being incorporated in the exhaust passage 3 of the diesel engine.
Exhaust gas emitted from a diesel engine is passed through a filter 1 arranged in an exhaust passage 3 to remove particulates such as carbon, soot, HC contained in the exhaust gas from the filter 1.
The collected particulates are heated and incinerated into gas, and the gas is discharged to the outside through the exhaust gas outlet passage 4.

As shown in FIG. 1, this diesel particulate filter has a case 2 incorporated in an exhaust pipe 15 and a cylindrical filter 1 arranged in the case 2. The tubular filter 1 is made of a ceramic non-woven fabric capable of collecting particulates contained in exhaust gas. The cylindrical filter 1 has an opening 7 formed at the upstream hollow end in the exhaust gas flow direction, and the downstream end is closed by a closing plate 8.
An annular passage 5 is formed between the outer surface of the cylindrical filter 1 and the inner surface of the case 2. Exhaust gas is in the exhaust passage 3
Is introduced into the hollow portion 6 of the cylindrical filter 1 through the opening 7, then the particulates in the exhaust gas are collected through the cylindrical filter 1, and the cleaned exhaust gas flows out to the annular passage 5. It is discharged to the outside through the exhaust gas outlet passage 4.

In this diesel particulate filter, as shown in FIG. 2, the tubular filter 1 has a felt made of a ceramic non-woven fabric which is sequentially folded in a circumferential direction between the inside and the outside to form a fold. It is formed in a shape with an increased collecting area. Examples of the ceramic non-woven fabric forming the tubular filter 1 include Al ₂ O ₃ and Si.
Ceramics such as mixed carbon / oxide of C, Si and Ti, and heat resistant and highly corrosion resistant such as SiO ₂ can be selected.

This diesel particulate filter can be manufactured as follows. Si-Ti-C
Ceramic short fibers containing an element of —O were processed into a non-woven felt by a needle punching method. Next, the felt is surrounded by a heat-resistant alloy wire net 16 in a sandwich structure, and the felt is sequentially folded into a fold shape,
As shown in FIG. Furthermore, the wire mesh 1 located on the wall surface 14 on the exhaust gas inflow side which is the upstream side of the exhaust gas flow
An electrode 9 was connected to 6 to form a wire mesh heater 10 to produce a cylindrical filter 1. The tubular filter 1 can be heated by energizing the wire mesh heater 10 through the electrode 9.

This diesel particulate filter is manufactured as described above, and the inner wall surface 14 on the exhaust gas inflow side for collecting the particulates contained in the exhaust gas of the tubular filter body 1 has a wire mesh heater over the entire area. 1
This means that 0 is placed. When the wire net heater 10 is arranged on the exhaust gas inflow side of the tubular filter 1, when the particulate matter collected in the tubular filter 1 is incinerated by heating, the temperature can be raised extremely well and the incineration time can be shortened. However, the cylindrical filter 1 may be provided in a state that it is embedded in the ceramic nonwoven fabric, that is, embedded. The wire net heater 10 can be made of, for example, a Ni—Cr heat resistant metal.

In this diesel particulate filter, the weight per unit area (weight per unit area of the fiber) of the ceramic non-woven fabric is optimized, and the weight per unit area is set in the range of 200 to 350 g / m ^2. It is a feature. By setting the basis weight of the ceramic non-woven fabric in the range of 200 to 350 g / m ² , the cylindrical filter 1 enables mixed filtration that is both cake filtration and deep layer filtration, as shown in FIG. 3. As can be seen from FIG. 6, the efficiency of collecting particulates can be improved and the pressure loss can be reduced. The cake filtration is a state in which particulates are collected as cake 11 on the wall surface 14 of the filter 1 on the exhaust gas inflow side. Further, in the deep-layer filtration, particulates are collected inside the filter 1, large particles 12 of particulates are collected in the upstream region of the filter 1, and small particles of particulates are collected in the downstream region. 13 have been collected.

With respect to this diesel particulate filter, the product of the present invention was prepared as a comparative product in which the basis weight of the ceramic non-woven fabric was out of the above range, and the results of testing the particulate collection state were as follows. It was As a comparative product 1, a filter having a low basis weight of ceramic non-woven fabric set to less than 200 g / m ² has a low fiber density and a large space between the fibers, so that the filtration on the wall surface 14 on the exhaust gas inflow side is difficult. As shown in FIG. 4, only the deep layer filtration inside the felt of the filter 1 is performed, and the large particles 12 of particulates are collected in the upstream region of the filter 1 and the particulates of the particulates are collected in the downstream region. Small particles 13 were collected. Comparative product 1
Then, as shown in FIG. 6, with respect to the collection of particulates in the exhaust gas, the pressure loss was reduced, but the collection efficiency was small.

Further, as Comparative product 2, a filter having a large basis weight of ceramic non-woven fabric set to a value exceeding 350 g / m ² has a large fiber density and a small space between the fibers, so that the filter in the exhaust gas is 5 cannot penetrate into the felt of the filter 1, and as shown in FIG. 5, it is only cake filtration on the wall surface 14 on the exhaust gas inflow side, and the cake 11 is on the exhaust gas inflow side of the filter 1. Although formed on the wall surface 14, deep filtration did not occur. In Comparative product 2, as shown in FIG. 6, the collection efficiency was good, but the pressure loss was large and the filter 1 clogged in a short time.

Further, in this diesel particulate filter, the fiber length of the ceramic non-woven fabric is adjusted to 35 mm or more, and as shown in FIG. 7, the entanglement between the fibers becomes complicated and the fibers are held together. , The scattering of fibers is reduced. When the fiber length of the ceramic non-woven fabric is shorter than 35 mm, the entanglement between the fibers does not become complicated, the number of scattered fibers increases, and the fibers are mixed in the exhaust gas discharged from the exhaust gas outlet passage 4. As a result, environmental pollution is caused and the durability of the filter is reduced, which is not preferable.

[0023]

The diesel particulate filter according to the present invention is constructed as described above and has the following effects. That is, since this diesel particulate filter is made of a ceramic non-woven fabric, the filter itself is a non-structured body and can prevent damage to the filter due to thermal stress or the like. In particular, the weight per unit area of the ceramic non-woven fabric that constitutes the filter is optimized,
Since it is set in the range of 0 to 350 g / m ² , both filtration functions of cake filtration and deep layer filtration can be achieved, collection efficiency can be improved, and pressure loss can be reduced. The filter body can be constantly controlled at an appropriate temperature at which particulates are incinerated.

Further, since the fiber length of the ceramic non-woven fabric is adjusted to 35 mm or more, it is possible to reduce the scattering of fibers and prevent environmental pollution. Furthermore, since the wire mesh heater is disposed at least on the exhaust gas inflow side in the felt made of the ceramics non-woven fabric that constitutes the ceramics filter, particulates such as carbon and smoke contained in the exhaust gas are collected. Sometimes
The particulates can be heated and incinerated in a short time, and the filter can be regenerated.

Further, since the entire surface of the felt on the exhaust gas inflow side is surrounded by the wire mesh heater, the entire surface of the felt can be uniformly and quickly heated by energizing the wire mesh heater. Prevents local heating and abnormal overheating to prevent melting damage,
Regeneration failure can be prevented, the filter can be maintained in a good condition at all times, exhaust gas can be purified, and the filter can be used continuously for a long time, and the durability of the filter can be improved.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a diesel particulate filter according to the present invention.

2 is a cross-sectional view taken along the line AA in FIG.

FIG. 3 is a partially enlarged sectional view of a tubular filter showing a state in which particulate matter in exhaust gas is collected by the diesel particulate filter according to the present invention.

FIG. 4 is a partially enlarged cross-sectional view of a tubular filter showing a state in which particulate matter in exhaust gas is collected by a diesel particulate filter of a comparative product.

FIG. 5 is a partially enlarged cross-sectional view of a tubular filter showing a state in which particulates in exhaust gas are collected by another diesel particulate filter of a comparative product.

FIG. 6 is a graph showing the relationship between pressure loss and collection efficiency with respect to the weight per unit area of a ceramic nonwoven fabric.

FIG. 7 is a graph showing the relationship between the fiber length of a ceramic nonwoven fabric and the number of scattered fibers.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylindrical filter 1M Inventive product 1C, 1D Comparative product 2 Case 3 Exhaust passage 4 Exhaust gas outlet passage 5 Annular passage 6 Hollow part 7 Opening 8 Closing plate 9 Electrode 10 Wire mesh heater 11 Cake 12 Particulate particles 13 Particulate Small particles 14 Inner wall surface 15 Exhaust pipe

Claims (4)

[Claims] 1. A diesel particulate filter for collecting particulates contained in exhaust gas discharged from a diesel engine by a ceramics filter, wherein the ceramics filter is made of a ceramics nonwoven fabric, and the weight of the ceramics nonwoven fabric is 200 to A diesel particulate filter characterized by being set in a range of 350 g / m ² . 2. The fiber length of the ceramic nonwoven fabric is 3
2. The thickness is adjusted to 5 mm or more.
Diesel particulate filter described in. 3. The diesel particulate according to claim 1 or 2, wherein the felt made of the ceramic non-woven fabric constituting the ceramic filter is provided with a wire mesh heater at least on the exhaust gas inflow side. filter. 4. The felt made of the ceramics non-woven fabric forming the ceramics filter has an exhaust gas inflow side entirely surrounded by a wire mesh heater. Diesel particulate filter.