JP2841803B2 - Particle trap media for diesel engine exhaust - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a trap medium used for trapping and removing fine particles exhausted from a diesel engine.

[Conventional technology]

Vehicle emissions are one of the major causes of air pollution,
Technology for removing harmful components contained in exhaust gas is extremely important.

Especially in diesel engine vehicles, NO
Removal of soot-like fine particles (particulates) mainly composed of _X and carbon is an important issue.

In order to remove these harmful components, supercharging, improvement of the fuel injection system, improvement of the shape of the combustion chamber, and efforts on the part of the engine are also being carried out. Removal is essential.

Among the harmful components of the exhaust gas, the fine particles are composed of solid carbon and a soluble organic substance dissolved in an organic solvent, and it is considered that a method of capturing and removing the fine particles by a filter trap is most practical.

By the way, as a filter trap medium for trapping fine particles contained in diesel engine exhaust, it is necessary to satisfy the following performance from the conditions used. First, it is necessary to have a trapping efficiency for particulates that can satisfy the required cleanliness of exhaust gas. Second, since the engine exhaust is discharged through this trap, it is necessary to reduce the ventilation pressure loss during the flow of the exhaust gas in order not to apply an excessive back pressure to the engine. It is required not only that the initial pressure loss is small, but also that the pressure loss hardly increase even if fine particles are trapped. That is, the first and second
The shape and structure of the filter trap must be designed to satisfy the requirements of (1).

Further, when fine particles are trapped in the trapping medium to a certain extent, it is necessary to remove and reproduce the trapped fine particles to recover the collecting ability. As a regeneration method, a method of burning and removing fine particles by electric heating or burner heating is considered to be the most effective method. Therefore,
As the third required performance, it is necessary to have durability against this repetitive reproduction processing.

At present, as the trap media, honeycomb-shaped porous body of cordierite ceramics is said to be the most practical material in terms of exhaust gas resistance, heat resistance, trapping performance and durability against regeneration. I have. However, when cordierite ceramics are used as a filter trap, local temperature distribution is likely to occur in the trapping media due to the burning of fine particles during regeneration, and regeneration conditions must be extremely controlled to prevent cracks due to thermal stress. It is difficult and not yet practical.

[Problems to be solved by the invention]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a particulate trap medium for diesel engine exhaust that has a low pressure loss, a high trapping efficiency, and can withstand thermal stress during regeneration.

[Means for solving the problem]

In order to solve the above-mentioned problems, the present invention provides a three-dimensional network porous body having continuous vents composed of a skeleton of a nickel-chromium alloy or an alloy obtained by adding 1 to 6% by weight of aluminum to a nickel-chromium-iron alloy. The diesel engine exhaust particulate trap medium is constituted by the continuous vents having an average pore diameter of 0.1 to 0.5 mm.

[Action]

As shown in FIG. 1, the above three-dimensional network porous body is a porous body composed of a skeleton and a pocket-like space connected to each other. Since the porosity is high, the gas flow resistance is extremely small. The particles trapped in the pocket-shaped space are hard to be detached from the space, and thus have excellent solids collecting performance. Also, it has excellent heat resistance.

〔Example〕

The performance of a filter using a three-dimensional network porous material as a filter is mainly determined by the following two factors.

One is the pore size of the three-dimensional network porous material used,
The pore diameter of the three-dimensional network porous body to be used is determined from the balance between enhancing the collection characteristics and reducing the pressure loss in the filter trap. The pore diameter of the three-dimensional network porous body must be an average pore diameter of 0.1 to 5 mm in order to satisfy the exhaust gas regulation value proposed in the United States and Japan in terms of collection efficiency. When the average pore diameter is 0.1 mm or less, the trapping efficiency is excellent, but the ventilation resistance becomes excessive. If the average pore diameter is 0.5 mm or more, the trapping efficiency at the initial stage or immediately after the regeneration treatment is insufficient, and it is difficult to satisfy the above-mentioned regulation value.

The ventilation resistance when the exhaust gas flows through the trap depends not only on the average pore diameter of the three-dimensional network structure porous body but also on its thickness. Generally, for a diesel engine, if a pressure loss of 0.04 kg / cm ² or more occurs in the trap section, an excessive back pressure will be applied to the engine, adversely affecting the operation of the engine. It is necessary to adjust the thickness so that the ventilation resistance is 0.04 kg / cm ² or less.

The second is a structural factor of the filter trap. That is, it is important not only to exhibit a better filter characteristic but also to make the interval of reproduction longer by taking a compact and larger filter area. At the same time, the structural design must be suitable for the three-dimensional network porous body and suitable for attachment to the engine exhaust pipe. From such a viewpoint, examples of the structure of the porous body having the three-dimensional network structure include examples as shown in FIGS.

The example shown in FIG. 2 and FIG. 3 shows a block-shaped three-dimensional network structure porous body 1 housed in a trap holder 2,
A hole 6 for a gas passage is formed from the gas inlet 3 to the gas outlet 4. The hole 6 may be formed from the gas outlet 4 side to the gas inlet 3 side, and as in the example shown in FIGS. 4 and 5, from the gas inlet 3 side. The hole 6 formed toward the gas outlet 4 may be adjacent to the hole 6 ′ formed from the gas outlet 4 toward the gas inlet 3.

With such a structure, a large filter area can be obtained and the thickness of the filter can be substantially reduced as compared with the case where the three-dimensional network structure porous body 1 has a simple block shape, so that the pressure loss at the time of passing exhaust gas is reduced. be able to. 4 and 5, the above effect is maximized by arranging the hole 6 from the inflow side and the hole 6 'from the outflow side as close as possible. It can be used for

In the example shown in FIGS. 6 and 7, a plurality of cylinders 7 having different diameters formed by the three-dimensional network structure porous body 1 are concentrically overlapped with a predetermined gap between the cylinders 7. The outermost cylindrical body 7 housed in the trap holder 2
Is formed between the outer peripheral surface and the inner peripheral surface of the trap holder 2, a gap formed at one end of each cylinder 7, and an end face opening of the innermost cylinder 7. ,
The gas inlet 3 and the gas inlet 4 are closed by a sealing member 8 so as to be alternately arranged, and the exhaust gas passes through the respective cylinders 7 as shown in FIG.

Further, in each of the above examples, the pore diameter of the three-dimensional network structure porous body 1 on the gas outlet 4 side is made smaller than the pore diameters of the other portions, so that the collection efficiency can be improved, and The so-called blow-off phenomenon in which the captured fine particles are discharged can be prevented. Reducing the hole diameter of the three-dimensional network structure porous body only at the gas outlet 4 side can be realized by, for example, forming a small hole once and then expanding the hole diameter by plastic deformation.

Cordierite ceramics have been studied as a particulate trap medium for diesel engine exhaust.However, the temperature at the exhaust gas inlet when used as a particulate filter trap depends on the load conditions during traveling. , 200 at most during normal 40-60km / h
Temperature of ~ 300 ° C. The temperature rises to 400 ° C to 500 ° C when running continuously or suddenly starting on many slopes.
When the collection of the specified amount of the fine particles is completed, a process of removing the fine particles by some combustion means is performed before the back pressure becomes too large. At this time, a regeneration gas up to 700 to 900 ° C. is introduced. Temperature rises to 1,000 ° C at one time. The combustion is completed in 5 to 15 minutes. In practice, when a diesel engine vehicle is run with such a particulate filter trap mounted thereon, the life of the trap material is required to be at least 5 years or more.

Although various materials have been developed as heat-resistant materials, in the present invention, a Ni-based alloy (Celmet, trade name, manufactured by Sumitomo Electric Industries, Ltd.) is used as a three-dimensional network porous body. The three-dimensional network porous body is obtained by subjecting the urethane foam to a conductive treatment, forming a skeleton by Ni plating, and burning off the base urethane foam to obtain a three-dimensionally connected structure. For these reasons, the basic composition of the substrate is Ni. For pure Ni, 70
Heat resistance of 0 ° C. or higher cannot be expected, and it cannot withstand corrosion by SO ₂ gas contained in exhaust gas for a long time.

However, a Ni three-dimensional network porous substrate can be alloyed with Ni by diffusion infiltration treatment.
An alloy in which each element of chromium, iron, aluminum, and rare earth elements (such as yttrium and cerium) is diffused and infiltrated into Ni can be produced. These elements can improve heat resistance and corrosion resistance by alloying in an appropriate amount or by adding a small amount thereof. There are combinations mainly composed of a nickel-chromium alloy and a nickel-chromium-iron alloy. These alloys contain a trace amount of rare earth elements such as yttrium metal element or cerium metal element of 0.1% or less in the surface layer by PVD (physical vapor deposition) method such as electron beam evaporation method or sputtering method or ion plantation,
Further, these elements can be diffused from the surface layer to the inside in an inert atmosphere or an H ₂ reducing atmosphere to obtain the alloy of the present invention. For rare earth elements such as yttrium element or cerium element of 0.1% or less, each metal is mixed with the raw material powder in the diffusion penetrant so as to be 0.2% or more of the total weight and diffused and infiltrated at a temperature of 1000 ° C or more. It is easily obtained by processing.

In addition, as a result of applying the ZrO ₂ ceramic layer to the coating of the three-dimensional network porous material by the sol-gel method using a metal alkoxide, there was no problem with the heat resistance at 1,000 ° C., and a highly reliable structure was obtained.

The structure coated with the above alloy and heat-resistant ceramic layer has strength as a structure at 700 ° C or higher, and oxidation in a high-temperature oxidizing atmosphere rarely progresses. It was confirmed by a running test that the material was excellent enough as a trapping medium material for fine particles in exhaust gas requiring corrosion resistance.

EXPERIMENTAL EXAMPLE 1 As shown in FIG. 8, a trap device and a regeneration gas supply device were attached to the exhaust system of a 6.4, 6-cylinder direct injection diesel engine. As shown in FIGS. 6 and 7, the trap device is a three-dimensional network porous material of nickel-chromium-aluminum alloy or nickel-chromium-iron-aluminum alloy having an average pore diameter of 0.2 mm (manufactured by Sumitomo Electric Industries, Ltd.) as a trapping medium. Name Celmet, Composition: Nickel
55%, chromium 40%, aluminum 5%, nickel 68
%, Chromium 15%, iron 13%, aluminum 4%)
After being formed into a cylindrical shape, as shown in FIG. 6, the exhaust gas is introduced from the gas inlet 3 side, passes through the three-dimensional mesh-structured porous body 1, and is then discharged from the gas outlet 4 through the flow path. The formed one was used.

The hot gas supply for regeneration is 60
A gas at 0 to 900 ° C. can be generated, and a hot gas for regeneration can be supplied to the trap when the exhaust gas is bypassed from the trap device.

In FIG. 8, reference numeral 10 denotes an engine, 5 denotes a trap device, 11 denotes a regeneration gas supply device, 12 denotes an exhaust pipe, and 13 denotes an exhaust bypass.

This device was used to repeatedly perform an exhaust test in the transient mode for heavy duty diesel engines in the United States, and the particle reduction effect was measured.As a result, it was 0.54 g / HPHr without a trap, but after 20 cycles, it became 0 .
It was 02g / HP · Hr. Efficiency of more than 83% in US EP
It was found that it satisfies the 1994 regulation value of A (0.1 g / HP · Hr). In addition, the pressure loss value is 0.04
It turned out that kg / cm ² was maintained. After 20 repetition cycles, the engine exhaust gas is bypassed from the trap device, and the trap device is supplied with heated air at an average temperature of 700 ° C or more from the regeneration hot gas supply device at a flow rate of 2 m ³ / min.
It was fed for 15 minutes and regenerated by burning the trapped particulates. The trap media after regeneration is dissolved,
No cracks, extreme oxidation or corrosion were observed. After this,
The exhaust circuit was switched again and an exhaust test was performed.
After the repetition cycle was performed 20 times, the exhaust circuit was switched again to the regeneration hot gas supply circuit, and the regeneration was performed.

The above test was repeated, and reproduction was performed 100 times. 100
The trap media of the present invention did not decrease the collection efficiency, showed no external damage such as melting and cracking, and did not show any deterioration in mechanical properties after repeated exhaust traps and regeneration.

In the examples, Celmet having two kinds of synthetic compositions was shown. However, the present invention is not necessarily limited to these compositions, and the same effects were obtained with alloys in the following ranges.

At about 100 times of regeneration, there is no significant difference in heat resistance even without the addition of Al.
_{Since a 2} O ₃ oxide film is formed, the amount of oxidation is reduced to a fraction of that in the case where no oxide film is added, and the life is shortened. Addition of Al can be easily obtained by diffusion infiltration treatment as in the case of Cr and Fe. Excessive addition is undesirable because it forms a hard intermetallic compound and deteriorates workability.

[Experimental Example 2] When alloying Cr, Fe, and Al by diffusion infiltration, a rare earth element such as yttrium and cerium is mixed with the diffusion infiltration material in a minute amount to perform coating diffusion treatment. Is possible. The amount of the rare earth element in the finally produced three-dimensional network porous material is 100 μm from the skeleton surface.
Another atmospheric oxidation test (800 ° C * 500 hours) found that the porous material had sufficient heat resistance compared to a non-treated porous material, only having a diffusion permeation amount of only 0.005 to 0.1% by weight. . No additional effect was observed. Using a three-dimensional network structure porous body in which cerium metal element among the rare earth elements was diffused and infiltrated, a test was performed up to 20 exhaust cycles and 100 regenerations under the same conditions as in Experimental Example 1. However, the regeneration gas temperature was 700 ° C. and the regeneration time was 15 minutes, and the regeneration gas temperature was 800 ° C. and 10 minutes. Combustion was sufficiently completed at both the regeneration gas temperature at 700 ° C and the regeneration temperature at 800 ° C, and even after 100 times of regeneration, there was no condition in which the appearance of Celmet was deteriorated at all. The conditions for diffusion and infiltration are almost the same as those for alloying Cr, Fe, and Al, and the diffusion and infiltration treatment can be performed sufficiently in a hydrogen gas atmosphere or an inert atmosphere gas such as an Ar gas.

Here, the diffusion and infiltration treatment of metal cerium among the rare earth elements is described. However, the same applies to the case where yttrium is added. He was not seen. Needless to say, the same effect was obtained by the addition of other rare earth elements.

[Experimental Example 3] Using a sol-gel method, a structure in which a skeleton surface of a three-dimensional network structure porous body made of a nickel-chromium alloy was coated with a heat-resistant ceramic of 3 to 20 µm was produced. Using a metal alkoxide solution obtained by mixing metal zirconium with methyl alcohol or butyl alcohol, degrease the three-dimensional mesh-structured porous body by ultrasonic cleaning, immerse it in the adjusted liquid, and then withdraw it at a constant pulling speed (3 m / min). )
A coating process was performed. In this treatment, the number of times of immersion was adjusted so that the thickness after final coating and gelation was 3 to 20 μm. After immersion and drying, the temperature was gradually raised from room temperature to form a stable film, followed by heating and curing at a final temperature of 400 ° C. for 30 minutes. Using the porous body having the three-dimensional network structure having the film formed thereon, a test was performed under the same conditions as in Experimental Example 1 up to 20 exhaust cycles and 100 regenerations. However, the regeneration gas temperature is 1
The playback time was 0 minutes. Even after 100 times of regeneration, the structure did not show any deterioration in appearance.

For comparison, the film thickness is 3 μm or less, or 20 μm.
m was prepared. It was found that, in the case of a film having a thickness of 3 μm or less, the rate of oxidation was increased at 850 ° C., and it was not possible to sufficiently improve the heat resistance. This is probably due to the three-dimensional structure that makes it difficult to provide sufficient coating, and only a non-uniform film can be obtained. Therefore, in order to obtain a uniform thick film, it is sufficient that the thickness is 3 μm or more, but if it is 20 μm or more, the film easily cracks due to shrinkage of the film during drying and curing, and the crack reaches the substrate surface. Some are not preferred. At the time of reproduction, cracks are spread, and it is necessary to determine the reproduction temperature condition based on the heat resistance temperature of the base material. The film obtained here is zirconium oxide (ZrO ₂ ) and has a linear expansion coefficient of 1 × 10 ⁻⁶ / ° C., which is the same as the expansion coefficient of a nickel-chromium alloy. No, and stable film properties were maintained.

〔The invention's effect〕

As described above, the three-dimensional network porous body of the present invention has a sufficient ability to capture fine particles exhausted from a diesel engine vehicle, and has a sufficient capacity to burn and remove the captured fine particles. It is effective when used as a particulate trap medium for diesel engine exhaust because heat resistance at up to 900 ° C is obtained.

[Brief description of the drawings]

FIG. 1 is an enlarged view of a porous body having a three-dimensional network structure, and FIGS. 2 and 3, FIGS. 4 and 5, FIGS. 6 and 7 are longitudinal front views and longitudinal sections showing an example of a trap device, respectively. Side view,
FIG. 8 is a schematic view showing an example in which a trap device and a regeneration gas supply device are provided in an exhaust system of a diesel engine. DESCRIPTION OF SYMBOLS 1 ... Porous body of three-dimensional network structure, 2 ... Trap holder, 3 ... Gas inlet, 4 ... Gas outlet, 5 ... Trap device, 6 ... Hole, 7 ... Cylindrical body, 8 ... ... Seal member.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Keichichi Komatsu 1-1-1 Kunyokita, Itami-shi, Itami-shi, Hyogo Sumitomo Electric Industries, Ltd. Itami Works (56) References JP-A-58-137424 (JP, A) JP-A-2-4413 (JP, A) JP-A-62-1737 (JP, U) JP-A-3-500527 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) ) F01N 3/02 B01D 39/20

Claims (4)

(57) [Claims] A three-dimensional network porous body having continuous pores comprising a skeleton of a nickel-chromium alloy or an alloy obtained by adding 1 to 6% by weight of aluminum to a nickel-chromium-iron alloy, wherein the continuous pores have an average pore diameter. Fine particle trap media for diesel engine exhaust, characterized in that the diameter is 0.1 to 0.5 mm. 2. The method according to claim 1, wherein said skeleton is provided with a rare earth element such as yttrium or cerium within a range of 0.005 to 100 μm from the surface of the skeleton.
The particulate trap medium for diesel engine exhaust according to claim 1, further comprising a diffusion layer distributed so as to be 0.1% by weight. 3. The skeletal surface is coated with 3 to 20 μm by a sol-gel method.
3. The trapping medium for diesel engine exhaust according to claim 1, comprising a heat-resistant ceramic layer coated with a thickness of m. 4. The trapping medium for diesel engine exhaust according to claim 3, wherein the heat-resistant ceramic layer is made of ZrO ₂ .