JPH04124419A - Particulate trap medium for diesel engine exhaust - Google Patents

Abstract

PURPOSE:To sufficiently seize particulates exhausted from a diesel engine vehicle and also to obtain heat resistance by using a three-dimensional network structure porous body having communication pores and comprising a skeleton in which a nickel-chrome alloy or a nickel-chrome-iron alloy is covered with heat resistant ceramics. CONSTITUTION:In a block shape three dimensional network structure porous body 1 housed in a trap holder 2, hole portions 6 for gas passage are formed from a gas flow-in port 3 side toward a gas flow-out port 4 side. As a trap medium for a trap device a three dimensional network structure of: (1) a nickel- chrome-aluminum alloy having an average pore diameter of 0.2 mm or (2) a nickel-chrome-iron-aluminum alloy is used, which is formed into a cylindrical shape. A device, wherein a flow passage is formed so that an exhaust gas is introduced in from the gas flow-in port 3 side and discharged from the gas flow-out port 4 side after passing through the three dimensional network structure porous body 1, is used. With this constitution, a particulate trap medium for a diesel engine exhaust with low pressure loss and high seizing efficiency and durable against thermal stress at the time of regeneration can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a trap medium used for capturing and removing particulates exhausted from a diesel engine.

[Conventional technology]

Automobile exhaust gas is one of the major causes of air pollution, and technology to remove harmful components contained in exhaust gas is extremely important.

In particular, in diesel engine vehicles, the removal of soot-like particulates (particulates) mainly composed of carbon is an important issue.

In order to remove these harmful components, efforts are being made on the engine side, such as supercharging, improving the fuel injection system, and improving the shape of the combustion chamber, but there is no drastic solution.
Removal by post-treatment is essential.

Among the harmful components of exhaust gas, fine particles consist of solid carbon and soluble organic matter that dissolves in organic solvents, and it is considered that the most practical method is to capture and remove them using a filter lamp.

By the way, filter trap media for capturing particulates contained in diesel engine exhaust include:
It is necessary to satisfy the following performance based on the usage conditions. First, it is necessary to have sufficient particle collection efficiency to satisfy the required cleanliness of exhaust gas. Secondly, since engine exhaust gas is exhausted through this trap, the ventilation pressure loss during exhaust gas flow must be small in order to avoid applying excessive back pressure to the engine. In addition to having a small initial pressure loss, it is also required that the pressure loss does not easily increase even when fine particles are tramped. That is, the shape and structure of the filter Trump must be designed to satisfy the first and second requirements.

Furthermore, when more than a certain amount of particles are trapped in the trap medium, it is necessary to remove and regenerate the trapped particles to recover the trapping ability. The most effective method of regeneration is considered to be to burn off the particulates using electric heat or burner heating. Therefore, the third required performance is durability against this repeated regeneration process.

At present, cordierite ceramic honeycomb porous bodies are said to be the material closest to practical use as trap media in terms of exhaust gas contact resistance, heat resistance, collection performance, and durability for regeneration. There is. However, when cordierite ceramics are used as a filter trap, local temperature distribution tends to occur in the trap media due to the combustion of fine particles during regeneration, and in order to prevent cracks from occurring due to thermal stress, it is necessary to control the regeneration conditions. The current situation is that it is extremely difficult and has not yet been put into practical use.

[Problem to be solved by the invention]

Therefore, this invention has low pressure loss and high collection efficiency.
The present invention aims to provide particulate trapping media for diesel engine exhaust that can withstand thermal stress during regeneration.

[Means to solve the problem]

In order to solve the above problems, this invention
Chromium alloys, nickel-chromium-iron alloys, alloys with trace amounts of rare earth elements such as aluminum, yttrium, or cerium added to these alloys, or skeletons made of these alloys coated with a heat-resistant ceramic layer using the sol-gel method. A three-dimensional network porous body with communicating holes is used as particulate trapping media for diesel engine exhaust.

[Effect]

As shown in FIG. 1, the above-mentioned three-dimensional network structure porous body has
It is a porous body consisting of connected skeletons and hollow-shaped spaces, and due to its high porosity, the gas flow resistance is extremely small.However, particles trapped in the hollow-shaped spaces are difficult to detach from the spaces, so they become solid. Excellent object collection performance. It also has excellent heat resistance.

〔Example〕

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

One is the pore diameter of the three-dimensional network structure porous material used, and the pore diameter of the three-dimensional network structure porous material used is determined from the balance between increasing collection characteristics and reducing pressure loss in the filter trap. It is decided. The average pore diameter of the three-dimensional network porous material needs to be 0.1 to 0.5+m++ in order to satisfy the exhaust gas regulation values proposed in the United States and Japan from the perspective of collection efficiency. . When the average pore diameter is 0.1 am or less, the collection efficiency is excellent, but the ventilation resistance becomes excessive. If the average pore diameter is 0.5 m11 or more, the collection 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 exhaust gas flows through playing cards is affected not only by the average pore diameter of the three-dimensional network porous material but also by its thickness. Generally, for diesel engines, if a pressure loss of 0.04 kg/crA or more occurs at the trap part,
Because excessive back pressure is applied to the engine and has a negative effect on engine operation, the thickness of the trap media must be adjusted according to the pore diameter so that the airflow resistance is 0.04 kg/cii or less. .

The second factor is the structural factor of the filter trap. In other words, being compact and taking up a larger filter area not only provides better filter characteristics, but also
This is also important from the point of view of lengthening the playback interval. At the same time, the structural design must be suitable for the three-dimensional network porous body and suitable for installation in the engine exhaust pipe.From this perspective, the structure of the three-dimensional network porous body is , there are examples as shown in FIGS. 2 to 7.

In the example shown in FIGS. 2 and 3, a block-shaped three-dimensional network structure porous body 1 housed in a playing card holder 2 is provided with a gas passage from a gas inlet 3 side to a gas outlet 4 side. A hole 6 is formed therein. The hole 6 may be formed from the gas outlet 4 side toward the gas inlet 3 side, or, as in the example shown in the fourth and FIG. 5, from the gas inlet 3 side. A hole 6 formed toward the gas outlet 4 side and a gas inlet 3 formed from the gas outlet 4 side oppositely.
The holes 6' formed toward the sides may be adjacent to each other.

With such a structure, compared to the case where the three-dimensional network structure porous body 1 is made into a simple block shape, a larger filter area can be obtained and the actual filter thickness can be reduced, thereby reducing pressure loss when exhaust gas passes through. be able to.

Furthermore, as shown in the examples shown in FIGS. 4 and 5, the above effects can be maximized by arranging the holes 6 from the inflow side and the holes 6' from the outflow side as close to each other as possible. It can be put to good use.

The example shown in FIGS. 6 and 7 is a three-dimensional network structure porous body 1
A plurality of cylinders 7 having different diameters are stacked concentrically with a predetermined gap between each cylinder 7 and accommodated in the trap holder 2, and one end of the outermost cylinder 7 is placed in the trap holder 2. A space formed between the outer circumferential surface of the trap holder 2 and the inner circumferential surface of the trap holder 2, a gap at one end formed between each cylinder 7, and an end face opening of the innermost cylinder 7, respectively, The gas inlet 3 side and the gas inlet 4 side are alternately closed by seal members 8, and the exhaust gas passes through each cylinder 7 as shown in FIG.

Furthermore, in each of the above examples, by making the pore diameter of the three-dimensional network structure porous body 1 of the four gas outlet ports smaller than the pore diameter of other parts, the collection efficiency can be improved, and - It is possible to prevent the so-called blow-off phenomenon in which fine particles once captured are discharged. The pore diameter of the three-dimensional network porous body can be reduced only on the gas outlet 4 side by, for example, first making small pores and then enlarging the pore diameter by plastic deformation.

In addition, cordierite ceramics have been considered as particulate Trump media for diesel engine exhaust, but the temperature at the exhaust gas inlet when used as a particulate filter trap depends on the load conditions during driving. , the temperature is at most 200 to 300°C during normal driving at 40 to 60 km/hour. 400°C to 500°C when driving continuously on slopes or when starting suddenly.
The temperature rises to "C". When the collection of a specified amount of fine particles is completed, the fine particles are removed by some combustion means before the back pressure becomes too large.

At this time, a regeneration gas at a temperature of 700 to 900°C is introduced. -Temperature rises up to 1,000°C during the period.

Combustion ends in 5 to 15 minutes. When a diesel engine vehicle is actually driven with such a particulate filter trap installed, the trap material is required to have a lifespan of at least five years.

Although various materials have been developed as heat-resistant materials, in the present invention, a Ni-based alloy (manufactured by Sumitomo Electric Industries, Ltd., trade name: CELMENT) is used as the three-dimensional network structure porous body. The three-dimensional network structure porous material is obtained as a three-dimensionally connected structure in which a urethane foam is subjected to conductive treatment and then Ni-plated to form a skeleton, and the urethane foam as a base material is burned off. For these reasons, the basic composition of the base material is Ni. Pure Ni cannot be expected to have heat resistance above 700'C, and cannot withstand long-term corrosion by SO□ gas contained in exhaust gas.

However, it is possible to alloy Ni with a three-dimensional network structure porous base material made of Ni by diffusion infiltration treatment, and each element such as chromium, iron, aluminum, and rare earth elements (yttrium, cerium, etc.) can be added to Ni. Diffusion-infiltrated alloys can be produced. Heat resistance and corrosion resistance can be improved by alloying or adding trace amounts of these elements in appropriate amounts. nickel-chromium alloy,
There are combinations based on nickel-chromate penta-iron alloys.

These alloys contain trace amounts of rare earth elements such as yttrium metal element or cerium metal element in the surface layer of 0.1% or less by electron beam evaporation method, sputtering method, PVD (physical vapor deposition) method such as ion plantidion. Furthermore, the alloy of the present invention can be obtained by diffusing these elements from the surface layer into the interior in an inert atmosphere or an H2 reducing atmosphere. Also, rare earth light such as 0.1% or less of yttrium element or cerium element.

The element can be easily obtained by mixing each metal in a raw material powder in a diffusion infiltration agent in an amount of 0.2% or more of the total weight and performing a diffusion infiltration treatment at a temperature of 1000° C. or more.

In addition, 2.0. As a result of applying the ceramic layer to the coating of a three-dimensional network structure porous body, a structure with high reliability was obtained with no problem in terms of heat resistance at 1,000'C.

The structure coated with the above alloy and heat-resistant ceramic layer has strength as a structure at temperatures above 700°C, and oxidation hardly progresses in a high-temperature oxidizing atmosphere. A running test confirmed that the material is suitable for use as a media material for trapping particulates in exhaust gas, which requires corrosion resistance.

[Experimental Example 1] A trap device and a regeneration gas supply device were installed in the exhaust system of a 6.41.6-cylinder direct injection diesel engine as shown in FIG. As shown in Figures 6 and 7, the trap device uses a medium with an average pore diameter of 0.2 mm as the trap media.
Nickel-chromium-aluminum alloy or nickel-chromium-iron-aluminum alloy three-dimensional porous body (manufactured by Sumitomo Electric, product name Celmet, composition: 55% nickel, 40% chromium, 5% aluminum, 68% nickel) , chromium 15%, iron 13%, aluminum 4%)
is formed into a cylindrical shape, and as shown in FIG. A type with a flow path formed therein was used.

The regeneration real gas supply equipment uses a light oil burner to produce 60
0-900° CO gas can be generated, and when the exhaust gas is bypassed from the trap device, regeneration hot gas can be supplied to the trap.

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

Using this device, we conducted repeated exhaust tests in transient mode for American heavy-duty diesel engines and measured the particulate reduction effect, which was 0.54 g/HP-Hr without a trap, compared to 20 g/HP-Hr. After cycling, it was 0.02 g/HP-Hr. The collection efficiency is over 83%, which is sufficient to meet the US EPA's 1994 regulation value (0
, 1g/HP・Hr). In addition, the pressure loss value is 0.04 k up to 20 cycles.
It was found that g/cd was maintained. After 20 repeated cycles, the engine exhaust is bypassed from the trap device, and the trap device is supplied with 2 rr of heated air with an average temperature of 700'C or more from the regeneration hot gas supply device.
! /mir+ for about 15 minutes, and regenerated by burning the traversed particulates. After regeneration, no melting, cracking, extreme oxidation, or corrosion was observed in the regenerated Tora and Pmedia. After this, switch the exhaust circuit again,
I did an exhaust test. After repeating the cycle 20 times, the exhaust circuit was again switched to the regeneration photogas supply circuit, and the above-mentioned regeneration was carried out.

The above test was repeated and played back 100 times. 1
The trap media of the present invention does not reduce the collection efficiency after 00 exhaust tramps and repeated regenerations, and has no effect on dissolution,
No external damage such as cracks was observed, and no deterioration of mechanical properties was observed.

In the example, Celmet having two types of alloy compositions was shown, but it is not necessarily limited to these compositions, and similar effects were observed with alloys in the following ranges.

Material Composition (wt%) Ni Cr Fe AlNi -Cr
-Al bal, 30~55 1~
6Ni-Cr-Fe-Al bat, 15-3
0 10~30 1~6100 times, the appearance is
Although there is no significant difference in heat resistance even without the addition of AI, a stable Al2O3 oxide film is formed with the addition of a few percent, so the amount of oxidation is reduced to a fraction of that without addition. , it is preferable to add it because it will prolong the service life. Like Cr and Fe, AI can be easily added by diffusion infiltration treatment. Excessive addition is undesirable because it forms a hard intermetallic compound and deteriorates workability.

[Experiment Example 2] When performing alloying treatment of Cr, Fe, and AI by diffusion treatment, by mixing a small amount of rare earth elements such as yttrium and cerium together with the diffusion treatment material, coating diffusion treatment can be performed. is possible. The amount of rare earth elements in the final three-dimensional network structure porous material was 10% from the skeleton surface.
Another atmospheric oxidation test (800
No further addition effect was observed. Using a three-dimensional network structure porous material in which metal cerium among rare earth elements was diffused and permeated, an exhaust cycle of 20 was carried out under the same conditions as in Experimental Example 1. times, 100 plays
Tests were conducted up to once. However, the regeneration gas temperature is 7
Two types of regeneration were carried out: one at 00'C for 15 minutes and the other at 800C for 10 minutes. 8 even at regeneration gas temperature of 700°C.
Combustion is fully completed even at the regeneration temperature of 00°C.
Further, even after regeneration 100 times, no deterioration in appearance was observed in the cellment. The conditions for diffusion and infiltration are almost the same as those for normal alloying of Cr, Fe, and AI, and the diffusion and infiltration process can be performed satisfactorily in a hydrogen gas atmosphere or in an inert atmospheric gas such as Ar gas.

Here, we have described products treated by diffusion and penetration of metallic cerium, one of the rare earth elements, but this also applies to cases where yttrium is added, and there is no appearance deterioration even after repeated regeneration with sufficient resistance to exhaust gas and regeneration gas atmospheres. It was never seen. Needless to say, the addition of other rare earth elements had similar effects.

[Experimental Example 3] A structure in which the skeleton surface of a three-dimensional network porous body made of a nickel-chromium alloy was coated with a heat-resistant ceramic having a thickness of 3 to 20 tnm was produced using a sol-gel method. Using a metal alkoxide solution made by mixing metal zirconium with methyl alcohol or butyl alcohol and turning it into a sol, the three-dimensional network structure porous material was degreased by ultrasonic cleaning, and then immersed in the prepared solution. It was pulled up after 5 h) and subjected to coating treatment. This treatment was the final coating, and the number of immersions was adjusted so that the thickness after gelation was 3 to 20 irm. After immersion drying, the temperature was gradually increased from room temperature to a final temperature of 400° C. for 30 minutes to form a stable film. Using the three-dimensional network structure porous material on which the film was formed, the exhaust cycle was carried out for 20 times under the same conditions as in Experimental Example 1.
Tests were conducted for up to 100 playbacks. However, the regeneration gas temperature was 850°C and the regeneration time was 10 minutes. 1
Even after 00 cycles of playback, no deterioration in the appearance of the structure was observed.

For comparison, structures were produced in which the film thickness was 3 nm or less or 20 nm or more.

It was found that in a film having a thickness of 3R or less, the rate of oxidation increases when regenerated at 850°C, and a sufficient improvement in heat resistance cannot be imparted. This is probably because it has a three-dimensional structure that makes it difficult to coat it sufficiently, and only uneven coatings can be obtained. For this reason, in order to obtain a film with a uniform thickness, it is sufficient to use 3n or more, but if it is 20μ or more, the film is more likely to crack due to shrinkage during drying and curing, and the cracks may reach the surface of the base material. There are some that are undesirable. At the time of regeneration, the cracks spread, and it is necessary to determine the re-exit temperature conditions based on the heat resistance temperature of the base material, and a thick film of 20 nm or more cannot contribute to improving heat resistance. The film obtained here is zirconium oxide (ZrOz) and has a linear expansion coefficient of lχ
Since the coefficient of expansion was 10-'/'C, which was the same as that of the nickel-chromium alloy, no peeling of the film occurred even after repeated regeneration, and stable film properties were maintained.

〔Effect of the invention〕

As explained above, the three-dimensional network structure porous body of the present invention has sufficient ability to capture particulates exhausted from diesel engine vehicles, and also has the ability to capture 600% of particulates necessary to burn and remove the captured particulates. Since it has heat resistance up to 900'C, it is effective when used as particulate trap media for diesel engine exhaust.

[Brief explanation of drawings]

Figure 1 is an enlarged view of a three-dimensional network structure porous material, Figures 2 and 3, Figures 4 and 5, Figures 6 and 7 are a vertical front view and a vertical cross-section showing an example of a trap device, respectively. Side view,
FIG. 8 is a schematic diagram showing an example in which a trap device and a regeneration gas supply device are provided in the exhaust system of a diesel engine. 1...Three-dimensional network structure porous body, 2...
Playing card holder 3... Gas inlet, 5... Playing card device, 7... Cylindrical body, 6... Hole, 4...・Gas outlet, 8... Seal member.

Claims (6)

[Claims] (1) Particulate trap media for diesel engine exhaust consisting of a three-dimensional network structure porous body with communicating holes made of a skeleton of nickel-chromium alloy or nickel-chromium-iron alloy. (2) The particulate trap media for diesel engine exhaust according to claim (1), wherein the communicating holes have an average pore diameter of 0.1 to 0.5 mm. (3) 1 to 10% of aluminum is added to the alloy according to claim (1).
Particulate trap media for diesel engine exhaust characterized by containing 6% by weight. (4) Claims (1) to 10 include a diffusion layer in which a rare earth element such as yttrium or cerium is distributed within 100 μm from the skeleton surface at a concentration of 0.005 to 0.1% by weight. (3) Particulate trap media for diesel engine exhaust according to any one of the above. (5) The particulate trap media for diesel engine exhaust according to claim 1 or 2, characterized in that the skeleton surface has a heat-resistant ceramic layer coated with a thickness of 3 to 20 μm by a sol-gel method. (6) The heat-resistant ceramic layer according to claim (5) is ZrO.
Particulate trap media for diesel engine exhaust characterized by consisting of _2.