JP3807224B2 - Particulate filter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a particulate filter that collects particulate matter (hereinafter referred to as “PM” unless otherwise specified) represented by, for example, suspended particulate matter contained in the exhaust of a diesel engine. .
[0002]
[Prior art]
Diesel engines are excellent in economy, but removal of PM contained in exhaust gas is an important issue. For this reason, a technique of providing a particulate filter for collecting PM in an exhaust system of a diesel engine so that PM is not released into the atmosphere is well known (see Japanese Patent Laid-Open No. 9-262414).
[0003]
This particulate filter is provided with the same number of non-woven fabrics as the non-woven fabric having a filter function of N sheets (N is an even number of 2 or more) made of heat-resistant metal fibers, and is somewhat smaller in width than the non-woven fabric. In addition, since it has a corrugated longitudinal section, it basically includes a heat-resistant metal plate generally called a corrugated plate.
[0004]
Further, the particulate filter is formed as follows.
[0005]
A corrugated sheet is alternately stacked on the nonwoven fabric one by one in the same direction to form a long laminated material, and then the long laminated material is rolled into a cylindrical shape (hereinafter referred to as a long laminated material). Is formed into a columnar shape, and is referred to as a “columnar laminate”.
[0006]
In addition, the cylindrical shape is maintained by the rigidity of the corrugated sheet. That is, the corrugated plate functions as an aggregate of the cylindrical laminate.
[0007]
And the said cylindrical laminated body alternates with the seam part which obstruct | occludes the front-end | tip of the nonwoven fabrics which adjoin in the radial direction by welding, and the non-mesh part which keeps the front-end | tip of adjacent nonwoven fabrics open similarly. Formed.
[0008]
Specifically, when the cylindrical laminate is viewed from one end thereof, the corrugated sheet positioned between the nonwoven fabrics is closed by the nonwoven fabric and cannot be seen, and the corrugated sheet can be seen because it is open. They are formed alternately with the seams. And also the other end side is alternately formed with a seam portion and a non-mesh portion. However, the place where the seam portion and the non-mesh portion are formed is different between the one end side and the other end side.
[0009]
That is, for a pair of adjacent non-woven fabrics that are sealed on one end side of the cylindrical laminate, a pair of non-woven fabrics that are not sealed on one end side are not sealed on the other end side. About each other, the other end side is sealed.
[0010]
As a result, the cylindrical laminate is formed with a plurality of layers in a swirling state (hereinafter referred to as “layer part”) in which corrugated sheets are placed in a space surrounded by a nonwoven fabric and open at one end and the other end. Then, such a cylindrical laminated body is put in a heat resistant metal container having the same diameter as the exhaust passage and open at both ends, and the inner surface of the heat resistant metal container and the outer peripheral surface of the cylindrical laminated body Are welded at their appropriate positions, whereby the cylindrical laminate is fixed to the heat-resistant metal container to form a particulate filter. In addition, in order to ensure the durability with respect to vibration, it forms so that there may be no gap as much as possible between a cylindrical laminated body and a heat-resistant metal container.
[0011]
Further, welding, brazing, or diffusion bonding is used for joining the nonwoven fabric and the corrugated sheet. Diffusion bonding refers to bonding two metals to be bonded, that is, a nonwoven fabric and a corrugated sheet, by heating and holding at an appropriate temperature in a pressurized state.
[0012]
And in the state where the exhaust passage is attached to the particulate filter, the exhaust gas that has flowed toward the particulate filter through the exhaust passage enters the layer portion from the non-sealing portion on the exhaust upstream side of the nonwoven fabric, and then Flows downstream of the exhaust passage. The downstream side in the layer portion is sealed by welding, and a very small gap formed between the nonwoven fabric fibers is closed in the portion. Therefore, the exhaust gas that has lost its destination flows from the layer portion that is marked on the downstream side toward another layer portion that is adjacent to the layer portion and that is the non-sealed portion on the downstream side. At that time, PM is collected in a very small gap of the nonwoven fabric, thereby removing PM from the exhaust.
[0013]
The exhaust gas from which PM has been removed and flowed into the other layer portion is released to the atmosphere after that, because the downstream side is an unsealed portion and is open in the other layer portion.
[0014]
On the other hand, when the amount of collected PM by the particulate filter increases, the filter may be clogged. This clogging occurs when a very small gap of the nonwoven fabric is blocked by the collected PM. When clogging occurs, the resistance when the exhaust gas passes through the filter increases, the pressure of the exhaust gas in the exhaust passage increases, and this pressure may damage the filter.
[0015]
The PM collected by the filter is reduced in combustion by the heat of the exhaust gas when the internal combustion engine is in a high rotation and high load state, but the exhaust temperature is low in the low rotation and low load state of the internal combustion engine. Since PM is low, PM does not burn but accumulates on the nonwoven fabric.
[0016]
Therefore, a technique is known in which the collected PM is periodically burned down by using exhaust heat, electric heater heat, etc., thereby preventing clogging and preventing PM collection by the particulate filter from being hindered. It is. This is called particulate filter regeneration.
[0017]
Further, the particulate filter can purify HC, CO, etc. in addition to collecting PM by supporting the catalyst on the surface of the corrugated sheet and the nonwoven fabric. In this way, the integration of the particulate filter and the catalytic converter can be realized, and the need for separately installing the catalytic converter can be eliminated.
[0018]
[Problems to be solved by the invention]
However, using a method of raising the temperature of the exhaust by means of fuel injection or an exhaust throttle valve, etc., in order to reduce the PM causes deterioration of fuel consumption and acceleration performance, and directly using a filter such as an electric heater. When the heating method is used, problems such as that the inside of the filter is not heated uniformly occur, and further, the apparatus becomes large and complicated.
[0019]
On the other hand, in order to carry the catalyst on the nonwoven fabric and purify HC, CO, etc., it is indispensable to increase the contact area between the exhaust and the nonwoven fabric. Has been done. However, in the process of attaching the porous material or the like to the nonwoven fabric, the porous material or the like may enter the void of the nonwoven fabric and narrow or close the void.
[0020]
Then, the resistance when the exhaust discharged from the internal combustion engine passes through the gap increases, the pressure of the exhaust on the upstream side of the filter increases, and the pressure of the exhaust is applied to the nonwoven fabric, There is a risk of causing damage.
[0021]
The present invention has been made in view of the above circumstances, and the problem to be solved is to prevent PM from being clogged by burning PM by the oxidation reaction heat of the catalyst without depending on external heating. Another object of the present invention is to provide a technique for preventing deformation and damage of the particulate filter.
[0022]
[Means for Solving the Problems]
The particulate filter of the present invention employs the following means in order to solve the above problems.
[0023]
That is, in the particulate filter that is provided in the exhaust passage of the internal combustion engine and collects particulate matter contained in the exhaust gas,
A nonwoven fabric Do Ri oxidation catalyst is not supported from a metal,
A metal plate carrying an oxidation catalyst on its surface;
Comprising
A bag-shaped upstream open bag-shaped portion having a upstream open portion that opens toward the upstream side of the exhaust passage and a downstream closed portion that is closed on the downstream side;
A bag-shaped downstream open bag-shaped portion having a downstream open portion opened toward the downstream and an upstream closed portion closed on the upstream side;
There are several forms, the Rukoto increasing the temperature of the nonwoven fabric by the oxidation reaction in the oxidation catalyst, wherein the metal plate is supported on the installed the metal plate while in contact with said nonwoven fabric constituting the upstream-side open bag portion Features.
[0024]
Moreover, in this invention, the said metal plate can be installed, contacting the said nonwoven fabric which comprises the said downstream open | release bag-shaped part.
[0025]
Here, the “nonwoven fabric” is a fabric made by mechanically / chemically / thermally treating a fiber sheet and joining it with an adhesive or the adhesive strength of the fiber itself without going through a thread form.
[0026]
For example, a corrugated plate having high rigidity is preferably used as the metal plate.
[0027]
In the particulate filter constructed in this way, the oxidation reaction of carbon monoxide CO, hydrocarbon HC, and SOF (Soluble Organic Fraction) in the exhaust gas by the catalyst supported on the metal plate. Occurs and the temperature of the metal plate rises. Since the nonwoven fabric in contact with the metal plate is made of metal and has high thermal conductivity, the heat generated by the oxidation reaction of the metal plate is transferred to the entire nonwoven fabric, and the temperature of the entire nonwoven fabric increases. Further, the temperature of the exhaust gas also increases due to the oxidation reaction heat of the catalyst carried on the metal plate. Therefore, the temperature of the nonwoven fabric also increases when the exhaust gas whose temperature has increased passes through the nonwoven fabric.
[0028]
Even when the exhaust temperature of the internal combustion engine is low and the load is low due to this oxidation reaction heat, the temperature of the nonwoven fabric can be increased to the temperature at which soot burns, and soot can be reduced.
[0029]
Further, since the catalyst is supported only on the metal plate, the nonwoven fabric can be prevented from being clogged due to adhesion of a porous substance or the like.
[0030]
Furthermore, when a metal plate carrying an oxidation catalyst is placed in contact with the downstream open bag-like portion in the same manner as the upstream open bag-like portion, the metal plate placed inside the upstream open bag-like portion is oxidized. The oxidation reaction of carbon monoxide CO, hydrocarbon HC, and SOF in the exhaust gas that has not reacted can be caused, and the temperature of the nonwoven fabric can be further increased.
[0031]
Thus, since a nonwoven fabric and a metal plate become high temperature, it is suitable to use the metal excellent in heat resistance for the material to be used.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
[First Embodiment]
1A is a view of the particulate filter 1 according to the present embodiment as viewed from the upstream side of the exhaust passage 7, and FIG. 1B is a cross-sectional view when the filter 1 is cut in the exhaust flow direction.
[0033]
The particulate filter 1 is a collector that is installed in, for example, an exhaust passage 7 of a diesel engine and mainly collects PM represented by soot, which is a suspended particulate matter contained in exhaust gas.
[0034]
The filter 1 includes a nonwoven fabric 5 made of a heat-resistant metal fiber, a corrugated plate 2 made of a heat-resistant metal, a metal inner tube 3, and a metal outer tube 4.
[0035]
The nonwoven fabric 5 has an upstream open end 5a that is open toward the upstream side of the exhaust passage 7 and an upstream open bag-like portion 5c that is open on the upstream side and has a downstream side closed end 5b that is closed on the downstream side. A plurality of diffracted inner cylinders are formed so as to be alternately formed with a downstream open end 5d opened toward the downstream side and a downstream open bag-like portion 5f opened downstream with an upstream closed end 5e closed upstream. 3 It is joined inside.
[0036]
Here, the bent portion is not limited to a clear joint formed by bending the nonwoven fabric 5, but includes a side portion that can have a certain width by being bent without a fold.
[0037]
The corrugated plate 2 is formed with a wave height in accordance with the bending width of the nonwoven fabric 5 constituting the upstream open end 5a and the downstream closed end 5b. The corrugated sheet 2 is upstream so that the peaks of the wave peaks and valleys are in contact with the nonwoven fabric 5 and the wave direction of the corrugated sheet 2 is parallel to the folds of the nonwoven fabric 5 constituting the upstream open end 5a. It is narrowly inserted into the open bag-like portion 5c.
[0038]
For example, an Fe—Cr—Al alloy having a thickness of 0.05 mm can be used for the corrugated plate 2, and the flat plate is formed to have a plurality of corrugated cross sections by diffracting a plurality of times.
[0039]
On the surface of the corrugated plate 2, an alumina slurry having a thickness of several μm to several tens of μm is formed by applying or dipping alumina slurry, and platinum Pt, palladium Pd, rhodium Rh is formed on the support layer. An oxidation catalyst metal such as is supported.
[0040]
The supported oxidation catalyst has a function of oxidizing carbon monoxide CO, hydrocarbon HC, and SOF contained in the exhaust gas.
[0041]
The nonwoven fabric 5 is made of a heat-resistant metal, and there is a gap of, for example, about 70% between the fibers of the nonwoven fabric 5, and the exhaust discharged from the internal combustion engine passes through the gap.
[0042]
Since the void is smaller than the size of the soot contained in the exhaust gas, the fine particles such as soot contained in the exhaust gas cannot be passed through the air gap and are collected by the nonwoven fabric.
[0043]
If an oxidation catalyst such as platinum is also carried on the nonwoven fabric 5, it becomes possible to purify HC, CO and the like. However, at this time, the contact area between the nonwoven fabric 5 and the exhaust gas is small and a sufficient exhaust purification effect cannot be obtained by simply carrying the oxidation catalyst without performing any processing on the nonwoven fabric 5. Therefore, it is indispensable to increase the contact area with the exhaust gas. For this reason, it is necessary to coat the surface of the nonwoven fabric 5 with a porous material such as alumina. However, in the process of coating alumina, alumina may enter the voids of the nonwoven fabric 5 to narrow or close the voids (see FIG. 3). Therefore, in the present embodiment, the nonwoven fabric 5 is not supported with an oxidation catalyst, but only the corrugated sheet 2 is coated with alumina, which is a porous material, to support the oxidation catalyst.
[0044]
The inner cylinder 3 is made of ferritic stainless steel, and is a circular cylinder having both open ends.
[0045]
The exhaust passage 7 is formed of a circular hollow tube, and has a joint portion 7a projecting outward. The exhaust passages 7 are joined to each other at the joint portion 7a.
[0046]
The outer cylinder 4 is a circular cylinder having both open ends, and a flange 4a projecting outward is formed at one end. The outer diameter of the outer cylinder 4 is slightly smaller than the inner diameter of the joint portion 7 a of the exhaust passage 7, and the outer cylinder 4 is fitted in the exhaust passage 7.
[0047]
On the other hand, there are a plurality of upstream-side open bag-like portions 5c, and the lengths in the fold direction of the nonwoven fabric 5 at the upstream-side open ends 5a are different from each other. . Therefore, it is necessary to prepare the corrugated plate 2 formed in accordance with this length for each upstream open bag-like portion 5c. And the corrugated sheet 2 is narrowly inserted in all the upstream open bag-like parts 5c.
[0048]
When the corrugated sheet 2 is placed in contact with the nonwoven fabric 5 in this way, the oxidation reaction heat generated by the oxidation catalyst carried on the corrugated sheet 2 is easily transferred to the nonwoven fabric 5, and the temperature of the corrugated sheet 2 increases. At the same time, the temperature of the nonwoven fabric 5 also rises.
[0049]
The outer diameter of the inner cylinder 3 is slightly smaller than the inner diameter of the outer cylinder 4, and the inner cylinder 3 is fitted into the outer cylinder 4. Then, by welding and joining the outer circumferences of the outer cylinder 4 and the inner cylinder 3, the exhaust passes through the gap between the inner cylinder 3 and the outer cylinder 4 without passing through the nonwoven fabric 5 and is released into the atmosphere. Is preventing.
[0050]
Moreover, if all the exhaust gas passing through the filter 1 does not pass through the air gaps of the nonwoven fabric 5, soot and the like in the exhaust gas will be released into the atmosphere. Therefore, the periphery of the nonwoven fabric 5 is welded to the inside of the inner cylinder 3 so that all the exhaust gas flowing through the exhaust passage 7 passes through the voids of the nonwoven fabric 5.
[0051]
The outer cylinder 4 is fitted into the exhaust passage 7 with the other end on which the flange 4a is not formed facing upstream from the joint portion 7a, and the flange 4a is sandwiched by the joint portion 7a. A highly heat insulating ceramic fiber sheet 6 is interposed between the flange 4a and the joint 7a to prevent the heat of the filter 1 from being transferred to the exhaust passage 7 and the temperature of the filter 1 from being lowered.
[0052]
If the catalyst is supported on the corrugated plate 2 in this way, the integration of the particulate filter and the catalytic converter can be realized, and the necessity of separately installing the catalytic converter can be eliminated.
[0053]
In addition, since the soot and the like attached to the filter can be burned by the oxidation reaction heat of the oxidation catalyst, there is no need for an increase in fuel for reducing the soot and the like, or heating means such as an electric heater.
[0054]
Next, the function and effect of the particulate filter 1 according to the embodiment having such a configuration will be described.
[0055]
Particulate matter called PM is contained in the exhaust discharged from the internal combustion engine. This PM consists of insoluble components such as soot or soluble components (SOF) such as unburned fuel components. Here, it is known that SOF has a lower oxidation / combustion temperature, for example, by about 200 ° C. than soot and the like.
[0056]
When the exhaust gas passes through the filter, PM contained in the exhaust gas is collected by the nonwoven fabric 5, and PM is deposited on the surface or inside of the nonwoven fabric 5. When a large amount of PM is deposited on the nonwoven fabric 5, the voids of the nonwoven fabric 5 are narrowed by PM and finally closed, and the resistance when exhaust passes through the filter 1 is increased. Then, the exhaust discharged from the internal combustion engine has no place to go, and the pressure of the exhaust in the exhaust passage 7 upstream of the nonwoven fabric 5 is increased. This pressure may induce deformation or damage of the filter 1.
[0057]
Therefore, it is necessary to reduce this PM before the filter 1 is clogged. One method of reducing the amount of PM is a sub-injection in which fuel is injected during an exhaust stroke or the like that does not become the output of the internal combustion engine, and the fuel is burned so that the exhaust is heated to a high temperature and the PM deposited on the nonwoven fabric 5 is reduced in combustion. (Post injection) is known. However, in this method, for example, it is necessary to send a high-temperature exhaust near 600 ° C. to the nonwoven fabric 5 for several tens of seconds, but it is difficult to maintain this state during actual running.
[0058]
In addition, other methods for directly heating the filter 1 with an electric heater or the like are also known, but there are problems such as the size of the apparatus being increased due to the installation of the heater or the like, and the inside of the filter 1 being unable to be heated uniformly.
[0059]
Therefore, in the filter 1 according to the present embodiment, platinum as an oxidation catalyst is carried on the surface of the corrugated plate 2, and the temperature of the nonwoven fabric 5 is increased by the oxidation reaction heat so that PM is burned down. .
[0060]
In the corrugated plate 2 installed in the upstream open bag-like portion 5 c that has become a bag shape by bending, the upstream open end 5 a opens toward the upstream side of the exhaust passage 7. For this reason, the exhaust before passing through the nonwoven fabric 5 comes into contact with the corrugated plate 2. HC, CO, and SOF contained in the exhaust gas are oxidized by the oxidation catalyst carried on the corrugated plate 2 to generate oxidation reaction heat. This heat of oxidation reaction is transferred to the corrugated plate 2 and the exhaust, and raises the respective temperatures. The exhaust gas whose temperature has risen flows directly toward the downstream nonwoven fabric 5, passes through the voids of the nonwoven fabric 5, and is discharged into the atmosphere. When this exhaust gas passes through the voids of the nonwoven fabric 5, the heat of the exhaust heat is transferred to the nonwoven fabric 5 and the temperature of the nonwoven fabric 5 rises.
[0061]
Further, since the nonwoven fabric 5 is in contact with the corrugated plate 2 whose temperature has risen, the heat of the corrugated plate 2 is efficiently transferred to the nonwoven fabric 5. Since the nonwoven fabric 5 is made of metal fibers and has a high thermal conductivity, the temperature of the entire nonwoven fabric 5 rises due to thermal conduction. The heat transferred to the non-woven fabric 5 is further transferred to the inner cylinder 3 and the outer cylinder 4, and a ceramic fiber sheet 6 as a heat insulating material is sandwiched between the flange of the outer cylinder 4 and the exhaust passage 7. In this way, heat is transferred to the exhaust passage 7 to prevent the temperature of the filter from decreasing.
[0062]
When the temperature of the nonwoven fabric 5 rises in this way, the accumulated PM is burned and reduced due to the high temperature.
[0063]
Since the temperature at which SOF is oxidized and burned by the oxidation catalyst is about 200 ° C. lower than that of soot, for example, the temperature increase due to oxidation and combustion of SOF can be utilized for soot oxidation and combustion.
[0064]
As described above, in the present embodiment, the temperature of exhaust gas is increased without using fuel injection or an increase in load due to an exhaust throttle in order to burn PM, so that fuel consumption and acceleration performance are deteriorated. Absent. And even when the temperature of the exhaust when the vehicle is traveling at a low speed and a light load of about 40 km / h is low (for example, 270 ° C. to 300 ° C.), the temperature of the nonwoven fabric is raised to a recyclable region (for example, 430 ° C. or more). The soot collected in the nonwoven fabric 5 can be burned and reduced.
[0065]
In addition, HC and CO discharged from the internal combustion engine can be purified by the oxidation catalyst carried on the corrugated plate 2.
[0066]
Further, since the corrugated sheet 2 is sandwiched between and in contact with the nonwoven fabric 5, the heating of the corrugated sheet 2 by the heat of oxidation reaction is more uniform and quicker than the heating from the outside of the filter 1 by a heater or the like. Can be heated. Therefore, even immediately after starting the internal combustion engine, the temperature of the nonwoven fabric 5 can be raised quickly, and the amount of soot can be reduced quickly.
[0067]
FIG. 2 shows the relationship between the running state of the vehicle and the temperature of the nonwoven fabric 5, but when the vehicle is decelerated and the exhaust gas temperature is low when the internal combustion engine has a low rotation and low load, This time, the heat of the nonwoven fabric 5 is transferred to the exhaust, and the temperature of the nonwoven fabric 5 is generally lowered. However, by arranging the corrugated sheet 2 carrying the catalyst, the heat of oxidation reaction is transferred to the nonwoven fabric 5 and the temperature of the nonwoven fabric 5 can be kept high.
[0068]
If it is not possible to completely reduce soot due to the above effects, for example, in combination with post-injection that increases the exhaust temperature by injecting fuel during the exhaust stroke of the internal combustion engine at a light load while traveling at 80 to 100 km / h. Soot accumulated with a small amount of fuel can be reduced.
[Second Embodiment]
In this embodiment, as shown in FIG. 4 in addition to the first embodiment, the corrugated plate 2 carrying the oxidation catalyst also on the downstream side open bag-like portion 5 f opened on the downstream side of the exhaust passage 7. Is narrowed in the same manner as in the first embodiment. In this way, the HC, CO, and SOF that have not been oxidized by the upstream corrugated plate 2 are oxidized by the downstream corrugated plate 2, so that the exhaust gas purification rate can be improved. Furthermore, since the oxidation reaction heat generated in the corrugated plate 2 on the downstream side is transferred to the nonwoven fabric 5, the nonwoven fabric 5 can be heated earlier and the amount of soot can be reduced.
[0069]
【The invention's effect】
According to the particulate filter according to the present invention, soot accumulated in the filter can be burned and reduced by the oxidation reaction heat of the catalyst.
[0070]
Further, since the catalyst is supported on the metal plate, the amount of carbon monoxide CO and hydrocarbon HC in the exhaust gas can be reduced.
[0071]
Since the nonwoven fabric and the metal plate are brought into contact with each other, the temperature of the nonwoven fabric can be increased evenly and quickly compared to heating from the outside such as an electric heater.
[Brief description of the drawings]
FIG. 1 (a) is a view of a particulate filter according to a first embodiment of the present invention as seen from the upstream side of an exhaust passage. FIG. 1B is a cross-sectional view showing the particulate filter according to the first embodiment of the present invention cut in the exhaust flow direction.
FIG. 2 is a diagram showing changes in the temperature of a nonwoven fabric depending on operating conditions.
FIG. 3 is a view showing alumina adhering to a gap between nonwoven fabrics.
FIG. 4 is a cross-sectional view showing a particulate filter according to a second embodiment of the present invention cut in the exhaust flow direction.
[Explanation of symbols]
1 Particulate filter (collector)
2 Corrugated plate 3 Inner tube 4 Outer tube 5 Non-woven fabric 6 Ceramic fiber sheet 7 Exhaust passage

Claims (2)

In the particulate filter that is provided in the exhaust passage of the internal combustion engine and collects particulate matter contained in the exhaust gas,
A nonwoven fabric Do Ri oxidation catalyst is not supported from a metal,
A metal plate carrying an oxidation catalyst on its surface;
Comprising
A bag-shaped upstream open bag-shaped portion having a upstream open portion that opens toward the upstream side of the exhaust passage and a downstream closed portion that is closed on the downstream side;
A bag-shaped downstream open bag-shaped portion having a downstream open portion opened toward the downstream and an upstream closed portion closed on the upstream side;
There are several forms, the Rukoto increasing the temperature of the nonwoven fabric by the oxidation reaction in the oxidation catalyst, wherein the metal plate is supported on the installed the metal plate while in contact with said nonwoven fabric constituting the upstream-side open bag portion A featured particulate filter. 2. The particulate filter according to claim 1, wherein the metal plate is placed in contact with the nonwoven fabric constituting the downstream open bag-shaped portion.

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