EP1979066A1 - A diesel soot particulate filter medium - Google Patents

A diesel soot particulate filter medium

Info

Publication number
EP1979066A1
EP1979066A1 EP06818902A EP06818902A EP1979066A1 EP 1979066 A1 EP1979066 A1 EP 1979066A1 EP 06818902 A EP06818902 A EP 06818902A EP 06818902 A EP06818902 A EP 06818902A EP 1979066 A1 EP1979066 A1 EP 1979066A1
Authority
EP
European Patent Office
Prior art keywords
layers
particulate filter
filter medium
diesel soot
soot particulate
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP06818902A
Other languages
German (de)
French (fr)
Inventor
Johan Vandamme
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Bekaert NV SA
Original Assignee
Bekaert NV SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Bekaert NV SA filed Critical Bekaert NV SA
Priority to EP06818902A priority Critical patent/EP1979066A1/en
Publication of EP1979066A1 publication Critical patent/EP1979066A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D39/00—Filtering material for liquid or gaseous fluids
    • B01D39/14—Other self-supporting filtering material ; Other filtering material
    • B01D39/20—Other self-supporting filtering material ; Other filtering material of inorganic material, e.g. asbestos paper, metallic filtering material of non-woven wires
    • B01D39/2027—Metallic material
    • B01D39/2041—Metallic material the material being filamentary or fibrous
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D39/00—Filtering material for liquid or gaseous fluids
    • B01D39/14—Other self-supporting filtering material ; Other filtering material
    • B01D39/20—Other self-supporting filtering material ; Other filtering material of inorganic material, e.g. asbestos paper, metallic filtering material of non-woven wires
    • B01D39/2027—Metallic material
    • B01D39/2041—Metallic material the material being filamentary or fibrous
    • B01D39/2044—Metallic material the material being filamentary or fibrous sintered or bonded by inorganic agents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D39/00—Filtering material for liquid or gaseous fluids
    • B01D39/14—Other self-supporting filtering material ; Other filtering material
    • B01D39/20—Other self-supporting filtering material ; Other filtering material of inorganic material, e.g. asbestos paper, metallic filtering material of non-woven wires
    • B01D39/2027—Metallic material
    • B01D39/2051—Metallic foam
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
    • B01D2239/06—Filter cloth, e.g. knitted, woven non-woven; self-supported material
    • B01D2239/065—More than one layer present in the filtering material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2275/00—Filter media structures for filters specially adapted for separating dispersed particles from gases or vapours
    • B01D2275/30—Porosity of filtering material

Definitions

  • the present invention relates to a diesel soot particulate filter medium, and in particular a diesel soot particulate filter medium for filtering diesel exhaust gasses of a diesel combustion device such as a diesel combustion engine, an automotive vehicle including the diesel soot filter medium as well as a method of manufacture and operating of the diesel soot filter medium.
  • Diesel soot particulate filter medium comprising metal fibers are known in the art.
  • WO03/047720 discloses a multilayered sintered metal fiber filter medium for filtration of diesel soot from exhaust gas of a diesel combustion engine.
  • this medium may have the disadvantage that only limited amount of soot can be held before the medium gets clogged.
  • electrical regeneration i.e. conducting electrical current through the medium, causing a heating of the medium due to the Joule effect
  • regeneration by injection of catalytic compounds in the diesel or exhaust gas e.g. by injection of catalytic compounds in the diesel or exhaust gas.
  • electrical regeneration i.e. conducting electrical current through the medium, causing a heating of the medium due to the Joule effect
  • An advantage of the present invention is the provision of diesel soot particulate filter media, which avoid holes being burned in the filter medium. For example, such holes can be caused by local combustion of too large amounts of filtered soot during a regeneration of the diesel soot particulate filter medium.
  • a diesel soot particulate filter medium having an inflow side and an outflow side, comprises at least n consecutive layers Lx of fiber media, x varying from 1 to n and n being more than 2.
  • L1 provides the inflow side of the diesel soot particulate filter and
  • Ln provides the outflow side of the diesel soot particulate filter medium.
  • Each layer Lx has a porosity Px. All layers Lx, for which 1 ⁇ x ⁇ n-1 , have a substantially equal porosity to Ph and layer Ln has a porosity Ps. The porosity Ph is larger than Ps.
  • Ln may be a sintered layer.
  • a diesel soot particulate filter medium may comprise non-sintered layers.
  • the presence of such layers avoids holes being burned in the filter medium during regeneration, for example in case locally a too large concentration of soot particulates is combusted during such regeneration phase.
  • the layers Lx for which 1 ⁇ x ⁇ n-1 may be non sintered layers.
  • Ph may be more than or equal to 93%, Ph may be less than or equal to 98%.
  • Ps may be more than or equal to 70%, Ps may be less than or equal to 87%.
  • a diesel soot particulate filter medium has an inflow side and an outflow side.
  • the diesel soot particulate filter medium comprises at least n consecutive layers Lx of fiber media, x varying between 1 and n and n being more than 3.
  • L1 provides the inflow side of the diesel soot particulate filter and
  • Ln provides the outflow side of the diesel soot particulate filter medium.
  • Each layer Lx has a porosity Px.
  • the porosity Pxi is smaller than its neighbouring layers.
  • all layers LXJ may have an equal porosity Ps.
  • Ps may be more than or equal to 70%, Ps may be less than or equal to 87%.
  • Pn may be equal to Ps.
  • Pn may be smaller than Pn-1.
  • a diesel soot particulate filter medium may comprise non-sintered layers. The presence of such layers avoids holes being burned in the filter medium during regeneration, for example in case locally a too large concentration of soot particulates is combusted during such regeneration phase.
  • the layers LX J may be sintered layers.
  • layer Ln may be a sintered layer.
  • the layers other than layers LX J and Ln are non-sintered layers.
  • m being at least 2
  • an identical number q of intermediate layers may be located, q may be larger than 1.
  • a substantially identical gradient of porosity ⁇ P may be provided over the q intermediate layers.
  • the gradient of porosity ⁇ P may be substantially zero or the gradient of porosity ⁇ P is a decreasing gradient in flow direction.
  • a diesel soot particulate filter medium has an inflow side and an outflow side.
  • the diesel soot particulate filter medium comprises at least n consecutive layers Lx of fiber media, x varying between 1 and n and n being more than 3.
  • L1 provides the inflow side of the diesel soot particulate filter and
  • Ln provides the outflow side of the diesel soot particulate filter medium.
  • Each layer Lx has a porosity Px.
  • LXJ 1 ⁇ i ⁇ m, m being at least 1 and m being less than n/2
  • Lxj is different from Ln and LX J being different from L1
  • the porosity PX J is smaller than its neighbouring layers.
  • the equivalent diameter of the fibers in the layer Lx ⁇ may be larger than the equivalent diameter of the fibers in the layer Lx i2 .
  • the equivalent diameter of the fibers in the layer Lxn may be larger than the equivalent diameter of the fibers in the layer Lx i2.
  • the layers between Lx M and Lx i2 may have the same equivalent diameter as the equivalent diameter of the fibers in the layer Lx i2 .
  • s may be equal to number q of intermediate layers.
  • a gradient of porosity over said s layers may be identical to the gradient of porosity ⁇ P.
  • t may be equal to the number q of intermediate layers.
  • the gradient of porosity over the t layers may be identical to the gradient of porosity ⁇ P.
  • the layers other than layers Lx 1 and Ln may have a porosity more than or equal to 93%, the layers other than layers LX J and Ln may have a porosity less than or equal to 98%.
  • the fibers of each of the layers Lx may have an equivalent diameter Dx, for all layers Lx, for which 1 ⁇ x ⁇ n-1 , Dx ⁇ Dx+1. At least one of the layers may comprise a catalyst.
  • the fiber media may comprise metal fibers.
  • the fiber media may consist out of metal fibers.
  • the metal fibers may be bundle drawn metal fibers.
  • the filter medium further comprises metal foam layers of porous medium layers out of hollow metal spheres.
  • the present invention further relates to the use of a diesel soot particulate filter as subject of the present invention in an automotive vehicle such as in a truck or a bus as well as the automotive vehicle including the particulate filter.
  • Fig. 1 is a schematically view of a cross section of a diesel soot particulate filter medium according to an embodiment of the present invention
  • Fig. 2 is a schematically view of a cross section of a diesel soot particulate filter medium according to another embodiment of the present invention.
  • Fig. 3 is a schematic view of a cross section of a diesel soot particulate filter medium according to another embodiment of the present invention.
  • porosity means the porosity which represents the average porosity, averaged out over the layer in width, length and depth of the layer.
  • the term "porosity P" of a layer is to be understood as 100-D, wherein D is the density of the layer.
  • the density D is the layer consisting from a given material, is the ratio, expressed in percentage, of the weight per volume of the layer over the theoretical weight of that same volume, in case this whole volume would have been provided completely out of said material.
  • substantially equal porosity of value% means the porosity having a preset value plus or minus 6%, e.g. plus or minus 5%, e.g. plus or minus 4%, preferably plus or minus 3%, e.g. plus or minus 3%, which is the normal variation obtained when producing a filter medium, aiming at a porosity of exactly the given value.
  • equivalent diameter of a fiber is to be understood as the diameter of an imaginary circle, having the same surface as the average surface of a radial cross section of the fiber.
  • coil shaved metal fiber is to be understood as a fiber obtainable by the method as described in EP319959A.
  • the term "bundle drawn" metal fiber is to be understood as a fiber obtainable by the method as described in EP280340A or US3379000.
  • melt extracted metal fiber is to be understood as a fiber obtainable by the method as described in US 5027886.
  • a device A coupled to a device B should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means.
  • the invention will now be described by a detailed description of several embodiments of the invention. It is clear that other embodiments of the invention can be configured according to the knowledge of persons skilled in the art without departing from the true spirit or technical teaching of the invention, the invention being limited only by the terms of the appended claims.
  • a diesel soot particulate filter medium 100 has an inflow side 110 and an outflow side 120.
  • the diesel soot particulate filter medium 100 comprises a number of layers of filter media, e.g. up to 4 consecutive layers Lx of filter media, so x varying from 1 to 4.
  • layers L1 (indicated 101 in Fig. 1 ), L2 (indicated 102 in Fig. 1 ), L3 (indicated 103 in Fig. 1 ) and L4 (indicated 104 in Fig. 1 ) are so provided.
  • L1 provides the inflow side 110 of the diesel soot particulate filter 100.
  • L4 provides the outflow side 120 of the diesel soot particulate filter medium 100.
  • Each of the layers L1 , L2 and L3 preferably has a substantially equal porosity Ph. For example, Ph can be 97%.
  • the fourth layer L4 has a porosity Ps being 70%.
  • the value of Ph is preferably larger than the value of Ps.
  • the porosities of each of the layers L1 , L2 and L3 may vary over a range of about 6%, still being understood as substantially equal porosities.
  • Layer L1 is a layer provided out of metal fibers of a bundle-drawn, melt extracted or coil shaved (machined) type having a FECRALLOY ® composition or equivalent heat-resistant composition having an equivalent diameter ranging from 20 ⁇ m to 75 ⁇ m, e.g. 35 ⁇ m or 65 ⁇ m.
  • a typical FECRALLOY® composition is along following lines: 20% Cr 1 5% Al, > 0.10% Y 1 0.30% Si 1 0.08% Mn 1 0.03% Cu, 0.03% C 1 the balance being Fe.
  • the layer has a thickness of 63 mm.
  • the Layer L1 is a non-sintered metal fiber layer.
  • Layer L2 is a layer provided out of metal fibers of a bundle-drawn, melt extracted or coil-shaved type with a FECRALLOY ® or equivalent composition having an equivalent diameter ranging from 10 ⁇ m to 30 ⁇ m but being lower than the diameter of layer L1 , e.g. 17 ⁇ m.
  • the layer has a thickness of 63 mm.
  • Layer L2 is a non-sintered metal fiber layer.
  • Layer L3 is a layer provided out of metal fibers of a bundle-drawn type with a FECRALLOY ® or equivalent composition having an equivalent diameter ranging from 5 ⁇ m to 20 ⁇ m but being smaller than the diameter of layer L2, e.g. 12 ⁇ m.
  • the layer has a thickness of 63 mm.
  • Layer L3 is a non-sintered metal fiber layer.
  • Layer L4 is a layer provided out of metal fibers of a bundle drawn type with a FECRALLOY ® or equivalent composition having an equivalent diameter ranging from 4 ⁇ m to 15 ⁇ m but being smaller than or equal to the diameter of layer L3, e.g. 8 ⁇ m.
  • the layer has a thickness of 0.5 mm.
  • Layer L4 is a sintered metal fiber layer.
  • a diesel soot particulate filter medium 200 has an inflow side 210 and an outflow side 220.
  • the diesel soot particulate filter medium 200 comprises up to 5 consecutive layers Lx of filter media, with x varying from 1 to 5.
  • layers L1 (indicated 201 in Fig. 2), L2 (indicated 202 in Fig. 2), L3 (indicated 203 in Fig. 2), L4 (indicated 204 in Fig. 2) and L5 (indicated 205 in Fig. 2) are so provided.
  • L1 provides the inflow side 210 of the diesel soot particulate filter 200.
  • each of the layers L1 , L2, L3 and L4 has a substantially equal porosity Ph, Ph being 97%.
  • the fifth layer L5 has a porosity Ps being 75%.
  • the value of Ph is larger than that of Ps.
  • the porosities of each of the layers L1 , L2, L3 and L4 may vary over a range of about 6%, still being understood as substantially equal porosities.
  • Layer L1 is a layer provided out of metal fibers of a bundle-drawn, melt extracted or coil shaved (machined) type having a FECRALLOY ® composition or equivalent heat-resistant composition having an equivalent diameter ranging from 20 ⁇ m to 70 ⁇ m, e.g. 35 ⁇ m.
  • the layer has a thickness of e.g. 37 mm.
  • the Layer L1 is a non-sintered metal fiber layer.
  • Layer L2 is a layer provided out of metal fibers of a bundle-drawn, melt extracted or coil shaved (machined) type having a FECRALLOY ® composition or equivalent heat-resistant composition type having an equivalent diameter ranging from 15 ⁇ m to 30 ⁇ m but being lower than the diameter of layer L1 , e.g. 22 ⁇ m.
  • the layer has a thickness of 37 mm.
  • Layer L2 is a non-sintered metal fiber layer.
  • Layer L3 is a layer provided out of metal fibers of a bundle-drawn, melt extracted or coil shaved (machined) type having a FECRALLOY ® composition or equivalent heat-resistant composition type having an equivalent diameter ranging from 10 ⁇ m to 25 ⁇ m but being lower than the diameter of layer L2, e.g. 17 ⁇ m.
  • the layer has a thickness of e.g. 37 mm.
  • Layer L3 is a non-sintered metal fiber layer.
  • Layer L4 is a layer provided out of metal fibers of a bundle drawn type having an equivalent diameter ranging between 5 ⁇ m and 20 ⁇ m but being lower than the diameter of the fibers in layer L3, e.g. 12 ⁇ m.
  • the layer has a thickness of e.g. 37 mm.
  • Layer L4 is a non-sintered metal fiber layer.
  • Layer L5 is a layer provided out of metal fibers of a bundle-drawn type having an equivalent diameter ranging from 4 ⁇ m to 15 ⁇ m but being lower than or equal to the diameter of layer L5, e.g. 8 ⁇ m.
  • the layer has a thickness of e.g. 0.5 mm.
  • Layer L5 is a sintered metal fiber layer.
  • the embodiments of Fig. 1 and Fig. 2 may be dimensioned so that they can fit into the volumes occupied by existing ceramic filters. Other examples of thickness configurations are for the embodiments as shown in Fig. 1 : 80 mm/40 mm/23 mm/0.5 mm or 140 mm/70 mm/44 mm/ 0.5 mm, wherein the thicknesses correspond with the layers L1/L2/L3/L4.
  • thickness configurations are for the embodiments as shown in Fig. 2: 75 mm/38 mm/20 mm/10 mm/ 0.5 mm or 134 mm/67 mm/35 mm/ 18 mm/ 0.5 mm wherein the thicknesses correspond with the layers L1/L2/L3/L4/L5.
  • a diesel soot particulate filter medium 300 has an inflow side 3100 and an outflow side 3200.
  • the diesel soot particulate filter medium 3000 comprises up to 12 consecutive layers Lx of filter media, with x varying from 1 to 12.
  • these layers are indicated as L3001 , L3002, L3003, L3004, L3005, L3006, L3007, L3008, L3009, L3010, L3011 and L3012, and represent respectively L1 , L2, L3, L4, L5, L6, L7, L8, L9, L10, L11 and L12.
  • the layer L1 provides the inflow side 3100 of the diesel soot particulate filter medium 3000, the layer L12 provided the outflow side 3200 of the diesel soot particulate filter medium 3000.
  • Each of the layers has a porosity, and is provided out of metal fibers having an equivalent diameter as shown in table 1.
  • Each of the layers is either sintered or not, as indicated in table 1. All layers are provided out of metal fibers, which fibers are obtained by using a production method as indicated in table 1 , the metal having a FECRALLOY ® composition alloy Table 1
  • the diesel soot particulate filter medium 3000 comprises 'm' being three layers, i.e. L3, L6 and L9, which layers are not the first layer L1 nor the last layer L12.
  • L3, L6 and L9 the porosity of each of these three layers is smaller than the porosities of its neighbouring layers, being respectively L2 and L4, L5 and L7, and L8 and L10.
  • the layers L3, L6 and L9 all have an equal porosity of 85%, and all these layers are sintered layers.
  • the other layers which are not L3, L6, and L9, nor the last layer L12, are not sintered.
  • L3 and L6, and between L6 and L9 an identical number of layers q, hereafter called intermediate layers, are located. More in particular, q is equal to two; this means two intermediate layers are located between each pair of consecutive layers.
  • an identical, decreasing gradient of the porosity ⁇ P is provided over the q intermediate layers, ⁇ P decreasing in the flow direction of the gasses to be filtered.
  • the identical gradient of the porosity ⁇ P is a porosity difference of 12%, divided as: • a decrease of 4% between the first and the second of the two intermediate layers, this is between L4 and L5, and between L7 and L8; • a decrease of 8% between the second of the two intermediate layers and the layer L6 or L9 as the case may be, this is between L5 and L6, and between L8 and L9.
  • a porosity gradient is provided over the layers between inflow side 3100 and the first of the layers L3, L6 and L9, being identical to the porosity gradient ⁇ P over the intermediate layers between each pair of consecutive layers L3, L6 and L9.
  • the layers in between comprises fibes having the same equivalent diameter as the layer of the pair closest to the outflow side, i.e. closest to L12.lin particular, this means that the layers between L3 and L6, i.e. L4 and L5 comprises fibers having the same equivalent diameter as L6.
  • the layers between L6 and L9, i.e. L7 and L8 comprises fibers having the same equivalent diameter as L9.
  • the layers are provided from fibers having en equivalent diameter equal to the layer of the pr closest to the outflow side, i.e. L2 has the same equivalent diameter as L3, and L10 and L11 comprises fibers having an equivalent diameter equal to the equivalent diameter of the fibers of L12.
  • the equivalent diameter of the fibers in the layer of this pair being located between L1 and the other layer of this pair is larger than the equivalent diameter of the fibers in the outer layer of this pair. More particular here, the equivalent diameter of the fibers in the L3, being located between L1 and L6 is larger than the equivalent diameter of the fibers in layer L6. The equivalent diameter of the fibers in the L6, being located between L1 and L9 is larger than the equivalent diameter of the fibers in layer L9.
  • the embodiment of Figure 3 is particularly suitable for diesel soot particulate filter in trucks and buses.
  • This embodiment has the particular advantage that the gas flow may be accelerated consecutively with each number of layers with a different diameter. This promotes the Browse movement in order to enhance the capture of diesel soot. It is to be understood that although preferred embodiments, specific constructions and configurations, as well as materials, have been discussed herein for devices according to the present invention, various changes or modifications in form and detail may be made without departing from the scope and spirit of this invention.

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  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Inorganic Chemistry (AREA)
  • Filtering Materials (AREA)
  • Processes For Solid Components From Exhaust (AREA)

Abstract

A diesel soot particulate filter medium as subject of the present invention has an inflow side and an outflow side, and comprises at least n consecutive layers Lx of fiber media, x varying from 1 to n, n being more than 2. L1 provides the inflow side of the diesel soot particulate filter and Ln provides the outflow side of the diesel soot particulate filter medium. Each layer Lx has a porosity Px. All layers Lx, for which 1≤x≤n-1, have a substantially equal porosity to Ph, layer Ln having a porosity Ps, Ph being larger than Ps. Also according to the present invention, a diesel soot particulate filter medium comprises at least n consecutive layers Lx of fiber media, x varying between 1 and n, n being more than 3. L1 provides the inflow side of the diesel soot particulate filter and Ln provides the outflow side of the diesel soot particulate filter medium. For at least m layers LXi, 1≤i≤m, m being at least 1 and m being less than n/2, Lxi being different from Ln and LXi being different from L1 , PXi is smaller than its neighboring layers.

Description

DIESEL SOOT PARTICULATE FILTER MEDIUM
Technical field of the invention
The present invention relates to a diesel soot particulate filter medium, and in particular a diesel soot particulate filter medium for filtering diesel exhaust gasses of a diesel combustion device such as a diesel combustion engine, an automotive vehicle including the diesel soot filter medium as well as a method of manufacture and operating of the diesel soot filter medium.
Background of the invention
Diesel soot particulate filter medium comprising metal fibers are known in the art.
As an example, WO03/047720 discloses a multilayered sintered metal fiber filter medium for filtration of diesel soot from exhaust gas of a diesel combustion engine. Although performing satisfactorily, this medium may have the disadvantage that only limited amount of soot can be held before the medium gets clogged. As a result, very frequent and numerous regeneration actions need to take place, e.g. by regeneration using electrical regeneration (i.e. conducting electrical current through the medium, causing a heating of the medium due to the Joule effect) or regeneration by injection of catalytic compounds in the diesel or exhaust gas. Other disadvantages are that this medium is limited in efficiency and is rather expensive.
An alternative, multilayered diesel soot particulate filter medium is described in WO04/104386. This medium has, due to its substantially larger thickness, an increased soot holding capacity. The medium has the disadvantage that in order to reach this increased soot holding capacity, large volumes are needed.
Summary of the invention
It is an object of the present invention to provide an improved diesel soot particulate filter medium and filter method, for example, solving at least some of the problems of the diesel soot particulate filter medium as known in the prior art. It is an advantage of some embodiments of the present invention to provide a diesel soot particulate filter medium, which has equal or better filter efficiency than the presently known media. It is as well an advantage of some embodiments of the present invention to provide a diesel soot particulate filter medium which is less expensive to produce. It is also an advantage of some embodiments of the present invention to provide a diesel soot particulate filter medium which has an equal or larger soot holding capacity, however requiring less volume as compared to presently known soot filter media. An advantage of the present invention is the provision of diesel soot particulate filter media, which avoid holes being burned in the filter medium. For example, such holes can be caused by local combustion of too large amounts of filtered soot during a regeneration of the diesel soot particulate filter medium.
The above objective is accomplished by a diesel soot particulate filter medium according to the present invention.
According to some embodiments of the present invention, a diesel soot particulate filter medium, having an inflow side and an outflow side, comprises at least n consecutive layers Lx of fiber media, x varying from 1 to n and n being more than 2. L1 provides the inflow side of the diesel soot particulate filter and Ln provides the outflow side of the diesel soot particulate filter medium. Each layer Lx has a porosity Px. All layers Lx, for which 1 <x≤n-1 , have a substantially equal porosity to Ph and layer Ln has a porosity Ps. The porosity Ph is larger than Ps.
According to some of the embodiments of the present invention, Ln may be a sintered layer.
According to embodiments of the present invention, a diesel soot particulate filter medium may comprise non-sintered layers. The presence of such layers avoids holes being burned in the filter medium during regeneration, for example in case locally a too large concentration of soot particulates is combusted during such regeneration phase. According to some of the embodiments of the present invention, the layers Lx for which 1<x≤n-1 may be non sintered layers. According to some of the embodiments of the present invention, Ph may be more than or equal to 93%, Ph may be less than or equal to 98%. According to some of the embodiments of the present invention, Ps may be more than or equal to 70%, Ps may be less than or equal to 87%. According to some embodiments of the present invention, a diesel soot particulate filter medium has an inflow side and an outflow side. The diesel soot particulate filter medium comprises at least n consecutive layers Lx of fiber media, x varying between 1 and n and n being more than 3. L1 provides the inflow side of the diesel soot particulate filter and Ln provides the outflow side of the diesel soot particulate filter medium. Each layer Lx has a porosity Px. For at least m layers LXj, 1<i<m, m being at least 1 and m being less than n/2, LXj is different from Ln and LXj being different from L1 , the porosity Pxi is smaller than its neighbouring layers. According to some embodiments of the present invention all layers LXJ may have an equal porosity Ps.
According to some embodiments of the present invention, Ps may be more than or equal to 70%, Ps may be less than or equal to 87%. According to some embodiments of the present invention, Pn may be equal to Ps. According to some embodiments of the present invention, Pn may be smaller than Pn-1. According to embodiments of the present invention, a diesel soot particulate filter medium may comprise non-sintered layers. The presence of such layers avoids holes being burned in the filter medium during regeneration, for example in case locally a too large concentration of soot particulates is combusted during such regeneration phase. According to some embodiments of the present invention, the layers LXJ may be sintered layers. According to some embodiments of the present invention, layer Ln may be a sintered layer. According to some embodiments of the present invention, the layers other than layers LXJ and Ln are non-sintered layers. According to some embodiments of the present invention, between each pair of consecutive layers LXJ of said m layers, m being at least 2, an identical number q of intermediate layers may be located, q may be larger than 1. According to some embodiments of the present invention, for all pairs of consecutive layers Lxf of said m layers, a substantially identical gradient of porosity ΔP may be provided over the q intermediate layers. The gradient of porosity ΔP may be substantially zero or the gradient of porosity ΔP is a decreasing gradient in flow direction. According to some embodiments of the present invention, a diesel soot particulate filter medium has an inflow side and an outflow side. The diesel soot particulate filter medium comprises at least n consecutive layers Lx of fiber media, x varying between 1 and n and n being more than 3. L1 provides the inflow side of the diesel soot particulate filter and Ln provides the outflow side of the diesel soot particulate filter medium. Each layer Lx has a porosity Px. For at least m layers LXJ, 1<i≤m, m being at least 1 and m being less than n/2, Lxj is different from Ln and LXJ being different from L1 , the porosity PXJ is smaller than its neighbouring layers. According to some embodiments, for which m is at least 2, for at least one pair of consecutive layers Lx^ and Lxi2 of the m layers, LxM being located between L1 and Lxi2, the equivalent diameter of the fibers in the layer Lxπ may be larger than the equivalent diameter of the fibers in the layer Lxi2. According to embodiments of the present invention, for each pair of consecutive layers Lxπ and Lxi2 of said m layers, Lxπ being located between L1 and Lxi2, the equivalent diameter of the fibers in the layer Lxn may be larger than the equivalent diameter of the fibers in the layer Lxi2.. The layers between LxM and Lxi2 may have the same equivalent diameter as the equivalent diameter of the fibers in the layer Lxi2.
According to some embodiments of the present invention, for the number of layers s, located between the inflow side of the medium and LXJ being located closest to the inflow side, s may be equal to number q of intermediate layers. According to some embodiments of the present invention, a gradient of porosity over said s layers may be identical to the gradient of porosity ΔP. According to some embodiments of the present invention, for the number of layers t, located between Ln and LXJ being located closest to the outflow side, t may be equal to the number q of intermediate layers. The gradient of porosity over the t layers may be identical to the gradient of porosity ΔP. According to some embodiments of the present invention, the layers other than layers Lx1 and Ln may have a porosity more than or equal to 93%, the layers other than layers LXJ and Ln may have a porosity less than or equal to 98%. According to some embodiments of the present invention, the fibers of each of the layers Lx may have an equivalent diameter Dx, for all layers Lx, for which 1<x≤n-1 , Dx≥Dx+1. At least one of the layers may comprise a catalyst.
According to some of the embodiments of the present invention, the fiber media may comprise metal fibers. The fiber media may consist out of metal fibers. According to some of the embodiments of the present invention, the metal fibers may be bundle drawn metal fibers.
According to some of the embodiments of the present invention, the filter medium further comprises metal foam layers of porous medium layers out of hollow metal spheres. The present invention further relates to the use of a diesel soot particulate filter as subject of the present invention in an automotive vehicle such as in a truck or a bus as well as the automotive vehicle including the particulate filter.
Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims.
Although there has been constant improvement, change and evolution of devices in this field, the present concepts are believed to represent substantial new and novel improvements, including departures from prior practices, resulting in the provision of more efficient, stable and reliable devices of this nature.
The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.
Brief description of the drawings
Fig. 1 is a schematically view of a cross section of a diesel soot particulate filter medium according to an embodiment of the present invention; Fig. 2 is a schematically view of a cross section of a diesel soot particulate filter medium according to another embodiment of the present invention; and
Fig. 3 is a schematic view of a cross section of a diesel soot particulate filter medium according to another embodiment of the present invention.
Definitions
The following terms are provided solely to aid in the understanding of the invention. These definitions should not be construed to have a scope less than understood by a person of ordinary skill in the art.
The term "porosity" means the porosity which represents the average porosity, averaged out over the layer in width, length and depth of the layer.
The term "porosity P" of a layer is to be understood as 100-D, wherein D is the density of the layer. The density D is the layer consisting from a given material, is the ratio, expressed in percentage, of the weight per volume of the layer over the theoretical weight of that same volume, in case this whole volume would have been provided completely out of said material.
The term "substantially equal porosity" of value% means the porosity having a preset value plus or minus 6%, e.g. plus or minus 5%, e.g. plus or minus 4%, preferably plus or minus 3%, e.g. plus or minus 3%, which is the normal variation obtained when producing a filter medium, aiming at a porosity of exactly the given value.
The term "equivalent diameter" of a fiber is to be understood as the diameter of an imaginary circle, having the same surface as the average surface of a radial cross section of the fiber.
The term "coil shaved" metal fiber is to be understood as a fiber obtainable by the method as described in EP319959A.
The term "bundle drawn" metal fiber is to be understood as a fiber obtainable by the method as described in EP280340A or US3379000.
The term "melt extracted" metal fiber is to be understood as a fiber obtainable by the method as described in US 5027886.
Description of illustrative embodiments
The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.
Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.
It is to be noticed that the term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.
Similarly, it is to be noticed that the term "coupled", also used in the claims, should not be interpreted as being restricted to direct connections only.
Thus, the scope of the expression "a device A coupled to a device B" should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. The invention will now be described by a detailed description of several embodiments of the invention. It is clear that other embodiments of the invention can be configured according to the knowledge of persons skilled in the art without departing from the true spirit or technical teaching of the invention, the invention being limited only by the terms of the appended claims. According to a first embodiment of the present invention, as shown in Fig. 1 , a diesel soot particulate filter medium 100 has an inflow side 110 and an outflow side 120. The diesel soot particulate filter medium 100 comprises a number of layers of filter media, e.g. up to 4 consecutive layers Lx of filter media, so x varying from 1 to 4. As such, layers L1 (indicated 101 in Fig. 1 ), L2 (indicated 102 in Fig. 1 ), L3 (indicated 103 in Fig. 1 ) and L4 (indicated 104 in Fig. 1 ) are so provided. L1 provides the inflow side 110 of the diesel soot particulate filter 100. L4 provides the outflow side 120 of the diesel soot particulate filter medium 100. Each of the layers L1 , L2 and L3 preferably has a substantially equal porosity Ph. For example, Ph can be 97%. The fourth layer L4 has a porosity Ps being 70%. The value of Ph is preferably larger than the value of Ps. As is understood by the skilled person, the porosities of each of the layers L1 , L2 and L3 may vary over a range of about 6%, still being understood as substantially equal porosities. Layer L1 is a layer provided out of metal fibers of a bundle-drawn, melt extracted or coil shaved (machined) type having a FECRALLOY® composition or equivalent heat-resistant composition having an equivalent diameter ranging from 20 μm to 75 μm, e.g. 35μm or 65 μm. A typical FECRALLOY® composition is along following lines: 20% Cr1 5% Al, > 0.10% Y1 0.30% Si1 0.08% Mn1 0.03% Cu, 0.03% C1 the balance being Fe. The layer has a thickness of 63 mm. The Layer L1 is a non-sintered metal fiber layer.
Layer L2 is a layer provided out of metal fibers of a bundle-drawn, melt extracted or coil-shaved type with a FECRALLOY® or equivalent composition having an equivalent diameter ranging from 10 μm to 30 μm but being lower than the diameter of layer L1 , e.g. 17μm. The layer has a thickness of 63 mm. Layer L2 is a non-sintered metal fiber layer.
Layer L3 is a layer provided out of metal fibers of a bundle-drawn type with a FECRALLOY® or equivalent composition having an equivalent diameter ranging from 5 μm to 20 μm but being smaller than the diameter of layer L2, e.g. 12μm. The layer has a thickness of 63 mm. Layer L3 is a non-sintered metal fiber layer.
Layer L4 is a layer provided out of metal fibers of a bundle drawn type with a FECRALLOY® or equivalent composition having an equivalent diameter ranging from 4 μm to 15 μm but being smaller than or equal to the diameter of layer L3, e.g. 8μm. The layer has a thickness of 0.5 mm. Layer L4 is a sintered metal fiber layer.
According to a second embodiment of the present invention, as shown in Fig. 2, a diesel soot particulate filter medium 200 has an inflow side 210 and an outflow side 220. The diesel soot particulate filter medium 200 comprises up to 5 consecutive layers Lx of filter media, with x varying from 1 to 5. As such, layers L1 (indicated 201 in Fig. 2), L2 (indicated 202 in Fig. 2), L3 (indicated 203 in Fig. 2), L4 (indicated 204 in Fig. 2) and L5 (indicated 205 in Fig. 2) are so provided. L1 provides the inflow side 210 of the diesel soot particulate filter 200. L4 provides the outflow side 220 of the diesel soot particulate filter medium 200. Each of the layers L1 , L2, L3 and L4 has a substantially equal porosity Ph, Ph being 97%. The fifth layer L5 has a porosity Ps being 75%. The value of Ph is larger than that of Ps. As is understood by the skilled person, the porosities of each of the layers L1 , L2, L3 and L4 may vary over a range of about 6%, still being understood as substantially equal porosities.
Layer L1 is a layer provided out of metal fibers of a bundle-drawn, melt extracted or coil shaved (machined) type having a FECRALLOY® composition or equivalent heat-resistant composition having an equivalent diameter ranging from 20 μm to 70 μm, e.g. 35μm. The layer has a thickness of e.g. 37 mm. The Layer L1 is a non-sintered metal fiber layer.
Layer L2 is a layer provided out of metal fibers of a bundle-drawn, melt extracted or coil shaved (machined) type having a FECRALLOY® composition or equivalent heat-resistant composition type having an equivalent diameter ranging from 15 μm to 30 μm but being lower than the diameter of layer L1 , e.g. 22μm. The layer has a thickness of 37 mm. Layer L2 is a non-sintered metal fiber layer.
Layer L3 is a layer provided out of metal fibers of a bundle-drawn, melt extracted or coil shaved (machined) type having a FECRALLOY® composition or equivalent heat-resistant composition type having an equivalent diameter ranging from 10 μm to 25 μm but being lower than the diameter of layer L2, e.g. 17μm. The layer has a thickness of e.g. 37 mm. Layer L3 is a non-sintered metal fiber layer.
Layer L4 is a layer provided out of metal fibers of a bundle drawn type having an equivalent diameter ranging between 5 μm and 20 μm but being lower than the diameter of the fibers in layer L3, e.g. 12 μm. The layer has a thickness of e.g. 37 mm. Layer L4 is a non-sintered metal fiber layer.
Layer L5 is a layer provided out of metal fibers of a bundle-drawn type having an equivalent diameter ranging from 4 μm to 15 μm but being lower than or equal to the diameter of layer L5, e.g. 8μm. The layer has a thickness of e.g. 0.5 mm. Layer L5 is a sintered metal fiber layer. The embodiments of Fig. 1 and Fig. 2 may be dimensioned so that they can fit into the volumes occupied by existing ceramic filters. Other examples of thickness configurations are for the embodiments as shown in Fig. 1 : 80 mm/40 mm/23 mm/0.5 mm or 140 mm/70 mm/44 mm/ 0.5 mm, wherein the thicknesses correspond with the layers L1/L2/L3/L4. Other examples of thickness configurations are for the embodiments as shown in Fig. 2: 75 mm/38 mm/20 mm/10 mm/ 0.5 mm or 134 mm/67 mm/35 mm/ 18 mm/ 0.5 mm wherein the thicknesses correspond with the layers L1/L2/L3/L4/L5.
According to another embodiment of the present invention, as shown in Fig. 3, a diesel soot particulate filter medium 300 has an inflow side 3100 and an outflow side 3200. The diesel soot particulate filter medium 3000 comprises up to 12 consecutive layers Lx of filter media, with x varying from 1 to 12. In Fig. 3, these layers are indicated as L3001 , L3002, L3003, L3004, L3005, L3006, L3007, L3008, L3009, L3010, L3011 and L3012, and represent respectively L1 , L2, L3, L4, L5, L6, L7, L8, L9, L10, L11 and L12. The layer L1 provides the inflow side 3100 of the diesel soot particulate filter medium 3000, the layer L12 provided the outflow side 3200 of the diesel soot particulate filter medium 3000. Each of the layers has a porosity, and is provided out of metal fibers having an equivalent diameter as shown in table 1. Each of the layers is either sintered or not, as indicated in table 1. All layers are provided out of metal fibers, which fibers are obtained by using a production method as indicated in table 1 , the metal having a FECRALLOY® composition alloy Table 1
wherein
(1 ) = bundle-drawn, melt extracted or machined
(2) = bundle-drawn
Another suitable configuration is given in Table 2.
Table 2
(1 ) = bundle-drawn, melt extracted or machined
(2) = bundle-drawn
The diesel soot particulate filter medium 3000 comprises 'm' being three layers, i.e. L3, L6 and L9, which layers are not the first layer L1 nor the last layer L12. For L3, L6 and L9, the porosity of each of these three layers is smaller than the porosities of its neighbouring layers, being respectively L2 and L4, L5 and L7, and L8 and L10. The layers L3, L6 and L9 all have an equal porosity of 85%, and all these layers are sintered layers.
The other layers, which are not L3, L6, and L9, nor the last layer L12, are not sintered.
Between each pair of consecutive layers L3, L6 and L9, this is between
L3 and L6, and between L6 and L9, an identical number of layers q, hereafter called intermediate layers, are located. More in particular, q is equal to two; this means two intermediate layers are located between each pair of consecutive layers.
Between each pair of consecutive layers L3, L6 and L9, an identical, decreasing gradient of the porosity ΔP is provided over the q intermediate layers, ΔP decreasing in the flow direction of the gasses to be filtered. The identical gradient of the porosity ΔP is a porosity difference of 12%, divided as: • a decrease of 4% between the first and the second of the two intermediate layers, this is between L4 and L5, and between L7 and L8; • a decrease of 8% between the second of the two intermediate layers and the layer L6 or L9 as the case may be, this is between L5 and L6, and between L8 and L9.
Between the inflow side 3100 of the medium 3000, being provided by layer L1 , and the layer of the group L3, L6 and L9 being located closest to the inflow side, this is layer L3, again 2 layers are located, being the layers L1 and
L2. This means that between inflow side 3100 of the medium 3000, and layer
L3, t layers are provided, for which t is equal to q.
A porosity gradient is provided over the layers between inflow side 3100 and the first of the layers L3, L6 and L9, being identical to the porosity gradient ΔP over the intermediate layers between each pair of consecutive layers L3, L6 and L9.
Between the layer L12 providing the outflow side 3200 of the medium
3000, and the layer of the group L3, L6 and L9 being located closest to the outflow side, this is layer L9, again 2 layers are located, being the layers L10 and L11. This means that between layers L12 providing the outflow side 3200 of the medium 3000 and L9, s layers are provided, for which s is equal to q.
Between each pair of consecutive layers L3 and L6, and L6 and L9, the layers in between comprises fibes having the same equivalent diameter as the layer of the pair closest to the outflow side, i.e. closest to L12.lin particular, this means that the layers between L3 and L6, i.e. L4 and L5 comprises fibers having the same equivalent diameter as L6. The layers between L6 and L9, i.e. L7 and L8 comprises fibers having the same equivalent diameter as L9. Similarly, between L1 and L3, and between L9 and L12, the layers are provided from fibers having en equivalent diameter equal to the layer of the pr closest to the outflow side, i.e. L2 has the same equivalent diameter as L3, and L10 and L11 comprises fibers having an equivalent diameter equal to the equivalent diameter of the fibers of L12.
For at least one, and in particular for each pair of consecutive layers L3 and L6, and L6 and L9, the layer of this pair being located between L1 and the other layer of this pair, the equivalent diameter of the fibers in the layer of this pair being located between L1 and the other layer of this pair is larger than the equivalent diameter of the fibers in the outer layer of this pair. More particular here, the equivalent diameter of the fibers in the L3, being located between L1 and L6 is larger than the equivalent diameter of the fibers in layer L6. The equivalent diameter of the fibers in the L6, being located between L1 and L9 is larger than the equivalent diameter of the fibers in layer L9. The embodiment of Figure 3 is particularly suitable for diesel soot particulate filter in trucks and buses. This embodiment has the particular advantage that the gas flow may be accelerated consecutively with each number of layers with a different diameter. This promotes the Browse movement in order to enhance the capture of diesel soot. It is to be understood that although preferred embodiments, specific constructions and configurations, as well as materials, have been discussed herein for devices according to the present invention, various changes or modifications in form and detail may be made without departing from the scope and spirit of this invention.

Claims

1.- A diesel soot particulate filter medium having an inflow side and an outflow side, said diesel soot particulate filter medium comprising at least n consecutive layers Lx of fiber media, x varying from 1 to n, n being more than 2, L1 providing the inflow side of said diesel soot particulate filter and Ln providing the outflow side of said diesel soot particulate filter medium, each layer Lx having a porosity Px, characterised in that all layers Lx, for which 1<x≤n-1 , have a substantially equal porosity to Ph, layer Ln having a porosity Ps, said Ph being larger than Ps.
2.- A diesel soot particulate filter medium as in claim 1 , wherein said fiber media comprises metal fibers.
3.- A diesel soot particulate filter medium as in claim 2, wherein said fiber media consists of metal fibers.
4.- A diesel soot particulate filter medium as in any one of the claims 2 to 3, wherein said metal fibers are bundle drawn metal fibers.
5.- A diesel soot particulate filter medium as in any one of the claims 1 to 4, wherein Ln is a sintered layer.
6.- A diesel soot particulate filter medium as in any one of the claims 1 to 5, wherein layers Lx for which 1<x≤n-1 are non sintered layers.
7.- A diesel soot particulate filter medium as in any one of the claims 1 to 6, wherein said Ph is more than or equal to 93%, said Ph is less than or equal to 98%.
8.- A diesel soot particulate filter medium as in any one of the claims 1 to 7, wherein said Ps is more than or equal to 70%, said Ps is less than or equal to 87%.
9.- A diesel soot particulate filter medium having an inflow side and an outflow side, said diesel soot particulate filter medium comprising at least n consecutive layers Lx of fiber media, x varying between 1 and n, n being more than 3, L1 providing the inflow side of said diesel soot particulate filter and Ln providing the outflow side of said diesel soot particulate filter medium, each layer Lx having a porosity Px1 characterised in that for at least m layers Lxι, 1<i<m, m being at least 1 and m being less than n/2, LXJ being different from Ln and LXJ being different from L1 , PXJ is smaller than its neighboring layers.
10.- A diesel soot particulate filter medium as in claim 9, wherein said fiber media comprises metal fibers.
11.- A diesel soot particulate filter medium as in claim 10, wherein said fiber media consists of metal fibers.
12.- A diesel soot particulate filter medium as in any one of the claims 10 to
11 , wherein said metal fibers are bundle drawn metal fibers.
13.- A diesel soot particulate filter medium as in any one of the claims 9 to 12, wherein all layers Lxi have an equal porosity Ps.
14.- A diesel soot particulate filter medium as in claim 13, wherein said Ps is more than or equal to 70%, said Ps is less than or equal to 87%.
15.- A diesel soot particulate filter medium as in any one of the claims 13 to 14, wherein Pn is equal to Ps.
16.- A diesel soot particulate filter medium as in any one of the claims 9 to 15, wherein Pn is smaller than Pn-1.
17.- A diesel soot particulate filter medium as in any one of the claims 9 to 16, wherein layers Lxι are sintered layers.
18.- A diesel soot particulate filter medium as in any one of the claims 9 to 17, wherein layer Ln is a sintered layer.
19.- A diesel soot particulate filter medium as in any one of the claims 9 to 18, wherein said layers other than layers Lx1 and Ln are non-sintered layers.
20.- A diesel soot particulate filter medium as in any one of the claims 9 to 19, wherein between each pair of consecutive layers LXJ of said m layers, m being at least 2, an identical number q of intermediate layers are located.
21.- A diesel soot particulate filter medium as in claim 20, wherein q is larger than i .
22.- A diesel soot particulate filter medium as in claim 21 , wherein for all pairs of consecutive layers LXJ of said m layers, a substantially identical gradient of porosity ΔP is provided over said q intermediate layers.
23.- A diesel soot particulate filter medium as in claim 22, wherein said gradient of porosity ΔP is substantially zero.
24.- A diesel soot particulate filter medium as in claim 22, said gradient of porosity ΔP is a decreasing gradient in flow direction.
25.- A diesel soot particulate filter medium as in any one of the claims 22 to
24, wherein for the number of layers s, located between the inflow side of said medium and LXJ being located closest to the inflow side, s is equal to said number q of intermediate layers.
26.- A diesel soot particulate filter medium as in claim 25, wherein gradient of porosity over said s layers is identical to said gradient of porosity ΔP.
27.- A diesel soot particulate filter medium as in any one of the claims 22 to 26, wherein for the number of layers t, located between Ln and LXJ being located closest to the outflow side, t is equal to said number q of intermediate layers.
28.- A diesel soot particulate filter medium as in claim 27, wherein gradient of porosity over said t layers is identical to said gradient of porosity ΔP.
29.- A diesel soot particulate filter medium as in any one of the claims 9 to 28, wherein said layers other than layers LXJ and Ln have a porosity more than or equal to 93%, said layers other than layers LXJ and Ln have a porosity less than or equal to 98%.
30.- A diesel soot particulate filter medium as in any one of the claims 1 to 29, wherein the fibers of each of said layers Lx have an equivalent diameter
Dx, for all layers Lx, for which 1<x≤n-1 , Dx≥Dx+1.
31.- A diesel soot particulate filter medium as in any one of the claims 1 to 30, wherein at least one of the layers comprises a catalyst .
32.- A diesel soot particulate filter medium as in any one of the claims 1 to 31 , wherein said filter medium further comprises metal foam layers of porous medium layers out of hollow metal spheres.
EP06818902A 2006-01-09 2006-11-29 A diesel soot particulate filter medium Withdrawn EP1979066A1 (en)

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