DE602004003975T2 - CONVERTER FOR EXHAUST GASES FROM INTERNAL COMBUSTION ENGINES - Google Patents

Description

The The invention relates to a converter for internal combustion engines and in particular a device for the oxidation of the exhaust gases of these engines can be used.

It It is known that the exhaust gases of internal combustion engines did not completely oxidize Contain gases such as CO and unburned hydrocarbons, wherein These gases are a cause for Pollution and current regulations are the use of systems for eliminating these emissions, which are to be completed the combustion of these gases are arranged after the engine, for example through converter, demand.

in the U.S. Patent 5,294,411 is an apparatus for treating exhaust gases discloses a honeycomb structure wound up like a spiral includes a catalytically active continuous surface has a ceramic or metallic substrate and in which the flow of exhaust gases follows linear paths, flowing through a multitude of channels formed by the structure itself, all parallel to each other and to this flow direction. A device of this type has essentially two problems: first is the for the total area available for contact with the gases, the the development of the spiral structure corresponds, not particularly large, and the relationship from volume of the device to the geometric surface on which the catalyst is spread is not advantageous; and secondly is the strictly linear geometry of the channels such that the gas flow Due to the structure is predominantly laminar, which is not optimal utilization of the catalyst allowed.

In Patent Application WO 97/02092 is an apparatus for treatment disclosed by exhaust gases, which consist of a perforated sheet metal or a metal grid is obtained, on which a preferably made of alumina or zirconia porous ceramic Layer was applied, then with a solution or Suspension of a catalyst precursor waterproof has been. Also in this case, however, is the available catalytic surface not very large, therefore the conversion efficiency is limited. That's why The invention is based on the object, a converter for exhaust gases to provide that is free of these disadvantages.

These Task is by a converter for the exhaust gases of internal combustion engines solved, which a housing comprising, with at least one inlet opening for the exhaust gases to be converted and with at least one outlet opening for the converted gases and contains a conversion system, characterized characterized in that the conversion system comprises a plurality of plates Fiber includes a metal core made with a layer of Oxides coated is on which catalytically active metals are present, wherein the plates are arranged so that they are substantially parallel to each other with an edge to the inlet opening and another edge to the outlet opening are directed and metallic spacers from each other be kept at a distance.

The with catalysts functionalized metallic inventive Plates have a contact surface, the opposite the perforated plates and metal grids of the known devices is significantly enlarged. About that In addition, the arrangement according to the invention causes the plates and Spacer comprises, such a turbulent gas flow in the converter, that the gas is on its way between the inlet and the outlet is forced to flow at least partially through these plates. By these features will be the contact between the gas stream and the catalyst and consequently the conversion efficiency, in particular the oxidation, of the converter according to the invention considerably improved.

The Advantages and features of the converter according to the invention will become apparent to those skilled in the art with reference to the following specific and not limiting the invention Description of some embodiments with reference to the attached drawings, wherein

1 an exploded view of a converter according to the invention,

2 a perspective view of a metal fiber plate used in the invention and

3 a cross section through a fiber from which the plate of 1 is constructed, shows and the

4 to 7 Details of the conversion system according to the invention show and

8th a preferred inventive conversion system shows.

In 1 is an exploded view of a converter according to the invention 10 shown a conversion system 11 includes a variety of plates 12 includes, wherein the converter 10 in a known manner, a housing 13 with at least one inlet opening 14 for the exhaust gases to be treated coming from an internal combustion engine and at least one outlet opening 15 for those of the system 11 treated gases. The plates are preferably of (not shown in this figure th) metal elements 16 surrounding, which form a frame, which is attached to the plate edges by any suitable means, for example by mechanical crimping, which helps to the flatness of the plate 12 to maintain heat cycles (both in the heat treatments for oxidizing and functionalizing the plates and in the post-engine operation heat cycles) and to avoid fiber losses at the plate edges. The converter 10 can be around the perimeter of the outlet opening 15 comprise a flange (not shown in this figure).

According to the invention, the system comprises 11 a variety of plates 12 , which are held by metallic spacers at the desired distance. It has been found by the inventors that good results are obtained if this distance is maintained in a range of between about 1 and 4 mm. At a distance of less than 1 mm, the plate pack becomes too dense and the system becomes too small 11 causes too high a drop in gas pressure. On the other hand, too great a distance has the disadvantage that the number of plates of the type 12 and thus reducing the catalytic surface active in the gas treatment; In addition, if the distance between the plates is too large, the effect of generating a turbulent motion in the gas flow is reduced and at least a portion of the gas can pass through the system 11 flow without being on the plates of the kind 12 arranged catalyst to come into contact. Optimum values of the distance between adjacent plates are in the range of between about 2 and 3 mm.

In 2 is a plate used in the system according to the invention 12 in the framing metal elements 16 comprehensive preferred embodiment shown. This plate is a mat of metallic fibers that have generally been adhered to each other by sintering. These fibers may contain steel or, preferably, an alloy containing iron, chromium and aluminum plus small percentages of other elements, and as Fecralloy ^® (registered trademark of UKAEA, Didcot, Great Britain) is known to be produced. It has been found that this alloy is particularly suitable for long-term use at high temperatures, such as uses intended for catalytic converters or filters for internal combustion engines. Plates made of Fecralloy ^® fibers can be obtained from the company NV Bekaert SA, Zwevegem, Belgium, which markets it under the name Bekipor ^®; these plates can be shaped according to different geometries and adapted to different uses.

In 3 is in cross-section one for the production of the plate 12 shown fiber used (here, the parts of the fiber not to scale), wherein in the figure, a fiber with a rectangular cross-section is shown, as the most typical form of Fecralloy ^® fibers, although the fibers of course also have a different cross section, for example a circular, can have. fiber 30 comprises a Fecralloy ^® core 31 that with a layer 32 coated with oxides, which is the catalyst 33 wearing. The oxide layer is generally multi-layered and composed of two or three oxide layers, each differing in chemical composition or physical properties. A first oxide layer 32 ' ^® is on the surface of the Fecralloy fibers were allowed to grow by a high temperature treatment in an oxidizing atmosphere, wherein the oxide layer formed by this treatment mainly of alumina whiskers having a length of generally from 0.5 to 5 micrometers (microns) depending on treatment time and temperature and the whiskers preferably have a length of less than 3 microns. The oxide forming this whisker is generally very dense and uniform. The subsequent process step consists in the formation of a second oxide layer 32 '' on the first. This second oxide layer, unlike the first, is porous and has a large specific surface area; it may again consist of alumina or of another oxide. The second oxide layer can be prepared by spraying a solution of a precursor compound of the oxide or by dipping the mat of sintered metallic fibers into this solution, followed by thermal decomposition of the precursor. Alternatively, the second oxide layer may be prepared by dipping the mat in a liquid suspension of precursor particles and then calcining. Optionally, a third layer 32 ''' of oxides on the second oxide layer forms GE. This layer also has a large specific surface area. The optional layer 32 ''' It consists generally of a cerium-zirconium mixed oxide (with optional addition of lanthanum) and has the property of limiting the sintering of the catalytic metals, thereby ensuring their dispersion over time and thus helping to maintain high efficiency of the converter, as well to represent an oxygen supply for the oxidation of the unburnt gases leaving the engine.

The outer oxide layer (either 32 '' or 32 ''' ) is an optimum support for catalytic metals due to its porous structure, it ensures the dispersion of the metal and its good anchoring on the fiber surface. The functionalization of the oxide layer with the catalyst 33 is required for the intended use of the fiberboard. The catalyst is preferably composed of one or more precious metals selected from those of the eighth group of the periodic table or their Ver are selected, wherein the use of platinum is preferred.

In 4 is a partial exploded view of a first possible embodiment of the system according to the invention 11 shown. In this embodiment, the system includes 11 a superposition of plates 12 that deal with metal sheets 40 alternate (only two plates and a metal sheet are shown; and metal elements of the type 16 are not shown), these sheets having a plurality of protrusions 41 . 41 ' , ..., which rise from both sides of a sheet. These projections all have the same height so that they provide a plurality of contact points on which two plates 12 (one per side of the sheet 40 ) can lie. The sheets 40 are made of high temperature resistant metals; Preferably, these sheets from the same Fecralloy ^®, which for producing the fibers of the plates 12 has been used. These sheets are generally as thin as possible and suitable for the necessary mechanical resistance at high temperatures, with optimum thicknesses of 0.15 to 0.45 mm.

In 5 is in one of the 4 similar view of a slightly different embodiment of the system 11 shown, in which case (to the sheets 40 analogous) sheets 50 next to protrusions 51 . 52 ' , ..., a variety of holes 52 . 52 ' , ..., and this arrangement in enhancing the turbulence of the flow of the gas as it passes through the system 11 supports, reducing the efficiency of contact of the gas with the plates 12 and consequently the efficiency of the system 11 is increased in the gas treatment, in 5 the holes are shown circular, but their shape can be essentially any. In a system 11 , the sheets of the type 50 It is preferred that the holes occupy no more than 50% of the surface area of the sheet so as not to cause any design problems in it when the system 11 works at high temperatures.

More preferable is the case where bumps and openings coincide. 6 is an example of this embodiment. In this case, the sheet has 60 holes 61 by partially cutting in the sheet, creating "flaps" 62 have been obtained, which are connected along at least one edge to the sheet, and bent the "flaps" along this edge wor formed, the dimensions of the "flaps" and their bending angle with respect to the sheet plane, the distance between the surface of sheet metal 60 and those of the adjacent plate 12 determine so that these "flaps" form the spacers in this embodiment, and 6 rectangular "flaps" (and openings), but of course any other suitable shape can be used. The cuts in the sheet metal 60 by which these "flaps" are formed may be attached by mechanical shearing, laser cutting or any other known method.

The various types of systems described so far 11 are preferably inserted into a metal box which surrounds the system on all sides except on the inlet and outlet sides, and in turn into the housing 13 is installed, preferably between this metal box and the housing 13 ceramic fiber boards are arranged for reasons of thermal insulation.

In 7 is a plate 12 shown for a still further embodiment of the system according to the invention 11 can be used, for clarity of illustration in this figure, the assembly of the plate is shown with only a few spacers. In this case, the spacers 70 Metal sheets with a geometric surface that forms a small part of the geometric surface of the sheets 12 (unlike the sheets 40 . 50 and 60 ) and wound in such a way that the points of contact with the adjacent plates are curved and smooth. The spacers 70 are held in place by countries (for example by spot welding) on Metallbän countries 71 be as narrow as possible and meet the requirements of being mechanically strong enough and a sufficient surface for the attachment of the spacers 70 to offer. In turn, the metal bands 71 held in place by (for example, again by spot welding) to two metal elements of the type 16 be attached by crimping on the two side edges of the plate 12 (in relation to the direction of the gas flow in the converter 10 , which is indicated by the arrow), while the other two elements of the type 16 (those who are in front of the inlet 14 and the outlet 15 the converter 10 can be connected to the plate before the thermal oxidation treatments of the fibers, wherein the two lateral elements of the type 16 the plate 12 better be added at the end of their production to prevent their oxidation and for the tapes 71 to ensure good welding properties. On the other side of the plate 12 are more spacers of the kind 70 not shown in the figure, with the spacers on all the plates of the converter system preferably arranged in the same positions so that by superposing a plurality of plates, the spacers form a kind of pillar with the overall effect of reinforcing the structure ,

In 8th is an exploded view of the preferred assembly of the system 11 shown when spacers of the type 70 are used, for reasons of clarity in this figure, no spacers are shown. In this case, it has been found that, to ensure the mechanical stability of the system, the panels fit better in two lateral retention means 80 . 80 ' be inserted with the shape of a meander.

The plates 12 can in the holding means 80 . 80 ' by mechanically crimping sections of the meander onto the lateral elements of the type 16 where the same elements are the bands 71 wear, be fastened. The assembly, which is made up of plates and holding means, turns into a metal box 81 inserted, which surrounds the four parallel to the gas flow sides of the assembly, but is open on the inlet and the outlet side. This arrangement leaves, the system 11 is bypassed, possible passages 82 for gases released, so from the outlet 15 emerge untreated. To avoid this danger, the passages become 82 filled with a high temperature resistant adhesive (not shown in the figure) which normally comprises a metal powder (eg, steel powder) in an inorganic binder, a suitable adhesive being Durabond 954, marketed by COTRONICS Corp. of Brooklyn, NY (USA). The assembly is completed by placing its back and its front each with a frame 83 . 83 ' This is to ensure that no passages are left for engine-sourced gases from the system 11 could bypass, with the framework 83 . 83 ' with front and back elements of the type 16 the plates 12 , the ends of the retaining means 80 . 80 ' and maybe the box 81 , again by gluing, be connected.

Of the converter according to the invention, by including plates made of metal fibers is special for one as close as possible Arrangement on the engine suitable (a configuration that is in the art as "Close Coupled Catalyst "or CCC known is), i. in the position in which it is ensured that the converter operates at maximum temperature, creating a high Conversion efficiency is obtained. Again, the Converter according to the invention due to its metallic construction sudden temperature changes endure, like those in modern systems for elimination expected from internal combustion engines pollutants are expected. Especially In the case of diesel engines, what is critical is the so-called "post-injection phase" resulting from injection of the fuel in the cylinders when they are in the exhaust stroke are located (exhaust valves are open) and so the fuel is not ignites in the cylinder, but unburned reaches the CCC converter, where he due to whose high temperature is catalytically oxidized. Thus, the the CCC leaving gases a very high temperature and can on the actual filter (known in the art as "diesel soot particulate filter" or DPF) burn accumulated particles, thereby enabling its regeneration; an example of one DPF filter is in Italian patent application MI2003A002211 the patent applicant described.

One Another important advantage, the converter system according to the invention offers, is the low weight of the carrier material compared with The honeycomb converter systems of the prior art, the same Occupy volume (and thus about the same amount of catalytic Metals and have substantially the same conversion efficiency). Various types of converter systems according to the invention are produced by the inventors as determined by measuring their weight and volume is that they have an average weight of 0.28 grams per cubic centimeter of the system; In contrast, revealed a similar one Measurement with prior art systems an average weight of about 0.62 grams per cubic centimeter. Apart from a lower ren Total weight (which is already an advantage in itself), this means the big one Advantage of a lower thermal inertia, so the systems of the invention the high temperatures at which the catalyst has the best properties own, reach faster, which mitigates the "cold start problem".

Claims (15)

Converter ( 10 ) for the exhaust gases of internal combustion engines, which a housing ( 13 ), which is provided with at least one inlet opening ( 14 ) for the exhaust gases to be converted and with at least one outlet ( 15 ) is provided for the converted gases and a conversion system ( 11 ) characterized in that the conversion system comprises a plurality of disks ( 12 ) of fibers ( 30 ) comprising a metal core ( 31 ), with a layer ( 32 ) is coated on oxides on which catalytically active metals ( 33 ) are arranged, wherein the plates are arranged so that they are directed substantially parallel to each other with an edge to the inlet opening and another edge to the outlet opening and of metallic spacers ( 41 . 41 '; 51 . 51 '; 62 ; 70 ) are kept apart from each other. A converter according to claim 1, wherein the core ( 31 ) from the fibers ( 30 ) made of an alloy containing iron, chromium and aluminum and coated with a multilayer ( 32 ) is covered by oxides comprising a first layer ( 32 ' ) of alumina, which is in contact with the alloy, a second oxide layer ( 32 '' ) and optionally a third layer ( 32 ''' ) of cerium, zirconium and optionally lanthanum oxide. Converter according to claim 2, wherein the multilayer ( 32 ) with one or more catalysts ( 33 ) selected from the precious metals of the eighth group of the periodic table or their compounds. Converter according to claim 3, wherein the catalyst made of platinum. Converter according to claim 1, wherein the conversion system ( 11 ) of metal elements ( 16 ) surrounded plates ( 12 ) is made. Converter according to claim 1, wherein the distance between two adjacent plates ( 12 ) of the conversion system ( 11 ) Is 1 to 4 mm. Converter according to claim 1, wherein the distance between two adjacent plates ( 12 ) of the conversion system ( 11 ) Is 2 to 3 mm. Converter according to claim 1, wherein the conversion system ( 11 ) an alternating superposition of plates ( 12 ) and on both sides projections ( 41 . 41 ' ) having metal sheets ( 40 ). Converter according to claim 1, wherein the conversion system ( 11 ) an alternating superposition of plates ( 12 ) and metal sheets ( 50 ) and these sheets projections ( 51 . 51 ' ) on both sides and holes ( 52 . 52 ' ), which allow passage of the gases to be converted from one side of the sheet to the other. A converter according to claim 9, wherein the projections and the holes coincide and by inserting cuts in the sheets ( 60 ), whereby flaps ( 62 ), which are connected along at least one edge to the metal sheet, and bending of the flaps along this edge, whereby the holes ( 61 ) have been formed. Converter according to claim 5, wherein the conversion system ( 11 ) a stack of plates ( 12 ), which is at the desired spacing of spacers ( 70 ), which are metal sheets having a geometric area smaller than that of the plates, and which have been wound so that the points of contact with the adjacent plates are curved and smooth. Converter according to claim 11, wherein the spacers ( 70 ) in their place by attachment to metal strips ( 71 ), which in turn can be held by attachment to two metal elements surrounding the plate ( 16 ) are held in their place. Converter according to claim 12, wherein the two metal elements ( 16 ) are those at the parallel to the gas flow in the converter sides of the plate. Converter according to Claim 13, in which the sides of the plate which are parallel to the gas flow in the converter are formed by two lateral holding means ( 80 . 80 ' ) are held in the shape of a meander consisting of plates ( 12 ) and holding means ( 80 . 80 ' ) constructed unit in a metal box ( 81 ) which surrounds the four sides of the unit parallel to the gas flow in the converter but is open on the inlet and outlet sides, the passages (FIG. 82 ) between the holding means ( 80 . 80 ' ) and the box ( 81 ) are filled with a high temperature resistant adhesive and two metal frames ( 83 . 83 ' ) with the front and back surrounding elements ( 16 ) of the plates ( 12 ), the ends of the holding means ( 80 . 80 ' ) and optionally the box ( 81 ) are connected. Converter according to one of the preceding claims, wherein the conversion system ( 11 ) in a box ( 81 ) installed in the housing ( 13 ) of the converter ( 10 ) is arranged, wherein between the box and the housing ceramic plates are inserted.