EP0386013A1

EP0386013A1 - Catalyzer with flow guiding body.

Info

Publication number: EP0386013A1
Application number: EP88907684A
Authority: EP
Inventors: Wolfgang Maus; Helmut Swars
Original assignee: Emitec Gesellschaft fuer Emissionstechnologie mbH
Current assignee: Vitesco Technologies Lohmar Verwaltungs GmbH
Priority date: 1987-10-02
Filing date: 1988-08-23
Publication date: 1990-09-12
Anticipated expiration: 2008-08-23
Also published as: EP0386013B1; US5150573A; JPH0791972B2; ES2009047A6; DE3733402A1; US5103641A; RU1839696C; DE3866244D1; WO1989002978A1; JPH02502110A

Abstract

Un agencement catalyseur, notamment pour moteurs à combustion interne, comprend un diffuseur qui s'élargit dans le sens de l'écoulement, en amont d'un corps catalyseur (23) en nid d'abeille, un convergeur (25) qui se rétrécit dans le sens de l'écoulement en aval du corps catalyseur (23) et au moins un corps de guidage de l'écoulement installé dans le diffuseur et/ou dans le convergeur. Afin d'assurer un afflux uniforme de la face frontale du corps catalyseur (23) sans étrangler trop fortement le courant de gaz d'échappement, on installe au moins dans le diffuseur un corps de guidage de l'écoulement (24) formé d'une pluralité de canaux adjacents et/ou concentriques qui présentent au moins en partie une section transversale croissante dans le sens de l'écoulement. Les canaux individuels présentent de préférence un angle d'ouverture alpha qui empêche un décollage de courant des parois des canaux individuels. Le corps de guidage de l'écoulement peut en outre être enduit d'une couche d'un matériau catalyseur actif, ce qui permet d'utiliser le volume du diffuseur, éventuellement du convergeur lui aussi, pour agencer des surfaces actives de catalyse, et d'améliorer entre autres, outre l'afflux du corps catalyseur principal (23), les propriétés de démarrage à froid de l'agencement catalyseur.A catalyst arrangement, in particular for internal combustion engines, comprises a diffuser which widens in the direction of flow, upstream of a honeycomb catalyst body (23), a convergent (25) which narrows in the direction of flow downstream of the catalyst body (23) and at least one flow guide body installed in the diffuser and / or in the converger. In order to ensure a uniform inflow of the front face of the catalyst body (23) without excessively throttling the flow of exhaust gas, at least one flow guide body (24) is formed in the diffuser. a plurality of adjacent and / or concentric channels which at least partly have an increasing cross section in the direction of flow. The individual channels preferably have an alpha opening angle which prevents current takeoff from the walls of the individual channels. The flow guide body can also be coated with a layer of active catalyst material, which makes it possible to use the volume of the diffuser, possibly also of the converger, to arrange active catalysis surfaces, and to improve inter alia, in addition to the inflow of the main catalyst body (23), the cold start properties of the catalyst arrangement.

Description

Catalyst arrangement with flow guide

The present invention relates to a catalyst arrangement, in particular for internal combustion engines, according to the preamble of claim 1 and a method for its production.

Such a catalyst arrangement is known for example from DE-A-34 30 399 or DE-A-34 30 400. Most conventional catalyst arrangements contain a honeycomb-like catalyst body with a multiplicity of parallel channels, which can either consist of a ceramic base material or of structured metal sheets. Because the usual

Exhaust pipes have a much smaller cross-section than a catalyst body, a conically widening diffuser section is usually arranged in front of each catalyst body and, correspondingly, a confusing section is arranged behind the catalyst body as a transition to the normal exhaust pipes.

A known problem with catalyst arrangements now consists in that the flow of the catalyst body is not uniform over its entire cross-sectional area, so that flow guide bodies, for example, are used for uniform utilization.

From DE-A-35 36 315 it is also known to use * flow guide bodies which generate a flow swirl in front of the catalyst body.

From DE-C-34 17 506 two divided catalyst bodies with different cross sections are also known, which allow adaptation to different installation conditions. Two-stage catalyst bodies are also known from DE-A-30 12 132 in order to achieve optimally matched conditions to the respective combustion exhaust gases.

Finally, from DE-OS-23 13 040 a catalyst body is known, which is made slightly conical for manufacturing reasons by being pressed into a slightly conical housing.

However, the problem of a uniform flow against the front of a catalyst body is still not satisfactorily solved in the case of catalyst arrangements. All known devices act like throttles in the exhaust gas flow and thus undesirably increase the exhaust gas back pressure, which affects the efficiency of the engine. Also, the known flow guide bodies still cannot achieve a uniform flow against the catalyst body. In addition, the space required for the diffuser or confuser cannot be optimally used.

The object of the present invention is therefore to create a catalytic converter arrangement which has an optimal flow against the

Catalyst body causes. In addition, the utilization of the volume required for the diffuser and the confuser is to be improved or this volume is to be reduced. Finally, a better light-off behavior of the catalyst should also

Cold start can be achieved.

To solve these problems, a catalytic converter arrangement according to the characterizing features of claim 1 is proposed. Flow guide bodies according to the invention can be used both in the diffuser and in the confuser. The open cross-sectional area of the flow guide body must increase in the diffuser, and it must decrease in the confuser, so that such a flow guide body only has to be arranged upside down. In the following, therefore, only the Flow guide considered in the diffuser, although all

Unless expressly stated otherwise, information also applies to the reverse arrangement in the confuser.

A flow guide body, which consists of a plurality of at least partially conically widening channels, can direct the flow much more uniformly onto the entire end face of a catalyst body than known arrangements can. The pressure loss caused by the flow guide remains relatively small, in some cases even below the pressure loss that a diffuser without a flow guide would cause. Flow guide bodies according to the invention are therefore honeycomb bodies, the individual channels of which, however, do not run parallel but at angles to one another and which overall have a cross section which increases in the flow direction. The shape of such honeycomb bodies must of course be adapted to the shape of the cross-sectional area of the catalyst body, so that, in addition to truncated cone shapes, flattened shapes are also possible.

Advantageous embodiments of the invention are specified in the subclaims and are explained in more detail below and with reference to the drawing.

A difficulty of the present invention lies first of all in the fact that the manufacturing techniques customary for catalyst bodies are not readily applicable to conical honeycomb bodies. Neither can conical bodies with conically widening channels be made from the usual nozzles with ceramic mass, nor can they be wound spirally out of sheet metal strips without problems. When manufacturing from metal sheets, as they are preferably used for catalyst bodies, new forms and manufacturing methods must therefore be found. The problem is that for the spiral winding of conical bodies, for example from alternating layers of smooth and corrugated sheets, there is no straight line Sheet metal strips are required, but sheet metal strips with a radius of curvature that decreases from layer to layer. The production of such metal strips is possible in principle, but not necessarily advantageous in terms of production technology. On the other hand, it should be noted that the flow guide only has to have a much smaller number of channels than that

Catalyst body itself, so that even relatively complicated

Manufacturing processes are still possible due to the small number of channels. Even the prefabrication of individual duct blocks and their later assembly are a possible way of producing the desired ones

Flow guide.

In any case, the manufacture of a conical flow guide body results in relatively complicated shapes and channel cross sections that differ in quantity and quality over the length. It is practically impossible to define an opening angle of the individual channels. Nevertheless, each channel has an effective opening angle, which results from its cross-sectional area at the entrance and its cross-sectional area at the exit, unless a channel at the entrance is divided into a plurality of channels at the exit, which also occurs in the present exemplary embodiments. Therefore, when the following refers to an opening angle of a channel, it means the solid angle that this channel delimits. The measure of this solid angle is the area that is cut out from this solid angle from the unit sphere around the apex as the center.

In terms of flow technology, of course, not only this opening angle but also the cross-sectional shape of the individual channels plays a role, so that a complete theoretical treatment of the various conceivable shapes is hardly possible. A decisive advantage of the flow guide body according to the invention is, however, that the individual channels can in any case have such small opening angles that the flow no longer separates from the walls. In the case of a conical diffuser, for example, the flow separates from the wall at an opening angle of approximately π / 17 and becomes turbulent. Common diffusers in catalyst arrangements have typical opening angles of ~ 2 π / 3, so that the

Flow always detaches, which leads to uneven distribution of the flow without a flow guide. For more complicated channel shapes, the separation angle must be determined empirically, but one according to the invention can be used

Always produce flow guide bodies from so many channels that the critical angle at which the flow separates from the walls is undershot. The subdivision of the diffusof into individual channels therefore reduces despite the installation of

Partitions the flow resistance in the diffuser and causes a very even distribution on the face of the

Catalyst body. If desired, even an uneven distribution of the flow, which may still be present, can even be counteracted by different opening angles of the inner and outer channels of the flow guiding body, or a desired non-uniform distribution can be targeted

Distribution over the end face of the catalyst body can be achieved.

As a result of the fact that the flow guide body has fewer channels than the catalyst body, it is possible, according to claim 2, to make the open cross-sectional areas of the individual channels of the flow guide body on the upstream side, for example, approximately the same size as the open cross-sectional areas of the channels of the catalyst body. In order to make the pressure loss at the flow guide body small, the open cross-sectional areas can even be chosen to be considerably larger there.

According to claim 3, the flow guide body and the catalyst body are to be separated by an intermediate space which swirls the exhaust gas between the flow guide body and catalyst body allows. This increases the turbulence when entering the catalyst body and thus the

Effectiveness of the catalyst.

According to claim 4 it is proposed that the opening angle of the individual channels should be smaller than the angle at which the flow separates from the walls. This measure optimizes the pressure losses caused by the flow guide body.

Alternatively, however, according to claim 5

Opening angle of the individual channels of the flow guide body can also be chosen so that turbulence is present, for example at the end of the channels, as a result of which better mixing of the exhaust gas is achieved. This configuration has particular advantages if, as mentioned below, the flow guide body is also coated with catalytically active material.

Claims 6 to 9 specify technically feasible forms of flow guide bodies according to the invention, as will be explained in more detail with reference to the drawing.

A very decisive advantage of the invention results in the configurations according to claims 10 and 11. By coating the flow guide body with catalytically active material, the total catalytically active surface available with unchanged volume is considerably increased. The volume required for the diffuser and possibly also the confuser can thus also be used for the attachment of catalytically active surfaces. The flow control function of the flow guide body is not impaired by this. Rather, the flow guide bodies also become catalyst bodies in addition to the actual catalyst body, which results in additional advantages. It has been shown in experiments that metallic catalyst carrier bodies with a small number of channels per cross-sectional area show better starting behavior than catalysts with a larger number of channels per cross-sectional area. These catalysts reach a high conversion rate more quickly on cold start, which is of considerable importance. If a flow guide body coated with catalytically active material is now connected upstream of the actual catalyst body, this can likewise significantly improve the starting properties. The catalytic reaction in the flow guide body begins earlier than that in the actual catalyst body. As a result, the reaction in the actual catalyst body may even be ignited earlier, since the exothermic reaction in the flow guide body accelerates the cold start in the actual catalyst body. In order to support this effect, the flow guide body can also be coated with a catalytically active material other than the actual catalyst body, for example with a material which in particular improves the cold start properties. Of course, this embodiment also does not apply in the same way to a catalytic coating of a flow guide body in the confuser, although a catalytically active coating also makes better use of the available volume there.

Finally, claim 12 describes a particularly preferred method for producing a flow guide body according to the invention, as will be explained in more detail with reference to the drawing.

Embodiments of the invention are shown in the drawing and show

FIG. 1 shows a typical catalyst arrangement with flow guide bodies according to the invention,

Figure 2 shows a catalyst arrangement with only one Flow guide in the diffuser,

Figure 3 is a slotted, corrugated sheet, such as

Production of flow guide bodies according to the invention is suitable,

FIG. 4 schematically shows a straightened position on the end face of a flow guide body,

FIG. 5 schematically and straightens a position on the outflow side of the flow guide body,

6 schematically shows a straightened position on the end face of a flow guide body produced differently, FIG. 7 schematically shows a straightened position on the outflow side of a flow guide body according to the invention in the central region,

Figure 8 schematically shows a straightened position in the outer area of the

Downstream side of this body,

FIG. 9 schematically shows the construction of flow guide bodies from individual prefabricated frustoconical channel modules,

Figure 10 shows schematically the structure of a flow guide body from individual prefabricated channels with a rectangular cross-section and

Figure 11 schematically shows the structure of a flow guide body of nested, concentrically arranged

Truncated cones with increasing opening angle.

FIG. 1 shows a catalyst arrangement with an inlet tube 1, an outlet tube 2, a customary honeycomb-shaped catalyst body 3, a flow guide body 4 in the diffuser and a flow guide body 5 in the confuser. Mixing gaps 6, 7 are provided between the flow guide bodies 4, 5 and the catalyst body 3.

FIG. 2 shows a catalyst arrangement consisting of an inlet pipe 21, an outlet pipe 22, a catalyst body 23 and a flow guide 24 in the diffuser, which is separated from the catalyst body 23 by a mixing column 26. This figure indicates the structure of the catalyst body from parallel channels and the structure of the flow guide body from widening in the direction of flow Channels with a room opening angle α. Basically, it is favorable if the flow guide body begins exactly at the end of the inlet pipe 21, but it may be necessary for manufacturing or fluidic reasons that the end face of the flow guide body is only slightly inside the diffuser. The schematic cross sections through catalyst arrangements shown apply equally to cylindrical or conical arrangements as well as to flattened shapes.

The following figures serve to illustrate how a flow guide body according to the invention can be produced from sheet metal, as is usually also used for metallic catalyst carrier bodies. An alternative is first illustrated in FIGS. 3, 4 and 5. The basic problem is that the overall conical flow guide body should not be created by compressing one end face, because then the ratio of open cross-sectional areas to cross-sectional areas closed by material would be very unfavorable on this end face, which considerably increases the pressure loss. For technically sensible solutions, it is therefore necessary to use specially designed sheets that produce the desired channel shapes with increasing cross-sections when assembling. According to FIG. 3, a corrugated sheet 31 is suitable for this, which. has slots 34 extending from its outflow side 33 along all or part of the troughs and / or peaks. Such a corrugated sheet 31 is first produced with as steep as possible flanks and a large amplitude. The slots 34 are then made. Now the corrugated sheet metal on its upstream side 32 can be pulled apart, as a result of which the slope and the amplitude are reduced. On the outflow side 33, the slotted sheet 34 is also pulled apart, and possibly further than on the inflow side 32. The slots 34 expand without the flanks or the amplitude changing. Wraps such a corrugated sheet 31 together with a smooth one

Sheet 35, which, however, does not have to be straight but increasingly curved, spirally on, possibly with increasing spreading of the slots 34, so a desired flow guide body with channels 36 is formed, which one in

Have flow direction increasing cross section. The

Figures 4 and 5 indicate the resulting cross-sectional shape on the

Upstream side 32 or on the downstream side 33. It became the

For the sake of simplicity, only one straightened position of a corrugated sheet 31 with two smooth sheets 35 is shown.

Another alternative for producing desired flow guide bodies is shown schematically in FIGS. 6, 7 and 8. In this exemplary embodiment, the flow guide body essentially consists of a corrugated plate 71 with a large amplitude and a corrugated plate 72 with the same wavelength and a smaller amplitude. These sheets are wound spirally, however, a narrow, smooth intermediate layer 73 is also wrapped on the outflow side, as a result of which the two corrugations cannot interlock there, resulting in a much faster growing end face than on the inflow side. In principle, the smooth intermediate layer is not a straight one. Sheet metal strip, but must have an increasing curvature, but in the case of a narrow sheet metal strip this can generally be achieved by plastic deformation. The resulting flow guide body shows on its front side a typical constellation of corrugated sheets lying one inside the other, as shown in FIG. 6 and on the outflow side in the inner region a constellation as in FIG. 7 and in the outer region a constellation as shown in FIG.

FIGS. 9 and 10 show schematically how flow guide bodies according to the invention can be constructed from individually prefabricated frustoconical channel modules 91 or from rectangular channel modules 101. Other channel cross sections are of course possible, but in addition the individual modules can also comprise entire rows of channels, not individual ones. Finally, FIG. 11 shows a further possibility of arranging a flow guide body according to the invention from nested, concentrically arranged truncated cone surfaces 111 with increasing opening angle. Such surfaces can be kept at the desired distances, for example by webs, corrugated intermediate layers or the like.

The exemplary embodiments mentioned here show only a few of many possibilities for the production of flow guide bodies according to the invention, wherein, of course, considerable variants in the sheet metal structures are possible in accordance with other known catalyst arrangements. In general, it will be advantageous to solder the sheets to one another, but other joining techniques such as gluing, welding and sintering can also be used. The flow guide body according to the invention can also have a jacket tube, as is usually the case with a catalyst body

Catalyst system then forms the confuser or is used in such.

Claims

1. Catalyst arrangement, in particular for internal combustion engines, with a diffuser widening in the direction of flow in front of a honeycomb-like catalyst body (3; 23) and an in

Confusor constricting the flow direction behind the catalyst body and at least one flow guide body in the diffuser and / or confuser, characterized by the following features: all or at least in part in the diffuser have a cross section increasing in the flow direction or in the confuser a cross section decreasing in the flow direction. b) The open cross-sectional area of the flow guide body is significantly larger on one side than on the other, for. B. more than twice as large, preferably about 4 to 6 times as large.

2. Catalyst arrangement according to claim 1, d a d u r c h g e k e n n z e i c h n e t that the open cross-sectional areas of the individual channels of

Flow guide bodies (4, 5; 24) on the side with the smaller cross-sectional areas are approximately as large as the open cross-sectional areas of the channels of the honeycomb-shaped catalyst body (3; 23), preferably even considerably larger.

3. A catalytic converter arrangement according to claim 1 or 2, characterized in that between the flow guide body (4, 5; 24) and the catalyst body (3; 23) a space serving for swirling the exhaust gas (6, 7; 26) of about 5 mm to 30 mm is present.

4. A catalyst arrangement according to claim 1, 2 or 3, characterized in that the channels of the flow guide body (4; 24), which have an increasing cross section, have opening angles (Qt) which are smaller than the angle at which the flow separates from the walls, for example in the case of simple cross sections smaller than π / 17, preferably smaller than π / 24.

5. Catalytic converter arrangement according to claim 1, 2 or 3, d a d u r c h g e k e n n z e i c h n e t that the channels of the flow guide body (4; 24) an increasing

Have cross-section, such opening angles (α) that just a turbulent flow is maintained in the channels or at the end of the channels.

6. Catalyst arrangement according to one of the preceding

Claims, characterized in that the channels, which have an increasing cross-section, are formed by alternately layered or wound smooth (35) and corrugated (31) sheets, in which the corrugated sheets (31) from the outflow side (33) approximately along the Wave crests or wave troughs are slit up to the upstream side (32) and spread out in the direction of flow, but the flanks of the corrugation on the upstream side (32) are less steep than on the downstream side (33).

7. Catalyst arrangement according to one of the preceding

Claims that the flow guide body consists of at least two corrugated elements

Sheets (71, 72) of approximately the same wavelength and significantly different amplitude is wound or layered, the corrugations on the side with less

Cross-sectional area interlock, but on the other side by an intermediate layer (73) made of a narrow, smooth

Metal strips are separated.

8. A catalyst arrangement according to claim 1, 2, 3 or 4, characterized in that the flow guide body (4, 5; 24) is composed of individually prefabricated channel modules (91; 101; 111) with increasing or decreasing cross-section, preferably of metallic modules made from sheet metal.

9. Catalytic converter arrangement according to claim 6, 7 or 8, that the plates (31, 35; 71, 72, 73) are soldered to one another at at least part of the contact points.

10. Catalytic converter arrangement according to one of the preceding claims, that the flow guide body (4, 5; 24) is coated with catalytically active material.

11. A catalyst arrangement according to claim 10, that the catalytically active material on the flow guide body (4; 24) in the diffuser is such that it improves in particular the cold start properties, ie. H. the beginning of catalytic reactions at low temperatures.

12. A method for producing a flow guide body, according to claim 5, characterized by the following steps: a) A corrugated sheet (31) with flanks that are as steep as possible is slit (34) from one side (33) along all or part of the wave crests or troughs. up to the other side (32), e.g. B. up to 10 mm. b) The sheet (31) is spread, more on the slotted side (33) than on the non-slotted (32). c) The spread sheet (31) is alternately wound or layered with a smooth sheet (35) to form a block with many channels (36) and on at least part of the Contact points connected by joining, preferably high temperature soldering.