SE542960C2 - Exhaust gas aftertreatment system - Google Patents

Abstract

The present disclosure relates to an exhaust gas aftertreatment system (4) comprising a first pipe section (11), a second pipe section (13) and a pipe fitting (15). The first pipe section has an outlet end (33) and comprises a reductant injector nozzle (17). The second pipe section has an inlet end (37) and comprises an SCR catalyst device (23). The pipe fitting is arranged to provide fluid communication between the first pipe section and the second pipe section. The pipe fitting comprises a retainer plate (25), an endcap (27) and a foraminous baffle (29). The retainer plate comprises an inlet orifice (31) connected to the outlet end of the first pipe and an outlet orifice (35) connected to the inlet end of the second pipe. The endcap extends from the retainer plate and encircles the inlet and outlet orifices. The endcap together with the retainer plate forms a semi-enclosed internal volume (26). The foraminous baffle is arranged to extend from the retainer plate and is arranged to extend over an area (A) of the outlet orifice.The disclosure further relates to a vehicle (1) comprising such an exhaust gas aftertreatment system.

Description

Exhaust gas aftertreatment system TECHNICAL FIELD The present invention relates to an exhaust gas aftertreatment system comprising a pipe fitting, as well as a vehicle comprising such anaftertreatment system.

BACKGROUND ART Emissions standards for motor vehicles are becoming increasingly stringent. Such standardstypically specify maximum emission levels for a number of tailpipe pollutants including carbonmonoxide (CO), hydrocarbons (HC), nitrogen oxides (NOX) and particulate matter (PM). lnorder to meet the requirements of the present and presumably future standards, vehicles arerequired to be equipped with emissions reduction technologies. Such emissions reductiontechnologies suitable for diesel vehicles include exhaust gas recirculation (EGR), particulatefilters, diesel oxidation catalysts (DOC), and selective catalytic reduction (SCR). Eachtechnology has its own distinct advantages and disadvantages, and may increase the incidenceof one pollutant while reducing the incidence of another. For example, EGR may reduce NOXemissions, but reduce fuel efficiency and increase particulate matter. Therefore, a number of technologies are commonly applied together in order to meet emissions standards.

Selective catalytic reduction (SCR) is an effective technology to reduce tailpipe nitrogen oxides(NOX) emissions. lt involves adding a reductant, such as ammonia, to the vehicle exhauststream. The reductant, with the aid of a catalyst, reduces NOX in the exhaust stream tonitrogen gas (NZ) and water. ln practical implementations in motor vehicles, an aqueous ureasolution is used as a reductant and this urea solution is thermally decomposed to ammonia and carbon dioxide in the hot exhaust stream.

Since SCR is implemented downstream ofthe engine as an exhaust aftertreatment, it does notaffect the combustion performance ofthe engine in the same manner as for example EGRdoes. Therefore, it is desirable to be able to remove substantially all NOX from the exhaust stream using only SCR, without the need for EGR. However, this is not without difficulties. ln 2 order to produce the quantities of ammonia required to reduce substantially all NOX, largequantities of urea solution must be injected into the exhaust stream. To be able to utilizeinjected urea and reduce NOx-emission with high efficiency over the SCR, effective distributionof reductant in the exhaust stream is essential. Non-uniform distribution can lead todeposition of urea and urea by-products on surfaces downstream of the injection site.I\/|oreover, if the reductant is not uniformly distributed over the SCR catalyst, the catalyst mayneed to be dimensioned to the maximum flux of reductant, meaning that some catalysts willbe over-dimensioned, which is environmentally and economically wasteful. Alternatively,excess urea will have to be injected to fully supply all catalysts with reductant. This excess ureawill require the use of a larger ammonia slip catalyst in order to prevent tailpipe ammoniaemissions. Therefore, there is a desire for aftertreatment systems that provide a more uniform mixing of reductant with the exhaust stream.

SUMMARY OF THE INVENTION The inventors of the present invention have identified a number of shortcomings in prior artsolutions for obtaining good mixing of reductant in the exhaust stream. The distance betweenthe reductant injector and the SCR catalyst surface is a primary factor in obtaining effectivemixing of reductant with the exhaust stream in combination with low backpressure. However,using an increased mixing length in order to obtain a high degree of mixing with lowbackpressure typically leads to an increase in system dimensions that is unacceptable orundesirable for many applications. ln order to utilize a shorter mixing distance for compactinstallations such as passenger cars, mixing devices that creates turbulence or swirls arecommonly used. However, the conversion efficiency of such systems is typically only in therange of 80%. Such solutions are therefore insufficient for attaining the high conversionsefficiencies required for many commercial vehicles in order to meet emissions standards.I\/|oreover, the larger engines typically used in commercial vehicles create high exhaust flowrates. High exhaust flow rates exasperate the problem of backpressure increase with mixer type solutions, leading to increased fuel consumption.

Therefore, it is an object ofthe present invention to remedy or alleviate at least some of the shortcomings described above. ln particular, it would be desirable to enable a means of 3mixing reductant with the exhaust stream that provides excellent mixing with low backpressure in a relatively compact system.

These objects are obtained by the exhaust aftertreatment system as defined in the appendedclaims. The exhaust gas aftertreatment system comprises a first pipe section, a second pipesection and a pipe fitting. The first pipe section has an outlet end and comprises a reductantinjector nozzle. The second pipe section has an inlet end and comprises an SCR catalyst device.The pipe fitting is arranged to provide fluid communication between the first pipe section andthe second pipe section. The pipe fitting comprises a retainer plate, an endcap and aforaminous baffle. The retainer plate comprises an inlet orifice connected to the outlet end ofthe first pipe and an outlet orifice connected to the inlet end ofthe second pipe. The endcapextends from the retainer plate and encircles the inlet and outlet orifices. The endcaptogether with the retainer plate forms a semi-enclosed internal volume. By semi-enclosedinternal volume it is meant a volume that would be fully enclosed if not for the orificesprovided in the retainer plate. The foraminous baffle is arranged to extend from the retainer plate, and extend over an area of the outlet orifice.

Providing a baffle within the endcap increases the distance travelled by the exhaust streambetween the urea injector and the SCR catalyst, while maintaining a compact design. However,a solid baffle would considerably increase the backpressure caused by the system due to thesharp rerouting ofthe exhaust stream. ln order to prevent an excessive rise in backpressure, itis required that the baffle is foraminous, i.e. perforated. Most ofthe exhaust stream still flowsaround the baffle in the extended mixing path. However, the perforation of the baffle providesa degree of pressure equalisation across the baffle, thus reducing the backpressure caused bythe system. As a side-effect of the perforations in the baffle, the bypassed gases passingthrough the perforation will collide with the gases following the extended path and thereby afurther increase in mixing is obtained. The solution outlined makes it possible to increasesystem performance from approximately 90% NOx reduction to greater than 95% NOxreduction with minimum backpressure increase, while maintaining the original system dimensions.

The foraminous baffle may be arranged to extend from the retainer plate at least at portion of the retainer plate arranged between the inlet orifice and the outlet orifice. This may for 4example be a proximal circumferential portion ofthe outlet orifice, wherein the proximalcircumferential portion is a portion ofthe outlet orifice circumference in closest proximity tothe in|et orifice. The foraminous baffle may be arranged to extend over a proximal area of theoutlet orifice, wherein the proximal area is an area of the outlet orifice in closest proximity to the in|et orifice.

The first pipe section may comprise a mixer device arranged between the reductant injectornozzle and the outlet end. This provides a rotating flow of exhaust gases prior to reaching the baffle, and may further improve the mixing obtained by the system.

The first pipe section may comprise a reductant vaporization element arranged between thereductant injector nozzle and the outlet end. This facilitates evaporation and decomposition ofthe urea injected from the nozzle, and may help prevent buildup of urea depositions in the first pipe.

The first pipe section may comprise a flow-directing vane arranged at the outlet end. Such avane may, together with the pipe fitting, assist in converting a rotational exhaust flow to a more laminar exhaust flow.

The first pipe section and the second pipe section may be arranged essentially parallel to each other. Thus, the system effectively utilizes the space available for the pipes.

The pipe fitting comprises a retainer plate, an endcap and a foraminous baffle. The retainerplate comprises an in|et orifice arranged to be connectable to a first pipe and an outlet orificearranged to be connectable to a second pipe. The endcap extends from the retainer plate andencircles the in|et and outlet orifices. The endcap together with the retainer plate forms asemi-enclosed internal volume. By semi-enclosed internal volume it is meant a volume thatwould be fully enclosed if not for the orifices provided in the retainer plate. The foraminousbaffle is arranged to extend from the retainer plate, and extend over an area ofthe outlet orifice.

The foraminous baffle may be arranged to extend from the retainer plate at least at portion ofthe retainer plate arranged between the in|et orifice and the outlet orifice. This may forexample be a proximal circumferential portion ofthe outlet orifice, wherein the proximal circumferential portion is a portion ofthe outlet orifice circumference in closest proximity to 5the inlet orifice. The foraminous baffle may be arranged to extend over a proximal area oftheoutlet orifice, wherein the proximal area is an area of the outlet orifice in closest proximity to the inlet orifice.

The retainer plate may be planar. This facilitates manufacture of the pipe fitting, as sheet or plate metal is widely available, thus reducing the cost of manufacture ofthe fitting.

The foraminous baffle may comprise a rim arranged to extend substantially outward from theretainer plate and a planar portion arranged to extend substantially parallel to the retainerplate. This helps ensure that the flow channels created within the internal volume ofthe pipe fitting are suitably dimensioned in order to provide good mixing with low backpressure.

By "substantially parallel to the retainer plate" it is meant at an angle of 30° or less withrespect to the plane of the retainer plate. For example, the planar portion may extend at anangle 0 relative to the retainer plate, wherein 0 is from about 0° to about 30°, preferably fromabout 0° to about 20°, such as approximately 5°. Having a slightly angled baffle assists inconverting a rotating gas flow to a more laminar flow and thus assists in preventing pressure drop across the pipe fitting.

The rim of the foraminous baffle may be non-apertured, i.e. without holes. This prevents exhaust gas from taking the shortest path between the inlet and outlet orifices and assists inrerouting the bulk of the exhaust gas around the foraminous baffle. The planar portion oftheforaminous baffle may be foraminous in order to ensure sufficient pressure-balancing across the baffle.

The internal volume has a maximum height h and the planar portion ofthe foraminous baffleis arranged at least at a distance d from the outlet orifice. The ratio h:d may be from about10:1 to about 1.511. This ensures suitable dimensioning ofthe flow channels formed by partitioning ofthe internal volume with the foraminous baffle.

The foraminous baffle may have an open area of from about 10% to about 70%, preferablyfrom about 20% to about 50%, such as about 35%. This ensures a suitable balance of pressureacross the baffle and thus assists in reducing backpressure while ensuring that a significantproportion ofthe exhaust gases travel the extended path around the baffle. ln some cases where fuel economy and backpressure are not a significant concern, the baffle could be non- 6foraminous. A non-foraminous baffle would still provide improved mixing in the compact space utilized, but at the cost of a significant rise in backpressure.

The foraminous baffle may cover from about 30% to about 90% of a total area ofthe out|etorifice, preferably from about 50% to about 80%, such as about 70%. This assists in ensuring a sufficient elongation ofthe exhaust flow path in order to provide improved mixing.

The dista| edge ofthe foraminous baffle may be essentially straight. This straight edge may bearranged to extend essentially perpendicular to a line extending between the centre ofthe inlet orifice and the centre of the out|et orifice.

The pipe fitting may further comprise a flow-directing vane. The vane may be arranged on aninterior wall portion of the endcap covering the inlet orifice. Such a flow-directing vane assistsin converting a rotating flow to a more laminar flow and thus helps avoid the generation of backpressure by the pipe fitting.

According to another aspect of the invention, the objects ofthe invention are achieved by avehicle comprising an exhaust aftertreatment system or pipe fitting as described in the appended claims.

Further objects, advantages and novel features of the present invention will become apparent to one skilled in the art from the following detailed description.BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the present invention and further objects and advantages of it,the detailed description set out below should be read together with the accompanyingdrawings, in which the same reference notations denote similar items in the various diagrams, and in which: Fig. 1 schematically illustrates a vehicle comprising an exhaust gas aftertreatmentsystem;Fig. 2 schematically illustrates a cross-sectional plan view of an exhaust gas afteftfeatmefit SyStemj 7 Fig. 3 schematically illustrates a cross-sectional plan view of an exhaust gasaftertreatment system comprising a single flow-directing vane; Fig. 4 schematically illustrates a cross-sectional plan view of an exhaust gasaftertreatment system comprising two flow-directing vanes; Fig. 5 schematically illustrates a cross-sectional plan view of a pipe fitting; Fig. 6 schematically illustrates a cross-sectional perspective view of an upper part of the exhaust gas aftertreatment system.

DETAILED DESCRIPTION The present invention concerns a compact exhaust gas aftertreatment system, and a pipefitting facilitating the provision of such a system. The invention is based on the discovery bythe inventors that a foraminous baffle arranged in the endcap ofthe pipe fitting mayconsiderably extend the flow path of the exhaust gases without a concomitant substantial increase in backpressure.

The exhaust gas aftertreatment system comprises a first pipe section, a second pipe sectionand a pipe fitting. Upstream and downstream respectively refer to positions in the exhaustaftertreatment system with reference to the typical direction of flow of exhaust gas from theengine to the tailpipe. A component is designated upstream of another if it is located in theexhaust system closer to the engine, whereas it is designated downstream if it is located in the exhaust system closer to the tailpipe.

The first pipe section contains a reductant injector nozzle for injection of a reductant into theexhaust stream in an upstream or transverse direction. The reductant is preferably dieselexhaust fluid comprising a solution of urea in water, in accordance with standard AUS 32 ofISO 22241. The reductant injector nozzle may be arranged to inject reductant such that acentral axis ofthe spray cone coincides with the central axis ofthe exhaust pipe, i.e. injectalong the length of the pipe. However, the injector nozzle may alternatively be positioned on a wall of the first pipe and be arranged to spray at an angle relative to the central axis of the 8pipe. The reductant injector may be of any type known in the art, such as air-assisted (e.g. jetspray) injectors, or a liquid-only (i.e. airless) injectors.

A vaporization element may be provided within the first pipe in order to assist in vaporizingand decomposing urea to ammonia. The vaporization element may be a surface arranged toreceive a proportion ofthe urea injected into the first pipe. For example, if the injector isarranged to spray essentially along the central axis of the pipe, the vaporization element maybe a tube arranged to receive a peripheral proportion of the spray cone on its surface.Alternatively, if the injector injects at an angle to the central axis of the pipe, the vaporizationelement may be a plate arranged to receive any urea spray not rapidly entrained in theexhaust flow. The walls of the vaporization element may be continuous, i.e. solid, or they maybe foraminous, e.g. mesh or perforated sheet. The vaporization element is preferablyconstructed of a material having good heat transfer properties, such as sheet metal or metal mesh.

A mixer device may be arranged in the first pipe in order to assist in mixing the reductant withthe exhaust stream. Note however that the present invention may in some cases obviate theneed for a mixer, and a mixer may therefore not be required. Suitable mixers are known in theart and include i.a. propeller-like, corkscrew-like and volute-like devices that induce rotation inthe exhaust stream. Depending on the mixer construction, it may be located upstream, downstream or essentially in line with the injector nozzle.

For example, the first pipe section may comprise an injector nozzle arranged to injectreductant along the central axis of the pipe section, propeller-type mixer device arranged inline with the injector nozzle, and a tubular vaporization element arranged coaxially with the pipe section.

The second pipe section comprises the SCR catalyst device. The SCR catalyst device may be ofany type known in the art. By SCR catalyst device, it is meant a device comprising a catalystcapable of catalysing the reduction of NOx to NZ using the reductant. The SCR catalyst devicemay be a dedicated SCR catalyst, or it may be a device combining the function of an SCRcatalyst with another function. For example, the SCR device may be an SCR-catalysed dieselparticulate filter (SDPF). The SCR device may comprise multiple SCR catalysts arranged in parallel or series. The second pipe section may comprise an ammonia slip catalyst arranged 9downstream (i.e. at the outlet side) ofthe SCR Catalyst. The second pipe section may alsocomprise further components, such as pressure, NOx or temperature sensors. The second pipe section typically may have a larger diameter than the first pipe section.

The pipe fitting is arranged to provide fluid communication between the first pipe and thesecond pipe, such that the exhaust stream may exit the first pipe and flow into the secondpipe section via the pipe fitting. The pipe fitting comprises a retainer plate, an endcap and a foraminous baffle.

The plate comprises an inlet orifice connected to the outlet end of the first pipe and an outletorifice connected to the inlet end of the second pipe. The orifices and relevant ends of thepipe sections may be machined or formed in any manner that enables connection of the pipeto the orifice. For example, each orifice may be machined to form a recess into which therelevant end ofthe pipe section may fit, each orifice and pipe end may be threaded, the pipemay be provided with a flange that may be fixed to the underside of the plate by welding, orthe pipe and retainer plate may simply be welded together. The retainer plate may preferablybe constructed from sheet or plate metal that is machined to form, and therefore preferably isplanar. The inlet orifice may be smaller than the outlet orifice. For example, the diameter ofthe inlet orifice may be approximately equal to the radius ofthe outlet orifice. The relativediameters of the first and second pipes obviously correspond to the size of the inlet and outlet orifices respectively.

The endcap extends from the retainer plate and encircles, i.e. surrounds the inlet and outletorifices, i.e. the endcap forms a cap or dome over the inlet and outlet orifices together. lndoing so, the endcap together with the retainer plate forms a semi-enclosed internal volume.By semi-enclosed internal volume it is meant a volume that would be fully enclosed if not forthe orifices provided in the retainer plate. This internal volume provides an enclosed volumeby which the exhaust gas may pass through on passing from the first pipe section to thesecond pipe section. The walls of the endcap may extend substantially outwards from theretainer plate. By "substantially outward from the retainer plate" it is meant at an angle ofgreater than 45° with respect to the plane ofthe retainer plate, such as an angle greater than 60°, greater than 75° or approximately 90° with respect to the plane of the retainer plate.

The walls of the endcap transition to a roof of the endcap. This transition may abrupt, i.e. theroof may appear perpendicular to the walls when seen from the side, the transition may besmooth such that when seen from the side the walls and roof resemble a continuous arc, orthe transition may be somewhere therebetween, such that the angle formed between thewalls and roof are somewhat rounded. The height h ofthe internal volume, measured normalto the plane of the retaining plate, may be essentially constant over essentially the entire areacovered by the endcap, or it may vary, decreasing with proximity to the walls of the endcap.The height h at its maximum may for example be from approximately V2 to approximatelytwice the radius of the inlet orifice. The endcap is fixed to the retainer plate by any means known in the art, such as by welding.

The foraminous baffle is arranged to extend from the retainer plate, and extend over an areaof the outlet orifice. The foraminous baffle may be arranged to extend from the retainer plateat a portion ofthe retainer plate arranged between the inlet orifice and the outlet orifice, thusblocking the most direct flow route between the inlet and outlet orifices. For example, theforaminous baffle may be arranged at a proximal circumferential portion of the outlet orifice,i.e. a portion ofthe outlet orifice circumference in closest proximity to the inlet orifice. Thisportion can be conceptualised as originating at a point of the circumference ofthe outletorifice that lies at the intersection of the circumference and a straight line connecting thecentres ofthe inlet and outlet orifice. The circumferential portion originates at this point andextends equally in both directions around the circumference ofthe outlet orifice for thedesired extent. The foraminous baffle extends over an area of the outlet orifice. Due to theforaminous baffle originating at a portion of the retainer plate arranged between the inletorifice and the outlet orifice, the foraminous baffle may extend over a proximal area of theoutlet orifice, wherein the proximal area is an area of the outlet orifice in closest proximity to the inlet orifice.

The distal edge ofthe foraminous baffle, i.e. the edge not in contact with the retainer plate, ornot running essentially along the circumference of the outlet orifice, may be straight orcurved. For example, it may be a straight line resembling a chord ofthe outlet orifice whenseen from above, or it may resemble an arc of a circle having the centre ofthe inlet orifice as its centre. 11 The foraminous baffle may comprise a rim extending substantially outwards from the retainerplate. By "substantially outward from the retainer plate" it is meant at an angle of greaterthan 45° with respect to the plane of the retainer plate, such as an angle greater than 60°,greater than 75° or approximately 90° with respect to the plane ofthe retainer plate. The rimmay transition to a planar portion of the baffle extending over the outlet orifice and arrangedsubstantially parallel to the retainer plate. By "substantially parallel to the retainer plate" it ismeant at an angle of less than 30° with respect to the plane of the retainer plate, such as anangle less than 20° but greater than or equal to 0°, such as approximately 5° with respect tothe plane ofthe retainer plate. Preferably, the planar portion ofthe baffle is slightly angledwith respect to the retainer plate in order to facilitate a transition from a rotational exhaust flow to a more laminar exhaust flow.

The rim functions as a spacer, determining the distance d between the retainer plate and theplanar portion of the baffle, measured normal to the plane of the retainer plate. The distanced may be constant along the entire planar portion ofthe baffle or may vary, depending onwhether the planar portion of the baffle is parallel or slightly angled with respect to theretainer plate. The ratio ofthe maximum height h of the internal volume as compared to thedistance d at the closest point of the planar portion of the baffle to the retainer plate is preferably from about 10:1 to about 1.511.

The rim of the baffle is preferably solid, i.e. without perforations, in order to prevent theexhaust flow taking the shortest possible path between the inlet and outlet orifices. Theplanar portion of the baffle is foraminous, i.e. comprises a multitude of small holes. The holesmay all be ofthe same size or vary in size. For example, the holes may all have the samediameter of from about 2 mm to about 8mm. An optional transitionary portion of the bafflearranged between the rim and the planar portion may be solid, i.e. non-foraminous, or it maybe foraminous. The open area of the baffle, i.e. the area ratio of holes to surface, may be fromabout 10% to about 70%, preferably from about 20% to about 50%, such as about 35%. The baffle may for example be formed of perforated sheet metal or mesh.

The baffle is fixed to the retainer plate either directly or indirectly. For example, a perforated sheet or mesh covering the entire area ofthe outlet orifice may be fixed to the retainer plate, 12and the baffle may be fixed to this sheet of mesh. Any relevant means of fixation, such as welding, may be utilized.

The exhaust gas aftertreatment system may comprise one or more flow-directing vanes, forexample one, two or three such vanes. These vanes may assist in converting a rotating orturbulent exhaust flow to more laminar flow through the pipe fitting, thus reducingbackpressure caused by the pipe fitting. They may also assist in mixing ammonia-rich volumesof the exhaust flow with ammonia-deficient volumes. For example, a cap vane may bearranged on the roof of the endcap. The vane may for example be arranged above the inletorifice, as seen normal to the plane of the retainer plate. Alternatively, or in addition, a pipevane may be arranged at the outlet end of the first pipe section. These vanes may bemanufactured in any suitable material, such as metal sheet or plate, and may be fixed to the relevant surface by any known fixing means.

The retainer plate, endcap, baffle and flow-directing vanes have heretofore been described asbeing manufactured as separate pieces prior to being assembled by means of fixations such aswelding. However, it is equally viable that two or more ofthese components, such as theretainer plate together with the endcap, or the retainer plate together with the baffle, or evenall ofthese components, are manufactured as a single piece. For example, two or more of thecomponents may be manufactured as a single piece by moulding or additive manufacturing techniques.

The invention will now be described in more detail with reference to certain exemplifyingembodiments and the drawings. However, the invention is not limited to the exemplifyingembodiments discussed herein and/or shown in the drawings, but may be varied within thescope ofthe appended claims. Furthermore, the drawings shall not be considered drawn to scale as some features may be exaggerated in order to more clearly illustrate certain features.

Figure 1 shows schematically a side view of a vehicle 1 according to an embodiment of theinvention. The vehicle 1 includes a combustion engine 2, and an exhaust gas aftertreatmentsystem 4 arranged in exhaust conduit 10. The exhaust conduit 10 leads exhaust gases fromthe engine 2, through the exhaust gas aftertreatment system 4 and onwards to expel thetreated exhaust gases. The vehicle 1 may be a heavy vehicle, e.g. a truck as herein illustrated, a tractor, or a bus. The vehicle 1 may alternatively be a passenger car. The vehicle may be a 13hybrid vehicle comprising an electric machine (not shown) in addition to the combustionengine 2. The vehicle may alternatively be a marine vessel, such as a ship. The invention mayalso be used in the exhaust aftertreatment of non-vehicular engine systems also, such as in geHeFatOFS.

Figure 2 schematically illustrates an exhaust gas aftertreatment system 4 in cross-sectionalplan view. The system 4 comprises a first pipe section 11, a second pipe section 13 and a pipefitting 15. The first pipe section 11 comprises a reductant injector nozzle 17 and a mixer 19arranged in-line with the injector nozzle (herein illustrated as a propeller-type mixer). Avaporization tube 21 is arranged within the first pipe section 11 to receive spray from theinjector nozzle 17. The second pipe section 13 comprises SCR catalyst 23. The pipe fitting 15comprises a retainer plate 25, an endcap 27 and a foraminous baffle 29. The retainer plate 25has an inlet orifice 31 connected to the outlet end 33 of the first pipe section 11, and an outletorifice 35 connected to the inlet end 37 ofthe second pipe section 13. The retainer plate 25together with the endcap 27 forms a semi-enclosed internal volume 26 within the pipe fitting .

Reductant is added to exhaust gas passing through first pipe section 11 by nozzle 17. Themixer 19 induces a rotational flow of the exhaust gas to facilitate mixing of the reductant inthe exhaust gas. Vaporization tube 21 assists in the vaporization and decomposition oftheinjected reductant. Upon entering pipe fitting, the exhaust flow is directed primarily aroundthe baffle 29 and onward into second pipe section where it enters the SCR catalyst 23. lt canbe seen that the presence of baffle 29 significantly increases the flow path ofthe exhaustfluid. For example, the length ofthe typical flow path as measured from the exit of thevaporization tube to the entrance of the SCR catalyst may be increased by a factor of 2 to 3.This greatly facilitates mixing of the reductant with the exhaust flow. At the same time, thepresence of holes in the foraminous baffle allows a proportion ofthe exhaust gas to passthrough. The primary function of the holes is to permit pressure equalisation across the baffle29, however, a degree of further mixing is also obtained by mixing of exhaust passing through the holes with exhaust passing around the baffle 29. 14Figure 3 schematically illustrates an embodiment ofthe invention identical to that illustratedin Figure 2, with the exception that a flow-directing vane 39 is arranged on the roof of the endcap 15.

Figure 4 schematically illustrates an embodiment of the invention identical to that illustratedin Figure 3, with the exception that a further flow-directing vane 41 is arranged at the outlet end 33 ofthe first pipe section 11.

Figure 5 schematically illustrates the pipe fitting 15. lt can be seen that the foraminous baffle29 has a rim 43 arranged at a circumferential portion of the outlet orifice 35 in c|osestproximity to the in|et orifice 31, and a planar portion 45 extending over an area of the outletorifice 35 in c|osest proximity to in|et orifice 31. The area covered by the baffle 29 is measurednormal to the plane ofthe retainer plate 25 and is indicated by arrow A. The planar portion 45forms an angle 6 with respect to the plane ofthe retainer plate 25, as illustrated, and isarranged at a minimum distance from the outlet orifice as indicated by arrow d. The endcap27 extends outwards from the retainer plate 27 at an angle oL relative to the plane of the retainer plate 25. The pipe fitting 15 has a maximum height as indicated by arrow h.

Figure 6 schematically illustrates an upper part of the exhaust aftertreatment system in crosssectional perspective view. Again, the pipe fitting 15 comprising retainer plate 25, endcap 27,foraminous baffle 29, in|et orifice 31 and outlet orifice 35 is illustrated, as well as fist pipe section11 and second pipe section 13. Here it can be clearly seen that the foraminous baffle 29arranged in pipe fitting 15 greatly increases the flow path ofthe exhaust gas as indicated by themultitude of arrows 47 indicating flow direction. lt can be further seen that a mesh 49 isarranged to cover the outlet orifice of the pipe fitting 15, and that the foraminous baffle 29 isfixed onto this mesh. Furthermore, it can be seen that a distal edge 51 ofthe foraminous baffle29 is straight and extends perpendicular to a line extending between the centre of the in|et orifice 31 and the centre of the outlet orifice 35.

Claims (4)

1. CLAll\/IS An exhaust gas aftertreatment system (4) characterized in that it comprises: A first pipe section (11) comprising a reductant injector nozzle (17), the first pipe section having an outlet end (33); a second pipe section (13) comprising an SCR catalyst device (23), the second pipe section having an inlet end (37); and a pipe fitting (15) arranged to provide fluid communication between the first pipe section and the second pipe section, the pipe fitting comprising: a retainer plate (25) comprising an inlet orifice (31) connected to the outlet end of the first pipe and an outlet orifice (35) connected to the inlet end ofthe second pipe; an endcap (27) extending from the retainer plate and encircling the inlet and outletorifices, the endcap together with the retainer plate forming a semi-enclosed internal volume (26); and a foraminous baffle (29) arranged to extend from the retainer plate, and arranged to extend over an area (A) of the outlet orifice. The exhaust gas aftertreatment system according to claim 1, wherein the first pipe section(11) comprises a mixer device (19) arranged in line with the reductant injector nozzle (17),and/or a reductant vaporization element (21) arranged between the reductant injector nozzle and the outlet end (33). The exhaust gas aftertreatment system according to any one of the preceding claims,wherein the first pipe section (11) comprises a flow-directing vane (41) arranged at the outlet end (33). The exhaust gas aftertreatment system according to any one of the preceding claims,wherein the first pipe section (11) and the second pipe section (13) are arranged essentially parallel to each other. 10. 11. 1

2. 1

3. The exhaust gas aftertreatment system according to any one of the preceding claims,wherein the foraminous baffle (29) comprises a rim (43) arranged to extend substantiallyoutward from the retainer plate (25) and a planar portion (45) arranged to extend substantially parallel to the retainer plate. The exhaust gas aftertreatment system according to claim 5, wherein the planar portion(45) extends at an angle 0 relative to the retainer plate (25), wherein 0 is from about 0° to about 30°, preferably from about 0° to about 20°, such as approximately 5°. The exhaust gas aftertreatment system according to any one of claims 5-6, wherein the rim (43) ofthe foraminous baffle (29) is non-apertured. The exhaust gas aftertreatment system according to any one claims 5-7, wherein theinternal volume (26) has a maximum height h, and wherein the planar portion (45) oftheforaminous baffle (29) is arranged at least at a distance d from the outlet orifice (35), wherein the ratio h:d is from about 1011 to about 1.5:1. The exhaust gas aftertreatment system according to any one of the preceding claims,wherein the foraminous baffle (29) has an open area of from about 10% to about 70%, preferably from about 20% to about 50%, such as about 35%. The exhaust gas aftertreatment system according to any one of the preceding claims,wherein the foraminous baffle (29) covers from about 30% to about 90% of a total area of the outlet orifice (35), preferably from about 50% to about 80%, such as about 70%. The exhaust gas aftertreatment system according to any one of the preceding claims,wherein a distal edge (51) of the foraminous baffle (29) is essentially straight and isarranged to extend essentially perpendicular to a line extending between the centre of the inlet orifice (31) and the centre of the outlet orifice (35). The exhaust gas aftertreatment system according to any one of the preceding claims,further comprising a flow-directing vane (39) arranged on an interior wall portion of the endcap (27) covering the inlet orifice (31).An engine system comprising: an internal combustion engine (2); and - an exhaust aftertreatment system (4) according to any one ofthe preceding claims. 1

4. A vehicle (1) comprising an engine system according to claim 13, or an exhaust aftertreatment system (4) according to any one of the preceding claims.