FR3097775A1 - Set of purification of an exhaust gas, exhaust line and vehicle - Google Patents

Abstract

Set for purifying an exhaust gas, exhaust line and vehicle The purification assembly comprises: - a mixer (19) whose inlet (21) has a central inlet axis (C1) defining with the 'central output axis (C2) an angle β of between 60 ° and 120 °; - the mixer (19) comprising an outer casing (29) and a deflector part (31) located inside the outer casing (29), the mixer (19) comprising a single circulation passage (33) s' extending from the inlet (21) to the outlet (23) extending about an axis of rotation (R) at an angle between 270 ° and 450 °; the mixer comprising an injector (35) arranged to inject a fluid inside the circulation passage (33) towards the deflector part (31). Figure for the abstract: 3

Description

Exhaust gas purification assembly, exhaust line and vehicle

The present invention relates to an assembly for purifying an exhaust gas.

• Un premier dispositif de purification de gaz d’échappement avec un premier axe central ;
• Un second dispositif de purification de gaz d’échappement avec un second axe central;
• Un mélangeur ayant une entrée de mélangeur de gaz d’échappement raccordé fluidiquement au premier dispositif de purification de gaz d’échappement et une sortie de mélangeur de gaz d’échappement raccordée fluidiquement au second dispositif de purification de gaz d’échappement, le mélangeur comprenant un injecteur de fluide.

Diesel vehicles can be fitted with an exhaust gas purification package comprising:

• A first exhaust gas purification device with a first central axis;
• A second exhaust gas purification device with a second central axis;
• A mixer having an exhaust gas mixer inlet fluidly connected to the first exhaust gas purification device and an exhaust gas mixer outlet fluidly connected to the second exhaust gas purification device, the mixer comprising a fluid injector.

The second exhaust gas purification device is typically a catalyst of the SCR (Selective Catalytic Reduction) type, in which the nitrogen oxides contained in the exhaust gas are converted catalytically into N ₂ Gas. . The injector injects a reducing agent between the two exhaust gas purification devices. For example, an aqueous solution of urea is injected, the urea being broken down and generating gaseous ammonia.

Sometimes vehicle manufacturers require that the exhaust gas purification assembly be located in the engine compartment. The engine compartment is generally very cluttered, and the space authorized for the installation of the exhaust gas purification assembly is very limited.

In addition, certain vehicle manufacturers sometimes impose a position for the injector substantially aligned with the first central axis, with the direction of injection pointing towards the outlet of the exhaust gas mixer.

FR3010137 discloses a mixer comprising an injector having an injection direction pointing towards the outlet of the exhaust gas mixer. This mixer comprises a deflector piece, having the shape of a “chistera”, arranged such that the exhaust gas forms two vortices on both sides of the deflector piece.

The FR3010137 mixer is very effective but can hardly be used in a very cluttered environment when the injector must be placed substantially on the first central axis. A relatively large space is imperative to house the “chistera”.

Additionally, the mixerFR3010137 must be symmetrical, so that both exhaust gas vortices are loaded with the same amount of reducing agent. In the engine compartment, it is not always possible to give a symmetrical shape to the mixer. In some cases, a recess must be provided in the mixer outer casing to accommodate other equipment close to the mixer.

In this context, the object of the invention is to provide an exhaust gas purification assembly which can be arranged in a very cluttered environment such as an engine compartment, and which offers good performance even when the injector must be located substantially along the first central axis, with the direction of injection pointing towards the exhaust gas mixer outlet.

To this end, the invention according to a first aspect relates to an exhaust gas purification assembly comprising:

- a first exhaust gas purification device with a first central axis;

- a second exhaust gas purification device with a second central axis;

- a mixer having an exhaust gas mixer outlet fluidly connected to the first exhaust gas purification device and an exhaust gas mixer outlet fluidly connected to the second exhaust gas purification device, the exhaust gas mixer inlet having a central inlet axis and the exhaust gas mixer outlet having a central outlet axis, the central inlet axis defining with the central outlet axis an angle β between 60° and 120°;

- the mixer comprising an outer casing defining the exhaust gas mixer inlet and the exhaust gas mixer outlet and a deflector part located inside the outer casing, the mixer comprising a circulation passage extending from the exhaust gas mixer inlet to the exhaust gas mixer outlet, defined by the deflector piece and the outer shroud and extending around an axis of rotation on an angle between 270° and 450°;

the mixer comprising an injector arranged to inject a fluid inside the circulation passage towards the deflector part.

In the event that the exhaust gas mixer outlet must be substantially perpendicular to the exhaust gas mixer inlet, the exhaust gas purification assembly allows very effective mixing of the fluid injected into the flow of exhaust gases.

The mixing performance remains very good even when, due to spatial constraints, the injection orifice must be arranged very low, the log of the first central axis.

The baffle piece prevents the fluid from flowing directly from the injector to the exhaust gas mixer outlet, along a straight line.

Following the circulation path, the exhaust gas flow changes from laminar flow to vortex flow at the exhaust gas mixer outlet, thus ensuring very good mixing performance.

Virtually all of the exhaust gas flow passes under the injection port. The fluid is thus dispersed in a large quantity of exhaust gases.

Virtually all of the exhaust gas flow passes along the baffle piece. When the fluid is a liquid, it evaporates quickly as the liquid droplets strike the surface of the baffle piece, which is kept hot by the high flow of exhaust gas.

The exhaust gas purification set is very compact, especially the mixer.

The external casing of the mixer does not have to have a symmetrical shape, which facilitates the arrangement of other equipment near the mixer. This is particularly valuable when the exhaust gas purification assembly is located in the engine compartment of a vehicle.

The exhaust gas purification assembly may also have one or more of the characteristics below, considered alone or in all technically possible combinations:

- the rotation axis defines with the central output axis an angle between 0° degree and 30° degree;

- the injector is fixed to an injection port of the outer casing located opposite the outlet of the exhaust gas mixer in an injection direction, the deflector part extending between said injection port and the exhaust gas mixer outlet following the direction of injection;

- the direction of injection defines with the axis of rotation an angle between 0° and 45°;

- the first exhaust gas purification device comprises a purification member and a tubular casing in which the purification member is housed, the tubular casing having an open downstream axial end, the outer casing of the mixer being directly attached at said downstream axial end and closing said downstream axial end;

- in projection in a plane perpendicular to the first central axis, the tubular casing defines a closed contour line around the first central axis and the injection orifice defines a projected orifice located inside the closed contour line, the closed contour line having a maximum distance from the first central axis, a distance between the projected orifice and the first central axis being between 0% and 50% of said maximum distance;

- the outer casing comprises a concave shell having an opening delimited by a free edge directly attached to the tubular casing;

- the concave shell comprises a first half-shell and a second half-shell fixed to each other and together defining the free edge, the first half-shell defining the exhaust gas mixer outlet;

- the second half-shell comprises a first planar zone bearing the injection orifice and extending substantially perpendicular to the axis of rotation, and a second planar zone substantially perpendicular to the first central axis;

- the outer casing comprises an outer deflector part fixed to the concave shell, the outer deflector part closing the opening except in a zone defining the inlet of the exhaust gas mixer.

According to a second aspect, the invention relates to an exhaust line comprising an exhaust gas purification assembly having the above characteristics.

According to a third aspect, the invention relates to a vehicle comprising an exhaust line having the above characteristics.

• [Fig 1] La figure 1 est une représentation schématique de ligne d’échappement comprenant un ensemble de purification de gaz d’échappement selon l’invention ;
• [Fig 2] La figure 2 est une vue de dessus de l’ensemble de purification de gaz d’échappement de la figure 1 ;
• [Fig 3] La figure 3 est une vue agrandie en perspective du mélangeur de la figure 2 ;
• [Fig 4] La figure 4 est une vue éclatée du mélangeur de la figure 3 ;
• [Fig 5] La figure 5 est une représentation schématique, montrant les projections de l’enveloppe tubulaire du premier dispositif de purification et de l’orifice d’injection, dans un plan perpendiculaire à l’axe central du premier dispositif de purification ;
• [Fig 5] La figure 6 est une vue similaire à la vue de la figure 4, le mélangeur étant assemblé, la moitié supérieure de l’enveloppe concave n’étant pas représentée ;
• [Fig 7] [Fig 8] Les figures 7 et 8 sont de vue en perspective montrant les lignes de flux de gaz d’échappement dans le mélangeur de l’invention et dans un mélangeur conçu selon les principes deFR3010137 ;
• [Fig 9] [Fig 10] Les figures 9 et 10 sont de vue en perspective montrant les lignes de flux de gaz d’échappement dans l’ensemble de purification de gaz d’échappement de la figure 2 et dans un ensemble de purification de gaz d’échappement conçu selon les principes deFR3010137 .

Other characteristics to the advantage of the invention will emerge from the detailed description which is given below, by way of indication and in no way limiting, with reference to the appended figures, among which:

• [Fig 1] Figure 1 is a schematic representation of an exhaust line comprising an exhaust gas purification assembly according to the invention;
• [Fig 2] Figure 2 is a top view of the exhaust gas purification assembly of Figure 1;
• [Fig 3] Figure 3 is an enlarged perspective view of the mixer of Figure 2;
• [Fig 4] Figure 4 is an exploded view of the mixer of Figure 3;
• [Fig 5] Figure 5 is a schematic representation, showing the projections of the tubular casing of the first purification device and of the injection orifice, in a plane perpendicular to the central axis of the first purification device;
• [Fig 5] Figure 6 is a view similar to the view of Figure 4, the mixer being assembled, the upper half of the concave envelope not being shown;
• [Fig 7] [Fig 8] Figures 7 and 8 are perspective views showing the exhaust gas flow lines in the mixer of the invention and in a mixer designed according to the principles of FR3010137 ;
• [Fig 9] [Fig 10] Figures 9 and 10 are perspective views showing the exhaust gas flow lines in the exhaust gas purification assembly of Figure 2 and in a exhaust gas designed according to the principles of FR3010137 .

The exhaust gas purification assembly 1 of the invention is designed to be arranged in the exhaust line 3 of a vehicle, as illustrated in Figure 1.

The vehicle is typically an automobile, a truck or a two-wheeler.

As illustrated in Figure 2, the exhaust gas purification assembly 1 comprises a first exhaust gas purification device 5 having a first central axis X1 and a second exhaust gas purification device 7 having a second central axis X2.

The first exhaust gas purification device 5 comprises a first exhaust gas purification device inlet 9, fluidly connected to an exhaust manifold 11 collecting the exhaust gases emitted by the engine 13. Equipment such a turbo compressor are typically arranged between the exhaust manifold 11 and the first exhaust gas purification device 5.

The second exhaust gas device 7 has a second exhaust gas purification device outlet 15, fluidly connected to a cannula 17 through which the purified exhaust gas is discharged into the atmosphere. Equipment such as a silencer is typically arranged between the nozzle 17 and the second exhaust gas purification device 7.

As shown in Figure 2, according to a first configuration, a plane perpendicular to the first central axis X1 intersects both the first exhaust gas purification device 5 and the second exhaust gas purification device 7. In addition , the second central axis X2 forms with the first central axis X1 an angle α comprised between 0° and 30°, preferably comprised between 0° and 15°.

In other words, the first exhaust gas purifying device 5 and the second exhaust gas purifying device 7 are arranged side by side, and are substantially parallel to each other.

Alternatively, the first exhaust gas purification device 5 and the second exhaust gas purification device 7 are not substantially parallel to each other. The first central axis X1 and the second central axis X2 form any angle with each other. For example, the first central axis X1 and the second central axis X2 are substantially perpendicular to each other.

The first exhaust gas purification device 5 is for example a diesel oxidation catalyst (DOC).

The second exhaust gas purification device 7 is typically an SCR (Selective Catalytic Reduction) or an SCRF (Selective Catalytic Reduction Filter)

The exhaust gas purification assembly 1 further comprises a mixer 19 having an exhaust gas mixer inlet 21 (FIG. 3) fluidly connected to the first exhaust gas purification device 5 and a exhaust gas 23 fluidically connected to the second exhaust gas purification device 7.

In the embodiment shown in the figure, the exhaust gas mixer outlet 3 is fluidly connected to the second exhaust gas purifying device inlet 25 of the second exhaust gas purifying device 7 through a conduit 27 (FIG. 2).

The exhaust gas mixer inlet 21 has an inlet centerline C1 and the exhaust gas mixer outlet 23 has an outlet centerline C2. The central input axis C1 defines with the central output axis C2 an angle β comprised between 60° and 120°, typically comprised between 75° and 105°, and for example substantially equal to 90°.

In other words, the exhaust gas mixer inlet 21 and the exhaust gas mixer outlet 23 face in mutually perpendicular directions.

The central input axis C1 is for example parallel to the first central axis X1.

The exhaust gas mixer inlet 21 is an orifice, which extends substantially in one plane. The central input axis C1 is the axis passing through the center of this orifice and which is perpendicular to the said plane.

Similarly, the exhaust gas mixer outlet 23 is a port which extends substantially in one plane. The central output axis C2 is the axis passing through the center of this orifice and which is perpendicular to the said plane.

As visible in Figures 3 and 4, the mixer comprises an outer casing 29 and a deflector part 31 placed inside the outer casing 29.

Outer shroud 29 defines exhaust mixer inlet 21 and exhaust mixer outlet 23.

The mixer 19 includes a single circulation passage 33 extending from the exhaust gas mixer inlet 21 to the exhaust gas mixer outlet 23, defined by the baffle piece 31 and the outer shroud 29.

At least 80%, typically at least 90%, and preferably at least 95% of the exhaust gas entering mixer 19 through exhaust mixer inlet 21 follows circulation passage 33 along its entire length. , to the exhaust gas mixer outlet 23.

A small part of the exhaust gas can enter the mixer 19 through an opening which is different from the exhaust gas mixer inlet 21, for example holes in the outer casing 29.

A small portion of the exhaust gas entering mixer 19 through exhaust mixer inlet 21 may not follow circulation passage 33 along its entire length. For example, it flows through openings in the baffle piece 31 directly to the exhaust gas mixer outlet 23.

The circulation passage 33 extends around an axis of rotation R over an angle comprised between 270° and 450°, preferably comprised between 330° and 390°, being for example substantially equal to 360°.

The axis of rotation R defines with the central output axis C2 an angle comprised between 0° and 30°, preferably comprised between 0° and 15°. For example, the rotation axis R is substantially aligned with the central output axis C2.

The circulation passage 33 thus describes a substantially complete revolution around the axis of rotation R.

The circulation passage 33 has substantially an intermediate shape between a helix and a spiral, with an inlet tangential to the axis of rotation R and an outlet along the axis of rotation R.

The mixer 19 further comprises an injector 35 (FIG. 1) arranged to inject a fluid into the circulation passage 33 towards the deflector part 31.

The fluid is typically a liquid. For example, it is an aqueous solution of urea. Such a solution is sold under the name Adblue ^TM . According to another embodiment, the liquid is an ammonia solution, or any other liquid.

According to another alternative embodiment, the fluid is a gas, for example gaseous ammonia or any other gas.

The injector 35 is attached to an injection port 37 of the outer casing 29 located opposite the outlet of the exhaust gas mixer 23 along the direction of injection I (Figure 2). The baffle piece 31 extends between the injection port 37 and the exhaust gas mixer outlet 23 along the injection direction I.

Accordingly, the baffle piece 31 stops the injected fluid inside the circulation passage 33 and prevents the fluid from flowing directly from the injector 19 to the outlet of the exhaust gas mixer 23.

Such an arrangement is particularly advantageous when the fluid is a liquid, which must be evaporated. Since the baffle part 31 is completely surrounded by exhaust gas, it is particularly hot. It is maintained at a high temperature by the exhaust gas flowing along the circulation passage 33. The droplets of fluid striking the deflector part 31 are evaporated under the effect of the heat transmitted by the deflector part 31.

The injection direction I defines with the axis of rotation R an angle γ comprised between 0° and 45°, preferably comprised between 0° and 30°, and for example equal to 15°.

The first exhaust gas purification device 5 comprises a purification member 39 and a tubular casing 41 in which the purification member 39 is housed (FIG. 2).

The first central axis X1 is the central axis of the tubular casing 41.

The tubular casing 41 has a section, considered perpendicular to the first central axis X1, which is circular, oval, elliptical, or which has any other shape.

The tubular casing 41 has an open upstream axial end 43 and an open downstream axial end 45.

An inlet cone 47 is attached to the upstream axial end 43 and defines the first exhaust gas purification device inlet 9.

The outer casing 29 of the mixer 19 is directly attached to the downstream axial end 45 and closes this downstream end 45.

In a typical variant embodiment, in projection in a plane perpendicular to the first central axis X1, the tubular casing 41 defines a closed contour line 49 around the first central axis X1 and the injection orifice 37 defines a projected orifice 51 located inside the closed contour line 49, as shown in Figure 5. The shape of the closed contour line 49 corresponds to the section of the tubular casing 41.

The closed contour line 49 has a maximum distance from the first central axis X1. In the example shown in Figure 5, the closed contour line 49 is a circle, the axis X1 being the center of this circle. The distance to the first central axis X1 is constant.

When the closed line 49 is an ellipse, the closed contour line 49 has a minimum distance from the first central axis X1, corresponding to the minor radius of the ellipse. The closed contour line also has a maximum distance from the first central axis X1, corresponding to half of the major axis of the ellipse.

The distance between the projected orifice 51 and the first central axis X1 is between 0% and 50% of the maximum distance, preferably between 0% and 25%, more preferably between 0% and 10%.

Such an arrangement is typically imposed by the vehicle manufacturer and is a constraint for the design of the mixer 19.

The outer casing 29 comprises a concave shell 53 having an opening 55 delimited by a free edge 57 directly fixed to the tubular casing 41 (FIGS. 3, 4 and 6). The concave shell 53 is concave towards the first exhaust gas purifying device 5.

The shape of the free edge 53 corresponds to the section of the tubular casing 41. In the example shown in the figures, the open downstream axial end 45 is engaged inside the free edge 57.

The free edge 57 is fixed directly to the open downstream axial end 45, for example by welding or brazing.

The concave shell 53 comprises a first half-shell 59 and a second half-shell 61 fixed to each other and together defining the free edge 57.

The first half-shell 59 defines the exhaust gas mixer outlet 23.

The first half-shell 59 defines a lower half of the free edge 57.

The second half-shell 61 defines an upper half of the free edge 57.

The second half-shell 61 comprises a first flat zone 63 bearing the injection orifice 37 and extending substantially perpendicular to the axis of rotation R.

The second half-shell 61 further comprises a second flat zone 65 substantially perpendicular to the first central axis X1. The second flat zone 65 is typically located entirely above the first flat zone 63, that is to say on the side of the first flat zone 63 opposite the first half-shell 59.

The first flat zone 63 extends opposite the exhaust gas mixer outlet 23.

The second flat zone 65 extends opposite the open downstream axial end 45.

The two half-shells 59, 61 are concave towards each other, and are attached to each other along respective edges 67, 69 having U-shapes. The edges 67, 69 are typically welded to one another.

The outer casing 29 further comprises an outer deflector part 71 fixed to the concave shell 53.

The outer baffle piece 71 closes the opening 55 defined by the free edge 57, except for an area defining the exhaust gas mixer inlet 21 (FIGS. 3, 4 and 6).

The operation of the exhaust gas purification assembly 1 will now be detailed, with reference to Figure 7.

The exhaust gas flow lines, at the outlet of the first purification device 5, are straight. The exhaust gas flow is laminar.

The exhaust gas flow is diverted to the exhaust gas mixer inlet 21 by the outer baffle piece 71.

After passing through the exhaust gas mixer inlet 21, the exhaust gas flow follows the circulation passage 33. The exhaust gas flow is guided around the rotation axis R, and follows a trajectory which is not very different from a propeller.

This trajectory is substantially the opposite of the trajectory followed by a fluid in a centrifugal pump. It is tangential in the upstream part, and along the axis of rotation in the downstream part.

Following the circulation passage 33, the exhaust gas flow changes from a laminar flow to a vortex flow when it arrives at the exhaust gas mixer outlet 23. The exhaust gas flow, when it leaves the mixer 19 forms a vortex around the axis of rotation R.

The fluid is injected through the injector in the middle of the circulation passage 33. The deflector piece 31 prevents the fluid from flowing directly to the outlet of the exhaust gas mixer 23, in a straight line.

Virtually all of the exhaust gas flow passes below the injection port 37, the fluid thus being dispersed in a large quantity of exhaust gas.

Virtually all of the exhaust gas flow passes along baffle piece 31. When the fluid is a liquid, it is rapidly evaporated as the liquid droplets strike the surface of baffle piece 31, which is held high. temperature by the large quantity of exhaust gas flowing in contact with it.

The operation of the exhaust gas purification assembly according toFR3010137 is illustrated in Figure 8. Said exhaust gas purification assembly is arranged taking into account the same spatial constraints as the exhaust gas purification assembly of the invention shown in Figure 7. In particular, the injection port is at the same position.

As visible in Figure 8, two vortices are formed, around respective axes of rotation parallel to the central exit axis.

However, because the space available for the vortices to develop is limited, the exhaust gas flow lines at the outlet of the mixer are substantially straight.

In the exhaust gas purification assembly of the invention, the flow of exhaust gas forms a vortex all along the duct 27, up to the second purification device 7 (FIG. 9).

In the exhaust gas purification assembly according to FR3010137 , the exhaust gas flow lines are substantially straight along the conduit 27, as shown in Figure 10.

The invention has been described with an injection orifice located along or close to the first central axis of the first purification device. According to a variant embodiment, the injection orifice is not located along or close to the first central axis.

Claims (12)

Exhaust gas purification kit, comprising:
- a first exhaust gas purification device (5) with a first central axis (X1);
- a second exhaust gas purification device (7) with a second central axis (X2);
- a mixer (19) having an exhaust gas mixer outlet (21) fluidly connected to the first exhaust gas purification device (5) and an exhaust gas mixer outlet (23) fluidly connected to the second exhaust gas purifying device (7), the exhaust gas mixer inlet (21) having an inlet center axis (C1) and the exhaust gas mixer outlet (23) having a central exit axis (C2), the central entry axis (C1) defining with the central exit axis (C2) an angle β of between 60° and 120°;
- the mixer (19) comprising an outer casing (29) defining the exhaust gas mixer inlet (21) and the exhaust gas mixer outlet (23) and a deflector part (31) located at the inside the outer casing (29), the mixer (19) comprising a single circulation passage (33) extending from the exhaust mixer inlet (21) to the exhaust mixer outlet exhaust gas (23), defined by the deflector part (31) and the outer casing (29) and extending around an axis of rotation (R) over an angle comprised between 270° and 450°;
the mixer comprising an injector (35) arranged to inject a fluid inside the circulation passage (33) towards the deflector piece (31). Exhaust gas purification assembly according to Claim 1, in which the axis of rotation (R) defines with the central outlet axis (C2) an angle comprised between 0° degree and 30° degree. Exhaust gas purification assembly according to claim 1 or 2, wherein the injector (35) is attached to an injection port (37) of the outer casing (29) located opposite the mixer outlet of exhaust gas (23) in an injection direction (I), the deflector piece (31) extending between said injection orifice (37) and the outlet of the exhaust gas mixer (23) along the direction of injection (I). Exhaust gas purification unit according to Claim 3, in which the direction of injection defines with the axis of rotation (R) an angle (γ) comprised between 0° and 45°. Exhaust gas purification assembly according to any one of Claims 1 to 4, in which the first exhaust gas purification device (5) comprises a purification member (39) and a tubular casing (41) in which the purification member (39) is housed, the tubular casing (41) having an open downstream axial end (45), the outer casing (29) of the mixer (19) being directly attached to said downstream axial end ( 45) and closing said downstream axial end (45). Exhaust gas purification assembly according to Claim 5 in conjunction with Claim 3 or 4, in which, in projection in a plane perpendicular to the first central axis (X1), the tubular casing (41) defines a closed contour line (49) around the first central axis (X1) and the injection orifice (37) defines a projected orifice (51) located inside the closed contour line (49), the closed contour line (49 ) having a maximum distance from the first central axis (X1), a distance between the projected orifice (51) and the first central axis (X1) being between 0% and 50% of said maximum distance. Exhaust gas purification assembly according to any one of claims 5 or 6, wherein the outer casing comprises a concave shell (53) having an opening (55) bounded by a free edge (57) directly attached to the tubular casing (41). Exhaust gas purification assembly according to claim 7, wherein the concave shell (53) comprises a first half-shell (59) and a second half-shell (61) fixed to each other and together defining the free edge (57), the first half-shell defining the exhaust gas mixer outlet (23). Exhaust gas purification assembly according to Claim 8, in which the second half-shell (61) comprises a first planar zone (63) carrying the injection orifice (37) and extending substantially perpendicular to the axis of rotation (R), and a second planar zone (65) substantially perpendicular to the first central axis (X1). An exhaust gas purification assembly according to any of claims 7 to 9, wherein the outer shroud (29) comprises an outer baffle piece (71) attached to the concave shell (53), the outer baffle piece ( 71) closing the opening (55) except in an area defining the exhaust gas mixer inlet (21). Exhaust line (3) comprising an exhaust gas purification assembly (1) according to any one of claims 1 to 10. Vehicle comprising an exhaust line (3) according to claim 11.