WO2018104278A1 - Device and method for injecting a mixing gas into an exhaust line - Google Patents

Abstract

A device for injecting a mixing gas into an exhaust gas exhaust line of an engine, the device comprising: one or more inlet openings, a plurality of walls comprising: o a first wall (31) and; o a second wall (32) having one or more outlet openings and being arranged downstream of the first wall, and means (36) for injecting the mixing gas between the first wall and the second wall, so as to allow the mixing gas and the exhaust gases to be mixed between the first wall and the second wall.

Description

 DEVICE AND METHOD FOR INJECTING A GAS TO MIX IN AN EXHAUST LINE

Field of the invention

The invention generally relates to the injection of a gas to be mixed, and in particular to an injection device, for example in an exhaust gas exhaust line of an engine. The invention further relates to an assembly, an exhaust line and a method thereof.

State of the art

Transmission-related pollutant emissions have been a major driver of industry progress for nearly 30 years. The gradual increase in the severity of the emission limits for the four regulated pollutants (CO, HC, NO _x , particles) has significantly improved air quality, particularly in large cities.

The ever-increasing use of the automobile requires continued efforts to further reduce these pollutant emissions. Having high-efficiency depollution technologies in all driving conditions is therefore a major challenge for the transport industry. In this context, the reduction of nitrogen oxides (NO _x ) to a lean mixture, that is to say a mixture comprising excess oxygen, represents an important issue associated with a complex problem.

In addition, fuel consumption, directly linked to CO2 emissions, has been propelled in a few years into a major automotive concern. Thus, regulations have been put in place at European level since 2012 on CO2 of private vehicles. It is already clear that this limit will be lowered regularly over the coming decades. Reducing CO2 emissions has therefore become the new engine of growth for the entire transport industry.

This double problem of reducing local pollution (NO _x ) and reducing fuel consumption (CO2) is particularly difficult to solve for the Diesel engine whose combustion in lean mixture is accompanied by emissions in NO _x difficult to treat. .

In this context, SCR (Selective Catalytic Reduction) after-treatment technology is used for both passenger cars and freight vehicles. It is then possible to position the engine on its optimal operation in efficiency, the high NO _x emissions being then treated in the exhaust by the SCR system allowing NOx reduction with high efficiency.

 SCR involves mixing an agent, for example a gas or a liquid, in particular a reducing agent such as a reducing gas, for example gaseous ammonia, with the exhaust gas and passing the mixture through or on a catalyst placed in the exhaust line.

At the catalyst level, the reducing agent converts the nitrogen oxides to nitrogen and water. When the reducing agent is NH 3 ammonia, the reaction is as follows:

It is possible to inject a solution of urea (and thus a liquid), which is converted into ammonia under the effect of the heat of the exhaust gas. An aqueous solution of urea retained and standardized for the operation of systems currently in series with SCR is referenced in AUS32 (the trade name in Europe being Adblue ®)

 This very efficient process, however, suffers from a number of disadvantages. It has a limited cold efficiency, whereas such a situation occurs in several cases, including that of buses in the city. The urea reservoir has a large mass and volume, typically 15 to 30L for a particular vehicle, 40 to 80L for a truck. Such a congestion causes a complexity of integration into the vehicle all the more important that the vehicle is small. This results in a high cost of depollution, as well as a surplus of mass which is detrimental to the fuel consumption of the vehicle and therefore of the CO2 emissions.

 The reducer can be injected as a gas to be mixed. This is possible for example by storing in solid form the reducing agent, for example ammonia, for example by absorption of the gas inside a material, for example a salt. Storage of gas, for example ammonia, is then carried out in the salt by the formation of ammonia-type chemical complexes.

 The storage of gas to be mixed, for example of reducing agent, in the form of absorbed gas has the advantage of a gain in volume with respect to a liquid, for example an aqueous solution, as well as an increased cold efficiency. a greater compactness of the mixing zone with the exhaust gases, in particular.

 If the agent is injected as a gas to be mixed, it is difficult to mix with the exhaust gas, which may affect the effectiveness of the reaction of interest, for example SCR. A mixer may be disposed downstream of the injection, however the effectiveness of the known devices remains limited.

Another problem associated with injecting a gas, for example gaseous ammonia, into the exhaust line comes from more and more important in the line as more elements are added (catalysts, filter, injector, sensors, etc.). This limits the possibilities of producing the elements necessary for a reaction, for example the SCR.

Summary of the invention

An object of the invention is to make more compact elements associated with the injection and the gas mixture along the exhaust line.

For this purpose, there is provided a device for injecting a gas to be mixed into an exhaust gas exhaust line of an engine, the device comprising for example:

 - one or more entrance openings,

 a plurality of walls comprising:

 o a first wall, and

 a second wall having one or more outlet openings and disposed downstream of the first wall, and

 means for injecting the gas to be mixed between the first wall and the second wall,

so as to allow mixing of the gas to be mixed and exhaust gas between the first wall and the second wall. Such a device is particularly compact. In particular, it no longer requires a mixer downstream of the injection, the injection device ensuring mixing of the gas to be mixed and exhaust gas. In addition, the mixture is particularly effective. The invention is advantageously completed by the following features, taken alone or in any of their technically possible combinations:

 - The plurality of walls comprises at least one intermediate wall disposed between the first wall and the second wall, the intermediate wall comprising one or more openings;

means for diverting at least one zone, at at least one opening, configured to form fluid communication between at least one opening of one wall of the plurality of walls upstream of the zone with at least one opening a wall of the plurality of walls downstream of the zone without passing through the zone;

 a side wall connecting the first wall and the second wall and delimiting with the first wall and the second wall an interior space,

 - The injection device is adapted to be disposed within the exhaust line, so as to allow the passage of exhaust gas between the side wall and the wall of the exhaust line;

 the side wall is distinct from the wall of the exhaust line;

 the device comprises means for fastening the device to the exhaust line;

 the device forms a section of the exhaust line,

the side wall is in contact with the exhaust line and / or forms a part of the wall of the exhaust line;

 gas supply means for mixing injection means,

 the fixing means comprise the feeding means;

the first wall and / or the side wall has one or more inlet openings. the injection means are arranged at the level of the first wall and / or extend between the first wall and the second wall from the first wall;

 for at least one wall of the plurality of walls, the dimensions of the openings and / or the total empty area and / or the total empty surface density and / or the total empty density and / or the quantity of openings varies. ;

 the dimensions of the openings and / or the total empty area and / or the total empty surface density and / or the total empty density and / or the quantity of openings of at least one wall varies (s) with respect to at least one other wall of the plurality of walls.

The invention also relates to an exhaust line comprising such a device.

The invention also relates to an assembly comprising a motor and a system and / or an exhaust line, the assembly comprising such a device. The invention is advantageously completed by the following features, taken alone or in any of their technically possible combinations:

 - a selective catalytic reduction system for exhaust gas, and / or an oxidation catalyst

The invention also relates to a vehicle comprising such a device and / or such an exhaust line and / or an assembly.

The invention also relates to a method of a gas to be mixed in an exhaust gas exhaust line of an engine implemented by means of such a device, comprising the following steps: - exhaust gas inlet between the first wall and the second wall,

 injecting the gas to be mixed between the first wall and the second wall,

 - mixture of the exhaust gases entered and the mixed gas injected,

 - Exit of the exhaust gas and the mixed gas mixed by the at least one opening of the second wall. Brief description of the figures

Other features and advantages of the invention will become apparent in the following description of an embodiment. In the accompanying drawings:

 FIG. 1 schematically represents an exhaust line according to an exemplary embodiment of the invention,

 FIG. 2 schematically represents a heat engine equipped with a selective catalytic reduction system for the exhaust gas of an engine according to an exemplary embodiment of the invention,

 FIGS. 3a, 3b and 3c schematically show side, front and rear views of an injection device according to an exemplary embodiment of the invention,

 FIG. 4 diagrammatically represents a perspective view of an injection device according to another exemplary embodiment of the invention,

FIG. 5 schematically represents a perspective view of an injection device according to yet another exemplary embodiment of the invention, FIGS. 6a, 6b and 6c schematically represent walls according to examples of embodiments of the invention,

 FIG. 7 schematically represents a side view of an injection device according to yet another exemplary embodiment of the invention,

 - Figure 8 schematically shows an injection method according to another example embodiment of the invention. Detailed description of the invention

Exhaust line and set

Referring to Figure 1, there is described an exhaust gas exhaust line of a motor 1, the exhaust line comprising a device for injecting a gas to be mixed in an exhaust line of exhaust gas from an engine as described below. Alternatively or in addition, there is described an assembly comprising such a motor and / or such an exhaust line, the assembly comprising the injection device. Alternatively or in addition, there is described a vehicle comprising such an exhaust line or such an assembly. The exhaust line comprises for example a wall.

 For example, the gas to be mixed is or comprises a reducing gas, or consists essentially of a reducing gas. The reducing gas is, for example, gaseous ammonia and / or gaseous hydrogen. The gas to be mixed is or comprises, for example, oxygen.

The engine 1 is for example a heat engine. The engine may be an internal combustion engine, for example a diesel engine, or a lean gasoline engine, such as a direct injection engine with a stratified mixture. The engine 1 is for example equipped with a selective catalytic reduction system for exhaust gas, for example by means of a reducing gas, for example gaseous ammonia and / or hydrogen, as described below. .

 The exhaust line or the assembly is for example configured so that, at the output of the engine 1, exhaust gases 12 from the engine are for example directed to a pollution control system 2. The line of Exhaust or the assembly comprises for example the pollution control system 2. The pollution control system 2 may comprise an oxidation catalyst, for example a diesel oxidation catalyst, and / or a three-way catalyst. The pollution control system 2 may further comprise a particulate filter.

 A device 3 for injecting the gas to be mixed, for example ammonia and / or hydrogen and / or gaseous oxygen, into an exhaust gas exhaust line of an engine as described below. after is for example disposed downstream of the output of the engine 1, for example downstream or upstream of the pollution control system 2. The exhaust line or the assembly comprises for example the device 3.

 Downstream means in the direction of flow of the exhaust gas along the exhaust line, that is to say in the direction from the engine to the outlet of the exhaust.

 Upstream means in the opposite direction of the flow of exhaust gas along the exhaust line, that is to say in the direction from the exhaust outlet to the engine.

The device 3 makes it possible to inject gas to be mixed at the level of the exhaust line of the engine and to mix it with the exhaust gases. The device 3 makes it possible, for example, to form a mixing gas / exhaust gas mixture 13. An additional mixer (not shown) may for example be added downstream of the device to further mix the gas to be mixed with the exhaust gas. However, the device 3 already allows mixing and the mixer is no longer necessary or can be greatly reduced in its dimensions.

 At least at the level of the device 3, the exhaust line comprises a portion having a section in which the exhaust gas flows, this section being delimited by an exhaust line wall.

 An SCR catalyst 4 may for example be arranged downstream of the device, for example downstream of the mixer. The exhaust line or the assembly comprises for example the SCR catalyst. The SCR catalyst is thus adapted to be traversed by the mixing gas / exhaust gas mixture. The catalyst SCR 4 is for example adapted to allow the reduction of NOx by the gas to be mixed. The device 3 can for example form an SCR catalyst, so that the SCR catalyst can be omitted or reduced in size.

At least one additional post-processing element, for example a plurality of such elements, can be positioned downstream of the SCR catalyst 4. The exhaust line or the assembly comprises, for example, the complementary element 5. The complementary element 5 may comprise a particulate filter or an oxidation catalyst. The exhaust gases are thus in the form of exhausted exhaust gases 14 at the outlet of the complementary element 5. Alternatively or in addition, the catalyst SCR 4 can comprise the complementary element 5. The catalyst SCR 4 can thus for example, comprising a particulate filter, in particular a diesel particulate filter (DPF), so as to form a SCR filter catalyst (SCRF, in the English terminology "selective catalytic reaction on filter "). It is thus possible to achieve a new space saving by making an exhaust line or a system without complementary element 5 or with a complementary element 5 of reduced size. The line may comprise an exhaust outlet 17 disposed downstream of the device 3, for example downstream of the catalyst SCR 4, for example downstream of the complementary element 5. The exhaust gases that have been decontaminated are, for example, subsequently directed towards the exhaust outlet 17. Thus the exhaust comprises, arranged from upstream, engine side 1, downstream, outlet side 17, for example the depollution element 2, the device 3, for example the catalyst SCR 4 , and for example the complementary element 5. System and together

Referring to Figure 2, there is described a system, for example a selective catalytic reduction system, for the exhaust gas of such a motor 1, comprising such an injection device as described below. Alternatively or in addition, there is described an assembly comprising such an engine and such a system. Alternatively or in addition, there is described a vehicle comprising such a system or such an assembly.

 The engine 1 is for example driven by an electronic computer 1 1. The system or assembly comprises, for example, the electronic computer 1 1.

The system or assembly may comprise a storage chamber 8 of gas to be mixed, for example ammonia and / or hydrogen and / or gaseous oxygen. The storage enclosure 8 may comprise and / or contain a storage structure 7. The storage structure 7 may, for example, be temperature-controlled by heating means 9, for example a heating element, the system or the heating element. together. It is thus possible to provide a feed and a dosage of the gas to be mixed at a gas inlet 16 mixing device 3, for example ammonia and / or hydrogen and / or oxygen gas. Alternatively or additionally, the heating means are or comprise, for example, means or an element of reheating and / or cooling. The heating means 9 comprise for example an electrical resistance or a heat exchanger supplied by a coolant such as the engine coolant.

 The heating means 9 make it possible, for example, to supply heat directly inside the storage enclosure 8. Alternatively or in addition, the heating means 9 make it possible, for example, to transmit heat from the outside. enclosure 8 towards the inside of the enclosure 8.

 In particular, the heating means 9 make it possible, for example, to supply heat to the storage structure 7.

 The storage structure 7 comprises for example a material adapted to allow solid storage of gas to be mixed. The material comprises, for example, a salt, for example an alkaline earth salt. The storage structure 7 comprises, for example, a layer of storage material, for example at least two layers of storage material, the storage material being, for example, a powdery salt, the at least two layers of powdered salt being, for example, separated from each other. one of the other by at least one layer of a thermally conductive and / or deformable material.

 The layers of the storage structure 7 may have a symmetry of revolution of the same axis. The storage structure 7 may for example have a recess within it, for example along an axis of symmetry of revolution, to ensure the storage and / or destocking of gas to be mixed at each salt layer.

 The storage structure 7 may comprise channels for conveying gas to be mixed, for example ammonia and / or hydrogen and / or oxygen gas, from the outside of the storage enclosure 8 to the layers salt and / or in the opposite direction.

The heating means 9 may comprise one or more heating modules (not shown), each heating module being adapted to heat a salt layer independently of the other heating module (s) and / or independently of the other salt layers.

 The storage enclosure 8 is for example connected to a pressure control element 6 of the storage and / or gas dosing chamber to be mixed, for example ammonia and / or hydrogen and / or gaseous oxygen, to the device 3. This element 6 can be controlled by a dedicated electronic controller 10 connected to the electronic computer 1 1 of the engine. In an alternative configuration not shown, the element 6 can be directly controlled by the engine computer 1 1.

 The element 6 is for example a valve, for example a solenoid valve.

 The system or assembly may thus comprise a gas supply system for mixing, for example ammonia and / or hydrogen and / or gaseous oxygen, comprising, from upstream to downstream in the direction of circulation. gas to be mixed, for example the storage enclosure 8, for example the element 6, and for example the device 3 for injecting gas to be mixed in the exhaust. Device

General structure

With reference to FIGS. 3a-c to 7, there is described a gas injection device for mixing, for example ammonia and / or hydrogen and / or gaseous oxygen, in a gas exhaust line. exhaust of an engine, for example the exhaust line and / or the engine as described above.

 The device comprises for example a plurality of walls.

 The plurality of walls comprises for example a first wall

31. The device comprises for example one or more inlet openings 31 1.

 The first wall 31 has for example one or more inlet openings 31 1, for example the single inlet opening or all of the inlet openings. The first wall 31 can thus form an input wall.

 The plurality of walls comprises for example a second wall 32. The second wall 32 has for example one or more outlet openings 321. The second wall is for example disposed downstream of the first wall. The second wall 32 can thus form an exit wall.

 The device comprises, for example, injection means 36 for mixing gases, for example ammonia and / or hydrogen and / or gaseous oxygen. The injection means are for example adapted to allow the injection of the gas to be mixed between the first wall and the second wall.

 The injection means and / or the plurality of walls and / or the device is or are, for example, configured so as to allow mixing of the gas to be mixed and exhaust gas between the first wall and the second wall. .

The inlet opening or openings may thus allow the exhaust gases coming from the upstream of the exhaust line to penetrate into a space between the first wall 31 and the second wall 32 where the gas to be mixed is also introduced. . The plurality of walls and the inlet openings 31 1 and outlet 321 make it possible to limit the space and the flow of fluid at the inlet and outlet of this space, so as to thus form a mixing zone. The outlet opening (s) 321 may thus allow the mixture of exhaust gas and gas to be mixed to exit the mixing zone towards the outlet 17 of the exhaust. Such a device is particularly compact. In particular, it no longer requires a mixer downstream of the injection, the injection device ensuring the mixing of the reducing gas and the exhaust gas. In addition, the mixture is particularly effective.

Plurality of walls

The plurality of walls may comprise at least one intermediate wall, for example a plurality of intermediate walls. Each intermediate wall is for example disposed between the first wall 31 and the second wall 32. Each intermediate wall may comprise one or more opening (s) intermediate (s). It is thus possible to adapt the flow between the first wall 31 and the second wall 32 to improve the mixing between the gas to be mixed and the exhaust gas, for example by modulating or controlling the flow, for example by limiting the decrease in gas flow. The plurality of intermediate walls may for example comprise a third wall 33 comprising one or more intermediate opening (s) 331 and a fourth wall 34 comprising one or more intermediate opening (s) 341.

The plurality of walls may thus comprise a total of at least three walls, for example four walls, for example five walls, for example more than five walls, for example ten walls, for example more than ten walls. The first wall 31 and / or the second wall 32 and / or the at least one intermediate wall, for example each wall of the plurality of walls, is for example separated from the adjacent wall (s) of the plurality of walls. for example separated from each other wall of the plurality of walls, for example so as to form with each adjacent wall a mixing zone. The plurality of walls can thus form a stack of walls spaced from each other by at least one zone. The zone disposed directly downstream of the first wall, for example between the first wall and the second wall in the absence of an intermediate wall, or otherwise between the first wall and the most upstream intermediate wall, forms for example the first zone. . In the case where the device comprises at least one intermediate wall, the next zone then forms the second zone, and so on by recurrence the n-th zone, until the last zone which is the zone between the intermediate wall arranged on the further downstream and the second wall. By n-th zone thus denotes at least one zone between the first and the last zone, including the first zone and the last zone. At least one nth zone forms, for example, an exchange zone between the exhaust gas entering the device and the gas to be mixed injected into the device.

 The first wall 31 and / or the second wall 32 and / or the at least one intermediate wall, for example each wall of the plurality of walls, may comprise an upstream face facing upstream and a downstream face facing towards the downstream. The upstream face can form an entrance face. The downstream face can form an exit face.

 The first wall 31 and / or the second wall 32 and / or the at least one intermediate wall is for example flat and / or has a plane upstream face and / or a flat downstream face.

The first wall 31 and / or the second wall 32 and / or the at least one intermediate wall is for example curved and / or has an upstream face and / or a curved downstream face, for example convex or concave. The first wall 31 is for example concave, the concavity being turned upstream. It is thus possible to concentrate the flow of exhaust gas, for example towards a central part of the section of the device and / or the exhaust line. The second wall 32 is for example concave, the concavity being turned downstream. It is thus possible to disperse the flow of exhaust gas, for example to the outside of the section of the device and / or the exhaust line or all over this same section.

 The first wall 31 and / or the second wall 32 and / or the at least one intermediate wall, for example each wall of the plurality of walls, for example has dimensions strictly smaller than that of the section of the exhaust line. , or substantially equal to those of the section of the exhaust line. The exhaust line, for example a motor vehicle, has for example a diameter of between 25 and 75 mm, for example about 50 mm.

The device may be devoid of sidewall. In this case, the injection and / or mixing zone is defined by the plurality of walls, which affect the gas flow.

 Alternatively, the device may further comprise a side wall 35. The side wall connects for example the first wall 31 and / or the second wall 32 and / or at least one intermediate wall, and / or all the walls of the plurality of walls. . The side wall 35 defines for example with the first wall 31 and the second wall 32 an interior space. This interior space is for example the one in which gas injection is performed to mix and mix with the exhaust gas. This interior space includes for example at least one nth zone, for example all the nth zones.

 The side wall may be distinct from the exhaust line and the device comprising means for fixing the device to the exhaust line. In this case, the device may have at least partly a section smaller than that of the section of the exhaust line. The device may then have for example a pommel shape.

The device 3 may extend over the entire section of the exhaust line, the side wall being for example in contact with the wall of the exhaust line and / or forming or being formed by a part of the wall of the exhaust line. exhaust line. The side wall is for example substantially cylindrical. The side wall is for example symmetrical of revolution. The side wall may have, in section passing through the central axis of the exhaust line portion and / or by the axis of the device and / or by the axis of symmetry of the side wall, a straight wall and / or or convex and / or concave.

 The device 3 and / or the side wall 35 has for example a section, for example an outer and / or internal section that is substantially constant, that is to say not varying more than 2% in area.

 The device 3 and / or the side wall 35 has for example a section, for example an outer and / or internal section, strictly increasing or decreasing from upstream to downstream. The device 3 and / or the side wall 35 has for example a section in the form of a truncated cone.

 The device 3 and / or the side wall 35 has for example a section, for example an external and / or internal section, comprising an increasing or decreasing portion and a substantially constant section, for example only two such portions. The device 3 and / or the lateral wall 35 has for example a section, for example an external and / or internal section, comprising from upstream to downstream an increasing portion, for example in the form of a truncated cone, and a substantially constant section. .

 The side wall 35 has for example one or more inlet openings, for example the single inlet opening or all of the inlet openings. The side wall 35 can thus form an inlet wall. These inlet openings may be arranged upstream of the outlet opening (s).

The side wall is for example full and devoid of lateral openings. Alternatively, the side wall has for example one or more lateral opening (s) 351. The lateral opening (s) 351 can thus also allow the exhaust gases coming from the upstream of the exhaust line to penetrate into the space between the first wall 31 and the second wall 32 where the gas to mix is also introduced. Alternatively or in addition, the, some, or the side openings (s) can also allow the mixture of exhaust gas and gas to mix out of the mixing zone towards the outlet 17 of the exhaust.

 Side openings may vary along the sidewall

35, for example from upstream to downstream. Thus, possibly in combination with the plurality of walls, it is possible to further adapt the flow between the first wall 31 and the second wall 32 to improve the mixing between the gas to be mixed and the exhaust gas, for example by modulating or by controlling the flow, for example by limiting the decrease in gas flow.

The injection device is for example adapted to be disposed inside the exhaust line, for example so as to allow the passage of exhaust gas out of the device, for example between the side wall and the wall of the device. exhaust line. It is thus possible to bring exhaust gases directly downstream of the device 3, so that they can mix with the mixture at the outlet of the device 3 and thus form a second mixing zone downstream of the device 3. device 3.

The first wall 31 and / or the second wall 32 and / or the at least one intermediate wall, for example each wall of the plurality of walls, and / or the side wall 35 is for example formed or comprises a plate.

The first wall 31 and / or the second wall 32 and / or the at least one intermediate wall, for example each wall of the plurality of walls, and / or the side wall 35 is for example made of metal, for example steel stainless steel, for example a composite material, for example a ceramic, for example coated with a catalytic impregnation for the in situ pollution control of the exhaust gas. Opening

At least one inlet opening 31 1 and / or outlet opening 321 and / or intermediate opening 331 and / or 341 and / or lateral opening 351, for example each such opening, may be or comprise a through orifice. In the description, unless otherwise indicated, opening means in particular an inlet opening 31 1 and / or outlet 321 and / or intermediate 331 and / or 341 and / or lateral 351.

 For example, it is possible to modify the distribution and the shape of the openings of one wall of the plurality of walls to the other and / or along the side wall and / or from one nth zone to the other. .

Each inlet opening 31 1 and / or outlet opening 321 and / or intermediate opening 331 and / or 341 and / or lateral opening 351 may have dimensions, for example substantially constant dimensions on the same wall and / or a wall with the other. The dimensions include or are for example the diameter and / or the length and / or the width. The dimensions of at least one opening, for example each inlet opening 31 1 and / or outlet 321 and / or intermediate 331 and / or 341 and / or lateral opening 351 are for example less than or equal to 5 cm, by for example less than or equal to 1 cm, for example less than or equal to 5 mm, for example greater than or equal to 0.05 mm, for example greater than or equal to 0.1 mm, for example greater than or equal to 0.5 mm, for example of the order of 1 mm, for example substantially equal to 1 mm.

For at least one wall of the plurality of walls, the dimensions, for example the diameter, of the at least one opening may vary, for example according to a gradient, for example from the center to the periphery. For example, the dimensions of the openings in a central zone of at least one wall of the plurality of walls may be greater than or equal to, for example, strictly greater than those of a peripheral zone of the same wall. For example, the dimensions of the openings in a peripheral zone of at least one wall of the plurality of walls may be greater than or equal to, for example, strictly greater than those of a central zone of the same wall. In particular, the dimensions of the openings of this wall can follow a gradient increasing or decreasing from the center to the periphery.

 For example, the plurality of walls may comprise an alternation of one or more walls whose dimensions of the openings in a central zone are greater than or equal to, for example strictly greater than, those of a peripheral zone, and one or more walls whose diameter of the openings in a peripheral zone are greater than or equal to, for example strictly greater than those of a central zone. For example, the plurality of walls may comprise an alternation of one or more walls whose diameters of the openings follow a gradient increasing from the center towards the periphery and one or more walls whose dimensions of the openings follow a decreasing gradient from the center towards the periphery.

Alternatively or in addition, the dimensions of the at least one opening of a wall of the plurality of walls, for example of the upstream or downstream face of this wall may vary from one wall to another and / or relative to the other, at least one or other walls of the plurality of walls or be substantially the same.

For example, the dimensions of the openings of at least one wall of the plurality of walls may be greater than or equal to, for example, strictly greater than those of the wall immediately upstream. It is thus possible to facilitate a suction effect and an upstream-downstream diffusion from the upstream openings, which improves the diffusion of the gas to be mixed and / or upstream exhaust gas downstream and thus their mixing.

 For example, the dimensions of the openings of each wall of the plurality of walls may be greater than or equal to, for example, strictly greater than those of the wall (s) of the plurality of upstream walls. This may allow to further increase the diffusion.

 For example, the dimensions of the openings of at least one wall of the plurality of walls may be less than or equal to, for example, strictly less than those of the wall immediately upstream. In this configuration, the dimensions of the orifices decrease from upstream to downstream, which makes it possible to increase the pressure gradient from upstream to downstream, and thus to cause disturbances of the flow and to avoid or limit a part of substantial flow does not pass directly through the device as under the effect of a bypass. The disturbed flows thus make it possible to promote the mixing of the gas to be mixed and the exhaust gases within the device.

 For example, the dimensions of the openings of each wall of the plurality of walls may be smaller than or equal to, for example, strictly less than those of the wall (s) of the plurality of upstream walls. This can further increase turbulence levels, including the establishment of many recirculation zones.

For a wall of the plurality of walls, or a portion of said wall, an empty total area is defined. The total empty area may be defined as the area occupied by the opening (s) of a wall, or part of said wall, at the upstream or downstream face, or the average of these measured surfaces for the upstream face and the downstream face.

For a wall of the plurality of walls, or a part of said wall, an empty total surface density is defined. The surface density total void can be defined as the ratio of the area occupied by the aperture (s) of a wall, or part of said wall, at the upstream face or the downstream face, or the average of these measured surfaces for the upstream face and the downstream face, with respect to the surface occupied by the material at the upstream face or the downstream face, or the average of these measured surfaces for the upstream face and the downstream face.

 For a wall of the plurality of walls, or a portion of said wall, an empty total volume density is defined. The total empty volume density can be defined as the ratio of the volume occupied by the opening or openings of a wall, or a part of said wall, relative to the volume occupied by the material.

 For a wall of the plurality of walls, or a portion of said wall, the number of distinct openings is defined as the number of openings.

 For at least one wall of the plurality of walls, the total void area and / or the total void density and / or the total void volume density and / or the amount of apertures may vary, for example according to a gradient, for example from the center to the periphery.

For example, the total void area and / or the total void density and / or the total void density and / or the amount of apertures in a central area of at least one wall of the plurality of walls may be greater than or equal to equal, for example strictly greater than that of a peripheral zone of the same wall. The central zone is further from the periphery than the peripheral zone, for example the central zone is included in the smallest solid surface comprising the peripheral zone on the wall considered. The central and / or peripheral zone is for example an annular zone. For example, the total void area and / or the total void density and / or the total void density and / or the amount of apertures in a peripheral area of at least one wall of the plurality of walls may be greater than or equal to equal, by example strictly superior to that of a central zone of the same wall. In particular, the total empty surface area and / or the total empty surface density and / or the total empty density and / or the amount of openings of this wall can follow a gradient increasing or decreasing from the center to the periphery.

 For example, the plurality of walls may comprise an alternation of one or more walls whose total void area and / or total empty surface density and / or the total void density and / or the amount of openings in a central area is greater than or equal to, for example strictly greater than, that of a peripheral zone, and of one or more walls whose total empty surface and / or the total empty surface density and / or the total empty density and / or the the amount of openings in a peripheral zone is greater than or equal to, for example, strictly greater than that of a central zone. It is thus possible, as illustrated in FIG. 5, to create currents alternately towards the center and towards the periphery of the device and / or the exhaust line, which allows even better mixing and lengthening of the distance over which the mixing takes place. For example, the plurality of walls may comprise an alternation of one or more walls whose total empty surface area and / or the total empty surface density and / or the total empty density density and / or the number of openings follows a gradient increasing from center to the periphery and one or more walls whose total void area and / or the total empty surface density and / or the total void volume density and / or the amount of openings follows a decreasing gradient from the center to the periphery.

For example, the total void area and / or the total empty surface density and / or the total void density and / or the amount of openings of at least one wall of the plurality of walls may be greater than or equal to, for example strictly superior to that of the wall immediately upstream. It is thus possible to facilitate a suction effect and a diffusion from upstream to downstream from the openings arranged upstream, which improves the diffusion of the gas to be mixed and / or upstream exhaust gas downstream and thus their mixing.

 For example, the total empty area and / or the total empty surface density and / or the total empty density and / or the quantity of openings of each wall of the plurality of walls may be greater than or equal to, for example, strictly greater, to that of the wall (s) of the plurality of walls upstream. This may allow to further increase the diffusion.

 For example, the total void area and / or the total void density and / or the total void density and / or the amount of apertures of at least one wall of the plurality of walls may be less than or equal to, for example strictly inferior to that of the wall immediately upstream. In this configuration, the pressure gradient can increase from upstream to downstream, and thus cause flow disturbances and avoid or limit the fact that a substantial part of the flow does not pass directly through the device as under the effect of a bypass. The disturbed flows thus make it possible to promote the mixing of the gas to be mixed and the exhaust gases within the device.

 For example, the total void area and / or the total void density and / or the total void volume density and / or the amount of apertures of each wall of the plurality of walls may be less than or equal to, for example, less than to that of the wall (s) of the plurality of walls upstream. This makes it possible to further increase the disturbances. With reference to FIGS. 6a to 6c, a wall of the plurality of walls may comprise a central portion, for example substantially elongated, for example ovoid.

The wall may further comprise at least one radial portion, for example a plurality of radial portions 621, 622, 623, 624, extending from the central portion to the periphery. The radial portion is for example an arm, for example a segment. The radial part is for example right. The wall may for example comprise one, two, three or four radial portions perpendicular and / or parallel to each other two by two.

 The wall may comprise at least one peripheral part 63, for example several peripheral parts 63, extending around the central part 61, for example without discontinuity, for example so as to form an annular band, for example defining an elongated shape, for example ovoidal. Each peripheral portion 63 comprises for example a plurality of sections 631, 632, 633, 634, for example of curved sections, connecting different radial portions. The peripheral portions may form different annular bands included one inside the other.

 The central portion 61 and / or the at least one radial portion and / or the at least one peripheral portion 63 are for example arranged so as to form between them or the openings of the wall considered.

 With reference to FIG. 6a, the dimensions of the openings of this wall may follow a gradient increasing from the center to the periphery, the total empty surface and / or the total empty surface density and / or the total empty density may vary according to a gradient growing from the center to the periphery. In particular, the spacing between the peripheral parts can follow a gradient increasing from the center to the periphery.

 With reference to FIG. 6b, the spacing between the peripheral portions may follow a decreasing gradient from the center to the periphery.

 With reference to FIG. 6c, the spacing between the peripheral portions may remain constant from the center to the periphery.

As illustrated in Figures 3b and 3c, at least a portion of the openings of a wall of the plurality of walls, for example all the openings of such a wall, are for example distributed in concentric circles. From one wall to the other, at least a portion of the openings of the walls of the plurality of walls are for example offset so as to modulate the flow. Catalyst

The device may comprise a catalyst arranged at at least one nth zone, for example at least the last zone. The first wall 31 and / or the second wall 32 and / or the at least one intermediate wall, for example each wall of the plurality of walls, and / or the side wall 35 may be covered at least partially by a coating ( "Washcoat" in English terminology), the coating comprising for example a porous structure, the coating supporting a catalyst and / or the catalyst impregnating the coating, for example an SCR catalyst and / or a catalyst of oxidation. It is thus possible for the device to ensure a SCR catalyst function and thus to eliminate or reduce the size of the possible SCR catalyst disposed downstream. The catalyst can form a coating. The catalyst may cover at least one wall face turned towards the inside of the device, that is to say a wall face which is not the face turned towards the outside of the first wall 31, of the second wall 32 or the side wall 35, in particular which is not the upstream face of the first wall 31, the downstream face of the second wall 32 or the outer face of the side wall 35. The zone at which the The catalyst is thus able to form an SCR catalyst.

Bypass

The device may comprise bypass means, that is to say bypass means, of at least one nth zone, for example a plurality of nth zones, at the level of at least one opening, configured to form fluid communication between at least one opening of a wall of the plurality of walls upstream of the n-th zone with at least one opening of a wall of the plurality of walls downstream of the n-th zone without passing through the n-th zone. The device may comprise a plurality of such bypass means of the same nth zone or nth different zones. Such bypass means make it possible to limit the mixing in one zone to a part of the flow, the other part of the flow being reinjected only in an area of the device situated downstream or downstream of the device, to be mixed. downstream.

 The device may comprise bypass or bypass means of the first zone and / or the second zone and / or the third zone and / or the nth zone and / or the last zone.

 The bypass means comprise, for example, a conduit, for example a tube, connecting the opening upstream and the opening downstream. Injection means

The injection means 36 comprise for example an injector, for example a multi-point injector. The injection means 36 comprise for example at least one branch, for example several branches. Each branch has for example at least one opening, for example a plurality of openings.

 The injection means 36 are for example arranged, for example at least in part, at, for example at a central portion of, the first wall 31 and / or the second wall 32. It is thus possible inject the gas to be mixed at a central section of the device.

The injection means are for example suitable for injecting the gas to be mixed between the first wall 31 and an intermediate wall, for example the upstream intermediate wall, for example the intermediate wall immediately downstream of the first wall 31. It is thus possible to form a first chamber of the device, for example the first zone, adapted for injection and a first possible mixture, and a second chamber of the device disposed downstream, for example downstream of the first zone, for thorough mixing.

 The injection means are for example suitable for injecting the gas to be mixed into a plurality of n-th zones, the injection varying for example from one zone to another, for example in terms of flow.

 Alternatively or in addition, the injection means 36 are for example arranged, for example at least in part, at the side wall 35. This allows for example to simplify the injection or to limit the amount of material required for its operation. manufacturing.

 The injection means 36 may not extend, or substantially not extend between the first wall 31 and the second wall 32. The injection means 36 may thus comprise one or more orifice (s) opening at the the first wall 31 and / or the second wall 32 and / or the side wall 35.

 Alternatively or in addition, the injection means 36 may extend between the first wall 31 and the second wall 32. The injection means 36 may for example extend in or along an intermediate wall. The injection means 36 may for example comprise an injection part extending between the first wall 31 and the second wall 32. The injection part comprises for example a pierced tube or a plurality of pierced tubes. Each pierced tube may comprise at least one gas injection orifice to be mixed, for example ammonia and / or hydrogen and / or oxygen gas, for example a plurality of gas injection orifices to be mixed. .

 The injection means 36 may for example extend from a central portion and / or the center of the first wall 31 and / or the second wall 32.

The device 3 and / or the exhaust line and / or the system may comprise supply means 361 for mixing gases, for example ammonia and / or hydrogen and / or gaseous oxygen, injection means. The supply means 361 comprise, for example, a supply duct.

Fixation

The device comprises for example fastening means to the exhaust line and / or the system, for example fastening means to the wall of the exhaust line.

 The fixing means comprising, for example, the injection means and / or the supply means.

 The fixing means comprise, for example, means for fixing the first wall and / or the second wall and / or at least one intermediate wall, for example disposed at the periphery of this wall or these walls.

 The first wall 31 and / or the second wall 32 and / or at least one intermediate wall is for example connected and / or fixed to another wall of the plurality of walls by means of connection and / or attachment between dedicated walls, these means being for example separate from the side wall 35. The connecting means and / or securing between walls comprise for example a connecting wall and / or fixing, for example in contact with and / or attached to a central portion of each wall connected and / or fixed. The connecting wall forms for example a tube. The fixing means of the device are for example in contact with the fixing means and / or connection between walls to ensure the attachment of the device.

Examples of devices

With reference to Figures 3a to 3c, there is described such a device 3. The arrow in Figure 3a shows the direction of flow. The first wall 31 and the second wall 32 are for example planar. The first wall 31 and the second wall 32 have for example dimensions strictly smaller than that of the section of the exhaust line. The injection device is for example adapted to be disposed inside the exhaust line, for example so as to allow the passage of exhaust gas out of the device, for example between the side wall and the wall of the device. exhaust line.

 The device may further comprise a side wall 35. The side wall connects for example the first wall 31 and the second wall 32. The side wall 35 defines for example with the first wall 31 and the second wall 32 an interior space. This interior space is for example the one in which gas injection is performed to mix and mix with the exhaust gas. This interior space includes for example the first zone. The side wall may be distinct from the exhaust line and the device comprising means for fixing the device to the exhaust line. In this case, the device may have at least partly a section smaller than that of the section of the exhaust line. The device may then have for example a pommel shape. The side wall is for example substantially cylindrical. The side wall is for example symmetrical of revolution. The device 3 and the side wall 35 have for example a decreasing section.

 Each wall of the plurality of walls is for example formed or comprises a plate, for example of metal.

 Each inlet opening 31 1 and / or outlet opening 321 may be a through orifice.

The total empty area and / or the total empty surface density and / or the total empty density and / or the quantity of openings of the second wall may be strictly greater than that of the first wall. The first wall 31 may comprise less than twenty inlet openings 31 1, for example less than ten openings. The second wall 32 may comprise at least forty, for example at least fifty, for example at least sixty outlet openings 321. The injection means 36 comprise for example an injector. The injection means 36 are for example arranged at a central portion of the first wall 31. The injection means 36 may not extend between the first wall 31 and the second wall 32. The device 3 and / or the exhaust line and / or the system may comprise means for supplying gas 361. mix injection means. The supply means 361 comprise, for example, a supply duct.

 The fixing means comprising, for example, the injection means and / or the supply means.

Referring to Figure 4, there is described another such device 3. The arrows in Figure 4 show the direction of flow and flow lines. The first wall 31 and the second wall 32 are for example curved, for example convex or concave. The first wall 31 is for example concave, the concavity being turned upstream. It is thus possible to concentrate the flow of exhaust gas, for example towards a central part of the section of the device and / or the exhaust line. The second wall 31 is for example concave, the concavity being turned downstream. It is thus possible to disperse the flow of exhaust gas, for example out of the section of the device and / or the exhaust line or over the entire section.

 The first wall 31 and the second wall 32 have for example dimensions strictly smaller than that of the section of the exhaust line. The injection device is for example adapted to be disposed inside the exhaust line, for example so as to allow the passage of exhaust gas out of the device, for example between the side wall and the wall of the device. exhaust line.

The device may further comprise a side wall 35. The side wall connects for example the first wall 31 and the second wall 32. The side wall 35 defines for example with the first wall 31 and the second wall 32 an interior space. This interior space is for example the one in which gas injection is performed to mix and mix with the exhaust gas. This interior space includes for example the first zone. The side wall may be distinct from the exhaust line and the device comprising means for fixing the device to the exhaust line. In this case, the device may have at least partly a section smaller than that of the section of the exhaust line. The device may then have for example a pommel shape. The side wall is for example substantially cylindrical. The side wall is for example symmetrical of revolution. The side wall may have, in section passing through the axis of the device and / or the axis of symmetry of the side wall, a straight wall. The device 3 and the side wall 35 have for example a substantially constant section. The side wall has for example several lateral openings 351.

 Each wall of the plurality of walls is for example formed or comprises a plate, for example of metal.

 Each inlet opening 31 1 and / or outlet 321 and / or lateral opening 351 may be a through orifice.

 Each inlet opening 31 1 and / or outlet 321 and / or intermediate 331 and / or 341 and / or lateral 351 may have substantially constant dimensions.

The injection means 36 comprise for example an injector. The injection means 36 may extend between the first wall 31 and the second wall 32. The injection means 36 may for example comprise an injection part extending between the first wall 31 and the second wall 32. The injection portion comprises for example a pierced tube. The device 3 and / or the exhaust line and / or the system may comprise gas supply means 361 to mix injection means. The supply means 361 comprise, for example, a supply duct. The fixing means comprising, for example, the injection means and / or the supply means.

With reference to FIG. 5, another such device 3 is described. The arrows in FIG. 5 represent the direction of flow and flow lines. The device 3 may comprise a plurality of intermediate walls. Each intermediate wall is for example disposed between the first wall 31 and the second wall 32. Each intermediate wall may comprise a plurality of intermediate openings. It is thus possible to adapt the flow between the first wall 31 and the second wall 32 to improve the mixing between the gas to be mixed and the exhaust gas, for example by modulating or controlling the flow, for example by limiting the decrease in gas flow. The plurality of intermediate walls may for example comprise a third wall 33 comprising a plurality of intermediate openings 331 and a fourth wall 34 comprising a plurality of intermediate openings 341.

 The plurality of walls may thus comprise a total of at least four walls, for example exactly four walls.

 The first wall 31, the second wall 32 and the intermediate walls 33 and 34 are for example flat.

 The first wall 31 and the second wall 32 have for example dimensions substantially equal to that of the section of the exhaust line. The injection device can extend over the entire section of the exhaust line

The device may further comprise a side wall 35. The side wall connects for example the first wall 31, the second wall 32, and the two intermediate walls 33 and 34. The side wall 35 delimits for example with the first wall 31 and the second wall 32 an interior space. This interior space is for example the one in which gas injection is performed to mix and mix with the exhaust gas. This interior space includes for example the first, second and third zones. The device 3 may extend over the entire section of the exhaust line, the side wall 35 being formed by a portion of the wall of the exhaust line. The side wall is for example substantially cylindrical. The side wall is for example symmetrical of revolution. The side wall may have, in section passing through the central axis of the exhaust line portion the axis of the device and / or the axis of symmetry of the side wall, a straight wall. The device 3 and the side wall 35 have for example a substantially constant section.

 Each wall of the plurality of walls and the side wall 35 are for example formed or each comprise a plate, for example metal.

 The plurality of walls may comprise an alternation of one or more walls whose diameters of the openings follow a gradient increasing from the center towards the periphery, for example the intermediate wall 33 and / or the second wall 32 and one or more walls of which the dimensions of the openings follow a decreasing gradient from the center to the periphery, for example the first wall 31 and / or the intermediate wall 34.

 Alternatively or in addition, the plurality of walls may comprise an alternation of one or more walls whose total empty surface area and / or the total empty surface density and / or the total empty density density and / or the number of openings follows a gradient increasing from the center to the periphery, for example the intermediate wall 33 and / or the second wall 32 and one or more walls whose total empty surface area and / or the total empty surface density and / or the total volume density empty and or the quantity of openings follows a gradient decreasing from the center to the periphery, for example the first wall 31 and the intermediate wall 34.

 The injection means 36 comprise for example an injector.

The injection means are for example adapted to inject the gas to mixing, for example ammonia and / or hydrogen and / or gaseous oxygen, between the first wall 31 and the intermediate wall 33 immediately downstream of the first wall 31. The injection means 36 are for example arranged at the side wall 35. The injection means 36 may not extend between the first wall 31 and the second wall 32. The injection means 36 may thus comprise an opening opening at the side wall 35.

Referring to Figure 7, there is described yet another such device 3. The arrows in Figure 7 show the direction of flow and flow lines. The device 3 may comprise a plurality of intermediate walls. Each intermediate wall is for example disposed between the first wall 31 and the second wall 32. Each intermediate wall may comprise a plurality of intermediate openings. It is thus possible to adapt the flow between the first wall 31 and the second wall 32 to improve the mixing between the gas to be mixed and the exhaust gas, for example by modulating or controlling the flow, for example by limiting the decrease in gas flow. The plurality of intermediate walls may for example comprise a third wall 33 comprising a plurality of intermediate openings 331 and a fourth wall 34 comprising a plurality of intermediate openings 341.

 The plurality of walls may thus comprise a total of at least four walls, for example exactly four walls.

 The first wall 31, the second wall 32 and the intermediate walls 33 and 34 are for example flat.

 The first wall 31 and the second wall 32 have for example dimensions substantially equal to that of the section of the exhaust line. The injection device can extend over the entire section of the exhaust line

The device may further comprise a side wall 35. The side wall connects for example the first wall 31, the second wall 32, and the two intermediate walls 33 and 34. The side wall 35 defines for example with the first wall 31 and the second wall 32 an interior space. This interior space is for example the one in which gas injection is performed to mix and mix with the exhaust gas. This interior space includes for example the first, second and third zones. The device 3 may extend over the entire section of the exhaust line, the side wall 35 being formed by a portion of the wall of the exhaust line. The side wall is for example substantially cylindrical. The side wall is for example symmetrical of revolution. The side wall may have, in section passing through the central axis of the exhaust line portion the axis of the device and / or the axis of symmetry of the side wall, a straight wall. The device 3 and the side wall 35 have for example a substantially constant section.

 Each wall of the plurality of walls and the side wall 35 are for example formed or each comprise a plate, for example metal.

 From upstream to downstream, the openings of the walls of the plurality of walls are becoming smaller and more numerous, without covering a larger surface. Thus, the dimensions of the openings of each wall of the plurality of walls may be smaller than or equal to, for example, strictly less than those of the wall (s) of the plurality of upstream walls. The total void area and / or the total void surface density and / or the total void volume density of each wall of the plurality of walls may be substantially less than that of the walls of the plurality of upstream walls. The amount of openings in each wall of the plurality of walls may be strictly greater than that of the walls of the plurality of upstream walls.

The device may comprise bypass or bypass means of the first zone only. The device may include bypass or bypass means of the first and second zones only. The device may include bypass or bypass means of the first, second and third zones. The bypass means comprise, for example, a conduit, for example a tube, connecting the opening upstream and the opening downstream.

 The injection means 36 comprise for example an injector.

The injection means are for example suitable for injecting the gas to be mixed, for example ammonia and / or hydrogen and / or gaseous oxygen, between the first wall 31 and the intermediate wall 33 immediately downstream of the first wall 31. The injection means 36 are for example arranged at the side wall 35. The injection means 36 may not extend between the first wall 31 and the second wall 32. The injection means 36 may thus comprise an opening opening at the side wall 35.

Referring to Figure 8, there is described a method of injecting gas to be mixed, for example ammonia and / or hydrogen and / or gaseous oxygen, into an exhaust gas exhaust line. an engine implemented by means of the device 3 as described above.

 The method comprises for example a first exhaust gas inlet step 801 between the first wall 31 and the second wall 32, for example by the at least one inlet opening 31 1 of the first wall. The exhaust gas thus enters the injection and mixing zone, for example according to a flow modified by the at least one inlet opening 31 1 and / or the shape of the inlet wall 31.

The method comprises for example a second stage 802 for injecting gas to be mixed, for example with ammonia and / or hydrogen and / or oxygen gas, between the first wall 31 and the second wall 32. possible to bring into contact in the same space the exhaust gas and the gas to be mixed. The method comprises for example a third stage 803 for mixing the exhaust gas entering and the injected mixing gas. An effective mixture directly during the injection is allowed by the structure of the device which delimits a mixing zone.

 The method comprises, for example, a fourth step 804 for discharging the exhaust and the gas to be mixed mixed by the at least one opening of the second wall. It is thus possible to obtain a homogeneous mixture of gas to be mixed and exhaust gas, which no longer requires additional mixing or which will require a mixer of reduced dimensions.

Claims

1. Device for injecting a gas to be mixed into an exhaust gas exhaust line (12) of an engine (1), the device comprising:  one or more inlet openings (31 1),  a plurality of walls comprising:  a first wall (31), and  a second wall (32) having one or more outlet openings (321) and disposed downstream of the first wall, and  - injection means (36) of the gas to be mixed between the first wall and the second wall, so as to allow mixing of the gas to be mixed and exhaust gas between the first wall and the second wall. 2. Device according to claim 1, wherein the plurality of walls comprises at least one intermediate wall (33, 34) disposed between the first wall and the second wall, the intermediate wall comprising one or more openings (331, 341). 3. Device according to claim 1 or 2, comprising means for bypassing at least one zone, at at least one opening, configured to form a fluid communication between at least one opening of a wall of the plurality of walls upstream of the zone with at least one opening of a wall of the plurality of walls downstream of the zone without passing through the zone. 4. Device according to any one of the preceding claims, further comprising a side wall (35) connecting the first wall (31) and the second wall (32) and delimiting with the first wall and the second wall an interior space, the injection device (36) being adapted to be disposed inside the exhaust line, so as to allow the passage of exhaust gas between the side wall and the wall of the exhaust line. 5. Device according to claim 4, wherein the device comprises means for fixing the device to the exhaust line. 6. Device according to one of claims 1 to 3, the device forming a section of the exhaust line, in particular the device comprising a side wall (35) connecting the first wall (31) and the second wall (32). and delimiting with the first wall and the second wall an interior space so that the side wall (35) is in contact with the exhaust line and / or forms a wall portion of the exhaust line. 7. Device according to claim 5, comprising gas supply means (361) for mixing injection means, the fixing means comprising the supply means. 8. Device according to any one of the preceding claims, wherein the first wall (31) and / or the side wall (35) has one or more of the one or more inlet openings (31 1). 9. Device according to any one of the preceding claims, wherein the injection means (36) are arranged at the level of the first wall (31) and / or extend between the first wall and the second wall (32). from the first wall. 10. Device according to one of the preceding claims, wherein for at least one wall of the plurality of walls the dimensions of the openings and / or the total empty surface and / or the total surface density void and / or the total void volume density and / or the amount of apertures vary (s). 1 1. Device according to one of the preceding claims, wherein the dimensions of the openings and / or the total void area and / or the total void density and / or the total void volume density and / or the amount of openings of at least a wall varies (s) with respect to at least one other wall of the plurality of walls. 12. An assembly comprising a motor and / or an exhaust line of the engine exhaust gas, the assembly comprising a device according to one of the preceding claims. 13. The assembly of claim 12, comprising a selective catalytic reduction system for exhaust gas, and / or an oxidation catalyst. 14. A method of injecting a gas to be mixed in an exhaust gas exhaust line of an engine implemented by means of a device according to one of claims 1 to 1 1, comprising the steps following:  inlet (801) of exhaust gas between the first wall and the second wall,  injecting (802) the gas to be mixed between the first wall and the second wall,  - mixture (803) of the exhaust gas entered and the mixed gas injected,  - outlet (804) of the exhaust gas and the mixed gas mixed by the at least one opening of the second wall.