Exhaust line injection and mixing device

Abstract

Exhaust line injection and mixing device The injection and mixing device comprises: - a casing (13) having an exhaust gas inlet (15) and an exhaust gas outlet (17), the casing (13) internally delimiting a passage (19) for the exhaust gases from the exhaust gas inlet (15) to the exhaust gas outlet (17), the exhaust gas inlet (15) opening into an inlet zone (45) of the passage (19); - an injector (21) of a liquid comprising a nitrogen oxide reducer or a precursor of such a reducer;- a deflector (39) housed inside the casing (13) and defining in the passage (19) a first passage (41) connecting the inlet area (45) to the exhaust gas outlet (17), in which the exhaust gases flow at a first average speed, and a second passage (43) connecting the inlet area (45) to the exhaust gas outlet (17), in which the exhaust gases flow at a second average speed lower than the first average speed, the injector (21) injecting the liquid into the second passage (43). Figure for the abbreviation: 2;

Description

Title of the invention: Exhaust line injection and mixing device

[0001] The invention relates to an exhaust line injection and mixing device, intended to inject a liquid containing a nitrogen oxide reducer or a precursor of such a reducer into the exhaust line.

[0002] Exhaust systems may include so-called SCR (Selective Catalytic Reduction) catalysts. These catalysts convert nitrogen oxides present in the exhaust gases, in the presence of the reducing agent, into nitrogen gas.

[0003] The reducing agent is typically ammonia.

[0004] The exhaust line then includes an injector for injecting the nitrogen oxide reducer into the exhaust gases upstream of the SCR catalyst. Alternatively, the injector injects a precursor of the nitrogen oxide reducer, for example urea, which generates gaseous ammonia after hydrolysis and thermolysis.

[0005] The nitrogen oxide reducer is typically injected in liquid form.

[0006] When the injector is of the low SMD (Sauter Mean Diameter) type, the dispersion of liquid droplets in the exhaust gas is not satisfactory.

[0007] Such injectors produce a jet of droplets with a small average diameter, typically between 20 and 30 micrometers.

[0008] These droplets are small, and therefore have a low mass and reduced kinetic energy. Consequently, they are easily deflected by the exhaust gas flow.

[0009] The droplets can thus easily be pressed against a so-called cold surface by the exhaust gas. In this case, they can settle there and form a deposit that disrupts the initial gas flow pattern and increases the back pressure.

[0010] In this context, the invention aims to provide an injection and mixing device whose operation is satisfactory for injectors of the low SMD type.

[0011] To this end, the invention relates, in a first aspect, to an injection and mixing device for an exhaust line, the device comprising: - an enclosure having an exhaust gas inlet and an exhaust gas outlet, the enclosure internally delimiting a passage for the exhaust gases from the exhaust gas inlet to the exhaust gas outlet, the exhaust gas inlet opening into an inlet zone of the passage; - an injector of a liquid containing a nitrogen oxide reducer or a precursor of such a reducer, the injector being mounted on a wall of the casing directed towards the exhaust gas outlet;

[0012] - a deflector housed inside the casing and defining in the passage a first pass connecting the inlet area to the exhaust gas outlet, in which the exhaust gases flow at a first average speed, and a second pass connecting the inlet area to the exhaust gas outlet, in which the exhaust gases flow at a second average speed lower than the first average speed, the injector injecting the liquid in the second pass.

[0013] Thus, the deflector allows the exhaust gas flow passing through the passage to be distributed into a low-speed flow and a high-speed flow. The injector injects the liquid containing the reducer or the reducer precursor into the low-speed flow.

[0014] The liquid jet is only slightly or not at all deflected by the low-speed gas flow.

[0015] When the injector is of the low SMD type, the injection and mixing of droplets The reduction in the exhaust gas flow is satisfactory.

[0016] Furthermore, only a portion of the exhaust gas flow circulates in the second pass. The other portion of the exhaust gas flow circulates in the first pass, and therefore undergoes only a slight reduction in speed.

[0017] As a result, the injection and mixing device generates a lower back pressure than if the entire exhaust gas flow were decelerated and circulating at low speed.

[0018] The injection and mixing device may further have one or more of the following characteristics, considered individually or in all technically possible combinations:

[0019] - the deflector comprises a perforated plate, through which the second passage communicates with the entry area;

[0020] - the perforated plate forms with a central axis of the exhaust gas inlet a angle between 0° and 60°, advantageously between 30° and 45°;

[0021] - the perforated plate has a void ratio between 10% and 70%, advantage between 40% and 55%;

[0022] - the deflector comprises an impactor plate, the injector injecting the liquid according to an injection direction oriented towards the exhaust gas outlet, the impactor plate being interposed between the injector and the exhaust gas outlet;

[0023] - the impactor plate is substantially flat and has a normal forming an angle of less than 25° with the injection direction;

[0024] - the envelope comprises a first envelope part and a second part of envelopes placed one on top of the other, the perforated plate being attached to the first part of the envelope, the plate forming the impactor being attached to the second part of the envelope, the perforated plate and the plate forming the impactor being free from each other;

[0025] - the casing includes a tubular casing portion defining the gas outlet exhaust, the deflector comprising a tubular deflector part engaged in the tubular envelope part and constituting a downstream section of the second passage;

[0026] - the tubular part of the deflector is coaxial with the tubular part of the envelope;

[0027] - the tubular part of the deflector and the tubular part of the casing delimit between they form an annular canal constituting a downstream section of the first passage;

[0028] - a flexible conduit is mounted on the tubular part of the casing, the tubular part of deflector extending beyond the tubular part of the casing inside the flexible duct;

[0029] - the first passage has a passage entrance leading into the area at the inlet, the inlet area presents a passage section narrowing from the exhaust gas inlet to the inlet of the first passage.

[0030] According to a second aspect, the invention relates to an exhaust line comprising an injection and mixing device having the above characteristics, the exhaust gas outlet being fluidly connected to the exhaust gas inlet of an SCR catalyst.

[0031] According to a third aspect, the invention relates to a manufacturing process having the above characteristics, the process comprising the following steps:

[0032] - obtaining the first part of the envelope;

[0033] - obtaining the second part of the envelope;

[0034] - fixing the perforated plate to the first part of the envelope;

[0035] - fixing the impactor plate to the second part of the casing

[0036] - fixing the first part of the envelope and the second part of the envelope to each other.

[0037] Other features and advantages of the invention will become apparent from the detailed description given below, by way of example and not limitation, with reference to the accompanying figures, among which:

[0038] - [Fig.1] Fig.1 is a schematic representation of an exhaust line according to the invention; - [Fig. 2] Fig. 2 is a side view of the injection and mixing device of [Fig.1], for a first embodiment of the invention, the deflector being visible by transparency through the envelope; - [Fig. 3] Fig. 3 is a perspective view of the injection device and mixture of [Fig.2], the deflector appearing transparent through the envelope; and - [Fig.4] Fig.4 is a perspective view of a second embodiment of the injection and mixing device.

[0039] The exhaust line 1 shown in [Fig. 1] includes an injection and mixing device 3, designed to inject a liquid containing a nitrogen oxide reducer or a precursor of such a reducer into the exhaust gases. Downstream of the injection and mixing device 3, the exhaust line 1 includes an SCR (Selective Catalytic Reduction) catalyst 5.

[0040] The SCR catalyst, in the presence of a nitrogen oxide reducing agent, reduces NOx to gaseous N2.

[0041] Upstream, the injection and mixing device 3 is fluidly connected to a manifold 7, collecting the exhaust gases exiting the combustion chambers of the engine 9. Downstream, the SCR catalyst is connected to a cannula 11 through which the purified exhaust gases are released into the atmosphere.

[0042] Equipment such as a turbocharger is interposed between the manifold 7 and the injection and mixing device 3.

[0043] Other equipment, for example silencers, are interposed between the SCR catalyst 5 and the cannula 11.

[0044] The injection device 3 is shown more precisely in Figures 2 and 3.

[0045] It comprises a casing 13 having an exhaust gas inlet 15 and an exhaust gas outlet 17.

[0046] The envelope 13 internally delimits a passage 19 for the exhaust gases from the exhaust gas inlet 15 to the exhaust gas outlet 17.

[0047] The injection and mixing device 3 further includes an injector 21 of a liquid comprising a nitrogen oxide reducer or a precursor of such a reducer.

[0048] Typically the liquid is an aqueous solution of urea. Urea is a precursor of a nitrogen oxide reducing agent, which after hydrolysis and thermolysis in contact with exhaust gases decomposes into gaseous ammonia.

[0049] By variation, the liquid is liquid ammonia, or is any other suitable liquid.

[0050] As can be seen in [Fig.2], the envelope 13 has a background 23.

[0051] The casing 13 also includes a tubular casing portion 25, defining the exhaust gas outlet 17. The tubular casing portion 25 connects to the bottom 23 and projects outward from the bottom 23 towards the outside of the casing.

[0052] The tubular part of the envelope 25 has a central axis CE.

[0053] Perpendicular to the central axis, the tubular part of the envelope 25 has circular sections.

[0054] Typically, a flexible conduit 27 is connected to the tubular part of the casing 25.

[0055] The flexible conduit 27 typically connects the outlet 17 to the inlet of the SCR catalyst 5.

[0056] The injector 21 is mounted on a wall 29 of the casing 13 directed towards the exhaust gas outlet 17.

[0057] By directed towards the exit, it is understood that the injector 21 is directed towards the exit with an angle of up to 60°, ideally 30° and preferably opposite, that is to say with an angle of substantially 0°.

[0058] The wall 29 is located opposite the exhaust gas outlet 17 along an elevation direction E.

[0059] The elevation direction E is typically parallel to the central axis CE.

[0060] More specifically, the envelope 13 has, opposite the bottom 23, another bottom 31.

[0061] In the example shown, the other background 31 is stepped. It comprises, in addition to the wall 29, another wall 33. The exhaust gas inlet 15 is provided in the other wall 33.

[0062] The wall 29 is, along the elevation direction E, relatively closer to the bottom 23 than the other wall 33. The walls 29 and 33 are connected to each other by an intermediate wall 35, which in the example shown is substantially parallel to the elevation direction E.

[0063] The wall 29 is substantially parallel to the bottom 23.

[0064] Similarly, the other wall 33 is substantially parallel to the bottom 23.

[0065] The bottom 23 and the other bottom 31 are connected to each other by a peripheral wall lateral 37. The lateral peripheral wall 37 has a closed contour.

[0066] The injection and mixing device 3 further includes a deflector 39 housed inside the casing 13 and defining in the passage 19 a first passage 41 and a second passage 43.

[0067] As can be seen in [Fig.2], the exhaust gas inlet 15 opens into an inlet zone 45, belonging to the passage 19. The inlet zone 45 corresponds to the upstream end of the passage 19.

[0068] The first passage 41 connects the input zone 45 to the output 17.

[0069] It is arranged so that the exhaust gases flow at a first average speed along said first passage 4L

[0070] The second passage 43 also connects the inlet zone 45 to the outlet 17. It is arranged so that the exhaust gases flow at a second average speed along the second passage 43.

[0071] The second average speed is lower than the first average speed.

[0072] The first average velocity can be calculated by averaging the velocities of all the gas molecules traversing the first pass. The velocity of each gas molecule considered here is the average velocity of the gas molecule throughout the first pass.

[0073] The second average speed is calculated in the same way, the important thing being to maintain a similar calculation method for the first and second average speeds

[0074] The gas flowing through the first passage therefore flows at high speed, typically at a speed of about 60 m / s. The gas flowing through the second passage therefore flows at low speed, typically at a speed of about 40 m / s. At the exhaust gas inlet 15 and the exhaust gas outlet 17, the gas typically flows at a speed of about 80 m / s.

[0075] Injector 21 is typically a low SMD injector.

[0076] In other words, the injector 21 is of the type that injects liquid droplets having an average diameter between 10 and 50 micrometers, preferably between 20 and 30 micrometers.

[0077] By varying, the injector is of a different type.

[0078] The injector injects the liquid along an injection direction I, shown in figures 2 and 3.

[0079] The injection direction I here corresponds to the general direction in which the liquid droplets are injected into the envelope 13.

[0080] When the injector 21 is of the conical jet type, the injection direction I corresponds to the central axis of the cone. When the injector 21 is of the type generating several conical jets, the injection direction I corresponds to the direction located at the midpoint of the respective axes of the cones.

[0081] The injection direction I is, for example, coincident with the central axis CE of the tubular casing portion 25. In the example shown, the injection direction I is not strictly parallel to the central axis CE. The injector 21 is not positioned in line with the central axis CE, but slightly offset to the side. The injection direction I then forms an angle of less than 25° with the central axis CE, preferably less than 15°.

[0082] The injector 21 injects the liquid into the second passage 43.

[0083] To do this, the part of passage 19 adjoining wall 29 belongs to the second passage 43.

[0084] On the other hand, the part of passage 19 adjoining the bottom 23 belongs to the first passage 4L

[0085] The deflector 39 comprises a perforated plate 47, through which the second passage 43 communicates with the inlet zone 45. As seen in [Fig.2], this plate is perforated with multiple holes 49. The holes 49 are distributed substantially over the entire surface of the perforated plate 47, preferably regularly distributed.

[0086] The perforated plate 47 therefore delimits the second passage 43 upstream.

[0087] In this application, upstream and downstream are understood in relation to the meaning of normal flow of exhaust gases.

[0088] The perforated plate 47 forms with a central axis E of the exhaust gas inlet 15 an angle between 0° and 60°, advantageously between 30° and 45°.

[0089] The central axis E corresponds to the axis perpendicular to the plane of the exhaust gas inlet 15, and passing through the center of the latter.

[0090] The perforated plate 47 has a void ratio of between 10% and 70%, advantageously between 40% and 55%.

[0091] The void ratio corresponds to the ratio of void area to solid area in the perforated plate.

[0092] The deflector 39 further comprises a plate 51 forming an impactor.

[0093] The impactor plate 51 is interposed between the injector 21 and the exhaust gas outlet 17.

[0094] More specifically, it is interposed along the injection direction I between the injector 21 and the exhaust gas outlet 17.

[0095] The impactor plate 51 is typically substantially parallel to the bottom 23.

[0096] The normal N to the impactor plate 51 forms an angle α of less than 25°, of preference less than 15° with injection direction I.

[0097] The deflector 39 still includes a tubular deflector part 53 engaged in the tubular envelope part 25 and constituting a downstream section of the second passage 43.

[0098] The tubular deflector part 53 is typically coaxial with the tubular envelope part 25. It has a central axis which is typically coincident with the central axis CE of the tubular envelope part.

[0099] Perpendicular to its central axis, the tubular part of the deflector 53 has circular sections of equal diameters.

[0100] The tubular part of the deflector 53 is integral with the plate forming the impactor 51. It protrudes from the plate 51, in a direction opposite to the injector 21.

[0101] More specifically, the impactor plate 51 has an orifice 55, one end of the tubular deflector portion 53 connecting to the edge of the orifice 55. Said end of the tubular portion 53 flares outwards and has a general quarter-torus shape. Such a shape is said to be tulip-shaped.

[0102] The tubular deflector portion 53 typically extends to the exhaust gas outlet 17. Advantageously, it extends beyond the exhaust gas outlet 17, and its end is engaged in the flexible conduit 27.

[0103] Thus, the tubular part of the deflector 53 and the tubular part of the casing 25 delimit between them an annular channel constituting a downstream section of the first passage 4L

[0104] The perforated plate 47 is delimited by a first longitudinal edge 57, a second longitudinal edge 59 and two lateral edges 61 connecting the longitudinal edges 57, 59 to each other.

[0105] The longitudinal direction L is perpendicular to the elevation direction E.

[0106] The first longitudinal edge 57 is rigidly fixed to the intermediate wall 35, at proximity to the other wall 33.

[0107] The second longitudinal edge 59 is located substantially at the level of the impactor forming plate 51.

[0108] The lateral edges 61 are pressed against and rigidly fixed to the peripheral wall 37.

[0109] The perforated plate 47 is inclined with respect to the elevation direction E. When following the perforated plate 47 from the first longitudinal edge 57 to the second longitudinal edge 59, this plate moves away from the intermediate wall 35 and the other wall 33. Thus, the first longitudinal edge 57 is not located under the exhaust gas inlet 15, along the elevation direction E, while the second longitudinal edge 59 is placed under the inlet 33.

[0110] The area 63 of the peripheral side wall 37 located opposite the perforated plate 47 along a transverse direction T is also inclined.

[0111] The transverse direction T is perpendicular to the elevation direction E and perpendicular to the longitudinal direction L.

[0112] More precisely, when following zone 63 from the other wall 33 towards the bottom 23, this zone 63 approaches transversely the perforated plate 47.

[0113] In other words, considered in section perpendicular to the longitudinal direction L as illustrated in [Fig.2], the perforated plate 47 and the area 63 converge towards each other.

[0114] Thus, the inlet zone 45 has a passage cross-section that gradually decreases from the exhaust gas inlet 15 to the inlet 64 of the first passage 4L

[0115] This allows the exhaust gas flow heading towards the first passage 41 to maintain a substantially constant speed, although part of the flow flows towards the second passage 43.

[0116] The impactor plate 51 is delimited by two transverse edges 65 and two longitudinal edges 67, 69.

[0117] The transverse edges 65, and the longitudinal edge 67 located opposite the perforated plate 47, are arranged along the lateral peripheral wall 37, and typically are in contact with this wall.

[0118] The longitudinal edge 69 extends opposite and along the longitudinal edge 59 of the perforated plate 47. A gap 71 separates the edges 59 and 69.

[0119] The impactor plate 51 is substantially flat, except for the edge 69 which is curved and rises towards the wall 29.

[0120] As indicated above, the impactor plate 51 is substantially perpendicular dicular to the elevation direction E. Along this elevation direction E, it is relatively closer to the bottom 23 than to the wall 29. For example, along the elevation direction E, the gap between the plate forming impactor 51 and the bottom 23 is between 30% and 50% of the gap separating the plate forming impactor 51 and the wall 29.

[0121] The envelope 13 comprises a first part of envelope 71 and a second part of envelope 73 placed one on top of the other.

[0122] The first part of the envelope 71 typically comprises the wall 29, the other wall 31, the intermediate wall 35 and a part 75 of the lateral peripheral wall 37.

[0123] The second envelope part 73 includes the bottom 23, the tubular envelope part 25, and another part 77 of the lateral peripheral wall 37.

[0124] The first envelope part 71 and the second envelope part 71 are in contact with each other along a closed contour line 79, illustrated in figures 2 and 3.

[0125] The two envelope parts 71, 73 are in contact with each other via parts 75, 77 of the lateral peripheral wall, these two parts joining at the closed contour line 79.

[0126] The two envelope parts 71, 73 are typically welded to each other.

[0127] Advantageously, the perforated plate 47 is integral with the first part of the envelope 71. The plate forming the impactor 51 is integral with the second part of the envelope 73.

[0128] Furthermore, as can be seen in the figures, the perforated plate 47 and the impactor plate 51 are free from each other. In other words, they are not directly connected to each other. The figures show that they are separated by the gap 71.

[0129] Such an arrangement allows for easy assembly of the injection and mixing device.

[0130] The low-speed circulation passage 43 comprises a first volume 81, into which the liquid is injected. This first volume 81 is delimited along the upward direction E between the impactor plate 51 and the wall 29. Along the transverse direction T, it is delimited between the perforated plate 47 and the lateral peripheral wall 37. Along the longitudinal direction L, it is delimited between two zones of the lateral peripheral wall 37.

[0131] The second passage 43 is extended by the internal volume of the tubular part of the deflector 53, which constitutes the downstream section of the second passage, as indicated above.

[0132] The first passage 41 comprises the volume 83 delimited between the impactor plate 51 and the bottom 23. This first volume 83 is extended by an annular channel 85, delimited between the tubular part of the deflector 53 and the tubular part of the casing 25. This annular channel 85 constitutes the downstream section of the first passage 4L

[0133] The operation of the injection and mixing device will now be described.

[0134] The exhaust gases enter the casing 13 through the exhaust gas inlet 15.

[0135] From this inlet 15, it flows into the inlet zone 45.

[0136] Part of the exhaust gas flow passes through the perforated plate 47, through the 49 orifices.

[0137] By doing so, the velocity of the exhaust gases is reduced.

[0138] This low-speed fraction of the exhaust gas flow follows the second pass 43. It first passes through the volume 81, then flows inside the tubular part of the deflector 53 to the exhaust gas outlet 17.

[0139] The injector 21 injects the liquid into the volume 81. Part of the liquid jet strikes the impactor plate 51, around the orifice 55. Another part is injected directly into the volume delimited by the tubular deflector portion 53. It is not intercepted by the impactor plate 51.

[0140] The portion of the exhaust gas flow that does not pass through the perforated plate 47 flows through the inlet area 45 to the inlet 64 of the first passage 4L. Because the passage cross-section narrows from the exhaust gas inlet 15 to the inlet 64 of the first passage 41, the exhaust gas velocity is not reduced. This high-velocity fraction of the exhaust gases follows the first passage 4L. It flows first into the volume 83, then is directed to the annular channel 85, and flows around the tubular deflector portion 53.

[0141] The high-speed fraction of the exhaust gases does not undergo pronounced acceleration or deceleration, so that the gas flow does not generate back pressure, or only very low back pressure.

[0142] The high-velocity flow exiting the annular channel 85 and the low-velocity flow exiting the tubular deflector portion 23 are substantially parallel to each other. This reduces the back pressure.

[0143] Typically, the fraction of the exhaust gas flow directed towards the second pass 43 is between 30% and 70% of the total flow, more preferably between 40% and 60%, and is for example 50%.

[0144] The injection and mixing device according to the first embodiment is mounted in the following manner.

[0145] The perforated plate 47 is first fixed to the first part of the envelope 71.

[0146] The impactor plate 51, carrying the tubular deflector part 53, is fixed to the second part of envelope 73.

[0147] The first and second envelope parts are then fixed to each other, the impactor plate and the perforated plate fitting together as illustrated in Figures 2 and 3.

[0148] A second embodiment of the invention will now be described, with reference to [Fig. 4]. Only the points by which this second embodiment differs from the first will be detailed below. Identical elements, or those performing the same function, will be designated by the same reference numerals.

[0149] In the second embodiment, the impactor plate 51 occupies the entire internal section of the envelope 13.

[0150] In other words, the outer edge of the plate forming the impactor 51 extends in the immediate vicinity of the lateral peripheral wall 37, and this over its entire periphery.

[0151] The perforated plate 47 is replaced by a perforated tube 87. The perforated tube 87 extends from the exhaust gas inlet 15 to an orifice 89 provided in the plate forming impactor 51.

[0152] The perforated tube 87 is substantially straight, and is perforated along its entire length and all its periphery.

[0153] The orifice 89 is offset longitudinally with respect to the orifice 55. It is located, along the elevation direction E, in the extension of the exhaust gas inlet 15.

[0154] The inlet area 45 here corresponds to the internal volume of the perforated tube 87.

[0155] The second passage 43 comprises the entire volume delimited between the impactor plate 51 and the other bottom 31, with the exception of the inlet zone 45. The first passage 41 comprises the entire volume located between the bottom 23 and the impactor plate 51.

[0156] In this embodiment, the perforated tube 87 is integral with the plate forming impactor 51.

[0157] The entire deflector assembly 39, i.e. the plate forming impactor 51, the perforated tube 87 and the tubular part of the deflector 53, is integral with the second part of the envelope 73.

[0158] The exhaust gases entering through the exhaust gas inlet 15 into the casing 13 flow into the inlet zone 45, i.e., the delimited zone inside the perforated tube 87. Part of this flow passes through the perforated tube 87 and follows the second passage 43. Another part of the exhaust gas flow flows along the perforated tube 87 to the orifice 89, and then flows into the first passage 4L

[0159] The injection and mixing device according to the second embodiment is mounted in the following manner.

[0160] The impactor plate 51, the perforated tube 87, and the tubular deflector portion 53 are first assembled together. This subassembly is rigidly fixed to the second casing portion 73. Finally, the first casing portion and the second casing portion are fixed to each other. The tube 87 is positioned opposite and in line with the exhaust gas inlet 15.

[0161] A variant of the first embodiment will now be described. This variant is not shown in the figures.

[0162] Only the points by which this variant differs from those of figures 2 and 3 will be detailed below.

[0163] In this embodiment, the perforated plate 47 and the impactor plate 51 are fixed to each other. In other words, the lower longitudinal edge 59 of the perforated plate is connected to the longitudinal edge 69 of the impactor plate 51. In contrast, the perforated plate 47 is not rigidly fixed to the lateral peripheral wall 37 of the casing. There is a slight gap between the upper longitudinal edge 57 and the edges 61 of the plate on the one hand, and the lateral peripheral wall 37 on the other.

[0164] In this variant, the deflector 39 is manufactured first. The deflector 39 comprises the perforated plate 47, the impactor plate 51 and the tubular deflector part 53. These different components are joined together.

[0165] The deflector 39 is then fixed on the second part of the envelope 73.

[0166] Finally, the first part of the envelope 71 and the second part of the envelope 73 are fixed to each other. The perforated plate 47 then fits inside the first part of the envelope 71, a slight gap remaining between the perforated plate 47 and this first part of the envelope 71.

[0167] The injection and mixing device has multiple advantages.

[0168] By appropriately choosing the angle of the perforated plate and / or the rate of In the vacuum, the distribution of the exhaust gas flow between the first and second passes is influenced. The flow in the second pass is chosen to only slightly deflect the liquid jet. Minimizing the deflection of the liquid jet ensures that it penetrates deeply into the second pass, towards the outlet.

[0169] When the envelope consists of a first envelope part and a second envelope part placed one on top of the other, the assembly of the injection and mixing device is facilitated.

[0170] Assembly is particularly easy when the impactor plate is attached to the second part of the envelope and the perforated plate is attached to the first part of the envelope, the perforated plate and the impactor plate being free from each other.

[0171] The fact that the deflector includes a tubular deflector portion forming a downstream section of the second pass allows for the re-acceleration of the low-speed fraction of the exhaust gases exiting the second pass. Indeed, the cross-sectional area offered to the exhaust gas by the tubular deflector portion is reduced compared to the volume of the second pass in which the injection takes place.

[0172] As mentioned above, the fact that the tubular part of the deflector is coaxial with The tubular section of the casing ensures that the flows exiting the first and second passes are parallel to each other. This helps to limit back pressure.

[0173] The first and second passes are located on either side of the impactor plate. The latter is therefore maintained at a high temperature by the exhaust gases, which reduces the risk of the formation of a solid deposit on the impactor plate.

[0174] The fact that the tubular deflector portion and the tubular envelope portion define an annular channel between them, constituting a downstream section of the first pass, means that the tubular deflector portion is also maintained at a high temperature. The risks of deposits are reduced.

[0175] Furthermore, the exhaust gases passing through the plate forming the impactor and flowing inside the tubular part of the deflector have a flow that is not disturbed by the high-speed gas flow.

[0176] The fact that the tubular portion of the deflector extends beyond the tubular portion of the casing, inside the flexible conduit, means that the attachment of the flexible conduit to the tubular portion of the casing is not exposed to the injected liquid. This is beneficial for the long-term durability of this attachment.

[0177] The presence of the tubular deflector part allows an impactor, or a mixing element, to be arranged inside this tubular deflector part.

[0178] Such a component could not be fixed in the flexible conduit, the latter not being rigid enough to allow such a fixing.

[0179] The fact that the inlet area has a narrowing passage section from the exhaust gas inlet to the inlet of the first passage helps to maintain the flow velocity and therefore avoids having to re-accelerate it afterwards, which is an additional energy expenditure.

[0180] The injection and mixing device can have multiple variants.

[0181] The exhaust gas inlet may not be on a wall of the casing located opposite the exhaust gas outlet. This inlet may be lateral, or even provided on the bottom of the casing.

[0182] The injection and mixing device is configured so that it is not necessary to place the injector precisely opposite the exhaust gas outlet. As explained above, this injector can be slightly offset, as the injection direction is not necessarily strictly parallel to the central axis.

Claims

Demands

1. Injection and mixing device for an exhaust line, the device comprising: - a casing (13) having an exhaust gas inlet (15) and an exhaust gas outlet (17), the casing (13) internally delimiting a passage (19) for the exhaust gases from the exhaust gas inlet (15) to the exhaust gas outlet (17), the exhaust gas inlet (15) opening into an inlet zone (45) of the passage (19); - an injector (21) of a liquid comprising a nitrogen oxide reducer or a precursor of such a reducer, the injector (21) being mounted on a wall (29) of the casing (13) directed towards the exhaust gas outlet (17);- a deflector (39) housed inside the casing (13) and defining in the passage (19) a first passage (41) connecting the inlet area (45) to the exhaust gas outlet (17), in which the exhaust gases flow at a first average speed, and a second passage (43) connecting the inlet area (45) to the exhaust gas outlet (17), in which the exhaust gases flow at a second average speed lower than the first average speed, the injector (21) injecting the liquid into the second passage (43), the deflector (39) comprising a perforated plate (47), through which the second passage (43) communicates with the inlet area (45), the perforated plate (47) having a void ratio between 10% and 70%.

2. Device according to claim 1, wherein the perforated plate (47) forms with a central axis of the exhaust gas inlet an angle between 0° and 60°, advantageously between 30° and 45°.

3. Device according to claim 1 or 2, wherein the perforated plate (47) has a void ratio of between 40% and 55%.

4. Device according to any one of claims 1 to 3, wherein the deflector (39) comprises an impactor plate (51), the injector (21) injecting the liquid in an injection direction (I) oriented towards the exhaust gas outlet (17), the impactor plate (51) being interposed between the injector (21) and the exhaust gas outlet (17).

5. Device according to claim 4, wherein the plate forming impactor (51) is substantially planar and has a normal forming with the injection direction (I) an angle of less than 25°.

6. Device according to claim 4 or 5, wherein the envelope (13) comprises a first envelope part (71) and a second envelope part (73) attached to one another, the perforated plate (47) being integral with the first envelope part (71), the impactor plate (51) being integral with the second envelope part (73), the perforated plate (47) and the impactor plate (51) being free with respect to each other.

7. Device according to any one of the preceding claims, wherein the casing (13) comprises a tubular casing portion (25) defining the exhaust gas outlet (17), the deflector (39) comprising a tubular deflector portion (53) engaged in the tubular casing portion (25) and constituting a downstream section of the second passage (43).

8. Device according to claim 7, wherein the tubular deflector part (53) is coaxial with the tubular envelope part (25).

9. Device according to claim 7 or 8, wherein the tubular deflector part (53) and the tubular envelope part (25) delimit between themselves an annular channel (85) constituting a downstream section of the first passage (41).

10. Device according to any one of claims 7 to 9, wherein a flexible conduit (27) is mounted on the tubular envelope portion (25), the tubular deflector portion (53) extending beyond the tubular envelope portion (25) inside the flexible conduit (27).

11. Device according to any one of the preceding claims, wherein the first passage (41) has a passage inlet (64) opening into the inlet zone (45), the inlet zone (45) having a passage section narrowing from the exhaust gas inlet (15) to the inlet of the first passage (64).

Images