Exhaust gas treatment device for an exhaust system of an internal combustion engine

Abstract

To provide an exhaust gas treatment device for an exhaust system of an internal combustion engine.SOLUTION: A treatment device 1 includes: a tubular duct 2 divided by a tubular side wall 4, and including an inlet opening portion 5, an outlet opening portion, and an injection opening portion 7 obtained through the tubular side wall 4 and designed to receive a reducing substance injection device; and a mixing body portion forming a reinforcement passage for an exhaust gas to pass so as to flow from the inlet opening portion 5 to the outlet opening portion. The mixing body portion includes a first base wall facing the outlet opening portion of the tubular duct 2, partially engaged with a cross-section of the tubular duct 2, and having a partially circular shape leaving only a half moon-shaped passage area, and a second base wall facing the inlet opening portion 5 of the tubular duct 2, completely engaged with the cross-section of the tubular duct 2, including a main hole 12 at its center, and having a circular shape.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This patent application claims priority to Italian Patent Application No. 102020000015346, filed June 25, 2020, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates to an exhaust gas treatment device for the exhaust system of an internal combustion engine. [Background technology]

[0003] International regulations relating to the control of pollutant emissions produced by motor vehicles limit the NOx that can be released into the atmosphere. x It specifies a very low limit for the numerator.

[0004] Compliance with such limit values ​​is particularly important for diesel motors, for this reason the exhaust systems of diesel engines must be fitted with NO x NO is designed to convert molecules (NO or NO) into the inert gas nitrogen (N) and water (H2O). x It has been proposed to equip the vehicle with an additional SCR (Selective Catalytic Reduction) catalytic converter for NO x The reduction reaction to molecular nitrogen (N2) is difficult to achieve without the use of a suitable reducing agent, commonly identified as ammonia (NH3), which must be injected into the exhaust system and upstream of the SCR catalytic converter so that it mixes with the exhaust gases before entering the converter.

[0005] However, storing ammonia on board a vehicle is not advisable for obvious safety reasons related to the fact that ammonia is toxic. As a result, it has been proposed to store and inject a solution of urea in water, since urea is decomposed into ammonia by the effect of the heat of the exhaust gases and also partly by catalytic effects.

[0006] To maximize the efficiency of an SCR catalytic converter, it is necessary for the ammonia concentration on the surface of the SCR catalytic converter monolith to be as uniform as possible. Furthermore, a problem associated with injecting urea-water solutions into exhaust systems relates to the fact that difficult-to-remove solid incrustations can form on the exhaust system walls, consisting of both urea and its possible decomposition derivative, isocyanic acid (HNCO).

[0007] In order to maximize the uniformity of the ammonia concentration on the surface of the monolith of the SCR catalytic converter (and to prevent the formation of solid incrustations on the inner walls of the exhaust system), it has been proposed to insert a mixer into the exhaust system and near the injection area of ​​the urea, said mixer creating turbulence in the exhaust gas, thereby favoring the uniform distribution of ammonia in the exhaust gas. International Application No. WO2018001789A1 describes an exhaust gas treatment device with a reducing additive injection device at a static mixer (i.e., containing no moving parts).

[0008] However, known mixers of the type described in the preceding paragraph have the disadvantage that they do not have an optimal balance between the opposing requirements of effectiveness (i.e., ensuring good mixing of the exhaust gases) and efficiency (i.e., limiting the pressure drop in the exhaust gases). In other words, known mixers of the type described in the preceding paragraph are either ineffective (i.e., do not ensure good mixing of the exhaust gases) or inefficient (i.e., cause a large pressure drop in the exhaust gases).

[0009] Chinese Patent Application No. CN109538337A describes an exhaust gas treatment device for an exhaust system of an internal combustion engine, in particular a mixing device is provided that brings about mixing of exhaust gas with urea injected by a specified injector. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Application No. WO2018001789A1 [Patent Document 2] Chinese Patent Application No. CN109538337A Summary of the Invention [Problem to be solved by the invention]

[0011] The object of the present invention is to provide an exhaust gas treatment device for the exhaust system of an internal combustion engine, which treatment device does not have the drawbacks explained in the previous paragraph and which is in particular easy and cost-effective to manufacture. [Means for solving the problem]

[0012] According to the present invention, an exhaust gas treatment device for an exhaust system of an internal combustion engine is provided as set out in the accompanying claims.

[0013] The claims describe preferred embodiments of the invention and form an integral part of the description of the invention.

[0014] The invention will now be described with reference to the accompanying drawings, which show non-limiting exemplary embodiments. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a perspective view of an exhaust gas treatment device manufactured in accordance with the present invention. [Figure 2] 2 is a further perspective view of the processing device of FIG. 1. [Figure 3] 2 is a perspective view of a mixing body of the processing device of FIG. 1. FIG. [Figure 4] 2 is a perspective view of a mixing body of the processing device of FIG. 1. FIG. [Figure 5] FIG. 5 is a perspective view of the mixing body of FIGS. 3 and 4 without the base wall. [Figure 6] FIG. 5 is a perspective view of the mixing body of FIGS. 3 and 4 without the base wall. [Figure 7] 2 is a longitudinal cross-sectional view of the processing device of FIG. 1; DETAILED DESCRIPTION OF THE INVENTION

[0016] In Figures 1 and 2, reference number 1 indicates as a whole an exhaust gas treatment device for the exhaust system of an internal combustion engine preferably operating according to the diesel cycle (i.e. powered by a diesel or the like).

[0017] The exhaust gas treatment device 1 comprises a tubular duct 2 having a longitudinal axis 3 and a cylindrical shape (i.e., a circular cross section of constant diameter). The tubular duct 2 is bounded by a tubular side wall 4 made from sheet metal and has an exhaust gas inlet opening 5 (illustrated in FIG. 1 ) arranged at a first base of the tubular duct 2, and an exhaust gas outlet opening 6 (illustrated in FIG. 2 ) opposite the inlet opening 5 and arranged at a second base of the tubular duct 2 (obviously opposite the first base of the tubular duct 2), so that, in use, exhaust gas enters the tubular duct 2 through the inlet opening 5, traverses the tubular duct 2, and exits the tubular duct 2 through the outlet opening 6.

[0018] The tubular duct 2 further has an injection opening 7 obtained through the tubular side wall 4 between the inlet opening 5 and the outlet opening 6 and designed to receive and house an injection device for the reducing material, and in particular a tubular housing 8 cantilevered out of the tubular side wall 4 and configured to receive and house the injection device is arranged around the injection opening 7.

[0019] The injector is designed to inject a reducing additive, in particular a urea solution (i.e. a solution of urea and water), into the tubular duct 2, so that in use, under the effect of the heat of the exhaust gases present inside the tubular duct 2, the urea spontaneously decomposes into isocyanic acid (HNCO) and ammonia (NH3), which acts as a reducing substance inside the subsequent SCR catalytic converter, resulting in the production of NO x It facilitates the decomposition reaction in which molecules break down into nitrogen (N2) and water (H2O).

[0020] As clearly illustrated in Figures 3 and 4, the treatment device 1 comprises a mixing body 9 (static, i.e. without moving parts) arranged inside the tubular duct 2 and forming a forced path followed by the exhaust gases flowing from the inlet opening 5 to the outlet opening 6. In particular, the mixing body 9 has the function of generating turbulence in the exhaust gases present inside the tubular duct 2, thereby increasing the efficiency of the subsequent SCR catalytic converter and making the distribution of ammonia in the exhaust gases more homogeneous.

[0021] The mixing body 9 is coaxial with the tubular duct 2 (i.e., with the longitudinal axis 3 of the tubular duct 2), has a partially circular shape, and comprises a base wall 10 facing the outlet opening 6 of the tubular duct 2, which partially engages with the cross section of the tubular duct 2, leaving only a single passage area of ​​half-moon shape and free of obstructions. In other words, the base wall 10 is obtained by starting from a circular disk of the same size as the cross section of the tubular duct 2 (so as to completely block said tubular duct 2), and then eliminating the half-moon shaped segment to form a passage area (apparently shaped like a half-moon). The partially circular and perforated base wall 10 only partially engages with (blocks) the cross section of the tubular duct 2, so that the exhaust gases can continue to pass beyond the base wall 10 and pass next to said base wall 10.

[0022] The mixing body 9 comprises a base wall 11, which is coaxial with the tubular duct 2 (i.e. with the longitudinal axis 3 of the tubular duct 2), has a (completely) circular shape, is parallel to and opposite the base wall 10, faces the inlet opening 5 of the tubular duct 2, completely engages with the cross section of the tubular duct 2, and has at its center a main hole 12, which is coaxial with the tubular duct 2 (i.e. with the longitudinal axis 3) and is a through hole for allowing the passage of exhaust gases. The base wall 11 completely engages (closes) the cross section of the tubular duct 2 (i.e. the exhaust gases can only continue beyond the base wall 11 through the main hole 12 in said base wall 11). In particular, the base wall 11 has at its center a single, and only one, main hole 12, which is the only path along which the exhaust gases must continue beyond the base wall 11.

[0023] 3 to 7, the mixing body 9 comprises a deflector wall 13 having a flat shape, which extends from the base wall 10 towards the base wall 11 and forms an acute angle α (illustrated in FIG. 7) with the base wall 10 and further with the base wall 11, so as to force the exhaust gases that have reached the outlet opening 6 (i.e., that have passed through the passage area of ​​the base wall 10) to take on the lateral and / or circumferential components of motion necessary to pass over the deflector wall 13. The deflector wall 13 is inclined and therefore forms, together with the side wall 4 of the tubular duct 2, a passage channel having an area available for the flow of exhaust gases that gradually increases as the outlet opening 6, i.e., the passage area of ​​the base wall 10, is approached. Apparently, the deflector wall 13 makes an acute angle α with the base wall 10 on one side, while the deflector wall 13 makes an obtuse angle (the complement of the acute angle α) with the base wall 10 on the other side.

[0024] According to a preferred embodiment, the deflector wall 13 has a cross extension, i.e., perpendicular to the longitudinal axis 3 of the tubular duct 2, which is smaller than the corresponding cross extension of the tubular duct 2, i.e., the deflector wall 13 is narrower than the tubular duct 2, leaving two regions of the tubular duct 2 arranged between the side edge of the deflector wall 13 and the side wall 4 (i.e., not engaged by the deflector wall 13).

[0025] The deflector wall 13 has a central band 14 that extends to the base wall 11 and two side bands 15 arranged on either side of the central band 14 and terminating short of, i.e., at a non-zero distance from, the base wall 11. Preferably, each side band 15 terminates at an outer edge facing the base wall 11 and has a semicircular shape in plane (as best illustrated in FIG. 7).

[0026] The deflector wall 13 has at one end a flange 16 arranged transversely to the remainder of the deflector wall 13 and resting against the base wall 10 to connect (secure) the deflector wall 13 to the base wall 10. Similarly, the deflector wall 13 has at the opposite end another flange 17 arranged transversely to the remainder of the deflector wall 13 and resting against the base wall 11 to connect (secure) the deflector wall 13 to the base wall 11; obviously, the flange 16 extends over the entire deflector wall 13, but the flange 17 extends only in the region of the central band 14 of the deflector wall 13.

[0027] According to a preferred, but non-limiting embodiment illustrated in the accompanying figures, the deflector wall 13 has a flat shape and is provided at two opposite edges with wings 18 arranged laterally and directed towards the nearest side wall 4 (i.e., the side facing the injection opening 7).

[0028] As clearly illustrated in Figures 5 and 6, the mixing body 9 comprises two deflector walls 19 that are arranged symmetrically around the longitudinal axis 3 of the tubular duct 2 and are at a non-zero distance from each other (i.e., the two deflector walls 19 do not touch each other but face each other), i.e., the two deflector walls 19 have mirror symmetry with respect to the longitudinal axis 3 of the tubular duct 2.

[0029] Each deflector wall 19 connects base wall 10 to base wall 11, is oriented crosswise with respect to deflector wall 13, is positioned beside deflector wall 13 at a non-zero distance from said deflector wall 13, and is connected to base wall 11 adjacent to main hole 12 (i.e., close to the edge of main hole 12).

[0030] Each deflector wall 19 has a cylindrical shape that is coaxial with the tubular duct 2, and as shown, each deflector wall 19 has an angular extent of approximately 15° to 25°.

[0031] According to a preferred, but non-limiting embodiment illustrated in the accompanying figures, each deflector wall 19 ends within the region of the mid-plane of the tubular duct 2 (i.e., the plane that bisects the tubular duct 2 into two symmetrical parts and passes through the longitudinal axis 3 of the tubular duct 2), i.e., overall the deflector walls 13 and 19 engage half of the internal volume of the tubular duct 2.

[0032] The deflector walls 19 have at one end a flange 20 that is arranged perpendicular to the remainder of the deflector wall 19 and rests against the base wall 10 to connect (secure) the deflector wall 19 to the base wall 10. Similarly, each deflector wall 19 has at its opposite end another flange 21 that is arranged perpendicular to the remainder of the deflector wall 19 and rests against the base wall 11 to connect (secure) the deflector wall 19 to the base wall 11. According to the embodiment illustrated in the accompanying figures, the flange 20 of each deflector wall 19 is narrower than the remainder of the deflector wall 19.

[0033] The injection opening 7 is arranged on the opposite side of the deflector wall 13 so as to be positioned at the farthest point relative to the deflector wall 13 and centrally relative to the two deflector walls 19, and in this way the jet of reducing agent sprayed by the injection device is directed to strike the deflector wall 13 and pass through the two deflector walls 19.

[0034] According to a preferred embodiment illustrated in Figures 3 and 4, the base wall 11 has a plurality of sub-holes 22, which are through-holes (substitutes for the main holes 12) allowing the passage of exhaust gases, have a diameter (much) smaller than the main holes 12 and are arranged around the main holes 12. In particular, the sub-holes 22 are distributed along two circumferences arranged one inside the other, are coaxial with the main holes 12 and surround said main holes 12, and are further arranged near the tubular side wall 4 so as to be (much) close to the tubular side wall 4 and (much) far from the main holes 12.

[0035] The base wall 11 has a large number of small sub-through holes 22 arranged side by side, in particular several tens of sub-through holes 22 (approximately 180-240 sub-through holes 22). Each sub-through hole 22 has a diameter ranging from 1 to 3 mm, and therefore the diameter of each sub-through hole 22 is significantly smaller than the diameter of the main hole 12 and the diameter of the tubular duct 2, for example the diameter of each sub-through hole 22 is equal to 0.5-3% of the diameter of the main hole 12.

[0036] The secondary holes 22 allow only a moderate proportion of the exhaust gases coming from the inlet opening 5 of the tubular duct 2 to pass through the base wall 11 of the mixing body 9, but it is important that the main part of the exhaust gases coming from the inlet opening 5 of the tubular duct 2 is forced to pass through the main holes 12 (which are much larger than the secondary holes 22 and therefore cause a much lower pressure drop when passing through). In other words, the secondary holes 22 are an alternative means to the main holes 12 for the exhaust gases to pass through the base wall 11 of the mixing body 9; therefore, instead of passing through the base wall 11 through the main holes 12, a small part of the exhaust gases passes through the base wall 11 through the secondary holes 22 which constitute a bypass for the main holes 12.

[0037] According to a different embodiment, not illustrated, the base wall 11 of the mixing body 9 does not have any secondary through holes 22 .

[0038] 4, base wall 11 has recessed sector 23 that is axially offset toward base wall 10 relative to the remainder of base wall 11, i.e., recessed sector 23 is not coplanar with the remainder of base wall 11 and is axially closer to base wall 10 than the remainder of base wall 11. Recessed circular sector 23 has an angular extent of 15° to 30° as shown.

[0039] According to the preferred, but non-limiting embodiment shown in the accompanying drawings, the base wall 10 of the mixing body 9 has an annular rim 24 that is perpendicular to the base wall 10, extends around the longitudinal axis 3 and is fixed (welded) against the inner surface of the tubular side wall 4 of the tubular duct 2.

[0040] Similarly, the base wall 11 of the mixing body 9 also has an edge 25 which is perpendicular to the base wall 11, extends less than 360° around the longitudinal axis 3 (as it is interrupted by the recessed sector 23) and is fixed (welded) against the inner surface of the tubular side wall 4.

[0041] The exhaust gas passes through the base wall 11 of the mixing body 9 via the main holes 12 and the secondary holes 22 in a completely axial motion (i.e. without any lateral / circumferential components), and then, due to the presence of the base wall 10 and the deflector wall 13 of the mixing body 9, the exhaust gas is split into two flows which pass laterally through the deflector wall 13 (and further through the deflector wall 19) in a circular motion so that it can reach the passage area located next to the base wall 10 (this represents the only possibility of passing through the base wall 10 and therefore reaching the outlet opening 6). The change in direction of motion imposed by the presence of the base wall 10 and the deflector wall 13 (and also partly by the presence of the deflector wall 19) gives the exhaust gases a (significant) circumferential motion component in addition to the predominant axial motion component which favours the mixing of the reducing agent sprayed by the injector arranged through the injection opening 7, i.e. the turbulent motion (due to the radial and tangential motion components induced by the particular shape of the mixing body 9) favours optimal mixing of the exhaust gases with the reducing additive injected from the injection opening 7.

[0042] According to a different embodiment not illustrated, the tubular duct 2 may be provided with an oxidation catalytic converter and / or a NO catalytic converter arranged upstream of the mixing body 9 (i.e., through which the exhaust gases first pass). xIt is also possible to accommodate an SCR (Selective Catalytic Reduction) catalytic converter arranged downstream of the mixing body 9 (i.e., the last one the exhaust gas passes through) for the aftertreatment of molecules (NO and NO2), which may also incorporate a particle filter.

[0043] The embodiments described herein may be combined with one another without departing from the scope of protection of the present invention.

[0044] The processing device 1 described above has a number of advantages.

[0045] First, the treatment device 1 described above has an optimal balance between the conflicting requirements of effectiveness (i.e., ensuring a favorable mixing of the exhaust gases) and efficiency (i.e., limiting the pressure drop in the exhaust gases). In other words, the treatment device 1 described above simultaneously has high effectiveness (i.e., ensuring a proper mixing of the exhaust gases) and high efficiency (i.e., creating a moderate pressure drop in the exhaust gases).

[0046] In addition, the processing device 1 described above is particularly robust (hence has a long service life and a very low risk of breakage) since it comprises only a few parts.

[0047] The processing device 1 described above has a particularly reduced bulk (especially in the axial direction) and a moderate overall weight.

[0048] Finally, the processing device 1 described above is easy and cheap to manufacture, as it is made up of a small number of parts that are not complex in shape and are easy to join using standard ring welds. [Explanation of symbols]

[0049] 1 Processing Device 2 Tubular duct 3 Longitudinal Axis 4 Tubular side wall 5 Inlet opening 6 Outlet opening 7 Injection opening 8 Tubular housing 9 Mixed body part 10 Base wall 11 Base wall 12 Main hole 13 Deflector wall 14 Central Band 15 Side Band 16 flange 17 Flange 18 Wing 19 Deflector wall 20 flange 21 flange 22 Secondary hole 23 Depressed Sector 24 Circular margin 25 Circular Rim

Claims

1. An exhaust gas treatment device (1) for an exhaust system of an internal combustion engine, said treatment device (1) comprising: a tubular duct (2) bounded by a tubular side wall (4) and having an exhaust gas inlet opening (5), an exhaust gas outlet opening (6) opposite said inlet opening (5), and an injection opening (7) obtained through said tubular side wall (4) between said inlet opening (5) and said outlet opening (6) and designed to receive an injection device for a reducing substance; a mixing body (9) arranged inside the tubular duct (2) and defining a forced path that the exhaust gas must follow to flow from the inlet opening (5) to the outlet opening (6); the mixing body (9) has a first base wall (10) of partially circular shape facing the outlet opening (6) of the tubular duct (2) and partially engaging with the cross section of the tubular duct (2) to leave a passage area; The mixing body (9) comprises a second base wall (11) of circular shape facing the inlet opening (5) of the tubular duct (2), fully engaging with the cross section of the tubular duct (2), centrally coaxial with the tubular duct (2), and having a main hole (12) through which the exhaust gas can pass; The mixing body (9) comprises a first deflector wall (13) extending from the first base wall (10) towards the second base wall (11); The processing device (1) the first deflector wall (13) forms an acute angle with the first base wall (10) and the second base wall (11); the first base wall (10) partially engages with the cross section of the tubular duct (2), leaving only one passage area free of obstructions, having a half-moon shape; An exhaust gas treatment device (1) characterized in that the second base wall (11) has a single, only one main hole (12) at its center.

2. 2. The processing device (1) of claim 1, wherein the first deflector wall (13) has a central band (14) extending to the second base wall (11) and two side bands (15) arranged on either side of the central band (14) and terminating in front of the second base wall (11).

3. 3. The treatment device (1) according to claim 1 or 2, wherein the first deflector wall (13) has a cross-extension, i.e. perpendicular to the longitudinal axis (3) of the tubular duct (2), which is smaller than the corresponding cross-extension of the tubular duct (2).

4. 4. The processing device (1) according to claim 1, 2 or 3, wherein the first deflector wall (13) has a flat shape and is provided at two opposite edges with wings (18) arranged vertically.

5. 5. The processing device (1) according to claim 1, wherein the mixing body (9) comprises at least one second deflector wall (19) that connects the first base wall (10) to the second base wall (11), is oriented in a transverse direction with respect to the first deflector wall (13), is arranged beside the first deflector wall (13) at a non-zero distance from the first deflector wall (13), and is connected to the second base wall (11) next to the main hole (12).

6. 6. The treatment device (1) according to claim 5, wherein the second deflector wall (19) has a cylindrical shape coaxial with the tubular duct (2).

7. 7. Treatment device (1) according to claim 5 or 6, wherein the second deflector wall (19) ends in the region of the mid-plane of the tubular duct (2).

8. 8. The treatment device (1) according to claim 5, 6 or 7, wherein the mixing body (9) comprises two second deflector walls (19) arranged symmetrically around the longitudinal axis (3) of the tubular duct (2) and at a non-zero distance from each other.

9. 9. The processing device (1) of claim 8, wherein the injection opening (7) is arranged on the opposite side of the first deflector wall (13) so as to be at the farthest point relative to the first deflector wall (13) and centered relative to the two second deflector walls (19).

10. The treatment device (1) according to any one of claims 1 to 9, wherein the second base wall (11) has a plurality of sub-holes (22) which are through holes that allow the exhaust gas to pass through, have a diameter smaller than that of the main hole (12), and are arranged around the main hole (12).

11. 11. The treatment device (1) according to claim 10, wherein the sub-holes (22) are coaxial with the main hole (12), are distributed circumferentially and surround the main hole (12).

12. 12. The treatment device (1) according to claim 10 or 11, wherein the sub-holes (22) are distributed along two circumferences arranged inside each other, coaxial with the main hole (12) and surrounding the main hole (12).

13. 13. The treatment device (1) according to claim 10, 11 or 12, wherein the secondary holes (22) are arranged near the tubular side wall (4) and away from the main holes (12).

14. 14. The processing device (1) according to any one of claims 1 to 13, wherein the injection opening (7) is arranged on the opposite side of the first deflector wall (13) so as to be at the furthest point relative to the first deflector wall (13).

15. 15. The processing device (1) according to any one of claims 1 to 14, wherein the second base wall (11) has a recessed sector (23) that is axially offset towards the first base wall (10) with respect to the remaining part of the second base wall (11).

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