Exhaust gas reducer mixer
The mixer design addresses space constraints and fluid deposit issues by creating a vortex for enhanced mixing and using a perforated tube to prevent deposits, improving exhaust gas treatment efficiency.
Patent Information
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- FAURECIA SYST DECHAPPEMENT SAS
- Filing Date
- 2022-06-30
- Publication Date
- 2026-06-12
AI Technical Summary
Existing exhaust gas mixers face challenges in optimizing the intimate mixing of reducing fluids with exhaust gases in limited space and preventing reducing fluid deposits on cold mixer walls.
A mixer design featuring a pipeline with upstream and downstream pipes and intermediate sub-pipes arranged to create a vortex, combined with a sprayer positioned at the junction to enhance mixing and a perforated tube to prevent fluid deposits.
The design improves mixing homogeneity and reduces fluid deposits, enhancing the efficiency of reducing fluid incorporation into exhaust gases while minimizing pressure loss.
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Abstract
Description
Title of the invention: Exhaust gas reducer mixer technical field
[0001] The invention relates to a reducing agent mixer for exhaust gases. Such a mixer is typically located in the exhaust line of an internal combustion engine. Its function is to mix a reducing fluid, conventionally ammonia or an aqueous urea solution (AUS 32, DEF), with the exhaust gases, in order to prepare the mixture for treatment by at least one selective catalytic reduction (SCR) agent to reduce nitrogen oxides. Previous technique
[0002] To construct such a mixer, a sealed mixing chamber is typically built, excluding an inlet, an outlet, and a spray nozzle. The exhaust gases flow through the mixing chamber from the inlet to the outlet. A sprayer is arranged in an outer wall of the mixing chamber so as to spray the reducing fluid, through the spray nozzle, into the exhaust gas flow.
[0003] Two problems are classically encountered when designing such a mixer.
[0004] First, it is necessary to optimize the intimate mixing of the reducing fluid with the exhaust gases. To achieve this, the length of the mixer is generally increased as much as possible in order to maximize the time the two components—reducing fluid and exhaust gas—are in contact. This is generally difficult in an environment, such as an engine and / or exhaust system, where space is very limited.
[0005] Secondly, spraying of the reducing fluid against an external, and therefore cold, wall of the mixer should be avoided, as this risks forming a film of reducing fluid on said wall, a precursor to a very harmful deposit of reducing fluid.
[0006] The invention proposes a new mixer architecture, which addresses these two problems in a particularly ingenious way. Summary of the invention
[0007] To this end, the invention relates to a mixer for mixing exhaust gas with a reducing fluid, comprising a pipe through which the exhaust gases flow from an inlet to an outlet and a spray sprayer for spraying the reducing fluid into the exhaust gas circulation, where the pipeline comprises, from upstream to downstream, an upstream pipe connecting the inlet to a junction, at least two intermediate subpipes connecting the junction to a junction and a downstream pipe connecting the junction to the outlet, where, at the junction, the at least two subpipes are arranged so that the exhaust gas circulation forms a vortex in the downstream pipe and where the sprayer is disposed at the junction so as to spray into the downstream pipe, preferably coaxially.
[0008] Specific features or embodiments, usable alone or in combination, are:
[0009] - the arrangement of the sub-pipes is achieved by a geometric offset, the pro projections of the axes of the sub-pipes onto a plane perpendicular to the axis of the downstream pipe, preferably the axes of the sub-pipes themselves, not passing through the axis of the downstream pipe,
[0010] - the arrangement of the sub-pipes is obtained by bending the sub-pipes at their arrival at the junction,
[0011] - at least upon arrival at the junction, the projections of the sub-pipes onto a plane perpendicular to the axis of the downstream pipeline, preferably the sub-pipes themselves, are arranged axisymmetrically relative to the axis of the downstream pipeline.
[0012] - the axis of the downstream pipe is substantially aligned with the axis of the upstream pipe,
[0013] - the downstream conduit includes an open tube, with a cross-section smaller than the cross-section of the downstream pipe, preferably perforated, arranged coaxially in the downstream pipe,
[0014] - the tube includes at least one protrusion extending axially from the tube in direction of the sprayer, said at least one protrusion not being placed opposite the inlet of a sub-pipe,
[0015] - the sections of the sub-pipes are identical to each other, preferably sen likely equal to the cross-section of the upstream pipe divided by the number of sub-pipes,
[0016] - the cross-section of the downstream pipe is substantially equal to or greater than the cross-section of upstream driving.
[0017] According to a second aspect of the invention, an exhaust line comprising such a mixer. Brief description of the drawings
[0018] The invention will be better understood upon reading the following description, given solely by way of example, and with reference to the figures in the appendix in which:
[0019] [Fig. 1] shows, in perspective view, a mixer according to the invention,
[0020] [Fig.2] shows, in perspective view, the mixer of [Fig.1] from another point of view,
[0021] [Fig.3] shows schematically, viewed along the axis of the downstream pipe, a first mode of offset,
[0022] [Fig.4] shows schematically, viewed along the axis of the downstream pipe, another mode of offset,
[0023] [Fig.5] shows, in perspective view, a detail of the mixer of Fig. 1, showing, in transparency, a tube. Description of the implementation methods
[0024] With reference to [Fig. 1], the invention relates to a mixer 1. A mixer 1 is intended to mix a reducing agent with exhaust gases. Such a mixer is typically located in the exhaust line of an internal combustion engine. Its function is to mix a reducing fluid, conventionally ammonia or any other ammonia precursor in gaseous or liquid form. A common solution is to use an aqueous urea solution: AUS 32, also known as DEF or commercially as AdBlue®.
[0025] The mixing of this reducing fluid with the exhaust gases prepares them to be treated by a selective catalytic reduction (SCR) in order to reduce nitrogen oxides.
[0026] To construct such a mixer 1, a closed, sealed mixing chamber is typically constructed, excluding an inlet orifice 2, an outlet orifice 3, and a spray orifice. The exhaust gases flow through the mixing chamber, from the inlet orifice 2 to the outlet orifice 3. A sprayer 4 is arranged in an outer wall of the mixing chamber so as to spray the reducing fluid, through the spray orifice, into the flow of exhaust gases.
[0027] The sprayer 4 can be a standard injector. It may or may not be heated, in order to preheat the reducing fluid during its spraying.
[0028] According to the invention, the mixer 1 comprises a pipe 5-8, forming the mixing chamber, connecting the inlet port 2 to the outlet port 3, through which the exhaust gases flow. The direction of flow, from upstream to downstream, corresponds to a direction from the inlet 2 to the outlet 3. The mixer 1 further comprises a sprayer 4 for spraying the reducing fluid into the pipe 5-8 and thus into the exhaust gas flow.
[0029] According to one feature, the pipeline 5-8 comprises, successively, from upstream to downstream, an upstream conduit 5, at least two intermediate sub-conduits 6, 7, and a downstream pipe 8. The upstream pipe 5 connects the inlet 2 to a junction 9. Said at least two intermediate sub-pipes 6, 7 connect the junction 9 to a junction 10. The downstream pipe 8 connects the junction 10 to the outlet 3.
[0030] At the junction 10, the at least two sub-pipes 6, 7 are arranged so that the exhaust gas flow forms a vortex in the downstream pipe 8. Due to the arrangement, detailed further below, the at least two exhaust gas flows, formed at the disjunction 9, meet at the junction 10. The arrangement is such that this meeting creates a vortex in the downstream pipe 8. Preferably, this vortex is centered on the axis A of the downstream pipe 8.
[0031] The sprayer 4 is positioned at the junction 10 so as to spray into the downstream pipe 8. Thus, the reducing fluid jet is advantageously sprayed into the exhaust gas vortex. This vortex is highly advantageous because it creates movement in the exhaust gases, increasing the mixing of the exhaust gases with the sprayed reducing fluid, thereby significantly improving the homogeneity of the exhaust gas / reducing fluid mixture. The spray axis of the sprayer 4 is preferably coaxial with the axis A of the downstream pipe 8, essentially coinciding with the axis of the vortex.
[0032] The arrangement is designed to create a swirling circulation of the exhaust gas flow. All methods are possible to obtain such a swirl. Two examples are given here by way of illustration.
[0033] According to a first embodiment, more particularly illustrated in [Fig. 3], showing a detail of a mixer 1 along the axis A of the downstream pipe 8, the arrangement of the sub-pipes 6, 7 is achieved by a geometric offset F between the axes of the sub-pipes 6, 7 and the axis A of the downstream pipe 8. In other words, the projections of the axes of the sub-pipes 6, 7, onto a plane perpendicular to the axis A of the downstream pipe 8, do not pass through the axis A of the downstream pipe 8 and do not intersect the axis A of the downstream pipe 8. This geometric offset F naturally creates a "lever arm" allowing a "torque" to be applied to the exhaust gas sub-flows from each of the sub-pipes 6, 7. This is true in projection. Moreover, according to a preferred embodiment, this is still true if the axes of the sub-pipes 6, 7 themselves do not pass through the axis A of the downstream pipe 8.
[0034] According to another embodiment, more particularly illustrated in [Fig. 4], showing a detail of a mixer 1 along the axis A of the downstream pipe 8, the arrangement of the subpipes 6, 7 is achieved by bends in the subpipes 6, 7 at, or slightly before, their arrival at the junction 10. Here, "slightly before" is understood to mean a length of subpipe 6, 7 less than twice the diameter of the subpipe 6, 7, preferably less than once the diameter of the subpipe 6, 7. conduit 6, 7 and preferably less than half the diameter of sub-conduit 6, 7. Such a configuration allows the creation of a non-homogeneous flow, which, when the sub-flows of exhaust gas meet, will allow the desired vortex to be created.
[0035] It is obvious to a person skilled in the art that it is possible to combine these two embodiments, by combining a curvature of the sub-pipes 6, 7 and a geometric offset F.
[0036] In order to optimize the energies arriving at the junction 10, with a view to creating a homogeneous vortex preferably centered on the axis A of the downstream pipe 8, it is important that the configuration at the junction 10 be axisymmetric.
[0037] Also, according to another feature, at least at, or a little before, the arrival at the junction 10, the projections of the sub-pipes 6, 7, on a plane perpendicular to the axis A of the downstream pipe 8, are arranged axisymmetrically relative to the axis A of the downstream pipe 8.
[0038] This is true in projection, and according to a preferred embodiment, this is also true if the sub-pipes 6, 7 themselves are arranged axisymmetrically relative to the axis A of the downstream pipe 8.
[0039] Such an axisymmetric characteristic implies that the sub-pipes 6, 7 have substantially identical shapes and cross-sections. This also implies that the sub-pipes 6, 7 are, in projection or per se, angularly equidistant around the axis A of the downstream pipe 8. Thus, two sub-pipes 6, 7 will be opposite each other, at 180°. Three sub-pipes 6, 7 will be equidistant, angularly separated by 120° according to an angular periodicity around the axis A.
[0040] Everything described above applies at least in projection, parallel to the axis A of the downstream pipe 8, on a plane perpendicular to the axis A of the downstream pipe 8. However, the more "regular" the configuration, the greater the vortex efficiency.
[0041] Also, according to a preferred configuration, the axes of the sub-pipes 6, 7 are advantageously arranged on a cone whose axis coincides with the axis A of the downstream pipe 8. In this case, the cone preferentially has an opening facing upstream in order to facilitate flows from the sub-pipes 6, 7, towards the downstream pipe 8.
[0042] According to another feature, the axes of the sub-pipes 6, 7 are coplanar, preferably in a plane perpendicular to the axis A of the downstream pipe 8. This latter feature, with a plane perpendicular to the axis A, is included in the previous one, in that it corresponds to a cone with an opening angle of 180°.
[0043] According to another feature, the axis A of the downstream pipe 8 is substantially aligned with the axis of the upstream pipe 5.
[0044] According to another feature, more particularly illustrated in [Fig. 5], where the The downstream pipe 8 is shown transparent. The downstream pipe 8 includes a tube 11. This tube 11 is open at both ends to allow the circulation of exhaust gases, reducing fluid, and a mixture of the two. The cross-sectional area of the tube 11 is smaller than that of the downstream pipe 8, so that the wall of the tube 11 is further away from the wall of the downstream pipe 8. The ratio of the cross-sectional area of the tube 11 to that of the downstream pipe 8 is advantageously between 40 and 80%. The tube 11 is arranged coaxially with and inside the downstream pipe 8. The tube 11 is preferably perforated.
[0045] The tube 11 performs a dual function. On the one hand, it prevents any potential projection of reducing fluid towards the cooler inner wall of the downstream pipe 8, thus limiting the risk of reducing fluid deposits on this inner wall. On the other hand, since the tube 11 is advantageously positioned within the exhaust gas flow, it is heated by the latter. Consequently, any potential projection of reducing fluid onto the tube 11 is advantageously vaporized by this heat, and no deposit is likely to occur on the tube 11.
[0046] It can be noted that at the level of the inlet of the tube 11, the parts of the tube 11 opposite the inlets of the sub-pipes 6, 7 are removed, in order not to create an obstruction to the circulation of the sub-flows from the sub-pipes 6, 7.
[0047] The tube 11 includes at least one protrusion 12 extending axially from said tube 11 towards the sprayer 4. Said at least one protrusion 12 is not placed opposite the outlet of the sub-pipes 6, 7.
[0048] It was unexpectedly observed that this at least one protrusion 12 reduces the back pressure by 20%. These results were obtained by simulation. Like the tube 11 itself, said at least one protrusion 12 also allows some of the reducer spray to be collected on the tube 11 and not on the inner wall of the downstream pipe 8. This is all the more advantageous as the proximity between said at least one protrusion 12 and the sprayer 4 increases.
[0049] According to another characteristic, the sections of the sub-pipes 6, 7 are identical to each other, preferably substantially equal to the section of the upstream pipe 5 divided by the number of sub-pipes 6, 7.
[0050] According to another feature, the cross-section of the downstream pipe 8 is substantially equal to or greater than the cross-section of the upstream pipe 5. The incoming exhaust gas flow is found at the outlet. A (slightly) larger cross-section of the downstream pipe 8 accommodates the negligible volume caused by the addition of reducing fluid and, above all, prevents the creation of further pressure losses or back pressure.
[0051] The invention further relates to an exhaust line comprising such a mixer 1.
[0052] The invention has been illustrated and described in detail in the drawings and the preceding description. This description is to be considered illustrative and given by way of example and not as limiting the invention to this single description. Numerous embodiments are possible. List of reference signs
[0053] 1: mixer,
[0054] 2: entry,
[0055] 3: exit,
[0056] 4: sprayer,
[0057] 5: upstream conduction,
[0058] 6, 7: intermediate sub-conductor,
[0059] 8: downstream conduction,
[0060] 9: disjunction,
[0061] 10: junction,
[0062] 11: tube,
[0063] 12: protuberance,
[0064] A: axis of the downstream pipe,
[0065] F: offset.
Claims
Demands
1. A mixer (1) for mixing exhaust gases with a reducing fluid, comprising a pipe (5-8) through which the exhaust gases flow from an inlet (2) to an outlet (3), and a sprayer (4) for spraying the reducing fluid into the exhaust gas flow. The pipe (5-8) comprises, from upstream to downstream, an upstream conduit (5) connecting the inlet (2) to a junction (9), at least two intermediate sub-pipes (6, 7) connecting the junction (9) to a junction (10), and a downstream conduit (8) connecting the junction (10) to the outlet (3). At the junction (10), the at least two sub-pipes (6, 7) are arranged so that the exhaust gas flow forms a vortex in the downstream conduit (8), and the sprayer (4) is disposed at the junction (10) so as to spray into the downstream pipe (8), preferably coaxially,characterized in that the downstream pipe (8) comprises an open tube (11) with a cross-section smaller than that of the downstream pipe (8), preferably perforated, arranged coaxially in the downstream pipe (8), the tube (11) comprising at least one protrusion (12) extending axially from the tube (11) towards the sprayer (4), said at least one protrusion not being placed opposite the inlet of a sub-pipe (6, 7).
2. Mixer (1) according to claim 1, wherein the arrangement of the subpipes (6, 7) is achieved by a geometric offset (F), the projections of the axes of the subpipes (6, 7), onto a plane perpendicular to the axis (A) of the downstream pipe (8), preferably the axes of the subpipes (6, 7) themselves, not passing through the axis (A) of the downstream pipe (8).
3. Mixer (1) according to any one of claims 1 or 2, wherein the arrangement of the subpipes (6, 7) is achieved by bends in the subpipes (6, 7) at, or slightly before, their arrival at the junction (10).
4. Mixer (1) according to any one of claims 1 to 3, wherein, at least at the arrival at the junction (10), the projections of the subpipes (6, 7) onto a plane perpendicular to the axis (A) of the downstream pipe (8), preferably the subpipes (6, 7) themselves, are arranged axisymmetrically with respect to the axis (A) of the downstream pipe (8).
5. Mixer (1) according to any one of claims 1 to 4, wherein the axis (A) of the downstream pipe (8) is substantially aligned with the axis of the upstream pipe (5).
6. Mixer (1) according to any one of claims 1 to 5, wherein the cross-sections of the sub-pipes (6, 7) are identical to each other, preferably substantially equal to the cross-section of the upstream pipe (5) divided by the number of sub-pipes (6, 7).
7. Mixer (1) according to any one of claims 1 to 6, wherein the cross-section of the downstream pipe (8) is substantially equal to or greater than the cross-section of the upstream pipe (5).
8. Exhaust line comprising a mixer (1) according to any one of the preceding claims.