CN102933810B - ring reducer mixer - Google Patents

Abstract

The present invention relates to an exhaust aftertreatment system employing a reductant for NOx reduction technology, the engine exhaust aftertreatment system including a ring disposed in an exhaust conduit. The ring facilitates the introduction and conversion of the reducing agent introduced by the injector, an outer surface of the ring being joined to a plurality of spacers in direct contact with an inner wall of the exhaust conduit, a gap being formed between the outer surface of the ring, the inner wall of the exhaust conduit and two of the plurality of spacers through which the gas flows.

Description

ring reducer mixer

technical field

The present invention relates to engine exhaust aftertreatment systems, and more particularly to exhaust aftertreatment systems employing reductants for NOx reduction technology.

Background technique

Selective catalytic reduction (SCR) systems may be included in exhaust treatment or aftertreatment systems for powertrain systems to remove or reduce nitrogen oxide (NOx or NO) emissions from engine exhaust. SCR systems use a reducing agent, such as urea, that is introduced into the exhaust system.

US patent US 7,581,387 discloses a mixing system comprising mixing blades for mixing urea with the exhaust gas flow.

Contents of the invention

The present invention provides an engine exhaust aftertreatment system including an injector configured to introduce a reductant into an exhaust conduit and a ring disposed in the exhaust flow.

Description of drawings

FIG. 1 is a schematic diagram of a powertrain including an engine and an aftertreatment system with a mixer.

Figure 2 is a front view of the mixer.

Figure 3 is a front view of another embodiment of a mixer.

Figure 4 is a front view of another embodiment of a mixer.

Figure 5 is a front view of another embodiment of a mixer.

Figure 6 is a front view of another embodiment of a mixer.

Fig. 7 is a schematic diagram of a double-branch aftertreatment system incorporating a mixer.

detailed description

As shown in FIG. 1 , a powertrain system 10 includes an engine 12 and an aftertreatment system 14 for treating an exhaust flow 16 produced by the engine 12 . Engine 12 may include other features not shown, such as controls, fuel system, air system, cooling system, peripherals, driveline components, turbochargers, exhaust gas recirculation systems, and the like.

Engine 12 may be any type of engine (internal combustion, gas, diesel, gaseous fuel, natural gas, propane, etc.), may be of any size, with any number of cylinders, and in any configuration ("V", inline, radial Wait). Engine 12 may be used to drive any machine or other device, including on-highway trucks or vehicles, off-road trucks or machinery, earth-moving equipment, generators, aerospace applications, locomotive applications, marine applications, pumps, stationary equipment, or other engine-driven applications.

The aftertreatment system 14 includes an exhaust conduit 18 and a selective catalytic reduction (SCR) system 20 . SCR system 20 includes SCR catalyst 22 , mixing conduit 24 , mixer 26 and reductant supply system 28 .

The SCR catalyst 22 includes a catalyst material disposed on a substrate. The substrate can be composed of cordierite, silicon carbide, other ceramics or metals. The substrate may include a plurality of channels therethrough and may form a honeycomb structure.

The reductant supply system 28 may include a reductant 30 , a reductant source 32 , a pump 34 , a valve 36 , a reductant line 38 and an injector 40 . Reductant 30 is drawn from reductant source 32 via pump 34 and delivery to injector 40 is controlled via valve 36 . The flow of reductant 30 may also be controlled by operation of pump 34 .

The mixing line 24 is the section of the exhaust line 18 into which the reducing agent 30 is introduced. The mixing duct 24 includes an inner wall 25 and an outer wall 27 . The mixing duct 24 is also defined by an inner width 29 .

Reductant supply system 28 may also include a thermal management system for thawing frozen reductant 30 , preventing reductant 30 from freezing, or preventing reductant 30 from overheating. Components of reductant supply system 28 may also be insulated to prevent overheating of reductant 30 . The reductant supply system 28 may also include an air assist system for introducing compressed air to assist in the formation of small droplets in the reductant spray 44 . An air assist system may also be used to drive reductant 30 to reductant line 38 and other reductant supply system 28 components when not in use.

The reductant 30 comes from a nozzle or injector tip 42 of the injector 40 to form a reductant spray 44 or is otherwise introduced into the exhaust gas flow 16 or the SCR catalyst 22 . The position of injector tip 42 may be such that reductant spray 44 is directed directly down the centerline of mixing conduit 24 and mixer 26 .

The aftertreatment system 14 may also include a diesel oxidation catalyst (DOC) 46 , a diesel particulate filter (DPF) 48 , and a purification catalyst 50 . DOC 46 and DPF 48 may be in the same tank as shown or separate. The SCR catalyst 22 and the purification catalyst 50 can also be located in the same tank as shown or be separate.

Aftertreatment system 14 is configured to remove, collect, or convert undesired components from exhaust stream 16 . The DOC 46 converts carbon monoxide (CO) and unburned hydrocarbons (HC) into carbon dioxide (CO2). DPF 48 collects particulate matter or soot. The SCR catalyst 22 is configured to reduce the amount of NOx reducing the exhaust gas flow 16 in the presence of the reductant 30 .

A heat source 52 may also be included to remove soot from the DPF 48 , thermally manage the SCR catalyst 22 , DOC 46 , or purge catalyst 50 to remove sulfur from the SCR catalyst 22 or to remove deposits of the reductant 30 that may have formed. Heat source 52 may embody a burner, a hydrocarbon metering system for creating an exothermic reaction on DOC 46, an electric heating element, a microwave device, or other heat source. The heat source 52 may also be embodied as operating the engine 12 in a condition that produces an elevated temperature of the exhaust flow 16 . The heat source 52 may also embody a backpressure valve or another restriction in the exhaust to increase the temperature of the exhaust stream 16 .

In the illustrated embodiment, exhaust gas flow 16 exits engine 12 , bypasses or passes heat source 52 , passes DOC 46 , DPF 48 , then passes SCR system 20 , and then passes purification catalyst 50 via exhaust conduit 18 .

Other exhaust gas treatment devices may also be provided upstream, downstream, or within the SCR system 20 . In the illustrated embodiment, SCR system 20 is located downstream of DPF 48 and DOC 46 is located upstream of DPF 48 . Heat source 52 is located upstream of DOC 46 . A cleanup catalyst 50 is located downstream of the SCR system 20 . In other embodiments, these means can be arranged in various orders and combined together. In one embodiment, the SCR catalyst 22 may be combined with the DPF 48 where the catalyst material is deposited on the DPF 48 .

Urea is the most common source of reductant 30, although other reductants 30 are possible. The urea reductant 30 decomposes or hydrolyzes to ammonia (NH 3 ) and is then absorbed or otherwise stored in the SCR catalyst 22 . Mixing conduit 24 may be long to assist in mixing or uniform distribution of reductant 30 into exhaust stream 16 and to provide residence time for conversion of urea reductant 30 to NH3. NH3 is consumed in the SCR catalyst 22 by reduction of NOx to nitrogen (N2).

The purification catalyst 50 may be embodied as an ammonia oxidation catalyst (AMOX). The purge catalyst 50 is configured to capture, store, oxidize, reduce, and/or convert NH 3 that may slip over or pass through the SCR catalyst 22 . Purification catalyst 50 may also be configured to capture, store, oxidize, reduce, and/or convert other components present.

A controller and sensor system may also be included to control engine 12 , heat source 52 , reductant supply system 28 , and other components of power system 10 or its application.

The mixer 26 includes a surrounding member or ring 54 . Ring 54 is shown flat, having a toroidal shape and a rectangular cross-section, similar to a washer. In other embodiments, ring 54 may have various other cross-sections, including circular.

Ring 54 includes a face surface 55 , an inner surface 56 and an outer surface 57 . The ring 54 is defined by a thickness 58 in the flow direction of the exhaust gas flow 16 , an inner diameter 60 , an outer diameter 61 , and a ring width 62 . Ring width 62 is the width of the components forming ring 54 and is half the difference between inner diameter 60 and outer diameter 61 . The inner diameter 60 of the ring 54 defines a central opening 64 .

Since the ring 54 may be flat, the surface of the ring may be consistent through the thickness 58 and identical to the front surface 55 . A transverse plane 65 passes through the mixer and cuts the mixing duct 24 . Transverse plane 65 includes a group of planes parallel to it. The transverse plane 65 may be disposed along the frontal surface 55 or may extend through another portion of the mixer 26 . The transverse plane 65 may be perpendicular to the exhaust flow 16 as shown. The transverse plane 65 may also be perpendicular to the inner wall 25 of the mixing duct 24 . In other embodiments, transverse plane 65 may be arranged at various angles to exhaust flow 16 and inner wall 26 .

While ring 54 is described and shown as toroidal and circular and has a "diameter," ring 54 may also be rectangular, octagonal, triangular, or any other shape. The shape of the ring 54 may conform to the inner circumference of the mixing duct 24 and may correspondingly match at least a portion of the shape of the mixing duct 24 that houses it. Ring 54 may also have a different shape than mixing duct 24 and be sized to fit within mixing duct 24 (eg, ring 54 may have a square shape that fits within circular mixing duct 24 ). Ring width 62 may or may not be constant. The outer shape of the ring 54 may also differ from the inner shape (eg, the outer shape may be circular while the inner shape and central opening 64 may be rectangular).

The mixer 26 may also include a spacer 66 separating the ring 54 from the inner wall 25 of the mixing conduit 24 . A spacer 66 may also be used to mount the ring 54 .

The separation between the outer surface 57 of the ring 54 and the inner wall 25 defines a gap 68 . The gap 68 may be annular or have a different shape. Gap 68 may have a gap width 70 . Gap width 70 may or may not be constant around ring 54 . In some embodiments, there may be no gap 68 at some locations of the ring 54 .

Some dimensions of mixer 26 are provided below. These dimensions may depend on a number of variables that may vary between different powertrains 10 . For example, appropriate mixer 26 size may depend on exhaust flow 16 velocity, mixing duct 24 size, engine 12 duty cycle, engine 12 backpressure requirements, reductant spray 44 droplet size, reductant spray 44 rate. To account for these variables, the following dimensions are defined and ranges are provided in terms of ratios.

Gap width 70 may be approximately 1/8 inch. In other embodiments, gap width 70 may be between 1/16 and 1/4 inch. In still other embodiments, gap width 70 may be between 1/16 and 1/2 inch.

The size of the gap width 70 can also be a function of the inner width 29 . In one embodiment, the area of the gap 68 along the transverse plane 65 may be approximately 1.3% of the area of the mixing duct along the transverse plane 65 . In other embodiments, the area of the gap 68 along the transverse plane 65 may be between 0.5% and 5%, between 0.1% and 10%, or between 0.7% and 2% of the area of the mixing duct along the transverse plane 65 .

Ring width 62 may be approximately 2 inches. In other embodiments, ring width 62 may be between 1 and 3 inches. In still other embodiments, ring width 62 may be between 0.5 and 5 inches.

The dimension of ring width 62 may also be a function of inner width 29 . In one embodiment, ring width 62 may be approximately 10% of inner width 29 . In other embodiments, ring width 62 may be between 5% and 15% or between 2% and 25% of inner width 29 .

Gap width 70 and ring width 62 may also be selected to achieve a given size of central opening 64 based on inner width 29 . In one embodiment, the area of the central opening 64 along the transverse plane 65 may be approximately 62% of the area of the mixing duct 24 along the transverse plane 65 . In other embodiments, the area of the central opening 64 along the transverse plane 65 may be between 50% and 70%, between 40% and 80%, between 30% and 80% of the area of the mixing duct 24 along the transverse plane 65. % or between 20% and 90%.

Ring 54 may be constructed of sheet metal, and thus thickness 58 may be relatively small, although it may be of various sizes. In one embodiment, the thickness may be less than 1 (one) inch. In another embodiment, the thickness may be less than 1/4 inch. Thickness 58 may also be less than ring width 62 .

2-6 illustrate various embodiments of mixer 26 having various features as described below. Mixer 26 may include any combination of the features described herein. Figure 2 shows the ring 54 as a solid surface. FIG. 2 also shows that spacer 66 may be formed by spot welds 72 that separate ring 54 from and fit or connect to inner wall 25 .

FIG. 3 shows that ring 54 may include one or more openings 73 through front surface 55 . Openings 73 may have various locations on ring 54 and may form various patterns. FIG. 3 also shows that the spacers 66 may be formed from tabs 74 extending from the outer surface 57 of the ring 54 . The distal end of tab 74 may then be welded, inserted, or otherwise connected to mixing duct 24 to separate and mount or connect ring 54 to inner wall 25 and form gap 68 .

FIG. 4 shows that mixer 26 may include a central structure 76 extending into central opening 64 . These central structures 76 may extend from the inner surface 56 of the ring 54 or from another location or body. The central structure 76 can be embodied as a large part, a small wire or a wire mesh.

FIG. 5 shows that a baffle 78 may be added to the mixer 26 . The baffle 78 includes a baffle opening 80 and a deflector 82 . The deflector 82 is disposed at an angle of less than 90 degrees to the exhaust flow 16 and thereby directs the exhaust flow 16 at an angle through the baffle opening 80 . The baffle 78 may be formed by bending a cutout 84 or stamping a scallop 86 . FIG. 6 shows that the deflector 82 can also be formed by the spacer 66 or the central structure 76 .

FIG. 1 shows the position of the mixer 26 in the mixing conduit 24 . The mixer 26 is arranged within the inner wall 25 at a mixer distance 88 from the injector tip 42 . The mixer distance 88 may be such that when the reductant spray 44 reaches the ring 54 , the size of the spray 44 as it expands is approximately the size of the central opening 64 .

FIG. 7 shows that mixer 26 may be used in a dual-leg aftertreatment system 90 . Dual-leg aftertreatment system 90 includes first and second SCR legs 91 and 92 that receive exhaust gas flow 16 and reductant 30 from reductant supply system 28 .

The exhaust flow 16 from the mixing duct 24 is divided or divided in a dividing section 93 of the exhaust duct 18 . Separation section 93 may be located at separation distance 94 downstream of mixer 26 . Separation distance 94 may be longer than mixer distance 88 . In one embodiment, the separation distance may be a function of the inner width 29 . Separation distance 94 may be approximately 1.2 times inner width 29 . In other embodiments, the separation distance 94 may be more than 1.2 times, between 1 and 2 times, or between 1 and 3 times the inner width 29 .

Dual-leg aftertreatment system 90 may also include first and second inlet legs 95 and 96 that deliver exhaust gas stream 16 to reductant supply system 28 . The exhaust flow 16 from the first and second inlet branches 95 and 96 is split or divided in a merged section 97 of the exhaust duct 18 .

The first and second inlet legs 95 and 96 are shown to include the DPF 48 and the DOC 46 , but may include neither, or may include other components. In one embodiment, first and second inlet legs 95 and 96 do not include DPF 48 . The first and second inlet legs 95 and 96 may also be shown arranged at right angles relative to the first and second SCR legs 91 and 92 , but may be arranged at various other angles or may be arranged linearly. The dual-leg aftertreatment system 90 may also be housed in a box structure with inner walls separating the exhaust flow.

The mixer 26 components may be constructed of steel or any other variety of materials. Mixer 26 may also be coated with a material that assists in the conversion or hydrolysis of reductant 30 to NH3.

Industrial Applicability

The mixer 26 helps to evenly distribute or mix the reductant 30 into the exhaust gas stream 16 , facilitates the conversion of the reductant 30 to NH 3 , and prevents the formation of deposits. The mixer 26 should also be cheap, small and create minimal back pressure. However, these features often conflict with each other. For example, large and complex structures can be effective at distributing reductant 30 evenly into exhaust gas stream 16 and promoting conversion of reductant 30 to NH 3 , but are not cheap, take up excessive space, and often create substantial back pressure.

Evenly distributing the reductant 30 into the exhaust gas flow 16 increases the efficiency of the SCR system 20 by directing the NH3 evenly to all channels of the SCR catalyst and thus enables a large amount of conversion to occur. Evenly distributing the reductant 30 into the exhaust flow 16 may also reduce the amount of reductant 30 needed to achieve greater efficiency. Evenly distributing the reductant 30 into the exhaust flow 16 also prevents too much NH 3 from being directed to a portion of the SCR catalyst area that could cause NH 3 to slip through.

Precipitates may form when the reducing agent 30 is not rapidly decomposed into NH 3 , and a thick layer of the reducing agent 30 accumulates. These layers can build up as more and more reductant 30 is injected or collected, which can have a cooling effect that prevents decomposition into NH3. As a result, the reducing agent 30 sublimates into crystals or otherwise converts into solid components to form a precipitate. The precipitate component may contain biuret (NH2CONHCONH2) or cyanuric acid ((NHCO)3) or another component, depending on temperature and other conditions. These deposits may form in or on surfaces where the reductant spray 44 impinges, settles, or stagnates.

These deposits may adversely affect the operation of power system 10 . The deposits can block the flow of the exhaust stream 16 , causing higher back pressure and reducing engine 12 and aftertreatment system 14 performance and efficiency. The deposits may also interrupt the flow and mixing of the reductant 30 into the exhaust stream 16, thereby reducing decomposition to NH3 and reducing NOx reduction efficiency. The formation of deposits also consumes the reductant 30 , making control of injection more difficult and potentially reducing NOx reduction efficiency. The deposits may also corrode and degrade the components of the SCR system 20 .

It is also important to limit the increase in back pressure. High back pressure can compromise engine 12 performance. High back pressure can also cause deposit formation and exhaust leaks.

The ring 54 may create limited back pressure while still achieving a higher degree of mixing of the reductant 30 into the exhaust flow 16 . The large size of the central opening 64 limits confinement and also creates tumbling of the exhaust flow 16 that is effective for mixing the reductant 30 into the exhaust flow 16 . Many other mixer designs achieve mixing by swirling or creating high turbulence levels. These mixers are of complex and bulky construction and thus tend to be expensive and generate back pressure. In contrast, tumbling via the ring 54 has been found to be effective for mixing while being cheap to produce and not creating as much back pressure as other mixers. The flat shape of the ring 54 facilitates its manufacture by cutting cheap simple sheet material. More complex mixers require expensive and more complex cutting, bending and welding.

Gap 68 may be employed to allow exhaust flow 16 to flow through while still achieving the tumbling effect described above. This flow-through prevents stagnant accumulation of reductant 30 that would otherwise form a precipitate. This flow also helps reduce back pressure. If the gap 68 is too large, the tumbling effect described above may be hindered because the bulk flow will only be done around the ring 54 rather than tumbling through the central opening 64 . If the gap 68 is too small, the flow through may not be sufficient to prevent deposits or achieve a significant reduction in back pressure.

The gap 68 may be located along the perimeter along the outer surface 57 of the ring 54 since this is where the reductant will collect. In some embodiments, gap 68 may be located only at the bottom of ring 54 where reductant 30 would otherwise collect.

The mixer distance 88 of the mixer 26 from the injector tip 42 can affect sediment formation and mixing effectiveness. If the mixer distance 88 is too short, the reductant spray 44 will be concentrated in a small space because the spray 44 has not yet expanded. Accordingly, reductant spray 44 may only pass through the exact central portion of central opening 64 . Since the spray 44 will be concentrated in a small space and only pass through the center of the central opening, the tumbling effect described above may not work and the mixing of the reductant 30 into the exhaust flow 16 may not be to the desired extent. If the mixer distance 88 is too long, the reductant spray 44 will have expanded to a larger volume and may impinge on the ring 54 or inner wall 25 before being converted to NH3. This impact may lead to the formation of precipitates as described above.

Opening 73 may be employed to help reduce back pressure and also reduce weight. The openings 73 can also be used to form flow-through and drain areas where the reducing agent 30 collects, thereby preventing deposits.

Central structure 76 may help fragment and atomize reductant spray 44, thereby facilitating conversion to NH3. The central structure 76 may also introduce turbulence into the exhaust flow 16 that may aid conversion to NH 3 . Central structures 76 may not form deposits because they are located in areas with high flow rates and high temperatures. Central structure 76 may also increase the rigidity and structural strength of mixer 26 .

Baffles 78 may be employed to introduce swirl into the exhaust flow 16 for additional mixing in addition to tumbling. In some embodiments, the baffles 78 can create counter-rotating swirls. Like the opening 73, the baffle 78 can also help reduce back pressure and can also save weight. Baffles 78 may also be used to create flow-through and drain areas where reducing agent 30 collects, thereby preventing deposits.

Mixer 26 may also be suitable for dual-leg aftertreatment system 90 . The dual branch aftertreatment system 90 is often used in conjunction with larger engine systems. The dual-leg aftertreatment system 90 may allow the use of smaller aftertreatment substrates. Since these substrates are often complex ceramic bodies, they can be produced more economically in smaller sizes. The smaller size also improves packaging options and improves flow distribution across the substrate.

Since the mixer 26 introduces limited back pressure, it can uniformly combine the exhaust stream 16 from the first and second inlet branches 95 and 96 . The tumbling created by the mixer 26 may also assist in the flow separation of the exhaust stream 16 into the first and second exit legs 91 and 92 . The mixer, which relies heavily on swirl and turbulence, can create a bias flow towards either of the first and second exit branches 91 and 92 .

Separation distance 94 may effect the flow uniform separation of exhaust gas stream 16 into first and second exit legs 91 and 92 and prevent the formation of deposits.

The separation distance 94 may affect the flow uniformity of the exhaust stream 16 into the first and second exit legs 91 and 92 . If the separation distance 94 is too short, the reductant 30 may not have time to convert to NH3 and the tumbling effect from the mixer 26 may be large. Poor conversion to NH3 prior to separation section 93 may produce precipitates as the reducing agent impinges on the walls. A large roll may cause a bias towards one of the first and second exit branches 91 and 92 . If the separation distance is too long, it may cause packaging difficulties for the dual-leg aftertreatment system 90 and may result in a loss of heat needed to activate the SCR catalyst 22 and prevent deposit formation.

While mixer 26 is described above as assisting in introducing reductant into the exhaust stream, it is also contemplated that mixer 26 may be used to assist in introducing any of a variety of substances into any of a variety of flows. Although embodiments of the invention as described herein may be combined without departing from the scope of the following claims, it will be apparent to those skilled in the art that various modifications and changes can be made. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the invention. It is intended that the specification and examples be considered exemplary only, with the true scope of the invention being indicated by the following claims and their equivalents.

Claims (8)

1. An engine exhaust aftertreatment system (14), comprising: an injector (40) configured to introduce a reductant (30) into the exhaust conduit (24) of the engine (12); and An annulus (54) disposed in said exhaust duct (24) downstream of said injector (40), wherein the outer surface (57) of the ring (54) is joined to a plurality of spacers (66) in direct contact with the inner wall (25) of the exhaust duct (24), A gap (68) for gas to flow is formed between the surface (57), the inner wall (25) of the exhaust pipe (24) and two spacers among the plurality of spacers (66), Therein, the ring (54) includes a plurality of openings (73), a deflector (82) and a central structure (76) extending into a central opening (64) in the ring (54). 2. The engine exhaust aftertreatment system (14) of claim 1, wherein the ring (54) is flat. 3. The engine exhaust aftertreatment system (14) of claim 1, wherein the ring (54) has a toroidal shape and has a rectangular cross-section. 4. The engine exhaust aftertreatment system (14) of any one of claims 1-3, wherein the ring (54) defines a central opening (64) along the exhaust The area of the transverse plane (65) of the duct (24) is between 50% and 70% of the area of said transverse plane (65) in said exhaust duct (24). 5. The engine exhaust aftertreatment system (14) of any one of claims 1-3, wherein the gap (68) has a width (70) of between 1/16 and 1/2 inch ). 6. The engine exhaust aftertreatment system (14) according to any one of claims 1-3, wherein the gap (68) is along the transverse plane (65) of the exhaust duct (24) The area is between 0.5% and 5% of the area of said transverse plane (65) within said exhaust duct (24). 7. The engine exhaust aftertreatment system (14) of any one of claims 1-3, wherein the ring (54) is located at a distance (88) from the injector (40), Such that when the spray (44) of the reducing agent (30) reaches the ring (54), the spray (44) is no larger than the central opening (64) of the ring (54). 8. The engine exhaust aftertreatment system (14) according to any one of claims 1-3, wherein the exhaust duct (24) is downstream of the ring (54) from the ring (54) Divided into 2 or more branch pipes (91, 92) at a distance (94) greater than the width (29) of said exhaust duct (24).