Patent Grant
9718037
The present disclosure relates to a mixing system, more specifically to a mixing system for an aftertreatment system.
An aftertreatment system is associated with an engine system. The aftertreatment system is configured to treat and reduce oxides of nitrogen (NOx) present in an exhaust gas flow, prior to the exhaust gas flow exiting into the atmosphere. In order to reduce NOx, the aftertreatment system may include a reductant delivery module, a reductant injector, and a Selective Catalytic Reduction (SCR) module.
The reductant injector is configured to inject a reductant into the exhaust gas flowing through a mixing tube of the aftertreatment system. In order to achieve improved levels of NOx conversion, better flow distribution and mixing of the reductant with the exhaust gases must be achieved. A mixing element is affixed inside the mixing tube so that increased turbulence and improved distribution of the reductant within the exhaust gases may be achieved within a short length of the mixing tube.
However, sometimes the mixing element may provide a surface for the reductant particles to collect thereon, leading to formation of solid deposits. Deposit formation may in turn lead to increased back pressure on the engine and reduce an overall effectiveness of the mixing element. Further, the functioning of the aftertreatment system may be affected as well, causing a reduction in NOx conversion capability and increase in ammonia slip.
U.S. Pat. No. 8,272,777 describes a method for mixing an exhaust gas flow with a fluid in an exhaust gas pipe of an exhaust gas system, in which the fluid is injected by means of an injection device into the exhaust gas pipe. The exhaust gas flow is guided in the exhaust gas pipe in the area of the injection device in a direction of flow parallel to the exhaust gas pipe. The fluid is injected directly onto a deflection element which is arranged in the exhaust gas pipe in a central direction of injection which deviates from the direction of flow by an angle, wherein by means of at least one sheet metal part which is provided on the deflection element and which is raised at least partially at an angle with reference to the direction of flow, the exhaust gas flow is diverted with reference to the direction of flow from its direction of flow into a central direction of distribution.
In one embodiment of the present disclosure, a mixing system for an aftertreatment system is disclosed. The mixing system includes a mixing tube. The mixing tube is provided in fluid communication with an exhaust conduit. The mixing system also includes a reductant injector positioned at an injection location on the mixing tube. The mixing system further includes a mixer assembly positioned downstream of the injection location. The mixer assembly includes a plurality of mixing elements provided in a series arrangement, such that each of the plurality of mixing elements is provided downstream of one another.
Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.
Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or the like parts. Referring to
The engine 102 may include other components (not shown), such as, a fuel system, an intake system, a drivetrain including a transmission system, and so on. The engine 102 may be used to provide power to any machine including, but not limited to, an on-highway truck, an off-highway truck, an earth moving machine, an electric generator, and so on. Accordingly, the engine system 100 may be associated with an industry including, but not limited to, transportation, construction, agriculture, forestry, power generation, and material handling.
Referring to
In the illustrated embodiment, the aftertreatment system 104 includes a first module 106 that is fluidly connected to an exhaust conduit 108 of the engine 102. During engine operation, the first module 106 is arranged to internally receive engine exhaust gas from the exhaust conduit 108. The first module 106 may contain various exhaust gas treatment devices, such as, a Diesel Oxidation Catalyst (DOC) 110 and a Diesel Particulate Filter (DPF) 112, but other devices may be used. The first module 106 and the components found therein are optional and may be omitted for various engine applications in which the exhaust treatment function provided by the first module 106 is not required.
In the illustrated embodiment, the exhaust gas flow provided to the first module 106 by the engine 102 may first pass through the DOC 110 and then through the DPF 112 before entering a mixing tube 114. The aftertreatment system 104 includes a reductant supply system 116. A reductant is injected into the mixing tube 114 by a reductant injector 118. The reductant may be a fluid, such as, Diesel Exhaust Fluid (DEF). The reductant may include urea, ammonia, or other reducing agent known in the art.
Referring to
Further, in order to promote mixing of the reductant with the exhaust gas flow, a mixing system 200 may be associated with the aftertreatment system 104. The mixing system 200 is provided within a portion of the mixing tube 114. The amount of the reductant that may be injected into the mixing tube 114 may be appropriately metered based on engine operating conditions. The aftertreatment system 104 disclosed herein is provided as a non-limiting example. It will be appreciated that the aftertreatment system 104 may be disposed in various arrangements and/or combinations relative to the exhaust manifold. These and other variations in aftertreatment system design are possible without deviating from the scope of the disclosure. The mixing system 200 will now be explained in detail with reference to
As shown in
It should be noted that the reductant injected in to the exhaust gas flow is generally in a liquid state. The each of the mixing elements 204, 206, 208 of the mixing system 200 is configured to break up and evaporate the reductant injected into the exhaust gas flow, such that before entering the SCR module 128, the reductant is in a gaseous state and is homogenously mixed with the exhaust gas flow.
The first mixing element 204 of the mixer assembly 202 is different from the second mixing element 206. Referring to
The first mixing element 204 also includes a plurality of attachment tabs 217. The attachment tabs 217 may be provided at different positions on the first mixing element 204 in order to mount the first mixing element 204 within the mixing tube 114. It should be noted that a number of shelves 213, number and orientation of the tabs 215, and the number of attachment tabs 217 may vary based on system requirements.
Referring now to
Referring now to
The second mixing element 206 includes a plurality of first support members 224. The first support members 224 extend along a first direction B-B′. In this example, the first support members 224 are attached between inner surfaces 218 of the wall 216 of the second mixing element 206. Further, each of the plurality of first support members 224 is parallel to each other. The second mixing element 206 also includes second support members 226. The second mixing element 206 disclosed herein includes a pair of second support members 226, however the number of second support members 226 may vary as per operational requirements. The second support members 226 extend along a second direction C-C′, such that the second direction C-C′ is perpendicular to the first direction B-B′. The second support members 226 are also attached between the inner surfaces 218 of the wall 216 of the second mixing element 206, and are parallel to each other.
The second mixing element 206 further includes a first set of fin elements 228 and a second set of fin elements 230. The fin elements 228, 230 have a trapezoidal shape. Alternatively, the fin elements 228, 230 may have any other shape known in the art that serves the purpose of mixing. The fin elements 228, 230 are attached to and extend from the first support members 224 of the second mixing element 206. Further, each of the fin elements 228, 230 are attached to the first support members 224 in an angled manner. An inclination of the fin elements 228, 230 with respect to a vertical axis Y-Y′ of the second mixing element 206 is defined as a fin angle “α”. Further, in the illustrated embodiment, the fin elements 228, 230 make an acute angle with respect to the axis Y-Y′. More specifically, the first set of fin elements 228 has the fin angle “α”, such that the fin elements 228 extend upwards from the first support members 224. Whereas the second set of fin elements 230 have the fin angle “α”, such that the fin elements 230 extend downwards from the first support members 224. In one example, the fin angle “α” may approximately lay between ±1° to 60°. However, the value of the fin angle “α” is not limited thereto, and may vary based on system requirements. It should be noted that the number of fin elements 228, 230 attached to the second mixing element 206 may also vary based upon a desired fin density. The term “fin density” used herein is calculated based upon the number of fin elements provided per unit area of a particular mixing element.
As shown in
Referring now to
Referring to
Further, in an exemplary embodiment, the fin density of the third mixing element 208 may be higher as compared to the fin density of the second mixing element 206, such that the third mixing element 208 includes higher number of fin elements 238, 240 compared to the number of fin elements 228, 230 of the second mixing element 206. In some embodiments, the fin angle “α” of the fin elements 228, 230, 238, 240 of each of the second and third mixing elements 206, 208 may also vary. In one example, the fin angle “α” of the fin elements 238, 240 of the third mixing element 208 may be lesser than the fin angle “α” of the fin elements 228, 230 of the second mixing element 206 (see
For better mixing and stratification of the reductant with the exhaust gas flow, the third mixing element 208 is provided at an optimum location within the mixing tube 114, so that the reductant may contact the fin elements 238, 240 of the third mixing element 208, instead of a wall 244 of the third mixing element 208. Accordingly, the third mixing element 208 is provided in the mixing tube 114 at the distance “X3” (see
In an alternate embodiment of the present disclosure, as shown in
Alternatively, the attachment surface 602 may be shaped as a bar member. One or more such bar members may be associated with the mixing elements 604, 606, 608 in order to couple the mixing elements 604, 606, 608 with each other. Further, in another embodiment, the attachment surfaces 602 may be embodied by extending only the first pair of sidewalls 610 of the first mixing element 604, and not the bottom wall 612 of the first mixing element 604.
In addition to the first and second mixing elements 504, 506, the mixer assembly 502 may include a pre-mixer 547. The pre-mixer 547 is embodied as a booster. The pre-mixer 547 is configured to impart a slight turbulence to the exhaust gas flow entering the mixing tube 114, before the reductant is injected therein. The pre-mixer 547 is provided at a distance “Y4” from the first mixing element 504. More particularly, the distance “Y4” may be defined as the distance between a downstream edge 548 of the pre-mixer 547 and an upstream edge 550 of the first mixing element 504. The distance “Y4” may lie approximately between 1 to 2 inches or 2 to 4 inches. In one example, the distance “Y4” may be approximately equal to 3 inches.
Referring now to
As shown in
However, it should be noted that each of the mixing elements 704, 706, 708, 710 are designed such that at least one parameter of the mixing elements 704, 706, 708, 710 may change or be adjusted along the exhaust gas flow direction “F”. The parameter may include the fin density, the fin angle “α”, the clocking of the mixing elements 704, 706, 708, 710 with respect to each other, or any combination of the parameters. The first mixing element 704 of the mixer assembly 702 is mounted within the mixing tube 114 at a distance “Z1” from the injection location 703, so that the first mixing element 704 may capture reductant at low exhaust flow rates and may prevent the reductant from contacting a circular wall of the first mixing element 704.
As shown in the accompanying figures, the first mixing element 704 is divided into portions, namely a top portion 744 and a bottom portion 746. The top portion 744 of the first mixing element 704 is embodied as an open space 748. Further, the bottom portion 746 of the first mixing element 704 includes the fin elements 728, 736 attached thereto. The first mixing element 704 is configured to break up large particles of the reductant at low exhaust gas flow rates while flowing through the fin elements 728, 736. Whereas, the reductant may be allowed to pass through the open space 748 of the first mixing element 704 during high exhaust flow rates.
The fin elements 728, 736 of the first mixing element 704 have a shallow fin angle “α” as compared to the fin angle “α” of the remaining mixing elements 706, 708, 710 provided downstream of the first mixing element 704. The fin angle “α” is decided such that, the fin elements 728, 736 may promote a break up of large particles of the reductant and also promote mixing of the reductant with the exhaust gas flow. Further, the first mixing element 704 has relatively lower fin density as compared to fin densities of the remaining mixing elements 706, 708, 710.
The second mixing element 706 of the mixer assembly 702 is mounted within the mixing tube 114 at a distance “Z2” from the first mixing element 704. The distance “Z2” is decided such that the reductant particles, at high exhaust gas flow rates, hit the fin elements 730, 738 instead of the circular wall of the second mixing element 706. Further, the second mixing element 706 is configured to continue breaking of the reductant particles at low exhaust flow rates, and also to initiate the breaking of the large particles of the reductant at high exhaust flow rates. For this purpose, the second mixing element 706 is designed such that the fin elements 730, 738 have a shallow fin angle “α” at a top portion of the second mixing element 706. Also, the fin density of the second mixing element 706 may be lower at the top portion. In one embodiment, the fin density of the second mixing element 706 may be greater than the fin density of the first mixing element 704. The arrangement of the fin elements 730, 738 at the top portion of the second mixing element 706 may promote the breakup of the large particles of the reductant at high exhaust flow rates.
The fin angle “α” of the fin elements 730, 738 may progressively get steeper towards a bottom portion of the second mixing element 706. Also, the fin density of the second mixing element 706 may increase progressively towards the bottom portion of the second mixing element 706. This arrangement may allow for the continual breakup of the small particles of the reductant that may have already passed through the first mixing element 704 at low exhaust gas flow rates.
The third mixing element 708 is mounted within the mixing tube 114 at a distance “Z3” from the second mixing element 706. The distance “Z3” is optimized and decided such that minimal deposit formation may occur on the third mixing element 708 and close to uniform mixing of the reductant with the exhaust gas flow may be obtained. The third mixing element 708 is configured to break up the small particles of the reductant that may still exist in the exhaust gas flow and start a gaseous phase mixing of the reductant with the exhaust gas flow.
The third mixing element 708 includes the fin elements 732, 740. In the illustrated embodiment, the fin angle “α” of the fin elements 732, 740 is steeper at a top portion of the third mixing element 708, as compared to the fin angle “α” of the fin elements 730, 738 of the second mixing element 706. Further, the fin angle “α” may progressively get steeper towards a bottom portion of the third mixing element 708. Also, the fin density of the third mixing element 708 may be optimally chosen in order to reduce or minimize back pressure and promote uniform mixing of the reductant with the exhaust gas flow. The fin density may be constant from the top portion to the bottom portion of the third mixing element 708; however, the fin density of the third mixing element 708 may be higher as compared to the fin density of the second mixing element 706.
As shown in the accompanying figures, the third mixing element 708 is mounted within the mixing tube 114 at a different angular orientation within the mixing tube 114 as compared to the second mixing element 706. More particularly, the third mixing element 708 is clocked at a certain angle about the longitudinal axis A-A′. In some examples, the fin angle “α” of the fin elements 732, 740 may be optimized such that the third mixing element 708 may be clocked approximately up to 90° with respect to the second mixing element 706, about the longitudinal axis A-A′. The clocking of the third mixing element 708 may promote the gaseous phase mixing of the reductant with the exhaust gas flow.
The mixer assembly 702 includes the fourth mixing element 710. The fourth mixing element 710 may be configured to continue the breaking of the small particles of the reductant present in the exhaust gas flow, and may also promote gaseous mixing of the reductant with the exhaust gas flow. Further, the fourth mixing element 710 is mounted within the mixing tube 114 at a distance “Z4” from an outlet 750 of the mixing tube 114. The distance “Z4” may be optimally decided so as to achieve maximum evaporation of the reductant and also promote close to uniform mixing of the reductant with the exhaust gas flow.
Further, the fin angle “α” of the fin elements 734, 742 of the fourth mixing element 710 may be steeper as compared to the fin angle “α” of the fin elements 732, 740 of the third mixing element 708. The fin density of the fourth mixing element 710 may be optimized in order to minimize backpressure and also to promote close to uniform mixing of the reductant with the exhaust gas flow. It should be noted that the fin density of the fourth mixing element 710 may be the highest as compared to the fin densities of the first, second, and third mixing elements 704, 706, 708. Further, the fin density of the fourth mixing element 710 may be uniform from a top portion to a bottom portion of the fourth mixing element 710. It should be further noted that the fin angle “α” of the fin elements 734, 742 may be optimized such that the fourth mixing element 710 may be clocked approximately up to 90° with respect to the third mixing element 708, about the longitudinal axis A-A′. The clocking of the fourth mixing element 710 may further promote the gaseous phase mixing of the reductant with the exhaust gas flow.
An optimum distribution of the reductant with the exhaust gas flow and the evaporation of the reductant in the mixing tube may be critical to the performance of the SCR module. Mixing systems are generally used for obtaining uniform flow distribution and thorough mixing of the reductant with the exhaust gas flow. However, an improper design of the mixing system may lead to increased formation of solid deposits of the reductant thereon. Deposit formation may lead to increased back pressure on the engine and reduce an effectiveness of the mixing system to blend the reductant with the exhaust gas flow, thereby leading to reduction in NOx conversion capability and increase in ammonia slip.
The present disclosure describes a low cost mixing system 200, 500, 700 which provides improved stratification of the reductant injected in the exhaust gas flow and also provides optimum mixing of the reductant with the exhaust gas flow in a multi-stage reductant break up arrangement. The mixing system 200, 500, 700 may be capable of achieving improved levels of NOx conversion through close to uniform distribution of the reductant with the exhaust gas flow, with minimal or no formation of solid deposits. The positioning of each of the mixing elements 204, 206, 208, 504, 506, 508, 547, 604, 606, 608, 704, 706, 708, 710 within the mixing systems 200, 500, 700 respectively may be optimized in order to achieve the higher levels of NOx conversion through close to uniform distribution of the reductant. The positioning of the mixing elements 204, 206, 208, 504, 506, 508, 547, 604, 606, 608, 704, 706, 708, 710 with respect to each other and/or the injection locations 203, 503, 703 respectively may also be adjusted as a function of an exhaust gas flow velocity and reductant particle diameter in order to control the residence time and evaporation rate of the reductant.
Also, it is possible to adjust the fin angle “α”, fin density, and positioning of each of the mixing elements 204, 206, 208, 504, 506, 508, 547, 604, 606, 608, 704, 706, 708, 710 based on a function of a length of the mixing tube 114, in order to achieve optimum mixing of the reductant with the exhaust gas flow. Further, the process of designing the mixing systems 200, 500, 700 is simpler as compared to current designs because optimized mixing and distribution of the reductant with the exhaust gas flow may be achieved by breaking the function of uniform distribution into multiple mixing stages formed in each of the mixing assemblies 202, 502, 702.
Further, utilization of the multiple mixing elements 204, 206, 208, 504, 506, 508, 547, 604, 606, 608, 704, 706, 708, 710 may cause the engine system 100 to heat up faster as compared to the current designs. This may be beneficial from a reductant deposit formation perspective, especially when the engine system 100 is transitioning from a cold condition to a high temperature condition. A person of ordinary skill in the art will appreciate that mixing systems 200, 500, 700 of the present disclosure may be used across multiple platforms, apart from engine applications allowing for less development time and a consistent approach to mixing tube designs. The design may also allow for mixing of the reductant with the exhaust gas flow within shorter mixing tube lengths as compared to current designs.
While embodiments of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.
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