Patent Publication Number: US-2017362987-A1

Title: Engine system having mixing mechanism for exhaust and injected fluid and engine exhaust treatment strategy

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to engine aftertreatment, and more particularly to apparatus for increasing mixing of engine exhaust and an injected fluid upstream of an exhaust aftertreatment mechanism. 
     BACKGROUND 
     A great many different exhaust aftertreatment strategies have been developed over the years to reduce certain undesired emissions from internal combustion engines. Such emissions have a number of different forms, notably various oxides of nitrogen collectively referred to as “NOx”, carbon monoxide or “CO”, unburned hydrocarbons, and particulate matter or “PM”. Mechanical trapping mechanisms and various catalyzed chemical treatments are used to reduce certain emissions to desired levels. Engine operating strategies are sometimes used in conjunction with aftertreatment to bring emissions levels down to jurisdictional requirements or objectives. 
     One aftertreatment strategy that has achieved widespread application is known as selective catalytic reduction or “SCR”. In SCR a reductant is delivered into an exhaust stream and adsorbed onto a catalyst. Nitrogen oxides are converted in the presence of the adsorbed reductant into diatomic nitrogen and water. In some systems a fluid containing urea and generally referred to as diesel emission fluid or “DEF” is injected into the exhaust stream. The urea decomposes into ammonia and water. Ammonia serves as the reductant that reacts with NOx with the assistance of the catalyst. United States Patent Application Publication No. 20110036082 to Collinot is directed to an exhaust element having a static device mounted therein for mixing an injected additive with exhaust gases. The static device includes a helicoid having an axis forming an angle with a direction of flow of the fluid through the exhaust element. While Collinot may achieve his stated objectives, there is always room for improvement. 
     SUMMARY 
     In one aspect, an engine system includes an internal combustion engine including an engine housing defining a plurality of engine cylinders, and an exhaust system coupled with the engine housing and including an exhaust conduit having an exhaust inlet, an exhaust outlet, a fluid injector structured to inject a fluid into the exhaust conduit, and an aftertreatment mechanism coupled with the exhaust conduit. The exhaust system further including a mixing mechanism positioned fluidly between the fluid injector and the aftertreatment mechanism, and having a turbulator positioned within a flow path of exhaust and injected fluid through the exhaust conduit at an upstream location, and a swirler positioned within the flow path at a downstream location. 
     In another aspect, a mixing mechanism for an engine aftertreatment system includes an exhaust conduit having an upstream end structured to receive a flow of exhaust gas and injected fluid, and a downstream end structured to convey the flow of exhaust gas and injected fluid to an aftertreatment mechanism. The mixing mechanism further includes a turbulator mounted within the exhaust conduit at an upstream location and including flow impingement surfaces structured to induce turbulence in the flow of exhaust gas and injected fluid, and a swirler positioned within the exhaust conduit at a downstream location and including flow impingement surfaces structured to induce swirl in the flow of exhaust gas and injected fluid. 
     In still another aspect, a method of treating exhaust from an internal combustion engine includes injecting a fluid into exhaust passing through an exhaust conduit, and feeding a flow of the exhaust and injected fluid toward an outlet of the exhaust conduit structured to fluidly connect with an emissions treatment mechanism. The method further includes increasing mixing of the exhaust gas and injected fluid at least in part by impinging the flow upon turbulence-inducing surfaces of a turbulator within the exhaust conduit, and impinging the turbulated flow upon swirl-inducing surfaces of a swirler within the exhaust conduit, prior to discharging the flow from the outlet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is diagrammatic view of an engine system, according to one embodiment; 
         FIG. 2  is a diagrammatic view of a swirler for a mixing mechanism in the engine system of  FIG. 1 , according to one embodiment; 
         FIG. 3  is an end view of a turbulator for a mixing mechanism in the engine system of  FIG. 1 , according to one embodiment; 
         FIG. 4  is an end view of a mixing mechanism, according to one embodiment; and 
         FIG. 5  is a sectioned side diagrammatic view of a mixing mechanism, according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , there is shown an engine system  10  according to one embodiment, and including an internal combustion engine  12  (or “engine  12 ”). Engine  12  includes an engine housing  14  defining a plurality of engine cylinders  16 . In the  FIG. 1  illustration only one cylinder  16  is shown, however, it will be appreciated that a plurality of substantially identical cylinders will be formed within engine housing  14 . In a practical implementation strategy engine  12  is a two-stroke engine where a piston  34  reciprocates within cylinder  16  to rotate a crankshaft  36  according to a conventional two-stroke engine cycle. An air intake conduit  32  is coupled with cylinder  16  and provides intake air for combustion. Engine system  10  further includes an exhaust system  18  coupled with engine housing  14  and including an exhaust conduit  20  having an exhaust inlet  22  at an upstream end  23  of exhaust conduit  20  coupled with cylinder  16 . Engine  12  may be a direct-injected compression ignition engine. A fuel injector  38  suitable for injecting a fuel such as a diesel fuel is shown positioned partially within cylinder  16  and supported within an engine head  40 . It should be appreciated that the illustration of  FIG. 1  is diagrammatic only, and features of engine  12 , and indeed any part of engine system  10 , may vary from the illustrated embodiments. For instance, those skilled in the art will be familiar with two-stroke engine configurations having one or more exhaust valves in an engine head, and engine  12  could be constructed according to such a configuration. In still other instances engine  12  might not be a two-stroke engine at all, and also could be spark-ignited rather than compression ignition. 
     Engine system  10  further includes an aftertreatment system  43  including an aftertreatment mechanism  28  coupled with exhaust conduit  20 . In a practical implementation strategy aftertreatment mechanism  28  includes a selective catalytic reduction (SCR) module, having a catalyst support element  31  with catalyst affixed thereon. Exhaust gases mixed with an injected fluid are conveyed from an exhaust conduit  20  by way of an outlet  25  in a downstream end  29  of exhaust conduit  20  into aftertreatment mechanism  28  such that the gases and injected fluid contact the catalyst. Exhaust gases having been treated to reduce emissions in aftertreatment mechanism  28  are discharged by way of a treated exhaust outlet  27 . The injected fluid may include urea or a urea mixture such as DEF. Other fluids containing other suitable reductants, or even a different fluid altogether such as fuel could be used depending upon the exhaust treatment strategy and objectives. Exhaust system  18  further includes a fluid injector  26  coupled with exhaust conduit  20  and structured to inject the fluid for mixing with exhaust. A fluid supply  30 , which may include a urea supply, is coupled with injector  26 . As will be further apparent from the following description engine system  10  is uniquely configured for increasing mixing of the injected fluid and exhaust gases so as to improve the operation and effectiveness of aftertreatment mechanism  28  without unduly increasing back pressure on engine  12 . 
     To this end, exhaust system  18  further includes a mixing mechanism  42  (or “mechanism  42 ”) positioned fluidly between fluid injector  20  and aftertreatment mechanism  28 , within a segment of exhaust conduit  20 . Mechanism  42  includes a turbulator  44  positioned within a flow path of exhaust and injected fluid through exhaust conduit  20  at an upstream location, and a swirler  46  positioned within the flow path at a downstream location. In the  FIG. 1  illustration solid arrows generally depict injected fluid, and open arrows generally depict exhaust gases. It can be seen that the flow of exhaust and injected fluid is not well mixed upstream from turbulator  44 , that turbulence is induced in the flow after passing through turbulator  44 , and that the flow of exhaust and injected fluid is better mixed and swirling after passing through swirler  46 . It can also be noted that mixing mechanism  42  is positioned upstream from a bend  48  in exhaust conduit  20 . At bend  48  and thereafter exhaust conduit  20  expands vertically and feeds into aftertreatment mechanism  28  by way of an exhaust outlet  25  of exhaust conduit  20 . It has been discovered that where mixing of an injected fluid and exhaust is relatively poor prior to a change in flow direction or a change in flow area, a high concentration of injected fluid in a pocket or portion of the flow of fluid can persist as the flow continues downstream and ultimately into aftertreatment mechanism  28 . Promoting mixing of injected fluid with the exhaust can reduce concentrations of injected fluid and generally improve the effectiveness of aftertreatment mechanism  28  at reducing certain emissions, notably NOx. The present disclosure enables such improved mixing without unduly increasing back pressure on engine  12  by both inducing or increasing turbulence in the flow of exhaust gases and injected fluid and inducing or increasing swirling. At least some minor turbulence in the flow of exhaust and fluid may exist prior to the flow reaching mixing mechanism  42 . The present concept can therefore be understood to induce extra or increased turbulence in many instances. The present techniques differ from certain known strategies which, while successful at mixing exhaust and injected fluid, could do so only at the expense of increased back pressure or undesirable economics of the mixing apparatus itself. 
     Referring also now to  FIG. 2  there is shown swirler  46  illustrating features in greater detail. Swirler  46  includes a frame  50  having an outer frame element  52  with a substantially cylindrical shape, and an inner frame element  54  with a substantially cylindrical shape and being coaxial with outer frame element  52  about a center axis  56 . Swirler  46  further includes a plurality of flow impingement surfaces  62  formed upon, for example, a plurality of swirl-inducing elements  58  in the nature of blades  58  (“elements  58 ” or “blades  58 ”), and structured for positioning within the flow path of exhaust and injected fluid through exhaust conduit  20  to induce swirl therein. As will be further apparent in view of subsequently described drawings, swirl-inducing elements  58  may be supported within exhaust conduit  20  in a stellate configuration, although the present disclosure is not thereby limited. Each of elements  58  further includes a leading edge  60  and a downstream surface  64  positioned opposite the corresponding upstream flow-impingement surface  62 . Trailing edges  61  of elements  58  are shown in  FIG. 4 , to be described in more detail below. In a practical implementation strategy, elements  58  are eight in number and are uniformly spaced circumferentially about axis  56 , and extend radially between frame element  54  and frame element  52 . As further discussed herein, elements  58  may be located and contoured in a manner considered optimal for inducing mixing, and structured to cooperate with turbulator  44 . 
     Referring now also to  FIG. 3 , there is shown a front view of turbulator  44  illustrating a plurality of flow impingement surfaces  76  structured to induce turbulence in the flow of exhaust gas and injected fluid, and located upon turbulence-inducing elements  74  (or “elements  74 ”). Elements  74  are positioned within a flow of the exhaust and injected fluid, and when turbulator  44  is positioned for service, within exhaust conduit  20  at locations spaced radially inward from an inner wall of exhaust conduit  20 . Each of elements  74  may be supported by way of support elements  72  coupled with an outer frame  70 . Support elements  72  can have the form of relatively thin metal strips welded or brazed, for example, to elements  74  and to frame  70  and providing only a relatively minor occlusion of a cross-sectional flow area through turbulator  44 . Collectively elements  74  and elements  72  may obstruct 25% or less of a cross-sectional flow area through turbulator  44 , and potentially about 10% or less of the cross-sectional flow area. Surfaces  76  may be understood as leading surfaces oriented to face the flow of exhaust gas and injected fluid when turbulator  44  is positioned for service in exhaust conduit  20 . Elements  78  and surfaces  76  can have rounded shapes, and in some embodiments may have hemispheric shapes. It can also be noted that elements  74  have substantially circular outer perimeters  78 , and are arranged in a rhomboid configuration. Elements  74  form with elements  72  and frame  70  a plurality of outer flow channels  75  and a center flow channel  77 . 
     Referring also now to  FIG. 4  there is shown mixing mechanism  42  with turbulator  44  and swirler  46  shown as they might appear positioned for service and centered upon axis  56 . Trailing edges  61  of elements  58  are shown in  FIG. 4 . It can also be seen from  FIG. 4  that blades  58  are positioned so as to align with elements  74 . In particular, it can be seen that blades  58  align with elements  74  and indeed overlap with elements  74  in the axial projection plane of  FIG. 4 . In a practical implementation strategy, at least some of blades  58  align with elements  74  and blades  58  are positioned such that leading edges  60  intersect elements  74  in the axial projection plane, and are circumferentially offset from elements  72 . Also illustrated in  FIG. 4  are inboard edges  63  of blades  58  and outboard edges  65 . It can be seen from  FIG. 4  that inboard edges  63  appear to have a relatively greater circumferential extent than outboard edges  65  in the axial projection plane. In actuality edges  63  and  65  may have similar or identical lengths, but because of a sculpted contour of blades  58  have the appearance of different circumferential extents. Referring also now to  FIG. 5 , illustrating a sectioned side view of mixing mechanism  42 , it can be seen that leading or upstream surfaces  62  and trailing or downstream surfaces  64  have non-linear profiles in a longitudinal section plane. Blades  58  may have a slight twist that results in the sculpted shapes and thus non-linear profiles so as to optimize the swirling induced in the flow of exhaust gas and injected fluid. As used herein, a sculpted surface should be understood as a surface having a shape that varies simultaneously in multiple dimensions. Thus, a surface having a curvature that is uniform along a length or width dimension of the surface would probably not be considered sculpted. A surface having a curvature that varies along a length or width dimension would likely be considered sculpted. Blades  58  or analogous swirl-inducing elements could be substantially planar in other embodiments, or have still other curved, non-curved, or twisted shapes. It can further be seen from  FIG. 5  that elements  74  have trailing surfaces or back surfaces that face a downstream direction and are substantially planar. Surfaces  76  face upstream and have rounded shapes as described, and in the illustrated embodiment surfaces  76  and elements  74  generally can be understood to have hemispheric shapes. 
     INDUSTRIAL APPLICABILITY 
     Referring to the drawings generally, but in particular to  FIG. 5  there are shown solid arrows representing injected fluid, and open arrows representing exhaust gas flow through a segment  21  of exhaust conduit  20  having turbulator  44  and swirler  46  coupled therewith. For clarity fluid flow is depicted only through the part of mechanism  42  toward the bottom of the page in  FIG. 5 . End flanges  82  and  84  are provided for mounting segment  21  to adjoining parts of exhaust system  20 . Reference numeral  21  indicates an inner wall of exhaust conduit  20 . As the flow of exhaust gas and injected fluid approaches turbulator  44  the constituents may experience some mixing but can also be expected to remain somewhat segregated, as a plume of injected fluid from injector  26  will mix with exhaust gases only relatively slowly as the flow of exhaust gases and injected fluid is fed through exhaust conduit  20  and toward outlet  25  to discharge into aftertreatment mechanism  28 . As the flow of exhaust and injected fluid reaches turbulator  44  some of the exhaust and injected fluid will impinge upon surfaces  76 . Due to the shape of surfaces  76 , exhaust and injected fluid will tend to flow around elements  74  relatively smoothly but typically begin to form eddies or other properties of turbulent flow, as illustrated near outer peripheral edge  78 , approximately upon or just after reaching edge  78 . 
     The turbulent flow properties can be expected to persist at least to some degree as the exhaust gas and injected fluid advance toward swirler  46  and begin to impinge upon blades  58 . The swirling flow that is induced in the exhaust gas and injected fluid can further increase mixing beyond the increase in mixing that results from the inducing of turbulence, and can be expected to persist temporarily after the exhaust gas and injected fluid exits swirler  46 . The swirling motion can, moreover, assist in distributing the exhaust and injected fluid mixture into the changing shape of exhaust conduit  20  as it approaches aftertreatment mechanism  28 . After exiting swirler  46 , and prior to discharging the flow from outlet  25  to feed into aftertreatment mechanism  28 , the exhaust gas and injected fluid mixture can change direction of flow at bend  48 , and thenceforth pass by way of outlet  25  into aftertreatment mechanism  28 . As discussed above certain features of mixing mechanism  42  are optimized to increase mixing sufficiently to improve performance of aftertreatment mechanism  28  while not substantially increasing back pressure on engine  12 . Those skilled in the art will appreciate the sensitivity to back pressure of certain engines, notably two-stroke engines that can have difficulty in successfully expelling exhaust and drawing in fresh intake air for combustion if there is too much back pressure. In coupling the turbulence inducing properties of turbulator  44  with the swirl inducing effect of swirler  46  the present disclosure enables robust mixing without unduly restricting fluid flow as is the case in certain other known designs. 
     The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. Other aspects, features and advantages will be apparent upon examination of the attached drawings and appended claims.