EXHAUST AFTERTREATMENT SYSTEM WITH IN-ELBOW

REDUCTANT INJECTION

Technical Field

The present disclosure relates generally to mixing of reductant and exhaust in an aftertreatment system, and more particularly to a tubeless mixer that includes a plurality of stacked rings distributed with increasing size as a distance from a reductant injector increases.

Background

In many exhaust aftertreatment systems, a reductant, such as liquid urea, is injected into exhaust flow. The urea droplets go through a vaporization and hydrolysis reactions to form ammonia gas. The ammonia adsorbs onto an SCR catalyst and then reacts with NOx in the exhaust flow, with the end result being water and nitrogen at the tailpipe after the selective catalytic reduction. In general, the urea injection site can be located at various positions, such as in the center of a straight segment of an exhaust conduit or at an elbow pipe in the exhaust conduit.

Those skilled in the art will appreciate that a successful mixing strategy of the urea droplets with the exhaust flow can be evaluated based upon the uniformity of ammonia gas distribution at the SCR catalyst combined with minimal or no urea deposits in the exhaust conduit upstream from the catalyst. One of the main issues associated with urea injection, especially in elbow pipe injection locations, are urea deposits. The occurrence of a deposit in the flow path may create severe issues related with performance, such as back pressure increases, reductions in ammonia distribution uniformity and maybe even structural damage if a deposit build up separates from the wall and hits a key component, such as the SCR catalyst itself. The problem is further complicated by the fact that spray distribution may be very dependent upon exhaust conditions, such as low flow conditions associated with idle versus high exhaust flow conditions associated with the engine operating at a rated condition. The main issues faced with in-elbow pipe injection include spray distribution variation with exhaust flow conditions, deposit issues due at an elbow bend, and deposit risk at the injector tip during low exhaust flow conditions.

The present disclosure is directed toward improved performance for in-elbow urea injection of exhaust aftertreatment systems.

Summary

In one aspect, an exhaust aftertreatment system includes an exhaust conduit with an elbow pipe positioned between an engine end and a tailpipe end. An SCR catalyst is positioned in the exhaust conduit between the elbow pipe and the tailpipe end. A reductant dosing system with a nozzle outlet of an injector is positioned in the elbow pipe of the exhaust conduit. A tubeless mixer is positioned in the exhaust conduit between the nozzle outlet and the SCR catalyst. The tubeless mixer includes a plurality of rings, all of which are distributed with increasing size as distance from the nozzle outlet increases.

In another aspect, an elbow pipe of an exhaust conduit includes a pipe with an inlet and an outlet. A centerline of the inlet is angled, at an angle greater than zero, with respect to a centerline of the outlet. The pipe defines an injector opening therethrough. A tubeless mixer is attached to an inner surface of the pipe and includes a plurality of rings, all of which are distributed with increasing size as distance from the injector opening increases.

In still another aspect, a method of operating an exhaust aftertreatment system includes moving exhaust in an exhaust conduit from an engine end toward a tailpipe end. Reductant is injected from an injector into an elbow pipe of the exhaust conduit. The reductant is mixed with exhaust at least in part by passing the exhaust and the reductant through a tubeless mixer that includes a plurality of rings distributed with increasing size as a distance from the injector increases. NOx is reacted in the exhaust with the reductant at an SCR catalyst positioned in the exhaust conduit.

Brief Description of the Drawings

Fig. 1 is a schematic view of an engine and exhaust aftertreatment system according to the present disclosure;

Fig. 2 is a schematic sectioned view of an elbow pipe of an exhaust conduit without a tubeless mixer during high exhaust flow conditions; Fig. 3 is a view similar to Fig. 2 except showing low exhaust flow conditions;

Fig. 4 is a view similar to that of Fig. 2, except with a tubeless mixer according to the present disclosure;

Fig. 5 is a view similar to Fig. 3, except with a tubeless mixer according to the present disclosure;

Fig. 6 is an end view of a tubeless mixer according to the present disclosure;

Fig. 7 is a side view of the tubeless mixer of Fig. 6;

Fig. 8 is a perspective view of the tubeless mixer of Figs. 6 and 7; and

Fig, 9 is an enlarged partial sectioned view of two adjacent rings of a tubeless mixer according to another embodiment of the present disclosure. Detailed Description

Referring initially to Fig. 1, an engine 10, such as a diesel engine, includes an exhaust aftertreatment system 11 attached thereto. Exhaust aftertreatment system 11 includes an exhaust conduit 20 that extends between an engine end 22 and a tailpipe end 23. Exhaust aftertreatment system 11 may include a diesel oxidation catalyst/diesel particulate filter 35, a reductant dosing system 40 and a selective catalytic reduction (SCR) catalyst 30 in a conventional manner. Reductant dosing system 40 includes a reductant supply 42 fluidly connected to an injector 41 by a supply line 43. Injector 41 is positioned for injection into an elbow pipe 21 of exhaust conduit 20.

Referring now in addition to Figs. 2 and 3, an enlarged view of elbow pipe 21 is shown with reductant spray from nozzle outlet 44 of injector 41 during high exhaust flow conditions and low exhaust flow conditions, respectively. Although other reductants could fall within the scope of the present disclosure, reductant dosing system 40 may include hardware and features typically associated with urea injection systems well known in the art. Fig. 2 illustrates a problem that can occur during high exhaust flow conditions where the urea spray droplets 46 from injector 41 may be pushed toward or impinge upon outside wall 76 of elbow pipe 21. The spray pattern shown in Figure 2 can be problematic if the spray droplets impinge upon the wall of the elbow pipe 21 of exhaust conduit 20 causing a deposit to develop. In addition, Figure 2 also shows that the urea spray droplets 46 may not be uniformly distributed across the cross section of the exhaust conduit 20, resulting in an less than uniform distribution of reductant at the SCR catalyst 30, and a

corresponding compromise in the efficiency of the NOx reduction reaction occurring at the SCR catalyst 30. Fig. 3 shows an example spray pattern when exhaust flow is low, such as when the engine 10 is operating at idle or low load conditions. In this case, the urea spray droplets 46 may be more uniformly distributed, but some of the spray may also impinge on the inside wall 77, which could lead to undesirable levels of deposits that could cause harm as discussed in the background section.

Referring now in addition to Figures 4 and 5, these views are equivalent to respective views shown in Figs. 2 and 3, except that a tubeless mixer 50 is attached to elbow pipe 21 in order to improve uniform spray distribution of the urea droplets 46 while also inhibiting impingement of liquid droplets onto the inner and outer walls 77, 76 of the portion of the exhaust conduit defined by elbow pipe 21 and/or downstream therefrom. In particular, tubeless mixer 50 may be positioned in exhaust conduit 20 between the nozzle outlet 44 of injector 41 and the SCR catalyst 30. Tubeless mixer 50 includes a plurality of rings 51 all of which are distributed with increasing size as distance from the nozzle outlet 44 increases. In the illustrated embodiment, tubeless mixer 50 includes a half ring 80 followed by five full rings 51. By including tubeless mixer 50, the undesirable flow patterns associated with Figs. 2 and 3 are improved upon both by improving spray distribution uniformity and by inhibiting impingement of the spray onto the interior wall of exhaust conduit 20 in order to avoid problems associated with deposit build ups.

Referring in addition to Figures 6-8, tubeless mixer 50 is shown before attachment to elbow pipe 21. In this embodiment, half ring 80 and individual rings 81, 82, 83, 84 and 85 are all attached to a common spine 86. A tubeless mixer 50 according to the present disclosure means a structure that is completely free of tubes. A tube according to the present disclosure means a cylindrical structure with a length to diameter ratio greater than one. This is to be contrasted with a ring, which according to the present disclosure means a cylindrical structure with a length to diameter ratio less than one. Those skilled in the art will appreciate that there exists a wide variety of strategies for constructing tubeless mixer 50, including attachment of individual rings 51 to a common spine 86 as illustrated. Tubeless mixer made 50 may also be made by cutting out an appropriate shape of sheet metal with a plurality of ribs, and then rolling the individual ribs back onto themselves to define the individual rings. The ends of the ribs could then be welded back onto each other to complete each individual ring. In the illustrated embodiment, the spine 86 comes in contact with and is attached to the inner surface 75 of elbow pipe 21, such as via welds, or maybe even mechanical fasteners. Elbow pipe 21 may be thought of as a pipe 70 with an inlet 71 and an outlet 72. Centerline 61 of the inlet is angled with respect to centerline 60 of the outlet. The angle in the illustrated embodiment is 90°, but is always greater than zero in order to fairly characterize pipe 70 as an elbow pipe 21. Pipe 70 defines an injector opening 74 therethrough that facilitates mounting an injector 41 so that the nozzle outlet 44 is positioned within exhaust conduit 20 at elbow pipe 21. The rings 51 increase in size with a distance from the injector opening 74. The rings 51 all have a ratio of length L to diameter D that is less than one. In addition, the rings may each have a circular cross section and may share a common centerline 60 that is shared with the centerline of the outlet 72 of pipe 70. Although not necessary, the leading edges 55 of consecutively increased size rings 51 may be located at distances that increase along common centerline 60 from the injector opening 74.

Likewise, although not necessary but shown in the illustrated embodiment, the trailing edges 56 of consecutively increased sized rings 51 are located at distances that increase along common centerline 60 from the injector opening 74.

The tubeless mixer 50 shown in Figs. 4-8 also shows rings 51 that are all regular cylindrical shapes in that each ring 51 has a constant diameter over its length. Nevertheless, rings having different shapes could also fall within the scope of the present disclosure. Also, tubeless mixer 50 of the illustrated embodiment shows a structure in which the trailing edge and leading edge of adjacent rings are coincident along common centerline 60. Nevertheless, a structure in which adjacent rings overlapped one another or were spaced apart from one another along common centerline 60 could also fall within the intended scope of the present disclosure. Finally, although the illustrated embodiment shows five complete rings, structures with less than that number or more than that number of rings 51 could also fall within the intended scope of the present disclosure. It is also important to note that tubeless mixer 50 includes a first small half ring 80 adjacent the nozzle outlet 44 of injector 41. While this structure may be preferable in certain applications, the inclusion of one or more half rings is not necessary in order to fall within the intended scope of the present disclosure.

Referring now in addition to Fig. 9, fragments of largest rings 84 and 85 are shown to illustrate some variations that would still fall within the intended scope of the present disclosure. The length L of each ring is the distance along common centerline 60 and the diameter D is the dimension of the ring perpendicular to common centerline 60. As discussed earlier, all the rings 51 in the illustrated embodiments include rings with a length L over diameter D ratio that is less than one. Fig. 9 is useful in illustrating some of the variables that can be changed to alter the performance of an individual tubeless mixer 50 according to the present disclosure. The AR between adjacent rings can be varied to change the flow gap between adjacent rings 51. In addition, although the illustrated embodiments shows the trailing edge 56 and the leading edge 55 of adjacent rings 51 being coincident along centerline 60, versions in which there is an overlap O such as dotted lines ring 85A would also fall within the intended scope of the present disclosure. In addition, also shown with dotted lines is another variation in which the adjacent rings 84 and 85 are separated by a distance S along common centerline 60 as shown in 85B. Rather than having leading edges 55 that are parallel to centerline 60, the leading edges 55 may have to be angled (positive or negative) as shown in Fig. 9 without departing from the present disclosure. In addition, the trailing edges 56 of the individual rings 51 may also be angled (positive or negative) with regard to centerline 60 without departing from the intended scope of the present disclosure. Thus, engineers can vary a number of rings, the sizes of adjacent rings, the change in diameter between adjacent rings, the circularity of the rings, whether there is an overlap or space between leading and trailing edges of adjacent rings to arrive at a construction with satisfactory performance for a specific application. Finally, although not necessary, the tubeless mixer 50 of the illustrated embodiment includes a half ring 80 closest to injector 41 in order to promote better mixing while also inhibiting spray from impinging on the inside wall 75 of pipe 70. This structure may also help prevent deposit formation on the injector 41 itself.

Industrial Applicability

Referring to Figs. 1, 4 and 5, exhaust aftertreatment system 11 may be operated by moving exhaust originating from engine 10 in the exhaust conduit 20 from the engine end 22 toward the tailpipe end 23. Reductant, such as urea, is injected from injector 41 into elbow pipe 21 of exhaust conduit 20. The reductant is mixed with the exhaust at least in part by passing the exhaust and the reductant through the tubeless mixer 50 as best shown in Figs 4 and 5. Thus, different portions of the exhaust and urea droplets 46 move through the gaps AR between different pairs of adjacent rings 51. Although not visible, the NOx in the exhaust will react with the reductant at SCR catalyst 30 positioned in exhaust conduit 20. The end result being nitrogen gas and water vapor exiting at tailpipe end 23 instead of undesirable NOx, due to the reduction reaction occurring at SCR catalyst 30.

When the exhaust flow is high as in Fig. 4 the mixing accomplished with tubeless mixer 50 helps to disperse the reductant toward inside wall 77 of elbow pipe 21. On the otherhand, when exhaust flow is low as in Fig. 5, the tubeless mixer 50 in general and half ring 80 in particular may serve to inhibit impingement of reductant onto the inside wall 77. Although not necessary, the mixing accomplished by the tubeless mixer 50 may in part be attributed to orienting the rings 51 to share a common centerline 60. In addition, this common centerline 60 may be oriented co-linear with the centerline of the exhaust conduit 20 immediately adjacent elbow pipe 21 as shown in Figs. 4 and 5. The tubeless mixer 50 of the present disclosure addresses several issues faced with in-elbow pipe injection, including but not limited to spray distribution variation with exhaust flow conditions being high or low or in between, deposit issues at the elbow bend and downstream, and a deposit risk at the injector tip at low flow conditions. By placing the first half ring 80 of the tubeless mixer close to the nozzle outlet 44 of injector 41 , it is believed that near tip velocities are increased in order to inhibit potential deposit risk at the injector tip.

As used in this disclosure, the tubeless mixer 50 is characterized as having a plurality of rings 51 , all of which are distributed with increasing size as distance from the nozzle outlet 44 of injector 41 increases. Also, tubeless mixer 50 also includes no structure that could be fairly characterized as a tube consistent with the definition set forth earlier in this disclosure. Thus, a tubeless mixer 50 according to the present disclosure means something other than a mixed flow guiding device of the type shown in Chinese Patent CN 202021015 that includes a central tube 7.

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 an examination of the attached drawings and appended claims.