Abstract:
In a land vehicle of the type having an engine and an exhaust system including an exhaust pipe, a flow diffuser for the exhaust pipe generally includes a substantially tubular body having an outer wall, an interior, and first and second ends, the first end being an exhaust inlet configured to be attachable to an exhaust pipe, the second end being an exhaust discharge portion having an exit plane, a plurality of radial struts extending inwardly from the inner surface of the outer wall to the center of the exit plane for dividing the exhaust discharge portion divided into a plurality of exit channels, and a plurality of air channels extending from the outer wall to the interior of the tubular body configured for delivering air to the interior of the tubular body.

Description:
BACKGROUND 
     New, more stringent emission limits for diesel engines necessitate the use of exhaust after-treatment devices, such as diesel particulate filters. Certain after-treatment devices include a regeneration cycle. During the regeneration cycle, the temperature of the exhaust gas plume may rise significantly above acceptable temperatures normally experienced by exhaust systems without such after-treatment devices. As an example, exhaust systems without after-treatment devices typically discharge exhaust gas at a temperature of around 650 degrees Kelvin. An exhaust system having an after-treatment device that includes a regeneration cycle may experience an exhaust gas plume temperature exceeding 900 degrees Kelvin at its center core. Exhaust gas at this high exit temperature creates a potentially hazardous operating environment. 
     Prior art and current exhaust pipe diffusers passively feed cooling ambient air directly through the duct wall, but do not optimally intermingle the cooling air with the hot core stream in the center of the exhaust pipe. The result at the exit plane is a cool ring of exhaust flow surrounding a very hot exhaust core. 
     Thus, there exists a need for a flow diffuser for an exhaust pipe for diffusing hot exhaust gas on exit from an exhaust pipe. 
     SUMMARY 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     In accordance with one embodiment of the present disclosure, in a land vehicle of the type having an engine and an exhaust system including an exhaust pipe, a flow diffuser for the exhaust pipe is provided. The flow diffuser generally includes a substantially tubular body having an outer wall, an interior, and first and second ends, the first end being an exhaust inlet configured to be attachable to an exhaust pipe, the second end being an exhaust discharge portion having an exit plane. The flow diffuser further includes a plurality of radial struts extending inwardly from the inner surface of the outer wall to the center of the exit plane for dividing the exhaust discharge portion into a plurality of exit channels. The flow diffuser further includes a plurality of air channels extending from the outer wall to the interior of the tubular body configured for delivering air to the interior of the tubular body. 
     In accordance with another embodiment of the present disclosure, in a land vehicle of the type having an engine and an exhaust system including an exhaust pipe, a flow diffuser for the exhaust pipe is provided. The flow diffuser generally includes a substantially tubular body having an outer wall, an interior, and first and second ends, the first end being an exhaust inlet configured to be attachable to an exhaust pipe, the second end being an exhaust discharge portion having an exit plane. The flow diffuser further includes a plurality of radial struts extending inwardly from the inner surface of the outer wall to the center of the exit plane for dividing the exhaust discharge portion into a plurality of exit channels, wherein the plurality of radial struts are substantially hollow and include a plurality of air channels extending from a plurality of inlets on the outer surface of the outer wall to a plurality of outlets in the interior of the tubular body. 
     In accordance with another embodiment of the present disclosure, in a land vehicle of the type having an engine and an exhaust system including an exhaust pipe, a flow diffuser for the exhaust pipe is provided. The flow diffuser generally includes a substantially tubular body having an outer wall, an interior, and first and second ends, the first end being an exhaust inlet configured to be attachable to an exhaust pipe, the second end being an exhaust discharge portion having an exit plane. The flow diffuser further includes a plurality of radial struts extending inwardly from the inner surface of the outer wall to the center of the exit plane for dividing the exhaust discharge portion into a plurality of exit channels, wherein the plurality of radial struts are substantially hollow and include a plurality of air channels extending from a plurality of inlets on the outer surface of the outer wall to a plurality of outlets in the interior of the tubular body, wherein the outlets are located in the interior of the tubular body at least ¼ of the radial distance inwardly from the outer wall of the tubular body. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The patent or application file contains at least one figure executed in color. Copies of this patent or patent application publication with color figures will be provided by the Office upon request and payment of the necessary fee. 
       The foregoing aspects and many of the attendant advantages of this disclosure will become more readily appreciated by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a side view of a flow diffuser formed in accordance with one embodiment of the present disclosure, showing the flow diffuser coupled to a vehicle of the type having an engine and an exhaust pipe; 
         FIG. 2  is a perspective view of the flow diffuser of  FIG. 1 ; 
         FIG. 3  is a perspective view of flow diffuser for an exhaust pipe formed in accordance with other embodiments of the present disclosure; and 
         FIG. 4  is a comparison exit temperature section plot for four different systems (from left to right): an expanding tapered diameter exhaust pipe, the flow diffuser of  FIG. 2 , an intra-stream ambient injector, and a standard straight diameter exhaust pipe; 
         FIGS. 5A ,  5 B,  5 C, and  5 D are individual plots for the four systems of  FIG. 4 ; and 
         FIGS. 6 and 7  are perspective views of the flow diffuser formed in accordance other embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     A flow diffuser  20  constructed in accordance with one embodiment of the present disclosure may be best understood by referring to  FIGS. 1 and 2 . The flow diffuser  20  includes a substantially tubular body  22  having an outer surface  24  and first and second ends  26  and  28 . The first end  26  is configured for attachment to an exhaust pipe  12 . The second end  28  includes a diffusion portion  30  having at least one diffusion port  32  and an optimized flow configuration for heat dissipation. During the operation of a vehicle, for example, the vehicle  10  shown in the illustrated embodiment of  FIG. 1 , exhaust gas travels through an exhaust pipe  12  and is diffused to the surrounding ambient air by the flow diffuser  20 . 
     Flow diffusers  20  of the present disclosure reduce temperature and velocity profiles of hot exhaust gas plumes after exiting an exhaust pipe to reduce the risk of danger associated with hot exhaust pipe discharge. As discussed in greater detail below, specifically, with reference to EXAMPLES 1-3 below, the flow diffusers described herein promote ready mixing and diffusion of hot exhaust gas with cooler surrounding ambient air for heat dissipation. Moreover, the embodiments described herein are also configured such that the combined flow area of the diffusion ports  32  is equal to or greater than the flow area of the inlet or first end  26  to maintain or reduce exhaust gas velocity at the diffusion ports  32  and prevent back pressure within the flow diffuser  20 . 
     Although illustrated and described in conjunction with under-chassis exhaust pipes, other configurations, such as vertical (i.e., stack) exhaust pipes, are also intended to be within the scope of the present disclosure. In a stack exhaust pipe application, exhaust gas diffusion is important to prevent combustion of ignitable objects nears the stack, such as a bridge, tree, etc. It should be appreciated that the first end  26  is an inlet, connectable to the exhaust pipe  12  (see  FIG. 1 ) by any means known to those having ordinary skill in the art, including by an interference fit, welding, or any suitable fastening devices, such as bolts, rivets, or other fasteners. 
     In the illustrated embodiment of  FIGS. 1 and 2 , the flow diffuser  20  is coupled to an exhaust pipe  12 , for example, a 5-inch diameter nominal pipe having a circular cross section. In the illustrated embodiment, the flow diffuser  20  has a flared end, for example, a 5-degree flare from a 5-inch diameter to a 7-inch diameter to increase the cross-sectional area of the second end  28  of the flow diffuser  20 . However, it should be appreciated that the flow diffuser may also have a substantially uniform cross-sectional area from the first end  26  to the second end  28  (see, e.g.,  FIG. 3 ). 
     As mentioned above, the flow diffuser  20  includes at least one diffusion port  32  having an exit plane  34  for exhaust gases to exit the flow diffuser  20 . In the illustrated embodiment, the flow diffuser  20  includes a flow diverter  40 , such as a plug, at or near the exit plane  34 . The flow diverter  40  is designed to physically interrupt the core stream in the center of the exhaust pipe  12  and flow diffuser  20  and promote turbulence in the exhaust stream for fluid mixing and heat dissipation. In the illustrated embodiment, the flow diverter  40  is located along the center longitudinal axis of the flow diffuser  20  at or near the exit plane  34 ; however, it should be appreciated that the flow diverter  40  need not be centered along the longitudinal axis of the flow diffuser at or near the exit plane  34 . In that regard, the placement of the flow diverter  40  may be used to direct exhaust gas from the flow diffuser  20 . For example, if positioned on the vehicle as shown in  FIG. 1 , it may be advantageous to position the flow diverter toward the top of the flow diffuser  20  to direct exhaust gas backwardly and downwardly away from areas of concern, such as the vehicle chassis, wiring, or cab. In addition, it should be appreciated that the flow diffuser  20  may include more than one flow diverter  40  in the exit plane  34 . 
     The flow diffuser  20  further encourages exhaust stream mixing by introducing flow dividers  42 , or struts, to further break up the hot exhaust gases and also to draw in cooling ambient air into the exhaust stream to encourage mixing at the exit plane  34 . In that regard, as seen in the illustrated embodiment, the flow diverter  40  is surrounded by a plurality of radial struts  42  connected to the second end  28  of the flow diffuser  20 . The struts  42  divide the exhaust diffusion portion  30  of the flow diffuser  20  into a plurality of diffusion ports  32 . 
     In the illustrated embodiment, the struts  42  have first and second ends  44  and  46 , which extend from an interior surface of the tubular body  22  of the flow diffuser  20  to the center axis of the flow diffuser  20 , meeting near the longitudinal axis of the flow diffuser  20 , e.g., at or near the flow diverter  40  (or center plug). The struts  42  are positioned in an obtuse angular relationship to the tubular body  22 . In the illustrated embodiment, eight struts  42  are shown; however, it should be appreciated that any number of struts are within the scope of the present disclosure, including, but not limited to three, four, five, six, seven, eight, or more. Moreover, it should be appreciated that the struts need not all be of equal length, but may have varying lengths, as described in greater detail below in conjunction with the embodiment shown in  FIG. 3 . 
     As seen in  FIG. 2 , the struts  42  are hollow struts having channels  48  therethrough with inlets  50  on the outside of the tubular body  22  of the flow diffuser  20  and outlets  52  in or near the exit plane  34  of the flow diffuser  20 . These inlets  50  and outlets  52  allow for the struts  42  to draw ambient air into the exhaust stream as a result of the pressure differential between the environment outside the diffuser  20  and the environment inside the diffuser  20 , such that the ambient air aids in heat dissipation of the exhaust stream. The struts  42  include tapered inlets  50  to enhance the flow of ambient air into the channels. The outlets  52  are spaced from the inlets  50  along the length of the struts  42  in or near the exit plane  34 . In that regard, the outlets  52  are suitably spaced in the exhaust stream to aid in heat dissipation. As mentioned above, one drawback of prior art diffusers is that they passively feed ambient air directly through the duct walls, but do not optimally intermingle the ambient air with the hot core streams in the center of the exhaust pipes. 
     In view of these deficiencies, the struts  42  and the outlets  52  in the struts  42  of the present disclosure are designed to optimally mix ambient air in the hot core of the exhaust stream. In one embodiment of the present disclosure, the outlets  52  are located in the interior of the tubular body  22  at least ¼ of the radial distance inwardly from the outer wall  24  of the tubular body  22 . In another embodiment of the present disclosure, the outlets  52  are located in the interior of the tubular body  22  at least ⅓ of the radial distance inwardly from the outer wall  24  of the tubular body  22 . (See  FIG. 6 ). In yet another embodiment of the present disclosure, the outlets  52  are located in the interior of the tubular body  22  at least ½ of the radial distance inwardly from the outer wall  24  of the tubular body  22 . (See  FIG. 7 ). 
     In the illustrated embodiment, the outlets  52  are shown to be substantially equidistant from the inlets  50  along the length of the struts  42 ; however, it should be appreciated that the outlets  52  may be at varying positions along the length of the struts  42 . In the illustrated embodiment, the outlets  52  mix ambient air with the exhaust stream in the direction of the exhaust stream. If the outlets  52  were facing the exhaust stream, then they would serve as inlets, with exhaust gases exiting along the outer surface  24  of the tubular body  22 . 
     The heat transfer and fluid mixing promoted by the flow diffuser  20  of the illustrated embodiment of  FIGS. 1 and 2  will now be described in greater detail. When in use, heat dissipation of hot exhaust gas is achieved through the flow diffuser  20  in at least four ways: (1) by heat conduction; (2) by velocity reduction; (3) by breaking up the exhaust stream to encourage turbulence and mixing with ambient air; and (4) by introducing ambient air into the exhaust stream. As will be described in greater detail below, velocity reduction and mixing with ambient air, in turn, result in reduction of the center core of the hot exhaust gas streams exiting the flow diffuser  20  to promote enhanced fluid mixing upon exit. Enhanced fluid mixing results in more rapid heat dissipation of the exhaust gas with the surrounding ambient air. It should be appreciated that fluid mixing contributes more significantly to the overall heat dissipation of the flow diffuser  20  than heat dissipation by conduction (for example, heat loss through the outer surface  24  of the flow diffuser  20 ). 
     First, heat is dissipated from the effective surface area of the flow diffuser  20  to the surrounding ambient air. The wall thickness of the diffusion portion  30  and the substantially tubular body  22 , as well as the thermal resistivity of the material from which the flow diffuser  20  is constructed, contribute to the conductive cooling achieved by the flow diffuser  20 , in accordance with the principles of heat transfer. It should further be appreciated that additional cooling of the flow diffuser  20  surface may be achieved by convective cooling. For example, if the vehicle  10  to which the flow diffuser  20  is attached is moving, the fluid flow of the surrounding ambient air over the flow diffuser  20  will further provide cooling to the flow diffuser  20 . 
     Second, because the flow area of the diffusion portion  30  may be greater than the flow area at the inlet or first end  26  of the flow diffuser  20 , the velocity of the exhaust gas may decrease as it exits the diffusion portion  30 . Decreased exhaust gas velocity allows for a decreased penetration distance of the jet exhaust streams, which further allows for enhanced mixing of the exhaust gas streams with the surrounding ambient air. In addition to the mixing advantages described herein, increased flow area at the diffusion portion  30  also helps decrease back pressure during the vehicle exhaust stroke. 
     Third and fourth, heat dissipation is promoted through breaking up the exhaust stream to encourage turbulence and mixing, as well as by introducing ambient air into the exhaust stream. With regard to the mixing effects, it should be appreciated that exhaust gas generally has a nonlaminar flow at a high velocity and, comparatively, the surrounding ambient air generally has a substantially quieter flow at a lower velocity. As the exhaust gas exits the flow diffuser  20 , the flow diverter  40  (or plug) and flow dividers  42  (or struts) create a plurality of separate exhaust gas streams through separate diffusion ports  32 . 
     Although the velocities of the separate exhaust gas streams decrease with increased flow area at or near the exit plane  34 , the exhaust gas still exits the flow diffuser  20  at a substantially higher velocity than the surrounding ambient air. When the exhaust gas streams exit the flow diffuser  20 , the shearing forces between the exhaust gas streams and the surrounding ambient air create a frictional drag at their barriers. This frictional drag creates a series of small vortices along the barriers of the exhaust gas streams, and the circulation of the vortices promotes mixing between the exiting streams and the surrounding ambient air to aid in the diffusion of the exhaust gas. Such mixing aids in significantly decreasing the temperature of the hot exhaust gas and the penetration distance of hot exhaust gas streams discharging from the flow diffuser  20 . 
     The more barriers and vortices that are created and the more ambient air present at the barriers for mixing, the greater the heat diffusion of the exhaust gas. Therefore, the combination flow diversion and flow dividing, as well as the introduction of ambient air promotes increased mixing of the exhaust gas with ambient air after exiting the flow diffuser  20 . In addition, if the vehicle  10  to which the flow diffuser  20  is attached is moving, the fluid mixing may be even more enhanced by the introduction of convective mixing principles, described above. 
     Referring to  FIG. 2 , the flow diverter  40  and the radial struts  42  divide the exhaust stream into a plurality of exhaust streams and create a series of barriers and vortices through the core of the exhaust stream. In addition, the channels  48  in the struts  42  draw ambient air into the core of the exhaust stream to provide a source of cooler air for mixing at the barriers and in the vortices. 
     Now returning to  FIG. 3 , a flow diffuser formed in accordance with another embodiment of the present disclosure will be described in greater detail. The flow diffuser is substantially identical in materials and operation as the previously described embodiment, except for differences regarding the diffusion portions of the flow diffusers, which will be described in greater detail below. For clarity in the ensuing descriptions, numeral references of like elements of the flow diffuser  20  are similar, but are in the  100  series for the illustrated embodiment of  FIG. 3 . 
     As mentioned above, the struts  142  may be configured in a variety of numbers and configurations to optimize heat dissipation at or near the exit plane  134  of the flow diffuser  120 . In the illustrated embodiment of  FIG. 3 , the struts  142  and  162  are configured in an alternating long and short pattern to provide enhanced mixing and turbulence in the exhaust stream at the exit plane  134 . In that regard, the long struts  142  extend to the longitudinal center axis of the flow diffuser  120 , while the short struts  162  extend only a portion of the way in the radial direction into the flow diffuser  120 . The advantage of this pattern is that the long and short struts  142  and  162  break up the exhaust stream to encourage turbulence and mixing, and also to introduce ambient into the exhaust stream at various radial distances. It should be appreciated that other patterns are also within the scope of the present disclosure, and varying strut length is also within the scope of the present disclosure. 
     EXAMPLE 
     Comparative Exhaust Temperature Section Plots 
     The heat transfer and fluid mixing promoted by the flow diffuser embodiments described herein may be further understood by referring to the exemplary temperature section plots of exhaust systems under simulated use conditions for modeling mass flow, inlet temperature, and exit port temperature of a diesel particulate filter undergoing regeneration. 
       FIG. 4  includes comparison exit temperature section plots for four different systems (from left to right): (A) an expanding tapered diameter exhaust pipe, which corresponds for  FIG. 5A ; (B) the flow diffuser  20  of  FIG. 2 , which corresponds for  FIG. 5B ; (C) an intra-stream ambient injector, which corresponds for  FIG. 5C ; and (D) a standard straight diameter exhaust pipe, which corresponds for  FIG. 5D . All four systems were subjected to simulated diesel particulate filter conditions of over 950 degrees Kelvin and a mass flow rate of about 1 kg/sec in a vertical stack application in a 20 mile/hr free stream. Ambient temperature is 273 degrees Kelvin. 
     Referring to  FIG. 5B , the hot core of the exhaust gas streams exiting the flow diffuser  20  has immediate heat dissipation from over 950 degrees Kelvin to less than about 850 degrees Kelvin within a vertical distance of less than about 4 inches from the exit plane  34  of the diffuser  20 . Referring to  FIG. 5D , the hot core of the exhaust gas stream exiting the standard exhaust pipe, on the other hand, has little to no heat dissipation from over 950 degrees Kelvin to less than 850 degrees Kelvin until the exhaust gas reaches a vertical distance of over 8 inches from the exit plane. Referring to  FIGS. 5A and 5C , the hot cores of the exhaust gas streams exiting the expanding tapered diameter exhaust pipe and intra-stream ambient injector have little to no heat dissipation from over 950 degrees Kelvin to less than 850 degrees Kelvin until the exhaust gas reaches a vertical distance of over 6.5 inches from the exit plane. 
     Referring now to the comparison graph in  FIG. 4 , not only does the hot core dissipate more quickly using the flow diffuser  20  (see  FIG. 5B ), but the hot stream fully dissipates to ambient temperatures within a vertical distance of about 9 inches from the exhaust plane  34 . All of the other systems have more gradual heat dissipation and do not achieve full heat dissipation until a vertical distance of well over 10 inches from the exhaust plane. 
     As best seen by comparing the temperature section plots in  FIG. 4  for the flow diffuser  20  and the various other exhaust systems, the mixing effects of the flow diffusers formed in accordance with embodiments of the present disclosure are significantly improved over the mixing effects of the other systems as a result of the following: the combination of decreased exhaust stream velocity, resulting in improved mixing at the barrier; increased cross-sectional area at the exit plane of the flow diffuser, resulting in a reduced core in the exhaust gas streams and an increased barrier for the flow area for enhanced mixing; and the introduction of ambient air through the struts, resulting in a greater amount of ambient air at the barrier of the exhaust gas streams for enhanced mixing with ambient air. 
     Referring to  FIG. 5D , by examining the limited expansion and mixing of the hottest core of the exhaust gas stream in the exit temperature section plot for a standard straight diameter exhaust pipe, the section plot indicates that significantly less mixing between the exhaust gas and the surrounding ambient air at the barrier is occurring, as compared to the mixing achieved with the flow diffuser  20  in  FIG. 5B , described above. Less mixing at the standard exhaust pipe outlet is a result of the substantially constant velocity of the exhaust gas at the exhaust pipe inlet and outlet for a standard exhaust pipe having a circular cross section. Although the cross-sectional diameter of the hot spot decreases in diameter with vertical distance from the exit port, the hot spot remains a penetrating jet of hot exhaust gas, even after traveling a vertical distance of over 8 mm from the exit plane. 
     While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the disclosure.