Abstract:
An apparatus and system are disclosed for efficiently recirculating an exhaust gas in a combustion engine. The apparatus includes an intake air conduit that accepts and promotes mixing of an intake air stream and an EGR stream. The intake air stream moves in the direction of the axis of the intake air conduit. The EGR stream enters the intake air conduit within a volute of decreasing area curled about the outside circumference of the intake air stream. The rate at which the volute encourages mixing of an EGR stream with an intake air stream is affected by the rate at which the volute&#39;s area decreases as the volute curls about the inside circumference of the intake air conduit, and by the angle of entry for the EGR stream as directed by the volute.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to exhaust gas recirculation (EGR) systems on combustion engines, and more particularly relates to the process of mixing the EGR with intake air. 
   2. Description of the Related Art 
   Environmental concerns motivate emissions requirements for internal combustion engines throughout much of the world. Governmental agencies, such as the Environmental Protection Agency (EPA) in the United States, carefully monitor the emission quality of engines and set acceptable emission standards, to which all engines must comply. One important group of regulated emission components is the class of nitrogen oxides (NO x ) formed during engine combustion. 
   A system presently in use on many internal combustion engines to retard the formation of NO x  is the exhaust gas recirculation (EGR) system. The EGR is mixed with air coming into the engine prior to the air entering the combustion chambers. The blending of EGR and intake air prior to combustion results in lower peak combustion temperatures due to lower concentrations of oxygen in the combustion chamber and the heat-sink effects of inert gas fractions, thus acting to prevent the formation of NO x  during combustion. Furthermore, the EGR stream may pass through an EGR cooler prior to mixing with the incoming air, to further lower combustion temperatures and improve the power density of the engine. To ensure the engine runs properly and the emissions are effectively reduced, it is essential to thoroughly mix the EGR with the incoming air such that each cylinder receives an equal gas mixture. 
   Blending EGR with incoming air introduces competing design constraints. Designs which optimize the mixing of EGR and intake air often introduce significant pressure drop in the system and reduce the performance and efficiency of the engine. Designs which optimize the pressure drop while mixing EGR and intake air often result in poor mixing and inconsistent combustion mixtures reaching each cylinder. Additionally, the available packaging space for installing an EGR system on an engine is often low. Some EGR systems are introduced on engine-vehicle designs that originally did not include EGR, and serious costs are incurred for any extra space consumed by the EGR system. Even where EGR systems are designed into an original vehicle package, space constraints are often significant because increased space usage results in other tradeoffs that increase the cost of the engine and vehicle system. 
   Further, complicated pipe routing schemes are disfavored because such schemes introduce other constraints into the design of a vehicle system. For example, a pipe carrying EGR gas will typically be hot, and a complex routing scheme for the pipe may limit the places where electronics and other system components can be installed in the engine compartment of a vehicle. Additionally, a complex routing scheme for an EGR system reduces the generality of the engine-EGR design, thereby making an engine-EGR system less able to be dropped into various vehicles without significant redesign costs. Also, complex internal routing schemes with various slots and internal conduits introduce significant machining and manufacturing costs into the system. Further, complex routing schemes reduce transient response times due to large EGR path volumes, reduce transient performance due to inconsistent EGR compositions across the EGR path, and induce pressure drops due to long pipe lengths in the EGR path. 
   In the current art, several EGR mixing systems are typically used. In a first system, a series of 90-degree straight turns in the EGR system provide some assistance in mixing and help reduce the EGR path volume, but induce significant pressure loss. In a second system, a Venturi is used at the EGR-intake air connection point to reduce the pressure on the intake air side, but these systems provide poor mixing of EGR and intake air. In a third system, a vortex is induced in the intake air where EGR is mixed in. Variations of the third system may introduce added pressure drop through internal conduit flows, and introduce significant manufacturing costs into the system. 
   SUMMARY OF THE INVENTION 
   From the foregoing discussion, Applicant asserts that a need exists for an apparatus and system for efficiently recirculating exhaust gas in a combustion engine. Beneficially, such an apparatus and system would provide thorough mixing of EGR and intake air, with low pressure drop, in a small and simple physical package. 
   The present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available methods. Accordingly, the present invention has been developed to provide an apparatus and system for efficiently recirculating an exhaust gas in a combustion engine that overcome many or all of the above-discussed shortcomings in the art. 
   An apparatus is disclosed to efficiently recirculate an exhaust gas stream for a combustion engine. The apparatus includes an intake air conduit receiving an intake air stream and an EGR stream, and directing a blended intake air and EGR stream to a combustion engine. The apparatus includes a volute having a reducing radius, width, and/or cross-section area to blend the EGR stream and intake air stream. In one embodiment, the volute has a large radius at the EGR conduit equal to the radius of the intake air conduit plus the diameter of the EGR conduit. In one embodiment, the volute has a small radius equal to the radius of the intake air conduit. The volute may engage the intake air conduit helically, perpendicularly, and/or at an acute angle with the direction of the intake air stream. The apparatus may further include multiple EGR streams intersecting the intake air conduit. The apparatus may further include an EGR path fluidly coupling the EGR valve to the volute, and the EGR path may be substantially arcuate. In one embodiment, the EGR path contains no turns greater than 60 degrees over any axial segment of the EGR path having a length equal to the diameter of the EGR conduit. In one embodiment, the EGR path is substantially straight. 
   A system is disclosed to efficiently recirculate an exhaust gas stream. The system includes an internal combustion engine receiving an intake air stream and producing an exhaust gas. The system includes an exhaust gas recirculation (EGR) stream that returns a portion of the exhaust gas to the intake air stream. The system further includes a volute that directs the EGR stream from an EGR conduit into the intake air conduit. In one embodiment, the system further includes a turbocharger, and a remainder of the exhaust gases pass through the turbocharger. 
   Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present invention should be or are in any single embodiment of the invention. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, discussion of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same embodiment. 
   Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention. 
   These features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which: 
       FIG. 1  is a schematic drawing depicting one embodiment of a system to efficiently recirculate an exhaust gas stream in accordance with the present invention; 
       FIG. 2  is an illustration taken from a perspective view depicting one embodiment of a mixer to efficiently recirculate an exhaust gas stream in accordance with the present invention; 
       FIG. 3  is an illustration depicting one embodiment of a cross-section of a mixer to efficiently recirculate an exhaust gas stream in accordance with the present invention; 
       FIG. 4  is an illustration depicting one embodiment of a cross-section of a mixer to efficiently recirculate an exhaust gas stream in accordance with the present invention; 
       FIG. 5  is a side view of a mixer used to efficiently recirculate an exhaust gas stream in accordance with the present invention; and 
       FIG. 6  is a schematic illustration depicting a volute engaging an air intake conduit in a helical manner. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   It will be readily understood that the components of the present invention, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the apparatus and system of the present invention, as presented in  FIGS. 1 through 6 , is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. 
   Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. 
   Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of materials, fasteners, sizes, lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention. 
     FIG. 1  is an illustration depicting one embodiment of a system  100  to efficiently recirculate an exhaust gas stream in accordance with the present invention. The system  100  comprises a combustion engine  102 , which may be any type of combustion engine  102  including a diesel engine  102 . The combustion engine  102  produces an exhaust gas  104 , a portion of which may be directed into an exhaust gas recirculation (EGR) conduit  106  as an EGR stream  107 . The system  100  may further include a turbocharger  114 , and a remainder of the exhaust gas  104  may pass through the turbocharger  114 . While the embodiment of  FIG. 1  illustrates the EGR stream  107  beginning the recirculation path upstream of the turbocharger  114  (a “high pressure” implementation), the EGR stream  107  may also begin the recirculation path from downstream of the turbocharger  114  (a “low pressure” implementation—not shown), or the EGR stream  107  may have any other routing understood in the art. 
   In one embodiment, the system  100  includes a mixer  110 . The mixer  110  includes a volute, a portion of an intake air conduit, and an area where the volute engages the intake air conduit. The volute directs the EGR stream  107  from the EGR conduit  106  into the intake air conduit. The volute has a reducing radius, and a small radius equal to a radius of the intake air conduit. 
   The system  100  may include an EGR path  109  that fluidly couples the EGR valve  108  to the volute of the mixer  110 . In one embodiment, the EGR path  109  is substantially arcuate, having a continuous curvature with no sharp turns. In one example, the EGR path  109  may turn less than 60 degrees in any given axial segment of the EGR path  109  with a length equal to the diameter of the EGR conduit  106 . For example, if the EGR conduit  106  is 3 inches in diameter, the EGR path  109  may have no turns of 60 degrees or more within any 3 inch segment of the EGR path  109 . The turns within the EGR path  109  may be measured by any description known within the art—for example by the mathematically calculated turns of a curve describing the geometric center of the EGR path  109 . In one embodiment, the EGR path  109  is substantially straight (not shown) and carries the EGR stream  107  directly from the EGR valve  108  to the volute of the mixer  110 . 
   The EGR valve  108  and the turbocharger  114  may be used to control the flow of exhaust gas  104  through the EGR conduit  106 . The turbocharger  114  may affect the flow of exhaust gas  104  through the EGR conduit  106  by the amount of the backpressure generated by the turbocharger  114  in the system  100 . The turbocharger  114  may manipulate backpressure in the exhaust gas  104  through adjustment of its geometry, as in a variable geometry turbo (VGT)  114 , or by rerouting exhaust gas  104  through a wastegate around the turbocharger  114 , as in a wastegate turbocharger  114 . 
     FIG. 2  is an illustration depicting one embodiment of the mixer  110  to efficiently recirculate a portion of the exhaust gas  104  in accordance with the present invention. The mixer  110  comprises an air inlet  202  configured to receive an intake air stream  112 , and the EGR conduit  106  configured to direct a portion of the exhaust gas  104  into an intake air conduit  204  through a volute  205 . In the embodiment of  FIG. 2 , the volute  205  engages the intake air conduit  204  at an acute angle with the flow direction of the intake air stream  112  in the intake air conduit  204 . The detail  210  emphasizes the angle of the intake air stream  112  and the entry angle  208  of the volute  205  forming an acute angle  212  according to the mixer  110  illustrated in  FIG. 2 . 
   The EGR conduit  106  may comprise a single EGR conduit  106 , or a plurality of EGR conduits  106 , and the mixer  110  may thereby include multiple volutes  205 . Each volute  205  may engage the intake air conduit  204  from opposite sides, the same side, and/or may be axially displaced along the length of the intake air conduit  204 . Each EGR conduit  106  may approach the intake air conduit  204  vertically up or down, horizontally, and/or at some other intermediate position. The mixer  110  further includes an air outlet  206  that may be coupled to an intake manifold supplying the blended intake air stream  112  and exhaust gas  104  to the combustion engine  102 . 
     FIG. 3  is an illustration depicting one embodiment of a mixer cross-section  300  in accordance with the present invention. The mixer cross-section  300  comprises the structure of the intake air conduit  204 , which contains the intake air stream  112  moving perpendicular to the plane of the illustration, and the EGR stream  107  curling around the inside circumference of the intake air conduit  204 . In one embodiment, the EGR stream  107  may enter the intake air conduit  204  perpendicular to the intake air stream  112 . In alternate embodiments, the EGR stream  107  may enter the intake air stream  112  at an acute angle  212  with the flow direction of the intake air stream  112 . The acute angle  212  comprises some angle greater than an identical flow direction angle of 0 degrees and less than the perpendicular angle of 90 degrees. The illustration of  FIG. 3  is a schematic illustration only, and does not necessarily show scale or other non-essential details. For example, where the volute  205  engages the intake air conduit  204  at an acute angle  208  less than 90 degrees, the volute large radius  302  and volute small radius  304  may not occur at the same point axially relative to the intake air conduit  204 . 
   The mixer cross-section  300  further includes a volute  205  comprising a reducing radius, wherein the large volute radius  302  is equal to a diameter of the EGR conduit  106  plus the radius of the intake air conduit  204 . The small volute radius  304  is equal to a radius of the intake air conduit  204 . The rate at which the volute  205  decreases its radius affects the rate at which the EGR stream  107  becomes mixed with the intake air stream  112 . One of skill in the art may determine for a particular application, using simple experimentation and the disclosures herein, the optimal rate for reducing the volute radius  302 ,  304  to minimize abrupt changes in the EGR stream  107  that may cause pressure drops in the system  100 . 
   In one embodiment of the mixer cross-section  300 , the volute  205  engages the intake air conduit  204  around about 360 degrees of the outside circumference of the intake air stream  112 , as shown in  FIG. 3 . In an alternate embodiment, the volute engages the intake air conduit  204  around about 180 degrees of the outside circumference of the intake air conduit  204  (refer to  FIG. 4 ). In other embodiments, the degree of curvature of the volute engaging the intake air conduit  204  may comprise angles between 180 degrees and 360 degrees, and may further comprise angles less than 180 degrees. In one embodiment, the volute  205  engages the intake air conduit  204  in a helical manner, and may comprise engage the intake air conduit  204  over angles greater than 360 degrees of the outside circumference of the intake air conduit  204 . Generally, the mixing of the EGR stream  107  with the intake air stream  112  may be accomplished in about 180 degrees of curvature. One of skill in the art may determine for a particular application the necessary curvature to adequately mix the EGR stream  107  with the intake air stream  112  through simple testing of the blended streams ( 107 ,  112 ) and/or through modeling and analysis to determine whether the each cylinder is receiving a mixed intake gas stream while minimizing pressure drop. 
     FIG. 4  is an illustration depicting one embodiment of a mixer cross-section  400  in accordance with the present invention. The mixer cross-section  400  comprises the structure of the intake air conduit  204 , the EGR conduit  106 , the intake air stream  112 , and the EGR stream  107 . The mixer cross-section  400  further includes the volute  205  comprising the large volute radius  302  and the small volute radius  304 .  FIG. 4  depicts the volute intersecting the intake air conduit  204  over about 180 degrees around the outside circumference of the intake air conduit  204 . The outer wall depicted in the embodiment of  FIG. 4  transitions  402  from volute  205  to intake air conduit  204  where the volute  205  has reduced to the small volute radius  304 . 
     FIG. 5  is an illustration depicting one embodiment of a mixer  110  side-view to efficiently recirculate an exhaust gas  104  stream in accordance with the present invention. The mixer  110  shows the EGR conduit  106  conveying the EGR stream  107  to the volute  205 , and the intake air conduit  204  receiving an intake air stream  112  and the EGR stream  107 .  FIG. 5  indicates an approximate region  502  where, in one embodiment, the large volute radius  302  begins. The large volute radius  302  may begin where the EGR conduit  106  begins to engage the intake air conduit  204 . From the region  502  the volute  205  comprises a reducing width, with a large width  504 A at the EGR conduit  106  and a small width  504 B at the intake air conduit  204 . The reducing width of the volute  205  acts to decrease the cross-sectional area of the volute  205 , thereby smoothly increasing the velocity of the EGR stream  107  and the rate of mixing the EGR stream  107  with the intake air stream  112  while introducing minimal pressure drop into the mixer  110 . 
   One of skill in the art may determine an optimal reduction of the reducing width for a particular application through simple experimentation (and/or through modeling and analysis) and the disclosures within. For example, a non-uniform intake air stream  112  composition after the mixer  300 ,  400  indicates that greater mixing is desirable, and the ratio of the large width  504 A of the volute to the small width  504 B of the volute could be increased to compensate. An increased pressure drop can be relieved with a lower ratio of the large width  504 A of the volute to the small width  504 B of the volute. 
     FIG. 6  is a schematic illustration depicting an apparatus  600  comprising a volute  205  engaging an intake air conduit  204  in a helical manner. The volute engages the intake air conduit  204  over an axial distance  602  and around an angle  604  of the circumference of the intake air conduit  204 . The apparatus  600  has an EGR path  109  fluidly connecting the EGR valve  108  to the volute  205 . For example, the EGR path  109  in  FIG. 6  ends at the approximate region  502  where the large volute radius  302  begins. The EGR path  109  is substantially arcuate. In one embodiment, a curve  606  describing the geometric center of the EGR path  109  turns less than 60 degrees through any axial section of the EGR path  109  having a length equal to a diameter of the EGR conduit  106 . In one embodiment, a curve  606  describing the geometric center of the EGR path  109  turns less than 60 degrees through any 2-inch section of the EGR path. 
   In one embodiment, the volute intersects the intake air conduit  204  over an axial distance  602  such that a curve describing the geometric center of the volute  205  turns less than 60 degrees through any axial section of the volute  205  having a length equal to the diameter of the EGR conduit  106 . In one embodiment, the volute  205  intersects the intake air conduit  204  over an axial distance  602  about equal to the radius of the intake air conduit  204 . The volute may have a reducing radius  302 ,  304 , a reducing width  504 A,  504 B, and or a reducing cross-sectional area. 
   The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.