Abstract:
An apparatus, a system, and a method for treating exhaust gases from an internal combustion engine. The system and method employing the use of a catalytic device coaxial-arranged dual leg apparatus comprising a housing having a first flow path and a second flow path having coaxially arranged portions, a device for selectively directing the exhaust gases between the first flow path and the second flow path, and a first NOx adsorbing catalyst contained in the first flow path.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a system and a method for treating exhaust gases from an engine. 
   2. Background Art 
   NOx adsorber technology is often times used to reduce the amount of NOx emission (content) in engine exhaust gases. A key component in this technology is the NOx adsorber catalyst, which functions as both an adsorbent and a three-way catalyst. During normal engine operations, the three-way catalyst first oxidizes NOx molecules using the excess oxygen in the engine exhaust, and then stores the oxidized NOx molecules on the adsorbent sites on the catalyst. 
   To ensure proper operability, the stored NOx must be removed chemically before the adsorbent becomes fully saturated, otherwise the NOx in the exhaust stream will bypass the adsorbent and exit directly to the atmosphere. A substantially oxygen free exhaust stream with adequate CO (carbon monoxide) and HC (hydrocarbon) is often times used to chemically release the stored NOx from the adsorbent sites and convert them to N 2  at the three-way catalyst sites. This NOx releasing/converting process is defined as NOx adsorber catalyst regeneration. 
   To obtain the substantially oxygen free exhaust stream, additional fuel is usually injected into either the engine cylinders or the exhaust pipe, upstream of the catalyst, to consume the oxygen. This additional fuel use typically results in at least an additional 2-6% fuel consumption increase, or a so-called fuel economy penalty, and results in a considerable operation cost for utilizing such an after treatment system. 
   In order to minimize the fuel economy penalty, the amount of oxygen in the exhaust gases during regeneration should be kept as low as possible. To this end, parallel-arranged dual leg NOx catalyst systems minimize the fuel required by only using a portion of the exhaust gases for catalyst regeneration. These systems have been demonstrated in the laboratory but are typically difficult to install in vehicles because of their space requirements, i.e., they require more space than is typically available. 
   It would be desirable to provide a system and method for treating exhaust gases from an engine which overcomes at least one of the problems in the prior art. 
   SUMMARY OF THE INVENTION 
   In at least one aspect, the present invention generally provides an apparatus, a system and a method for treating exhaust gases from an engine. The present invention reduces the typical space required for a NOx adsorbing catalyst using a coaxial-arranged dual leg treatment apparatus. In at least one embodiment, the coaxial-arranged dual leg apparatus comprises a housing having a first flow path and a second flow path having coaxially arranged portions, a device for selectively directing the exhaust gases between the first flow path and the second flow path, and a first NOx adsorbing catalyst contained in the first flow path. 
   The above features, and other features and advantages of the present invention are readily apparent from the following detailed descriptions thereof when taken in connection with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in greater detail in the following way of example only and with reference to the attached drawings, in which: 
       FIG. 1  is a schematic block diagram of the use of a catalyst system in accordance with the present invention; 
       FIG. 2  is a cross sectional view of a component shown in  FIG. 1 ; 
       FIG. 3  is a view similar to  FIG. 2  showing the operation of the component under a first condition; 
       FIG. 4  is a view similar to  FIG. 3  showing the operation of the component under a second condition; and 
       FIG. 5  is a view similar to  FIG. 2  illustrating another embodiment in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   As required, detailed embodiments of the present invention are disclosed herein. However, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale, some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for the claims and/or as a representative basis for teaching one skilled in the art to variously employ the present invention. 
   With reference to the Figures, the present invention will now be described in greater detail. As shown schematically in  FIG. 1 , the present invention relates to a NOx adsorbing catalyst treatment system  10  for treating exhaust gases from an engine  12 . The system  10  can be used for engines that use various types of fuel, including, but not necessarily limited to, diesel and other gasoline engines such as gas direct-injection engines (GDI). These types of engines include, but are not necessarily limited to, car, truck, boat, and other types of engines such as locomotive, generator set, and mining, and construction vehicles. At least some, if not all, of the components of the treatment system  10  are generally downstream from the engine  12 . The engine  12  and the treatment system  10  are in communication via an exhaust conduit  16 . The treatment system  10  treats the exhaust gases from the engine  12  and then exhausts the treated gases to the atmosphere via output conduit  18 . 
     FIG. 2  illustrates a first embodiment of the treatment system  10  in accordance with at least one aspect of the present invention. The treatment system  10  includes a catalytic device  20 . The catalytic device  20  includes a housing  22 . The housing  22  extends between and connects the conduits  16  and  18 . The housing  22  includes an outer wall  24  which helps to define a first portion  30 , an interchange portion  32 , and a second portion  34 . The first portion  30  generally extends between and connects the conduit  16  and the interchange portion  32 . The interchange portion  32  generally extends between and connects the first portion  30  of the housing  22  and the second portion  34  of the housing. The second portion  34  of the housing  22  generally extends between and connects the interchange portion  32  of the housing  22  and the output conduit  18 . 
   The housing  22  further includes a first interior wall  40  and a second interior wall  42 , both of which are spaced axially inward of the outer wall  24  and help to define a main flow path  46  and a secondary flow path  48  of the housing  22 . Generally, the main flow path  46  and the secondary flow path  48  run throughout the catalytic device  20  in a generally coaxial arrangement. As shown in an embodiment shown in  FIG. 2 , the main flow path  46  is axially inward the second flow path  48  in the first portion  30  of the housing  22  while the main flow path  46  is axially outward the secondary flow path in the second portion  34  of the housing. The change in the relative orientation of the main and secondary flow paths  46  and  48  generally occurs in the interchange portion  32  of the housing  22 . It should be understood by those skilled in the art that either the main flow path  46  or the secondary flow path  48  could initially be spaced axially outward of the other flow path without departing from the spirit of the present invention. The catalytic device  20  and its operation will be explained in greater detail below. 
   The first interior wall  40  helps to define a first main flow path portion  46   a  in the first portion  30  of the housing  22 . The walls  24  and  40  help to define a first secondary flow path portion  48   a  in the first portion  30  of the housing  22 . In the first portion  30  of the housing  22 , the first main flow path portion  46   a  is axially inward of the first secondary flow path  48   a.    
   The first housing portion  30  contains a main catalyst diesel particulate filter  52  and a main NOx adsorbing catalyst  54 . As shown in  FIG. 2 , the main catalyst diesel particulate filter  52  is upstream of the NOx adsorbing catalyst  54  and both are housed within a chamber formed by and within the first interior wall  40 . In this arrangement, gases flowing through the first main flow path portion  46   a  pass through both the main catalyst diesel particulate filter  52  and the NOx adsorbing catalyst  54 . Any suitable filter  52  and catalyst  54  known to those of ordinary skill in the art can be used. Suitable samples of filter  52  includes, but are not necessarily limited to, Cordierite, Silicon carbide, fiber ceramic and sintered metal filters. Suitable samples of catalyst include, but are not necessarily limited to, barium or strontium based catalyst, preferably coated onto honeycomb ceramic substrates. 
   In the interchange portion  32  of the housing  22 , a first conduit  60  is provided that extends axially inward from the outer wall  24  and the first inner wall  40  towards the center axis of the housing  22  such that the second flow path  48  is directed axially inward. Also in the interchange portion  32  of the housing  22 , the main flow path  46  communicates with a second conduit  62  that extends axially outward from the center axis of the housing  22  up to the outer wall  24  and the second interior wall  42 . The conduits  60  and  62  redirect the flow paths  46  and  48  transversely (i.e., angled) away from their respective locations in the first portion  30  of the housing  22 . 
   The second interior wall  42  is located in the second portion  34  of the housing  22  longitudinally spaced from the first inner wall  40 . The second interior wall  42  helps to define a second secondary flow path portion  48   b  in the second portion  34  of the housing  22 . The walls  24  and  42  help to define a second main flow path portion  46   b  in the second potion  34  of the housing  22 . In the second portion  34  of the housing  22 , the second main flow path portion  46   b  is axially outward the second secondary flow path portion  48   b.    
   The second housing portion  34  contains a secondary catalyzed diesel particulate filter  66  and a secondary NOx adsorbing catalyst  68 . As shown in  FIG. 2 , the secondary catalyzed diesel particulate filter  66  is upstream of the secondary NOx adsorbing catalyst  68  and both are housed within a chamber formed by and within the second interior wall  42 . In this arrangement, gases passing through the second secondary flow path portion  48   b  pass through both the secondary catalyst diesel particulate filter  66  and the secondary NOx adsorbing catalyst  68 . In this arrangement, the second main flow path portion  46   b  is axially outward the secondary catalyst diesel filter  66  and the secondary NOx adsorbing catalyst  68 . The secondary catalyst diesel filter  66  can be the same type of filter as the main catalyst diesel filter  52  but may be smaller in size. The filters  52  and  66  can have any relative size, however, preferably, the secondary filter  66  is about one-tenth to about the same size of the main filter  52 , and is more preferably about one-quarter to one-half the size of the main filter  52 . Likewise, the secondary NOx adsorbing catalyst  68  can be the same type of catalyst as the main NOx adsorbing catalyst  54  but may be smaller in size. The catalysts  54  and  68  can have any relative size, however, preferably, the secondary catalyst  68  is about one-tenth to about the same size of the main catalyst  54 , and is more preferably about one-quarter to one-half the size of the main catalyst  54 . 
   The second portion  34  of the housing  22  also includes a third conduit  72  that extends axially inward from the outer wall  24  and the second wall  42  towards the center axis of the housing  22 . The third conduit  72  directs gases flowing from the second main flow path portion  46   b  into chamber  76 . The gases flowing from the second secondary flow path  48   b  also flow into chamber  76 . The second portion  34  also includes a diesel oxidizing catalyst  80 . The diesel oxidizing catalyst  80  is located between the chamber  76  and the output conduit  18  such that the gases from the second main and secondary flow path portions  46   b  and  48   b , respectively, ultimately flow into and through diesel oxidizing catalyst  80 . It should be understood that while the diesel oxidizing catalyst (DOC)  80  is shown to be within the housing  22 , the DOC could be outside the housing as long as the gases from the flow paths  46  and  48  are able to pass through the DOC, if desired. 
   As shown in  FIG. 2 , the exhaust conduit  16  includes a valve  82  for directing, i.e., splitting, the majority of the exhaust gases from the engine  12  into the main flow path  46  or the secondary flow path  48 . It should be understood by those skilled in the art that other devices can be used to selectively direct the exhaust gases without departing from the spirit of the present invention. Suitable examples include, but are not necessarily limited to, two-way valves. It should also be understood by those skilled in the art that the value  82  could be incorporated in the housing  22  rather than conduit  16 . 
   Under normal operating conditions, the valve  82  will be in the closed position to the secondary flow path so that the majority of the exhaust gases (typically about 85-95%) from the engine  12  will flow from the engine into the main flow path  46 , while the remainder (typically about 5-15%) will flow into the secondary flow path  48 . It should be understood that the relative amounts of the flow into paths  46  and  48  can vary from the typical amounts stated herein. This configuration is shown schematically in FIG.  3 . As the gases flow through the main flow path  46  into the housing  22 , they first go through the main catalyzed diesel particulate filter  52  to remove large particulate material such as solid carbon, oil ash, and soluble organic fraction. After exiting the filter  52 , the gases then flow through the main NOx adsorbing catalyst  54  where NO in the exhaust gases are catalyzed to NO 2 . The NO 2  is then adsorbed by the sites on the catalyst  54 . The gases then moves through the housing  22  into the interchange portion  32  through second conduit  62  and are diverted axially outward and around the secondary filter  66  and the secondary NOx adsorbing catalyst  68  which are located in the secondary flow path  48 . The gases then flow back down through the third conduit  72  into chamber  76  and then through diesel oxidizing catalyst  80  where the exhaust gases are further purified, i.e., oxidized and catalyzed. The exhaust gases are then outputted to the environment in the normal course through the output conduit  18 . 
   Because of the type of catalyst that is employed in the NOx adsorbing catalyst  54 , the catalyst requires periodic chemical regeneration. A source of fuel  86  is provided for regenerating the catalyst  54 . A control system (not shown), including sensors in communication with control logic, determines timing of the periodic regeneration of the main and secondary NOx adsorbing catalysts  54  and  66 , respectively. To chemically regenerate catalyst  54 , fuel from fuel source  86  is injected through first fuel injector  88  into the main flow path  46 . It should be understood by those skilled in the art that reductant agents other than fuel, such as CO and H 2 , can also be an used to regenerate the NOx adsorbing catalysts without departing from the spirit of the present invention. It should be understood by those skilled in the art that devices other than fuel injectors can be used to selectively direct fuel or another reducing agent to flow into the NOx adsorbing catalysts without departing from the spirit of the present invention. To minimize the amount of fuel that is required during this fuel injection step, the valve  82  is essentially opened ( FIG. 4 ) for the secondary flow path  48  and essentially closed for the main flow path  46  so that at least a substantial portion, (typically at least a majority, and more preferably about 85-95%), of the exhaust gases are diverted into the secondary flow path with the remainder flowing into the main flow path. The fuel from the fuel source  86  then proceeds through the catalyst  54  in an essentially, or at least substantially, undiluted manner for maximum catalytic generation. 
   When the valve  82  is essentially opened and the majority of the exhaust gases flow through the secondary flow path  48 , the majority of exhaust gases are routed through the first portion  30  of the housing  22  through the first secondary flow path portion  48   b  at a location spaced axially from the main particulate filter  52  and the main NOx adsorbing catalyst  54 . As the gases flow into the interchange portion  32  of the housing  22 , the gases flow through the first conduit  60  axially inward through the second secondary flow path portion  48   b  into the secondary particulate filter  66  and then through the second NOx adsorbing catalyst  68 , where the gases are subjected to the filtering and catalyzing in a similar fashion as in the main filter  52  and the main NOx adsorbing catalyst  54 . The exhaust gases then proceed through chamber  76  and diesel oxidizing catalyst  80  where further oxidizing and catalyzation occurs, and then out through the output conduit  18 . While this can vary depending upon the relative size of the flow paths and other components (such as catalysts), this type of operation, i.e., flowing the majority of exhaust gas through the secondary flow path  48 , occurs typically about 15% of the time so the catalyst  54  can be periodically regenerated without appreciably effecting the catalytic operation of the catalytic device  20 . The remainder of the time, i.e., under normal operating conditions, the majority of the exhaust gases flows through the main flow path  46 . During normal operating conditions, as necessary, the control system regenerates the secondary NOx adsorbing catalyst  68  in a similar fashion by injecting fuel from fuel source  86  into the secondary flow path  48  using the second injector  90 . Those skilled in the art will recognize that required regeneration periods will be specific to individual systems and operating conditions and that the above percentages are illustrations rather than limitations of the present invention. 
     FIG. 5  shows a catalytic device  20   a  made in accordance with a second embodiment of the present invention. The second embodiment is similar to the first embodiment of the present invention illustrated in  FIGS. 2-4 . Accordingly, parts that are the same or similar are generally given the same reference numeral with the suffix “a” attached. 
   The catalytic device  20   a  differs from the catalytic device  20  of the first embodiment in that it does not have a secondary catalyzed diesel particulate filter or a secondary NOx adsorber and only has one fuel injector. This type of configuration while still having excellent NOx conversion has a lower NOx conversion than the device  20  of the first embodiment since the bypass exhaust (through the secondary flow path) will go untreated. The catalytic device  20   a  will be explained below in greater detail. The catalytic device  20   a  includes a housing  22   a . The housing  22   a  extends between and connects the conduits  16   a  and  18   a . The housing  22   a  includes an outer wall  24   a  which helps to define a first portion  30   a , an interchange portion  32   a , and a second portion  34   a . The first portion  30   a  generally extends between and connects the conduit  16   a  and the interchange portion  32   a.  The interchange portion  32   a  generally extends between and connects the first portion  30   a  of the housing  22   a  and the second portion  34   a  of the housing. The second portion  34   a  of the housing  22   a  generally extends between and connects the interchange portion  32   a  of the housing  22   a  and the output conduit  18   a.    
   The housing  22   a  further includes a first interior wall  40   a  spaced axially inward of the outer wall  24   a  which helps to define a main flow path  146  and a secondary flow path  148  of the housing  22   a . Generally, the main flow path  146  and the secondary flow path  148  run throughout the catalytic device  20   a  in a generally coaxial arrangement. As shown in an embodiment shown in  FIG. 5 , the main flow path  146  is axially inward the second flow path  148  in the first portion  30   a  of the housing  22   a . It should be understood by those skilled in the art that the secondary flow path  148  could initially be spaced axially inward of the main flow path  146  without departing from the spirit of the present invention. The catalytic device  20   a  and its operation will be explained in greater detail below. 
   The first interior wall  40   a  helps to define a first main flow path portion  146   a  in the first portion  30   a  of the housing  22   a . The walls  24   a  and  40   a  help to define a first secondary flow path portion  148   a  in the first portion  30   a  of the housing  22   a . In the first portion  30   a  of the housing  22   a , the first main flow path portion  146   a  is axially inward of the first secondary flow path  148   a.    
   The first housing portion  30   a  contains a catalyst diesel particulate filter  52   a  and a NOx adsorbing catalyst  54   a . As shown in  FIG. 5 , the catalyst diesel particulate filter  52   a  is upstream of the NOx adsorbing catalyst  54   a  and both are housed within a chamber formed by and within the interior wall  40   a . In this arrangement, gases flowing through the first main flow path portion  146   a  pass through both the main catalyst diesel particulate filter  52   a  and the NOx adsorbing catalyst  54   a.    
   In the interchange portion  32   a  of the housing  22   a , a first conduit  60   a  is provided that extends axially inward from the outer wall  24   a  and the first inner wall  40   a  towards the center axis of the housing  22   a  such that the second flow path  148  is directed axially inward. The conduit  60   a  redirects the flow path  148  transversely (i.e., angled) toward the center of the housing  22   a , so that the gases flowing from the first secondary flow path portion  148   a  are directed into chamber  76   a.    
   The gases flowing from the first main flow path portion  146   a  also flow into chamber  76   a . The second portion  34   a  also includes a diesel oxidizing catalyst  80   a . The diesel oxidizing catalyst  80   a  is located between the chamber  76   a  and the output conduit  18   a  such that the gases from the main and secondary flow paths  146  and  148 , respectively, ultimately flow into and through diesel oxidizing catalyst  80   a.    
   As shown in  FIG. 5 , the exhaust conduit  16   a  includes a valve  82   a  for directing the exhaust gases from the engine  12  into either the main flow path  146  or the secondary flow path  148 . It will be clear to those skilled in the art that other devices can be used to selectively direct the exhaust gases without departing from the spirit of the present invention. 
   Under normal operating conditions, the valve  82   a  will be in the essentially closed position so that the majority of the exhaust gases from the engine  12  will flow from the engine into the main flow path  146 . As the gases flow through the main flow path  146 , they first go through the catalyzed diesel particulate filter  52   a  to remove large particulate material. After exiting the filter  52   a , the gases then flow through the NOx adsorbing catalyst  54   a  where the exhaust gases are catalyzed to remove the NOx from the exhaust gases. The gases then moves through the housing  22   a  passing axially inward of the interchange portion  32   a  into chamber  76   a  and then through diesel oxidizing catalyst  80   a  where the exhaust fumes are further purified. The exhaust gases are then outputted to the environment in the normal course through the output conduit  18   a.    
   A source of fuel  86   a  is provided for regenerating the catalyst  54   a . A control system (not shown), including sensors in communication with control logic, determines timing of the periodic regeneration of the NOx adsorbing catalyst  54   a . To chemically regenerate catalyst  54   a , fuel from fuel source  86   a  is injected through fuel injector  88   a  into the main flow path  146 . To minimize the amount of fuel that is required during this fuel injection, the valve  82   a  is essentially opened for the secondary flow path  148  and essentially closed for the main flow path  146  so that the majority of the exhaust gases are diverted into the secondary flow path instead of the main flow path. The fuel from the fuel source  186  then proceeds through the catalyst  54   a  in an essentially, or at least substantially, undiluted manner for maximum catalytic generation. 
   When the valve  82   a  is essentially opened and the majority of the exhaust gases flow through the secondary flow path  148 , the exhaust gases are routed through the first portion  30   a  of the housing  22   a  through the first secondary flow path portion  148   b  at a location spaced axially outward from the particulate filter  52   a  and the NOx adsorbing catalyst  54   a . As the gases flow into the interchange portion  32   a  of the housing  22   a , the gases flow through the conduit  60   a  axially inward into and through the chamber  76  and through the diesel oxidizing catalyst  80   a  where oxidizing and catalyzation occurs, and then out through the output conduit  18 . 
   While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.