Abstract:
A fuel cell system comprises a main body including a first partial header and a fastening point. The main body is adapted to be coupled to a plurality of plates forming a fuel cell stack, allowing a single plate design to be used for multiple fuel cell stack lengths having a large differential of energy requirements, affording a durable alignment mechanism for the fuel cell stack, and providing integration flexibility for components and configurations of the fuel cell system.

Description:
FIELD OF THE INVENTION 
       [0001]    The present disclosure relates to a fuel cell assembly and more particularly to header manifolds for reactants and coolant supplied to and removed from a fuel cell stack. 
       BACKGROUND OF THE INVENTION 
       [0002]    Fuel cell systems are increasingly being used as a power source in a wide variety of applications. Fuel cell systems have been proposed for use in power consumers such as vehicles as a replacement for internal combustion engines, for example. Such a system is disclosed in commonly owned U.S. patent application Ser. No. 10/418,536, hereby incorporated herein by reference in its entirety. Fuel cells may also be used as stationary electric power plants in buildings and residences, as portable power in video cameras, computers, and the like. Typically, the fuel cells generate electricity used to charge batteries or to provide power for an electric motor. 
         [0003]    Fuel cells are electrochemical devices which combine a fuel such as hydrogen and an oxidant such as oxygen to produce electricity. The oxygen is typically supplied by an air stream. The hydrogen and oxygen combine to result in the formation of water. Other fuels can be used such as natural gas, methanol, gasoline, and coal-derived synthetic fuels, for example. 
         [0004]    The basic process employed by a fuel cell is efficient, substantially pollution-free, quiet, free from moving parts (other than an air compressor, cooling fans, pumps and actuators), and may be constructed to leave only heat and water as by-products. The term “fuel cell” is typically used to refer to either an individual cell or a plurality of cells depending upon the context in which it is used. The plurality of cells is typically bundled together and arranged to form a stack with the plurality of cells commonly arranged in electrical series. Since individual fuel cells can be assembled into stacks of varying lengths, systems can be designed to produce a desired energy output level providing flexibility of design for different applications. 
         [0005]    The stacks may comprise of more than one hundred individual bipolar plates, wherein successive plates and a membrane-electrode-assembly (MEA) disposed therebetween form the individual cell. Typically, apertures formed in successive bipolar plates cooperate to form a “header” running the length of the fuel cell stack. The plate formed header distributes reactants (such as oxygen and hydrogen) and coolant to the individual cells. A first end of the plate formed header is sealingly disposed against an end unit, wherein an injector, a recycler, a reactant source, a humidifier, or other support system is typically disposed. A second end of the plate formed header is sealingly disposed against an end plate or a second end unit. 
         [0006]    Bipolar plates include active and inactive areas formed thereon. The electrochemical reaction occurs in active areas of the bipolar plates. Inactive areas are used to guide reactants and coolants across portions of the plate, provide sealing surfaces for gasket material, form apertures in the plate, and provide structural support for the plate. Large areas of inactive areas on plates result in an inefficient use of the plate and a gasket used to form the individual cells. 
         [0007]    Fuel cell stacks of varying number of cells require different amounts of reactants and coolant to operate properly. Apertures formed in the bipolar plates may be sized to optimize reactant and coolant flow rates to and from the fuel cell stack. A stack having a larger number of cells, and thus a longer stack length requires plate formed headers capable of carrying more reactants and coolant, necessitating larger apertures in the plates. As a result, a particular plate design is limited to a relatively narrow range of stack lengths, and a manufacturer may be required to support multiple plate designs to accommodate a number of vehicles having a large differential of energy requirements. 
         [0008]    Fuel cell stacks require a close stacking alignment and adequate sealing between successive plates. Sealing surfaces formed on the plates and the MEAs must be properly aligned to form the fuel cell stack that operates efficiently, militates against leakage of reactants and coolant, and electrically isolates successive plates from one another. 
         [0009]    Plate formed headers have a consistent cross-sectional shape along a header length when a single plate design is used to form the fuel cell stack. A consistent cross sectional shape may be undesirable for to the fuel cell stack because a pressure differential may exist along the length of the header, causing differences in reactant and coolant flow rates into individual cells. Additionally, plate formed headers limit header access to ends of the fuel cell stack for placement of components such as a distribution manifold, a water separator, and an infector, for example, necessary for operation of the fuel cell stack. 
         [0010]    It would be desirable to produce a discrete header for a fuel cell stack, wherein the discrete header minimizes use of the plate and the gasket materials, allows a single plate design to be used for multiple stack lengths having a large differential of energy requirements, provides a durable alignment mechanism for the fuel cell stack, and provides integration flexibility for components and configurations of the fuel cell stack. 
       SUMMARY OF THE INVENTION 
       [0011]    Presently provided by the invention, a discrete header for a fuel cell system that minimizes use of the plate and the gasket materials, allows a single plate design to be used for multiple fuel cell stack lengths having a large differential of energy requirements, provides a durable alignment mechanism for the fuel cell stack, and provides integration flexibility for components and configurations of the fuel cell system, has surprisingly been discovered. 
         [0012]    In a first embodiment, the fuel cell system, comprises a fuel cell plate including a first partial header, and a main body including a second partial header and a fastening point, the fastening point coupled to the plate, the fastening point of the main body securing the main body to the plate to form a header between the first partial header and the second partial header. 
         [0013]    In another embodiment, the fuel cell system comprises a plurality of fuel cell plates aligned to form a fuel cell stack, the stack including a first partial header and a channel, a plurality of membrane electrode assemblies at least partially formed from a gasket material, the membrane electrode assemblies disposed between the fuel cell plates, a discrete header section including a second partial header, and a fastening point disposed on the discrete header section, the fastening point extending along a length of the discrete header section, the fastening point being a flanged protuberance substantially conforming to a shape of the channel, wherein the fastening point is coupled to the channel to form a header from the first partial header and the second partial header. 
         [0014]    In a further embodiment, a fuel cell system comprises a plurality of fuel cell plates aligned to form a fuel cell stack, the stack including a first partial header and a channel, a plurality of membrane electrode assemblies at least partially formed from a gasket material, the membrane electrode assemblies disposed between the fuel cell plates, a discrete header section including a second partial header and one of a fluid inlet and a fluid outlet formed in the second partial header at an intermediate position along a length of the discrete header section, a fastening point disposed on the discrete header section, the fastening point extending along the length of the discrete header section, the fastening point being a flanged protuberance substantially conforming to a shape of the channel, and a fastening keyway formed in the fastening point, the fastening keyway extending along a length of the discrete header for receiving a header key, wherein the fastening point expands when the header key is inserted into the fastening keyway, the fastening point abutting one of the channel and the plurality of membrane electrode assemblies disposed between the plurality of fuel cell plates, securing the discrete header section to the stack to form a header from the first partial header and the second partial header. 
     
    
     
       DRAWINGS 
         [0015]    The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of embodiments of the invention when considered in the light of the accompanying drawings in which: 
           [0016]      FIG. 1  is an exploded perspective view of an illustrative fuel cell stack known in the art; 
           [0017]      FIG. 2  is an exploded perspective view of an illustrative fuel cell stack according to the present invention; 
           [0018]      FIG. 3  is an enlarged, fragmentary top plan view of the fuel cell stack shown in  FIG. 2 , with a clamping plate, a first end seal, and a second end seal removed from the fuel cell stack; 
           [0019]      FIG. 4  is an enlarged, fragmentary top plan view of the fuel cell system shown in  FIG. 2 , with a clamping plate, a first end seal, and a second end seal removed from the fuel cell stack and showing a plurality of header keys inserted into a plurality of fastening points; 
           [0020]      FIG. 5  is an enlarged, fragmentary top plan view of a discrete header according to another embodiment of the present disclosure; 
           [0021]      FIG. 6  is an enlarged, fragmentary top plan view of the discrete header shown in  FIG. 5 , shown coupled to a fuel cell stack; 
           [0022]      FIG. 7  is an enlarged, fragmentary top plan view of a fuel cell stack including a discrete header according to another embodiment of the present disclosure; and 
           [0023]      FIG. 8  is an enlarged, fragmentary top plan view of the fuel cell stack including the discrete header shown in  FIG. 7 , including a sealant disposed between the fuel cell stack and the discrete header. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    The following detailed description and appended drawings describe and illustrate various embodiments of the invention. The description and drawings serve to enable one skilled in the art to make and use the invention, and are not intended to limit the scope of the invention in any manner. 
         [0025]      FIG. 1  depicts a fuel cell stack  10  having a pair of membrane electrode assemblies  12  separated from each other by an electrically conductive bipolar plate  14 . For simplicity, only a two-cell stack (i.e. one bipolar plate) is illustrated and described in  FIG. 1 , it being understood that the fuel cell stack  10  will typically have many more cells and bipolar plates. 
         [0026]    The membrane electrode assemblies  12  and bipolar plate  14  are stacked together between a pair of clamping plates  16 ,  18  and a pair of unipolar end plates  20 ,  22 . The clamping plates  16 ,  18  are electrically insulated from the end plates  20 ,  22  by a seal or a dielectric coating (not shown). The unipolar end plate  20 , both working faces of the bipolar plate  14 , and the unipolar end plate  22  include respective active areas  24 ,  26 ,  28 ,  30 . The active areas  24 ,  26 ,  28 ,  30  are typically flow fields for distributing gaseous reactants such as hydrogen gas and air over an anode and a cathode, respectively, of the membrane electrode assemblies  12 . 
         [0027]    The bipolar plate  14  is typically formed by a conventional process for shaping sheet metal such as stamping, machining, molding, or photo etching through a photolithographic mask, for example. In one embodiment, the bipolar plate  14  is formed from unipolar plates which are then joined by any conventional process such as welding or adhesion. It should be further understood that the bipolar plate  14  may also be formed from a composite material. In one particular embodiment, the bipolar plate  14  is formed from a graphite or graphite-filled polymer. 
         [0028]    A plurality of nonconductive gaskets  32 , which may be a component of the membrane electrode assemblies  12 , are disposed between the bipolar plate  14  and the unipolar end plates  20 ,  22 . The gaskets  32  militate against fuel cell leakage and provide electrical insulation between the plates  14 ,  20 ,  22  of the fuel cell stack  10 . Gas-permeable diffusion media  34  are disposed adjacent the membrane electrode assemblies  12 . The end plates  20 ,  22  are also disposed adjacent the diffusion media  34 , respectively, while the active areas  26 ,  28  of the bipolar plate  14  are disposed adjacent the diffusion media  34 . 
         [0029]    The bipolar plate  14 , unipolar end plates  20 ,  22 , and the membrane electrode assemblies  12  each include a cathode supply aperture  36  and a cathode exhaust aperture  38 , a coolant supply aperture  40  and a coolant exhaust aperture  42 , and an anode supply aperture  44  and an anode exhaust aperture  46 . A conventional supply header  48  of the fuel cell stack  10  is formed by an alignment of the respective apertures  36 ,  42 ,  46  in the bipolar plate  14 , unipolar end plates  20 ,  22 , and the membrane electrode assemblies  12 . A conventional exhaust header  50  of the fuel cell stack  10  is formed by an alignment of the respective apertures  38 ,  40 ,  44  in the bipolar plate  14 , unipolar end plates  20 ,  22 , and the membrane electrode assemblies  12 . The hydrogen gas is supplied to an anode supply header via an anode inlet conduit  52 . The air is supplied to a cathode supply header of the fuel cell stack  10  via a cathode inlet conduit  54 . An anode outlet conduit  56  and a cathode outlet conduit  58  are also provided for an anode exhaust header and a cathode exhaust header, respectively. A coolant inlet conduit  60  is provided for supplying liquid coolant to a coolant supply header. A coolant outlet conduit  62  is provided for removing coolant from a coolant exhaust header. It should be understood that the configurations of the various inlets  52 ,  54 ,  60  and outlets  56 ,  58 ,  62  in  FIG. 1  are for the purpose of illustration, and other configurations may be chosen as desired. 
         [0030]      FIG. 2  depicts a fuel cell stack  110  according to an embodiment of the present invention having a pair of membrane electrode assemblies  112  separated from each other by an electrically conductive bipolar plate  114 . For simplicity, only a two-cell stack (i.e. one bipolar plate) is illustrated and described in  FIG. 2 , it being understood that the fuel cell stack  110  will typically have many more cells and bipolar plates. 
         [0031]    The membrane electrode assemblies  112  and the bipolar plate  114  are stacked together between a pair of clamping plates  116 ,  118  and a pair of unipolar end plates  120 ,  122 . The clamping plates  116 ,  118  are typically electrically insulated from the end plates  120 ,  122  by a seal or a dielectric coating (not shown). As illustrated, the clamping plates  116 ,  118  may be one of a cap plate and a header plate. The unipolar end plate  120 , both working faces of the bipolar plate  114 , and the unipolar end plate  122  include respective active areas  124 ,  126 ,  128 ,  130 . The active areas  124 ,  126 ,  128 ,  130  are typically flow fields for distributing gaseous reactants such as hydrogen and air over an anode and a cathode, respectively, of the membrane electrode assemblies  112 . 
         [0032]    The bipolar plate  114  is typically formed by a conventional process for shaping sheet metal such as stamping, machining, molding, or photo etching through a photolithographic mask, for example. In one embodiment, the bipolar plate  114  is formed from unipolar plates which are then joined by any conventional process such as welding or adhesion. It should be further understood that the bipolar plate  114  may also be formed from a composite material or other materials. In one particular embodiment, the bipolar plate  114  is formed from a graphite or graphite-filled polymer. 
         [0033]    A plurality of nonconductive gaskets  132 , which may be a component of the membrane electrode assemblies  112 , is disposed between the bipolar plate  114  and the unipolar end plates  120 ,  122 . The gaskets  132  militate against fuel cell leakage and provide electrical insulation between the plates  114 ,  120 ,  122  of the fuel cell stack  10 . Gas-permeable diffusion media  134  are disposed adjacent the membrane electrode assemblies  112 . The end plates  120 ,  122  are also disposed adjacent the diffusion media  134 , respectively, while the active areas  126 ,  128  of the bipolar plate  114  are disposed adjacent the diffusion media  134 . 
         [0034]    The bipolar plate  114 , unipolar end plates  120 ,  122 , and the membrane electrode assemblies  112  each include a cathode supply region  136  and a cathode exhaust region  138 , a coolant supply region  140  and a coolant exhaust region  142 , and an anode supply region  144  and an anode exhaust region  146 . A first plurality of partial first headers of the fuel cell stack  110  is formed by an alignment of the respective regions  136 ,  142 ,  146  in the bipolar plate  114 , unipolar end plates  120 ,  122 , and the membrane electrode assemblies  112 . A first discrete header section  147  having a second plurality of partial first headers is sealingly engaged with the bipolar plate  114 , the unipolar end plates  120 ,  122 , and the membrane electrode assemblies  112  to form a plurality of first headers  148 . A first plurality of partial headers of the fuel cell stack  110  is formed by an alignment of the respective region  138 ,  140 ,  144  in the bipolar plate  114 , unipolar end plates  120 ,  122 , and the membrane electrode assemblies  112 . A second discrete header section  149  having a second plurality of partial first headers is sealingly engaged with the bipolar plate  114 , unipolar end plates  120 ,  122 , and the membrane electrode assemblies  112  to form a plurality of second headers  150 . The hydrogen gas is supplied to an anode supply header via an anode inlet conduit  152 . The air is supplied to a cathode supply header of the fuel cell stack  110  via a cathode inlet conduit  154 . An anode outlet conduit  156  and a cathode outlet conduit  158  are also provided for an anode exhaust header and a cathode exhaust header, respectively. A coolant inlet conduit  160  is in fluid communication with the discrete header section  147  for supplying liquid coolant to a coolant supply header. A coolant outlet conduit  162  is in fluid communication with the discrete header section  149  for removing coolant from a coolant exhaust header. It should be understood that the configurations of the various inlets  152 ,  154 ,  160  and outlets  156 ,  158 ,  162  in  FIG. 2  are for the purpose of illustration, and other configurations may be chosen as desired. For example, the coolant inlet conduit  160  and the coolant outlet conduit  162  may be formed on the clamping plates  116 ,  118 . 
         [0035]    Adequate sealing must be provided between the discrete header sections  147 ,  149  and the clamping plates  116 ,  118 . A plurality of end seals  163  is disposed at a first end and a second end of the discrete header sections  147 ,  149 . The end seals  163  are disposed between the discrete header sections  147 ,  149  and one of the clamping plates  116 ,  118 . The end seals  163  may be disposed in one of recesses (not shown) formed in the clamping plates  116 ,  118  corresponding to a shape of the end seals  163  and recesses formed in the first end and the second end of the discrete header sections  147 ,  149 . Alternately, a recess (not shown) may be formed in the end seals  163  corresponding to one of the first end and the second end of the discrete header sections  147 ,  149 , one of the first end and the second end of the discrete header sections  147 ,  149  disposed in the recess formed in the end seals  163 . 
         [0036]    Adequate sealing must also be provided between the discrete header sections  147 ,  149  and the plates  114 ,  120 ,  122 . Sealing between the discrete header sections  147 ,  149  and the plates  114 ,  120 ,  122  militates against a mixing of the reactants and the coolant. Further, sealing between the discrete header sections  147 ,  149  and the plates  114 ,  120 ,  122  militates against the reactants and the coolant from leaking from the fuel cell stack  110 . 
         [0037]      FIG. 3  depicts a first embodiment of the discrete header section  147 . The discrete header section  147  comprises a unitary main body  168 . The discrete header section  147  includes a partial header  170  and a fastening point  172 . The discrete header section  147  includes three partial headers  170  and four fastening points  172 . Only two partial headers  170  and three fastening points  172  are shown in  FIG. 3 . The discrete header section  147  is typically formed from a non-conductive material such as a plastic and a plastic composite, for example. The discrete header section  147  may be produced by any conventional process such as a molding process and a machining process, for example. 
         [0038]    The partial headers  170  illustrated are substantially semi-circular in cross section, and extend along a length of the discrete header section  147 . Other arcuate shapes, rectangular shapes, angular shapes, or any combination thereof may be used. The shape of the partial headers  170  may also vary along the length of the discrete header section  147 . The partial headers  170  may be formed to increase or decrease a cross-sectional area of the supply headers and the exhaust headers over a length of the discrete header section  147 . A plurality of liquid management features  171  is disposed on an inner wall of the partial header  170  to militate against liquid retention within the supply headers and the exhaust headers. The liquid management features  171  may be integrally formed with the partial header  170 , formed separate from the partial header  170  and coupled thereto, or formed on the partial header  170  by a secondary operation. One of a hydrophilic coating and a hydrophobic coating may also be applied to the partial header  170  to facilitate liquid management within one of the supply headers and the exhaust headers. As shown, the discrete header section  170  includes the coolant inlet conduit  160  integrally formed therewith at an intermediate position along the length of the discrete header section  147 . It should be understood that the configuration of the coolant inlet conduit  160  shown in  FIG. 2  is for the purpose of illustration, and other configurations of the conduits  152 ,  154 ,  156 ,  158 ,  160 ,  162  formed with the discrete header sections  147 ,  149  may be chosen as desired. 
         [0039]    An interface of the discrete header sections  147 ,  149  and the plates  114 ,  120 ,  122  is formed by a fastening point  172  formed on the discrete header sections  147 ,  149  and a fastening channel  173  formed in the plates  114 ,  120 ,  122 . The fastening point  172  extends along a length of the discrete header and slidingly engages the fastening channel  173  to secure the discrete header section  147  to the fuel cell stack  110 . A plate partial header  174  is formed adjacent the fastening channel  173 . The plate partial header  174  includes one of inlets and outlets of the plates  114 ,  120 ,  122  that are in fluid communication with one of the active areas  124 ,  126 ,  128 ,  130  and an interior cavity of the bipolar plate  114 . As shown, four fastening channels  173  are located between and on each side of the plate partial headers  174 , but any configuration of the fastening channels  173  and the plate partial headers  174  may be chosen as desired. 
         [0040]    As shown, the fastening point  172  is integrally formed with the discrete header section  147 . Alternately, the fastening point  172  may be formed separate from and coupled to the discrete header section  147 . The discrete header section  147  including the fastening point  172  is slidingly disposed in the fastening channel  173  of the fuel cell stack  110 . As shown, the fastening point  172  is a bifurcated flanged rectangular protuberance substantially corresponding to a shape of the fastening channel  173 , but any other shape may be used. A fastening keyway  176  is formed by the bifurcations in the fastening point  172 , the fastening keyway  176  extending along a length of the discrete header section  147 . The fastening keyway  176  is shown as being substantially rectangular in shape and having an open side to allow for expansion of the fastening point  172 , but any shape may be used. The fastening point  172  includes at least one retention notch  177 . As shown, the fastening point  172  includes two retention notches  177  formed therein. The retention notches  177  are rectangularly shaped and formed in opposing sides of the fastening point  172 , but other shapes and arrangements of the retention notches  177  may be used. 
         [0041]    The fastening channel  173  is formed by the alignment of a plurality of plate slots formed in the plates  114 ,  120 ,  122 . The fastening channel  173  is rectangular in shape and substantially corresponds to a shape of the fastening point  172 . The plate slots each include at least one retention protuberance  178 . As shown, each plate slot includes retention protuberances  178  having a rectangular shape and substantially corresponding to a shape of the retention notches  177  formed in the fastening points  172 , but other shapes and arrangements of the retention protuberances  178  may be used. 
         [0042]      FIG. 4  depicts the discrete header section  147  illustrated in  FIG. 3  having a header key  180  disposed in the fastening keyway  176 . The fastening keyway  176  has a width smaller than a width of the header key  180 . A tapered or chamfered end of the header key  180  may be formed thereon to facilitate insertion of the header key  180  into the fastening keyway  176 . The insertion of the header key  180  into the fastening keyway  176  causes the width of the fastening keyway  176  to increase until the bifurcations of the fastening point  172  contact the fastening channel  173 , thereby securing the discrete header section  147  to the plates  114 ,  120 ,  122 . The discrete header section  147  secured to the plates  114 ,  120 ,  122  by the insertion of the header key  180  militates against a movement of the discrete header section  147  in relation to the plates  114 ,  120 ,  122  along a length of the discrete header section  147 . 
         [0043]    The header key  180  inserted into the fastening keyway  176  also creates a seal between the discrete header section  147  and the plates  114 ,  120 ,  122 . MEAs  112  (not shown) disposed between the plates  114 ,  120 ,  122  are shaped to allow a portion of the MEAs  112  to enter the fastening channel  173 . When the header key  180  is inserted into the fastening channel  173 , the expanding fastening point  172  compresses the portion of the MEAs  112  entering the fastening channel  173 , creating a seal between the discrete header section  147  and the plates  114 ,  120 ,  122 . 
         [0044]      FIGS. 5 and 6  show another embodiment of the invention similar to that shown in  FIGS. 2 ,  3 , and  4 . Reference numerals for similar structure in respect of the description of  FIGS. 2 ,  3 , and  4  are repeated in  FIGS. 5 and 6  with a prime (′) symbol. 
         [0045]    The discrete header section  147 ′ shown includes the fastening points  172 ′ having a plurality of sealing ridges  190 . The fastening point  172 ′ slidingly engages the fastening channel  173 ′ to secure the discrete header section  147 ′ to the fuel cell stack  110 ′. The fastening point  172 ′ is integrally formed with the discrete header section  147 ′. Alternately, the fastening point  172 ′ may be formed separate and coupled to the discrete header section  147 ′. As shown, the fastening point  172 ′ is a flanged rectangular protuberance substantially corresponds to a shape of the fastening channel  173 ′. The fastening point  172 ′ includes the sealing ridges  190 . Four sealing ridges  190  are formed on each of the fastening points  172 ′ as illustrated in  FIGS. 5 and 6 , but any number may be used. The sealing ridges  190  are triangular in shape and are integrally formed with the fastening point  172 ′. Alternately, the sealing ridges  190  may be formed separately and coupled to the fastening point  172 ′. 
         [0046]      FIG. 6  depicts the fastening points  172 ′ of the discrete header section  147 ′ illustrated in  FIG. 5  inserted into the fastening channels  173 ′. The fastening point  172 ′ having the plurality of sealing ridges  190  has a width substantially corresponding to a width of the fastening channel  173 ′. Insertion of the discrete header section  147 ′ creates a seal between the discrete header section  147 ′ and the plates  114 ′,  120 ′,  122 ′. MEAs  112 ′ disposed between the plates  114 ,  120 ′,  122 ′ are shaped to allow a portion of the MEAs  112 ′ to enter the fastening channel  173 ′. As shown, when the fastening point  172 ′ is inserted into the fastening channel  173 ′, the sealing ridges  190 ′ compress the portion of the MEAs  112 ′ entering the fastening channel  173 ′, creating a seal between the discrete header section  147 ′ and the plates  114 ′,  120 ′,  122 ′. Alternately, the sealing ridges  190  may cut into the portion of the MEAs  112 ′ entering the fastening channel  173 ′, creating a seal between the discrete header section  147 ′ and the plates  114 ′,  120 ′,  122 ′. Frictional forces between the sealing ridges  190  and the portion of the MEAs  112 ′ entering the fastening channel militate against a movement of the discrete header section  147 ′ in relation to the plates  114 ′,  120 ′,  122 ′ along a length of the discrete header section  147 ′. 
         [0047]      FIGS. 7 and 8  show another embodiment of the invention similar to that shown in  FIGS. 2 ,  3 , and  4 . Reference numerals for similar structure in respect of the description of  FIGS. 2 ,  3 , and  4  are repeated in  FIGS. 7 and 8  with a double prime (″) symbol. 
         [0048]    The discrete header section  147 ″ shown in  FIG. 7  includes the fastening points  172 ″. The fastening point  172 ″ slidingly engages the fastening channel  173 ″ to secure the discrete header section  147 ″ to the fuel cell stack  110 ″. The fastening point  172 ″ is substantially “T” shaped and is integrally formed with the discrete header section  147 ″. Alternately, the fastening point  172 ″ may be formed separate and coupled to the discrete header section  147 ″. Other shapes such as a circular, a triangular, or a bifurcated shaped may be used, for example. As shown, the fastening point  172 ″ corresponds to at least a portion of the fastening channel  173 ′ and includes at least one fastening flange  200 . As shown, two fastening flanges  200  form a portion of the fastening point  172 ″ having a width greater than at least a portion of the fastening channel  173 ″. A sealant cavity  202  corresponds to the portion of the fastening channel  173 ″ not occupied by the fastening point  172 ″. 
         [0049]      FIG. 8  depicts the sealant cavity  202  having a sealant  204  disposed therein. The sealant  204  forms a seal between the fastening point  172 ″ of the discrete header section  147 ″ and the plates  114 ″,  120 ″,  122 ″. Any dielectric sealant insoluble to one of the reactants and the coolant used in the fuel cell stack  110 ″ may be used. The sealant  204  is disposed in the sealant cavity  202  through an injection process, a potting process, or other process, for example. After an appropriate curing time the sealant  204  solidifies, securing the discrete header section  147 ″ to the plates  114 ″,  120 ″,  122 ″. As shown, the sealant  204  is also applied in a bead between the partial header  170 ″ and the plate partial header  174 ″. The bead is applied along a length of the discrete header section  147 ″. The sealant  204  militates against a mixing of the reactants and the coolant. Further, the sealant  204  militates against the reactants and the coolant from leaking from one of the supply and the exhaust headers through the interface of the discrete header sections  147 ″ and the plates  114 ″,  120 ″,  122 ″. 
         [0050]    In use, the discrete header section  147 ,  147 ′,  147 ″,  149  for the fuel cell stack  110 ,  110 ′,  110 ″ minimizes the amount of material used to form the fuel cell plates  114 ,  120 ,  120 ′,  120 ″,  122  and a gasket portion of the MEAs  112 ,  112 ′. The material used to form the fuel cell plates  114 ,  120 ,  120 ′,  120 ″,  122  and a gasket portion of the MEAs  112 ,  112 ′ is reduced because the fuel cell plates  114 ,  120 ,  120 ′,  120 ″,  122  and the MEAs  112 ,  112 ′ do not encircle one of the supply and the exhaust headers for the fuel cell stack  110 ,  110 ′,  110 ″ including the discrete header section  147 ,  147 ′,  147 ″,  149 . The fuel cell plates  114 ,  120 ,  120 ′,  120 ″,  122  used with the discrete header section  147 ,  147 ′,  147 ″,  149  require the plate partial header  174 ,  174 ′,  174 ″ and a plate slot (which collectively form the fastening channels  173 ,  173 ′,  173 ″), minimizing an amount of inactive area on the fuel cell plates  114 ,  120 ,  120 ′,  120 ″,  122  and a plurality of sealing surfaces required for operation of the fuel cell stack  110 ,  110 ′,  110 ″. The plurality of sealing surfaces required for the fuel cell stack  110 ,  110 ′,  110 ″ including the discrete header section  147 ,  147 ′,  147 ″,  149  are limited to a bead seal which encloses the active areas  124 ,  126 ,  128 ,  130  of each fuel cell and the interfaces located between the discrete headers section  147 ,  147 ′,  147 ″,  149  and the fastening channels  173 ,  173 ′,  173 ″. As a result of minimizing the plurality of sealing surface required, reliability and cost effectiveness of the fuel cell stack  110 ,  110 ′,  110 ″ is increased. 
         [0051]    The fuel cell stack  110 ,  110 ′,  110 ″ including the discrete header section  147 ,  147 ′,  147 ″ increases the design flexibility of a fuel cell system into which the fuel cell stack  110 ,  110 ′,  110 ″ is incorporated, Fuel cell systems having different fuel cell stack lengths may be produced to achieve a desired power requirement. The required amount of fuel and cooling needs of the fuel cell system may vary considerably depending on a length of the fuel cell stack. The fuel cell stack  110 ,  110 ′,  110 ″ including the discrete header section  147 ,  147 ′,  147 ″,  149  permits the fuel cell plates  114 ,  120 ,  120 ′,  120 ″,  122  and the MEAs  112 ,  112 ′ to be used for fuel cell systems having different fuel cell stack lengths. As a non-limiting example, a fuel cell stack comprising of 300 fuel cells may have the supply headers and the exhaust headers about 50% larger in cross-sectional area (having the discrete header with an increased size of the partial header  170 ,  170 ′,  170 ″) than a fuel cell stack comprising of 200 fuel cells, where both the fuel cell stack comprising of 300 fuel cells and the fuel cell stack comprising of 200 fuel cells use a common fuel cell plate and a common MEA. The fuel cell stack  110 ,  110 ′,  110 ″ including the discrete header section  147 ,  147 ′,  147 ″,  149  promotes proper and sustained alignment of the fuel cell plates  114 ,  120 ,  120 ′,  120 ″,  122 . During assembly of the fuel cell stack  110 ,  110 ′,  110 ″ an assembly fixture or a guide is used to align the fuel cell plates  114 ,  120 ,  120 ′,  120 ″,  122  and MEAs  112 ,  112 ′ that form the fuel cell stack  110 ,  110 ′,  110 ″. The discrete header sections  147 ,  147 ′,  147 ″,  149  are then secured to the fuel cell plates  114 ,  120 ,  120 ′,  120 ″,  122  according to one of the embodiments of the invention illustrated in  FIGS. 2-4 ,  FIGS. 5-6 , and  FIGS. 7-8 . The discrete header sections  147 ,  147 ′,  147 ″,  149  militate against movement of the one of the fuel cell plates  114 ,  120 ,  120 ′,  120 ″,  122  and the MEAs  112 ,  112 ′ in relation to the discrete header sections  147 ,  147 ′,  147 ″,  149 . The fastening points  172 ,  172 ′,  172 ″ of the discrete header sections  147 ,  147 ′,  147 ″,  149  maintain contact with each of the fuel cell plates  114 ,  120 ,  120 ′,  120 ″,  122  and the MEAs  112 ,  112 ′ to stabilize the fuel cell stack  110 ,  110 ′,  110 ″. The fuel cell stack  110 ,  110 ′,  110 ″ stabilized by the discrete header sections  147 ,  147 ′,  147 ″,  149  militates against leakage of the reactants and the coolant that may occur as a result of the fuel cell stack  110 ,  110 ′,  110 ″ shifting. Further, the fuel cell stack  110 ,  110 ′,  110 ″ stabilized by the discrete header sections  147 ,  147 ′,  147 ″,  149  militates against electrical shorting that may occur as a result of the fuel cell stack  110 ,  110 ′,  110 ″ shifting. 
         [0052]    A size of the partial headers  170 ,  170 ′,  170 ″ may vary along the length of the discrete header sections  147 ,  147 ′,  147 ″,  149  to control the cross-sectional area and the volume of the supply headers and the exhaust headers. The cross-sectional area of the supply headers and the exhaust headers that varies along the length of the discrete header sections  147 ,  147 ′,  147 ″,  149  allows a pressure differential existing along the length of the supply headers and the exhaust headers to be minimized, affording substantially equal flow rates of the reactants and the coolant into and out of the fuel cells at any point along the length of the supply headers and the exhaust headers. Further, the inlet conduits  152 ,  154 ,  160 ,  160 ′,  160 ″, the outlet conduits  156 ,  158 ,  162 , or other equipment may be incorporated into the discrete header sections  147 ,  147 ′,  147 ″,  149  to simplify operation of the fuel cell system including the discrete header section  147 ,  147 ′,  147 ″,  149 . As shown in  FIGS. 2-8 , the coolant inlet conduit  160 ,  160 ′,  160 ″ is integrally formed with the discrete header section  147 ,  147 ′,  147 ″, eliminating the need for the inlet conduit formed in the clamping plate  118 . The supply inlet conduits  152 ,  154 ,  160 ,  160 ′,  160 ″ the outlet conduits  156 ,  158 ,  162 , or other equipment incorporated into the discrete header section  147 ,  147 ′,  147 ″,  149  permits greater design flexibility of the fuel cell stack  110 ,  110 ′,  110 ″ and minimizes “crowding” that may occur in an end unit the supply inlet conduits  152 ,  154 ,  160 ,  160 ′,  160 ″ the outlet conduits  156 ,  158 ,  162 , or other equipment is incorporated in. As a non-limiting example, the discrete header section  147 ,  147 ′,  147 ″,  149  may include an ejector integrally formed with the discrete header section  147 ,  147 ′,  147 ″,  149 , where the ejector is in fluid communication with an injector disposed in the end unit of the fuel cell system. 
         [0053]    While certain representative embodiments and details have been shown for purposes of illustrating the invention, it will be apparent to those skilled in the art that various changes may be made without departing from the scope of the disclosure, which is further described in the following appended claims.