Patent Document

FIELD OF THE INVENTION 
     The invention relates generally to a fuel cell system, and more particularly, to a fuel cell system having a fuel cell assembly heated by a fluid in the fuel cell system during a starting operation of the fuel cell system. 
     BACKGROUND OF THE INVENTION 
     Fuel cell assemblies convert a fuel and an oxidant to electricity. One type of fuel cell system employs a proton exchange membrane (hereinafter “PEM”) to catalytically facilitate reaction of fuels (such as hydrogen) and oxidants (such as oxygen or air) to generate electricity. The PEM is a solid polymer electrolyte membrane that facilitates transfer of protons from an anode to a cathode in each individual fuel cell normally deployed in a fuel cell system. 
     In a typical fuel cell assembly (stack) within a fuel cell system, individual fuel cell plates include flow channels through which various reactants and cooling fluids flow. In subzero temperatures, water vapor in the fuel cell assembly may condense in the flow channels. Further, the condensate may form ice in the fuel cell assembly. The presence of condensate and ice may affect the performance of the fuel cell assembly and may also cause damage to the fuel cell assembly. 
     During typical operation of the fuel cell assembly in subzero temperatures, waste heat from the fuel cell reaction heats the fuel cell assembly and mitigates against vapor condensation and ice formation in the assembly. However, during a starting operation or low power operation of the fuel cell assembly in subzero temperatures, water vapor may condense and the condensate may form ice within the fuel cell assembly before the waste heat from the fuel cell reaction heats the fuel cell assembly. 
     Typical fuel cell assemblies are in cathode fluid communication with a compressor including surge control hardware and software. The compressor increases the pressure of a fluid flowing therethrough by reducing a volume of the fluid within the compressor. Increasing the pressure of the fluid increases the temperature of the fluid. The surge control hardware of the compressor mitigates against compressor surge, or the reverse flow of the fluid through the compressor, caused by a pressure drop or back pressure in the fuel cell assembly. Current fuel cell assemblies having compressor systems use a system bypass valve to reduce the amount of fluid caused to flow to the fuel cell assembly. The bypass valve facilitates obtaining a desired fluid pressure to mitigate against compressor surge. The fluid caused to flow through the bypass valve is purged to a vehicle exhaust system. 
     The fluid purged to the environment from the exhaust system of the fuel cell system is also a concern. Unconsumed hydrogen (H 2 ) is the most important emission consideration from the fuel cell system of the vehicle. The hydrogen exiting the vehicle must be kept below a lower flammability limit (LFL) of approximately 4% molar concentration of hydrogen in air. If the exhaust from the fuel cell assembly is above 4% molar concentration of hydrogen, the fuel cell assembly can be operated at increased airflows to dilute the hydrogen in the exhaust stream. Operating the fuel cell assembly at an increased stack airflow may dry out the fuel cell assembly. 
     It would be desirable to produce a fuel cell system heated by a fluid in the fuel cell system during a starting operation to mitigate against vapor condensation and ice formation in a fuel cell assembly and to decrease a warm up time of the fuel cell system. 
     SUMMARY OF THE INVENTION 
     Concordant and congruous with the present invention, a fuel cell system heated by a fluid in the fuel cell system during a starting operation to mitigate against vapor condensation and ice formation in a fuel cell assembly and to decrease a warm up time of the fuel cell system has surprisingly been discovered. 
     In one embodiment, a fuel cell system comprises a fuel cell assembly in fluid communication with an exhaust system; a compressor adapted to compress and heat a first fluid; a heat exchanger disposed between and in fluid communication with said compressor and said fuel cell assembly; and a first means for regulating flow in fluid communication with said heat exchanger, wherein said first means for regulating flow facilitates a flow of at least a portion of the first fluid from said heat exchanger to said compressor. 
     In another embodiment, a fuel cell system comprises, a fuel cell assembly in fluid communication with an exhaust system; a compressor adapted to compress and heat a first fluid; a charge air cooler disposed between and in fluid communication with said compressor and said fuel cell assembly; and a first means for regulating flow in fluid communication with said charge air cooler, wherein said first means for regulating flow facilitates a flow of at least a portion of the first fluid from said charge air cooler to said compressor. 
     The invention also provides a method of heating a fuel cell assembly that comprises the steps of providing a compressor adapted to compress and heat a first fluid; providing a heat exchanger disposed between and in fluid communication with the compressor and the fuel cell assembly; providing a first means for regulating flow in fluid communication with the heat exchanger and an inlet of the compressor; causing the first fluid to flow from the compressor and through the heat exchanger; causing a second fluid to flow through the heat exchanger to control a temperature of the first fluid exiting the heat exchanger; selectively causing at least a portion of the first fluid to flow from the heat exchanger back to the compressor using the first means for regulating flow to control a temperature of the first fluid entering the compressor; causing a portion of the first fluid to flow from the heat exchanger through the first means for regulating flow and to the compressor; permitting the remaining portion of the first fluid to flow from the heat exchanger to the fuel cell assembly to heat the fuel cell assembly and mitigate against vapor condensation and ice formation in the fuel cell assembly. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       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 a preferred embodiment when considered in the light of the accompanying drawings in which: 
         FIG. 1  is a schematic flow diagram of a fuel cell system according to the prior art; 
         FIG. 2  is a schematic flow diagram of a fuel cell system according to an embodiment of the invention; 
         FIG. 3  is a schematic flow diagram of a fuel cell system according to another embodiment of the invention; and 
         FIG. 4  is an exploded perspective view of a PEM fuel cell assembly, showing two fuel cells, illustrative of the fuel cell assemblies shown in  FIGS. 1-3 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following detailed description and appended drawings describe and illustrate various exemplary 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. It is understood that materials other than those described can be used without departing from the scope and spirit of the invention. In respect of the methods disclosed, the steps presented are exemplary in nature, and thus, the order of the steps is not necessary or critical. 
       FIG. 1  shows a fuel cell system  10  according to the prior art. The fuel cell system  10  is typically used in fuel cell powered vehicles (not shown). The fuel cell system  10  includes a fuel cell assembly  12 , a first means for regulating flow  14 , a compressor  16 , a heat exchanger  18 , a mass flow meter  20 , and a filter  22 . System conduit  25  is in communication with the system components as described herein, and the system conduit  25  facilitates the flow of a first fluid from one component of the fuel cell system  10  to another. 
     The fuel cell assembly  12  is in fluid communication with an outlet  20   b  of the mass flow meter  20  and an exhaust system  24 . In the prior art embodiment shown in  FIG. 1 , the fuel cell assembly  12  is a PEM fuel cell assembly. It is understood that other fell cell types can be used as desired. 
       FIG. 4  is an exploded view illustrative of the fuel cell assembly  12 , including two fuel cells. It is understood that the number of fuel cells in the fuel cell assembly  12  may vary. As shown, the fuel cell assembly  12  has a pair of membrane electrode assemblies (MEA)  26  and  28  separated from each other by an electrically conductive fuel distribution element  30 , hereinafter a bipolar plate. The MEAs  26 ,  28  and bipolar plate  30  are stacked together between stainless steel clamping plates or end plates  32 ,  34  and end contact elements  36 ,  38 . The end contact element  36  is a cathode, while the end contact element  38  is an anode. The end contact elements  36 ,  38 , as well as both working faces of the bipolar plate  30 , contain a plurality of grooves or channels  40  for distributing fuel and oxidant gases (i.e. hydrogen and oxygen) to the MEAs  26 ,  28 . The bipolar plate  30  may be made from metal but the plate  30  can also be manufactured from other materials, if desired. For example, bipolar plates may be fabricated from graphite or other conductive composites which are lightweight, corrosion resistant, and electrically conductive in the environment of a PEM fuel cell assembly  12 . 
     The fuel cell assembly  12  also includes diffusion media  44  that include a flange  42 . The flanges  42  of the diffusion media  44  provide seals and insulation between components of the fuel cell assembly  12 . One of the diffusion media  44  is disposed between the end contact element  36  and the MEA  26 . One of the diffusion media  44  is disposed between the MEA  26  and an anode side of the bipolar plate  30  and another diffusion medium  44  is disposed between a cathode side of the bipolar plate  30  and the MEA  28 . Yet another diffusion medium  44  is disposed between the MEA  28  and the end contact element  38 . It is understood that the fuel cell assembly  12  may include any number of fuel cells and the components of the fuel cell assembly  12  may be formed from any conventional materials. Further, the fuel cell assembly  12  may be any conventional fuel cell assembly including a reformed methanol fuel cell, an alkaline fuel cell, and a solid oxide fuel cell, for example. 
     The first means for regulating flow  14  includes an inlet  14   a  and an outlet  14   b . In the prior art embodiment shown in  FIG. 1 , the first means for regulating flow  14  is a flow control valve, although other flow regulating devices can be used such as a globe valve, a ball valve, a positive displacement pump, or a centrifugal pump, for example. The first means for regulating flow  14  is disposed between the compressor  16  and the exhaust system  24 . The inlet  14   a  of the first means for regulating flow  14  is in fluid communication with an outlet  16   b  of the compressor  16 . The outlet  14   b  of the first means for regulating flow  14  is in fluid communication with the exhaust system  24 . 
     The compressor  16  includes an inlet  16   a  and the outlet  16   b . In the embodiment shown the compressor  16  is a centrifugal air compressor. The inlet  16   a  of the compressor  16  is in fluid communication with an outlet  22   b  of the filter  22  and the outlet  16   b  of the compressor  16  is in fluid communication with an inlet  18   a  of the heat exchanger  18 . The compressor  16  may be any conventional means for compressing a fluid such as turbomachine, centrifugal, mixed flow, blower or fan compressor, for example. In the embodiment shown, the compressor  16  is operated by a motor  17 . 
     The heat exchanger  18  shown in  FIG. 1  includes the inlet  18   a  and an outlet  18   b . The inlet  18   a  of the heat exchanger  18  is in fluid communication with the outlet  16   b  of the compressor  16 , and the outlet  18   b  of the heat exchanger  18  is in fluid communication with an inlet  20   a  of the mass flow meter  20 . In the embodiment shown, the heat exchanger  18  is a charge air cooler. It is understood that any conventional heat exchanger may be used such as a shell and tube heat exchanger, an air-cooled heat exchanger, or other heat exchanger device, as desired. 
     The mass flow meter  20  includes the inlet  20   a  and the outlet  20   b . The inlet  20   a  of the mass flow meter  20  is in fluid communication with the outlet  18   b  of the heat exchanger  18 , and the outlet  20   b  of the mass flow meter  20  is in fluid communication with the fuel cell assembly  12 . It is understood that a volumetric flow meter or no flow meter may be used, as desired. The mass flow meter  20  may be a curved tube flow meter or straight tube flow meter, as desired. 
     The filter  22  includes an inlet  22   a  and the outlet  22   b . The inlet  22   a  is in fluid communication with the first fluid from a fluid source  23 , and the outlet  22   b  of the filter  22  is in fluid communication with the inlet  16   a  of the compressor  16 . In the embodiment shown the filter  22  is an air filter, the first fluid is air, and the fluid source  23  is ambient air. It is understood that the air filter  22  may be a paper filter, a foam filter, a cotton filter, or other fluid filtering device, as desired. It is also understood that the first fluid may be pure oxygen (O 2 ), compressed oxygen or air, cryogenic oxygen or air, or other fluid, as desired. Also, the fluid source  23  may be a fluid storage tank or other vessel adapted to store a fluid, as desired. 
     In use, the first fluid is caused to flow from the fluid source  23 , through the system conduit  25 , and to the inlet  22   a  of the filter  22 . As the first fluid passes through the filter  22 , contaminants such as pollen, dust, mold, bacteria, chemicals and dirt are removed from the first fluid. The filtered first fluid is then caused to flow through system conduit  25  to the inlet  16   a  of the compressor  16 . In the compressor  16 , the volume of the first fluid is reduced to increase the pressure and temperature thereof. 
     As the first fluid exits the outlet  16   b  of the compressor  16 , a portion of the first fluid is selectively caused to flow through the system conduit  25  to the inlet  14   a  of the first means for regulating flow  14 . The portion of the first fluid selectively flows through the first means for regulating flow  14  from the compressor  16  to maintain a desired pressure in the compressor  16  to mitigate against compressor surge. The portion of the first fluid flows through the outlet  16   b  of the compressor  16 , through the first means for regulating flow  14 , and to the exhaust system  24 . A remaining portion of the first fluid is caused to flow through system conduit  25  to the inlet  18   a  of the heat exchanger  18 . 
     In the heat exchanger  18 , the first fluid passes through sealed passageways (not shown) inside the heat exchanger  18 , while a second fluid is caused to flow across the passageways. The second fluid may be air, a coolant, water, or other fluid, as desired. The second fluid may cool or heat the first fluid in the heat exchanger  18 . The first fluid will be cooled by the second fluid during low power operation of the fuel cell system  10  and during a start up operation of the fuel cell system  10 . When the fuel cell system  10  is at an elevated temperature, approximately 65° F. or higher, the first fluid from the outlet  16   b  of the compressor  16  may be below a temperature of the fuel cell assembly  12 . Accordingly, the first fluid stream may absorb energy and be heated in heat exchanger  18 . Upon exiting the heat exchanger  18 , the first fluid is caused to flow to the inlet  20   a  of the mass flow meter  20 . In the mass flow meter  20 , the amount of the first fluid flowing to the fuel cell assembly  12  is measured. The first fluid is then caused to flow through a cathode side of the fuel cell assembly  12  to facilitate the catalytic reaction within the fuel cell assembly  12  to generate electricity. Unused first fluid is then caused to flow out of the fuel cell assembly  12  and to the exhaust system  24  and is removed from the fuel cell system  10 . 
       FIG. 2  shows a fuel cell system  210  according to an embodiment of the invention. The fuel cell system  210  is used in fuel cell powered vehicles. The fuel cell system  210  includes a fuel cell assembly  212 , a first means for regulating flow  214 , a compressor  216 , a heat exchanger  218 , a mass flow meter  220 , and a filter  222 . System conduit  225  is in communication with the system components as described herein. The system conduit  225  facilitates the flow of a first fluid from one component of the fuel cell system  210  to another. 
     The fuel cell assembly  212  is in fluid communication with an outlet  220   b  of the mass flow meter  220  and an exhaust system  224 . The fuel cell assembly  212  shown in  FIG. 2  is a PEM fuel cell assembly. The fuel cell assembly  212  is similar to the fuel cell assembly  12  described above and illustrated in  FIG. 4 . It is understood that the fuel cell assembly  212  may include any number of fuel cells and may be formed from any conventional materials. Further, the fuel cell assembly  212  may be any conventional fuel cell assembly including a reformed methanol fuel cell, an alkaline fuel cell, and a solid oxide fuel cell, for example. 
     The first means for regulating flow  214  includes an inlet  214   a  and an outlet  214   b . In the embodiment shown in  FIG. 2 , the first means for regulating flow  214  is a bypass valve. The first means for regulating flow  214  is disposed between the heat exchanger  218  and the compressor  216 . The inlet  214   a  of the first means for regulating flow  214  is in fluid communication with an outlet  218   b  of the heat exchanger  218 . The outlet  214   b  of the first means for regulating flow  214  is in fluid communication with an inlet  216   a  of the compressor  216 . The first means for regulating flow  214  may be any conventional fluid controlling device such as a globe valve, a ball valve, a positive displacement pump, or a centrifugal pump, for example. 
     The compressor  216  includes the inlet  216   a  and an outlet  216   b . In the embodiment shown the compressor  216  is a centrifugal air compressor. The inlet  216   a  of the compressor  216  is in fluid communication with an outlet  220   b  of the mass flow meter  220  and the outlet  214   b  of the first means for regulating flow  214 . The outlet  216   b  of the compressor  216  is in fluid communication with an inlet  218   a  of the heat exchanger  218 . The compressor  216  may be any conventional means for compressing a fluid such as scroll compressor or a diaphragm compressor, for example. In the embodiment shown, the compressor  216  is operated by a motor  217 . 
     The heat exchanger  218  shown in  FIG. 2  includes the inlet  218   a  and an outlet  218   b . The inlet  218   a  of the heat exchanger  218  is in fluid communication with the outlet  216   b  of the compressor  216 , and the outlet  218   b  of the heat exchanger  218  is in fluid communication with the fuel cell assembly  212  and the inlet  214   a  of the first means for regulating flow  214 . In the embodiment shown, the heat exchanger  218  is a charge air cooler. It is understood that any conventional heat exchanger may be used such as a shell and tube heat exchanger, an air-cooled heat exchanger, or other heat exchange device, as desired. 
     The mass flow meter  220  includes an inlet  220   a  and the outlet  220   b . The inlet  220   a  of the mass flow meter  220  is in fluid communication with an outlet  222   b  of the filter  222 , and the outlet  220   b  of the mass flow meter  220  is in fluid communication with the inlet  216   a  of the compressor  216 . It is understood that a volumetric flow meter or no flow meter may be used, as desired. The mass flow meter  220  may be a curved tube flow meter or straight tube flow meter, as desired. 
     The filter  222  includes an inlet  222   a  and the outlet  222   b . The inlet  222   a  is in fluid communication with a fluid from a fluid source  223 , and the outlet  222   b  of the filter  222  is in fluid communication with the inlet  220   a  of the mass flow meter  220 . In the embodiment shown the filter  222  is an air filter, the fluid is air, and the fluid source  223  is ambient air. It is understood that the air filter  222  may be a paper filter, a foam filter, a cotton filter, or other fluid filtering device, as desired. It is also understood that the fluid may be pure oxygen (O 2 ), compressed oxygen or air, cryogenic oxygen or air, or other fluid, as desired. Also, the fluid source  223  may be a fluid storage tank or other vessel adapted to store a fluid, as desired. 
     In use, the fluid is caused to flow from the fluid source  223  through system conduit  225  to the inlet  222   a  of the filter  222 . As the fluid passes through the filter  222  contaminants such as pollen, dust, mold, bacteria, chemicals and dirt are removed from the fluid. The filtered fluid is then caused to flow through system conduit  225  to the inlet  220   a  of the mass flow meter  220 . In the mass flow meter  220 , the amount of the fluid flowing to the compressor  216  from the fluid source  223  is measured. The fluid is then caused to flow from the outlet  220   b  of the mass flow meter  220  to the inlet  216   a  of the compressor  216 . In the compressor  216  the volume of the fluid is reduced to increase a pressure and temperature thereof. 
     Next, the fluid is caused to flow from the outlet  216   b  of the compressor  216  through the system conduit  225  to the inlet  218   a  of the heat exchanger  218 . In the heat exchanger  218 , the fluid passes through sealed passageways (not shown) inside the heat exchanger  218 . A second fluid is caused to flow across the passageways. The second fluid may be air, a coolant, water, or other fluid, as desired. The second fluid may cool or heat the fluid in the heat exchanger  218 . The fluid is typically cooled by the second fluid during low power operation of the fuel cell system  210  and during a start up operation of the fuel cell system  210 . When the fuel cell system  210  is at an elevated temperature, typically around 65° F. or higher, the fluid from the outlet  216   b  of the compressor  216  may be below a temperature of the fuel cell assembly  212 . Accordingly, the fluid stream may absorb energy and be heated in heat exchanger  218 . As the fluid exits the outlet  218   b  of the heat exchanger  218 , a portion of the fluid is selectively caused to flow through the system conduit  225  to the inlet  214   a  of the first means for regulating flow  214 . The fluid then flows through the outlet  214   b  of the first means for regulating flow  214  and rejoins the flow of the fluid from the outlet  220   b  of the mass flow meter  220  entering into the inlet  216   a  of the compressor  216 . A remaining portion of the fluid exiting the heat exchanger  218  is then caused to flow through the system conduit  225  to the fuel cell assembly  212 . The fluid is then caused to flow through a cathode side of the fuel cell assembly  212  to facilitate the catalytic reaction within the assembly  212  to generate electricity. Unused fluid is then caused to flow out of the fuel cell assembly  212  and to the exhaust system  224 , and is exhausted from the fuel cell system  210 . 
     Because the portion of the fluid flowing through the first means for regulating flow  214  has been heated by the compressor  216 , when the fluid is caused to mix with the flow of fluid from the outlet  220   b  of the mass flow meter  220  the temperature and pressure of the fluid flowing into the compressor  216  is increased. As the temperature and pressure of the fluid entering the compressor  216  increases, the temperature and pressure of the fluid exiting the compressor  216  also increases, thereby resulting in an increase in energy entering the heat exchanger  218  and the fuel cell assembly  212  and minimizing a required time to warm up the fuel cell assembly  212 . A minimized warm up time allows the compressor  216  to run at a lower power state, drawing less electric power, allowing the system to warm up with higher efficiency. The minimized time to warm up the fuel cell assembly  212  minimizes the amount of time it takes for a vehicle (not shown) powered by the fuel cell system  210  powered vehicle (not shown) to be able to be driven away and increases the heat available for a passenger cabin (not shown) of the vehicle. 
     Another advantage of the fuel cell system  210  over the prior art fuel cell system  10  is that the mass flow meter  220  is in fluid communication with the inlet  216   a  of the compressor  216  and not in communication with the outlet  218   b  of the heat exchanger  218 , thereby removing the mass flow meter  220  from a high pressure and high temperature fluid flow. A further advantage of the fuel cell system  210  over the prior art fuel cell system  10  is that the first means for regulating flow  214  is in fluid communication with the outlet  218   b  of the heat exchanger  218 , while the first means for regulating flow  14  is in fluid communication with the outlet  16   b  of the compressor  16 . By moving the first means for regulating flow  214  to the outlet  218   b  of the heat exchanger  218 , the fluid caused to flow through the first means for regulating flow  214  is at a reduced temperature, whereas the fluid exiting the compressor  16  of the prior art fuel cell system  10  has an increased temperature. During the initial system  310  cold start, the heat exchanger  318  temperature is below the fluid leaving the compressor outlet  316   b . The air temperature leaving the heat exchanger outlet  318   b  is reduced as the heat energy from the air stream transfers into the heat exchanger  318 . The lower air temperature into the inlet of the first means for regulating flow  314   a  is preferred over the warmer temperature because lower convective heat losses occur to ambient in the system conduit  325  and the first means for regulating  314 . 
       FIG. 3  shows a fuel cell system  310  according to another embodiment of the invention. The fuel cell system  310  is typically used in fuel cell powered vehicles (not shown). The fuel cell system  310  includes a fuel cell assembly  312 , a first means for regulating flow  314 , a second means for regulating flow  315 , a compressor  316 , a heat exchanger  318 , a mass flow meter  320 , and a filter  322 . A system conduit  325  is in communication with the system components as described herein, and the system conduit  325  facilitates the flow of a first fluid from one component of the fuel cell system  310  to another. 
     The fuel cell assembly  312  is in fluid communication with an outlet  320   b  of the mass flow meter  320  and an exhaust system  324 . The fuel cell assembly  312  shown in  FIG. 3  is a PEM fuel cell assembly. The fuel cell assembly  312  is similar to the fuel cell assembly  12  described above and illustrated in  FIG. 4 . It is understood that the fuel cell assembly  312  may include any number of fuel cells and may be formed from any conventional materials. Further, the fuel cell assembly  312  may be any conventional fuel cell assembly including a reformed methanol fuel cell, an alkaline fuel cell, and a solid oxide fuel cell, for example. 
     The first means for regulating flow  314  includes an inlet  314   a  and an outlet  314   b . In the embodiment shown in  FIG. 3 , the first means for regulating flow  314  is a bypass valve. The first means for regulating flow  314  is disposed between the compressor  316  and the second means for regulating flow  315 . The inlet  314   a  of the first means for regulating flow  314  is in fluid communication with an outlet  318   b  of the heat exchanger  318 . The outlet  314   b  of the first means for regulating flow  314  is in fluid communication with an inlet  315   a  of the second means for regulating flow  315 . The first means for regulating flow  314  may be any conventional fluid regulating device such as a globe valve, a ball valve, a positive displacement pump, or a centrifugal pump, for example. 
     The second means for regulating flow  315  includes the inlet  315   a  and a first outlet  315   b , and a second outlet  315   c . In the embodiment shown in  FIG. 3 , the second means for regulating flow  315  is a three-way valve. The inlet  315   a  of the second means for regulating flow  315  is in fluid communication with the outlet  314   b  of the first means for regulating flow  314 . The first outlet  315   b  of the second means for regulating flow  315  is in fluid communication with an inlet  316   a  of the compressor  316 . The second outlet  316   c  of the second means for regulating flow  315  is in fluid communication with the exhaust system  324 . The second means for regulating flow  315  may be any conventional fluid regulating device adapted to selectively cause the fluid flowing through the second means for regulating flow  315  to flow to a plurality of destinations. 
     The compressor  316  includes the inlet  316   a  and an outlet  316   b . In the embodiment shown, the compressor  316  is a centrifugal air compressor. The inlet  316   a  of the compressor  316  is in fluid communication with an outlet  320   b  of the mass flow meter  320  and the outlet  315   b  of the second means for regulating flow  315 . The outlet  316   b  of the compressor  316  is in fluid communication with an inlet  318   a  of the heat exchanger  318 . The compressor  316  may be any conventional means for compressing a fluid such as turbomachine, centrifugal, mixed flow, blower or fan compressor, for example. In the embodiment shown, the compressor  316  is operated by a motor  317 . 
     The heat exchanger  318  shown in  FIG. 3  includes the inlet  318   a  and an outlet  318   b . The inlet  318   a  of the heat exchanger  318  is in fluid communication with the outlet  316   b  of the compressor  316 , and the outlet  318   b  of the heat exchanger  318  is in fluid communication with the fuel cell assembly  312  and the inlet  314   a  of the first means for regulating flow  314 . In the embodiment shown, the heat exchanger  318  is a charge air cooler. It is understood that any conventional heat exchanger may be used such as a shell and tube heat exchanger, an air-cooled heat exchanger, or other heat exchange device, as desired. 
     The mass flow meter  320  includes an inlet  320   a  and the outlet  320   b . The inlet  320   a  of the mass flow meter  320  is in fluid communication with an outlet  322   b  of the filter  322 , and the outlet  320   b  of the mass flow meter  320  is in fluid communication with the inlet  316   a  of the compressor  316 . It is understood that a volumetric flow meter or no flow meter may be used, as desired. The mass flow meter  320  may be a curved tube flow meter or straight tube flow meter, as desired. 
     The filter  322  includes an inlet  322   a  and the outlet  322   b . The inlet  322   a  is in fluid communication with a fluid from a fluid source  323 , and the outlet  322   b  of the filter  322  is in fluid communication with the inlet  320   a  of the mass flow meter  320 . In the embodiment shown the filter  322  is an air filter, the fluid is air, and the fluid source  323  is ambient air. It is understood that the air filter  322  may be a paper filter, a foam filter, a cotton filter, or other fluid filtering device, as desired. It is also understood that the fluid may be pure oxygen (O 2 ), compressed oxygen or air, cryogenic oxygen or air, or other fluid, as desired. Also, the fluid source  323  may be a fluid storage tank or other vessel adapted to store a fluid, as desired. 
     In use, the fluid is caused to flow from the fluid source  323  through system conduit  325  to the inlet  322   a  of the filter  322 . As the fluid passes through the filter  322  contaminants such as pollen, dust, mold, bacteria, chemicals and dirt are removed from the fluid. The filtered fluid is then caused to flow through system conduit  325  to the inlet  320   a  of the mass flow meter  320 . In the mass flow meter  320 , the amount of the fluid flowing to the compressor  316  from the fluid source  323  is measured. The fluid is then caused to flow from the outlet  320   b  of the mass flow meter  320  to the inlet  316   a  of the compressor  316 . In the compressor  316 , the volume of the fluid is reduced to increase a pressure and temperature thereof. 
     Next, the fluid is caused to flow from the outlet  316   b  of the compressor  316  through the system conduit  325  to the inlet  318   a  of the heat exchanger  318 . In the heat exchanger  318 , the fluid passes through sealed passageways (not shown) inside the heat exchanger  318 , while a second fluid is caused to flow across the passageways. The second fluid may be air, a coolant, water, or other fluid, as desired. The second fluid may cool or heat the fluid in the heat exchanger  318 . The fluid is typically cooled by the second fluid during low power operation of the fuel cell system  310  and during a start up operation of the fuel cell system  310 . When the fuel cell system  310  is at an elevated temperature, typically about 65° F. or higher, the fluid from the outlet  316   b  of the compressor  316  may be below a temperature of the fuel cell assembly  312 . Accordingly, the fluid stream may absorb energy and be heated in heat exchanger  318 . As the fluid exits the heat exchanger  318 , a portion of the fluid is selectively caused to flow through the system conduit  325  to the inlet  314   a  of the first means for regulating flow  314 . The fluid then flows through the outlet  314   b  of the first means for regulating flow  314  to the inlet  315   a  of the second means for regulating flow  315 . A remaining portion of the fluid exiting the heat exchanger  318  is caused to flow through the system conduit  325  to the fuel cell assembly  312 . The fluid is then caused to flow through a cathode side of the fuel cell assembly  312  to facilitate the catalytic reaction within the assembly  312  to generate electricity. Unused fluid is then caused to flow out of the fuel cell assembly  312  and to the exhaust system  324  and is exhausted from the fuel cell system  310 . 
     The portion of the fluid flowing to the second means for regulating flow  315  is caused to selectively flow to the first outlet  315   b  and the second outlet  315   c . The fluid caused to flow through the first outlet  315   b  joins the flow of the fluid from the outlet  320   b  of the mass flow meter  320  entering into the inlet  316   a  of the compressor  316 . The fluid caused to flow through the second outlet  315   c  of the second means for regulating flow  315  is mixed with the flow of fluid from the fuel cell assembly  312  to the exhaust system  324  and is exhausted from the fuel cell system  310 . 
     Because the portion of the fluid flowing through the first means for regulating flow  314  has been heated by the compressor  316 , when the portion of the fluid from the outlet  315   b  of the second means for regulating flow  315  is caused to mix with the flow of fluid from the outlet  320   b  of the mass flow meter  320 , the temperature and pressure of the fluid flowing into the compressor  316  is increased. As the temperature and pressure of the fluid entering the compressor  316  increases, the temperature and pressure of the fluid exiting the compressor  316  also increases, thereby resulting in an increase in energy entering the heat exchanger  318  and the fuel cell assembly  312  and facilitating a minimization of a time to warm up the fuel cell assembly  312 . A minimized warm up time allows the compressor  316  to be run at a lower power state, drawing less electric power allowing the system to warm up with higher efficiency. The minimization of time required to warm up the fuel cell assembly  312  minimizes the amount of time it takes for a vehicle (not shown) powered by the fuel cell system  310  powered vehicle (not shown) to be able to be driven away and increases the heat available for a passenger cabin (not shown) of the vehicle. 
     The portion of the fluid flowing through the outlet  315   c  of the second means for regulating flow  315  is caused to flow to the exhaust system  324 , thereby increasing the volume of fluids in the exhaust and facilitating a dilution of the hydrogen concentration. A controller (not shown) adjusts the second means for regulating flow  315  in response to the fuel cell system  310  requirements. The controller determines a desired amount of the fluid required for dilution of hydrogen in the exhaust system  324 , if any. If the amount of hydrogen in the exhaust system  324  is above the lower flammability limit of 4% molar concentration, the outlet  315   c  of the second means for regulating flow  315  is opened to permit the fluid to flow to the exhaust system  324 . If the hydrogen being emitted to the exhaust system  324  is below the lower flammability limit, the controller causes the outlet  315   c  to close and causes all of the flow of fluid through the second means for regulating flow  315  to flow to the inlet  316   a  of the compressor  316 . 
     Another advantage of the fuel cell system  310  over the prior art fuel cell system  10  is that the mass flow meter  320  is in fluid communication with the inlet  316   a  of the compressor  316  and not in communication with the outlet  318   b  of the heat exchanger  318 , thereby removing the mass flow meter  320  from a high pressure and high temperature fluid flow. A further advantage of the fuel cell system  310  over the prior art fuel cell system  10  is that the first means for regulating flow  314  is in fluid communication with the outlet  318   b  of the heat exchanger  318 , while the first means for regulating flow  14  is in fluid communication with the outlet  16   b  of the compressor  16 . By moving the first means for regulating flow  314  to the outlet  318   b  of the heat exchanger  318 , the fluid caused to flow through the first means for regulating flow  314  is at a reduced temperature whereas the fluid exiting the compressor  16  of the prior art fuel cell system  10  has an increased temperature. During the initial system  310  cold start, the heat exchanger  318  temperature is below the fluid leaving the compressor outlet  316   b . The air temperature leaving the heat exchanger outlet  318   b  is reduced as the heat energy from the air stream transfers into the heat exchanger  318 . The lower air temperature into the inlet of the first means for regulating flow  314   a  is preferred over the warmer temperature because lower convective heat losses occur to ambient in the system conduit  325  and the first means for regulating  314 . 
     From the foregoing description, one ordinarily skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications to the invention to adapt it to various usages and conditions.

Technology Category: h