Abstract:
The invention relates to a fuel cell system comprising a housing including a chamber for accommodating a fuel cell stack. The fuel cell system has various features that can also be independently embodied, namely: a U-shaped air channel including air inlet channels and air outlet channels which include an inlet or outlet on the same side of the housing of the fuel cell system; at least two fans or compressors that are disposed downstream of each other in an air flow direction in the air inlet channel or in the air outlet channel; a housing that has two additional, separate housing sections apart from a chamber for a fuel cell stack and an air inlet channel and an air outlet channel; and an air bypass channel which is arranged between an air inlet channel for introducing ambient air into a chamber for the fuel cell stack and an air outlet channel for discharging air from the chamber for the fuel cell stack.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. National Stage of International Application Number PCT/EP2009/054683 filed on Apr. 20, 2009, which was published on Oct. 22, 2009 under International Publication Number WO 2009/127743. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    The invention relates to a fuel cell system for a fuel cell stack. The invention relates less to the fuel cell stack itself, but rather to additional components of the fuel cell system for media supply and for setting operating parameters for a fuel cell stack, like in particular a housing and a media supply with water and hydrogen and its control. 
         [0004]    2. Discussion of Related Art 
         [0005]    Typical components of a fuel cell system are a fuel cell stack which includes the actual fuel cell configured form a plurality of particular cells respectively configured with a cathode and anode and an electrolyte disposed there between, e.g. configured as a membrane, and a housing. The housing includes the necessary components, e.g. air channels and hydrogen conduit which are necessary to supply the required hydrogen to the anodes of the fuel cell stack and to supply the necessary oxygen to the cathodes of the fuel cell stack, e.g. as a portion of the supplied ambient air. Furthermore the fuel cell system includes devices for controlling the respectively provided volume flow of hydrogen and air and for temperature and humidity management, since released reactive heat and water generated have to be removed. For a fuel cell it is important to maintain an advantageous operating temperature if possible during operations. 
         [0006]    In this context the invention particularly relates to a fuel cell system with a fuel cell stack with an open cathode in which the anodes to be supplied with hydrogen are connected with channels for a central hydrogen supply, while the cathodes to be supplied with oxygen are quasi freely accessible and disposed adjacent to one another in layers, so that an oxygen supply has to come from the housing of the fuel cell system. The water generated on the cathode side from a reaction of oxygen and hydrogen has to be removed as moisture. Fuel cell stack with an open cathode are known in principle. 
       DISCLOSURE OF INVENTION 
       [0007]    It is the object of the invention to provide a fuel cell system for a fuel cell stack with an open cathode which facilitates simple and efficient operations. 
         [0008]    According to the invention the object is achieved through a fuel cell system which has various features that can also be implemented independently from one another, namely:
       a U-shaped air duct including air inlet channels and air outlet channels which include an inlet opening or an outlet opening on the same side of the housing of the fuel cell system, so that air is conducted from this side of the housing through an air inlet channel to a chamber for the fuel cell stack and from there through an air outlet channel back again to the same side of the housing;   at least two fans or compressors that are disposed downstream from one another in airflow direction in the air inlet- or air outlet channel, preferably configured as axial fans or diagonal fans;   a housing that has two additional, separate housing sections apart from a chamber for a fuel cell stack and an air inlet channel and an air outlet channel; namely a housing section for receiving a preferably electronic control and a second housing section for receiving all components which are being used for introducing hydrogen into the fuel cell stack and discharging hydrogen from the fuel cell stack; and   a bypass air channel which is arranged between an air inlet channel for introducing ambient air into a chamber for a fuel cell stack and an air outlet channel for discharging air from the chamber for the fuel cell stack.       
 
         [0013]    All these features by themselves or in combination with one another provide optimized air ducting. How this is done can be derived from the subsequent descriptions of preferred embodiments. 
         [0014]    Additional aspects of the invention which can also be implemented independently from one another relate to:
       a chamber for receiving a fuel cell stack, the chamber configured so that the fuel cell stack is disposed slanted relative to the housing and the chamber; and   a closed, in particular thermally insulated housing.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The particular aspects of the invention which can also be implemented independently from one another and particularly preferred variants of the particular aspects and particularly preferred combination of the aspects are subsequently described in more based on embodiments with reference to drawing figures, wherein: 
           [0018]      FIG. 1 : illustrates a schematic lateral view through a preferred fuel cell system; 
           [0019]      FIG. 2  illustrates a view similar to  FIG. 1  for illustrating additional housing sections of the fuel cell system of  FIG. 1 ; 
           [0020]      FIGS. 3   a - 3   c  illustrates a fuel cell system similar to  FIG. 1   with  an additional bypass air channel; 
           [0021]      FIGS. 4   a  &amp;  4   b  illustrate a modular fuel cell system in a detailed view; 
           [0022]      FIG. 5  illustrates a schematic view, wherein plural lifters are being used in an air inlet channel or in an air outlet channel for an air supply to a fuel cell stack; 
           [0023]      FIG. 6  illustrates a fuel cell stack with an open cathode and air scoops connected thereto; 
           [0024]      FIG. 7  illustrates an advantageous embodiment of the fuel cell stacks and the air scoops; 
           [0025]      FIG. 8  illustrates a particular preferred variant for a chamber for a fuel cell stack; 
           [0026]      FIG. 9  illustrates a schematic view of a relative arrangement of an air inlet channel and a air out let channel for a fuel cell stack; 
           [0027]      FIG. 10  illustrates a schematic view of a preferred relative arrangement of a chamber for a fuel cell stack and additional components for controlling the fuel cell system and for components for hydrogen supply. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]      FIG. 1  illustrates a schematic horizontal sectional view of a fuel cell system  10  with a chamber  12  for a fuel cell stack  14  and an air inlet channel  16  to a chamber  12  and an air outlet channel  18  from the chamber  12 . Between the air inlet channel  16  and the chamber  12  a deflection channel  17  is disposed through which the air flowing though the air inlet channel  16  is deflected in a U-shape by 180°. Furthermore a compressor or fan  20  is schematically illustrated in the air inlet channel  16 . These components are enclosed by a schematically illustrated housing  22 . 
         [0029]    According to an independent feature of the invention the air inlet channel  16 , the deflection channel  17 , the air outlet channel  18 , the chamber  12  and the fan  20  are configured as independent modules which are exchangeable and combinable with one another any manner. 
         [0030]    Thus  FIG. 1  illustrates an first feature of the invention according to which the air inlet channel  16  and the air outlet channel  18  originate respectively on the same side of the housing  22  (the left side in the figure). This provides an advantageous U-shaped air duct which facilitates disposing the fuel cell system in a space in any arrangement, wherein optionally the air inlet channel and the air outlet channel can lead into the ambient or into the space. Accordingly the fuel cell system can be disposed in the space. 
         [0031]      FIG. 2  illustrates a fuel cell system  10 ′ similar to the one illustrated in  FIG. 1 , wherein on the one hand the fan  20  configured as an axial fan  20 ′ is illustrated. Furthermore  FIG. 2  illustrates that the housing  22 ′ includes a proper housing section  24  for receiving control components, this means particularly configured for receiving control electronics, and a third additional housing section  26  for receiving the components for the hydrogen supply. As can already be derived from  FIG. 2 , the third housing section  26  for receiving the components for hydrogen supply preferably includes a hydrogen connection  28 , which is not disposed on the same housing side, like the openings of the air inlet channel  16  and the air outlet channel  18 , but which is disposed on another, preferably opposite housing side. On the side of the chamber  12  for the fuel cell stack  14 , a connection terminal  30  is provided through which the fuel cell stack  14  has to be connected with the components for the hydrogen supply (not illustrated in  FIG. 2 ) in the third housing component  26 , so that the required hydrogen can be supplied to the fuel cell stack  14  through the connection terminal  30 . Providing proper housing sections for control components and for components for hydrogen supply represents a second feature of the invention which can also be implemented independently. 
         [0032]      FIGS. 3   a - 3   c  eventually illustrate a third feature of the invention which can also be implemented independently, wherein the feature includes a bypass air channel  32 , which connects the air inlet channel  16  with the air outlet channel  18 . As can also be derived from the three figures, an air supply flap  34  is provided in the air inlet channel  16 , an air outlet flap  36  is provided in the air outlet channel  18 , and a recirculation flap  38  is provided in the air bypass channel  32 . An air inlet flap, air outlet flap and recirculation air flap in the sense of the invention designates any device through which a hydraulic diameter of the air inlet channel, air outlet channel or bypass channel can be changed in a controlled manner, thus e.g. also an iris aperture or a slide. 
         [0033]    Also the bypass channel  32  and the air inlet flap  34  and the air outlet flap  36  can be configured as exchangeable modules that can be combined in any manner, so that a modular configuration of the fuel cell system is provided overall. 
         [0034]      FIG. 3   a  illustrates an operating condition in which the air inlet flap  34  and the air outlet flap  36  are completely open and the recirculation air flap  38  is completely closed, so that the bypass air channel  32  is de facto ineffective and the fuel cell system operates like a conventional fuel cell system. 
         [0035]    For cold ambient temperatures, e.g. ambient temperatures of less than 10° C., the air inlet flap  34  and the air outlet flap  36  can be closed for starting the fuel system  10  and the recirculation air flap  38  can be opened, so that de facto no ambient air is sucked into the air inlet channel  16 , but so that air rather circulates through the air inlet channel  16 , the chamber  12  for the fuel cell stack  14  the air outlet channel  18  and the air bypass channel  32 . This way, the heat generated in the fuel cell stack  14  can be used effectively and the fuel system  10  can be brought to an advantageous operating temperature of e.g. 50° C. to 60° C. in an advantageous manner as quickly as possible. This is illustrated in  FIG. 3   b.    
         [0036]    As illustrated in  FIG. 3   c , a partial recirculation of the air run through the chamber  12  can also be provided by opening or closing the air inlet flap  34  and the air outlet flap  36  or closing it, while the recirculation flap  28  is open. 
         [0037]    A fuel cell system  10  with a bypass air channel  32  provides the following possible operating modes. 
         [0038]    For example, the air can be recirculated in the system several times, e.g. 10-fold until the fuel cell stack  14  has reached an acceptable temperature of at least e.g. 20° C. Thus, as illustrated in  FIG. 3   b , the air inlet flap  34  and the air outlet flap  36  are closed and the recirculation flap  38  is open. When a fuel cell stack temperature of approximately 20° C. is reached, the air inlet flap  34  and the air outlet flap  36  in turn can be opened completely or partially in order to partially or completely provide ambient air to the fuel cell stack. 
         [0039]    Instead of closing the air inlet flap  34  and the air outlet flap  36  completely, when starting the fuel cell system as illustrated in  FIG. 3   b , the air inlet flap  34  and the air outlet flap  36  can also be partially closed and opened as illustrated in  FIG. 3   c.    
         [0040]    With respect to  FIGS. 3   a - 3   c , it is appreciated that in case of a bypass air channel  32 , a required fan has to be disposed behind the port of the bypass air channel into the air inlet channel  16  and/or in front of the port of the bypass air channel  32  into the air outlet channel  18 , so that the fan can also be effective in the operating mode illustrated in  FIG. 3   b.    
         [0041]      FIGS. 4   a  and  4   b  illustrate a modular fuel cell system in a detailed illustration. 
         [0042]    According to the preferred embodiment of the chamber  12  illustrated in  FIGS. 4   a  and  4   b , the chamber  12  is formed by two shells  12 . 1  and  12 . 2 . This facilitates assembly. When the upper shell is removed (shell  12 . 1 ) all components are easily accessible. The lower shell  12 . 2  illustrates an opening and a circumferential frame  42  with a seal surface  44 . This frame forms a support  42  for the fuel cell stack  14 , which closes the opening as soon as the frame is applied. The shell  12 . 1  includes press contours  52 , which press upon the fuel cell stack  14  and press it onto the seal surface  44  of the lower shell  12 . 2  as soon as the chamber  12  is closed. 
         [0043]    Ideally, the contact surface  42  and also the press contours  52  adapt precisely to the geometry of the fuel cell stack. Thus, fixating the fuel cell stack in the chamber is performed through form locking as soon as the chamber is closed and no separate elements are required for attaching the fuel cell stack. 
         [0044]    By slanting the fuel cell stack, the chamber  12  is divided, so that two intermediary spaces are created, which are sealed relative to one another through inserting the fuel cell stack. The support  42  for the fuel cell stack simultaneously forms the seal surface. The chamber  12  does not have to be sealed completely any more in outward direction. Air flowing into the first intermediary cavity can only reach the intermediary cavity by flowing through the fuel cell stack  14 . A short circuit flow past the fuel cell stack is thus not possible. 
         [0045]    Slanting the fuel cell stack provides a very low installation height for the assembly and simultaneously provides optimum air distribution. The fuel cell stack acts like a “divider wall” and forms a tapering first intermediary space  50 . 1  on the side of the air entry and an expanding second intermediary space  50 . 2  on the side of the air exit. This assembly provides optimum flow through for the fuel stack itself, and there is no air blockage in the intermediary cavities. 
         [0046]    The chamber concept is easily adaptable to different stack sizes of the same type. Only one dimension has to be changed, which can be implemented through accordingly configured intermediary components at the chamber walls. 
         [0047]    The chamber concept implements a portion of the preferred modularity in that an air filter  54  or the fan  20 ″ is easily exchangeable. 
         [0048]    A fourth feature of the invention, which can also be implemented independently relates to the compressor  20  schematically illustrated in  FIG. 1 . According to the feature, plural compressors, e.g. provided in the form of axial compressors, are disposed behind one another in the air cycle (cascaded instead of the typical one compressor). For example, two compressors  20 . 1  and  20 . 2  can be disposed behind one another in an air supply channel or two compressors  20 . 3  and  20 . 4  can be disposed behind one another in the air outlet channel. By the same token, a first compressor  20 . 1  can be disposed in the air inlet channel and a second compressor  20 . 4  can be disposed in the air outlet channel.  FIG. 4  illustrates an embodiment with a total of four compressors  20 . 1 - 20 . 4 , of which two are respectively disposed in the inlet channel  16  and in the outlet channel  18 . Between the inlet channel  16  and the outlet channel  18 , a fuel cell stack  14 ′ is schematically illustrated. 
         [0049]    When the compressors are respectively configured as particular modules, they can be combined with one another in any manner and can be adapted in an optimum manner to different operating conditions or fuel cell stacks. 
         [0050]    The compressors  20 . 2 - 20 . 4  are preferably axial fans and furthermore preferably have different nominal or maximum power. 
         [0051]    By using plural compressors or fans instead of the typical singular compressor or fan, the subsequent problems typically occurring when using only one fan can be avoided:
       the minim startup volume flow of the compressor is too high;   the maximum volume flow of the compressor for high ambient temperatures, e.g. more than 35° C. is not sufficient; and   additional pressure losses by including additional conduits after installing the fuel cell system onsite influence the compressor power negatively, and cannot be easily compensated by a single compressor.       
 
         [0055]    When using two compressors, the problem of minimum startup volume flow can be solved in that for minimum air requirement in a partial load range of the fuel flow system only one of the two fans is being operated. When using axial fans, overall a higher pressure difference between inlet and outlet can be generated because the two axial fans are connected in series, so that pressure delivery of the combined compressor arrangement is increased. Alternatively, two compressors can also be disposed in parallel with one another in order to increase volume flow. Thus, the required fan power can be implemented in a more efficient manner through a respective arrangement of the compressors or through controlled switching them on and off, than this would be possible with a single fan, which may have to be operated in partial load operation with a reduced efficiency. This way, also the total efficiency of the fuel cell system can be increased. Overall, thus any power points can be easily controlled through single controlling of the compressors. 
         [0056]    In this respect, another feature of the invention can be helpful, which is not depicted in the figures, and which is comprised in that the fan or compressor is associated with an air flap that is spring loaded in operating condition and which acts as a pressure reducer and for optimizing the operating point of the fan in partial load operation, wherein the air flap can be opened under full load, so that it does not operate as a pressure reducer then. 
         [0057]    When at least one compressor is disposed in a push mode in the air inlet channel  16  and the other compressor is disposed in the air outlet channel  18  in a suction mode as illustrated in  FIG. 5 , so that one compressor is disposed on the pressure side and the other compressor is disposed on the suction side, this furthermore provides an improvement of the uniform distribution of the flow over the fuel cell stack  14 . Overall, it is advantageous that the volume flow and the pressure of the supply are easily scalable. Furthermore, a simple configuration with low installation size is provided, since also axial fans can be used, which are otherwise rather unfavorable. Eventually, also the even distribution of the airflow over the stack can be improved. 
         [0058]    A fifth embodiment of the invention which can also be implemented independently from the other embodiments relates to optimizing the arrangement of the fuel cell stacks  14  in the chamber  12  or the housing  22 . 
         [0059]    For the fuel cell systems known in the art with a fuel cell stack with an open cathode, typically air scoops  40 . 1  and  40 . 2  are provided as they are illustrated in combination with a stack  14  in  FIG. 6 . Air is supplied to a first air scoop  40 . 1  and inducted through the air scoop  40 . 1  into the stack  14  and flows past the open cathodes through the stack to the second air scoop  40 . 2 . 
         [0060]    In order to arrive at optimum housing dimensions, which facilitate overall a small exterior housing and thus also overall small heat losses through the housing wall, the fifth embodiment provides disposing the stack  14  at a slant angle as illustrated in  FIG. 7 . The outsides of the air scoops  40 . 1  and  40 . 2  thus extend preferably parallel to an outer wall, e.g. a topside or bottom side of a housing  20  of a fuel cell system  10 . 
         [0061]      FIG. 7  additionally illustrates a radial fan  20 ″ configured as a compressor, which is connected to the air inlet scoop  40 . 1 . 
         [0062]      FIG. 8  eventually illustrates a particularly optimized variant of an assembly of a fuel cell stack  14  in a particular chamber  12  of the housing  22 . Thus, the chamber  12  is aligned, so that its chamber walls  12 . 1  and  12 . 2  extend approximately parallel to outer walls of the housing  22 . The fuel cell stack  14  is disposed in the chamber  12  at a slant angle. As can be derived from  FIG. 7 , furthermore an air inlet channel  16  and an air outlet channel  18  are connected to the chamber  12 , so that this yields in top view ( FIG. 7  represents a vertical sectional view) an assembly of a chamber  12  for a fuel cell stack  14  and an air outlet channel  18  as schematically illustrated in  FIG. 9 . Furthermore, the U-shaped air duct according to the invention is illustrated which has already been described with reference to  FIGS. 1 and 2 .  FIG. 9  in turn illustrates a radial fan  20 ″ configured as a compressor  20  in a schematic manner. Advantageously, an assembly of plural fans can be provided instead of a single radial fan  20 ″ as described in more detail with reference to  FIG. 5 . 
         [0063]      FIG. 10  eventually illustrates an embodiment again which includes dividing the housing  22  into at least three housing sections, wherein one housing section includes the chamber  12  and the air channels  16  and  18  and a housing section  24  that is separate there from includes control components, and a third housing section  26  eventually includes the components for the hydrogen supply. 
         [0064]    When all embodiments which can also be implemented independently from one another are simultaneously implemented in a fuel cell system is provided which has a compact housing with small dimensions. This is preferably made from a heat insulating material for further reducing the heat losses. 
         [0065]    The particular embodiments by themselves and in particular in combination with one another implement a fuel cell system which has a high efficiency also in partial load ranges and which can be brought to an optimum operating temperature quickly, also for low ambient temperatures.