Patent Publication Number: US-2019181478-A1

Title: Apparatus for reducing hydrogen concentration in exhaust gas of an exhaust system for a fuel cell vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. patent application Ser. No. 15/640,723 entitled “APPARATUS FOR REDUCING HYDROGEN CONCENTRATION IN EXHAUST GAS OF AN EXHAUST SYSTEM FOR A FUEL CELL VEHICLE”, filed Jul. 3, 2017, which claims priority to and the benefit of Korean Patent Application No. 10-2016-0165280 filed in the Korean Intellectual Property Office on Dec. 6, 2016. The entire contents of these prior filed applications are incorporated herein by reference. 
    
    
     BACKGROUND 
     Field of the Disclosure 
     The present disclosure relates to an apparatus for reducing hydrogen concentration in exhaust gas of an exhaust system of a fuel cell vehicle. 
     Description of the Related Art 
     In general, a fuel cell system is a kind of a power generating system that supplies air and hydrogen to a fuel cell to generate electrical energy by an electrochemical reaction between hydrogen and oxygen by the fuel cell. For example, the fuel cell system is used to drive a driving source such as an electric motor in a vehicle, a ship, a train, or a plane. 
     The fuel cell system includes a stack in which fuel cells are stacked, a hydrogen supply unit that supplies hydrogen to fuel electrodes of the fuel cells, an air supply unit that supplies air to air electrodes of the fuel cells, and a heat/water management unit that controls an operating temperature of the stack by removing heat and water resulting from fuel cell reaction. 
     Meanwhile, in the case of a polymer fuel cell, an appropriate amount of moisture allows an ion exchange membrane of a membrane-electrode assembly (MEA) to smoothly operate. To this end, the air supply device of the fuel cell system includes a humidification device for humidified air supplied to the fuel cell. 
     For example, the humidification device humidifies dried air supplied through an air compressor of the air supply device using moisture in high temperature and high humidity air exhausted from the cathode of the fuel cell, and supplies the humidified air to the cathode of the fuel cell. 
     Further, the fuel cell system includes a hydrogen re-circulating unit that mixes hydrogen discharged from the fuel electrodes of the fuel cells with hydrogen supplied from the hydrogen supply unit to supply the mixture to the fuel electrodes. 
     Meanwhile, impurities such as nitrogen and water vapor are accumulated to decrease a concentration of hydrogen in the fuel electrodes of the fuel cells during an operation of the fuel cell system, and when the concentration of the hydrogen is excessively decreased, cell omission may occur in the fuel cell stack. 
     In order to address this problem, in the fuel cell system, a purge valve is provided on the hydrogen discharge side of the fuel cell stack. By periodically opening the purge valve, the impurities and the hydrogen are discharged. The hydrogen concentration of the fuel electrodes is thus maintained at more than a certain level. 
     When the purge valve is opened to purge the fuel electrodes, the fuel electrodes discharge the impurities and the hydrogen, and the purge gas is introduced into the humidifying device together with the air discharged from the fuel cell stack. 
     Thereafter, water vapor in the impurities is used as a humidifying source of the reactant gas for the electrochemical reaction of the fuel cell in the humidifying device, and gases such as hydrogen and nitrogen are discharged into the atmosphere through an exhaust line of the humidifying device. 
     Accordingly, such a hydrogen purge method is a technique for obtaining a dilution effect of purge hydrogen by mixing hydrogen discharged from the fuel electrode with air discharged through the air discharge line from the fuel cell stack. 
     While starting and stopping of the fuel cell system or in an idle condition (for example, an Idle, Stop, and Go (ISG) condition of the fuel cell vehicle) of a fuel cell vehicle employing the fuel cell system, a substantive amount of hydrogen that crosses over from the fuel electrode to the air electrode through a membrane may be exhausted. 
     In this case, the hydrogen together with the air is exhausted from the air electrode of the fuel cells to a humidifying device, diluted by air at the humidifier, and then exhausted to an atmosphere with reduced concentration. 
     However, according to the conventional scheme, although the hydrogen exhausted from the fuel cell system is mixed in the humidifier with air exhausted from the air electrode so as to reduce the hydrogen concentration, it is difficult to realize a sufficient mixing effect and the hydrogen concentration may not be sufficiently reduced. 
     Therefore, hydrogen concentration exhausted from the fuel cell system may not be effectively reduced, and highly dense hydrogen may be exhausted depending on the driving condition of the fuel cell system, which implies a possibility of ignition and explosion of the exhaust gas. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure. Therefore the Background section may contain information that does not constitute prior art. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure provides an apparatus for reducing hydrogen concentration in exhaust gas of an exhaust system of a fuel cell vehicle. The apparatus may be useful for effectively reducing the hydrogen concentration of exhaust gas of a fuel cell system of a fuel cell vehicle. 
     An apparatus for reducing hydrogen concentration in exhaust gas of an exhaust system of a fuel cell vehicle according to an embodiment may include a bumper cover and an exhaust gas guiding unit. The bumper cover may be disposed at a rear portion of the fuel cell vehicle, and the bumper cover forms a streamlined exterior surface. The exhaust gas guiding unit may interconnect the exhaust system and the bumper cover and guide the exhaust gas to the streamlined exterior surface of the bumper cover. 
     While the exhaust gas may be guided to the streamlined exterior surface of the bumper cover, hydrogen in the exhaust gas may flow along the streamlined exterior surface of the bumper cover, thereby being diffused to, and diluted by, an exterior air. 
     The exhaust gas guiding unit may include an extension portion formed by extending an exhaust end of the exhaust system and connected with a bottom of the bumper cover. 
     An apparatus for reducing hydrogen concentration in exhaust gas of an exhaust system of a fuel cell vehicle according to another embodiment may include a bumper cover and an air amplifier. The bumper cover may be disposed at a rear portion of a vehicle, forming a closed space connected with an exhaust end of the exhaust system, and forming a streamlined exterior surface where the close space may be connected with a rear of the bumper cover by a gap formed along a length direction of the bumper cover. The air amplifier may exhaust the exhaust gas to the streamlined exterior surface through the gap and guiding an exterior air to the streamlined exterior surface. 
     The air amplifier may guide the exhaust gas to stick to, and flow along, the streamlined exterior surface of the bumper cover. As a result, hydrogen in the exhaust gas is diffused to, and diluted by, the exterior air. 
     The bumper cover may be formed in a shape of a hollow loop in cross-section. The streamlined curved surface may be formed as a rear surface of the bumper cover. The rear surface may be overlapped by a front surface with the gap at a bottom of the bumper cover. 
     A blocking protrusion may be formed at a top of the bumper cover so as to block hydrogen contained in the exhaust gas from flowing upward. 
     An apparatus for reducing hydrogen concentration in exhaust gas of an exhaust system of a fuel cell vehicle according to yet another embodiment may include a collecting member, at least one passage member, and an exhaust portion. The collecting member may be installed at an interior of a bumper cover disposed at a rear portion of the fuel cell vehicle and collect the exhaust gas exhausted from the exhaust system. 
     The at least one passage member may be disposed in a length direction of the bumper cover at the interior of the bumper cover and be connected with the collecting member so as to allow the collected gas to flow along the length direction. The exhaust portion may be connected with the at least one passage member, formed along the length direction of the bumper cover, exhaust the exhaust gas inside the at least one passage member, and guide the exhausted gas toward the streamlined exterior surface of the bumper cover. 
     The collecting member may be fixed to the bumper cover at an interior of the bumper cover. The at least one passage member may be fixed to the bumper cover at the interior of the bumper cover. 
     The collecting member may be formed as a housing that includes a first port connected with the exhaust system, a second port connected with the at least one passage member, and a third port for draining moisture contained in the collected exhaust gas. 
     A water trap valve for selectively opening/closing the third port may be provided at the third port. 
     The exhaust portion may include an exhaust slit formed along the length direction of the bumper cover. 
     Each of the at least one passage member may be provided with a connection slit formed along the length direction of the bumper cover, where the connection slit may be connected with the exhaust slit. 
     The exhaust slit may be located upward and rearward with respect to the connection slit, such that the exhaust gas may move upward and rearward while flowing from the connection slit to the exhaust slit. 
     The connection slit and the exhaust slit may be interconnected by a connection passage. 
     The exhaust portion may include a plurality of exhaust holes formed with a predetermined spacing along the length direction of the bumper cover. 
     Each of the at least one passage member may be provided with a plurality of connection holes that are formed in the length direction and respectively connected with the plurality of exhaust holes. 
     The plurality of exhaust holes may be located upward and rearward with respect to the plurality of connection holes, such that the exhaust gas may move upward and rearward while flowing from the plurality of connection holes to the plurality of exhaust holes. 
     The plurality of connection holes and the plurality of exhaust holes may be interconnected by a plurality of connection passages. 
     An apparatus for reducing hydrogen concentration in exhaust gas of an exhaust system of a fuel cell vehicle according to yet another embodiment may include a collecting member and an exhaust portion. The collecting member may be installed at an interior of a bumper cover disposed at a rear portion of the fuel cell vehicle, collect exhaust gas exhausted from the exhaust system, and exhaust the collected exhaust gas to the interior of the bumper cover. The bumper cover may form a streamlined exterior surface. The exhaust portion may include a mesh screen formed at the bumper cover, discharge exhaust gas at the interior of the bumper cover to an exterior of the bumper cover, and guide the discharged gas to the streamlined exterior surface of the bumper cover. 
     According to disclosed embodiments, exhaust gas containing hydrogen and air is guided to a streamlined exterior surface of a rear bumper cover, and diffused to and diluted by an exterior air. 
     Thus, by utilizing the bumper at a rear portion of a fuel cell vehicle in order to reduce hydrogen concentration in the exhaust gas by diluting the exhaust gas by an exterior air, hydrogen concentration in the exhaust gas may be effectively reduced. 
     Further effects that can be obtained or expected from the disclosed embodiments are directly or suggestively described in the following detailed description. That is, various effects expected from the disclosed embodiments will be described in the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a fuel cell system in which an apparatus in accordance with the disclosed embodiments is applied. 
         FIG. 2  is a schematic view of an apparatus for reducing hydrogen concentration in exhaust gas of an exhaust system of a fuel cell vehicle according to a first disclosed embodiment. 
         FIG. 3A  and  FIG. 3B  are a schematic views of an apparatus for reducing hydrogen concentration in exhaust gas of an exhaust system of a fuel cell vehicle according to a second disclosed embodiment. 
         FIG. 4  is a schematic view of an apparatus for reducing hydrogen concentration in exhaust gas of an exhaust system of a fuel cell vehicle according to a third disclosed embodiment. 
         FIG. 5  is a perspective view of an example of an apparatus for reducing hydrogen concentration in exhaust gas of an exhaust system of a fuel cell vehicle according to a third disclosed embodiment. 
         FIG. 6  is a perspective view of another example of an apparatus for reducing hydrogen concentration in exhaust gas of an exhaust system of a fuel cell vehicle according to a third disclosed embodiment. 
         FIG. 7  is a perspective view of a yet another example of an apparatus for reducing hydrogen concentration in exhaust gas of an exhaust system of a fuel cell vehicle according to a third disclosed embodiment. 
         FIG. 8  is a schematic view of an apparatus for reducing hydrogen concentration in exhaust gas of an exhaust system of a fuel cell vehicle according to a fourth disclosed embodiment. 
     
    
    
     The following reference symbols are used throughout the drawings and the following Detailed Description section: 
     
       
         
           
               
               
             
               
                   
               
             
            
               
                 1: fuel cell system 
                 2: fuel cell stack 
               
               
                 2a: air electrode 
                 2b: fuel electrode 
               
               
                 2c: fuel cell 
                 3: air supply unit 
               
               
                 4: hydrogen supply unit 
                 5: humidifier 
               
               
                 6: hydrogen recirculation unit 
                 7: heat/water management unit 
               
               
                 8: purge valve 
                 9: exhaust system 
               
               
                 9a: exhaust line 
                 9b: exhaust end 
               
               
                 101: bumper 
                 103, 203, 303, 403: bumper cover 
               
            
           
           
               
            
               
                 110, 210, 310, 410: exhaust gas guiding unit 
               
            
           
           
               
               
            
               
                 111: extension portion 
                   
               
               
                 201: closed space 
                 205: front surface 
               
               
                 207, 307, 407: rear surface 
                 209: blocking protrusion 
               
               
                 211: air amplifier 
                 213: gap 
               
               
                 311, 411: collecting member 
                 313: first port 
               
               
                 315: second port 
                 317: third port 
               
               
                 321: water trap valve 
                 331: passage member 
               
               
                 333: connection slit 
                 333a: connection hole 
               
               
                 351, 451: exhaust portion 
                 353: exhaust slit 
               
               
                 353a: exhaust hole 
                 371: connection passage 
               
               
                 413: intake port 
                 490: mesh screen 
               
               
                   
               
            
           
         
       
     
     DETAILED DESCRIPTION 
     The present disclosure will be described more fully hereinafter with reference to the accompanying drawings, in which disclosed embodiments are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present disclosure. 
     The drawings and description are to be regarded as illustrative in nature and not restrictive, and like reference numerals designate like elements throughout the specification. 
     The size and the thickness of each component illustrated in the drawings are arbitrarily illustrated in the drawings for better understanding and ease of description, but the present disclosure is not limited to the illustration. In the drawings, the thicknesses of various portions and regions are enlarged for clarity. 
     In the following description, dividing names of components into first, second and the like is to divide the names because the names of the components are the same as each other and an order thereof is not particularly limited. 
     In addition, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. 
     In addition, the terms “˜unit”, “˜means”, “˜part”, and “member” described in the specification mean units of a comprehensive configuration for performing at least one function and operation. 
       FIG. 1  is a block diagram of a fuel cell system in which an apparatus in accordance with disclosed embodiments is applied. 
     Referring to  FIG. 1 , a fuel cell system  1  applied with the disclosed embodiments is an electricity generator system generating electrical energy by an electrochemical reaction of fuel and an oxidizer, and may be installed in a fuel cell vehicle that drives an electric motor by electrical energy. 
     In the disclosed embodiments, fuel used in the fuel cell system  1  is called hydrogen gas (hereinafter, called “hydrogen” for convenience), and an oxidizer used in the fuel cell system  1  is called air. 
     Such a fuel cell system  1  includes a fuel cell stack  2 , an air supply unit  3 , a hydrogen supply unit  4 , a humidifier  5 , a hydrogen recirculation unit  6 , and a heat/water management unit  7 . 
     The fuel cell stack  2  is an accumulated assembly of fuel cells  2   c , respectively including a membrane (not shown), an air electrode  2   a , and a fuel electrode  2   b . The fuel cells  2   c  are supplied with hydrogen by the fuel electrode  2   b  and air by the air electrode  2   a , and generates electrical energy by an electrochemical reaction of hydrogen and oxygen. 
     The air supply unit  3  is driven by electricity and supplies atmospheric air to the air electrode  2   a  of the fuel cells  2   c . The air supply unit  3  may include an air compressor or an air blower. The hydrogen supply unit  4  stores compressed hydrogen and may include a hydrogen tank for supplying the compressed hydrogen to the fuel electrode  2   b  of the fuel cells  2   c.    
     The humidifier  5  may include a membrane humidifier that humidifies air supplied from the air supply unit  3  by using an exhaust air containing moisture and exhausted from the air electrode  2   a  of the fuel cells  2   c , and supplies the humidified air to the air electrode  2   a.    
     The hydrogen recirculation unit  6  recirculates hydrogen exhausted from the fuel electrode  2   b  of the fuel cells  2   c  to the fuel electrode  2   b . The hydrogen recirculation unit  6  may mix the hydrogen exhausted from the fuel electrode  2   b  and the hydrogen supplied from the hydrogen supply unit  4  and supply the mixed hydrogen to the fuel electrode  2   b.    
     The heat/water management unit  7  eliminates heat and water formed by the electrochemical reaction of the fuel cells  2   c , and thereby controls an operating temperature of the fuel cell stack  2 . 
     The above constituent elements of such a fuel cell system  1  may be formed as known in the art. 
     When a fuel cell vehicle installed with the fuel cell system is being started, the fuel cell system  1  exhausts hydrogen by a cross-over together with air from the air electrode  2   a  of the fuel cells  2   c , and exhausts purge hydrogen from the fuel electrode  2   b  of the fuel cells  2   c.    
     In addition, the fuel cell system  1  exhausts only purge hydrogen from the fuel electrode  2   b  of the fuel cells  2   c  during a driving of the vehicle. When the vehicle is stopped or in an idle state (for example, in the case of an Idle, Stop, and Go (ISG) condition), the fuel cell system  1  exhausts hydrogen by a cross-over together with air from the air electrode  2   a  of the fuel cells  2   c.    
     The cross-over hydrogen means hydrogen that crosses over from the fuel electrode  2   b  of the fuel cells  2   c  to the air electrode  2   a  through the membrane by a residual pressure. 
     The purge hydrogen means hydrogen exhausted from the fuel electrode  2   b  together with impurities by an operation of the purge valve  8 , so as to remove impurities such as nitrogen and water vapor accumulated in the fuel electrode  2   b  of the fuel cells  2   c.    
     The hydrogen exhausted from the fuel cells  2   c  may be supplied to the humidifier  5 , and exhausted from the humidifier  5  together with air. Therefore, hydrogen concentration may be reduced in the exhaust gas due to dilution by air. 
     That is, when the vehicle is being started, driven, and stopped or in an idle state, the hydrogen exhausted from the fuel cells  2   c  inflows to the humidifier  5  together with the air exhausted from the fuel cells  2   c , and hydrogen concentration is reduced by the air. 
     The fuel cell system  1  includes an exhaust system  9  so as to exhaust the gas (a gas containing hydrogen and air; hereinafter called an “exhaust gas”) exhausted from the humidifier  5  to an atmosphere. Here, the exhaust gas contains water and water vapor as well as hydrogen and air. 
     The exhaust system  9  may include an exhaust line  9   a  arranged at a bottom of the vehicle from a front to a rear of the vehicle. The exhaust line  9   a  guides the exhaust gas from the front to the rear of the vehicle, and emits the exhaust gas to the atmosphere. 
     The exhaust line  9   a  may be formed as a pipe, and various parts, such as a muffler to reduce an exhaust noise, a sensor to detect a hydrogen concentration, may be installed in the exhaust line  9   a.    
     When the vehicle is being started and stopped or in the idle state, the exhaust gas is exhausted from the exhaust system  9  at a low flow rate, which is a low flow rate and low pressure condition of the exhaust gas, and in this case, the exhaust gas contains hydrogen with relatively high concentration. 
     When the vehicle is driven, the exhaust gas is exhausted from the exhaust system  9  at a high flow rate, which is a high flow rate and high pressure condition of the exhaust gas, and in this case, the exhaust gas contains hydrogen with relatively low concentration. 
     Here, low flow rate/low pressure condition and high flow rate/high pressure condition of the exhaust gas may be determined by a consumed power by the air compressor or air blower of air supply unit  3 . 
     In the disclosed embodiments, the above-described low flow rate/low pressure condition and high flow rate/high pressure condition may be clearly identified depending vehicle state (staring, driving, stopping, idle state), and thus the low flow rate/low pressure condition and the high flow rate/high pressure condition may not be limited to a specific value or range. 
     An apparatus  100  for reducing hydrogen concentration for an exhaust system of a fuel cell vehicle may be connected with an exhaust system  9  at a rear of the fuel cell vehicle. 
     By forming the apparatus  100  for reducing hydrogen concentration for an exhaust system of a fuel cell vehicle at the rear of the fuel cell vehicle, condensate water containing moisture in the exhaust gas may be exhausted rearward, and thus the condensate water may not be frozen in the course of the exhaust line. 
     By forming the apparatus  100  for reducing hydrogen concentration to be connected with the exhaust system  9  at the rear of the vehicle, the hydrogen contained in the exhaust gas may be maximally diluted by exterior air. 
     According to an apparatus  100  for reducing hydrogen concentration for an exhaust system of a fuel cell vehicle according to the disclosed embodiments, the hydrogen in the exhaust gas exhausted through the exhaust system  9  is diffused to, and diluted by, the exterior air, and thereby the hydrogen concentration may be effectively reduced. 
     Hereinafter, a surface toward a front of the fuel cell vehicle is called a front surface, and a surface toward a rear of the fuel cell vehicle is called a rear surface. In addition, “end” may be interpreted as a literal end or an area/section/region/portion that includes the literal end. 
     According to disclosed embodiments that are hereinafter described, the exhaust gas exhausted through the exhaust system  9  is guided toward a bumper at a rear portion of a vehicle and the hydrogen contained in the exhaust gas is diffused to, and diluted by, exterior air. In this regard, the bumper may be construed as a component of an exhaust system. 
     According to an apparatus  100  ( 200 ,  300 ,  400 ) for reducing hydrogen concentration for an exhaust system of a fuel cell vehicle according to the disclosed embodiments, the exhaust system  9  and the bumper at a rear portion of a vehicle  101  are connected. In addition, the apparatus  100  ( 200 ,  300 ,  400 ) may include an exhaust gas guiding unit  110  ( 210 ,  310 ,  410 ) to guide the exhaust gas exhausted through the exhaust system  9  toward a streamlined exterior surface of the bumper  101 . 
       FIG. 2  is a schematic view of an apparatus for reducing hydrogen concentration in exhaust gas of an exhaust system of a fuel cell vehicle according to a first disclosed embodiment. 
     Referring to  FIG. 1  and  FIG. 2 , an apparatus  100  for reducing hydrogen concentration for an exhaust system of a fuel cell vehicle according to a first disclosed embodiment includes an exhaust gas guiding unit  110  that guides the exhaust gas containing hydrogen along a streamlined exterior surface of the bumper cover  103  and diffuses the hydrogen to the exterior air to be diluted by the exterior air. 
     The bumper cover  103  is arranged at the bumper  101  at a rear portion of a fuel cell vehicle, where, for example, a front side of the bumper cover  103  is open and a rear surface forms a streamlined exterior surface upward. That is, the rear surface of the bumper cover  103  forms a curved surface in a vertical direction. 
     The exhaust gas guiding unit  110  includes an extension portion  111  that is formed by extending the exhaust end  9   b  of the exhaust system  9  toward a bottom of the bumper cover  103 . 
     The extension portion  111  is provided at the rear end of the exhaust line  9   a  that is below the bumper  101  at a rear of the fuel cell vehicle, and extends the exhaust end  9   b  illustrated by a single-dot chain line to the bottom of the bumper cover  103 . 
     Thus, the extension portion  111  connects the exhaust end  9   b  with the bottom of the bumper cover  103 . By such a configuration, a diameter of the exhaust line  9   a  becomes larger as the exhaust line  9   a  goes rearward. 
     Because the extension portion  111  extending the exhaust end  9   b  of the exhaust system  9  to the bottom of the bumper cover  103  is formed at the rear end of the exhaust line  9   a , the hydrogen contained in the exhaust gas exhausted by the exhaust end  9   b  may flow upward along the streamlined exterior surface of the bumper cover  103 . Such a flow is enabled by a Coanda effect in which a stream close to a wall sticks to the wall. 
     The hydrogen exhausted together with the air through the exhaust line  9   a  of the exhaust system  9 , being lighter than the air, flows upward along the streamlined exterior surface of the bumper cover  103  by the Coanda effect. The air and water are exhausted to an atmosphere through the exhaust end  9   b.    
     Thus, according to a disclosed embodiment, the hydrogen contained in the exhaust gas exhausted by the exhaust end  9   b  of the exhaust system  9  flows upward along the streamlined exterior surface of the bumper cover  103 , and therefore, the hydrogen is diffused to, and diluted by, ambient air (exterior air). 
     Therefore, hydrogen concentration in the exhaust gas exhausted to the atmosphere through the exhaust system  9  may be effectively reduced. 
       FIG. 3A  and  FIG. 3B  are schematic views of an apparatus for reducing hydrogen concentration in exhaust gas of an exhaust system of a fuel cell vehicle according to a second disclosed embodiment. 
     Referring to  FIG. 3A  and  FIG. 3B , an apparatus  200  for reducing hydrogen concentration for an exhaust system of a fuel cell vehicle according to a second disclosed embodiment includes a closed space  201  and a bumper cover  203 . The closed space  201  is connected with the exhaust end  9   b  of the exhaust system  9 . The bumper cover  203  has a streamlined exterior surface at a rear portion of a vehicle. 
     The present disclosed embodiment is provided with an air amplifier  211  for accelerating exterior air toward the streamlined exterior surface of the bumper cover  203 . 
     The bumper cover  203  has a shape of a hollow round loop forming the closed space  201  as an interior space, and includes a front surface  205  formed as a flat surface and a rear surface  207  formed as the streamlined curved surface. 
     A side surface (not shown) of the bumper cover  203  opposite to a side connected to the exhaust end  9   b  is closed. A bottom of the bumper cover  203  where the streamlined curved surface (i.e., the rear surface  207 ) meets the front surface  205  has a roundish form. The exhaust end  9   a  of the exhaust system  9  is connected with a side (shown in the left) of the bumper cover  203 , and the exhaust gas flows from the exhaust system  9  to the closed space  201  of the bumper cover  203 . 
     The air amplifier  211  is formed at the bottom of bumper cover  203  along a length direction of the bumper cover  203 . The air amplifier  211  forms a gap  213  along the length direction of the bumper cover  203  between the front surface  205  and the rear surface  207  of the streamlined curved surface. That is, the front surface  205  partially overlaps the rear surface  207  with the gap  213 , and this overlapping portion forms the air amplifier  211 . 
     While the exhaust gas flows from the exhaust system  9  into the closed space  201  of the bumper cover  203 , the air amplifier  211  exhausts the inflowing exhaust gas to the streamlined exterior surface of the rear surface  207  through the gap  213 , and also guides exterior air to the streamlined exterior surface. 
     The air amplifier  211  enables the exhaust gas emitted through the gap  213  to flow along the streamlined exterior surface of the rear surface  207 , and thus hydrogen in the emitted gas is diffused to, and diluted by, the exterior air. 
     A blocking protrusion  209  is formed at a top of the bumper cover  203 , so as to block the hydrogen flowing upward along the streamlined exterior surface of the rear surface  207 , such that the hydrogen may not reach a trunk space (not shown). 
     The blocking protrusion  209  is integrally formed at the top of the bumper cover  203  along the length direction of the bumper cover  203 , and is formed to be slanted downward to the rear of the bumper cover  203 . Thus, the blocking protrusion  209  may block the hydrogen in the exhaust gas flowing along the streamlined exterior surface of the rear surface  207  and guide the hydrogen in the exhaust gas downward. 
     According to an apparatus  200  for reducing hydrogen concentration for an exhaust system of a fuel cell vehicle according to a second disclosed embodiment, the exhaust gas exhausted through the exhaust system  9  first flows in the closed space  201  of the bumper cover  203 . 
     When the exhaust gas is emitted through the gap  213 , a flow speed of the emitted exhaust gas is accelerated due to the round shape of the bulgy rear surface  207 . 
     The acceleration of flow speed of the emitted gas inhales the exhaust gas from the closed space  201 , and consequently, the exhaust gas is emitted from the closed space  201  through the gap  213  of the air amplifier  211  at a very high speed. The exhaust gas emitted through the gap  213  sticks to, and flows upward along, the streamlined exterior surface of the rear surface  207  by the Coanda effect. By emitting the exhaust gas at a high speed, a pressure at a rear of the streamlined curved surface of the rear surface  207  becomes lowered. Therefore, the air in vicinity of the rear surface  207  of the streamlined curved surface is inhaled toward the curved surface, and thereby a very strong stream is formed in an upward direction along the curved surface. 
     Such an air amplifier action to form the strong stream is apparent to a person of ordinary skill in the art, in view of the above-described arrangement of the present embodiment. 
     Thus, according to the present embodiment, the exhaust gas flowing into the bumper cover  203  is emitted through the gap  213  of the air amplifier  211  and flows upward along the streamlined exterior surface of the rear surface  207 . At the same time, ambient air (exterior air) is guided along the streamlined exterior surface of the rear surface  207  by a strong stream. 
     As a result, the hydrogen in the exhaust gas emitted through the gap  213  of the air amplifier  211  is diffused to, and diluted by, the exterior air. 
     Meanwhile, while the exhaust gas flows upward along the streamlined exterior surface of the rear surface  207  and the hydrogen in the exhaust gas is diluted, the blocking protrusion  209  at the top of the bumper cover  203  blocks the exhaust gas to flow further upward, e.g., to flow into a trunk space (not shown). Then, the exhaust gas blocked by the blocking protrusion  209  flows into the atmosphere in a downward direction. 
       FIG. 4  is a schematic view of an apparatus for reducing hydrogen concentration in exhaust gas of an exhaust system of a fuel cell vehicle according to a third disclosed embodiment. 
     Referring to  FIG. 4 , an apparatus  300  for reducing hydrogen concentration for an exhaust system of a fuel cell vehicle according to a third disclosed embodiment is provided with an exhaust gas guiding unit  310 . The exhaust gas guiding unit  310  receives the exhaust gas exhausted from the exhaust system  9  inside an interior space of the bumper cover  303 , and guides the exhaust gas toward the streamlined exterior surface of the rear surface  307  of the bumper cover  303 . The exhaust gas guiding unit  310  includes a collecting member  311 , a passage member  331 , and an exhaust portion  351 . 
     The bumper cover  303  has an open front side and a closed rear surface  307 . The rear surface  307  forms a streamlined exterior surface (curved surface). 
     In the present embodiment, the collecting member  311  collects the exhaust gas exhausted through the exhaust system  9 . The collecting member  311  is provided at an interior of the bumper cover  303 , and fixed to the bumper cover  303 . 
     The collecting member  311  is in the form of a closed housing, e.g., in a shape of a rectangular parallelepiped, although  FIG. 5  and  FIG. 6  illustrate the collecting member  311  to be open for the purpose of better understanding and illustration. Such a collecting member  311  includes a first port  313  connected with the exhaust system  9 , a second port  315  connected with the passage member  331 , and a third port  317  for draining moisture (water) contained in the exhaust gas. 
     The third port  317  is formed at a bottom surface of the collecting member  311 , and a water trap valve  321  is installed at the third port  317  so as to open and close the third port  317  by an electrical signal. 
     When the third port  317  is closed by the water trap valve  321 , moisture or water in the exhaust gas is collected inside the collecting member  311 . When the third port  317  is opened by the water trap valve  321 , the collected water in the collecting member  311  is drained through the third port  317 . 
     In the present embodiment, the passage member  331  is formed along the length direction of the bumper cover  303  at an interior of the bumper cover  303 , and is connected with the second port  315  of the collecting member  311 . The passage member  331  allows the exhaust gas in the collecting member  311  to flow in a length direction of bumper cover  303 , and one end of the passage member  331  is fixed to the bumper cover  303 . 
     The passage member  331  is provided with a connection slit  333  formed along the length direction of the bumper cover  303 , in order for exteriorly exhausting the exhaust gas. The connection slit  333  is connected with the exhaust portion  351 . 
     As an example of an apparatus  300  for reducing hydrogen concentration for an exhaust system of a fuel cell vehicle according to a third disclosed embodiment, a single passage member  331  may be provided at the interior of the bumper cover  303 , as shown in  FIG. 4  and  FIG. 5 . 
     As another example of an apparatus  300  for reducing hydrogen concentration for an exhaust system of a fuel cell vehicle according to a third disclosed embodiment, a plurality of passage members  331  (e.g., three passage members  331 ) may be provided at the interior of the bumper cover  303 , as shown in  FIG. 6 . 
     By employing the plurality of passage members  331  as shown in  FIG. 6 , a pressure difference for exhausting the exhaust gas from the exhaust system  9  to the passage member  331  through the collecting member  311  may be reduced, and noise caused by the flow of the exhaust gas may also be reduced. 
     As shown in  FIG. 4  to  FIG. 6 , in the present embodiment, the exhaust portion  351  exhausts the exhaust gas through the connection slit  333  of the passage member  331  to an exterior of the rear surface  307  of the bumper cover  303 . 
     The exhaust portion  351  includes an exhaust slit  353  connected with the connection slit  333  of the passage member  331 . The exhaust slit  353  is formed at the rear surface  307  of the bumper cover  303  along the length direction thereof. 
     The exhaust slit  353  of the exhaust portion  351  is located upward and rearward with respect to the connection slit  333  of the passage member  331 , and the exhaust slit  353  and the connection slit  333  are interconnected by the connection passage  371 . 
     By connecting the connection slit  333  and the exhaust slit  353  in a slope by the connection passage  371 , the exhaust gas exhausted through the exhaust slit  353  through the connection slit  333  and the connection passage  371  may easily flow upward along the streamlined exterior surface of the rear surface  307  of the bumper cover  303 . 
     According to an apparatus  300  for reducing hydrogen concentration for an exhaust system of a fuel cell vehicle according to a third disclosed embodiment, the exhaust gas exhausted through the exhaust system  9  first flows into the collecting member  311  through the first port  313  of the collecting member  311 . 
     Then, the exhaust gas flows into the passage member  331  through the second port  315  of the collecting member  311 , and after flowing through the passage member  331 , is exhausted to the exhaust slit  353  of the exhaust portion  351  through the connection slit  333  and the connection passage  371 . Subsequently, the exhaust gas is exhausted to an exterior of the rear surface  307  of the bumper cover  303  through the exhaust slit  353 . 
     Since the connection slit  333  and the exhaust slit  353  is interconnected by the connection passage  371  in a slope in the present embodiment, the exhaust gas exhausted from the exhaust slit  353  may be easily guided to the streamlined exterior surface of the rear surface  307  of the bumper cover  303 . 
     As described above, the exhaust gas exhausted through the exhaust slit  353  of the exhaust portion  351  is guided to the streamlined exterior surface of the rear surface  307  of the bumper cover  303 , and accordingly, the exhaust gas sticks to, and flows upward along, the streamlined exterior surface of the rear surface  307  by the Coanda effect. 
     In the present embodiment as described above, the exhaust gas flows upward along the streamlined exterior surface of the rear surface  307  of the bumper cover  303 , and the hydrogen in the exhaust gas may be diffused to, and diluted by, the ambient air (exterior air). 
     In the present embodiment, moisture in the exhaust gas flowing into the collecting member  311  may be collected by closing the third port  317  of the collecting member  311  by the water trap valve  321 . 
     In the present embodiment, water collected in the collecting member  311  may be drained through the third port  317  by opening the third port  317  of the collecting member  311  by the water trap valve  321 . 
     As a yet another example of an apparatus  300  for reducing hydrogen concentration for an exhaust system of a fuel cell vehicle according to a third disclosed embodiment, a plurality of connection holes  333   a  with a predetermined spacing may be formed along the length direction of the bumper cover  303 , as the passage member  331  as shown in  FIG. 7 . 
     As the exhaust portion  351 , a plurality of exhaust holes  353   a  may be formed along the length direction of the rear surface  307  of the bumper cover  303 . The plurality of exhaust holes  353   a  may be formed apart by a predetermined spacing and connected with the connection holes  333   a  of the passage member  331 . 
     The exhaust holes  353   a  are located upward and rearward with respect to the connection holes  333   a , and are connected with the connection holes  333   a  by the connection passages  371  (refer to  FIG. 4 ). 
       FIG. 8  is a schematic view of an apparatus for reducing hydrogen concentration in exhaust gas of an exhaust system of a fuel cell vehicle according to a fourth disclosed embodiment. 
     Referring to  FIG. 8 , an apparatus  400  for reducing hydrogen concentration for an exhaust system of a fuel cell vehicle according to a disclosed embodiment may include a exhaust gas guiding unit  410  including a collecting member  411  and a mesh type exhaust portion  451 . The collecting member  411  is installed at an interior of the bumper cover  403 , and the mesh type exhaust portion  451  is formed at a rear surface  407  of the bumper cover  403 . 
     The collecting member  411  collects the exhaust gas exhausted from the exhaust system  9 , and exhausts the exhaust gas toward an interior of the bumper cover  403 . 
     The collecting member  411  is formed with an intake port  413  through which the exhaust gas exhausted from the exhaust system  9  flow into the collecting member  411 . In addition, the collecting member  411  has an open face toward an interior of the bumper cover  403  such that the exhaust gas may be exhausted toward the interior of the bumper cover  403 . 
     In the present embodiment, the exhaust portion  451  exhausts the exhaust gas exhausted to the interior of the bumper cover  403  through the collecting member  411  toward an exterior of the rear surface  407  of the bumper cover  403  and guides the exhaust gas to the streamlined exterior surface of the rear surface  407 . The exhaust portion  451  may be realized as a mesh screen  490  formed at the rear surface  407  of the bumper cover  403 . 
     According to an apparatus  400  for reducing hydrogen concentration for an exhaust system of a fuel cell vehicle according to a fourth disclosed embodiment, the exhaust gas exhausted from the exhaust system  9  is collected in the collecting member  411 , and the collected exhaust gas is exhausted toward the interior of the bumper cover  403  through the open face of the collecting member  411 . 
     Then, the exhaust gas is exhausted from the interior to the exterior of the rear surface  407  of the bumper cover  403  through the exhaust portion  451 , and guided to the streamlined exterior surface of the rear surface  407 . Then the exhausted gas sticks to and flows upward along the streamlined exterior surface of the rear surface  407  by the Coanda effect. 
     In the present embodiment as described above, the exhaust gas is exhausted to an exterior of the rear surface  407  of the bumper cover  403  through the mesh type exhaust portion  451 , and flows upward along the streamlined exterior surface of the rear surface  407 . Therefore, the hydrogen in the exhaust gas may be diffused to, and diluted by, the ambient air (exterior air). 
     While this disclosure has been described in connection with what are presently considered to be useful disclosed embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.