Patent Publication Number: US-2023160773-A1

Title: Arrangement and method for detecting a hydrogen leak in a hydrogen supply system

Description:
TECHNICAL FIELD 
     The disclosure herein relates to an arrangement for detecting a hydrogen leak in a hydrogen supply system. Further, the disclosure herein relates to a method for detecting a hydrogen leak in a hydrogen supply system. The disclosure herein is in particular applicable for a hydrogen supply system of an aircraft. 
     BACKGROUND 
     By using hydrogen as a fuel for propelling aircrafts, gas emissions which have an impact on the climate can be drastically reduced. The hydrogen can be supplied e.g. to fuel cells or fuel cell engines for propelling the aircraft. 
     The use of hydrogen in aircrafts needs to fulfil strong safety requirements. In particular, a leak in the hydrogen supply system for fuel cells or for combustion engines must be detected as soon as possible in order to implement adequate measures. Pipe or equipment containment failures not detected in a short time could lead to a loss of hydrogen flowing into the surrounding equipment space and thus very quickly to a hazardous situation. 
     SUMMARY 
     It is an object of the disclosure herein to timely detect a leak in a hydrogen supply system so that steps can be taken immediately in order to ensure the safety of the hydrogen supply system and in particular of an aircraft comprising the system. In particular, a leak in a hydrogen supply system for propelling an aircraft shall be detected in a very short time. 
     The object is achieved by an arrangement for detecting a hydrogen leak in a hydrogen supply system, comprising a hydrogen tank for providing hydrogen, a hydrogen supply line designed for supplying the hydrogen from the hydrogen tank to a hydrogen consumption unit, a restrictor unit arranged in the supply line for limiting the flow of the hydrogen in the supply line, a pressure difference sensor unit designed for generating a pressure difference signal representing a pressure difference across the restrictor unit, and a control unit coupled to the pressure sensor unit, the control unit being configured for comparing the pressure difference signal with a predefined threshold value, and for providing a leak detection signal if the pressure difference signal exceeds the threshold value. 
     The disclosure herein enables a timely and reliable detection of the leak so that steps can be taken to ensure the safety of the hydrogen supply system and in particular of the aircraft. These steps may e.g. comprise an activation of shut-off valves from supply, turning off equipment, venting compartments, etc. In particular, a depressurization of the system, which may be large and sudden depending on the leak, and a loss of hydrogen into the surrounding space can be avoided by the disclosure herein. 
     Preferably, the restrictor unit comprises a reduced internal cross-section or cross-sectional area for the flow of hydrogen compared to the cross section or cross-sectional area of the supply line adjacent to the restrictor. In particular, the internal cross-sectional area of the restrictor is reduced compared to the cross-sectional area of the supply line upstream of the restrictor. 
     Preferably, the restrictor unit comprises a Venturi tube and/or an orifice member. 
     The Venturi tube or other orifice member sized correctly and e.g. located at an inlet to a suitable volume of pipes, can limit the flow from the tank e.g. by using the Venturi effect. 
     Preferably, the predefined threshold value is higher than the pressure difference across the restrictor unit at normal operation. 
     Preferably, the arrangement comprises a purge valve configured for purging the supply system, and a pressure difference sensor unit configured for detecting a pressure difference across the purge valve. 
     Preferably, the control unit is adapted to trigger a safety procedure if the pressure difference across the purge valve is lower than a predefined value. Preferably, the control unit is configured for combining the pressure difference signal with a purge valve signal representing the status of the purge valve before the pressure difference signal is compared with the threshold value. 
     According to an aspect of the disclosure herein, a method for detecting a hydrogen leak in a hydrogen supply system is provided, comprising the steps: providing hydrogen in a tank and supplying the hydrogen through a supply line to a hydrogen consumption unit; limiting the flow of the hydrogen in the supply line by a restrictor unit; generating a pressure difference signal representing a pressure difference across the restrictor unit; comparing the pressure difference signal with a predefined threshold value; and providing a leak detection signal if the pressure difference signal exceeds the threshold value. 
     Preferably, the flow of the hydrogen is limited by a restrictor unit comprising a reduced internal cross-sectional area for the flow of hydrogen. 
     In particular, the restrictor unit may comprise a reduced cross-sectional area for the flow of hydrogen compared to the cross-sectional area of the supply line upstream of the restrictor unit. 
     Preferably, the flow of the hydrogen is limited by a Venturi tube and/or by an orifice member used as the restrictor unit. 
     Preferably, the predefined threshold value is higher than the pressure difference across the restrictor unit at normal operation. 
     Preferably, the pressure difference signal is combined with a purge valve signal representing the status of a purge valve before the pressure difference signal is compared with the threshold value. 
     Preferably, a pressure difference across the purge valve is detected. 
     In particular, the purge valve is configured for purging the supply system. For detecting the pressure difference across the purge valve, a pressure difference sensor unit may be provided. 
     Preferably, a safety procedure is triggered if the pressure difference across the purge valve is lower than a predefined value. 
     Preferably, a pressure difference signal representing the pressure difference across the purge valve is combined with a purge valve signal representing the status of the purge valve, before the pressure difference signal representing the pressure difference across the restrictor unit is compared with the threshold value. 
     According to a further aspect of the disclosure herein, an aircraft is provided which comprises the arrangement according to the disclosure herein and/or which is operated by using the method according to the disclosure herein. 
     The disclosure herein is based on the following thoughts: If a member with a reduced internal cross-section like e.g. a Venturi tube or an orifice member is provided in a hydrogen supply line, the pressure difference e.g. across the Venturi tube or orifice member under normal fuel cell use can be predicted. It will always remain under a small threshold. However, when a burst or significant leak occurs, the pressure difference across such a member will rise sharply due to the orifice choking and hence limiting the flow rate. Since the speed of sound in gaseous hydrogen is extremely fast, any sudden leak in the system can be detected very quickly in this way. Any larger leakages or pipe bursts downstream of the restrictor will be quickly detected as well. 
     The disclosure herein prevents that e.g. pipe or equipment containment failures could lead to a large and sudden depressurisation of the system and a loss of hydrogen into the surrounding equipment space, which could lead very quickly to a hazardous situation. 
     A further advantage of the disclosure herein is that the pressure sensor arrangement used here can be easily and quickly interpreted by a relatively simple controller module leading to correct and reliable results. 
     In particular, the disclosure herein provides a technical solution for the implementation of safe hydrogen supply systems in particular for use in aircrafts and aircraft propulsion systems. 
     Characteristics and advantages described in relation to the arrangement for detecting a hydrogen leak in a hydrogen supply system are also related to the method for detecting a hydrogen leak in a hydrogen supply system, and vice versa. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, example embodiments of the disclosure herein showing further advantages and characteristics are described in detail with reference to the accompanying figures, in which: 
         FIG.  1    shows a schematic diagram of a hydrogen supply system for a fuel cell stack comprising a leak detection arrangement according to a first preferred embodiment of the disclosure herein; 
         FIG.  2    shows a schematic diagram of a hydrogen supply system for a hydrogen driven engine comprising a leak detection arrangement according to a second preferred embodiment of the disclosure herein; 
         FIG.  3    shows an enlarged schematic sectional view of a pressure difference sensor arrangement attached to a restrictor unit according to a preferred embodiment of the disclosure herein. 
         FIG.  4    shows an example schematic diagram of pressure signals upstream and downstream of a restrictor unit and their pressure difference signal at a time period in which a leak occurs; and 
         FIG.  5    shows a schematic block diagram of an example leak detection logic. 
     
    
    
     DETAILED DESCRIPTION 
     In the figures, similar or identical elements and features are designated by the same reference numbers. The same applies for elements having the same or a similar function. Their description will only be repeated where it seems useful for understanding. Technical features described in one embodiment of the disclosure herein may also apply to one or more of the other embodiments described herein. 
       FIG.  1    shows an arrangement  10  for detecting a leak in a hydrogen supply system  11  according to a preferred embodiment of the disclosure herein. The arrangement  10  comprises a hydrogen tank  12  for providing hydrogen  13  which is stored in the tank  12 . A hydrogen supply line  14  extends from tank  12  to a hydrogen consumption unit  15 . The hydrogen supply line  14  is designed for supplying the hydrogen  13  from hydrogen tank  12  to the hydrogen consumption unit  15 . In the hydrogen supply line  14 , a restrictor unit  16  is arranged, which is configured for limiting the flow of the hydrogen in the supply line  14 . 
     The arrangement  10  further comprises a pressure difference sensor unit  17  which is designed for generating a pressure difference signal  18  representing a pressure difference across the restrictor unit  16 . The pressure difference sensor unit  17  is coupled to a control unit  19  which is configured for comparing the pressure difference signal  18  received from pressure difference sensor unit  17  with a predefined threshold value, and for providing a leak detection signal  20  if the pressure difference signal  18  exceeds the threshold value. 
     In the preferred embodiment, the restrictor unit  16  is formed as a Venturi tube or may comprise a Venturi tube. It is sized correctly and located at the inlet to a suitable volume of pipes  21 . However, the restrictor unit  16  may also be formed as an orifice member. 
     The restrictor unit  16  comprises a reduced internal cross-sectional area for the flow of hydrogen compared to the cross-sectional area of the adjacent supply line  14  upstream of the restrictor unit  16 . Further details of restrictor or Venturi unit  16  are described below with reference to  FIG.  3   . 
     The hydrogen consumption unit  15  being connected to supply line  14  comprises a fuel cell stack to which the hydrogen is fed through supply line  14  after it has passed the restrictor unit or Venturi restrictor  16 . 
     The predefined threshold value to which the pressure difference signal  18  is compared by control unit  19  is higher than the pressure difference across the restrictor unit  17  during normal operation of the hydrogen supply system  11 , i.e. when there is no leak in the hydrogen supply system. 
     A pipe arrangement  21  located downstream of restrictor unit  16  comprises a pump or recirculation pump  22  which is configured to provide a circular flow of hydrogen through the consumer or fuel cell stack  15 . 
     The hydrogen supply system  11  further comprises a purge valve  23  for providing a purge function within the system  11 , and it may also comprise conditioning equipment not shown in the figure. During a purge operation, the purge valve  23  is open so that a gas flow  24  exits from the system  11  to the atmosphere. 
     Preferably, a purge valve signal  25  indicating when the purge valve  23  is open is supplied via a signal connection to control unit  19 . In this way, a pressure drop across the restrictor unit  16  which is caused by a purge event will not be mistaken for a burst, i.e. it will not be interpreted by the control unit  19  as a leak in the hydrogen supply system  21 . 
     A second pressure difference sensor unit  27  may be provided for detecting a pressure difference across the purge valve  23 , i.e. it determines the difference between the pressure upstream and downstream of the purge valve  23 . Pressure difference signal  28  representing the pressure difference is also provided to the control unit  19 . In this way, during the purge period which may last e.g. for a few seconds, a leak can be detected by the second pressure difference sensor arrangement or unit  27  across the purge valve  23 . When the pressure difference detected by pressure difference sensor arrangement  27  is lower than expected, i.e. lower than a predefined threshold value, the control unit  19  triggers emergency safety procedures. 
     Further details of the control unit  19  will be explained below. 
     Referring now to  FIG.  2   , a second preferred embodiment of the disclosure herein will be described in detail. Here, the arrangement  10  comprises a hydrogen supply system  51 , in which the hydrogen consumer is formed by at least one engine  29  using hydrogen as fuel. Tank  12  containing the hydrogen  13  is connected via supply line  14  to engine  29 . 
     A hydrogen fuel pump  31  is arranged in supply line  14  in order to pump the hydrogen to the engine  29 , which is for example a fuel cell propulsion system or a combustion engine that uses hydrogen as a fuel. 
     Arranged in the supply line  14  are two restrictor units  16  which may comprise or be formed by a Venturi tube and/or an orifice member. One of them is positioned upstream of pump  31  and the other one is positioned downstream of pump  31 . For each restrictor unit  16 , a pressure difference sensor unit or sensor arrangement  17  is provided for generating a pressure difference signal  18  representing the pressure difference across the respective restrictor unit  16 , i.e. the difference of the pressure upstream and downstream of each restrictor unit  16 . Details of restrictor unit  16  and of pressure sensor units  17  have already been described above with reference to  FIG.  1   . 
     It is noted that also only one restrictor unit  16  provided with a pressure difference sensor unit  17  can be arranged in supply line  14 . 
     Like in the embodiment shown in  FIG.  1   , control unit  19  is coupled to the pressure sensor unit or units  17  and configured for comparing the respective pressure difference signal  18  with a predetermined threshold value, and for providing leak detection signal  20  if the pressure difference signal  18  exceeds the predefined threshold value. 
       FIG.  3    shows a schematic sectional view of the restrictor unit  16  provided with the pressure difference sensor unit  17  as used in the embodiments described above with reference to  FIGS.  1  and  2   . The restrictor unit  16  comprises a Venturi tube having a reduced internal cross-sectional area  30  compared to the cross-sectional area  32  and  33  upstream and downstream thereof. Arrow  34  indicates the hydrogen flow from tank  12  upstream of the restrictor unit  16 , and arrow  35  indicates the hydrogen flow to the hydrogen consumer  15 ,  29  downstream of the restrictor unit  16  (see  FIGS.  1  and  2   ). 
     The pressure difference sensor arrangement or unit  17  comprises a first pressure port  36  which is connected to supply line  14  upstream of Venturi tube or orifice  31 , and a second pressure port  37  which is connected to supply line  14  downstream of the Venturi tube or orifice  31 . Both pressure parts  36  and  37  are connected to a pressure difference sensor  38  which determines the pressure difference between pressure ports  36  and  37  and which provides pressure difference signal  18  for being received by control unit  19 , as depicted in  FIGS.  1  and  2   . 
     The second pressure difference sensor unit  27  described above with reference to  FIG.  2    is preferably configured in the same way, however arranged across the purge valve. 
       FIG.  4    depicts the pressures at the restrictor unit  16  shown in  FIGS.  1  and  2    over the time t. A first pressure signal  41  represents the pressure upstream of restrictor or Venturi unit  16  and a second pressure signal  42  represents the pressure downstream of the restrictor unit  16 . Pressure difference signal  18  represents the difference of the pressure upstream and downstream of the restrictor unit  16 , i.e. the difference between pressure signals  41  and  42 . 
     The control scheme compares pressure difference  18  to a threshold value which is determined exactly for the respective system and the sizing of the restrictor unit or Venturi tube  16 . Key is to detect a pressure drop that indicates that the Venturi has choked, but not to detect small pressure drops which are expected in normal operation. 
     As shown in  FIG.  4   , a pressure drop is indicated by pressure signal  42  at a time t 1 . That causes immediately a sharp increase of the pressure difference signal  18  at the same time. 
     If the pressure difference indicated by pressure difference signal  18  exceeds the predefined threshold, a signal is sent to e.g. an engine supervisor or other control system in order to trigger mitigation procedures and to protect the engine and aircraft. The signal is e.g. indicated by reference number  20  in  FIGS.  1  and  2   . 
     The exact control system may vary while still using the pressure difference detection method. Possible mitigation measures may e.g. comprise one or more of the following measures: turning off the hydrogen supply to the affected section of the system; venting the system with outside air by opening some external flaps or redirecting ram air or compressed air from the engine; inert the system with a readily available inert gas like e.g. nitrogen; consume the spare oxygen in the engine cavity with a fast chemical reaction; turn off the engine; alert the pilot; and/or reconfigure the propulsion system. The engine is for example a fuel cell propulsion system or a combustion engine that uses hydrogen as fuel. 
     Referring now to  FIG.  5   , a preferred example of a leak detection logic realised for example by control unit  19  is explained in detail. The logic is configured for dealing with a pressure drop in purge events in fuel cell systems as shown for example in  FIG.  1   . 
     During a purge event, which may happen at regular intervals like e.g. around every 2 to 5 minutes during normal operation, purge valve  23  is opened and may produce a change in the pressure difference signal  18  (see  FIG.  1   ). This may, depending on the design of the system, lead to a pressure drop across the Venturi or restrictor unit  16  that could be taken for a burst. 
     To avoid this situation, the purge valve signal  25 , which may also be a purge valve control signal, is combined with pressure difference signal  18  to neutralize the detection during the purge period. 
     The exact implementation depends on the control system being used. A solution which is shown here is to negate the pressure drop signal during a purge event by subtracting the purge opening signal, increased by a large gain from the pressure difference (see first subtraction  46  in  FIG.  4   ). 
     The purge valve signal  25  indicates for example 1 if purge valve  23  is open and 0 if it is closed. After passing gain 45, the purge valve signal  25  is combined with pressure difference signal  18  to neutralize the detection during the purge period. 
     Then, the resulting signal is combined with threshold pressure difference value  48  as indicated by reference number  49  in  FIG.  4   . Here, a second subtraction takes place. If the pressure difference exceeds the threshold, mitigation actions will be started. 
     The pressure sensor arrangement  17  shown in  FIGS.  1  and  2    is a general solution for detecting a hydrogen leak by measuring the pressure drop across the Venturi tube or restrictor unit  16 , which is e.g. located at the inlet to are contained part of the system were the leak needs to be detected, or within that system. 
     During the purge period, which may last e.g. for a few seconds, a leak can be detected by the second pressure difference sensor arrangement  27  across purge valve  23  as depicted in  FIG.  1   . If the pressure difference detected by the second pressure difference sensor arrangement  27  is lower than expected, i.e. lower than a predefined threshold value, emergency safety procedures are started. 
     Referring again to  FIGS.  1  and  2   , a preferred example of a method for detecting a hydrogen leak in a hydrogen supply system is described. 
     In the method, hydrogen  13  is provided in tank  13  and supplied through supply line  14  to hydrogen consumption unit  15 ,  29 , which is for example a fuel cell unit or engine using hydrogen as fuel. 
     The flow of hydrogen  13  in supply line  14  is limited by restrictor unit  16 . Restrictor unit  16  comprises for example a reduced internal cross-sectional area  30  as shown in  FIG.  3   . Preferably it is formed by a Venturi tube or by an orifice member. 
     The pressure difference sensor unit  17  generates a pressure difference signal  18  representing a pressure difference across the restrictor unit  16 . The pressure difference signal  18  is compared with a predefined threshold value by control unit  19 . If the pressure difference signal exceeds the threshold value, leak detection signal  20  is provided by the control unit  19 . 
     In order to avoid that leak detection signal  20  is erroneously provided due to a purge operation, purge valve signal  25  indicating the purge operation is generated and being processed by a logic. In this case, no leak detection signal  20  is generated. 
     In order to detect a leak during the purge operation, the pressure difference across purge valve  23  is detected by second pressure difference sensor arrangement  27 . If that pressure difference is lower than a predefined threshold value, a safety procedure is triggered. 
     The method is preferably performed by using the arrangement as described above in detail. 
     Further advantages of the disclosure herein are for example a quick and inexpensive pressure difference reading in one location, and a purge function which could give similar readings to a sudden pipe leakage can be compensated by zeroing the pressure difference signal during purge opening. 
     While at least one example embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the example embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a”, “an” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority. 
     LIST OF REFERENCE NUMBERS 
     
         
         
           
               10  arrangement 
               11  hydrogen supply system 
               12  tank 
               13  hydrogen 
               14  supply line 
               15  consumption unit 
               16  restrictor unit 
               17  pressure difference sensor unit 
               18  pressure difference signal 
               19  control unit 
               20  leak detection signal 
               21  pipe arrangement 
               22  pump 
               23  purge valve 
               24  gas flow 
               25  purge valve signal 
               27  second pressure difference sensor unit 
               28  Pressure difference signal 
               29  engine 
               31  hydrogen fuel pump 
               30  cross-sectional area 
               32 ,  33  cross-sectional areas upstream/downstream 
               34  hydrogen flow from tank 
               35  hydrogen flow to consumer 
               36 ,  37  pressure ports 
               38  pressure difference sensor 
               41 ,  42  pressure signals 
               45  gain 
               48  threshold pressure difference value 
               51  hydrogen supply system