Method for reducing losses by hydrogen evaporation

Abstract

The invention relates to a method for reducing hydrogen losses in a liquid hydrogen tank (10), this tank being refillable and on board a vehicle (V), by being provided with a vent for discharging the gaseous hydrogen from the tank in the event of overpressure, the method comprising the steps of: providing data for the next filling of the tank as a function of a next planned parking of the vehicle after the next filling, this data providing at least one target filling level to be reached for the next filling, this target filling level being determined so that at the start of parking of the vehicle after a possible journey of the vehicle between filling to the target filling level and the start of parking, the tank has a filling level at the start of parking adapted so that, during the duration of this parking, the loss of hydrogen via the vent is minimized. Figure for abstract: Fig.1.

Description

Title of the invention: Method for reducing losses by hydrogen evaporation

[0001] The present invention relates to a method for reducing losses by evaporation of hydrogen in a liquid hydrogen tank, this tank being filled with sand and mounted on a vehicle.

[0002] Cryogenic storage of hydrogen in a vehicle (car, truck, boat, train, plane, etc.) provides increased autonomy for vehicle journeys. A significant drawback related to this storage method is the evaporation of hydrogen (a phenomenon called "boil-off"), caused by the transfer of heat between the exterior and the hydrogen which is stored at temperatures ranging from 20 to 150 Kelvins. Evaporation results in losses via the vent, which increases the carbon footprint and furthermore operating costs. There is a crucial need to reduce these losses.

[0003] The present invention aims in particular to remedy this problem.

[0004] The invention thus relates to a method for reducing losses by evaporation of hydrogen in a liquid hydrogen tank, this tank being filled with sand and carried on a vehicle (land, sea, air or space) to supply for example a fuel cell of the vehicle, the tank being provided with a vent to evacuate the gaseous dihydrogen outside the tank in the event of overpressure, the method comprising the following steps: - providing data for the next filling of the liquid hydrogen tank based on a planned next parking of the vehicle after the next filling, these next filling data providing at least one target filling level (L-targ) to be reached for the next filling of the tank, this target filling level (L-targ) being determined so that at the start of parking of the vehicle after a possible journey of the vehicle between filling to the target filling level (L-targ) and the start of parking, the tank has a filling level at the start of parking (L-park) adapted so that, during the duration of this next parking of the vehicle, the loss of dihydrogen via the tank vent is minimized.

[0005] The invention advantageously makes it possible to guide, using the data on the next filling of the tank, the driver / pilot of the vehicle equipped with the cryogenic liquid hydrogen tank in order to optimize the refueling strategy and minimize losses linked to evaporation. The invention is particularly advantageous for intensive use applications, for example for a truck used all day, between driving phases and parking phases.

[0006] It is important that, during the phases of parking of the vehicle during which the phenomenon of hydrogen evaporation can occur, the tank is placed in conditions allowing losses via the vent to be minimized. This is what the present invention allows.

[0007] In the present invention, during the parking phase (i.e. the vehicle is stationary with the engine off), the liquid hydrogen tank stops supplying the fuel cell. A parking phase is different in particular from a simple stop at a red light or a short stop at the service station to recharge the tank with hydrogen. During parking within the meaning of the invention, the fuel cell is at rest.

[0008] According to one aspect of the invention, the parking duration is at least one hour or two hours, or even more, for example at least 5 hours or 8 hours.

[0009] It is noted that, when the vehicle is moving, the hydrogen intake by the cell lowers the pressure in the tank. In addition, the thermodynamic phenomenon of stratification (development of a thermal gradient in the height of the tank) causes the pressure to rise more quickly in a static tank than in a moving tank. Thus, when the vehicle is moving, the "boil-off" phenomenon is less critical.

[0010] In the invention, the objective is to determine the target filling level (L-targ) to be reached for the next filling of the tank, so that at the time of the start of parking, the tank is filled to the filling level at the start of parking (L-park). In fact, the user / driver does not necessarily need to know the value of the filling level at the start of parking (L-park). The user / driver needs to know the target filling level (L-targ) to be reached for the next filling of the tank, since he will fill it knowing this target level. The user / driver can for example enter the level value (L-targ) on ​​the charging station and this station automatically fills it up to the level (L-targ). This level (L-targ) can also be reached manually by the user.Alternatively, in the case where filling is done completely automatically, the user / driver would not need to know the target filling level (L-targ) to be reached, and it is the charging station which receives this data to fill automatically.

[0011] According to one aspect of the invention, the vehicle equipped with the liquid hydrogen tank is a road motor vehicle such as a truck, in particular of at least 3.5 tonnes, or a bus, in particular of at least 8 seats.

[0012] According to one aspect of the invention, the vehicle equipped with the liquid hydrogen tank is a train or a ship or an airplane.

[0013] According to one aspect of the invention, the target fill level (L-targ) provided by the next fill data is correlated to a time (date / time) planned for the next fill.

[0014] According to one aspect of the invention, the next filling data are determined at least as a function of the duration of the next parking of the vehicle.

[0015] According to one aspect of the invention, the parking duration is at least one hour or two hours, or even more, for example at least 5 hours or 8 hours.

[0016] According to one aspect of the invention, the next filling data are determined at least as a function of a dormancy parameter which represents the latency time before the tank undergoes ventilation (via the vent) due to the pressure in the tank which increases as the hydrogen evaporates.

[0017] The higher the value of this dormancy parameter, for a given situation, the more the release of evaporated hydrogen outside the tank is delayed. This is beneficial because it helps reduce losses due to evaporation.

[0018] According to one aspect of the invention, the determination of the next filling data uses a thermodynamic model providing a relationship between the dormancy parameter and the filling level at the start of parking (L-park), and possibly also in relation to the pressure inside the tank.

[0019] According to one aspect of the invention, the thermodynamic model is presented in the form of a correspondence table associating the percentage of filling of the tank (or filling level at the start of parking (L-park)) with values ​​of the dormancy parameter, and possibly also the pressure inside the tank.

[0020] The method according to the invention makes it possible, by providing next filling data for filling the tank at the refueling station, to ensure that, when the vehicle is next parked, the target filling level (L-targ) of the tank is adapted to the parking duration. The evaporation of hydrogen occurring during this parking phase is minimized thanks to the thermodynamic model and the anticipation of the vehicle's path, more generally of the vehicle's route plan.

[0021] According to one aspect of the invention, the next filling data is determined according to two different thermodynamic models, using one of the models for example if the duration of the next parking is less than a predetermined threshold, and using the other of the models if the duration of the next parking of the vehicle is greater than this predetermined threshold.

[0022] One of the models may use, as described above, the dormancy parameter and the other of the thermodynamic models may use, for example, a parameter of accumulation of evaporated hydrogen which is vented outside the tank.

[0023] Thus, depending in particular on the duration of the next parking of the vehicle, the determination of the next filling data can be based on one or other of the models depending on the duration of the next parking.

[0024] The dormancy parameter is for example maximized to a value of 50% if the liquid hydrogen is stored in the tank under a pressure of 10 bars.

[0025] The thermodynamic model uses for example a parameter of accumulation of evaporated hydrogen which is ventilated outside the tank.

[0026] According to one aspect of the invention, in the case where the next parking of the vehicle must last N hours, the next filling data is determined by taking into account this duration of parking of the vehicle.

[0027] According to one aspect of the invention, the next filling data also takes into account the consumption of liquid hydrogen during a journey of the vehicle between the moment when the next filling data is provided and the moment when the vehicle reaches a liquid hydrogen refueling station.

[0028] According to one aspect of the invention, the next filling data also takes into account a possible journey that the vehicle must travel between the refueling station and the vehicle's parking location, for example a parking lot or a garage.

[0029] According to one aspect of the invention, the next filling data are also determined as a function of vehicle journey data and / or vehicle environment data, for example the outside temperature.

[0030] According to one aspect of the invention, the next filling data is also determined based on data relating to a history of journeys of the vehicle.

[0031] According to one aspect of the invention, the vehicle journey data is, for example, the average mileage traveled by the vehicle during a normal day of travel.

[0032] According to one aspect of the invention, the journey data also includes, for example, the usual parking time of the vehicle, for example at 7 p.m. after the working day.

[0033] The parking duration or parking time can be set at 8 or 12 hours for example when the vehicle is parked overnight.

[0034] According to one aspect of the invention, the next filling data are determined based on data entered by the user via a human-machine interface. These entered data relate, for example, to the journey that the user plans to take, in particular the journeys just before and just after the next filling.

[0035] The invention also relates to a system for reducing losses by evaporation of hydrogen (boil-off) in a liquid hydrogen tank, this tank being refillable and on board a vehicle (land, sea, air or space) to supply for example a fuel cell of the vehicle, the tank being provided with a vent to evacuate the gaseous dihydrogen outside the tank in the event of overpressure, the system being configured to: - providing data for the next filling of the liquid hydrogen tank based on a planned next parking of the vehicle after the next filling, these next filling data providing at least one target filling level (L-targ) to be reached for the next filling of the tank, this target filling level (L-targ) being determined so that at the start of parking of the vehicle after a possible journey of the vehicle between filling to the target filling level (L-targ) and the start of parking, the tank has a filling level at the start of parking (L-park) adapted so that, during the duration of this next parking of the vehicle, the loss of dihydrogen via the tank vent is minimized.

[0036] According to one aspect of the invention, the system comprises a data processing unit, in particular a computer, configured to receive data on the duration of the next parking of the vehicle, and to determine target filling level data (L-targ) of the tank for the next filling at least as a function of the duration of the next parking of the vehicle.

[0037] According to one aspect of the invention, the data processing unit is configured to receive vehicle journey data and / or vehicle environment data, for example the outside temperature, and use this data in determining the target filling level data (L-targ) of the tank for the next filling.

[0038] According to one aspect of the invention, the data processing unit is on board the vehicle (being an on-board computer of the vehicle), and can possibly communicate with a remote server.

[0039] The data processing unit on board the vehicle is connected to software based on a remote server for heavier calculation operations.

[0040] According to one aspect of the invention, the data processing unit is remote (connected remotely from the vehicle).

[0041] In particular, the data processing unit is a remote computing unit which contains in memory the typical driving cycles.

[0042] According to one aspect of the invention, the system comprises a human-machine interface for providing the driver with target filling level information. (L-targ) of the tank for the next refill.

[0043] According to one aspect of the invention, the system is configured to perform at least some of the following steps: - process data from sensors such as liquid hydrogen level gauges in the tank; - process data related to a driving cycle; - retrieve a vehicle journey history; - communicate with a database concerning a liquid hydrogen refueling network and GPS; - calculate next filling data including in particular a next refueling location, a time, information on the target filling level (L-targ) of the tank; - present this next filling data to the user via a human-machine interface.

[0044] According to one aspect of the invention, at least one pressure sensor and / or one level sensor is placed in the liquid hydrogen tank.

[0045] Other characteristics, details and advantages of the invention will emerge more clearly on reading the description which follows on the one hand, and several exemplary embodiments given for informational and non-limiting purposes with reference to the appended schematic drawings on the other hand, in which:

[0046] [Fig.l] [Fig.l] is a schematic representation of a system for reducing hydrogen losses according to the invention;

[0047] [Fig.2] [Fig.2] represents dormancy curves used by the system of the [Fig.l];

[0048] [Fig.3] [Fig.3] represents curves of quantity of stale hydrogen;

[0049] [Fig.4] [Fig.4] is a block diagram illustrating a method according to an example of a realization lization of the invention.

[0050] The features, variants and different embodiments of the invention may be combined with each other, in various combinations, provided that they are not incompatible or mutually exclusive. In particular, variants of the invention may be imagined comprising only a selection of features described below in isolation from the other features described, if this selection of features is sufficient to confer a technical advantage and / or to differentiate the invention from the prior art.

[0051] [Fig.l] shows a system 100 for reducing losses by evaporation of hydrogen (or “boil-off”) in a tank 10 of liquid hydrogen, this tank 10 being refillable and mounted on a road vehicle V, here a truck, to power a fuel cell (not shown) of the vehicle V.

[0052] The tank 10 is provided with a vent 11 for evacuating the gaseous dihydrogen outside the tank 10 in the event of overpressure.

[0053] The system 100 is configured to provide data for the next filling of the liquid hydrogen tank 10 as a function of a next planned parking of the vehicle after the next filling, these next filling data providing at least one target filling level (L-targ) to be reached for the next filling of the tank 10, this target filling level (L-targ) being determined so that at the start of parking of the vehicle V after a possible journey of the vehicle between filling to the target filling level (L-targ) and the start of parking, the tank 10 has a filling level at the start of parking (L-park) adapted so that, during the duration D of this next parking of the vehicle, the loss of dihydrogen via the vent of the tank 10 is minimized. These aspects will be described in detail below.

[0054] The system 100 comprises a data processing unit 101, such as a computer, configured to: - receive data on the duration of the next parking of the vehicle, and determine target filling level data (L-targ) of the tank 10 for the next filling at least as a function of the duration of the next parking of the vehicle, and / or - receive vehicle trip data and / or vehicle environment data, e.g. outside temperature, and use this data in determining the target fill level (L-targ) data of the tank for the next fill.

[0055] The data processing unit 101 is on board the vehicle V and can communicate with a remote server 120, also called “Cloud” in English.

[0056] The data processing unit 101 on board the vehicle V is connected to a computer 130 on the remote server 120 for heavier calculation operations.

[0057] The remote server 120 contains in a memory 135 data on histories of driving and / or filling cycles.

[0058] Thus the next filling data are determined, where appropriate, by taking into account data relating to a history of journeys of the vehicle V.

[0059] The journey data of the vehicle V are, for example, the average mileage traveled by the vehicle during a normal day of travel.

[0060] The journey data also includes, for example, the usual parking time of the vehicle, for example at 6 p.m. or 7 p.m. after the working day.

[0061] The parking duration or parking time can be set at 8, 10 or 12 hours for example when the vehicle is parked overnight.

[0062] The next filling data can also be determined based on data entered by the user via a human-machine interface 105. This entered data relates, for example, to the journey that the user plans to take, in particular the journeys just before and just after the next filling.

[0063] The human-machine interface 105, for example a touch screen permanently installed on the vehicle V or a smartphone in the hands of the driver C, makes it possible to provide the driver with information on the target filling level (L-targ) of the tank for the next filling.

[0064] The remote server 120 contains in a database 137 on the location of the liquid hydrogen refueling stations, for example in the form of a map of the network of liquid hydrogen refueling stations. This database 137 can be updated regularly.

[0065] The system 100 is configured to perform the following steps: - processing data from sensors 111 such as liquid hydrogen level gauges in the tank 10; - process data related to a driving cycle; - retrieve a vehicle journey history from memory 135; - communicate with database 137 concerning a liquid hydrogen refueling network and GPS; - calculate next filling data including in particular a next refueling location, a time, information on the target filling level (L-targ) of the tank; - present this next filling data to the user via the human-machine interface 105.

[0066] At least one pressure sensor 111 and / or one liquid hydrogen level sensor 111 is placed in the liquid hydrogen tank 10.

[0067] The system 100 makes it possible to implement a method for reducing losses by evaporation of hydrogen via the vent 11 of the tank 10, the method comprising the following steps: - providing data for the next filling of the liquid hydrogen tank 10 as a function of a next parking of the vehicle V planned after the next filling, these next filling data providing at least one target filling level (L-targ) to be reached for the next filling of the tank, this target filling level (L-targ) being determined so that at the start of parking of the vehicle after a possible journey of the vehicle between filling to the target filling level (L-targ) and the start of parking, the tank has a filling level at the start of parking (L-park) adapted so that, for the duration of this next parking of vehicle V, the loss of dihydrogen via the tank vent is minimized.

[0068] The invention advantageously makes it possible to guide, using the data on the next filling of the tank 10, the driver / pilot of the vehicle equipped with the cryogenic liquid hydrogen tank in order to optimize the refueling strategy and minimize losses via the vent 11. The invention is particularly advantageous for intensive use applications, for example for a truck used all day, between driving phases and parking phases.

[0069] It is important that, during the phases of parking of the vehicle during which the phenomenon of hydrogen evaporation can occur, the tank is placed in conditions allowing losses via the vent to be minimized. This is what the present invention allows.

[0070] In the present invention, during the parking phase (i.e. the vehicle is stationary with the engine off), the liquid hydrogen tank stops supplying the fuel cell. A parking phase is different in particular from a simple stop at a red light or a short stop at the service station to recharge the tank with hydrogen. During parking within the meaning of the invention, the fuel cell is at rest.

[0071] According to one aspect of the invention, the parking duration is at least one hour or two hours, or even more, for example at least 5 hours or 8 hours.

[0072] In the invention, the objective is to determine the target filling level (L-targ) to be reached for the next filling of the tank, so that at the time of the start of parking, the tank is filled to the filling level at the start of parking (L-park). In fact, the user / driver does not necessarily need to know the value of the filling level at the start of parking (L-park). The user / driver needs to know the target filling level (L-targ) to be reached for the next filling of the tank, since he will fill it knowing this target level. The user / driver can for example enter the level value (L-targ) on ​​the charging station and this station automatically fills it up to the level (L-targ). This level (L-targ) can also be reached manually by the user.Alternatively, in the case where filling is done completely automatically, the user / driver would not need to know the target filling level (L-targ) to be reached, and it is the charging station which receives this data to fill automatically.

[0073] Preferably, the target fill level (L-targ) provided by the next fill data is correlated to a time (date / time) expected for the next fill.

[0074] Preferably, the next filling data are determined at least in depending on the duration of the vehicle's next parking.

[0075] Preferably, the parking duration is at least one hour or two hours, or even more, for example at least 5 hours or 8 hours.

[0076] In the example described, the next filling data are determined at least as a function of a dormancy parameter DORM which represents the latency time before the tank undergoes ventilation (via the vent 11) due to the pressure in the tank which increases as the hydrogen evaporates.

[0077] The dormancy parameter DORM is taken here with, as unit, the number of days and the assumption that the thermal inputs of the reservoir are 5 Watts.

[0078] [Fig.2] shows curves C1 to C4 with, on the abscissa, the filling level of the L-park reservoir (expressed as a percentage of filling of the reservoir 10), and on the ordinate, the dormancy parameter DORM (expressed as a number of days).

[0079] The higher the value of this dormancy parameter DORM, for a given situation, the more the release of evaporated hydrogen outside the tank is delayed. This is beneficial because it helps reduce losses via vent 11.

[0080] Curve Cl corresponds to a modeling of the variation of the dormancy parameter DORM for liquid hydrogen LH2 at a pressure between 6 and 10 bars, except at the 100% filling value for which the pressure is between 8 and 10 bars.

[0081] Curve C2 corresponds to a modeling of the variation of the dormancy parameter DORM for subcooled liquid hydrogen sLH2 at a pressure between 6 and 20 bars, except at the 100% filling value for which the pressure is between 16 and 20 bars.

[0082] Curve C3 corresponds to a modeling of a liquid hydrogen LH2 case for a pressure varying from 1 to 10 bars.

[0083] Curve C4 corresponds to a modeling of a hydrogen case sLH2 for a pressure varying from 1 to 20 bars.

[0084] For example, on curve Cl, we see that the dormancy parameter DORM is maximum for a filling level corresponding to 80%.

[0085] On curve C2, we see that the dormancy parameter DORM is maximum for a filling level corresponding to 50%.

[0086] It is unexpectedly found that it is not always desirable to fill the tank to 100% if the risk of hydrogen loss through the vent is to be reduced.

[0087] The determination of the next filling data uses a thermodynamic model providing a relationship between the dormancy parameter and the filling level at the start of parking (L-park), and possibly also in relation to the pressure inside the tank.

[0088] In the example described, the thermodynamic model is presented in the form of a correspondence table associating the percentage of filling of the tank (or filling level at the start of parking (L-park)) with values ​​of the dormancy parameter, and possibly also the pressure inside the tank.

[0089] The method according to the invention makes it possible, by providing next filling data for filling the tank at the refueling station, to ensure that, when the vehicle is next parked, the target filling level (L-targ) of the tank is adapted to the parking duration. The evaporation of hydrogen occurring during this parking phase is minimized thanks to the thermodynamic model and the anticipation of the vehicle's path, more generally of the route plan of the vehicle V.

[0090] In an exemplary embodiment of the invention, the next filling data is determined according to two different thermodynamic models, using one of the models for example if the duration of the next parking is less than a predetermined threshold, and using the other of the models if the duration of the next parking of the vehicle is greater than this predetermined threshold.

[0091] One of the models may use, as described above, the dormancy parameter and the other of the thermodynamic models may use, for example, a parameter of accumulation of evaporated hydrogen which is vented outside the tank 10.

[0092] Thus, depending in particular on the duration of the next parking of the vehicle, the determination of the next filling data can be based on one or other of the models depending on the duration of the next parking.

[0093] Another thermodynamic model is now described.

[0094] [Fig.3] shows curves SI to S3 with, on the abscissa, the duration D in hours since the start of parking, and on the ordinate, the cumulative quantity CQ of hydrogen vented via vent 11, expressed in kg.

[0095] Curves SI to S3 model the behavior for subcooled liquid hydrogen (sLH2) with a maximum permissible working pressure (also referred to as MAWP) of 20 bars, with the assumption that the pressure at the start of parking at D = 0 is 6 bars.

[0096] These curves were obtained for a thermal input of 30 Watts.

[0097] Curve SI corresponds to a filling level of the L-park tank of 20% at the start of parking (D=0).

[0098] Curve S2 corresponds to a filling level of the L-park tank of 50% at the start of parking (D=0).

[0099] Curve S3 corresponds to a filling level of the L-park tank of 80% at the start of parking (D=0).

[0100] It is noted that beyond, for example, 45 hours of parking, an initial tank initially filled to 20% (curve SI) presents less cumulative losses of stale hydrogen than in the case where the tank is filled to 50% at the start of parking (curve S2).

[0101] Thus, depending on the parking duration, it may be more judicious to fill the tank to a lower level to reduce losses due to stale flow.

[0102] Other parameters may be taken into account.

[0103] For example, in the case where the next parking of the vehicle must last N hours, the next filling data is determined by taking into account this duration of parking of the vehicle.

[0104] The next refill data also takes into account the consumption of liquid hydrogen during a journey of the vehicle between the moment when the next refill data is provided and the moment when the vehicle reaches a liquid hydrogen refueling station.

[0105] The next refill data also takes into account a possible journey that the vehicle must travel between the refueling station and the vehicle's parking location, for example a parking lot or a garage.

[0106] The next filling data is also determined based on vehicle travel data and / or vehicle environment data, for example the outside temperature.

[0107] We will now describe, with reference to [Fig.4], different steps of a method according to an example of implementation of the invention.

[0108] In this method, we start from the beginning (step 200) of a daily cycle of use of the vehicle V.

[0109] At the start of this daily cycle, a lower limit (L-min) and an upper limit (L-max) of the filling level of the tank 10 are calculated (step 201), limits recommended for the end of the day, just before the start of parking. This is an initialization.

[0110] While the vehicle V is running during the day, the system 100 checks, in real time or at regular time intervals, whether the current filling level (L-real) of the tank 10 is smaller than the lower limit (L-min), or whether L-real <L-min (étape 202).

[0111] As long as the current filling level L-real does not fall below the lower limit L-min, it is monitored (step 203) whether a next parking begins.

[0112] Until the time to start parking has arrived, step 202 is repeated.

[0113] If the current filling level L-real falls below the lower limit L-min, then it is deduced that a next filling of the tank 10 is necessary.

[0114] At this time, in step 204, the parking start filling level L- park is calculated.

[0115] Then in step 205, it is determined whether the parking start filling level L-park is smaller than the upper limit L-max.

[0116] If L-park is smaller than L-max, then L-targ is given the value of 100% (step 206).

[0117] Then a step 206 occurs for filling the tank which is filled to a level of 100%. In other words, the L-targ level is set at the level of 100%.

[0118] In the case where in step 205, it is determined that L-park is greater than L-max, then we move on to step 208 which is to calculate a target filling level L-targ to be reached for the next filling.

[0119] Once this step 208 has been completed, the tank is filled in step 207.

[0120] In step 203, if the time to start parking arrives, step 210 is carried out in which a comparison is made between the current filling level L-real and the lower limit L-min.

[0121] If the current filling level L-real (which then corresponds substantially to L-park) is greater than the lower limit L-min then parking can actually begin at step 211.

[0122] On the other hand, if the current filling level L-real is smaller than the lower filling limit L-min then the recommendation is issued to fill the tank 10 up to the target filling level L-targ (step 212).

[0123] Optionally, it is possible to park with a tank filled to a value different from L-targ, for example to avoid filling up before the parking phase if this is not necessary.

[0124] The steps described aim to maximize the dormancy parameter.

Claims

Claims

1. Method for reducing losses by evaporation of hydrogen in a liquid hydrogen tank (10), this tank being refillable and on board a vehicle (V) to supply for example a fuel cell of the vehicle, the tank (10) being provided with a vent to evacuate the gaseous dihydrogen from the tank in the event of overpressure, the method comprising the following steps: - providing data for the next filling of the liquid hydrogen tank as a function of a next parking of the vehicle planned after the next filling, this next filling data providing at least one target filling level (L-targ) to be reached for the next filling of the tank, this target filling level (L-targ) being determined so that at the start of parking of the vehicle after a possible journey of the vehicle between filling to the target filling level (L-targ) and the start of parking,the tank has a start-of-park filling level (L-park) adapted so that, during the duration of this next parking of the vehicle, the loss of dihydrogen via the tank vent is minimized.,

2. Method according to the preceding claim, in which the next filling data are determined at least as a function of a dormancy parameter (DORM) which represents the latency time before the tank undergoes ventilation due to the pressure in the tank which increases as the hydrogen evaporates.

3. Method according to the preceding claim, in which the determination of the next filling data uses a thermodynamic model providing a relationship between the dormancy parameter and the filling level at the start of parking (L-park), and possibly also in relation to the pressure inside the tank.

4. Method according to the preceding claim, in which the thermodynamic model is presented in the form of a correspondence table associating the percentage of filling of the tank, or level of filling- parking start pleating (L-park), with dormancy parameter values, and possibly still the pressure inside the tank.

5. Method according to one of the preceding claims, in which the next filling data is determined according to two different thermodynamic models, using one of the models for example if the duration of the next parking is less than a predetermined threshold, and using the other of the models if the duration of the next parking of the vehicle is greater than this predetermined threshold.

6. Method according to one of the preceding claims, in which the next filling data also takes into account the consumption of liquid hydrogen during a journey of the vehicle between the moment when the next filling data is provided and the moment when the vehicle reaches a liquid hydrogen refueling station.

7. Method according to one of the preceding claims, in which the next filling data is also determined on the basis of data relating to a journey history of the vehicle.

8. Method according to one of the preceding claims, in which the next filling data are determined based on data entered by the user via a human-machine interface. These entered data relate, for example, to the journey that the user plans to take, in particular the journeys just before and just after the next filling.

9. System (100) for reducing losses by evaporation of hydrogen in a tank (10) of liquid hydrogen, this tank (10) being refillable and on board a vehicle to supply for example a fuel cell of the vehicle, the tank being provided with a vent to evacuate the gaseous dihydrogen outside the tank in the event of overpressure, the system (100) being configured to: - provide data for the next filling of the liquid hydrogen tank as a function of a next parking of the vehicle planned after the next filling, this next filling data providing at least one target filling level (L-targ) to be reached for the next filling of the tank, this target filling level (L-targ) being determined so that at the start of parking of the vehicle (V) after a possible journey of the vehicle between the filling filling to the target filling level (L-targ) and the start of parking, the tank has a parking start filling level (L-park) adapted so that, during the duration of this next parking of the vehicle, the loss of dihydrogen via the tank vent is minimized.

10. System (100) according to the preceding claim, in which the system comprises a data processing unit (101), in particular a computer, configured to receive data on the duration of the next parking of the vehicle, and to determine target filling level data (L-targ) of the tank for the next filling at least as a function of the duration of the next parking of the vehicle.

11. System (100) according to the preceding claim, wherein the data processing unit (101) is configured to receive vehicle journey data (V) and / or vehicle environment data, for example the outside temperature, and use this data in determining the target filling level data (L-targ) of the tank for the next filling.

12. System (100) according to one of claims 9 to 11, wherein the system is configured to perform at least some of the following steps: - process data from sensors (111) such as liquid hydrogen level gauges in the tank; - process data related to a driving cycle; - retrieve a journey history of the vehicle (V); - communicate with a database concerning a liquid hydrogen refueling network and the GPS; - calculate next filling data including in particular a next refueling location, a schedule, target filling level information (L-targ) of the tank; - present this next filling data to the user via a human-machine interface (105).

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