Inerting system, aircraft and method for inerting hydrogen system of aircraft by means of inerting system

Abstract

The invention relates to an inerting system, an aircraft and a method for inerting a hydrogen system of an aircraft by means of an inerting system. The present invention relates to a hydrogen system, and in particular to an improved inerting system that reuses inert gas that has been supplied to the hydrogen system through a fluid recirculation system.

Description

Technical Field

[0001] The present invention relates to an inerting system for an aircraft and a method of inerting a hydrogen system, and in particular to an improved inerting system which reuses inert gas that has been supplied to the hydrogen system through a fluid recirculation system. Background Art

[0002] It is well known to those skilled in the art that an explosive or flammable gas atmosphere on an aircraft, such as a fuel tank or a fuel cell, is inerted with an inert gas by providing an inert gas (such as nitrogen) to the interior of a housing containing a hydrogen-based system. Hydrogen is a gas with a very high permeability, which makes it difficult to contain it within their working interface or volume. The inerting is performed to avoid the risk of explosion or combustion in the housing containing the fuel tank or fuel cell. Nitrogen is usually used as an inerting gas, and then the inert gas is provided by a nitrogen bottle or a nitrogen generation system. Nitrogen circulates in the fuel tank or fuel cell housing at a nominal rate, which is determined based on the worst case (i.e., with the maximum expected leakage). This positioning is to ensure that the limit value of the volume concentration of a flammable mixture of hydrogen and oxygen will never be reached in the gas atmosphere. The gas atmosphere mixture inside the fuel tank or fuel cell housing is then discharged to the outside of the aircraft. The concentration of hydrogen and oxygen in the gas atmosphere is maintained at many times below the safety policy limit required for fire extinguishing.

[0003] The arrangement of these nitrogen cylinders or nitrogen generation systems takes up space on the aircraft for their installation and also contributes to the onboard weight of the aircraft.

[0004] In addition, known hydrogen-based system housings are provided with a bottle of halon for discharging the halon in the event of a fire inside the housing. However, halon as a fire extinguishing agent is configured for large volumes, while hydrogen-based system housings involve smaller volumes. Furthermore, the use of halon as a fire extinguishing agent has begun to be disregarded for environmental reasons.

[0005] The present invention attempts to improve the above and other problems by improving the inerting of the fuel tank and the fuel cell housing.In addition, it is also necessary to find alternatives to extinguish fire in the event of a fire inside the housing of the fuel tank or fuel cell. Summary of the invention

[0006] The present invention provides a solution to the above mentioned problems by an inerting system according to a first aspect, an aircraft according to a second aspect and a method for inerting a hydrogen system according to a third aspect. In the present invention, preferred embodiments of the invention are also defined.

[0007] In a first inventive aspect, the present invention provides an inerting system for an aircraft, the inerting system comprising:

[0008] - a housing at least partially housing the hydrogen system, the housing comprising at least one inlet and a first outlet configured to connect the interior of the housing with the exterior of the aircraft;

[0009] - a pure inert gas supply device configured to supply pure inert gas to the interior of the housing through an inlet conduit connected to the pure inert gas supply device and to at least one inlet of the housing;

[0010] - a sensing device configured to measure an oxygen concentration and a hydrogen concentration of a fluid located inside the housing;

[0011] - an inert fluid regulating device configured to regulate the passage of pure inert gas flowing through the inlet duct to the interior of the housing;

[0012] - an outlet valve configured to regulate an outlet flow rate of a fluid located inside the housing through the first outlet;

[0013] a fluid recirculation system configured to recirculate a portion of the fluid located inside the housing to the inlet duct for supplying the recirculated fluid mixed with the pure inert gas to the interior of the housing; and

[0014] - a control device in data communication with the sensing device and configured to independently control at least the outlet valve and the fluid recirculation system based on the oxygen concentration and the hydrogen concentration inside the housing;

[0015] Therein, the control device is configured to activate the recirculation in the fluid recirculation system only when the oxygen concentration and / or the hydrogen concentration of the fluid located inside the housing is respectively below a first preset threshold value.

[0016] The inerting system is arranged to inert a hydrogen system (or hydrogen-based system) of an aircraft, such as a fuel tank or a fuel cell housing, wherein the fuel is hydrogen. The inerting system will be suitable for inerting any enclosure in an aircraft that has a relatively small free volume and needs to be inerted. In an embodiment, the hydrogen system is a fuel tank or a fuel cell.

[0017] The inerting system comprises a housing that at least partially contains or encloses the hydrogen system. The housing refers to an enclosure that contains the hydrogen system or a portion of the hydrogen system. The housing is used to contain hydrogen that may leak so that it does not diffuse outside the housing. The housing includes at least one inlet for allowing at least inert gas to be supplied to the housing. In addition, the inerted housing has a ventilation line for purging the gas atmosphere, and the ventilation line is usually connected to the outside of the aircraft.

[0018] In the gas atmosphere inside the housing, the oxygen concentration and the hydrogen concentration, respectively, must not exceed limit values ​​defined for safety reasons. In particular, oxygen must not exceed a volume concentration of 4% and hydrogen must not exceed a volume concentration of 4%.

[0019] At least one inlet is adapted with respect to its position, shape, orientation etc., to obtain as turbulent a flow as possible inside the housing, thereby avoiding local accumulations of oxygen and hydrogen.

[0020] Hydrogen systems, such as fuel cells, require hydrogen and air supplies (including oxygen) to operate. Inside the housing where the fuel cell is mounted, there are air supply pipes and hydrogen supply pipes. These pipes have a nominal leakage rate, and the inerting system is sized to take into account the worst case of the nominal leakage rate. These hydrogen supply pipes and the connections of the fuel cell are the main sources of leakage.

[0021] In order to inertate the interior of the housing, the inerting system comprises a supply device for distributing pure inert gas to the interior of the housing through the inlet by means of an inlet conduit. The inlet conduit connects the pure inert gas supply device with the inlet of the housing. There is an inert fluid regulating device for regulating the passage of the pure inert gas through the inlet conduit to the interior of the housing.

[0022] In an embodiment, the inert fluid regulating means comprises an inlet valve for regulating the flow of pure inert gas supplied to the interior of the housing through the inlet conduit. In another embodiment, the inert fluid regulating means comprises an orifice of a predetermined diameter that always allows the same flow rate to pass therethrough.

[0023] In an embodiment, the pure inert gas supplied by the supply device is nitrogen.

[0024] In an embodiment, the housing comprises a plurality of inlets (flow distributors) connected to the inlet ducts, so that the supply of pure inert gas to the interior of the housing is carried out through all of these inlets. Because the plurality of inlets allows a good mixing of the gas atmosphere in the housing to be obtained in different areas of the housing, the plurality of inlets reduces the local accumulation of oxygen and / or hydrogen inside the housing, and in some cases, turbulence flows in the housing to obtain better fluid mixing.

[0025] The inerting system also includes a sensing device for measuring the concentration of oxygen and hydrogen of a gas atmosphere or fluid contained in the housing. The fluid located inside the housing is understood to be a gaseous fluid, such as a pure gas or a gas mixture. These oxygen and hydrogen concentrations refer to the volume concentration inside the housing and are expressed as a percentage.

[0026] The inerting system further comprises an outlet valve for regulating the discharge of the fluid located inside the housing through the first outlet of the housing. The outlet valve, even in its most tight position, has a minimum orifice for letting the flow through to exit the housing.

[0027] Furthermore, the inerting system comprises a fluid recirculation system adapted to recirculate a portion of the fluid located inside the housing through the inerting system. A portion of the fluid located in the housing is recirculated to the inlet duct so as to be supplied back into the housing in a mixture with pure inert gas, thereby keeping the interior of the housing inerted.

[0028] The inerting system also includes a control device, which is connected to the sensing device so that the control device controls each of the inlet valve, the outlet valve and the fluid recirculation system individually as needed according to the data on the oxygen concentration and the hydrogen concentration provided by the sensing device. That is, if the oxygen concentration and / or hydrogen concentration conditions are suitable, a part of the fluid of the shell is recirculated by extracting a part of the fluid from the shell and re-injecting it in the case of mixing with the pure inert gas supplied by the pure inert gas supply device. When the oxygen concentration and / or the hydrogen concentration are respectively lower than the first preset threshold value, they are considered to be suitable for allowing a part of the fluid contained in the shell to be recirculated. Therefore, the control device only activates the recirculation when the oxygen concentration and / or the hydrogen concentration of the fluid of the shell is lower than such a first preset threshold value. Specifically, the term "activation" is understood to be a part of the fluid located inside the shell recirculated toward the inlet duct.

[0029] Depending on the hydrogen concentration and / or the oxygen concentration, the fluid recirculation system recirculates more or less mass flow of the fluid from the housing. If both the hydrogen concentration and the oxygen concentration of the fluid to be recirculated are below a first preset threshold, more mass flow of the fluid from the housing is recirculated and less pure inert gas is required. However, if only the hydrogen concentration or the oxygen concentration of the fluid to be recirculated is below the corresponding first preset threshold, less fluid from the housing is recirculated and more pure inert gas is required.

[0030] These first preset threshold values ​​are based on a safety policy, so that if the oxygen concentration and / or the hydrogen concentration is sufficiently far from the limit values ​​considered by the safety policy, the gas atmosphere located inside the enclosure will be partially recirculated.

[0031] Additionally, the control device is further configured to control regulation of at least the first outlet valve based on the measured concentrations of oxygen and hydrogen.In an embodiment, the control device is further configured to control regulation of the inlet valve.

[0032] The inerting system is therefore provided for inerting a volume surrounding the hydrogen system or a part of the hydrogen system in a controlled manner in order to prevent fires or the creation of a flammable gas atmosphere in undesired areas of said volume.

[0033] Advantageously, the present inerting system requires less installation space in the aircraft, since it reduces the amount of pure inert gas required for inerting by providing the possibility of partially recirculating the fluid located inside the housing. In addition, this reduction in the pure inert gas supply means (bottles or generation systems) in turn reduces the weight of the aircraft.

[0034] By means of the sensing means and the control means, the inerting system advantageously allows both the hydrogen concentration and the oxygen concentration inside the enclosure to be measured and monitored at any time, in order to be able to recirculate the fluid and prevent a fire inside the enclosure.

[0035] Furthermore, the inerting system allows providing a greater mass flow into the housing and a lower mass flow from the pure inert gas supply due to the recirculation of the fluid located inside the housing. This allows limiting local accumulations of oxygen and / or hydrogen by increasing the flow of the inerted gas circulating in the housing. It can also allow obtaining a more turbulent flow, thereby also increasing the homogeneity of the mixture of inert gas (nitrogen), oxygen and hydrogen. This homogenization advantageously prevents instantaneous points that could lead to a greater concentration of a local flammable mixture inside the housing.

[0036] Furthermore, since there is a higher mass flow entering the housing through the inlet channel, the flow velocity through the housing is greater and then the arrival time of the inerted gas atmosphere or fluid containing dangerous concentrations of oxygen or hydrogen flowing through the housing will be detected faster because it will reach the sensing device faster. Thus, the present inerting system provides for rapid detection of oxygen concentration values ​​and hydrogen concentration values ​​that may indicate a risk to the interior of the housing. For example, if a mixture of oxygen and hydrogen is present in the gas atmosphere of the housing and these gases have sufficient volume concentrations, the risk of starting a fire is higher. To this end, the present invention allows taking action before one of the first preset threshold value of oxygen concentration and the first preset threshold value of hydrogen concentration is locally reached.

[0037] Furthermore, the inerting system advantageously has the capability to adjust and vary the mass flow from the pure inert gas supply as required, based on information provided by the sensing means to the control means. Fluid inlet and outlet controls allow for continuous purging of the gas atmosphere inside the enclosure.

[0038] In an embodiment, the fluid recirculation system comprises:

[0039] a recirculation conduit connecting the interior of the housing with an inlet conduit upstream of at least one inlet of the housing;

[0040] a compressor inserted in the recirculation conduit; and

[0041] A recirculation valve located on the recirculation duct between the connection of the recirculation duct and the inlet duct and the compressor, the recirculation valve being configured to regulate the flow of the recirculation fluid towards the inlet duct.

[0042] The recirculation conduit of the fluid recirculation system connects the interior of the housing with the inlet conduit so as to mix the recirculated fluid with the pure inert gas before supplying the mixture to the housing through the inlet of the housing. The recirculation conduit of the recirculation system is connected to the inlet conduit in a section of the inlet conduit between the pure inert gas supply device and the inlet of the housing, that is, upstream of the inlet of the housing.

[0043] The recirculation system further comprises a compressor which is inserted on the recirculation conduit and is configured to compress the fluid from the interior of the housing to a pressure lower than the pressure of the pure inert gas supplied to the inlet conduit. The compressor ensures pumping of the recirculation fluid through the fluid recirculation system. The supply of the recirculation fluid to the inlet conduit must be at a lower pressure than the pure inert gas supply to prevent the recirculation fluid from flowing back in the inlet conduit to the pure inert gas inlet.

[0044] In addition, the fluid recirculation system comprises a recirculation valve, which is used to regulate the passage of the fluid from the recirculation conduit to the inlet conduit. Specifically, the recirculation valve is connected to the recirculation conduit between the connection of the recirculation conduit and the inlet conduit and the compressor.

[0045] The opening of the recirculation valve and / or the flow rate of the fluid recirculated through the compressor depends on the measured hydrogen concentration and / or oxygen concentration.

[0046] More specifically, the inerting system further comprises a mixer interposed on the inlet duct, between the inert fluid regulating device and at least one inlet of the housing, and connected to the recirculation duct, such that the mixer is configured to mix pure inert gas from the pure inert gas supply device and recirculating fluid from the fluid recirculation system.

[0047] A mixer is understood to be an enclosure inserted on the inlet duct and in fluid communication with the pure inert gas supply, the fluid recirculation system and the interior of the housing. The mixer is where the recirculating fluid is mixed with the pure inert gas before entering the interior of the housing. In an embodiment, the inlet valve regulates the passage of the pure inert gas towards the mixer, and the recirculation valve regulates the passage of the recirculating fluid towards the mixer.

[0048] The inerting system provides a flushing mode in which the flow rate of pure inert gas is increased so as to reduce the hydrogen concentration and / or oxygen concentration to below the preset flammable limit in a short time and extinguish the fire.

[0049] In an embodiment, the inerting system further comprises a fire detection device in data communication with the control device and configured to detect a fire inside the enclosure. The control device is further configured to open the inlet valve and the outlet valve at a maximum flow rate if the fire detection device detects a fire.

[0050] In another embodiment, the control device is further configured to open the inlet valve and the outlet valve at a maximum flow rate when a high concentration of oxygen or hydrogen is detected by the sensing device, that is, when the concentration of oxygen or hydrogen exceeds a third preset threshold.

[0051] In the case of opening the outlet valve at a maximum flow rate, the flammable gases are advantageously discharged from the interior of the housing. In addition, in the case of opening the inlet valve at a maximum flow rate, the flammable gases are purged from the housing and the interior of the housing is rapidly inerted again. Furthermore, in the case of opening the outlet valve at a maximum flow rate, an overpressure is avoided in the interior of the housing.

[0052] In addition, by providing the present inerting system, the use of any fire extinguishing agent (such as halon) is replaced. In addition, since the fire extinguishing agent bottle has been replaced by the fluid recirculation system that is required for shell inerting anyway, the installation space and weight of the fire extinguishing agent bottle are also saved.

[0053] The fact of having a first outlet valve for increasing the larger outlet flow portion in case of a malfunction provides an additional margin in terms of safety, since the pressure is released faster from the casing.

[0054] Furthermore, the reaction time for extinguishing the fire and re-inerting the interior of the housing by means of the inerting system is shorter compared to prior art solutions or nominal flow, ie compared to the case where the inlet valve is not opened at the maximum flow rate.

[0055] More specifically, the fire detection device may include an overpressure sensor for detecting overpressure inside the housing. In the event that overpressure inside the housing is detected, the inlet valve and the outlet valve are adjusted to release the generated overpressure.

[0056] In an embodiment, the inerting system further comprises a pressure measuring device which is in data communication with the control device and is configured to measure the pressure inside the housing, wherein the control device is configured to open the outlet valve at a flow rate higher than a preset flow rate threshold when the measured pressure exceeds a preset pressure threshold. That is, if an overpressure is detected inside the housing, the inlet valve of the housing is adjusted to release the generated overpressure and thereby achieve a greater purge of the gas atmosphere inside the housing. In addition, when an overpressure is detected inside the housing, the inlet valve may also be opened at a flow rate higher than a preset flow rate threshold to continue to inert the interior of the housing to a maximum. In this case, the outlet flow of the outlet valve is greater than the inlet flow of the inlet valve to prevent an increase in pressure in the housing.

[0057] In an embodiment, the sensing means comprises at least a first sensor for measuring oxygen concentration and at least a second sensor for measuring hydrogen concentration. Advantageously, the sensing means allow measuring hydrogen concentration and oxygen concentration so that the control means determines whether the fluid contained in the enclosure can be recirculated.

[0058] In an embodiment, the sensing device is located in the housing, and / or in the fluid recirculation system, and / or in an exhaust duct connected to the first outlet of the housing. Providing sensing devices in the housing, the fluid recirculation system and the exhaust duct allows measuring the concentration of oxygen and hydrogen at different points of the fluid flow contained in the housing in the inerting system.

[0059] In an embodiment, the sensing device is located in the housing and / or in a recirculation duct of the fluid recirculation system upstream of the compressor.

[0060] In an embodiment, there are multiple sensing devices located in the housing in order to cover several areas in the housing and thus avoid local accumulation of oxygen and hydrogen.

[0061] In a second inventive aspect, the invention provides an aircraft comprising an inerting system according to the first inventive aspect.

[0062] In a third inventive aspect, the invention provides a method for inerting a hydrogen system of an aircraft by means of an inerting system, the hydrogen system being at least partially accommodated in an enclosure, wherein the method comprises:

[0063] (a) supplying pure inert gas through a pure inert gas supply device;

[0064] (b) discharging a portion of the fluid located inside the housing through the first outlet by means of the first outlet valve;

[0065] (c) monitoring the oxygen concentration and hydrogen concentration inside the housing by means of a sensing device;

[0066] (d) recirculating a portion of the fluid located inside the housing through a fluid recirculation system of the inerting system when the hydrogen concentration and / or oxygen concentration of the fluid to be recirculated is below a first preset threshold value; and

[0067] (e) Supplying a recirculating fluid mixed with pure inert gas to the interior of the housing.

[0068] The method aims at inerting a hydrogen system or a part of a hydrogen system, in particular a housing enclosing a hydrogen system or a part of a hydrogen system, such as a fuel tank or a fuel cell housing in which the fuel is hydrogen, by means of an inerting system. In an embodiment, the inerting system for inerting a hydrogen system or a part of a hydrogen system is according to the first inventive aspect. The hydrogen system of an aircraft is enclosed in an inerted housing in order to keep the hydrogen system inert.

[0069] The method comprises the step of supplying pure inert gas by means of a pure inert gas supply device so that the pure inert gas flows to the interior of the housing through at least one inlet of the housing. This step is used to establish an inert gas atmosphere inside the housing containing the hydrogen system or a part of the hydrogen system. Once the interior of the housing is inerted, the hydrogen system starts its normal operation. In an embodiment, the pure inert gas is nitrogen.

[0070] The method also includes the step of discharging a portion of the fluid located inside the housing through a first outlet of the housing. The first outlet of the housing connects the interior of the housing with the exterior of the aircraft. That is, a portion of the gas atmosphere generated inside the housing is released toward the exterior of the aircraft.

[0071] The method further comprises the step of recirculating a portion of the fluid contained inside the housing through a fluid recirculation system of the inerting system. This recirculation is performed only if the hydrogen concentration and / or oxygen concentration inside the housing is below a first preset threshold value. After this step, the method comprises supplying the interior of the housing with the recirculated fluid mixed with pure inert gas.

[0072] Advantageously, the method allows reusing pure inert gas that has been supplied and mixed with other gases in the enclosure as long as the conditions of the fluid contained in the enclosure allow, ie as long as the hydrogen concentration and the oxygen concentration remain below a first preset threshold value.

[0073] In an embodiment, the fluid recirculation system recirculates fluid from the housing as long as the sensing device measures a hydrogen concentration below a first hydrogen preset threshold and / or an oxygen concentration below a first oxygen preset threshold.

[0074] The sensing means is adapted to measure the hydrogen concentration and the oxygen concentration to enable the control means to determine whether the fluid contained in the enclosure may be recirculated.

[0075] In another embodiment, the method further comprises the step of monitoring the pressure inside the housing by means of a pressure measuring device in data communication with the control device, wherein, in the case where the pressure inside the housing is determined by the control device to exceed a preset pressure threshold, the control device opens a first outlet valve for discharging pressure from the housing until the pressure inside the housing is the same as the pressure outside the aircraft. The control device determines whether there is an overpressure inside the housing based on the pressure measured by the pressure measuring device. More specifically, when it is determined that the pressure inside the housing exceeds a preset pressure threshold, the control device also opens an inlet valve for supplying pure inert gas to the interior of the housing. In addition, when an overpressure inside the housing is detected, the first outlet valve and / or the inlet valve are opened at a flow rate higher than a preset flow rate threshold. According to a normal working mode of the inerting system, the pressure inside the housing is slightly higher than outside so as to limit the intake of oxygen from the air surrounding the housing in the case of limited leakage of the housing.

[0076] In an embodiment, when the hydrogen concentration inside the shell exceeds a second preset threshold and / or the oxygen concentration inside the shell exceeds a second preset threshold, the control device opens the first outlet valve at a flow rate higher than a preset threshold to discharge the fluid from the shell, and opens the inlet valve to supply pure inert gas to the interior of the shell until the hydrogen concentration and the oxygen concentration are lower than the second preset threshold.

[0077] When the oxygen concentration or the hydrogen concentration or both exceed the second preset threshold, the system is reconfigured to discharge the fluid contained in the shell and re-inert the inside of the shell, but without recirculation, that is, the recirculation system stops working.

[0078] In an embodiment, in case the hydrogen concentration and / or oxygen concentration inside the enclosure exceeds a third preset threshold, or in case a fire is detected inside the enclosure, the control device opens the inlet valve and the first outlet valve at a maximum flow rate.

[0079] In an embodiment, if the hydrogen concentration and the oxygen concentration are below corresponding first preset thresholds, the mass flow rate for recirculation through the compressor of the fluid recirculation system is increased, and the mass flow rate from the pure inert gas supply device is reduced in the inlet duct to reduce the oxygen concentration and the hydrogen concentration inside the shell as needed.

[0080] In an embodiment, if the hydrogen concentration or the oxygen concentration is below the corresponding first preset threshold, the mass flow rate recirculated through the compressor of the fluid recirculation system is reduced, and the mass flow rate from the pure inert gas supply device is increased in the inlet duct to reduce the oxygen concentration or the hydrogen concentration inside the shell as needed.

[0081] In an embodiment, the first preset threshold is consistent with the second preset threshold, so that there is a single preset threshold that sets whether the fluid in the housing can be recirculated. That is, if the oxygen concentration and the hydrogen concentration are below the preset threshold, then recirculation can be performed, but if the oxygen concentration and the hydrogen concentration are above the threshold, then recirculation cannot be performed. In addition, if only one of the oxygen concentration or the hydrogen concentration is below the above threshold, then recirculation can be performed, but less fluid is recirculated as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] These and other features and advantages of the present invention will be clearly understood in view of the detailed description of the present invention which will become apparent from the preferred embodiments of the present invention, which are given by way of example only and not limited thereto, with reference to the accompanying drawings.

[0083] Figure 1 : The figure shows a schematic diagram of an inerting system according to an embodiment of the present invention.

[0084] Figure 2 : The figure shows a schematic diagram of an inerting system according to another embodiment of the present invention.

[0085] Figure 3 : The figure shows a schematic diagram of an aircraft having an inerting system according to the invention. DETAILED DESCRIPTION

[0086] Figure 1 and Figure 2 An inerting system suitable for inerting the housing 1 of a hydrogen fuel cell 12 is shown, the inerting system having Figure 1 and Figure 2 The fluid recirculation system S is arranged differently in each of the embodiments. The inerting system is configured to be installed in the aircraft 10. Specifically, Figure 3 shows suitable for including according to Figure 1 and Figure 2 Any inerting system of the aircraft 10 is included in the inerting system.

[0087] There is a housing 1 in which a hydrogen fuel cell 12 is housed. The housing 1 comprises one inlet 1.1 and a first outlet 1.2 allowing a fluid to flow through the housing 1. The inlet 1.1 is connected to an inlet duct 3 and the first outlet 1.2 is connected to an exhaust duct 14. The inlet duct 3 is in turn connected to a pure inert gas supply 2 adapted to supply nitrogen to inertate the interior of the housing 1. On the other hand, the first outlet 1.2 is configured to be connected to the exterior of the aircraft 10. The inlet flow rate of the fluid through the inlet 1.1 corresponds to the mass flow rate or m into the housing 1. in The outlet flow rate of the fluid through the first outlet 1.2 corresponds to the mass or m leaving the aircraft 10 and not returning.out .

[0088] The inertization system also shows an inlet valve 7 of the inert fluid regulating device inserted on the inlet conduit 3, and the inlet valve 7 is used to regulate the flow rate of nitrogen supplied by the pure inert gas supply device 2 to the interior of the housing 1. That is, nitrogen is supplied to the interior of the housing 1 through the inlet conduit and the flow rate of nitrogen is regulated by the inlet valve 7. This inlet flow rate of nitrogen through the inlet conduit 3 corresponds to the mass flow rate or m from the pure inert gas supply device 2. a .

[0089] These Figure 1 and Figure 2 The inerting system also shows an outlet valve 8 inserted in the exhaust duct 14 for regulating the outlet flow of the fluid from the interior of the housing 1 through the first outlet 1 . 2 .

[0090] The inerting system further comprises a fluid recirculation system S for recirculating a portion of the fluid contained in the housing 1. This recirculation comprises recirculating the fluid from inside the housing 1 to the inlet duct 3 and back into the housing 1 together with nitrogen supplied by the pure inert gas supply 2. The inerting system further shows a mixer 11 inserted on the inlet duct 3. In particular, the mixer 11 is arranged between the inlet valve 1.1 and the inlet 1.1 of the housing 1.

[0091] The fluid recirculation system S comprises a recirculation conduit 5 connecting the interior of the housing 1 with the mixer 11. Figure 1 , the recirculation duct 5 is arranged between the second outlet 1.3 of the housing 1 and the mixer 11, and according to Figure 2 , the recirculation duct 5 is arranged between the exhaust duct 14 and the mixer 11. Figure 1 and Figure 2 In both, the fluid recirculation system S further includes a compressor 6, which is inserted on the recirculation conduit 5 and is configured to pump the fluid from the interior of the housing 1 and is used to adjust the pressure of the recirculation fluid so as to adjust the pressure of the recirculation fluid to be lower than the pressure of the supplied nitrogen. The inlet flow rate of the recirculation flow through the outlet of the recirculation conduit 5 corresponds to the mass flow rate or m recirculated by the compressor 6. c .

[0092] The fluid recirculation system S further comprises a recirculation valve 9 arranged between the connection of the recirculation duct 5 and the mixer 11 and the compressor 6. The regulating valve 9 is arranged for regulating the inlet of the recirculation fluid towards the recirculation duct 3.

[0093] The inerting system further comprises a sensing device 4 for measuring the oxygen concentration and the hydrogen concentration inside the housing 1. In particular, the sensing device 4 comprises a first sensor 4.1 for measuring the oxygen concentration and a second sensor 4.2 for measuring the hydrogen concentration. Figure 1 , the first sensor 4.1 and the second sensor 4.2 are located on the housing 1, the recirculation duct 5 and the exhaust duct 14. In contrast, in Figure 2 In the embodiment, the first sensor 4 . 1 and the second sensor 4 . 2 are located on the housing 1 and the recirculation duct 5 .

[0094] The inerting system further comprises a control device 13 which independently controls the inlet valve 7, the outlet valve 8, the compressor 6 and the recirculation valve 9. In addition, the control device 13 performs data communication with the sensing device 4 in order to determine the oxygen concentration and the hydrogen concentration inside the housing 1 and whether the fluid recirculation system S can be actuated. That is, only when the control device 13 determines that the oxygen concentration and / or the hydrogen concentration are respectively lower than the first preset threshold value, the fluid can be recirculated from the interior of the housing 1 toward the inlet duct 3 to be supplied to the interior of the housing 1 again in the case of mixing with nitrogen.

[0095] according to Figure 1 and Figure 2 The inerting system further comprises a fire detection device (not shown) arranged in contact with the housing 1. The fire detection device is also in data communication with the control device 13, so that if the fire detection device detects a fire inside the housing 1, the control device 13 opens the inlet valve 7 at a maximum flow rate in order to supply nitrogen at the maximum possible flow rate, and also opens the outlet valve 8 at a maximum flow rate in order to allow the gas atmosphere contained in the housing 1 to be quickly discharged.

[0096] Furthermore, the inerting system comprises a pressure measuring device (not shown) which is arranged in contact with the housing 1 and is configured to measure the pressure inside the housing 1. The pressure measuring device is also in data communication with the control device 13, so that if the control device 13 determines that there is an overpressure inside the housing 1, that is, the pressure inside the housing 1 exceeds a preset pressure threshold, the control device 13 opens the inlet valve 7 or opens the inlet valve 7 and the outlet valve 8 at a flow rate higher than a preset flow rate threshold, so as to reduce the pressure of the fluid contained inside the housing 1.

[0097] Method for inerting a hydrogen system of an aircraft

[0098] The present invention also provides a method for inerting a hydrogen system of an aircraft 10 by means of an inerting system. An example of a method for inerting a housing 1 of a fuel cell 12 in an aircraft 10 is explained below, wherein the inerting is carried out by the above description of Figure 1 and Figure 2 Any of the inerting systems described herein is performed.

[0099] The method comprises a first step a of supplying nitrogen to the interior of the housing 1 through the inlet 1.1 by means of a pure inert gas supply 2. The control device 13 controls the operation of the inlet valve 7 for regulating the flow rate of nitrogen supplied through the inlet duct 3 towards the interior of the housing 1, that is to say for regulating m a If the inert gas atmosphere is to be generated in the housing 1 for the first time, the inlet valve 7 is opened to its maximum flow rate to allow rapid inerting of the housing 1 and, in this case, m a With m in same.

[0100] During the inerting process, there must be not only a fluid inlet but also a fluid outlet inside the housing 1 so that the fluid flows continuously through the housing 1. To this end, the method comprises a step b of discharging a portion of the fluid contained inside the housing 1 through the first outlet 1.2 of the housing 1. The control device 13 also controls the operation of the outlet valve 8 for regulating the outlet flow from the housing 1, that is, for regulating m out The control device 13 controls the operation of both the inlet valve 7 and the outlet valve 8 so that there is always a fluid flow through the housing 1, thereby maintaining m in the housing 1. a Equal to m out balance.

[0101] During the inerting, the method also monitors, according to step (c), the oxygen concentration and the hydrogen concentration inside the enclosure 1. This monitoring is performed by means of sensing means 4 which continuously measure these concentrations.

[0102] Based on the data measured by the sensing device 4, the control device 13 determines whether a portion of the fluid contained in the housing 1 can be recirculated by the fluid recirculation system S. That is, according to step d of the method, if the control device 13 determines that the oxygen concentration and / or hydrogen concentration of the fluid or gas atmosphere inside the housing 1 is lower than the first preset threshold value, the control device 13 controls the recirculation of a portion of the fluid located inside the housing 1, that is, the recirculation system S starts to work.

[0103] While inerting is being performed, if the control device 13 determines that fluid recirculation can be performed, the compressor 6 is operated to pump fluid from the interior of the housing 1 along the recirculation conduit 5, that is, to pump m c , and then control the recirculation valve 9 to adjust the passage of the recirculating fluid to the mixer 11. During fluid recirculation, control the inlet valve 7 to reduce m a , in order to compensate for some of the nitrogen not supplied by the recirculating fluid. In the case of recirculation, m a +m c Equal to min .

[0104] In an embodiment, according to the safety policy limits required for fire extinguishing, the first preset threshold value for oxygen is below 4%, and according to the safety policy the first preset threshold value for hydrogen is below 4%. For both oxygen concentration and hydrogen concentration, the concentration limit that may create a flammable risk inside the enclosure is 4%.

[0105] In the inerting method, there is also a step of monitoring the pressure inside the housing 1 by means of a pressure measuring device (not shown), which performs data communication with the control device 13. If the control device 13 determines that the pressure inside the housing 1 exceeds a preset pressure threshold based on the data (measured pressure) provided by the pressure measuring device, the first outlet valve 8 is opened at a flow rate higher than a preset threshold for exhausting the pressure from the housing 1. At the same time, the inlet valve 7 may also be opened at a flow rate higher than a preset threshold for supplying nitrogen to the inside of the housing 1 until the pressure in the housing 1 reaches the same pressure as outside the aircraft 10. The preset pressure threshold and the preset flow rate threshold may vary depending on the configuration of the housing and the hydrogen system.

[0106] Furthermore, if the control device 13 determines that the hydrogen concentration and / or oxygen concentration inside the housing 1 exceeds a second preset threshold, both the inlet valve 7 and the first outlet valve 8 are opened at a flow rate higher than a preset threshold to quickly purge the fluid contained in the housing 1 until the hydrogen concentration and / or oxygen concentration inside the housing 1 reach a hydrogen concentration and an oxygen concentration below the second preset threshold. In the example, the second preset threshold is a hydrogen volume concentration of 0.75% and an oxygen volume concentration of 2%.

[0107] Furthermore, the method comprises the step of extinguishing a fire inside the housing 1 when the fire detection device of the inerting system detects a fire inside the housing 1. For example, to cause a fire, there must be an air supply leak inside the housing 1, there must be an overpressure inside the housing 1, and there must also be a small amount of hydrogen leak. All of these can cause a fire, thereby locally consuming a portion of the oxygen inside the housing 1. Although the hydrogen fuel cell 12 is cut off at the moment of the fire, there is always residual hydrogen in the pipeline of the hydrogen fuel cell 12.

[0108] In order to extinguish the fire in the housing 1, both the inlet valve 7 and the first outlet valve 8 are opened at a maximum flow rate to exhaust the affected gas atmosphere inside the housing 1 as quickly as possible and to generate a new inerted gas atmosphere. Specifically, the first outlet valve 8 is first opened for flushing oxygen and / or hydrogen, but the pressure in the housing 1 increases due to the fire. Then, the inlet valve 7 is fully opened to smother the fire, with the aim of obtaining a lower oxygen concentration and hydrogen concentration inside the housing 1. In an embodiment, when the inerting system is operated to extinguish the fire inside the housing 1 as described above, the oxygen concentration drops below 4%. Therefore, when the volume concentration of oxygen is lower than 4%, the fire cannot stably occur inside the housing 1. In an embodiment, according to the safety policy restrictions required for fire extinguishing, the flammability limit for hydrogen concentration is 4%, and the flammability limit for oxygen concentration is 4%.

[0109] The nitrogen mass flow rate can be increased as required and is related to the free volume of the enclosure and the time required to inert the enclosure again in the event of a fault or fire inside the enclosure.

Claims

1. An inerting system, the inerting system being used for an aircraft (10), the inerting system comprising: A housing (1) at least partially containing a hydrogen system, the housing (1) comprising at least one inlet (1.1) and a first outlet (1.2), the first outlet (1.2) being configured to connect the interior of the housing (1) with the exterior of the aircraft (10); a pure inert gas supply device (2), the pure inert gas supply device (2) being configured to supply pure inert gas to the interior of the housing (1) via an inlet duct (3) connected to the pure inert gas supply device (2) and to at least one inlet (1.1) of the housing (1); a sensing device (4) configured to measure the oxygen concentration and the hydrogen concentration of the fluid located inside the housing (1); an inert fluid regulating device configured to regulate the passage of pure inert gas flowing through the inlet conduit (3) to the interior of the housing (1); an outlet valve (8), the outlet valve (8) being configured to regulate an outlet flow rate of a fluid located inside the housing (1) through the first outlet (1.2); a fluid recirculation system (S) configured to recirculate a portion of the fluid located inside the housing (1) to the inlet duct (3) for supplying the recirculation fluid mixed with the pure inert gas to the interior of the housing (1); as well as a control device (13) in data communication with the sensing device (4) and configured to independently control at least the outlet valve (8) and the fluid recirculation system (S) based on the oxygen concentration and the hydrogen concentration inside the housing (1); The control device (13) is configured to activate recirculation in the fluid recirculation system (S) only when the oxygen concentration and / or hydrogen concentration of the fluid inside the housing (1) is respectively lower than a first preset threshold value.

2. Inerting system according to the preceding claim, wherein: The fluid recirculation system (S) comprises: a recirculation duct (5) connecting the interior of the housing (1) with the inlet duct (3) upstream of at least one inlet (1.1) of the housing (1); a compressor (6) inserted into the recirculation conduit (5); and A recirculation valve (9) is located on the recirculation duct (5) between the connection between the recirculation duct (5) and the inlet duct (3) and the compressor (6), and the recirculation valve (9) is configured to regulate the flow of the recirculating fluid toward the inlet duct (3).

3. The inerting system according to the preceding claim further comprises a mixer (11) which is inserted on the inlet duct (3), between the inert fluid regulating device and at least one inlet (1.1) of the housing (1), and is connected to the recirculation duct (5), such that the mixer (11) is configured to mix pure inert gas from the pure inert gas supply (2) and recirculating fluid from the fluid recirculation system (S).

4. An inerting system according to any one of the preceding claims, wherein: The inert fluid regulating device comprises an inlet valve (7), and the control device (13) is also configured to control the inlet valve (7).

5. The inerting system according to the preceding claim, further comprising a fire detection device which is in data communication with the control device (13) and is configured to detect a fire inside the housing (1), wherein: The control device (13) is also configured to open the inlet valve (7) and the outlet valve (8) at a maximum flow rate if the fire detection device detects a fire.

6. The inerting system according to any one of claims 4 to 5, further comprising a pressure measuring device, which is in data communication with the control device (13) and is configured to measure the pressure inside the housing (1), wherein: The control device (13) is configured to open the outlet valve (8) above a preset flow rate threshold if the measured pressure exceeds a preset pressure threshold.

7. An inerting system according to any one of the preceding claims, wherein: The sensing device (4) comprises at least a first sensor (4.1) for measuring the oxygen concentration and at least a second sensor (4.2) for measuring the hydrogen concentration.

8. An inerting system according to any one of the preceding claims, wherein: The sensing device (4) is located in the housing (1), and / or in the fluid recirculation system (S), and / or in an exhaust duct (14) connected to a first outlet (1.2) of the housing (1).

9. An inerting system according to any one of the preceding claims, wherein: The pure inert gas is nitrogen.

10. An inerting system according to any one of the preceding claims, wherein: The hydrogen system is a fuel tank or a fuel cell (12).

11. An aircraft (10) comprising an inerting system according to any one of the preceding claims.

12. A method for inerting a hydrogen system of an aircraft (10) by means of an inerting system, the hydrogen system being at least partially accommodated in a housing (1), wherein: The method comprises: (a) supplying pure inert gas through a pure inert gas supply device (2); (b) discharging a portion of the fluid inside the housing (1) through a first outlet (1.2) by means of a first outlet valve (8); (c) monitoring the oxygen concentration and hydrogen concentration inside the housing (1) by means of a sensing device (4); (d) recirculating a portion of the fluid located inside the housing (1) through the fluid recirculation system (S) of the inerting system when the hydrogen concentration and / or oxygen concentration of the fluid to be recirculated is below a first preset threshold value; and (e) supplying the recirculating fluid mixed with pure inert gas to the interior of the housing (1).

13. The method according to the preceding claim, wherein: The fluid recirculation system (S) recirculates fluid from the housing (1) as long as the sensing device (4) measures a hydrogen concentration below a first hydrogen preset threshold and / or an oxygen concentration below a first oxygen preset threshold.

14. The method according to claim 12, further comprising the step of monitoring the pressure inside the housing (1) by means of a pressure measuring device in data communication with the control device (13), wherein: When the control device (13) determines that the pressure inside the housing (1) exceeds a preset pressure threshold, the control device (13) opens the first outlet valve (8) to discharge the pressure from the housing (1) until the pressure inside the housing (1) is the same as the pressure outside the aircraft (10).

15. The method according to claim 12 or 14, wherein: When the hydrogen concentration inside the housing (1) exceeds a second preset threshold value and / or the oxygen concentration inside the housing (1) exceeds a second preset threshold value, the control device (13) opens the first outlet valve (8) at a flow rate higher than a preset threshold value to discharge the fluid from the housing (1), and opens the inlet valve (7) to supply pure inert gas to the interior of the housing (1) until the hydrogen concentration and the oxygen concentration are lower than the second preset threshold value.

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