Patent Application
20250229910
This application claims the benefit of European Patent Application Number 24382043.8 filed on Jan. 17, 2024, the entire disclosure of which is incorporated herein by way of reference.
The present invention relates to an inerting system for an aircraft and a method of inerting fuel cell systems. More particularly, the invention relates to an improved inerting system that injects inert gas around fuel cells in a distributed manner to ensure a correct dissolution of flammable agents that could appear around the fuel cells.
It is well-known to those skilled in the art to inert explosive or flammable atmospheres on-board an aircraft with inert gas (such as nitrogen), such as for example fuel tanks or fuel cells, by providing inert gas to the inside of the casings housing the hydrogen-based systems. Hydrogen is a gas with a very high permeability. This makes it challenging to contain hydrogen gas inside an enclosure. The inerting is performed in order to avoid risks of explosion or flames in casings housing fuel cells. It is common to use nitrogen as inerting gas, the inert gas being provided by nitrogen bottles or nitrogen generation systems. The nitrogen circulates in the fuel cells casing at a nominal rate, determined based on a worst case scenario (i.e., with the maximum nominal case scenario leakages). This sizing is made to ensure that the limits of a flammable mixture of hydrogen and oxygen in volumetric concentration are never reached in this atmosphere. The mix of the atmosphere or fluid inside the fuel tank or fuel cell casing is then expelled to the outside of the aircraft. The concentration of hydrogen and oxygen in this atmosphere is maintained many times below the required safety policy limits.
The injection of inert gas is currently performed as a generic injection of inert gas in the enclosure of the fuel cells. This enclosure could be defined as a “container” or “casing”. The term “injector” is used to define the inlet of inert gas (such as nitrogen) in the volume to be inerted. This injection is usually made taking into account a generic position and the capacity to supply the different flows needed. The quantity of inert gas injected is calculated to be able to dissolve a certain quantity of nominal leaks that can occur in such volume.
A common way to integrate fuel cells inside a casing is vertically placing such fuel cells side by side inside the casing according to a direction parallel to the longitudinal direction of an aircraft when the casing is on-board of the aircraft. In this case, the inert gas flow is injected from the inferior part of the casing, that is, bellow the fuel cells and an outlet is provided above the fuel cells. With this configuration, the risk of locally hydrogen accumulation surrounding the fuel cells is lower compared with other configuration of fuel cells inside the casing. However, such a solution cannot be adopted for fuel cells arranged horizontally, stacked one over the other in the casing.
The present invention seeks to solve the problems mentioned above and others by improving the inerting of fuel cells casing with a distributed injection of inert gas.
The present invention provides an inerting system according to one or more embodiments described herein, an aircraft according to one or more embodiments described herein, and a method for inerting a fuel cell system according to one or more embodiments described herein.
In a first inventive aspect, the present invention provides an inerting system adapted for inerting a fuel cell system for an aircraft, the fuel cell system comprising a set of fuel cells stacked next to each other along a longitudinal direction X-X′ and with a free space between consecutive fuel cells; the inerting system comprising:
the first outlet of the casing is arranged over the stack of fuel cells according to the longitudinal direction X-X′; and
the fluid injection device comprises,
each distribution channel comprises a plurality of injectors distributed longitudinally along the distribution channel and configured to inject fluid towards the free space between two fuel cells or the free space between a fuel cell and the casing.
The present inerting system is provided for inerting any enclosure that has a relatively small free volume and that needs to be inerted in an aircraft, and specifically for inerting fuel cell systems for aircraft wherein the fuel is hydrogen. For the present invention, the fuel cell system comprises a set of fuel cells stacked next to each other in a longitudinal direction X-X′ with a free space between each two fuel cells, i.e., the fuel cells are arranged horizontally, stacked one over the other along the longitudinal direction X-X′, with a free space between each two consecutive fuel cells.
The longitudinal direction X-X′ is the stacking direction of the fuel cells inside the casing. When the present inerting system is on-board the aircraft, the longitudinal direction X-X′ is substantially parallel to the vertical direction of the aircraft. This vertical direction of the aircraft is orthogonal to the horizontal plane containing the longitudinal direction of the aircraft. According to this longitudinal direction or stacking direction of the fuel cells, the casing comprises a bottom or lower surface, a top or upper surface and a plurality of lateral walls or lateral surfaces enclosing such lower and upper surfaces. For the present invention, relative terms such as “upper, lower, lateral, above, over etc.” are referred with respect to the longitudinal direction X-X′ or stacking direction of the fuel cells.
The inerting system comprises a casing that houses or encloses a fuel cell system or at least the set of fuel cells. Casing means an enclosure, which houses the fuel cell system or at least the set of fuel cells. This casing is used to contain a potential leak of hydrogen so that it does not extend outside the casing. The casing comprises a bottom, a top and a plurality of lateral walls, wherein each lateral wall extends from the bottom to the top in the longitudinal direction X-X′. That is, the bottom is connected to the top through the lateral walls.
The set of fuel cells is provided inside the casing keeping a free space between each fuel cell and any of the bottom, top and lateral walls of the casing. In this sense, inside the casing there are free spaces between fuel cells and between the fuel cells and the surfaces of the casing, i.e., free spaced between fuel cells and any of the following: bottom, top and lateral walls of the casing.
In an embodiment, the fuel cell system comprises a balance of plant arranged partially inside the casing and separated from the fuel cells. There is also a free space surrounding the balance of plant. The balance of plant is understood as the systems for regulating flows of hydrogen and air before being injected at their reaction sites in the fuel cells.
The casing comprises a first outlet configured to connect the inside of the casing with the outside of the aircraft. Specifically, this first outlet is understood as a vent line to purge the fluid inside the casing and this vent connects with the outside of the aircraft. In addition, this first outlet of the casing is arranged over the stack of fuel cells according to the longitudinal direction X-X′, i.e., the first outlet is far away from the stack of fuel cells. In this sense, the first outlet is at a distance from the bottom of the casing that is greater than the distance between the bottom and the last fuel cells of the stack furthest from the bottom. In an embodiment, the stack of fuel cells is arranged inside the casing closer to the bottom of the casing. In an embodiment, the first outlet is at the top of the casing to take advantage of the fact that hydrogen is a lighter gas and will tend to go to the top of the casing naturally.
In the fluid housed inside the casing the oxygen concentration and the hydrogen concentration shall not be respectively higher than limits defined for safety reasons. In particular, oxygen shall not overpass 4% of volumetric concentration and hydrogen shall not overpass 4% of volumetric concentration.
Inside the casing, where the fuel cells are installed, are placed air supply pipes and hydrogen supply pipes. The joints between these pipes may also have nominal leakages and the inerting system is sized taking into consideration the worst case scenario of nominal leakages. The connectors of these hydrogen supply pipes and the fuel cells are the main sources of leakages.
For inerting the inside of the casing, the inerting system comprises supplying means for supplying inert gas to the present system and a fluid injection device for dispensing a fluid to the inside of the casing. In addition, the inerting system comprises an inlet channel through which a fluidic connection is maintained between the inert gas supplying means and the fluid injection device. The fluid dispensed inside the casing comprises mainly inert gas. In an embodiment, the inert gas is nitrogen. In an embodiment, the inert gas is pure nitrogen. In an embodiment, the inert gas is a combination of pure nitrogen with recirculated fluid from the casing. The meaning of “recirculated fluid” is defined below regarding a fluid recirculation system. Moreover, the fluid located inside the casing is understood as a gas fluid such as a pure gas or a gas mix.
Specifically, the fluid injection device comprises a main channel and at least two distribution channels. The main channel is connected to the inlet channel. The distribution channels are connected to the main channel and arranged in a distributed manner one above the other according to the longitudinal direction X-X′. The term “distributed” is not necessarily equal to evenly distributed. According to the invention, each distribution channel is located at a different height along the longitudinal direction X-X′.
Each distribution channel comprises a plurality of injectors longitudinally distributed along the distribution channel so that there are rows of injectors distributed at different heights along the longitudinal direction X-X′. These injectors are configured to inject fluid towards the free space between two fuel cells or the free space between a fuel cell and the casing.
The injectors are arranged in different rows so that the injectors of a distribution channel are arranged along one row. In an embodiment, a row of injectors is arranged in an area inside the casing comprised in any of the free space.
Furthermore, the inerting system comprises means for regulating fluid flowing through the inerting system, specifically for regulating fluid at least partially comprising inert gas.
The inerting system is therefore provided for inerting the volume around the fuel cells in a distributed manner to prevent the local accumulation of hydrogen and/or oxygen, which may otherwise create a flammable fluid in this volume.
Advantageously, the present inerting system is provided with a specific and improved fluid injection device to inject inert gas into the casing in a distributed manner so that the inert gas flows around the fuel cells in a way that ensures the correct dilution of possible flammable agent. The present fluid injection device is able to inject the inert gas towards the free spaces already mentioned above to have a good drag of the fluid surrounding the fuel cells. That is, the inert gas is not directly sent towards the outlet of the casing but provides a circulation of inerted fluid in the casing that allow to minimize non-ventilated volumes in the casing, thereby minimizing local accumulation of flammable gases. Turbulences may also be created inside the casing in order to increase the dilution of potentially local accumulation of flammable gases, giving as result a very homogeneous mixture in all the casing volume
Moreover, the present fluid injection device allows injecting inert gas inside the casing homogeneously enough to drag the fluid close to the interfaces where the leak of flammable fluid can be present. The inert gas flow that is injected has enough velocity around the surfaces where the leak can be present.
In an embodiment, the outlet of the injectors inside the casing is arranged separated from the lower surface of a fuel cell a distance preferably higher than 10 mm and lower than a half of the distance between the lower surface of a top fuel cell and the top surface of the lower fuel cell.
In an embodiment, the fluid injection device is located outside the casing so that the injectors of each distribution channel pass through the casing for injecting fluid inside the casing, each injector being an inlet to the inside of the casing. In this embodiment, the main channel and the distribution channels are located outside the casing whilst the injectors or at least part of the injectors is/are located inside the casing. In an embodiment, the injectors pass through the at least one of the lateral walls of the casing.
In an embodiment, the fluid injection device is located inside the casing so that the inlet channel passes through the casing. In this embodiment, the main channel and the distribution channel are located with the injectors inside the casing. In an embodiment, the inlet channel passes through any of the lateral walls of the casing.
In an embodiment, the fluid injection device is built into the casing.
In an embodiment, the main channel is partially arranged parallel to the longitudinal direction X-X′. In an embodiment, the distribution channels are arranged perpendicular to the longitudinal direction X-X′.
In an embodiment,
Specifically, the additional injectors injects fluid from the bottom of the casing along a free space between the stack of fuel cells and one of the lateral walls of the casing according to the longitudinal direction X-X′.
Advantageously, the additional distribution channel evacuates fluid more quickly preventing inside the casing the accumulation of flammable gas which can leak out.
In an embodiment, the distribution channels are arranged on a same side of the stack of fuel cells. In this embodiment, the injectors are configured to inject fluid according to a same first direction from one lateral wall of the casing to an opposite lateral wall of the casing. In this sense, the fluid is injected only from one lateral wall of the casing, that is, from one side of the stack of fuel cells relative to the longitudinal direction X-X′. The term “side” will be understood as the space beside the stack of fuel cells for each of the faces of the stack, that is, the side of the stack of fuel cells is the area next to the stack. If the fluid injection device is located inside the casing, the distribution channels and their respective injectors are all positioned on the same side of the stack of fuel cells, i.e., between the stack of fuel cells and at least one of the lateral walls of the casing. On the other hand, if the fluid injection device is located outside the casing, the distribution channels are positioned beyond one of the casing lateral walls while the respective injectors are located between these distribution channels and said lateral wall of the casing. In any of these embodiments, the fluid is injected from a same side of the stack of fuel cells.
In an embodiment, at least
In other words, the distribution channels are arranged alternatively between two different sides of the stack of fuel cells so that for each free space fluid is injected from different sides of the stack of fuel cells. According to the longitudinal direction X-X′, there is a first row of injectors for injecting fluid in a first direction for a first free space inside the casing. A second row of injectors for injecting fluid in a second direction for a second free space consecutive to the first free space, and so on, alternating injection from at least two sides of the stack of fuel cells. The first direction of injection being different from the second direction. In this embodiment, there are not two rows of injectors on the same side of the stack of fuel cells for the same free space to inject fluid into but alternate from each side of the stack for each free space.
In this embodiment, for each free space between fuel cells and between a fuel cell and the casing, there is a row of injectors located at any of the two sides of the stack of fuel cells, i.e., injecting fluid from any of two lateral walls of the casing. According to the longitudinal direction X-X′, for a first free space, such as the free space between the casing bottom of the casing and a first fuel cell, a first row of injectors is located on a first side of the stack of fuel cells for injecting fluid from a first side of the stack in a first direction. For a second free space, consecutive to the first free space, such as a free space between the first fuel cell and a second fuel cell, a second row of injectors is located on a second side of the stack of fuel cells, for injecting fluid from the second side in a second direction different. The second side being different from the first side and the second direction being different from the first direction. For a third free space, consecutive to the second free space, such as a free space between the second fuel cell and a third fuel cell, a third row of injectors is located on the first side of the stack of fuel cells for injecting fluid from the first side according to the first direction. This would continue in a similar manner for each additional fuel cell in the stack, that is, alternating which side of the stack the fluid is injected from.
With the configuration of the above embodiment of alternating rows of injectors in height (according to the longitudinal direction X-X′), a wave or snake shaped fluid flow in the inside of the casing around the fuel cells is achieved. Thus ensuring that all or almost all of the fluid around the fuel cells is swept.
In an embodiment, the first side of the stacked fuel cells is opposite to the second side. In an embodiment, the first direction is opposite to the second direction. In an embodiment, the first lateral wall of the casing is opposite to the second lateral wall.
In an embodiment, the distribution channels and the respective injectors are arranged on two different sides of the stack of fuel cells and for each free space so that each free space can be injected with fluid from either side of the stack of fuel cells. For each free space between two fuel cells or between a fuel cell and the casing, the fluid injection device is configured to selectively actuate only the injectors located at one of the sides of the stack of fuel cells.
In this embodiment, although there are injectors on both sides of the stack of fuel cells the fluid injection device allows to inject fluid only from one side of the stack of fuel cells selectively. This means that the fluid injection device chooses whether to actuate the injectors on one side or the other side of the stack of fuel cells for each free space.
In an embodiment, each injector comprises an injecting channel and a nozzle. The nozzle is oriented and opened to the inside of the casing. The injecting channel is connected to the distribution channel and the nozzle.
In an embodiment, the nozzle comprises a nozzle opening for the injector fluid outlet, wherein a cross section area of the nozzle opening is larger than a cross section area of the injecting channel.
The above difference cross section are between the injecting channel and the nozzle opening allows the fluid diffusion to be homogeneous and with sufficient velocity to sweep the fluid inside the casing.
In an embodiment, each distribution channel and its respective injectors are comprised in an enclosing structure, the enclosing structure comprising a common outlet open to the casing and a common space upstream of the common outlet, and wherein the nozzle opening of each injector is open to said common space. Advantageously, this configuration allows it to be manufactured in one piece for easy assembly into the system.
In an embodiment, the inerting system comprises:
The sensing means measures the concentration of oxygen and hydrogen of the fluid housed in the casing where the fuel cells are placed. These concentrations of oxygen and hydrogen refer to the volumetric concentration inside the casing and are expressed as a percentage.
The control means is connected to the sensing means so that according to the data provided by the sensing means, regarding the oxygen and hydrogen concentrations, the control means controls at least the fluid regulating means as needed. That is, if the oxygen and/or hydrogen concentration conditions are above a first pre-set threshold, part of the fluid of the casing is exhausted by extracting it from the casing and inert gas or pure inert gas is supplied by the inert gas supplying means. Therefore, the control means actuate at least the fluid regulation means at least when the concentration of oxygen and/or the concentration of hydrogen of the fluid of the casing are above said first pre-set thresholds. Specifically, the term “to actuate” is understood as to recirculate part of the fluid located inside the casing towards the inlet channel.
Depending on the hydrogen concentration and/or oxygen concentration, the fluid injection device injects more or less mass flow into the casing. If only the concentration of hydrogen or the concentration of oxygen inside the casing is above a corresponding first pre-set threshold more inert gas or pure inert gas is needed to be injected.
Thus, the inerting system is therefore provided for inerting the volume around fuel cells in a controlled manner to prevent the occurrence of a fire or the creation of a flammable fluid in an undesired area of said volume inside the casing.
These first thresholds are based on the safety policy.
By means of the sensing means and the control means, the inerting system advantageously allows to measure and monitor the concentration of both hydrogen and oxygen inside the casing at any time, both to be able to prevent a fire from occurring inside the casing.
In an embodiment, the inerting system comprises a fluid regulation system configured to recirculate part of the fluid located inside the casing to the inlet channel for supplying the recirculated fluid mixed with the inert gas to the inside of the casing through the fluid injection device; wherein the control means is further configured to:
This fluid recirculation system partially recirculates fluid located inside the casing through the inerting system. Part of the fluid located in the casing is recirculated to the inlet channel in order to be supplied back into the casing by the fluid injection device but mixed with inert gas or pure inert gas in such a way that the inside of the casing is kept inert.
In an embodiment, the control means are configured to independently control at least the fluid regulating means and the fluid recirculation system based on the concentration of oxygen and the concentration of hydrogen inside the casing. In such a way that the control means is configured to actuate the recirculation in the fluid recirculation system only when the concentration of oxygen and/or the concentration of hydrogen of the fluid located inside the casing are below second pre-set thresholds respectively.
Therefore, according to the data provided by the sensing means, regarding the oxygen and hydrogen concentrations, the control means controls the fluid regulating means and fluid recirculation system separately as needed. That is, if the oxygen and/or hydrogen concentration conditions are suitable, part of the fluid of the casing is recirculated by extracting it from the casing and re-injecting it mixed with pure inert gas or inert gas supplied by the inert gas supplying means. The oxygen and/or hydrogen concentrations are considered suitable for allowing the recirculation of part of the fluid housed in the casing when they are below a second pre-set threshold respectively. Therefore, the control means actuate the recirculation only when the concentration of oxygen and/or the concentration of hydrogen of the fluid of the casing are below such second pre-set thresholds.
Depending on the hydrogen concentration and/or oxygen concentration, the fluid recirculation system recirculates more or less mass flow of fluid from the casing. If the concentration of hydrogen and the concentration of oxygen of the fluid to be recirculated are below second pre-set thresholds, more mass flow of fluid from casing is recirculated and less pure inert gas or inert gas is needed. Whereas if only the concentration of hydrogen or the concentration of oxygen of the fluid to be recirculated is below the corresponding second pre-set threshold, less fluid from the casing is recirculated and more inert gas or pure inert gas is needed.
These second pre-set thresholds are based on the safety policy, so that if the concentration of oxygen and/or the concentration of hydrogen are sufficiently far away from the limits considered by the safety policy, the gas located inside the casing will be partially recirculated.
In the embodiment where the inerting system comprises a fluid recirculation system, advantageously the present inerting system requires less installation space in the aircraft as it reduces the amount of inert gas or pure inert gas needed for inerting by providing the possibility of partially recirculating the fluid located inside the casing. In addition, this reduction in the inert gas supplying means (bottles or generation system) in turn reduces the weight for the aircraft.
Moreover, the present inerting system allows to provide bigger mass flow entering the casing and lower mass flow coming from the inert gas supplying means thanks to the recirculation of fluid located inside the casing. This allows to limit the local build-up of oxygen and/or hydrogen by increasing the flow of inerted gas circulating in the casing. It may also allow to obtain a more turbulent flow, thereby also increasing the homogeneity of the mix of inert gas (nitrogen), oxygen and hydrogen. This homogenization advantageously prevents punctual points of bigger concentrations that could lead to locally flammable mixture inside the casing.
Furthermore, as there is a higher mass flow entering the casing by the fluid injection device, the flow velocity through the casing is bigger and then the arrival time of an inerted fluid flowing through the casing containing risky concentrations of oxygen or hydrogen, will be detected much quicker, as it will arrive faster to the sensing means. Therefore, the present inerting system provides rapid detection of oxygen and hydrogen concentration values that may be indicative of risk to the inside of the casing. For example, if a mixture of oxygen and hydrogen with enough volumetric concentration of these gases in the fluid of the casing happens, there are higher risks of a fire to be triggered. For this reason, the present invention allows to take action before one of the first or second pre-set thresholds of concentrations of oxygen and concentrations of hydrogen is reached locally.
Additionally, the present inerting system advantageously has the capacity to regulate and variate, as needed, the mass flow coming from the inert gas supplying means depending on the information provided by the sensing means to the control means. The fluid regulating means control allows continuous sweeping of the fluid inside the casing. In an embodiment, the fluid regulating means comprises:
In another embodiment, the fluid regulating means comprise an inlet orifice with a predefined diameter that always allows the same flow rate to pass through.
The first outlet valve regulates the exhaust of fluid located inside the casing through the first outlet of the casing. This first outlet valve even in its closest position has a minimal aperture that lets pass a flow for exhausting the casing.
In an embodiment, the control means are also configured to control at least the regulation of the first outlet valve based on the measured concentration of oxygen and hydrogen.
In an embodiment, the control means are also configured to control the regulation of the inlet valve.
In an embodiment, the fluid recirculation system comprises:
The recirculation channel of the fluid recirculation system connects the inside of the casing with the inlet channel in order to mix the recirculated fluid with inert gas or pure inert gas before being this mixture supplied to the casing through the fluid injection device. The recirculation channel of the recirculation system connects with the inlet channel in a section of this inlet channel between the inert gas supplying means and the inlet of the casing, that is, upstream the inlet of the casing.
The recirculation system further comprises a compressor interposed on the recirculation channel and being configured to compress the fluid coming from the inside of the casing to a pressure lower than the pressure at which the inert gas or pure inert gas is supplied to the inlet channel. This compressor ensures pumping of recirculated fluid through the fluid recirculation system. The supplying of the recirculated fluid to the inlet channel must be at a lower pressure than the inert gas or pure inert gas supply to prevent the recirculated fluid from flowing backwards in the inlet channel to the inert gas inlet.
Moreover, the fluid recirculation system comprises a recirculation valve for regulating the passage of fluid from the recirculation channel to the inlet channel. Specifically, this recirculated valve is connected to the recirculation channel between the compressor and the connection of the recirculation channel with the inlet channel.
The opening of the recirculation valve and/or the flow of fluid recirculated by the compressor depends on the measured hydrogen concentration and/or oxygen concentration.
More particularly, the inerting system further comprises a mixer interposed on the inlet channel, between the inert fluid regulating means and the at least one inlet of the casing. The mixer is connected to the recirculation channel and is configured to mix inert gas or pure inert gas from the inert gas supplying means and recirculated fluid from the fluid recirculation system.
The mixer is understood as an enclosure interposed on the inlet channel and in fluid communication with the inert gas supplying means, the fluid recirculation system and the inside of the casing by the fluid injection device. This mixer is where the recirculated fluid is mixed with the inert gas or pure inert gas before going to the inside of the casing. In an embodiment, the inlet valve regulates the passage of inert gas or pure inert gas toward the mixer and the recirculation valve regulates the passage of the recirculated fluid towards the mixer.
The present inerting system provides a flushing mode increasing the flow rate of inert gas or pure inert gas in order to diminish the concentrations of hydrogen and/or oxygen under pre-set flammability limits in a short time and extinguish a fire.
In an embodiment, the inerting system further comprises fire detection means in data communication with the control means and configured to detect fire inside the casing. The control means are further configured to open at maximum flow rate the inlet valve and the first outlet valve if the fire detection means detects a fire.
In another embodiment, the control means are further configured to open at maximum flow rate the inlet valve and first outlet valve if a high concentration of oxygen or hydrogen is detected by the sensing means, that is, if the concentration of oxygen or hydrogen is above fourth pre-set thresholds.
With the maximum flow rate opening of the first outlet valve flammable gases are advantageously exhausted from inside the casing. In addition, with the maximum flow rate opening of the inlet valve the flammable gases are swept out of the casing and the inside of the casing is quickly inerted again. Moreover, with the maximum flow rate opening of the first outlet valve the creation of an overpressure inside the casing is avoided.
Furthermore, with the provision of the present inerting system, replacing the use of any fire extinguishing agent (such as halon) is achieved. In addition, the installation space and weight of the fire extinguishing agent bottle is also spared since it has been replaced by the fluid recirculation system, which is anyway required for the inerting of the casing.
The fact of having a first outlet valve to enhance a bigger section of outflow in case of failure, gives an extra margin in terms of safety since the pressure releases quicker from the casing.
Moreover, the reaction time for extinguishing a fire and re-inerting the inside of the casing is shorter with the present inerting system compared to the prior art solutions or with a nominal flow, that is, without opening the inlet valve at its maximum flow rate. In addition, with the new fluid injection device it is possible to supply the fluid inside the casing in a more homogeneous and effective way by quickly sweeping the fluid surrounding the fuel cells inside of the casing.
More particularly, the fire detection means may comprise an overpressure sensor for detecting overpressure inside the casing. In case an overpressure inside the casing is detected, the inlet and outlet valves are adjusted to release the generated overpressure.
In an embodiment, the inerting system further comprises pressure measuring means in data communication with the control means and configured to measure the pressure inside the casing, wherein the control means is configured to open the outlet valve above a pre-set flow rate threshold if the pressure measured is over a pre-set pressure threshold. That is, if an overpressure is detected inside the casing, the inlet valve of the casing is regulated to release the generated overpressure and thus achieve a greater sweep of the fluid inside the casing. In addition, when an overpressure is detected inside the casing the inlet valve may be also opened above a pre-set flow rate threshold to continue inerting the inside of the casing to the maximum. In this case, the outflow of the outlet valve is greater than the inlet flow of the inlet valve to prevent pressure increase in the casing.
In an embodiment, the sensing means comprises at least a first sensor for measuring the concentration of oxygen and at least a second sensor for measuring the concentration of hydrogen. Advantageously, the sensing means allows measuring the concentration of hydrogen and the concentration of oxygen in order to determine the control means if the fluid contained in the casing can be recirculated.
In an embodiment, the sensing means is located in the casing and/or in the fluid recirculation system and/or in an exhaust channel connected to the first outlet of the casing. The provision of sensing means in the casing, in the fluid recirculation system and in the exhaust channel allows to measure the concentration of oxygen and hydrogen at different points in the inerting system where the fluid contained in the casing flows.
In an embodiment, the sensing means is located in the casing and/or in the recirculation channel of the fluid recirculation system upstream the compressor.
In an embodiment, there is a plurality of sensing means located in the casing with the aim to cover several areas in the casing, thus avoiding localized accumulation of oxygen and hydrogen.
In a second inventive aspect, the invention provides an aircraft comprising an inerting system according to the first inventive aspect.
In a third inventive aspect, the invention provides a method for inerting a fuel cell system by an inerting system that comprises a fluid injection device, wherein:
wherein in step a) at least the inert gas supplied by the supplying means is injected inside the casing through the injectors, towards the free space between fuel cells and/or the free space between a fuel cell and the casing.
The present method is intended for inerting a fuel cell system, particularly, a casing enclosing a fuel cell system or a part of the fuel system, where the fuel is hydrogen, by injecting inert gas in a homogeneous way and sweeping the fluid surrounding the fuel cells as fast as possible. In an embodiment, the inerting system used for inerting the fuel cell system or part of the same is according to the first inventive aspect. The fuel cell system of an aircraft is enclosed in a casing, which is inerted in order to keep the fuel cell system inert.
In an embodiment, the method comprises:
In an embodiment, the inert gas is pure inert gas.
Advantageously, the method according to the above embodiment allows reuse of inert gas already supplied and mixed in the casing with other gases as long as the conditions of the fluid housed in the casing allow it, i.e., as long as the concentration of hydrogen and the concentration of oxygen remain below second pre-set thresholds.
In an embodiment, as long as the sensing means measures a concentration of hydrogen below a second hydrogen pre-set threshold and/or a concentration of oxygen below a second oxygen pre-set threshold, the fluid recirculation system recirculates fluid from the casing.
In an embodiment, the recirculation of step (d) is carried out if the concentration of hydrogen and the concentration of oxygen of the fluid (located inside the casing) to be recirculated are below second pre-set thresholds.
In another embodiment, the method further comprises a step of monitoring the pressure inside the casing by pressure measuring means in data communication with the control means, wherein if a pressure over a pre-set pressure threshold inside the casing is determined by the control means, the control means opens the first outlet valve for exhausting pressure from the casing until the pressure inside the casing is the same as outside the aircraft. The control means determines if there is an overpressure inside the casing based on the pressure measured by the pressure measuring means. More particularly, when a pressure over a pre-set pressure threshold inside the casing is determined, the control means also opens the inlet valve for supplying inert gas to the inside of the casing. Additionally, the first outlet valve and/or the inlet valve are/is opened above a pre-set flow rate threshold when an overpressure inside the casing is detected. According to normal working mode of the inerting system, the pressure inside the casing is slightly higher than outside in order to limit intake of oxygen from air surrounding the casing in case of limited leak of the casing.
In an embodiment, if the concentration of hydrogen inside the casing is above a third pre-set threshold and/or the concentration of oxygen inside the casing is above a third pre-set threshold, the control means opens, above a pre-set flow rate threshold, the first outlet valve for exhausting fluid from the casing and the inlet valve for supplying inert gas to the inside of the casing, until the concentration of hydrogen and the concentration of oxygen are below the third pre-set thresholds.
When the concentration of oxygen or concentration of hydrogen or both are above the third pre-set thresholds, the present system is reconfigured to exhaust the fluid housed inside the casing and re-inert the inside of the casing but without recirculation, that is, the recirculation system stops working.
In an embodiment, if the concentration of hydrogen and/or the concentration of oxygen inside the casing are above fourth pre-set thresholds, or if a fire inside the casing is detected, the control means opens at maximum flow rate the inlet valve and the first outlet valve.
In an embodiment, if the concentration of hydrogen and the concentration of oxygen are below the corresponding second pre-set threshold, the mass flow recirculated passing through a compressor of the fluid recirculation system is increased and the mass flow coming from the inert gas supplying means is lowered in the inlet conduct to diminish the concentration of oxygen and hydrogen inside the casing as needed.
In an embodiment, if the concentration of hydrogen or the concentration of oxygen is below the corresponding second pre-set threshold, the mass flow recirculated passing through a compressor of the fluid recirculation system is lowered and the mass flow coming from the inert gas supplying means is increased in the inlet conduct to diminish the concentration of oxygen or hydrogen inside the casing as needed.
In an embodiment, the second pre-set thresholds coincide with the third pre-set thresholds, so that there is a single pre-set threshold that sets whether the fluid located in the casing can be recirculated or not. That is, if the oxygen concentration and hydrogen concentration are below this pre-set threshold, recirculation is possible, but if the oxygen concentration and the hydrogen concentration are above the threshold, recirculation is not possible. In addition, if only the concentration of one of both, oxygen or hydrogen, is below the mentioned threshold, recirculation is possible, although less fluid is recirculated as indicated above.
These and other characteristics and advantages of the invention will become clearly understood in view of the detailed description of the invention which becomes apparent from a preferred embodiment of the invention, given just as an example and not being limited thereto, with reference to the drawings.
For any of the embodiments shown in
The casing (2) comprises one inlet (2.2) and a first outlet (2.1) which allow a fluid flow through the casing (2). The inlet (2.2) is connected to an inlet channel (11) and the first outlet (2.1) is connected to an exhaust channel (19). The inlet channel (11) is in turn connected with inert gas supplying means (4) adapted for supplying nitrogen for inerting the inside of the casing (2). On the other hand, the first outlet (2.1) is configured to be connected to the outside of the aircraft (20). The flow inlet of fluid through the inlet (2.2) corresponds to the mass flow entering the casing (2) or min. The flow outlet of fluid through the first outlet (2.1) corresponds to the mass going outside the aircraft (20) and not coming back or mout.
The inerting system shown in
The inerting system of these
The fluid injection device (10) shown in these
The inerting system of
Furthermore, the inerting system also comprises control means (13) that independently controls at least the inlet valve (5) and the outlet valve (6). The control means (13) are in data communication with the sensing means (12) in order to determine the concentration of oxygen and hydrogen inside the casing (2).
According to the embodiment of
This fluid recirculation system(S) comprises a recirculation conduct (18) that connects the inside of the casing (2) with the mixer (15). The recirculation conduct (18) is arranged between the exhaust channel (19) and the mixer (15). The fluid recirculation system(S) also comprises a compressor (16) interposed on the recirculation conduct (18) and configured to pumping the fluid from the inside of the casing (2) and for regulate the pressure of the recirculated fluid in order to adjust the pressure of this recirculated fluid to be lower than that of the supplied nitrogen. The flow inlet of recirculated flow through the outlet recirculation conduct (18) corresponds to the mass flow recirculated passing through the compressor (16) or mc.
The fluid recirculation system(S) further comprises a recirculation valve (17) arranged between the compressor (16) and the connection of the recirculation conduct (18) with the mixer (15). This recirculation valve (17) is provided for regulating the inlet of recirculated fluid towards the recirculation conduct (18).
The control means (13) shown in
The embodiment of
With the configuration of the fluid injection device (10) shown in
For the embodiment of this
For the embodiments of
The present invention further provides a method for inerting a fuel cell system of an aircraft (20) by an inerting system. An example of a method for inerting a fuel cell (1) casing (2) in an aircraft (20) is explained below, wherein the inerting is performed by any of the inerting systems described above regarding
The method comprises a first step a) of supplying nitrogen to the fluid injection device (10) by means of inert gas supplying means (4). The control means (13) control the operation of the inlet valve (5) for regulating the flow of nitrogen that is supplied through the inlet channel (11) towards the fluid injection device (10), that is, for regulating ma. If it is the first time that an inert fluid is to be generated in the casing (2), the inlet valve (5) is opened to its maximum flow rate to allow inerting the casing (2) quickly, and in this case, ma is the same as min.
Specifically, in this step (a) the nitrogen supplied by the supplying means (4) is injected inside the casing (2) towards the free spaces between fuel cells (1) and the bottom (2.3) of the casing (2) and a fuel cell (1). This fluid injection is performed by the fluid injection device (10).
In the inerting process, there must not only be a fluid inlet inside the casing (2) but also a fluid outlet so that there is a continuous flow of fluid through the casing (2). For this reason, the method comprises the step (b) of exhausting part of a fluid housed inside the casing (2) through the first outlet (2.1) of the casing (2). The control means (13) control also the operation of the outlet valve (6) for regulating the outlet flow from the casing (2), that is, for regulating the mout. The control means (13) controls the operation of both inlet valve (5) and outlet valve (6) so that there is always fluid flowing through the casing (2) so that a balance is maintained within the casing (2) being ma equal to mout.
In an embodiment based on the inerting system shown in
Based on the data measured by the sensing means (12), the control means (13) determines if part of fluid housed in the casing (2) can be recirculated by a fluid recirculation system(S). That is, according to a step (d) of the method, if the control means (13) determines that the concentration of oxygen and/or the concentration of hydrogen of the fluid inside the casing (2) are/is below second pre-set thresholds, then the control means (13) controls the recirculation of part of the fluid located inside the casing (2). That is, the recirculation system(S) starts working.
While inerting is carried out, if the control means (13) determines that a fluid recirculation can be performed, the compressor (16) is operated to pump fluid from the inside of the casing (2) along the recirculation conduct (18), that is, to pump mc. Then the recirculation valve (17) is controlled to regulate the passage of recirculated fluid to the mixer (15). During the fluid recirculation, the inlet valve (5) is controlled to reduce ma with the aim to compensate for some of the nitrogen that is not supplied by the recirculated fluid. In the case of recirculation, ma+mc is equal to min.
In this inerting method, there is also a step of monitoring the pressure inside the casing (2) by pressure measuring means (not shown) which are in data communication with the control means (13). If the control means (13) determines that the pressure inside the casing (2) is over a pre-set pressure threshold based on the data (measured pressure) provided by the pressure measuring means, the first outlet valve (6) is opened above a pre-set flow rate threshold for exhausting pressure from the casing (2). At the same time the inlet valve (5) may be also opened above the pre-set flow rate threshold for supplying nitrogen to the fluid injection device (10) for injecting this fluid into the casing (2) until the pressure in the casing (2) achieves the same pressure as outside the aircraft (20). The pre-set pressure threshold and the pre-set flow rate threshold may vary depending on the configuration of the casing and the fuel cell system.
Moreover, if the control means (13) determines that the concentration of hydrogen and/or the concentration of oxygen inside the casing (2) is/are above a third pre-set thresholds, both inlet valve (5) and first outlet valve (6) are opened above a pre-set flow rate threshold. This is to rapidly sweep the fluid contained in the casing (2) until it reaches concentrations of hydrogen and oxygen below the second pre-set thresholds. In an example, the third pre-set threshold is 0.75% volumetric concentration of hydrogen and 2% volumetric concentration of oxygen.
Furthermore, the method comprises a step of extinguishing a fire inside the casing (2) if fire detection means of the inerting system detects that a fire is generated inside the casing (2). For example, for a fire to start there has to be an air supply leak inside the casing (2), an overpressure inside the casing (2) and also a small leakage of hydrogen. All this triggers the start of a fire locally consuming part of the oxygen located inside the casing (2). Although at the moment a fire starts the hydrogen fuel cells (1) are shut down, there is always residual hydrogen in the pipes of the fuel cells (1).
To extinguish the fire in the casing (2), both the inlet valve (5) and the first outlet valve (6) are opened at maximum flow rate to evacuate the affected fluid inside the casing (2) as soon as possible and generate a new inerted fluid. Specifically, firstly the first outlet valve (6) is opened for flushing the oxygen and/or hydrogen but the pressure in the casing (2) increases due to the fire. Then, the inlet valve (5) is completely opened to suffocate the fire with the objective to obtain a lower concentration of oxygen and hydrogen inside the casing (2). In an embodiment, when the inerting system is operated to extinguish a fire inside the casing (2) as already described above, the concentration of oxygen is diminished below a 4%. Thus, when the volumetric concentration of oxygen is under 4%, no fire can be stabilize inside the casing (2). In an embodiment, the flammability limits are 4% for the hydrogen concentration and 4% for the oxygen concentration according to required safety policy limits regarding fire extinguishing.
The mass flow of nitrogen can be increased as needed. This mass flow of nitrogen is related to the free volume of the casing and the time required to inert again the casing in case of failure or fire inside the casing.
The systems and devices described herein may include a controller or a computing device comprising a processing unit and a memory which has stored therein computer-executable instructions for implementing the processes described herein. The processing unit may comprise any suitable devices configured to cause a series of steps to be performed so as to implement the method such that instructions, when executed by the computing device or other programmable apparatus, may cause the functions/acts/steps specified in the methods described herein to be executed. The processing unit may comprise, for example, any type of general-purpose microprocessor or microcontroller, a digital signal processing (DSP) processor, a central processing unit (CPU), an integrated circuit, a field programmable gate array (FPGA), a reconfigurable processor, other suitably programmed or programmable logic circuits, or any combination thereof.
The memory may be any suitable known or other machine-readable storage medium. The memory may comprise non-transitory computer readable storage medium such as, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. The memory may include a suitable combination of any type of computer memory that is located either internally or externally to the device such as, for example, random-access memory (RAM), read-only memory (ROM), compact disc read-only memory (CDROM), electro-optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM) or the like. The memory may comprise any storage means (e.g., devices) suitable for retrievably storing the computer-executable instructions executable by processing unit.
The methods and systems described herein may be implemented in a high-level procedural or object-oriented programming or scripting language, or a combination thereof, to communicate with or assist in the operation of the controller or computing device. Alternatively, the methods and systems described herein may be implemented in assembly or machine language. The language may be a compiled or interpreted language. Program code for implementing the methods and systems described herein may be stored on the storage media or the device, for example a ROM, a magnetic disk, an optical disc, a flash drive, or any other suitable storage media or device. The program code may be readable by a general or special-purpose programmable computer for configuring and operating the computer when the storage media or device is read by the computer to perform the procedures described herein.
Computer-executable instructions may be in many forms, including modules, executed by one or more computers or other devices. Generally, modules include routines, programs, objects, components, data structures, etc., that perform particular tasks or implement particular abstract data types. Typically, the functionality of the modules may be combined or distributed as desired in various embodiments.
It will be appreciated that the systems and devices and components thereof may utilize communication through any of various network protocols such as TCP/IP, Ethernet, FTP, HTTP and the like, and/or through various wireless communication technologies such as GSM, CDMA, Wi-Fi, and WiMAX, is and the various computing devices described herein may be configured to communicate using any of these network protocols or technologies.
While at least one exemplary 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 exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 24382043.8 | Jan 2024 | EP | regional |
