FR3159595A1 - System for securing an aircraft fluid circuit at risk, associated mounting method and method of use - Google Patents

Abstract

A system (2) for securing a portion (1P) of a fluid circuit (1) in which a fluid that is hazardous to an aircraft circulates, the securing system (2) comprising: at least one first flexible casing (3), configured to be mounted around the portion (1P); at least one second flexible casing (4), configured to be mounted around the portion (1P) in the first casing (3), a buffer volume (9) being defined between the first casing (3) and the second casing (4); a thermally insulating material (5) filling the buffer volume (9); and at least one drainage conduit (6), configured to be mounted along the portion (1P) of the fluid circuit (1) and mounted at least partly in the second casing (4), the drainage conduit (6) being configured to evacuate leaks of hazardous fluid from the portion (1P) of the fluid circuit (1). Abstract figure: Figure 2

Description

System for securing an aircraft fluid circuit at risk, associated mounting method and method of use

The present invention relates to the field of securing installations in which a hazardous fluid circulates, for example a flammable or explosive fluid. The invention applies in particular to securing an aircraft fuel circuit.

Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new aircraft types and those already in operation, requiring the implementation of technological solutions to ensure their compliance with current regulations. Civil aviation has been mobilizing for several years now to contribute to the fight against climate change.

Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into consideration the impact factors in all phases of design and development to obtain less energy-intensive, more environmentally friendly aeronautical components and products whose integration and use in civil aviation have moderate environmental consequences with the aim of improving the energy efficiency of aircraft.

Consequently, the Applicant is constantly working to reduce its negative climate impact by using methods and operating virtuous development and manufacturing processes and minimizing greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

This sustained research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, particularly through the materials used and lighter on-board equipment, the development of the use of electrical technologies to ensure propulsion, and, as an essential complement to technological progress, aeronautical biofuels.

To this end, the invention is the result of technological research aimed at significantly improving aircraft performance and, in this sense, contributes to reducing the environmental impact of aircraft. For this purpose, the invention applies in particular to a cryogenic fuel circuit for supplying an aircraft turbomachine.

It is known to store fuel, for example hydrogen or methane, in liquid form to limit the size and mass of an aircraft's tanks. To this end, the fuel is stored in a cryogenic tank of the aircraft and is conveyed to the turbomachine by a fluid circuit. For example, the fuel flow is stored in the cryogenic tank at a temperature of the order of -253 to -251°C (20 to 22 Kelvins).

In order to be able to circulate in the structure of the aircraft to the combustion chamber of the turbomachine M, the fuel Q must be conditioned, that is to say pressurized and heated, to pass into the gaseous state. For this, with reference to the FIG. 1 , a fuel flow Q circulates in the fluid circuit CQ and successively passes through a mechanical pump PO and a heat exchanger EC. The mechanical pump PO is configured to circulate the fuel flow Q in the fluid circuit CQ. The heat exchanger EC is configured to provide calories to the fuel flow Q in order to heat it so that it can be injected into the turbomachine M.

In practice, the fuel flow Q is heated in the heat exchanger EC using calories from hot sources in the aircraft. For example, as shown in the FIG. 1 , it is known to heat the fuel flow Q from calories transferred, by the exhaust air flow coming from the turbine stage TU of the turbomachine M, the exhaust air flow coming from the combustion, in the combustion chamber CC, between the fuel flow Q and a compressed air flow. The transfer of calories is carried out, in a known manner, in a second heat exchanger (not shown) mounted in the exhaust nozzle, by means of a heat transfer fluid FC, for example an inert gas such as nitrogen, which makes it possible to avoid the risk of contact, in the heat exchanger EC, between an oxidizing fluid and a reducing fluid.

However, between the cryogenic tank R and the heat exchanger EC, the fuel flow Q circulates at very low temperatures, close to cryogenic temperatures. Such temperatures do not allow the use of flexible material seals to tightly connect the various equipment in the fluid circuit CQ, such as the mechanical pump PO, the heat exchanger EC or even a shut-off valve V that controls the circulation and flow rate of the fuel flow Q in the fluid circuit CQ. As a result, it is not possible to ensure the absence of fuel leaks in the fluid circuit CQ, which can be a significant disadvantage.

In addition, at cryogenic temperatures, it is necessary to thermally isolate the CQ fluid circuit from the ambient air to limit the risk of ice or frost formation on the pipes and equipment. In the CQ fluid circuit, the mechanical pump PO and the heat exchanger EC are also equipment that produce heat and must be thermally insulated to avoid heating the pipes and ensure that an efficient cryogenic fluid circuit is maintained.

To achieve this, it is known to use so-called "double-walled" pipes or to add insulating foam around the pipes and/or equipment that needs to be insulated to form a thermal barrier. However, double-walled pipes significantly increase the weight of the aircraft. Furthermore, the addition of insulating foam, which is complex to implement, has limited effectiveness.

Also known in the prior art is a security system using a box 100, also shown in the FIG. 1 , which extends around all the cryogenic equipment in the CQ fluid circuit and isolates it from the air. A vacuum pump 101 creates a vacuum inside the box 100 and drains any fuel Q leaks that may appear at the equipment junctions to the outside. The drainage prevents the fuel Q from accumulating in the box 100. A vacuum box also provides effective thermal insulation.

In practice, it is necessary for the vacuum pump 101 to operate continuously to ensure the vacuum and drain the fuel leaks Q to the outside of the box 100. It is then necessary to use a high-performance vacuum pump, which has many drawbacks. Indeed, such a vacuum pump has a large footprint, which is impractical, particularly in an aeronautical environment. In addition, the vacuum pump is heavy, which increases the aircraft's fuel consumption and therefore its greenhouse gas emissions. In addition, such a pump is energy-intensive and represents a source of heat, which is not desirable in the presence of a fuel such as hydrogen or methane. Furthermore, fuel leaks Q in the sealed box 100 can impact the maintenance of the vacuum, which can affect the thermal insulation of the fluid circuit CQ.

The invention thus aims to eliminate at least some of these drawbacks by proposing a reliable and efficient system for securing a high-risk fluid circuit of an aircraft, which ensures both thermal insulation of the fluid circuit and optimal drainage of fluid leaks. The invention aims in particular at a high-performance vacuum pump-free security system.

PRESENTATION OF THE INVENTION

• au moins une première enveloppe flexible, configurée pour être montée autour de la portion du circuit de fluide, la première enveloppe flexible définissant autour de la portion du circuit de fluide une enceinte extérieure étanche,
• au moins une deuxième enveloppe flexible, configurée pour être montée autour de la portion du circuit de fluide dans la première enveloppe, la deuxième enveloppe flexible définissant autour de la portion du circuit de fluide une enceinte intérieure étanche, un volume tampon étant défini entre la première enveloppe et la deuxième enveloppe,
• un matériau thermiquement isolant remplissant le volume tampon, et
• au moins un conduit de drainage, configuré pour être monté le long de la portion du circuit de fluide et monté au moins en partie dans la deuxième enveloppe, le conduit de drainage étant configuré pour évacuer les fuites de fluide à risque issues de la portion du circuit de fluide.

The invention relates to a system for securing a portion of a fluid circuit in which a fluid at risk for an aircraft circulates, the securing system comprising:

• at least one first flexible envelope, configured to be mounted around the portion of the fluid circuit, the first flexible envelope defining around the portion of the fluid circuit a sealed external enclosure,
• at least one second flexible envelope, configured to be mounted around the portion of the fluid circuit in the first envelope, the second flexible envelope defining around the portion of the fluid circuit a sealed inner enclosure, a buffer volume being defined between the first envelope and the second envelope,
• a thermally insulating material filling the buffer volume, and
• at least one drainage conduit, configured to be mounted along the portion of the fluid circuit and mounted at least partly in the second casing, the drainage conduit being configured to evacuate risky fluid leaks from the portion of the fluid circuit.

Two flexible enclosures make it possible to form a lightweight safety system with a reduced footprint compared to the prior art system in which a heavy and bulky rigid box was used. The safety system is therefore simpler to implement. In addition, two flexible enclosures are easier to handle, which limits both assembly time and the strain on operators. Storing the flexible enclosures is also simpler. A double sealed enclosure around the fluid circuit portion allows for a reliable safety system in which the risk of a leak spreading is limited. In other words, the equipment in the fluid circuit portion is isolated thanks to a compact system that provides an optimal level of safety and insulation.

The thermally insulating material that fills the buffer volume limits the thermal emissivity coming from the fluid circuit portion, which makes it possible, in the case of transporting a cryogenic fuel, for example, to limit the formation of frost on the pipes. The service life of the fluid circuit is thus increased and the risk of failure is limited.

The second casing mounted between the portion to be secured and the thermally insulating material eliminates any risk, in the event of a leak, of bringing the fluid at risk into contact with the thermally insulating material, which avoids the risk of soiling it and lowering its insulating characteristics. In addition, the second casing protects the equipment in the portion of the fluid circuit, for example, avoiding any risk of corrosion or damage.

The drainage pipe installed in the second casing, as close as possible to the equipment in the fluid circuit section, allows any leaks to be drained and eliminates any risk of accumulation of hazardous fluid leaks near heat sources. The drainage pipe thus effectively drains leaks from pipes and/or equipment installed on the section to be secured, for example following damage or at the level of the connecting joints between the pipes and the equipment.

In one embodiment, the thermally insulating material is a polyurethane foam, which allows for a lightweight material with known and effective insulating properties. An expanding polyurethane foam is also simple to install by injection, for example.

According to a preferred aspect, the safety system comprises at least one cutting device mounted at least partly in the first casing and configured to cut the thermally insulating material. Such a cutting device makes it possible to remove the thermally insulating material in the event of maintenance, for example. The cutting device directly integrated into the safety system makes it possible to avoid any risk of damage to the equipment in the portion of the fluid circuit at risk.

In one embodiment, the cutting device is mounted at least partly in the second casing, which makes it possible to ensure the removal of all of the thermally insulating material by means of a single cutting device. The thermally insulating material can thus be removed simply and quickly.

In one embodiment, the securing system comprises two cutting devices mounted on either side of the portion of the fluid circuit, so as to form two cuts in the thermally insulating material. The latter can thus be removed without being damaged. This makes it possible, for example, to reposition the thermally insulating material after maintenance by joining the cut pieces and gluing them, for example, using adhesive tape or specific glue.

Preferably, the cutting device is in the form of a flexible metal wire, which allows it to be easily mounted inside the second casing. The cutting device is thus light and compact and does not present any risk of damaging the equipment in the fluid circuit portion.

According to a preferred aspect, the cutting device comprises at least one gripping member, allowing simple and safe handling by an operator to cut the thermally insulating material. The gripping member also allows the operator to apply sufficient force to the cutting device to cut the thermally insulating material in a practical, efficient and rapid manner.

Preferably, the cutting device comprises a gripping member at each of its ends, which makes it possible to cut the thermally insulating material along its entire length in a single pass.

Preferably, the gripping member extends outside the first envelope, allowing optimal accessibility for an operator, even when the securing system is entirely mounted around the portion to be secured.

In a preferred embodiment, the drainage conduit is made of a material whose modulus of elasticity is between 100 MPa and 3400 MPa. Such a modulus of elasticity makes it possible to form a drainage conduit that is both sufficiently soft and flexible to fit the contours of the equipment in the portion of the fluid circuit while being sufficiently rigid not to be crushed by the thermally insulating material.

Preferably, the drainage conduit is made of a porous or micro-aerated material, allowing it to absorb the fluid at risk in the event of a leak in the portion of the fluid circuit.

Preferably, the drainage conduit is made of a plastic material, for example of the Polyvinyl Chloride type, known by the acronym PVC. Such materials make it possible to form a drainage conduit that is both sufficiently porous to effectively absorb leaks of fluid at risk while being sufficiently flexible to fit the contours of the equipment in the portion of the fluid circuit and sufficiently rigid not to be crushed by the thermally insulating material.

According to a preferred aspect, the inner enclosure of the second envelope has an internal pressure lower than atmospheric pressure. The inner enclosure is thus placed under vacuum, which allows the second envelope to be pressed against the equipment of the fluid circuit. A vacuum environment makes it possible, in the event of a risky fluid leak, to avoid its coming into contact with air in a confined environment. The vacuum also makes it possible to improve the thermal insulation of the portion to be secured.

The invention also relates to a fluid circuit connecting a cryogenic tank to an aircraft turbomachine and comprising at least one safety system as described previously, securing a portion of the fluid circuit.

Preferably, the fluid circuit comprises several securing systems securing the portion of the fluid circuit, the drainage conduits being fluidically connected.

In one embodiment, the fluid circuit comprises, at least between the cryogenic tank and the safety system, a double-walled pipe comprising an outer pipe and an inner pipe mounted in the outer pipe, the outer pipe having an inner pressure lower than atmospheric pressure. The outer pipe is thus under vacuum, which allows the double-walled pipe to convey the fluid at risk to the portion secured by the safety system, in complete safety.

Thanks to the security system, the use of double-walled pipes is limited, which helps to limit costs while ensuring an optimal level of security.

The invention also relates to an aircraft comprising at least one turbomachine, a cryogenic tank and a fluid circuit as described previously mounted between the cryogenic tank and the turbomachine.

• monter le conduit de drainage le long de la portion de circuit de fluide,
• monter la deuxième enveloppe autour de la portion de circuit de fluide et du conduit de drainage,
• monter la première enveloppe autour de la deuxième enveloppe et de la portion de circuit de fluide, et
• remplir le volume tampon défini entre la première enveloppe et la deuxième enveloppe avec le matériau thermiquement isolant.

The invention also relates to a method of mounting a security system as described above, the mounting method comprising the steps of:

• install the drainage pipe along the fluid circuit portion,
• mount the second casing around the fluid circuit portion and the drainage pipe,
• mount the first envelope around the second envelope and the fluid circuit portion, and
• fill the buffer volume defined between the first envelope and the second envelope with the thermally insulating material.

Preferably, the fluid circuit comprising at least one piece of equipment and/or at least one pipe, the drainage conduit is mounted along the portion of the fluid circuit as close as possible to said piece of equipment and/or said pipe, preferably in a dedicated position substantially adjacent to the portion of the fluid circuit.

In one embodiment, the assembly method comprises, after filling the buffer volume, a step consisting of sealing on either side of the first envelope and the second envelope to form the sealed inner enclosure and the sealed outer enclosure.

• absorber la fuite dans le conduit de drainage, et
• drainer la fuite via le conduit de drainage hors du système de sécurisation.

Finally, the invention relates to a method of using a security system as described above, the method of use comprising the steps of:

• absorb the leak in the drainage pipe, and
• drain the leak via the drainage pipe outside the safety system.

Thermal insulation is thus ensured thanks to the flexible double envelope and the thermally insulating material, even in the event of a leak, the latter being effectively drained by means of a compact system.

PRESENTATION OF FIGURES

The invention will be better understood on reading the description which follows, given by way of example, and referring to the following figures, given by way of non-limiting examples, in which identical references are given to similar objects.

There FIG. 1 is a schematic representation of a system for securing a portion of a fluid circuit at risk according to the prior art.

There FIG. 2 is a schematic representation of a system for securing a portion of a fluid circuit at risk according to a first embodiment of the invention.

There FIG. 3 is a schematic representation of a system for securing a portion of a fluid circuit at risk according to a second embodiment of the invention.

There FIG. 4 is a schematic representation of a system for securing a portion of a fluid circuit at risk according to a third embodiment of the invention.

There FIG. 5 is a schematic representation of a system for securing a portion of a fluid circuit at risk according to a fourth embodiment of the invention.

There FIG. 6 is a schematic representation of the steps of a method of assembling the security system of the FIG. 4 .

There FIG. 7 is a schematic representation of the steps of a method of using the security system of the FIG. 4 .

It should be noted that the figures set out the invention in detail to implement the invention, said figures can of course be used to better define the invention where appropriate.

DETAILED DESCRIPTION OF THE INVENTION

As is known, an aircraft comprises one or more gas turbine engines to enable its movement from the acceleration of an upstream to downstream air flow. For this, as shown in the FIG. 2 , the turbomachine M is powered by a fuel flow Q from a fuel tank R. In this example, the fuel Q is dihydrogen but it goes without saying that the invention applies to any type of high-risk fuel, in particular methane. In general, the invention applies to any circuit for transporting a high-risk fluid.

Such fuel Q is stored in tank R at cryogenic temperatures. For example, the fuel stream Q is stored in the cryogenic tank R at a temperature of the order of -253 to -251°C (20 to 22 Kelvins). At this temperature, the fuel stream Q is liquid. In order to be introduced into a combustion chamber of the turbomachine M, the fuel Q must be heated.

For this, always with reference to the FIG. 2 , the aircraft comprises a fuel circuit 1 which connects the cryogenic tank R to the turbomachine M. The fuel flow Q circulates from upstream to downstream in the fuel circuit 1 by means of a mechanical pump PO and passes through a heat exchanger EC, in which it exchanges calories with a heat transfer fluid FC. In this example, the heat exchanger EC is configured to heat the fuel flow Q to a vaporization temperature. It goes without saying that the fuel flow Q could pass through more than one heat exchanger EC to heat, for example, the fuel flow Q gradually. In this example, a control valve W makes it possible to control the flow rate of the fuel flow Q in the fuel circuit 1. It goes without saying that the fuel circuit 1 could comprise a different number of equipment items.

In this example, the fuel circuit 1 comprises a portion 1P likely to generate fuel leaks Q which must be contained to ensure the safety of the aircraft. In this example, the mechanical pump PO, the control valve W and the heat exchanger EC are mounted on the portion 1P of the fuel circuit 1. It goes without saying that the portion 1P could comprise a variety of equipment. Similarly, it goes without saying that the fuel circuit 1 could comprise a plurality of portions 1P likely to generate leaks. The portion 1P extends in this example to the ambient air.

In one embodiment, the fuel circuit 1 comprises a double-walled pipe 10 (shown in the FIG. 3 ), mounted between the tank R and the portion 1P. The double-walled pipe 10 comprises a concentric inner pipe 11 and an outer pipe 12, the inner pipe 11 being mounted in the outer pipe 12. In this example, the fuel Q circulates in the inner pipe 11 and the outer pipe 12 has a pressure lower than atmospheric pressure. In other words, the outer pipe 12 is under vacuum, making it possible, in the event of a leak for example in the inner pipe 11, to prevent the spread of fuel Q outside the fuel circuit 1. The vacuum also makes it possible to form effective thermal insulation for the inner pipe 11 in which fuel Q circulates in a cryogenic state. In this example, the fuel circuit 1 also comprises a double-walled pipe 10 as described previously, mounted between the portion 1P and the turbomachine M, as shown in the FIG. 3 .

According to one aspect of the invention, the portion 1P of the fuel circuit 1 is secured by a security system 2 which will now be presented in detail.

In reference to the FIG. 2 , the securing system 2 comprises a first flexible envelope 3 and a second flexible envelope 4 mounted around the portion 1P of the fuel circuit 1 to be secured.

The first envelope 3 defines around the portion 1P of the fuel circuit 1 a sealed external enclosure.

The dimensions of the first envelope 3 are determined to correspond to the portion 1P to be secured.

Preferably, the first envelope 3 is made of a polymer-type material (single layer, multi-layer, composite or other), for example, polypropylene, TFE (or Teflon ®), natural or synthetic rubber, silicone, etc., making it possible to form a flexible first envelope 3. In order to increase its mechanical strength, the first envelope 3 may comprise reinforcement (a composite mesh, a belt or other), for example, with polyester, nylon, aramid or steel. A flexible first envelope 3 makes it possible to limit the size of the security system 2 while being easier to handle by an operator.

Preferably, the first casing 3 comprises an opening 31 to allow the insertion of the portion 1P. In this example, the first casing 3 has a shape similar to a sleeve to insert the portion 1P to be secured in a manner similar to a sock. The opening 31 is thus mounted at the upstream end 1A of the fuel circuit 1. In practice, in this example, the first casing 3 comprises two openings 31A, 31B (shown in the FIG. 2 ), each opening 31A, 31B being positioned respectively at an upstream end 1A and at a downstream end 1B of the portion 1P. In this example, each opening 31A, 31B is closed by a sealing member, for example a ring or a clamping flange, as will be described in more detail later.

As described above, the second casing 4 is mounted around the portion 1P of the fuel circuit 1 to be secured. More specifically, the second casing 4 is mounted around the portion 1P in the first casing 3 and defines around the portion 1P a sealed inner enclosure. Thus, the first casing 3 and the second casing 4 define a double protection for the portion 1P of the fuel circuit 1.

The dimensions of the second envelope 4 are determined to correspond to the portion 1P to be secured.

Preferably, the second casing 4 is made of a polymer-type material (single layer, multilayer, composite or other), for example, polypropylene, TFE (or Teflon®), natural or synthetic rubber, silicone, etc. In order to increase its mechanical strength, the first casing 3 may comprise a reinforcement (a composite mesh, a belt or other), for example, with polyester, nylon, aramid or steel. The second casing 4 is deformable, in particular, to match the shape of the portion 1P of the fuel circuit 1, as will be described in more detail below.

Preferably, the second casing 4 has an opening 41 to allow the insertion of the portion 1P. In this example, in a manner similar to the first casing 3, the second casing 4 has a shape similar to a sleeve to facilitate the insertion of the portion 1P to be secured. The opening 41 is thus mounted at the upstream end 1A of the fuel circuit 1. In practice, in this example, the second casing 4 has two openings 41A, 41B (shown in the FIG. 2 ), each opening 41A, 41B being positioned respectively at the upstream end 1A and at the downstream end 1B of the portion 1P. In this example, each opening 41A, 41B is closed by a sealing member, for example a ring or a clamping flange, as will be described in more detail later.

In this example, the second envelope 4 has an internal pressure lower than atmospheric pressure. In other words, the internal enclosure is under vacuum, so as to press the second envelope 4 against the equipment of the fuel circuit 1 and thus avoid any risk of fuel leaks Q coming into contact with air in a confined environment.

As shown in the FIG. 2 , the safety system 2 comprises a first sealing member 20A, mounted at the upstream end 1A of the portion 1P of the fuel circuit 1, and a second sealing member 20B mounted at the downstream end 1B of the portion 1P of the fuel circuit 1. In this example, the safety system 2 also comprises a third sealing member 20C mounted at an inlet in the casings 3, 4 of the heat transfer fluid circuit FC and a fourth sealing member 20D mounted at an outlet of the heat transfer fluid circuit FC of the casings 3, 4. In practice, each sealing member 20 makes it possible to close each opening 31, 41 to seal the first casing 3 and the second casing 4, so as to respectively define the closed and sealed inner enclosure and the outer enclosure. It goes without saying that the safety system 2 can comprise a different number of sealing members 20. In particular, if the fuel circuit 1 and/or the heat transfer fluid circuit FC has(have) more than one inlet and one outlet in the first casing 3 and the second casing 4, the latter comprises as many sealing members 20.

In this example, each sealing member 20 is in the form of an elastic ring inside which an end 1A, 1B of the portion 1P of the fuel circuit 1 or the inlet or outlet of the heat transfer fluid circuit FC can extend. It goes without saying that each sealing member 20 could be in a different form, for example, in the form of a clamp, in particular, forming an integral part of a flange between two components of the fuel circuit 1.

In this example, a single first envelope 3 and a single second envelope 4 are described, however, it goes without saying that the security system 2 could alternatively comprise a third envelope to define triple protection for the portion 1P of the fuel circuit 1.

According to one aspect of the invention, a buffer volume 9 is defined between the first envelope 3 and the second envelope 4. The buffer volume 9 is a closed volume.

Still referring to the FIG. 2 , the safety system 2 comprises a thermally insulating material 5 which fills the buffer volume 9 between the envelopes 3, 4, so as to limit the heat flow coming from outside the fuel circuit 1 where the temperatures are higher than the temperatures of the cryogenic fuel Q which circulates in the portion 1P of the fuel circuit 1.

Preferably, the thermally insulating material 5 is a cellular plastic foam configured to expand upon contact with air. In other words, the thermally insulating material 5 is configured to be initially in the liquid or viscous state and to increase in volume and change to the solid state upon contact with air.

In this example, the thermally insulating material 5 is chosen from: a polyurethane foam, polystyrene beads or aerogel powder. More specifically, in this example, the thermally insulating material 5 is an expanding polyurethane foam which has significant insulating properties while being lightweight. For this purpose, the first envelope 3 preferably comprises an insertion orifice 32 (shown in the FIG. 2 ) to allow, for example, the passage of an injection nozzle to inject the thermally insulating material 5 into the buffer volume 9. The insertion orifice 32 can be closed in a sealed manner.

In practice, the volume of thermally insulating material 5 is determined according to the material used and the equipment of the portion 1P of the fuel circuit 1 to be insulated.

According to one aspect of the invention, still with reference to figures 2 and 3, the safety system 2 comprises a drainage conduit 6 for evacuating fuel leaks Q from the portion 1P of the fuel circuit 1.

For this, the drainage duct 6 is mounted along the portion 1P of the fuel circuit 1, partly in the second casing 4. In other words, the drainage duct 6 extends into the inner enclosure and is mounted at a predetermined position as close as possible to the equipment and pipes of the portion 1P of the fuel circuit 1, so as to be in contact with the equipment of the portion 1P to be secured.

Preferably, the drainage duct 6 is made of a material whose modulus of elasticity is between 100 MPa and 3400 MPa. The drainage duct 6 is thus both sufficiently flexible to fit the contours of the equipment of the portion 1P to be secured and sufficiently rigid not to be crushed against the equipment of the portion 1P by the thermally insulating material 5.

Preferably, the drainage conduit 6 is made of a porous or micro-aerated material to be able to capture fuel leaks Q from the equipment of the portion 1P.

In practice, the drainage conduit 6 is preferably made of a plastic material. In this example, the drainage conduit 6 is made of Polyvinyl Chloride, known by the acronym PVC.

In one embodiment, with reference to the FIG. 3 , the safety system 2 comprises a mechanical pump 7 fluidically connected to the drainage duct 6. The mechanical pump 7 is configured to drain any fuel leaks Q and to evacuate them outside the safety system 2. The mechanical pump 7 is for example in the form of a hydraulic pump, an electric pump or a passive pump operating for example by the venturi effect. An external tapping of the drainage duct makes it possible for example to create a vacuum to suck up the leaks.

In this example, the mechanical pump 7 connected to the drainage duct 6 is also configured to place the inner enclosure under vacuum, for example by suction via the drainage duct 6. It goes without saying that the vacuum inside the second envelope 4 could alternatively be achieved by a vacuum pump connected via a connection orifice that can be closed in a sealed manner, for example.

In reference to the FIG. 4 , the securing system 2 preferably comprises a cutting device 8 mounted partly in the first casing 3 and configured to cut the thermally insulating material 5, for a maintenance operation for example. In this example, the cutting device 8 is mounted partly in the second casing 4 and extends over the length of the portion 1P to be secured. In practice, the two ends of the cutting device 8 extend outside the casings 3, 4 through the openings 31, 41.

In the second casing 4, the cutting device 8 preferably extends longitudinally between the drainage duct 6 and the thermally insulating material 5. The cutting device 8 is configured to allow the removal of the thermally insulating material 5 by forming a cut over its entire depth from the portion 1P to the outside of the first casing 3, so as, for example, to allow access to the equipment of the portion 1P of the fuel circuit 1 in the event of maintenance. It goes without saying that the security system 2 could alternatively comprise several cutting devices 8 mounted on either side of the portion 1P to divide the thermally insulating material 5 into several parts and remove it simply and quickly.

In this example, the cutting device 8 is in the form of a flexible metal wire, making it possible to cut the thermally insulating material 5 efficiently while being light and compact. In other words, the cutting device 8 is similar to a butter cutter. It goes without saying that the cutting device 8 could be in a different form, for example an abrasive wire or a heating wire.

To be able to be easily handled by an operator, always with reference to the FIG. 4 , the cutting device 8 preferably comprises a gripping handle 80, which extends outside the inner enclosure. In this example, the cutting device 8 comprises two gripping handles 80, mounted respectively at each end of the cutting device 8, i.e. on either side of the openings 31, 41.

Preferably, the safety system 2 comprises a device (not shown) for detecting a fuel leak Q. Preferably, the detection device is mounted in the fuel circuit 1 and is configured to measure, for example, a pressure difference with a predetermined pressure.

In one embodiment, the safety system 2 comprises a leak warning and isolation device (not shown), so as to limit the fuel leak Q. In this example, the detection device is in the form of a pressure sensor connected to a computer (also not shown) of the aircraft. The computer is configured to emit a warning signal, in particular to the pilot. Preferably, the computer is configured to command, for example, a stoppage of the circulation of fuel Q in the portion 1P of the fuel circuit 1.

A single securing system 2 is described mounted around the portion 1P of the fuel circuit 1, however it goes without saying that several securing systems 2 could be mounted to secure the portion 1P. Such an embodiment, shown in the FIG. 5 , makes it possible to individually isolate different parts 1P-A, 1P-B, for example different equipment, from the portion 1P of the fuel circuit 1. The size of the casings 3, 4 is therefore limited, which makes it easier to mount the safety system 2A, 2B around the portion 1P of the fuel circuit 1.

In this embodiment, the thermally insulating material 5 may be different in each buffer volume 9 and chosen according to the temperature resistance of the material, the thermal conductivity of the equipment of the portion 1P mounted in each buffer volume 9 or even the available buffer volume 9. Alternatively, the thermally insulating material 5 is identical in all the buffer volumes 9.

Likewise, in this embodiment, the different drainage conduits 6A, 6B can be independent or fluidically connected, as shown in the FIG. 5 , to limit the space requirement in the fuel circuit 1. Preferably, a mechanical pump 7 is connected to each drainage pipe 6, for example via a common suction pipe.

A method of mounting the security system 2 as described previously will now be described, with reference to the FIG. 6 .

In a first step E1, an operator positions the drainage conduit 6 along the portion 1P of the fuel circuit 1. Preferably, the drainage conduit 6 is mounted at a predetermined position as close as possible to the portion 1P of the fuel circuit 1, so as to be attached to the equipment and pipes of the portion 1P, to allow effective drainage in the event of leaks.

In this example, the operator positions, in this same step E1, a cutting device 8 along the portion 1P of the fuel circuit 1. The cutting device 8 is preferably mounted along the drainage duct 6. The drainage duct 6 and the cutting device 8 are, in this example, held in position by means of two fixing members, for example clip clamps, mounted on either side of the portion 1P.

In a second step E2, the portion 1P of the fuel circuit 1 is positioned in the second casing 4. In practice, the second casing 4 is inserted around the portion 1P through one of the openings 41 in the manner of a sleeve. The second casing 4 is positioned so that the drainage conduit 6 protrudes from the downstream end 1B of the portion 1P to be secured. The drainage conduit 6 is preferably mounted at the upstream end 1A, inside the second casing 4 to allow the drainage of leaks from upstream to downstream. In other words, the second casing 4 is positioned so that the drainage conduit 6 extends both into the second casing 4 and out of the second casing 4 via the downstream opening 41. Likewise, preferably, the cutting device 8 is positioned in the second envelope 4, so as to extend both into the second envelope 4 and out of the second envelope 4 via the two openings 41A, 4AB. Two gripping handles 80 then preferably extend on either side of the openings 41A, 41B.

It goes without saying that the second casing 4 could alternatively first be mounted around the portion 1P of the fuel circuit 1 and the drainage duct 6 (if applicable, also the cutting device 8) could be inserted into the second casing 4 after the latter has been mounted.

The portion 1P of the fuel circuit 1, the drainage conduit 6, the cutting device 8 and the second casing 4 are then positioned in the first casing 3, in a step E3. In practice, in a manner similar to the second casing 4, the first casing 3 is inserted around the second casing 4 through one of the openings 31 in the manner of a sleeve.

Each sealing member 20A, 20B, 20C, 20D is then mounted respectively at the upstream end 1A and the downstream end 1B of the portion 1P of the fuel circuit 1 and at the inlet and outlet of the heat transfer fluid circuit FC in the casings 3, 4. The first casing 3 and the second casing 4 are then sealed, so as to form the sealed inner enclosure and the sealed outer enclosure. The cutting device 8 extends into the sealed inner enclosure and outside the casings via the openings 31A, 31B, 41A and 41B. The drainage conduit 8 extends into the sealed inner enclosure via the downstream openings 31B and 41B but without passing through the upstream openings 31A and 41A.

In this example, the drainage duct 6 is connected to a mechanical pump 7, in a step E4. The mechanical pump 7 sucks the air present in the interior enclosure to create a vacuum there. In this step, the drainage duct 6 and the cutting device 8 are pressed against the equipment of the portion 1P to be secured. Thanks to its flexible material, the drainage duct 6 can adapt to best fit the contours of the portion 1P without deforming. The buffer volume 9 is then defined between the first envelope 3 and the second envelope 4.

In a fifth step E5, the operator connects, in this example, an injection nozzle to the insertion orifice 32 and injects the thermally insulating material 5 into the buffer volume 9. The thermally insulating material 5 is in this example in the form of an expanding foam, for example a polyurethane foam. When it is injected into the buffer volume 9, the thermally insulating material 5 expands and hardens to form a cellular foam in the solid state. When the buffer volume 9 is completely filled with thermally insulating material 5, the injection nozzle is withdrawn and the insertion orifice 32 is closed tightly.

The safety system 2 then forms an effective assembly for thermally insulating the portion 1P of the fuel circuit 1 while being able to drain fuel leaks Q as will now be described.

A method of using the security system 2 as described above will now be described, with reference to the FIG. 7 . Preferably, the mechanical pump 7 fluidly connected to the drainage conduit 6 operates continuously, so as to continuously suck the interior of the drainage conduit 6.

In this example, the drainage duct 6 and the cutting device 8 extend into the inner enclosure, the second casing 4 is pressed against the drainage duct 6, itself pressed against the portion 1P of the fuel circuit 1, the thermally insulating material 5 fills the buffer volume 9. A drainage pump 7 is connected to the drainage duct 6.

In reference to the FIG. 7 , in this example, a leak F of fuel Q is detected in the portion 1P to be secured, in a first step EA. In this example, a detection device detects the leak and emits for example an alert signal, via a computer. In particular, the alert signal is received by the pilot who can implement countermeasures, for example by ordering a stoppage of the circulation of fuel Q in the portion 1P of the fuel circuit 1.

In a step EB, the leak F is absorbed by the drainage duct 6, made of a porous or micro-aerated material, and evacuated via the drainage duct 6 out of the safety system 2, by means of the mechanical pump 7. The vacuum environment of the inner enclosure makes it possible to limit any risk of the fuel Q coming into contact with an air flow in a confined space.

Thanks to the safety system 2 according to the invention, an optimal level of safety is maintained in the fuel circuit 1, even in the event of a leak appearing in the portion to be secured.

In one embodiment, a maintenance operation of the portion 1P of the fuel circuit 1 is scheduled. It is then necessary to remove the safety system 2. For this, the sealing members 20 are first removed. The operator then grasps the gripping handles 80 of the cutting device 8 and forms a cut in the thermally insulating material 5 from the portion 1P of the fuel circuit 1 to the outside of the safety system 2. The cut is made substantially radially, as shown in the FIG. 6 . The thermally insulating material 5 can then be completely dismantled by pulling manually or using specific tools from the cutout. The first envelope 3 and the second envelope 4 are also cut and removed. The envelopes 3, 4 as well as the thermally insulating material 5 can be repositioned and a new seal can be created using a specific adhesive or glue, for example for later use. These can also be replaced.

Claims (15)

Securing system (2) for a portion (1P) of a fluid circuit (1) in which a fluid at risk for an aircraft circulates, the securing system (2) comprising:

• at least one first flexible envelope (3), configured to be mounted around the portion (1P) of the fluid circuit (1), the first flexible envelope (3) defining around the portion (1P) of the fluid circuit (1) a sealed external enclosure,
• at least one second flexible envelope (4), configured to be mounted around the portion (1P) of the fluid circuit (1) in the first envelope (3), the second flexible envelope (4) defining around the portion (1P) of the fluid circuit (1) a sealed inner enclosure, a buffer volume (9) being defined between the first envelope (3) and the second envelope (4),
• a thermally insulating material (5) filling the buffer volume (9), and
• at least one drainage duct (6), configured to be mounted along the portion (1P) of the fluid circuit (1) and mounted at least partly in the second casing (4), the drainage duct (6) being configured to evacuate the risky fluid leaks from the portion (1P) of the fluid circuit (1).

Securing system (2) according to claim 1, wherein the thermally insulating material (5) is a polyurethane foam. Securing system (2) according to one of claims 1 to 2, the securing system (2) comprising at least one cutting device (8) mounted at least partly in the first casing (3) and configured to cut the thermally insulating material (5). Securing system (2) according to claim 3, wherein the cutting device (8) is mounted at least partly in the second casing (4). Securing system (2) according to one of claims 3 to 4, in which the cutting device (8) is in the form of a flexible metal wire. Securing system (2) according to one of claims 3 to 5, in which the cutting device (8) comprises at least one gripping member (80). Securing system (2) according to one of claims 1 to 6, in which the drainage conduit (6) is made from a material whose modulus of elasticity is between 100 MPa and 3400 MPa. Securing system (2) according to one of claims 1 to 7, in which the drainage conduit (6) is made from a porous or micro-aerated material. Securing system (2) according to one of claims 1 to 8, in which the inner enclosure of the second casing (4) has an inner pressure lower than atmospheric pressure. Fluid circuit (1) connecting a cryogenic tank (R) to an aircraft turbomachine (M) and comprising at least one securing system (2) according to one of claims 1 to 8 securing a portion (1P) of the fluid circuit (1). Fluid circuit (1) according to claim 10, the fluid circuit (1) comprising several securing systems (2) securing the portion (1P) of the fluid circuit (1), the drainage conduits (6) being fluidically connected. Fluid circuit (1) according to claim 9, in which the fluid circuit (1) comprises, at least between the cryogenic tank (R) and the safety system (2), a double-walled pipe (10) comprising an outer conduit (12) and an inner conduit (11) mounted in the outer conduit (12), the outer conduit (12) having an internal pressure lower than atmospheric pressure. Aircraft comprising at least one turbomachine (M), a cryogenic tank (R) and a fluid circuit (1) according to one of claims 10 to 12 mounted between the cryogenic tank (R) and the turbomachine (M). Method for mounting a security system (2) according to one of claims 1 to 9, the mounting method comprising the steps consisting of:

• mount (E1) the drainage pipe (6) along the portion (1P) of the fluid circuit (1)
• mount (E2) the second casing (4) around the portion (1P) of the fluid circuit (1) and the drainage conduit (6),
• mounting (E4) the first casing (3) around the second casing (4) and the portion (1P) of the fluid circuit (1), and
• filling (E6) the buffer volume (9) defined between the first envelope (3) and the second envelope (4) with the thermally insulating material (5).

Method of using a security system (2) according to one of claims 1 to 9, the method of use comprising the steps of:

• absorb the leak (F) in the drainage pipe (6), and
• drain the leak (F) via the drainage pipe (6) out of the safety system.