FR3060652A1 - NACELLE FOR AIRCRAFT TURBOJET ENGINE EQUIPPED WITH A FIRE EXTINGUISHING DEVICE - Google Patents

Abstract

The present invention relates to a nacelle (41) for a turbojet, comprising: an upstream section forming an air inlet, a median section, downstream from said upstream section, comprising: a fan cowl, surrounding a fan casing; a turbojet, a median annular space delimited by said fan cowl and said fan case, said median annular space defining a median fire zone of the nacelle, a downstream section comprising a fixed internal structure (25) surrounding a central compartment (21) of said turbojet, forming a downstream annular space defined by said fixed internal structure and an outer wall (27) of said turbojet, said central compartment defining a downstream fire zone (29) of the nacelle. The nacelle according to the invention is remarkable in that it comprises a fire extinguishing device designed to stifle a fire by constriction when a fire is triggered in said zones (29) of fire.

Description

© Publication no .: 3,060,652 (to be used only for reproduction orders)

©) National registration number: 16 63068 ® FRENCH REPUBLIC

NATIONAL INSTITUTE OF INDUSTRIAL PROPERTY

COURBEVOIE

©) Int Cl ⁸ : F02 C 7/25 (2017.01), B 64 D 29/00

A1 PATENT APPLICATION

©) Date of filing: 21.12.16. ©) Applicant (s): SAFRAN NACELLES Company by (30) Priority: simplified actions - FR. @ Inventor (s): GONIDEC PATRICK and GONTHIER GILLES. (43) Date of public availability of the request: 22.06.18 Bulletin 18/25. (56) List of documents cited in the report preliminary research: Refer to end of present booklet (© References to other national documents ©) Holder (s): SAFRAN NACELLES Joint-stock company related: simplified. ©) Extension request (s): @) Agent (s): CABINET GERMAIN & MAUREAU.

NACELLE FOR AN AIRCRAFT TURBOREACTOR EQUIPPED WITH A FIRE EXTINGUISHING DEVICE.

FR 3 060 652 - A1

The present invention relates to a nacelle (41) for a turbojet engine, comprising:

- an upstream section forming an air inlet,

- a middle section, downstream of said upstream section, comprising:

a fan cover, surrounding a fan casing of a turbojet engine, a median annular space, delimited by said fan cowl and by said fan casing, said median annular space defining a median fire zone of the nacelle,

- a downstream section, comprising a fixed internal structure (25) surrounding a central compartment (21) of said turbojet engine, forming a downstream annular space delimited by said fixed internal structure and by an external wall (27) of said turbojet engine, said central compartment defining a downstream light zone (29) of the nacelle.

The nacelle according to the invention is remarkable in that it comprises a fire extinguisher device designed to smother a fire by constriction when a fire is started in said fire zones (29).

i

The present invention relates to a nacelle for an aircraft turbojet engine equipped with a fire extinguishing device, and a propulsion unit equipped with such a nacelle.

An aircraft is powered by several turbojets each housed in a nacelle. The propulsion unit constituted by a turbojet engine and the nacelle which receives it is shown in FIG. 1.

The propulsion unit 1 comprises a nacelle 3 supporting a turbojet engine 5. The propulsion unit 1 is connected to the aircraft fuselage (not visible) for example by means of a pylon 7 or engine mast intended to be suspended under a wing of the 'plane.

The nacelle 3 generally has a tubular structure comprising an upstream section 9 defining an air inlet 10 upstream of the turbojet engine 5, a middle section 11 intended to surround a fan of the turbojet engine, a downstream section 13 comprising an external cover 15 which can house a thrust reverser device and intended to surround the combustion chamber of the turbojet engine and all or part of the compressor and turbine stages of the turbojet engine, and is generally terminated by an ejection nozzle whose outlet is located downstream of the turbojet engine.

2 shows the propulsion unit 1 of Figure 1, seen in a longitudinal section. The nacelle 3 houses the turbojet 5 which can be of the double flow type, capable of generating, by means of blades of a blower 17, a flow of hot air (also called primary flow), coming from the combustion chamber 19 of the turbojet and circulating downstream of the propulsion unit in a compartment of substantially tubular shape called “core” compartment or central compartment 21, and a flow of cold air (secondary flow) from the blower which circulates outside of the turbojet engine through an annular passage, also called a vein 22, formed between an internal structure defining a fairing of the turbojet engine and an internal wall of the external cowling 15 of the nacelle. The two air flows are ejected from the turbojet engine from the rear of the nacelle.

The central compartment 21 of the turbojet or “core” compartment forms a downstream annular space delimited by an internal wall 23 fixed internal structure 25 of the nacelle or “IFS” (acronym of “Internai Fixed Structure”) surrounding the central compartment 21 and the delimiting the vein 22, and by an external wall 27 of the turbojet engine.

The fixed internal structure 25 of the nacelle typically comprises one or more panels integral with each other. There are mainly two types of composition of a fixed internal structure panel with, on the one hand, the fixed metallic internal structure, comprising a metallic honeycomb sandwich (NIDA) type panel caught between two metallic layers such as skins aluminum, possibly acoustically pierced on the vein side and, on the other hand, the composite fixed internal structures built on the same principle as their metallic equivalent, but for which the metallic layers are replaced by internal skins (central compartment or "core" side ) and external (vein side) made of composite materials (for example: carbon / epoxy or carbon / BMI).

Since the fixed internal structure is subjected to high thermal stresses, it is necessary to protect the panels which make up the fixed internal structure by a thermal protection typically placed on the central compartment or “core” side, this in order to locally maintain the temperatures at acceptable levels and to extend the life of the equipment.

The role of thermal protections is to protect the components of the nacelle from the engine environment, these components can be impacted by the convection of air from the central or “core” compartment, the temperature of which can typically reach 400 ° C. , and by the radiation from the crankcase, the temperature of which can typically reach 750 ° C.

The assembly formed by the IFS covered by a thermal protection also acts as a fire barrier.

In order to strengthen the protection of the components of the nacelle from the engine environment, the nacelles generally include a fire extinguisher device for extinguishing a fire started in certain areas of the nacelle.

The fire extinguishing devices of the prior art are typically designed to allow the extinction of a fire started in a downstream fire zone 29 of the nacelle, defined by the central compartment 21 of the turbojet engine, or even in a zone of central fire 31, defined by a median annular space delimited by an internal wall 33 of a fan cowl 35 and by an external wall 37 of a fan casing 39 of the turbojet engine.

According to an embodiment known from the prior art, such fire extinguishing devices comprise several cylinders containing a chemical extinguisher gas such as Halon. These cylinders are typically distributed in the reactor mast of the nacelle.

The routing of the gaseous fluid from these cylinders to the fire zones is carried out by means of a set of pipes for supplying the extinguishing fluid, disposed within the reactor mast. On the pilot's order, the extinguishing fluid is brought from these cylinders to the fire zones.

A first drawback of such a fire extinguisher device of the prior art is linked to the mass of this extinguishing system.

In fact, the cylinders and the set of pipes for supplying the extinguishing fluid give the propulsion unit an additional mass which should be reduced.

A second drawback of such a fire extinguisher device of the prior art is that the aerodynamic profile of the parts of the mast which receive these cylinders, in particular the trailing edge of the reactor mast, is affected thereby.

Indeed, the presence of these cylinders greatly thickens the aerodynamic lines of the nacelle, in particular the trailing edge area of the engine mast, an area which should be as fine as possible to give the nacelle good aerodynamic properties.

A third disadvantage of this fire extinguisher device of the prior art is that the Halon gas used today as a chemical extinguisher gas is a very high greenhouse gas extinguishing gas which is today incompatible with the current European Union standard "REACH" (English acronym for "Registration, Evaluation and Authorization of Chemicals").

The present invention aims to overcome the aforementioned drawbacks of the prior art, by proposing a fire extinguisher device of reduced mass compared to the extinguishing devices of the prior art, which satisfies the regulations in force in ecological matters and which improves the aerodynamic profile of the nacelle when the fire extinguisher device is installed in the nacelle.

To do this, the present invention relates to a nacelle for an aircraft turbojet engine, comprising:

an upstream section forming an air inlet, a middle section, downstream of said upstream section, comprising:

• a fan cover, intended to surround a fan casing of a turbojet engine, • a median annular space, delimited by an internal wall of said fan casing and by an external wall of said fan casing when said nacelle supports said turbojet engine, said median annular space defining a median fire zone of the nacelle, a downstream section, downstream of said middle section, comprising a fixed internal structure intended to surround a central compartment of said turbojet engine, said central compartment being positioned downstream of a combustion of said turbojet engine and forming a downstream annular space delimited by an internal wall of said fixed internal structure and by an external wall of said turbojet engine when said nacelle supports said turbojet engine, said central compartment defining a zone of fire downstream from the nacelle, said nacelle being remarkable in that it includes an extinguishing device A fire designed to suppress a fire by constriction when a fire breaks out in said fire areas.

Thus, by planning to equip the nacelle with a fire extinguishing device designed to suffocate by constriction a fire started in the fire areas of the nacelle, it is therefore no longer necessary to have recourse to a gas chemical fire extinguisher incompatible with current ecological and environmental regulations.

According to all optional features of the invention: the fire extinguisher device comprises:

• a flexible extinguishing wall, comprising a flexible fabric resistant to heat and fire and at least partially covering the fixed internal structure of the nacelle when said flexible extinguishing wall is in a rest position according to which no fire is 'is triggered in the downstream fire zone of the nacelle, and • a gas generator system, designed to propel a gas inside said flexible extinguishing wall, said flexible extinguishing wall being further designed to moving from its rest position to a so-called active position, towards the downstream fire zone of the nacelle, when a gas is propelled inside said flexible extinguishing wall;

Thus, by providing a flexible extinguishing wall which moves under the effect of a propellant gas towards the fire zone downstream of the nacelle when a fire is started, it is no longer necessary to provide a rich extinguishing gas. chemical extinguishing agents as is the case in the prior art. Thus, the mass of the chemical extinguishing device is considerably reduced compared to the prior art;

the flexible extinguishing wall may advantageously be made of ceramic fabric of the “Nextel” type or of metallic fabric or of metallic felt or of glass fabric;

the flexible extinguishing wall has at least one zone which is impermeable to the gas propelled by the gas generating system and at least one zone which is permeable to an extinguishing gas. By providing a porous zone capable of letting an extinguishing gas escape from the flexible wall, the extinguishing gas crosses the porous zone of the flexible extinguishing wall, which makes it possible to complete the extinction of the fire made by constricting the zone of fire, obtained by displacement of the flexible extinguishing wall. We thus manage to reach certain areas of the nacelle which cannot be completely reached by the flexible extinguishing wall; the flexible extinguishing wall comprises a plurality of compartments and the gas generating device is further designed to move said compartments independently of one another from the rest position to the active position of said flexible wall, in the direction of the area of downstream light of the nacelle, when a gas is propelled inside said flexible extinguishing wall;

the gas generating device is also designed to move:

• a first compartment of the flexible extinguishing wall, positioned at the level of a ventilation air inlet for the fire zone downstream of the nacelle, then • a second compartment of said flexible wall, positioned at a central portion of said downstream fire zone, then • a third compartment of said flexible wall, positioned at an air outlet from said downstream fire zone.

the gas is propelled at a relative pressure of between approximately 0.1 bar and approximately 0.3 bar. By planning to inflate the flexible wall at such a low pressure, the deployment time of the entire flexible extinguishing wall is close to one second, which makes it possible to avoid a deflagration which could occur in the event of inflation at higher pressure, as would be the case using a range of pressure values on the order of that used in the automotive field in order to trigger an airbag;

the internal wall of the fixed internal structure of the nacelle comprises:

• a first so-called cold wall;

• a second so-called hot wall, intended to come into contact with the central compartment of the turbojet engine, constituted by the flexible extinguishing wall, and • an insulating element taken between the first and second walls, integral with said first wall, • a member for retainer, designed to keep the flexible extinguishing wall in contact with the insulating element when the flexible extinguishing wall is in its rest position;

the retaining member comprises at least one fusible portion, designed to rupture when a gas is propelled inside said flexible extinguishing wall;

the flexible extinguishing wall is non-elastic and in that the retaining member is elastic and is designed to bring the flexible extinguishing wall from its active position to its rest position;

the flexible wall is folded, according to a fold-by-fold folding method, when the flexible wall is in its rest position; alternatively, the internal wall of the fixed internal structure of the nacelle is covered at least partially by an intumescent paint designed to thicken when the temperature of the downstream fire zone exceeds a predetermined value;

the fixed internal structure comprises two annular half-covers separated by an internal wall of a lower bifurcation of the nacelle, and the internal wall of said bifurcation is covered at least partially by an intumescent paint designed to thicken when the temperature of the downstream fire zone exceeds a predetermined value;

according to a characteristic common to the embodiments of the invention, the internal wall of the fan cover is covered at least partially by an intumescent paint designed to thicken when the temperature of the middle fire zone exceeds a predetermined value.

The present invention also relates to a propulsion unit for an aircraft comprising a turbojet engine supported by a nacelle according to the invention.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows for the understanding of which reference will be made to the appended drawings in which:

FIG. 1 illustrates a propulsion unit of the prior art in isometric view;

Figure 2 is a longitudinal sectional view of a propulsion unit of the prior art;

Figure 3 is a schematic front view of the propulsion unit according to a first embodiment of the invention, the extinguishing device being in the rest position;

FIG. 4 represents a portion of the fixed internal structure obtained according to the first embodiment of the invention, in a rest position of the fire extinguisher device;

Figure 5 is a view similar to that of Figure 4, the nacelle being illustrated in an active position;

Figure 6 is a view similar to that of Figure 3, the extinguishing device being in the active position;

Figure 7 is a schematic front view of the propulsion unit according to a second embodiment of the invention, the extinguishing device being in the rest position;

Figure 8 is a view similar to that of Figure 7, the extinguishing device being in the active position;

FIG. 9 is a schematic front view of the propulsion unit centered on a center fire zone of the nacelle, the extinguishing device being in the rest position;

Figure 10 is a view similar to that of Figure 9, the extinguishing device being in the active position.

In the description and the claims, the expressions “internal” and “external” are used without limitation with reference to the radial distance from the longitudinal axis of the nacelle, the expression “internal” defining a zone radially closer to the longitudinal axis of the nacelle, as opposed to the expression "external".

It should also be noted that in the description and in the claims, the terms “upstream” and “downstream” must be understood with respect to the circulation of the air flow inside the propulsion unit formed by the nacelle and the turbojet, that is to say from left to right with reference to Figure 2 of the prior art.

In addition, in all of the figures, identical or analogous references represent identical or analogous members or sets of members.

Reference is made to FIGS. 3 to 6 illustrating a propulsion unit obtained according to a first embodiment according to which the fire zone of the nacelle is the central compartment of the turbojet engine.

Reference is made to FIG. 3, illustrating a propulsion unit 40 seen from the front, in a so-called rest position, according to which no fire has yet started.

The nacelle 41 conforms to that described in FIG. 2, that is to say that the nacelle comprises an upstream section forming an air inlet, a middle section, downstream from the upstream section, and a downstream section, downstream of said middle section.

The downstream section comprises the fixed internal structure 25 intended to surround the central compartment 21 of the turbojet engine 5. The central compartment 21 of the turbojet engine 5 forms a downstream annular space delimited by the internal wall 23 of the fixed internal structure 25 and by the external wall Y1 of the turbojet engine. The central compartment thus defines a downstream fire zone 29 of the nacelle, zone in which a fire is likely to be started.

According to a first embodiment of the invention, the nacelle comprises a fire extinguishing device operating in the manner of an airbag which is deployed when a fire is triggered in the downstream fire zone 29 of the nacelle.

By deploying like an airbag, the fire extinguishing device smothers the fire by constriction, that is to say by expelling the oxygen present in the fire zone downstream from the nacelle.

To do this, the fire extinguishing device according to the first embodiment of the invention comprises a flexible extinguishing wall 43 and a gas generator device 45 (visible in FIG. 4) designed to propel a gas to the inside the flexible extinguishing wall 43 and the detailed operation of which is described below.

Reference is made to FIG. 4 in which a portion of the internal wall 23 of the fixed internal structure 25 is shown, equipped with the fire extinguishing device according to the invention, in the rest position, that is to say when no fire is started in the downstream fire area.

The internal wall 23 is equipped with a thermal protection 47 fixed on the internal wall 23, on the side of the central compartment 21 or “core” compartment of the turbojet engine.

The thermal protection 47 comprises an insulating element 49 or thermal mattress, which may be made of silica fibers, ceramic or a microporous material, caught between a first wall 51 known as cold due to its distance relative to the central compartment 21 or compartment "Core" of the turbojet and integral with it, and between a second wall 53 called hot intended to come into contact with the central compartment 21 of the turbojet.

The thermal protection 47 is typically fixed to the internal wall 23 of the fixed internal structure 25 by means of fixing systems, not shown, such as rivets which cooperate punctually with the internal wall 23 over the entire surface of the protection.

Depending on the structure of its constituents, the thermal protection may also comprise a plurality of retaining members 55, keeping the second wall 53 in contact with the insulating element when the fire extinguishing device is at rest, this is i.e. when no fire is started in the downstream fire area.

According to the invention, the second wall 53, called hot wall, is constituted by the flexible extinguishing wall 43.

The flexible extinguishing wall is in the form of a flexible fabric resistant to heat and fire. This fabric can be of the “Nextel” type obtained by weaving ceramic fibers. As a variant, the flexible extinguishing wall can be made of metallic fabric, metallic felt or even glass fabric. The fabric can advantageously be treated so as to be waterproof or water-repellent and oil-repellent in order to avoid any accumulation of fluid by the thermal insulator.

The fabric is advantageously flexible. It can be elastic, so that it has the capacity to return to its initial position after it has been extended. The fabric can alternatively be a non-elastic fabric as will be seen in the following description.

When no fire is started in the downstream fire zone of the nacelle, the flexible extinguishing wall 43 is in a rest position and covers the fixed internal structure of the nacelle at least in part.

Furthermore, the gas generating device 45 is arranged in the propulsion unit so as to propel a gas inside the flexible extinguishing wall 43 when a fire is started. This device can be controlled analogously to the current extinction, that is to say by the pilot.

Reference is made to FIG. 5 in which the internal wall 23 of FIG. 4 is shown in a configuration where a fire has started in the downstream fire zone of the nacelle corresponding to the central compartment 21 of the turbojet engine.

When a fire starts in the downstream fire zone of the nacelle, the gas generating device 45 propels the gas 57 which it contains.

Under the effect of the pressure generated by the propulsion of gas 57 from the gas generating device 45, the flexible extinguishing wall 43 moves in the direction of the downstream fire zone. The flexible extinguishing wall 43 thus passes from its rest position to a so-called active position.

In order to allow the flexible extinguishing wall 43 to move, the retaining members 55 each have a fusible portion 59. This fusible portion is designed to rupture when a tensile force is applied to the retaining member, this tensile force being obtained in the context of the invention when the gas 57 is propelled inside the flexible extinguishing wall 43 when a fire is started in the downstream fire zone of the nacelle.

Additional retaining means (not shown) are provided in order to retain certain portions of the flexible extinguishing wall, this in order to avoid its total displacement towards the downstream fire zone of the nacelle.

Reference is now made to FIG. 6 in which the propulsion unit 40 of FIG. 3 has been represented, after a fire has started in the downstream fire zone 29 of the nacelle defined by the central compartment 21 of the turbojet engine. or "core" compartment.

The flexible extinguishing wall 43 has been moved towards the fire zone 29 downstream of the nacelle under the effect of the pressure generated by the gas 57 propelled by the gas generating device inside the flexible extinguishing wall .

The flexible wall 43 substantially matches the shape of the external wall Yl of the turbojet when it is in its active position when a fire is started in the downstream fire zone of the nacelle corresponding to the central compartment of the turbojet. The flexible extinguishing wall surrounds in its active position the external wall Yl of the turbojet engine, including the engine equipment 61.

In order to allow the smothering of the fire which has started in the downstream fire zone of the nacelle, it is envisaged to move the flexible extinguishing wall 43 towards the downstream fire zone 29 in two stages. To do this, the wall 43 may comprise several separate compartments.

Initially, it is envisaged that the flexible extinguishing wall will move so as to obstruct the air inlet of the downstream fire zone 29, corresponding to an upstream portion of the downstream fire zone 29 of the gondola.

In a second step, it is envisaged that the flexible extinguishing wall 43 continues its movement in the downstream fire zone 29 of the nacelle, until it comes to obstruct the air outlet from the downstream fire zone 29, corresponding to a downstream portion of the downstream light zone 29 of the nacelle.

By providing for such a two-stage deployment of the flexible wall 43, the fire started in the downstream fire zone 29 is extinguished due to the lack of oxygen obtained by constricting the air inlet and outlet of the fire zone downstream of the nacelle.

In order to allow such a displacement in two stages of the flexible extinguishing wall 43 and such a sequenced obstruction of the downstream light zone 29 of the nacelle, the gas generating device comprises a plurality of chambers (not shown). Each chamber contains at least one solid tablet which, once activated, chemically produces the propellant gas 57. The chambers are distributed in the nacelle near the air inlet of the downstream fire zone and near the outlet of air from said fire zone in the rest position of the extinguishing device. The propellant can also be stored in tablets in the liquid state or in pressurized bottles.

The gas generators can advantageously be distributed in the nacelle and in the compartments of the flexible extinguishing wall 43 so that the flexible wall 43 comes to obstruct, when the extinction is controlled, first a first compartment of the flexible extinguishing wall 43 positioned at a ventilation air inlet of the fire zone downstream of the nacelle, corresponding to an upstream portion of the downstream zone, then a second compartment of the flexible extinguishing wall 43 positioned at a central portion of the downstream fire zone, then a third compartment of the flexible extinguishing wall 43 positioned at an air outlet from the downstream fire zone of the nacelle, corresponding to a downstream portion of the downstream fire zone of the nacelle.

Furthermore, the partitioning into compartments of the flexible extinguishing wall 43 also makes it possible, in the event of damage to the fixed internal structure (by perforation for example), to preserve the swelling of the flexible extinguishing wall in the neighboring compartment. to the damaged one. In the event of perforation of the fixed internal structure of the nacelle, the extinguishing fluid leaks at the level of the damaged walls. However, the fact of providing for compartmentalizing the flexible extinguishing wall makes it possible to ensure extinction even in the event of degradation of the fixed internal structure.

The fabric of the flexible wall may be elastic, so that the displacement of the flexible wall towards the downstream fire zone of the nacelle is obtained by extension of the fabric from the rest position of the flexible wall to its active position. Being elastic, the flexible wall has the capacity to return to its initial position after it has been extended, for example by propelling gas from the gas generating device.

Alternatively, the fabric of the flexible wall may be non-elastic. When it is in the rest position, that is to say when no fire is started, the flexible wall is thus folded back on itself, according to a folding process called fold over fold, folding process known to those skilled in the art and which is akin to folding a sail or a parachute.

When the flexible wall is not elastic, the retaining members 55 of the flexible extinguishing wall 43 can be elastic. They are designed to bring the flexible extinguishing wall 43 from its active position to its rest position. The transition from the active position to the rest position is obtained by depressurization of the flexible extinguishing wall. This depressurization can be carried out on the ground or controlled in flight, for example by an air valve remotely controlled at the level of the gas generator (s).

Furthermore, other retention members 55 of longer size can be provided in order to act only when the device is pressurized, in the manner of a mattress ticking, this in order to minimize the effects of the pressurization of the mattress on the surrounding structures. The flexible wall can also be dimensioned in this direction to just outcrop taking up a large part of the pressure forces instead of compressing the surrounding structures.

When a gas from the gas generator device is propelled inside the flexible non-elastic extinguishing wall, the latter unfolds and deploys, from its rest position to its active position, towards the downstream fire zone of the gondola.

The gas used in the context of the present invention to cause the displacement (by extension or by unfolding) of the flexible extinguishing wall is a non-toxic gas for the environment and compatible with the European Union standard in force " REACH ".

By way of example, this gas can be nitrogen. By planning to use a gas such as nitrogen, the mass and the volume relating to the fire extinguishing device are considerably reduced compared to the standards of the prior art, because the gas stored in the device d extinction, which is a propellant gas and not extinguisher, does not include any extinguishing agent and has fewer ingredients than in the prior art.

It is envisaged that the flexible extinguishing wall includes one or more zones which are impermeable to the propellant gas.

As a variant, the flexible extinguishing wall comprises one or more zones permeable to an extinguishing gas. For this purpose, some pellets of the fire extinguisher device can be filled with an extinguishing gas which is non-toxic for the environment, which makes it possible to extinguish the fire by means of an extinguishing gas, in addition to the extinction by smothering of the fire discussed above. When the propellant is inert, it can also play a complementary choking role. This will be the case with nitrogen for example.

The propellant gas produced by the gas generators of the extinguishing device is also advantageously propelled inside the flexible extinguishing wall at a pressure of approximately 0.1 bar.

By planning to inflate the flexible wall at such a low pressure, the deployment time of the entire flexible extinguishing wall is close to one second, which makes it possible to avoid a deflagration which could occur in the event of inflation at higher pressure, as would be the case using a range of pressure values on the order of that used in the automotive field in order to trigger an airbag.

In the context of the present invention, it has moreover been found that the inflation is satisfactory up to a pressure of the order of 0.3 bar. Higher pressures can be envisaged for partitioned walls. On the other hand, the inflation time must avoid any violent unsteady phenomenon potentially penalizing the surrounding structure.

According to a second embodiment of the invention shown in Figures 7 and 8 illustrating a propulsion unit 62 seen from the front, the internal wall 63 of the fixed internal structure 65 of the nacelle 66 is covered with an intumescent paint 67 coming under the thermal protection 69 and coming from the side of the central compartment 21 or “core” compartment of the turbojet engine.

The thermal protection 69 comprises an insulating element or thermal mattress, which may be made of silica fibers, ceramic or a microporous material, caught between a first so-called cold wall due to its distance relative to the central compartment 21 or compartment "core »Of the turbojet engine and integral with it, and between a second so-called hot wall intended to come into contact with the central compartment 21 of the turbojet engine.

The first cold wall and the second hot wall can for example be made of stainless steel.

As shown in FIG. 8, the intumescent paint 67 thickens when the temperature in the downstream fire zone 29 exceeds a predetermined value.

Thus, in the event of a fire starting in the downstream fire zone, the intumescent paint covering the internal wall of the fixed internal structure of the nacelle thickens, until the fire is suppressed by constriction which has started.

Furthermore, in order to reinforce the capacity of the fire extinguishing device according to this second embodiment, it is envisaged to cover the internal wall 71 with a lower bifurcation 73 of the nacelle with intumescent paint when the internal structure is fixed comprises two annular half-covers 68, 70.

According to a characteristic applicable to the two embodiments of the nacelle which precedes and represented in FIGS. 9 and 10 illustrating a propulsion unit 75 seen from the front, the internal wall 33 of the fan hood 35 is covered at least partially by an intumescent paint 77 coming from on the side of the middle fire zone 31 defined by a median annular space delimited by the internal wall 33 of the fan cowl 35 and by an external wall 37 of the fan casing 39 of the turbojet engine.

As shown in Figure 10, the intumescent paint 77 thickens when the temperature in the middle fire zone 31 exceeds a predetermined value.

Thus, in the event of a fire in the middle fire zone, the intumescent paint covering the internal wall of the fan cover thickens, until the fire is suppressed by constriction which has started. It is also possible to coat the fan casing with this intumescent paint. In this case, the inflation will take place from the engine to the fan cover. This variant is particularly well suited to the lower part of the fan hood and where the intumescent paint can be spread in front of a ventilation outlet to obstruct it in priority during a fire.

This embodiment by intumescent paint is particularly suitable for the fan cover where the thickness of the compartment is often quite small and where the paint can be used alone.

It goes without saying that the present invention is not limited to the sole embodiments of this nacelle and of this propulsion unit, described above only by way of illustrative examples, but on the contrary embraces all the variants involving the technical equivalents of the means described as well as their combinations if these fall within the scope of the invention.

Claims (15)

1. Nacelle (41, 66) for an aircraft turbojet engine, comprising: an upstream section forming an air inlet, a middle section, downstream of said upstream section, comprising: • a fan cover (35), intended to surround a fan casing (39) of a turbojet engine, • a median annular space, delimited by an internal wall (33) of said fan cover (35) and by an external wall (37) of said fan casing (39) when said nacelle supports (41, 66) said turbojet engine, said median annular space defining a median fire zone (31) of the nacelle, a downstream section, downstream of said middle section, comprising a fixed internal structure (25) intended to surround a central compartment (21) of said turbojet engine, said central compartment being positioned downstream of a combustion chamber of said turbojet engine and forming a downstream annular space delimited by an internal wall (23) of said fixed internal structure (25) and by an external wall (27) of said turbojet when said nacelle supports said turbojet, said central compartment defining a downstream light zone (29) of the nacelle, said na that being characterized in that it comprises a fire extinguishing device designed to smother a fire by constriction when a fire starts in said fire zones (29, 31). 2. Nacelle (41) according to claim 1, characterized in that the fire extinguishing device comprises: a flexible extinguishing wall (43), comprising a flexible fabric resistant to heat and fire and at least partially covering the fixed internal structure (25) of the nacelle when said flexible extinguishing wall (43) is in a rest position according to which no fire is started in the downstream fire zone of the nacelle (29), and a gas generating device (45), designed to propel a gas (57) inside said flexible wall extinguisher (43), said flexible extinguishing wall (43) being further designed to move from its rest position to a so-called active position, towards the downstream light zone (29) of the nacelle, when a gas (57) is propelled inside said flexible extinguishing wall (43). 3. Nacelle (41) according to claim 2, characterized in that the flexible extinguishing wall (43) is made of ceramic fabric of the "Nextel" type or metallic fabric or metallic felt or glass fabric. 4. Nacelle (41) according to one of claims 2 or 3, characterized in that the flexible extinguishing wall (43) has at least one gas-tight zone (57) propelled by the gas generator system and at least an area permeable to an extinguishing gas. 5. Nacelle (41) according to any one of claims 2 to 4, characterized in that the flexible extinguishing wall (43) comprises a plurality of compartments and in that the gas generating device (45) is furthermore designed to move said compartments independently of each other from the rest position to the active position of said flexible wall, in the direction of the downstream light zone (29) of the nacelle, when a gas (57) is propelled to the inside said flexible extinguishing wall (43). 6. Nacelle (41) according to claim 5, characterized in that the gas generating device (45) is further designed to move: a first compartment of the flexible extinguishing wall (43), positioned at the level of a ventilation air inlet for the fire zone downstream of the nacelle, then a second compartment of said flexible wall, positioned at a central portion of said downstream fire zone, then a third compartment of said flexible wall, positioned at an air outlet from said downstream fire zone. 7. Nacelle according to (41) any one of claims 2 to 6, characterized in that the gas (57) is propelled at a relative pressure between about 0.1 bar and about 0.3 bar. 8. Nacelle (41) according to any one of claims 2 to 7, characterized in that the internal wall of the fixed internal structure of the nacelle comprises: a first wall (51) called cold; a second wall (53) called hot, intended to come into contact with the central compartment (21) of the turbojet engine, constituted by the flexible extinguishing wall (43), and an insulating element (49) taken between the first and second walls, integral with said first wall (51), a retaining member (55), designed to keep the flexible extinguishing wall (43) in contact with the insulating element (49) when the flexible extinguishing wall (43) is is in its rest position. 9. Nacelle (41) according to claim 8, characterized in that the retaining member (55) comprises at least one fusible portion (59), designed to rupture when a gas (57) is propelled inside of said flexible extinguishing wall (43). 10. Nacelle (41) according to claim 8, characterized in that the flexible extinguishing wall (43) is non-elastic and in that the retaining member (55) is elastic and is designed to bring the flexible wall d extinction (43) from its active position to its rest position. 11. Nacelle (41) according to any one of claims 2 to 10, characterized in that the flexible extinguishing wall (43) is folded, according to a fold-by-fold folding method, when said flexible wall (43) is in its rest position. 12. Nacelle (66) according to claim 1, characterized in that the internal wall (23) of the fixed internal structure (25) of the nacelle is covered at least partially by an intumescent paint (67) designed to thicken when the temperature of the downstream fire zone (29) exceeds a predetermined value. 13. Nacelle (66) according to claim 12, in which the fixed internal structure (25) comprises two annular half-covers (68, 70) separated by an internal wall (71) of a lower bifurcation (73) of the nacelle , characterized in that the internal wall of said bifurcation is covered at least partially by 5 an intumescent paint designed to thicken when the temperature of the downstream fire zone (29) exceeds a predetermined value. 14. Nacelle (41, 66) according to any one of claims 1 to 13, characterized in that the internal wall (33) of the fan cover (35) is covered At least partially by an intumescent paint (77) designed to thicken when the temperature of the middle fire zone (31) exceeds a predetermined value. 15. Propulsion unit (40, 62, 75) for aircraft, characterized in that it 15 comprises a turbojet engine supported by a nacelle (41, 66) according to any one of claims 1 to 14. PRIOR ART 2/5