EP1609507B1 - System to extinguish a fire by injection of a gas generated by the combustion of a pyrotechnical charge - Google Patents

Description

TECHNICAL FIELD AND PRIOR ART

The invention relates to fire-fighting apparatus, ie fire extinguishers. In particular, the invention finds its application in stationary fire extinguishing devices that can be triggered remotely.

The invention relates more particularly to the generation of an inert gas by combustion of a pyrotechnic composition and the diffusion of this gas in the fire zone with a controlled flow rate; the invention relates to an extinguisher comprising a combustion chamber, a control system and diffusion means in the fire zone, in particular used in the field of aeronautics.

STATE OF THE PRIOR ART

Most of the time, extinguishing devices include a tank containing an extinguishing agent that is diffused over the fire zone to extinguish it, but also prevent its extension.

Agent tank extinguishers are classified into two broad categories. The first category concerns permanent pressure devices in which a gas ensures the constant pressurization of the agent within a single bottle that serves as a reservoir. The extinguishing agent is released by a valve at the outlet of said bottle. In the In the second category, a propellant is released only when the extinguisher is put into service and propels the extinguishing agent, which is therefore not stored under pressure.

By way of illustration, as fire extinguisher of the first type, extinguishers currently used to extinguish an aircraft engine fire can be considered. These devices use halon as an extinguishing agent, stored in liquid form because of the level of pressurization of the bottle used as a reservoir. Depending on the safety requirements, two or more fire extinguishers may be installed. One or more distribution lines connected to each bottle allow the distribution of the agent to the area or areas to be protected. At the bottom end of the bottle, a calibrated seal is used to seal the distribution line to keep the halon in the bottle. A pressure sensor is also installed to continuously check the pressurization of the bottle. When a fire is detected, a pyrotechnic detonator is triggered: the shock wave generated by this detonator pierces the shutter seal, which causes the emptying of the bottle and the evacuation of the extinguishing agent under the effect pressure to the areas to be protected via the distribution pipes.

For second category extinguishers, they use a separate pressurizing device. These fire-fighting devices are generally equipped with a first compressed gas tank and a second tank for the extinguishing agent. When the device is used, the gas contained in the first tank is communicated through an orifice with the second tank, which allows the pressurization of the bottle containing the extinguishing agent. Sometimes the first compressed gas tank is replaced by a gas generator as described in the document WO 98/02211 . In all cases, when the extinguishing agent is pressurized, it is ejected fire extinguishers of the second category for fire fighting, as for appliances of the first category.

The patent US 6,257,341 discloses an extinguisher comprising a closed chamber 1 which contains an inert gas composition 2 before use, that is to say before the burning of the propellant gas 3 begins.

The document US 2002/070035 discloses an extinguishing system comprising two closed enclosures 1 which each contain compressed nitrogen before use, that is to say before opening the quenching device 5 regulating the flow of nitrogen.

The disadvantages of these extinguishers, whatever the category considered, is the continuous storage of the extinguishing agent, with the necessary monitoring and verification operations, such as periodic weighing. For the devices used for the extinction of fires on board aircraft, belonging to the first category, are added the requirements related to the pressure storage of the extinguishing agent, and in particular the problems caused by their sensitivity to micro leaks.

STATEMENT OF THE INVENTION

The invention aims to overcome the drawbacks mentioned fire extinguishers, including fires in aircraft engines, among other benefits.

To do this, the invention relates in one aspect to a fire extinguishing device whose extinguishing agent is an inert gas produced only when necessary, that is to say at the time of use of the fire extinguisher, by burning a pyrotechnic material appropriately selected. It is thus possible to generate a large quantity of inert gas whose composition depends on the nature of the pyrotechnic material; in particular, the gas may comprise more than 20% nitrogen or more than 20%, or even 40%, of a mixture of neutral gases such as nitrogen, carbon monoxide and / or dioxide. Preferably, the inert gas generated will consist essentially of nitrogen given its relative ease of production by pyrotechnic combustion.

The generated nitrogen is injected into the areas where the fire has been detected. To ensure reliable extinguishing, the inert gas is expelled from the extinguishing device according to a regulated pressure, in order to be able in particular to bring the quantity of oxygen in the fire zones to follow a predetermined profile as a function of time, for example a concentration stage. quasi-constant for a non-zero time period.

The device according to the invention therefore comprises a pyrotechnic gas generator associated with means for distributing the gas generated as extinguishing agent and means for regulating the pressure therein.

Advantageously, the gas generator comprises an enclosure comprising a propellant block and a pyrotechnic igniter. The ignition of the pyrotechnic igniter by electric current allows for example the start of the combustion of the propellant whose decomposition allows the generation of an inert gas.

Preferably, the extinguishing device comprises filters located in the enclosure of combustion or in the distribution means, so that the soot and ash also produced by the combustion of the pyrotechnic composition do not reach the fire zone.

Advantageously, the device comprises means for cooling the generated gas.

The extinguishing device may comprise a variable number of gas generators, which are connected to the same distribution means. It is also possible to have several pyrotechnic materials of different compositions in the same enclosure.

The regulation means are parameterized beforehand by determining the pressure at which the inert gas is expelled from the chamber, directly related to the flow rate of the gas ejected on the fire zone and the concentration, oxygen or other component, sought in the areas to be treated. Depending on the geometry of the distribution network, the dimensions and the ventilation of the zones to be treated, taking into account the head losses or the arrangement of the zones to be treated, those skilled in the art can determine the required pressure. These calculations can be refined during experiments.

According to one embodiment, the pressure regulation means consist of at least one control valve located in the dispensing means, whose opening is controlled during the trigger sequence of the extinguisher, or by an order outside, or by pressurizing the combustion chamber. The control valve is advantageously controlled according to a given law and defined by the user, possibly using the information from sensors, which for example measure the oxygen concentration in the areas to be treated; this allows a closed loop regulation, even finer, of the gas pressure.

The opening of the valve can be controlled remotely, by manual control, or by a control mechanism coupled to the firing means of the pyrotechnic composition.

The geometry of the pyrotechnic material block also makes it possible to generate combustion gases according to a predetermined law. The regulating means can thus, alternatively or alternatively, consist of a determination of the various parameters of the gas generator, and in particular of the geometry of the propellant block, which ensures a controlled generation of inert gas injected into the zones to be protected.

In this case, it is possible to replace the regulating valve by a calibrated orifice: once triggered, the combustion of the block of pyrotechnic material no longer requires control, and the calibrated orifice makes it possible to control the pressure at which the combustion of the propellant so as to ensure the flow of agent necessary for the inert gas of the fire zones.

The regulation can also, alternatively or in addition, be provided by other regulating devices such as a regulator associated or not with a device that creates a pressure difference (diaphragm, nozzle).

Whatever the means of regulation, they make it possible to optimize the time during which the concentration of inert agent will lead, for example, to an oxygen content of less than 12% in the fire zones under consideration. In this way, it is also possible to create concentration slots of varying shape and to precisely control the duration and level of protection of the area.

In one aspect of the invention, the extinguisher can be triggered by a remote operator. It can also be put into operation directly by an ignition device receiving the information of a sensor which detects the conditions related to the probability of a fire. To avoid undesired triggering, especially during maintenance operations, the device may be equipped with neutralization means.

The extinguishing device according to the invention is preferably used in aircraft, more particularly in turbojet engines where it makes it possible to dispense with the halogenated extinguishing agents currently used.

BRIEF DESCRIPTION OF THE DRAWINGS

• La figure 1 représente un dispositif d'extinction conforme à l'un des modes de réalisation de l'invention.
• La figure 2 montre une alternative au dispositif d'extinction selon l'invention.
• La figure 3 montre un autre mode de réalisation de l'extincteur selon l'invention.
• La figure 4 montre schématiquement le montage à bord d'un aéronef d'un dispositif d'extinction feu moteur selon l'invention.
• Les figures 5 représentent les courbes d'évolution de la concentration en oxygène dans deux zones feu équipées d'un dispositif d'extinction suivant l'invention.

The appended figures and drawings will make it possible to better understand the invention, but are given only as an indication and are in no way restrictive.

• The figure 1 represents an extinguishing device according to one of the embodiments of the invention.
• The figure 2 shows an alternative to the extinguishing device according to the invention.
• The figure 3 shows another embodiment of the extinguisher according to the invention.
• The figure 4 schematically shows the mounting on board an aircraft of a fire extinguishing device according to the invention.
• The figures 5 represent the evolution curves of the oxygen concentration in two fire zones equipped with an extinction device according to the invention.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

As shown in figure 1 , the extinguishing device or fire extinguisher 1, comprises an inert gas generator 2 associated with gas distribution means 4. The gas distribution means 4 may consist of a pipe long enough to reach the fire zone 6, or coupled to any known dispensing device 8, such as for example a multi-outlet pipe.

The gas generator 2 is constituted by a combustion chamber 10, for example cylindrical, in which is placed a pyrotechnic cartridge 12, usually consisting of propellant. The combustion of the propellant, initiated by the ignition device 14, generates an inert gas which flows into the distribution means 4 via an outlet orifice 16.

The inert gas, largely composed of nitrogen and / or carbon monoxide, produced by the combustion decomposition of pyrotechnic compositions, is at a high temperature, and a Rapid cooling may be necessary before introduction into fire zones. Cooling means can thus be provided, for example an "active" filter, that is to say a chemical compound introduced into or outside the combustion chamber 10 and absorbing part of the heat of combustion, or a metal filter. Moreover, it may be desirable for filters, chemical and / or mechanical, to be present in order to filter the soot.

These different filters 18 may be located upstream and / or downstream of the gas outlet orifice 16, in the enclosure 10 or in the distribution means 4.

Advantageously, the outlet orifice 16 of the combustion chamber 10 can be closed by a closure device 20, in order to isolate the propellant from the external environment as long as its action is not required. In particular, the closing device 20 may be a tared cover, that is to say a membrane which breaks or opens after ignition as soon as the pressure inside the combustion chamber 10 reaches a certain level. threshold.

The pressure inside the chamber 10 is advantageously atmospheric pressure when the extinguishing device 1 is not used. As soon as the ignition device 14 is triggered, the propellant block 12 begins to burn and to generate a pressure in the chamber 10. The ignition device 14 may consist of any known device. It can be triggered manually, by direct action on the device 14.

Preferably, the ignition device 14 is triggered remotely via a control line 22, which can be coupled to a control unit 24. Advantageously, a signal 26 from a fire detector can be used as an automatic release via the control unit 24. In this case of automatic triggering, it may be preferable to provide a device 28 for disabling the control means 22. It may also be useful to provide a device manual release 30 on the control box 24 and / or the ignition device 14.

In order to extinguish the fire, the supply of oxygen in the burned zone 6 is restricted. For this purpose, the gas generated by the combustion of the pyrotechnic unit 12 and ejected by the dispensing device 8 makes it possible to reduce the relative concentration of 'oxygen. It is desirable that the gas generated is inert, but also that it is not polluting or corrosive, especially in the context of a fire zone 6 located in an aircraft engine. In this regard, the gas generated therefore comprises a nitrogen portion, at least 20% or even 40%, obtained by the combustion of a pyrotechnic composition strongly "nitrogenous"; it is also possible to associate the nitrogen, for example with carbon dioxide to increase the concentration of injected neutral gas and reach the desired thresholds.

It is commonly accepted, for example, that below an oxygen concentration of 12%, no fire can survive. It is possible to determine the amount of gas to be injected into the fire zone 6 in order to reach this O _{2 level} ; in case of fire zones ventilation, the rate of air renewal is taken into account when calculating the quantity of gas to be injected. This makes it possible to determine the quantity of pyrotechnic product 12 to be placed in the fire extinguisher under consideration.

In order to optimize the extinguishing capabilities, a fire extinguisher 1 according to the invention is provided with a system for regulating the flow of gas at the outlet of line 8 in the fire zone 6, that is to say means for regulating the pressure prevailing in the distribution means 4. By virtue of such a pressure control, it is possible to minimize the quantity of pyrotechnic material 12 and / or the size of the enclosure 10 while ensuring that the fires are off. For example, the pressure regulating means make it possible to obtain a predetermined profile of the oxygen concentration in the fire zone, such as a plateau during a non-zero period of time, or a slotted profile; it is clear that each of the concentrations can have a margin of error with respect to the theoretical fixed value of the plateau. Thus, a bearing may be a "flattened Gaussian", or a curve between two values separated by less than 10% of the value of the bearing.

According to a preferred embodiment, the closing device 20 of the gas generator 2 can thus be a control valve, advantageously controlled remotely by first control means 32. Such control valves are known for example from WO 93/25950 or US-A-4,877,051 , and commercially available.

The first control means 32 may be a control line coming from a control unit 24, advantageously confused with that used to trigger the ignition device 14. The information input into the control unit 24 makes it possible to modify manually or automatically, according to a predetermined sequence or as a function of measured parameters, the degree of opening and / or closing of the valve 20.

For example, it is possible to provide a sensor measuring the oxygen concentration in the fire zone 6: by the control line 34, the unit 24 can modify the signal sent by the first control means 32 to regulate the opening of the valve 20.

Extinguishing devices 1 according to the invention can be connected in parallel and for example be connected to the same distribution device 8. Another embodiment, presented on the figure 2 , relates to the presence of several generators 2a-2e of inert gas within the same extinguishing device 1. The pyrotechnic material blocks 12a-12e of each of these generators can be of nature (composition, geometry, as it will be explained later) similar or different. The ignition devices 14a-14e of each of the generators 2a-2e can be triggered independently or simultaneously. Advantageously, control means can trigger selectively combustion and thus optimize the number of generators 2a-2e used according to the detection and fire parameters, or choose the most appropriate generator if the nature of the propellant blocks 12 is different.

In this embodiment, it is possible for each gas generator 2a, 2b to be placed in communication with the distribution means 4 by its own duct 4a, 4b provided with its regulation valve 20a, 20b. It is also possible to provide a single valve 20f located on a conduit 4f leading to generators 2c, 2d, 2e coupled together via conduits 4c, 4d, 4e. As for the embodiment presented in figure 1 , the regulation can be carried out in open or closed loop.

Another possibility for realizing the regulation of the pressure according to the invention is to calibrate the block of pyrotechnic material in order to generate a pressure in the enclosure 10 conforming to a defined profile. This pressure P (stop pressure) is transmitted directly, and in a parameterized and controlled manner, to the distribution means 4 and thus to the fire zone 6.

As it is known for example from the propulsion of the rockets, it is indeed possible, by judiciously choosing the nature of the propellant and the geometry of the block, to obtain a controlled flow rate of generated gas, and therefore a regulated pressure. in the enclosure 10. In this case, even if a control valve 20 can be provided, it is possible to have between the combustion chamber 10 and the distribution means 4 than a simple closure device such as a tared cap, or even directly connect the outlet port 16 to the distribution means 4. An embodiment of such a extinguishing device is presented in the figure 3 .

Advantageously, the outlet orifice 16 is provided with a nozzle 36, shaped if possible so that the speed of sound is reached at the minimum section of the nozzle 36. This allows to isolate the gas generator 2 distribution means 4; the pressure fluctuations in the distribution pipe 4 do not therefore disturb the combustion of the pyrotechnic material 12, which allows better control of the parameters.

In particular, it is possible to calibrate the block of combustible material 12 so as to obtain a flow of gas leaving the enclosure 10 through the opening 16 equal to a determined value. The means for regulating the pressure, and therefore the flow rate of the inert agent in the fire zone 6, are then directly integrated into the gas generator 2: a simple control on the ignition device 14 makes it possible to ensure that the flow rate is fixed beforehand. .

avec :

Q :

débit (kg/s);

ρ :

masse volumique du propergol (kg/m³) ;

S_c :

surface de combustion du propergol (m²) ;

V_c :

vitesse de combustion du propergol (m/s).

Indeed, mathematical formulas make it possible to link together the various parameters (pressure, speed and combustion surface, flow rate of gas generated, etc.) in order to optimize the geometry of a block of combustible material, of its enclosure. combustion, and the initial conditions for a given pyrotechnic material in order to achieve the flow of desired inert gas. Thus the flow of gas generated by the combustion of a pyrotechnic material 12 such as propellant is: $$\mathrm{Q}\mathrm{=}\mathrm{\rho }{\mathrm{S}}_{\mathrm{VS}}{\mathrm{V}}_{\mathrm{VS}}\mathrm{,}$$

with:

Q:

flow rate (kg / s);

ρ:

density of the propellant (kg / m ³ );

S _c :

propellant combustion surface (m ² );

V _c :

propellant burning rate (m / s).

It should be noted that the surface S _c depends on the shape of the block; in particular, it can be scalable during combustion.

avec :

a,n :

coefficients dépendant de la composition du propergol et déterminés expérimentalement ;

P :

pression d'arrêt (Pa) régnant dans la chambre de combustion 10.

On the other hand, the burning rate of the propellant V _c is a function of the pressure prevailing in the combustion chamber, namely: $${\mathrm{V}}_{\mathrm{VS}}\mathrm{=}\mathrm{at}\mathrm{.}{\mathrm{P}}^{\mathrm{not}}\mathrm{,}$$

with:

a, n:

coefficients depending on the composition of the propellant and determined experimentally;

P:

stopping pressure (Pa) in the combustion chamber 10.

avec

P :

pression d'arrêt (Pa) ;

A_t :

surface de la tuyère 36 au col (m²) ;

1/C_et :

coefficient de débit (s/m), dépendant de la nature du gaz généré ;

C_d :

coefficient inhérent à la nature de la tuyère.

Finally, the flow of gas passing through a nozzle is expressed by: $$\mathrm{Q}\mathrm{=}\frac{{\mathrm{PA}}_{\mathrm{t}}}{{\mathrm{VS}}_{\mathrm{and}}}\mathrm{.}{\mathrm{VS}}_{\mathrm{d}}\mathrm{,}$$

with

P:

stop pressure (Pa);

At _t :

surface of the nozzle 36 at the neck (m ² );

1 / C _and :

flow coefficient (s / m), depending on the nature of the gas generated;

C _d :

coefficient inherent to the nature of the nozzle.

It suffices to solve these equations according to the intrinsic characteristics of the propellant chosen (p, a, n, C _and ) and the ejection conditions of the desired gases (A _t , P, V _c ) to define the geometry of the gas generator to provide the desired flow profile for the required time.

The device according to the invention is particularly suitable for application in aircraft. The figure 4 schematically shows the mounting on board a turbine engine 40 of an aircraft of a device 1 for extinguishing engine fire according to the invention, which can be triggered on detection of fire and / or smoke.

Example : Application of the invention to extinguishing engine fire for aircraft.

The generation of inert gas, preferably nitrogen, and more than 20%, or even 30% or 40%, is obtained by the combustion of a pyrotechnic composition "highly nitrogenous". The main characteristics to consider when choosing a pyrotechnic composition are the efficiency in terms of gas production, the density of the material, the combustion temperature and the secondary species generated by the combustion. The toxic or / and corrosive appearance of the fumes must also be taken into account, which leads to the automatic elimination of certain compositions. In particular, a composition recommended in the context of aircraft relates to a mixture of sodium azide and copper oxide (NaN ₃ / CuO) which gives by combustion 40.1% nitrogen. Another possibility relates to guanidine nitrate associated with strontium nitrate (NG / Sr (NO ₃ ) ₂ ) whose combustion gives 32.5% of nitrogen and 20% of carbon dioxide. Is also possible the association of basic copper nitrate and guanidine nitrate (BCN / NG) to produce a gas containing 24.7% N ₂ and 16.9% CO ₂ .

To evaluate the quantity of nitrogen to be injected, the ventilation rate and the size of the zone (s) concerned are taken into account. For example, a motor 40 will be considered according to the figure 4 with both fire zones A and B having the following characteristics: Volume
V (m ³ ) Ventilation Q _R (m ³ / s)
(air change rate) Zone A 1,416 0.212 Zone B 0.476 0.285

The inert agent generator is constituted as previously described by a combustion chamber 10, provided with a block 12 of pyrotechnic product as specified above, an ignition device 14 and a filter 18, equipped to an end of a nozzle 36 shaped so that the speed of sound is reached at the minimum section of the nozzle.

• une phase d'extinction E (phase « booster ») : diminution du taux d'oxygène de 21 % (concentration nominale en oxygène de l'air en volume) à 11 % en 1,5 s.
• une phase de maintien M (phase « d'inertage », ou « sustainer ») : maintien de la concentration en oxygène à 11 % pendant 3,5 s.

It is desired that the inerting of the fire zones 6, lasts 5 seconds. Other settings over time are often preferred or even imposed by the regulations, and in this case, we wish:

• an extinction phase E ("booster" phase): reduction of the oxygen content by 21% (concentration nominal oxygen in the air volume) at 11% in 1.5 s.
• a maintenance phase M ("inerting" phase, or "sustainer"): maintaining the oxygen concentration at 11% for 3.5 s.

It can thus be noted that during the maintenance phase M, the flow rate of nitrogen (or of inert gas) is lower than during the extinction phase E. This two-phase regime can be obtained in various ways, such as the use of two different pyrotechnic compositions. Preferably, and as described below, the evolution of the combustion profile of the propellant block (geometrical evolution of the burning surface) makes it possible to obtain such a regime.

ce qui donne (par définition, le débit du générateur ne contient pas d'oxygène et CI = 0) : $$\mathrm{C}\left(\mathrm{t}\right)\mathrm{=}\mathrm{k}\mathrm{.}\exp \left(\mathrm{-}\left(\frac{{\mathrm{Q}}_{\mathrm{R}}\mathrm{+}{\mathrm{Q}}_{\mathrm{I}}}{\mathrm{V}}\right)\mathrm{t}\right)\mathrm{+}\frac{{\mathrm{Q}}_{\mathrm{I}}{\mathrm{C}}_{\mathrm{I}}\mathrm{+}{\mathrm{Q}}_{\mathrm{R}}{\mathrm{C}}_{\mathrm{R}}}{{\mathrm{Q}}_{\mathrm{R}}\mathrm{+}{\mathrm{Q}}_{\mathrm{I}}}\mathrm{=}\mathrm{k}\mathrm{.}\exp \left(\mathrm{-}\frac{{\mathrm{Q}}_{\mathrm{S}}\mathrm{t}}{\mathrm{V}}\right)\mathrm{+}\frac{{\mathrm{Q}}_{\mathrm{R}}{\mathrm{C}}_{\mathrm{R}}}{{\mathrm{Q}}_{\mathrm{S}}}$$

The evolution over time of the oxygen concentration C (t) in a fire zone 6 as schematized in figure 3 as a function of the fresh air flow (renewal of air in the zone) Q _R , of the flow from the gas generator injected into the fire zone Q _I (these two flows being removed from the fire zone 6 by the flow rate Q _S = Q _R + Q _I ), and relative oxygen concentrations C _R and C _I of these two input rates can be expressed by the differential equation: $$\mathrm{VS}\left(\mathrm{t}\mathrm{+}\mathrm{dt}\right)\mathrm{=}\mathrm{VS}\left(\mathrm{t}\right)\mathrm{+}\frac{{\mathrm{VS}}_{\mathrm{R}}{\mathrm{Q}}_{\mathrm{R}}\mathrm{+}{\mathrm{VS}}_{\mathrm{I}}{\mathrm{Q}}_{\mathrm{I}}}{\mathrm{V}}\mathrm{dt}\mathrm{-}\mathrm{VS}\left(\mathrm{t}\right)\mathrm{.}\frac{{\mathrm{Q}}_{\mathrm{S}}}{\mathrm{V}}\mathrm{dt}$$

which gives (by definition, the flow of the generator does not contain oxygen and CI = 0): $$\mathrm{VS}\left(\mathrm{t}\right)\mathrm{=}\mathrm{k}\mathrm{.}\exp \left(\mathrm{-}\left(\frac{{\mathrm{Q}}_{\mathrm{R}}\mathrm{+}{\mathrm{Q}}_{\mathrm{I}}}{\mathrm{V}}\right)\mathrm{t}\right)\mathrm{+}\frac{{\mathrm{Q}}_{\mathrm{I}}{\mathrm{VS}}_{\mathrm{I}}\mathrm{+}{\mathrm{Q}}_{\mathrm{R}}{\mathrm{VS}}_{\mathrm{R}}}{{\mathrm{Q}}_{\mathrm{R}}\mathrm{+}{\mathrm{Q}}_{\mathrm{I}}}\mathrm{=}\mathrm{k}\mathrm{.}\exp \left(\mathrm{-}\frac{{\mathrm{Q}}_{\mathrm{S}}\mathrm{t}}{\mathrm{V}}\right)\mathrm{+}\frac{{\mathrm{Q}}_{\mathrm{R}}{\mathrm{VS}}_{\mathrm{R}}}{{\mathrm{Q}}_{\mathrm{S}}}$$

In the extinction phase E, we want that in a well defined time (in the example 1.5 s), we have reaches a concentration of 11% (by volume) of oxygen. Now, C _R = 0.21, and when t = 0, C (t) = C _R , where k = C _{R ·} (Q _S - Q _R ) / Q _S.

.So we have ${\mathrm{VS}}_{\mathrm{E}}\left(\mathrm{t}\right)\mathrm{=}{\mathrm{VS}}_{\mathrm{R}}\left(\mathrm{1}\mathrm{-}\frac{{\mathrm{Q}}_{\mathrm{R}}}{{\mathrm{Q}}_{\mathrm{S}}}\right)\mathrm{.}\exp \left(\mathrm{-}\frac{{\mathrm{Q}}_{\mathrm{S}}\mathrm{t}}{\mathrm{V}}\right)\mathrm{+}\frac{{\mathrm{Q}}_{\mathrm{R}}{\mathrm{VS}}_{\mathrm{R}}}{{\mathrm{Q}}_{\mathrm{S}}}\mathrm{.}$

.

In the maintenance phase M, it is desired that during a well-defined time (in the 3.5 s example), the oxygen concentration be maintained at a level very close to that reached at the end of the booster phase and below the minimum rate. necessary for combustion. In the same way, C _R = 0.21, and at any time, C _M (t) = C _min = 0.11, where k = C _min - (Q _{R ·} C _R ) / Q _S.

The quantity of inert gas to be injected during this phase is therefore directly obtained: Q _IM = (Q _R / C _min ) _· (C _R - C _min ).

All calculations made, the following values are obtained for the volume flow of inert gas to be injected in the fire zones: Diet Duration (s) Q _I (m ³ / s) Zone A Q _I (m ³ / s) Zone B Total (m ³ / s) V _total (m ³ ) Booster E 1.5 0.7 0.35 1.05 1.58 M maintenance 3.5 0.192 0.259 0.45 1.58 3.16

The evolution of oxygen concentration at one point for these two fire zones is shown in Figure 5A for zone A and in Figure 5B for zone B, where the horizontal line represents the level of oxygen concentration to be reached to secure the fire zone considered, ie 12%.

It is clear that it would also be possible with an extinguishing device according to the invention to manage the rate of inert agent so as to have an oxygen concentration in the evolutive fire zone following a given profile, for example in crenellations.

There are many pyrotechnic compositions whose combustion generates a large quantity of inert gas consisting mainly of nitrogen and / or carbon dioxide and / or carbon monoxide, in the example presented 3.16 m ³ , while limiting very strongly the production of undesired additional compounds (see for example above). Those skilled in the art, specialist propellant, will be able to make the most appropriate choice or define new compositions depending on the intended application.

• C_et = 1034 m/s
• ρ = 1600 Kg/m³
• a = 1,7.10^-6
• n = 0,5
• rendement gazeux de gaz généré par masse brûlée à la température de combustion : 1,2 1/g.

For the example treated here, the design calculations will be carried out with a propellant, chosen solely for illustrative and non-limiting purposes, whose ballistic characteristics are as follows:

• C _and = 1034 m / s
• ρ = 1600 Kg / m ³
• a = 1.7.10 ^-6
• n = 0.5
• gas yield of gas generated by burnt mass at the combustion temperature: 1.2 l / g.

Moreover, the flow difference between the two phases E and M is in a ratio of 20; or the outlet orifice 16 (calibrated nozzle 36) of the combustion chamber 10 is identical in both cases. The operating pressure P of the gas generator 10 will thus also evolve in a ratio of 20.

In other words, to avoid going too low in the combustion chamber during the holding phase M, which would be detrimental to the ejection conditions, it is possible to set an operating pressure for this phase, for example 5 bars (5.10 ⁵ Pa). For the extinction phase E, the pressure will then reach 100 bars (100.10 ⁵ Pa).

The volume flow rate that is desired for the booster phase E is Q _I = 1.05 m ³ / s = 1050 l / s, ie a mass flow rate of gas leaving the generator 875 g / s. The burning rate of the propellant at 100 bar is V _cE = aP ⁿ = 1.7.10 ^-6 . (100.10 ⁵ ) ^0.5 = 5.4 × 10 ^-3 m / s.

The thickness of propellant to be burned during this booster phase E of 1.5 s is therefore _{E E} = 8.1 mm. The burning surface S _c is deduced from equation (1), ie S _cE = 0.1 m ² .

The dimensioning of the nozzle uses equation (3), that is, A _t = (Q _Im, C _and ) / (P, C _d ), with C _d = 0.99, or a passage surface at neck A _t = 91.4.10 ⁶ m ² , or a diameter d = 10.8 mm.

For the maintenance phase M, the desired volume flow rate is 0.05 m ³ / s or 50 l / s, which gives a mass flow rate of gas leaving the generator Q _Im = 42 g / s for a pressure of 5 bar . The combustion rate is V _cM = aP ⁿ = 1.2 × 10 ^-3 m / s, and the thickness of propellant to be burned during this phase 3.5 s is Ep _M = 4.2 mm, ie a combustion area S _cM = 0.022 m ² .

The combustion surfaces, different in the E booster and M maintenance phases (of a ratio of 4.55), can be obtained in several ways, with blocks burning on one side "in cigarette", on several sides, etc. . The shape to give the block depends on the conditions of manufacture, the surface evolution, but also the mode of ignition. It is possible to optimize the evolution of the combustion surface over time to obtain a desired flow law.

As specified above, it is also possible to provide two different types of propellants for the two combustion phases.

The description presented above does not exclude all the alternatives that the skilled person will not fail to raise to achieve a device according to the invention. In particular, various combinations are possible between the various embodiments presented. It is clear, for example, that it is conceivable not to have a control box 24, but separate sensors and controls for each device to be controlled. Similarly, for a device 1 comprising several gas generators 2, it can be envisaged that certain generators are designed to have a regulated gas production, while others, connected to the same distribution means, have a gas generation. regulated by valves 20. Furthermore, depending on the profiles sought, it is possible to have more than two different compositions in a propellant block 12.

Claims (21)

1. Extinction device (1), characterized in that it comprises:

   - a gas generator (2) comprising an enclosure (10) equipped with a gas outlet port (16), the pressure within the enclosure being the atmospheric pressure when the extinction device (1) is not used, and a block of pyrotechnic material (12) which generates propellant gas, the inert gas being generated only during the use of the extinction device and comprising at least 20% of nitrogen and/or of carbon monoxide and/or of carbon dioxide ;

   - means of distributing (4) said generated gas coupled to the gas outlet port (16);

   - means of regulating (12, 20, 36) the pressure created by the gas generated in the distribution means (4).
2. Device according to claim 1, comprising a plurality of gas generators (2a-2e) each comprising an enclosure (10) equipped with a gas outlet port (16), a block of pyrotechnic material (12a-12e) which generates propellant gas and connection means (4a-4e) for coupling each gas outlet port (16) to the distribution means (4).
3. Device according to claim 2, comprising at least one control valve (20a, 20b) in the connection means (4a, 4b).
4. Device according to one of claims 1 to 3, comprising at least one control valve (20, 20f) in the distribution means (4).
5. Device according to one of claims 3 or 4, comprising first control means (32) capable of controlling the control valve (20) according to control parameters.
6. Device according to claim 5, in which the first control means (26) comprise means for measuring the concentration of oxygen in the zone to be treated and said concentration (36) is one of the control parameters.
7. Device according to one of claims 5 to 6, comprising at least one control unit (24) connected to the first control means (32).
8. Device according to one of claims 1 to 7, comprising at least one combustion trigger (14) of at least one block of pyrotechnic material (12).
9. Device according to claim 8, comprising second control means (22) for setting off the combustion trigger (14).
10. Device according to claim 7, comprising at least one device for triggering the combustion of at least one block of pyrotechnic material, and second control means (22) for setting off the combustion trigger (14) connected to the control unit (24).
11. Device according to one of claims 9 or 10, in which the second control means (22) comprise means for detecting a fire, and said detection (34) is one of the control parameters of the trigger (14).
12. Device according to one of claims 9 to 11, in which the second control means (22) comprise manual triggering means, and the manual triggering (30) is one of the control parameters.
13. Device according to one of claims 9 to 12, in which the second control means (22) comprise neutralisation means (28).
14. Device according to one of claims 1 to 13, in which the regulation means are an integral part of at least one first gas generator (2) and the following parameters of the first generator (2) are selected so that the flow rate law of gas (Q) stemming from the combustion of its block of pyrotechnic material (12) in the distribution means (4) follows a predetermined and controlled profile: stagnation pressure (P) in the enclosure (10), size (A_t) of the port (16) and surface area (S_c) of the block of pyrotechnic material (12).
15. Device according to claim 14, comprising a nozzle (36) at the outlet port (16) of the enclosure (10) of the first gas generator (2).
16. Device according to claim 15, in which the nozzle (36) is tailored in such a way that at the minimum cross section of the nozzle (36), the gases generated by the combustion of pyrotechnic material (12) from the first generator (2) have a speed equal to the speed of sound.
17. Device according to one of claims 1 to 16, in which at least one block of pyrotechnic material (12) comprises two materials of different composition.
18. Device according to one of claims 1 to 17, comprising at least one tared disc (20) at the level of an outlet port (16).
19. Device according to one of claims 1 to 18, comprising at least one filter (18) for retaining particles.
20. Device according to one of claims 1 to 19, comprising means of cooling (18) the generated gas.
21. Turbojet engine comprising a device according to one of claims 1 to 20.

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