GB2585346A - Fire suppression system - Google Patents

Abstract

A fire suppression system 10 comprises a container 11 for storing a fire suppressing agent and is fluidly connected to an aerosoliser 14 for aerosolising the fire suppressing agent. The system further includes a supply of heated gas 12 and a conduit 13 for conveying a mixture of the aerosolised fire suppressing agent and the gas to a fire. The aerosoliser may comprise an aperture in the flow path of the fire suppressing agent, such that the fire suppressing agent is aerosolised when the fire suppressing agent passes through the aperture. In a preferred embodiment, the tube is positioned within the conduit such that the aerosolised fire suppressing agent is directly introduced into a flow of heated gas from the gas supply.

Description

FIRE SUPPRESSION SYSTEM Field of the Invention

The invention relates to a fire suppression system, in particular to a fire suppression system for use in aircraft.

Background

Halons are a class of chemical agents which are commonly used in fire suppression systems used to control and extinguish fires. In particular these may be steaming or total flooding systems, where streaming encompasses handheld fire extinguishers and any discharge where the agent is directed towards a target as a stream, and where total flooding encompasses applications such as computer rooms and other spaces where a specific airborne vapor concentration is desired to extinguish a fire anywhere within the protected enclosure. One particular chemical agent which is in common use for total flooding fire suppression systems in aircraft is Halon 1301 (bromotrifluoromethane) which is an effective fire suppressant with a low toxicity.

However, it is now known that many Halons, including Halon 1301, contribute to the depletion of the Earth's ozone layer and also to the greenhouse effect, and so use of these agents is being phased out and alternative fire suppressing agents sought.

Examples of alternative agents include HFC-227ea (heptafluoropropane) and HFC-236fa (hexafluoropropane), which have been successfully tested for use in handheld and lavatory fire suppressing systems in aircraft, and 2-BTP (2-brommo3,3,3,-trifluoropropene), which has been successfully tested for use in handheld fire extinguishers.

However, no chemical agent and fire suppressing system has yet been identified which is suitable for aircraft engines, in civilian aircraft in particular, to replace Halon 1301. Many agents which have previously been tested cannot be used for aircraft engines because they are too heavy, require a larger storage volume, and because of concerns relating to their global warming potential. Furthermore, other halon alternatives such as FK-5-1-12 and sodium bicarbonate aerosol have been tested for engine nacelles, but have been found to be unable to suppress fires under certain test conditions, and so are deemed to be unsuitable for this application. In particular, temperatures can be low at the flying altitude of aircraft and while FK-5-1-12 can pass all required tests under standard ambient conditions, it lacks the required vapour pressure to properly reach its design concentration at the cold temperatures at altitude. Sodium bicarbonate, which is finely ground and dispersed as an aerosol, does not need to vaporise like a halogenated agent and so works well in a standard Federal Aviation Authority (FAA) engine test fixture. This fixture comprises stabiliser ribs and other elements to create a semi-cluttered space. However, when sodium bicarbonate is tested in the more highly cluttered space of an actual engine nacelle, it has been found that the solid particles are unable to disperse through the space and extinguish test fires.

Summary of the Invention

The present invention aims to address the problems associated with known halon-alternative fire suppression systems. At its most general, the present invention relates to a delivery system for a mixture of a fire suppressing agent and a gas.

According to a first aspect of the invention, there is provided a fire suppression system comprising a container for storing a fire suppressing acent, the container being fluidly connected to an aerosoliser for aerosolising the fire suppressing agent; a supply of heated gas; and a conduit for conveying a mixture of the aerosolised fire suppressing agent and the heated gas to a source of a fire. An aersoliser in this context means a device or piece of apparatus which is capable of transforming the fire suppressing agent, usually supplied as a liquid, into an aerosol, or fine liquid droplets. By aerosolising the fire suppressing agent and delivering a mixture of the fire suppressing agent and a heated gas to a source of fire, the fire suppressing agent may be delivered to the source of fire in a gaseous form, as the aerosolised fire suppressing agent readily evaporates into a gas, greatly enhancing its efficacy. The fire suppression system of the present invention may therefore be used with fire suppressing agents which may otherwise be considered unsuitable for use in certain applications, such as in aircraft, or under certain conditions, such as at low temperatures. Furthermore, by more effectively using the fire suppressing agent, the fire suppression system is able to effectively operate despite having a reduced mass and volume, increasing its suitability for use cases with strict mass and/or volume requirements.

Advantageously, the aerosoliser is configured to produce a droplet size of 100 micrometres or less, for example 50 micrometres or less. Preferably, the aerosoliser comprises an aperture in the flow path of the fire suppressing agent, such that the fire suppressing agent is aerosolised when the fire suppressing agent passes through the aperture. In this way, the aerosoliser does not require any additional electronics or components to operate, and so the fire suppression system is resistant to failure, and maintenance of the system is minimised. Resistance to failure and low maintenance are particularly advantageous as a fire suppression system is an important safety feature which may be in place for a long time without use. Advantageously, the aerosoliser comprises a tube having a plurality of apertures in a sidewall thereof. Optionally, the tube is positioned within the conduit such that the aerosolised fire suppressing agent is directly introduced into a flow of heated gas from the gas supply. By providing the aerosoliser as a tube within the conduit, the fire suppressing agent mixes with the heated gas as soon as it has been aerosolised, that is, transformed into fine liquid droplets, and so the droplets of fire suppressing agent quickly evaporate to form a gas. The mixture of heated gas and gaseous fire suppressing agent are then conveyed to the source of fire through the conduit.

Advantageously, the gas supply is a solid propellant gas generator (SPGG). Preferably, the SPGG is configured to produce an inert gas, such as nitrogen gas, or the SPGG may be configured to produce a mixture comprising nitrogen gas, carbon dioxide, and water vapour. Optionally, the SPGG produces a heated gas which is filtered of particulates. A POOP is able to produce large volumes of gas very quickly, which ensures that the fire suppression system is able to deliver the mixture of heated gas and gaseous fire suppressing agent to the source of fire very soon after a fire has been detected. This is particularly advantageous to ensure that a fire is contained, and does not spread to other areas.

Optionally, the container may comprise a solid propellant gas generator configured to expel the fire suppressing agent from within the container. In this way, the fire suppression system is hereby able to deliver the mixture of heated gas and gaseous fire suppressing agent to the source of fire very soon after a fire has been detected. In addition, this may allow the container to be compact, reducing the overall volume of the fire suppression system. Preferably the container comprises a rupture disc such that, when the rupture disc is broken, the fire suppressing agent is able along to flow along a fluid flow path to the aerosoliser. In some embodiments, the rupture disc is configured to break when a pressure within the container reaches a predetermined level. In this way, the rupture disc is configured to break without any external input due to pressure from within the container when the fire suppression system is activated to allow fire suppressing liquid to flow to the aerosoliser. Alternatively, the fire suppression system may comprise a pyrotechnical charge configured to break the rupture disc. The pyrotechnical charge may be detonated when the fire suppression system is activated to allow fire suppressing agent to flow from the container to the aerosoliser.

Preferably, the solid propellant gas generator is configured to provide enough gas to vaporise the liquid fire suppressing agent. For example, the container may be configured to store a volume of fire suppressing agent equal to more than three times the volume of heated gas supplied by the gas supply. This ensures that the fire suppression system is configured to produce a gas and fire suppressing agent mixture which has an optimal ratio of the components. In particular, the fire suppression system may be configured to supply a mixture comprising up to 30% by volume of heated gas and at least 50% by volume of fire suppressing agent to the source of a fire. In particular, the first suppression system may be configured to supply a mixture of fire suppressing agent and heated gas comprising no more than 35% by volume of heated gas and at least 65 by volume of fire suppressing agent.

Preferably, the fire suppressing agent may be 2-BTP (-brommo-3,3,3,-trifluoropropene), which has a boiling point of around 34°C, and does not contribute to ozone depletion or to global warming. In some embodiments FK-5-1-12 may be used, though 2-BTP may be preferable as it requires less agent weight and volume. Alternatively, the fire suppressing agent may be chosen from trifluoroiodomethane, and dodecafluoro-2-methylpentan-3-one. To overcome any potential issues due to cold temperatures which are present at altitude, waste heat from the SPGG may advantageously be used to heat and vaporise a spray of fire suppressing agent droplets prior to discharge to the source of a fire, for example into an engine nacelle.

According to a second aspect of the invention, there is a provided an aircraft comprising the fire suppression system according to the first aspect of the invention.

Preferably, the conduit is configured to convey the mixture of the aerosolised fire suppressing agent and the gas to an engine nacelle. Optionally, the container and the supply of gas may be located within a wing of the aircraft. Alternatively, the container of gas may be located between the wing and engine in a supporting strut. In other embodiments, the container may be located in the fuselage of the aircraft, and the mixture of gas and fire suppressing agent may be conveyed to any engine nacelle of the aircraft.

The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

Brief Description of the Drawings

So LhaL Lhe inven Lion may be undersLood, and so LhaL further aspects and features thereof may be appreciated, embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a diagram of a fire suppressing system according to an embodiment of the present invention; Figure 2 shows a diagram of a fire suppressing system according to an embodiment of the present invention mounted within an engine nacelle of an aircraft.

Detailed Description and Further Optional Features of the Invention Fig. 1 shows a schematic diagram of a fire suppression system 10 according to an embodiment of the present invention. The fire suppression system 10 comprises a container of a fire suppressing agent 11, such as 2-BTP, a solid propellant gas generator (SPGG) 12, an outflow conduit 13 and a suppressant discharge tube 14.

The SPGG 12 contains a solid propellant which, when ignited, generates a large volume of a heated gas, preferably an inert gas such as nitrogen gas, though the SPGG 12 may alternatively produce a mixture of nitrogen, carbon dioxide, and water vapour. For example, the solid propellant may be 5-aminotetrazole or BTATz (C,H4li4) The gas which is generated by the SPGG 12 is at a high temperature, and the temperature of the gas is prefereably higher than the boiling point of the fire suppressing chemical agent. For example, 2-BTP has a boiling point of around 34°C at atmospheric pressure. By producing gas with a temperature higher than the boiling point of the chemical agent, it can be ensured that the chemical agent is delivered to the fire in a gaseous form which, as discussed below, produces an optimal fire suppressing effect.

The higher the temperature of the gas produced by the SPGG 12, the quicker the liquid agent will evaporate to form a gas. For example, the SPGG 12 may generate gas at a temperature of around 1000 °C. Although this temperature is high enough to cause decomposition of 2-BTP, the SPGG 12 is configured to produce an amount of gas which delivers just enough thermal energy to 2-BTP to ensure that the fire suppressing agent is vaporised but does not decompose. However, it may also be desirable for the mixture of gas and chemical agent delivered to the fire to be capable of absorbing heat from the fire. A balance must therefore be struck between quick evaporation of the chemical agent and the temperature of the mixture. In particular, a mixture having a lower temperature will be able to absorb more heat from the fire. In order to achieve the desired balance between these factors and the evaporation rate of the fire suppressing agent, the SPGG 12 may be limited in size to limit the amount of heated gas produced, and heat absorbing materials may be incorporated into the SPGG 12 if it is necessary to limit the temperature of the generated gas.

The SPGG 12 is connected to a first end of the outflow conduit 13, through which the gas generated by the SPGG 12 is directed, and the suppressant discharge tube 14 is positioned within the outflow conduit 13 downstream of the SPGG 12. The container 11 of chemical agent is fluidly connected to the suppressant discharge tube 14 such that when the fluid suppression system 10 is activated, the fire suppressing agent is introduced directly into the flow of gas generated by the SPGG 12.

The outer surface of the suppressant discharge tube 14 comprises a number of radial discharge ports to introduce the chemical agent into the gas flowing through the outflow conduit 13. Preferably the radial discharge ports are dimensioned such that the chemical agent is aerosolised as it passes into the gas flow from the SPGG 12. This creates a mist of small liquid particles of the chemical agent which quickly evaporate to form a gas. The smaller the droplets which are formed by the radial discharce ports, the quicker the liquid agent will evaporate to form a gas. In this way, it can be ensured that the chemical agent is delivered to a fire in gaseous form, which greatly enhances its fire suppressing properties thereby reducing the extinguishing concentration of the chemical agent. In turn, this allows a smaller amount of chemical agent to be used, which is particularly desirable where the fire suppression system 10 is to be used in aircraft, which may have strict mass and/or size restrictions for the fire suppression system 10. Preferably, the radial discharge ports are dimensioned to produce a droplet size of 100 micrometres of less.

The container 11 of fire suppressing agent may be pressurised to ensure rapid discharge of fire suppressing agent through the discharge tube 14. This helps aerosolise the chemical agent as it passes through the radial discharge ports discussed above. The container 11 may be pressurised by filling the headspace of the container 11 with a pressurised gas, preferably an inert gas such as nitrogen, such that when the fire suppression system 10 is activated, the chemical agent is delivered into the discharge tube 14 by opening a valve, or breaking a rupture disc (e.g. with a pyrotechnical cartridge) and allowing the cas in the headspace to expand. Alternatively, the container 11 may contain a solid propellant gas generator (not shown), similar to SPGG 12, which may be ignited to produce a gas, which may comprise substantially entirely nitrogen gas or could be a mixture of nitrogen, carbon dioxide, and water vapour, when the fire suppression system 10 is activated. At the same time, a valve is opened to allow the chemical agent to flow into the discharge tube 14.

Alternatively, the container 11 may comprise a rupture disc, which is configured to break at a certain pressure which occurs when the solid propellant gas generator within the container 11 is activated. When the rupture disc breaks, the chemical agent is free to flow through the discharge conduit 14.

When the fire suppression system 10 is activated, for example in response to a fire in an engine nacelle of an aircraft, the solid propellant of the SPGG 12 is ignited and a rupture disc on the container 11 is broken to allow 2-BIT to flow from the container 11 and be dispersed into the flow of gas. As discussed above, the 2-BTP may be delivered from the container 11 by way of pressurised gas within the headspace of the container 11. The gas and chemical agent mixture then passes from the outflow tube 13 and is piped into the engine nacelle to extinguish the fire.

2-BTP has a boiling point of approximately 34°C and the gas generated by the SPGG 12 is produced at a higher temperature than this which, in combination with the discharge ports in the discharge tube 14 which aerosolise the 2-BTP, ensures that the chemical agent is introduced to the engine nacelle in gaseous form. In particular, these features allow the fire suppression system 10 to be effective in extinguishing fires in an encine nacelle under cold-soak conditions, where the temperature of the wings and engine nacelles of an aircraft may be below -50°C due to the presence of low atmospheric temperatures experienced when commercial aircraft are flying at an altitude above 10 kilometres.

The relative volume of gas produced by the SPGG 12 compared to the volume of agent stored in the container 11 may be selected to ensure maximum fire extinguishing efficiency of the overall mixture which is delivered to the engine nacelle.

However, particularly in aircraft applications, size and weight restrictions on the overall fire suppression apparatus 10 must also be considered. For example, although a larger volume of fire suppressing agent may be more effective for fire suppression, a large amount of agent may be too voluminous or heavy for a particular application. The volumes of each are therefore chosen to minimise the extinguishing concentration of the mixture delivered as well as the overall volume and mass of the fire suppression system 10. It has been found that, where the fire suppressing agent is 2-BTP, the mixture of gas and 2-BTP delivered to the engine nacelle preferably comprises at least 50% by volume of 2-BT? in gaseous form and no more than 50% by volume of heated gas. This is approximately equivalent to at least 86% by weight of 2-BTP and no more than 14% by weight of heated nitrogen gas,

for example.

Fig. 2 shows a schematic diagram of a fire suppression system according to an embodiment of the present invention mounted within an engine nacelle 20 of an aircraft. The engine nacelle is supported underneath a wing 21 of an aircraft by a support strut 22.

In this example, the container 11 of chemical agent and the SPGG 12 are both mounted within the wing, and the outflow conduit 13 is positioned within the support strut to direct a gas/chemical agent mixture to the engine nacelle 20. As shown in Fig. 1, the discharge tube 14 is located within the outflow conduit 13, but has been omitted from Fig. 2 for clarity.

At the distal end of the outflow conduit 13, within the engine nacelle 20, the fire suppression system 10 comprises two nozzles 15a, 15b which each distribute the gas and chemical agent mixture within the engine nacelle 20 to extinguish a fire.

The nozzles 15a, 15b may be located within the nacelle 20 to ensure that the heated gas and chemical agent mixture may be distributed to reach all components which may be present within the nacelle, such as fan blades, the surfaces of the compression and combustion chambers, turbines etc. Of course, it is envisaged that any other number of nozzles may be used as required, and two nozzles 15a, 15b are shown simply as an illustrative example. Indeed, the present invention is not limited to nozzles within the engine nacelle 20, and nozzles may be positioned at any suitable location.

Although a few preferred embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purposes, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclose is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims (1)

1. Claims 1. A fire suppression system comprising: a container for storing a fire suppressing agent, the container being fluidly connected to an aerosoliser for aerosolising the fire suppressing agent; a supply of heated gas; and a conduit for conveying a mixture of the aerosolised fire suppressing agent and the gas to a fire 2. The fire suppression system of claim 1, wherein the aerosoliser comprises an aperture in the flow path of the fire suppressing agent, such that the fire suppressing agent is aerosolised when the fire suppressing agent passes through the aperture.3. The fire suppression system of claim 2, wherein the aerosoliser comprises a tube having a plurality of apertures in a sidewall thereof.4. The fire suppression system of claim 3, wherein the tube is positioned within the conduit such that the aerosolised fire suppressing agent is directly introduced into a flow of heated gas from the gas supply.5. The fire suppression system of any preceding claim, wherein the supply of heated gas is a solid propellant gas generator.6. The fire suppression system of claim 5, wherein the solid propellant gas generator is configured to produce a heated gas which is filtered of particulates.7. The fire suppression system of any preceding claim, wherein the container comprises a solid propellant gas generator configured to expel the fire suppressing agent from within the container.8. The fire suppression system of any preceding claim wherein the container comprises a rupture disc.9. The fire suppression system of claim 8, wherein the rupture disc is configured to break when a pressure within the container reaches a predetermined value.10. The fire suppression system of claim 8, further comprising a pyrotechnical charge configured to break the rupture disc.11. The fire suppression system of any preceding claim, wherein the fire suppression system is configured to supply a mixture of fire suppressing agent and heated gas comprising no more than 50% by volume of heated gas and at least 50% by volume of fire suppressing acent.12. The fire suppression system of any preceding claim, wherein the fire suppression system is configured to supply a mixture of fire suppressing agent and heated gas comprising no more than 35% by volume of heated gas and at least 65% by volume of fire suppressing agent.13. The fire suppression system of any preceding claim, wherein the fire suppressing agent is selected from the group consisting of 2-bromo-3,3,3-trifluoropropene, trifluoroiodomethane, and dodecafluoro-2-methylpentan-3-one.14. An aircraft comprising the fire suppression system of any of claims 1 to 12.15. The aircraft of claim 13, wherein the conduit is configured to convey the mixture of the aerosolised fire suppressing agent and the gas to an engine nacelle.