Patent Application
20210244978
The present disclosure relates generally to fire suppression in an aircraft cargo hold. More specifically, the disclosure relates to a green fire suppression system in an aircraft cargo hold that does not require Halon 1301.
Currently, all US airlines are required to have engine inerting systems, which decrease the oxygen level in the fuel tanks to below the concentration required for ignition. The primary system currently in use utilizes a fiber membrane material that separates supplied air into nitrogen-enriched air and oxygen-enriched air.
The FAA also requires that all cargo holds have a fire detection and suppression system. Current fire suppression systems utilize a high-rate discharge bottle of hydrofluorocarbon (HFC) to knock down the fire, then a low-rate metered discharge bottle of HFC designed to keep the fire suppressed until the plane can safely land.
With the ban of Halon 1301 for aircraft use, the aerospace industry is facing difficulties in identifying HFC alternatives that satisfy the FAA requirements for fire suppression. Other industries, such as HVAC, are already facing regulations to use low Global Warming Potential (GWP) materials, and some countries such as Switzerland have pushed to ban the use of HFCs altogether. With the ongoing focus on global climate change issues, the development of green fire suppression systems is additionally desirable.
A system for fire suppression includes a fuel tank inerting system configured to produce an inert gas mixture, a water source, and a low pressure misting nozzle directed into a cargo hold. The low pressure misting nozzle being configured to produce a mist solution using the inert gas mixture and water.
Fire suppression systems are required in the cargo holds of all US airlines. Because current fires suppression systems utilize HFCs, and HFCs will be banned in the future, new fire suppression systems are required. The FAA requires that these new systems be at least as good as current systems at fire knock down and suppression.
Gas only fire suppression systems require that the flow rate of the gas, typically nitrogen, be high in order to effectively knock down a fire. Therefore, many designs require pressurized gas tanks to obtain the high flow rates. Pressurized gas tanks are large and heavy, and therefore, a lighter and more space efficient method of environmentally friend fire suppression is desired. Aircraft currently have a fuel inerting system, which reduces the oxygen level in the fuel tank to a level below that required for ignition of the fuel. Utilizing the fuel inerting system already present on the aircraft to provide the gas for the fire suppression system would remove the need for pressurized gas tanks, however it is difficult to obtain the high flow rates required in the knock down stage of the fire suppression.
As described herein, in order to utilize the inerting system to provide the gas mixture and still be effective at a low flow rate, water mist is additionally utilized in the fire knock down stage. Specifically, the inerting gas mixture is diverted to a low pressure water mist nozzle to form a water mist. In some embodiments, the inerting gas mixture can be supplemented or replaced by a hydrofluorocarbon. The combination water mist/inerting gas mixture is then pumped into the cargo hold to complete the fire knock down stage. After the fire has been knocked down, inerting gas mixture can be flowed into the cargo hold at a relatively low flow rate to maintain a low oxygen environment or specific agent concentration level during the fire suppression stage. The system described herein effectively knocks down and suppresses fires at a lower total agent amount compared to bottled nitrogen fire suppression systems, allowing for the utilization of gas from the fuel inerting system. As a result, pressurized gas tanks are not necessary, reducing the weight and environmental impact of the fire suppression system.
Inerting process 100 is performed in the fuel tank. The inerting process can be a selective membrane, catalytic, or electrochemical process. A selective membrane process uses a membrane which selectively allows nitrogen through to reduce the oxygen level of the gas mixture in the fuel tank below 12%. In some embodiments, for example, the oxygen level is below 10%, below 9% or below 7%. In a catalytic inerting system, the system reacts on-board jet fuel to make a gas mixture of carbon dioxide, nitrogen, and water. The generated gas mixture reduces the oxygen level of the gas mixture in the fuel tank below 12%. In some embodiments, for example, the oxygen level is below 10%, below 9% or below 7%. In an electrochemical process with water and air, an electrochemical potential is used to separate oxygen from the air. The generated gas mixture reduces the oxygen level of the gas mixture in the fuel tank below 12%. In some embodiments, for example, the oxygen level is below 10%, below 9% or below 7%. In embodiments where water is produced in the inerting process, the water must be removed from fuel tank inerting in order to prevent fuel fouling issues. The water can be stored in condensation tanks. The stored water can then be utilized in fire suppression or other non-potable usages (e.g. sanitation).
Effervescing process 102 creates water mist using the water, the inert gas mixture, and/or hydrofluorocarbon. The fuel tank is functionally connected to an effervescent system such that the inerting gas mixture can be transferred between them. In the effervescent system, the inerting gas mixture is bubbled through water inside the injection nozzle at a low pressure. Water can be sourced from a condensation tank or from the onboard water stores (e.g. for cooking, sanitation, drinking, etc.). Low pressure can be less than 4 atm, less than 3 atm or less than 2 atm. The low pressure effervescent system produces a water mist which is delivered to the cargo hold. The water mist has a droplet size, for example, of no greater than 1000 microns, no greater than 500 microns, or no greater than 100 microns.
In fire knock down stage 104, the water mist can be delivered through a low pressure nozzle driven by the inerting gas. The flow rate of the water mist and inerting gas can be, for example, between 200 cubic feet per minute and 40 cubic feet per minute, or between 150 cubic feet per minute and 50 cubic feet per minute. Additional inerting gas can be provided through additional low pressure nozzles without water mist. The flow rate of the inerting gas can be, for example, between 200 cubic feet per minute and 40 cubic feet per minute, or between 150 cubic feet per minute and 50 cubic feet per minute. The fire knock down stage continues until the fire is suppressed or reduced to acceptable level. The water mist coupled with the inerting gas effectively knocks down fires by directly cooling the fire with water and dilution, thereby reducing the fire temperature through physical heat absorption and water vaporization, and by inhibiting the fire by displacing the oxygen rich atmosphere with an oxygen poor inerting gas environment.
After the fire is knocked down, fire suppression stage 106 controls any remaining fire and prevents any new fires until the plane can safely land. In the fire suppression stage, inerting gas is pumped into the cargo hold at a relatively low rate to maintain agent concentration and overcome leakage from the cargo hold. The addition of inerting gas may be continuous or intermittent. The flow rate of the inerting gas can be, for example, between 200 cubic feet per minute and 40 cubic feet per minute, or between 150 cubic feet per minute and 50 cubic feet per minute. The inerting gas in the fire suppression stage can be provided through the low pressure water mist nozzles and/or through inerting gas specific nozzles. The inerting gas flow reduces the oxygen level of the gas mixture in the cargo hold below 16%. In some embodiments, for example, the oxygen level is below 12%, below 9% or below 7%. The fire suppression step can continue as long as is required to land safely. The oxygen level or agent concentration level can be monitored continuously or intermittently to ensure the oxygen or agent level of the gas mixture is in the target design range.
The following are non-exclusive descriptions of possible embodiments of the present invention.
A system for fire suppression, the system comprising: a fuel tank inerting system configured to produce an inert gas mixture; a water source; and a low pressure misting nozzle directed into a cargo hold; wherein the low pressure misting nozzle is configured to produce a mist solution using the inert gas mixture and water.
The system of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:
A further embodiment of any of the foregoing systems, wherein the fuel tank inerting system is a catalytic inerting system or an electrochemical inerting system.
A further embodiment of any of the foregoing systems, wherein the water source is condensation from the inerting system.
A further embodiment of any of the foregoing systems, wherein the fuel tank inerting system is an inerting membrane.
A further embodiment of any of the foregoing systems, wherein the water source is a primary aircraft water system.
A further embodiment of any of the foregoing systems, wherein the low pressure misting nozzle is configured to create a mist solution at a pressure of less than 2 atm.
A further embodiment of any of the foregoing systems, wherein the inert gas mixture comprises no greater than 16% oxygen.
A further embodiment of any of the foregoing systems, wherein the inert gas mixture comprises carbon dioxide, nitrogen, or a combination thereof.
A further embodiment of any of the foregoing systems, wherein the mist solution consists of water particles no larger than 1000 microns.
A further embodiment of any of the foregoing systems, wherein the mist solution has an average particle size of no greater than 100 microns.
A method of fire suppression, the method comprising: creating a mist solution including water and an inert gas mixture; flowing the mist solution into a cargo hold to suppress a fire; and flowing the inert gas mixture into the cargo hold after the fire is suppressed to maintain a low oxygen environment or target agent concentration.
The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:
A further embodiment of the foregoing method, further comprising the step of producing the inert gas mixture through a fuel tank inerting process.
A further embodiment of any of the foregoing methods, wherein the fuel tank inerting process is a catalytic inerting process or an electrochemical inerting process.
A further embodiment of any of the foregoing methods, wherein the water is a condensation product from the fuel tank inerting process.
A further embodiment of any of the foregoing methods, wherein the fuel tank inerting process is a membrane inerting process.
A further embodiment of any of the foregoing methods, wherein the mist solution is created using a low pressure effervescent system.
A further embodiment of any of the foregoing methods, wherein the mist solution is created at no greater than 2 atm.
A further embodiment of any of the foregoing methods, wherein the mist solution is flowed into the cargo hold at a rate of between 200 cubic feet per minute and 40 cubic feet per minute.
A further embodiment of any of the foregoing methods, wherein the inert gas mixture is flowing into the cargo hold at a rate of between 200 cubic feet per minute and 40 cubic feet per minute.
A further embodiment of any of the foregoing methods, wherein the low oxygen environment comprises no greater than 16% oxygen.
A further embodiment of any of the foregoing methods, further comprising flowing the inert gas mixture into the cargo hold containing to suppress the fire.
While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
