Abstract:
An aircraft fire prevention system provides oxygen depleted (hypoxic) air for the fuel tank and/or cargo compartment protection; the system does not employ compressed air for the production of hypoxic air, which allows to save energy and fuel and to reduce negative impact on the earth atmosphere.

Description:
[0001]    The present application is a continuation-in-part of U.S. patent application Ser. No. 11/183,948 titled “Hypoxic Fire Suppression System for Aerospace Applications” filed Jul. 19, 2005 and U.S. patent application Ser. No. 12/079,224 titled “Method of Producing Hypoxic Environments in Enclosed Compartments Employing Fuel Cell Technology” filed Mar. 24, 2008, which are continuations-in-part of U.S. Pat. No. 7,900,709 titled “Hypoxic Aircraft Fire Prevention and Suppression System with Automatic Emergency Oxygen Delivery System” filed Dec. 3, 2003 and issued Mar. 8, 2011, which claims benefit of and priority to U.S. Provisional Application Ser. No. 60/461,450 filed Apr. 9, 2003. U.S. patent application Ser. Nos. 11/183,948 and 12/079,224, U.S. Pat. No. 7,900,709, and U.S. Provisional Application Ser. No. 60/461,450 are incorporated by reference herein in their entirety for all purposes. 
     
    
     FIELD 
       [0002]    The present invention relates to a method, equipment, and composition of Hypoxic Aircraft Fire Prevention System (HAFPS) that utilizes Hypoxic Air Venting (HAV) to provide fire protection (inerting) of fuel tanks and to provide fire-preventive environment in a cargo compartment. 
         [0003]    With its mode of action based on the automatic release of hypoxic air, this system is completely non-toxic, simple and reliable. Consequently, it is ideally suited to provide fire protection for any aircraft or airspace vehicle. 
       BACKGROUND 
       [0004]    Solutions to the challenge of fire safety are discussed in U.S. Pat. No. 7,900,709, and U.S. patent application Ser. Nos. 11/183,948 and 12/079,224 (all of which are incorporated herein by reference in their entirety). U.S. Pat. No. 7,900,709, and U.S. patent application Ser. Nos. 11/183,948 and U.S. Ser. No. 12/079,224 describe establishing a hypoxic fire-preventive environment in different compartments of an aircraft during its operation. 
         [0005]    The concept of inerting aircraft fuel tanks with hypoxic air up to 12% oxygen content has been adopted by the aviation community. The FAA (Federal Aviation Administration) requires installation of such systems for fuel tank protection on all commercial airplanes, which illustrates a practical implementation of the solutions provided in the patent and applications disclosed above. 
         [0006]    However, all currently proposed systems require compressed air for feeding of an air separation device that produces hypoxic air for inerting of the fuel tanks. This requires energy and additional fuel has to get burned on the aircraft, which cost money and provides a negative impact on the Earth&#39;s atmosphere. 
       SUMMARY 
       [0007]    The principal objects of the present invention are as follows: 
         [0008]    The provision of an aircraft fire prevention and suppression system that overcomes the above-described deficiencies in the prior art. 
         [0009]    The provision of an onboard system that allows to constantly generating hypoxic air in an air separation device utilizing the pressure difference between an internal compartment of an aircraft (cabin) and fuel tank and cabin and external atmosphere. 
         [0010]    The provision of a membrane based air separation device utilizing the pressure difference between an internal compartment of an aircraft and external atmosphere and said internal compartment and a fuel tank. 
         [0011]    The provision of a PSA or VPSA based air separation device utilizing the pressure difference between an internal compartment of an aircraft, fuel tank and external atmosphere. 
         [0012]    The provision of a fuel cell based air separation device utilizing the pressure differences between an internal compartment of an aircraft and a fuel tank and internal compartment and external atmosphere. 
         [0013]    According to one embodiment, a system for providing fire prevention for a fuel tank on an aircraft by using cabin air for producing oxygen-depleted (hypoxic) air from the cabin air comprises an air-separation device having an inlet and first and second outlets; said air-separation device employing a first pressure difference between said inlet and said first outlet, and a second pressure difference between said inlet and said second outlet; said first pressure difference and said second pressure difference providing a driving force for separating said cabin air into oxygen-enriched and oxygen-depleted gas mixtures without preliminary compression; said inlet communicating with an interior atmosphere of the aircraft, said first outlet communicating with a fuel tank, and said second outlet communicating with the atmosphere outside of the said aircraft; said inlet receiving said cabin air and said first outlet transmitting an oxygen-reduced gas mixture and said second outlet transmitting an oxygen-enriched gas mixture; said oxygen-enriched gas mixture being normally vented outside the aircraft; and said oxygen-reduced gas mixture, when in use, being supplied into said fuel tank for maintaining therein a hypoxic environment in order to prevent fuel ignition or explosion; wherein an oxygen content in said oxygen-reduced gas mixture is maintained in a range from 9% to 15% and, preferably, below 12% and above 10%. 
         [0014]    According to a further embodiment, said oxygen-reduced gas mixture, when in use, is constantly supplied into said fuel tank for maintaining therein a hypoxic environment in order to prevent fuel ignition or explosion. 
         [0015]    According to a further embodiment, said air separation device employing a hollow fiber air separation membrane. 
         [0016]    According to a further embodiment, said air separation device employing one of fuel cell technology, a PSA technology, or a VPSA technology. 
         [0017]    According to a further embodiment, said air separation device employing a combination of membrane and one of VPSA technology or PSA technology. 
         [0018]    According to a further embodiment, said inlet of the air separation device being provided with a compressed air when the aircraft is on the ground or at an altitude below 3 km above sea level, in order to provide continuous fire protection. 
         [0019]    According to a further embodiment, said first outlet being provided with a vacuum pump. 
         [0020]    According to a further embodiment, said first outlet communicating with a compartment onboard of the aircraft for providing fire protection. 
         [0021]    According to a further embodiment, said inlet being provided with an additional fan for oxygen content regulation. 
         [0022]    According to a further embodiment, the system further comprises an oxygen content monitoring system provided for measuring the oxygen content of the oxygen-reduced gas mixture transmitted via said first outlet; and a computerized control panel for receiving and analyzing data from said oxygen content monitoring system. 
         [0023]    According to one embodiment, a method for providing fire prevention for a fuel tank on an aircraft by using cabin air for producing oxygen-depleted (hypoxic) air from said cabin air comprises employing a first pressure difference, by an air-separation device having an inlet and first and second outlets, between said inlet and said first outlet, employing a second pressure difference by the air-separation device between said inlet and said second outlet; receiving said cabin air by said inlet; separating said cabin air, by using said first pressure difference and said second pressure difference as a driving force, without preliminary compression, into oxygen-enriched and oxygen-depleted gas mixtures; said inlet communicating with an interior atmosphere of the aircraft, said first outlet communicating with a fuel tank, and said second outlet communicating with the atmosphere outside of the said aircraft; transmitting by said first outlet an oxygen-reduced gas mixture; and transmitting by said second outlet an oxygen-enriched gas mixture; said oxygen-enriched gas mixture being normally vented outside the aircraft; said oxygen-reduced gas mixture, when in use, being supplied into said fuel tank for maintaining there a hypoxic environment in order to prevent fuel ignition or explosion; wherein the oxygen content in said oxygen-reduced gas mixture is maintained in the range from 9% to 15% and, preferably, below 12% and above 10%. 
         [0024]    According to one embodiment, an apparatus for producing hypoxic air comprises an air-separation device having an inlet and first and second outlets; said air-separation device employing a first pressure difference between said inlet and said first outlet, and a second pressure difference between said inlet and said second outlet; said first pressure difference and said second pressure difference providing a driving force for separating said cabin air into oxygen-enriched and oxygen-depleted gas mixtures without preliminary compression; said inlet communicating with an interior atmosphere of the aircraft, said first outlet communicating with a fuel tank, and said second outlet communicating with the atmosphere outside of the said aircraft; said inlet receiving said cabin air and said first outlet transmitting an oxygen-reduced gas mixture and said second outlet transmitting an oxygen-enriched gas mixture; said oxygen-enriched gas mixture being normally vented outside the aircraft; and said oxygen-reduced gas mixture, when in use, being constantly supplied into said fuel tank for maintaining therein a hypoxic environment in order to prevent fuel ignition or explosion; wherein an oxygen content in said oxygen-reduced gas mixture is maintained in a range from 9% to 15% and, preferably, below 12% and above 10%. 
         [0025]    According to one embodiment, a method of producing hypoxic air for fuel tank fire prevention on an aircraft comprises extracting, by an air separation device according to an embodiment described herein, hypoxic air out of air contained in an interior compartment of an aircraft without preliminary pressurization of the air; supplying said hypoxic air into said fuel tank and creating there a fire preventative atmosphere; and expelling an oxygen-enriched fraction of the air as a byproduct of the air separation into an atmosphere outside of said aircraft. 
         [0026]    According to a further embodiment, a vacuum pump is provided at said first outlet for improved performance and oxygen content regulation. 
         [0027]    According to a further embodiment, an additional fan is provided on said inlet for improving performance of the system and oxygen content regulation. 
         [0028]    According to a further embodiment, during a flight at altitudes above 3 km above sea level, said inlet receiving cabin air without preliminary pressurization and separating it into oxygen enriched fraction and oxygen reduced fraction; said oxygen reduced fraction being provided into said fuel tank, via said first outlet, for fire prevention and said oxygen enriched fraction being expelled into atmosphere outside of said aircraft, via said second outlet; said inlet having upstream a valve that switches from a non-pressurized cabin air supply to a pressurized air supply; a compressor that can supply said air separation device, via said valve, with compressed air when aircraft is on the ground or at an altitude below 3 km above sea level; said valve closing compressed air supply when aircraft reaches an altitude high enough to provide air separation using pressure difference between cabin air and outside atmosphere and using suction provided by the fuel consumption in said fuel tank. 
         [0029]    According to one embodiment, a method of producing hypoxic air for fuel tank or cargo compartment fire prevention on an aircraft comprises extracting, by an oxygen-consuming device according to an embodiment described herein, some oxygen out of air contained in an interior compartment of an aircraft without preliminary pressurization of the air and expelling some of byproducts of said oxygen consummation into an atmosphere outside of said aircraft; supplying remaining hypoxic air into said fuel tank and creating there a fire preventative atmosphere. 
         [0030]    According to various embodiments, said cabin air can be partially supported or replaced by bleed air available on some types of aircraft. 
     
    
     
       BRIEF DESCRIPTION 
         [0031]      FIG. 1  illustrates a schematic view of the present fire prevention system for a fuel tank protection integrated into a compartment on an aircraft, according to one embodiment. 
           [0032]      FIG. 2  illustrates a further improved embodiment of the present system for the fuel tank allowing fire protection during all positions of an aircraft, according to one embodiment. 
           [0033]      FIG. 3  illustrates an alternate embodiment of the present system for fire protection of a cargo or other compartment on an aircraft, according to one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    The present disclosure includes a reliable and low-cost solution that allows for the design and building of fire safe aircraft and is particularly valuable by allowing converting most of existing passenger airplanes into a fire-protected aircraft. The present invention allows this without spending energy and fuel on generating hypoxic air needed for fire prevention. 
         [0035]    The present invention overcomes limitations of currently proposed systems due to the fact that it does not require compressed air for the air separation process. 
         [0036]    Current airplanes fly most of the time on high altitudes, still providing low-altitude atmospheric pressure inside its compartments, mostly for the passengers&#39; comfort and safety. The present invention is based on the use of the Hypoxic Air Generator principle described in the previous line of the patents provided above and incorporated herein by reference. It is also based on the fact that an air separation unit, required for hypoxic air generation, needs some pressure difference on its inlet and outlets. 
         [0037]    The previous line of the patents describes in detail how to utilize compressed ambient air, ether from bleed, received though the inlet of such a unit, for generation of hypoxic air on first outlet and oxygen enriched air on the second outlet. Such an air separation unit is being called in the aviation industry IGGS (Inert Gas Generation System), which is scientifically not correct. Almost all living organisms can perfectly utilize hypoxic air with 12% oxygen in it. Therefore, the term “inert” is not correct. A term “hypoxic” is more appropriate. 
         [0038]    However, generation of the compressed air for the air separation costs energy, which requires more fuel to be burned. The present invention proposes the use of an Air Separation unit that works without a compressor. The present invention particularly applies to providing a fire preventative atmosphere in aircraft fuel tanks and, with some modification, for cargo and other compartments of an aircraft. 
         [0039]    The main principle of the present invention is to utilize a lower atmospheric pressure outside of the aircraft as a driving force on the permeate side of the air separation unit, along with the suction created in the fuel tank, when the aircraft consumes fuel during the flight, on the retentate side. 
         [0040]    For example, if the air separation unit (hypoxic generator) utilizes a hollow fiber membrane, then an oxygen enriched fraction results on the first (permeate) outlet, which communicates with the outside atmosphere, and an oxygen reduced fraction results on the second (retentate) outlet communicating with the fuel tank interior. The same applies to other hypoxic generators that may use PSA (Pressure Swing Adsorption) and other air separation techniques, some of them having also an oxygen enriched retentate and oxygen-depleted permeate. 
         [0041]    When an aircraft, after its cabin (interior compartment of an aircraft) is pressurized, climbs to a higher altitude, the difference in atmospheric pressures inside and outside of the aircraft force the cabin air through an air separation device expelling its oxygen-enriched fraction into the outside atmosphere. At the same time the fuel level in a fuel tank gradually decreases providing some suction on the oxygen-reduced (hypoxic) side of the air separation unit (hypoxic generator). 
         [0042]      FIG. 1  illustrates a schematic view of the present system provided for fuel tank fire prevention on an aircraft, according to one embodiment. An interior cabin  10  accommodates a hypoxic generator unit  11  that communicates with a fuel tank  12  via an hypoxic outlet  15 . Cabin air is drawn into the hypoxic generator unit  11  via inlet  13  due to the suction on an outlet  14  communicating with the outside atmosphere and suction created in the fuel tank  12  when fuel level decreases. A vacuum pump (not shown here) may be installed before fuel tank  12  on the outlet  15  in order to draw hypoxic air when the fuel from this tank is not consumed and/or for improving performance of the system and/or for oxygen content regulation. In an additional outlet  16  is necessary from the fuel tank  12  in order to release some internal atmosphere out of the tank  12  into the outside atmosphere. The same outlet  16  can be employed as a dive valve that opens when the aircraft loses altitude in order to equalize pressure and prevent damage of the fuel tank  12 . The system can be adjusted such that it can provide, via outlet  15 , hypoxic air with oxygen content in the range above 9% and below 18% and in particular, from 12% to 15% of oxygen by volume. In some cases, oxygen concentrations from 10% to 12% are most preferred. 
         [0043]    Hypoxic generator  11  unit may accommodate an air separation device described above or an oxygen consuming device, such as a rebuilt fuel cell, etc. In this case the outlet  14  can be used for removal of byproducts of the oxygen consummation. 
         [0044]      FIG. 2  illustrates a further improved embodiment of the present system that provides a hypoxic fire prevention atmosphere inside of the fuel tank at all times, even on the ground and during flight on lower altitudes (mainly below 2.7 km above sea level). The further embodiment includes similar components: a cabin  20 , an air separation unit or hypoxic generator  21  having outlets  24  and  25 , an inlet  23 , a fuel tank  22  with an outside (dive) valve  26 . The difference between the further embodiment and the embodiment depicted in  FIG. 1 , is that the further embodiment includes a three way valve  29  that allows an input of compressed air from a compressor (or bleed air from the aircraft engine)  27 , via conduit  28 . This is utilized when the aircraft is on the ground or at lower altitudes (mainly below 3 km above sea level) where no driving force would be applied from the pressure difference between the inlet  23  and outlet  24  and/or  25 . 
         [0045]    When aircraft cruises at a high altitude, the 3-way valve  29  closes the conduit  28  and opens the inlet  30 , which allows cabin air to enter the hypoxic generator  21 . This configuration saves fuel that otherwise would be burned to provide compressed air during the entire duration of the flight. As an example, this saving would apply to at least 7 hours during 8 hours of a trans-Atlantic flight. 
         [0046]    The inlets  13  and  30  can be equipped with a small capacity fan or blower having low energy consumption, which can improve performance of the air separation unit (IGGS) and/or can be used for oxygen content regulation. 
         [0047]    The same configuration can be applied to an aircraft cargo compartment instead of the fuel tank  12  and  22 , using a vacuum pump on hypoxic outlet  15  or  25 . 
         [0048]      FIG. 3  illustrates a hypoxic fire prevention system for a cargo compartment  37  on an aircraft or other enclosed compartment. An air separation unit  31  utilizes the pressure difference between inlet  33  and oxygen-enriched outlet  34  exposed to the outside. However, in this case, suction must be provided on the hypoxic outlet  35 , which is perfectly achievable by attaching a vacuum pump  36 . 
         [0049]    The same embodiment can be used with an additional compressed air supply, via 3-way valve  29 , similar to that depicted in  FIG. 2 . 
         [0050]    A preferable air separation device for the unit  11 ,  21  and  31  is a hollow fiber membrane with a large surface capable working on a minimal pressure difference between the inlet and outlets. PSA (pressures swing adsorption), VPSA (vacuum pressure swing adsorption) and other air separation techniques and their combinations can be used as well. 
         [0051]    Oxygen-enriched byproduct can be used for improving fuel burning process in the aircraft engines and/or for power generation using fuel cells or other power generation techniques. 
         [0052]    The air separation device  11 ,  21  and  31  can also employ an electric current or electro-chemical separation technology, such as modified fuel cell, etc. In this case a fuel cell needs to be redesigned to accommodate an inlet ( 13 ,  23 ,  33 ) and first ( 15 ,  25 ,  35 ) and second ( 14 ,  24 ,  34 ) outlets. Cabin air can be delivered to such a modified fuel cell ( 11 ,  21 ,  31 ) via this inlet, some oxygen can be used in the electro-chemical process creating electric energy, and oxygen-depleted air can be supplied into a fuel tank or cargo compartment ( 12 ,  22  or  37 ) via first outlet ( 15 ,  25 ,  35 ). The second outlet ( 14 ,  24  and  34 ) can be used to remove byproducts of oxygen consummation and to provide sufficient suction on the inlet ( 13 ,  23 ,  33 ). The air movement through the system is supported by the pressure differences between the inlet and outlets. 
         [0053]    Second outlet ( 14 ,  24  and  34 ) can be communicating directly to the outside of an aircraft or in any internal space of it that communicates with the outside atmosphere (wheel bay, etc.). 
         [0054]    The oxygen content in the oxygen depleted gas mixture transmitted through outlet  15 ,  25  and  35  can be measured by an in-line oxygen monitor (not shown here) and data transmitted to a computerized controller for possible regulation.