System and method for reducing the concentration of fuel vapor in the hollow of a fuel tank

Abstract

This description generally relates to a system for removing fuel from a mixture of air and fuel vapor in a hollow space within an aircraft fuel tank. The system includes a compressor for drawing the air-fuel vapor mixture from the hollow space and directing it through a heat exchanger where the mixture is cooled. The system also includes a turbine configured to be driven by the air-fuel mixture from the heat exchanger. Power from the turbine can be fed back to the compressor to assist in its rotation. The system further includes a separator for receiving the air-fuel vapor mixture from the turbine and separating at least some of the liquid fuel from the mixture.From the separator, a separated liquid fuel and a mixture of air and fuel vapor with a reduced fuel vapor concentration are returned to the aircraft fuel tank. Figure for the abbreviation: Fig. 1.

Description

Title of the invention: System and method for reducing the concentration of fuel vapor in the hollow of a fuel tank technical field

[0001] The present description relates generally to a system and a method for rendering a hollow in a fuel tank non-flammable and more particularly to a system and a method for reducing the concentration of fuel vapor in the hollow of a fuel tank.

[0002] CONTEXT

[0003] It is well known how to treat the trough (i.e., the portion of a tank above the liquid) of an aircraft fuel tank to prevent the tank from burning. In these types of aircraft fuel tanks, it is desirable to keep the fuel concentration in the trough mixture low. Systems have been developed to improve fuel tank safety. Examples of such systems are described in US patents Nos. 7,918,358, 9,016,078, and 7,955,424, and US patent publication No. 20130341465.

[0004] It is well known to use one or more filters or "air separation modules" (ASMs) that allow the separation of an intake air supply into a portion of nitrogen-enriched air (NEA) and a portion of oxygen-enriched air (OEA). In order for air separation modules to operate efficiently, they must be supplied with intake air at a relatively high pressure (typically 40 psig (2.76 x 10⁵ Pag) or higher). It is possible to operate at lower pressures, but this would mean that several air separation modules would be required, with the consequent increase in weight and complexity, which is undesirable.

[0005] Some conventional flammability reduction systems move air into the cavity along with air enriched with inert nitrogen, which is generated using an air separation device such as a system employing hollow fiber membranes. Hollow fiber membrane technology can be used to separate air into oxygen and nitrogen, and to provide nitrogen-enriched air in which the nitrogen concentration is higher than that of ambient air, and the oxygen concentration is lower. These systems can be complex and have components with limited lifespans, which can lead to significant ownership costs.

[0006] There is a need for improved systems to efficiently remove fuel vapor such that the vapor / air mixture in the hollow of a tank of fuel is non-flammable.

[0007] SUMMARY

[0008] The systems and methods described herein have features that render a fuel tank cavity gas mixture non-flammable by removing fuel vapor from the fuel tank to maintain the cavity gas mixture below the lower flammability limit specified by Federal Aviation Administration (FAA) regulations. These regulations require that the fuel tanks of a civil aircraft be rendered inert, meaning that the flammability hazard posed by the fuel tank is reduced.

[0009] Aspects of this description relate to an improved aircraft system for increasing fuel tank safety. The system may also include one or more of the following features individually or in non-exclusive combinations.

[0010] The system includes a fuel tank with a gaseous mixture of cavities in a cavity region and a quantity of fuel in a fuel region, and a compressor which has a compressor inlet in fluidic communication with the fuel tank to receive a portion of the gaseous mixture of cavities from the fuel tank. During operation, the compressor increases the pressure and temperature of the gaseous mixture of cavities.

[0011] The system may include a heat exchanger positioned downstream of the compressor. The compressor includes a compressor outlet in fluidic communication with a heat exchanger inlet where the compressor outlet is operational during use to supply the heat exchanger with a compressed cavity gas mixture. The cavity gas mixture is passed through the heat exchanger, which is cooled by atmospheric air or exhausted from the cabin.

[0012] The system may include a turbine positioned downstream of the heat exchanger. The turbine has a turbine inlet to receive the hollow gas mixture, where the hollow gas mixture expands through the turbine and reaches a temperature below the tank temperature such that the fuel vapor in the hollow gas mixture condenses into liquid fuel. The turbine includes a turbine outlet to pass the hollow gas mixture out of the turbine into a moisture separator.

[0013] The moisture separator has a moisture separator inlet in fluidic communication with the turbine outlet and first and second moisture separator outlets in fluidic communication with the fuel tank. The moisture separator is operational during use to separate the liquid fuel from the gaseous mixture. The liquid fuel flows through the first moisture separator from the return moisture separator outlet into the tank. fuel and the hollow gas mixture flows from the moisture separator through the second return moisture separator outlet into the fuel tank.

[0014] The system includes an energy transfer arrangement which allows energy to be recovered from the turbine and transferred back to the compressor to drive the compressor.

[0015] The compressor and the turbine can be mounted on a common shaft through which the power from the turbine can be transferred back to the compressor.

[0016] Aspects of this description also relate to a method for reducing the concentration of fuel vapor in the trough of an aircraft fuel tank. The method may include the following sequence of operations: receiving a portion of the trough gas mixture from the aircraft fuel tank via a compressor in fluidic communication with the aircraft fuel tank; channeling the trough gas mixture portion to a heat exchanger downstream of the compressor where the heat exchanger is in fluidic communication with the compressor; removing the thermal energy from the trough gas mixture portion at the heat exchanger;the expansion of the hollow gas mixture portion through a turbine such that the hollow gas mixture has a temperature below the tank temperature and the fuel vapor in the hollow gas mixture condenses into liquid fuel; the passage of the hollow gas mixture out of the turbine into a moisture separator in which the moisture separator has first and second moisture separator outlets in fluidic communication with the aircraft fuel tank; the separation of the liquid fuel from the hollow gas mixture where the liquid fuel flows from the moisture separator through the first moisture separator outlet into the aircraft fuel tank and the hollow gas mixture flows from the moisture separator through the second moisture separator outlet into the aircraft fuel tank;and the recovery of energy from the turbine via an energy transfer arrangement, in which energy is transferred back to the compressor to drive the compressor.

[0017] These and other features and advantages will become apparent upon reading the following detailed description and examining the accompanying drawings. It is understood that the preceding general description and the following detailed description are provided by way of example and explanation only and are not exhaustive of the major concepts on which the embodiments described herein are based. Brief description of the drawings

[0018] The accompanying drawings, which are incorporated into the description and form part thereof The drawings, which illustrate several aspects of the present invention, provide a brief description of the drawings:

[0019] [Fig.1] illustrates a top cross-sectional view of an example aircraft with an aircraft fuel system given as an example in accordance with the principles of this description;

[0020] [Fig.2] illustrates a schematic view of a system used to reduce the concentration of fuel vapor in the hollow of a fuel tank in accordance with the principles of this description; and

[0021] [Fig. 3] illustrates a schematic view of another system that includes a gear train in accordance with the principles of the present invention. DETAILED DESCRIPTION

[0022] Reference is now made in detail to the embodiments of the present invention illustrated in the accompanying drawings. Where possible, the same reference numbers will be used in all drawings to refer to identical or similar structures.

[0023] The systems and methods described herein have features that continuously extract a proportion of the hollow gas mixture from a fuel tank to remove fuel vapor and ensure that the hollow gas mixture is below the lower flammability limit specified by Federal Aviation Administration (FAA) regulations. The fuel vapor in the system is condensed into liquid fuel, separated, and returned to the fuel tank. Furthermore, the system operates with an energy transfer arrangement that allows energy to be recovered within the system.

[0024] [Fig. 1] illustrates an example of a top view of an aircraft 100 which includes an example of a system 102 for reducing the concentration of fuel vapor in the hollow of a fuel tank. Although the example of system 102 is shown to be applicable to an aircraft, it is understood that the principles of this description can be applied to reduce the flammability of any fuel tank.

[0025] The system 102 includes a first fuel tank 104 that occupies most of a first wing volume 106 of the aircraft 100, a second fuel tank 108 that occupies most of a second wing volume 110 of the aircraft 100, and a central fuel tank 112 positioned within an aircraft fuselage 114. In some examples, the aircraft fuel tanks may have an alternative arrangement while still allowing the aircraft 100 to operate as described herein. In some examples, the first fuel tank 104, the second fuel tank 108, and the central fuel tank 112 each include the system 100 described herein to reduce vapor content of fuel within each fuel tank. In other examples, System 100 can be used for the first fuel tank 104, the second fuel tank 108, and the central fuel tank 112. System 100 renders a fuel tank cavity non-flammable by removing fuel vapor such that the vapor / air mixture is below a lower flammability limit. As such, a fuel tank cavity can be considered non-flammable when it is equal to or below a lower flammability limit.

[0026] [Fig.2] is a schematic illustration of an example of a 200 system used on Aircraft 100, shown in [Fig. 1], is used to render a fuel tank cavity non-flammable by reducing the concentration of fuel vapor within the cavity. The system 200 includes a fuel tank 202, a compressor 204, a heat exchanger 206, an expansion turbine 208, a moisture separator 210, and a motor 212. In some examples, the motor 212 is an electric motor.

[0027] The fuel tank 202 contains a hollow gas mixture (i.e., a mixture of fuel and air) in a hollow region 214 and a quantity of fuel in a fuel region 216. During system operation, the hollow gas mixture can be drawn from an outlet 218 of the fuel tank 202 by the compressor 204. The compressor 204 has a compressor inlet 220 that is in fluidic communication with the fuel tank 202 to receive a portion of the hollow gas mixture. In some examples, the compressor 204 may be a positive displacement compressor or pump. The hollow gas mixture is compressed by the compressor 204, which increases the pressure and temperature of the hollow gas mixture. The compressor 204 supplies the heat exchanger 206 with the hollow gas mixture through a compressor outlet 222.In some examples, a compressor 204 drive shaft is driven by an electric motor.

[0028] The heat exchanger 206 is positioned downstream of the compressor 204. The compressor outlet 222 is in fluidic communication with a heat exchanger inlet 224. The compressor outlet 222 is operational when in use to supply the heat exchanger 206 with a cavity gas mixture via the heat exchanger inlet 224. Atmospheric or exhaust air from the cabin can be ducted through the heat exchanger 206 for cooling. The heat exchanger 206 operates to reduce the temperature of the cavity gas mixture. An air blower 226 can be integrated into the system 200 to increase the flow of cabin air to the heat exchanger 206 when the cabin pressure is insufficient to provide the required cooling flow or to promote the flow of atmospheric air through the heat exchanger 206. The air The cooling system absorbs heat from the gas mixture in high-pressure and high-temperature hollows that must be removed from the system 200.

[0029] The coupling of the expansion turbine 208 to the compressor 204 and the inclusion of the motor 212 to increase the power required to drive the compressor 204 will now be described.

[0030] The expansion turbine 208 is positioned downstream of the heat exchanger 206. The expansion turbine 208 has a turbine inlet 228 to receive the hollow gas mixture. The expansion turbine 208 is configured to be driven by the hollow gas mixture from the heat exchanger 206. The hollow gas mixture expands through the expansion turbine 208 to a temperature below the tank temperature such that the fuel vapor in the hollow gas mixture condenses into liquid fuel. The hollow gas mixture also expands to a lower pressure. The expansion turbine 208 includes a turbine outlet 230 to discharge the hollow gas mixture from the expansion turbine 208. The expansion turbine 208 can generate power for the compressor 204.Namely, the power from the expansion turbine 208 can be transferred back to the compressor 204 to help drive the rotation of the compressor 204. The compressor 204 can be driven at least partially or totally by shaft power supplied from the expansion turbine 208.

[0031] The system 200 may include a power transfer arrangement 232 designed to recover energy from the expansion turbine 208 to be transferred back to the compressor 204 to drive the compressor 204. The power transfer arrangement 232 may include the motor 212 coupled to the system 200 between the expansion turbine 208 and the compressor 204 to provide additional power to drive the compressor 204.

[0032] In some examples, an output shaft 234 of the expansion turbine 208 is connected via the motor 212 to the drive shaft of the compressor 204. In some examples, the output shaft 234 of the expansion turbine 208 has a direct shaft connection to the drive shaft of the compressor 204. In other examples, the output shaft 234 of the expansion turbine 208 may be connected to the compressor 204 via a gear train 236 (see [Fig. 3]), such as a planetary gear train or another type of gear train. One end of the output shaft 234 of the expansion turbine 208 may connect to the gear train 236.

[0033] The motor 212 may have a motor shaft 238 passing through it such that one end of the motor shaft 238 connects either to the expansion turbine 208 or to the gear train 236 and an opposite end of the motor shaft 238 connects to the compressor 204. In some examples, the shaft of Motor 238 may also have a gear for meshing with the gear train 236, which is connected to the output shaft 234 of the expansion turbine 208. As such, the motor shaft 238 and the output shaft 234 are not required to rotate at the same speed, allowing the gear ratio to be changed. The gear train 234 can provide a smooth transition between drive ratios. In other examples, a battery can be charged by motor 212 to provide backup or supplementary power to the electric motor.

[0034] The liquid fuel condensed out of the expansion turbine 208 can be separated from the fuel vapor in the moisture separator 210. The moisture separator 210 can include a moisture separator inlet 240 in fluidic communication with the turbine outlet 230, a first moisture separator outlet 242, and a second moisture separator outlet 244. The first and second moisture separator outlets 242, 244 can be in fluidic communication with the fuel tank 202 to provide a closed-loop system.

[0035] The moisture separator 210 is operational when used to separate the liquid fuel from the hollow gas mixture while returning both separately to the fuel tank 202. From the moisture separator 210, a separated liquid fuel and a hollow gas mixture of air and fuel vapor with a reduced fuel vapor concentration are returned to the aircraft fuel tank separately. Namely, the liquid fuel can flow through the first return outlet of the moisture separator 210 to the fuel tank 202, and the hollow gas mixture can flow from the moisture separator 210 through the second return outlet of the moisture separator 244 to the fuel tank 202. The coupling of the turbine to the compressor and the inclusion of the engine increase the power required to drive the compressor.

[0036] Another aspect of the present description relates to a method for making a fuel tank cavity non-flammable by reducing the concentration of fuel vapor in a cavity of an aircraft fuel tank.The method may include a sequence of start-ups which include the following: 1) receiving a portion of the hollow gas mixture from the aircraft fuel tank via a compressor in fluidic communication with the aircraft fuel tank; 2) piping the portion of the hollow gas mixture to a heat exchanger downstream of the compressor, where the heat exchanger is in fluidic communication with the compressor; 3) removing the thermal energy from the portion of the hollow gas mixture at the heat exchanger; 4) expanding the portion of the hollow gas mixture through a turbine such that the hollow gas mixture has a temperature below the temperature of . tank and that the fuel vapor in the hollow gas mixture condenses into liquid fuel; 5) the passage of the hollow gas mixture out of the turbine into a moisture separator where the moisture separator has first and second moisture separator outlets in fluidic communication with the aircraft fuel tank; 6) the separation of the liquid fuel from the hollow gas mixture where the liquid fuel flows from the moisture separator through the first moisture separator outlet into the aircraft fuel tank and the hollow gas mixture flows from the moisture separator through the second moisture separator outlet into the aircraft fuel tank; and 7) the recovery of energy from the turbine by means of a power transfer arrangement where the energy is transferred back to the compressor to drive the compressor.

[0037] Various modifications and changes to this description will become obvious to a person skilled in the art without departing from the scope and spirit of this description, and it must be understood that the inventive scope of this description should not be unduly restricted to the illustrative embodiments presented herein.

Claims

Demands

1. 1 System for reducing the concentration of fuel vapor in a hollow part of an aircraft fuel tank comprising: a fuel tank including a gaseous mixture of hopper in a hopper region and a quantity of fuel in a fuel region; a compressor having a compressor inlet in fluidic communication with the fuel tank to receive a portion of the gaseous mixture from the fuel tank; a heat exchanger positioned downstream of the compressor, the compressor including a compressor outlet in fluidic communication with a heat exchanger inlet, in which the compressor outlet is operational when in use to supply the heat exchanger with gaseous mixture of hollow; a turbine positioned downstream of the heat exchanger, the turbine having a turbine inlet to receive the hollow gas mixture, the hollow gas mixture extending through the turbine, in which the hollow gas mixture has a temperature below the tank temperature such that the fuel vapor in the hollow gas mixture condenses into liquid fuel, the turbine including a turbine outlet to pass the hollow gas mixture out of the turbine; a moisture separator having a moisture separator inlet in fluidic communication with the turbine outlet and first and second moisture separator outlets in fluidic communication with the fuel tank, the moisture separator being operational when used to separate liquid fuel from the gaseous cavity mixture, wherein the liquid fuel flows from the moisture separator through the first moisture separator outlet into the fuel tank and the gaseous cavity mixture flows from the moisture separator through the second moisture separator outlet into the fuel tank; and an energy transfer arrangement that allows energy to be recovered from the turbine and transferred back to the compressor to drive the compressor.

2. 2 System according to claim 1, wherein the compressor is suitable for increasing the pressure and temperature of gas mixtures hollow.

3. 3 System according to claim 1, wherein atmospheric air or air rejected from the cabin is channeled through the heat exchanger for cooling.

4. 4 System according to claim 1, wherein the energy transfer arrangement includes a motor coupled to the system between the turbine and the compressor.

5. 5 System according to claim 4, wherein the motor is an electric motor.

6. 6 System according to claim 4, wherein the motor includes a motor shaft which passes through it, in which one end of the motor shaft is connected to the compressor.

7. 7 System according to claim 6, wherein an opposite end of the motor shaft is connected to the turbine.

8. 8 System according to claim 6, wherein one opposite end of the motor shaft is connected to a gear train.

9. 9 System according to claim 8, wherein the gear train is a planetary gear train.

10. 10 System according to claim 4, further comprising a battery, in which the motor is adapted to charge the battery with excess energy.

11. 11 A method for reducing the concentration of fuel vapor in a hollow of an aircraft fuel tank, the method comprising: receiving a portion of the hollow gas mixture from the aircraft fuel tank via a compressor in fluidic communication with the aircraft fuel tank; channeling the portion of the hollow gas mixture to a heat exchanger downstream of the compressor, wherein the heat exchanger is in fluidic communication with the compressor; removing the thermal energy from the portion of the hollow gas mixture at the heat exchanger; expanding the portion of the hollow gas mixture through a turbine such that the hollow gas mixture has a temperature below the tank temperature and the fuel vapor in the hollow gas mixture condenses into liquid fuel;the passage of the gaseous mixture from the turbine out of the turbine into a moisture separator, the moisture separator having first and; second moisture separator outlets in fluidic communication with the aircraft fuel tank; separation of liquid fuel from hollow gas mixture, in which the liquid fuel flows from the moisture separator through the first moisture separator outlet into the aircraft fuel tank and the hollow gas mixture flows from the moisture separator through the second moisture separator outlet into the aircraft fuel tank; and recovery of turbine energy by means of an energy transfer arrangement, in which energy is transferred back to the compressor to drive the compressor.

12. 12 Method according to claim 11, wherein, in the step of receiving a portion of gaseous hollow mixture through the compressor, a temperature and pressure of the gaseous hollow mixture increase.

13. 13 Method according to claim 11, wherein, in the step of channeling the gas mixture portion from the cavity to the heat exchanger, the heat exchanger is cooled by atmospheric air or air expelled from the cabin.

14. 14 Method according to claim 11, wherein the power transfer arrangement includes a motor between the turbine and the compressor.

15. 15 Method according to claim 14, wherein the motor includes a motor shaft which passes through it, in which one end of the motor shaft is connected to the compressor.

16. 16 Method according to claim 15, wherein an opposite end of the motor shaft is connected to the turbine.

17. A system for removing fuel from a mixture of air and fuel vapor in a hollow space of an aircraft fuel tank, the system comprising: a compressor for drawing the mixture of air and fuel vapor from the hollow space and directing the mixture of air and fuel vapor through a heat exchanger where the mixture of air and fuel vapor is cooled; a turbine configured to be driven by the mixture of air and fuel from the heat exchanger, in which the mixture of air and fuel vapor expands and cools to a temperature below the temperature in the aircraft fuel tank as the mixture of air and fuel passes through the turbine, and in in which the power from the turbine is transferred back to the compressor to help drive the rotation of the compressor; and a separator to receive the air and fuel vapor mixture from the turbine and separate at least a portion of the liquid fuel from the air and fuel vapor mixture, in which, from the separator, a separated liquid fuel and an air and fuel vapor mixture having a reduced concentration of fuel vapor are returned to the aircraft fuel tank.

18. 18 System according to claim 17, wherein the compressor and turbine are mounted on a common shaft through which power from the turbine can be transferred back to the compressor.

19. 19 System according to claim 17, wherein the compressor is driven by an electric motor, and wherein the power from the turbine helps the electric motor to drive the compressor.

20. 20 System according to claim 17, wherein the mixture of air and fuel vapor is cooled in the heat exchanger by atmospheric air or air expelled from the cabin.