Aircraft fuel tank inerting system

Abstract

An aircraft fuel tank inerting system and a method of inerting an aircraft fuel tank. The aircraft fuel tank inerting system having an on-board inerting gas generation system arranged in fluid communication between a fuel tank vent system and an aircraft fuel tank.

Claims

1. An aircraft fuel tank inerting system having an on-board inerting gas generation system arranged in fluid communication between a fuel tank vent system and the aircraft fuel tank, wherein the fuel tank vent system includes a NACA duct arranged to supply the on-hoard inerting gas generation system with atmospheric air and wherein the on-board inerting gas generation system additionally comprises an air pressure reduction device.

2. The aircraft fuel inerting system of claim 1 wherein the on-board inerting gas generation system comprises an air separation module.

3. The aircraft fuel inerting system of claim 1 wherein the air pressure reduction device is a venturi based vacuum generator.

4. The aircraft fuel inerting system of claim 1 wherein the air pressure reduction device is a vacuum pump.

5. The aircraft fuel inerting system of claim 1 wherein the fuel tank vent system includes a flame arrestor.

6. The aircraft fuel inerting system of claim 1 having an air separation module filter arranged in fluid communication between the fuel tank vent system and the on-board inciting gas generation system.

7. An aircraft fuel tank inerting system having an on-board inerting gas generation system arranged in fluid communication between a fuel tank vent system and the aircraft fuel tank, the aircraft fuel tank inerting system further comprising an alternate vent pathway between the fuel tank vent system and the aircraft fuel tank.

8. The aircraft fuel inerting system of claim 7 having a climb/dive valve arranged in the alternate vent pathway between the fuel tank vent system and the aircraft fuel tank, bypassing the on-board inerting gas generation system.

9. An aircraft having the aircraft fuel inerting system of claim 1.

10. A method of inerting an aircraft fuel tank comprising the steps of: providing an on-board inerting gas generation system in fluid communication between a fuel tank vent system and the aircraft fuel tank; providing an air pressure reduction device in fluid communication with the on-board inerting gas generation system; supplying the on-board inerting gas generation system with atmospheric air via the fuel tank vent system, wherein the on-board inerting gas generation system is supplied with atmospheric air via a NACA duct in the fuel tank vent system; and supplying the aircraft fuel tank with inerted air from the on-board inerting gas generation system.

11. A method of inerting an aircraft fuel tank according to claim 10 further comprising the step of: providing an air separation module in the on-board inerting gas generation system; wherein the air separation module is supplied with atmospheric air via the NACA duct in the fuel tank vent system and the air separation module exhausts oxygen depleted air to the fuel tank.

12. A method of inerting an aircraft fuel tank according to claim 10 comprising the further steps of: passing a first proportion of the atmospheric air through the air pressure reduction device to produce a supply of reduced pressure air passing a second proportion of the atmospheric air along one side of a membrane of the air separation module, exposing the other side of the membrane of the air separation module to the reduced pressure air, so that oxygen passes from the air on one side of the membrane to the reduced pressure air on the other side of the membrane and the air separation module exhausts an oxygen depleted air to the fuel tank.

Description

(1) Aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic of a typical passenger aircraft cross-section taken along the aircraft wing-span at the mid plane between the aircraft nose and tail;

(3) FIG. 2 is a block diagram of the aircraft fuel tank inerting system of a first embodiment of the present invention; and

(4) FIG. 3 is a block diagram of the aircraft fuel tank inerting system of a second embodiment of the present invention.

(5) In FIG. 1, a large passenger aircraft 1 has a fuselage 2, divided into a pressurised cabin region 3 and a non-pressurised centre wingbox 4. A starboard and a port wing 5, 6 extend from a wing root section 5a, 6a either side of the centre wingbox 4 to respective wing tips 5b, 6b. Each wing 5, 6 houses a wing fuel tank 8. A centre wingbox fuel tank 7 is housed within the centre wingbox 4.

(6) The wing fuel tanks 8 and centre wing fuel tank 7 are interconnected via crossfeed systems as is known in the art such that fuel may pass between the tanks 7, 8 and together the tanks 7, 8 supply fuel to the aircraft engines (not shown) and auxiliary power unit (also not shown). The tanks 7, 8 are vented to the atmosphere through respective NACA ducts 9 arranged on a lower surface of the port and starboard wings 5, 6, adjacent the respective wing tips 5b, 6b. The wing fuel tanks 8 and centre wingbox fuel tank 7 may themselves comprise multiple separate fuel cells, but for simplicity of description will be termed collectively as aircraft fuel tank 40.

(7) The aircraft fuel tank inerting system 10, (see FIG. 2) comprises an on-board inerting gas generation system 20 arranged in fluid communication between a fuel tank vent system 30 and an aircraft fuel tank 40. The on-board inerting gas generation system 20 arranged between an atmospheric opening in the fuel tank vent system 30 and the aircraft fuel tank 40.

(8) In use, the aircraft fuel tank inerting system 10 operates as follows: the atmospheric air enters the fuel tank vent system 30 via air intake 50. The on-board inerting gas generation system 20 is supplied with atmospheric air from the fuel tank vent system 30 via atmospheric air supply conduit 60. The on-board gas generation extracts a proportion of the oxygen (O.sub.2) from the atmospheric air and exhausts the remaining inert, Oxygen Depleted Air (ODA), to the aircraft fuel tank 40 via inerting gas supply conduit 80. The extracted oxygen is ejected from the on-board inerting gas generation system 20 to the atmosphere via an oxygen exhaust vent 70.

(9) In FIG. 3, an alternate aircraft fuel tank inerting system 110 also has an on-board inerting gas generation system 120 arranged in fluid communication between a fuel tank vent system 130 and an aircraft fuel tank 140. Parts corresponding to parts in FIG. 2 bear the same reference numerals, but preceded with a “1”.

(10) The fuel tank inerting system 110 differs from the aircraft fuel tank inerting system 10 in a number of ways as will be described below.

(11) The fuel tank vent system 130 includes a flame arrestor 132.

(12) The on-board inerting gas generation system 120 comprises an air separation module 121, as is known in the art. The air separation module 121 includes an air separation module filter 122 arranged at its inlet. The air separation module 121 includes a molecular sieve 123 illustrated across the air separation module mid-plane, defining an inerting side 124 and an O.sub.2 extraction side 125. In reality, the air separation module 121 comprises a cylindrical conduit packed with hollow fibres. The walls of the fibres provide the molecular sieve, generally termed 123, which separates the channels within the hollow fibres, collectively designated as inerting side 124 and the regions external to the hollow fibres, collectively designated as O.sub.2 extraction side 125.

(13) The fuel tank inerting system 110 further includes an air pressure reduction device 136. The air pressure reduction device 136 is a vacuum generator, the function of which will be described in more detail below.

(14) The fuel tank inerting system 110 further includes a climb/dive valve 142 as is known in the art, the function of which will be described in more detail below.

(15) In use, the aircraft fuel tank inerting system 110 operates as follows: the atmospheric air enters the fuel tank vent system 130 via air intake 150. A proportion of the atmospheric air is routed from the flame arrestor 132 in the fuel tank vent system 130 to the air separation module filter 122 via supply conduit 160. The remainder of the atmospheric air is routed from the fuel tank vent system 130 to the air pressure reduction device 136 via conduit 151.

(16) The air separation module filter 122 removes atmospheric particulates to provide a filtered atmospheric air supply from conduit 162 to the inerting side 124 of air separation module 121. The air separation module in the on-board inerting gas generation system 120 is thereby supplied with filtered atmospheric air.

(17) The air pressure reduction device 136 is venturi based, and generates a supply of reduced pressure air by passing the remainder of the atmospheric air through a constriction. The reduced pressure air is exposed to the O.sub.2 extraction side 125 of the air separation module 121 by conduit 138.

(18) In use, the filtered atmospheric air is supplied from conduit 162 to the inerting side 124 of the molecular sieve 123, and the reduced pressure air is exposed to the O.sub.2 extraction side 125 of the molecular sieve 123 by conduit 138. This arrangement boosts the pressure differential across the molecular sieve 123 to increase the rate of extraction of oxygen across the molecular sieve 123 from the inerting side 124 to the O.sub.2 extraction side 125. The extracted oxygen is collected on the O.sub.2 extraction side 125 of the air separation module 121 and ejected to the atmosphere via an oxygen exhaust vent 170. The remaining inert, Oxygen Depleted Air (ODA), is supplied from the inerting side 124 of the air separation module 121 to the aircraft fuel tank 140 via inerting gas supply conduit 180.

(19) The climb/dive valve 142 provides a bypass 164 from the aircraft fuel tank 140 to the supply conduit 160 between the flame arrestor 132 and the air separation module filter 122.

(20) In use, the climb/dive valve 142 provides an additional vent pathway from the fuel tank 140 when necessary, for example during ascent or during refuel operations, by opening to allow fuel vapour to exit the fuel tank 140 via the bypass 164. The climb/dive valve 142 also provides relief by opening during descent if insufficient inerting gas is supplied to the fuel tank 140 from the on-board inerting gas generation system 120, to prevent the fuel tank pressure to atmospheric pressure differential from exceeding a pre-determined value.

(21) In an alternate embodiment, a vacuum pump may be used as an air pressure reduction device.