The present invention relates to treating fuel for use in aircraft and other vehicles, such that the fuel is self inerting.
Conventional fuel tanks for aircraft have ullages which contain explosive mixtures of atmospheric air and fuel vapors during various stages of operation of the aircraft. The fuel tanks are vented to atmosphere to relieve ascent and descent pressure changes, allowing the atmospheric air to enter into the ullages and mix with the fuel vapors above the liquid levels of the volatile fuels contained within the fuel tanks. These explosive mixtures are highly flammable and are easily ignited by a spark or other ignition source, which can result in massive explosions and loss of life to those onboard the aircraft.
The risks due to explosives mixtures being contained within fuel tank ullages may be increased as ambient temperatures increase, raising the temperature of the volatile fuels contained within the aircraft. Fuel temperatures may also be increased due to various processes, such as those employed for deicing the aircraft. U.S. Pat. No. 5,558,303, entitled xe2x80x9cMethod And Apparatus For Using Hot Fuels To De-Ice Aircraft,xe2x80x9d invented by Koethe, et al., and issued on Sep. 24, 1996 discloses a method whereby hot fuels are used to de-ice aircraft. The hot fuels are provided in aircraft fuel tanks, and then heat is transferred from the hot fuels to exterior surfaces of the aircraft to warm and thus de-ice the exterior surfaces. This hot fuel de-icing technique has proven effective for both removing and preventing in-flight icing, icing on the ground in cold and warm weather, as well as moisture condensation within fuel tanks. Use of hot fuels to de-ice aircraft may provide a more environmentally friendly and often times more effective technique than the currently employed commercial method of spraying warm antifreeze fluids onto the exterior surfaces of the aircraft. However, the use of hot fuels for de-icing aircraft is subject to safety requirements, which later may prevent the use of raised temperature fuels if such use is later found to create increased safety concerns regarding explosive mixtures in fuel tank ullages.
Previous attempts have been made to reduce the risks of explosion within the non-vented ullages of aircraft fuel tanks. One such attempt fills the ullages with an inert gas, such as nitrogen (N2), to blanket the liquid fuel and prevent air from entering the ullages so that the fuel vapors in the ullages will not have a readily available oxygen source. The inert gases were provided by on-board tanks or generating systems which proved inefficient and ultimately impractical due to the size of large, heavy tanks used for on-board storage or generating of the inerting gases, and the heavy logistics support required for such systems. This type of system also required alteration of existing aircraft to accommodate such equipment.
A second problem exists is that the range of aircraft, or the distance which the aircraft can fly, is limited due to the limited volumetric storage capacity of onboard fuel tanks. While in-flight refueling is possible today with some types of aircraft, most refueling is performed on the ground. Such refueling stops prolong travel time and ruin the economics of operating an airplane. It is therefore desirable to increase the amount of fuel that can be stored on the aircraft, preferably with no or only minimal alteration to the aircraft structure. On such method is that set forth in PCT International Patent Application Serial Number PCT/US97/04091, filed on Mar. 17, 1997, entitled xe2x80x9cREFRIGERATED FUEL FOR ENGINES,xe2x80x9d invented by Terence Lee Koethe, published on Oct. 9, 1997 and claiming a priority date of Mar. 18, 1996, as set forth above in the section entitled xe2x80x9cCross Reference To Related Applications,xe2x80x9d and to which the present application claims priority as a Continuation-in-Part.
A method and apparatus are disclosed for providing inert loading jet fuel for use in cold fuel, hot fuel or conventional temperature fuel applications for aircraft. Inert loading jet fuel is preferably provided by direct contact injection, in which an inerting material, such as, for example, nitrogen (xe2x80x9cN2), is directly into the jet fuel as the fuel is being loaded aboard the aircraft. The inerting material is preferably injected directly into the jet fuel by injection nozzles which are in direct contact with a flow of the jet fuel. The inert material is metered to accommodate an entrained level of the inerting material which will outgas as an inert gas into a ullage of an onboard, vented fuel tank of the aircraft, rendering the mixture of gases in the ullage nonexplosive for a period of time.
The inerting material can be injected into fuels which are used to provide cold temperature fuels, which are cooled to temperatures that are less than ambient temperatures so that the unit volume of the fuel per pound of fuel is reduced. The fuel is preferably cooled externally to the aircraft at a ground location, and then stored in onboard fuel tanks at the reduced temperatures, allowing more fuel to be held in the storage tanks and increasing the energy value of the fuel per unit volume over fuel at ambient temperatures. A heat transfer surface may also cooled below ambient temperature using the cold fuel or the inerting material, and then ambient air is passed over the heat transfer surface and cooled for passing into the passenger compartment of the aircraft.
The inerting material may also be injected into fuels which are used to provide hot fuel for de-icing aircraft. The hot fuel is provided by heating fuel to elevated temperatures which are sufficiently high enough to transfer heat from the fuel stored in onboard fuel tanks within the wings of the aircraft to the exterior of the wings to de-ice the aircraft. The inerting material may be injected directly into the fuel either prior to or after heating to the elevated temperatures.