Abstract:
A method of optimizing a fuel system on a vehicle is provided. The fuel system includes a fuel tank configured to receive and contain a quantity of fuel, and the method includes determining a property associated with the quantity of fuel contained within the fuel system, comparing the determined property with a nominal value for that fuel property, and modifying at least one vehicle sub-system setting in response to the determined fuel property.

Description:
BACKGROUND OF THE DISCLOSURE 
       [0001]    The field of the invention relates generally to gas turbine engine fuel systems and more specifically to the optimization of such fuel systems dependent upon the type of fuel being used in the system. 
         [0002]    The various jet fuel types are governed by standards developed by the American Society for Testing and Materials (ASTM). These standards set specification constraints for the quality of aviation turbine fuels and describes the fuels found satisfactory for the operation of aircraft and turbine engines. To be utilized for aviation, each jet fuel type must meet or exceed the standards for aviation fuels. Current gas turbine engine and commercial aircraft research and development efforts are focusing on the practicality of using alternative fuels in near-term, mid-term, and far-term aircraft. However, most known alternative fuels do not comply with the ASTM established standards, and many are non-compliant outside of the established specifications by 2-20%. To bring such fuels into compliance, significant processing steps may need to be taken to convert such fuels into the allowable specification range. Such additional processing steps may render the alternative fuels financially impractical. 
         [0003]    Current efforts are underway to certify “drop in” jet fuels as alternatives to typical aircraft fuels, such as Jet-A, for example. A “drop in” fuel, i.e. direct replacement, is a fuel that is capable of being blended with, or completely replacing Jet-A fuel without necessitating any substantial modifications to the aircraft or engine. Some known “drop in” fuels, which consist primarily of a blend of kerosene and other synthetic fuels, are currently available for use in existing and near-term aircraft. 
         [0004]    However, future mid-term and long-term aircraft development projects propose using a wide variety of bio-jet and synthetic fuels (as blends and in unmixed or “neat” form) for use in ultra-efficient airplane designs. Such fuels are substantially similar in performance to conventional jet fuel, but may have a near-zero sulfur and aromatics content resulting in substantially lower particulate exhaust emissions. In addition, synthetic fuels exhibit excellent low-temperature properties, maintaining a low viscosity at lower ambient temperatures. 
         [0005]    As mentioned above, many alternative fuels have properties that do not fit within current ASTM fuel specifications, or that vary within specification limits and have different relationships between properties. Such fuels may be considered “near drop-in” fuels, as their usage would require only minor system adjustments to aircraft systems to allow for safe and efficient use. Some known methods of optimizing fuel systems in response to these differing fuel properties include conducting a major ground and flight test program to obtain approval of each alternative fuel or fuel combination. Additionally, alternative fuels may be heavily processed to attempt to meet all or nearly all fuel specification limits, which can add significant cost to the fuel. Currently, there is no reliable way to quickly determine the type of fuel being used in the aircraft in combination with adjusting aircraft and engine systems to use “near drop-in” fuels. Such a method would add flexibility to aviation fuel specifications, and enable a wider variety of alternative fuels to be utilized in military and commercial aircraft. The above-mentioned flexibility could broaden options for a more environmentally friendly aviation fuel supply, reduce fuel cost, improve fuel quality assurance, and provide a more robust supply if conventional fuel supplies are disrupted. 
       BRIEF DESCRIPTION OF THE DISCLOSURE 
       [0006]    One aspect is directed to a method of optimizing a fuel system on a vehicle. The fuel system includes a fuel tank configured to receive and contain a quantity of fuel, and the method includes determining a property of the quantity of fuel within the fuel system, comparing the determined property with a nominal value for the fuel property, and modifying the vehicle in response to the determined fuel property. 
         [0007]    Another aspect is directed to a computer readable medium that includes a process to be executed by a processor for use in optimizing a fuel system on a vehicle. The vehicle includes a fuel tank configured to receive and contain a quantity of fuel, and the processor, when executing said process, is programmed to determine a property of the quantity of fuel within the fuel system, compare the determined property with a nominal value for the fuel property, and modify the vehicle in response to the determined fuel property. 
         [0008]    Another aspect is directed to an alternative fuel-powered vehicle that includes a mission planning system configured to determine a range of the vehicle, a fuel system comprising at least one sensor. The fuel system is optimized by a computer system that is programmed to determine a property of a fuel within the fuel system, compare the determined property with a nominal value for the fuel property, and modify the fuel gaging system and mission planning system in response to the determined fuel property. 
         [0009]    Various refinements exist of the features noted in relation to the above-mentioned aspects of the present invention. Further features may also be incorporated in the above-mentioned aspects of the present invention as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to any of the illustrated embodiments of the present invention may be incorporated into any of the above-described aspects of the present invention, alone or in any combination. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0010]      FIG. 1  is an internal perspective view of an exemplary aircraft fuel system. 
           [0011]      FIG. 2  is a schematic illustration of an exemplary optimizer assembly that may be used in the aircraft fuel system shown in  FIG. 1 . 
           [0012]      FIG. 3  is a flow diagram of an exemplary method of optimization that may be used in the aircraft fuel system shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION  
       [0013]    Referring to  FIGS. 1 and 2 ,  FIG. 1  is an internal perspective view of an aircraft  10  with exemplary aircraft fuel system  12 , and  FIG. 2  is a schematic illustration of an exemplary optimizer assembly  14  that may be used in aircraft fuel system  12  shown in  FIG. 1 . Aircraft fuel system  12  includes a first fuel tank  16  and a second fuel tank  18  positioned proximate a respective wing  20 ,  22  of aircraft  10 , and a center fuel tank  24  positioned within an aircraft fuselage  26 . Alternatively, aircraft  10  may have any fuel tank configuration to allow aircraft  10  to function as described herein. In the exemplary embodiment, first fuel tank  16 , second fuel tank  18  and center fuel tank  24  each include a sensor assembly  28  for use in determining the fuel type contained in each tank and to facilitate optimizing fuel system  12  using data regarding determined the fuel type, as described in more detail herein. 
         [0014]    As shown in  FIG. 2 , and in the exemplary embodiment, a fuel tank  30  contains a quantity of fuel  32 , and a known optical sensor assembly  34  that includes a source  36 , a mirror  38  and a sensor element  40  arranged in sequence such that a light  42  emitted from source  36  is directed by the mirror  38  towards sensor  40 . Sensor element  40  measures a physical variable of light  42  emitted through the quantity of fuel  32 , for example water content of the fuel  32 . Fuel tank  30  also includes a thermometer  44 , a densitometer  46  and a fixed capacitor  48  that measure temperature, density and dielectric constant respectively. Specifically, fixed capacitor  48  measures the dielectric constant of the fuel  32  by measuring the capacitance of the fuel. Since capacitance is a function of the dielectric constant and the geometry of the fixed capacitor, the fuel dielectric constant can be calculated. Each of the sensor element  40 , thermometer  44 , densitometer  46  and a fixed capacitor  48  are in communication with a property comparator  50  positioned within aircraft  10  that receives the measurements from each of the sensor element  40 , thermometer  44 , densitometer  46  and fixed capacitor  48 . Property comparator  50  is programmed for determination of further fuel properties such as, for example, fuel acidity, fuel aromatics content, fuel flash point, fuel freeze point, fuel viscosity and fuel heat of combustion. Property comparator  50  is also programmed to compare the received measured properties with pre-determined nominal values for the measured properties and resolve the type of fuel contained in the fuel system. A Vehicle Management System (VMS)  52  positioned within aircraft  10  is in communication with property communicator  50 . Based upon the determined fuel type contained in the system, VMS  52  determines aircraft subsystem adjustments that must be made to accommodate the fuel type, as described in more detail herein. The determined subsystem adjustments are then communicated to the various aircraft sub-systems, such as a fuel system  54 , an engine  56 , a mission planning system  58  and maintenance system  60 . 
         [0015]      FIG. 3  is a flow diagram  100  of an exemplary method for fuel optimization that may be used in aircraft fuel system  12  shown in  FIG. 2 . In the exemplary embodiment, nominal fuel properties are provided  102  to the property comparator  50  (shown in  FIG. 2 ) from a database of standard fuel properties for conventional aviation fuels, synthetic and biofuels, and any blend combination of these known fuels. In the exemplary embodiment, the provided standard fuel properties include fuel acidity, fuel aromatics content, fuel flash point, fuel density, fuel freeze point, fuel viscosity, fuel heat of combustion, fuel conductivity, fuel water content, and dielectric. Alternatively, any property may be provided that enables the fuel type to be determined as described herein. Additionally, fuel operating specifications are provided  102  to the property comparator  50  (shown in  FIG. 2 ). In the exemplary embodiment, engine specification values are provided in ASTM D1655 (Jet A, Jet A-1) and MIL-DTL-83133E (JP-8). 
         [0016]    Fuel properties associated with the fuel contained in the aircraft fuel system  12  are then determined  104  by the property comparator  50  (shown in  FIG. 2 ). In the exemplary embodiment, an optical sensor assembly and various other property measurement devices, i.e. a thermometer, a densitometer and a fixed capacitor, are included within the fuel tank (as shown in  FIG. 2 ). In the exemplary embodiment, fuel density, fuel conductivity, water content and a dielectric constant are measured using the sensor assembly and the included measurement devices. Specifically, the optical sensor assembly operates to determine fuel water content, and a thermometer  44 , a densitometer  46  and a fixed capacitor  48  measure temperature, density and dielectric constant respectively. From these measurements, the type of fuel provided in the aircraft fuel tank can be determined  104 . Alternatively, any fuel property may be measured therewith to enable the type of fuel provided in the fuel tank to be determined  104  such as, for example, fuel acidity, fuel aromatics content, fuel flash point, fuel freeze point, fuel viscosity and fuel heat of combustion. In another embodiment, the type of sensor is not limited to the following, but may be for example, an infrared sensor or a laser sensor, or any other sensor that enables the fuel type to be determined as described herein. 
         [0017]    The determined  104  fuel properties are then compared  106  with the provided  102  nominal fuel properties. The property comparator  50  (shown in  FIG. 2 ) determines the most likely fuel type using the determined and provided data, and determines whether the results of the comparison  106  are expected  108 . If the determined fuel type is not expected, a fault signal is transmitted  110  externally wherein the fault signal is subsequently displayed and used to alert ground crew personnel, or a pilot, that the fuel type is not expected. If the determined fuel type is expected, the determined fuel properties are then compared  112  to a fuel specification for engine operation. In the exemplary embodiment, engine specification values are provided in ASTM D1655 (Jet A, Jet A-1) and MIL-DTL-83133E (JP-8). If the determined fuel property values are determined  114  to be unsafe following comparison  112 , a fault signal is transmitted  110  externally where the fault signal is displayed, thus alerting ground crew personnel, or a pilot, that the fuel type is not expected. 
         [0018]    If the determined fuel property values are determined  114  to be safe following comparison  112 , aircraft system adjustment factors are then calculated  116  using the comparisons  112  between the determined fuel properties and the specifications. Fuel-dependent aircraft sub-systems must then be adjusted to account for differences in the determined fuel properties. In the exemplary embodiment, the aircraft fuel system, mission planning system, and engine operational settings will be modified. Specifically, the property comparator with calculate  116  adjustment factors for these systems based upon the comparisons  106 ,  112 , and these calculated system adjustments are transmitted  118  to the VMS for dissemination to the various aircraft systems and sub-systems. 
         [0019]    In the exemplary embodiment, the aircraft systems and/or sub-systems autonomously execute the adjustments to ensure the aircraft fuel system is optimized and operating within safe and efficient parameters depending upon the determined fuel type in the system. 
         [0020]    Further, although the present invention is described with respect to processors and computer programs, as will be appreciated by one of ordinary skill in the art, the present invention may also apply to any system and/or program that is configured to optimize gas turbine engine fuel system performance and efficiency for a range of conventional, synthetic and bio-fuels, or any fuel-blend combination. For example, as used herein, the term processor is not limited to just those integrated circuits referred to in the art as processors, but broadly refers to computers, processors, microcontrollers, microcomputers, programmable logic controllers, application specific integrated circuits, and other programmable circuits. The processor may be part of a computer that may include a device, such as; a floppy disk drive or compact disc-read-only memory (CD-ROM) drive, for reading data from a computer-readable medium, such as a floppy disk, a CD-ROM, a magneto-optical disk (MOD), or a digital versatile disc (DVD). 
         [0021]    Exemplary embodiments of optimization techniques for use in aircraft fuel systems are described in detail above. The above-described fuel systems that include a system for automatically measuring fuel characteristics in the fuel tank to determine fuel properties, compare these properties to acceptable limits, and signal these properties to the fuel gaging system and engines to allow adjustment to optimize performance, enhance safety and efficiency for a range of conventional, synthetic, and biofuels and any blend combination. Moreover, this system is particularly useful for sensing key fuel properties while the fuel is in the fuel tank, rather then requiring outside laboratory testing. The system described herein would allow the use of a much wider range of “near drop-in” alternative fuels that currently can not be accommodated, as well as determining how the aircraft and engine parameters need to be changed to safely and efficiently accommodate the alternative fuel, and would allow a determination to be made whether the fuel is within specifications and safe to fly. 
         [0022]    Although the foregoing description contains many specifics, these should not be construed as limiting the scope of the present invention, but merely as providing illustrations of some of the presently preferred embodiments. Similarly, other embodiments of the invention may be devised which do not depart from the spirit or scope of the present invention. Features from different embodiments may be employed in combination. The scope of the invention is, therefore, indicated and limited only by the appended claims and their legal equivalents, rather than by the foregoing description. All additions, deletions and modifications to the invention as disclosed herein which fall within the meaning and scope of the claims are to be embraced thereby. 
         [0023]    As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
         [0024]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.