Patent Publication Number: US-10766760-B2

Title: Systems and methods for supplying fuel to a vehicle

Description:
FIELD 
     The present disclosure generally relates to systems and methods for supplying fuel to a vehicle, and more particularly to refueling systems and methods for supplying fuel to a vehicle based on a level of ionization of an air medium in a fuel tank of the vehicle. 
     BACKGROUND 
     During a refueling operation, a fuel source supplies fuel to a fuel tank of a vehicle. As the fuel flows in a fuel line from the fuel source to the fuel tank, an electrostatic charge may be generated in the fuel due to, among other factors, friction between the fuel and the fuel line. When the fuel arrives in the fuel tank the electrostatic charge may accumulate on the surface of the fuel. The accumulated electrostatic charge may present a risk of electrical discharge between the fuel and the fuel tank and, thus, a risk of an explosion hazard. To mitigate the risk of electrical discharge, a rate of fuel flow in the fuel line is limited so that the accumulated charge remains relatively low. 
     SUMMARY 
     In an example, a method of supplying fuel to a fuel tank of a vehicle is described. The method includes supplying, via a fuel line, fuel to a fuel tank of a vehicle at an initial rate of fuel flow. The act of supplying the fuel causes an electrostatic charge to accumulate on a surface of the fuel in the fuel tank. The method also includes exposing, using an ionization radiation source, an air medium in the fuel tank to ionizing radiation to increase a level of ionization of the air medium in the fuel tank and thereby increase a rate of dissipation of the electrostatic charge accumulated on the surface of the fuel. Responsive to exposing the air medium in the fuel tank to the ionizing radiation, the method includes determining the level of ionization of the air medium in the fuel tank. The method further includes determining an increased rate of fuel flow based on a difference between the determined level of ionization and a baseline level of ionization. The electrostatic charge accumulated on the surface of the fuel dissipates at an increased rate when the determined level of ionization of the air medium is higher than the baseline level of ionization. The method also includes supplying, via the fuel line, the fuel to the fuel tank at the determined increased rate of fuel flow to reduce a time for supplying the fuel to the fuel tank. 
     In another example, a system for supplying fuel to a fuel tank of a vehicle is described. The system includes a fuel line configured to supply fuel to a fuel tank of a vehicle. A flow of the fuel in the fuel line causes an accumulation of an electrostatic charge on a surface of the fuel in the tank. The system also includes an ionization radiation source configured to expose an air medium in the fuel tank to ionizing radiation, and a sensor configured to determine a level of ionization of the air medium in the fuel tank and generate a sensor signal indicating the determined level of ionization. 
     The system further includes a control device in communication with the sensor and configured to: (i) cause the fuel line to supply the fuel to the fuel tank at an initial rate of fuel flow, (ii) cause the ionization radiation source to expose the air medium in the fuel tank to the ionizing radiation and increase the level of ionization of the air medium in the fuel tank, (iii) receive the sensor signal indicating the determined level of ionization, (iv) determine an increased rate of fuel flow based on a difference between the determined level of ionization and a baseline level of ionization, and (v) cause the fuel line to supply the fuel to the fuel tank at the determined increased rate of fuel flow to reduce a time for supplying the fuel to the fuel tank. The electrostatic charge accumulated on the surface of the fuel dissipates at an increased rate when the determined level of ionization of the air medium is higher than the baseline level of ionization. 
     In another example, a method of supplying fuel to a fuel tank of a vehicle is described. The method includes exposing air in an air tank to ionizing radiation to form ionized air. The air tank is external to the fuel tank of the vehicle. The method also includes supplying the ionized air into the fuel tank to increase a level of ionization of an air medium in the fuel tank. Responsive to supplying the ionized air into the fuel tank, the method includes determining the level of ionization of the air medium in the fuel tank. The method further includes determining, based on the determined level of ionization, a rate of fuel flow at which to supply the fuel to the fuel tank and supplying, via a fuel line, the fuel to the fuel tank at the determined rate of fuel flow. The act of supplying the fuel causes an electrostatic charge to accumulate on a surface of the fuel in the fuel tank. Determining the rate of fuel flow includes determining, based on the determined level of ionization, the rate of fuel flow that is configured to maintain the accumulated electrostatic charge below a threshold value. The threshold value is related to a potential for electrical discharge between the surface of the fuel and a structure of the fuel tank due to the accumulated electrostatic charge. 
     The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The novel features believed characteristic of the illustrative embodiments are set forth in the appended claims. The illustrative embodiments, however, as well as a preferred mode of use, further objectives and descriptions thereof, will best be understood by reference to the following detailed description of an illustrative embodiment of the present disclosure when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  illustrates a simplified block diagram of a refueling system according to an example embodiment. 
         FIG. 2  illustrates a perspective view of the refueling system shown in  FIG. 1  according to an example embodiment. 
         FIG. 3A  illustrates a simplified block diagram of a refueling system according to an example embodiment. 
         FIG. 3B  illustrates a simplified block diagram of a refueling system according to an example embodiment. 
         FIG. 4  illustrates a simplified block diagram of a refueling system according to an example embodiment. 
         FIG. 5  illustrates a perspective view of the refueling system shown in  FIG. 4  according to an example embodiment. 
         FIG. 6A  illustrates a perspective view of a nozzle and an ionization radiation source in a first position according to an example embodiment. 
         FIG. 6B  illustrates a perspective view of the nozzle and the ionization radiation source in second position according to the example embodiment shown in  FIG. 6A . 
         FIG. 7  illustrates a perspective view of the refueling system shown in  FIG. 4  according to an example embodiment. 
         FIG. 8  illustrates a simplified block diagram of a refueling system according to an example embodiment. 
         FIG. 9  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle according to an example embodiment. 
         FIG. 10  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIG. 9 . 
         FIG. 11  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIG. 10 . 
         FIG. 12  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIGS. 9-11 . 
         FIG. 13  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIG. 12 . 
         FIG. 14  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIG. 13 . 
         FIG. 15  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIGS. 11-12 . 
         FIG. 16  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIGS. 9-15 . 
         FIG. 17  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIGS. 9-16 . 
         FIG. 18  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle according to an example embodiment. 
         FIG. 19  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIG. 18 . 
         FIG. 20  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIG. 19 . 
         FIG. 21  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle according to an example embodiment. 
         FIG. 22  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIG. 21 . 
         FIG. 23  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIGS. 21-22 . 
         FIG. 24  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIG. 23 . 
         FIG. 25  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIG. 24 . 
         FIG. 26  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIGS. 21-25 . 
         FIG. 27  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIG. 26 . 
         FIG. 28  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIGS. 21-27 . 
         FIG. 29  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIGS. 21-28 . 
         FIG. 30  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIGS. 21-29 . 
         FIG. 31  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle according to an example embodiment. 
         FIG. 32  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIG. 31 . 
         FIG. 33  illustrates a flow chart of an example process for supplying fuel to a fuel tank of a vehicle that can be used with the process shown in  FIGS. 31-32 . 
     
    
    
     DETAILED DESCRIPTION 
     Disclosed embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all of the disclosed embodiments are shown. Indeed, several different embodiments may be described and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are described so that this disclosure will be thorough and complete and will fully convey the scope of the disclosure to those skilled in the art. 
     The systems and methods of the present disclosure provide refueling systems and methods for supplying fuel to a fuel tank of a vehicle. As noted above, during refueling of the vehicle, the fuel flows in a fuel line from the fuel source to the fuel tank. As the fuel flows in the fuel line, an electrostatic charge may be generated in the fuel due to, among other factors, friction between the fuel and the fuel line. When the fuel is received in the fuel tank, the electrostatic charge may accumulate on the surface of fuel. The accumulated electrostatic charge may present a risk of electrical discharge between the fuel and the fuel tank and, thus, may present safety issues. 
     Because the fuel has a relatively low conductivity, the accumulated static charge on the surface of the fuel in the fuel tank may dissipate relatively slowly. To mitigate the risk of electrical discharge, existing refueling systems limit a rate of fuel flow in the fuel line so that the accumulated charge remains relatively low. In particular, for example, many refueling systems limit the rate of fuel flow to a rate of fuel flow that is based on an assumption that an air medium in the fuel tank is a non-ionized air medium. However, a non-ionized air medium in the fuel tank dissipates the accumulated electrostatic charge at lower rate of dissipation than an ionized air medium in the fuel tank. 
     The refueling systems and methods described in the present disclosure can beneficially determine the level of ionization of the air medium in the fuel tank, and determine a rate of fuel flow based on the determined level of ionization. Because the rate of dissipation of the electrostatic charge increases as the level of ionization of the air medium increases, the refueling systems and methods described in the present disclosure can increase the rate of fuel flow while maintaining the accumulated electrostatic charge on the surface of the fuel at or below a relatively safe level. By increasing the rate of fuel flow, the refueling systems and methods described in the present disclosure can reduce a time for supplying the fuel to the fuel tank of the vehicle. 
     Reducing the time for supplying the fuel to the fuel tank of the vehicle can further provide significant efficiencies for operating transportation facilities. For example, aircraft are generally refueled at airports between flights with an amount of fuel required to complete the aircraft&#39;s next flight. To increase the revenue generated by the aircraft, it may be desirable to reduce (or minimize) the amount of time the aircraft spends on the ground between flights. The time spent refueling the aircraft can be a significant contributor to the time required between flights and, thus, it is generally desirable to reduce (or minimize) the amount of time required to refuel the aircraft. Similar considerations may be applicable to other types of vehicles. 
     Also, within examples, the refueling systems and methods described in the present application provide for increasing the level of ionization of the air medium in the fuel tank of the vehicle. By increasing the level of ionization of the air medium, the rate at which the accumulated electrostatic charge dissipates can be further increased such that the rate of fuel flow also can be increased. 
     Referring now to  FIG. 1 , a simplified block diagram of a refueling system  100  for supplying fuel to a fuel tank of a vehicle is depicted according to an example embodiment. As shown in  FIG. 1 , the refueling system  100  includes a vehicle  110  having a fuel tank  112  for storing fuel  114 . Within examples, the vehicle  110  can be an aircraft, a helicopter, an automobile (e.g., a car, a truck, a bus, and/or a van), a railed vehicle (e.g., a train and/or a tram), a watercraft (e.g., a ship and/or a boat), and/or a spacecraft. In an implementation in which the vehicle  110  is an aircraft, the fuel tank  112  can be in a fuselage and/or a wing of the aircraft. 
     The type of fuel  114  that is stored in the fuel tank  112  can be based, at least in part, on the type of vehicle  110  to be powered by the fuel  114 . As examples, the fuel  114  can include aviation gasoline, jet propellant, diesel fuel, and/or automotive gasoline. More generally, the fuel  114  can be any material that can provide energy for operating the vehicle  110 . 
     As also shown in  FIG. 1 , the refueling system  100  includes a fuel source  116  that can store and deliver the fuel  114  to the fuel tank  112  of the vehicle  110  during a refueling operation. In  FIG. 1 , the fuel source  116  includes a fuel storage device  118  coupled to a fuel delivery device  120 . The fuel storage device  118  stores the fuel  114 , which is to be supplied to the fuel tank  112  of the vehicle  110  during the refueling operation. As one example, the fuel storage device  118  can include one or more storage tanks above and/or below ground (e.g., a fuel farm at an airport). The fuel delivery device  120  can couple the fuel storage device  118  to the fuel tank  112  of the vehicle  110  via a fuel line  122 . For example, the fuel delivery device  120  can include a fixed refueling system (e.g., a hydrant refueling system) and/or a mobile refueling system (e.g., a refueling truck and/or a tanker aircraft). 
     The fuel source  116  is coupled to the fuel tank  112  by the fuel line  122 . In an example, the fuel line  122  can be a fueling hose having a nozzle  124  for coupling to a fuel inlet  126  of the fuel tank  112 . The fuel inlet  126  provides access to an interior space of the fuel tank  112 . In an example in which the vehicle  110  is an aircraft, the fuel inlet  126  can be positioned on the aircraft to facilitate over-the-wing refueling and/or under-the-wing refueling. In this arrangement, during a refueling operation, the fuel line  122  can supply the fuel  114  to the fuel tank  112  of the vehicle  110  via the coupling between the nozzle  124  and the fuel inlet  126 . 
     To control the flow of the fuel  114  from the fuel source  116  to the fuel tank  112  of the vehicle  110 , the fuel delivery device  120  can include a flow rate control device  128  along the flow path between the fuel storage device  118  and the fuel tank  112 . Within examples, the flow rate control device  128  is operable to start, stop, increase, and/or decrease a rate of fuel flow in the fuel line  122 . For instance, the flow rate control device  128  can include one or more valves and/or fuel pumps along the flow path between the fuel storage device  118  and the fuel tank  112 . The valve(s) and/or fuel pump(s) can be actuatable to start, stop, increase, and/or decrease the rate of fuel flow. 
     As noted above, the flow of the fuel  114  in the fuel line  122  causes an accumulation of an electrostatic charge on a surface  130  of the fuel  114  in the fuel tank  112 . For example, as the fuel  114  flows in the fuel line  122  from the fuel source  116  to the fuel tank  112 , friction between the fuel  114  and the fuel line  122  (and/or other components of the fuel source  116  such as, e.g., a filter) generates an electrostatic charge in the fuel  114 . When the fuel  114  arrives in the fuel tank  112 , the conductivity of the fuel  114  is relatively low and thus the electrostatic charge accumulates on the surface  130  of the fuel  114 . 
     The accumulated electrostatic charge dissipates at a rate of dissipation that is based, at least in part, on a level of ionization of an air medium  132  in the fuel tank  112 . For instance, when the air medium  132  has a relatively high level of ionization, the air medium  132  dissipates the accumulated electrostatic charge at a higher rate than when the air medium  132  has a relatively low level of ionization. 
     The level of ionization of the air medium  132  can be related to an extent of ionizing radiation in an environment proximate to the fuel tank  112 . (e.g., in an environment at the location of the fuel tank  112  and/or an environment within a radius of several miles from the fuel tank  112 ). For example, the decay of naturally occurring terrestrial radioactive materials, radiation from the sun, and/or cosmic radiation can strip electrons from air molecules and thus ionize the environment proximate to the fuel tank  112 . Additionally, for example, winds and/or weather fronts can impart friction forces and ionize the air molecules in the environment proximate to the fuel tank  112 . Accordingly, the level of ionization of the air medium  132  may naturally vary over time and/or at different locations of the vehicle  110  due to various factors such as those described above. 
     As noted above, the refueling system  100  is configured to supply the fuel  114  to the fuel tank  112  at a rate of fuel flow that is based on the level of ionization of the air medium  132  in the fuel tank  112 . To that end, the refueling system  100  can include an ion sensor  134 , which can determine the level of ionization of the air medium  132  in the fuel tank  112  and generate a sensor signal indicating the determined level of ionization. As one example, the ion sensor  134  can include an air ion counter (e.g., a positive ion detector and/or a negative ion detector), which measures the level of ionization of the air medium  132 . Additionally, for example, the sensor signal can indicate the determined level of ionization by indicating an ion density of the air medium  132  (e.g., a number of ions per cubic centimeter of air). 
     In one implementation, the ion sensor  134  can be coupled to an inner wall of the fuel tank  112 . In another implementation, the ion sensor  134  can be inserted into the fuel tank  112  during the refueling operation. For example, the ion sensor  134  can be integrated with the nozzle  124  so that the ion sensor  134  is inserted into the fuel tank  112  when the nozzle  124  is coupled to the fuel inlet  126 . In another example, the ion sensor  134  can be coupled to the fuel tank  112  separately from the nozzle  124  such as, for instance, via an access port on the inner wall of the fuel tank  112  (which is separate from the fuel inlet  126 ). 
     As shown in  FIG. 1 , the refueling system  100  further includes a control device  136 , which is in communication with the fuel delivery device  120  and the ion sensor  134 . The control device  136  can receive the sensor signal from the ion sensor  134  and cause the fuel delivery device  120  to supply the fuel  114  through the fuel line  122  at one of a fuel flow rate based on the determined level of ionization indicated by the sensor signal. For example, the flow rate control device  128  and the fuel line  122  can be operable to supply the fuel  114  at a plurality of different rates of fuel flow. The control device  136  can transmit, to the flow rate control device  128 , a control signal indicating one of the rates of fuel flow. Responsive to the control signal, the flow rate control device  128  and the fuel line  122  can supply the fuel  114  at the rate of fuel flow indicated by the control signal. 
     In one implementation, the control device  136  can transmit a first control signal to the fuel delivery device  120  to cause the fuel line  122  to supply the fuel  114  at an initial rate of fuel flow. The initial rate can be a rate of fuel flow that is configured to maintain the accumulated electrostatic charge below a threshold value when the air medium  132  is at a baseline level of ionization. The threshold value can be related to a potential for electrical discharge between the surface  130  of the fuel  114  and a structure of the fuel tank  112  due to the accumulated electrostatic charge. As one example, the initial rate can be configured to maintain the accumulated electrostatic charge below a threshold value of approximately 30 Coulombs per square meter. Additionally, for example, in aviation, the fuel  114  is typically supplied at a rate of fuel flow of approximately 7 feet per second to approximately 10 feet per second (i.e., approximately 2.13 meters per second to approximately 3.05 meters per second), depending on the type of fuel  114 , the diameter of the fuel line  122 , and/or the composition of the fuel line  122  to maintain the accumulated electrostatic charge below the threshold value at which an electrical discharge may occur. In one implementation, for instance, the initial rate of fuel flow can be approximately 700 gallons per minute to approximately 1000 gallons per minute for a fuel line  122  having a six inch diameter (i.e., a 15.24 centimeter diameter). 
     In one example, the baseline level of ionization can be a level of ionization of non-ionized air (i.e., approximately no ionization of the air medium  132 ). As noted above, the rate of dissipation of the accumulated electrostatic charge increases as the level of ionization of the air medium  132  increases. Thus, when the air medium  132  is at the level of ionization of non-ionized air, the rate of dissipation is at or close to a minimum, and the rate of fuel flow should be relatively low to maintain the accumulated electrostatic charge below the threshold value. By basing the initial rate of fuel flow on an assumption that the air medium  132  is non-ionized air, the control device  136  can conservatively cause the fuel line  122  to supply the fuel  114  at a relatively low rate of fuel flow during an initial portion of the refueling operation. This can help to reduce (or eliminate) the risk of the accumulated electrostatic charge reaching the threshold value prior to determining the level of ionization of the air medium  132 . 
     The control device  136  can receive the sensor signal indicating the determined level of ionization, and determine an increased rate of fuel flow based on a difference between the determined level of ionization and the baseline level of ionization. For example, the control device  136  can determine, based on the sensor signal, that the determined level of ionization is higher than the baseline level of ionization. In this scenario, the electrostatic charge accumulated on the surface  130  of the fuel  114  dissipates at an increased rate when the determined level ionization of the air medium  132  is higher than the baseline level of ionization. As such, the rate of fuel flow can be increased while maintaining the accumulated electrostatic charge below the threshold value. This is because the increased accumulation of electrostatic charge (e.g., due to the increased friction at the increased rate of fuel flow) is offset, at least in part, by the higher rate of dissipation of the accumulated electrostatic charge at the determined level of ionization of the air medium  132 . 
     In general, the control device  136  can determine, based on the determined level of ionization, the increased rate such that the accumulated electrostatic charge remains below the threshold value when the fuel line  122  supplies the fuel  114  at the increased rate. In one example, the control device  136  can store in memory and/or access a lookup table, which includes records providing a correspondence between a plurality of levels of ionization and the rates of fuel flow that can be achieved by the fuel delivery device  120  and the fuel line  122 . In this example, the control device  136  can determine the increased rate of fuel flow by determining the record in the lookup table that corresponds to the determined level of ionization indicated by the sensor signal. 
     In another example, the control device  136  can implement an algorithm that outputs the increased rate of fuel flow based on the determined level of ionization and the baseline level of ionization as inputs. For instance, an example algorithm can be in the form of the following equation:
 
 R=R   b   +K *( X   i   −X   b )  (1)
 
     where R represents the increased rate of fuel flow, R b  represents the baseline rate of fuel flow, X i  represents the determined level of ionization, X b  represents the baseline level of ionization, and K represents a constant. Constant K depends on geometry of the fuel tank and on the pressure, temperature, and humidity of the air medium. 
     After the control device  136  determines the increased rate of fuel flow, the control device  136  can cause the fuel line  122  to supply the fuel  114  to the fuel tank  112  at the increased rate of fuel flow to reduce a time for supplying the fuel  114  to the fuel tank  112 . For example, the control device  136  can transmit a second control signal to cause the fuel delivery device  120  and the fuel line  122  to supply the fuel  114  at the increased rate of fuel flow. 
     In general, the control device  136  is a computing device that is configured to control operation of the refueling system  100 . As such, the control device  136  can be implemented using hardware, software, and/or firmware. For example, the control device  136  can include one or more processors and a non-transitory computer readable medium (e.g., volatile and/or non-volatile memory) that stores machine language instructions or other executable instructions. The instructions, when executed by the one or more processors, cause the refueling system  100  to carry out the various operations described herein. The control device  136 , thus, can receive data (including data indicated by the sensor signal) and store the data in memory (including the lookup table) as well. 
     Additionally, as shown in  FIG. 1 , the fuel tank  112  can include a vent  138 . The vent  138  can provide for venting a portion of the air medium  132  out of the fuel tank  112  while the fuel line  122  supplies the fuel  114  into the fuel tank  112 . The vent  138  can thus help to relieve a pressure in the fuel tank  112  and thereby facilitate supplying the fuel  114  at the rate of fuel flow determined by the control device  136 . Within examples, the vent  138  can be at an elevated location relative to the surface  130  of the fuel  114  in the fuel tank  112 . 
     In the example described above, the baseline level of ionization was that of non-ionized air. In another example, the baseline level of ionization can be a relatively low level of ionization based on, for instance, the type of vehicle  110  and/or a location of the vehicle  110 . For example, the baseline level of ionization can be approximately 1000 ions per cubic centimeter of air to approximately 2000 ions per cubic centimeter of air. More generally, the baseline level of ionization can be an assumed level of ionization that is expected to be below the actual level of ionization that will be determined by the ion sensor  134 . In this way, the control device  136  can initially start supplying the fuel  114  at a relatively conservative rate of fuel flow and then increase the rate of fuel flow based on the determined level of ionization of the air medium  132 . The baseline level of ionization can be based on, for example, past historical measurements of levels of ionization at the particular refueling location of the vehicle  110 , the type of vehicle  110  that will be refueled, terrestrial weather (e.g. wind blowing from an ocean may have relatively low ionization but wind blowing down from a mountain range may have relatively high ionization), and current solar weather (e.g. low solar activity increases the flux of cosmic rays striking the earth, which increases the level of ionization). 
       FIG. 2  depicts a perspective view of the refueling system  100  during a refueling operation in accordance with an example embodiment. In  FIG. 2 , the vehicle  110  is an aircraft  210  and the fuel source  116  is a fuel truck  216 ; however, the vehicle  110  and the fuel source  116  can take other forms in alternative examples. The aircraft  210  includes the fuel tank  112  in a wing  240 , which is coupled to a fuselage  242  of the aircraft  210 . The fuel tank  112  can additionally or alternatively be located in the fuselage  242  of the aircraft  210 . 
     As shown in  FIG. 2 , the fuel source  116  is coupled to the aircraft  210  via the fuel line  122 . For example, in  FIG. 2 , the fuel inlet  126  can be accessed by opening a fuel cover  244  over the fuel inlet  126  and removing a cap  246 . With the fuel cover  244  opened and the cap  246  removed, the nozzle  124  is inserted into the fuel inlet  126  to couple the fuel line  122  to the fuel tank  112 . After refueling is completed, the cap  246  can be coupled to the fuel inlet  126  to facilitate sealing the fuel inlet  126 , and the fuel cover  244  can be closed. The fuel cover  244  and the cap  246  can thus help to protect the fuel tank  112  when the fuel  114  is not being supplied to the fuel tank  112 . 
     Additionally, as shown in  FIG. 2 , the refueling system  100  includes a plurality of electrical conductors  248 ,  250 ,  252  for providing a conductive path to equalize the electrical potential between the fuel source  116  and the vehicle  110 . For example, a first electrical conductor  248  electrically couples the nozzle  124  to the aircraft  210 , a second electrical conductor  250  electrically couples the fuel truck  216  to the aircraft  210 , and a third electrical conductor  252  electrically couples the fuel truck  216  to a ground (e.g., a grounding post). The second electrical conductor  250  can also be coupled to the ground. Equalizing the electrical potential between the aircraft  210 , the fuel truck  216 , and the nozzle  124  using the electrical conductors  248 ,  250 ,  252  can reduce the risk of a discharge of the electrostatic charge, which accumulates while supplying the fuel  114  from the fuel truck  216  to the aircraft  210 . 
     In the examples described above, the refueling system  100  can increase the rate of fuel flow based on the determined level of ionization of the air medium  132  in the fuel tank  112  being higher than the baseline level of ionization. As described above, the determined level of ionization of the air medium  132  may be higher than the baseline level of ionization due to, for example, an extent of ionizing radiation in the environment proximate to the fuel tank  112 . Thus, in the example above, the refueling system  100  can beneficially increase the rate of fuel flow based naturally occurring conditions at the time of refueling allowing for the increased rate of fuel flow while maintaining a relatively low risk of electrical discharge. 
     In additional or alternative examples, the refueling system  100  can facilitate increasing the level of ionization of the air medium  132  in the fuel tank  112 . By increasing the level of ionization of the air medium  132  in the fuel tank  112 , the refueling system  100  can further increase the rate at which the accumulated electrostatic charge dissipates from the surface  130  of the fuel  114 . Accordingly, increasing the level of ionization of the air medium  132  can facilitate the refueling system  100  providing for greater increases to the rate of fuel flow while maintaining the accumulated electrostatic charge below the threshold value during a refueling operation. 
       FIG. 3A  and  FIG. 3B  depict simplified block diagrams of refueling systems  300 A,  300 B for increasing the level of ionization of the air medium  132  and supplying the fuel  114  to the fuel tank  112  of the vehicle  110  according to example embodiments. As shown in  FIGS. 3A-3B , the refueling systems  300 A,  300 B include the vehicle  110 , the fuel tank  112 , the fuel  114  having the surface  130 , the fuel source  116 , the fuel storage device  118 , the fuel delivery device  120 , the fuel line  122 , the nozzle  124 , the fuel inlet  126 , the flow rate control device  128 , the air medium  132  in the fuel tank  112 , the ion sensor  134 , the control device  136 , and the vent  138  arranged and configured as described above. 
     Additionally, as shown in  FIGS. 3A-3B , the refueling systems  300 A,  300 B include a blower  354  and an ambient air sensor  356  in communication with the control device  136 . The blower  354  can supply, from an environment external to the fuel tank  112 , ambient air  358  into the fuel tank  112 . As examples, the blower  354  can include one or more centrifugal blowers, positive displacement blowers, air compressors, and/or air flow dampers. 
     In  FIG. 3A , the blower  354  is coupled to the fuel delivery device  120 . In this arrangement, the fuel delivery device  120  can receive the ambient air  358  from the blower  354  and supply a mixture of the ambient air  358  and the fuel  114  to the fuel tank  112  via the fuel line  122 . Whereas, in  FIG. 3B , the blower  354  is configured to supply the ambient air  358  to the fuel tank  112  separately from the fuel  114  in the fuel line  122 . For example, in  FIG. 3B , the blower  354  is coupled to an air inlet  360  of the fuel tank  112  via an air line  362 . Supplying the ambient air  358  via the fuel line  122  (e.g., as shown in  FIG. 3A ) can reduce the number of inlets  126 ,  360  to the fuel tank  112 . Whereas, supplying the ambient air  358  via separate air line  362  (e.g., as shown in  FIG. 3B ) can simplify the fuel delivery device  120 . 
     In  FIGS. 3A-3B , the vent  138  can vent a portion of the air medium  132  out of the fuel tank  112  while the blower  354  supplies the ambient air  358  into the fuel tank  112  (e.g., via the fuel delivery device  120  and/or the air line  362 ). This can facilitate relieving pressure in the fuel tank  112  while supplying the fuel  114  and the ambient air  358  into the fuel tank  112 . Venting the air medium  132  while supplying the ambient air  358  to the fuel tank  112  can also help to increase the level of ionization of the air medium  132  as the vented air medium  132  is replaced by the supplied ambient air  358 . 
     The ambient air sensor  356  can determine a level of ionization of the ambient air  358  in the environment external to the fuel tank  112  and transmit to the control device  136  an ambient-air signal indicating the determined level of ionization of the ambient air  358 . For example, the ambient air sensor  356  can include an ion counter, which can measure an ion density of the ambient air  358 . Based on the ambient-air signal received from the ambient air sensor  356  and the sensor signal received from the ion sensor  134 , the control device  136  can determine that the determined level of ionization of the air medium  132  in the fuel tank  112  is less than the determined level of ionization of the ambient air  358 . In such instances, it can be beneficial to supply the ambient air  358  into the fuel tank  112  to increase the level of ionization of the air medium  132  in the fuel tank  112  and thus increase the rate for dissipating the accumulated electrostatic charge on the surface  130  of the fuel  114 . 
     Accordingly, responsive to a determination that the determined level of ionization is less than the level of ionization of the ambient air, the control device  136  can cause the blower  354  to supply the ambient air  358  into the fuel tank  112  to increase the level of ionization of the air medium  132  in the fuel tank  112 . By increasing the level of ionization of the air medium  132  using the ambient air  358 , the refueling systems  300 A- 300 B can increase the rate for dissipating the electrostatic charge accumulated on the surface  130  of the fuel  114 . This in turn allows for the control device  136  to increase the rate of fuel flow by greater magnitudes while maintaining the accumulated electrostatic charge below the threshold amount. 
     In one implementation, the control device  136  can iteratively repeat (i) causing the blower  354  to supply the ambient air  358  and increase the level of ionization of the air medium  132  in the fuel tank  112 , (ii) receiving, from the ion sensor  134 , the sensor signal indicating the determined level of ionization of the air medium  132 , (iii) determining the increased rate of fuel flow based on the determined level of ionization, and (iv) causing the fuel line  122  to supply the fuel  114  at the increased rate of fuel flow one or more times to iteratively increase the increased rate of fuel flow and further reduce the time for supplying the fuel  114  to the fuel tank  112  during the refueling operation. 
       FIG. 4  depicts a refueling system  400  for increasing the level of ionization of the air medium  132  and supplying the fuel  114  to the fuel tank  112  of the vehicle  110  according to another example embodiment. As shown in  FIG. 4 , the refueling system  400  includes the vehicle  110 , the fuel tank  112 , the fuel  114  having the surface  130 , the fuel source  116 , the fuel storage device  118 , the fuel delivery device  120 , the fuel line  122 , the nozzle  124 , the fuel inlet  126 , the flow rate control device  128 , the air medium  132  in the fuel tank  112 , the ion sensor  134 , the control device  136 , and the vent  138  arranged and configured as described above. 
     Additionally, as shown in  FIG. 4 , the refueling system  400  includes an ionization radiation source  462  in communication with the control device  136 . The ionization radiation source  462  can expose the air medium  132  in the fuel tank  112  to ionizing radiation to increase the level of ionization of the air medium  132  in the fuel tank  112  and thereby increase the rate of dissipation of the electrostatic charge accumulated on the surface  130  of the fuel  114 . As examples, the ionizing radiation can be at least one of x-ray radiation, gamma ray radiation, alpha particles, or beta particles. 
     In one example, the ionization radiation source  462  can transmit the ionizing radiation to the air medium  132  in the fuel tank  112  through a surface of the vehicle  110  and the fuel tank  112 .  FIG. 5  depicts a perspective view of the refueling system  400  during a refueling operation for one implementation of this example. In  FIG. 5 , the ionization radiation source  462  is depicted as a portable x-ray radiation source  562  positioned on a surface  564  of the vehicle  110  adjacent to the fuel tank  112 . While positioned on the surface  564  of the vehicle  110 , the portable x-ray radiation source  562  can transmit x-ray radiation through the surface  564  of the vehicle  110  to the air medium  132  in the fuel tank  112 . 
     In  FIG. 5 , the vehicle  110  includes a designated area for positioning the portable x-ray radiation source  562  (or another ionization radiation source  462 ). More particularly, the portable x-ray radiation source  562  is positioned on a window portion  566  of the surface  564  of the vehicle  110 . The window portion  566  has a higher x-ray radiation transmissivity than a portion  568  of the surface  564  of the vehicle  110  adjacent to the window portion  566 . For example, the window portion  566  can be thinner than the portion  568  adjacent to the window portion  566 , and/or the window portion  566  can be made from a different material than the portion  568  adjacent to the window portion  566 . 
     Additionally, the vehicle  110  includes a window cover  570 , which is actuatable between an open state and a closed state. In the open state, the window cover  570  provides access to the window portion  566 . Whereas, in the closed state, the window cover  570  inhibits access to the window portion  566 . In the closed state, the window cover  570  can thus protect the window portion  566  before and/or after the refueling operation. For instance, when the window cover  570  is closed the thickness of the surface  564  at the window portion  566  is increased and, thus, a combination of the window cover  570  and the window portion  566  can provide a lower x-ray radiation transmissivity into the fuel tank  112  when the window cover  570  is closed than the x-ray transmissivity of the window portion  566  alone when the window cover  570  is open. 
     In additional or alternative examples, the nozzle  124  of the fuel line  122  can include the ionization radiation source  462 . In such examples, the ionization radiation source  462  can expose the air medium  132  to the ionizing radiation when the nozzle  124  is coupled to the fuel inlet  126 .  FIGS. 6A-6B  depict an example in which the nozzle  124  includes the ionization radiation source  462 . As shown in  FIGS. 6A-6B , the fuel line  122  is coupled to the fuel inlet  126  via the nozzle  124 . The nozzle  124  includes a handle  672  and a spout  674  extending from the handle  672 . The handle  672  can facilitate handling of the nozzle  124  by an operator, and the spout  674  can facilitate coupling the nozzle  124  to the fuel inlet  126 . 
     Also, as shown in  FIGS. 6A-6B , the ionization radiation source  462  is coupled to the spout  674  of the nozzle  124 . As such, when the spout  674  is inserted in the fuel inlet  126 , the ionization radiation source  462  can extend into and/or directly access the fuel tank  112 . In this way, the ionization radiation source  462  can expose the air medium  132  in the fuel tank  112  to the ionizing radiation transmitted by the ionization radiation source  462 . Although the ionization radiation source  462  is on an end of the spout  674  in  FIGS. 6A-6B , the ionization radiation source  462  can be additionally or alternatively coupled to a different portion of the nozzle  124  in another example. 
     In  FIGS. 6A-6B , the nozzle  124  also includes a retractable shield  676  on the spout  674 . The retractable shield  676  can limit exposure to the ionizing radiation from the ionization radiation source  462  when the nozzle  124  is decoupled from the fuel tank  112 . This can beneficially provide additional protection to operators and equipment in the vicinity of the nozzle  124 . Within examples, the retractable shield  676  can be made from one or more materials that inhibit and/or block the ionizing radiation transmitted by the ionization radiation source  462  such as, for instance, lead, depleted uranium, thorium, and/or barium sulfate. 
     The retractable shield  676  is actuatable between a first position in which the retractable shield  676  covers the ionization radiation source  462 , and a second position in which the retractable shield  676  retracts from the ionization radiation source  462 . The retractable shield  676  can be in the first position when the nozzle  124  is decoupled from the fuel tank  112 , and the retractable shield  676  can be in the second position when the nozzle  124  is coupled to the fuel inlet  126  of the fuel tank  112 . Accordingly, prior to inserting the nozzle  124  into the fuel tank  112 , the retractable shield  676  can limit exposure to the ionizing radiation from the ionization radiation source  462 . Whereas, when the nozzle  124  is inserted into the fuel tank  112 , the retractable shield  676  can expose the ionization radiation source  462  to transmit the ionizing radiation to the air medium  132  in the fuel tank  112 . 
     As one example, the retractable shield  676  can be actuated between the first position and the second position by an engagement between the retractable shield  676  and a portion of the fuel inlet  126 . For instance, in  FIGS. 6A-6B , the fuel inlet  126  includes a shoulder portion  678 , which is configured to engage with the retractable shield  676  when the nozzle  124  is inserted in the fuel inlet  126 . In  FIG. 6A , the spout  674  is partially inserted in the fuel inlet  126 . As shown in  FIG. 6A , the retractable shield  676  does not engage the shoulder portion  678  and, thus, the retractable shield  676  is in the first position covering the ionization radiation source  462 . 
     In  FIG. 6B , the spout  674  is fully inserted in the fuel inlet  126 . While inserting the spout  674  from the partially-inserted position shown in  FIG. 6A  to the fully-inserted position shown in  FIG. 6B , the retractable shield  676  engages the shoulder portion  678  and retracts away from the ionization radiation source  462 . Accordingly, in  FIG. 6B , the retractable shield  676  is in the second position exposing the ionization radiation source  462 . In one implementation, the retractable shield  676  can be spring-biased towards the first position so that the retractable shield  676  returns to the first position covering the ionization radiation source  462  when the nozzle  124  is decoupled from the fuel inlet  126  of the fuel tank  112 . 
     In an additional or alternative example, the ionization radiation source  462  can be in the fuel tank  112 .  FIG. 7  depicts the refueling system  400  during a refueling operation for one implementation of this example. As shown in  FIG. 7 , the ionization radiation source  462  is in the fuel tank  112  of the vehicle  110 . For example, the ionization radiation source  462  can be coupled to an inner wall of the fuel tank  112 . By locating the ionization radiation source  462  in the fuel tank  112 , the ionization radiation source  462  can directly transmit the ionizing radiation to the air medium  132  in the fuel tank  112 . Additionally, locating the ionization radiation source  462  in the vehicle  110  can facilitate more rapidly increasing the level of ionization of the air medium  132  as compared to examples in which the ionization radiation source  462  is coupled to the vehicle  110  during the refueling operation (e.g., as described above with respect to  FIGS. 5-6B  and below with respect to  FIG. 8 ). 
     Also, in additional or alternative examples, the ionization radiation source  462  can increase the level of ionization of the air medium  132  by forming ionized air in an air tank external to the fuel tank  112 , and then supplying the ionized air from the air tank into the fuel tank  112 .  FIG. 8  depicts a simplified block diagram of a refueling system  800  including an air tank  878  for supplying ionized air to the fuel tank  112  to increase the level of ionization of the air medium  132 . As shown in  FIG. 8 , the refueling system  800  includes the vehicle  110 , the fuel tank  112 , the fuel  114  having the surface  130 , the fuel source  116 , the fuel storage device  118 , the fuel delivery device  120 , the fuel line  122 , the nozzle  124 , the fuel inlet  126 , the flow rate control device  128 , the air medium  132  in the fuel tank  112 , the ion sensor  134 , the control device  136 , and the vent  138  arranged and configured as described above. 
     Additionally, as shown in  FIG. 8 , the refueling system  800  includes the ionization radiation source  462 , the air tank  878 , an air line  862 , and an air inlet  860 . The air tank  878  is coupled the air inlet  860  of the fuel tank  112  via the air line  862 . The ionization radiation source  462  can expose air in the air tank  878  to the ionizing radiation to form ionized air  880 . For example, as described above, the ionization radiation source  462  can transmit at least one of one of x-ray radiation, gamma ray radiation, alpha particles, or beta particles to the air in the air tank  878  to form the ionized air  880 . As another example, the ionization radiation source  462  can supply a radioactive gas into the air tank  878  to form the ionized air  880 . 
     As yet another example, the ionization radiation source  462  can include a sparker in the air tank  878 . In one implementation, the sparker can include a plurality of electrodes separated by a relatively small gap. When activated, the sparker can generate a spark, which can form plasma and, thus, the ionized air  880  in the air tank  878 . 
     Responsive to the ionization radiation source  462  forming the ionized air  880  in the air tank  878 , the air tank  878  can supply the ionized air  880  to the fuel tank  112  via the air line  862  and the air inlet  860 . In  FIG. 8 , the air tank  878  is in communication with the control device  136 . In this example, the control device  136  can transmit a control signal to the air tank  878  to control the supply of the ionized air  880  into the fuel tank  112 . In another example, the air tank  878  can be manually operated to supply the ionized air  880  into the fuel tank  112 . 
     Although the air tank  878  is coupled to the fuel tank  112  via the air line  862  and the air inlet  860 , the air tank  878  can be coupled to the fuel delivery device  120  in an additional or alternative example. In this example, the air tank  878  can supply the ionized air  880  to the fuel delivery device  120  and the fuel delivery device  120  can then supply a mixture of the ionized air  880  and the fuel  114  to the fuel tank  112  via the fuel line  122 . 
     In the examples described above, the refueling systems  100 ,  300 A,  300 B,  400 , and  800  include an ion sensor  134  that can measure the level of ionization of the air medium  132  in the fuel tank  112 . In another example, the refueling systems  100 ,  300 A,  300 B,  400 , and  800  can additionally or alternatively calculate the level of ionization of the air medium  132  in the fuel tank  112 . More generally, the refueling systems  100 ,  300 A,  300 B,  400 , and  800  can determine the level of ionization of the air medium  132  by measuring or calculating the level of ionization of the air medium  132 , and then use the determined level of ionization of air medium  132  as a basis for determining and/or increasing the rate of fuel flow. 
     In one example, the control device  136  can calculate the level of ionization of the air medium  132  in the fuel tank  112  by (a) calculating the types and average concentrations of radioisotopes in ambient air along various flight segments since the last fueling (e.g., one segment may be “cruise 4,000 miles at 37,000 feet over the mid-Pacific ocean on May 3, 2017” or “climb eastward from Boston to 12,000 feet on Jun. 12, 2017”), (b) calculating an amount of air drawn into the fuel tank  112  during each flight segment, (c) computing an amount of each radioisotope remaining in the air medium  132 , given the decay rate of each radioisotope and the elapsed time since each flight segment, (d) calculating a power level of ionizing radiation produced by the total amount of radioisotope (e.g. 0.2 watts of radioactive decay), (e) dividing the power level of ionizing radiation by 33 electron volts, which is the average energy lost by an ionizing particle per ion pair created in a gas, (f) multiplying by two to calculate the rate of ion production in the air medium (each ion pair has one positive and one negative ion), (g) dividing by the volume of the fuel tank  112  to calculate a rate of ion production per unit volume of air medium, and (h) dividing by the mean lifetime λ 1  of an ion in the air medium in the tank, which is a measurable or calculable function of the tank size, the tank geometry, and the amount of fuel in the tank. Within examples, the types and average concentrations of radioisotopes in ambient air can be calculated from the recent history of a given body of air, such as time near a geologic region with abundant granite or shale (prominent sources of radon-222 which has half-life if 4 days) or at high altitude and high latitude (heavily exposed to cosmic radiation which produces a variety of radioisotopes). Also, within examples, the recent history of a given body of air can be estimated from meteorological data, e.g. wind measurements and vertical mixing measurements. 
     In another example in which the blower  354  increases the level of ionization, the control device  136  can calculate the level of ionization of the air medium  132  by (a) calculating the average concentration of radon-222 in ambient air, (b) calculating the amount of air blown into the fuel tank  112  by the blower  354  operating for a given period of time, (c) calculating the amount of radon-222 remaining in the air medium given the 4-day half-life of radon-222 and the elapsed time since the blower  354  was active, (d) computing the power level of ionizing radiation produced by the total amount of radon-222 and its shorter-lived decay products, (e) dividing this power level by 33 electron volts, which is the average energy lost by an ionizing particle per ion pair created in a gas, (f) multiplying by two to calculate the rate of ion production in the air medium (each ion pair has one positive and one negative ion), (g) dividing by a volume of the fuel tank  112  to get rate of ion production per unit volume of air medium  132 , and (h) dividing by the mean lifetime λ 1  of an ion in the air medium  132  in the fuel tank  112 , which is a measurable or calculable function of a size of the fuel tank  112 , a geometry of the fuel tank  112 , and/or an amount of fuel  114  in the fuel tank  112 . The average concentration of radon-222 in ambient air can be measured and/or calculated from a recent history of a given body of air, such as time near a geologic region with abundant granite or shale (prominent sources of radon-222). 
     In yet another example in which the ionization radiation source  462  increases the level of ionization, the control device  136  can calculate the level of ionization of the air medium  132  by (a) calculating the power level of ionizing radiation produced by ionization radiation source  462  (e.g. 5 watts of x-ray output) that enters the air medium  132 , (b) dividing this power level by 33 electron volts, which is the average energy lost by an ionizing particle per ion pair created in a gas, (c) multiplying by two to calculate the rate of ion production in the air medium  132  (each ion pair has one positive and one negative ion), (d) dividing by the volume of the fuel tank  112  to get rate of ion production per unit volume of air medium  132 , and (e) dividing by the mean lifetime λ of an ion in the air medium  132  in the fuel tank  112 , which is a measurable and/or calculable function of the size of the fuel tank  112 , the geometry of the fuel tank  112 , the amount of fuel  114  in the fuel tank  112 , and/or the location and orientation of ionization radiation source  462 . 
     In operation, a refueling operation can begin by coupling the electrical conductors  248 ,  250 ,  252  to bond the vehicle  110  and the fuel source  116 . This equalizes the electrical potential between the vehicle  110  and the fuel source  116  and thereby reduces the risk of an electrical discharge while supplying the fuel  114  from the fuel source  116  to the fuel tank  112  of the vehicle  110 . 
     After bonding the vehicle  110  and the fuel source  116 , the control device  136  can transmit a control signal to the fuel delivery device  120  to cause the fuel line  122  to supply the fuel  114  to the fuel tank  112  of the vehicle  110  at the initial rate of fuel flow. As noted above, supplying the fuel  114  causes an electrostatic charge to accumulate on the surface  130  of the fuel  114  in the fuel tank  112 . Also, as noted above, the control device  136  can determine the initial rate of fuel flow to be a rate of fuel flow, which maintains the accumulated electrostatic charge below the threshold value when the air medium  132  is at the baseline level of ionization. 
     Before and/or while supplying the fuel  114  at the initial rate of fuel flow, the ion sensor  134  determines the level of ionization of the air medium  132  in the fuel tank  112  and transmits the sensor signal to the control device  136 . The control device  136  receives, from the ion sensor  134 , the sensor signal indicating the determined level of ionization of the air medium  132 . Additionally or alternatively, before and/or while supplying the fuel  114  at the initial rate of fuel flow, the control device  136  performs calculations to determine the level of ionization. 
     The control device  136  then determines the increased rate of fuel flow based on a difference between the determined level of ionization and the baseline level of ionization. For example, the control device  136  can determine, based on the determined level of ionization, the increased rate such that the accumulated electrostatic charge remains below the threshold value when supplying the fuel at the increased rate. For instance, the control device  136  can use the lookup table and/or the algorithm stored in memory to determine the increased rate of fuel flow. The control device  136  can then transmit another control signal to the fuel delivery device  120  to cause the fuel line  122  to supply the fuel  114  to the fuel tank  112  at the increased rate of fuel flow to reduce a time for supplying the fuel  114  to the fuel tank  112 . 
     In some examples, the refueling system  300 A,  300 B,  400 ,  800  also increases the level of ionization of the air medium  132  in the fuel tank  112  to increase the rate at which the electrostatic charge accumulated on the surface  130  of the fuel  114  dissipates. For example, before and/or while supplying the fuel  114  from the fuel source  116  to the fuel tank  112 , the control device  136  can cause the blower  354  of the ambient air  358  and/or the ionization radiation source  462  to increase the level of ionization of the air medium  132  in the fuel tank  112 . Responsive to increasing the level of ionization of the air medium  132 , the ion sensor  134  can determine the level of ionization of the air medium  132 , the control device  136  can receive the sensor signal indicating the determined level of ionization, the control device  136  can determine the increased rate of fuel flow based on the determined level of ionization, and the control device  136  can cause the fuel line  122  to supply the fuel  114  to the fuel tank  112  at the increased rate of fuel flow. 
     In one implementation, the refueling system  300 A,  300 B,  400 ,  800  can increase the level of ionization of the air medium  132  and responsively perform the acts described above to increase the rate of fuel flow once during the refueling operation. In another implementation, the refueling system  300 A,  300 B,  400 ,  800  can iteratively repeat (i) increasing the level of ionization using the blower  354  of ambient air  358  and/or the ionization radiation source  462 , (ii) determining the level of ionization (e.g., by measuring the level of ionization using the ion sensor  134  and/or by calculating the level of ionization using the control device  136 ), (iii) determining the increased rate of fuel flow by the control device  136 , and (iv) supplying the fuel  114 , via the fuel line  122 , at the increased rate of fuel flow one or more times during the refueling operation to iteratively increase the increased rate of fuel flow and further reduce the time for supplying the fuel  114  to the fuel tank  112 . 
     In the example refueling operation described above, the refueling system  100 ,  300 A,  300 B,  400 ,  800  first supplies the fuel at an initial rate of fuel flow and then increases the rate of fuel flow based on the determined level of ionization of the air medium. In an additional or alternative example, the refueling system  100 ,  300 A,  300 B,  400 ,  800  determines a rate of fuel flow based on the determined level of ionization before, during, or after initially supplying the fuel  114  to the fuel tank  112 . 
     In this example, the refueling operation can include the ion sensor  134  determining the level of ionization of an air medium  132  in a fuel tank  112  and transmitting the sensor signal indicating the determined level of ionization to the control device  136 . The control device  136  then determines, based on the determined level of ionization, a rate of fuel flow at which to supply the fuel  114  to the fuel tank  112 . For example, the control device  136  can determine, based on the determined level of ionization, the rate of fuel flow that is configured to maintain the accumulated electrostatic charge below the threshold value, which is related to the potential for electrical discharge between the surface  130  of the fuel  114  and a structure of the fuel tank  112  due to the accumulated electrostatic charge. For instance, the control device  136  can use the lookup table and/or the algorithm stored in memory to determine the rate of fuel flow. Responsive to determining the rate of fuel flow, the control device  136  causes the fuel source  116  to supply, via the fuel line  122 , the fuel  114  to the fuel tank  112  of the vehicle  110  at the determined rate of fuel flow. 
     In another example, a refueling operation can include exposing air in the air tank  878  to ionizing radiation to form ionized air  880 . For example, the ionization radiation source  462  can expose the air in the air tank  878  to a radioactive gas to form the ionized air  880 . In another example, the ionization radiation source  462  can expose the air in the air tank  878  to at least one of x-ray radiation, gamma ray radiation, alpha particles, or beta particles to form the ionized air  880 . 
     The air tank  878  can then supply the ionized air  880  into the fuel tank  112  to increase a level of ionization of an air medium  132  in the fuel tank  112 . Responsive to the air tank  878  supplying the ionized air  880  into the fuel tank  112 , the ion sensor  134  determines the level of ionization of the air medium  132  in the fuel tank  112  and/or the control device  136  performs calculations to determine the level of ionization of the air medium  132 . The control device  136  then determines, based on the determined level of ionization, a rate of fuel flow at which to supply the fuel  114  to the fuel tank  112 . For example, the control device  136  can determine, based on the determined level of ionization, the rate of fuel flow that is configured to maintain the accumulated electrostatic charge below the threshold value, which is related to the potential for electrical discharge between the surface of the fuel and a structure of the fuel tank  112  due to the accumulated electrostatic charge. For instance, the control device  136  can use the lookup table and/or the algorithm stored in memory to determine the rate of fuel flow. 
     After determining the rate of fuel flow based on the determined level of ionization, the control device  136  transmits a control signal to the fuel source  116  to cause the fuel line  122  to supply the fuel  114  to the fuel tank  112  at the determined rate of fuel flow. 
     Referring now to  FIG. 9 , a flowchart for a process  900  of supplying fuel to a fuel tank of a vehicle is illustrated according to an example embodiment. As shown in  FIG. 9 , at block  910 , the process  900  includes supplying, via a fuel line, fuel to a fuel tank of a vehicle at an initial rate of fuel flow. The act of supplying the fuel causes an electrostatic charge to accumulate on a surface of the fuel in the fuel tank. At block  912 , the process  900  includes determining a level of ionization of an air medium in the fuel tank. 
     At block  914 , the process  900  includes determining an increased rate of fuel flow based on a difference between the determined level of ionization and a baseline level of ionization. The electrostatic charge accumulated on the surface of the fuel dissipates at an increased rate when the determined level of ionization of the air medium is higher than the baseline level of ionization. At block  916 , the process  900  includes supplying, via the fuel line, the fuel to the fuel tank at the determined increased rate of fuel flow to reduce a time for supplying the fuel to the fuel tank. 
       FIGS. 10-17  depict additional aspects of the process  900  according to further examples. As shown in  FIG. 10 , supplying the fuel at the initial rate at block  910  can include supplying the fuel at a rate that maintains the accumulated electrostatic charge below a threshold value when the air medium is at the baseline level of ionization at block  918 . The threshold value can be related to a potential for electrical discharge between the surface of the fuel and a structure of the fuel tank due to the accumulated electrostatic charge. 
     As shown in  FIG. 11 , determining the increased rate of fuel flow at block  914  can include determining, based on the determined level of ionization, the increased rate such that the accumulated electrostatic charge remains below the threshold value when supplying the fuel at the increased rate at block  920 . 
     As shown in  FIG. 12 , the process  900  can also include increasing the level of ionization of the air medium in the fuel tank to increase the rate at which the electrostatic charge accumulated on the surface of the fuel dissipates at block  922 . 
     As shown in  FIG. 13 , prior to increasing the level of ionization of the air medium at block  922 , the process  900  can include determining that the determined level of ionization of the air medium in the fuel tank is less than a level of ionization of ambient air external to the fuel tank at block  924 . Also, as shown in  FIG. 13 , to increase the level of ionization of the air medium in the fuel tank at block  920 , the process  900  can include supplying the ambient air, which is external to the fuel tank, into the fuel tank at block  926 . 
     As shown in  FIG. 14 , increasing the level of ionization of the air medium in the fuel tank at block  920  can also include venting a portion of the air medium out of the fuel tank while supplying the ambient air into the fuel tank at block  928 . 
     As shown in  FIG. 15 , the process  900  can further include, at block  930 , iteratively repeating (i) the increasing the level of ionization at block  920 , (ii) the determining the level of ionization at block  912 , (iii) the determining the increased rate of fuel flow at block  914 , and (iv) the supplying the fuel at the increased rate of fuel flow at block  916  one or more times to iteratively increase the increased rate of fuel flow and further reduce the time for supplying the fuel to the fuel tank. 
     As shown in  FIG. 16 , determining the increased rate of fuel flow based on the difference between the determined level of ionization and the baseline level of ionization at block  914  can include determining the increased rate of fuel flow based on the difference between the determined level of ionization and a level of ionization of non-ionized air at block  932 . As shown in  FIG. 17 , supplying the fuel to the fuel tank of the vehicle at block  916  can include supplying the fuel to the fuel tank of an aircraft at block  934 . 
     Referring now to  FIG. 18 , a flowchart for a process  1800  of supplying fuel to a fuel tank of a vehicle is illustrated according to an example embodiment. As shown in  FIG. 18 , at block  1810 , the process  1800  includes determining a level of ionization of an air medium in a fuel tank. At block  1812 , the process  1800  includes determining, based on the determined level of ionization, a rate of fuel flow at which to supply the fuel to the fuel tank. At block  1814 , the process  1800  includes supplying, via a fuel line, fuel to a fuel tank of a vehicle at the rate of fuel flow. 
     In the process  1800 , supplying the fuel at block  1814  causes an electrostatic charge to accumulate on a surface of the fuel in the fuel tank. As shown in  FIG. 18 , determining the rate of fuel flow at block  1812  includes determining, based on the determined level of ionization, the rate of fuel flow that is configured to maintain the accumulated electrostatic charge below a threshold value at block  1816 . The threshold value is related to a potential for electrical discharge between the surface of the fuel and a structure of the fuel tank due to the accumulated electrostatic charge. 
       FIGS. 19-20  depict additional aspects of the process  1800  according to further examples. As shown in  FIG. 19 , the process  1800  can also include determining that the determined level of ionization of the air medium in the fuel tank is less than a level of ionization of ambient air external to the fuel tank at block  1818 . Responsive to determining that the determined level of ionization is less than the level of ionization of the ambient air at block  1818 , the process  1800  can include supplying the ambient air into the fuel tank to increase the level of ionization of the air medium in the fuel tank at block  1820 . As shown in  FIG. 20 , supplying the ambient air into the fuel tank at block  1820  can include supplying, using the fuel line, a mixture of the fuel and the ambient air to the fuel tank at block  1822 . 
     Referring now to  FIG. 21 , a flowchart for a process  2100  of supplying fuel to a fuel tank of a vehicle is illustrated according to an example embodiment. As shown in  FIG. 21 , at block  2110 , the process  2100  includes supplying, via a fuel line, fuel to a fuel tank of a vehicle at an initial rate of fuel flow. The act of supplying the fuel causes an electrostatic charge to accumulate on a surface of the fuel in the fuel tank. At block  2112 , the process  2100  includes exposing, using an ionization radiation source, an air medium in the fuel tank to ionizing radiation to increase a level of ionization of the air medium in the fuel tank and thereby increase a rate of dissipation of the electrostatic charge accumulated on the surface of the fuel. 
     Responsive to exposing the air medium in the fuel tank to the ionizing radiation at block  2112 , the process  2100  includes determining the level of ionization of the air medium in the fuel tank at block  2114 . At block  2116 , the process  2100  includes determining an increased rate of fuel flow based on a difference between the determined level of ionization and a baseline level of ionization. The electrostatic charge accumulated on the surface of the fuel dissipates at an increased rate when the determined level of ionization of the air medium is higher than the baseline level of ionization. At block  2118 , the process  2100  includes supplying, via the fuel line, the fuel to the fuel tank at the determined increased rate of fuel flow to reduce a time for supplying the fuel to the fuel tank. 
       FIGS. 22-30  depict additional aspects of the process  2100  according to further examples. As shown in  FIG. 22 , supplying the fuel at the initial rate at block  2110  can include supplying the fuel at a rate that maintains the accumulated electrostatic charge below a threshold value when the air medium is at the baseline level of ionization at block  2120 . The threshold value is related to a potential for electrical discharge between the surface of the fuel and a structure of the fuel tank due to the accumulated electrostatic charge. Also, as shown in  FIG. 22 , determining the increased rate of fuel flow at block  2116  can include determining, based on the determined level of ionization, the increased rate such that the accumulated electrostatic charge remains below the threshold value when supplying the fuel at the increased rate at block  2122 . 
     As shown in  FIG. 23 , exposing the air medium in the fuel tank to the ionizing radiation at block  2112  can include (i) positioning a portable x-ray radiation source on a surface of the vehicle adjacent to the fuel tank at block  2124 , and (ii) while positioning the portable x-ray radiation source on the surface of the vehicle at block  2124 , transmitting x-ray radiation from the portable x-ray source to the air medium in the fuel tank at block  2126 . 
     As shown in  FIG. 24 , positioning the portable x-ray radiation source at block  2124  can include positioning the portable x-ray radiation source on a window portion of the surface of the vehicle at block  2128 . The window portion has a higher x-ray radiation transmissivity than a portion of the surface of the vehicle adjacent to the window portion. As shown in  FIG. 25 , positioning the portable x-ray radiation source at block  2128  can include opening a cover to access the window portion at block  2130 . A combination of the cover and the window portion provides a lower x-ray radiation transmissivity into the fuel tank when the cover is closed than the x-ray transmissivity of the window portion alone when the cover is open. 
     As shown in  FIG. 26 , exposing the fuel tank to the ionizing radiation at block  2112  can include inserting a nozzle of the fuel line into the fuel tank at block  2132 . In the process  2100  of  FIG. 26 , the nozzle includes the ionization radiation source. 
     As shown in  FIG. 27 , prior to inserting the nozzle into the fuel tank at block  2132 , the process  2100  can include using a shield on the nozzle to limit exposure to the ionizing radiation from the ionization radiation source at block  2134 . Responsive to inserting the nozzle into the fuel tank at block  2132 , the process  2100  can include retracting the shield on the nozzle to expose the ionization radiation source at block  2136 . As shown in  FIG. 28 , exposing the air medium to the ionizing radiation at block  2112  can include exposing the air medium to at least one of gamma ray radiation, alpha particles, or beta particles at block  2138 . 
     As shown in  FIG. 29 , determining the increased rate of fuel flow based on the difference between the determined level of ionization and the baseline level of ionization at block  2116  can include determining the increased rate of fuel flow based on the difference between the determined level of ionization and a level of ionization of non-ionized air at block  2140 . As shown in  FIG. 30 , supplying the fuel to the fuel tank of the vehicle at block  2118  can include supplying the fuel to the fuel tank of an aircraft at block  2142 . 
     Referring now to  FIG. 31 , a flowchart for a process  3100  of supplying fuel to a fuel tank of a vehicle is illustrated according to an example embodiment. As shown in  FIG. 31 , at block  3110 , the process  3100  includes exposing air in an air tank to ionizing radiation to form ionized air. The air tank is external to the fuel tank of the vehicle. At block  3112 , the process  3100  includes supplying the ionized air into the fuel tank to increase a level of ionization of an air medium in the fuel tank. 
     Responsive to supplying the ionized air into the fuel tank at block  3112 , the process  3100  includes determining the level of ionization of the air medium in the fuel tank at block  3114 . At block  3116 , the process  3100  includes determining, based on the determined level of ionization, a rate of fuel flow at which to supply the fuel to the fuel tank. At block  3118 , the process  3100  includes supplying, via a fuel line, the fuel to the fuel tank at the determined rate of fuel flow. 
     Supplying the fuel at block  3118  causes an electrostatic charge to accumulate on a surface of the fuel in the fuel tank. As shown in  FIG. 31 , determining the rate of fuel flow at  3116  includes determining, based on the determined level of ionization, the rate of fuel flow that is configured to maintain the accumulated electrostatic charge below a threshold value at block  3120 . The threshold value is related to a potential for electrical discharge between the surface of the fuel and a structure of the fuel tank due to the accumulated electrostatic charge. 
       FIGS. 32-33  depict additional aspects of the process  3100  according to further examples. As shown in  FIG. 32 , exposing the air in the air tank to ionizing radiation at block  3110  can include exposing the air to a radioactive gas at block  3122 . As shown in  FIG. 33 , exposing the air in the air tank to ionizing radiation at block  3110  can include exposing the air in the air tank to at least one of x-ray radiation, gamma ray radiation, alpha particles, or beta particles at block  3124 . 
     Any of the blocks shown in  FIGS. 9-33  may represent a module, a segment, or a portion of program code, which includes one or more instructions executable by a processor for implementing specific logical functions or steps in the process. The program code may be stored on any type of computer readable medium or data storage, for example, such as a storage device including a disk or hard drive. Further, the program code can be encoded on a computer-readable storage media in a machine-readable format, or on other non-transitory media or articles of manufacture. The computer readable medium may include non-transitory computer readable medium or memory, for example, such as computer-readable media that stores data for short periods of time like register memory, processor cache and Random Access Memory (RAM). The computer readable medium may also include non-transitory media, such as secondary or persistent long term storage, like read only memory (ROM), optical or magnetic disks, compact-disc read only memory (CD-ROM), for example. The computer readable media may also be any other volatile or non-volatile storage systems. The computer readable medium may be considered a tangible computer readable storage medium, for example. 
     In some instances, components of the devices and/or systems described herein may be configured to perform the functions such that the components are actually configured and structured (with hardware and/or software) to enable such performance. Example configurations then include one or more processors executing instructions to cause the system to perform the functions. Similarly, components of the devices and/or systems may be configured so as to be arranged or adapted to, capable of, or suited for performing the functions, such as when operated in a specific manner. 
     The description of the different advantageous arrangements has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different advantageous embodiments may describe different advantages as compared to other advantageous embodiments. The embodiment or embodiments selected are chosen and described in order to explain the principles of the embodiments, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.