Patent Publication Number: US-8991446-B2

Title: Pump assisted refilling system for LPG fuel tanks

Description:
TECHNICAL FIELD 
     The present invention relates to liquefied petroleum gas (LPG) fuel systems, and more particularly to a pump assisted refilling system for LPG fuel tanks. 
     BACKGROUND OF THE INVENTION 
     Motor vehicle designers continually strive to create vehicles which have lower emissions of noxious and greenhouse gases than vehicles currently in use. One means of reducing vehicular emissions is to utilize alternative fuels. Commonly used fuels such as gasoline and diesel fuel, are mixtures of complex hydrocarbons which may also contain unwanted chemicals, such as sulfur. One form of alternative fuel available is LPG. LPG is primarily composed of propane, a three carbon hydrocarbon, and butane, a four carbon hydrocarbon. These hydrocarbons have a lower carbon to hydrogen ratio than gasoline or diesel fuel. Because the carbon to hydrogen ratio is lower, less carbon dioxide is produced in the burning of LPG than in the burning of gasoline or diesel fuel. The longer chain hydrocarbons of gasoline and diesel fuel are much more likely to produce unwanted particulate emissions in the exhaust gas. Relative to LPG, gasoline and diesel fuel do have two advantages, namely: (i) they are both liquids at STP (standard temperature and pressure), whereas under typical ambient operating conditions LPG must be stored in a pressure vessel to be in a liquefied state; and: (ii) gasoline and diesel fuel produce more energy per unit volume of fuel as compared to LPG, even when LPG is in a liquid state. This means that in dealing with LPG fueled vehicles, one must manage the difficulties encountered with temperatures and pressures far from the ambient range. 
     A key physical factor in the management of LPG fuel conditions is the liquid/gas equilibrium. The ambient conditions will dictate the mixture of LPG vapor and LPG liquid found in the fueling system. Additional measures must be taken to ensure the correct balance of liquid and vapor for the operation of the fuel consumer, as for example the internal combustion engine of a motor vehicle. For example, the ignition system of the engine can be designed to use either a gas phase LPG or a liquid phase LPG. Components may be added to the fueling system to either condense vapor into the liquid state or to ensure that all the liquid state has been evaporated and heated into a gaseous state, depending on which phase of the fuel is required. 
       FIG. 1  schematically depicts an exemplar prior art LPG fuel system  10  providing fuel to a consumer, for example the engine of a motor vehicle, the system being shown undergoing refilling of the fuel tank via a conventional filler neck. 
     A pressurized fuel tank (or vessel)  12  holds LPG fuel  14  in a liquid phase  14 ′ and a vapor phase  14 ″. The fuel tank  12  is equipped with a pressure relief valve  15 , and may be equipped with a temperature sensor  16  and a pressure sensor  18 . The LPG fuel  14  within the fuel tank  12  may be subject to external heat  20  as for example coming from the motor vehicle exhaust system, outside of the fuel tank  12 , as well as heat  22  from components within the fuel tank  12 , as for example, produced by a fuel pump  24 . All of these sources of heat increase the temperature inside the fuel tank  12 , thereby increasing the vapor pressure inside the fuel tank. 
     By way of example, contained within the fuel tank  12  are components that make up a fuel delivery system  26 . These components may be simply a filter  28  at a lead end of the fuel line  30 , or may be a fuel pumping system  32  connected to the fuel line  30 , including, merely by way of example, the filter  28 , the fuel pump  24  (typically engaged to boost fuel feed pressure when the pressure inside the fuel tank  12  is below a predetermined level), a check valve  34 , a filter  36 , and a fuel pressure regulator  38  so that a desired fuel pressure differential across the fuel pump is maintained. External to the fuel tank  12 , the fuel line  30  connects with various safety and fuel conditioning components well known in the art (not shown) which are suitable to the particular fuel delivery application that pertains to the fuel consumer  40 . 
     An LPG refilling source or bowser  42  is schematically shown connected by means of a bowser nozzle  44 , to a pressure sealed release refilling fitting  46  of the fuel tank filler neck  48 . The fuel flow  50  is from the bowser  42  through the refilling fitting  46  and into the interior of the fuel tank  12 , wherein an internal fill level valve  52 , as for example in the form of a float valve, provides automatic shut-off of the fuel flow when the liquid phase  14 ′ reaches a predetermined level in the fuel tank  12 . 
     For rapid refilling to occur, the fuel pressure of the bowser nozzle  44  should be well in excess of the fuel vapor pressure within the fuel tank  12 . As the fuel vapor pressure within the tank approaches the bowser nozzle fuel pressure, the rate of refilling decreases and, if the fuel vapor pressure becomes high enough relative to the bowser nozzle pressure, refilling may become impossible. Impossible to refill, or no-fill situations, in which fuel cannot flow from the bowser nozzle into the fuel tank because of excessive backpressure caused by the fuel vapor pressure within the tank, are highly undesirable. If such a no-fill situation is encountered, then a technique used in the prior art to overcome this problem is to cool the contents of the fuel tank down in order to reduce the vapor pressure inside the fuel tank. Methods of the prior art to do this include pouring cold water over the fuel tank or placing ice or wet rags on the fuel tank. Such methods can be difficult and time-consuming to implement, and may be unacceptable, impractical or unavailable, depending on the circumstances. 
     Concern over ability to refill the fuel tank is exacerbated for fuels having multiple chemical components of varying volatility. LPG and other fuels which are stored at vapor pressure typically have multiple chemical components, each having differing vapor pressures. Examples of high vapor pressure components which may be present in LPG fuels include: ethane, nitrogen and carbon dioxide; and manufacture or servicing may introduce air (or other contaminant gases such as nitrogen used for leak detection) into the tank, which may not have been completely purged out. The vapor pressure inside the fuel tank is the vapor pressure of the fuel mixture, however the individual chemical components may have a vapor pressure which is higher or lower than the vapor pressure of the mixture. If the vapor pressure of a chemical component is higher than the mixture, then the component will tend to remain in its gaseous phase and the concentration (mole fraction) of that chemical component will be higher in the vapor phase relative to the liquid phase. Conversely, if the vapor pressure of a chemical component is lower than the mixture, then the concentration (mole fraction) of that chemical component will be lower in the vapor phase relative to the liquid phase. The chemical composition of the vapor phase inside the fuel tank will typically be different in relation to the chemical composition of the liquid phase because the vapor phase will contain a higher concentration (mole fraction) of high vapor pressure chemical components relative to the liquid phase. As a result, the rate at which high vapor pressure chemical components can be withdrawn from the fuel tank is less when liquid fuel is extracted as compared to when fuel vapor is extracted. Accordingly, as a fuel tank is emptied, the final vapor pressure will be related to the ratio of the chemical components, and that will depend upon the ratio of the liquid fuel to fuel vapor extracted. If high volatility (high vapor pressure causing) chemical components have been favored to remain in their gaseous phase and therefore ‘compress’ rather than ‘condense’ as the pressure inside the fuel tank increases, ability to refill the fuel tank is adversely affected. If the fuel tank pressure approaches the bowser nozzle pressure before the fuel tank can be filled up, then it will not be possible to fully refill (refuel) the fuel tank. Thus, if high vapor pressure components are allowed to accumulate inside a fuel tank, then the rate of refilling will be slow, or refilling may even be prevented (a no-fill situation). This problem is exacerbated for the next refill if during the present refill, a relatively larger quantity of high vapor pressure chemical components are added to the fuel tank than will be removed during operation of the fuel consumer. Therefore, it is desirable to keep the concentration of high vapor pressure chemical components at low levels in the fuel supplied; however, this may impose increased fuel costs, and the desired low levels from the perspective of fuel tank refilling, may not always be met in practice. 
     In the case of fuels which are stored at, or near their vapor pressure, the pressure in both the bowser supply tank and the fuel tank being refilled (refueled) will be close to the vapor pressure of the fuel, and both tanks will contain a mixture of liquid fuel and fuel vapor. 
     Variables which can affect the likelihood of a no-fill situation include: 1) the pressure differential across the bowser; 2) the height of the liquid fuel level in the bowser supply tank, relative to that of the fuel tank being refilled (for example, the bowser supply tank may be located underground, whereas the fuel tank being refilled is typically located above ground); 3) the chemical composition of the fuel in the bowser supply tank (fuel vapor pressure varies with chemical composition and the feed pressure at the bowser nozzle, may be reduced if the bowser supply tank contains low vapor pressure fuel); 4) the temperature of the fuel in the bowser supply tank (a lower fuel temperature will reduce the vapor pressure in the bowser tank and hence the feed pressure at the bowser nozzle; 5) the chemical composition of fuel in the fuel tank being refilled (fuel vapor pressure varies with chemical composition and the backpressure at the bowser nozzle to fuel tank interface will increase if the fuel tank being refueled contains high vapor pressure fuel); and, 6) the temperature of fuel in the fuel tank being refilled (a high fuel temperature will increase the backpressure at the bowser nozzle to fuel tank interface). 
     Factors which can affect this sixth variable (the temperature of the fuel in the fuel tank being refilled) include: 1) ambient temperature (higher ambient temperature tends toward higher fuel temperature), 2) proximity of the exhaust system to the fuel tank (reduced separation typically results in increased heat transfer to the fuel tank), 3) engine load (a higher engine load can result in increased heat transfer from the exhaust system to the fuel tank, 4) airflow over the fuel tank (increased airflow results in better convective cooling), and 5) engine run time (a longer time may translate to more heat transfer to the fuel tank. 
       FIG. 2  is a graph  60  of probability  62  (as an increasing percent) versus pressure  64  (in bar), which exemplifies how refilling (or refueling) of an LPG fuel tank may be affected by the vapor pressure within the fuel tank. Distribution curve  66  represents a hypothetical probability distribution of bowser nozzle pressure of a bowser (or fuel supply station), and distribution curve  68  represents a hypothetical probability distribution of the fuel vapor pressure within an LPG fuel tank under prior art operational conditions, both immediately prior to commencement of refilling, and wherein point  70  represents a hypothetical maximum safe tank pressure. Both distribution curves  66 ,  68  are affected by factors such as ambient temperature and fuel chemical composition, which can vary from fill-to-fill and from market-to-market. By way of example only, to facilitate fuel flow from the bowser nozzle into the fuel tank, the bowser nozzle pressure should be greater than preferably about 5 bar or more over that of the fuel vapor pressure inside the fuel tank in order to facilitate rapid refilling of the fuel tank in a filling station environment. 
     Accordingly, what remains needed in the art of LPG fuel systems, is to somehow selectively modify the pressure differential between the bowser feed pressure of the fuel entering the fuel storage tank and the vapor pressure within the fuel tank so that rapid refilling is always assured. 
     SUMMARY OF THE INVENTION 
     The present invention is a pump assisted refilling system for LPG and other fuels wherein the fuel storage pressure is at, or close to, the vapor pressure of the fuel. The present invention provides selective modification of the pressure differential as between the bowser feed pressure of the fuel entering the fuel storage tank and the vapor pressure within the fuel tank so as to assure rapid refilling will always occur. 
     The present invention consists of a refilling fuel pump disposed, preferably, in the fuel tank filler neck, wherein the refilling fuel pump is activated (that is, it is switched on) whenever: a) the sensed pressure differential as between the bowser feed nozzle pressure and the fuel vapor pressure in the fuel tank interior is at or below a predetermined differential pressure, or 2) the fuel tank vapor pressure is at or above a predetermined fuel tank vapor pressure, collectively referred to herein as a predetermined fuel pressure assistance condition, wherein the activation of the refilling fuel pump assists delivery of the fuel from the bowser to the interior of the fuel tank. For differential pressures above the predetermined differential pressure, or for fuel tank vapor pressure below the predetermined fuel tank vapor pressure, collectively referred to herein as a predetermined fuel pressure non-assistance condition, the fuel delivery rate is deemed to be acceptably fast, so the refilling fuel pump is not activated (that is, it is switched off). 
     The implementation of the refilling fuel pump at the fuel tank filler neck can have differing configurations. 
     In one exemplar configuration, the operational states of a three-way solenoid valve are responsive to a controller having fuel pressure data input and appropriate programming, wherein in a first state of the valve, fuel delivered from the bowser is piped into the refilling fitting and then through a main conduit directly to the interior of the fuel tank; and in a second state of the valve, fuel delivered from the bowser is diverted, after the refilling fitting, to an auxiliary conduit interfaced with the refilling fuel pump, which is activated to thereby pump fuel from the refilling fitting into the fuel tank interior. 
     In another exemplar configuration, the operational states of a shuttle or check valve are responsive to directly sensed fuel pressure, wherein in a first state of the valve, fuel delivered from the bowser is piped into the refilling fitting and then through a main conduit directly to the interior of the fuel tank; and in a second state of the valve, fuel delivered from the bowser is diverted, after the refilling fitting, to an auxiliary conduit interfaced with the refilling fuel pump, which is activated to thereby pump fuel from the refilling fitting into the fuel tank interior. 
     In yet another exemplar configuration, fuel delivered from the bowser is piped into the refilling fitting and then through a conduit directly to the interior of the fuel tank, wherein the conduit is interfaced with the refilling fuel pump. In response to sensed fuel pressure, the refilling fuel pump is selectively activated to thereby pump fuel from the refilling fitting into the fuel tank interior. 
     Once the level of liquid fuel inside the tank reaches a predetermined level, the fill level valve will terminate the filling process in the normal, conventional manner. 
     Further according the methodology of the present invention, the liquid fuel entering the LPG fuel storage tank from the bowser will provide fuel tank cooling as a result of the fuel expanding as it passes into the LPG fuel storage tank, whereby in the event that the refilling fuel pump has been activated because the sensed pressure is the predetermined fuel pressure assistance condition, this cooling will encourage its deactivation once the sensed pressure becomes the predetermined fuel pressure non-assistance condition. 
     Accordingly, it is an object of the present invention to provide a pump assisted refilling system for LPG fuel tanks which provides selective modification of the pressure differential as between the bowser feed pressure of the fuel entering the fuel storage tank and the vapor pressure within the fuel tank so as to assure rapid refilling will always occur. 
     This and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an exemplar prior art LPG fuel system, shown in refilling mode, and showing in particular a conventional fuel tank filler neck connected to the bowser nozzle of a bowser. 
         FIG. 2  depicts graphically the probability distribution of exemplar bowser LPG fuel delivery pressure and of LPG fuel vapor pressure inside the fuel tank. 
         FIG. 3  is a schematic diagram of an LPG fuel system similar to that of  FIG. 1 , but now showing in particular a fuel tank filler neck equipped with a pump assisted refilling system according to the present invention. 
         FIG. 4  is a detailed schematic diagram of a first exemplar pump assisted refilling system according to the present invention. 
         FIG. 5  is a detailed schematic diagram of a second exemplar pump assisted refilling system according to the present invention. 
         FIG. 6  is a detailed schematic diagram of a third exemplar pump assisted refilling system according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the Drawings,  FIGS. 3 through 6  depict aspects for implementing a pump assisted fuel tank refilling system  100  according to the present invention. 
     The pump assisted fuel tank refueling system  100  can be implemented with any fuel tank having fuel contents generally in both the liquid and vapor phase, wherein the fuel storage pressure is at, or close to, the vapor pressure of the fuel. Fuels which may be stored this way include, but are not limited to: propane, butane, liquefied petroleum gas (LPG), and dimethyl ether. Application of the present invention is intended to include all such fuel systems which store fuel at, or close to, the vapor pressure of the fuel, and the exemplar LPG fuel systems presented herein are merely for purposes of illustration. Thus, any reference herein to ‘LPG’ should be widely taken to mean any fuel stored at or near its vapor pressure&#39; and not as restricting the scope of the present invention to LPG fuel systems. Similarly, reference herein to motor vehicle fuel systems should not be taken as restricting the scope of the invention thereto, as the present invention applies to any gaseous phase fuel system application utilizing a fuel consumer which may or may not be an internal combustion engine. 
     By way merely of exemplification,  FIG. 3  schematically depicts a fuel system as in  FIG. 1  with like functioning parts having like reference numerals, now including the pump assisted fuel tank refilling system  100  of the present invention, which is disposed, preferably, at the fuel tank filler neck  48 ′. An LPG refilling source or bowser  42  is schematically shown connected by means of a bowser nozzle  44 , to a pressure sealed release refilling fitting  46  of the fuel tank filler neck  48 ′. The fuel flow  50  is from the bowser  42  to the refilling fitting  46 , through the pump assisted fuel tank refilling system  100  and then into the interior of the fuel tank  12 , wherein an internal fill level valve  52 , as for example in the form of a float valve, provides automatic shut-off of the fuel flow when the liquid phase  14 ′ reaches a predetermined level in the fuel tank  12 . 
     The pump assisted fuel tank refilling system  100  includes a refilling fuel pump  102  (see  FIGS. 4 through 6 ), wherein the refilling fuel pump is activated (that is, it is switched on) whenever: a) the sensed pressure differential as between the bowser feed nozzle pressure and the fuel vapor pressure in the interior of the fuel tank  12  is at or below a predetermined differential pressure, or 2) the fuel vapor pressure in the interior of the fuel tank  12  is at or above a predetermined fuel tank vapor pressure, collectively referred to herein as a predetermined fuel pressure assistance condition, wherein the activation of the refilling fuel pump assists delivery of the fuel from the bowser  42  (at the refilling fitting  46 ) to the interior of the fuel tank  12 . For differential pressures above the predetermined differential pressure, or for fuel tank vapor pressure below the predetermined fuel tank vapor pressure, collectively referred to herein as being a predetermined fuel pressure non-assistance condition, the fuel delivery rate is deemed to be acceptably fast, so the refilling fuel pump  102  is not activated (that is, it is switched off). Once the level of liquid fuel  14 ′ inside the fuel  12  tank reaches a predetermined level, the fill level valve  52 , will terminate the filling process in the normal, conventional manner. 
     By way merely of exemplification and not limitation the following pressure threshold examples are provided. Where a predetermined differential pressure is used, then the predetermined differential pressure may be about 5 bar, wherein for differential pressures in which the bowser fuel delivery pressure at the refilling fitting is less than the about 5 bar above the fuel vapor pressure within the fuel tank, then the predetermined fuel pressure assistance condition is present and the refilling fuel pump is activated; otherwise, for bowser fuel delivery pressure at the refilling fitting greater than the about 5 bar above the fuel vapor pressure within the fuel tank, then the predetermined fuel pressure non-assistance condition is present (that is, the predetermined fuel pressure assistance condition is absent) and the refilling fuel pump is not activated. Where a predetermined fuel vapor pressure within the fuel tank is used, then predetermined fuel vapor pressure may be set at about 8 bar, as per the exemplar bowser pressure probabilities exemplified at  FIG. 2 , wherein for fuel vapor pressures within the fuel tank above about 8 bar, then the predetermined fuel pressure assistance condition is present and the refilling fuel pump is activated; otherwise, for vapor pressures within the fuel tank below the about 8 bar, then the predetermined fuel pressure non-assistance condition is present (that is, the predetermined fuel pressure assistance condition is absent) and the refilling fuel pump is not activated. The selected pressure threshold value for determining the presence and absence of the predetermined fuel pressure assistance condition would be determined by modeling or empirical testing as per the particular application. 
     According the methodology of the present invention, the fuel flow  50  of the liquid fuel entering the LPG fuel storage tank  12  from the bowser  42  will provide fuel tank cooling as a result of the fuel expanding as it passes into the LPG fuel storage tank, whereby in the event that the refilling fuel pump  102  has been activated because the sensed pressure is the predetermined fuel pressure assistance condition, this cooling will encourage deactivation of the refilling fuel pump once the sensed pressure becomes the predetermined fuel pressure non-assistance condition. 
     It will occur to those skilled in the art that the pump assisted fuel tank refilling system  100  can be implemented in a number of ways; accordingly,  FIGS. 4 through 6  depict exemplar implementations for instructive purposes to those skilled in the art. 
       FIG. 4  depicts a first implementation  100 ′ of the pump assisted fuel tank refilling system  100 , which includes a three-way solenoid valve  104 . The operational states of a three-way solenoid valve  104  are responsive to a controller  106  having a fuel pressure data input (from pressure sensor  108  sensing fuel vapor pressure within the fuel tank, and optionally from pressure sensor  108 ′ sensing fuel vapor pressure at the refilling fitting  46 , via data line(s)  110 . In a first state of the three-way solenoid valve  104  responsive to the sensed pressure and signal sent via data line  112  from the controller  106  to the solenoid  104 ′ of the three-way solenoid valve, fuel flow  50  delivered from the bowser  42  (see  FIG. 3 ) enters the refilling fitting  46 , passes into an inlet  114  and exits at a first outlet  116 , thereupon being piped through a main conduit  118  and past the fill level valve  52  into the interior of the fuel tank  12 . In a second state of the three-way solenoid valve  104  responsive to the sensed fuel pressure and signal sent via the data line  112  from the controller  106  to the solenoid  104 ′ of the three-way solenoid valve, fuel flow  50  delivered from the bowser  42  (see  FIG. 3 ), enters the refilling fitting  46 , passes into the inlet  110  and exits at a second outlet  120 , thereupon being piped through an auxiliary conduit  122 , through the refilling fuel pump  102 , past the fill level valve  52  into the interior of the fuel tank  12 , wherein the refilling fuel pump is activated via data line  124  and the refilling fuel pump activation circuit  126  so as to pump fuel from the bowser into the fuel tank interior. The first state of the three-way solenoid valve  104  (with deactivation of the refilling fuel pump) is provided by the controller  106  whenever the sensed pressure is the predetermined fuel pressure non-assistance condition; the second state of the three-way solenoid valve with activation of the refilling fuel pump  102  is provided by the controller whenever the sensed pressure is the predetermined fuel pressure assistance condition. 
       FIG. 5  depicts a second implementation  100 ″ of the pump assisted fuel tank refilling system  100 , which includes a shuttle or check valve  130 . The operational states of the valve  130  are responsive to directly sensed fuel pressure, wherein in one state of the valve  130 , fuel flow  50  delivered from the bowser to the refilling fitting  46 , piped through a main conduit  132  and past the fill level valve  52  into the interior of the fuel tank  12 . In a second of the valve  130  responsive to the directly sensed fuel pressure, fuel flow  50  delivered from the bowser  42  (see  FIG. 3 ) to the refilling fitting  46 , then piped through an auxiliary conduit  134 , through the refilling fuel pump  102 , and then past the fill level valve  52  into the interior of the fuel tank  12 , wherein the refilling fuel pump is activated so as to pump fuel from the bowser into the fuel tank interior, wherein fuel pressure is sensed  136  and, via data line  138 , provides a signal to the refilling fuel pump activation circuit  140  to activate the refilling fuel pump  102 . The first state of the valve  130  (with deactivation of the refilling fuel pump) is provided automatically whenever the sensed pressure is the predetermined fuel pressure non-assistance condition; the second state of the valve with activation of the refilling fuel pump  102  is provided automatically whenever the sensed pressure is the predetermined fuel pressure assistance condition. 
       FIG. 6  depicts a third implementation  100 ′″ of the pump assisted fuel tank refilling system  100 , wherein the refilling fuel pump  102  is disposed in a conduit  150 , free of valving, wherein the fuel flow  50  from the bowser  42  (see  FIG. 3 ) goes into the refilling fitting  46 , through the refilling fuel pump, past the fill level valve  52  into the interior of the fuel tank  12 . Fuel pressure data input (from pressure sensor  152  sensing fuel vapor pressure within the fuel tank, and optionally from pressure sensor  152 ′ sensing fuel vapor pressure at the bowser nozzle  44  (See  FIG. 3 ), via data line(s)  154 , deliver a signal to the refilling fuel pump activation circuit  156  to activate the refilling fuel pump  102 . The refilling fuel pump  102  is deactivated whenever the sensed pressure is the predetermined fuel pressure non-assistance condition; the refilling fuel pump  102  is activated whenever the sensed pressure is the predetermined fuel pressure assistance condition. 
     To those skilled in the art to which this invention appertains, the above described preferred embodiment may be subject to change or modification. Such change or modification can be carried out without departing from the scope of the invention, which is intended to be limited only by the scope of the appended claims.