Patent Publication Number: US-2012042848-A1

Title: Fuel stabalizer metering device and method

Description:
BACKGROUND 
     During prolonged periods of time in which an engine is not used, fuel remaining within the engine may become stale. Such stale fuel may cause corrosion of internal carburetor parts such as jets, seats, needles, o-rings and the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an internal combustion engine system according to an example embodiment. 
         FIG. 2  is a schematic illustration of another embodiment of the internal combustion engine system of  FIG. 1 . 
         FIG. 3  is a schematic illustration of another embodiment of the internal combustion engine system of  FIG. 1 . 
         FIG. 4  is a schematic illustration of another embodiment of the internal combustion engine system of  FIG. 1 . 
         FIG. 5  is a first fragmentary side elevational view of another embodiment of the internal combustion engine system of  FIG. 1 . 
         FIG. 6  is a second fragmentary side elevational view of the internal combustion engine system of  FIG. 5 . 
         FIG. 7  is a sectional view of the internal combustion engine system of  FIG. 5  illustrating a metering device in a loading state. 
         FIG. 8  is an enlarged sectional view of the internal combustion engine of  FIG. 7 . 
         FIG. 9  is a sectional view of the internal combustion engine system of  FIG. 5  illustrating the metering device in an unloading state. 
         FIG. 10  is an enlarged sectional view of the internal combustion engine of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS 
       FIG. 1  schematically illustrates an internal combustion engine system  10  according to an example embodiment. System  10  uses fuel stabilizer to reduce corrosion or other damage to a carburetor resulting from stale fuel within the engine. As will be described hereafter, system  10  meters fuel stabilizer to the carburetor of the engine during or after shutdown of the engine. Because the fuel stabilizer is metered during or after shutdown of the engine, fuel within the carburetor is reliably treated without inconveniencing the user and wasteful consumption of fuel stabilizer is reduced. 
     As shown by  FIG. 1 , internal combustion engine system  10  includes engine  20 , fuel stabilizer reservoir (FSR)  24  and fuel stabilizer metering device (FSMD)  28 . Engine  20  (schematically represented) comprises an internal combustion engine having a carburetor  30  with a carburetor bowl  32  (both of which are schematically represented). Engine  20  supplies power or torque to a powered appliance, examples of which include, but are not limited to, riding and walk behind lawnmowers, snow blowers, tillers, pumps, generators and power washers, or other engine powered equipment. Carburetor  30  is a component of engine  20  and provides the required air-fuel mixture to a combustion chamber of the engine based upon engine operating speed and load. Bowl  32  contains or stores fuel prior to the fuel being mixed with air by the carburetor  30 . 
     Fuel stabilizer reservoir  24  comprises a tank, container, chamber or other volume configured to contain and store a fuel stabilizer. Fuel stabilizer reservoir  24  is connected to fuel stabilizer metering device  28  so as to deliver fuel stabilizer to fuel stabilizer metering device  28 . Reservoir  24  may have various sizes, shapes and configurations. Reservoir  24  may comprise a reservoir that is refillable while connected to metering device  28  or may be a type that requires disconnection from metering device  28  for refilling or replacement. 
     Fuel stabilizer metering device  28  comprises a device configured to meter or supply a predetermined amount or volume of fuel stabilizer to bowl  32  of carburetor  30  after initiation of engine shutdown. In one embodiment, metering device  28  does not deliver any stabilizer to engine  20  or bowl  32  of carburetor  30  while engine  20  is running (prior to any initiation of shutdown of engine  20 ). In another embodiment, fuel stabilizer metering device  28  meters fuel stabilizer to bowl  32  of carburetor  30  only after engine shutdown has been completed. In some embodiments, metering device  28  may meter a predefined quantity of fuel stabilizer to bowl  32  of carburetor  30  while the engine is being shut down (but not prior to initiation of engine shutdown) and after shutdown has been completed. 
     Because of fuel stabilizer metering device  28  meters a predefined quantity or volume of fuel stabilizer, a user of the appliance having engine  20  is not inconvenienced by having to measure the appropriate amount of fuel stabilizer and by having to manually supply fuel stabilizer to anything other than reservoir  24 . Because fuel stabilizer metering device  28  meters a predefined quantity or volume of fuel stabilizer only at least after initiation of engine shut down or after completion of engine shutdown, most, if not all, of the fuel stabilizer added to bowl  32  of carburetor  30  remains within bowl  32  to stabilize fuel and is not consumed immediately prior to shutdown of engine  20 . As a result, wasteful consumption of fuel stabilizer is reduced. 
     According to one embodiment, fuel stabilizer metering device  28  delivers a metered amount of fuel stabilizer to bowl  32  in response to user input (either by a manual actuation of a mechanical input such as a lever, squeezing or compression of a compressible fluid fillable bulb filled with the fuel stabilizer or by actuation of an electrical switch or other electrical device causing release or metering of fuel stabilizer). In such embodiments, metering device  28  is configured to inhibit such manual input until at least after initiation of engine shutdown or is configured to delay the delivery of fuel stabilizer to bowl  32  from a time that the manual input is provided to at least after initiation of engine shutdown. 
     In yet other embodiments, fuel stabilizer metering device  28  may alternatively be configured to automatically deliver a metered amount of fuel stabilizer to bowl  32  of carburetor  30  until at least after initiation of engine shutdown. For purposes of this disclosure, such “automatic” delivery of fuel stabilizer means that the fuel stabilizer is delivered to carburetor  30  without a person (user) having to take any action to initiate the delivery of fuel stabilizer to carburetor  30 , other than making sure that the fuel stabilizer reservoir  24  contains the fuel stabilizer and other than initiating engine shutdown. In one embodiment, parameters associated with the shutting down or completion of shutdown of engine  20  may be sensed by one or more sensors, wherein a controller generates control signals causing an actuator to deliver the metered fuel stabilizer to bowl  32  of carburetor  30 . In yet another embodiment, the parameters associated with shutting down or completion of shutdown of engine  20  may themselves actuate or directly cause an actuator to deliver the metered amount of fuel stabilizer to bowl  32  of carburetor  30 . Examples of such engine shutdown parameters may include, but are not limited to, vacuum or pressure, temperature, fuel flow, electrical current flow and the like. 
       FIG. 2  schematically illustrates internal combustion engine system  110 , a particular embodiment of system  10 . Those elements or components of system  110  which are the same as elements or components of system  10  are numbered similarly. System  110  includes fuel stabilizer metering device  128 , a particular embodiment of fuel stabilizer metering device  28 . 
     As shown by  FIG. 2 , fuel stabilizer metering device  128  includes a volume  140  (schematically illustrated). Volume  140  comprises a cavity, container, channel, groove, bore, reservoir, chamber or other volume configured to receive and contain a predefined stationary (non-flowing) volume or amount fuel stabilizer from reservoir  24 . As indicated by arrows  141 , fuel stabilizer metering device  128  moves volume  140  between a loading position  143  and an unloading position  145 . In the loading position  143 , volume  140  is located so as to be connected or connectable to fuel stabilizer reservoir  24 . In the unloading position  145  (shown in broken lines), volume  140  is located so as to be connected or connectable to bowl  32  of carburetor  30  to allow the release, delivery or discharge of the fuel stabilizer within volume  140  to bowl  32  of engine  20 . In one embodiment, volume  140  moves to the unloading position  145  during (after initiation of) engine shutdown. In other words, volume  140  does not begin moving towards the unloading position until at least after initiation of engine shutdown. In another embodiment, volume  140  moves to the unloading position  145  only after completion of engine shutdown. In such embodiments, volume  140  may be filled (either fully or least partially) during operation of engine  20  or after engine shutdown has been initiated. 
       FIG. 3  schematically illustrates internal combustion engine system  210 , a particular embodiment of system  110 . Internal combustion engine system  210  includes engine  220 , fuel stabilizer reservoir  24  and fuel stabilizer metering device  228 . Engine  220  is similar to engine  20  in that engine  220  includes a carburetor  30  having a bowl  32 . Engine  220  additionally includes or is associated with a sensor  234 , a user input  236  and a controller  238 . 
     Sensor  234  comprises one or more sensors configured to sense or detect an engine shutdown parameter  239  and to transmit signals, such electrical signals, to controller  238  indicating the status of the sensed shutdown parameter. Shutdown parameter  239  comprises a parameter or characteristic of engine  220  that changes in response to initiation of engine shutdown or completion of engine shutdown. Examples of an engine shutdown parameter  239  include, but are not limited to, vacuum or pressure, temperature, fuel flow, electrical current flow and the like. For example, in one embodiment, sensor  234  senses a drop in negative pressure or vacuum in the intake manifold of engine  220 . In response to detecting a drop in the vacuum in the intake manifold of engine  220 , indicating that engine  220  is in the process of being shut down or has completed shut down, sensor  234  transmits a signal to controller  238 . In other embodiments, other shutdown parameters  239  may be detected or sensed by sensor  234 . 
     User input  236  comprises a mechanism or device associated with or provided as part of engine  220  which is configured to receive input from a person. In one embodiment, user input  236  is configured to receive such input from a person initiating or causing shutdown of engine  220 . In yet another embodiment, input  236  is configured to receive such input for a person indicating that engine  220  has been shut down or is in process of being shut down or requesting metering of fuel stabilizer to carburetor  30  by metering device  228 . User input  236  is operatively or communicatively connected or coupled to controller  238 . 
     For purposes of this disclosure, the term “coupled” shall mean the joining of two members directly or indirectly to one another. Such joining may be stationary in nature or movable in nature. Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate member being attached to one another. Such joining may be permanent in nature or alternatively may be removable or releasable in nature. The term “operably coupled” or “operatively coupled” shall mean that two members are directly or indirectly joined such that motion may be transmitted from one member to the other member directly or via intermediate members. The term “fluidly coupled” shall mean that two or more fluid transmitting volumes are connected directly to one another or are connected to one another by intermediate volumes or spaces such that fluid may flow from one volume into the other volume. The term “communicatively coupled” shall mean that two devices are directly or indirectly connected on another such that electrical signals may be transmitted therebetween. 
     In one embodiment, user input  236  may comprise a lever, key ignition, a pushbutton, switch, touchpad, touch screen, keypad or an automatic shutdown mechanism. Examples of an automatic shutdown mechanism include a kill bar or other safety mechanism that automatically shuts down the engine such as when a sufficient amount of weight is no longer on the seat of the mower. In other embodiments, other mechanical or electrical mechanisms may be utilized for user input  236 . 
     Controller  238  comprises one or more processing units configured to receive input or signals from sensor  234  and user input  236  and to further generate control signals for directing the operation of fuel stabilizer metering device  228  based upon such input from sensor  234  and user input  236 . For purposes of this application, the term “processing unit” shall mean a presently developed or future developed processing unit that executes sequences of instructions contained in a memory. Execution of the sequences of instructions causes the processing unit to perform steps such as generating control signals. The instructions may be loaded in a random access memory (RAM) for execution by the processing unit from a read only memory (ROM), a mass storage device, or some other persistent storage. In other embodiments, hard wired circuitry may be used in place of or in combination with software instructions to implement the functions described. For example, controller  238  may be embodied as part of one or more application-specific integrated circuits (ASICs). Unless otherwise specifically noted, the controller is not limited to any specific combination of hardware circuitry and software, nor to any particular source for the instructions executed by the processing unit. 
     Fuel stabilizer metering device  228  is a particular embodiment of fuel stabilizer metering device  128 . As shown by  FIG. 3 , fuel stabilizer metering device  228  is specifically illustrated as including an actuator  260 . Actuator  260  comprises one or more mechanisms continue to move volume  140  between the loading position  143  and the unloading position  145 . In one embodiment, actuator  260  may comprise a pneumatically, hydraulically or electrically powered device. Examples of such devices include hydraulic or pneumatic piston-cylinder assemblies or electric solenoids. 
     In another embodiment, actuator  260  may comprise one or more mechanisms that utilize forces naturally produced by engine  220  to move volume  140 . For example, negative and/or positive air or gas pressures within engine  220  may be utilized to move volume  140 . Alternatively, force or motion produced by engine  220  may be transmitted via one or more cams, linkages, transmissions, power trains or the like so to move volume  140 . In each of such embodiments, volume  140  may be biased to one of the loading or unloading positions by a spring or similar mechanism, wherein the hydraulic, pneumatic, electrical or engine produced force moves volume  140  against the bias to the other of the loading or unloading position. Actuator  260  moves volume  140  to the unloading position  145  at least after initiation of engine shut down or after completion of engine shutdown. 
     In the example illustrated, internal combustion engine system  210  is configured to operate in a selected one of multiple available modes or settings which may be set by the person using system  210 . In a first selectable mode, controller  238  generates control signals causing actuator  260  to move volume  140  to the unloading position  145  in response to signals from user input  236  initiating or causing shutdown of engine  220 . For example, in one embodiment a person may turn the ignition key to shut engine  220  off. Such action results in signals being transmitted to controller  238 , where the controller  238  generates signals causing actuator  260  to move volume  140  to the unloading position  145  so as to discharge fuel stabilizer to bowl  32  of carburetor  30 . In some embodiments, a delay timer or other delay mechanism may be provided such that the actual movement of volume  140  to the unloading position  145  occurs at a predetermined time period following receipt of user input  236  shutting down engine  220  by controller  238 . During operation of engine  220 , or during start up of engine  220 , controller  238  generates control signals causing actuator  260  to move volume  140  to the filling or loading position  143 , wherein volume  140  is filled with a predetermined volume of fuel stabilizer from reservoir  24 . 
     In a second selectable mode, controller  238  generates control signals causing actuator  260  to move volume  140  to the unloading position  145  in response to signals received from user input  236  requesting that fuel stabilizer be provided to bowl  32  of carburetor  30  by metering device  228 . In such an embodiment, if such user input is received prior to initiation of engine shut down, input of the request at user input  236  is inhibited or prevented or actual actuation of volume  140  to the unloading position by actuator  260  is paused or delayed until initiation of engine shutdown has occurred or until engine shutdown has been completed. In one embodiment, controller  238  may simply delay the transmission of control signals to actuator  260 . In another embodiment, actuator  260 , itself, may delay actuation or movement of volume  140 . 
     In a third selectable mode, controller  238  generates control signals causing actuator  260  to move volume  140  to the unloading position  145  in response to receiving signals from sensor  234  based upon one of more sensed shut down parameters  239  indicating that engine shutdown has been initiated or has been completed. For example, in one embodiment, sensor  234  senses a drop in vacuum pressure in the intake manifold of engine  220 . When the drop in vacuum is to such an extent that it indicates that engine  220  is being shutdown, controller  238  generates control signals causing actuator  260  to move volume  140  to the unloading position  145 . 
     In a fourth selectable mode, actuator  260  is directly connected to engine  220  so as to utilize forces or changes in engine parameters such that the forces naturally occurring during engine shut down are what actually move volume  140 . For example, negative and/or positive air or gas pressures within engine  220  may be utilized to move volume  140 . Alternatively, force or motion produced by engine  220  may be transmitted via one or more cams, linkages, transmissions, power trains or the like so to move volume  140 . In each of such embodiments, volume  140  may be biased to one of the loading or unloading positions by a spring or similar mechanism, wherein the hydraulic, pneumatic, electrical or engine produced force moves volume  140  against the bias to the other of the loading or unloading position. Actuator  260  moves volume  140  to the unloading position  145  at least after initiation of engine shut down or after completion of engine shutdown. 
     Although internal combustion engine system  210  is illustrated and described as having each of the above for selectable modes or settings, in other embodiments, internal combustion engine system  210  may include a fewer number of such available modes. Although fuel stabilizer metering device  228  is schematically illustrated as being separate from engine  220 , in other embodiments, fuel stabilizer metering device  228  may be embodied as part of engine  220  or may be provided as a module or add-on including the illustrated components, including some of the components of engine  220  or including less than all the components illustrated. For example, in one embodiment, metering device  228  may be incorporated as part of a carburetor unit which is configured to be mounted to a remainder of an engine. 
       FIG. 4  schematically illustrates internal combustion engine system  310 , another embodiment of internal combustion engine system  210 . Internal combustion engine system  310  is similar to internal combustion engine system  210  except that internal combustion engine system  310  includes volume  340  and valves  342 ,  344  in place of volume  140  and further includes actuator  360  in place of actuator  260 . Unlike volume  140 , volume  340  is substantially stationary. Valve  342  comprises a mechanism configured selectively connect volume  340  to fuel stabilizer reservoir  24 . Valve  342  is actuatable between an open position or state, allowing fuel stabilizer to flow from reservoir  24  into volume  340  and a closed state blocking the flow of fuel stabilizer from fuel stabilizer  24  into volume  340 . Valve  344  comprises a mechanism configured selectively connect volume  340  to bowl  32  of carburetor  30 . Valve  344  is actuatable between an open position or state, allowing fuel stabilizer to flow from volume  340  to or at least towards bowl  32  of carburetor  30  and a closed position or state blocking or occluding flow of fuel stabilizer from volume  340 . 
     Actuator  360  comprises one or more actuators or mechanisms configured to selectively actuate valves  342 ,  344  between their open and closed states. In one embodiment, actuator  360  may comprise a pneumatically, hydraulically or electrically powered device. Examples of such devices include hydraulic or pneumatic piston-cylinder assemblies or electric solenoids. 
     In another embodiment, actuator  360  may include mechanisms that utilize forces naturally produced by engine  220  to move valves  342 ,  344 . For example, negative and/or positive air or gas pressures within engine  220  are what actually move valves  342 ,  344 . Alternatively, force or motion produced by engine  220  may be transmitted via one or more cams, linkages, transmissions, power trains or the like so to move valves  342 ,  344 . In each of such embodiments, valves  342 ,  344  may be biased to one of the open or closed positions by a spring or similar mechanism, wherein the hydraulic, pneumatic, electrical or engine produced force moves valves  342 ,  344  against the bias to the other of the open or closed position. Actuator  360  moves or actuates valve  344  to the open state at least after initiation of engine shut down or after completion of engine shutdown. Prior to valve  344  being actuated to the open state, actuator  360  also actuates valve  342  to its closed state. Closing of valve  342  may occur immediately preceding the opening of valve  344  or may occur well before the opening of valve  344  during the operation of engine  220 . Likewise, actuator  360  closes  344  prior to opening valve  342 . Valve  342  may be actuated to its open state to at least partially fill volume  340  at any time while valve  344  is closed. 
     Internal combustion engine system  310  offers each of the selectable modes described above with respect to system  210 . Unlike the modes described above with respect to system  210 , the modes of operation for system  310  actuate valve  342 ,  344  instead of moving a metering volume. As with system  210 , system  310  may include a fewer of such selectable modes. In one embodiment, system  310  may include a single mode of operation. 
       FIGS. 5-10  illustrate internal combustion engine system  410 , a particular embodiment of internal combustion engine system  20 . As shown by  FIGS. 5 and 6 , internal combustion engine system  410  includes engine  420 , fuel stabilizer reservoir  424  (shown in  FIG. 6 ) and fuel stabilizer metering device  428  (shown in  FIG. 5 ). Engine  420  comprises an internal combustion engine having a carburetor  430  with a carburetor bowl  432 , and an intake manifold  434 . Engine  420  supplies power or torque to a powered appliance, examples of which include, but are not limited to, riding and walk behind lawnmowers, snow blowers, tillers, pumps and power washers, or other engine powered equipment. Intake manifold comprise a component of engine  420  that distributes an air-fuel mixture from carburetor  30  to one or more cylinders of engine  420 . Carburetor  430  is a component of engine  420  and provides the required air-fuel mixture to a combustion chamber of the engine based upon engine operating speed and load. Bowl  432  contains or stores fuel prior to the fuel being mixed with air by the carburetor  430 . 
     Intake manifold  434  comprises engine component that distributes the air-fuel mixture from carburetor  430  to cylinders of engine  420 . As shown by  FIGS. 5 and 6 , intake manifold  434  is pneumatically connected or fluidly coupled to fuel stabilizer metering device  428  by conduit  437 , such as a tubing or hose. In other embodiments, metering device  428  may be fluidly coupled to the intake manifold  434  at other locations or in other manners. After initiation of engine shut down, vacuum pressure within intake manifold  434  decreases until reaching atmospheric pressure. As will be described hereafter, fuel stabilizer metering device  428  utilizes this drop in vacuum pressure within manifold  434  during an engine shutdown, as communicated and transmitted to metering device  428  by conduit  437 , to automatically meter fuel stabilizer to bowl  432  of carburetor  430 . 
     Fuel stabilizer reservoir  424  (shown in  FIG. 6 ) comprises a tank, container, chamber or other volume configured to contain and store a fuel stabilizer. Fuel stabilizer reservoir  424  is connected to fuel stabilizer metering device  428  so as to deliver fuel stabilizer to fuel stabilizer metering device  428 . Reservoir  424  may have various sizes, shapes and configurations. In the example illustrated, reservoir  424  comprises a reservoir that is refillable while connected to engine  420  and metering device  428 . In other embodiments, reservoir  424  may be a type that requires disconnection from metering device  428  and/or engine  420  for refilling or replacement. As shown by  FIGS. 5 and 6 , fuel stabilizer reservoir  424  is connected or fluidly coupled to fuel stabilizer metering device  428  by a conduit  439 , such as a tubing or hose. In other embodiments, fuel stabilizer reservoir  424  is fluidly coupled to metering device  428  in other fashions. 
     Fuel stabilizer metering device  428  comprises a device configured to meter or supply a predetermined amount or volume of fuel stabilizer to bowl  432  of carburetor  430  after initiation of engine shutdown. In one embodiment, metering device  428  does not deliver any stabilizer to engine  420  or bowl  432  of carburetor  430  while engine  420  is running (prior to any initiation of shutdown of engine  420 ). In another embodiment, fuel stabilizer metering device  428  meters fuel stabilizer to bowl  432  of carburetor  430  only after engine shutdown has been completed. In some embodiments, metering device  428  may meter a predefined quantity of fuel stabilizer to bowl  432  of carburetor  430  while the engine is being shut down (but not prior to initiation of engine shutdown) and after shutdown has been completed. 
       FIGS. 7-10  illustrate fuel stabilizer metering device  428  in more detail. As shown by  FIG. 7 , metering device  428  comprises body  464 , piston or plunger  466 , bias  468  and retainer  470 . Body  464  comprises a structure having a bowl connecting portion  472 , a reservoir connecting portion  474 , an intake manifold connecting portion  476 , a discharge port  478 , plunger guiding cavity  480 , plunger passage  482  and fill port  484 . Bowl connecting portion  472  comprises that portion of device  428  that is configured to connect to bowl  432  of carburetor  430 . In the example illustrated, portion  472  comprises an externally threaded stem configured to thread into an internally threaded bore within bowl  430 . In other embodiments, the relationship between portion  472  and bowl  432  may be reversed or other mechanisms may be used to connect portion  472  to bowl  432 . 
     Reservoir connecting portion  474  comprises that portion of metering device  428  configured to be connected to conduit  439  and ultimately to fuel stabilizer reservoir  424  (shown in  FIG. 6 ). Similarly, intake manifold connecting portion  476  comprises that portion of metering device  428  configured to be connected to conduit  437  and ultimately to intake manifold  434  as shown in  FIG. 5 . In the example illustrated, portion  474  and  476  comprise barbed nipples that sealingly fit into conduits  439  and  437 , respectively. In other embodiments, portions  474  and  476  may have other configurations for connecting to conduits  439  and  437 , respectively. 
     Discharge port  478  comprises an internal volume within portion  472  extending from plunger passage  482  and opening into an interior of bowl  432 . Plunger guiding cavity  480  comprises a bore configured to receive and guide linear, translating movement of plunger  466 . In some embodiments, body  464  may omit cavity  480  where other structures are provided for guiding movement of plunger  466 . Plunger passage  482  comprises a passage through which plunger  466  extends and moves. In one embodiment, plunger passage  482  seals about outer circumferential portions of plunger  466 . In the example illustrated, additional sealing rings  486  are provided on opposite sides of plunger passage  482  to seal about and against plunger  466  while allowing plunger  466  to slide or move through passage  482 . Fill port  484  comprises a passage extending from an interior of portion  474  to an interior of plunger passage  482 . In the example illustrated, metering device  428  is substantially T-shaped with plunger passage  482  extending along a central axis and fill port  484  extending substantially perpendicular to the central axis. In another embodiment, fill port  484  may have other configurations. 
     Plunger  466  comprises a member movable through plunger passage  482 . Plunger  466  includes shank portion  490 , head portion  492  and volume  440 . Shank portion  490  extends from head portion  492  and extends through plunger passage  482 . Volume  440  comprises an opening or chamber formed within a circumferential portion of shank portion  490 . Volume  440  has a predefined volume configured for the purpose of metering a predetermined amount of fuel stabilizer. The actual predetermined volume of volume  440  may vary depending upon characteristics of engine  420  and carburetor  430 . In the example illustrated, volume  440  comprises a circumferential groove completely encircling shank portion  490 . In other embodiments, volume  440  may comprise a notch or other cavity only partially extending about shank portion  490 . In yet another embodiment, volume  440  may comprise a bore partially or completely extending through shank portion  490  in a radial direction. 
     Head portion  492  extends from shank portion  490  and includes a neck portion  494  and a collar  496 . Neck portion  494  extends from collar  496  and projects into bias  468  to seat bias  468  against plunger  466 . Collar  496  projects radially outward from that portion  494  into contact with interior sides of cavity  480 . Collar  496  outer peripheral surfaces that cooperate with surfaces of cavity  480  to guide movement of plunger  466 . Collar  496  further provides a surface or shoulder against which bias  468  may apply force to plunger  466 . In addition, collar  496  sufficiently seals against sides of cavity  480  such that changes in vacuum pressure communicated from intake manifold  434  by conduit  437  may move plunger  466 . In other embodiments, plunger  466  may have other configurations. 
     As shown by  FIGS. 8 and 10 , plunger  466  is movable between a loading position (shown in  FIG. 8 ) in which volume  440  is fluidly coupled to fill port  484 , allowing volume  440  to at least be partially filled with fuel stabilizer through port  484 , and a discharge or unloading position (shown in  FIG. 10 ) in which volume  440  is fluidly coupled to discharge port  478 , allowing fuel stabilizer within volume  440  to be released or discharged into port  478  and into bowl  432 . Although plunger  466  is illustrated as linearly moving (without rotation about axis  498 ) between the loading and unloading positions along central axis  498 , in other embodiments, plunger  466  may alternatively rotate about axis  498  between the loading and unloading positions. For example, in another embodiment, plunger passage  482  may be internally threaded, while shank portion  490  is externally threaded, wherein force applied to plunger  466  in a direction parallel to axis  498  causes rotation of plunger  466  about axis  498  and also causes plunger  466  to move along axis  498 . 
     Bias  468  comprises a member configured to resiliently bias plunger  466  towards the unloading position shown in  FIG. 10 . In the example illustrated, bias  468  comprises a compression spring captured between collar  496  of plunger  466  and retainer  470 . The spring of bias  468  has a spring constant such that during operation of engine  420 , the vacuum pressure applied to plunger  466  from intake manifold  434 ) shown in  FIG. 5 ) through conduit  437  is sufficiently strong so to resist bias  468  and retain plunger  460 , against the bias of bias  468 , in the loading position shown in  FIG. 8 . 
     In other embodiments, bias  468  may have other configurations. For example, in other embodiments, bias  468  may comprise a tension spring operatively couple to plunger  466  on an opposite side of plunger passage  482 . In yet other embodiments, bias  468  may alternatively be configured to bias plunger  466  towards the loading position, wherein forces resulting from the shutdown of engine  420  are utilized to overcome the force of bias  468  to move plunger  466  to the unloading position when the engine is shut down. 
     Retainer  470  comprises a member inserted and fixedly retained in cavity  480 . Retainer  470  is configured to capture bias  468  between retainer  470  and collar  496  of plunger  466 . Retainer  470  includes an internal bore  499  through which vacuum pressure is transmitted through conduit  437  and may be applied to plunger  466  to retain plunger  466  in the loading position while the engine is running. In other embodiments, retainer  470  may have other configurations or may be omitted where other mechanisms or surfaces are used to bear against bias  468 . 
     During running of engine  420 , a vacuum pressure exists within intake manifold  434  (shown in  FIG. 5 ) of sufficient strength to hold plunger  466  in the loading position against the force of bias  468 . As shown by  FIGS. 7 and 8 , during this time, fuel stabilizer flows from reservoir  424 , through conduit  439 , and into volume  440  of plunger  466  through fill port  484 . Upon initiation of the shutdown of engine  420 , vacuum pressure within intake manifold  434  begins to decline or drop. 
     As shown by  FIGS. 9 and 10 , in response to the vacuum pressure within intake manifold  434  dropping below a predetermined threshold value, bias  468  is able to overcome the decreased vacuum pressure, urging plunger  466  to the unloading position. In the unloading position, the fuel stabilizer within volume  440  is released into bowl  432  of carburetor  430 . At the same time, fill port  484  is substantially closed off or sealed by shank portion  490 . In one embodiment, the spring constant of bias  468  is such that plunger  466  moves to the unloading position during shutdown of engine  420 . In another embodiment, the spring constant of bias  468  is such that plunger  466  moves to the unloading position only after complete shutdown of engine  420 , wherein the interior of intake manifold  434  is at atmospheric pressure. During startup of engine  420 , the vacuum within intake manifold  434  causes plunger  466  to return to the loading position against bias  468 . 
     Although the present disclosure has been described with reference to example embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the claimed subject matter. For example, although different example embodiments may have been described as including one or more features providing one or more benefits, it is contemplated that the described features may be interchanged with one another or alternatively be combined with one another in the described example embodiments or in other alternative embodiments. Because the technology of the present disclosure is relatively complex, not all changes in the technology are foreseeable. The present disclosure described with reference to the example embodiments and set forth in the following claims is manifestly intended to be as broad as possible. For example, unless specifically otherwise noted, the claims reciting a single particular element also encompass a plurality of such particular elements.