Abstract:
Systems and methods for providing heated fuel to a fuel injector of an engine are provided. According to the approaches described herein, adequate cold-start fuel atomization may be provided without compromising driver satisfaction due to excessive pre-ignition delay, while at the same time reducing unnecessary heating of fuel during warm engine off conditions.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional of U.S. patent application Ser. No. 12/332,154 filed Dec. 10, 2008, the entire contents of which are incorporated herein by reference for all purposes. 
    
    
     TECHNICAL FIELD 
     The present application relates to the fields of motor-vehicle fuel systems and motor-vehicle emissions control. 
     BACKGROUND AND SUMMARY 
     Emissions-control performance in a motor-vehicle engine system depends on effective atomization of the liquid fuel. When fuel entering the combustion chamber of an engine is inadequately atomized, increased hydrocarbon and/or other emissions may result. This effect may be especially evident shortly after a cold start of the engine, when the fuel and the engine are both cold. Moreover, ignition of the fuel under cold-start conditions may be unreliable when the fuel is inadequately atomized. 
     Achieving adequate cold-start fuel atomization may be especially difficult in a gasoline direct-injection (GDI) engine, where the air/fuel mixing interval is short, and in engines where high surface-tension, low-volatility alcohol fuels are used in place of gasoline. It is known, however, that a heated fuel may be atomized more easily than a cold fuel. Approaches for improving cold-start fuel atomization have therefore included heating the fuel as soon as a cold start is requested, e.g., when a driver of the motor vehicle turns the ignition key. The fuel may be heated via one or more resistively heated engine elements—injection impingement plates, ports, injectors, for example. Alternatively, the fuel may be heated via the combustion air. 
     These approaches all share a common feature: a wait-to-start interval beginning when the cold-start is requested and continuing until a liquid or solid body has reached a given temperature. By delaying ignition until after the wait-to-start interval, a disadvantageous trade-off between motor-vehicle cost and driver satisfaction may be manifest. Specifically, driver satisfaction may require a short wait-to-start interval, so that ignition occurs promptly after the cold-start request. But a short wait-to-start interval may require significant power-delivery from fuel-heating engine elements, resulting in increased motor-vehicle cost. 
     The inventors herein have recognized the disadvantages noted above and have provided an approach to address this paradox. In one embodiment, a method for providing heated fuel to a fuel injector of an engine is provided. The method comprises maintaining a volume of fuel above a start-ready temperature during a pre-start interval, the pre-start interval beginning after the engine is turned off, beginning automatically, and ending when the engine is restarted, the start-ready temperature greater than a lowest temperature of the engine during the pre-start interval. The method further comprises delivering some of the volume of fuel to the fuel injector when the engine is about to be restarted. Other embodiments of the present disclosure provide more particular methods and systems for providing heated fuel to an engine. According to the various approaches described herein, adequate cold-start fuel atomization may be provided without compromising driver satisfaction due to excessive pre-ignition delay, while at the same time reducing unnecessary heating of fuel during warm engine off conditions. Further, the approaches described herein may be enacted inexpensively in a wide variety of motor-vehicle configurations. 
     It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a first example system for providing fuel to an engine of a motor vehicle, in accordance with the present disclosure. 
         FIG. 2  shows a second example system for providing fuel to an engine of a motor vehicle, in accordance with the present disclosure. 
         FIG. 3  shows a third example system for providing fuel to an engine of a motor vehicle, in accordance with the present disclosure. 
         FIG. 4  shows a fourth example system for providing fuel to an engine of a motor vehicle, in accordance with the present disclosure. 
         FIG. 5  shows a fifth example system for providing fuel to an engine of a motor vehicle, in accordance with the present disclosure. 
         FIG. 6  shows a sixth example system for providing fuel to an engine of a motor vehicle, in accordance with the present disclosure. 
         FIG. 7  illustrates an example method for providing fuel to an engine of a motor vehicle, in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a first example system  10  for providing fuel to an engine of a motor vehicle. More specifically, system  10  is one example of a local, pumped-circulation fuel-delivery system with an added pump. The system includes container  12 , which is configured to store a volume of fuel. The container may have any capacity ranging from a few milliliters to several liters. Further, the capacity of the container may be matched to one or more characteristics of the engine and/or the motor vehicle in which the engine is installed. For example, the container may be configured to store sufficient fuel to allow the engine to operate under normal speed and load conditions over a warm-up interval, where the warm-up interval may correspond to the time required for a coolant of the engine to warm from a cold, ambient temperature to a nominal operating temperature. 
     Container  12  may be configured to store a hydrocarbon fuel (gasoline, diesel fuel, etc.), an alcohol fuel (methanol, ethanol, etc.), and/or a mixture thereof (E15, E85, etc.). Further, the container may be configured to store such fuels at greater-than-ambient temperatures. For, example, the container may be configured to store the hydrocarbon and/or alcohol fuel over a temperature range that includes an ambient temperature and approaches a boiling point of the fuel. Therefore, an interior of container may be fabricated from materials resistant to heated hydrocarbon and/or alcohol fuels. 
     Container  12  may be insulated to limit a transport of heat through the walls thereof. For example, the container may be wrapped or covered with a thermally insulating material—glass wool, polystyrene foam, etc. The container may include a heat-reflective foil or other coating. In some examples, the container may be a vacuum-enclosing vessel such as a Thermos® or Dewar-type vessel. 
       FIG. 1  shows heater  14 , which is configured to maintain a temperature of the volume of fuel above a start-ready temperature during a pre-start interval. The pre-start interval may be any period of time beginning automatically after the engine is turned off and ending when the engine is restarted. The term ‘beginning automatically,’ is used herein to indicate that the pre-start interval may begin independent of any action of an operator of the motor vehicle—independent of a driver door opening, independent of an ignition key turning, etc. For example, the pre-start interval may begin when the engine is turned off. In other examples, the pre-start interval may begin some predetermined period of time after the engine is turned off (2 hours after, 30 minutes after, etc.). In still other examples, the pre-start interval may begin when an engine temperature (an engine-component temperature, an engine-coolant temperature, etc.) drops below a threshold temperature; the threshold temperature may be set a few degrees above the start-ready temperature. 
     The start-ready temperature may be any desirable fuel temperature for the fuel supplied to the engine when the engine is restarted. In one example, the start-ready temperature may be chosen so that the fuel, if supplied at or above the start-ready temperature, may be effectively atomized via a fuel injector of the engine, thereby enabling satisfactory emissions-control and/or cold-start performance. In this example, fuel injected at the start-ready temperature is not cold enough to impair emissions-control performance of the motor vehicle due to inadequate atomization. In another example, the start-ready temperature may be chosen so that the fuel, if supplied to the engine below the start-ready temperature, may not be effectively atomized via a fuel injector of the engine. Therefore, it may be advantageous to supply the fuel at or above the start-ready temperature in order to enable satisfactory emissions-control and/or cold-start performance. 
     Depending on the motor-vehicle configuration, on ambient conditions, and on the period of time elapsed since the engine was turned off, the start-ready temperature may be greater than a lowest temperature of the engine during the pre-start interval. Therefore, the heater may be configured to supply heat to the volume of fuel in the container during the pre-start interval, either continuously or intermittently. The heat supplied by the heater may be derived from any suitable energy source. For example, the heater may be an electrical resistive heater, deriving energy from an electrical power supply—a plug-in power supply external to the motor vehicle, a battery and/or alternator of the motor vehicle, etc. In other examples, the heater may be a heat exchanger deriving heat energy from the engine or from an exhaust system of the motor vehicle. In still other examples, the heater may be a heat exchanger deriving energy from a solar panel mounted on the motor vehicle. 
     Although heater  14  is shown in  FIG. 1  schematically disposed within container  12 , it will be understood from the above examples that the heater may comprise a plurality of components disposed inside as well as outside the container. Further, the heater may be operatively coupled to other motor-vehicle components—an electronic control unit, a temperature sensor, etc. 
       FIG. 1  shows fuel rail  16  of the engine, which is coupled to a plurality of fuel injectors. Fuel may be supplied to the fuel rail from a fuel-storage tank via a lift pump (not shown in  FIG. 1 ), and provided to a plurality of combustion chambers in the engine via fuel injectors  18 . Thus, the engine that is provided fuel in this embodiment may be a GDI engine. In other embodiments, one or more fuel injectors may supply fuel to an intake manifold: thus, the engine may be port-injected as well. 
       FIG. 1  shows a fuel-handling system coupled to the container and configured to cause the fuel to flow from the container to the fuel rail when the engine is about to be restarted. One or more elements of the fuel-handling system may be triggered by other motor-vehicle components configured to sense when the engine is about to be restarted. Various readily detectable conditions or events may indicate that the engine is about to be restarted: a turning of an ignition key or ignition switch, a depression of a brake pedal when the engine is turned off, an opening of the driver&#39;s door from the outside, for example. In one embodiment, an electronic control unit of the motor vehicle may be configured to detect such a condition (or conditions), and in response, trigger the fuel-handling system. As indicated above, heater  14  is configured to maintain the temperature of a volume of fuel at or above the start-ready temperature during the pre-start interval, which extends to the time that the engine is restarted. It follows that the fuel supplied to the fuel rail when the fuel-handling system is triggered may be at or above the start-ready temperature. 
     In the embodiment illustrated in  FIG. 1 , the fuel-handling system includes pump  20 , which is configured to pump the fuel from fuel rail  16  to container  12  when the engine is about to be restarted. The pump may be configured to move the fuel from the fuel rail to the container faster than the fuel is supplied from the fuel-storage tank or consumed by the engine. Therefore, pumping the fuel from the fuel rail to the container may result in a substantially equivalent counterflow of fuel at or above the start-ready temperature from the container to the fuel rail. In this manner, the fuel-handling system is configured to exchange at least some of the fuel in the container with the fuel in the fuel rail when the engine is about to be restarted. 
     In the embodiment illustrated in  FIG. 1 , the fuel-handling system includes one-way pressure-actuated valves  22  and  24 , provided to limit convective heat transfer from container  12 . Each of the one-way, pressure-actuated valves referred to herein may be any valve configured to transmit fuel in one direction when the pressure across the valve exceeds a threshold pressure, but to block transmission of the fuel when the pressure does not exceed the threshold pressure. Thus, a one-way pressure-actuated valve may transmit fuel in one direction only. Similarly, a check valve is a species of one-way pressure-actuated valve in which the threshold pressure is a small (e.g., small relative to the pressure rating of the valve). In the embodiment illustrated in  FIG. 1 , one or both of the one-way pressure-actuated valves may be check valves. 
     It will be understood that  FIG. 1  and subsequent drawings are schematic and not intended to represent spatial relationships among system components in any embodiment. Further, the various system components may and will include structure that is not shown in the drawings. In some embodiments, the conduit through which fuel enters container  12  from pump  20  may be at least partly different than the conduit through which fuel exits the container to fuel rail  16 . Further, the disposition of the conduits may be determined by the placement of heater  14  and other configurational details. In particular, the conduits may be configured so that colder fuel enters the container from the bottom (via a dip tube, for example), and heated fuel is drawn off from the top. 
       FIG. 2  shows a second example system  26  for providing fuel to an engine of a motor vehicle. More specifically, system  26  is one example of a global, pumped-circulation fuel-delivery system, which uses a conventional lift pump. In this and subsequent embodiments, elements that are substantially the same as in a previous embodiment are rendered, labeled, and named the same as in the previous embodiment, and are described no further. In will be understood, however, that identically named elements in different embodiments of the present disclosure may be at least partly different. Likewise, functional aspects of this and subsequent embodiments, if substantially the same as in a previous embodiment, are presented with a minimum of functional description. 
       FIG. 2  shows a fuel-storage tank  28  and associated lift pump  30 . In this embodiment, the fuel-storage tank is configured to receive fuel from fuel rail  16 , and the lift pump is configured to pump the fuel from the fuel-storage tank to container  12  when the engine is about to be restarted. Fuel at or above the start-ready temperature, thereby displaced from the container, is forced into the fuel rail and supplied to the plurality of fuel injectors  18 ; unused fuel from the fuel rail may re-enter the fuel-storage tank via return path  32 . In this manner, fuel entering the container forces fuel maintained above the start-ready temperature into the fuel rail, which forces fuel from the fuel rail into the fuel-storage tank when the engine is about to be restarted. 
     In the embodiment illustrated in  FIG. 2 , the return path includes an additional one-way, pressure-activated valve  33 . This valve is configured to maintain pressurization in the fuel rail while permitting fuel to return to the fuel-storage tank. In another embodiment, a regulator may be used in place of one-way, pressure-activated valve  33 . 
     In various embodiments, lift pump  30  may be configured to move the fuel not only when the engine is about to be restarted, but during other periods as well. In one example, the pump may be configured to pump the fuel whenever the engine is operating in addition to when the engine is about to be restarted. However, by activating the pump at least when the engine is about to be restarted, a volume of fuel substantially at or above the start-ready temperature may be provided to the plurality of fuel injectors  18  when the engine is restarted. 
       FIG. 3  shows a third example system  34  for providing fuel to an engine of a motor vehicle. More specifically, system  34  is one example of a vapor push-out system having no extra pumps. Subsequent embodiments (vide infra) show other such examples. In this embodiment, the fuel-handling system includes lift pump  30  configured to draw fuel from fuel-storage tank  28 , GDI pump  36  configured to supply the fuel to fuel rail  16 , and a normally closed valve  38  configured to admit fuel from the fuel rail to the fuel-storage tank when the engine is about to be restarted. In this embodiment, the GDI pump and the normally closed valve are disposed in parallel and coupled to an outlet of the lift pump via two-way pressure-actuated valve  40 . A two-way pressure-actuated valve may be any valve that is a functional equivalent of two one-way pressure-actuated valves disposed in parallel, with the inlet of each valve coupled to the outlet of the other valve. A two-way pressure-actuated valve may admit of a threshold pressure for flow in one direction that differs from the threshold pressure for flow in the opposite direction. 
     Continuing in  FIG. 3 , normally closed valve  38  may be directly or indirectly controllable via an electronic control unit of the motor vehicle; it may be a hydraulically or electrically actuated valve—a solenoid-actuated valve, for example. In this embodiment, opening normally closed valve  38  allows cold fuel from fuel rail  16  to be flushed into fuel-storage tank  28  by the pressurized fuel in container  12 . Therefore, two-way pressure-actuated valve  40  may have a threshold pressure for return of fuel to the fuel tank which is on the order of the vapor pressure of the fuel at the start-ready temperature. 
     In this embodiment, the vapor pressure of the heated fuel in container  12  is the motive force used to push the heated fuel into fuel rail  16 . In other words, vapor pressure of fuel maintained above the start-ready temperature pushes the fuel from the container to the fuel rail, and from the fuel rail to the fuel-storage tank, when the engine is about to be restarted. In moving from the container to the fuel rail, the heated fuel passes through one-way, pressure activated valve  42 , which is configured to provide relatively little restriction to the flow of fuel in the indicated direction. In other, similar embodiments, a float-actuated valve may be used to stop heated fuel from exiting the container once the level has dropped to a near-empty position. This aspect relieves the control system from the task of estimating how much fuel is pushed out when normally closed valve  38  is opened. 
     In this and similar embodiments, the capacity of container  12  may be greater than that of fuel rail  16  so that the fuel rail may be purged multiple times prior to engine start, for increased heating efficacy. Further, GDI pump  36  may include an integrated outlet check valve. Other, similar embodiments may include a pressure-relief valve for container  12 , to prevent the pressure inside the container from exceeding the ratings of various components. In the embodiment of  FIG. 3 , normally closed valve  38  may be used for pressure relief at fuel rail  16 , to control fuel injector leakage, etc. Further, in embodiments where a pressurized gaseous fuel is available, the pressure of the gaseous fuel may be used to exchange the cold fuel for the heated fuel. 
     After the heated volume of fuel is discharged from container  12 , fuel from the fuel rail may refill the container via orifice  43 . The restriction in the orifice is configured to control the refill rate and allow fuel rail  16  to be pressurized by GDI pump  36  before the container is filled. Further, the heater may be operatively coupled to other motor-vehicle components—an electronic control unit, a temperature sensor, etc. 
       FIG. 4  shows a fourth example system  44  for providing fuel to an engine of a motor vehicle. This embodiment does not include a GDI pump; it may be appropriate for a port-injection engine, for example. In other respects, this embodiment is similar to the previous embodiment. The fuel-handling system in  FIG. 4  includes lift pump  30  configured to draw fuel from fuel-storage tank  28 , and normally closed valve  46  configured to admit fuel from container  12  to fuel rail  16  when the engine is about to be restarted. Opening normally closed valve  46  allows cold fuel from fuel rail  16  to be flushed into fuel-storage tank  28  by the pressurized fuel in container  12 . 
     The embodiment illustrated in  FIG. 4  shows a single conduit linking container  12  to normally closed valve  46 . In other embodiments, however, the fuel may pass into the container via a restrictive orifice, and out of the container via a one-way, pressure activated valve presenting relatively little restriction to the flow, as shown in  FIG. 3 . Refilling is controlled such that it does not drop pressure in the rail precipitously during engine operation. 
       FIG. 5  shows a fifth example system  48  for providing fuel to an engine of a motor vehicle. The fuel-handling system in  FIG. 5  includes lift pump  30  configured to draw fuel from fuel-storage tank  28 , first normally closed valve  50  configured to admit fuel from fuel rail  16  to fuel-storage tank  28  when the engine is about to be restarted, GDI pump  52  configured to supply fuel to the fuel rail, two-way pressure-actuated valve  40  disposed between the lift pump and the GDI pump, second normally closed valve  54  configured to admit the fuel from the container to the GDI pump when the engine is about to be restarted, and one-way, pressure-actuated valve  56 , also known as a ‘pressure-relief valve,’ disposed parallel to the second normally closed valve and configured to release the fuel from container  12  when the container is over-pressurized. 
     In this and other embodiments, GDI pump  52  may include integrated components not shown in the drawing: an outlet check valve, a pressure-relief valve, and a controllable inlet check valve, as examples. In the embodiment illustrated in  FIG. 5 , container  12  is disposed on the low pressure side of GDI pump  52 . This configuration provides for minimal injector leak at key-off because the fuel rail pressure can remain low while the heated fuel is at or above its vapor pressure. Normally closed valves  50  and  54  may be actuated as described in the previous embodiment, when the engine is about to be restarted. In addition, second normally closed valve  54  may be actuated when the container is refilled. 
     In the embodiment illustrated in  FIG. 5 , cold fuel from the fuel rail is returned to a point that is downstream of lift pump  30  but downstream of two-way, pressure-activated valve  40  (relative to the normal fuel supply flow). In other embodiments, the conduit that returns the fuel may be plumbed to the other side of the two-way, pressure activated valve for reduced fuel-handling system cost. 
       FIG. 6  shows a sixth example system  58  for providing fuel to an engine of a motor vehicle. In this embodiment, the fuel-handling system is similar to that of the previous embodiment, but further includes a second one-way pressure-actuated valve  60  configured to admit the fuel from the fuel rail  16  to container  12  when the fuel rail is over-pressurized. 
     Normally closed valves  50  and  54  are actuated as described in the previous embodiment. One-way pressure-actuated valve  56  may be configured as a pressure-relief valve. In this embodiment, one-way pressure-actuated valve  60  is configured to control the refilling of container  12 . As such, it may have a relatively high threshold pressure, e.g., 300 p.s.i. to open. Further, GDI pump  52  may include integrated components as described in the previous embodiment. As in the previous embodiment, container  12  is disposed on the low-pressure side of the GDI pump. In this and other embodiments, the pressure in the fuel rail may be driven to a default pressure even in the event that a fuel rail pressure sensor should fail. 
       FIG. 7  shows an example method  62  for providing heated fuel to an engine. The method may be enabled via one or more of the embodiments described herein. Therefore, continued reference is made to various aspects of the embodiments. It will be understood, however, that the method may be enabled by other configurations as well. 
     The method begins at  64 , where fuel is flowed into a container, e.g. container  12 . The fuel may be flowed into the container via a fuel-handling system substantially as set forth above. The method continues to  66 , where it is determined whether power for heating the fuel inside the container is available. The availability of power may be assessed in a variety of different ways, depending on the particular configuration in use. It may include, for example, measuring a battery voltage, measuring an engine coolant temperature, a temperature of fluid in a heat exchanger, etc. 
     If power for heating the fuel inside the container is available, then at  68 , it is determined whether the temperature of the fuel in the container is above or below the start-ready temperature. In some examples, the temperature of the fuel may be measured directly, as with a thermocouple or other temperature sensor operatively coupled to an electronic control unit of the motor vehicle. If the fuel in the container is below the start-ready temperature, then at  70 , heat is applied to the fuel in the container. Heat may be applied in any manner set forth in the example configurations herein, or in any other suitable manner. In this way, a volume of fuel may be maintained above a start-ready temperature during a pre-start interval, the pre-start interval beginning automatically after the engine is turned off and ending when the engine is restarted. Further, the start-ready temperature may be greater than a lowest temperature of the engine during the pre-start interval. 
     Execution of method  62  continues at  72 , where it is determined whether the engine is about to be restarted. The determination of whether the engine is about to be restarted may be based on a trigger from an ignition system of the motor vehicle, as described above, or based on a driver-side door opening from the outside, etc. If it is determined that the engine is not about to be restarted, then execution resumes at  66 . However, if it is determined that the engine is about to restarted, then at  74 , fuel from the insulated container is flowed into the fuel rail of the engine, and the method returns to  64 . The fuel may be flowed into the fuel rail via a fuel-handling system as described above in various example embodiments. In this manner, a volume of heated fuel may be delivered to the engine when the engine is restarted. 
     It will be understood that the example control and estimation routines disclosed herein may be used with various system configurations. These routines may represent one or more different processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, the disclosed process steps (operations, functions, and/or acts) may represent code to be programmed into computer readable storage medium in a control system. It will be understood that some of the process steps described and/or illustrated herein may in some embodiments be omitted without departing from the scope of this disclosure. 
     Thus, a particularly simple method for providing heated fuel to a fuel injector of an engine, which is fully consistent with this disclosure, includes, at least under selected conditions, heating the fuel to above a temperature of the engine prior to any indication from the driver that the engine is about to be restarted, and delivering some of the fuel maintained above the start-ready temperature to the fuel injector when the driver restarts the engine. 
     Likewise, the indicated sequence of the process steps may not always be required to achieve the intended results, but is provided for ease of illustration and description. One or more of the illustrated actions, functions, or operations may be performed repeatedly, depending on the particular strategy being used. 
     Finally, it will be understood that the systems and methods described herein are exemplary in nature, and that these specific embodiments or examples are not to be considered in a limiting sense, because numerous variations are contemplated. Accordingly, the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and methods disclosed herein, as well as any and all equivalents thereof.