Abstract:
Methods and systems for detecting leakage of a liquid fuel into a gas fuel rail of a dual-fuel system for an internal combustion engine are disclosed. The methods and systems include sending an injection signal from a controller to a fuel injector and subsequently injecting gas fuel and liquid fuel into a cylinder for combustion. A pressure in the gas rail detects the pressure in the gas rail over a pre-determined time period after the injection event. A controller measures pressure fluctuations in the gas rail over a pre-determined time period after the injection event. If the pressure in the gas rail fluctuates by more than the pre-determined amount, the controller is programmed to take at least one mitigating action to prevent or limit damage to the engine.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates generally to dual fuel common rail systems, and more particularly to a diesel only method of operation that includes strategies to address liquid fuel leakage into the gas fuel side of the system. 
       BACKGROUND 
       [0002]    Diesel engines are the most popular type of compression ignition engines. Diesel engines introduce fuel directly into the combustion chamber. Diesel engines are very efficient because they provide high compression ratios without knocking, which is the premature detonation of the fuel mixture inside the combustion chamber. Because diesel engines introduce fuel directly into the combustion chamber, the fuel injection pressure must be greater than the pressure inside the combustion chamber. For liquid fuels such as diesel, the pressure must be significantly higher so that the fuel is atomized for efficient combustion. 
         [0003]    Diesel engines are favored by industry because of their excellent combination of power, performance, efficiency and reliability. For example, diesel engines are generally much less expensive to operate compared to gasoline fueled, spark-ignited engines, especially in commercial applications where large quantities of fuel are used. However, one disadvantage of diesel engines is pollution, such as particulate matter (soot) and NOx gases, which are subject to increasingly stringent regulations that require NOx emissions to be progressively reduced over time. To comply with these increasingly stringent regulations, engine manufacturers are developing catalytic converters and other after-treatment devices to remove pollutants from diesel exhaust streams. 
         [0004]    Improvements to diesel fuels are also being introduced to reduce the amount of sulfur in diesel fuel, to prevent sulfur from de-activating the catalysts of catalytic converters and to reduce air pollution. Research is also being conducted to improve combustion efficiency to reduce engine emissions, for example by making refinements to engine control strategies. However, most of these approaches add to the capital cost of the engine and/or the operating costs. 
         [0005]    Other recent developments have been directed to substituting some of the diesel fuel with cleaner burning gas fuels such as, for example, natural gas, methane, butane, propane, hydrogen, and blends thereof. Since gas fuels typically do not auto-ignite at the same temperature and pressure as diesel fuel, a small amount of pilot diesel fuel can be introduced into the combustion chamber to auto-ignite and trigger the ignition of the gas fuel. Another approach for consuming gas fuel on board a vehicle involves introducing the gas fuel into the engine&#39;s intake air manifold at relatively low pressures. However, this approach has been unable to match the performance and efficiency of currently available diesel engines, particularly at high gas:diesel ratios. Thus, fuel injectors have been developed that provide a simultaneous delivery of both diesel fuel and gas fuel to combustion chambers, with the diesel acting as a pilot fuel. 
         [0006]    For example, U.S. Pat. No. 7,627,416 appears to teach a dual fuel common rail system in which liquid diesel fuel and natural gas fuel are both injected from a single fuel injector associated with each engine cylinder. This reference recognizes that there may be instances in which the engine will need to operate solely on liquid diesel fuel due to exhaustion of the natural gas fuel supply or possibly some fault in the natural gas portion of the system. However, one problem this reference does not recognize is the migration of diesel or the liquid fuel into the gas fuel delivery system or gas rail. If liquid fuel migrates or leaks into the gas rail, the gas:liquid fuel ratio changes, engine performance suffers and damage to the engine is possible. 
       SUMMARY 
       [0007]    Thus, there is a need for a methods and systems for detecting when liquid fuel has leaked or migrated into the gas rail so the operation of the engine can be changed to mitigate or prevent damage and/or so the operator can be notified that such a problem exists. 
         [0008]    In one aspect, a method for detecting leakage of a liquid fuel into a gas rail of a dual-fuel system for an internal combustion engine is disclosed. The method may include sending an injection signal from the controller to a fuel injector and injecting gas fuel and liquid fuel into a cylinder for combustion. The method may further include detecting the pressure in the gas rail over a pre-determined time period after the injection event. The method may further include measuring pressure fluctuations in the gas rail over the pre-determined time period and, if the pressure in the gas rail fluctuates by more than the pre-determined amount, the method may further include taking at least one mitigating action. 
         [0009]    In another aspect, a system for detecting leakage of a liquid fuel into a supply of a gas fuel of a dual-fuel internal combustion engine is disclosed. The system may include a gas rail that is coupled to a pressure sensor. The gas rail may also be in communication with a gas nozzle chamber of a fuel injector for delivering gas fuel to the gas nozzle chamber. The system may also include a liquid rail in communication with a liquid nozzle chamber of the fuel injector for delivering a liquid fuel to the liquid fuel chamber. Further, the system may include a controller linked to the pressure sensor. The controller may have a memory programmed to receive signals from the pressure sensor and to determine if the pressure in the gas rail is fluctuating more than the pre-determined amount. The memory may also be programmed to initiate a mitigating action if the pressure in the gas rail is fluctuating more than the pre-determined amount. 
         [0010]    A vehicle is also disclosed which may include an engine which may include a plurality of cylinders and a plurality of fuel injectors. Each cylinder may be in communication with one of the fuel injectors. Each fuel injector may include a liquid nozzle chamber and a gas nozzle chamber for simultaneously injecting liquid fuel and gas fuel respectively into its respective cylinder. Each fuel injector may also be in communication with a gas rail and a liquid rail. The gas rail may be used for delivering gas fuel from a gaseous fuel tank to the plurality of fuel injectors. The liquid rail may be used for delivering liquid fuel from a liquid fuel tank to the plurality of fuel injectors. The gas rail may be coupled to a pressure sensor. The pressure sensor may be linked to the controller. The controller may have a memory programmed to receive signals from the pressure sensor and to determine if a pressure in the gas rail is fluctuating more than a pre-determined amount. The memory may also be programmed to initiate a mitigating action if the pressure in the gas rail is fluctuating more than a pre-determined amount. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic view of a dual fuel engine according to this disclosure. 
           [0012]      FIG. 2  is a sectional perspective view of a portion of the engine housing shown to reveal a structure for one quill assembly, a disclosed fuel injector and an engine cylinder. 
           [0013]      FIG. 3  is a sectional side view through the co-axial quill assembly shown in  FIG. 2 . 
           [0014]      FIGS. 4-9  are sectional views through a disclosed fuel injector. 
           [0015]      FIG. 10  graphically illustrates the differences in the pressure waves or fluctuations generated by an injection event with no liquid in the gas rail and with liquid in the gas rail. 
       
    
    
     DESCRIPTION 
       [0016]    Referring initially to  FIGS. 1-3 , a dual fuel engine  20  may include a dual fuel common rail system  21  mounted to an engine block  22  that may define a plurality of engine cylinders  23 . Each cylinder  23  may include a fuel injector  24  positioned for direct injection into each its respective cylinder  23 . A gas fuel common rail  25  and a liquid fuel common rail  26  may be fluidly connected to each fuel injector  25  and therefore each cylinder  23 . 
         [0017]    The gas fuel common rail  25  may be in communication with a manifold  27  which may be in communication with an isolation valve  28 . The isolation valve  28  may be used to shut off the gas fuel supply in the event that the gas fuel pressure drops to an undesirable level and the engine  20  must convert to a “limp home” mode where the engine  20  runs on liquid fuel only. The isolation valve  28  may be connected to a fuel conditioning module  29  which may be linked with the isolation valve  28  to the controller  31 . The controller  31  may be an engine control module (ECM). A filter  32 , an accumulator  33 , a pump  35  and a pressurized cryogenic gas fuel tank  36  may be disposed upstream of the conditioning module  29 . The fuel tank  36  may be equipped with a pressure relief valve  37 . The controller  31  may also be linked to a gas fuel rail pressure sensor  38  that monitors the pressure in the gas rail  25 . 
         [0018]    The liquid fuel common rail  26  may also be in communication with a manifold  27  which may be in communication with a high pressure fuel pump  41 . The fuel pump  41  may be linked to the controller  31  and may also be disposed upstream or downstream from a filter  42 . In the embodiment shown in  FIG. 1 , the pump  41  draws liquid fuel from a liquid fuel tank  43  and through the filter  42  before delivering the liquid fuel to the manifold  27  and the liquid fuel common rail  26 . 
         [0019]    The controller  31  may control each fuel injector  24 , the isolation valve  28 , the fuel conditioning module  29 , and the pump  41  in a known manner. The gas fuel pump  35  may be a unidirectional variable displacement cryogenic pump while the liquid fuel pump  41  may be a unidirectional variable displacement hydraulic pump. The fuel conditioning module  29  may be used to control the supply and pressure of gas fuel to gas fuel common rail  25 . 
         [0020]    Turning to  FIGS. 1-3 , a cylinder  23  is shown coupled to a fuel injector  24  which, may be coupled to a coaxial quill assembly  44 . As shown in  FIG. 1 , each cylinder  23  may be associated with its own quill assembly  44 , and as shown in  FIGS. 1-2 , each quill assembly  44  may include a block  45 . Turning to  FIG. 3 , the co-axial quill assembly  44  may include an inner quill  46  and an outer quill  47  in sealing contact with a common conical seat  48  of each fuel injector  25  (see also  FIG. 2 ). The blocks  45  of the co-axial quill assemblies  44  may be coupled together by the gas fuel rail  25  and the liquid fuel rail  26 . The blocks  45  may also be in communication with the fuel conditioning module  29  as shown in  FIG. 2 . It will be noted here that the gas fuel rail  25  and liquid fuel rail  26  need not be unitary structures but may be segments coupled together at the various blocks  45 . 
         [0021]    Each block  45  of each co-axial quill assembly  44  may define a segment of the gas common rail  25  which may be oriented perpendicular to the axis  51  of the inner quill  46 . One end of a gas fuel passage  52  opens at the gas fuel common rail  25 , proceeds through the check valve  53 , passes between the inner quill  46  and the outer quill  47  before opening at its other end into the gas fuel inlet  54  of the fuel injector  24 . Thus, a segment of the gas fuel rail  25  is located between the inner quill  46  and the outer quill  47 . Each of the blocks  45  also defines a segment of liquid fuel common rail  26 . One end of a liquid fuel passage  55  opens at the liquid common rail  26 , and may open at its opposite end into liquid fuel inlet  56  of the fuel injector  24 . 
         [0022]    Referring to  FIGS. 4-9  and primarily to  FIG. 4 , a disclosed fuel injector  24  may include a nozzle body  57  that defines a gas nozzle outlet  58  and a liquid nozzle outlet  61 . The injector  24  may include an injector body  63  coupled to the nozzle body  57  and that defines a liquid drain outlet  62  and a gas drain outlet  60 . The injector body  63  may also define the gas fuel inlet  54  and the liquid fuel inlet  56 , which can be seen in  FIG. 3  opening through the common seat  48  of fuel injector  24 . The gas and liquid fuel inlets  54 ,  56  are also shown in  FIGS. 6-9 . 
         [0023]    Returning to  FIG. 4 , the injector body  63  may include a gas control chamber  64  and a liquid control chamber  65  defined by the plate  59  and closing hydraulic surfaces  67 ,  73  of a gas check valve  66  and a liquid check valve  72  respectively. The closing hydraulic surface  67  is exposed to fluid (gas) pressure in the gas control chamber  64 . The gas check valve  66  is movable between a closed position, as shown in  FIGS. 4-9 , in contact with a gas seat  68  to fluidly block flow from the gas fuel inlet  54  ( FIG. 3  and  FIGS. 6-9 ) to the gas nozzle outlet  58 , and an open position (not shown) out of contact with the gas seat  68  to fluidly connect the gas fuel inlet  54  ( FIG. 3  and  FIGS. 6-9 ) to the gas nozzle outlet  58 . 
         [0024]    The liquid check valve  72  has a closing hydraulic surface  73  ( FIG. 4 ) exposed to fluid pressure in the liquid control chamber  65 . The liquid check valve  72  may also be movable between a closed position, as shown in  FIGS. 4-9 , in contact with a liquid seat  74  to fluidly block the liquid fuel inlet  56  to the liquid nozzle outlet  61 , and an open position out of contact with the liquid seat  74  to fluidly connect the liquid fuel inlet  56  to the liquid nozzle outlet  61  via a liquid supply passage  75  not visible in  FIG. 4  but shown in  FIGS. 5-9 . 
         [0025]    Thus, an injection of a gas fuel (e.g., natural gas) to a cylinder  23  through the gas nozzle outlet  58  is facilitated by movement of the gas check valve  66 , while an injection of a liquid fuel (e.g., diesel) through the liquid nozzle outlet  61  is facilitated by movement of the liquid check valve  72 . Those skilled in the art will appreciate that the gas and liquid nozzle outlets  58 ,  61  might be expected to each include several nozzle outlets arranged around respective centerlines in a manner well known in the art. However, the gas and liquid nozzle outlets  58 ,  61  could each include as few as one nozzle outlet or any number of nozzle outlets in any arrangement without departing from the scope of this disclosure. 
         [0026]    A gas control valve  77  may be positioned in the injector body  63  and may be movable axially between a closed position in contact with a seat  78  at which the gas control chamber  64  is fluidly blocked from the gas drain outlet  60 , and an open position where the gas control chamber  64  is fluidly connected to the gas drain outlet  60  via the control passage  76  as shown in  FIGS. 5-7  and  9 . When the gas control chamber  64  is fluidly connected to gas drain outlet  60  in the open position, pressure in gas control chamber  64  drops, relieving pressure on the closing hydraulic surface  67  to allow the gas check valve  66  to lift with the assistance of the spring or biasing element  69  to facilitate an injection of the gas fuel (e.g. natural gas) through the gas nozzle outlet  58 . 
         [0027]    A liquid control valve  81  may be positioned in the injector body  63  and movable axially between a closed position in contact with a seat  82  so the liquid control chamber  65  is fluidly blocked from the liquid drain outlet  62  as shown in  FIG. 4 , and an open position out of contact with the seat  82  at which the liquid control chamber  65  is fluidly connected to the liquid drain outlet  62  via the liquid control passage  93  as shown in  FIGS. 4-5 . When the liquid control chamber  65  is fluidly connected to liquid drain outlet  62 , fluid pressure acting on the closing hydraulic surface  73  is relieved to allow the liquid check valve  72  to lift to an open position to facilitate injection of the liquid fuel (e.g., diesel) through the liquid nozzle outlet  61 . 
         [0028]    In the illustrated embodiment, the gas and liquid control valve members  77 ,  81  may be moved to one of their respective closed and open positions with the gas and liquid electrical actuators  83 ,  84  respectively. The control valves  77 ,  81  may be biased to their closed position by a spring(s) or biasing member(s)  85 . A liquid armature  86  may be attached to a pusher  87  in contact with the liquid control valve  81 . The liquid armature  86 , the pusher  87  and the liquid control valve  81  may be biased to the position shown in contact with the seat  82  by the spring  85 . Thus, the liquid armature  86  can be thought of as being operably coupled to move the liquid control valve  81 . Similarly, a gas armature  88  may be operably coupled to move the gas control valve  77  by way of the pusher  91 . A common stator  92  separates the liquid armature  86  from the gas armature  88 . 
         [0029]    The liquid control valve  81  may be in contact and out of contact with the seat  82  in its open and closed positions respectively. Likewise, the gas control valve  77  may be in contact and out of contact with the seat  78  in its closed and open positions, respectively. The liquid control valve  81  may be coupled to move with the liquid armature  86  in response to a de-energizing of the liquid actuator  84  mounted in the common stator  92 . When the liquid actuator  84  is energized, the armature  86  and pusher  87  are lifted upward (or shifted to the right in  FIGS. 4-9 ) thereby allowing the high pressure in control passage  93  ( FIGS. 4-5 ) to push the liquid control valve  81 out of contact with the seat  82  to fluidly connect the liquid control chamber  65  to drain outlet  62 . 
         [0030]    The gas nozzle chamber  94  may be fluidly connected to gas fuel inlet  54  via the passage  71  (see  FIGS. 6-9 ). The liquid nozzle chamber  96  may be fluidly connected to the liquid fuel inlet  56  via the liquid fuel supply passage  75  (see  FIGS. 5-9 ). Some amount of leakage of liquid fuel may occur from the liquid nozzle chamber  96  into the gas nozzle chamber  94  during a regular mode of operation. However, substantial leakage may cause damage to the engine  20  and various components thereof. In one aspect, a method for determining when such leakage occurs may include detecting fluctuations in the pressure in the gas common rail  25  as shown in  FIG. 10  and discussed below. 
         [0031]    Dual fuel common rail fuel systems may also have a single fuel mode of operation in which only liquid diesel fuel is utilized to power the engine  20 . This mode of operation may be referred to as a “limp home” mode, as this mode of operation may only be preferable when there is some fault in the gas fuel system. A fault may include a malfunction of one or more of gas supply pressure control devices such as the pressure relief valve  37 , the pump  35 , the heat exchanger  34 , the filter  32 , the fuel conditioning module  29  or the isolation valve  28 . A malfunction may also simply relate to a lack of sufficient gas fuel in the tank  36  to continue operating in a regular mode. When operating in a limp home mode, the controller  31  may maintain the liquid rail  26  at a high pressure (e.g., 80 MPa), whereas the pressure in gas rail  25  may be allowed to decay, and may slowly drop as low as atmospheric pressure. 
         [0032]    During the limp home mode, the engine  20  is operated as a conventional diesel engine in which liquid diesel fuel is injected through the liquid nozzle outlets  61  in sufficient quantities and at timings to compression ignite the liquid fuel. On the other hand, during the regular mode of operation, one might expect a relatively small pilot liquid injection through the liquid nozzle outlets  61  to be compression ignited to ignite a much larger charge of gas fuel injected through gas nozzle outlets  58  to power the engine  20  in a regular mode of operation. Due to the higher pressure differential between the liquid fuel and the gas fuel that exists during the limp home mode of operation, more leakage of liquid fuel from the upper liquid nozzle chamber  102  to the gas nozzle chamber  94  is expected as opposed to a regular mode of operation with a smaller pressure differential between the two fuels. 
         [0033]    Referring back to  FIG. 1 , although not necessary, the dual fuel common rail system  30  may also include an electronically controlled isolation valve  28  operably positioned between the fuel conditioning module  29  and the manifold  27 . The isolation valve  28  may be mechanically biased toward a closed position but movable to an open position responsive to a control signal from the controller  31 . When the dual fuel common rail fuel system  21  is being operated in a regular mode, the electronic controller  31  may maintain the isolation valve  28  in an open position. However, in the event that the system transitions into a limp home mode of operation, the electronic controller  31  may close the isolation valve  28  to fluidly isolate the gas supply from any leaked liquid fuel that may find its way into the gas side of dual fuel common rail system  21 . As an alternative, a mechanical check valve may be employed to isolate the gas supply from the dual fuel common rail system  21 . 
         [0034]    Turning to  FIG. 10 , the line  95  represents the pressure in the gas common rail  25  during a normal operation. However, the line  97  represents the pressure in the gas common rail  25  when a significant leakage of liquid fuel into the gas common rail  25  has occurred. As noted above, such leakage may predominantly occur between liquid nozzle chamber  102  and the gas nozzle chamber  94 . Accordingly, detection of the pressure spikes and drops in the gas common rail  25  as shown by the line  97  provides a means for detecting when leakage of liquid fuel into the gas common rail  25  is occurring or has recently occurred. The reader will note that the spikes and drops in gas rail  25  may occur after an injection signal is sent by the controller  31  as indicated by the line  98 . The magnitude of the wave may be indicative of the amount of liquid fuel that has leaked into the gas rail  25 . 
         [0035]    Further, while leakage from the liquid nozzle chamber  96  to the gas nozzle chamber  94  may be the primary location where liquid fuel leaks into the gas rail  25 , other areas of the disclosed injectors  24  and other fuel injectors that differ in design from the disclosed injector  24  may be the source of such leakage and those skilled in the art will be able to examine a fuel injector design and determine where such leakage may occur. 
       INDUSTRIAL APPLICABILITY 
       [0036]    A system and method for detecting liquid fuel leakage from the liquid rail  26  to the gas rail  25  is disclosed. When such leakage occurs, the pressure in the gas rail  25  will fluctuate and such fluctuations can be detected by the gas rail pressure sensor  38  and may be communicated to the controller  31 . The gas rail pressure sensor  38  may be in continuous or regular communication with the controller  31 . 
         [0037]    Therefore, a dual fuel system is disclosed that is configured to: (1) monitor the pressure in the gas rail  25 ; (2) evaluate pressure waves in the gas rail  25  after injections to determine if liquid fuel is present in the gas rail  25 ; and (3) take one or more mitigating actions. Detecting liquid fuel or diesel in the gas rail  25  will allow the engine controller  31  to take any one or more of the following mitigating actions, such as: (1) entering a diagnostic mode to determine the leak location; (2) entering a liquid fuel or diesel only mode operation; (3) reducing fuel delivered to the effected cylinder(s) to prevent or reduce engine damage; (4) derating the engine or reducing the power output of the engine to prevent engine damage; and/or (5) notifying the operator that a problem exists. The controller  31  may be programmed to take other corrective actions as well, as will be apparent to those skilled in the art.