Dual-fuel common rail system and operating procedures therefor in diesel mode

Abstract

Method for operating a dual-fuel engine (10), comprising the following steps: Operating a dual-fuel common rail system (20) in a regular mode; Operating the dual-fuel common rail system (20) in an emergency mode; leaking more liquid fuel into a gas fuel part of the dual-fuel system (20) when operating in limp-home mode compared to regular mode; Injecting liquid fuel from a first nozzle outlet set (103) and injecting gaseous fuel from a second nozzle outlet set (104) into an engine cylinder (12) when the dual-fuel common rail system (20) is operating in regular mode; Injecting liquid fuel from the first nozzle outlet set (103) and injecting liquid fuel, but no gaseous fuel, from the second nozzle outlet set (104) into the engine cylinder (12) when the dual-fuel common rail system (20) is operating in limp home mode.

Description

Technical area

[0001] The present disclosure relates generally to dual-fuel common rail systems, and more particularly to a diesel-only operating method that employs strategies to address leakage of liquid fuel to the gaseous fuel side of the system. background

[0002] A relatively new class of engines attempts to use two different fuels to achieve the efficiencies associated with compression ignition combined with the benefits associated with natural gas fuel combustion. In particular, one type of dual-fuel engine uses a small pilot injection of liquid diesel fuel, which is compression-ignited to, in turn, ignite a much larger charge of natural gas fuel in each engine cylinder. In one strategy for this type of engine, both fuels are injected directly from a single fuel injector associated with each engine cylinder. For example, US Pat. No. 7,627,416 B2 apparently teaches 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 document recognizes that there may be cases where the engine must operate solely on diesel fuel due to the natural gas fuel supply being depleted or due to a possible failure in the natural gas portion of the system. However, this document neither recognizes some of the problems associated with operating the engine in a diesel-only fuel supply mode nor teaches solutions to some of the associated challenges.

[0003] Furthermore, CA 2 773 651 A1 discloses a method and apparatus for controlling the fuel pressure in an internal combustion engine consuming gaseous and liquid fuel, comprising the steps of: determining a setpoint for the pressure of the gaseous fuel as a function of an engine operating condition; bringing the liquid fuel to a liquid fuel pressure based on the setpoint; and regulating the pressure of the gaseous fuel based on the liquid fuel pressure such that the pressure of the gaseous fuel corresponds to the setpoint within a predetermined tolerance range.

[0004] The present disclosure is directed to one or more of the problems set forth above. Summary

[0005] The object of the present invention is achieved by a method and a system according to the main claims. The subclaims relate to preferred embodiments of the invention. A method for operating a dual-fuel engine comprises operating a dual-fuel common rail system in a regular mode and in a limp-home mode. When operating in limp-home mode, more liquid fuel leaks into a gaseous fuel portion of the dual-fuel system than in regular mode. The injection of liquid fuel from a first nozzle outlet set and the injection of gaseous fuel from a second nozzle outlet set into an engine cylinder is described when operating the dual-fuel common rail system in regular mode.When operating the dual-fuel common rail system in limp home mode, liquid fuel is injected into the engine cylinder from the first nozzle outlet set, and liquid fuel, but not gaseous fuel, is injected into the engine cylinder from the second nozzle outlet set.

[0006] According to another aspect, a dual-fuel common rail system includes a gaseous fuel common rail and a liquid fuel common rail. A plurality of fuel injectors are each fluidly connected to both the gaseous fuel common rail and the liquid fuel common rail. A liquid fuel supply and pressure control system is fluidly connected to the liquid fuel common rail. A gaseous fuel supply and pressure control system is fluidly connected to the gaseous fuel common rail. An electronic control device is in control communication with the plurality of fuel injectors, with the liquid fuel supply and pressure control system, and with the gaseous fuel supply and pressure control system.The electronic control device includes a limp-home algorithm configured to transmit liquid injection control signals to inject liquid fuel from a first nozzle outlet set and gas injection control signals to inject gaseous fuel from a second nozzle outlet set. The electronic control device also includes a regular algorithm configured to transmit liquid injection control signals to inject liquid fuel from the first nozzle outlet set and gas injection control signals to inject gaseous fuel from the second nozzle outlet set. Short description of the drawings Fig. 1 is a schematic view of a dual-fuel engine according to the present disclosure, Fig. 2 is a perspective view of a portion of the engine and the dual-fuel common rail system for the engine of the Fig. 1; Fig. 3 is a sectioned perspective view of a part of the Fig. 2 to illustrate the structure for a fuel injector and an engine cylinder; Fig. 4 is a sectional side view through a coaxial web line assembly according to another aspect of the present disclosure, Fig. 5 is a front cross-sectional view of a fuel injector according to one aspect of the present disclosure; and Fig. 6 is a logic flow diagram illustrating a method of operating the motor of the Fig. 1 shows. Detailed description

[0007] Initially with reference to Fig. 1-3, a dual-fuel engine 10 includes a dual-fuel common rail system 20 mounted on an engine housing 11 that defines a plurality of engine cylinders 12. The dual-fuel common rail system 20 includes one fuel injector 25 arranged for direct injection into each of the plurality of engine cylinders 12. A gaseous fuel common rail 21 and a liquid fuel common rail 22 are fluidly connected to each of the fuel injectors 25. The dual fuel common rail system 20 also includes gas supply and pressure control devices 16 fluidly connected to the gaseous fuel common rail 21 as well as liquid supply and pressure control devices 17 fluidly connected to the liquid fuel common rail 22.The fuel injectors 25, the gas pressure supply and control devices, and the liquid supply and pressure control devices 17 are in control communication with and controlled by an electronic engine control device 15 in a known manner. The gas supply and pressure control devices 16 may include a pressurized, refrigerated or cryogenic liquefied natural gas tank 40 having an outlet fluidly connected to a variable-flow cryogenic pump 41. The devices 16 may also include a heat exchanger 42, an accumulator 44, a gas filter 43, and a fuel conditioning module 45 that control the supply and pressure of the gaseous fuel common rail 21.The liquid supply and pressure control devices 17 may include a diesel fuel tank 50, fuel filter 51, and an electronically controlled high-pressure fuel pump 52 that supplies liquid fuel to the liquid fuel common rail 22 and controls the pressure therein.

[0008] Additionally on Fig. 4, the dual-fuel common rail system 20 may include a coaxial ridge assembly 30 having an inner ridge 32 and an outer ridge 33 in sealing contact with a common conical seat 27 of each fuel injector 25. The blocks 31 of the coaxial ridge assembly 30 may be connected together in series with gaseous fuel line segments 18 and liquid fuel line segments 19 to define the gaseous fuel common rail 21 and the liquid fuel common rail 22, respectively. The last coaxial ridge assembly 30 in the series connection may include a set of plugs instead of the plugs shown in Fig. 2. A coaxial web assembly 30 is fluidly positioned between each of the plurality of fuel injectors 25 and both the gaseous fuel common rail 21 and the liquid fuel common rail 22.

[0009] Each coaxial web assembly 30 may include a load adjustment clamp 34 with a pivot surface 75 in contact with a block 31 at a load adjustment position 56 intersected by the axis 29 of the inner web 32. The load adjustment clamp 34 may define a fastener slot 77 and a fastener bore 76 that receive a first fastener 81 and a second fastener 80, respectively. The load adjustment clamp 34 pivots at the load adjustment position 56 in response to adjustments of the first and second fasteners 81, 80. The fasteners 80 and 81 are received in the fastener bore 54 and the fastener slot 55, respectively, of the blocks 31.

[0010] Each block 31 of each coaxial land assembly 30 defines a segment of a gaseous fuel common rail 21 oriented perpendicular to the axis 19 of the inner land 32. A gaseous fuel passage 60 opens at one end into the gaseous fuel common rail 21 and opens at its other end into the first fuel inlet 101 of the fuel injector 25. A segment of the gaseous fuel passage 60 is located between the inner land 32 and the outer land 33. Each of the blocks 31 also defines a segment of the liquid fuel common rail 22. A liquid fuel passage 61 opens at one end into the liquid fuel common rail 22 and opens at its opposite end into the second fuel inlet 102 of the fuel injector 25.

[0011] To capture metallic debris that is often released into the fuel stream during initial operation of the engine 10 after it is built, the coaxial fin assembly 30 may include a gaseous fuel edge filter 36 and a liquid fuel edge filter 37. In the illustrated embodiment, the liquid fuel edge filter 37 may be positioned within the inner fin 32. The gaseous fuel edge filter 36 is shown positioned within the outer fin 33. Those skilled in the art will recognize that the edge filters 36 and 37 may be arranged differently, or omitted, without departing from the scope of this disclosure.

[0012] Additionally on Fig. 5, a fuel injector 25 according to the present disclosure includes an injector body 100 defining a first nozzle outlet set 103, a second nozzle outlet set 104, and a drain outlet 105. The injector body 100 also defines a first fuel inlet 101 and a second fuel inlet 102, which in the sectional view of Fig. 4, which open through the common conical seat 27 of the fuel injector 25. Disposed within the injector body 100 are a first control chamber 106 and a second control chamber 107. A first check valve member 110 has a hydraulically closing surface 112 exposed to the fluid pressure in the first control chamber 106. The first check valve member 110 is movable between a closed position, as shown, in contact with a first seat 108 to fluidly block the first fuel inlet 101 from the first nozzle outlet set 103, and an open position out of contact with the first seat to fluidly connect the first fuel inlet 101 to the first nozzle outlet set 103 via a passage shown in the sectional view of Fig. 5 is not visible. A second check valve member 120 has a hydraulic closure surface 121 which is exposed to the fluid pressure in the second control chamber 107. The second check valve member 120 is movable between a closed position, as shown, in contact with a second seat 113 to fluidly block the second fuel inlet 102 from the second nozzle outlet set 104, and an open position out of contact with the second seat 113 to fluidly connect the second fuel inlet 102 to the second nozzle outlet set 104 via a passage which is not shown in the sectional view of Fig. 5. Thus, injection of a first fuel (e.g., natural gas) through the first nozzle outlet set 103 is enabled by movement of the first check valve member 110, while injection of the second fuel (e.g., liquid diesel) through the second nozzle outlet set 104 is enabled by movement of the second check valve member 120. Those skilled in the art will appreciate that the first and second nozzle outlet sets 103, 104 may each be considered to include six nozzle outlet sets arranged about respective centerlines in a manner known in the art. However, the nozzle outlet sets 103 and 104 may each include only one nozzle outlet or any number of nozzle outlets in any arrangement without departing from the scope of the present disclosure.

[0013] A first check valve member 130 is positioned within the injector body 100 and is movable along a common centerline 125 between a first position in contact with the flat seat 151, where the first control chamber 106 is fluidly blocked from the drain outlet 105, and a second position where the first control chamber 106 is fluidly connected to the drain outlet 105 via the control passage 133. When the first control chamber 106 is fluidly connected to the drain outlet 105, the pressure in the first control chamber 106 drops, relieving the pressure on the hydraulic closure surface 112, allowing the first check valve member 110 to lift to enable injection of the first fuel (e.g., natural gas) through the first nozzle outlet set 103.A second control valve member 135 is positioned within the injector body 100 and is movable along the common centerline 125 between a first position in contact with the flat seat 156, in which the second control chamber 107 is fluidly blocked from the drain outlet 105, and a position out of contact with the flat seat 156, in which the second control chamber 107 is fluidly connected to the drain outlet 105. When the second control chamber 107 is fluidly connected to the drain outlet 105, the fluid pressure acting on the hydraulic closure surface 121 is relieved, allowing the second check valve member 120 to lift to an open position to enable injection of the second fuel (e.g., liquid diesel) through the second nozzle outlet set 104.

[0014] In the illustrated embodiment, the second control valve member 135 is intersected by the common centerline 125, but the first control valve member 130 defines a bore 131 therethrough that is concentric with the common centerline 125. In the illustrated fuel injector 25, the respective control valve members 130, 135 can be moved to one of the corresponding first and second positions with the first and second electrical actuators 111, 122, respectively. The control valve members 130, 135 can be biased to the other of their respective first and second positions by a spring(s) 146, 147. In particular, a first armature 141 can be attached to a plunger 145 in contact with the first control valve member 130.The first armature 141, the plunger 145, and the first control valve member 130 may be biased to the position shown, which is in contact with the flat seat 151, by biasing the spring 146. The control valve member 130 may rotate slightly about an axis perpendicular to the common centerline 125 by action of a self-aligning feature 136 that allows the convex surface 137 to move on a concave bearing surface 138 each time the control valve member 130 contacts the flat seat 151. Thus, the first armature 141 may be said to be operatively connected or coupled to move the first control valve member 130, and a second armature 142 may be said to be operatively coupled to move the second control valve member 135 by means of a plurality of plungers 143. A common stator 144 separates the first armature 141 from the second armature 142.

[0015] The first control valve member 130 is in contact with and out of contact with the flat seat 151 at the first position and the second position, respectively. Similarly, the second control valve member 135 is in contact with and out of contact with the flat seat 156 at its first position and its second position, respectively. Either one or both of the seats 151 and 156 may be conical seats. The first control valve member 130 may be coupled or connected to move with the first armature 141 in response to de-energization of the lower coil attached to the common stator 144.When the lower coil attached to the common stator 144 is energized, the armature 141 and plunger 145 are lifted upward, allowing the high pressure in the control passage 133 to force the first control valve member 130 out of contact with the flat seat 151, thereby fluidly connecting the control chamber 106 to the drain outlet 105. The first control chamber 106 and the second control chamber 107 may always be fluidly connected to the second fuel inlet 102 via passages shown in the sectional view of FIG. Fig. 5 are not visible. In this way, the liquid diesel originating from the second fuel inlet 102 can be used as a control fluid to control the operation of the first check valve member 110 to enable gaseous fuel injections, and the second member 120 to enable liquid fuel injections.

[0016] A hydraulically locking seal 132 in the form of a ring, which is continuously fluidly connected to the second fuel inlet 102, may be useful to prevent the migration of gaseous fuel from the gas nozzle chamber 115 up into the control chamber 106. The gas nozzle chamber 115 is continuously fluidly connected to the first fuel inlet 101 via passages that are not in Fig. 5 are visible. Back to Fig. 4 and Fig. 5, the present disclosure teaches a strategy to prevent liquid fuel from migrating from the respective fuel injectors 25 to the gaseous fuel common rail 21. When the dual-fuel common rail system 20 is operating in a regular mode, the liquid fuel common rail 22 may be maintained at a medium-high pressure (e.g., about 40 MPa), and the gaseous fuel common rail 21 may be maintained at a medium-low pressure (e.g., about 35 MPa). This slight pressure differential is intended to prevent leakage of gaseous fuel into the liquid fuel portions of the fuel injector 25 and, consequently, into the entire dual-fuel common rail fuel system 20.The provision of the hydraulically locking seal 132 is another feature to prevent gaseous fuel from migrating to the liquid fuel side of the dual-fuel common rail system 20. Nevertheless, some leakage of liquid fuel onto the gas fuel side of the system could be expected during regular operating mode, but this small amount of leakage may be allowed to allow for proper lubrication of the moving parts. For example, a small amount of liquid diesel fuel may leak from the hydraulically locking seal 132 down into the gas nozzle chamber 115 during regular operating mode. This small amount of liquid diesel is expected to be expelled from the nozzle outlet set 103 with each gas injection event.This small amount of leaking liquid diesel may serve to assist in lubricating the guide movement of the first check valve member 110 and the seat 108 during regular operating mode.

[0017] The dual-fuel common rail system may also have a single-fuel operating mode in which only liquid diesel fuel is used to power the engine 10. This operating mode may be referred to as limp-home mode, as this mode is only preferable if there is any fault in the gaseous fuel system. According to the present disclosure, a fault may include a malfunction of one or more of the gas supply pressure control devices 16, a malfunction elsewhere in the dual-fuel common rail system 20, or may simply refer to a lack of sufficient gaseous fuel for continued operation in regular mode.When operating in a limp-home mode, the electronic control device 15 may maintain the liquid fuel common rail 22 at a high pressure (for example, approximately 80 MPa), while the pressure in the gaseous fuel common rail 21 may decrease and slowly drop to only atmospheric pressure. During the limp-home mode, the engine 10 is operated as a conventional diesel engine, with liquid diesel fuel injected through the nozzle outlet set 104 in sufficient quantities and at appropriate times to ignite by compression. On the other hand, during the regular operating mode, a relatively small pilot injection of diesel liquid through the nozzle outlet set 104 is expected to be ignited by compression to, in turn, ignite a much larger charge of gaseous fuel injected through the nozzle outlet set 103 to operate the engine 10 in a regular operating mode.Due to the higher pressure differential between the liquid fuel and the gaseous fuel that exists during the limp home mode of operation, more liquid fuel is expected to leak into the gas side of the dual-fuel common rail system 20 than would leak during a regular operating mode with a smaller pressure differential between the two fuels. Because little or no gaseous fuel is used during the limp home mode of operation, and because leakage of liquid fuel to the gaseous fuel side is greater, the present disclosure teaches the provision of a check valve 66 or 67 to prevent a buildup of leaked liquid diesel in the gas nozzle chamber 115 from eventually reaching and entering the gaseous fuel common rail 21. With particular reference to FIG. Fig. 4, a valve 66 may, in a specific embodiment, be located in the passageway extending from the first fuel inlet 101 to the gas nozzle chamber 115 within the respective fuel injector body 100. On the other hand, Fig. 4 also shows an alternative location where the check valve 67 may be located in the gaseous fuel passage 60, such as within the block 31. Those skilled in the art will appreciate that the check valve 66 or 67 blocks leaked liquid fuel from migrating to the gaseous fuel common rail 21 during a limp home mode of operation, but is open during the regular mode of operation and allows the free flow of gaseous fuel to the gas nozzle chamber 115.

[0018] Back on Fig. 1, although not required, the dual-fuel common rail system 20 may also include an electronically controlled isolation valve 46 operatively positioned between the gaseous fuel supply and pressure control devices 16 and the gaseous fuel common rail 21. The isolation valve 46 may be mechanically biased to a closed position but movable to an open position in response to a control signal from the electronic control device 15. When the dual-fuel common rail fuel system 20 is operating in a regular mode, the electronic control device 15 may maintain the isolation valve 46 in an open position.However, in the event that the system enters a limp-home mode of operation, the electronic control device 15 may close the isolation valve 46 to fluidly isolate the gas supply and pressure control devices 16 from any escaping liquid diesel fuel that may find its way onto the gas side of the dual-fuel common rail system 20.

[0019] The present disclosure recognizes that leaked liquid diesel fuel during limp home mode tends to increase the pressure in the gas fuel side of the dual-fuel common rail system 20. For example, the gas fuel side of the dual-fuel common rail system 20 may be designed to withstand a regular operating pressure (e.g., about 35 MPa), but may not reliably withstand or seal the higher liquid fuel pressures (e.g., about 80 MPa) associated with the liquid fuel common rail 22 during limp home mode. To prevent the gas fuel side of the dual-fuel common rail system 20 from becoming over-pressurized during a limp home mode of operation, the present disclosure teaches periodic small injections of accumulated leaked liquid fuel in the gas nozzle chamber 115 through the nozzle outlet set 103 into the engine cylinder 12.Due to the provision of the check valve(s) 66, 67, the pressure downstream of the check valve(s) 66 or 67 may be considerably higher than the residual pressure in the common rail 21 for gaseous fuel when operating in the limp home mode. Furthermore, the pressure downstream of the respective check valve(s) 66, 67 associated with different fuel injectors may vary due to different leakage rates. Thus, the present disclosure teaches a possible need for some experimentation to determine what leakage rates might be expected, as well as the expected variance around the average leakage rate, in order to determine potential worst-case scenarios regarding pressure buildup downstream of the check valve(s) 66, 67.This information could then be used to develop an open-loop control strategy to develop pressure downstream of the check valve(s) 66, 67 by opening the first check valve member 110 to inject liquid fuel from the gas nozzle outlet set 103 when engine cylinder conditions are suitable. For example, the present disclosure could also attempt to implement an injection strategy that avoids potential entrapment of cylinder gases into the gas nozzle chambers 115 of the individual fuel injectors. Thus, the frequency and timing of controlled injection events for lowering the liquid fuel pressure in the gas nozzle chamber 115 during the limp home mode of operation can be selected to prevent gas entrapment.Gas inflow and excessive pressure in one or more of the fuel injectors are avoided even under worst-case leakage rates. For example, a strategy could simply instruct liquid diesel fuel that has leaked into the gas nozzle chamber 115 to be injected in a short injection event at the beginning of each intake stroke in each engine cycle to ensure that the injected quantity is too small to cause any early ignition in the respective engine cylinder, but the frequency of the injections could be sufficient to prevent pressure buildup and potentially excessive pressure even under worst-case leakage scenarios.Furthermore, such a strategy could also ensure that no cylinder gases enter one or more of the fuel injectors 25 because the cylinder pressures are low and the leakage rate associated with one or more of the fuel injectors 25 may also be relatively low, resulting in a significant variance in pressure downstream of the respective check valve(s) 66, 67 between the different fuel injectors.

[0020] An alternative strategy could be to omit the check valve(s) 66, 67 and rely on pressure information transmitted from the pressure sensor 24 to the electronic control device 15 to controllably monitor the pressure and inject accumulated liquid diesel fuel by monitoring the possible increase in the common rail 21 for gaseous fuel as transmitted from a pressure sensor 24 ( Fig. 1). In other words, when the shutoff valve 46 is closed during a limp-home mode, leaked or ingressed liquid diesel fuel in the respective gas nozzle chamber 115 could be expected to slowly increase the pressure in the gaseous fuel common rail 21, as accumulated liquid has migrated from the respective fuel injectors to the gaseous fuel common rail 21. When the pressure in the gaseous fuel common rail 21 has reached a certain threshold (e.g., approximately 35 MPa), the various fuel injectors 25 could be actuated at appropriate times and for appropriate durations to utilize the accumulated pressure to force or inject accumulated leaked liquid diesel from the respective gas nozzle chambers 115 into the engine cylinders 12.Because the injection pressure would be known, and because the engine cylinders are predictable, the timing and duration of the injection events for injecting the leaked liquid diesel from the gas nozzle outlet sets could be selected to both avoid cylinder gas flow into the respective fuel injectors and to inject amounts that do not contribute significantly to the heat rejection or heat input into the individual cylinder, rather than undermining the control logic associated with the majority of the fuel delivery that occurs during the limp home mode of operation.

[0021] The present disclosure, in turn, recognizes that the liquid diesel leakage rate associated with the different fuel injectors 25 can vary considerably, resulting in a relatively high degree of uncertainty regarding which fuel injector 25 contributes most to the leakage and pressure buildup. Thus, an embodiment of the present disclosure could include both a check valve(s) 66, 67 and a shutoff valve 46. Additionally, the present disclosure recognizes that the pressure sensor 24 itself may be faulty, rendering a control strategy for injecting leaked diesel relatively unsustainable or unreliable.Thus, an embodiment of the present disclosure will include an open loop control strategy for injecting liquid diesel fuel accumulated downstream of each respective check valve 66, 67, and may or may not also include a closed loop control strategy that causes liquid injection events through the gas nozzle outlet sets 103 in response to a pressure in the gaseous fuel common rail 21 in a controlled manner.

[0022] The electronic control device 15 according to the present disclosure may include a limp-home algorithm configured to transmit liquid injection control signals for injecting liquid fuel from the liquid nozzle outlet sets 104 and gas injection control signals for injecting liquid fuel from the gas nozzle outlet sets 103. Additionally, the electronic control device 15 could be expected to include a regular algorithm configured to transmit liquid injection control signals for injecting liquid fuel from the liquid nozzle outlet set 104 and gas injection control signals for injecting gaseous fuel from the gas nozzle outlet set 103. The limp-home algorithm is also expected to be configured to maintain a high ratio of the liquid fuel common rail pressure to the gaseous fuel common rail pressure.Additionally, the regular algorithm could be configured to maintain a low ratio of the liquid fuel common rail pressure to the gaseous fuel common rail pressure. The limp home algorithm may or may not be configured to control the timing and / or duration of liquid fuel injection from the gas nozzle outlet set 103 in response to a gaseous fuel common rail pressure communicated to the electronic control device 15 from the pressure sensor 24.

[0023] In the illustrated embodiment, the first check valve member 110 and the second check valve member 120 move along corresponding lines parallel to, but spaced from, the common centerline 125. Nevertheless, those skilled in the art will recognize that the construction could vary. For example, double concentric check valve members concentric with the common centerline 125 would also be within the scope of the present disclosure. Industrial applicability

[0024] The present disclosure is broadly applicable to any engine that utilizes two fluidly distinct common rails to deliver fuel to a single fuel injector associated with each engine cylinder. The contents of the respective common rails may differ in either pressure and / or chemistry and / or phase without departing from the present disclosure. In the illustrated example, the respective common rails may differ in all three, containing pressurized natural gas fuel and liquid diesel fuel, respectively, at different pressures.The present disclosure is also applicable to a dual-fuel common rail system capable of operating in a regular mode utilizing both fuels, as well as in a limp-home mode in which the engine is supplied with only one of the fuels. For example, a limp-home mode may correspond to the use of liquid diesel fuel due to the unavailability of gaseous fuel. The present disclosure is particularly applicable to preventing overpressure of a gaseous fuel side of a dual-fuel common rail system due to leakage of liquid fuel from the liquid fuel side to the gaseous fuel side when operating in a limp-home mode.

[0025] Again with reference to all Fig. 1-5, a regular method of operating the dual-fuel engine 10 begins with mounting a dual-fuel common rail system 20 to an engine casing 11. Gaseous fuel is delivered to the gaseous fuel common rail 21 to each of the plurality of fuel injectors 25 through a respective coaxial spar assembly 30. Similarly, liquid fuel is delivered from a liquid fuel common rail 22 to each of the plurality of fuel injectors 25 through the same respective coaxial spar assemblies 30. In the regular mode of operation, gaseous fuel from each fuel injector 25 is injected into an engine cylinder 12 in response to a gaseous fuel injection signal communicated from the electronic engine controller 15 to the fuel injector 25.Liquid fuel from fuel injector 25 is injected directly into engine cylinder 12 from the same fuel injector 25 in response to a liquid fuel injection signal from electronic engine control unit 15. One method of operating dual-fuel engine 10 includes operating dual-fuel system 20 in a regular mode, preferably a majority of the time. Preferably, dual-fuel common rail system 20 is operated in a limp-home mode for a minor portion of the time, which may be due to a depleted gas fuel supply or some fault in the gas fuel system causing a switch to a single-fuel mode. In any event, one might expect more fuel to leak into the gas fuel portion of dual-fuel common rail system 20 when operating in limp-home mode compared to regular mode.When operating in regular mode, liquid fuel is injected from liquid nozzle outlet set 104, and gaseous fuel is injected from gas nozzle outlet set 103 into an engine cylinder 12. When operating the dual-fuel common rail system 20 in limp-home mode, liquid fuel is injected from liquid nozzle outlet set 104 into the engine cylinder 12, and liquid fuel, but not gaseous fuel, is injected from gas nozzle outlet set 103 into the engine cylinder 12. When operating in limp-home mode, the electronic control device 15 will operate to maintain a high ratio of the liquid fuel common rail pressure to the gaseous fuel common rail pressure, but will maintain the ratio low when the dual-fuel common rail system 20 is operating in regular mode.When operating in limp home mode, the check valve(s) 66, 67 will act to prevent leaked liquid fuel from reaching the gaseous fuel common rail 21. If a shutoff valve 46 is provided, the method of operation may include isolating the gas fuel supply and pressure control devices 16 from the gaseous fuel common rail 21 in limp home mode, but not in regular mode. Depending on preference or if desired, the timing and / or duration of injection of leaked liquid fuel from the gas nozzle outlet set 103 may be controlled in response to the pressure in the gaseous fuel common rail 21, such as a pressure communicated from the sensor 24 to the electronic control device 15.On the other hand, when the leaked liquid fuel is ejected or injected in an open loop manner, the timing and duration of injection of the leaked liquid fuel from the gas nozzle outlet set 103 can be controlled in terms of timing and / or duration without taking into account the pressure in the gaseous fuel common rail 21.

[0026] Now, with particular reference to Fig.6 illustrates an example of a fuel supply control algorithm 160 according to the present disclosure. The logic starts at oval box 163 and proceeds to block 164, where the electronic controller 15 would determine whether the dual-fuel common rail system 20 should be operated in a regular mode or in a limp home mode. If operation according to a regular algorithm 161 is intended, query 165 will advance the logic to block 166, where the isolation valve 46 is opened. In block 167, the electronic controller 15 will maintain the liquid fuel rail pressure at a medium-high level, such as 40 MPa. In block 168, the electronic controller 15 will maintain the gaseous fuel rail pressure at a medium-low level, such as 35 MPa.Depending on factors such as engine speed and load, and other considerations, the electronic controller 15 will determine liquid injection control signals at block 169. At block 170, the electronic controller 15 will determine gaseous injection control signals. For example, a typical regular operating mode might include a small pilot injection of liquid diesel fuel at or near top dead center of an individual cylinder 12. The small amount of liquid diesel fuel will immediately ignite through compression, and then the electronic controller will command a gaseous fuel injection event to deliver a much larger charge of gaseous fuel to the individual cylinder 12. The compression ignition of the pilot charge of liquid diesel fuel will serve to ignite the much larger charge of gaseous fuel.At query 171, the logic may query whether a gas system fault has occurred. For example, according to the present disclosure, a gas system fault could simply mean that the gas fuel supply is empty. Other gas fuel system faults include, but are not limited to, a malfunction of one or more of the gas supply and pressure control devices 16 or any other fault known in the art. If no gas system fault has occurred, the logic will return to block 167 and continue operation in regular mode according to the regular algorithm 161. On the other hand, if a gas system fault is detected, the logic may return to block 164 to again determine whether to continue operation in regular mode or to transition to a limp home mode of operation.

[0027] If query 165 determines that the system is operating in limp home mode, the logic will proceed to block 172 to begin execution of limp home algorithm 162. At block 172, the isolation valve 46 is closed. Next, the electronic controller 15 will maintain the liquid fuel rail pressure high, such as on the order of about 80 MPa. At block 174, the electronic controller 15 will determine liquid injection control signals to deliver the necessary fuel supply of liquid diesel to the engine 10 according to the engine speed and load requirements needed at a particular time. When operating in limp home mode, for example, much larger injections of liquid fuel are to be expected than might occur in regular operating mode. At block 175, a purge orAn open-loop liquid discharge control strategy from the gas side of the common rail fuel system 20 may be achieved by commanding gaseous fuel injection control signals to the individual fuel injectors 25 without considering the pressure in the gaseous fuel common rail 21. For example, small injections could occur periodically when cylinder pressures are appropriate to inject small amounts of leaked liquid diesel fuel from the individual fuel injectors 25 periodically to prevent a significant buildup of liquid diesel in the gas nozzle chambers 115 of the individual fuel injectors 25. In block 176, the electronic controller may sense or determine the gaseous fuel rail pressure through the sensor 24.If the gaseous fuel rail pressure has exceeded a certain threshold, such as 35 MPa, query 177 may determine that the gas side of the fuel system 20 is being overpressurized, and if so, a controlled purge or blast of leaked liquid fuel from the gas side of the fuel system may be achieved at block 178 by injecting leaked liquid fuel, but not gaseous fuel, from the gas nozzle outlet set 103 by communicating gas injection control signals to the individual fuel injectors 25. If query 177 returns a negative answer, meaning that the gaseous fuel common rail does not appear to be overpressurized, the logic may proceed to query 179 to determine if there has been a fault or failure of the gaseous fuel rail pressure sensor 24.If so, the logic may proceed to oval box 180 and terminate. On the other hand, if the query returns a negative result, the logic may return to block 173 and continue operating in the limp mode according to the limp mode algorithm 162.

Claims

[1] A method for operating a dual-fuel engine (10), comprising the following steps: Operating a dual-fuel common rail system (20) in a regular mode; Operating the dual-fuel common rail system (20) in an emergency mode; leaking more liquid fuel into a gas fuel part of the dual-fuel system (20) when operating in limp-home mode compared to regular mode; Injecting liquid fuel from a first nozzle outlet set (103) and injecting gaseous fuel from a second nozzle outlet set (104) into an engine cylinder (12) when the dual-fuel common rail system (20) is operating in regular mode; Injecting liquid fuel from the first nozzle outlet set (103) and injecting liquid fuel, but no gaseous fuel, from the second nozzle outlet set (104) into the engine cylinder (12) when the dual-fuel common rail system (20) is operating in limp home mode. [2] Method according to claim 1, comprising the following steps: Maintaining a ratio of the common rail pressure for liquid fuel to the common rail pressure for gaseous fuel high when the dual fuel system (20) is operating in limp home mode; Maintaining the ratio of the liquid fuel common rail pressure to the gaseous fuel common rail pressure low when the dual fuel system (20) is operating in regular mode; and blocking movement of liquid fuel into the gaseous fuel common rail (21). [3] A method according to claim 2, comprising isolating gas fuel supply and pressure control devices from the gaseous fuel common rail (21) in limp home mode, but not in regular mode; and controlling the timing and / or duration of liquid fuel injection from the second nozzle outlet set (104) in response to the gaseous fuel common rail pressure. [4] Method according to claim 1, which comprises controlling a time and / or a duration of an injection of liquid fuel from the second nozzle outlet set (104) taking into account the common rail pressure for gaseous fuel. [5] Dual-fuel common rail system (20), comprising: a common rail (21) for gaseous fuel; a common rail (22) for liquid fuel; a plurality of fuel injectors (25) each fluidly connected to both the gaseous fuel common rail (21) and the liquid fuel common rail (22); Liquid fuel supply and pressure control devices (17) fluidly connected to the liquid fuel common rail (22); Gas fuel supply and pressure control devices (16) fluidly connected to the gaseous fuel common rail (22); an electronic control device (15) in control communication with the plurality of fuel injectors (25), with the liquid fuel supply and pressure control devices (17) and with the gaseous fuel supply and pressure control devices (16), having a limp home algorithm (162) configured to generate liquid injection control signals for injecting liquid fuel from the first nozzle outlet set (103) and Gas injection control signals for injecting liquid fuel from a second nozzle outlet set (104), and comprising a regular algorithm (161) configured to transmit liquid injection control signals for injecting liquid fuel from the first nozzle outlet set (103) and To transmit gas injection control signals for injecting gaseous fuel from a second nozzle outlet set (104). [6] The dual-fuel common rail system (20) of claim 5, wherein the limp home algorithm (162) is configured to maintain a ratio of liquid fuel common rail pressure to gaseous fuel common rail pressure high; wherein the regular algorithm (161) is configured to keep the ratio of the liquid fuel common rail pressure to the gaseous fuel common rail pressure low; a check valve (66, 67) operatively positioned to block movement of liquid fuel from each of the plurality of fuel injectors (25) to the gaseous fuel common rail (21). [7] A dual fuel common rail system (20) as claimed in claim 6, including an electronically controlled shut-off valve (46) operatively positioned between the gaseous fuel supply and pressure control devices (16) and the gaseous fuel common rail (21). [8] The dual-fuel common rail system (20) of claim 7, including a gaseous fuel rail pressure sensor (24) in communication with the electronic control device (15); and wherein the limp home algorithm (162) is configured to control a timing and / or duration of liquid fuel injection from the second nozzle outlet (104) in response to a gaseous fuel common rail pressure. [9] The dual fuel common rail system (20) of claim 5 including a check valve (66, 67) operatively positioned to block movement of liquid fuel from each of the plurality of fuel injectors (25) to the gaseous fuel common rail (21). [10] The dual fuel common rail system (20) of claim 5, including a coaxial land assembly (30) fluidly positioned between each of the plurality of fuel injectors (25) and both the gaseous fuel common rail (21) and the liquid fuel common rail (22).

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