Systems and methods for reverse flow detection

Abstract

A system and method for reverse flow detection in a dual-fuel engine are disclosed. The engine may include an intake manifold, a liquid fuel supply line, and a gaseous fuel supply line, the gaseous fuel supply line including a gaseous fuel supply and a gaseous fuel rail. The method may include receiving sensed values ​​of a gaseous fuel supply pressure, an intake manifold pressure, and a gaseous fuel rail pressure; determining a threshold value based on the sensed value of the gaseous fuel supply pressure; determining reverse flow in the gaseous fuel supply line based on the sensed values ​​of the gaseous fuel supply pressure and the gas rail pressure and the determined threshold value; and outputting an indication of reverse flow in response to a determination of reverse flow.

Description

Technical Field

[0001] The present invention relates generally to dual fuel engines and, more particularly, to systems and methods for reverse flow detection in dual fuel engines. Background Art

[0002] Some internal combustion engines, known as dual-fuel engines, are configured to operate with two different fuels. For example, such engines can operate with both diesel fuel supplied through a diesel fuel supply system and natural gas supplied through a gas supply system. When switching from natural gas mode to diesel fuel-only mode, it is important to prevent reverse flow of air from the intake system into the gas supply system during diesel fuel-only mode. Reverse flow in the gas supply system could result in the creation of a flammable mixture, potentially posing a safety risk when the engine returns to natural gas mode.

[0003] U.S. Publication No. 2018 / 0149096 (the “'096 Publication”), published by Johns on May 31, 2018, describes a hybrid fuel supply system for diesel and other fuel-injected internal combustion engines. The system of the '096 Publication includes separate sources of liquid fuel and compressed hydrogen. The system includes a hydrogen supply module that calculates or “maps” an instantaneous liquid fuel demand based on engine size and capacity and at least one parameter output from an engine control unit (ECU). The system uses the mapped instantaneous liquid fuel demand to derive an instantaneous volume of hydrogen for addition to the engine's fuel injection system. The system further controls the hydrogen pressure to be suitable for mixing with the intake air at low engine speeds, and increases the hydrogen pressure when the air pressure in the intake manifold is boosted by a turbocharger. However, the system of the '096 Publication does not disclose a method for determining whether reverse flow occurs through the gas supply line.

[0004] The system and method for reverse flow detection of the present invention may solve one or more of the above problems and / or other problems in the art. However, the scope of the present invention is defined by the appended claims, rather than by the ability to solve any specific problem. Summary of the Invention

[0005] In one aspect, a method for detecting reverse flow in a dual-fuel engine is disclosed. The engine includes an intake manifold, a liquid fuel supply line, and a gaseous fuel supply line, the gaseous fuel supply line including a gaseous fuel supply and a gaseous fuel rail. The method may include receiving sensed values ​​of gaseous fuel supply pressure, intake manifold pressure, and gaseous fuel rail pressure; determining a threshold value based on the sensed value of the gaseous fuel supply pressure; determining reverse flow in the gaseous fuel supply line based on the sensed values ​​of the gaseous fuel supply pressure and the gas rail pressure and the determined threshold value; and outputting an indication of reverse flow in response to determining reverse flow.

[0006] In another aspect, a method for detecting reverse flow in a dual-fuel engine is disclosed, the engine comprising an intake manifold, a liquid fuel supply line, and a gaseous fuel supply line, the gaseous fuel supply line comprising a gaseous fuel supply and a gaseous fuel rail. The method may include: receiving sensed values ​​of gaseous fuel supply pressure, intake manifold pressure, and gaseous fuel rail pressure; comparing the sensed values ​​of the intake manifold pressure and the gaseous fuel supply pressure; determining a threshold value based on the sensed value of the gaseous fuel supply pressure when the intake manifold pressure is greater than the gaseous fuel supply pressure, wherein the threshold value is determined based on a mapping of empirical data representing threshold values ​​for the gaseous fuel supply pressure and at least one of the intake manifold pressure, engine load, or an amount of liquid fuel supplied to one or more cylinders of the engine; comparing the gaseous fuel rail pressure to the sensed value of the gaseous fuel supply pressure plus the threshold value; determining reverse flow in the gaseous fuel supply line when the gaseous fuel rail pressure is greater than or equal to the gaseous fuel supply pressure plus the threshold value; and outputting an indication of reverse flow in response to the determination of reverse flow.

[0007] In yet another aspect, a reverse flow detection system for a dual-fuel engine is disclosed. The system may include: an intake manifold for supplying intake air to the engine; a liquid fuel supply line for supplying liquid fuel to the engine; a gaseous fuel supply line including a gaseous fuel supply and a gaseous fuel rail for supplying gaseous fuel to the engine; and a controller configured to: receive sensed values ​​of gaseous fuel supply pressure, intake manifold pressure, and gaseous fuel rail pressure; determine a threshold value based on the sensed value of the gaseous fuel supply pressure; determine reverse flow in the gaseous fuel supply line based on the sensed values ​​of the gaseous fuel supply pressure and the gas rail pressure and the determined threshold value; and output an indication of reverse flow in response to a determination of reverse flow. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various exemplary embodiments and, together with the description, serve to explain the principles of the disclosed embodiments.

[0009] Figure 1 is a schematic diagram of a dual fuel engine system with a reverse flow detection system according to aspects of the present invention.

[0010] Figure 2 is used for Figure 1 Schematic diagram of an exemplary reverse flow detection system for a dual-fuel engine system.

[0011] Figure 3 Provides a description for detection Figure 1 A flow chart of an exemplary method of reverse flow of a system. DETAILED DESCRIPTION

[0012] The foregoing general description and the following detailed description are exemplary and illustrative only and do not limit the claimed features. As used herein, the terms "comprises," "comprising," "has," "having," "includes," "including," or other variations thereof are intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but may also include other elements not expressly listed or inherent to such process, method, article, or apparatus. In this disclosure, unless otherwise indicated, relative terms such as "about," "substantially," and "approximately" are used to indicate a possible variation of ±10% in the stated value.

[0013] Figure 1 A schematic diagram of a dual fuel engine system 10 with a reverse flow detection system 100 is shown. The dual fuel engine system 10 can be an internal combustion engine that can run on two fuels. For example, the dual fuel engine system 10 can use liquid fuel and / or gaseous fuel, or a combination of liquid fuel and gaseous fuel. Although diesel fuel is used in the exemplary embodiment, it should be understood that any type of liquid fuel can be used, such as gasoline, methanol, ethanol, or any other type of liquid fuel. Further, as used herein, "gaseous fuel" can include fuel supplied to the engine system 10 in gaseous form. The gaseous fuel can include, for example, natural gas, propane, biogas, landfill gas, carbon monoxide, hydrogen, or a mixture thereof. It should be understood that the engine system 10 can use only a single fuel (liquid or gaseous fuel) at a time, or can use both liquid fuel and gaseous fuel consistently.

[0014] like Figure 1 As shown, the dual fuel engine system 10 includes a diesel fuel delivery system 12 and a gaseous fuel delivery system 14. The dual fuel engine system 10 may also include an intake system 16 and a plurality of engine cylinders 18 ( Figure 118 ). A single engine cylinder 18 is depicted in FIG. 1 . A diesel fuel delivery system 12 can deliver diesel fuel to the cylinder 18, a gaseous fuel system 14 can deliver gaseous fuel to the cylinder 18, and an intake system 16 can deliver intake air to the cylinder 18, as described in further detail below. Each engine cylinder 18 can include a piston 20 slidably and reciprocally disposed to form a combustion chamber 22 of the cylinder 18. The piston 20 of each cylinder 18 can be connected to a crankshaft 24 via a connecting rod 26 and can provide power to a flywheel (not shown) of the engine system 10, as described in further detail below. The cylinder 18 can also include an intake port 28 for providing a mixture of air (e.g., intake air) and fuel (e.g., gaseous fuel) to the combustion chamber 22. The cylinder 18 can also include an exhaust port 30 for exhausting combustion gases from the cylinder 18 to an exhaust system 32.

[0015] The diesel fuel delivery system 12 may include a diesel fuel supply 36, such as a diesel fuel tank, a fuel pump, a fuel rail, and a diesel fuel supply line 38 for supplying diesel fuel from the supply 36 to the cylinders 18. For example, diesel fuel may be supplied to each cylinder 18 via a diesel fuel injector 40. It should be appreciated that the diesel fuel delivery system 12 may include any number and / or combination of valves or other components known in the art.

[0016] The gaseous fuel delivery system 14 may include a gaseous fuel supply 42 (e.g., a gas tank) and a gaseous fuel supply line 44 for supplying gaseous fuel from the supply 42 to the cylinders 18. For example, gaseous fuel may be supplied to each cylinder 18 through the intake system 16 via a gaseous fuel injector 46 (such as a solenoid-operated gas admission valve (SOGAV)), as described in further detail below. Thus, gaseous fuel may flow from the supply 42 through the supply line 44 into the intake system 16. The gaseous fuel delivery system 14 may also include a manual shutoff valve 43, a filter 48, a gaseous shutoff valve (GSOV) 50, a regulator 52, a gaseous fuel rail 54, and a check valve 56.

[0017] A manual shutoff valve 43 may be provided downstream of the supply 42. The valve 43 may include a ball valve or the like for preventing flow from the supply 42 into the gas fuel supply line 44 and toward the cylinder 18. Thus, the valve 43 may include a closed state for preventing flow from the supply 42 and an open state for allowing flow from the supply 42. The valve 43 may be manually actuated from an open state to a closed state to shut off or otherwise prevent the flow of gas fuel from the supply 42 to the cylinder 18. Similarly, the valve 43 may be manually actuated from a closed state to an open state to enable the flow of gas fuel from the supply 42 to the cylinder 18. Note that the valve 43 may be in an open state by default. The filter 48 may remove suspended liquids, dirt, and / or other particles from the gas fuel to prevent the suspended liquids, dirt, and / or other particles from clogging or damaging components of the gas fuel delivery system 14. A gas shutoff valve 50 may be provided in the gas fuel supply line 44 downstream of the supply 42. The valve 50 may include a closed state ( Figure 1 In the closed state, valve 50 can prevent gaseous fuel from supply 42 from flowing into supply line 44.

[0018] The valve 50 may include a check valve or the like for preventing flow from the supply 42 toward the cylinder 18 when the valve 50 is in a closed state, while allowing high-pressure flow in the opposite, reverse direction (e.g., if the pressure in the gaseous fuel supply line 44 is greater than the pressure of the supply 42). In an open state, the valve 50 may enable gaseous fuel to flow from the supply 42 into the supply line 44. In some embodiments, the valve 50 may include a solenoid-actuated valve such that the valve 50 may be automatically actuated in response to a signal received from, for example, the controller 104. The regulator 52 may include a valve for reducing and regulating the pressure of the gaseous fuel leaving the supply 42 and reducing the pressure to a predetermined level. The gaseous fuel rail 54 may distribute the gaseous fuel to the gaseous fuel injectors 46 ( Figure 1 Only one injector is shown.) It should be understood that valve 43, valve 50, regulator 52, and injector 46 may comprise any type of valve known in the art.

[0019] Check valve 56 can allow flow in one direction (e.g., from supply 42 toward intake system 16) and automatically prevent reverse flow or backflow. As used herein, "reverse flow" is any type of flow that returns upstream to gaseous fuel supply line 44 in the opposite direction (e.g., from intake system 16 toward supply 42). Check valve 56 can include any type of check valve, such as a ball check valve, a disc check valve, a diaphragm check valve, or any other type of valve for preventing flow in at least one direction.

[0020] Intake system 16 may include an air intake manifold 58. Intake manifold 58 may supply intake air to cylinders 18. In some embodiments, gaseous fuel supply line 44 may be connected to intake manifold 58 (e.g., via injectors 46) for providing gaseous fuel to intake manifold 58. Thus, intake manifold 58 may supply a gaseous fuel and air mixture to cylinders 18 (e.g., via intake ports 28). Intake system 16 may also include a turbocharger 60 and an air cooler 62. Turbocharger 60 may include a turbine and a compressor for compressing the intake air, and air cooler 62 may cool the compressed air. The turbine may also receive exhaust gas from exhaust ports 30 of cylinders 18. Thus, cooled compressed air or boosted air at high pressure may be provided to intake manifold 58, and therefore to cylinders 18, to promote greater energy production. It should be understood that intake system 16 may include any number of valves or other components and / or combinations thereof known in the art.

[0021] Reverse flow detection system 100 includes a controller 104 (such as an engine control module (ECM)) and a sensor system 34 connected to controller 104. Sensor system 34 may include one or more pressure sensors and one or more flow sensors. The pressure sensors and flow sensors may be existing sensors already installed in engine system 10. For example, sensor system 34 may include a first pressure sensor 64, a second pressure sensor 66, and a third pressure sensor 68, and may also include a flow sensor 70. First pressure sensor 64 may be located in gaseous fuel supply line 44, immediately downstream of gaseous fuel supply 42, and may sense gaseous fuel supply pressure. Second pressure sensor 66 may be located in intake manifold 58 and may sense intake manifold pressure. Third pressure sensor 68 may be located in gaseous fuel rail 54 and may sense gaseous fuel rail pressure. It should be understood that sensors 64, 66, and 68 may include any type of sensor for sensing pressure, such as a resistive sensor, a capacitive sensor, a piezoelectric sensor, an optical sensor, a micro-electromechanical system sensor, and the like.

[0022] A flow sensor 70 may be located in or otherwise connected to the gas fuel supply line 44, immediately downstream of the gas fuel supply 42, and may sense the flow of gas fuel in the gas fuel supply line 44. The flow sensor 70 may include, for example, a flow meter that measures the amount of gas fuel passing through the flow meter over a period of time to determine the flow rate (e.g., ft) of the gas fuel in the gas fuel supply line 44. 3 / hr). It should be understood that the flow sensor 70 may include any type of sensor for sensing or measuring the flow rate of the gaseous fuel, such as an obstruction-type flow meter, a derivation-type flow meter, an electromagnetic sensor, a volumetric sensor, a fluid dynamic sensor, a mass flow meter, etc. Further, the sensor system 34 may include any number and / or combination of sensors as needed.

[0023] Figure 2 A schematic diagram of an exemplary reverse flow detection system 100 for operation and / or control of at least a portion of a dual fuel engine system 10 is shown. The system 100 may include an input 102, a controller 104, and an output 106. The input 102 may include, for example, a gas fuel supply pressure (P SUPPLY ) signal 110, the intake manifold pressure (P IM ) signal 112, and the gaseous fuel rail pressure (P RAIL ) signal 114. While the exemplary embodiment includes signals 110-114 from various pressure sensors 64-68, it should be understood that input 102 may include other signals and / or derived values. For example, intake manifold pressure may be related to or otherwise correspond to engine load and the amount of liquid fuel injected or supplied to cylinder 18. Thus, input 102 may include an engine load signal and / or a liquid fuel signal. As used herein, "engine load" may be the ability of engine system 10 to produce power (e.g., torque) associated with a rated or maximum load at various speeds of engine system 10. Controller 104 may determine or derive engine load from various inputs, including, for example, intake manifold pressure, torque produced by engine system 10, speed of engine system 10, amount of liquid fuel injected into cylinder 18, or any other input. Further, controller 104 may control the amount of liquid fuel injected into cylinder 18 and, therefore, may determine or derive the amount of liquid fuel injected into cylinder 18. Output 106 may include, for example, a reverse flow indication signal. The controller 104 also includes a reverse flow detection module 108. Figure 3 As depicted, the reverse flow detection module 108 may receive the input 102 , implement the method 300 for detecting reverse flow, and control the output 106 .

[0024] The controller 104 may be embodied as a single microprocessor or multiple microprocessors, which may include means for detecting reverse flow in a dual fuel engine system. For example, the controller 104 may include a memory, an auxiliary storage device, a processor such as a central processing unit, or any other means for implementing the tasks consistent with the present invention. The memory or auxiliary storage device associated with the controller 104 may store data and / or software routines that may assist the controller 104 in performing its functions, such as Figure 3 The functions of the method 300 are implemented in accordance with the present invention. Furthermore, the memory or secondary storage device associated with the controller 104 may also store data received from the various inputs 102 associated with the reverse flow detection system 100. Many commercially available microprocessors can be configured to perform the functions of the controller 104. It should be understood that the controller 104 can readily be embodied as a general-purpose machine controller capable of controlling numerous other machine functions. Various other known circuits may be associated with the controller 104, including signal conditioning circuitry, communication circuitry, hydraulic or other actuation circuitry, and other suitable circuitry.

[0025] The controller 104 may also include stored and / or derived values ​​used by the module 108. For example, the stored values ​​may include an offset (e.g., a threshold) and a debounce time. The offset may include a first offset and a second offset. The first and second offsets may be fixed (e.g., constant, unchanging) scalar values ​​that are thresholds (e.g., pressure values) that are added to the gas fuel supply pressure (P SUPPLY ) value to avoid false trips in the reverse flow detection method 300. For example, the first offset may be a first threshold added to the gas fuel supply pressure during a first check, and the second offset may be a second threshold added to the gas fuel supply pressure during a second check, as described in detail below. According to one aspect of the present invention, in the event of a relatively low pressure from the gas supply 42 and / or when the gas supply 42 is shut off, for example, for P SUPPLY and P IM Using a constant, unchanging second threshold value for all pressure levels may not be sufficient to determine reverse flow during the second examination. For example, a constant, unchanging second threshold value for all pressure levels may allow for false positives (e.g., determining reverse flow when reverse flow is not actually present) and / or false negatives (e.g., not determining reverse flow when reverse flow is actually present) in some pressure levels.

[0026] Based on this, the present invention may include a map or lookup table that provides a variable second threshold value as a function of the gaseous fuel supply pressure and the intake manifold pressure. The second threshold value based on these variable maps can then be used to trigger a determination of reverse flow. For example, the map may be the intake manifold pressure (P IM ) relative to the gas fuel supply pressure (PSUPPLY ) are plotted as the x-axis and y-axis respectively. IM Relative to P SUPPLY The output of each value of is a value that module 108 can use to determine a corresponding second threshold value for reverse flow, as described in detail below. The information used to derive the second threshold value for the mapping or lookup table can be determined by empirical analysis. Such empirical data can be obtained, for example, by operating the test engine system 10 under predetermined conditions (e.g., under specific operating conditions) during, for example, bench testing. For example, the second threshold value can be related to P IM Relative to P SUPPLY It will be appreciated that the first threshold may be a constant, unchanging threshold and / or may also be a variable first threshold that is mapped (or in a lookup table) as a function of various inputs.

[0027] To help determine the second threshold and compare it with P IM Relative to P SUPPLY , module 108 may receive a gas fuel supply line flow signal from flow sensor 70 that indicates a flow rate in gas fuel supply line 44, in association with a value of . The flow threshold may include one or more flow thresholds in gas fuel supply line 44 for determining a threshold based on the mapping during testing. When gas fuel supply 42 is shut off, the flow threshold may be calibrated to account for a small amount of sensed flow in gas fuel supply line 44 due to sensor resolution.

[0028] During testing, the technician and / or module 108 may IM Relative to P SUPPLY For each test, the technician and / or module 108 may compare the flow rate in the gas fuel supply line 44 to the flow rate threshold. If the flow rate is greater than the threshold (e.g., reverse flow is actually present in the gas fuel supply line 44), the technician and / or module 108 may determine the value of P. IM Relative to P SUPPLY If the flow rate is less than the threshold value (eg, there is no reverse flow in the gas fuel supply line 44), the technician and / or module 108 may determine the second threshold value for P IM Relative to P SUPPLY The technician and / or module 108 may test the new second threshold value for P based on the flow rate sensed in the gas fuel supply line 44. IM Relative to P SUPPLY The second threshold can be improved for various values ​​of P. IM Relative to P SUPPLYAdditionally or alternatively, in some embodiments, the technician and / or module 108 may determine the second threshold by determining the point at which the flow indicates reverse flow. For example, the technician and / or module 108 may determine the second threshold at the moment (e.g., or shortly thereafter) when the flow rate becomes greater than the flow rate threshold.

[0029] Although the exemplary embodiment details the IM Relative to P SUPPLY However, it should be understood that a mapping or lookup table can provide a variable second threshold value as a function of the gaseous fuel supply pressure and various other inputs and / or values. For example, as detailed above, the intake manifold pressure is related to or otherwise corresponds to the engine load and / or the amount of liquid fuel injected. Thus, a mapping or lookup table can provide a variable second threshold value as a function of the gaseous fuel supply pressure and the engine load or the amount of liquid fuel injected. SUPPLY The engine load and relative to P SUPPLY A mapping or lookup table for the amount of fuel injected can be derived using techniques similar to those described above. It will be appreciated that a mapping or lookup table can provide a variable second threshold as a function of any type of input as desired.

[0030] The debounce time may include a predetermined time value for which a condition must be met within a predetermined amount of time to avoid a false trip in the reverse flow detection method 300 , as described in detail below.

[0031] The reverse flow indication signal output 106 may include controlling aspects of the engine system 10. For example, the reverse flow indication signal output 106 may include the controller 104 outputting a warning, such as a light, an audible warning, a warning on a display, etc., when a reverse flow condition is triggered. The reverse flow indication signal output 106 may also include the controller 104 adjusting the engine system 10. For example, the controller 104 may reduce or shut down the engine system 10 and / or may prevent or stop the engine system 10 from operating in the gaseous fuel mode.

[0032] Industrial Applicability

[0033] The disclosed aspects of the reverse flow detection system 100 of the present invention may be used in any dual fuel engine system 10 .

[0034] refer to Figure 1During operation of engine system 10, the engine system can be switched to a diesel fuel-only mode. During this switchover, controller 104 can send a signal to close gas shutoff valve 50 and injector 46, thereby preventing gaseous fuel from flowing from gas supply 42 through supply line 44. Additionally, or alternatively, as described above, valve 43 can be manually actuated to a closed position to shut off gas supply 42. In diesel fuel-only mode, only diesel fuel is supplied to cylinder 18. For example, controller 104 can control aspects of diesel fuel delivery system 12, such as opening a diesel fuel control valve to allow diesel fuel to flow through supply line 38 to cylinder 18 (e.g., through injector 40). Further, intake air from intake system 16 can be supplied to cylinder 18 via intake manifold 58. Thus, during the intake stroke of piston 20, an air and diesel fuel mixture can be drawn or forced into combustion chamber 22. The piston 20 can cycle through compression and power (combustion) strokes, and byproducts of combustion (e.g., exhaust gas) can be pushed through the exhaust port 30 during the exhaust stroke. As such, the piston 20 can drive the crankshaft 24 to provide useful mechanical work motion to the flywheel. Thus, the controller 104 can operate the engine system 10 in a diesel fuel-only mode via the supply line 38. During this diesel fuel-only mode, the injector 46, regulator 52, and gas shutoff valve 50 may not be sufficient or designed to prevent reverse flow through the supply line 44. Therefore, the check valve 56 prevents reverse flow of diesel fuel or intake air through the supply line 44.

[0035] Figure 3 A flow chart depicting an exemplary method 300 for detecting reverse flow in a dual fuel engine system 10 is shown. It should be understood that the steps of method 300 may be performed when the engine system 10 is operating in a diesel fuel only mode. In step 305, module 108 may receive sensor information. For example, module 108 may receive the gaseous fuel supply pressure (P SUPPLY ) signal 110, intake manifold pressure (P IM ) signal 112 and the gas fuel rail pressure (P RAIL ) signal 114. In some embodiments, module 108 may also receive or derive an engine load signal and / or a quantity of liquid fuel signal.

[0036] In step 310, the module 108 may perform a first check and compare the intake manifold pressure (P IM ) and gas fuel supply pressure (P SUPPLY ) plus the first threshold. In an exemplary embodiment, the first threshold may include a constant, unchanging first threshold (e.g., fixed). However, it should be understood that the first threshold may include a variable first threshold based on various inputs and / or may be omitted in some embodiments. If the intake manifold pressure (P IM) is less than the gas fuel supply pressure (P SUPPLY ) plus the first threshold (step 310: No), the module 108 can continue to receive sensor information. IM ) is greater than the gas fuel supply pressure (P SUPPLY ) plus a first threshold (eg, offset) (step 310: yes), the module 108 may determine a second threshold (step 315) and perform a second check (step 320). While the first check determines whether there is an inequality (P IM >P SUPPLY + first threshold), but it will be appreciated that the first check may include other variations of the inequality. For example, the first check may determine whether P IM -P SUPPLY > first threshold, and / or it may be determined whether P IM -First threshold>P SUPPLY .

[0037] In step 315, module 108 may generate a SUPPLY and P IM Determine the second threshold. For example, module 108 may receive P SUPPLY and P IM The value of P is obtained by using a mapping or lookup table as described above. SUPPLY and P IM In some embodiments, module 108 may determine the second threshold value based on the value of P SUPPLY and the engine load or the amount of liquid fuel injected into the cylinder 18 to determine the second threshold. For example, the module 108 may receive P SUPPLY and engine load or the amount of liquid fuel injected into the cylinder 18, and using a corresponding map or lookup table, as described above, based on the received P SUPPLY The second threshold is determined by the value of the engine load or the amount of liquid fuel injected into the cylinder 18 .

[0038] In step 320, when the second threshold has been determined, the module 108 may then perform a second check and compare the gaseous fuel rail pressure (P RAIL ) and gas fuel supply pressure (P SUPPLY ) plus a variable second threshold value based on the mapping. The module 108 may continuously receive sensor information (step 305), then perform a first check (step 310), determine a second threshold value (step 315), and / or if the gas fuel rail pressure (P RAIL ) is not greater than the gas fuel supply pressure (P SUPPLY ) plus the second threshold (step 320: No), then a second check is performed (step 320). If the gas fuel rail pressure (P RAIL) is greater than or equal to the gas fuel supply pressure (P SUPPLY ) plus a second threshold (eg, offset) (step 320: YES), the module 108 may determine reverse flow in the gas fuel supply line 44. While the second check determines whether there is an inequality (P RAIL ≥P SUPPLY + second threshold), but it will be appreciated that the second check may include other variations of the inequality. For example, the second check may determine P RAIL -P SUPPLY ≥ second threshold, and / or it may be determined that P RAIL - Second threshold ≥ P SUPPLY .

[0039] In response to the determination of reverse flow, the module 108 may output an indication of reverse flow in step 325. For example, the module 108 (via the controller 104) may send a warning signal to a display or other user interface, reduce the power of the engine system 10, and / or send a signal to shut down the engine system 10.

[0040] When in diesel fuel only mode, if the check valve 56 fails, intake air can flow back into the supply line 44. When intake air leaks past the check valve 56 into the gaseous fuel supply line 44, the gaseous fuel supply pressure (P SUPPLY ) can be reduced to the intake manifold pressure (P IM ) below. Similarly, the gas fuel rail pressure (P RAIL ) can be increased to the gas fuel supply pressure (P SUPPLY ) or more. If the intake air flows back into the gaseous fuel supply line 44, the intake air may mix with the gaseous fuel in the gaseous fuel supply line 44. Therefore, when the engine is again operated in the gaseous fuel mode, a combustible mixture may be produced due to the excess air in the gaseous fuel and air mixture. The module 108 may perform a first check for redundancy (step 310) to avoid a false trip when a reverse flow is detected. For example, if the gaseous fuel supply pressure (P SUPPLY ) is greater than the intake manifold pressure (P IM ), there will be no reverse flow of intake air into the gaseous fuel supply line 44. However, if the check valve 56 is functioning correctly (eg, not leaking), then even if the intake manifold pressure (P IM ) is greater than the gas fuel supply pressure (P SUPPLY ) will also not have reverse flow (e.g., check valve 56 will prevent reverse flow into supply line 44). Therefore, when intake air flows back into supply line 44 (e.g., check valve 56 is leaking), the gaseous fuel rail pressure (P RAIL ) will increase to the intake manifold pressure (P IM) or higher. Therefore, module 108 may perform a second check (step 320) to determine whether check valve 56 has failed (e.g., check valve 56 is leaking) and intake air is flowing reversely into supply line 44. Although both the first and second checks are performed by module 108 in the exemplary embodiment, it should be understood that module 108 may only perform the second check (step 320) to determine reverse flow in gaseous fuel supply line 44.

[0041] To avoid false tripping when reverse flow is determined, the module 108 may also include a predetermined debounce time. For example, the module 108 may calculate the intake manifold pressure (P IM ) and gas fuel supply pressure (P SUPPLY ) plus a first threshold value (eg, a predetermined offset) for comparison. IM ) is greater than the gaseous fuel supply pressure (P SUPPLY ) plus the first threshold (step 310), the module 108 may determine a second threshold (step 315) and perform a second check (step 320). Similarly, if the gaseous fuel rail pressure (P RAIL ) is greater than or equal to the gas fuel supply pressure (P SUPPLY ) plus a second threshold (step 320), the module 108 can determine reverse flow in the gas fuel supply pipeline 44.

[0042] The reverse flow detection system 100 may enable detection of reverse flow in the gaseous fuel delivery system 14. For example, the reverse flow detection system 100 may detect and / or indicate that the check valve 56 or other valve in the gaseous fuel supply line 44 is malfunctioning or has malfunctioned, and that intake air (e.g., charge air) is leaking into the gaseous fuel delivery system 14. Further, the reverse flow detection system 100 may be robust because it may be configured for P SUPPLY and P IM Different thresholds are determined for various values ​​of the gas flow rate, engine load, or the amount of liquid fuel injected into the cylinder 18. Thus, false tripping of reverse flow detections can be prevented, and false negatives where no reverse flow is detected can be avoided. Thus, when / if reverse flow occurs in the gaseous fuel delivery system 14, the reverse flow detection system 100 can help mitigate and / or prevent safety risks associated with combustible mixtures. Furthermore, the reverse flow detection system 100 can utilize existing sensors of the engine system 10, and thus, no additional components may be required or added.

[0043] It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed system without departing from the scope of the present invention. Other embodiments of the system will become apparent to those skilled in the art through consideration of the specification and practice of the system disclosed herein. It is intended that the specification and examples be considered exemplary only, with the true scope of the invention being indicated by the following claims and their equivalents.

Claims

1. A method for detecting reverse flow in a dual fuel engine, the engine comprising an intake manifold, a liquid fuel supply line, and a gaseous fuel supply line, the gaseous fuel supply line comprising a gaseous fuel supply and a gaseous fuel rail, the method comprising: receiving sensed values ​​of gaseous fuel supply pressure, intake manifold pressure, and gaseous fuel rail pressure; determining a threshold value based on said sensed value of the gaseous fuel supply pressure; determining reverse flow in the gaseous fuel supply line based on the sensed values ​​of gaseous fuel supply pressure and gas rail pressure and the determined threshold value; as well as An indication of reverse flow is output in response to the determination of reverse flow.

2. The method of claim 1 , wherein the threshold is determined based on a map of empirical data representing thresholds for gaseous fuel supply pressure and at least one of intake manifold pressure, engine load, or an amount of liquid fuel supplied to one or more cylinders of the engine.

3. The method according to any one of the preceding claims, wherein said determining said reverse flow comprises: comparing the sensed value of the gaseous fuel rail pressure to the gaseous fuel supply pressure plus the threshold; as well as Reverse flow in the gaseous fuel supply line is determined when the gaseous fuel rail pressure is greater than or equal to the gaseous fuel supply pressure plus the threshold.

4. The method of claim 3, wherein said comparison of said sensed value of gaseous fuel rail pressure and gaseous fuel supply pressure plus said threshold value is a second check, and Wherein said determination of reverse flow further comprises a first check including a comparison of intake manifold pressure and said sensed value of gaseous fuel supply pressure.

5. The method of claim 4, wherein the threshold is a second threshold, and the first checking comprises: comparing the sensed values ​​of intake manifold pressure and gaseous fuel supply pressure plus a first threshold; as well as The intake manifold pressure is determined to be greater than the gaseous fuel supply pressure plus the first threshold before determining the second threshold.

6. The method according to claim 5, further comprising: It is determined that the intake manifold pressure is greater than the gaseous fuel supply pressure plus the first threshold for a predetermined amount of time prior to determining the second threshold.

7. The method according to claim 5, further comprising: The reverse flow in the gaseous fuel supply line is determined when the gaseous fuel rail pressure is greater than or equal to the gaseous fuel supply pressure plus the second threshold for a predetermined amount of time.

8. The method of any preceding claim, wherein said outputting said indication comprises shutting down said engine.

9. A reverse flow detection system for a dual-fuel engine, comprising: an intake manifold for supplying intake air to the engine; a liquid fuel supply line for supplying liquid fuel to the engine; a gaseous fuel supply line including a gaseous fuel supply and a gaseous fuel rail for supplying gaseous fuel to said engine; as well as A controller configured to: receiving sensed values ​​of gaseous fuel supply pressure, intake manifold pressure, and gaseous fuel rail pressure; determining a threshold value based on said sensed value of the gaseous fuel supply pressure; determining reverse flow in the gaseous fuel supply line based on the sensed values ​​of gaseous fuel supply pressure and gas rail pressure and the determined threshold value; as well as An indication of reverse flow is output in response to the determination of reverse flow.

10. The system of claim 9, wherein the threshold is determined based on a map of empirical data representing thresholds for gaseous fuel supply pressure and at least one of intake manifold pressure, engine load, or an amount of liquid fuel supplied to one or more cylinders of the engine.

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