Dual fuel engine control system and dual fuel engine control method

Abstract

To provide a control system of a dual fuel engine suitable for a one-machine / one-axis type marine power system, and a control method of the dual fuel engine.SOLUTION: A control system 3 of a dual fuel engine comprises: an electronic governor 32 having a liquid fuel operation mode and a fuel gas operation mode; a mechanical governor 37 having a backup operation mode; and a liquid fuel adjustment mechanism 38 for selecting either of a liquid fuel injection command which is inputted via the electronic governor 32, and a backup liquid fuel injection command which is inputted via the mechanical governor 37, and increases and decreases a supply quantity of liquid fuel. When there occurs a malfunction at least at either of the liquid fuel operation mode by the electronic governor 32, and the fuel gas operation mode, the liquid fuel adjustment mechanism 38 switches an operation mode to the backup operation mode by the mechanical governor 37.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a control system for a dual fuel engine and a control method for a dual fuel engine. [Background technology]

[0002] The most important requirement for a ship's power system is redundancy. This is because, unlike a car, if an engine malfunction occurs during a voyage and the ship stops operating, there is a risk of distress. Therefore, a ship's power system needs a method to continue operation or a method to immediately repair the system when an abnormality occurs.

[0003] As one solution to this problem, the marine power system described in Patent Document 1 employs a dual-engine, dual-shaft system. The dual-engine, dual-shaft system is a system in which a single vessel has two power systems, each including a propeller, clutch, dual fuel engine, etc., and if an abnormality occurs in one system, the other system continues to operate, allowing the vessel to return to port or undergo repairs. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 175951 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, due to the cost and downsizing of ships, there is a demand for single-engine, single-shaft marine power systems using dual fuel engines. The single-engine, single-shaft system is a system in which only one power system is used in one ship, and it is not possible to continue operation by switching the system as in the case of the two-engine, two-shaft system. In particular, the control system of a dual fuel engine is equipped with an electronic governor to switch between liquid fuel operation mode and fuel gas operation mode, and a method of continuing operation is required even if an abnormality occurs in this electronic governor.

[0006] The present invention has been made in consideration of the above problems, and has an object to provide a dual-fuel engine control system and a dual-fuel engine control method suitable for a single-engine, single-shaft marine power system. [Means for solving the problem]

[0007] A control system for a dual-fuel engine according to one aspect of the present invention includes a dual-fuel engine having a liquid fuel injection valve that injects liquid fuel and a fuel gas injection valve that injects fuel gas, an electronic governor having a liquid fuel operation mode for operating the dual-fuel engine with the liquid fuel and a fuel gas operation mode for operating the dual-fuel engine with the fuel gas, a mechanical governor having a backup operation mode for operating the dual-fuel engine with the liquid fuel, and a liquid fuel regulating mechanism that selects one of a liquid fuel injection command input via the electronic governor and a backup liquid fuel injection command input via the mechanical governor and increases or decreases the amount of liquid fuel supplied, and when an abnormality occurs in at least one of the liquid fuel operation mode and the fuel gas operation mode controlled by the electronic governor, the liquid fuel regulating mechanism switches to the backup operation mode controlled by the mechanical governor.

[0008] The dual fuel engine control system according to this embodiment incorporates two systems, an electronic governor and a backup mechanical governor, to provide a duplicated control system. Therefore, when an abnormality occurs in at least one of the liquid fuel operation mode and the fuel gas operation mode by the electronic governor, control is switched to the backup mechanical governor, allowing the dual fuel engine to continue operating using liquid fuel. This makes it possible to establish a dual fuel engine control system suitable for a single-engine, single-shaft marine power system.

[0009] In the above-described dual fuel engine control system, the liquid fuel regulating mechanism may select one of the liquid fuel injection command and the backup liquid fuel injection command, whichever has a lower command value.

[0010] In the normal liquid fuel operation mode, the liquid fuel adjustment mechanism receives two commands: a liquid fuel injection command from the electronic governor and a backup liquid fuel injection command input via the mechanical governor, and selects the one with the lower command value to operate. Therefore, if an abnormality occurs in either governor, the control entity switches over, preventing the engine from stalling.

[0011] In the above-described dual-fuel engine control system, the electronic governor may decrease the output electrical signal when increasing the command value of the liquid fuel injection command, and increase the output electrical signal when decreasing the command value of the liquid fuel injection command.

[0012] In this case, if an abnormality such as a break occurs in the signal line of the electronic governor, the electrical signal input from the electronic governor becomes zero. This causes the command value of the liquid fuel injection command to reach its maximum, and the liquid fuel regulating mechanism selects a backup liquid fuel injection command with a lower command value, so that the control entity can automatically switch to the mechanical governor. Also, in this case, no special sensors or signals are required to switch the control entity.

[0013] In the above-mentioned dual fuel engine control system, the backup liquid fuel injection command Command value of To, The command value is set to be higher than the liquid fuel injection command. Equipped with a signal converter that adds a correction value Etc. Good too.

[0014] In this case, since a predetermined correction value is added to the backup liquid fuel injection command, the liquid fuel regulating mechanism always selects and operates on the liquid fuel injection command from the electronic governor, which makes it possible to prevent unintentional switching to control of the backup mechanical governor in the normal liquid fuel operation mode.

[0015] In the above-mentioned dual fuel engine control system, when the backup liquid fuel injection command is selected by the liquid fuel adjusting mechanism, the signal converter outputs the backup liquid fuel injection command Command value of The addition of the correction value to the

[0016] If control were to be switched from the electronic governor to the mechanical governor while a correction value was being added to the backup liquid fuel injection command, the command value input to the liquid fuel injector would jump up, causing the rotation speed of the dual fuel engine to increase sharply.For this reason, by stopping the addition of the correction value when control is switched from the electronic governor to the mechanical governor, it is possible to suppress fluctuations in the rotation speed of the dual fuel engine, enabling a smooth switchover of the control entity.

[0017] In the above-mentioned dual fuel engine control system, the signal converter outputs the backup liquid fuel injection command Command value of The correction value for the load on the rotation speed of the dual fuel engine is When the load on the rotation speed of the dual fuel engine is small, the load is increased. You may do so.

[0018] If a correction value is set to minimize the increase in rotation speed that occurs when switching from an electronic governor to a mechanical governor when the load on the rotation speed of the dual-fuel engine is high, the increase in rotation speed may be large when switching from the electronic governor to the mechanical governor when the load on the rotation speed of the dual-fuel engine is low. For this reason, by making it possible to change the correction value added to the backup liquid fuel injection command according to the load on the rotation speed, it is possible to suppress fluctuations in the rotation speed of the dual-fuel engine.

[0019] In the above-mentioned dual fuel engine control system, in the fuel gas operation mode, the signal converter outputs the backup liquid fuel injection command Command value of The addition of the correction value to may be increased.

[0020] When switching from the fuel gas operation mode to the liquid fuel operation mode, the rotation speed of the dual fuel engine temporarily drops while fuel gas injection is reduced and the injection of the amount of liquid fuel required to maintain the rotation speed is started. For this reason, the command value of the liquid fuel injection command immediately after switching to the liquid fuel operation mode becomes high, but at this time, it may exceed the command value of the backup liquid fuel injection command from the mechanical governor, which has a lower responsiveness than the electronic governor. For this reason, by setting the correction value added to the backup liquid fuel injection command to a larger correction value than normal in the fuel gas operation mode, it is possible to prevent unintentional switching to control of the backup mechanical governor.

[0021] In the above-described dual fuel engine control system, the signal converter may return to the original correction value after a predetermined time has elapsed since the fuel gas operation mode was switched to the liquid fuel operation mode.

[0022] In this case, after a predetermined time has elapsed since switching from the fuel gas operation mode to the liquid fuel operation mode, once the rotation speed of the dual-fuel engine has settled down, the correction value added to the backup liquid fuel injection command can be restored to its original value, thereby returning the system to the normal state.

[0023] In the above-mentioned dual fuel engine control system, in the liquid fuel operation mode, the signal converter outputs the liquid fuel injection command The command value of Increase per unit time This prevents the command value of the liquid fuel injection command from exceeding the command value of the backup liquid fuel injection command that has not yet reached its full potential. Furthermore, the correction value may be increased by adding it to the backup liquid fuel injection command.

[0024] When the command value of the liquid fuel injection command input via the electronic governor suddenly increases, it may exceed the command value of the backup liquid fuel injection command from the mechanical governor, which has a lower responsiveness than the electronic governor. Therefore, by setting the correction value added to the backup liquid fuel injection command to a larger correction value than normal, it is possible to prevent unintentional switching to control of the backup mechanical governor.

[0025] The control system for a dual fuel engine according to one aspect of the present invention may increase the addition of the correction value and then return it to the original correction value after a predetermined time has elapsed.

[0026] In this case, after a predetermined time has elapsed since the correction value was increased, once the rotation speed of the dual-fuel engine has settled down, the correction value added to the backup liquid fuel injection command can be returned to its original state, thereby restoring the normal state.

[0027] The control system for the dual fuel engine is 、 The electronic governor may send a liquid fuel injection command corresponding to a rotational speed of the dual fuel engine being zero to stop injection from the liquid fuel injection valve, and the fuel gas injection valve may increase or decrease the amount of fuel gas supplied based on the fuel gas injection command input via the electronic governor.

[0028] Even in the normal fuel gas operation mode, two types of commands are input to the liquid fuel regulation mechanism: a liquid fuel injection command from the electronic governor and a backup liquid fuel injection command input via the mechanical governor. Since the electronic governor transmits a liquid fuel injection command corresponding to a rotation speed of zero, the liquid fuel regulation mechanism selects the command value of the electronic governor, which is the lower command value, and stops injection from the liquid fuel injector. Therefore, when an abnormality occurs in the electronic governor, the control entity switches, and it is possible to prevent the engine from stalling.

[0029] In the above-mentioned dual fuel engine control system, in the fuel gas operation mode, the electronic governor may increase the output electrical signal when increasing the command value of the fuel gas injection command, and decrease the output electrical signal when decreasing the command value of the fuel gas injection command.

[0030] If an abnormality such as a break occurs in the signal line of the electronic governor, the electrical signal input from the electronic governor becomes zero. When this happens, the command value of the fuel gas injection command also becomes zero, and the operation of the fuel gas injection valve stops. Meanwhile, the liquid fuel regulation mechanism selects a backup liquid fuel injection command with a lower command value, so that the main control entity can automatically switch to the mechanical governor.

[0031] A control method for a dual-fuel engine according to one aspect of the present invention includes a dual-fuel engine including a liquid fuel injector that injects liquid fuel and a fuel gas injector that injects fuel gas, an electronic governor having a liquid fuel operation mode for operating the dual-fuel engine with the liquid fuel and a fuel gas operation mode for operating the dual-fuel engine with the fuel gas, a mechanical governor having a backup operation mode for operating the dual-fuel engine with the liquid fuel, and , the lower the command valueand a liquid fuel adjusting mechanism for increasing or decreasing the amount of liquid fuel supplied, the electronic governor decreases an output electrical signal when increasing a command value of the liquid fuel injection command, and increases an output electrical signal when decreasing a command value of the liquid fuel injection command, When an abnormality occurs in at least one of the liquid fuel operation mode and the fuel gas operation mode controlled by the electronic governor, the operation mode is switched to the backup operation mode controlled by the mechanical governor.

[0032] The control method for a dual-fuel engine according to this aspect incorporates two systems, an electronic governor and a backup mechanical governor, to duplicate the control system. When an abnormality occurs in at least one of the liquid fuel operation mode and the fuel gas operation mode by the electronic governor, control is switched to the backup mechanical governor to continue operation of the dual-fuel engine using liquid fuel. This makes it possible to establish a control method for a dual-fuel engine suitable for a single-engine, single-shaft marine power system. Effect of the Invention

[0033] According to the above aspect of the present invention, it is possible to provide a dual-fuel engine control system and a dual-fuel engine control method suitable for a single-engine, single-shaft marine power system. [Brief description of the drawings]

[0034] [Figure 1] 1 is a configuration diagram of a marine vessel power system according to an embodiment; [Diagram 2] 1 is a configuration diagram of a marine vessel equipped with a marine vessel power system according to an embodiment. [Diagram 3] FIG. 4 is an explanatory diagram illustrating the operation of a liquid fuel operation mode of a dual-fuel engine according to one embodiment. [Figure 4] FIG. 4 is an explanatory diagram illustrating the operation of a fuel gas operation mode of a dual-fuel engine according to one embodiment. [Diagram 5] FIG. 1 is a configuration diagram of a control system according to an embodiment. [Figure 6]5 is a graph showing changes in each command value and rotation speed in a liquid fuel operation mode according to one embodiment. [Figure 7] 6 is a graph showing changes in each command value and rotation speed in a fuel gas operation mode according to one embodiment. [Figure 8] FIG. 2 is a diagram illustrating an example of an abnormality that occurs in an electronic governor of a control system according to an embodiment. [Figure 9] 5 is a graph showing changes in each command value and rotation speed when an abnormality occurs in an electronic governor in a liquid fuel operation mode according to one embodiment. [Figure 10] 11 is a graph showing changes in each command value and rotation speed when an abnormality occurs in an electronic governor in a fuel gas operation mode according to one embodiment. [Figure 11] 11 is a graph showing changes in each command value and rotation speed when a problem occurs when switching from a fuel gas operation mode to a liquid fuel operation mode according to one embodiment. [Figure 12] 13 is a graph showing changes in each command value and the rotation speed when a correction value to be added to a backup liquid fuel injection command is changed to a second correction value in a fuel gas operation mode according to one embodiment. [Figure 13] 11 is a graph showing changes in each command value and rotation speed when the increase in the liquid fuel injection command per unit time is large and problematic in a liquid fuel operation mode according to one embodiment. [Figure 14] 11 is a graph showing changes in each command value and rotation speed when the correction value added to the backup liquid fuel injection command is changed to a third correction value in a liquid fuel operation mode according to one embodiment when the increase per unit time of the liquid fuel injection command is large. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, an example is given of the dual-fuel engine control system of the present invention being applied to a single-engine, single-shaft marine power system; however, the control system may also be applied to systems other than single-engine, single-shaft marine power systems.

[0036] Fig. 1 is a configuration diagram of a marine vessel power system 1 according to one embodiment. Fig. 2 is a configuration diagram of a marine vessel 100 equipped with the marine vessel power system 1 according to one embodiment. As shown in FIG. 1, a marine power system 1 includes a dual fuel engine 2 and a control system 3 thereof.

[0037] The dual-fuel engine 2 is capable of switching between a liquid fuel operation mode in which it runs on liquid fuel and a fuel gas operation mode in which it runs on fuel gas under the control of the control system 3, except when it is started or stopped.

[0038] The control system 3 starts the dual fuel engine 2 in the liquid fuel operation mode, and after it is confirmed that a gas pressure equal to or greater than a reference value is being supplied, switches the operation mode to the fuel gas operation mode using fuel gas. When the vessel 100 is stopped, the control system 3 switches the operation mode back to the liquid fuel operation mode before shutting it down.

[0039] The dual-fuel engine 2 includes a crankshaft 13, a piston 14 connected to the crankshaft 13, a cylindrical cylinder block 15 that guides the piston 14, and a cylinder head 16 that closes the upper end opening of the cylinder block 15. The crankshaft 13 is connected to a rotating shaft of a propeller 101 of a boat 100 shown in FIG.

[0040] The piston 14, the cylinder block 15, and the cylinder head 16 form a combustion chamber 17 of the dual fuel engine 2. A liquid fuel injector 11 that injects liquid fuel into the combustion chamber 17 is provided in the cylinder head 16. An ignition device 18 is also provided in the cylinder head 16. The ignition device 18 is, for example, a micro pilot oil injection valve, and is used in the fuel gas operation mode.

[0041] An intake valve 19 and an exhaust valve 20 are also installed in the cylinder head 16. An intake pipe 21 is connected to an intake port in which the intake valve 19 is installed in the cylinder head 16. An exhaust pipe 22 is connected to an exhaust port in which the exhaust valve 20 is installed in the cylinder head 16. A fuel gas injection valve 12 that injects fuel gas therein is installed in the intake pipe 21.

[0042] An air cooler 23 is installed in the intake pipe 21 upstream of the fuel gas injection valve 12. In addition, a turbocharger 24 is installed in the intake pipe 21 upstream of the air cooler 23. The turbocharger 24 includes a turbine that is rotated by at least a portion of the exhaust gas supplied from the exhaust pipe 22, and a compressor that is connected to the turbine via a rotating shaft and supplies compressed air to the intake pipe 21.

[0043] As shown in Fig. 2, the ship 100 is equipped with a single-engine, single-shaft ship power system 1 (main engine) and its auxiliary engine 102. The auxiliary engine 102 is an engine that generates electricity by driving a generator 103. The generator 103 supplies electric power to the ship power system 1 and other onboard equipment 105 via an inboard bus 104.

[0044] FIG. 3 is an explanatory diagram illustrating the operation of the dual-fuel engine 2 in the liquid fuel operation mode according to one embodiment. As shown in Fig. 3, in the liquid fuel operation mode, liquid fuel such as heavy oil is injected from the liquid fuel injector 11 into the combustion chamber 17, and the compressed air compressed by the piston 14 is ignited and burned. At this time, the fuel gas injector 12 is stopped.

[0045] FIG. 4 is an explanatory diagram illustrating the operation of the dual-fuel engine 2 in the fuel gas operation mode according to one embodiment. As shown in Figure 4, in fuel gas operation mode, Fuel gas injector 12Fuel gas such as natural gas is injected into the intake pipe 21 from the engine, and is premixed with air just before the combustion chamber 17. Next, liquid fuel for ignition is injected from the ignition device 18 into the combustion chamber 17, and the premixed gas compressed by the piston 14 is ignited and burned. At this time, the liquid fuel injection valve 11 is stopped.

[0046] FIG. 5 is a configuration diagram of a control system 3 according to an embodiment. As shown in FIG. 5, the control system 3 includes a rotation command unit 31, an electronic governor 32, a fuel gas injection valve driver 33, a PLC (Programmable Logic Controller) 34, a signal converter 35, an electro-pneumatic converter 36, a mechanical governor 37, and a liquid fuel adjustment mechanism 38.

[0047] The rotation command unit 31 outputs a rotation command S1 that controls the rotation speed of the dual-fuel engine 2. In this embodiment, the rotation command unit 31 outputs the rotation command S1 in response to a handle operation.

[0048] The electronic governor 32 is the main controller of the control system 3, and has a liquid fuel operation mode in which the dual-fuel engine 2 is operated with liquid fuel, and a fuel gas operation mode in which the dual-fuel engine 2 is operated with fuel gas.

[0049] In the liquid fuel operation mode, the electronic governor 32 outputs an actuator command S4 based on the rotation command S1. The actuator command S4 is an electric signal input to an actuator 38b of a liquid fuel regulating mechanism 38, which will be described later.

[0050] Furthermore, in the fuel gas operation mode, the electronic governor 32 outputs a fuel gas injection command S6 based on the rotation command S1. The fuel gas injection command S6 is an electric signal input to a fuel gas injector driver 33. The fuel gas injector driver 33 opens and closes the fuel gas injector 12 based on the fuel gas injection command S6.

[0051] The PLC 34 receives a contact signal S8 from the electronic governor 32 and monitors whether or not there is an abnormality in the electronic governor 32. In addition, the PLC 34 outputs a contact signal S9 based on the contact signal S8 to notify the signal converter 35 of the occurrence of an abnormality (such as a broken wire) in the electronic governor 32.

[0052] The signal converter 35 outputs a backup rotation command S2 based on the rotation command S1. The rotation command S2 is an electric signal input to the electro-pneumatic converter 36. The electro-pneumatic converter 36 outputs a backup rotation command S3 based on the rotation command S2. The rotation command S3 is a mechanical signal input to a mechanical governor 37. Note that the term "mechanical" here is a concept that includes hydraulic pressure and pneumatic pressure in addition to mechanical operations.

[0053] The mechanical governor 37 is a backup controller for the control system 3, and has a backup operation mode in which the dual-fuel engine 2 is operated with liquid fuel. The mechanical governor 37 outputs a backup liquid fuel injection command S5 based on the rotation command S3. The backup liquid fuel injection command S5 is a mechanical signal input to a selection mechanism 38a of a liquid fuel adjustment mechanism 38, which will be described later. The backup liquid fuel injection command S5 is, for example, an operation signal for the mechanical governor 37 based on the rotation command S3 (air pressure).

[0054] The liquid fuel regulating mechanism 38 switches to a backup operation mode using the mechanical governor 37 when an abnormality occurs in at least one of the liquid fuel operation mode and the fuel gas operation mode using the electronic governor 32 .

[0055] The liquid fuel regulating mechanism 38 includes an actuator 38b such as a torque motor system. The actuator 38b outputs a liquid fuel injection command S10 based on an actuator command S4 input from the electronic governor 32.

[0056] The liquid fuel injection command S10 is a mechanical signal input to the selection mechanism 38a of the liquid fuel regulating mechanism 38. The liquid fuel injection command S10 is, for example, an operation signal for the actuator 38b based on the actuator command S4 (electrical signal).

[0057] The liquid fuel adjustment mechanism 38 includes a selection mechanism 38a to which the liquid fuel injection command S10 is input via the electronic governor 32 and the backup liquid fuel injection command S5 is input via the mechanical governor 37. The selection mechanism 38a selects the liquid fuel injection command S10 or the backup liquid fuel injection command S5, whichever has the lower command value, and operates the liquid fuel injector 11.

[0058] In other words, the selection mechanism 38a has a structure that balances the mechanical signal of the liquid fuel injection command S10 and the mechanical signal of the backup liquid fuel injection command S5, and selects the one with the lower command value.

[0059] The actuator command S4 (electrical signal) input from the electronic governor 32 increases the command value of the liquid fuel injection command S10 when the electric signal decreases, and decreases the command value of the liquid fuel injection command S10 when the electric signal increases.

[0060] That is, when an abnormality occurs in the electronic governor 32 and the actuator command S4 (electrical signal) becomes zero, the command value of the liquid fuel injection command S10 becomes maximum and the backup liquid fuel injection command S5 is selected.

[0061] In the normal liquid fuel operation mode (main control by the electronic governor 32), the signal converter 35 adds a predetermined correction value S51 (see Figure 6(a) described later) to the backup liquid fuel injection command S5 so that the selection mechanism 38a of the liquid fuel regulating mechanism 38 always selects the liquid fuel injection command S10 from the electronic governor 32.

[0062] For example, when the liquid fuel injection command S10 is set to 800 min -1 When this is the case, the correction value S51 is 50 min -1The backup liquid fuel injection command S5 is set to 850 min -1 It will be considerable.

[0063] Fig. 6 is a graph showing the change in each command value and the rotation speed in the liquid fuel operation mode according to one embodiment. Fig. 6(a) shows the change in the command values ​​of the backup liquid fuel injection command S5, the fuel gas injection command S6, and the liquid fuel injection command S10 during a certain time period. Fig. 6(b) shows the change in the electrical signals of the rotation commands S2, S3, and the actuator command S4 during the same time period. Fig. 6(c) shows the change in the command value of the rotation command S1 and the change in the rotation speed S7 of the dual fuel engine 2 during the same time period.

[0064] As shown in Fig. 6(c), when the rotation speed S7 of the dual-fuel engine 2 is increased over time, the rotation command unit 31 increases the command value of the rotation command S1 over time. The signal converter 35 and the electro-pneumatic converter 36 increase the command values ​​of the rotation commands S2 and S3 over time based on the input rotation command S1, as shown in Fig. 6(b). On the other hand, the electronic governor 32 decreases the electric signal of the actuator command S4 over time, in contrast to the rotation commands S2 and S3, based on the input rotation command S1.

[0065] As described above, the liquid fuel injection command S10 increases in response to a decrease in the actuator command S4, so the command value of the liquid fuel injection command S10 is increased over time, as shown in Fig. 6(a). The mechanical governor 37 increases the command value of the backup liquid fuel injection command S5 over time, just like the input rotation command S3. Note that the command value of the fuel gas injection command S6 is zero because the liquid fuel operation mode is selected.

[0066] Here, a predetermined correction value S51 is added in advance to the command value of the backup liquid fuel injection command S5 in the signal converter 35. Therefore, the command value of the backup liquid fuel injection command S5 is always higher than the command value of the liquid fuel injection command S10, and the selection mechanism 38a of the liquid fuel regulating mechanism 38 selects the liquid fuel injection command S10, which has a lower command value. As described above, the dual fuel engine 2 can be operated in the liquid fuel operation mode in which the electronic governor 32 is the main control element.

[0067] Here, the correction value S51 added to the command value of the backup liquid fuel injection command S5 can be changed according to the load on the rotation speed of the dual fuel engine 2. The amount of liquid fuel injection required to maintain the rotation speed of the dual fuel engine 2 increases as the load on the rotation speed increases. Therefore, if the correction value S51 is set to minimize the increase in rotation speed that occurs when switching from the electronic governor to the mechanical governor when the load on the rotation speed of the dual fuel engine 2 is high, the increase in rotation speed becomes large when switching from the electronic governor to the mechanical governor when the load on the rotation speed of the dual fuel engine is low. Therefore, by making the correction value S51 added to the backup liquid fuel injection command changeable according to the load on the rotation speed, the fluctuation in the rotation speed of the dual fuel engine 2 can be suppressed. In other words, the correction value S51 is increased when the load on the rotation speed of the dual fuel engine 2 is large, and is decreased when the load on the rotation speed of the dual fuel engine 2 is small.

[0068] Fig. 7 is a graph showing the change in each command value and the rotation speed in the fuel gas operation mode according to one embodiment. Fig. 7(a) shows the change in the command values ​​of the backup liquid fuel injection command S5, the fuel gas injection command S6, and the liquid fuel injection command S10 during a certain time period. Fig. 7(b) shows the change in the electrical signal of the rotation commands S2, S3, and the actuator command S4 during the same time period. Fig. 7(c) shows the change in the command value of the rotation command S1 and the change in the rotation speed S7 of the dual fuel engine 2 during the same time period.

[0069] As shown in Fig. 7(c), when the rotation speed S7 of the dual-fuel engine 2 is increased over time, the rotation command unit 31 increases the command value of the rotation command S1 over time. Based on the input rotation command S1, the signal converter 35 and the electro-pneumatic converter 36 increase the command values ​​of the rotation commands S2 and S3 over time, as shown in Fig. 7(b). At this time, the electronic governor 32 holds the electric signal of the actuator command S4 at its maximum in order to stop the liquid fuel injector 11.

[0070] Based on the input rotation command S1, the electronic governor 32 increases the command value of the fuel gas injection command S6 over time, as shown in Fig. 7(a). The mechanical governor 37 increases the command value of the backup liquid fuel injection command S5 over time, similar to the input rotation command S3. Here, since the current of the actuator command S4 (electrical signal) is at a maximum, the command value of the liquid fuel injection command S10 is zero, and the selection mechanism 38a of the liquid fuel regulating mechanism 38 selects the lower command value, so the liquid fuel injector 11 does not operate. As described above, the dual fuel engine 2 can be operated in the fuel gas operation mode mainly controlled by the electronic governor 32.

[0071] Next, an operation when an abnormality occurs in the electronic governor 32 will be described.

[0072] FIG. 8 is a diagram showing an example of an abnormality that occurs in the electronic governor 32 of the control system 3 according to an embodiment. 8 illustrates an example in which a break 51 occurs in the signal line 50 of the electronic governor 32. In such a case, the PLC 34, which monitors the current of the actuator command S4, detects the break 51 in the signal line 50 and outputs a contact signal S9 to the signal converter 35, notifying the signal converter 35 of an abnormality in the electronic governor 32. In addition, in the case of a break in a rotation sensor or the like, the electronic governor 32 detects the break and transmits a contact signal S8 to the PLC 34, notifying the PLC 34 of an abnormality in the electronic governor 32.

[0073] 9 is a graph showing changes in each command value and rotation speed when an abnormality occurs in the electronic governor 32 in the liquid fuel operation mode according to one embodiment. Note that the vertically extending dashed dotted line in FIG. 9 indicates the timing when an abnormality occurs in the electronic governor 32. As shown in FIG. 9(b), when an abnormality (here, a disconnection 51) occurs in the electronic governor 32, the electric signal of the actuator command S4 of the electronic governor 32 becomes zero.

[0074] 9(a), the command value of the liquid fuel injection command S10 becomes maximum. As a result, the command value of the liquid fuel injection command S10 becomes higher than the command value of the backup liquid fuel injection command S5, and the selection mechanism 38a of the liquid fuel regulating mechanism 38 selects the backup liquid fuel injection command S5, which has the lower command value. As a result, the dual fuel engine 2 can be operated in the backup operation mode in which the mechanical governor 37 is the main control element.

[0075] Here, a predetermined correction value S51 is added in advance to the command value of the backup liquid fuel injection command S5 in the signal converter 35. If control is switched from the electronic governor 32 to the mechanical governor 37 while the correction value S51 is being added to the backup liquid fuel injection command S5, the supply amount of liquid fuel input to the liquid fuel injector 11 will suddenly increase, causing the rotation speed S7 of the dual-fuel engine 2 to increase sharply.

[0076] Therefore, when the signal converter 35 receives a notification of an abnormality in the electronic governor 32 from the PLC 34, it stops adding the correction value S51. When the addition of the correction value S51 is stopped, the command values ​​of the rotation commands S2 and S3 decrease as shown in Fig. 9(b), and the backup liquid fuel injection command S5 transitions to be continuous with the liquid fuel injection command S10 before the occurrence of the abnormality as shown in Fig. 9(a). This makes it possible to suppress fluctuations in the rotation speed S7 of the dual fuel engine 2 immediately after the occurrence of the abnormality as shown in Fig. 9(c), and enables smooth switching of the control subject.

[0077] 10 is a graph showing changes in each command value and rotation speed when an abnormality occurs in the electronic governor 32 in the fuel gas operation mode according to one embodiment. Note that the vertically extending dashed dotted line in FIG. 10 indicates the timing when an abnormality occurs in the electronic governor 32. 10(a), when an abnormality occurs in the electronic governor 32, the electric signal of the fuel gas injection command S6 of the electronic governor 32 becomes zero, which causes the fuel gas injector 12 to stop.

[0078] Furthermore, when an abnormality occurs in the electronic governor 32, the command value (current) of the actuator command S4 of the electronic governor 32 also becomes zero. Therefore, as shown in Fig. 10(a), the command value of the liquid fuel injection command S10 becomes maximum.

[0079] As a result, the command value of the liquid fuel injection command S10 becomes higher than the command value of the backup liquid fuel injection command S5, and the selection mechanism 38a of the liquid fuel regulating mechanism 38 selects the backup liquid fuel injection command S5 having the lower command value. As a result, the dual fuel engine 2 can be operated in the backup operation mode in which the mechanical governor 37 is the main control element.

[0080] Furthermore, when the signal converter 35 receives a notification of an abnormality in the electronic governor 32 from the PLC 34, it stops adding the correction value S51. When the addition of the correction value S51 is stopped, the command values ​​of the rotation commands S2 and S3 decrease as shown in Fig. 10(b), and the backup liquid fuel injection command S5 transitions to be continuous with the fuel gas injection command S6 before the occurrence of the abnormality as shown in Fig. 10(a). This makes it possible to suppress fluctuations in the rotation speed S7 of the dual fuel engine 2 immediately after the occurrence of the abnormality as shown in Fig. 10(c), and to realize a smooth switching of the control subject.

[0081] Next, a problem that may arise when switching from the fuel gas operation mode to the liquid fuel operation mode in the above-mentioned control system 3 will be described with reference to FIG. 11, and a countermeasure therefor will be described with reference to FIG.

[0082] FIG. 11 is a graph showing changes in each command value and rotation speed when a problem occurs when switching from the fuel gas operation mode to the liquid fuel operation mode according to one embodiment. 11(a), when switching from the fuel gas operation mode to the liquid fuel operation mode, the electric signal of the fuel gas injection command S6 of the electronic governor 32 becomes zero. As a result, the injection amount of the fuel gas injector 12 gradually decreases and then stops.

[0083] 11(c), the rotation speed S7 temporarily drops while the injection amount of fuel gas decreases and the injection amount of liquid fuel increases to an amount that can maintain the rotation speed S7 of the dual-fuel engine 2. For this reason, as shown in FIG 11(a), the command value of the liquid fuel injection command S10 immediately after switching to the liquid fuel operation mode becomes high, but at this time, it may exceed the command value of the backup liquid fuel injection command S5 from the mechanical governor 37, which has a lower responsiveness than the electronic governor 32. This response difference is caused by the difference in the change speed between the electrical signal and the mechanical signal.

[0084] For this reason, if the peak value P10 of the liquid fuel injection command S10 immediately after switching to the liquid fuel operation mode exceeds the peak value P5 of the backup liquid fuel injection command S5 from the mechanical governor 37, which has not yet fully risen, the selection mechanism 38a of the liquid fuel regulating mechanism 38 may select the backup liquid fuel injection command S5, and unintentionally switch to control from the backup mechanical governor 37. In other words, the increase in the rotation speed is limited by the mechanical governor 37.

[0085] FIG. 12 is a graph showing changes in each command value and rotation speed when the correction value S51 added to the backup liquid fuel injection command S5 is changed to a second correction value S52 in the fuel gas operation mode according to one embodiment. In order to address the problem described in Figure 11, as shown in Figure 12(a), the signal converter 35 of this embodiment adds a second correction value S52 larger than the correction value S51 to the backup liquid fuel injection command S5 in the fuel gas operation mode.

[0086] This makes it possible to prevent the peak value P10 of the liquid fuel injection command S10 immediately after switching to the liquid fuel operation mode from exceeding the peak value P5 that has not yet fully risen of the backup liquid fuel injection command S5 from the mechanical governor 37. Therefore, the selection mechanism 38a of the liquid fuel regulating mechanism 38 selects the liquid fuel injection command S10, and therefore it is possible to prevent an unintentional switch to control from the backup mechanical governor 37.

[0087] After a predetermined time has elapsed since the operation mode was switched from the fuel gas operation mode to the liquid fuel operation mode, the signal converter 35 restores the second correction value S52 to the original correction value S51 and adds it to the backup liquid fuel injection command S5. This makes it possible to return to the normal state as shown in Figs. 6 and 9.

[0088] Next, a case in which a problem occurs when the liquid fuel injection command S10 increases a large amount per unit time in the above-mentioned control system 3 will be described with reference to FIG. 13, and a countermeasure therefor will be described with reference to FIG.

[0089] FIG. 13 is a graph showing changes in each command value and rotation speed in a case where the increase in the liquid fuel injection command S10 per unit time is large and problematic in the liquid fuel operation mode according to one embodiment. As shown in Figure 13(a), when the load or rotation speed of the dual-fuel engine 2 increases suddenly, the liquid fuel injection command S10 becomes high. At this time, however, it may exceed the command value of the backup liquid fuel injection command S5 from the mechanical governor 37, which has a lower responsiveness than the electronic governor 32.

[0090] For this reason, the selection mechanism 38a of the liquid fuel regulating mechanism 38 may select the backup liquid fuel injection command S5, and unintentionally switch to control by the backup mechanical governor 37. In other words, the mechanical governor 37 limits the increase in load relative to the rotation speed.

[0091] FIG. 14 is a graph showing changes in each command value and rotation speed when the correction value added to the backup liquid fuel injection command S5 is changed to a third correction value S53 when the increase per unit time of the liquid fuel injection command is large in a liquid fuel operation mode according to one embodiment. To address the problem described in FIG. 13, as shown in FIG. 14(a), the signal converter 35 of this embodiment adds a third correction value S53 larger than the correction value S51 to the backup liquid fuel injection command S5.

[0092] This makes it possible to prevent the peak value P10 of the liquid fuel injection command S10 from exceeding the peak value P5 that has not yet reached the full value of the backup liquid fuel injection command S5 from the mechanical governor 37. Therefore, the selection mechanism 38a of the liquid fuel regulating mechanism 38 selects the liquid fuel injection command S10, and therefore it is possible to prevent unintentional switching to the control of the backup mechanical governor 37.

[0093] After a predetermined time has elapsed since the load on the rotation speed suddenly increased, the signal converter 35 returns the third correction value S53 to the original correction value S51 and adds it to the backup liquid fuel injection command S5, thereby making it possible to return to the normal state.

[0094] As described above, the control system 3 for the dual fuel engine 2 according to this embodiment includes the dual fuel engine 2 having the liquid fuel injection valve 11 that injects liquid fuel and the fuel gas injection valve 12 that injects fuel gas, the electronic governor 32 having a liquid fuel operation mode in which the dual fuel engine 2 is operated with liquid fuel and a fuel gas operation mode in which the dual fuel engine 2 is operated with fuel gas, the mechanical governor 37 having a backup operation mode in which the dual fuel engine 2 is operated with liquid fuel, and a liquid fuel adjustment mechanism 38 that selects one of the liquid fuel injection command S10 input via the electronic governor 32 and the backup liquid fuel injection command S5 input via the mechanical governor 37, and increases or decreases the amount of liquid fuel supplied, and when an abnormality occurs in at least one of the liquid fuel operation mode and the fuel gas operation mode controlled by the electronic governor 32, the liquid fuel adjustment mechanism 38 switches to the backup operation mode controlled by the mechanical governor 37.

[0095] The control system 3 for the dual-fuel engine 2 according to this embodiment incorporates two systems, an electronic governor 32 and a backup mechanical governor 37, making the control system 3 redundant. Therefore, when an abnormality occurs in at least one of the liquid fuel operation mode and the fuel gas operation mode by the electronic governor 32, control is switched to the backup mechanical governor 37, and the operation of the dual-fuel engine 2 can be continued using liquid fuel. Therefore, it is possible to establish a control system 3 for the dual-fuel engine 2 suitable for the single-engine, single-shaft marine power system 1.

[0096] In the present embodiment, the liquid fuel regulating mechanism 38 selects the lower command value between the liquid fuel injection command S10 and the backup liquid fuel injection command S5 and operates accordingly.

[0097] According to this configuration, in the normal liquid fuel operation mode, two commands are input to the liquid fuel regulating mechanism 38: the liquid fuel injection command S10 from the electronic governor 32 and the backup liquid fuel injection command S5 input via the mechanical governor 37, and the mechanism selects and operates the one with the lower command value. Therefore, if an abnormality occurs in either governor, the control entity switches, making it possible to prevent the engine from stalling.

[0098] In addition, in this embodiment, the electronic governor 32 decreases the electrical signal it outputs when increasing the command value of the liquid fuel injection command S10, and increases the electrical signal it outputs when decreasing the command value of the liquid fuel injection command S10.

[0099] According to this configuration, if an abnormality such as a break 51 occurs in the signal line 50 of the electronic governor 32, the electrical signal input from the electronic governor 32 becomes zero. This causes the command value of the liquid fuel injection command S10 to become maximum, and the liquid fuel regulating mechanism 38 selects the backup liquid fuel injection command S5, which has a lower command value, so that the control subject can automatically be switched to the mechanical governor 37. In this case, no special sensor or signal is required to switch the control subject.

[0100] Furthermore, in this embodiment, a signal converter 35 is provided that adds a predetermined correction value S51 to the backup liquid fuel injection command S5, making the backup liquid fuel injection command S5 higher than the liquid fuel injection command S10.

[0101] According to this configuration, because a predetermined correction value S51 is added to the backup liquid fuel injection command S5, the liquid fuel regulating mechanism 38 always selects and operates based on the liquid fuel injection command S10 from the electronic governor 32. This makes it possible to prevent unintentional switching to control of the backup mechanical governor in the normal liquid fuel operation mode.

[0102] Furthermore, in this embodiment, when the backup liquid fuel injection command S5 is selected by the liquid fuel regulating mechanism , the signal converter stops adding the correction value S51 to the backup liquid fuel injection command S5.

[0103] If control is switched from the electronic governor 32 to the mechanical governor 37 while the correction value S51 is being added to the backup liquid fuel injection command S5, the command value input to the liquid fuel injector 11 will jump up, causing a sudden increase in the rotation speed S7 of the dual-fuel engine 2. For this reason, by stopping the addition of the correction value S51 when control is switched from the electronic governor 32 to the mechanical governor 37, it becomes possible to suppress fluctuations in the rotation speed S7 of the dual-fuel engine 2, and a smooth switchover of the control entity can be achieved.

[0104] In the present embodiment, the signal converter 35 changes the correction value S51 for the backup liquid fuel injection command S5 in accordance with the load on the rotation speed of the dual-fuel engine 2.

[0105] If the correction value S51 is set to minimize the increase in rotation speed that occurs when switching from the electronic governor 32 to the mechanical governor 37 when the load on the rotation speed of the dual-fuel engine 2 is high, the increase in rotation speed may be large when switching from the electronic governor 32 to the mechanical governor 37 when the load on the rotation speed of the dual-fuel engine 2 is low. For this reason, by making it possible to change the correction value S51 added to the backup liquid fuel injection command S5 according to the load on the rotation speed, it is possible to suppress fluctuations in the rotation speed of the dual-fuel engine 2.

[0106] In this embodiment, in the fuel gas operation mode, the signal converter 35 increases the addition of the correction value S51 to the backup liquid fuel injection command S5.

[0107] When switching from the fuel gas operation mode to the liquid fuel operation mode, the rotation speed S7 of the dual fuel engine 2 temporarily drops while the injection of fuel gas is reduced and the injection of the amount of liquid fuel required to maintain the rotation speed is started. For this reason, the command value of the liquid fuel injection command S10 immediately after switching to the liquid fuel operation mode becomes high, but at this time, it may exceed the command value of the backup liquid fuel injection command S5 from the mechanical governor 37, which has a lower responsiveness than the electronic governor 32. For this reason, by setting the correction value S51 to be added to the backup liquid fuel injection command S5 in the fuel gas operation mode to a second correction value S52 that is larger than normal, it is possible to prevent unintentional switching to the control of the backup mechanical governor 37.

[0108] Furthermore, in this embodiment, in the liquid fuel operation mode, when the increase per unit time of the liquid fuel injection command S10 is large, the signal converter 35 increases the correction value added to the backup liquid fuel injection command S5.

[0109] When the command value of the liquid fuel injection command S10 input via the electronic governor 32 suddenly increases, it may exceed the command value of the backup liquid fuel injection command S5 from the mechanical governor 37, which has a lower responsiveness than the electronic governor 32. For this reason, by setting the correction value S51 to be added to the backup liquid fuel injection command S5 to a third correction value S53 that is larger than normal, it is possible to prevent unintentional switching to control of the backup mechanical governor 37.

[0110] Furthermore, in this embodiment, the signal converter 35 increases the addition of the correction value S51, and then returns it to the original correction value S51 after a predetermined time has elapsed.

[0111] According to this configuration, after a predetermined time has elapsed since the addition of the correction value S51 has been increased, when the rotation speed S7 of the dual-fuel engine 2 has stabilized, the correction value S51 added to the backup liquid fuel injection command S5 can be returned to its original value, thereby returning the system to the normal state.

[0112] In addition, in this embodiment, in the fuel gas operation mode, the liquid fuel regulating mechanism 38 selects the lower command value of the liquid fuel injection command S10 or the backup liquid fuel injection command S5, the electronic governor 32 sends the liquid fuel injection command S10 corresponding to a rotation speed of the dual fuel engine 2 of zero to stop injection from the liquid fuel injector, and the fuel gas injector increases or decreases the amount of fuel gas supplied based on the fuel gas injection command input via the electronic governor 32.

[0113] Even in the normal fuel gas operation mode, two sets of commands are input to the liquid fuel regulating mechanism 38: the liquid fuel injection command S10 from the electronic governor 32 and the backup liquid fuel injection command S5 input via the mechanical governor 37. Since the electronic governor 32 transmits the liquid fuel injection command S10 corresponding to a rotation speed of zero, the liquid fuel regulating mechanism 38 selects the command value of the electronic governor 32, which is the lower command value, and stops injection from the liquid fuel injector. Therefore, if an abnormality occurs in either governor, the control entity switches, making it possible to prevent the engine from stalling.

[0114] Furthermore, in this embodiment, in the fuel gas operation mode, the electronic governor 32 increases the electrical signal it outputs when increasing the command value of the fuel gas injection command, and decreases the electrical signal it outputs when decreasing the command value of the fuel gas injection command.

[0115] According to this configuration, if an abnormality such as a break 51 occurs in the signal line 50 of the electronic governor 32, the electrical signal input from the electronic governor 32 becomes zero. When this happens, the command value of the fuel gas injection command also becomes zero, and the operation of the fuel gas injector stops. Meanwhile, the liquid fuel regulating mechanism 38 selects the backup liquid fuel injection command S5, which has a lower command value, so that the control subject can automatically be switched to the mechanical governor 37.

[0116] Furthermore, the control method for a dual-fuel engine 2 according to the present embodiment is a control method for a dual-fuel engine 2 including: a liquid fuel injection valve 11 that injects liquid fuel and a fuel gas injection valve 12 that injects fuel gas; an electronic governor 32 having a liquid fuel operation mode for operating the dual-fuel engine 2 with liquid fuel and a fuel gas operation mode for operating the dual-fuel engine 2 with fuel gas; a mechanical governor 37 having a backup operation mode for operating the dual-fuel engine 2 with liquid fuel; and a liquid fuel adjustment mechanism 38 that selects one of the liquid fuel injection command S10 input via the electronic governor 32 and the backup liquid fuel injection command S5 input via the mechanical governor 37, and increases or decreases the amount of liquid fuel supplied, and when an abnormality occurs in at least one of the liquid fuel operation mode and the fuel gas operation mode controlled by the electronic governor 32, the operation mode is switched to the backup operation mode controlled by the mechanical governor 37.

[0117] The control method for the dual-fuel engine 2 according to this embodiment incorporates two systems, an electronic governor 32 and a backup mechanical governor 37, to duplicate the control system 3. When an abnormality occurs in at least one of the liquid fuel operation mode and the fuel gas operation mode by the electronic governor 32, control is switched to the backup mechanical governor 37 to continue operation of the dual-fuel engine 2 using liquid fuel. This makes it possible to establish a control method for the dual-fuel engine 2 that is suitable for a single-engine, single-shaft marine power system.

[0118] Although preferred embodiments of the present invention have been described and illustrated above, it should be understood that these are illustrative of the present invention and should not be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the scope of the present invention. Thus, the present invention should not be considered as limited by the foregoing description, but rather by the scope of the claims. [Explanation of symbols]

[0119] 1. Marine Power Systems 2 Dual fuel engine 3. Control System 11 Liquid fuel injector 12 Fuel gas injector 13 Crankshaft 14 Piston 15 Cylinder block 16 Cylinder head 17 Combustion chamber 18 Igniter 19 Intake valve 20 Exhaust valve 21 Intake pipe 22 Exhaust pipe 23 Air cooler 24 Turbocharger 31 Rotation control unit 32 Electronic Governor 33 Fuel gas injector driver 35 Signal Converter 36 Electropneumatic converter 37 Mechanical Governor 38 Liquid fuel adjustment mechanism 38a Selection mechanism 38b Actuator 50 Signal Line 51 Disconnection 100 ships 101 Propeller 102 Auxiliary Engine 103 Generator 104 Inboard busbar 105 Onboard Equipment P5 Peak value P10 Peak value S1 Rotation command S2 rotation command S3 Rotation command S4 Actuator command S5 Backup liquid fuel injection command S6 Fuel gas injection command S7 Rotation Speed S8 Contact signal S9 Contact signal S10 Liquid fuel injection command S51 Correction value S52 Second correction value S53 Third correction value

Claims

1. A dual fuel engine including a liquid fuel injector that injects liquid fuel and a fuel gas injector that injects fuel gas; an electronic governor having a liquid fuel operation mode for operating the dual fuel engine with the liquid fuel and a fuel gas operation mode for operating the dual fuel engine with the fuel gas; a mechanical governor having a backup operating mode for operating the dual fuel engine on the liquid fuel; a liquid fuel regulating mechanism which selects a lower command value between the liquid fuel injection command input via the electronic governor and the backup liquid fuel injection command input via the mechanical governor, and increases or decreases the amount of liquid fuel supplied, the electronic governor decreases an output electrical signal when increasing a command value of the liquid fuel injection command, and increases an output electrical signal when decreasing a command value of the liquid fuel injection command, A control system for a dual-fuel engine, wherein the liquid fuel regulating mechanism switches to the backup operation mode controlled by the mechanical governor when an abnormality occurs in at least one of the liquid fuel operation mode controlled by the electronic governor and the fuel gas operation mode.

2. 2. The dual fuel engine control system according to claim 1, further comprising a signal converter that adds a correction value to the command value of the backup liquid fuel injection command to make the command value higher than the liquid fuel injection command.

3. 3. The dual-fuel engine control system according to claim 2, wherein the signal converter stops adding the correction value to the command value of the backup liquid fuel injection command when the backup liquid fuel injection command is selected by the liquid fuel regulating mechanism.

4. 4. The dual-fuel engine control system according to claim 2, wherein the signal converter increases the correction value for the command value of the backup liquid fuel injection command when a load on the rotational speed of the dual-fuel engine is large, and decreases the correction value when the load on the rotational speed of the dual-fuel engine is small.

5. In the fuel gas operation mode, 5. The dual fuel engine control system according to claim 2, wherein the signal converter increases an addition of the correction value to a command value of the backup liquid fuel injection command.

6. 6. The dual fuel engine control system according to claim 5, wherein the signal converter restores the original correction value after a predetermined time has elapsed since the fuel gas operation mode was switched to the liquid fuel operation mode.

7. In the liquid fuel operation mode, 7. The dual fuel engine control system according to claim 2, wherein the signal converter increases the addition of the correction value to the backup liquid fuel injection command so that an increase per unit time in the command value of the liquid fuel injection command does not cause the command value of the liquid fuel injection command to exceed a command value of the backup liquid fuel injection command that has not yet fully increased.

8. 8. The dual fuel engine control system according to claim 7, wherein the signal converter increases the addition of the correction value and then returns the correction value to the original value after a predetermined time has elapsed.

9. In the fuel gas operation mode, the electronic governor transmits a liquid fuel injection command corresponding to a rotation speed of the dual fuel engine being zero to stop injection from the liquid fuel injector; 9. The control system for a dual fuel engine according to claim 1, wherein the fuel gas injector increases or decreases the amount of fuel gas supplied in response to a fuel gas injection command input via the electronic governor.

10. In the fuel gas operation mode, 10. The dual fuel engine control system according to claim 9, wherein the electronic governor increases the electrical signal it outputs when the command value of the fuel gas injection command is increased, and decreases the electrical signal it outputs when the command value of the fuel gas injection command is decreased.

11. A dual fuel engine including a liquid fuel injector that injects liquid fuel and a fuel gas injector that injects fuel gas; an electronic governor having a liquid fuel operation mode for operating the dual fuel engine with the liquid fuel and a fuel gas operation mode for operating the dual fuel engine with the fuel gas; a mechanical governor having a backup operating mode for operating the dual fuel engine on the liquid fuel; a liquid fuel regulating mechanism which selects one of the liquid fuel injection command input via the electronic governor and the backup liquid fuel injection command input via the mechanical governor, whichever has a lower command value, and increases or decreases the amount of liquid fuel supplied; a signal converter that adds a correction value to a command value of the backup liquid fuel injection command to make the command value higher than the liquid fuel injection command, the liquid fuel regulating mechanism switches to the backup operation mode by the mechanical governor when an abnormality occurs in at least one of the liquid fuel operation mode and the fuel gas operation mode by the electronic governor, In the fuel gas operation mode, A dual-fuel engine control system, wherein the signal converter increases the addition of the correction value to the command value of the backup liquid fuel injection command.

12. A dual fuel engine including a liquid fuel injector that injects liquid fuel and a fuel gas injector that injects fuel gas; an electronic governor having a liquid fuel operation mode for operating the dual fuel engine with the liquid fuel and a fuel gas operation mode for operating the dual fuel engine with the fuel gas; a mechanical governor having a backup operating mode for operating the dual fuel engine on the liquid fuel; a liquid fuel regulating mechanism which selects a lower command value between the liquid fuel injection command input via the electronic governor and the backup liquid fuel injection command input via the mechanical governor, and increases or decreases the amount of liquid fuel supplied, the liquid fuel regulating mechanism switches to the backup operation mode by the mechanical governor when an abnormality occurs in at least one of the liquid fuel operation mode and the fuel gas operation mode by the electronic governor, In the fuel gas operation mode, the electronic governor transmits a liquid fuel injection command corresponding to a rotation speed of the dual fuel engine being zero to stop injection from the liquid fuel injector; A control system for a dual fuel engine, in which the fuel gas injection valve increases or decreases the amount of fuel gas supplied in response to a fuel gas injection command input via the electronic governor.

13. A dual fuel engine including a liquid fuel injector that injects liquid fuel and a fuel gas injector that injects fuel gas; an electronic governor having a liquid fuel operation mode for operating the dual fuel engine with the liquid fuel and a fuel gas operation mode for operating the dual fuel engine with the fuel gas; a mechanical governor having a backup operating mode for operating the dual fuel engine on the liquid fuel; a liquid fuel regulating mechanism which selects a lower command value between a liquid fuel injection command input via the electronic governor and a backup liquid fuel injection command input via the mechanical governor, and increases or decreases an amount of the liquid fuel supplied, comprising: the electronic governor decreases an output electrical signal when increasing a command value of the liquid fuel injection command, and increases an output electrical signal when decreasing a command value of the liquid fuel injection command, A control method for a dual-fuel engine, comprising: switching to the backup operation mode by the mechanical governor when an abnormality occurs in at least one of the liquid fuel operation mode and the fuel gas operation mode by the electronic governor.

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