JP7522084B2 - Dual Fuel Engine System - Google Patents

Description

This disclosure relates to a dual fuel engine system.

Dual fuel engines use, for example, liquid fuel and gas fuel. For example, Patent Document 1 discloses a dual fuel engine that can select between diesel operation and gas operation. This engine is equipped with a compression ratio control valve that can adjust the effective compression ratio in the main combustion chamber. When the engine is switched from diesel operation to gas operation, the amount of liquid fuel injected is gradually reduced to the set value of the pilot amount, and the main fuel is switched to gas fuel. Simultaneously with this switching operation, the compression ratio control valve is controlled so that an effective compression ratio according to the operating conditions of the engine during gas operation is obtained.

JP 2002-4899 A

Dual fuel engines may experience issues when switching between liquid and gaseous fuels, such as delayed mode transitions or misfires, and may not be able to switch fuels smoothly.

The present disclosure aims to disclose a dual fuel engine system that can smoothly switch between fuels.

A dual-fuel engine system according to one aspect of the present disclosure includes a dual-fuel engine that uses liquid fuel and gas fuel, and a control device for the dual-fuel engine that adjusts the fuel ratio between the liquid fuel and the gas fuel, the compression ratio of a mixture including the fuel and intake air, and the injection timing of pilot fuel when the fuel of the dual-fuel engine is switched between liquid fuel and gas fuel , and the control device advances the injection timing of pilot fuel in a gas fuel mode in which gas fuel is used as the main fuel compared to the injection timing of pilot fuel in a liquid fuel mode in which liquid fuel is used .

When switching the fuel of a dual-fuel engine from liquid fuel to gas fuel, the control device may simultaneously adjust the fuel ratio, compression ratio, and pilot fuel injection timing.

When switching the fuel of a dual-fuel engine from liquid fuel to gas fuel, the control device may complete the switching of the compression ratio before completing the switching of the fuel ratio and the injection timing of the pilot fuel.

The control device may adjust the fuel ratio so that the total heat value of the liquid fuel and gaseous fuel corresponds to the heat value required depending on the operating state of the dual-fuel engine.

When switching the fuel of a dual-fuel engine from gas fuel to liquid fuel, the control device may first adjust the fuel ratio, and then adjust the compression ratio and the injection timing of the pilot fuel.

The dual fuel engine may include a piston rod and a crosshead connected to the piston rod, the crosshead including a liquid flow path that generates a hydraulic pressure that changes the extension length of the piston rod from the crosshead, and the control device may adjust the geometric compression ratio by changing the extension length of the piston rod.

The dual fuel engine may be a two-stroke engine, and the control device may adjust the opening timing of the exhaust valves of the dual fuel engine according to the geometric compression ratio.

The control device may adjust the exhaust valve closing timing of a dual fuel engine according to the geometric compression ratio.

This disclosure allows for smooth fuel switching.

FIG. 1 is a schematic diagram of a dual fuel engine system. FIG. 2 is a schematic enlarged view of a portion X in FIG. 1 when the piston rod is in a first position. FIG. 3 is a schematic cross-sectional view taken along line III-III in FIG. FIG. 4 is a schematic enlarged view of a portion X in FIG. 1 when the piston rod is in a second position. FIG. 5 shows a graph illustrating the change in parameters when the operating mode is changed from the liquid fuel mode to the gas fuel mode. FIG. 6 shows a graph illustrating the change in parameters when the operating mode is changed from the gas fuel mode to the liquid fuel mode. FIG. 7 is a flowchart showing the operation of the control device when the operating mode is changed from the liquid fuel mode to the gas fuel mode. FIG. 8 is a flowchart showing the operation of the control device when the operation mode is changed from the gas fuel mode to the liquid fuel mode.

Below, an embodiment of the present disclosure will be described in detail with reference to the attached drawings. Specific dimensions, materials, values, etc. shown in the embodiment are merely examples for ease of understanding, and do not limit the present disclosure unless otherwise specified. In this specification and drawings, elements having substantially the same functions and configurations are denoted by the same reference numerals to avoid duplicated explanations. Furthermore, elements that are not directly related to the present disclosure are not illustrated.

FIG. 1 is a schematic diagram of a dual fuel engine system 100. In this embodiment, the dual fuel engine system 100 is applied to a two-stroke dual fuel engine E. In other embodiments, the dual fuel engine E may be a four-stroke engine. Hereinafter, the dual fuel engine system 100 will be simply referred to as the "system" and the dual fuel engine E will be simply referred to as the "engine". The system 100 includes an engine E and a control device 50.

In this embodiment, the engine E is a uniflow scavenging engine in which the working gas flows in one direction inside the cylinder 1. For example, the engine E is used in a ship. The engine E includes the cylinder 1, a cylinder head 2, a piston 3, a piston rod 4, a crosshead 5, a connecting rod 6, and a cylinder jacket 7.

The cylinder 1 houses a piston 3. The piston 3 reciprocates within the cylinder 1. A first end 1a of the cylinder 1 is closed by a cylinder head 2. A combustion chamber R is defined by the cylinder 1, the cylinder head 2, and the piston 3. A second end 1b of the cylinder 1 is disposed within a cylinder jacket 7. The piston 3 is connected to a first end 4a of a piston rod 4. A second end 4b of the piston rod 4 is connected to a crosshead 5.

In this disclosure, the length of the piston rod 4 that protrudes from the crosshead 5 is referred to as the "protrusion length." The direction in which the piston rod 4 extends, i.e., the direction in which the piston 3 reciprocates, is referred to as the "stroke direction." As will be described in detail later, in this embodiment, the top dead center position and bottom dead center position of the piston 3 can be changed by the compression ratio variable mechanism M.

The crosshead 5 reciprocates together with the piston 3. The crosshead 5 includes a crosshead pin 5a and a crosshead shoe 5b. The crosshead pin 5a is connected to the piston rod 4. The crosshead shoe 5b restricts the movement of the crosshead 5 in a direction perpendicular to the direction of reciprocation. The crosshead pin 5a is connected to one end of a connecting rod 6. The other end of the connecting rod 6 is connected to a crankshaft (not shown).

In the engine E described above, a mixture of fuel and intake air is burned in the combustion chamber R. The piston 3 reciprocates in the cylinder 1 due to combustion. During one reciprocating motion of the piston 3, exhaust, intake, compression, and combustion expansion occur. The crosshead 5 reciprocates together with the piston 3. The reciprocating motion of the crosshead 5 is converted into the rotational motion of the crankshaft via the connecting rod 6.

The cylinder head 2 includes an exhaust port 21 and an exhaust valve 22. The exhaust port 21 guides exhaust gas generated in the combustion chamber R to the exhaust pipe 8. The exhaust valve 22 opens and closes the exhaust port 21. The operation of the exhaust valve 22 is controlled by a drive device A. The drive device A is communicatively connected to the control device 50 and is controlled by the control device 50. The exhaust gas in the exhaust pipe 8 is supplied to the turbine of the turbocharger C and then exhausted to the outside.

The cylinder 1 includes a plurality of scavenging ports 11. In the cylinder 1, the scavenging ports 11 are formed in an area within the cylinder jacket 7. The scavenging ports 11 are through holes that penetrate from the outer peripheral surface to the inner peripheral surface of the cylinder 1. The plurality of scavenging ports 11 are spaced apart from one another along the circumferential direction of the cylinder 1. The scavenging ports 11 draw active gas into the cylinder 1 in response to the sliding motion of the piston 3. The active gas includes an oxidizing agent such as oxygen or ozone, or a mixture thereof. For example, the active gas is air.

The cylinder jacket 7 is connected to the scavenging tank 9. The scavenging tank 9 receives pressurized active gas from the compressor of the turbocharger C. A cooler 91 is provided in the scavenging tank 9. The cooler 91 cools the active gas in the scavenging tank 9. The cooled active gas flows into the scavenging chamber 71 of the cylinder jacket 7. The active gas is drawn into the cylinder 1 from the scavenging port 11 due to the pressure difference between the scavenging chamber 71 and the cylinder 1.

The cylinder head 2 is provided with a first injection valve V1. The first injection valve V1 injects liquid fuel into the combustion chamber R. For example, the liquid fuel may be heavy oil or light oil. The first injection valve V1 is communicatively connected to the control device 50, and the injection amount and injection timing of the liquid fuel are controlled by the control device 50.

The cylinder 1 is provided with a second injection valve V2. In this embodiment, the second injection valve V2 is provided in a region away from the top dead center of the piston 3. Specifically, the second injection valve V2 is provided outside the cylinder jacket 7 in a region approximately in the middle in the central axial direction of the cylinder 1. In other embodiments, the second injection valve V2 may be provided inside the cylinder jacket 7 in a region near the scavenging port 11. Although not shown in FIG. 1, multiple second injection valves V2 may be arranged spaced apart from each other in the circumferential direction of the cylinder 1. The second injection valve V2 injects gaseous fuel into the combustion chamber R. For example, the gaseous fuel may be produced by gasifying LNG (liquefied natural gas), LPG (liquefied petroleum gas), ammonia, hydrogen, light oil, or heavy oil. The second injection valve V2 is communicatively connected to the control device 50, and the injection amount and injection timing of the gaseous fuel are controlled by the control device 50.

Engine E has a liquid fuel mode as an operating mode in which liquid fuel from the first injector V1 is used. Engine E also has a gas fuel mode as another operating mode in which gas fuel from the second injector V2 is used as the main fuel. Engine E transitions between the liquid fuel mode and the gas fuel mode.

In the liquid fuel mode, the first injector V1 injects liquid fuel as the main fuel into the combustion chamber R. The first injector V1 also injects a small amount of liquid fuel into the combustion chamber R as pilot fuel prior to the main fuel. In the liquid fuel mode, the piston 3 reciprocates due to the expansion pressure caused by the combustion of the liquid fuel.

In the gas fuel mode, the second injection valve V2 injects gas fuel as the main fuel into the combustion chamber R. Also, the first injection valve V1 injects a small amount of liquid fuel into the combustion chamber R as pilot fuel prior to the main fuel. In the gas fuel mode, the piston 3 reciprocates mainly due to the expansion pressure caused by the combustion of the gas fuel.

Generally, gaseous fuels burn more easily than liquid fuels and at a lower compression ratio. Therefore, the compression ratio suitable for liquid fuels and the compression ratio suitable for gaseous fuels are different from each other. In this embodiment, the engine E is equipped with a compression ratio variable mechanism M for geometrically changing the compression ratio depending on the fuel.

Figure 2 is a schematic enlarged view of part X in Figure 1 when the piston rod 4 is in the first position P1. At the first position P1 shown in Figure 2, the protruding length of the piston rod 4 is the longest. Also, Figure 3 is a schematic cross-sectional view taken along line III-III in Figure 2. Figures 2 and 3 show the compression ratio variable mechanism M.

Referring to FIG. 2, the second end 4b of the piston rod 4 is slidably connected to the crosshead pin 5a. Specifically, the piston rod 4 includes, in order from closest to the second end 4b, a small diameter section 41, a large diameter section 42, and a medium diameter section 43. The small diameter section 41 includes the second end 4b of the piston rod 4. The large diameter section 42 is formed continuously with the small diameter section 41. The diameter of the large diameter section 42 is larger than the diameter of the small diameter section 41. The medium diameter section 43 is formed continuously with the large diameter section 42. The diameter of the medium diameter section 43 is larger than the diameter of the small diameter section 41 and smaller than the diameter of the large diameter section 42.

The crosshead pin 5a includes a connecting hole 51 that extends in the stroke direction. As described below, the connecting hole 51 defines a hydraulic chamber. The connecting hole 51 includes a large diameter hole 51a and a small diameter hole 51b.

The large diameter hole 51a is configured to accommodate the large diameter portion 42 of the piston rod 4. The large diameter hole 51a has a diameter that is approximately the same as or slightly larger than the diameter of the large diameter portion 42 of the piston rod 4. A seal member such as an O-ring may be provided between the large diameter hole 51a and the large diameter portion 42. With this configuration, the large diameter portion 42 seals the large diameter hole 51a and slides within the large diameter hole 51a.

The small diameter hole 51b is configured to accommodate the small diameter portion 41 of the piston rod 4. The small diameter hole 51b has a diameter that is approximately the same as or slightly larger than the diameter of the small diameter portion 41 of the piston rod 4. A seal member such as an O-ring may be provided between the small diameter hole 51b and the small diameter portion 41. With this configuration, the small diameter portion 41 seals the small diameter hole 51b and slides within the small diameter hole 51b.

Referring to FIG. 3, the crosshead pin 5a includes a groove 51c extending in the stroke direction. The groove 51c is formed to be continuous with the connecting hole 51. The groove 51c accommodates the fixed lid 52. The connecting hole 51 is liquid-tightly closed by the fixed lid 52. The fixed lid 52 includes a through hole 52a. The through hole 52a has a diameter that is approximately the same as or slightly larger than the diameter of the medium diameter portion 43 of the piston rod 4. A seal member such as an O-ring may be provided between the through hole 52a and the medium diameter portion 43. With this configuration, the medium diameter portion 43 seals the through hole 52a and slides within the through hole 52a. With the above configuration, the second end 4b of the piston rod 4 is slidably connected to the crosshead pin 5a.

The crosshead pin 5a includes a first hydraulic chamber 53a and a second hydraulic chamber 53b. Specifically, the large diameter hole 51a is divided by the large diameter portion 42 of the piston rod 4 into a first hydraulic chamber 53a that partially accommodates the small diameter portion 41 and a second hydraulic chamber 53b that partially accommodates the medium diameter portion 43.

Referring to FIG. 2, the first hydraulic chamber 53a is connected to the first oil passage 54a and the second oil passage 54b. The first oil passage 54a is connected to a pump (not shown). The second oil passage 54b is connected to a spill valve (not shown). The second hydraulic chamber 53b is connected to the auxiliary oil passage 54c. The auxiliary oil passage 54c is connected to a pump (not shown).

When hydraulic oil is supplied from the first oil passage 54a to the first hydraulic chamber 53a and the spill valve connected to the second oil passage 54b is closed, the piston rod 4 maintains the first position P1 shown in FIG. 2.

Figure 4 is a schematic enlarged view of part X in Figure 1 when the piston rod 4 is in the second position P2. In the second position P2 shown in Figure 4, the protruding length of the piston rod 4 is the shortest. In the first position P1, when the spill valve connected to the second oil passage 54b is opened, the hydraulic oil in the first hydraulic chamber 53a is discharged from the first hydraulic chamber 53a through the second oil passage 54b. When the hydraulic oil is discharged from the first hydraulic chamber 53a, the second end 4b of the piston rod 4 moves from the first position P1 to the second position P2 shown in Figure 4.

When the piston 3 reaches the top dead center in the state shown in FIG. 4, the piston rod 4 has a play equal to the width of the second hydraulic chamber 53b. Therefore, if the inertia force of the piston rod 4 is large, the piston rod 4 may compress the hydraulic oil in the second hydraulic chamber 53b and move to the first position P1 relative to the crosshead pin 5a. When the piston rod 4 moves, the top dead center position of the piston 3 shifts. To reduce such a shift, hydraulic pressure is supplied to the second hydraulic chamber 53b from the hydraulic pump via the auxiliary oil passage 54c. Therefore, the piston rod 4 maintains the second position P2 shown in FIG. 4.

As described above, the positions of the top and bottom dead centers of the piston 3 change by changing the relative position between the piston rod 4 and the crosshead pin 5a, i.e., the protruding length of the piston rod 4. The compression ratio variable mechanism M adjusts the geometric compression ratio of the engine E by changing the positions of the top and bottom dead center of the piston 3. In this disclosure, "geometric compression ratio" means the value obtained by dividing the volume of the combustion chamber R at bottom dead center by the volume of the combustion chamber R at top dead center.

The components of the variable compression ratio mechanism M, such as the pump and spill valve, are communicatively connected to the control device 50, and the protruding length of the piston rod 4, i.e., the top dead center and bottom dead center positions of the piston 3, are controlled by the control device 50. In other words, the control device 50 controls the geometric compression ratio. Note that the variable compression ratio mechanism M is not limited to the above configuration, and can have various configurations as long as the relative positions of the piston rod 4 and the crosshead pin 5a can be changed by hydraulic pressure.

Referring to FIG. 1, the control device 50 includes, for example, an ECU (Engine Control Unit). The control device 50 includes components such as a processor (e.g., a CPU) 50a, a storage device (e.g., a hard disk, a ROM storing programs, etc., and a RAM as a work area) 50b, and a connector 50c, and controls the system 100. The control device 50 may further include other components (e.g., a display device such as a liquid crystal display or a touch panel, and an input device such as a keyboard, buttons, or a touch panel). For example, the operation of the control device 50 shown below may be realized by having the processor 50a execute a program stored in the storage device 50b.

The control device 50 adjusts the injection ratio between liquid fuel and gas fuel and the compression ratio of the mixture depending on the liquid fuel mode and the gas fuel mode. In this embodiment, the control device 50 further adjusts the injection timing of the pilot fuel depending on the liquid fuel mode and the gas fuel mode. In this embodiment, the control device 50 further adjusts the closing timing and opening timing of the exhaust valve 22 depending on the liquid fuel mode and the gas fuel mode.

Figure 5 shows graphs that explain the changes in parameters when the operating mode is shifted from liquid fuel mode to gas fuel mode. From top to bottom, Figure 5 shows graphs of the fuel ratio, geometric compression ratio, pilot fuel injection timing, and exhaust valve operation timing. In each graph, the horizontal axis indicates time. In the fuel ratio graph, the solid line indicates the liquid fuel ratio, and the dashed line indicates the gas fuel ratio. The liquid fuel ratio as pilot fuel is not shown in Figure 5. In the exhaust valve operation timing graph, the solid line indicates the opening timing of the exhaust valve 22, and the dashed line indicates the closing timing of the exhaust valve 22.

In FIG. 5, engine E operates in liquid fuel mode before time t1. Therefore, the gas fuel ratio is 0. The compression ratio, liquid fuel injection timing, and exhaust valve operation timing are each set to values suitable for the liquid fuel mode.

At time t1, the control device 50 transitions the operating mode of the engine E from the liquid fuel mode to the gas fuel mode. In FIG. 5, the transition is performed between time t1 and time t2. For example, the period between time t1 and time t2 may include several strokes of the piston 3.

The control device 50 controls the first injection valve V1 and the second injection valve V2 to reduce the ratio of liquid fuel and increase the ratio of gas fuel. The ratio of liquid fuel and gas fuel is adjusted so that the total heat generation amount of the liquid fuel and the gas fuel corresponds to the heat generation amount required according to the operating state of the engine E. With this configuration, the fuel of the engine E is switched from liquid fuel to gas fuel.

As the ratio of gaseous fuel increases, the control device 50 controls the compression ratio variable mechanism M to shorten the protruding length of the piston rod 4, i.e., to reduce the geometric compression ratio. This configuration prevents abnormal combustion, such as knocking.

The control device 50 also controls the first injection valve V1 to advance the injection timing of the pilot fuel. In the gas fuel mode, abnormal combustion such as knocking or pre-ignition or misfire is more likely to occur than in the liquid fuel mode. Therefore, in the gas fuel mode, it is effective to control combustion by advancing the injection timing of the pilot fuel. In FIG. 5, the control device 50 gradually advances the injection timing of the pilot fuel between time t1 and time t2. In other embodiments, the control device 50 may advance the injection timing instantaneously at time t1.

The control device 50 also controls the exhaust valve 22 to delay both the closing and opening times of the exhaust valve 22.

By delaying the closing timing of the exhaust valve 22, it is possible to further reduce the effective compression ratio of the mixture. Such a configuration further prevents abnormal combustion such as knocking. In this disclosure, "effective compression ratio" means the value obtained by dividing the capacity of the combustion chamber R when the mixture actually starts to be compressed, i.e., when the exhaust valve 22 closes, by the volume of the combustion chamber R at top dead center. For example, the memory device 50b of the control device 50 may store a table showing the relationship between the geometric compression ratio and the closing timing of the exhaust valve 22, and the processor 50a may read the closing timing of the exhaust valve 22 from the table according to the geometric compression ratio.

By delaying the opening timing of the exhaust valve 22, the effective expansion ratio of the mixture can be increased. In this disclosure, "effective expansion ratio" means the value obtained by dividing the volume of the combustion chamber R when the mixture actually finishes expanding, i.e., when the exhaust valve 22 is opened, by the volume of the combustion chamber R at top dead center. For example, the memory device 50b of the control device 50 may store a table showing the relationship between the geometric compression ratio and the opening timing of the exhaust valve 22, and the processor 50a may read the opening timing of the exhaust valve 22 from the table according to the geometric compression ratio.

As shown in FIG. 5, when the operating mode is shifted from the liquid fuel mode to the gas fuel mode, the fuel ratio, the geometric compression ratio, the pilot fuel injection timing, and the exhaust valve operation timing are switched simultaneously and gradually. With this configuration, it is possible to suppress fluctuations in the output of the engine E.

When the operating mode is shifted from the liquid fuel mode to the gas fuel mode, among the fuel ratio, the geometric compression ratio, the pilot fuel injection timing, and the exhaust valve operation timing, the geometric compression ratio switching may be completed earlier than time t2. Depending on the operating conditions of engine E, the change in the compression ratio may not be in a proportional relationship as shown in FIG. 5, and it may be difficult to control all parameters on the same time axis. Therefore, by completing the geometric compression ratio switching earlier, the robustness of engine E can be improved. In addition to the geometric compression ratio, the switching of the pilot fuel injection timing may also be completed earlier than time t2.

Figure 6 shows graphs that explain the change in parameters when the operating mode is shifted from the gas fuel mode to the liquid fuel mode. Like Figure 5, Figure 6 shows graphs of the fuel ratio, the geometric compression ratio, the pilot fuel injection timing, and the exhaust valve operation timing, in that order from top to bottom. In each graph, the horizontal axis indicates time. In the fuel ratio graph, the solid line indicates the liquid fuel ratio, and the dashed line indicates the gas fuel ratio. The ratio of liquid fuel as pilot fuel is not shown in Figure 6. In the exhaust valve operation timing graph, the solid line indicates the opening timing of the exhaust valve 22, and the dashed line indicates the closing timing of the exhaust valve 22.

In FIG. 6, engine E operates in gas fuel mode before time t3. Therefore, the liquid fuel ratio is 0. The compression ratio, liquid fuel injection timing, and exhaust valve operation timing are each set to values suitable for the gas fuel mode.

At time t3, the control device 50 transitions the operating mode of the engine E from the gas fuel mode to the liquid fuel mode. In FIG. 5, the transition is performed between time t3 and time t5. For example, the period between time t3 and time t5 may include several strokes of the piston 3.

The control device 50 controls the first injection valve V1 and the second injection valve V2 to decrease the ratio of gas fuel and increase the ratio of liquid fuel. With this configuration, the fuel of the engine E is switched from gas fuel to liquid fuel. In FIG. 6, the fuel switch is quickly completed by time t4, which is before time t5. For example, the period from time t3 to time t4 may be the duration of one stroke of the piston 3.

After the fuel is switched, the control device 50 controls the compression ratio variable mechanism M to increase the protruding length of the piston rod 4, i.e., to increase the geometric compression ratio. This configuration prevents abnormal combustion such as misfires.

The control device 50 also controls the first injection valve V1 to delay the injection timing of the pilot fuel.

The control device 50 also controls the exhaust valve 22 to advance the closing and opening timings of the exhaust valve 22. As described above, the processor 50a may read the opening and closing timings of the exhaust valve 22 from each table according to the geometric compression ratio.

As shown in FIG. 6, when the operating mode is shifted from the liquid fuel mode to the gas fuel mode, the fuel ratio is first adjusted quickly between time t3 and time t4, and then the geometric compression ratio, the pilot fuel injection timing, and the exhaust valve operation timing are gradually adjusted between time t4 and time t5. The combustion of gas fuel may be more unstable than the combustion of liquid fuel, which may lead to combustion abnormalities such as misfires. According to the above configuration, when a combustion abnormality occurs in the gas fuel mode, the fuel can be quickly switched from gas fuel to liquid fuel. In other embodiments, the geometric compression ratio, the pilot fuel injection timing, and the exhaust valve operation timing may be adjusted in separate periods. In still other embodiments, the fuel ratio may be gradually adjusted at the same time as the geometric compression ratio, the pilot fuel injection timing, and the exhaust valve operation timing.

Next, the operation of the system 100 will be explained.

Figure 7 is a flowchart showing the operation of the control device 50 when the operating mode is changed from the liquid fuel mode to the gas fuel mode. The operation shown in Figure 7 may be initiated, for example, when an instruction is input from an operator to change the operating mode from the liquid fuel mode to the gas fuel mode.

The processor 50a controls the first injector V1 and the second injector V2 to adjust the ratio of liquid fuel and gas fuel (step S100). Specifically, the processor 50a controls the first injector V1 to reduce the ratio of liquid fuel, and controls the second injector V2 to increase the ratio of gas fuel.

In parallel with step S100, the processor 50a controls the compression ratio variable mechanism M to adjust the geometric compression ratio (step S102). Specifically, the processor 50a controls the compression ratio variable mechanism M to reduce the geometric compression ratio.

In parallel with steps S100 and S102, the processor 50a controls the first injector V1 to adjust the injection timing of the pilot fuel (step S104). Specifically, the processor 50a controls the first injector V1 to advance the injection timing of the pilot fuel.

In parallel with steps S100 to S104, the processor 50a controls the drive device A to adjust the closing timing of the exhaust valve 22 (step S106). Specifically, the processor 50a reads the closing timing of the exhaust valve 22 from a table according to the geometric compression ratio, and controls the drive device A to delay the closing timing of the exhaust valve 22 based on the read timing.

In parallel with steps S100 to S106, the processor 50a controls the drive device A to adjust the opening timing of the exhaust valve 22 (step S108), and ends the series of operations. Specifically, the processor 50a reads the opening timing of the exhaust valve 22 from a table according to the geometric compression ratio, and controls the drive device A to delay the opening timing of the exhaust valve 22 based on the read timing.

Figure 8 is a flowchart showing the operation of the control device 50 when the operating mode is changed from the gas fuel mode to the liquid fuel mode. The operation shown in Figure 8 may be initiated, similar to the operation shown in Figure 7, for example, when an instruction is input from an operator to change the operating mode from the gas fuel mode to the liquid fuel mode.

The processor 50a controls the first injector V1 and the second injector V2 to adjust the ratio of liquid fuel and gas fuel (step S200). Specifically, the processor 50a controls the first injector V1 to increase the ratio of liquid fuel, and controls the second injector V2 to decrease the ratio of gas fuel.

After step S200, the processor 50a controls the compression ratio variable mechanism M to adjust the geometric compression ratio (step S202). Specifically, the processor 50a controls the compression ratio variable mechanism M to increase the geometric compression ratio.

In parallel with step S202, the processor 50a controls the first injector V1 to adjust the injection timing of the pilot fuel (step S204). Specifically, the processor 50a controls the first injector V1 to retard the injection timing of the pilot fuel.

In parallel with steps S202 and S204, the processor 50a controls the drive device A to adjust the closing timing of the exhaust valve 22 (step S206). Specifically, the processor 50a reads the closing timing of the exhaust valve 22 from a table according to the geometric compression ratio, and controls the drive device A to advance the closing timing of the exhaust valve 22 based on the read timing.

In parallel with steps S202 to S206, the processor 50a controls the drive device A to adjust the opening timing of the exhaust valve 22 (step S208), and ends the series of operations. Specifically, the processor 50a reads the opening timing of the exhaust valve 22 from a table according to the geometric compression ratio, and controls the drive device A to advance the opening timing of the exhaust valve 22 based on the read timing.

The above-described system 100 includes an engine E that uses liquid fuel and gaseous fuel, and a control device 50 for the engine E that adjusts the fuel ratio between the liquid fuel and the gaseous fuel and the compression ratio of the mixture including the fuel and the intake air, for example, the geometric compression ratio and the effective compression ratio, when the fuel of the engine E is switched between the liquid fuel and the gaseous fuel. As described above, gaseous fuel burns more easily than liquid fuel and burns at a lower compression ratio. Therefore, the compression ratio suitable for liquid fuel and the compression ratio suitable for gaseous fuel are different from each other. According to the configuration of the system 100, when the fuel is switched, the compression ratio is adjusted in addition to the fuel ratio. Therefore, when the fuel is switched, a compression ratio according to the fuel ratio is used. Therefore, it is possible to smoothly switch the fuel by suppressing combustion abnormalities such as knocking or misfire.

In addition, in the system 100, the control device 50 further adjusts the injection timing of the pilot fuel. Therefore, the mixture can be ignited at the optimal time depending on the fuel ratio used.

In addition, in the system 100, when the fuel for the engine E is switched from liquid fuel to gas fuel, the control device 50 simultaneously adjusts the fuel ratio, compression ratio, and pilot fuel injection timing. With this configuration, fluctuations in the output of the engine E can be suppressed.

In addition, in the system 100, when the fuel for engine E is switched from liquid fuel to gas fuel, the control device 50 adjusts the fuel ratio so that the total heat generation amount of the liquid fuel and the gas fuel corresponds to the heat generation amount required according to the operating state of engine E. With this configuration, it is possible to suppress fluctuations in the output of engine E.

In addition, in the system 100, when the fuel for the engine E is switched from gas fuel to liquid fuel, the control device 50 first adjusts the fuel ratio, and then adjusts the compression ratio and the injection timing of the pilot fuel. With this configuration, if a combustion abnormality occurs in the gas fuel mode, the fuel can be quickly switched from gas fuel to the more stable liquid fuel.

In the system 100, the engine E includes a piston rod 4 and a crosshead 5 connected to the piston rod 4, the crosshead 5 including hydraulic oil flow paths 53a, 53b, 54a, 54b, 54c that generate hydraulic pressure that changes the extension length of the piston rod 4 from the crosshead 5, and the control device 50 adjusts the geometric compression ratio by changing the extension length of the piston rod 4. With this configuration, the compression ratio can be adjusted more flexibly.

In addition, in the system 100, the engine E is a two-stroke engine, and the control device 50 adjusts the opening timing of the exhaust valve 22 of the engine E according to the geometric compression ratio. With this configuration, the effective expansion ratio can be adjusted according to the operating conditions of the engine E.

In addition, in the system 100, the control device 50 adjusts the closing timing of the exhaust valve 22 of the engine E according to the geometric compression ratio. With this configuration, the effective compression ratio can be adjusted according to the operating conditions of the engine E.

Although the embodiments of the present disclosure have been described above with reference to the attached drawings, it goes without saying that the present disclosure is not limited to such embodiments. It is clear that a person skilled in the art can conceive of various modified or amended examples within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure. In addition, the operations of the control device 50 shown above do not have to be performed in the above order, and may be performed in a different order as long as no technical contradiction occurs.

By promoting the use of multiple fuels, this disclosure can contribute, for example, to Sustainable Development Goal (SDG) Goal 7 "Ensure access to affordable, reliable, sustainable and modern energy" and Goal 9 "Build resilient infrastructure, promote sustainable industrialization and foster innovation."

4 Piston rod 5 Crosshead 22 Exhaust valve 50 Control device 53a First hydraulic chamber (liquid flow path)
53b Second hydraulic chamber (liquid flow path)
54a First oil passage (liquid passage)
54b Second oil passage (liquid passage)
54c Auxiliary oil passage (liquid passage)
100 Dual fuel engine system E Dual fuel engine

Claims (8)

A dual fuel engine that uses liquid fuel and gas fuel;
a control device for the dual-fuel engine, the control device adjusting a fuel ratio between the liquid fuel and the gas fuel, a compression ratio of a mixture including the fuel and intake air, and an injection timing of pilot fuel when switching fuel of the dual-fuel engine between the liquid fuel and the gas fuel;
Equipped with
the control device advances the injection timing of the pilot fuel in a gas fuel mode in which the gas fuel is used as a main fuel, compared to the injection timing of the pilot fuel in a liquid fuel mode in which the liquid fuel is used.
Dual fuel engine system. The dual fuel engine system of claim 1, wherein the control device simultaneously adjusts the fuel ratio, the compression ratio, and the injection timing of the pilot fuel when the fuel of the dual fuel engine is switched from the liquid fuel to the gas fuel. The dual fuel engine system according to claim 1, wherein when the fuel of the dual fuel engine is switched from the liquid fuel to the gas fuel, the control device completes the switching of the compression ratio before completing the switching of the fuel ratio and the injection timing of the pilot fuel. The dual fuel engine system according to claim 2 or 3, wherein the control device adjusts the fuel ratio so that the total heat value of the liquid fuel and the gaseous fuel corresponds to the heat value required according to the operating state of the dual fuel engine. The dual fuel engine system according to any one of claims 1 to 4, wherein the control device, when switching the fuel of the dual fuel engine from the gas fuel to the liquid fuel, first adjusts the fuel ratio, and then adjusts the compression ratio and the injection timing of the pilot fuel. The dual fuel engine is
A piston rod;
A crosshead connected to the piston rod, the crosshead including a liquid flow path that generates a hydraulic pressure that changes the extension length of the piston rod from the crosshead;
Including,
The control device adjusts a geometric compression ratio by changing the extension length of the piston rod.
6. A dual fuel engine system according to any one of claims 1 to 5. The dual fuel engine is a two-stroke engine,
The control device adjusts an opening timing of an exhaust valve of the dual fuel engine in accordance with the geometric compression ratio.
7. The dual fuel engine system of claim 6. The control device adjusts a closing timing of the exhaust valve of the dual fuel engine in accordance with the geometric compression ratio.
8. The dual fuel engine system of claim 7.

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