Controller of marine engine and method for operating vessel

Abstract

To reduce fuel consumption and methane slip, and suppress generation of knocking during transient operation from a low-load operation to a high-load operation when entering or leaving a port, in a marine engine operated with gas fuel.SOLUTION: When entering a coast C2 in a general sea area, a tuning state of a marine engine 1 is switched from a first tuning state to a second tuning state which has worse fuel consumption and less NOX emissions than the first tuning state.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to a marine engine control device and a method for operating a marine engine. [Background technology]

[0002] Marine engines are subject to the SO X No X Emissions of SO are regulated in certain marine areas (Emission Control Areas (ECAs)). X No X Emissions from ECAs are subject to particularly strict regulations. Emission regulations in ECAs are also called Tier 3, and are distinguished from Tier 2, which is the emission regulation in other sea areas (general sea areas).

[0003] For example, the following Patent Document 1 discloses an invention in which an automatic ship position detection means is used to identify the positional relationship between the ship and the boundary of exhaust gas regulation-related sea areas (ECA and general sea areas), and the engine exhaust gas purification state is switched to a state that complies with the regulations according to this positional relationship. When entering a regulated sea area, the purification state is automatically switched to one that clears the regulations, and when leaving the regulated sea area, the purification state is automatically switched to one that cancels the regulation-clearing state. This makes it possible to accurately and quickly clear regulations related to exhaust gas. The exhaust gas purification state is switched, for example, by switching the type of fuel (heavy oil A or heavy oil C), switching the purification device ON / OFF, or switching the type of purification device.

[0004] In addition, the following Patent Document 2 describes how the NO X The technology to switch the emission of NO in diesel engines has been presented. X There is a trade-off between emissions and fuel efficiency. X Tuning to reduce NO emissions will result in poorer fuel economy, while tuning to improve fuel economy will result in poorer NO emissions. X Therefore, in the invention of the same document, the first tuning state is compared with a second tuning state which has worse fuel economy than the first tuning state and has a higher NO XIn general waters (Tier 2), the first tuning state allows for good fuel economy, while in ECAs (Tier 3), the second tuning state allows for low NO emissions. X emissions can be kept below the Tier 3 standard. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2010-69999 A [Patent Document 2] Patent Publication No. 2021-32209 Summary of the Invention [Problem to be solved by the invention]

[0006] By the way, marine engines have traditionally used heavy oil, but in response to recent demands for environmental protection, X The use of gas fuel (LNG), which emits less carbon dioxide and soot, is on the rise. Compared to heavy fuel oil, LNG has a lower CO 2 This can reduce CO emissions by about 25-30%, but there is a problem of methane slip, where unburned gas fuel (methane gas) remains in the exhaust gas. 2 methane has a higher greenhouse effect than CO 2 The reduction effect of this would be wiped out.

[0007] For example, methane slip can be reduced by tuning to improve fuel efficiency, but in that case, knocking becomes more likely to occur. In particular, during bow thruster operation, which moves the ship sideways when entering and leaving port, the load on the engine is greater than during normal operation, so the load on the engine fluctuates greatly when switching from normal operation (low load operation) to bow thruster operation (high load operation). During such transient operation with large load fluctuations, knocking can occur even with tuning that improves fuel efficiency, making operation difficult.

[0008] Therefore, an object of the present invention is to reduce methane slip in a marine engine operated with gas fuel and to suppress the occurrence of knocking during transient load operation from low load operation to high load operation when entering or leaving port. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides a control device for a marine engine operated with gas fuel, the control device being configured to change the tuning state of the marine engine from a first tuning state to a second tuning state that is worse in fuel economy than the first tuning state and has NOx when the marine engine enters a coastal port of a general sea area. X The present invention provides a control device for a marine engine that switches to a second tuning state in which emissions are lower.

[0010] In the above Patent Document 2, the tuning state was switched at the boundary between sea areas with different emission regulations (general sea areas and ECAs). In this way, when switching the tuning based on emission regulations, when entering or leaving a coast of a general sea area with looser regulations, there is no need to switch to the second tuning state, and the first tuning state with good fuel efficiency may be maintained. In contrast, in the present invention, by focusing on the problem of knocking occurring during transitional operation from low load operation to high load operation when entering or leaving a port, a new idea of ​​switching the tuning state when entering a coast of a general sea area that is not an ECA has been reached. As a result, during normal navigation (other than entering or leaving a port), the first tuning state allows the ship to navigate in a fuel-efficient state, and when entering or leaving a port, the second tuning state allows the ship to suppress the occurrence of knocking even during transitional operation with large engine load fluctuations.

[0011] Specifically, for example, a tuning switching line is set on the boundary between coastal areas of general sea areas where engine load fluctuations are relatively large and coastal areas where engine load fluctuations are relatively small, and when the ship is offshore from the tuning switching line, the ship is in a first tuning state, and when the ship reaches the tuning switching line, the state is switched from the first tuning state to the second tuning state.

[0012] For example, the tuning state can be changed by changing the timing of supplying pilot fuel to the combustion chamber. In this case, the timing of supplying pilot fuel to the combustion chamber is earlier in the first tuning state than in the second tuning state.

[0013] Also, the tuning state can be switched by changing the temperature of the air supplied to the combustion chamber (intake air temperature). In this case, the intake air temperature in the first tuning state is higher than that in the second tuning state.

[0014] Also, the tuning state can be switched by changing the pressure of the air supplied to the combustion chamber (intake pressure). In this case, the first tuning state has a lower intake pressure than the second tuning state.

[0015] The present invention relates to a method of operating a marine vessel having an engine operated with gas fuel, the method comprising the steps of: When entering a coastal port in a general sea area, the tuning state of the engine is changed from a first tuning state to a state having a worse fuel economy than the first tuning state and having NO X The method may also be characterized as a method of operating a vessel by switching to a second tuning state that has lower emissions. Effect of the Invention

[0016] As described above, according to the present invention, it is possible to suppress the occurrence of knocking during transitional operation from low load operation to high load operation when entering or leaving port, and to reduce fuel consumption and methane slip during normal navigation other than when entering or leaving port. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram of a marine dual fuel engine. [Diagram 2] FIG. 2 is a cross-sectional view of a cylinder of the marine dual-fuel engine. [Diagram 3]FIG. 2 is a block diagram of the marine dual-fuel engine and a control device. [Figure 4] FIG. 4 is a diagram showing the state of the engine when the air excess ratio and the load applied to the engine are changed. [Diagram 5] 4 is a graph showing a relationship between the opening and closing timing of the intake valve and the exhaust valve and the timing of injecting gas fuel. [Figure 6] 4 is a graph showing the relationship between the timing of pilot fuel injection and the rate of improvement in fuel economy and methane slip. [Figure 7] 4 is a graph showing the relationship between intake air temperature and the improvement rate of fuel efficiency and methane slip. [Figure 8] 4 is a graph showing the relationship between intake pressure and the improvement rate of fuel efficiency and methane slip. [Figure 9] FIG. 1 is a plan view showing a ship entering a coastal port in an Emission Control Area (ECA). [Figure 10] FIG. 2 is a plan view showing a ship entering a coastal port in a general sea area. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0019] 1 shows a marine engine 1 (hereinafter simply referred to as “engine 1”) to be installed on a ship. The engine 1 has an engine body 2, a supercharger 3, an intake air temperature adjustment means 4, and an intake air pressure adjustment means 5.

[0020] The engine body 2 has a plurality of (six in the illustrated example) cylinders 6. As shown in Fig. 2, each cylinder 6 has a cylinder liner 7, a cylinder cover 8, a piston 9, an intake port 10, an intake valve 11, an exhaust port 12, and an exhaust valve 13. The space defined by the cylinder liner 7, the cylinder cover 8, and the piston 9 forms a combustion chamber 14.

[0021] A fuel supply means is provided for each cylinder 6. In this embodiment, two fuel supply means are provided: a liquid fuel supply means 21 that supplies liquid fuel (e.g., heavy oil), and a gas fuel supply means 22 that supplies gas fuel (e.g., LNG). That is, the engine 1 of this embodiment is a so-called dual fuel engine that can be switched between a diesel operation mode in which the engine is operated with liquid fuel and a gas operation mode in which the engine is operated with gas fuel.

[0022] Liquid fuel supply means 21 includes liquid fuel injection unit 21a having an injection port that opens into combustion chamber 14 in cylinder 6, and pump 21b that pressure-feeds liquid fuel to liquid fuel injection unit 21a. The amount of liquid fuel injected from the injection port of liquid fuel injection unit 21a is adjusted by an injection amount adjustment unit (e.g., a control rack) built into pump 21b.

[0023] The gas fuel supplying means 22 has a gas fuel injection unit 22a having an injection port opening into the intake port 10, and a gas compressor 22b that pressure-feeds gas fuel to the gas fuel injection unit 22a. An injection amount adjustment unit (e.g., a solenoid) provided in the gas fuel injection unit 22a adjusts the amount of liquid fuel injected from the injection port of the gas fuel injection unit 22a.

[0024] Since a mixture of gas fuel and air does not ignite simply by being compressed by the piston 9, each cylinder 6 is provided with an ignition means. In this embodiment, pilot fuel supply means 23 that supplies pilot fuel (e.g., heavy oil) to the combustion chamber 14 is provided as the ignition means. Pilot fuel supply means 23 has pilot fuel injection section 23a having an injection port opening into the combustion chamber 14, and pump 23b that pressure-feeds pilot fuel to pilot fuel injection section 23a. The amount of liquid fuel injected from the injection port of pilot fuel injection section 23a is adjusted by an injection amount adjustment section (e.g., a solenoid) provided in pilot fuel injection section 23a. In addition, an ignition plug may be provided as the ignition means.

[0025] 1, the turbocharger 3 has a compressor 31, a turbine 32, and a rotating shaft 33 connecting them. Exhaust gas discharged from the engine body 2 is supplied to the turbine 32 via the exhaust pipe 17, and the turbine 32, the rotating shaft 33, and the compressor 31 are rotated integrally by the pressure of the exhaust gas. As a result, air taken in from the outside is compressed by the compressor 31 and supplied to the intake port 10 of each cylinder 6 via the intake pipe 15.

[0026] The intake temperature adjusting means 4 adjusts the temperature of air (intake temperature) supplied to each cylinder 6. The intake temperature adjusting means 4 of this embodiment adjusts the temperature of air flowing through the intake pipe 15, and has a high-temperature cooling section 41 using jacket cooling water as a refrigerant and a low-temperature cooling section 42 using cooler cooling water as a refrigerant. The high-temperature cooling section 41 has, for example, a high-temperature cooling water passage 41a through which water discharged from the cooling water passage of the engine body 2 (water that has cooled the engine body 2) flows. The low-temperature cooling section 42 has a low-temperature cooling water passage 42a provided downstream of the high-temperature cooling section 41, and a flow rate adjustment valve 42b that adjusts the flow rate of cooling water supplied to the low-temperature cooling water passage 42a.

[0027] The high-temperature cooling section 41 removes rough heat from the air in the intake pipe 15 by continuously flowing the water that has cooled the engine body 2 into the high-temperature cooling water passage 41a, and does not control the temperature of the air in the intake pipe 15. Therefore, for example, a temperature sensor is provided to detect the temperature of the air in the intake pipe 15 cooled by the high-temperature cooling section 41, and the air in the intake pipe 15 can be kept at a predetermined temperature by adjusting the opening degree of the flow rate control valve 42b of the low-temperature cooling section 42 based on the detection result of this temperature sensor to adjust the amount of water flowing into the low-temperature cooling water passage 42a.

[0028] The intake pressure adjusting means 5 adjusts the pressure of air (intake pressure) supplied to the cylinders 6. In this embodiment, a bypass pipe 18 branched from an exhaust pipe 17 connecting each cylinder 6 and the turbine 32 is provided, and the intake pressure adjusting means 5 is provided in this bypass pipe 18. The intake pressure adjusting means 5 has a flow rate adjusting valve 50 (wastegate valve) provided in the bypass pipe 18. The flow rate of the exhaust gas supplied to the turbine 32 is adjusted by adjusting the opening degree of the flow rate adjusting valve 50. This adjusts the rotation speed of the turbocharger 3 to adjust the compression rate by the compressor 31, and as a result, the intake pressure is adjusted. For example, a pressure sensor that detects the pressure in the intake pipe 15 is provided in the engine body 2, and the opening degree of the flow rate adjusting valve 50 is adjusted based on the detection result of this pressure sensor, thereby making it possible to set the intake pressure to a predetermined value.

[0029] The engine 1 is controlled by a control device 60 according to an embodiment of the present invention. As shown in Fig. 3, the control device 60 is connected to the liquid fuel supply means 21, the gas fuel supply means 22, the pilot fuel supply means 23, the intake air temperature adjustment means 4, and the intake air pressure adjustment means 5, and controls them. The control device 60 of this embodiment is connected to the injection amount adjustment section of the pump 21b of the liquid fuel supply means 21, the injection amount adjustment section of the gas fuel injection section 22a of the gas fuel supply means 22, the injection amount adjustment section of the pilot fuel injection section 23a of the pilot fuel supply means 23, the flow rate adjustment valve 42b of the low-temperature cooling section 42 of the intake air temperature adjustment means 4, and the flow rate adjustment valve 50 of the intake air pressure adjustment means 5, and controls the opening degree of these.

[0030] The control device 60 operates the engine 1 in either a diesel operation mode or a gas operation mode. In the diesel operation mode, with the gas fuel supply means 22 stopped, liquid fuel and pilot fuel are supplied to the combustion chamber 14 by the liquid fuel supply means 21 and the pilot fuel supply means 23. On the other hand, in the gas operation mode, with the liquid fuel supply means 21 stopped, gas fuel and pilot fuel are supplied to the combustion chamber 14 by the gas fuel supply means 22 and the pilot fuel supply means 23.

[0031] When the control device 60 operates the engine 1 in the gas operation mode, it is possible to switch between a first tuning state, which is tuned to make the gas fuel relatively easier to burn, and a second tuning state, which makes the gas fuel less flammable than in the first tuning state. In the first tuning state, fuel economy and methane slip are lower than in the second tuning state, and in the second tuning state, NOx emissions are lower than in the first tuning state, and knocking is less likely to occur even during transient operation. Table 1 below shows the parameters to be adjusted when switching the tuning state and the relative state of each tuning state.

[0032] [Table 1]

[0033] FIG. 4 shows the state of engine 1 when the excess air ratio in the mixture and the load on the engine are changed. As shown in the figure, if the excess air ratio is too small (too rich in fuel), knocking occurs in engine 1, and if the excess air ratio is too large (too lean in fuel), engine 1 misfires. The range of excess air ratios in which such knocking and misfires do not occur is the operable range (scattered region) in which engine 1 operates. The greater the load on the engine, the smaller the range of excess air ratios in the operable range. Within this operable range, a first tuning state in which the excess air ratio is relatively low (i.e., the proportion of fuel in the mixture is high) and a second tuning state in which the excess air ratio is relatively high (i.e., the proportion of fuel in the mixture is low) are set.

[0034] For example, if the engine is in the first tuning state during a transition from normal operation to bow thruster operation, the engine load increases rapidly, causing the intake air to be unable to keep up and the amount of air in the mixture to decrease, causing the engine to move from the line of the first tuning state to the upper left in the figure and enter the knocking region (see arrow A1). After that, the intake air catches up, the proportion of air in the mixture increases, and the engine returns to the line of the first tuning state (see arrows A2 and B2).

[0035] On the other hand, when the engine is in the second tuning state during transient operation, the engine load also increases rapidly, causing the line of the second tuning state to be displaced in the upper left direction in the figure (see arrow B1). However, since the second tuning state is farther away from the knocking region than the first tuning state, it is less likely to enter the knocking region even during transient operation, and therefore knocking can be avoided.

[0036] 5, in this embodiment, the period during which gas fuel is injected from the gas fuel injection unit 22a is set between closing the exhaust valve 13 and closing the intake valve 11. That is, the injection of gas fuel from the gas fuel injection unit 22a is started after the exhaust valve 13 is closed, and the injection of gas fuel from the gas fuel injection unit 22a is completed before the intake valve 12 is closed. This prevents the gas fuel from blowing by (leaking into the exhaust system) and remaining in the intake port 10.

[0037] Figure 6 shows the relationship between the timing of pilot fuel injection and the improvement rate of fuel economy and methane slip. The figure uses as a reference the fuel economy and methane slip when pilot fuel injection starts when the piston 9 of the cylinder 6 reaches near top dead center (for example, 10 degrees before top dead center), and shows the improvement rate of fuel economy and methane slip when the pilot fuel injection start timing is advanced from this. The horizontal axis of the figure represents how much the pilot fuel injection start timing is advanced from the reference (10 degrees before top dead center) in terms of the rotation angle of the crankshaft. It can be seen from this figure that the earlier the pilot fuel injection start timing is, the higher the improvement rate of fuel economy and methane slip.

[0038] In this embodiment, the injection amount adjustment section (e.g., the timing of exciting a solenoid) of the pilot fuel injection section 23a of the pilot fuel supply means 23 is controlled so that the timing of starting the supply of pilot fuel in the first tuning state is earlier than the timing of starting the supply of pilot fuel in the second tuning state. Specifically, the timing of injection of pilot fuel is set to the end of the compression stroke when the piston 9 reaches from the bottom dead center to the top dead center (immediately before the top dead center). For example, the timing of starting the pilot fuel injection in the first tuning state is set to 15° before the top dead center, and the timing of starting the pilot fuel injection in the second tuning state is set to 10° before the top dead center. As a result, the first tuning state improves fuel economy and methane slip more than the second tuning state, while the NO X Emissions will increase and knocking will become more likely to occur.

[0039] FIG. 7 shows the relationship between the intake air temperature and the improvement rate of fuel economy and methane slip. The figure shows the improvement rate of fuel economy and methane slip when the intake air temperature is increased relative to a reference value. It can be seen from this figure that the higher the intake air temperature, the higher the improvement rate of fuel economy and methane slip. In this embodiment, the flow rate regulating valve 42b of the low-temperature cooling section 42 of the intake air temperature adjusting means 4 in each tuning state is controlled so that the intake air temperature in the first tuning state is higher than the intake air temperature in the second tuning state. As a result, in the first tuning state, fuel economy and methane slip are improved more than in the second tuning state, while NO X Emissions will increase and knocking will become more likely to occur.

[0040] FIG. 8 shows the relationship between intake pressure and the improvement rate of fuel economy and methane slip. The figure shows the improvement rate of fuel economy and methane slip when the intake pressure is reduced from a reference value. It can be seen from this figure that the lower the intake pressure, the higher the improvement rate of fuel economy and methane slip. In this embodiment, the flow rate regulating valve 50 of the intake pressure regulating means 5 in each tuning state is controlled so that the intake pressure in the first tuning state is lower than the intake pressure in the second tuning state. As a result, in the first tuning state, fuel economy and methane slip are improved more than in the second tuning state, while NO X Emissions will increase and knocking will become more likely to occur.

[0041] FIG. 9 shows a ship S having the engine 1 and the control device 60 entering the coast C1 of an emission control sea area (Tier 3). In this case, the tuning state is switched based on the boundary line L1 between the general sea area (Tier 2) and the emission control sea area (Tier 3). Specifically, when the ship S is offshore from the boundary line L1, the engine 1 is in a first tuning state with good fuel efficiency (the number in parentheses after the symbol S in the figure indicates the tuning state). Then, when the ship S approaches the boundary line L1, the engine 1 is switched from the first tuning state to a second tuning state that satisfies the Tier 3 standard by a command from the control device 60. After that, when the ship S berths, a high-load operation (such as a bow thruster operation) is performed in which a large load is applied to the engine 1. At this time, the engine 1 undergoes a transitional operation from a low-load operation to a high-load operation, which results in a large load fluctuation, but the engine 1 can enter the port smoothly because it is in the second tuning state in which knocking is unlikely to occur. Note that. When departing from the coast C1 of the emission control area, the above-mentioned procedure is reversed to switch from the second tuning state to the first tuning state.

[0042] 10 shows the ship S entering port C2 on the coast of a general sea area (Tier 2). In this case, if only emission regulations are considered as in the past, there is no need to switch the tuning state of the engine 1, and the ship may enter port in the first tuning state with good fuel efficiency. In this embodiment, focusing on the fact that the second tuning state is less likely to cause knocking during transient operation than the first tuning state, the first tuning state is switched to the second tuning state even when the ship S enters port C2 on the coast of a general sea area.

[0043] Specifically, a tuning switching line L2 is set in advance on the boundary between the coastal area C2 of the general sea area, which is an area near the coast where the engine load fluctuation is relatively large, and the offshore area where the engine load fluctuation is relatively small. Since the switching from the first tuning to the second tuning can be performed immediately before the transient operation in which low-load operation is switched to high-load operation (bow thruster operation), the distance of the tuning switching line L2 from the coastline of the coast C2 is much shorter than the distance of the boundary line L1 in Fig. 9 from the coastline of the coast C1, and is set to, for example, 1 km or less.

[0044] When the vessel S is offshore from the tuning switching line L2, the engine 1 is in a first tuning state with good fuel efficiency. Then, when the vessel S reaches the tuning switching line L2, the engine 1 is switched from the first tuning state to the second tuning state by a command from the control device 60. This suppresses knocking during transitional operation in which low-load operation is switched to high-load operation (bow thruster operation) when entering the coastal waters C2, allowing for smooth entry into the port. When departing from the coastal waters C2 in the general sea area, the engine 1 is switched from the second tuning state to the first tuning state in the reverse procedure to that described above.

[0045] The present invention is not limited to the above embodiment. For example, in the above embodiment, the control device 60 automatically switches from the first tuning state to the second tuning state, but the tuning state may be switched manually. For example, when entering the coast C2 of the general sea area (see FIG. 10), the tuning state may be manually switched from the first tuning state to the second tuning state immediately before starting a transitional operation in which low-load operation is switched to high-load operation. Also, when leaving the coast C2 of the general sea area, the tuning state may be manually switched from the second tuning state to the first tuning state immediately after the high-load operation is completed.

[0046] In the above embodiment, the tuning state is switched by adjusting the pilot fuel supply timing, the intake temperature, and the intake pressure. However, it is not necessary to adjust all of these items. The tuning state may be switched by adjusting one or more selected from these items.

[0047] The present invention is not limited to so-called dual fuel engines having two fuel supply means for liquid fuel and gas fuel, but can also be applied to gas engines that do not have liquid fuel supply means 21 and are operated only with gas fuel. [Explanation of symbols]

[0048] 1. Marine engines 2 Engine body 3. Turbocharger 4. Intake temperature control means 5. Intake pressure adjustment means 6 cylinders 7 Cylinder Liner 8 Cylinder cover 9 Piston 10 Intake port 11 Intake valve 12 Exhaust port 13 Exhaust valve 14 Combustion chamber 15 Intake pipe 17 Exhaust pipe 18 Bypass pipe 21 Liquid fuel supply means 21a Liquid fuel injection part 21b Pump 22 Gas fuel supply means 22a Gas Compressor 22b Pump 23 Pilot fuel supply means 23a Pilot fuel injection section 23b Pump 31 Compressor 32 Turbine 33 Rotation axis 41 High temperature cooling section 41a High temperature cooling waterway 42 Low temperature cooling section 42a Low temperature cooling waterway 42b Flow control valve 50 Flow control valve 60 Control device C1 Coastal areas of emission control areas C2 Coastal waters of general sea areas L1 Boundary between emission control areas and general sea areas L2 Tuning switch line S ship

Claims

1. A control device for a marine engine operated with gas fuel, comprising: When entering a coastal port of a general sea area, the tuning state of the marine engine is changed from a first tuning state to a state in which fuel consumption is worse than that of the first tuning state and NO Ｘ A control device for a marine engine that switches to a second tuning state having lower emissions.

2. a tuning switching line is set at a boundary between an area of ​​the coast where the engine load fluctuation is relatively large and an area of ​​the coast where the engine load fluctuation is relatively small; When the vessel is offshore from the tuning switching line, the vessel is in the first tuning state, 2. The control device for a marine engine according to claim 1, wherein the tuning state is switched from the first tuning state to the second tuning state when the marine vessel reaches the tuning switch line.

3. 2. The control device for a marine engine according to claim 1, wherein the timing of supplying pilot fuel to the combustion chamber of the marine engine in the first tuning state is earlier than that in the second tuning state.

4. 2. The control device for a marine engine according to claim 1, wherein the temperature of air supplied to the combustion chamber of the marine engine is higher in the first tuning state than in the second tuning state.

5. 2. The control device for a marine engine according to claim 1, wherein a pressure of air supplied to a combustion chamber of the marine engine is lower in the first tuning state than in the second tuning state.

6. 1. A method of operating a marine vessel having a gas-fueled engine, comprising the steps of: When entering a coastal port in a general sea area, the tuning state of the engine is changed from a first tuning state to a state in which fuel efficiency is worse than that of the first tuning state and NO Ｘ A method for operating a vessel, comprising: switching to a second tuning state in which emissions of

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