Marine internal combustion engine

Abstract

The present invention relates to a marine internal combustion engine. The engine (1) of the marine internal combustion engine includes: a main engine (10); an exhaust gas turbocharger (4) that uses the exhaust gas supplied to the turbine (42) to drive the compressor (41); an EGR passage (81) that connects a portion on the downstream side of the turbine in the exhaust passage (31) and a portion on the upstream side of the compressor in the intake passage (21); an EGR valve (82) that opens and closes the EGR passage; an exhaust gas regulating system (9) that regulates the flow rate of the exhaust gas supplied to the turbine; and a controller (100) that controls the exhaust gas regulating system according to the opening degree of the EGR valve. Compared with the case where the EGR valve is in a closed state, when the EGR valve is in an open state, the controller increases the flow rate of the exhaust gas supplied to the turbine. Thus, in a marine internal combustion engine including an exhaust gas turbocharger, EGR operation and normal operation can be balanced.

Description

Technical Field

[0001] The present disclosure relates to a marine internal combustion engine. Background Art

[0002] In Patent Document 1, as an example of an internal combustion engine not limited to marine use, a supercharged engine including an EGR device is disclosed. Specifically, the following is disclosed in Patent Document 1: Based on the intake air temperature of the supercharger, the breakage boost pressure corresponding to the breakage temperature that causes breakage of the supercharger is obtained, and the boost pressure of the supercharger is limited with the maximum boost pressure set lower than the breakage boost pressure as the upper limit.

[0003] According to Patent Document 1 above, in the case of an engine including an EGR device, depending on the performance of the EGR cooler, the EGR gas flowing back into the intake passage may become high temperature. Therefore, when the supercharger sucks in the EGR gas, the temperature of the air sucked in by the supercharger (intake air temperature) becomes too high, which may cause breakage of the supercharger.

[0004] In response to such a problem, the engine disclosed in Patent Document 1 above can prevent breakage of the supercharger by limiting the boost pressure of the supercharger based on the intake air temperature. Here, the engine related to this document is configured to include a bypass valve that allows air to flow around the supercharger as a mechanism for limiting the boost pressure of the supercharger.

[0005] Patent Document 1: Japanese Patent Laid-Open Gazette No. 2009-299537 Summary of the Invention

[0006] -Technical Problem to be Solved by the Invention-

[0007] As a specific countermeasure for dealing with the above problem, for example, when returning the EGR gas, the opening of the bypass valve is considered, etc., so as to reduce the flow rate or flow velocity of the exhaust gas flowing into the rotor, turbine, etc. constituting the supercharger, thereby preventing the boost pressure from becoming too high.

[0008] In addition, not limited to the bypass valve, it is also possible to consider appropriately adjusting the flow velocity of the exhaust gas flowing into the supercharger by using a so-called variable nozzle turbine depending on whether the EGR gas is returned.

[0009] However, the above problem is caused by the performance of the EGR cooler. Therefore, in the case of a marine internal combustion engine that can use a large and high-performance cooling device, for example, the above-described control is usually not required.

[0010] As a method for overcoming the NOx limit, especially the Tier 3 limit, imposed on ships, a marine internal combustion engine with an EGR device as disclosed in the above-mentioned Patent Document 1 was studied.

[0011] When the above marine internal combustion engine further includes an exhaust gas turbocharger, the specific heat ratio of the air compressed by the compressor decreases due to the EGR gas contained in the air. The decrease in the specific heat ratio causes a decrease in the scavenging pressure (boost pressure). The decrease in the scavenging pressure leads to deterioration of fuel economy, generation of smoke in the exhaust gas, etc., which is not preferable.

[0012] Therefore, it is speculated that the EGR gas will be recirculated, thereby setting the fuel injection pressure relatively high in advance, or reducing the nozzle area upstream of the turbine (hereinafter referred to as "turbine nozzle area") in advance to compensate for the scavenging pressure that decreases with the decrease in the specific heat ratio.

[0013] However, the sea areas where ships navigate are not limited to the sea areas regulated by the above-mentioned Tier 3 limit (hereinafter referred to as "Tier 3 sea areas"). It is also conceivable to navigate in the sea areas regulated by the Tier 2 limit (hereinafter referred to as "Tier 2 sea areas") where the NOx emission limit is looser than the Tier 3 limit, or to travel back and forth between Tier 3 sea areas and Tier 2 sea areas.

[0014] To cope with the above situation, it can be considered to control the internal combustion engine so that the EGR valve is opened to recirculate the EGR gas in the Tier 3 sea area, while the EGR valve is closed in the Tier 2 sea area to prevent the EGR gas from recirculating.

[0015] However, in order not to cause problems related to the specific heat ratio during EGR operation (operation suitable for Tier 3 sea areas) in which the EGR gas is recirculated, if the fuel injection pressure is set relatively high as described above, during normal operation in which the EGR gas is not recirculated (operation suitable for Tier 2 sea areas), there will be a problem of increased NOx emissions.

[0016] Therefore, it is conceivable to reduce the turbine nozzle area in advance as described above instead of increasing the fuel injection pressure. However, in this case, the scavenging pressure rises excessively during normal operation, and the in-cylinder pressure may exceed the range allowed by the design.

[0017] In this way, the inventors of the present application conducted research from a different perspective from the above-mentioned Patent Document 1, and as a result, newly discovered technical problems peculiar to marine internal combustion engines. After further intensive research, the inventors of the present application finally created a control method different in structural nature from that described in the document.

[0018] The present disclosure is accomplished to solve the above problems, and its object is to balance EGR operation and normal operation in a marine internal combustion engine including an exhaust gas turbocharger.

[0019] -Technical solutions for solving technical problems-

[0020] The first aspect of the present disclosure relates to a marine internal combustion engine. The marine internal combustion engine includes a two-stroke main engine, an intake passage and an exhaust passage, an exhaust gas turbocharger, an EGR passage, an EGR valve, an exhaust gas regulation system, and a controller. The intake passage and the exhaust passage are connected to the main engine. The exhaust gas turbocharger has a compressor arranged in the intake passage and a turbine arranged in the exhaust passage, and drives the compressor by using the exhaust gas supplied to the turbine. The EGR passage connects a portion on the downstream side of the turbine in the exhaust passage and a portion on the upstream side of the compressor in the intake passage. The EGR valve opens and closes the EGR passage. The exhaust gas regulation system regulates the flow rate or flow velocity of the exhaust gas supplied to the turbine. The controller controls the exhaust gas regulation system according to the opening degree of the EGR valve.

[0021] According to the first aspect of the present disclosure, compared with the case where the EGR valve is in the open state, when the EGR valve is in the closed state, the controller reduces the flow rate or flow velocity of the exhaust gas supplied to the turbine.

[0022] Here, the "exhaust gas regulation system" includes a bypass pipeline that regulates the flow rate of the exhaust gas by bypassing the turbine, a variable nozzle that regulates the flow velocity of the exhaust gas by changing the nozzle area upstream of the turbine, and the like.

[0023] According to the first aspect, compared with the case of performing EGR operation (the case where the EGR valve is in the open state) such as sailing in Tier 3 waters where EGR gas is recirculated, when performing normal operation (the case where the EGR valve is in the closed state) such as sailing in Tier 2 waters where EGR gas is not recirculated, the controller reduces the flow rate or flow velocity of the exhaust gas supplied to the turbine.

[0024] In this way, even if the turbine nozzle area is pre-reduced to achieve a scavenging pressure suitable for EGR operation, by reducing the flow rate or flow velocity of the exhaust gas supplied to the turbine during normal operation, it is possible to suppress an excessive increase in the scavenging pressure during normal operation, so that the in-cylinder pressure can converge within an allowable range.

[0025] In other words, compared with the case of performing normal operation, when performing EGR operation, the controller increases the flow rate or flow velocity of the exhaust gas supplied to the turbine.

[0026] In this way, even if the flow rate of the exhaust gas is set low, such as by using a bypass line, in order to achieve a scavenging pressure suitable for normal operation, by closing the bypass line during EGR operation, an appropriate scavenging pressure can be maintained during EGR operation.

[0027] According to a second aspect of the present disclosure, it may also be the case that the exhaust gas regulating system has a bypass passage and a bypass valve. The bypass passage connects a portion upstream of the turbine in the exhaust passage and a portion downstream of the turbine. The bypass valve adjusts the flow rate of the exhaust gas supplied to the turbine by opening and closing the bypass passage.

[0028] According to the second aspect described above, when the bypass valve is in the open state, the flow rate of the exhaust gas supplied to the turbine can be relatively reduced. On the other hand, when the bypass valve is in the closed state, the flow rate of the exhaust gas supplied to the turbine can be relatively increased. By appropriately opening and closing the bypass valve, the scavenging pressure can be maintained at an appropriate value when shifting from EGR operation to normal operation (or vice versa).

[0029] According to a third aspect of the present disclosure, it may also be the case that the exhaust gas turbocharger is configured such that when either the EGR valve or the bypass valve is in the open state, the ejection pressure of the exhaust gas turbocharger converges within a specified appropriate range.

[0030] The "ejection pressure" referred to here means the pressure of the air ejected from the compressor of the exhaust gas turbocharger (boost pressure). The magnitude of the ejection pressure is substantially equal to the above-mentioned scavenging pressure. The "appropriate range" referred to here is a pressure range set to ensure that the in-cylinder pressure of the main engine does not exceed the allowable range.

[0031] According to the third aspect described above, for example, by reducing the turbine nozzle area during the design phase, the ejection pressure of the exhaust gas turbocharger is set relatively high in advance. In this way, it is possible to predict a decrease in the ejection pressure when the EGR valve is in the open state (or when the bypass valve is in the open state), so that the ejection pressure can converge within an appropriate range.

[0032] According to a fourth aspect of the present disclosure, it may also be the case that when the EGR valve changes from the open state to the closed state, the controller causes the bypass valve to be at least temporarily fully open.

[0033] According to the fourth aspect described above, by making the bypass valve fully open immediately after shifting from EGR operation to normal operation or during the transition, the EGR gas remaining in the main engine can be discharged, and it can be discharged early. In this way, the shift from EGR operation to normal operation can be carried out smoothly.

[0034] According to a fifth aspect of the present disclosure, it may also be the case that the marine internal combustion engine includes an exhaust gas throttling mechanism that adjusts the ratio of the flow rate of the exhaust gas passing through the turbine to the flow rate of the exhaust gas bypassing the turbine via the bypass passage. The exhaust gas throttling mechanism is configured such that, regardless of whether the bypass valve is in an open state, the flow rate of the exhaust gas bypassing the turbine is less than the flow rate of the exhaust gas passing through the turbine.

[0035] When the bypass valve is in an open state, the exhaust gas bypasses the turbine via the bypass passage. However, if more exhaust gas than necessary bypasses the turbine, the scavenging pressure will decrease, which is not conducive to maintaining the scavenging pressure.

[0036] According to the above fifth aspect, even when the bypass valve is in an open state, the exhaust gas throttling mechanism causes the flow rate of the exhaust gas bypassing the turbine to be less than the flow rate of the exhaust gas passing through the turbine. In this way, the flow rate required to drive the turbine can be ensured, which is conducive to maintaining the scavenging pressure.

[0037] According to a sixth aspect of the present disclosure, it may also be the case that a throttle hole that narrows the passage cross-sectional area of the bypass passage is provided in the bypass passage, and the exhaust gas throttling mechanism is constituted by the throttle hole.

[0038] The above sixth aspect is effective in maintaining the scavenging pressure.

[0039] According to a seventh aspect of the present disclosure, it may also be the case that, for the marine internal combustion engine, the exhaust gas turbocharger includes variable nozzles that adjust the flow velocity of the exhaust gas supplied to the turbine by changing the passage area around the turbine, and the exhaust gas adjustment system is constituted by the variable nozzles.

[0040] According to the above seventh aspect, when the variable nozzles are narrowed, the flow velocity of the exhaust gas supplied to the turbine can be relatively increased. On the other hand, when the variable nozzles are opened, the flow velocity of the exhaust gas supplied to the turbine can be relatively decreased. With this configuration, when shifting from EGR operation to normal operation (or vice versa), the scavenging pressure can be maintained at an appropriate value.

[0041] According to an eighth aspect of the present disclosure, it may also be the case that the exhaust gas turbocharger is configured such that when the EGR valve is in an open state and the passage area is narrowed using the variable nozzles, or when the EGR valve is in a closed state and the passage area is enlarged using the variable nozzles, the discharge pressure of the exhaust gas turbocharger converges within a specified range.

[0042] According to the eighth aspect described above, for example, by reducing the area of the turbine nozzle during the design stage, the ejection pressure of the exhaust gas turbocharger is set relatively high in advance. In this way, it is possible to predict the reduction in scavenging pressure that occurs when the EGR valve is in the open state or when the passage area is enlarged by the variable nozzle, and thus the scavenging pressure can be converged within an appropriate range.

[0043] - Effects of the Invention -

[0044] As described above, according to the present disclosure, in a marine internal combustion engine including an exhaust gas turbocharger, EGR operation and normal operation can be achieved in a balanced manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a system diagram showing a schematic structure of a marine internal combustion engine;

[0046] Figure 2 is a flowchart showing a switching sequence from EGR operation to normal operation;

[0047] Figure 3 is a flowchart showing a switching sequence from normal operation to EGR operation;

[0048] Figure 4 is a diagram corresponding to a modified example of a marine internal combustion engine Figure 1 of.

[0049] - REFERENCE SIGNS -

[0050] 1 - Engine (marine internal combustion engine); 1' - Engine (modified example of marine internal combustion engine); 10 - Main engine; 21 - Intake passage; 31 - Exhaust passage; 4 - Exhaust gas turbocharger; 41 - Compressor; 42 - Turbine; 43 - Variable nozzle (modified example of exhaust gas regulation system); 81 - EGR passage; 82 - EGR valve; 9 - Exhaust gas regulation system; 91 - Bypass passage; 92 - Throttle hole (exhaust gas throttling mechanism); 93 - Bypass valve; 100 - Controller. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. It should be noted that the following description is only for illustrative purposes.

[0052] Figure 1 is a system diagram showing a schematic structure of a marine internal combustion engine (hereinafter simply referred to as "engine 1").

[0053] The engine 1 is an in-line multi-cylinder diesel engine including a plurality of cylinders 11. The engine 1 is configured as a direct-current scavenging two-stroke cycle internal combustion engine and is installed on large ships such as tankers, container ships, and vehicle carriers.

[0054] The engine 1 installed on the ship includes a main engine 10 for propelling the ship. Therefore, the output shaft of the main engine 10 is connected to the propeller (not shown) of the ship through a propeller shaft (not shown). When the engine 1 operates, the output of the engine 1 is transmitted to the propeller to propel the ship forward.

[0055] The engine 1 is also configured as an engine with a turbocharger. That is, as Figure 1 shown, the engine 1 according to the present embodiment is configured to include an exhaust gas turbocharger 4.

[0056] (1) Main structure

[0057] Next, the main parts of the engine 1 will be described.

[0058] As Figure 1 shown, the engine 1 includes: the above-mentioned main engine 10, an intake system 2 and an exhaust system 3 connected to the main engine 10, an exhaust gas turbocharger 4 that operates using the exhaust gas flowing in the exhaust system 3, an EGR (Exhaust Gas Recirculation) system 8 that returns the exhaust gas, an exhaust gas regulation system 9 that regulates the flow rate or velocity of the exhaust gas, and a controller 100 that controls each part of the engine 1.

[0059] Among them, the main engine 10 has a plurality of cylinders 11 (only four cylinders 11 are shown in Figure 1 ). The main engine 10 is a two-stroke main engine. Pistons (not shown) are respectively inserted into each cylinder 11, and the pistons can reciprocate. A combustion chamber is defined in each cylinder 11 by the inner wall of each cylinder 11, the ceiling surface of the cylinder head (not shown), and the top surface of the piston.

[0060] The main engine 10 further includes a scavenging air box 18 and an exhaust manifold 19. The scavenging air box 18 communicates with the combustion chamber of the main engine 10 and is configured to supply scavenging air to the combustion chamber 12. The exhaust manifold 19 communicates with the combustion chamber of the main engine 10 and can discharge the burned gas (exhaust gas) from the combustion chamber. The main engine 10 is connected to the intake system 2 (specifically, the intake passage 21 described later) via the scavenging air box 18, and on the other hand, the main engine 10 is connected to the exhaust system 3 (specifically, the exhaust passage 31 described later) via the exhaust manifold 19.

[0061] The intake system 2 has an intake passage 21 connected to the main engine 10. The intake system 2 is configured to send air into the main engine 10 via this intake passage 21. Specifically, in the intake passage 21 according to this embodiment, a compressor 41 and an air cooler 22 are sequentially provided from the upstream side. The compressor 41 compresses the air (fresh air) inhaled from the atmosphere together with the EGR gas described later, and the air cooler 22 cools the air compressed by the compressor 41. The air cooled by the air cooler 22 reaches the combustion chamber via the above-mentioned scavenging box 18.

[0062] The exhaust system 3 has an exhaust passage 31 connected to the main engine 10. The exhaust system 3 is configured to discharge the exhaust gas from the main engine 10 via this exhaust passage 31. Specifically, in the exhaust passage 31 according to this embodiment, a first branch portion (the connection portion of the upstream end of the bypass passage 91 and the exhaust passage 31) 31a that branches to the bypass passage 91 described later, a turbine 42 that drives the compressor 41 and is connected to the compressor 41, a confluence portion (the connection portion between the downstream end of the bypass passage 91 and the exhaust passage 31) 31b that converges with the bypass passage 91, and a second branch portion (the connection portion between the upstream end of the EGR passage 81 and the exhaust passage 31) 31c that branches to the EGR passage 81 described later are sequentially provided from the upstream side. The exhaust gas discharged from the combustion chamber flows into the exhaust passage 31 via the above-mentioned exhaust manifold 19, and then is released to the atmosphere through the turbine 42.

[0063] The exhaust gas turbocharger 4 has a compressor 41 arranged in the intake passage 21 and a turbine 42 arranged in the exhaust passage 31, and the exhaust gas turbocharger 4 is configured to drive the compressor 41 using the exhaust gas supplied to the turbine 42. Here, the compressor 41 is connected to the turbine 42 and rotates synchronously with each other. Therefore, when the compressor 41 is driven to rotate by the exhaust gas passing through the turbine 42, the air passing through this compressor 41 can be compressed.

[0064] The EGR system 8 has an EGR passage 81 that connects a portion downstream of the turbine 42 in the exhaust passage 31 (the second branch portion 31c) and a portion upstream of the compressor 41 in the intake passage 21. The EGR system 8 is configured as a so-called low-pressure EGR system, and the EGR system 8 is configured to circulate the exhaust gas via the EGR passage 81. Specifically, in the EGR passage 81 according to this embodiment, an EGR valve 82 and an EGR unit 83 are sequentially provided from the upstream side in the flow direction of the recirculated exhaust gas (hereinafter also referred to as "EGR gas").

[0065] Among them, the EGR valve 82 opens and closes the EGR passage 81. This EGR valve 82 operates according to the control signal input from the controller 100.

[0066] The EGR unit 83 is a combination of a scrubber that removes soot, SOx, etc. from the EGR gas, an EGR cooler that cools the EGR gas, and a blower that boosts the pressure of the EGR gas. It should be noted that when the pressure loss in the scrubber or the EGR cooler is small and the necessary amount of EGR gas can be circulated only by adjusting the opening degree of the EGR valve 82, the blower is not necessary.

[0067] The exhaust gas regulating system 9 controls the boost pressure of the exhaust gas turbocharger 4 (specifically, the pressure of the air ejected from the compressor 41) by regulating the flow rate or velocity of the exhaust gas supplied to the turbine 42. Specifically, the exhaust gas regulating system 9 according to the present embodiment is configured to regulate the flow rate of the exhaust gas supplied to the turbine 42, and the exhaust gas regulating system 9 includes a bypass passage 91, a bypass valve 93, and an exhaust gas throttling mechanism 92. It should be noted that, as described below, the exhaust gas throttling mechanism 92 is not necessary in the exhaust gas regulating system 9.

[0068] Among them, the bypass passage 91 connects a portion (first branch portion 31a) upstream of the turbine 42 in the exhaust passage 31 and a portion (confluence portion 31b) downstream of the turbine 42. On this bypass passage 91, an exhaust gas throttling mechanism 92 and a bypass valve 93 are arranged in order from the upstream side.

[0069] The bypass valve 93 opens and closes the bypass passage 91. The bypass valve 93 operates according to a control signal input from the controller 100.

[0070] The exhaust gas throttling mechanism 92 regulates the ratio of the flow rate of the exhaust gas passing through the turbine 42 (first flow rate) to the flow rate of the exhaust gas bypassing the turbine 42 via the bypass passage 91 (second flow rate). Specifically, regardless of whether the bypass valve 93 is in the open state, the exhaust gas throttling mechanism 92 is configured to make the second flow rate less than the first flow rate. By adopting the above structure, it is possible to ensure the minimum flow rate (first flow rate) required to drive the exhaust gas turbocharger 4, and only the flow rate (second flow rate) used to suppress the boost pressure can bypass the turbine 42.

[0071] The exhaust gas throttling mechanism 92 according to the present embodiment is composed of a throttle hole that narrows the passage cross-sectional area of the bypass passage 91. As described above, the exhaust gas throttling mechanism 92 is arranged upstream of the bypass valve 93 in the bypass passage 91.

[0072] It should be noted that the exhaust gas throttling mechanism 92 can also be arranged downstream of the bypass valve 93 and upstream of the confluence portion 31b. Additionally, the exhaust gas throttling mechanism 92 is not essential. It is also possible to endow the bypass valve 93 with the function of the exhaust gas throttling mechanism 92 to replace the arrangement of the exhaust gas throttling mechanism 92. In this case, by controlling the opening degree of the bypass valve 93, the flow rate of the exhaust gas supplied to the turbine 42 (specifically, the ratio of the first flow rate to the second flow rate) is adjusted.

[0073] It should be noted that when the EGR gas is circulated, the load of the exhaust gas turbocharger 4 is reduced by an amount corresponding to the flow rate of the exhaust gas flowing through the EGR passage 81, resulting in a decrease in the scavenging pressure. A decrease in the scavenging pressure will cause a decrease in the amount of air introduced into the cylinder 11, leading to deterioration of fuel economy, generation of smoke, etc., so it is not preferred. A similar problem also occurs when a part of the exhaust gas bypasses the turbine 42 (when the bypass valve 93 is opened).

[0074] Therefore, in the present embodiment, the above-mentioned decrease in the scavenging pressure is estimated, and adjustment is implemented in the design stage to reduce the turbine nozzle area of the exhaust gas turbocharger 4. The exhaust gas turbocharger 4 according to the present embodiment is configured such that when either the EGR valve 82 or the bypass valve 93 is in an open valve state (in other words, when one of the EGR valve 82 and the bypass valve 93 is in an open valve state and the other is in a closed valve state), the discharge pressure of the exhaust gas turbocharger 4 converges within a specified appropriate range. In this way, the decrease in the scavenging pressure generated when the EGR valve 82 is in an open valve state (or when the bypass valve 93 is in an open valve state) can be estimated, and thus the scavenging pressure can be converged within an appropriate range.

[0075] The controller 100 is electrically connected to at least the EGR valve 82 and the bypass valve 93. The controller 100 controls the exhaust gas regulation system 9 according to the opening degree of the EGR valve 82.

[0076] Specifically, the controller 100 is composed of a processor, a volatile memory, a non-volatile memory, an input / output bus, etc. The controller 100 receives a signal representing the opening degree of the EGR valve 82 and generates a control signal, and controls the exhaust gas regulation system 9 by inputting this control signal to the bypass valve 93.

[0077] Next, the processing related to the operation mode of the engine 1 in the control performed by the controller 100 will be described.

[0078] (2) Operation mode of the engine

[0079] The controller 100 can be used to distinguish the operating modes of the engine 1 by controlling various operating parameters of the engine 1, so as to use the EGR operation suitable for Tier 3 and the normal operation suitable for Tier 2. The EGR operation is an operation mode suitable for reducing the NOx emission amount compared with the normal operation. The normal operation is an operation mode with a relatively higher specific heat of air compared with the EGR operation.

[0080] During the EGR operation, the controller 100 makes the EGR valve 82 in an open valve state. In this way, the EGR gas circulates in the engine 1. During the EGR operation, the controller 100 controls the exhaust gas regulation system 9 so that the flow rate or velocity of the exhaust gas supplied to the turbine 42 is relatively higher than that in the normal operation. Specifically, the controller 100 makes the bypass valve 93 in a closed valve state. In this way, it is possible to suppress the exhaust gas from bypassing the turbine 42 via the bypass passage 91.

[0081] During the normal operation, the controller 100 makes the EGR valve 82 in a closed valve state. In this way, the EGR gas stops circulating. During the normal operation, the controller 100 controls the exhaust gas regulation system 9 so that the flow rate or velocity of the exhaust gas supplied to the turbine 42 is relatively lower than that in the EGR operation. Specifically, the controller 100 makes the bypass valve 93 in an open valve state. In this way, part of the exhaust gas bypasses the turbine 42 via the bypass passage 91.

[0082] When transferring from the EGR operation to the normal operation (or during the transfer transition), the EGR valve 82 changes from the open valve state to the closed valve state. At this time, the controller 100 makes the bypass valve 93 at least temporarily in a fully open state just after the transfer to the normal operation is completed or during the transfer transition.

[0083] Similarly, when transferring from the normal operation to the EGR operation (or during the transfer transition), the EGR valve 82 changes from the closed valve state to the open valve state. At this time, the controller 100 makes the bypass valve 93 in a closed valve state just after the transfer to the EGR operation is completed or during the transfer transition.

[0084] (3) Specific examples of operation mode switching

[0085] Figure 2 It is a flowchart showing the switching sequence from the EGR operation to the normal operation.

[0086] First, as Figure 2 shown in step S11, it is assumed that the ship is sailing in a state where the operating mode of the engine 1 is the EGR operation (in particular, the stable state of the EGR operation).

[0087] In the next step S12, it is determined whether to shift from EGR operation to normal operation. When this determination is "Yes", the process proceeds to step S13. On the other hand, when this determination is "No", the controller 100 ends the control process.

[0088] In step S13, the EGR valve 82 becomes a closed valve state. As a result, the EGR gas stops circulating. In the next step S14, the controller 100 outputs a control signal to the bypass valve 93, causing the bypass valve 93 to be at least temporarily fully open. As a result, the flow rate of the exhaust gas supplied to the turbine 42 decreases. Although there is a concern that the scavenging pressure may become excessive due to the closing of the EGR valve 82, this concern can be eliminated by opening the bypass valve 93.

[0089] When the EGR gas in the engine 1 is discharged by closing the EGR valve 82, the process proceeds from step S14 to step S15. In this step S15, various operating parameters (parameters for controlling various actuators of the engine 1) change from parameters suitable for EGR operation to parameters suitable for normal operation.

[0090] Finally, in step S16 after step S15, navigation starts in normal operation (in particular, the steady state of normal operation), and the controller 100 ends the control process.

[0091] It should be noted that steps S13, S14, and S15 can also be implemented simultaneously in parallel.

[0092] Figure 3 It is a flowchart showing the switching sequence from normal operation to EGR operation.

[0093] First, as Figure 3 shown in step S21, it is assumed that the ship is navigating in a state where the operating mode of the engine 1 is normal operation (in particular, the steady state of normal operation).

[0094] In the next step S22, it is determined whether to shift from normal operation to EGR operation. When this determination is "Yes", the process proceeds to step S23. On the other hand, when this determination is "No", the controller 100 ends the control process.

[0095] In step S23, the controller 100 outputs a control signal to the bypass valve 93, causing the bypass valve 93 to be at least temporarily fully closed. In the next step S24, the EGR valve 82 is made an open valve state.

[0096] In step S23, the controller 100 outputs a control signal to the bypass valve 93, so that the bypass valve 93 becomes at least temporarily fully closed. In this way, the flow rate of the exhaust gas supplied to the turbine 42 increases. In the next step S24, the EGR valve 82 is opened. In this way, the EGR gas starts to circulate. Although there is a concern that the scavenging pressure may decrease due to the opening of the EGR valve 82, this concern can be eliminated by closing the bypass valve 93.

[0097] When the EGR gas starts to circulate by opening the EGR valve 82, the process proceeds from step S24 to step S25. In this step S25, various operating parameters change from the parameters suitable for normal operation to the parameters suitable for EGR operation.

[0098] Finally, in step S26 after step S25, when starting to sail in EGR operation (in particular, the steady state of EGR operation), the controller 100 ends the control process.

[0099] It should be noted that steps S23, S24, and S25 can also be implemented simultaneously in parallel.

[0100] (4) Regarding maintaining the scavenging pressure

[0101] As described above, as shown in steps S13 - S14 of Figure 2 , compared with the case of performing EGR operation (when the EGR valve 82 is open), in the case of performing normal operation (when the EGR valve 82 is closed), the controller 100 according to the present embodiment reduces the flow rate of the exhaust gas supplied to the turbine 42.

[0102] In this way, even if the turbine nozzle area is pre - reduced to achieve the scavenging pressure suitable for EGR operation, by reducing the flow rate of the exhaust gas supplied to the turbine 42 during normal operation, it is possible to suppress the excessive increase in the scavenging pressure during this normal operation, so that the in - cylinder pressure converges within the allowable range.

[0103] In other words, as shown in steps S23 - S24 of Figure 3 , compared with the case of performing normal operation, in the case of performing EGR operation, the controller 100 increases the flow rate of the exhaust gas supplied to the turbine 42.

[0104] In this way, even if the flow rate of the exhaust gas is set low using the bypass passage 91 to achieve the scavenging pressure suitable for normal operation, by closing the bypass passage 91 during EGR operation, it is possible to maintain an appropriate scavenging pressure during EGR operation.

[0105] As shown in Figure 1As shown, an exhaust gas regulation system 9 is constituted by using a bypass valve 93. When the bypass valve 93 is in the open valve state, the flow rate of the exhaust gas supplied to the turbine 42 can be relatively reduced. On the other hand, when the bypass valve 93 is in the closed valve state, the flow rate of the exhaust gas supplied to the turbine 42 can be relatively increased. By appropriately opening and closing the bypass valve 93, the scavenging pressure can be maintained at an appropriate value when shifting from EGR operation to normal operation (or when making the opposite shift).

[0106] As described above, by reducing the turbine nozzle area in the design stage, the ejection pressure of the exhaust gas turbocharger 4 is set relatively high in advance. By setting it in this way, as described above, it is possible to estimate the reduction in the ejection pressure that occurs when the EGR valve 82 is in the open valve state or when the bypass valve 93 is in the open valve state, so that the ejection pressure can be converged within an appropriate range.

[0107] As Figure 2 As shown in step S14, by making the bypass valve 93 fully open immediately after shifting from EGR operation to normal operation or during the transition, the EGR gas remaining in the main engine 10 can be discharged, and it can be discharged early. In this way, the shift from EGR operation to normal operation can be smoothly carried out.

[0108] When the bypass valve 93 is in the open valve state, the exhaust gas bypasses the turbine 42 via the bypass passage 91. However, if the exhaust gas bypasses the turbine 42 more than necessary, the scavenging pressure will decrease, which is not conducive to maintaining the scavenging pressure.

[0109] Therefore, by providing a throttle hole 92 in the bypass passage 91, even when the bypass valve 93 is in the open valve state, the flow rate of the exhaust gas bypassing the turbine 42 is less than the flow rate of the exhaust gas passing through the turbine 42. In this way, the flow rate required to drive the turbine 42 can be ensured, which is conducive to maintaining the scavenging pressure.

[0110] 《Other Embodiments》

[0111] Figure 4 is a diagram corresponding to a modified example of a marine internal combustion engine (hereinafter, it will also be referred to as “engine 1’”). The exhaust gas regulation system 9 related to the above-described embodiment is constituted by a bypass passage 91 and a bypass valve 93 for opening and closing the bypass passage 91, etc., but the present disclosure is not limited to such a structure. Figure 1 For example, when the exhaust gas turbocharger 4 is configured as a so-called variable nozzle turbocharger (Variable Nozzle Turbo: VNT), the variable nozzle 43 can also constitute the exhaust gas regulation system 9’.

[0112]

[0113] ​Specifically, the exhaust gas turbocharger 4' according to the modified example includes a variable nozzle 43. The variable nozzle 43 is constituted by a so-called variable nozzle ring. The variable nozzle ring includes a plurality of nozzle vanes, and these nozzle vanes are arranged in a ring shape around the inlet of the turbine 42. On each nozzle vane, a shaft that functions as the rotation axis of each nozzle vane is provided. A rod is mounted on this shaft, and by operating this rod, the rotation angle of the nozzle vane is changed. Since the rotation angle of each nozzle vane changes, the throat area of the variable nozzle 43 increases or decreases. In this way, the passage area around the inlet of the turbine 42 increases or decreases. By changing the passage area around the turbine 42, the flow rate of the exhaust gas supplied to the turbine 42 can be adjusted. The exhaust gas regulation system 9' according to the modified example is constituted by this variable nozzle 43.

[0114] The exhaust gas turbocharger 4' according to the modified example is configured such that when the EGR valve 82 is in the open state and the passage area around the turbine 42 is reduced by using the variable nozzle 43, or when the EGR valve 82 is in the closed state and the passage area around the turbine 42 is enlarged by using the variable nozzle 43, the scavenging pressure of the exhaust gas turbocharger 4' converges within a specified range. In this way, similar to the above-described embodiment, it can be inferred that the scavenging pressure decreases when the EGR valve 82 is in the open state or when the passage area is enlarged by using the variable nozzle 43, so that the scavenging pressure can be converged within an appropriate range.

[0115] Similar to the above-described embodiment, during EGR operation, the controller 100 opens the EGR valve 82 and, by controlling the exhaust gas regulation system 9', makes the flow rate of the exhaust gas supplied to the turbine 42 relatively lower than that in normal operation. Specifically, the controller 100 operates the variable nozzle 43 that is the exhaust gas regulation system 9' to enlarge the above-described passage area.

[0116] On the other hand, during normal operation, the controller 100 closes the EGR valve 82 and, by controlling the exhaust gas regulation system 9', makes the flow rate of the exhaust gas supplied to the turbine 42 relatively higher than that in EGR operation. Specifically, the controller 100 operates the variable nozzle 43 that is the exhaust gas regulation system 9' to reduce the above-described passage area.

[0117] In this way, even if the turbine nozzle area is pre-reduced in order to achieve a scavenging pressure suitable for EGR operation, by reducing the flow rate of the exhaust gas supplied to the turbine 42 during normal operation, it is possible to suppress an excessive increase in the scavenging pressure during this normal operation, so that the in-cylinder pressure can be converged within an allowable range.

[0118] Similarly, even if the flow rate of the exhaust gas is set low by using the variable nozzle 43 in order to achieve a scavenging pressure suitable for normal operation, by operating the variable nozzle 43 during EGR operation to increase the flow rate, it is possible to maintain an appropriate scavenging pressure during EGR operation.

Claims

1. A marine internal combustion engine installed on a ship, characterized in that: The marine internal combustion engine includes a two-stroke main engine, an intake passage and an exhaust passage, an exhaust gas turbocharger, an EGR passage, an EGR valve, an exhaust gas regulating system, and a controller. The intake passage and the exhaust passage are connected to the main engine. The exhaust gas turbocharger has a compressor arranged in the intake passage and a turbine arranged in the exhaust passage, and drives the compressor by using the exhaust gas supplied to the turbine. The EGR passage connects a portion downstream of the turbine in the exhaust passage and a portion upstream of the compressor in the intake passage. The EGR valve opens and closes the EGR passage. The exhaust gas regulating system controls the boost pressure of the exhaust gas turbocharger by regulating the flow rate or flow velocity of the exhaust gas supplied to the turbine. The controller controls the exhaust gas regulating system according to the opening degree of the EGR valve. The exhaust gas regulating system has a bypass passage that connects a portion upstream of the turbine in the exhaust passage and a portion downstream of the turbine. The controller controls the EGR valve and the exhaust gas regulating system according to the sea area where the ship sails, thereby distinguishing between EGR operation in which EGR gas is recirculated by setting the EGR valve to the open state and normal operation in which EGR gas is not recirculated by setting the EGR valve to the closed state. In the case of EGR operation, the controller suppresses the exhaust gas from bypassing the turbine via the bypass passage by relatively increasing the flow rate or flow velocity of the exhaust gas supplied to the turbine compared to the case of normal operation. In the case of normal operation, the controller allows part of the exhaust gas to bypass the turbine via the bypass passage in such a way as to maintain the boost pressure in both the normal operation case and the EGR operation case.

2. The marine internal combustion engine according to claim 1, characterized in that: The exhaust gas regulating system has a bypass valve. The bypass valve regulates the flow rate of the exhaust gas supplied to the turbine by opening and closing the bypass passage.

3. The marine internal combustion engine according to claim 2, characterized in that: The exhaust gas turbocharger is configured such that when either the EGR valve or the bypass valve is in the open state, the discharge pressure of the exhaust gas turbocharger converges within a specified appropriate range.

4. The marine internal combustion engine according to claim 2, characterized in that: When the EGR valve changes from the open state to the closed state, the controller makes the bypass valve at least temporarily fully open.

5. The marine internal combustion engine according to claim 3, characterized in that: When the EGR valve changes from the open state to the closed state, the controller makes the bypass valve at least temporarily fully open.

6. The marine internal combustion engine according to any one of claims 2 to 5, characterized in that: The marine internal combustion engine includes an exhaust gas throttling mechanism that adjusts the ratio of the flow rate of the exhaust gas passing through the turbine to the flow rate of the exhaust gas bypassing the turbine via the bypass passage. The exhaust gas throttling mechanism is configured such that, regardless of whether the bypass valve is in the open state, the flow rate of the exhaust gas bypassing the turbine is less than the flow rate of the exhaust gas passing through the turbine.

7. The marine internal combustion engine according to claim 6, wherein: A throttle hole for narrowing the passage cross-sectional area of the bypass passage is provided in the bypass passage. The exhaust gas throttling mechanism is constituted by the throttle hole.

8. The marine internal combustion engine according to claim 1, wherein: The exhaust gas turbocharger includes variable nozzles that adjust the flow velocity of the exhaust gas supplied to the turbine by changing the passage area around the turbine. The exhaust gas adjustment system is constituted by the variable nozzles.

9. The marine internal combustion engine according to claim 8, wherein: The exhaust gas turbocharger is configured such that when the EGR valve is in the open state and the passage area is reduced using the variable nozzles, or when the EGR valve is in the closed state and the passage area is enlarged using the variable nozzles, the discharge pressure of the exhaust gas turbocharger converges within a specified range.

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