JP7503976B2 - Marine internal combustion engine - Google Patents

Description

This disclosure relates to a marine internal combustion engine.

Patent Document 1 discloses a supercharged engine equipped with an EGR device as an example of an internal combustion engine not limited to marine use. Specifically, Patent Document 1 discloses that a damage supercharging pressure corresponding to the damage temperature at which the supercharger is damaged is calculated based on the intake air temperature of the supercharger, and the supercharging pressure of the supercharger is limited so that the upper limit is set to a maximum supercharging pressure that is set lower than the damage supercharging pressure.

According to Patent Document 1, in the case of an engine equipped with an EGR device, depending on the performance of the EGR cooler, the EGR gas recirculated to the intake passage may become hot. Therefore, when the turbocharger draws in EGR gas, the temperature of the air drawn into the turbocharger (intake air temperature) becomes excessively high, which may cause damage to the turbocharger.

To address these issues, the engine disclosed in Patent Document 1 is able to prevent damage to the turbocharger by limiting the turbocharger's boost pressure based on the intake air temperature. Here, the engine described in this document is configured with a bypass valve that allows air to circumvent the turbocharger as a means for limiting the turbocharger's boost pressure.

JP 2009-299537 A

Specific measures to address the above-mentioned problem could, for example, open a bypass valve when recirculating EGR gas, thereby reducing the flow rate or flow velocity of the exhaust gas flowing into the rotor, turbine, etc. that make up the turbocharger, and thus preventing the turbocharger pressure from becoming excessively high.

In addition, instead of using a bypass valve, it is also possible to use a so-called variable nozzle turbo to appropriately adjust the flow rate of the exhaust gas flowing into the turbocharger depending on whether or not EGR gas is recirculated.

However, the above-mentioned problem is caused by the performance of the EGR cooler. Therefore, when a large, high-performance cooling device can be used, such as in a marine internal combustion engine, the above-mentioned control is usually not necessary.

Meanwhile, marine internal combustion engines equipped with an EGR device such as that disclosed in the above-mentioned Patent Document 1 are being considered as a means of complying with NOx regulations, particularly Tier 3 regulations, which are currently in place for ships.

When such a marine internal combustion engine is further equipped with an exhaust turbine supercharger, the specific heat ratio of the air compressed by the compressor decreases due to the EGR gas contained in the air. The decrease in specific heat ratio leads to a decrease in scavenging pressure (supercharging pressure). The decrease in scavenging pressure is undesirable because it leads to a deterioration in fuel efficiency and the generation of smoke in the exhaust.

In anticipation of recirculating EGR gas, it is possible to set the fuel injection pressure high in advance, or to narrow the nozzle area upstream of the turbine (hereinafter referred to as the "turbine nozzle area") in advance to compensate for the decrease in scavenging pressure that accompanies the decrease in the specific heat ratio.

However, the waters in which a ship operates are not limited to those where the aforementioned Tier 3 regulations are in place (hereafter referred to as "Tier 3 waters"). It is also conceivable for the ship to operate in waters where Tier 2 regulations (Tier 2 waters) are in place, which have looser NOx emission limits than the Tier 3 regulations, or to travel between Tier 3 waters and Tier 2 waters 2.

To deal with this, it is conceivable to control the internal combustion engine so that the EGR valve is opened in Tier 3 waters to allow the EGR gas to be recirculated, while the EGR valve is closed in Tier 2 waters to prevent the EGR gas from being recirculated.

However, if the fuel injection pressure is set high in advance as described above to avoid problems related to the specific heat ratio during EGR operation in which EGR gas is recirculated (operation suitable for Tier 3 waters), then during normal operation in which EGR gas is not recirculated (operation suitable for Tier 2 waters), the problem of increased NOx emissions will arise.

Instead of increasing the fuel injection pressure, it is possible to reduce the turbine nozzle area in advance, as mentioned above. However, in this case, the scavenging pressure may rise excessively during normal operation, causing the in-cylinder pressure to exceed the design tolerance.

As described above, the inventors of the present application conducted research from a different perspective than that of Patent Document 1, and as a result discovered a new problem specific to marine internal combustion engines. After further intensive research, the inventors of the present application came up with a control method that is different from the configuration described in Patent Document 1.

This disclosure has been made in light of these points, and its purpose is to achieve compatibility between EGR operation and normal operation in a marine internal combustion engine equipped with an exhaust turbine supercharger.

The first aspect of the present disclosure relates to a marine internal combustion engine. This marine internal combustion engine includes a two-stroke main engine, an intake passage and an exhaust passage connected to the main engine, an exhaust turbine supercharger having a compressor disposed in the intake passage and a turbine disposed in the exhaust passage, and driving the compressor with exhaust gas supplied to the turbine, an EGR passage connecting a portion of the exhaust passage downstream of the turbine and a portion of the intake passage upstream of the compressor, an EGR valve that opens and closes the EGR passage, an exhaust regulation system that regulates the flow rate or flow velocity of the exhaust gas supplied to the turbine, and a controller that controls the exhaust regulation system based on the opening degree of the EGR valve.

And, according to the first aspect of the present disclosure, when the EGR valve is in a closed state, the controller reduces the flow rate or flow velocity of the exhaust gas supplied to the turbine compared to when the EGR valve is in an open state.

Here, the "exhaust adjustment system" includes a bypass line that adjusts the exhaust flow rate by making the exhaust bypass the turbine, and a variable nozzle that adjusts the exhaust flow rate by varying the nozzle area upstream of the turbine.

According to the first aspect, when performing normal operation without recirculating EGR gas (when the EGR valve is closed), such as when operating in Tier 2 waters, the controller reduces the flow rate or flow velocity of the exhaust gas supplied to the turbine, compared to when performing EGR operation with recirculating EGR gas (when the EGR valve is open), such as when operating in Tier 3 waters.

As a result, even if the turbine nozzle area is narrowed in advance 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 scavenging pressure during normal operation and keep the in-cylinder pressure within an acceptable range.

In other words, when EGR operation is performed, the controller increases the flow rate or flow velocity of the exhaust gas supplied to the turbine compared to when normal operation is performed.

As a result, even if the exhaust flow rate is set low using a bypass line or the like to achieve a scavenging pressure suitable for normal operation, by closing the bypass line or the like during EGR operation, it becomes possible to maintain an appropriate scavenging pressure even during EGR operation.

According to a second aspect of the present disclosure, the exhaust adjustment system may also have a bypass passage that connects a portion of the exhaust passage upstream of the turbine with a portion of the exhaust passage downstream of the turbine, and a bypass valve that adjusts the flow rate of exhaust gas supplied to the turbine by opening and closing the bypass passage.

According to the second aspect, when the bypass valve is opened, the flow rate of the exhaust gas supplied to the turbine can be relatively reduced, while when the bypass valve is closed, 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 transitioning from EGR operation to normal operation (or vice versa).

Furthermore, according to a third aspect of the present disclosure, the exhaust turbocharger may be configured so that the discharge pressure of the exhaust turbocharger falls within a predetermined appropriate range when either the EGR valve or the bypass valve is in an open state.

The "discharge pressure" here refers to the pressure of the air discharged from the compressor of the exhaust turbocharger (supercharging pressure). The magnitude of the discharge pressure is substantially equal to the scavenging pressure mentioned above. Furthermore, the "appropriate range" here refers to the pressure range set so that the internal cylinder pressure of the main engine does not exceed the allowable range.

According to the third aspect, the discharge pressure of the exhaust turbocharger is set higher in advance, for example by narrowing the turbine nozzle area at the design stage. This allows for a configuration that anticipates a drop in discharge pressure that occurs when the EGR valve is opened (or when the bypass valve is opened), making it possible to keep the discharge pressure within an appropriate range.

According to a fourth aspect of the present disclosure, the controller may also at least temporarily open the bypass valve when the EGR valve is changed from an open state to a closed state.

According to the fourth aspect, by fully opening the bypass valve immediately after or during the transition from EGR operation to normal operation, it is possible to promote the discharge of EGR gas remaining in the main engine and discharge it early. This allows for a smooth transition from EGR operation to normal operation.

According to a fifth aspect of the present disclosure, the marine internal combustion engine may include an exhaust throttling means for adjusting the ratio between the flow rate of exhaust gas passing through the turbine and the flow rate of exhaust gas bypassing the turbine via the bypass passage, and the exhaust throttling means may be configured to make the flow rate of exhaust gas bypassing the turbine less than the flow rate of exhaust gas passing through the turbine, regardless of whether the bypass valve is in an open state.

When the bypass valve is open, the exhaust gas bypasses the turbine through the bypass passage. However, if more exhaust gas than necessary is bypassed, this will result in a decrease in scavenging pressure, which will be inconvenient in maintaining it.

According to the fifth aspect, the exhaust throttling means reduces the flow rate of exhaust bypassing the turbine to less than the flow rate of exhaust passing through the turbine even when the bypass valve is open. This ensures the flow rate required to drive the turbine, which is advantageous in maintaining the scavenging pressure.

According to a sixth aspect of the present disclosure, the bypass passage may be provided with an orifice that narrows the cross-sectional area of the bypass passage, and the exhaust throttling means may be constituted by the orifice.

The sixth aspect is effective in maintaining the scavenging pressure.

According to a seventh aspect of the present disclosure, the marine internal combustion engine may be configured such that the exhaust turbine supercharger includes a variable nozzle that adjusts the flow rate of the exhaust gas supplied to the turbine by changing the passage area around the turbine, and the exhaust adjustment system is configured by the variable nozzle.

According to the seventh aspect, when the variable nozzle is narrowed, the flow rate of the exhaust gas supplied to the turbine can be relatively increased, while when the variable nozzle is opened, the flow rate of the exhaust gas supplied to the turbine can be relatively decreased. By configuring in this way, it becomes possible to maintain the scavenging pressure at an appropriate value when transitioning from EGR operation to normal operation (or vice versa).

According to an eighth aspect of the present disclosure, the exhaust turbocharger may be configured such that the discharge pressure of the exhaust turbocharger falls within a predetermined range when the EGR valve is open and the passage area is reduced by the variable nozzle, or when the EGR valve is closed and the passage area is expanded by the variable nozzle.

According to the eighth aspect, the discharge pressure of the exhaust turbocharger is set higher in advance, for example by narrowing the turbine nozzle area at the design stage. This allows for a configuration that anticipates a drop in scavenging pressure that occurs when the EGR valve is opened or the passage area is expanded by the variable nozzle, making it possible to keep the scavenging pressure within an appropriate range.

As described above, according to the present disclosure, it is possible to achieve both EGR operation and normal operation in a marine internal combustion engine equipped with an exhaust turbine supercharger.

FIG. 1 is a system diagram illustrating a schematic configuration of a marine internal combustion engine. FIG. 2 is a flowchart illustrating a procedure for switching from EGR operation to normal operation. FIG. 3 is a flowchart illustrating a procedure for switching from normal operation to EGR operation. FIG. 4 is a view corresponding to FIG. 1, showing a modified example of a marine internal combustion engine.

Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. Note that the following description is merely an example.
FIG. 1 is a system diagram illustrating a schematic configuration of a marine internal combustion engine (hereinafter, also simply referred to as "engine 1").

Engine 1 is an in-line multi-cylinder diesel engine equipped with multiple cylinders 11. This engine 1 is configured as a two-stroke, one-cycle engine with a uniflow scavenging system, and is installed on large ships such as tankers, container ships, and car carriers.

The engine 1 installed on the ship is equipped with a main engine 10 for propelling the ship. Therefore, the output shaft of the main engine 10 is connected to the ship's propeller (not shown) via a propeller shaft (not shown). When the engine 1 is operating, its output is transmitted to the propeller, propelling the ship.

The engine 1 is also configured as a turbocharged engine. That is, the engine 1 according to this embodiment is configured with an exhaust turbine supercharger 4, as shown in FIG. 1.

(1) Main Configuration The main parts of the engine 1 will now be described.

As shown in FIG. 1, the engine 1 includes the main engine 10, an intake system 2 and an exhaust system 3 connected to the main engine 10, an exhaust turbine supercharger 4 that operates using exhaust gas flowing through the exhaust system 3, an EGR (Exhaust Gas Recirculation) system 8 that recirculates the exhaust gas, an exhaust regulation system 9 that adjusts the flow rate or flow speed of the exhaust gas, and a controller 100 that controls each part of the engine 1.

Of these, the main engine 10 has multiple cylinders 11 (only four cylinders 11 are illustrated in FIG. 1). The main engine 10 is a two-stroke engine. A piston (not shown) is inserted into each cylinder 11 so that it can reciprocate. A combustion chamber is defined for 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.

The main engine 10 also has a scavenging trunk 18 and an exhaust manifold 19. The scavenging trunk 18 is connected to the combustion chamber of the main engine 10 and is configured to supply scavenging air to the combustion chamber 12. The exhaust manifold 19 is connected to the combustion chamber of the main engine 10 and can discharge burnt gas (exhaust) from the combustion chamber. The main engine 10 is connected to the intake system 2 (specifically, the intake passage 21 described below) via the scavenging trunk 18, and is connected to the exhaust system 3 (specifically, the exhaust passage 31 described below) via the exhaust manifold 19.

The intake system 2 has an intake passage 21 connected to the main engine 10. The intake system 2 is configured to send air to the main engine 10 through this intake passage 21. Specifically, in this embodiment, the intake passage 21 is provided with, from the upstream side, a compressor 41 that compresses air (fresh air) taken in from the atmosphere together with EGR gas described below, and an air cooler 22 that cools the air compressed by the compressor 41. The air cooled by the air cooler 22 reaches the combustion chamber via the scavenging trunk 18 described above.

The exhaust system 3 has an exhaust passage 31 connected to the main engine 10. The exhaust system 3 is configured to discharge exhaust from the main engine 10 through this exhaust passage 31. Specifically, the exhaust passage 31 according to this embodiment is provided with, in order from the upstream side, a first branch section (connection section between the upstream end of the bypass passage 91 and the exhaust passage 31) 31a branching to a bypass passage 91 described later, a turbine 42 drivingly connected to the compressor 41, a junction section (connection section between the downstream end of the bypass passage 91 and the exhaust passage 31) 31b merging with the bypass passage 91, and a second branch section (connection section between the upstream end of the EGR passage 81 and the exhaust passage 31) 31c branching to an EGR passage 81 described later. The exhaust discharged from the combustion chamber flows into the exhaust passage 31 through the exhaust manifold 19 described above, passes through the turbine 42, and is released to the atmosphere.

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

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

Of these, the EGR valve 82 opens and closes the EGR passage 81. This EGR valve 82 operates according to a control signal input from the controller 100.

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 pressurizes the EGR gas. Note that if there is little pressure loss in the scrubber or EGR cooler and the required amount of EGR gas can be circulated simply by adjusting the opening of the EGR valve 82, the blower is not essential.

The exhaust regulation system 9 controls the boost pressure of the exhaust turbine supercharger 4 (specifically, the pressure of the air discharged from the compressor 41) by adjusting the flow rate or flow speed of the exhaust gas supplied to the turbine 42. Specifically, the exhaust regulation system 9 according to this embodiment is configured to adjust the flow rate of the exhaust gas supplied to the turbine 42, and has a bypass passage 91, a bypass valve 93, and an exhaust throttling means 92. Note that, as described below, the exhaust throttling means 92 is not essential to the exhaust regulation system 9.

Of these, the bypass passage 91 connects the portion of the exhaust passage 31 upstream of the turbine 42 (first branch portion 31a) to the portion downstream of the turbine 42 (junction portion 31b). In this bypass passage 91, an exhaust throttle means 92 and a bypass valve 93 are arranged in this order from the upstream side.

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

The exhaust throttle means 92 adjusts the ratio between the flow rate of exhaust gas passing through the turbine 42 (first flow rate) and the flow rate of exhaust gas bypassing the turbine 42 via the bypass passage 91 (second flow rate). Specifically, the exhaust throttle means 92 is configured to make the second flow rate less than the first flow rate, regardless of whether the bypass valve 93 is open or not. By configuring it in this way, it becomes possible to bypass the turbine 42 by the amount of flow rate (second flow rate) required to suppress the supercharging pressure while ensuring the minimum flow rate (first flow rate) required to drive the exhaust turbocharger 4.

The exhaust throttle means 92 according to this embodiment is configured by an orifice that narrows the cross-sectional area of the bypass passage 91. As described above, the exhaust throttle means 92 is disposed upstream of the bypass valve 93 in the bypass passage 91.

The exhaust throttling means 92 may be disposed downstream of the bypass valve 93 and upstream of the junction 31. Furthermore, the exhaust throttling means 92 is not essential. Instead of disposing the exhaust throttling means 92, the bypass valve 93 may also serve its function. In that case, the flow rate of the exhaust gas supplied to the turbine 42 (specifically, the ratio between the first flow rate and the second flow rate) is adjusted by controlling the opening degree of the bypass valve 93.

When EGR gas is circulated, the load on the exhaust turbocharger 4 is reduced by the amount of exhaust gas flowing through the EGR passage 81, and the scavenging pressure is reduced. A decrease in scavenging pressure is undesirable because it reduces the amount of air introduced into the cylinder 11, leading to poor fuel economy and the generation of smoke. A similar problem can occur when part of the exhaust gas is made to bypass the turbine 42 (when the bypass valve 93 is opened).

In this embodiment, therefore, in anticipation of the drop in scavenging pressure as described above, tuning is performed at the design stage to reduce the turbine nozzle area of the exhaust turbocharger 4. The exhaust turbocharger 4 according to this embodiment is configured so that when either the EGR valve 82 or the bypass valve 93 is opened (in other words, when one of the EGR valve 82 and the bypass valve 93 is opened and the other is closed), the discharge pressure of the exhaust turbocharger 4 falls within a predetermined appropriate range. In this way, a configuration can be achieved that anticipates the drop in scavenging pressure that occurs when the EGR valve 82 is opened (or when the bypass valve 93 is opened), and it becomes possible to keep the scavenging pressure within an appropriate range.

The controller 100 is electrically connected to at least the EGR valve 82 and the bypass valve 93. The controller 100 controls the exhaust regulation system 9 based on the opening degree of the EGR valve 82.

Specifically, the controller 100 is composed of a processor, a volatile memory, a non-volatile memory, an input/output bus, etc., and receives a signal indicating the opening degree of the EGR valve 82, generates a control signal, and inputs it to the bypass valve 93 to control the exhaust regulation system 9.

The following describes the processing performed by the controller 100 that is related to the operating mode of the engine 1.

(2) Engine Operation Modes The controller 100 controls various operation parameters of the engine 1, and thereby can selectively use EGR operation conforming to Tier 3 regulations (Tier 3) and normal operation conforming to Tier 2 regulations (Tier 2) as operation modes of the engine 1. The EGR operation is an operation mode more suitable for reducing NOx emissions than the normal operation. The normal operation is an operation mode in which the specific heat ratio of air is higher than that of the EGR operation.

In EGR operation, the controller 100 opens the EGR valve 82. This allows EGR gas to circulate within the engine 1. In addition, in EGR operation, the controller 100 controls the exhaust regulation system 9 to relatively increase the flow rate or flow velocity of the exhaust gas supplied to the turbine 42 compared to normal operation. Specifically, the controller 100 closes the bypass valve 93. This prevents the exhaust gas from bypassing the bypass passage 91.

In normal operation, the controller 100 closes the EGR valve 82. This stops the circulation of EGR gas. In addition, in normal operation, the controller 100 controls the exhaust regulation system 9 to reduce the flow rate or flow velocity of the exhaust gas supplied to the turbine 42 relatively compared to the EGR operation. Specifically, the controller 100 opens the bypass valve 93. This causes a portion of the exhaust gas to bypass the turbine 42 via the bypass passage 91.

In addition, when transitioning from EGR operation to normal operation (or during the transitional period), the EGR valve 82 is changed from an open state to a closed state. At this time, the controller 100 at least temporarily opens the bypass valve 93 immediately after the transition to normal operation is completed or during the transitional period.

Similarly, when transitioning from normal operation to EGR operation (or during the transition period), the EGR valve 82 is changed from a closed state to an open state. At this time, the controller 100 closes the bypass valve 93 immediately after the transition to EGR operation is completed or during the transition period.

(3) Specific Example of Switching Operation Mode FIG. 2 is a flowchart illustrating a procedure for switching from the EGR operation to the normal operation.

First, as illustrated in step S11 of FIG. 2, it is assumed that the ship is operating with the engine 1 operating mode in EGR operation (particularly, in the steady state of EGR operation).

In the next step S12, it is determined whether or not to transition from EGR operation to normal operation. If the determination is YES, the process proceeds to step S13, whereas if the determination is NO, the controller 100 ends the control process.

In step S13, the EGR valve 82 is closed. This stops the circulation of EGR gas. In the following step S14, the controller 100 outputs a control signal to the bypass valve 93, thereby fully opening the bypass valve 93 at least temporarily. This reduces the flow rate of exhaust gas supplied to the turbine 42. There is a concern that closing the EGR valve 82 may cause the scavenging pressure to become excessive, but this concern is eliminated by opening the bypass valve 93.

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 step S15, the various operating parameters (parameters for controlling the various actuators of the engine 1) are changed from parameters suitable for EGR operation to parameters suitable for normal operation.

Finally, in step S16, which follows step S15, normal operation (particularly, steady state normal operation) begins, and the controller 100 ends the control process.

Note that steps S13, S14, and S15 can also be performed simultaneously.

Figure 3 is a flowchart illustrating the procedure for switching from normal operation to EGR operation.

First, as illustrated in step S21 of FIG. 3, it is assumed that the ship is operating with engine 1 in normal operation mode (particularly, in the steady state of normal operation).

In the following step S22, it is determined whether or not to transition from normal operation to EGR operation. If the determination is YES, the process proceeds to step S23, whereas if the determination is NO, the controller 100 ends the control process.

In step S23, the controller 100 outputs a control signal to the bypass valve 93 to at least temporarily close the bypass valve 93. In the following step S24, the EGR valve 82 is opened.

In step S23, the controller 100 outputs a control signal to the bypass valve 93 to at least temporarily close the bypass valve 93. This increases the flow rate of exhaust gas supplied to the turbine 42. In the following step S24, the EGR valve 82 is opened. This starts the circulation of EGR gas. There is a concern that opening the EGR valve 82 may cause a drop in scavenging pressure, but closing the bypass valve 93 eliminates this concern.

When the EGR gas starts circulating by opening the EGR valve 82, the process proceeds from step S24 to step S25. In step S25, the various operating parameters are changed from parameters suitable for normal operation to parameters suitable for EGR operation.

Finally, in step S26, which follows step S25, operation with EGR operation (particularly, steady state EGR operation) is started, and the controller 100 ends the control process.

Note that steps S23, S24, and S25 can also be performed simultaneously.

(4) Regarding maintenance of scavenging pressure As described above, as shown in steps S13 to S14 of FIG. 2, when normal operation is performed (when the EGR valve 82 is in a closed state), the controller 100 according to this embodiment reduces the flow rate of exhaust gas supplied to the turbine 42 compared to when EGR operation is performed (when the EGR valve 82 is in an open state).

As a result, even if the turbine nozzle area is narrowed in advance to achieve a scavenging pressure suitable for EGR operation, by reducing the flow rate of exhaust gas supplied to the turbine 42 during normal operation, excessive increases in scavenging pressure during normal operation can be suppressed, and the in-cylinder pressure can be kept within an acceptable range.

In other words, as shown in steps S23 to S24 of FIG. 3, when EGR operation is performed, the controller 100 increases the flow rate of exhaust gas supplied to the turbine 42 compared to when normal operation is performed.

As a result, even if the exhaust flow rate is set low using the bypass passage 91 to achieve a scavenging pressure suitable for normal operation, by closing the bypass passage 91 during EGR operation, it is possible to maintain an appropriate scavenging pressure even during EGR operation.

As shown in FIG. 1, by configuring the exhaust adjustment system 9 using the bypass valve 93, when the bypass valve 93 is opened, the flow rate of the exhaust gas supplied to the turbine 42 can be relatively decreased, while when the bypass valve 93 is closed, 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, it becomes possible to maintain the scavenging pressure at an appropriate value when transitioning from EGR operation to normal operation (or vice versa).

Also, as mentioned above, by narrowing the turbine nozzle area at the design stage, the discharge pressure of the exhaust turbocharger 4 is set high in advance. By setting it in this way, it is possible to create a configuration that anticipates the drop in discharge pressure that occurs when the EGR valve 82 or the bypass valve 93 is opened, as mentioned above, and it becomes possible to keep the discharge pressure within an appropriate range.

In addition, as shown in step S14 of FIG. 2, by fully opening the bypass valve 93 immediately after or during the transition from EGR operation to normal operation, the discharge of EGR gas remaining in the main engine 10 is promoted, and the gas can be discharged early. This allows for a smooth transition from EGR operation to normal operation.

When the bypass valve 93 is open, the exhaust gas bypasses the turbine 42 via the bypass passage 91. However, if more exhaust gas than necessary is bypassed, this will result in a decrease in the scavenging pressure, which will be inconvenient in maintaining it.

Therefore, by providing an orifice 92 on the bypass passage 91, the flow rate of exhaust gas bypassing the turbine 42 is made smaller than the flow rate of exhaust gas passing through the turbine 42 even when the bypass valve 93 is open. This ensures the flow rate required to drive the turbine 42, which is advantageous in maintaining the scavenging pressure.

Other Embodiments
Fig. 4 is a view showing a modified example of a marine internal combustion engine (hereinafter, also referred to as "engine 1'") corresponding to Fig. 1. The exhaust gas regulation system 9 according to the embodiment is configured with the bypass passage 91 and the bypass valve 93 for opening and closing the bypass passage 91, etc., but the present disclosure is not limited to such a configuration.

For example, if the exhaust turbine supercharger 4 is configured as a so-called variable nozzle turbo (VNT), the exhaust adjustment system 9' may be configured using the variable nozzle 43.

Specifically, the exhaust gas turbine supercharger 4' according to the modified example has a variable nozzle 43. This variable nozzle 43 is configured by a so-called variable nozzle ring. The variable nozzle ring is made up of a number of nozzle vanes arranged in a ring shape around the inlet of the turbine 42. Each nozzle vane is provided with a shaft that functions as the rotation axis of each nozzle vane. A lever is attached to this shaft, and the rotation angle of the nozzle vane changes by operating the lever. By changing the rotation angle of each nozzle vane, the throat area of the variable nozzle 43 increases or decreases. This increases or decreases the passage area around the inlet of the turbine 42. 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 adjustment system 9' according to the modified example is configured by this variable nozzle 43.

The exhaust turbocharger 4' according to the modified example is configured so that the scavenging pressure of the exhaust turbocharger 4' falls within a predetermined range when the EGR valve 82 is opened and the passage area around the turbine 42 is reduced by the variable nozzle 43, or when the EGR valve 82 is closed and the passage area around the turbine 42 is expanded by the variable nozzle 43. In this way, as in the above embodiment, a configuration can be created that anticipates a decrease in scavenging pressure that occurs when the EGR valve 82 is opened or the passage area is expanded by the variable nozzle 43, making it possible to keep the scavenging pressure within an appropriate range.

As in the above embodiment, in EGR operation, the controller 100 opens the EGR valve 82 and controls the exhaust regulation system 9' to relatively increase the flow velocity of the exhaust gas supplied to the turbine 42 compared to normal operation. Specifically, the controller 100 operates the variable nozzle 43 as the exhaust regulation system 9' to reduce the passage area.

On the other hand, in normal operation, the controller 100 closes the EGR valve 82 and controls the exhaust gas regulation system 9' to reduce the flow velocity of the exhaust gas supplied to the turbine 42 relatively compared to that in the EGR operation. Specifically, the controller 100 operates the variable nozzle 43 as the exhaust gas regulation system 9' to increase the passage area.

As a result, even if the turbine nozzle area is narrowed in advance to achieve a scavenging pressure suitable for EGR operation, the flow rate of the exhaust gas supplied to the turbine 42 during normal operation is reduced, thereby preventing an excessive increase in scavenging pressure during normal operation and keeping the in-cylinder pressure within an acceptable range.

Similarly, even if the exhaust flow rate is set low using the variable nozzle 43 so that a scavenging pressure suitable for normal operation is achieved, the variable nozzle 43 can be operated during EGR operation to increase the flow rate, making it possible to maintain an appropriate scavenging pressure even during EGR operation.

1. Engine (marine internal combustion engine)
1' Engine (variant of marine internal combustion engine)
10 Main engine 21 Intake passage 31 Exhaust passage 4 Exhaust turbine supercharger 41 Compressor 42 Turbine 43 Variable nozzle (a modified example of the exhaust adjustment system)
81 EGR passage 82 EGR valve 9 Exhaust gas regulation system 91 Bypass passage 92 Orifice (exhaust gas throttling means)
93 Bypass valve 100 Controller

Claims (5)

A two-stroke main engine;
an intake passage and an exhaust passage connected to the main engine;
an exhaust turbocharger including a compressor disposed in the intake passage and a turbine disposed in the exhaust passage, the compressor being driven by exhaust gas supplied to the turbine;
an EGR passage connecting a portion of the exhaust passage downstream of the turbine and a portion of the intake passage upstream of the compressor;
an EGR valve that opens and closes the EGR passage;
an exhaust conditioning system for adjusting the flow rate or velocity of exhaust gas supplied to the turbine;
a controller that controls the exhaust gas regulation system based on an opening degree of the EGR valve,
the controller maintains a pressure of air discharged from the compressor between an open state and a closed state of the EGR valve by reducing a flow rate or velocity of exhaust gas delivered to the turbine when the EGR valve is in a closed state compared to when the EGR valve is in an open state ;
The exhaust regulation system includes:
a bypass passage connecting a portion of the exhaust passage upstream of the turbine and a portion of the exhaust passage downstream of the turbine;
a bypass valve that adjusts a flow rate of exhaust gas supplied to the turbine by opening and closing the bypass passage,
The controller at least temporarily opens the bypass valve when the EGR valve is changed from an open state to a closed state.
A marine internal combustion engine characterized by: 2. A marine internal combustion engine according to claim 1 ,
The exhaust turbo-supercharger is configured such that, when either the EGR valve or the bypass valve is opened, a discharge pressure of the exhaust turbo-supercharger falls within a predetermined appropriate range. A two-stroke main engine;
an intake passage and an exhaust passage connected to the main engine;
an exhaust turbocharger including a compressor disposed in the intake passage and a turbine disposed in the exhaust passage, the compressor being driven by exhaust gas supplied to the turbine;
an EGR passage connecting a portion of the exhaust passage downstream of the turbine and a portion of the intake passage upstream of the compressor;
an EGR valve that opens and closes the EGR passage;
an exhaust conditioning system for adjusting the flow rate or velocity of exhaust gas supplied to the turbine;
a controller that controls the exhaust gas regulation system based on an opening degree of the EGR valve,
the controller reduces a flow rate or a flow velocity of exhaust gas supplied to the turbine when the EGR valve is in a closed state compared to when the EGR valve is in an open state;
The exhaust regulation system includes:
a bypass passage connecting a portion of the exhaust passage upstream of the turbine and a portion of the exhaust passage downstream of the turbine;
a bypass valve that adjusts a flow rate of exhaust gas supplied to the turbine by opening and closing the bypass passage,
the exhaust turbo-supercharger is configured such that, when either the EGR valve or the bypass valve is opened, a discharge pressure of the exhaust turbo-supercharger falls within a predetermined appropriate range,
The marine internal combustion engine, wherein the controller at least temporarily brings the bypass valve into a fully open state when the EGR valve is changed from an open state to a closed state. A marine internal combustion engine according to any one of claims 1 to 3 ,
an exhaust throttle means for adjusting a ratio between a flow rate of exhaust gas passing through the turbine and a flow rate of exhaust gas bypassing the turbine via the bypass passage,
the exhaust throttling means is configured to make a flow rate of exhaust gas bypassing the turbine less than a flow rate of exhaust gas passing through the turbine, regardless of whether the bypass valve is in an open state or not. 5. A marine internal combustion engine according to claim 4 ,
The bypass passage is provided with an orifice that narrows a cross-sectional area of the bypass passage,
2. A marine internal combustion engine, comprising: a first exhaust throttling means for throttling said first exhaust gas;

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