Internal combustion engine

Abstract

To provide an internal combustion engine with a system for exhaust gas recirculation, and a method for operating the internal combustion engine.SOLUTION: The present invention relates to an internal combustion engine comprising a system for exhaust gas recirculation with an EGR path 11 arranged between an exhaust outlet 3 and an air inlet 4 of the cylinder 1. The internal combustion engine comprises a turbocharger 5 with a turbine 6 and a compressor 7. The system for exhaust gas recirculation is a low-pressure system, wherein exhaust gas is guidable via the turbine 6 of the turbocharger 5 and at least a part of the exhaust gas is guidable to the air inlet 4 of the cylinder 1 through the compressor 7 of the turbocharger 5. The EGR path 11 comprises a flow regulating valve 12, arranged upstream of the compressor 7, and a shut-off valve 13, arranged downstream of the turbine 6 and upstream of the flow regulating valve 12. The internal combustion engine comprises an air-supply system 20 for guiding scavenging air from a scavenge air-line 8 and / or from a scavenge air-receiver 9 into the EGR path 11 on demand.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an internal combustion engine comprising a system for exhaust gas recirculation, and a method for operating an internal combustion engine.

Background Art

[0002] The present invention preferably relates to an internal combustion engine such as a large marine or stationary engine having cylinders with an inner diameter of at least 200 mm. The engine is preferably a two-stroke engine or a two-stroke crosshead engine. The engine can be a diesel engine or a gas engine, and can be a dual-fuel engine or a multi-fuel engine. Combustion of liquid fuel and / or gas fuel in such an engine can also be by self-ignition or forced ignition.

[0003] The engine has at least one cylinder having a piston therein. The piston is connected to a crankshaft. The piston reciprocates between top dead center (TDC) and bottom dead center (BDC) during operation of the engine. The cylinder generally has at least one air passage opening for intake, specifically with an air inlet disposed in the cylinder liner, and at least one air passage opening for exhaust, specifically with an exhaust outlet disposed in the cylinder cover.

[0004] The internal combustion engine can be a longitudinally scavenged two-stroke engine.

[0005] [[ID=2,3]] The term internal combustion engine also refers to large engines that can be operated not only in diesel mode, which is characterized by self-ignition of fuel, but also in Otto mode, which is characterized by positive ignition of fuel, or a mixture of the two. Further, the term internal combustion engine specifically includes dual-fuel engines and large engines in which self-ignition of fuel is used for positive ignition of another fuel.

[0006] The engine speed is preferably below 800 RPM (4-stroke), and more preferably below 200 RPM (2-stroke), which indicates a low-speed engine.

[0007] The fuel may be diesel oil or marine diesel oil or heavy oil, or emulsion or slurry or methanol or ethanol, or gases such as liquefied natural gas (LNG) or liquefied petroleum gas (LPG).

[0008] Further possible fuels that may be added upon request include liquefied biogas (LBG), biofuels (e.g., algal fuel or seaweed oil), hydrogen, and synthetic fuels made from CO2 (e.g., produced by Power-To-Gas or Power-To-Liquid).

[0009] To reduce the reactivity of the gas / air mixture and methane slip, exhaust gas recirculation (EGR), specifically low-pressure exhaust gas recirculation (EGR) as shown in EP3722572A1, is known to be implemented. A portion of the exhaust gas is recirculated to the cylinder, while another portion is guided to the chimney and released into the environment.

[0010] After switching off exhaust gas recirculation, exhaust gas may remain in the EGR path pipes. As the pipes cool, condensation may occur on the inner walls of the pipes. This can lead to corrosion or damage to the EGR path and compressor components when exhaust gas recirculation is restarted.

[0011] Furthermore, when the engine is shut down, no exhaust fumes should remain in the system to prevent crew members from being exposed to exhaust fumes if any maintenance needs to be performed.

[0012] Therefore, any remaining exhaust gases should be purged.

[0013] DE10260220A1 is known to guide air through the high-pressure EGR system. The engine control module controls the intake pressure relative to the exhaust pressure so that air is selectively guided through the EGR system. DE102013225133B4 teaches flushing the EGR path during fuel supply interruptions.

[0014] However, an air supply that does not interrupt the fuel supply may be required. [Prior art documents] [Patent Documents]

[0015] [Patent Document 1] EP3722572A1 [Patent Document 2] DE10260220A1 [Patent Document 3] DE102013225133B4 [Overview of the project] [Problems that the invention aims to solve]

[0016] The object of the present invention is to avoid the drawbacks of the prior art, and more specifically, to provide an internal combustion engine equipped with a system for exhaust gas recirculation, and a method for operating the internal combustion engine to supply air to the EGR path in order to avoid or minimize the accumulation or condensation of EGR gas in the EGR path. [Means for solving the problem]

[0017] According to the present invention, an internal combustion engine, particularly a large ship engine or a stationary engine, comprises at least one cylinder having an inner diameter of at least 200 mm.

[0018] The internal combustion engine comprises a turbocharger having a turbine and a compressor. During operation, the turbine is driven by the exhaust gas and the compressor supplies the pressurized gas that is to be guided into the cylinders.

[0019] The internal combustion engine comprises a system for exhaust gas recirculation having an EGR passage fluidly arranged between the exhaust outlet and the air inlet of the cylinders.

[0020] According to a first aspect of the invention, the system for exhaust gas recirculation is a low-pressure system, the exhaust gas can be guided through the turbine of the turbocharger, at least a part of the exhaust gas can be branched downstream of the turbine and can be guided through the compressor of the turbocharger to the air inlet of the cylinders.

[0021] For example, 10% to 70%, preferably 30% to 60% of the exhaust gas is recirculated.

[0022] The low-pressure EGR passage preferably comprises a flow control valve arranged upstream of the compressor and a shut-off valve preferably arranged upstream of the flow control valve and downstream of the turbine.

[0023] In this context, the terms upstream and downstream relate to the flow direction of the recirculated exhaust gas.

[0024] The EGR passage may further comprise an exhaust gas cooling device arranged between the flow control valve and the shut-off valve.

[0025] The internal combustion engine comprises an air supply system for guiding the scavenging air from the scavenging line and / or the scavenging receiver into the EGR passage as required. [[ID=२९]]

[0026] The scavenging air can be collected in the scavenging receiver before being introduced into or sucked into the cylinders.

[0027] The scavenging line fluidly connects the compressor of the turbocharger that pressurizes fresh air to the air inlet of the cylinders or the scavenging receiver.

[0028] The air supply system may provide scavenging air to purge the EGR path in order to clean the EGR path from exhaust gas residues and / or condensates, specifically after exhaust gas recirculation has finished or before exhaust gas recirculation has started.

[0029] Alternatively, a small amount of scavenging may also be applied to establish pressure in the EGR path to avoid exhaust gas leakage through a closed but unsealed shut-off valve.

[0030] Generally, flow control valves and shut-off valves have a leakage of 0.5% of their total capacity. Therefore, even when a shut-off valve is closed, some exhaust gas may enter the EGR path. The sealing pressure in the EGR path can prevent this unwanted recirculation.

[0031] For purging, the air supply system may provide a large amount of scavenging air for a limited time, but to establish sealing pressure, the air supply system may provide a small amount of scavenging air for the duration that the internal combustion engine is operating without exhaust gas recirculation.

[0032] The air supply system may include an air supply line for guiding the scavenging. The air supply line may be fluidly connected to the EGR path upstream of the flow control valve.

[0033] The air supply line may be fluidly connected to the scavenging line and / or scavenging receiver.

[0034] The scavenging air contains fresh air. If the exhaust gases are recirculated or have been recirculated, the scavenging air may also contain some exhaust gases.

[0035] A flow limiting device, preferably comprising at least one valve, may be placed in the air supply line.

[0036] The flow limiting device controls the amount of scavenging air that is directed into the EGR path.

[0037] The flow limiting device may be configured to take on at least one state in which a first flow rate sufficient to purge the EGR path is permitted through the flow limiting device. The flow limiting device may also be configured to take on a further state in which no flow rate is permitted through the flow limiting device.

[0038] Preferably, the flow limiting device is capable of accommodating various flow rates passing through it.

[0039] The flow limiting device may be configured to take on at least three states. In the first state, a first flow rate is allowed through the flow limiting device, preferably a flow rate sufficient to allow purging of the EGR path. In the second state, a second flow rate is allowed through the flow limiting device, which is preferably smaller than the first flow rate, suitable for establishing a sealing pressure in the EGR path. In the third state, no flow rate is allowed through the flow limiting device, and the air supply line is closed.

[0040] The state of the flow limiting device may correspond to the respective positions or opening degrees of at least one valve.

[0041] Alternatively, a flow limiting device can be operated to provide the required flow rate for each state of the air supply system. The flow limiting device can be actively controlled, for example, based on concentration signals, flow rate signals, temperature signals, or pressure signals measured in the scavenging line, scavenging receiver, air supply line and / or EGR path.

[0042] The air supply system may include an air supply control unit configured to control the amount of scavenging air flowing into the EGR path.

[0043] The air supply control unit is configured, in detail, to configure at least one valve located in the air supply line. The air supply control unit may be configured to configure a flow limiting device as described above.

[0044] For purging, a scavenging volume of 1 to 3 times the volume of the EGR path is required. This can cause a drop of approximately 0.2 bar in the scavenging line, but this is not significant.

[0045] A decrease of approximately 0.2 bar in the scavenging line roughly corresponds to a 4% reduction in the engine's air flow.

[0046] For purging with the above parameters, the flow limiting device must be open for approximately 1 to 5 minutes while the engine is operating at full load.

[0047] For sealing purposes, the flow limiting device should allow a continuous flow of 0.3% to 0.8%, preferably 0.55% to 0.65%, of the engine's air consumption.

[0048] A system for exhaust gas recirculation may include an EGR control unit configured to control the amount of exhaust gas recirculated to the air inlet. Specifically, the EGR control unit may be configured to set valves. The EGR control unit may be configured to set flow control valves, shut-off valves, back pressure valves between the EGR path and the chimney, and / or blowers located in the EGR path.

[0049] The air supply control unit may be part of the EGR control unit, or the air supply control unit and the EGR control unit may be part of the engine control unit.

[0050] Preferably, the scavenging line includes a scavenging cooling device. The scavenging cooling device may include a scavenging cooler and a water mist collector.

[0051] The air supply line can be branched from the scavenging line upstream of the scavenging-cooling device. In this case, warm air can be supplied to the EGR path. For the same mass of gas, the hotter gas has a larger volume. If the scavenging is branched upstream of the scavenging-cooling device, scavenging losses can be minimized.

[0052] Alternatively, the air supply line may be branched downstream of the scavenging cooling device from the scavenging line, for example from the scavenging receptacle, and the cooled scavenging gas may be guided to the EGR path.

[0053] As described above, the air supply line of an internal combustion engine may be connected to an EGR path between the exhaust gas cooling device and the flow control valve. Alternatively, the air supply line may be connected to an EGR path between the shut-off valve and the exhaust gas cooling device.

[0054] When the air supply line is connected to the EGR path between the exhaust gas cooling device and the flow control valve, the flow control valve may be closed to purge the EGR path, and the scavenging air may be guided through an open shut-off valve to the chimney. In this case, the scavenging air is guided against the direction of the recirculated exhaust gas, i.e., in the opposite direction.

[0055] When the air supply line is connected to the EGR path between the shut-off valve and the exhaust gas cooling device, the shut-off valve may be closed to purge the EGR path, and the scavenged air may be guided through an open flow control valve to the compressor and air inlet. In this case, the scavenged air is guided in the direction of the recirculated exhaust gas, i.e., in the forward direction.

[0056] In this case, exhaust gas residue released from the EGR path is guided through the cylinder, so it takes longer for the cylinder to stop receiving exhaust gas.

[0057] When both the shut-off valve and the flow control valve are closed, pressure is established in the EGR path, preventing exhaust gas from entering the EGR path through the unsealed shut-off valve.

[0058] The internal combustion engine may include an exhaust gas back pressure valve located between the EGR path and the chimney, and / or a blower in the EGR path. The rate of EGR may be influenced by the opening and closing of the back pressure valve and / or the speed of the blower, preferably by an EGR control unit as described above.

[0059] Alternatively, the internal combustion engine may be equipped with a low-pressure system for exhaust gas recirculation, and the internal combustion engine may be equipped with an ambient air supply system for guiding ambient air into the EGR path as required. The air supply system may be equipped with an ambient air supply line for guiding ambient air, the ambient air supply line being fluidly connected to the EGR path upstream of a flow control valve, and the air supply line being fluidly connected to the environment.

[0060] A flow limiting device, preferably comprising at least one valve, may be placed in the ambient air supply line.

[0061] According to a second aspect of the present invention, the system for recirculating exhaust gases from an internal combustion engine is a high-pressure system.

[0062] In high-pressure systems, the exhaust gases are diverted upstream of the turbocharger turbine. At least a portion of the exhaust gases can be guided to the cylinder air inlet and mixed with scavenging gases downstream of the turbocharger compressor.

[0063] The high-pressure EGR path comprises an EGR blower, a first high-pressure EGR valve located upstream of the EGR blower, and / or a second high-pressure EGR valve located downstream of the EGR blower.

[0064] The high-pressure EGR path may consist of only a first high-pressure EGR valve or only a second high-pressure EGR valve. To enable exhaust gas recirculation, the high-pressure EGR valve is opened and the EGR blower is switched on.

[0065] Preferably, the high-pressure EGR path includes a first high-pressure EGR valve and a second high-pressure EGR valve. To enable exhaust gas recirculation, the first and second high-pressure EGR valves are opened and the EGR blower is switched on.

[0066] The internal combustion engine includes a purge control unit configured to allow scavenging from the scavenging line and / or scavenging chamber to be directed to the EGR path as needed. The purge control unit may be configured to switch an EGR blower to set a first high-pressure EGR valve and / or a second high-pressure EGR valve.

[0067] Under normal operating conditions for a large two-stroke engine, the scavenging pressure is higher than the pressure in the exhaust manifold. Therefore, for EGR operation, the EGR blower must be switched on.

[0068] In a high-pressure EGR system, if the first high-pressure EGR valve and / or the second high-pressure EGR valve are left temporarily open after switching to non-EGR operation and turning off the EGR blower, the scavenging flow will purge the EGR path in the reverse direction. Reverse direction means flow in the opposite direction to the flow direction of the recirculated exhaust gas.

[0069] In the case of two high-pressure EGR valves, one of the two high-pressure EGR valves, the first and the second, can be used as a flow limiting device (e.g., a position-controlled valve), while the other only requires an open / close function.

[0070] When switching the high-pressure EGR operation from on to off, the EGR blower is deactivated. The first and second high-pressure EGR valves may remain open when either one of them is in its flow limiting position.

[0071] Since the scavenging pressure is higher than the exhaust pressure, a smaller flow of scavenging air flows in the opposite direction through the EGR path, thereby purging exhaust gases from the system.

[0072] After a suitable length of time, the first high-pressure EGR valve and / or the second high-pressure EGR valve can be completely closed, completing the purging process. A sealing function is not required because leakage from the two valves causes a slight, natural sealing flow of scavenging air.

[0073] The high-pressure EGR system may include an EGR control unit for operating a first high-pressure EGR valve, a second high-pressure EGR valve, and / or an EGR blower.

[0074] The purge control unit may be part of the EGR control unit. The purge control unit and / or the EGR control unit may be part of the engine control unit.

[0075] According to a further aspect of the present invention, a method for operating an internal combustion engine as described above includes the following steps: Exhaust gas recirculation is switched on, and at least a portion of the exhaust gas is recirculated from the exhaust outlet to the air inlet; and exhaust gas recirculation is switched off. Subsequently, scavenging is guided from the scavenging line and / or scavenging receiver to the EGR path.

[0076] In the case of an internal combustion engine having a low-pressure EGR system as described above, a flow limiting device may be opened, allowing scavenging air to be guided through the flow limiting device located in the air supply line. The flow limiting device may then be closed.

[0077] To switch on exhaust gas recirculation of the low-pressure EGR system, the shut-off valve and flow control valve of an internal combustion engine having a low-pressure EGR system as described above may be opened.

[0078] Furthermore, an exhaust gas back pressure valve located between the EGR path and the chimney may be at least partially closed, and / or the blower may be switched on.

[0079] The flow control valve can be closed to switch off exhaust gas recirculation in the low-pressure EGR system.

[0080] Furthermore, when the flow control valve is closed or after it is closed, the exhaust gas back pressure valve may be fully opened and / or the blower may be switched off.

[0081] After the scavenging air has been guided to the EGR path, the shut-off valve may be closed, preferably before the flow limiting device is closed.

[0082] The scavenging can be guided through the EGR path in either the reverse or forward direction.

[0083] In the case of an internal combustion engine with a high-pressure EGR system as described above, the EGR blower may be shut down.

[0084] The first high-pressure EGR valve and / or the second high-pressure EGR valve may be opened or left open so that scavenging air can be guided through the EGR path to purge the EGR path.

[0085] At least one of the first high-pressure EGR valve and the second high-pressure EGR valve may be set to the fully open position, and the other valve may be set to the partially open position so as to limit the purge flow rate.

[0086] Subsequently, the first high-pressure EGR valve and the second high-pressure EGR valve may be closed.

[0087] Even after closing the first and second high-pressure EGR valves, a small amount of scavenging air may enter the EGR path, and pressure can be established in the EGR path to prevent exhaust gas from entering the EGR path when EGR recirculation is switched off.

[0088] The present invention will be further described below with reference to examples illustrated by the figures. The same reference numerals indicate functionally corresponding features. [Brief explanation of the drawing]

[0089] [Figure 1] This is a schematic diagram of an internal combustion engine. [Figure 2] This diagram schematically illustrates the first example of a low-pressure EGR system. [Figure 3] This diagram schematically illustrates a second example of a low-pressure EGR system. [Figure 4]This diagram provides a schematic representation of a high-voltage EGR system. [Figure 5] This diagram schematically illustrates the first example of a flow limiting device. [Figure 6] This diagram schematically illustrates a second example of a flow limiting device. [Figure 7] This diagram schematically illustrates a third example of a low-pressure EGR system. [Modes for carrying out the invention]

[0090] Figure 1 shows an internal combustion engine 100, particularly a large marine engine, which comprises at least one cylinder 1 having an inner diameter 2 of at least 200 mm.

[0091] The internal combustion engine 100 is equipped with a turbocharger 5 which has a turbine 6 driven by exhaust gas and a compressor 7 for supplying pressurized scavenging air.

[0092] The internal combustion engine 100 includes a low-pressure system 10 for exhaust gas recirculation, which has an EGR path 11 located between the exhaust outlet 3 and the air inlet 4 of the cylinder 1.

[0093] Figure 2 schematically shows a first example of a low-pressure EGR system, corresponding to the low-pressure system 10 for exhaust gas recirculation shown in Figure 1.

[0094] The exhaust gas is guided through the turbine 6 of the turbocharger 5. At least a portion of the exhaust gas is guided through the compressor 7 to the air inlet 4 of the cylinder 1, and another portion is released into the environment by the chimney 17.

[0095] The low-pressure EGR path 11 includes a flow control valve 12 located upstream of the compressor 7 and a shut-off valve 13 located downstream of the turbine 6 and upstream of the flow control valve 12. The shut-off valve 13 is opened to recirculate the exhaust gas. The amount of exhaust gas recirculated can be influenced by setting the opening degree of the flow control valve 12 and a back pressure valve 15 located between the EGR path 11 and the chimney 17.

[0096] The low-pressure EGR path 11 includes an exhaust gas cooling device 18 positioned between the shut-off valve 13 and the flow control valve 12.

[0097] The internal combustion engine 100 includes an air supply system 20 for guiding scavenging air from the scavenging line 8 to the EGR path 11 as needed. The air supply system 20 includes an air supply line 21, one end of which is fluidly connected to the EGR path 11 upstream of the flow control valve 12, and the other end of which is fluidly connected to the scavenging line 8.

[0098] Alternatively, the air supply line 21 can be fluidly connected to the scavenging receiver 9 (indicated by the dashed line).

[0099] The flow limiting device 22 is placed in the air supply line 21.

[0100] The scavenging line 8 includes a scavenging cooling device 28.

[0101] In this example, the air supply line 21 branches off from the scavenging line 8 upstream of the scavenging cooling device 28. The air supply line 21 is connected to the EGR path 11 between the exhaust gas cooling device 18 and the flow control valve 12.

[0102] The internal combustion engine 100 includes an air supply control unit 23 configured to set a flow limiting device 22, thereby controlling the amount of scavenging air flowing into the EGR path 11. The air supply control unit 23 is part of an EGR control unit 14, configured to set a flow control valve 12, a shut-off valve 13, and a back pressure valve 15.

[0103] When exhaust gas recirculation is complete, the shut-off valve 13 and the flow control valve 12 are generally closed. While the flow control valve 12 remains closed, the shut-off valve 13 may be opened, allowing a large amount of scavenged air to be guided into the EGR path 11, which then purges exhaust gas residues out of the EGR path to the chimney 17 via the open shut-off valve 13.

[0104] Alternatively or continuously, the shut-off valve 13 and the flow control valve 12 may be closed, and the flow limiting device 22 may be opened so that a small amount of scavenging air can be guided into the EGR path 11. A pressure may be established in the EGR path 11, which prevents the exhaust gas from overpowering the shut-off valve 13, which is closed but not sealed.

[0105] The purging direction is opposite to the flow direction during recirculation. Therefore, this example concerns what is known as "reverse purging."

[0106] Conversely, Figure 3 schematically illustrates a second example of a low-pressure EGR system relating to "forward purging."

[0107] In this example, the air supply line 21 also branches off from the scavenging line 8 upstream of the scavenging cooling device 28. A water mist catcher 31 is located downstream of the scavenging cooling device 28.

[0108] In this example, the air supply line 21 is connected to the EGR path 11 between the shut-off valve 13 and the exhaust gas cooling device 18, and particularly between the shut-off valve 13 and the economizer 19 which is located upstream of the exhaust gas cooling device 18 in the direction of the flow of the recirculated exhaust gas.

[0109] The exhaust gas cooling device 18 is supplied by the cooling circuit 32.

[0110] Once exhaust gas recirculation is complete, the shut-off valve 13 and the flow control valve 12 are closed. While the shut-off valve 13 remains closed, the flow control valve 12 may be opened, allowing a large amount of scavenging air to be guided into the EGR path 11. This scavenging air then purges exhaust gas residue out of the EGR path to the turbocharger 5 and scavenging receiver 9 via the open flow control valve 12.

[0111] Alternatively, or continuously, the flow limiting device 22 may be opened so that the shut-off valve 13 and the flow control valve 12 remain closed, and a small amount of scavenging air can be guided into the EGR path 11. A pressure may be established in the EGR path 11, which prevents the exhaust gas from overpowering the shut-off valve 13, which is closed but not sealed.

[0112] The purging direction corresponds to the flow direction during recirculation. Therefore, this example concerns what is known as "forward purging."

[0113] Figure 4 schematically shows an example of a high-voltage EGR system 40.

[0114] The EGR path 41 is also located between the exhaust gas receiver 29 and the scavenging receiver 9.

[0115] The exhaust gas recirculation system 40 is a high-pressure system in which the exhaust gas is diverted upstream of the turbine 6 of the turbocharger 5, and at least a portion of the exhaust gas is guided to the scavenging line 8, where it is mixed with fresh air downstream of the compressor 7 of the turbocharger 5.

[0116] The high-pressure EGR path 41 includes an EGR blower 49, a first high-pressure EGR valve 43 located upstream of the EGR blower 49, a second high-pressure EGR valve 42 located downstream of the EGR blower 49, and an exhaust gas cooling device 18 located between the EGR blower 49 and the second high-pressure EGR valve 42.

[0117] The purge control unit 44 is configured to allow scavenging from the scavenging line 8 to the EGR path 41 as needed.

[0118] The purge control unit 44 is configured to switch the EGR blower 49 in order to set the first high-pressure EGR valve 43 and the second high-pressure EGR valve 42.

[0119] The purge control unit 44 is part of the EGR control unit 14, which is also configured to switch the EGR blower 49 to set a first high-pressure EGR valve 43 and a second high-pressure EGR valve 42 in order to allow or prevent exhaust gas recirculation.

[0120] To recirculate the exhaust gas, the first high-pressure EGR valve 43 and the second high-pressure EGR valve 42 are opened, and the blower is switched on.

[0121] To stop exhaust gas recirculation, the first high-pressure EGR valve 43 and the second high-pressure EGR valve 42 may be closed, and the blower 49 may be switched off.

[0122] Since the pressure in the scavenging line 8 is higher than the pressure in the exhaust gas line 36 upstream of the turbine 6, the first high-pressure EGR valve 43 and the second high-pressure EGR valve 42 may be opened after exhaust gas recirculation is completed so that the scavenging is guided in the reverse direction to the turbine 6 and chimney 17 through the EGR path 41.

[0123] Figure 5 schematically shows a first example of a flow limiting device 22 equipped with a position-controllable butterfly valve 33. The flow area, and therefore the allowable flow, varies with the angle of the butterfly valve 33.

[0124] By setting the angle of the butterfly valve 33, various flow rates can be selected, for example, a flow rate sufficient to purge the EGR path, a flow rate for sealing, or no flow rate at all.

[0125] Figure 6 schematically shows a second example of the flow limiting device 22. Two on / off butterfly valves 34, 35 are arranged in parallel. Either the small or large section can be opened.

[0126] By selecting which of the butterfly valves 34 and 35 is opened, and which of the butterfly valves 34 and 35 is closed, a larger flow, a smaller flow, or no flow can be set.

[0127] Figure 7 schematically shows a third example of the low-pressure EGR system 10.

[0128] In this example, the ambient air supply line 51 is fluidly connected to the environment. The ambient air supply line 51 is connected to the EGR path 11 between the shut-off valve 13 and the flow control valve 12, and in particular between the shut-off valve 13 and the economizer 19, which is located upstream of the exhaust gas flow direction and adjacent to the exhaust gas cooling device 18.

[0129] The ambient air supply line 51 is equipped with a valve 52.

[0130] After a command to switch off exhaust gas recirculation, the shut-off valve 13 closes, but valve 52 receives a command to open from a control unit not explicitly shown in the figure.

[0131] Similarly, the back pressure valve 15 opens, allowing the entire exhaust gas flow to pass through. The flow control valve 12 remains open.

[0132] The compressor 7 continues to draw in gas, and therefore ambient air from the environment. Thus, the EGR path 11 is purged. Furthermore, the EGR path 11 may be equipped with an EGR blower 49 to establish sufficient pressure within the EGR path 11 and move the gas through the EGR path 11.

[0133] Valves 13 and 52 are scheduled to open and close in such a manner that exhaust gases do not flow into the environment through the ambient air path 51. During normal operation, the pressure upstream of the back pressure valve 15 exceeds atmospheric pressure. Therefore, the shut-off valve 13 should be closed before the ambient air valve 52 opens.

[0134] After a predefined purge time, valve 52 and flow control valve 12 are closed. The time can also be determined by measuring the gas composition in the EGR path 11.

[0135] The EGR path 11 can be pressurized between the shut-off valve 13 and the flow control valve 12 to the required level to protect the EGR path 11 from the ingress of ambient air or exhaust gas, using an air supply system 20 as shown in one of Figures 1 to 3.

Claims

1. An internal combustion engine (100), in particular a large marine engine or a stationary engine, comprising at least one cylinder (1) with an internal diameter (2) of at least 200 mm, The internal combustion engine (100) comprises a system (10) for exhaust gas recirculation having an EGR path (11) arranged between an exhaust outlet (3) of the cylinder (1) and an air inlet (4), and the internal combustion engine (100) comprises a turbocharger (5) having a turbine (6) and a compressor (7), the system (10) for exhaust gas recirculation is a low-pressure system in which exhaust gases can be guided through the turbine (6) of the turbocharger (5) and at least a portion of the exhaust gases can be guided through the compressor (7) of the turbocharger (5) to the air inlet (4) of the cylinder (1); the EGR path (11) includes a flow control valve (12) arranged upstream of the compressor (7), and a shutoff valve (13) arranged downstream of the turbine (6) and upstream of the flow control valve (12); In an internal combustion engine (100), The internal combustion engine (100) comprises an air supply system (20) for directing scavenging air from at least one of a scavenging line (8) and a scavenging air receiver (9) to the EGR path (11) on demand. An internal combustion engine (100).

2. The air supply system (20) comprises an air supply line (21) for guiding scavenging air, in which: the air supply line (21) is fluidly connected to the EGR path (11) upstream of the flow control valve (12); the air supply line (21) is fluidly connected to at least one of the scavenging line (8) and the scavenging air receiver (9); A flow restriction device (22) is disposed in the air supply line (21).

2. The internal combustion engine according to claim 1.

3. An internal combustion engine as described in claim 1, wherein the flow restriction device (22) comprises at least one valve (22).

4. The internal combustion engine of claim 2 , wherein the flow restriction device (22) is configured to have at least one state in which a first flow rate is permitted through the flow restriction device (22).

5. The flow restriction device (22): a first state in which a first flow rate is permitted through the flow restriction device (22); a second state in which a second flow rate less than the first flow rate is permitted through the flow restriction device (22); a third state in which no flow is permitted through said flow restriction device (22); configured to assume at least three states:

5. The internal combustion engine according to claim 4.

6. 2. The internal combustion engine of claim 1, wherein the air supply system (20) comprises an air supply control unit (23) configured to control the amount of scavenged air flowing into the EGR path (11).

7. An internal combustion engine as described in claim 6, wherein the air supply control unit (23) is configured to set at least one valve (22) arranged in the air supply line (21).

8. 2. An internal combustion engine according to claim 1, wherein the scavenging air line (8) is provided with a scavenging air cooling device (28).

9. 9. An internal combustion engine according to claim 2 and claim 8, wherein the air supply line (21) branches off from the scavenging air line (8) upstream of the scavenging air cooling device (28).

10. 2. The internal combustion engine of claim 1, wherein the EGR path (11) comprises an exhaust gas cooling device (18).

11. The air supply line (21) of the internal combustion engine is connected to the EGR path (11) between the exhaust gas cooling device (18) and the flow control valve (12), or the air supply line (21) of the internal combustion engine is connected to the EGR path (11) between the shut-off valve (13) and the exhaust gas cooling device (18); An internal combustion engine according to claims 2 and 10.

12. An internal combustion engine (100), in particular a large marine engine or a stationary engine, comprising at least one cylinder (1) with an internal diameter (2) of at least 200 mm, the internal combustion engine (100) comprises a system (40) for exhaust gas recirculation having an EGR path (41) arranged between the exhaust outlet (3) and the air inlet (4) of the cylinder (1); The internal combustion engine (100) comprises a turbocharger (5) having a turbine (6) and a compressor (7); the system (40) for exhaust gas recirculation is a high-pressure system in which exhaust gases are branched off upstream of the turbine (6) of the turbocharger (5), and at least a portion of the exhaust gases can be guided to the air inlet (4) of the cylinder (1) and can be mixed with scavenging air downstream of the compressor (7) of the turbocharger (5), the EGR path (41) includes at least one of an EGR blower (49), a first high-pressure EGR valve (43) disposed upstream of the EGR blower (49), and a second high-pressure EGR valve (42) disposed downstream of the EGR blower (49); In an internal combustion engine (100), The internal combustion engine (100) comprises a purge control unit (44) configured to allow scavenging air from at least one of a scavenging line (8) and a scavenging air receiver (9) to be directed to the EGR path (41) on demand. An internal combustion engine (100).

13. An internal combustion engine (100) as described in claim 12, wherein the purge control unit (44) is configured to do at least one of switching the EGR blower (49), setting the first high-pressure EGR valve (43), and setting the second high-pressure EGR valve (42).

14. 2. A method for operating an internal combustion engine (100) according to claim 1, comprising: switching on exhaust gas recirculation; recirculating at least a portion of the exhaust gas from the exhaust outlet (3) to the air inlet (4); switching off exhaust gas recirculation; guiding scavenging air from at least one of the scavenging line (8) and the scavenging air receiver (9) to the EGR path (11, 41); A method comprising:

15. Opening the flow restriction device (22) disposed in the air supply line of the internal combustion engine according to claim 2; guiding scavenging air through said air supply line (21); closing the flow restriction device (22); 15. The method of claim 14, comprising:

16. 15. The method according to claim 14, wherein the shut-off valve (13) and the flow regulating valve (12) of an internal combustion engine according to claim 1 are opened to switch on exhaust gas recirculation.

17. 15. The method according to claim 14, wherein the flow regulating valve (12) of an internal combustion engine according to claim 1 is closed to switch off exhaust gas recirculation.

18. 15. The method according to claim 14, wherein the shut-off valve (13) of the internal combustion engine according to claim 1 is closed after guiding scavenging air into the EGR path (11).

19. A method as described in claim 18, wherein the shut-off valve (13) of the internal combustion engine described in claim 1 is closed before the flow restriction device (21) of the internal combustion engine described in claim 2 is closed.

20. deactivating the EGR blower (49) of the internal combustion engine of claim 13; guiding scavenging air through the EGR path (41); 15. The method of claim 14, comprising:

21. A method for producing an internal combustion engine according to claim 13, comprising the steps of: opening at least one of the first high-pressure EGR valve (43) and the second high-pressure EGR valve (42); and Closing at least one of the first high pressure EGR valve (43) and the second high pressure EGR valve (42).

21. The method of claim 20, further comprising at least one of:

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