JP2015086869A - Large-sized, low-speed turbocharged two-stroke internal combustion engine equipped with crosshead and exhaust gas recirculation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a large-sized, low-speed two-stroke uniflow combustion engine equipped with a crosshead and an EGR, simpler, excellent in reliability, and having an inexpensive structure.SOLUTION: Provided is a crosshead-type large-scale, low-speed, two-stroke uniflow internal combustion engine including: a plurality of cylinders 2 each connected to a scavenge air port 11 and an exhaust gas port 6; a turbocharger 7 that includes a turbine T and a compressor C; a scavenge air channel introducing high-pressure scavenge air from an outlet of the compressor C to the scavenge air port 11; an exhaust-gas recirculation channel recirculating at least part of the exhaust gas from each cylinder 2 or the exhaust gas port 6 to the scavenge air port 11; a blower 30 forcing out an EGR flow to the scavenge air port 11; a sensor 51 providing a signal representing an oxygen concentration or a carbon dioxide concentration in the scavenge air port 11; and an electronic control unit ECU receiving a signal from the sensor 51, the electronic control unit ECU being configured to control the EGR flow in response to the signal from the sensor 51.

Description

  The present invention relates to a large low-speed turbocharged two-stroke internal combustion engine having an exhaust gas recirculation system and a crosshead. Furthermore, the present invention relates to an exhaust gas recirculation system and a method of operating a crosshead large low speed turbocharged two-stroke internal combustion engine.

  Typical use cases for crosshead large low speed two-stroke internal combustion engines are found in large ship propulsion systems and power plant prime movers. This type of engine has a crosshead between the piston and the crankshaft.

Meeting the emission requirements, especially the emission requirements for nitrogen oxide (NO _x ) levels, has been difficult today.

Currently, in a large low-speed turbocharged internal combustion engine, options for reducing NO _x generation there are some theoretical. These options should be applied to the engine process, in particular:
・ Recirculation of exhaust gas or combustion gas (EGR)
・ Use of water emulsion fuel ・ Humidification of fresh air, that is, Scavenging Air Moisturization (SAM)
・ Selective Catalyst Reactor method (SCR)

Exhaust gas recirculation (EGR), in order to reduce the exhaust gas containing NO _x, are known as a means for assisting a small high-speed diesel engine. However, few large two-stroke diesel engines operating on a commercial basis use exhaust gas recirculation. The reason is that it has been found difficult to perform exhaust gas recirculation in a large two-stroke diesel engine. One of the reasons why exhaust gas recirculation is so difficult in large two-stroke diesel engines is that they are generally operated with heavy oil with a high content of sulfur. There is. The exhaust gas sulfur content of these engines is much higher than small diesel engines that are operated with fuel oils that contain no or low sulfur content. The high concentration of sulfur significantly narrows the choice of cleaning methods and equipment, but most of these cleaning methods and equipment are in the exhaust of large two-stroke diesel engines, where heavy oils with a high content of sulfur are burned. This is because they cannot withstand the existing sulfur and sulfuric acid concentrations.

  One technique for cleaning exhaust gases in large two-stroke diesel engines that could withstand these high sulfur concentrations is wet cleaning. Wet cleaning refers to a technique of passing exhaust gas through a so-called wet scrubber that uses water as a cleaning solution.

  Another challenge was the power required to transfer the recirculated exhaust gas from the exhaust gas receiver to the scavenging airflow. The scavenging pressure of a large two-stroke diesel engine is typically up to about 0.3 bar higher than the pressure in the exhaust gas receiver of the large two-stroke diesel engine. Accordingly, a blower installation or other means is required to push the recirculated exhaust gas from the exhaust gas receiver to the scavenging system. In a large bore 12 or 14 cylinder 2-stroke diesel engine such as a MAN B & W 12K98MC-C engine, the output required to drive such a blower is expected to be about 0.5 MW. The amount of energy required to use an electric motor in an exhaust gas system is considerably large. When the blower is driven with such a large output requirement, an enormous cost increase is caused.

  Thus, the initial cost of machines such as wet scrubbers and blowers is significant in large diesel engine exhaust gas recirculation systems, depending on the size of these parts.

  Large low-speed two-stroke combustion engines depend on engine and turbocharger characteristics, but scavenging is sufficient when operating under low to medium load conditions such as 25 to 45% or less of the engine's maximum continuous rating. In order to obtain a high scavenging pressure, an auxiliary blower for assisting the turbocharger compressor is required. For this reason, an existing large-sized low-speed internal combustion engine is provided with a dedicated auxiliary blower for guaranteeing operation under a low load to a medium load condition.

  In view of such a background, an object of the present invention is to provide a large-sized low-speed two-stroke uniflow internal combustion engine having a crosshead type EGR and having a simpler, more reliable, and less expensive structure.

  This object is achieved by providing a crosshead large low speed two stroke uniflow combustion engine as follows. The engine includes a plurality of cylinders respectively connected to a scavenging receiver and an exhaust gas receiver; a turbocharger having a turbine that receives exhaust gas from the exhaust gas receiver and a compressor that supplies high-pressure scavenging; A scavenging passage for guiding the high-pressure scavenging from an outlet to the scavenging receiver; an exhaust gas recirculation passage for recirculating at least a portion of the exhaust gas from the cylinder or the exhaust gas receiver to the scavenging receiver; and EGR in the scavenging receiver A blower that pushes the flow; a sensor that provides a signal representative of the oxygen or carbon dioxide concentration in the scavenging receiver; and an electronic control unit that receives the signal from the sensor. The electronic control unit is configured to control the EGR flow in response to a signal from the sensor.

  An electronic control unit having an oxygen sensor or a carbon dioxide sensor in the scavenging receiver and configured to receive signals from these sensors in combination with these sensors and control, for example, the flow in response to the signals It is possible to provide a simple and reliable control system for operating at an appropriate EGR rate by providing a large-sized low-speed two-stroke uniflow internal combustion engine.

  In some implementations, the electronic control unit is configured to increase the EGR rate when the sensed oxygen concentration exceeds a first threshold and to decrease the EGR rate when the sensed oxygen concentration is less than a second threshold. The

  In some embodiments, the electronic control unit is configured to decrease the EGR rate when the sensed carbon dioxide concentration exceeds a first threshold and to increase the EGR rate when the sensed carbon dioxide concentration is less than a second threshold. Composed.

  Further objects, features, advantages and characteristics of the large low-speed turbocharged two-stroke internal combustion engine according to the present invention will become apparent from the detailed description.

In the following detailed part of the invention, the invention will be explained in more detail with reference to exemplary embodiments shown in the drawings.
FIG. 2 is a schematic diagram of an engine according to an exemplary embodiment. FIG. 2 is a detailed view of an electronic control unit and a control valve of the engine shown in FIG. 1. 2 is a schematic diagram of an engine according to another exemplary embodiment. FIG.

Detailed Description of the Preferred Embodiment

  In the following, a detailed description of a crosshead large low speed turbocharged two-stroke (diesel) combustion engine according to the present invention will be given using a preferred embodiment.

  The structure and operation of a crosshead large low speed turbocharged two-stroke combustion engine is well known per se and need not be further described as background to the present invention. Further details regarding the operation of the exhaust gas system are described below.

  FIG. 1 shows a first embodiment of a uniflow-type large-scale low-speed turbocharged two-stroke (diesel) internal combustion engine 1. The engine 1 can be used as a main engine for ocean-going ships or as a stationary engine for driving a power plant generator. The total power of the engine can range from, for example, 2,000 kW to 110,000 kW.

  The engine 1 is provided with a plurality of cylinders 2 arranged in series. Each cylinder 2 is provided with an exhaust valve 3 connected to its cylinder cover. The exhaust path can be opened and closed by the exhaust valve 3. For the engine 1, a crosshead 4a and a connecting rod 4b connecting the piston rod to the large end of the crankshaft are also described. The exhaust bent pipe 5 is connected to the exhaust gas receiver 6. The exhaust gas receiver 6 is arranged in parallel with the row of the plurality of cylinders 2. Exhaust gas is guided at least in a substantial part from the exhaust gas receiver 6 via the exhaust pipe toward the turbine T of the turbocharger 7 (even if two or more turbochargers 39 are present). Good). Another portion of the exhaust gas is recycled and enters an exhaust gas recirculation flow path, described in further detail below. The exhaust gas is discharged into the atmosphere downstream of the turbine of the turbocharger 7 via the exhaust gas bypass 54 and the outlets 9a, 9b or the outlet 9c.

  The turbocharger 7 also includes a compressor C connected to the fresh air intake port 10a. The compressor C sends high-pressure scavenging to the scavenging receiver 11 through the scavenging flow path. In some embodiments, the scavenging flow path includes a cooler 12 and a water mist collector 13. The water mist collector 13 removes all moisture that condenses when the scavenging air is cooled. The scavenging flow path continues from the water mist collector to the mixing chamber 25 via the check valve 24. The mixing chamber 25 also receives recirculated exhaust gas from an exhaust gas recirculation flow path described in further detail below.

  The scavenging flow path includes a branch point 23 downstream of the water mist collector 13 and upstream of the check valve 24. The air duct 26 is provided between the branch point 23 and the inlet of the blower 30. The blower conduit 26 allows some or all of the scavenging to be directed to the blower 30 inlet. The blower conduit 26 includes a check valve 27 and a blower control valve 28.

  The scavenging enters the mixing chamber 25 from the branch point through the check valve 24 or the air duct 26 and the blower 30.

  The scavenging gas that enters the mixing chamber 25 via the check valve 24 is mixed with the recirculated exhaust gas by the EGR operation. The outlet of the mixing chamber 25 is connected to the scavenging receiver 11 via a check valve 31. The scavenging flow path forms part of the scavenging unit 36. In some embodiments, the scavenging unit 36 includes a scavenging cooler 12, a water mist collector 13, a branch point 23, a check valve 24, a mixing chamber 25, and a check valve 31.

  The scavenging gas or the scavenging gas mixed with the recirculated exhaust gas is sent from the scavenging receiver 11 to the scavenging port 14 of each cylinder 2.

  The exhaust gas bypass 54 is provided to rapidly reduce the engine speed. Further, the exhaust gas bypass 54 may be used in combination with a turbocharger suitable for the exhaust gas bypass in order to prevent overloading of the turbocharger during high load operation.

  In order to reduce the pressure difference between the exhaust gas receiver 6 and the scavenging receiver 11, a cylinder bypass 47 can be additionally provided. When the hot air is bypassed from the outlet of the compressor C of the turbocharger 7 to the exhaust gas receiver 6, the differential pressure is reduced, so that less power is required for the blower 30 to overcome the differential pressure. The bypass inlet 61 leading to the exhaust gas receiver 6 is provided away from the inlet 62 of the exhaust gas recirculation unit 37 so as not to reduce the carbon dioxide concentration of the exhaust gas guided to the exhaust gas recirculation unit 37.

  Further, the exhaust gas receiver 6 is connected to the exhaust gas recirculation flow path by an outlet 62. This outlet forms part of the exhaust gas recirculation unit 37. The exhaust gas recirculation unit 37 can be arranged in the upper part of the engine or in the vicinity of the engine. The recirculation flow path includes a press scrubber 15, followed by an EGR cooler 16, a scrubber 17, a water mist collector 18, and a gas suction chamber 19. Depending on the implementation Keita, the scrubbers 15 and 17 are wet scrubbers, and the cleaning droplets and vapor are sprayed from one or more nozzles and evaporated into the exhaust gas, thereby mixing with the exhaust gas. Cleaning droplets and vapors are usually based on water. The cleaning droplets and vapors absorb catalyst fines, particles such as residual fuel and soot particles, gases such as sulfur compounds, and thereby clean the gases. In addition to cleaning the exhaust gas, the wet cleaning also has an action of cooling the exhaust gas. Since the EGR cooler 16 cools the exhaust gas, moisture may condense in the EGR cooler 16. The water mist collector (water mist separating means) 18 collects condensed water and small water droplets that may be carried from the scrubber by the gas flow. The water recovered by the water mist collector 18 is discharged through an outlet drain pipe (not shown) and reused after the rinsing stage.

The exhaust gas recirculation unit 37 can be used in the following two methods, which are basically different from each other.
・ Normal operation ・ EGR operation

Further details regarding the operation of the exhaust gas recirculation unit 37 are described below.
[Normal operation]

  The exhaust gas recirculation unit 37 can operate as an outside air cooling unit. In that case, the valve 43 is closed, the valves 41 and 42 are opened, and the turbocharger 39 is also operating. When the load is medium to high, the outside air is sent to the exhaust gas recirculation unit 37 without the support of the scrubber and finally guided to the scavenging receiver 11 via the check valve 29. When the load is low, the outside air passes through the conduit 21 and the blower 30, enters the mixing chamber 25, passes through the check valve 31, and is sent to the scavenging receiver 11. Therefore, the exhaust gas recirculation unit 37 operates as an outside air cooling unit. The shutoff valve 41 and the shutoff valve 42 are used for connecting and shutting off the second turbocharger 39. When the second turbocharger 39 is in operation, the compressor C sends compressed air directly to the EGR cooler 16 and bypasses the press clubber 15. For this purpose, the shutoff valve 43 in the conduit 62 provided between the exhaust gas receiver 6 and the press clubber 15 is closed. Operation without EGR may be selected if the engine meets Tier-II exhaust requirements without EGR.

The blower 30 can be used as an auxiliary blower when the load is low. That is, if the scavenging pressure provided by both turbochargers 7 and 39 is insufficient to ensure proper combustion, it can be used as an auxiliary blower. In such a case, the outside air passes from the EGR cooler 16 through the blower 30 to the mixing chamber 25 via the scrubber 17, the water mist collector 18, the gas suction chamber 19, and the conduit 21 that are stopped. Further, the gas is sent to the scavenging receiver 11 via the check valve 31.
[EGR operation]

  The exhaust gas recirculation unit 37 can operate as an exhaust gas cleaning device. In this case, the valve 43 is open, the valves 41 and 42 are closed, and the turbocharger 39 is not operating. The exhaust gas passes from the exhaust gas receiver 6 through the opening 62 and is sent to the press club 15. The gas is cooled and washed in the press scrubber 15 and directed to the EGR cooler 16 to further cool the moisture and gas. The gas stream is further washed through the scrubber 17. Most of the scrubber water is collected from the exhaust gas. The exhaust gas after cleaning and cooling enters the suction chamber 19 through an additional water mist collector 18. Since the pressure in the suction chamber 19 is lower than the pressure in the scavenging receiver 11, the check valve 29 is closed. The outlet of the gas suction chamber 19 is connected to a conduit 21 that leads to the inlet of the blower 30. The conduit 21 includes a check valve 20 and an EGR control valve 22. The check valve 20 prevents backflow during the blower operation.

  The blower 30 receives exhaust gas from the EGR flow path and branch scavenging from the blower path (conduit) 26. The blower 30 is driven by an electric drive motor, a hydraulic drive motor, a steam turbine or an exhaust gas expander to increase the pressure of exhaust gas and / or scavenging gas received by the blower, and gas is supplied to the scavenging gas receiver 11 via the check valve 31. Operates to extrude. The operation of the blower (the speed of the blower and / or the position of the diffuser) is controlled by an electronic control unit (ECU) shown in FIG.

The electronic control unit receives a signal representing the oxygen concentration (content) or the carbon dioxide concentration (content) of the gas in the scavenging receiver 11 from the sensor 51. The electronic control unit receives a signal representing the pressure in the scavenging receiver 11 from the pressure sensor 52. As shown in FIG. 2, the electronic control unit issues control signals to the blower control valve 28 in the conduit 26 and / or the EGR control valve 22 in the conduit 21. The electronic control unit is configured to ensure that the engine operates (depending on the EGR rate) such that the scavenging includes predetermined oxygen or carbon dioxide. The electronic control unit is also configured to ensure that the engine operates with sufficient scavenging pressure. The engine 1 can freely change its operation so as to operate at various EGR rates under the control of the electronic control unit. If the engine is a marine engine, this condition may be advantageous to meet geographically different exhaust gas requirements, such as limitations on NO _x emissions. Examples of such requirements are based on IMO NO _x Tier-II and Tier-III regulations.

  When the pressure drop from the turbocharger compressor C to the inlet of the blower 30 is lower than the pressure drop from the exhaust gas receiver 6 through the EGR module 37 to the inlet of the blower 30 (this is a common phenomenon) ) The blower control valve 28 may restrict the amount of scavenging that enters from the branch point. Adjusting the opening degree of the blower control valve 28 balances the flow rate from the scavenging module 36 and the flow rate from the EGR module 37, thereby controlling the EGR rate.

  The total flow rate of the mixed gas is controlled by the speed of the blower 30 and / or the position of the diffuser of the blower 30 according to a command from the electronic control unit.

  With the blower control valve 28 fully open, the flow through the conduit 26 is adapted to provide the required EGR rate for high EGR flow at a load just before the normal auxiliary blower set point (approximately (Tier-III mode with 25-30% loading).

In the Tier-III mode with strict NO _x emission limits, the EGR rate should be increased by the blower flow to achieve the desired oxygen content within the scavenging pan 11. The conduit 26 is also used to support the turbocharger 7 at low loads. In order to obtain an appropriate scavenging pressure and an appropriate oxygen content in the scavenging receiver 11, the air blow control valve 28 may be adjusted.
[Simplified configuration]

  FIG. 3 shows another embodiment that is similar to the above embodiment, but with a simplified configuration. In this embodiment, the EGR system always operates. This embodiment simplifies the structure and uses components in a double structure, such as an EGR cooler, under constant wet operating conditions. Since the wet cooler surface also functions as a scrubber, it is not necessary to install the scrubber 17. This embodiment does not include the EGR valves 43 and 22 because the blower always operates and the flow is completely controlled by the EGR blower 30 regardless of the mode and the load range. One check valve 20 is provided to prevent backflow to the EGR unit 37, which is a phenomenon associated with low load operation or blower failure. However, the second turbocharger, the shutoff valves 41 and 42, and the check valve 29 that directly connects the EGR unit 37 to the scavenging receiver 11 are not necessary and are not mounted. The turbocharger 7 can be adapted by several adaptation strategies. The adaptation strategy may depend on how the conduit 54 is used. In the simplest configuration, the turbocharger can be properly installed without the conduit 54. Further, in the embodiment that does not include the exhaust gas bypass 54, it is assumed that the engine control system can perform the deceleration operation fast enough to prevent overspeed operation of the turbocharger 7. This embodiment uses a single blower or multiple blowers 30 in parallel for auxiliary and EGR blowing. Depending on the setting of the EGR blower 30, the conduit 47 may not be used. In this embodiment, the EGR cooler 16 operates continuously under moist operating conditions. The wet cooler surface also functions as a scrubber, so a separate scrubber 17 is not required. The throttle / control valve 22 is not required for the EGR conduit 21 because the blower 30 is always in operation and the flow is fully controlled by the blower 30 and the control valve 28 regardless of mode and load range.

  The following table shows examples of possible modes of operation of the embodiment of FIG.

  Mode 2 is a fail-safe mode, which is a mode when the blower fails and modes 3 and 4 cannot be used. In mode 2, the load is limited by the maximum capacity of the turbocharger 7.

Mode 3 is a low EGR mode to satisfy the exhaust requirements of IMO, for example, Tier-II. The engine can operate with a load range of 0-110%. The blower 30 is used to provide a low flow recirculation exhaust gas but a sufficient flow recirculation exhaust gas to reach an EGR rate that results in a cycle value of NO _x exhaust below the Tier-II threshold. The EGR rate is, for example, in the range of 0 to 15%. In this mode, if the engine is operated at medium to high loads (eg, over 25%) and it is not necessary to assist the compressor C of the turbocharger 7 to reach the required scavenging pressure, the blower control Valve 28 is closed. When the load is low, for example, when adding 0 to 25%, the air blowing control valve 28 is opened or adjusted. At this time, the blower 30 plays a dual role. This is because the blower 30 assists the compressor C of the turbocharger 7 to reach the required scavenging pressure.

Mode 4 is a high EGR mode for satisfying the exhaust requirements of IMO Tier-III. The engine 1 can operate in a load range of 0 to 110%. The blower 30 is used to provide a significant amount of recirculated exhaust gas. That is, it is used to provide a significant amount of recirculated exhaust gas in order to reach an EGR rate that results in NO _x exhaust cycle values below the stringent Tier-III threshold. The EGR rate is in the range of 30 to 40%, for example. Even in this mode, when the engine is operated at a medium load to a high load (for example, exceeding 25%) and it is not necessary to assist the compressor C of the turbocharger 7 to reach the required scavenging pressure, The control valve 28 is closed. When the load is low, for example, when adding 0 to 25%, the air blowing control valve 28 is opened or adjusted. At this time, the blower 30 plays a dual role. This is because the blower 30 assists the compressor C of the turbocharger 7 to reach the required scavenging pressure.

  The technical idea of the present invention has many advantages. Depending on the embodiment or implementation, one or more of the following advantages are provided. It should be noted that this is not a comprehensive list and that there may be other benefits other than those described herein.

  An advantage of the technical idea of the present invention is to provide a gas exchange system for a large low-speed two-stroke combustion engine having exhaust gas recirculation with a simpler structure. Another advantage is to increase the degree of freedom of operation of a large low speed two-stroke combustion engine with exhaust gas recirculation and allow fuel optimization operation in the exhaust mode of the IMO Tier-II at partial load. . However, the obvious advantage is that many parts can be reduced to reduce the final cost.

  Although the present invention has been described in detail for purposes of illustration, such detailed description is merely for purposes of the invention and modifications may be made by those skilled in the art without departing from the scope of the invention. Please understand that you may. For example, it is possible to adapt the principles of the invention to larger engines, in which case more turbochargers and exhaust gas systems will be required in parallel to meet the flow requirements . The introduction of a blower can be similarly considered. In other words, it will be common to install multiple blowers to meet the demand for the required flow rate and simple requirements for redundancy of auxiliary blower operation.

  It should be noted that there are many alternative ways of implementing the technical idea of the present invention. For example, a blower that increases the pressure of both recirculated exhaust gas and scavenging gas may be installed by modifying an existing engine. It is good also as an engine system which integrated a blower. Alternatively, a single exhaust gas unit including a blower may be provided in the vicinity of the engine and connected to the engine by a conduit.

  In another embodiment, the crosshead large low-speed two-stroke uniflow combustion engine 1 includes a plurality of cylinders 2 connected to a scavenging receiver 11 and an exhaust gas receiver 6; and a turbine T that receives exhaust gas from the exhaust gas receiver 6 And a turbocharger 7 having a compressor C for supplying high-pressure scavenging; a scavenging flow path for guiding the high-pressure scavenging from the outlet of the compressor C to the scavenging receiver 11; from the cylinder 2 or the exhaust gas receiver 6 An exhaust gas recirculation flow path for recirculating at least a portion of the exhaust gas to the scavenging receiver 11; a blower 30 for pushing an EGR flow to the scavenging receiver 11; and a signal representing the oxygen concentration or carbon dioxide concentration in the scavenging receiver 11 And an electronic control unit ECU that receives the signal from the sensor 51. The electronic control unit ECU is configured to control the EGR flow in response to a signal from the sensor 51.

  When the oxygen concentration is measured, in some embodiments, the electronic control unit ECU is configured to increase the EGR rate when the oxygen concentration of the scavenging pan 11 exceeds a first threshold. Further, in some cases, the EGR rate is configured to decrease when the oxygen concentration of the scavenging receiver 11 falls below a specific second threshold.

  When the carbon dioxide concentration is measured, depending on the implementation Keita, the electronic control unit ECU is configured to decrease the EGR rate when the carbon dioxide concentration in the scavenging receiver 11 exceeds a first threshold. Further, in some cases, the EGR rate is increased when the carbon dioxide concentration of the scavenging receiver 11 is less than a specific second threshold value.

  As a modification of the present embodiment, the electronic control unit ECU is configured to operate the EGR rate by controlling the speed of the blower 30.

  As used in the claims, “comprising” does not exclude other elements or steps. The number of each element used in the claims does not exclude a plurality of cases.

  The electronic control unit can be some of the means recited in the claims.

  Any reference signs in the claims should not be construed as limiting the scope.

  Although the present invention has been described in detail for purposes of illustration, such detailed description is merely for purposes of illustration and modifications will be apparent to those skilled in the art without departing from the scope of the invention. Please understand that you may.

Claims (4)

A plurality of cylinders (2) respectively connected to the scavenging receiver (11) and the exhaust gas receiver (6);
A turbocharger (7) having a turbine (T) receiving exhaust gas from the exhaust gas receiver (6) and a compressor (C) supplying high pressure scavenging;
A scavenging flow path for guiding the high-pressure scavenging from the outlet of the compressor (C) to the scavenging receiver (11);
An exhaust gas recirculation flow path for recirculating at least a portion of the exhaust gas from the cylinder (2) or the exhaust gas receiver (6) to the scavenging receiver (11);
A blower (30) for pushing an EGR flow into the scavenging pan (11);
A sensor (51) providing a signal representative of the oxygen concentration or carbon dioxide concentration in the scavenging pan (11);
An electronic control unit (ECU) that receives the signal from the sensor (51);
A crosshead large low-speed two-stroke uniflow internal combustion engine (1), wherein the electronic control unit (ECU) is configured to control the EGR flow in response to the signal from the sensor 51.   The engine (1) according to claim 1, wherein the electronic control unit (ECU) is configured to manipulate an EGR rate by controlling a speed of the blower (30).   The electronic control unit (ECU) is configured to increase the EGR rate when the sensed oxygen concentration exceeds a first threshold, and to decrease the EGR rate when the sensed oxygen concentration is less than a second threshold. The engine (1) according to claim 1.   The electronic control unit (ECU) is configured to decrease the EGR rate when the sensed carbon dioxide concentration exceeds a first threshold and to increase the EGR rate when the sensed carbon dioxide concentration is less than a second threshold. The engine (1) according to claim 1, wherein:

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