DK202170181A1

DK202170181A1 - A large turbocharged two-stroke internal combustion engine with egr system

Info

Publication number: DK202170181A1
Application number: DKPA202170181A
Authority: DK
Inventors: Schmuttermair Herbert
Original assignee: Man Energy Solutions Filial Af Man Energy Solutions Se Tyskland
Priority date: 2021-04-21
Filing date: 2021-04-21
Publication date: 2022-09-23
Also published as: CN115217617A; JP7308326B2; JP2022166819A; CN115217617B; DK181014B1; KR20220145268A; KR20240054250A

Abstract

A large turbocharged multi-cylinder two-stroke internal combustion engine (100) of the uniflow type with an EGR system for conveying a flow of exhaust gas from the exhaust system to the intake system. The EGR system comprises an EGR blower (29) and an electronically adjustable EGR throttling valve (32,43). An AC electric drive motor (33) is coupled to the EGR blower (29) for driving the EGR blower (29). The AC electric drive motor (33) is configured to operate at a predetermined constant speed. A sensor (27) provides a signal representative of the oxygen concentration in the scavenge gas receiver (2), and a controller (50) in receipt of said signal and is coupled to the electronically adjustable EGR throttling valve (32). The said controller (50) is configured to regulate the flow of exhaust gas through the EGR system by adjusting the position of the electronically adjustable EGR throttling valve (32,43) as a function of the first signal as a primary measure.

Description

. DK 2021 70181 A1 A LARGE TURBOCHARGED TWO-STROKE INTERNAL COMBUSTION ENGINE

WITH EGR SYSTEM

TECHNICAL FIELD The present disclosure relates a method and large turbocharged two-stroke internal combustion engine with an exhaust gas recirculation (EGR) system, and more particularly to control of the operation of the EGR system.

BACKGROUND Large turbocharged two-stroke internal combustion engines are typically used in propulsion systems of large ships (as a marine engine) or as a prime mover in power plants. Their sheer size, weight, and power output render them completely different from common combustion engines and place large two-stroke turbocharged compression-ignited internal combustion engines in a class for themselves. The height of these engines is typically not crucial, and therefore they are constructed with crossheads in order to avoid lateral loads on the pistons. Typically, these engines are dual-fuel engines configured to operate with fuel oil and one of natural gas, petroleum gas, methanol, and ethane. Emissions from marine diesel engines are subject to restriction due to awareness of the environmental effects of the emissions. The Tier III restrictions, limiting the emission of NOx from marine diesel engines in selected areas, as was presented by International Maritime Organization were introduced in 2016. Meeting these emission restrictions requires the use of technologies that reduce the emissions of NOx. One such technology is Exhaust Gas Recirculation (EGR) which has been applied to four-

, DK 2021 70181 A1 stroke engines in the automotive industry for several decades.

The principle of EGR is to recirculate part of the exhaust gas back to the scavenge manifold of the engine. This decreases the scavenging oxygen level in the scavenging gas and in turn decreases the formation of NOx gas during combustion. Unfortunately, lowering the oxygen content of the scavenging gas also affects combustion efficiency. At excessively low scavenge air oxygen levels the engine will produce undesirable visible smoke. In four-stroke automotive engine, there is a positive pressure difference between the exhaust gas side and the intake side, i.e. the positive pressure difference will cause the exhaust gas to be recirculated to flow to the intake side without the need for blowers or the like. However, in a large turbocharged two-stroke internal combustion engines there is a negative pressure difference between the exhaust gas side and the intake side, and the charging air would flow towards the exhaust side if there was established a simple conduit between the intake side and the exhaust side, as is done in four-stroke automotive engines. Thus, an EGR system of a two-stroke turbocharged internal combustion engine requires a blower or pump to force a portion of the exhaust gas into the charging air i.e. in a large turbocharged two-stroke diesel engine, the exhaust gas is recirculated by blowers to overcome the pressure difference between the exhaust system and intake system. Hence, in a large turbocharged two-stroke > internal combustion engine, a blower or compressor is required to force the exhaust gas that is to be recirculated from the

DK 2021 70181 A1 exhaust system to the intake system. These enormous engines require very large blowers to perform this task, and these very large blowers require a large drive motor for performing the task of forcing the exhaust gas from the 5 exhaust system to the intake system. In order to meet the emission requirements for both NOx and soot, it is necessary to control the oxygen concentration in the scavenge gas receiver accurately because soot formation will exceed the acceptable limit if the oxygen concentration is too low and NOx emissions will exceed the acceptable limit if the oxygen concentration is too high. Known large turbocharged two-stroke internal combustion engines with EGR rely on a controllable and variable speed FGR blower to regulate the EGR flow and thereby arrive at the oxygen concentration setpoint.

SUMMARY It is an object of the invention to provide a large turbocharged two-stroke internal combustion engine of the uniflow type that overcomes or at least reduces the problems indicated above.

The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description, and the figures.

According to a first aspect, there is provided a large turbocharged two-stroke internal combustion engine of the uniflow type, the engine comprising: a plurality of cylinders with scavenge ports at their lower end and an exhaust valve at their upper end, an intake system through

2 DK 2021 70181 A1 which scavenging gas is introduced into the cylinders, the intake system comprising a scavenge gas receiver connected to the cylinders via the scavenge ports, an exhaust system through which exhaust gas produced in the cylinders is exhausted, the exhaust system comprising an exhaust gas receiver connected to the cylinders via the exhaust valves, at least one turbocharger having turbine in the exhaust system driving a compressor in the intake system, a fuel system for delivering a flow of fuel to the cylinders, an

EGR system for conveying a flow of exhaust gas from the exhaust system to the intake system, the EGR system comprising an EGR blower and an electronically adjustable EGR throttling valve, an AC electric drive motor coupled to said EGR blower for driving said EGR blower, said AC electric drive motor being directly coupled to an AC grid by an electrical switch, said electric drive motor being configured to operate at a constant speed determined by the AC frequency, a sensor providing a signal representative of the oxygen concentration in the scavenge gas receiver, and a controller in receipt of the signal and coupled to the electronically adjustable EGR throttling wvalve, the controller being configured to regulate the flow of exhaust gas through the EGR system by adjusting the position of the electronically adjustable EGR throttling valve as a function of the signal as a primary measure to regulate the flow of exhaust gas through the EGR system.

By providing a large turbocharged two-stroke internal combustion engine with an EGR blower that is directly driven by an AC electric drive motor that is directly coupled to the grid and that has a controller that is configured to regulate the EGR flow by adjusting the position of electrically adjustable EGR valve as a primary measure, without changing the speed of the EGR blower, it

- DK 2021 70181 A1 becomes possible to do without expensive equipment that enables the EGR blower to be a variable speed EGR blower, such as a variable mechanical, or electric drive, for example, a variable speed mechanical transmission between the AC electric drive motor and the EGR blower, and/or a variable frequency electric drive powering the AC electric drive motor. The resulting engine is less complicated, more reliable, and less expensive.

A load-dependent scavenge oxygen concentration setpoint is predefined. The actual oxygen concentration is measured or estimated and the setpoint is reached by feedback and/or feed forward control of this measurement, by adjusting the electrically adjustable FGR throttling valve.

In a possible implementation form of the first aspect, the controller 1s configured to move the electronically adjustable EGR throttling valve in a closing direction for reducing the flow of exhaust gas through the EGR system and to move the electronically adjustable EGR throttling valve in an opening direction for increasing the flow of exhaust gas through the EGR system.

In a possible implementation form of the first aspect, the controller is configured to regulate the flow of exhaust gas through the EGR system by adjusting the opening degree of an electronically controlled cylinder bypass throttling valve or orifice that is arranged in a bypass conduit that connects to the intake system downstream of the compressor and to the exhaust system upstream of the turbine as a primary or secondary measure to regulate the flow of exhaust gas through the EGR system.

. DK 2021 70181 A1 In a possible implementation form of the first aspect, the controller åis configured to move the electronically controlled cylinder bypass throttling valve or orifice in a closing direction for increasing the flow of exhaust gas through the EGR system and to move the electronically controlled cylinder bypass throttling valve or orifice in an opening direction for decreasing the flow of exhaust gas through the EGR system.

In a possible implementation form of the first aspect, the controller is configured to control the flow of exhaust gas through the EGR system to keep the oxygen concentration in the scavenge gas receiver close to an oxygen concentration setpoint.

In a possible implementation form of the first aspect, the controller is configured to use the signal from the first sensor in feedback/feedforward control to keep the oxygen concentration in the scavenge gas receiver close to a scavenge oxygen con morning centration setpoint, the scavenge oxygen concentration setpoint preferably being adjusted to engine load.

In a possible implementation form of the first aspect, the AC electric drive motor is an asynchronous electric motor. In a possible implementation form of the first aspect, the AC electric drive motor is an synchronous electric motor.

In a possible implementation form of the first aspect, the AC electric drive motor is directly coupled to a driveshaft of the EGR blower.

; DK 2021 70181 A1 In a possible implementation form of the first aspect, the electronically adjustable FGR throttling valve is arranged downstream of the EGR blower.

In a possible implementation form of the first aspect, the electronically adjustable FGR throttling valve is arranged upstream of the EGR blower.

In a possible implementation form of the first aspect, the engine comprises an electronically adjustable EGR throttling valve downstream of the EGR blower and an electronically adjustable EGR throttling valve upstream of the EGR blower.

In a possible implementation form of the first aspect, the the AC electric drive motor is coupled to the AC grid without involving equipment for varying frequency and/or voltage.

In a possible implementation form of the first aspect, the FGR blower layout is according to the operating point with lowest pressure ratio and volume flow at predefined exhaust gas bypass valve and cylinder bypass valve position, required to achieve related oxigen set point in the scavenge air receiver, covered by the fixed speed of the exhaust gas recirculation blower, and the controller is configured to control the EGR flow as a function of oxigen set points for all other operating points by opening the controlled exhaust gas bypass valve.

In a possible implementation form of the first aspect, the EGR blower layout is in the range where auxiliary blowers are normally running, according to the operating point with lowest pressure ratio and volume flow with auxiliary blower

2 DK 2021 70181 A1 or blowers switched off, needed to achieve related 02 set point in the scavenge air receiver, covered by the fixed speed of the EGR blower, and the controller is configurd to control the EGR flow as a function of oxigen set points for this and other operating points by switching off one or more of the auxiliary blowers, and /or throttling the flow of the auxiliary blower or blowers.

These and other aspects of the invention will be apparent from and the embodiments described below.

BRIEF DESCRIPTION OF THE DRAWINGS In the following detailed portion of the present disclosure, the invention will be explained in more detail with reference to the example embodiments shown in the drawings, in which: Fig. 1 is an elevated front view of a large two-stroke internal combustion engine according to an example embodiment. Fig. 2 is an elevated side view of the large two-stroke internal combustion engine of Fig. 1. Fig. 3 is a diagrammatic representation of the large two- stroke internal combustion engine according to Fig. 1. Fig. 4 is a diagrammatic representation of an embodiment of the large two-stroke internal combustion engine with an EGR system, and Fig. 5 is a diagrammatic representation of another embodiment of the large two-stroke internal combustion engine with an EGR system.

DETAILED DESCRIPTION Figs. 1, 2, and 3 show a large low-speed turbocharged two- stroke diesel engine with a crankshaft 8 and crossheads 9.

2 DK 2021 70181 A1 Fig. 3 shows a diagrammatic representation of a large low- speed turbocharged two-stroke diesel engine with its intake and exhaust systems. In this example embodiment, the engine has six cylinders 1 in line. Large low-speed turbocharged two-stroke diesel engines have typically between four and fourteen cylinders 1 in line, carried by a cylinder frame 23 that is carried by an engine frame 11. The engine may e.g. be used as the main engine in a marine vessel or as a stationary engine for operating a generator in a power station. The total output of the engine may, for example, range from 1,000 to 110,000 kW.

The engine is in this example embodiment a compression- ignited engine of the two-stroke uniflow type with scavenging ports 18 at the lower region of the cylinder liners 1 and a central exhaust valve 4 at the top of each cylinder liner 1. However, it is understood that the engine does not need to be compression ignited but can alternatively be spark ignited. Hence, in the present embodiment, the compression pressure of the engine will be sufficiently high for compression ignition, but it is understood that the engine can operate with lower compression pressure and ignited by spark or similar means.

The intake system of the engine comprises a scavenge air receiver 2. The scavenge air is passed from the scavenge air receiver 2 to the scavenge ports 18 of the individual cylinders 1. A piston 10 that reciprocates in the cylinder liner 1 between the bottom dead center (BDC) and top dead center (TDC) compresses the scavenge air. Fuel is injected through fuel valves 55 that are arranged in the cylinder cover 22. Combustion follows, and exhaust gas is generated.

i DK 2021 70181 A1 An exhaust valve 4 centrally arranged in the cylinder cover 22 with a plurality of fuel valves 55 is distributed around the central exhaust valve 4 ( (preferably two or three fuel valves 55 per cylinder for each type of fuel used). The exhaust valve 4 is actuated by an electrohydraulic exhaust valve actuation system (not shown) that is controlled by a controller 50. The controller 50, is in an embodiment, the electronic control unit, such as an electronic computer comprising one or more microprocessors, memory, and other hardware required for the operation of such a control unit. The controller 50 is connected to various sensors and to various devices that influence the operation of the engine

100. The connection between the controller 50 and these sensors and devices can be in the form of signal lines or wireless connections that have not been shown in the drawings for reasons of simplicity. The controller 50 can be formed by a combination of various control units or can be a single control unit.

The fuel valves 55 are part of the fuel supply system. If the engine is a dual or multi-fuel engine, there will be multiple fuel systems. In an embodiment, the controller 50 is also configured to control the operation of the fuel valves 55.

When an exhaust valve 4 is opened, the exhaust gas flows through an exhaust system that includes an exhaust duct associated with the cylinders 1 into the exhaust gas receiver 3 and onwards through a first exhaust conduit 19 to a turbine 8 of a turbocharger 5 (an embodiment, the engine is provided with a plurality of turbochargers), from which the exhaust gas flows away through a second exhaust conduit via an economizer 20 to an outlet 21 and into the atmosphere.

DK 2021 70181 A1 Through a shaft, the turbine 8 drives a compressor 7 supplied with fresh air via an air inlet 12. The compressor 7 delivers pressurized scavenge air to a scavenge air conduit 13 leading to the scavenge air receiver 2. The scavenge air in the scavenge air conduit 13 passes an intercooler 14 for cooling the scavenge air.

The cooled scavenge air passes via an auxiliary blower 16 driven by an electric motor 17 that pressurizes the scavenge air flow when the compressor 7 of the turbocharger 5 does not deliver sufficient pressure for the scavenge air receiver 2, i.e. in low or partial load conditions of the engine.

At higher engine loads the turbocharger compressor 7 delivers sufficient compressed scavenge air and then the stopped auxiliary blower 16 is passed via a non-return valve 15. Scavenging gas is introduced into the cylinders 1 through the intake system, the intake system comprising the scavenge gas receiver 2 connected to the cylinders 1 via the scavenge ports 18. Exhaust gas produced in the cylinders is exhausted through the exhaust system, the exhaust system comprising the exhaust gas receiver 3 connected to the cylinders 1 via the exhaust valves 4. With reference to the embodiment of Fig. 4, the engine comprises an exhaust gas recirculation system, that comprises an exhaust gas recirculation path 60 that extends from the exhaust system a position upstream of the turbine 8 of the turbocharger 5 to the intake system at a position downstream of the compressor 7 of the turbocharger 5. Thus,

i.

DK 2021 70181 A1 the exhaust gas that needs to be recirculated can flow from the exhaust system to the intake system.

In this embodiment, structures and features that are the same or similar to corresponding structures and features previously described or shown herein are denoted by the same reference numeral as previously used for simplicity.

The exhaust gas recirculation system comprises an exhaust gas recirculation unit 61 that is configured for treating the recirculated exhaust gas.

The exhaust gas to be used recirculated typically needs to be cleaned before it is allowed to enter the intake system in order to avoid damage to the engine 100. Hereto, the exhaust gas recirculation unit 61 will typically comprise a water-based wet scrubber, the inflow and outflow of water being illustrated by the horizontal arrows in Fig. 4. A water mist catches 63 removes the water that is used in the wet scrubber.

Thus, relatively clean water is supplied to the exhaust gas recirculation unit 61 and relatively polluted water is removed from the exhaust gas recirculation unit 61. An exhaust gas recirculation blower 29 is provided to force the recirculated exhaust gas from the exhaust system to the intake system.

The exhaust gas recirculation blower 29 is needed since the pressure in the exhaust system of a large two-stroke internal combustion engine is typically lower than the charging pressure in the intake system.

The exhaust gas recirculation blower 29 is driven by an AC electric drive motor 33. The AC electric drive motor 33 is in an embodiment directly coupled to the EGR blower 29 for driving said EGR blower 29. The AC electric drive motor 33 is directly coupled to an AC grid (for example an AC electric grid of the marine vessel in which the large two-

i. DK 2021 70181 A1 stroke internal combustion engine 100 is installed or an AC electric grid of a building or other facility in which the large two-stroke internal combustion engine 100 is installed), by an electrical switch (35), The AC electric drive motor 33 is configured to operate at a constant speed determined by the AC frequency, when powered with AC power from the electrical grid determined by the AC . Since the EGR blower I 29 is directly mechanically coupled to the AC electrical drive motor 33, the EGR blower 29 is also configured to operate at a predetermined constant speed. In an embodiment, a driveshaft of the AC electric drive motor 33 is directly coupled to a driveshaft of the EGR blower 29. The AC electric drive motor 33 is configured to operate at predetermined constant speed, i.e. when it is supplied with electric power AC with a constant frequency.

The rotational speed of the AC electric drive motor 33 is dictated by thefrequency of the AC power delivered to the AC electric drive motor 33. In an embodiment, the AC power of the grid has a constant frequency and hence the operating speed of the AC electric drive motor 33 is constant.

In embodiment, The AC electric drive motor 33 is an asynchronous motor in which, at steady state, the rotation of the output shaft is slightly below an integral number of AC cycles of the supplied current.

In embodiment, the AC electric drive motor33 is a synchronous motor in which, at steady state, the rotation of the shaft is synchronized with the frequency of the y DK 2021 70181 A1 supply current. The rotation period is exactly equal to an integral number of AC cycles.

Thus, there 1s neither a variable mechanical nor an electric variable drive, for example, a variable speed mechanical transmission between the AC electric drive motor 33 and the EGR blower 29 and/or a variable frequency electric drive (VFD) in the electric power supply system for the AC electric drive motor 33. There is no need for equipment for varying frequency and/or voltage of the current supplied form the grid to the AC electric drive motor 33. In an embodiment, the AC power for the AC electric drive motor 33 is generated by an electric generator driven by the engine 100 and that powers the grid. In another embodiment, the AC power is generated by an auxiliary engine that powers the grid (not shown), i.e. by a generator set. In another embodiment, the AC power is provided by other sources coupled to the grid. In the embodiment of Fig. 4 the EGR blower 29 is shown to be downstream of the EGR unit 61, but it is understood that the EGR blower 29 may just as well be located upstream of the EGR unit 61. An electronically adjustable EGR throttling valve 32, is arranged in the EGR path 60 downstream of the EGR blower

29. The adjustable EGR throttling valve 32 is preferably motorized for opening valve and coupled to the controller 50 so that the controller can control the position of the EGR throttling valve 32 via a command signal and thereby dictate the control the degree of throttling that the EGR throttling valve 32 applies to the flow of recirculated

. DK 2021 70181 A1 exhaust gas through the EGR path 60. Thus, the controller 50 can increase or reduce the throttling effect of the EGR throttling valve 32 through a control signal. The controller 50 is connected to various sensors so that it is informed about the operating conditions of the engine 100 (e.g. engine load, engine speed, ambient temperature, scavenging pressure, etc.). The controller 50 is in receipt of a signal from a sensor 27, that provides a signal representative of the oxygen concentration in the scavenge gas receiver (2).

The controller 50 is configured to regulate the flow of exhaust gas through the EGR system by adjusting the position of the electronically adjustable EGR throttling valve 32 as a function of the signal as a primary measure to regulate the flow of exhaust gas through the EGR system. The controller 50 is preferably configured to control the flow of exhaust gas through the EGR system with the aim of maintaining the oxygen concentration in the scavenge gas receiver 2 close to a given oxygen concentration setpoint. The oxygen concentration setpoint is in an embodiment a function of the engine load, or of other operating conditions, such as temperature, humidity, scavenging pressure in the scavenge air receiver, cylinder pressures and mean effective pressure, and the emission requirements that apply for the geographical location in which the engine is operating.

The controller 50 is configured to use the signal from the sensor 27 in feedback control, optionally combined with feedforward control, to maintain the oxygen concentration in the scavenge gas receiver 2 close to the scavenge oxygen concentration setpoint.

Cc DK 2021 70181 A1 The controller 50 can be configured to move the electronically adjustable EGR throttling valve 32 in a closing direction (increase throttling) for reducing the flow of exhaust gas through the EGR system and to move the electronically adjustable EGR throttling valve 32 in an opening direction (less throttling) for increasing the flow of exhaust gas through the EGR system.

In an embodiment, the engine 100 comprises a cylinder bypass 47 that connects to the intake system downstream of the compressor 7 and to the exhaust system upstream of the turbine 8. The cylinder bypass conduit 47 comprises an electronically adjustable cylinder bypass throttling valve 42 and/or an electronically adjustable orifice 49. The controller 50 can be configured to regulate the flow of exhaust gas through the EGR system by adjusting the opening degree of the electronically controlled cylinder bypass throttling valve 42 or orifice 49 as a primary measure to regulate the flow of exhaust gas through the EGR system, in particular, to reduce EGR variation and thus throttle losses.

The controller 50 is configured to move the electronically controlled cylinder bypass throttling valve 42 or orifice 49 in a closing direction for increasing the flow of exhaust gas through the EGR system and to move the electronically controlled cylinder bypass throttling valve 42 or orifice 49 in an opening direction for decreasing the flow of exhaust gas through the EGR system.

In a possible implantation of this embodiment, the engine comprises an exhaust bypass that comprises an

- DK 2021 70181 A1 electronically adjustable exhaust gas bypass throttling valve 41 controlled by the controller 50.

The engine 100 and the controller 50 can be configured to control the EGR flow in accordance with the following scenarios: - The EGR blower layout is according to operating point with highest pressure ratio and volume flow at open electronically adjustable EGR throttling valve 32, needed to achieve related oxygen (02) set point in the scavenge air receiver 2, covered by the EGR blower 29 at its predetermined operating speed. The FGR flow is controlled by the controller 50 as a function of oxygen (02) setpoints for all other engine operating points by closing the electronically adjustable EGR throttling valve 32 and thereby running the EGR blower 29 at the correct pressure ratio to achieve the correct flow in the EGR flow path 60. In this scenario the controller 50 is configured to operate with the following optimization strategy: Open the electronically controlled cylinder bypass throttling valve 42 or orifice 49 to the admissible extent according to engine performance in order to reduce the operating points at highest pressure ratio and volume flow, to reduce EGR variation and thus throttle losses. - The EGR blower layout is according to the operating point with lowest pressure ratio and volume flow at open electronically adjustable EGR throttling valve 32, needed to achieve related oxygen (02) set point in the scavenge air receiver 2, covered by the EGR blower 29 at its predetermined operating speed and the electronically controlled cylinder bypass throttling valve 42 or orifice

DK 2021 70181 A1 49 being closed. The EGR flow is controlled by the controller 50 as a function of to oxygen (02) setpoints for all other engine operating points by opening electronically controlled cylinder bypass throttling valve 42 or orifice 49 and thereby running the EGR blower 29 at the correct pressure ratio to achieve the correct flow in the EGR flow path 60. In this scenario the controller 50 is configured to operate with the following optimization strategy: Open the electronically controlled cylinder bypass throttling valve 42 or orifice 49 to the admissible extent according to engine performance to control oxygen level and use the EGR throttling valve 32 if the admissible extent of cylinder bypass is exceeded.

Fig. 5 shows another embodiment of the engine that is similar to the embodiment of Fig. 4. In this embodiment, structures and features that are the same or similar to corresponding structures and features previously described or shown herein are denoted by the same reference numeral as previously used for simplicity. However, in this embodiment the valve for throttling the EGR flow in the EGR flow path 60 is arranged upstream of the EGR blower 29, and the sensor 27 is arranged upstream of the scavenge air received 2, but downstream of the position in the intake system where the recirculated exhaust gas is mixed with the alr coming from the turbine 7.

In this embodiment, the engine 100 and the controller 50 can be configured to control the EGR flow in accordance with the following scenario: The EGR blower layout is according to operating points with highest pressure ratio and volume flow at open

0 DK 2021 70181 A1 electronically adjustable EGR valve throttling 43, needed to achieve related oxygen (02) set point in the scavenge air receiver 2, covered by the EGR blower 29 at its predetermined operating speed. The FGR flow is controlled by the controller 50 as a function of oxygen (O2) setpoints for all other engine operating points by closing the electronically adjustable EGR throttling valve 43 and thereby running the EGR blower 29 at the correct pressure ratio to achieve the correct flow in the EGR flow path 60.

In this scenario the controller 50 is configured to operate with the following optimization strategy: Open the electronically controlled cylinder bypass throttling valve 42 or orifice 49 to the admissible extent according to engine performance in order to reduce the operating points at highest pressure ratio and volume flow, to reduce EGR variation and thus throttle losses. In an embodiment, the EGR blower layout is according to the operating point with lowest pressure ratio and volume flow at predefined exhaust gas bypass valve 41 and cylinder bypass valve 42 position, required to achieve related 02 set point in the scavenge air receiver 2, covered by the fixed speed of the EGR blower 29. The controller 50 is configured to control the EGR flow as a function of 02 set points for all other operating points by opening the controlled exhaust gas bypass valve 41 and thereby running the EGR blower 29 at the correct pressure ratio to achieve the EGR correct flow. A non-return valve (not shown) in the EGR flow path 60 is provided to close the EGR flow path 60 in an emergency case. The controller 50 is configured to open the cylinder bypass valve 42 as a function of the engine performance, and to deploy other measures to reduce

>0 DK 2021 70181 A1 FGR variation that are applicable within the IMO NOx cycle admissible limits. In an embodiment, the EGR blower layout is according to the operating point with lowest pressure ratio and volume flow with auxiliary blower (s) 16 switched off, needed to achieve related 02 set point in the scavenge air receiver 2, covered by the fixed speed of the EGR blower 29. The controller 50 is configured to control the EGR flow controlled as a function of 02 set points for other operating points by switching off the auxiliary blower (s) 16, throttling the flow of the auxiliary blower (s) 16, thereby running the EGR blower 29 close to the correct pressure ratio to achieve the correct flow in the EGR flow path 60. The controller 50 is configured to deploy additional control measures to run the EGR blower 29 accurately at the correct pressure ratio especially in the load range where no auxiliary blower(s) 16 are required to be running for maintaining scavenging pressure.

In an embodiment, (not shown) the engine 100 comprises an electronically adjustable EGR throttling valve 32 downstream of the EGR blower 29 and an electronically adjustable EGR throttling valve 43 upstream of the EGR blower 29. The method and engine have been described in conjunction with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a

DK 2021 70181 A1 plurality.

A single controller, processor or other unit may fulfill the functions of several items recited in the claims.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

The reference signs used in the claims shall not be construed as limiting the scope.

Claims

> DK 2021 70181 A1 CLAIMS

1. A large turbocharged two-stroke internal combustion engine (100) of the uniflow type, said engine (100) comprising: a plurality of cylinders (1) with scavenge ports (18) at their lower end and an exhaust valve (4) at their upper end, an intake system through which scavenging gas is introduced into the cylinders (1), said intake system comprising a scavenge gas receiver (2) connected to said cylinders (1) via said scavenge ports (18), an exhaust system through which exhaust gas produced in the cylinders is exhausted, said exhaust system comprising an exhaust gas receiver (3) connected to said cylinders (1) via said exhaust valves (4), at least one turbocharger (5) having turbine (8) in the exhaust system driving a compressor (7) in the intake system, a fuel system for delivering a flow of fuel to said cylinders (1), an EGR system for conveying a flow of exhaust gas from the exhaust system to the intake system, said EGR system comprising an EGR blower (29) and an electronically adjustable EGR throttling valve (32,43), an AC electric drive motor (33) coupled to said EGR blower (29) for driving said EGR blower (29), said AC electric

> DK 2021 70181 A1 drive motor (33) being directly coupled to an AC grid by an electrical switch (35), said AC electric drive motor (33) being configured to operate at a predetermined constant speed determined by the AC frequency, a sensor (27) providing a signal representative of the oxygen concentration in said scavenge gas receiver (2), and a controller (50) in receipt of said signal and coupled to said electronically adjustable EGR throttling valve (32), said controller (50) being configured to regulate the flow of exhaust gas through said EGR system by adjusting the position of said electronically adjustable EGR throttling valve (32,43) as a function of said signal as a primary measure to regulate the flow of exhaust gas through said EGR system.

2. An engine according to claim 1, wherein said controller (50) is configured to move said electronically adjustable FGR throttling valve (32,43) in a closing direction for reducing the flow of exhaust gas through said EGR system and to move said electronically adjustable EGR throttling valve (32,43) in an opening direction for increasing the flow of exhaust gas through said EGR system.

3. An engine according to claim 1 or 2, wherein said controller (50) is configured to regulate the flow of exhaust gas through said EGR system by adjusting the opening degree of an electronically controlled cylinder bypass throttling valve (42) or orifice (49) that is arranged in a bypass conduit (47) that connects to the intake system downstream of the compressor (7) and to the exhaust system upstream of the turbine (8) as a primary or

> DK 2021 70181 A1 secondary measure to regulate the flow of exhaust gas through said FGR system.

4, An engine according to claim 3, wherein said controller (50) is configured to move said electronically controlled cylinder bypass throttling valve (42) or orifice (49) in a closing direction for increasing the flow of exhaust gas through said FGR system and to move said electronically controlled cylinder bypass throttling valve (42) or orifice (49) in an opening direction for decreasing the flow of exhaust gas through said EGR system.

5, An engine according to any one of claims 1 to 4, wherein said controller (50) is configured to control the flow of exhaust gas through said EGR system to maintain the oxygen concentration in said scavenge gas receiver (2) close to an oxygen concentration setpoint, said scavenge oxygen concentration setpoint preferably being adjusted to engine load.

6. An engine according to any one of claims 1 to 5, wherein sald controller (50) is configured to use the signal from said first sensor (27) in feedback and/or feedforward control to maintain the oxygen concentration in the scavenge gas receiver (2) close to a scavenge oxygen concentration setpoint, said scavenge oxygen concentration setpoint preferably being adjusted to engine load.

7. An engine according to any one of claims 1 to 6, wherein said AC electric drive motor (33) is a synchronous electric drive motor or an asynchronous electric drive motor.

J DK 2021 70181 A1

8. An engine according to claim 7, wherein a driveshaft of said AC electric drive motor (33) is directly coupled to a driveshaft of said EGR blower (29).

9. An engine according to any one of claims 1 to 8, wherein said electronically adjustable EGR throttling valve (32) is arranged downstream of the EGR blower (29).

10. An engine according to any one of claims 1 to 8, wherein said electronically adjustable EGR throttling valve (43) is arranged upstream of the EGR blower (29).

11. An engine according to any one of claims 1 to 8, comprising an electronically adjustable EGR throttling valve (32) downstream of the EGR blower (29) and an electronically adjustable EGR throttling valve (43) upstream of the EGR blower (29).

12. An engine according to any one of claims 1 to 11, wherein said AC electric drive motor (33) is coupled to the AC grid without involving equipment for varying frequency and/or voltage.

13. An engine according to any one of claims 1 to 12, wherein the EGR blower layout is according to the operating point with lowest pressure ratio and volume flow at predefined exhaust gas bypass valve (41) and cylinder bypass valve (42) position, required to achieve related oxygen set point in the scavenge air receiver (2), covered by the fixed speed of the exhaust gas recirculation blower (29), and the controller (50) is configured to control the EGR flow as a function of oxygen setpoints for all other operating points by opening the controlled exhaust gas bypass valve (41).

Je DK 2021 70181 A1

14. An engine according to any one of claims 1 to 12, wherein the EGR blower layout is in the range where auxiliary blowers are normally running, according to the operating point with lowest pressure ratio and volume flow with auxiliary blower or blowers (16) switched off, needed to achieve related 02 set point in the scavenge air receiver (2), covered by the fixed speed of the EGR blower (29), and the controller (50) is configured to control the EGR flow as a function of oxygen setpoints for this and other operating points by switching off one or more of the auxiliary blowers (16), and /or throttling the flow of the auxiliary blower or blowers (16).