Single-flow large turbocharged two-stroke internal combustion engine and method of operating the same

Abstract

A large turbocharged two-stroke internal combustion engine (100) of the uniflow type and a method for operating such an engine (100) are provided, the engine having a controller (50) and a plurality of turbochargers (5), at least one of the plurality of turbochargers being a selectively activatable turbocharger (5), the controller being configured to activate and deactivate the selectively activatable turbocharger (5) at relatively high engine loads and to reduce the risk of surging or stalling of the selectively activatable turbocharger (5).

Description

Technical Field

[0001] The present disclosure relates to a method and a large turbocharged two-stroke internal combustion engine equipped with a plurality of exhaust-gas driven turbochargers for supplying scavenging air and a method of operating such an engine. Background Art

[0002] Large turbocharged two-stroke internal combustion engines are generally used in propulsion systems of large ships or as prime movers in power plants. The huge size, weight and power output of this large turbocharged two-stroke internal combustion engine make them completely different from ordinary internal combustion engines, and make large two-stroke turbocharged compression ignition internal combustion engines sui generis. The height of these engines is usually not crucial, and therefore these engines are built with crossheads to avoid side loads on the piston. Usually, these engines use natural gas, petroleum gas, methanol, ethane or (heavy) fuel oil to operate.

[0003] Large turbocharged two-stroke internal combustion engines can be operated with compression ignition, i.e. according to the Diesel principle, or as a premixed engine, i.e. according to the Otto principle, in which scavenging gases are mixed with fuel during the piston's stroke from bottom dead center (BDC) to top dead center (TDC).

[0004] It is relatively simple to optimize the turbocharger performance in such an engine for a single engine load. However, large turbocharged two-stroke internal combustion engines need to operate over a wide range of engine loads and operating conditions, and it is difficult to achieve optimal turbocharger efficiency over a large engine load range if a single (non-variable geometry) turbocharger is installed. Variable geometry turbochargers can alleviate some of the problems, but also have other disadvantages, such as increased cost, maintenance and complexity. It has proven to be useful to be able to increase the scavenging air pressure at part load, especially when optimizing engine efficiency at part load. Therefore, it has become common to use an exhaust bypass to influence the scavenging air pressure. This effect is obtained by matching the turbocharger to a specific pressure at 100% load with the bypass open. This results in a reduction in the power of the turbocharger because a portion of the exhaust gas bypasses the turbine of the turbocharger. From the perspective of the cylinder, this corresponds to installing the turbocharger at a lower efficiency, and the scavenging is therefore negatively affected. However, when the bypass is closed at part load, the turbine of the turbocharger receives all available exhaust mass flow, and then the turbine of the turbocharger converts the received exhaust mass flow into a higher air mass flow, thereby generating a higher scavenging air pressure at part load. However, at high engine load, it is obviously not desirable to reduce scavenging. One way to avoid this problem is to install multiple turbochargers and selectively use one or more turbochargers in the turbocharger, so as to use a selected part of the total turbocharger capacity in a way that produces the best performance at the actual engine load. By selectively enabling and disabling the turbocharger, the one or more turbochargers enabled always obtain all exhaust power, and avoid the reduction of scavenging quality at high load. The one or more turbochargers enabled and disabled do not necessarily have the same size (capacity) as the remaining turbochargers (the remaining turbochargers are always enabled turbochargers). The relative size / capacity of the one or more turbochargers that are selectively enabled and disabled is selected according to the required impact on the scavenging air pressure.

[0005] Therefore, if multiple turbochargers are installed and the number of turbochargers in operation is controlled, high turbocharger efficiency can be achieved over a large engine load range, thereby improving fuel consumption compared to a single (non-variable geometry) turbocharger, thereby reducing engine operating costs and environmental loads.

[0006] 100% engine load is not necessarily possible when a turbocharger is deactivated. The remaining one or more activated turbochargers simply do not have enough capacity to handle the total exhaust gas volume. This means that when increasing the engine load towards the maximum engine load, one or more turbochargers need to be activated at a relatively high load, typically between 50% and 75% of the maximum engine load (maximum continuous rating). The same applies to the reverse process of deactivating a turbocharger, which typically also needs to be done at a similar or the same relatively high engine load.

[0007] However, in practice it has been shown to be difficult to enable or disable the turbocharger at such high engine loads, because it is critical to keep the compressor operating point within the compressor diagram of the compressor of the turbocharger during cut-in and cut-out. If the turbocharger speed becomes too low for the current pressure ratio, the compressor will be pushed into a surge / stall state. Surge is an interruption of stable flow in the compressor, which usually occurs at low flow rates. Surge occurs when the compressor deviates from the design point and surge affects the entire turbocharger, which is aerodynamically and mechanically undesirable. Surge can damage the turbocharger. Surge can cause high temperatures, high vibrations and cause reverse flow, which means that the flow will go backwards and flow out of the compressor muffler. This will cause high loads on the mechanical components of the turbocharger. Although a single surge / stall is not necessarily serious for the turbocharger, multiple surges over time may jeopardize the reliability of the turbocharger.

[0008] In the prior art, this problem has not been solved, namely that it is not possible to keep the compressor operating point in a desired position or region in the compressor map, and therefore, in the prior art, this problem has been circumvented by activating and deactivating the turbocharger at relatively low engine loads, typically around 10% of maximum continuous power or less. However, this means that each activation or deactivation of the turbocharger requires the engine to be decelerated to 10% engine load, which is highly undesirable and often impossible in practice, for example when the engine is used as main propulsion for an ocean-going vessel, it is undesirable that the engine needs to be decelerated to 10% engine load before it can be operated at an engine load above, for example, 65%.

[0009] US2010 / 0281862 discloses a marine engine equipped with multiple turbochargers, wherein the turbochargers are switched from single operation to parallel operation or from parallel operation to single operation, and it is claimed that surge in the turbochargers to be started or stopped is prevented. The marine diesel engine includes: an exhaust pipe, through which an exhaust manifold mounted on the engine body communicates with a turbine part; a turbine inlet valve, which is connected somewhere in the exhaust pipe; a supply pipe, through which a compressor part communicates with a supply manifold mounted on the engine body; a check valve, which is connected somewhere in the supply pipe and opens when the outlet pressure of the compressor part reaches or exceeds the outlet pressure of the compressor part; a vent pipe, one end of which is connected somewhere in the supply pipe between the compressor part and the check valve; and a vent valve, which is connected somewhere in the vent pipe. When the turbocharger is started, the vent valve closes when the turbine inlet valve almost reaches the open position of the turbine inlet valve, and when the turbocharger is stopped, the vent valve opens just before the turbine inlet valve starts to close. However, tests by the inventors of the present disclosure have shown that turbocharger surge cannot be reliably prevented by following the teachings of US2010 / 0281862.

[0010] JPWO2015162840A1 discloses an engine system, wherein, starting from a state in which a main supercharger and an auxiliary supercharger are operating, an auxiliary turbine inlet valve and an auxiliary compressor outlet valve are closed, and the auxiliary supercharger is stopped while the main supercharger is kept in operation; when the number of superchargers to be operated is reduced, a stop time reference pressure with a specified surge margin is determined based on the rotation speed of the auxiliary supercharger, and when the outlet pressure of the auxiliary compressor is higher than the stop time reference pressure, the discharge valve is opened, and when the outlet pressure of the auxiliary compressor is lower than the stop time reference pressure, the discharge valve is closed. Summary of the invention

[0011] The object of the present invention is to provide a large turbocharged two-stroke internal combustion engine of the uniflow type which allows activation and deactivation of the turbocharger at relatively high engine loads with a minimum risk of turbocharger surge / stall.

[0012] The foregoing and other objects are achieved by various aspects of the present disclosure.Other possible implementation forms will become apparent through, for example, the description and the drawings.

[0013] According to a first aspect, there is provided a large turbocharged two-stroke internal combustion engine of the uniflow type, the engine comprising:

[0014] a plurality of cylinders having a scavenging port at a lower end of the cylinder and an exhaust valve at an upper end of the cylinder,

[0015] an intake system through which scavenging gas is introduced into the cylinder, the intake system comprising a scavenging gas receiver connected to the cylinder via a scavenging port,

[0016] an exhaust system through which the exhaust gas generated in the cylinder is discharged, the exhaust system comprising an exhaust receiver connected to the cylinder 1 via an exhaust valve,

[0017] a plurality of turbochargers, each having an exhaust gas driven turbine operatively coupled to the compressor, wherein an inlet of the turbine is connected to an exhaust gas receiver and an outlet of the compressor is connected to an intake system to deliver a pressurized scavenging gas flow to the scavenging gas receiver,

[0018] At least one of the plurality of turbochargers is a selectively activatable turbocharger having:

[0019] an activatable turbine selectively connected to the exhaust gas receiver via an electronically controlled turbine control valve,

[0020] an enableable compressor, wherein an outlet of the enableable compressor is selectively connected to

[0021] Each of the following:

[0022] an air intake system to which an outlet of the activatable compressor is connected via an electronically controlled compressor control valve, and

[0023] atmosphere, the outlet of the enableable compressor being connected to atmosphere via an electronically controlled air release valve connected to the outlet of the enableable compressor upstream of the compressor control valve,

[0024] the air release valve is a variable valve, thereby providing a controllably variable restriction to the flow of gas through the air release valve, and

[0025] A controller coupled to:

[0026] Turbine control valve,

[0027] Compressor control valves, and

[0028] Air release valve,

[0029] Wherein, when the selectively enabled turbocharger is enabled, the controller is configured to:

[0030] Move the turbine control valve from the closed position to the open position,

[0031] Move the compressor control valve from the closed position to the open position,

[0032] The air is released according to a function of at least one of the following:

[0033] The valve moves continuously towards the closed position:

[0034] the measured or estimated pressure at the outlet of the enabled compressor,

[0035] as well as

[0036] Measured or estimated speed of the optionally activated turbocharger.

[0037] By continuously moving the air release valve from an open position to a closed position according to the function, the pressure at the outlet of the enableable compressor can be controlled, and thus the pressure ratio on the enableable compressor can be controlled at a level that ensures that the compressor operating point defined by a combination of the pressure ratio on the compressor and the turbocharger / compressor speed is at a distance from the operating point at which the compressor surges / stalls, i.e., has a surge / stall margin, thereby significantly reducing the risk of the compressor surge / stall occurring during activation of the enableable compressor.

[0038] In a possible implementation form of the first aspect, the function is obtained from an operating point of the enableable compressor known to be at a safe distance from the occurrence of surge or stall.

[0039] In a possible implementation form of the first aspect, the function is obtained from a compressor characteristic, for example a compressor characteristic defined in a compressor map associated with the enableable compressor.

[0040] By controlling the pressure at the outlet of the enableable compressor as a function obtained from a compressor map, activation of the turbocharger may be controlled in such a way that the occurrence of stall and / or surge is prevented or at least reduced.

[0041] In a possible implementation form of the first aspect, when the selectively enabled turbocharger is deactivated, the controller is configured to:

[0042] Move the compressor control valve from the open position to the closed position,

[0043] moving the turbine control valve from an open position to a closed position, preferably after the compressor control valve has been closed,

[0044] The air release valve is moved toward the open position as a function of at least one of:

[0045] the measured and / or estimated pressure at the outlet of the enabled compressor,

[0046] as well as

[0047] A measured and / or estimated speed of a selectively enabled turbocharger.

[0048] By continuously moving the air release valve from a closed position to an open position according to the function, the pressure at the outlet of the enableable compressor can be controlled, and thus the pressure ratio on the enableable compressor can be controlled at a level that ensures that the compressor operating point defined by the combination of the pressure ratio and the turbocharger speed is at a distance from the operating point at which the compressor surges / stalls, i.e., has a surge / stall margin, thereby significantly reducing the risk of the compressor surge or stalling during deactivation of the enableable compressor.

[0049] In a possible implementation form of the first aspect, for a given speed of the selectively activatable turbocharger within a speed range of the selectively activatable turbocharger, the controller is informed of a target pressure at the outlet of the activatable compressor.

[0050] In a possible implementation form of the first aspect, the controller moves the air release valve to a position such that the actual pressure at the outlet of the enableable compressor corresponds to the target pressure for the actual speed of the selectively enableable turbocharger. By ensuring that the actual pressure at the outlet of the enableable compressor corresponds to the target pressure, the operating point can be kept at an optimal position, for example, a position corresponding to the highest compressor efficiency. In addition, by keeping the operating point of the enableable compressor at or near the optimal operating position, the risk of stalling is also significantly reduced.

[0051] In a possible implementation form of the first aspect, the target pressure for a given speed of the selectively activatable turbocharger is spaced apart by a surge margin from a pressure at which the activatable compressor surges at the same given speed of the selectively activatable turbocharger.

[0052] In a possible implementation form of the first aspect, the target pressure at a given speed of the selectively activatable turbocharger corresponds to a pressure at which the activatable compressor has the highest efficiency at the same given speed of the selectively activatable turbocharger.

[0053] In a possible implementation form of the first aspect, the engine comprises: a pressure sensor providing a signal representing the pressure at the outlet of an enableable compressor; and / or a speed sensor configured to provide a signal representing the rotational speed of a selectively enableable turbocharger.

[0054] In a possible implementation form of the first aspect, the controller is configured to determine the target pressure based on a signal from a speed sensor.

[0055] In a possible implementation form of the first aspect, the controller is configured to determine a difference between the target pressure and a signal from the pressure sensor and to determine a set point of the air release valve depending on the difference.

[0056] In a possible implementation form of the first aspect, the controller is configured to determine a set point of the turbine control valve and / or the compressor control valve depending on the determined difference from the set point.

[0057] In possible implementation forms of the first aspect, the turbine control valve is arranged upstream of an enableable turbine and / or wherein the compressor control valve is arranged downstream of an enableable compressor and / or wherein the air release valve is arranged in an air release duct which is located downstream of the compressor of a selectively enabled turbocharger and upstream of the compressor control valve.

[0058] In a possible implementation form of the first aspect, the estimated pressure and / or the estimated speed of the selectively activatable turbocharger are pre-stored values ​​obtained from one or more tests and / or simulations or through experience.

[0059] In a possible implementation form of the first aspect, the engine comprises a fuel system for delivering fuel to the cylinders.

[0060] In a possible implementation form of the first aspect, the turbine control valve is configured to control the exhaust gas flow to the enableable turbine.

[0061] In a possible implementation form of the first aspect, the compressor control valve is configured to control a purge gas flow from the activateable compressor to the purge gas receiver.

[0062] In a possible implementation form of the first aspect, the engine comprises a pressure sensor for sensing the scavenging gas pressure in the scavenging gas receiver and / or an observer for estimating the scavenging gas pressure in the scavenging gas receiver.

[0063] In a possible implementation form of the first aspect, the controller is configured to enable and disable the selectively enableable turbocharger according to the operating conditions of the engine. Preferably, the controller is configured to enable and disable the selectively enableable turbocharger according to the engine load, the scavenging air pressure or the load set point.

[0064] In a possible implementation form of the first aspect, the controller is configured to determine the actual engine turbocharging efficiency based on the sensed or observed scavenging gas pressure and / or the sensed or observed exhaust temperature. The term "engine turbocharging efficiency" refers to the turbocharging efficiency experienced / felt by the engine, regardless of ambient conditions.

[0065] In a possible implementation form of the first aspect, the compressor control valve is a variable valve so as to form a controllable variable restriction on the gas flow through the compressor control valve, and when the selectively activatable turbocharger is activated, the controller is configured to move the compressor control valve toward the open position according to the following two:

[0066] the measured or estimated pressure at the outlet of the enabled compressor,

[0067] as well as

[0068] Measured or estimated speed of the optionally activated turbocharger.

[0069] According to a second aspect, there is provided a method of operating a large turbocharged two-stroke internal combustion engine of the uniflow type, the engine comprising:

[0070] a plurality of cylinders having a scavenging port at a lower end of the cylinder and an exhaust valve at an upper end of the cylinder,

[0071] an intake system through which scavenging gas is introduced into the cylinder, the intake system comprising a scavenging gas receiver connected to the cylinder via a scavenging port,

[0072] an exhaust system through which exhaust gas generated in the cylinder is discharged, the exhaust system comprising an exhaust receiver connected to the cylinder via an exhaust valve, and

[0073] a plurality of turbochargers, each turbocharger having an exhaust gas driven turbine operatively connected to the compressor, wherein an inlet of the turbine is connected to an exhaust gas receiver and an outlet of the compressor is connected to an intake system to deliver a pressurized scavenging gas flow to the scavenging gas receiver,

[0074] At least one of the plurality of turbochargers is a selectively activatable turbocharger having:

[0075] an activatable turbine selectively connected to the exhaust gas receiver via an electronically controlled turbine control valve,

[0076] an enableable compressor, the outlet of the enableable compressor selectively connected to:

[0077] an air intake system to which an outlet of the activatable compressor is connected via an electronically controlled compressor control valve, and

[0078] atmosphere, the outlet of the enableable compressor being connected to atmosphere via an electronically controlled air release valve connected to the outlet of the enableable compressor upstream of the compressor control valve,

[0079] The air release valve is a variable valve, thereby forming a controllable and variable restriction on the flow of gas through the air release valve.

[0080] The method includes:

[0081] measuring or estimating at least one of a pressure at an outlet of an activatable compressor and a rotational speed of a selectively activatable turbocharger,

[0082] At least one selectively activatable turbocharger is activated by:

[0083] Move the turbine control valve from the closed position to the open position,

[0084] moving the compressor control valve from a closed position to an open position, preferably after the turbine control valve has been opened,

[0085] The air release valve is continuously moved from a closed position to an open position according to at least one of the following:

[0086] a measured or estimated pressure at the outlet of the selectively activatable compressor, and a measured or estimated speed of the selectively activatable turbocharger.

[0087] In a possible implementation form of the second aspect, the method includes:

[0088] At least one selectively activated turbocharger is deactivated by:

[0089] Move the compressor control valve from the open position to the closed position,

[0090] moving the turbine control valve from an open position to a closed position, preferably after the compressor control valve has been closed,

[0091] The air release valve is continuously moved from an open position to a closed position according to at least one of the following:

[0092] the measured or estimated pressure at the outlet of the enabled compressor,

[0093] as well as

[0094] Measured or estimated speed of the optionally activated turbocharger.

[0095] These and other aspects of the invention will become apparent from the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0096] In the following detailed description of the present disclosure, various aspects, embodiments and implementations will be described in more detail with reference to exemplary embodiments shown in the accompanying drawings, in which:

[0097] Figure 1 is a front elevation view of a large two-stroke internal combustion engine equipped with multiple turbochargers according to an exemplary embodiment,

[0098] Figure 2 yes Figure 1 A side elevation view of a large two-stroke internal combustion engine.

[0099] Figure 3 is based on Figure 1 Schematic diagram of a large two-stroke internal combustion engine ( Figure 3 Only one turbocharger of the plurality of turbochargers is shown in order to keep the figure as simple as possible),

[0100] Figure 4 and Figure 5 is a graph showing scavenging pressure, valve movement and stall margin during testing,

[0101] Figure 6 yes Figure 1 The control diagram of the engine,

[0102] Figure 7 yes Figure 1 Schematic diagram of an embodiment of a large two-stroke internal combustion engine with two turbochargers,

[0103] Figures 8 to 10 It shows that according to Figure 1 Graphs of examples of scavenging pressure, operating line set point, actual operating line, valve movement, and surge margin for an engine of FIG. 1 , and

[0104] Fig.11 is a schematic diagram of another embodiment of a large two-stroke internal combustion engine having three turbochargers. DETAILED DESCRIPTION

[0105] Figure 1 , Figure 2 and Figure 3 A large, low speed, turbocharged, two-stroke diesel engine 100 is shown having a crankshaft 8 and a crosshead 9 . Figure 3A schematic diagram of a large, low-speed, turbocharged, two-stroke diesel engine with an intake system and an exhaust system is shown. In this exemplary embodiment, the engine 100 has six cylinders 1 in line. Large, low-speed, turbocharged, two-stroke diesel engines typically have four to fourteen cylinders 1 in line carried by a cylinder frame 23, which is carried by an engine frame 11. The engine 100 can be used, for example, as a main engine in a marine vessel or as a stationary engine in a power station for operating a generator. The total output of the engine 100 can be, for example, in the range of 1,000 kW to 110,000 kW.

[0106] In this exemplary embodiment, the engine 100 is a two-stroke uniflow compression ignition engine 100 having scavenging ports 18 located at the lower region of the cylinder liners 1 and a central exhaust valve 4 located at the top of each cylinder liner 1. However, it should be understood that the engine 100 need not be compression ignited (diesel principle) but may instead be a premixed engine (Otto principle). Thus, in this embodiment, the compression pressure of the engine 100 will be high enough for compression ignition, but it should be understood that the engine 100 may be operated at a lower compression pressure and may be a premixed engine ignited by spark or similar means.

[0107] Scavenging air is introduced into the cylinder 1 by an intake system comprising a scavenging gas receiver 2 connected to the cylinder 1 via a scavenging port 18 .

[0108] The exhaust gas generated in the cylinder is discharged through an exhaust system, which includes an exhaust gas receiver 3 connected to the cylinder 1 via an exhaust valve 4 .

[0109] The intake system of the engine 100 includes a receiver 2 for scavenging gas or scavenging air (if EGR is not used, the receiver 2 will only receive air, and in the case of using EGR, the receiver 2 will receive a mixture of exhaust gas and scavenging air, hence the name scavenging gas receiver). The scavenging air is delivered from the scavenging gas receiver 2 to the scavenging port 18 of each cylinder 1. The piston 10 reciprocating between the bottom dead center (BDC) and the top dead center (TDC) in the cylinder liner 1 compresses the scavenging air. The fuel is injected through the fuel valve 55 arranged in the cylinder head 22, and then burns and produces exhaust gas. Alternatively, the fuel valve 55 is arranged in the cylinder liner, and the fuel is allowed to enter during the stroke of the piston from BDC to TDC, the mixture of scavenging air and fuel is compressed and ignition is triggered when the piston is at or close to TDC, and then burns and produces exhaust gas.

[0110] A central exhaust valve 4 is arranged in a central opening in the cylinder head 22. A plurality of (preferably three or four) fuel valves 55 are distributed in the cylinder head 22 around the central opening / exhaust valve 4. The exhaust valve 4 is actuated by an electro-hydraulic exhaust valve actuation system 29 controlled by a controller 50 (electronic control unit). The fuel valve 55 is supplied with fuel by a fuel supply system 30. The controller 50 is also configured to control the operation of the fuel valve 55.

[0111] When the exhaust valve 4 is opened, the exhaust gas flows from the central opening in the cylinder head 22 through the exhaust system including the exhaust duct associated with each cylinder 1 and enters the exhaust receiver 3, and continues to flow through the first exhaust duct 19 to the turbine 8 of the turbocharger 5 (the engine 100 is provided with multiple turbochargers 5, but not all turbochargers must be enabled at the same time), and the exhaust gas flows from the turbine 8 through the second exhaust duct via the economizer 20 to the outlet 21 and then enters the atmosphere.

[0112] The turbine 8 of the activated turbocharger 5 drives the compressor 7 via a shaft in each turbocharger 5, and the compressor 7 is supplied with fresh air via an air inlet 12. The compressor 7 delivers the pressurized scavenging air to a scavenging air duct 13 leading to the scavenging gas receiver 2. Usually, a scavenging air duct 13 is provided for each compressor 7. The scavenging air in the scavenging air duct 13 passes through an intercooler 14 and a water mist collector 63 to cool the scavenging air.

[0113] The engine 100 includes a controller 50 and two or more turbochargers 5. At least one of the turbochargers 5 is a selectively enabled turbocharger 5. The controller 50 is configured to deactivate at least one selective turbocharger 5 below a deactivation engine load threshold so that only one turbocharger 5 with a suitable flow area operates at a low engine load. The controller 50 is also configured to enable at least one selectively enabled turbocharger 5 when the engine load is above an activation engine load threshold. The activation engine load and the deactivation engine load may be the same or different and are selected so that the flow area of ​​the activated turbocharger 5 matches the engine load.

[0114] Figure 7 An embodiment of an engine 100 is shown having two turbochargers 5 , each in a separate scavenging air train. Figure 7 The turbocharger 5 on the left side of the center is a selectively activated turbocharger. Figure 7The turbocharger 5 on the right side of the center is always enabled. The selectively enabled turbocharger 5 and the always enabled turbocharger 5 may have the same capacity or different capacities. In particular, the selectively enabled turbocharger 5 may have a smaller capacity than the always enabled turbocharger 5. The controller 50 is configured to enable and disable the selectively enabled turbocharger 5 according to the actual operating conditions of the engine, in particular according to the actual engine load, with the aim of achieving the best turbocharging efficiency of the engine 100.

[0115] An electronically controlled turbine control valve 35 is arranged in a conduit connecting the inlet of the enableable turbine 8 of the selectively enableable turbocharger 5 with the exhaust gas receiver 3. The turbine control valve 35 is connected to a controller 50, and the position of the turbine control valve 35 is controlled by the controller 50 via a signal to the turbine control valve 35. Via the turbine control valve 35, the controller 50 enables and disables the exhaust gas flow from the exhaust gas receiver 3 to the inlet of the enableable turbine 8.

[0116] An electronically controlled compressor control valve 36 is arranged in a conduit connecting the outlet of the enableable compressor 7 of the selectively enabled turbocharger 5 to the scavenging gas receiver 2 via the scavenging air cooler 14 and the water mist trap 63. The compressor control valve 36 is connected to the controller 50, and the position of the compressor control valve 36 is controlled by the controller 50 through a signal to the compressor control valve 36. Through the compressor control valve 36, the controller 50 can enable and disable the scavenging air flow from the outlet of the enableable compressor 7 to the scavenging gas receiver 2.

[0117] At least the selectively enabled turbocharger 5 is provided with a rotation speed sensor, which generates a signal representing the rotation speed of the selectively enabled turbocharger 5, and the signal is transmitted to the controller 50. The pressure sensor 33 is arranged to measure the pressure at the outlet of the enabled compressor 7. The pressure sensor 33 is arranged upstream of the compressor control valve 36. The signal of the pressure sensor 33 is transmitted to the controller 50.

[0118] An electronically controlled air release valve 37 is arranged between the outlet of the enableable compressor 7 and, for example, the atmosphere or other environment having a pressure substantially equal to atmospheric pressure, such as the exhaust system downstream of the turbocharger 5 or the inlet side of the selectively enableable compressor 7, the air release valve 37 being fluidly connected to the outlet of the enableable compressor 7 upstream of the compressor control valve 36. Preferably, the air release valve 37 is arranged in an air release conduit 39 that branches off from a conduit connecting the outlet of the enableable compressor 7 with the compressor control valve 36. The air release valve 37 is a variable valve, thereby forming a controllable variable restriction to the gas flow through the air release valve 37. Therefore, the controller 50 controls the restriction of the air flowing through the air release valve 37 by adjusting the position of the air release valve 37.

[0119] Figure 4 and Figure 5 The results of attempting to activate and deactivate the selectively activated turbocharger 5 using only the turbine control valve 35 (TCV) and the compressor control valve 36 (CCV) are shown. Figure 4 is a graph showing the purge gas pressure in bar in the purge gas receiver 2 as a function of time, and Figure 5 is a graph showing the opening and closing of the turbine control valve 35 and the compressor control valve 36 over time, wherein 0 on the vertical axis corresponds to a fully closed valve and 1 on the vertical axis corresponds to a fully open valve. Figure 5 The stall margin is also plotted in FIG. The stall margin is an indicator showing how close the compressor is to stalling. Figure 5 It is clearly shown that the stall margin is negative in the time span of about 4 seconds to 13 seconds after the turbine control valve 35 and the compressor control valve 36 are opened, causing the compressor to stall. Different opening curves and timings for the turbine control valve 35 and the compressor control valve 36 were tried, but no result was obtained that the surge / stall margin can be kept above zero during the activation and deactivation of the selectively activatable turbocharger 5.

[0120] The compressor efficiency can be described by a constant efficiency line in a graph, where the pressure ratio across the compressor 7 is plotted against the air flow through the compressor 7 (compressor graph). The constant efficiency line is an elliptical curve in the compressor graph, along which the efficiency of the compressor 7 remains constant. The pressure ratio is the ratio of the pressure at the outlet of the compressor 7 divided by the pressure at the inlet of the compressor 7. Since the pressure at the inlet of the compressor 7 is substantially equal to atmospheric pressure, it can be assumed that the pressure at the inlet of the compressor 7 is substantially constant, so only the pressure at the outlet of the compressor 7 needs to be determined by measurement (e.g. using a pressure sensor) or estimation (e.g. using an observer) in order for the controller 50 to determine the pressure ratio across the compressor 7. The air flow through the compressor 7 is difficult to measure directly, but in an embodiment is determined (calculated) by the controller 50 based on the rotational speed of the compressor 7, i.e. the rotational speed of the turbocharger 5.

[0121] In an embodiment, within a range of turbocharger speeds, the optimal pressure ratio on the enableable compressor 7 that produces the highest compressor efficiency relative to the rotational speed of the selectively enabled turbocharger 5 is stored in the controller 50, for example as an operating line that can be represented in a graph in which the optimal pressure ratio is plotted relative to the turbocharger speed.

[0122] In another embodiment, the optimum pressure at the outlet of the enableable compressor 7 that produces the highest compressor efficiency relative to the rotational speed of the selectively enabled turbocharger 5 over a range of turbocharger speeds is stored in the controller 50, since the (atmospheric) pressure at the inlet of the enableable compressor 7 is known and constant.

[0123] Figure 6A control diagram for controlling the position of a turbine control valve 35 (TCV), a compressor control valve 36 (CCV) and an air release valve 37 (ARV) is shown. The measured or estimated rotational speed of the turbocharger 5 is provided to a target pressure estimator, which may be a separate control unit or part of the controller 50. The target pressure estimator calculates the optimum pressure at the outlet of the enableable compressor 7 for the actual turbocharger speed, for example using the above-mentioned stored working line. The target pressure is compared with the actual pressure measured or determined at the outlet of the enableable compressor 7 to determine the difference between the two signals. The difference is sent to a valve controller. The valve controller may be a separate controller or part of the controller 50. The valve controller adjusts the position of the air release valve 37 accordingly. To control the air release valve 37, the valve controller may be proportional (P), proportional and integral (PI) or proportional, integral and differential (PID) to increase the restriction on flow caused by the air release valve 37 when the pressure at the outlet of the enabled compressor 7 is lower than the target pressure, and to reduce the restriction on flow caused by the air release valve 37 when the pressure at the outlet of the enabled compressor is higher than the target pressure. Thus, the turbocharger speed is used for the first feedback control loop, and the compressor outlet pressure is used for the second feedback control loop. Thus, in this embodiment, the control diagram forms a dual feedback loop control.

[0124] In an embodiment, the valve controller controls the opening and closing of the turbine control valve 35 and the compressor control valve 36 according to a predetermined curve and sequence. The curves or operating lines for enabling the selectively enabled turbocharger 5 and deactivating the selectively enabled turbocharger 5 can be determined by testing or simulation, and these predetermined curves and sequences are stored in the controller 50.

[0125] Figure 8An example of the valve movement over time resulting from enabling and disabling a selectively enabled turbocharger 5 when the engine is operated at 50% engine load (50% of maximum continuous power) is shown. The selectively enabled turbocharger 5 is enabled, for example, when the engine load rises to exceed an engine load threshold. In this example, the controller 50 is configured to enable the selectively enabled turbocharger 5 by moving the turbine control valve 35 from a fully closed position to a fully open position. The controller 50 is configured to move the compressor control valve 36 from a fully closed position to a fully open position within a time span after the turbine control valve 35 has been opened. This is not a fixed predetermined time span. When the pressure set point is no longer increasing, the compressor control valve 36 is opened. The time when this occurs depends on the acceleration of the turbocharger 5. The air release valve 37 starts from the open position and is closed according to the above-mentioned control method, that is, according to a function of the speed of the selectively enabled turbocharger 5 and the pressure at the outlet of the enabled compressor 7. This function is determined by the compressor characteristics, which can be described as described above, for example using a compressor diagram, and which allows an operating point where the compressor operates optimally (efficiently) or at least without any risk of stalling / surge determined by the speed of the enableable compressor 7 and the pressure at the outlet of the enableable compressor 7.

[0126] In the present example, the compressor control valve 36 opens after the turbine control valve 35. However, it should be pointed out that this is not always the case, but depends on the situation, in particular on the acceleration of the turbocharger 5.

[0127] The selectively activatable turbocharger 5 is deactivated, for example, when the engine load drops below an engine load threshold (which may be different from the engine load threshold used to activate the selectively activatable turbocharger 5). In this example, the controller 50 is configured to start the process of deactivating the selectively activatable turbocharger 5 by moving the compressor control valve 36 from a fully open position to a fully closed position. The controller 50 is configured to move the turbine control valve 35 from a fully open position to a fully closed position within a time span after the turbine compressor control valve 36 has been closed. The air release valve 37 starts from a closed position and opens according to the control method described above, i.e., according to the rotational speed of the selectively activatable turbocharger 5 and the pressure at the outlet of the activatable compressor 7.

[0128] Fig. 9 The purge gas pressure generated in the purge gas receiver 2 , the duty line set point of the air relief valve 37 and the actual duty line of the air relief valve 37 are shown as a function of time. Fig.10The surge margin is shown over time and is shown to be positive both during activation of the selectively activated turbocharger 5 and during deactivation of the selectively activated turbocharger 5 , thereby significantly reducing the risk of surge. The surge margin is an indicator of how close the compressor 7 is to surging.

[0129] The controller can therefore adjust the position of the air release valve in such a way that the actual pressure at the outlet of the enableable compressor 7 is kept close to a target pressure that follows the peak efficiency line of the enableable compressor 7 .

[0130] The behavior of the selectively enabled turbocharger 5 can be predicted based on testing of the engine in a test bench and / or computer simulations, and thus the appropriate opening curve of the relief valve 37 can be based on stored data without the need to measure or determine in real time the turbocharger speed and / or the pressure at the outlet of the enabled compressor 7. Here, the controller 50 can be provided with one or more operating lines for opening the pressure relief valve 37. Preferably, each of these curves is adapted to a specific engine load.

[0131] In an embodiment, the compressor control valve 36 is a variable valve, thereby forming a controllable variable restriction on the flow of gas through the compressor control valve 36. In this embodiment, the controller 50 is configured to move the compressor control valve 36 from the closed position toward the open position based on the measured or estimated pressure at the outlet of the selectively activatable compressor 7 and the measured or estimated speed of the selectively activatable turbocharger 5 when the selectively activatable turbocharger 5 is activated to assist the air release valve 37 in the task of controlling the pressure at the outlet of the selectively activatable compressor 7.

[0132] Fig.11 is a schematic diagram of an engine 100 according to another embodiment, the engine 100 including two always enabled turbochargers 5 and one selectively enabled turbocharger 5. For simplicity, in this embodiment, structures and features that are the same or similar to the corresponding structures and features previously described or shown herein are represented by the same reference numerals as the reference numerals used previously. Except for the additional always enabled turbocharger 5, the engine 100 according to this embodiment is basically the same as the above-mentioned engine. Due to the additional always enabled turbocharger, the engine load at which the selectively enabled turbocharger 5 is enabled and the engine load at which the selectively enabled turbocharger 5 is disabled are different from the above-mentioned engine. The engine load at which the selectively enabled turbocharger 5 is enabled and disabled will depend on the capacity and characteristics of the corresponding turbocharger 5.

[0133] The method and the engine have been described in conjunction with various embodiments herein. However, other variations of the disclosed embodiments may be understood and effected by a person skilled in the art in practicing the claimed subject matter, by studying the drawings, the present 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 plurality. A single controller or other unit may perform the functions of several items recited in a claim. The fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0134] The reference numerals used in the claims should not be construed as limiting the scope. Unless otherwise indicated, the drawings are intended to be read together with the specification (e.g., section lines, component arrangements, proportions, degrees, etc.) and are considered part of the entire written description of the present disclosure. The terms "horizontal", "vertical", "left", "right", "upper" and "lower" as used in the specification refer only to the orientation of the structure shown when a particular figure faces the reader.

Claims

1. A single-flow large-scale turbocharged two-stroke internal combustion engine (100), the engine (100) comprising: A plurality of cylinders (1), each cylinder (1) having a scavenging port (18) and an exhaust valve (4), wherein the scavenging port (18) is located at a lower end of the cylinder (1) and the exhaust valve (4) is located at an upper end of the cylinder (1), an intake system through which scavenging gas is introduced into the cylinder (1), the intake system comprising a scavenging gas receiver (2), the scavenging gas receiver (2) being connected to the cylinder (1) via the scavenging port (18), an exhaust system through which the exhaust gas generated in the cylinder (1) is discharged, the exhaust system comprising an exhaust receiver (3), the exhaust receiver (3) being connected to the cylinder (1) via the exhaust valve (4), a plurality of turbochargers (5), each turbocharger (5) having an exhaust gas driven turbine (8) operatively coupled to a compressor (7), wherein an inlet of the turbine (8) is connected to the exhaust gas receiver (3), and an outlet of the compressor (7) is connected to the intake system to deliver a pressurized scavenging gas flow to the scavenging gas receiver (2), At least one of the plurality of turbochargers (5) is a selectively activatable turbocharger (5), the selectively activatable turbocharger (5) having: an activatable turbine (8) selectively connected to the exhaust gas receiver (3) via an electronically controlled turbine control valve (35), An activatable compressor (7), wherein the outlet of the activatable compressor (7) is selectively connected to: the air intake system, the outlet of the activatable compressor (7) being connected to the air intake system via an electronically controlled compressor control valve (36), and atmosphere, the outlet of the enableable compressor (7) being connected to the atmosphere via an electronically controlled air release valve (37) connected to the outlet of the enableable compressor (7) upstream of the compressor control valve (36), The air release valve (37) is a variable valve, thereby providing a controllably variable restriction to the flow of gas through the air release valve (37), and A controller (50) coupled to: The turbine control valve (35), the compressor control valve (36), and The air release valve (37), It is characterized in that when the selectively activatable turbocharger (5) is activated, the controller (50) is configured to: moving the turbine control valve (35) from a closed position to an open position, moving the compressor control valve (36) from a closed position to an open position, The air release valve (37) is continuously moved from an open position toward a closed position according to a function of: a measured or estimated pressure at the outlet of the enableable compressor (7), as well as a measured or estimated rotational speed of the selectively activatable turbocharger (5), wherein, for a given rotational speed of the selectively activatable turbocharger (5), the controller (50) is informed of the target pressure at the outlet of the activatable compressor (7), and The target pressure at a given speed of the selectively activatable turbocharger (5) corresponds to a pressure at which the activatable compressor (7) has the highest efficiency at the same given speed of the selectively activatable turbocharger (5).

2. The engine (100) according to claim 1, wherein: When the selectively enabled turbocharger (5) is deactivated, the controller (50) is configured to: moving the compressor control valve (36) from an open position to a closed position, moving the turbine control valve (35) from an open position to a closed position, The air release valve (37) is continuously moved toward an open position as a function of at least one of: a measured or estimated pressure at the outlet of the enableable compressor (7), as well as A measured or estimated rotational speed of the selectively activatable turbocharger (5).

3. The engine (100) according to claim 1, wherein: The function moves the air release valve (37) to a position such that the actual pressure at the outlet of the activatable compressor (7) corresponds to the target pressure for the actual speed of the selectively activatable turbocharger (5).

4. The engine (100) according to claim 1, wherein: The target pressure for a given speed of the selectively activatable turbocharger (5) is separated from the pressure at which the activatable compressor (7) surges at the same given speed of the selectively activatable turbocharger (5) by a surge margin.

5. The engine (100) according to claim 1, comprising at least one of a pressure sensor (33) and a speed sensor, wherein the pressure sensor (33) is configured to provide a signal representing the pressure at the outlet of the enableable compressor (7), and the speed sensor is configured to provide a signal representing the rotational speed of the selectively enableable turbocharger (5).

6. The engine (100) according to claim 5, wherein: The controller (50) is configured to determine the target pressure based on a signal from the speed sensor.

7. The engine (100) according to claim 6, wherein: The controller (50) is configured to determine a difference between the target pressure and a signal from the pressure sensor (33), and to determine a set point for the air release valve (37) based on the difference.

8. The engine (100) according to claim 7, wherein: The controller (50) is configured to determine a set point of the turbine control valve (35) and / or the compressor control valve (36) based on the difference.

9. The engine (100) according to claim 1, wherein: The turbine control valve (35) is arranged upstream of the enableable turbine (8), and / or wherein the compressor control valve (36) is arranged downstream of the enableable compressor (7), and / or wherein the air release valve (37) is arranged in an air release duct (39) which is located downstream of the compressor (7) of the selectively enableable turbocharger (5) and upstream of the compressor control valve (36).

10. The engine (100) according to claim 1, comprising a pressure sensor (34) and / or an observer, wherein the pressure sensor (34) is used to sense the scavenging gas pressure in the scavenging gas receiver (2), and the observer is used to estimate the scavenging gas pressure in the scavenging gas receiver (2).

11. The engine (100) according to claim 1, wherein: The controller (50) is configured to activate and deactivate the selectively activatable turbocharger (5) according to operating conditions of the engine.

12. The engine (100) according to claim 1, wherein: The compressor control valve (36) is a variable valve, thereby forming a controllably variable restriction on gas flow through the compressor control valve (36), and wherein, when the selectively activatable turbocharger (5) is activated, the controller (50) is configured to move the compressor control valve (36) from a closed position toward an open position based on: a measured or estimated pressure at the outlet of the enableable compressor (7), and A measured or estimated rotational speed of the selectively activatable turbocharger (5).

13. A method of operating a large turbocharged two-stroke internal combustion engine (100) of the uniflow type, the engine (100) comprising: A plurality of cylinders (1), each cylinder (1) having a scavenging port (18) and an exhaust valve (4), wherein the scavenging port (18) is located at a lower end of the cylinder (1) and the exhaust valve (4) is located at an upper end of the cylinder (1), an intake system through which scavenging gas is introduced into the cylinder (1), the intake system comprising a scavenging gas receiver (2), the scavenging gas receiver (2) being connected to the cylinder (1) via the scavenging port (18), an exhaust system through which the exhaust gas generated in the cylinder is discharged, the exhaust system comprising an exhaust receiver (3), the exhaust receiver (3) being connected to the cylinder (1) via the exhaust valve (4), and a plurality of turbochargers (5), each turbocharger (5) having an exhaust gas driven turbine (8) operatively coupled to a compressor (7), wherein an inlet of the turbine (8) is connected to the exhaust gas receiver (3), and an outlet of the compressor (7) is connected to the intake system to deliver a pressurized scavenging gas flow to the scavenging gas receiver (2), At least one of the plurality of turbochargers (5) is a selectively activatable turbocharger (5), the selectively activatable turbocharger (5) having: an activatable turbine (8) selectively connected to the exhaust gas receiver (3) via an electronically controlled turbine control valve (35), An activatable compressor (7), wherein the outlet of the activatable compressor (7) is selectively connected to: the air intake system, the outlet of the activatable compressor (7) being connected to the air intake system via an electronically controlled compressor control valve (36), and atmosphere, the outlet of the enableable compressor (7) being connected to the atmosphere via an electronically controlled air release valve (37) connected to the outlet of the enableable compressor (7) upstream of the compressor control valve (36), The air release valve (37) is a variable valve, thereby forming a controllable and variable restriction on the gas flow through the air release valve (37), The method comprises: measuring or estimating at least one of the following: the pressure at the outlet of the activatable compressor (7) and the rotational speed of the selectively activatable turbocharger (5), It is characterized in that at least one of the selectively activatable turbochargers (5) is activated in the following manner: moving the turbine control valve (35) from a closed position to an open position, moving the compressor control valve (36) from a closed position to an open position, During activation of at least one of the selectively activatable turbochargers (5), the air release valve (37) is continuously moved from an open position toward a closed position according to at least one of the following: the measured or estimated pressure at the outlet of the enableable compressor (7), as well as the measured or estimated rotational speed of the selectively activatable turbocharger (5), wherein, for a given rotational speed of the selectively activatable turbocharger (5), a controller (50) is informed of a target pressure at the outlet of the activatable compressor (7), and The target pressure at a given speed of the selectively activatable turbocharger (5) corresponds to a pressure at which the activatable compressor (7) has the highest efficiency at the same given speed of the selectively activatable turbocharger (5).

14. The method according to claim 13, comprising: At least one of the selectively activatable turbochargers (5) is deactivated by: moving the compressor control valve (36) from an open position to a closed position, moving the turbine control valve (35) from an open position to a closed position, The air release valve (37) is continuously moved from a closed position to an open position according to at least one of the following: a measured and / or estimated pressure at the outlet of the enableable compressor (7), as well as A measured and / or estimated rotational speed of the selectively activatable turbocharger (5).

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