JP7596433B2 - Large turbocharged two-stroke internal combustion engine having a turbocharger and method of operating same - Google Patents

Description

The present disclosure relates to a large two-stroke internal combustion engine having multiple exhaust-driven turbochargers for supplying scavenging air, and a method of operating such an engine.

background

Large turbocharged two-stroke internal combustion engines are often used in the propulsion systems of large ships and as prime movers in power plants. Their size, weight and power output set them apart from other combustion engines and place them in a unique category. These engines are constructed with a crosshead to avoid side pressure on the pistons, as increased height is less of a problem. Such engines are usually run on natural gas, petroleum gas, methanol, ethane or (heavy) fuel oil.

Large two-stroke turbocharged internal combustion engines can be operated as compression ignition, i.e. on the Diesel principle, or as premixed engines, i.e. on the Otto principle, where scavenging gases are mixed with fuel during the piston stroke from bottom dead centre (BDC) to top dead centre (TDC).

In such engines, it is relatively easy to optimize the turbocharger performance for a single engine load. However, large turbocharged two-stroke internal combustion engines must operate over a wide range of engine loads and operating conditions, and it is difficult to achieve optimal turbocharging efficiency over a wide range of engine loads if only a single (non-variable geometry) turbocharger is installed. Variable geometry turbochargers can alleviate some of the problems, but at the expense of increased cost, maintenance, and complexity. For example, it has been found to be useful to increase the scavenging pressure at partial loads when optimizing engine efficiency at partial loads. For this reason, it has become common to use exhaust bypasses to influence the scavenging pressure. The effect is achieved by adapting the turbocharger to a specific pressure, at 100% load, with the bypass open. However, the turbocharger's capacity is reduced because some of the exhaust gas bypasses the turbocharger turbine. From the cylinder point of view, this results in a less efficient turbocharger, which also has a negative effect on scavenging. Closing the bypass at part load results in a higher scavenging pressure at part load, since the turbocharger turbine receives the entire available exhaust gas mass flow and converts it to a higher air mass flow. However, a reduction in scavenging at high load is of course undesirable. One way to avoid this problem is to have multiple turbochargers and selectively use one or more of the turbochargers, using a selected percentage of the total turbocharger power in a way that provides the best performance depending on the engine load. By selectively starting and stopping the turbochargers, the operating turbocharger or turbochargers always get all the exhaust gas power, and a reduction in scavenging quality at high load is avoided. The turbochargers that are activated and deactivated are not necessarily the same size (capacity) as the remaining turbochargers (where the remaining turbochargers mean the turbochargers that are always activated). The relative size/capacity of the selectively activated and deactivated turbochargers is selected according to the desired magnitude of the effect on the scavenging air pressure.

Therefore, by installing multiple turbochargers and controlling the number of them in operation, high turbocharger efficiency can be achieved over a wide range of engine loads, improving fuel efficiency and reducing engine operating costs and environmental impact compared to a single (non-variable geometry) turbocharger.

When the turbocharger is shut down, 100% engine load is not always possible. The remaining turbocharger does not have enough capacity to handle the full amount of exhaust gas. This means that the turbocharger needs to be operated at a relatively high load, typically between 50% and 75% of maximum engine load (maximum continuous rating), as the engine load approaches maximum engine load (maximum continuous rating). The same applies to the reverse process of shutting down the turbocharger, which also typically needs to be performed at a similar or the same relatively high engine load.

In practice, however, it is known to be difficult to start or stop a turbocharger at such high engine loads, since it is important to keep the turbocharger compressor operating point in the compressor diagram during cut-in and cut-out. If the turbocharger speed becomes too low for the current pressure ratio, the compressor is forced to surge/stall. Surge is the destruction of the steady flow in the compressor. It usually occurs at low flow rates, when the compressor is operated outside of its design values, and it affects the entire turbocharger, which is unfavorable aerodynamically and mechanically. It may even damage the turbocharger. Surge not only leads to high temperatures and high vibrations, but can also cause flow reversal, i.e. the flow can reverse and go out of the compressor silencer. This results in high loads on the mechanical components of the turbocharger. A single surge/stall will not be fatal to a turbocharger, but many surges/stalls over a long period of time will compromise the reliability of the turbocharger.

This problem has not been solved in the art, i.e., the compressor operating point cannot be maintained at a desired position or area in the compressor diagram. For this reason, the art has circumvented this problem by starting and stopping the turbocharger at a relatively low engine load, typically around 10% of the maximum continuous rating. However, this means that the engine must be slowed down to 10% engine load every time the turbocharger is started or stopped, which is highly undesirable and often impossible in practice. For example, if the engine is used as the main propulsion engine of an ocean-going vessel, it is undesirable to have to slow down the engine to 10% engine load before it can operate at, for example, 65% engine load or more.

US2010/0281862 discloses a marine engine equipped with multiple turbochargers. It is described that in this engine, the turbochargers are switched from single operation to parallel operation or from parallel operation to single operation, and surge of the turbochargers being started or stopped is prevented. This marine diesel engine is equipped with an exhaust pipe where an exhaust manifold mounted on the engine body connects to a turbine section, a turbine inlet valve connected somewhere in the exhaust pipe, a supply pipe where a compressor section connects to a supply manifold mounted on the engine body, a check valve connected somewhere in the supply pipe and opens when the pressure reaches or exceeds the outlet pressure of the compressor section, an air bleed pipe with one end connected somewhere in the supply pipe between the compressor section and the check valve, and an air bleed valve connected somewhere in the air bleed pipe. The air bleed valve is closed when the turbine inlet valve reaches a substantially open position when the turbocharger is started, and is opened just before the turbine inlet valve starts to close when the turbocharger is stopped. However, testing by the inventors of this application has shown that following the teachings of US2010/0281862 does not reliably prevent turbocharger surge.

The engine disclosed in JP2015162840A1 starts with the main turbocharger and auxiliary turbocharger in operation, closes the auxiliary turbine inlet valve and auxiliary compressor outlet valve while keeping the main turbocharger in operation, and stops the auxiliary turbocharger. In addition, when reducing the number of operating turbochargers, a stop reference pressure having a predetermined surge margin is determined based on the rotation speed of the auxiliary turbocharger, and the blow-off valve is opened when the outlet pressure of the auxiliary compressor is higher than the stop reference pressure, and the blow-off valve is closed when the outlet pressure of the auxiliary compressor is lower than the stop reference pressure.

Abstract

The object of the present invention is to provide a large uniflow type turbocharged two-stroke internal combustion engine that allows the turbocharger to be turned on/off at relatively high engine loads while minimizing the risk of turbocharger surge/stall.

This and other objects are achieved by the features of the present disclosure. Various possible implementations will become apparent from the specification and drawings.

According to a first aspect, there is provided a large uniflow type turbocharged two-stroke internal combustion engine as follows. This engine comprises:
a plurality of cylinders, each having a scavenging port at a lower end and an exhaust valve at an upper end;
an intake system having a scavenging receiver connected to the cylinder through the scavenging port, through which scavenging gas is introduced into the cylinder;
an exhaust system including an exhaust receiver connected to the cylinder through the exhaust valve, through which exhaust gas generated within the cylinder is exhausted;
a plurality of turbochargers each having an exhaust driven turbine coupled to a compressor to power the compressor, an inlet of the turbine connected to the exhaust system, and an outlet of the compressor connected to the intake system for delivering a pressurized scavenging flow to the scavenging receiver;
Equipped with
At least one of the plurality of turbochargers is a selectively operable/shutdown turbocharger, and the selectively operable/shutdown turbocharger is
a turnable and shuttable turbine selectively connected to the exhaust receiver by an electronically controlled turbine control valve;
A compressor that can be turned on and off,
having
an outlet of the turnable/disable compressor is selectively connected to the intake system by an electronically controlled compressor control valve and to the outside air by an electronically controlled air bleed valve connected to the outlet of the turnable/disable compressor upstream of the compressor control valve;
the air bleed valve being a variable valve that forms a controllable variable restriction on the flow of gas through the air bleed valve;
The engine further comprises a controller coupled to the turbine control valve, the compressor control valve, and the air bleed valve;
The controller further comprises, when starting the selectively turnable turbocharger,
transitioning the turbine control valve from a closed state to an open state;
transitioning the compressor control valve from a closed state to an open state;
- causing the air bleed valve to move successively towards a closed state as a function of at least one of a measured or estimated pressure at the outlet of the turnable/disable compressor and a measured or estimated rotational speed of the selectively turnable/disable turbocharger.
It is configured as follows.

By continuously switching the air bleed valve from an open state to a closed state according to the function, it becomes possible to control the pressure at the outlet of the operable/stoppable compressor, and in turn, it becomes possible to control the pressure ratio (upstream to downstream) of the operable/stoppable compressor to a certain level. This level is a level where the compressor operating point, defined by the combination of the compressor pressure ratio and the turbocharger or compressor speed, is a certain distance away from the operating point where the compressor surges/stalls, i.e., a level where there is a margin to surge/stall. Therefore, the risk of surge/stall occurring in the operable/stoppable compressor when the compressor is started can be significantly reduced.

In one implementation of the first approach, the function is derived from an operating point of the compressor that can be turned on and off and that is known to be a safe distance from surge or stall.

In one example implementation of the first approach, the function is derived from compressor characteristics, e.g., compressor characteristics defined in a compressor diagram associated with a compressor that can be turned on and off.

By controlling the pressure at the outlet of the compressor, which can be turned on and off, as a function derived from the compressor diagram, it is possible to control the start-up of the turbocharger so as to prevent or at least reduce the occurrence of stall and surge.

In one example of an implementation form of the first approach, when shutting down the selectively operable turbocharger, the controller:
transitioning the compressor control valve from an open state to a closed state;
transitioning the turbine control valve from an open state to a closed state, preferably after the compressor control valve has closed;
- switching said air bleed valve to an open state as a function of at least one of a measured and/or estimated pressure at the outlet of said turnable/disable compressor and a measured and/or estimated rotational speed of said selectively turnable/disable turbocharger.
It is configured as follows.

By continuously switching the air bleed valve from a closed state to an open state according to the function, it becomes possible to control the pressure at the outlet of the operable/stoppable compressor, and in turn, it becomes possible to control the pressure ratio (upstream to downstream) of the operable/stoppable compressor to a certain level. This level is a level where the compressor operating point, defined by the combination of the pressure ratio and the turbocharger speed, is a certain distance away from the operating point where the compressor surges/stalls, i.e., a level where there is a margin to surge/stall. Therefore, the risk of surge or stall occurring in the operable/stoppable compressor when the compressor is stopped can be significantly reduced.

In one implementation of the first approach, the controller is notified of a target pressure at the outlet of the startable/stopable compressor for a given rotational speed of the selectively operable/stopable turbocharger within a range of rotational speeds of the selectively operable/stopable turbocharger.

In one implementation of the first approach, the controller moves the air bleed valve to a position where the actual pressure at the outlet of the turnable compressor corresponds to the target pressure for the actual rotational speed of the selectively turnable turbocharger. By making the actual pressure at the outlet of the turnable compressor correspond to the target pressure, it is possible to maintain an operating point at an optimal position, e.g., a position corresponding to maximum compressor efficiency. Also, by maintaining the operating point of the turnable compressor at or near an optimal operating position, the risk of stalling is significantly reduced.

In one example of an implementation of the first approach, the target pressure for a given rotational speed of the selectively operable turbocharger is a surge margin away from the pressure at which the selectively operable compressor surges at the same given rotational speed of the selectively operable turbocharger.

In one example of an implementation of the first approach, the target pressure at a given rotational speed of the selectively operable turbocharger corresponds to the pressure at which the turnable compressor has the highest efficiency at the same given rotational speed of the selectively operable turbocharger.

In one example of an implementation of the first approach, the engine includes a pressure sensor that provides a signal representative of the pressure at the outlet of the turnable and deactivatable compressor, and a speed sensor that is configured to provide a signal representative of the rotational speed of the selectively turnable and deactivatable turbocharger.

In one example implementation of the first approach, the controller is configured to determine the target pressure based on a signal from the speed sensor.

In one example implementation of the first approach, the controller is configured to determine a difference between the target pressure and a signal from the pressure sensor and determine a setting value for the air bleed valve as a function of the difference.

In one example implementation of the first approach, the controller is configured to determine a setpoint for the turbine control valve and/or the compressor control valve as a function of the determined difference from the setpoint.

In one example of an implementation of the first approach, the turbine control valve is disposed upstream of the turnable/stopable turbine, and/or the compressor control valve is disposed downstream of the turnable/stopable compressor, and/or the air bleed valve is disposed in an air bleed pipe downstream of the compressor of the selectively turnable/stopable turbocharger and upstream of the compressor control valve.

In one example of an implementation of the first approach, the estimated pressure and/or estimated rotational speed of the selectively operable turbocharger are pre-stored values obtained from one or more tests and/or simulations, or experience.

In one example of an implementation of the first approach, the engine includes a fuel system for supplying fuel to the cylinders.

In one example implementation of the first approach, the turbine control valve is configured to control the flow of exhaust gas to a turbine that can be turned on and off.

In one example of an implementation of the first approach, the compressor control valve is configured to control the flow of scavenging gas from the turnable compressor to the scavenging receiver.

In one example of an implementation of the first approach, the engine is equipped with a pressure sensor for detecting the scavenging gas pressure in the scavenging receiver and/or an observation device for estimating the scavenging gas pressure in the scavenging receiver.

In one implementation of the first approach, the controller is configured to activate and deactivate the selectively operable turbocharger as a function of engine operating conditions, preferably as a function of engine load, scavenging pressure or load set point.

In one implementation of the first approach, the controller is configured to determine an actual engine turbocharging efficiency as a function of the sensed or observed scavenging pressure and/or the sensed or observed exhaust temperature, where the term "engine turbocharging efficiency" refers to the turbocharging efficiency experienced or felt by the engine regardless of ambient conditions.

In one example of an implementation of the first approach, the compressor control valve is a variable valve that forms a controllable variable restriction on the flow of gas through the compressor control valve, and the controller is configured to move the compressor control valve in an opening direction when starting the selectively operable turbocharger as a function of two things: a measured or estimated pressure at the outlet of the selectively operable compressor and a measured or estimated rotational speed of the selectively operable turbocharger.

According to a second aspect, there is provided a method of operating a large turbocharged two-stroke internal combustion engine of the uniflow type, said engine comprising:
a plurality of cylinders, each having a scavenging port at a lower end and an exhaust valve at an upper end;
an intake system having a scavenging receiver connected to the cylinder through the scavenging port, through which scavenging air is introduced into the cylinder;
an exhaust system including an exhaust receiver connected to the cylinder through the exhaust valve, through which exhaust gas generated within the cylinder is exhausted;
a plurality of turbochargers each having an exhaust driven turbine coupled to a compressor to power the compressor, an inlet of the turbine connected to the exhaust system, and an outlet of the compressor connected to the intake system for delivering a pressurized scavenging flow to the scavenging receiver;
Equipped with
At least one of the plurality of turbochargers is a selectively operable/shutdown turbocharger, and the selectively operable/shutdown turbocharger is
a turnable and shutable turbine selectively connected to the exhaust receiver via an electronically controlled turbine control valve;
A compressor that can be turned on and off,
having
an outlet of the turnable/disable compressor is selectively connected to the intake system by an electronically controlled compressor control valve and to the outside air by an electronically controlled air bleed valve connected to the outlet of the turnable/disable compressor upstream of the compressor control valve;
the air bleed valve is a variable valve that forms a controllable variable restriction in the flow of gas through the air bleed valve;
And the method further comprises:
Measuring or estimating at least one of a pressure at an outlet of the turnable and deactivatable compressor and a rotational speed of the selectively turnable and deactivatable turbocharger;
starting the at least one selectively operable turbocharger;
transitioning the turbine control valve from a closed state to an open state;
transitioning the compressor control valve from a closed state to an open state, preferably after the turbine control valve has opened;
- causing the air bleed valve to transition continuously from a closed state to an open state as a function of at least one of a measured or estimated pressure at the outlet of the turnable/deactivatable compressor and a measured or estimated rotational speed of the selectively turnable/deactivatable turbocharger;
and
Includes.

In one example implementation of the second aspect, the method includes shutting down the at least one selectively operable turbocharger, the method comprising:
transitioning the compressor control valve from an open state to a closed state;
transitioning the turbine control valve from an open state to a closed state, preferably after the compressor control valve has closed;
said air bleed valve being continuously transitioned from an open state to a closed state as a function of at least one of a measured or estimated pressure at the outlet of said turnable/disable compressor and a measured or estimated rotational speed of said selectively turnable/disable turbocharger;
This includes stopping by

The above and other aspects of the present invention will become more apparent from the embodiments described below.

Various aspects, embodiments and implementations are described in detail below with reference to example embodiments illustrated in the drawings.
FIG. 1 is a front overhead view of a large two-stroke internal combustion engine with multiple turbochargers according to an exemplary embodiment. FIG. 2 is a rear view of the large two-stroke internal combustion engine of FIG. 1 . 2 is a diagrammatic representation of a large two-stroke internal combustion engine according to Figure 1, in which only one of several turbochargers is shown in order to keep the illustration as simple as possible. 1 is a graph showing scavenging pressure during testing. 1 is a graph showing valve movement and stall margin during testing. FIG. 2 is a control diagram of the engine of FIG. 2 is a schematic representation of an embodiment of the large two-stroke internal combustion engine of FIG. 1 having two turbochargers; 2 is a graph showing an example of the movement of the valves of the engine according to FIG. 1; 2 is a graph showing an example of the scavenging pressure, the work line set value, and the actual work line of the engine shown in FIG. 1; 2 is a graph showing an example of a surge margin of the engine according to FIG. 1; 1 is a schematic representation of another embodiment of a large two-stroke internal combustion engine, this embodiment being equipped with three turbochargers.

Detailed explanation

Figures 1-3 depict a turbocharged large slow-speed two-stroke diesel engine 100. The engine has a crankshaft 8 and a crosshead 9. Figure 3 is a schematic representation of a turbocharged large slow-speed two-stroke diesel engine with its intake and exhaust systems. In this embodiment 100, the engine has six cylinders 1 in series. A turbocharged large slow-speed two-stroke diesel engine typically has four to fourteen cylinders arranged in series. The cylinders are carried on a cylinder frame 23. The cylinder frame 23 is carried on an engine frame 11. The engine 100 can be used, for example, as a main engine on a ship or as a stationary engine for driving a generator in a power plant. The total power output of the engine 100 can be, for example, between 1000 kW and 110000 kW.

The engine 100 in this embodiment is a two-stroke uniflow compression ignition engine, with each cylinder liner 1 having a scavenging port 18 in its lower region and an exhaust valve at the top center. However, the engine 100 does not necessarily have to be compression ignition (Diesel principle) and may be a premixed engine (Otto principle) in some embodiments. In the embodiment presented here, the compression pressure of the engine 100 is high enough to provide compression ignition. However, the engine 100 may be a premixed engine operating at a lower compression pressure and ignited by a spark or similar means.

Scavenging air is introduced into the cylinder 1 through the intake system. The intake system includes a scavenging receiver 2 that is connected to the cylinder 1 via a scavenging port 18.

The exhaust gas generated in the cylinder is exhausted through the exhaust system. The exhaust system includes an exhaust receiver 3 connected to the cylinder 1 via an exhaust valve 4.

The intake system of the engine 100 includes a receiver 2 for scavenging gas or scavenging air. When EGR is not used, the receiver 2 receives only air, and when EGR is used, the receiver 2 receives a mixture of exhaust gas and scavenging air. The receiver 2 is therefore called a "scavenging receiver". The scavenging air is led through the scavenging receiver 2 to the scavenging ports 18 of each cylinder 1. The piston 10 reciprocates between bottom dead center (BDC) and top dead center (TDC) in the cylinder liner 1, compressing the scavenging air. Fuel is injected from a fuel valve 55 located in the cylinder cover 22. Combustion then ensues and exhaust gases are produced. Alternatively, the fuel valve 55 is located in the cylinder liner and fuel is introduced during the piston stroke from BDC to TDC. The mixture of scavenging air and fuel is compressed and ignition is induced when the piston is at or near TDC, combustion ensues and exhaust gases are produced.

A central exhaust valve 4 is disposed in the central opening of the cylinder cover 22. A plurality of fuel valves 55 (preferably three or four) are also disposed in the cylinder cover 22 around the central opening or the central exhaust valve 4. The exhaust valves 4 are actuated by an electrohydraulic exhaust valve actuation system 29 controlled by a controller (electronic control unit) 50. The fuel valves 55 are supplied with fuel by a fuel supply system 30. The controller 50 is also configured to control the operation of the fuel valves 55.

When the exhaust valve 4 is opened, the exhaust gas flows from the central opening of the cylinder cover 22 through an exhaust system having an exhaust duct (provided for each cylinder 1) into the exhaust receiver 3, and then through the first exhaust pipe 19 toward the turbine 8 of the turbocharger 5. From there, the exhaust gas passes through the second exhaust pipe, passes through the economizer 20, and heads toward the outlet 21, where it is released into the atmosphere. Note that although the engine 100 is equipped with multiple turbochargers 5, not all of the turbochargers are necessarily operating at the same time.

When in operation, the turbine 8 of the turbocharger 5 drives the compressor 7 through the shaft of the turbocharger 5. The compressor 7 is supplied with outside air through an air intake 12. The compressor 7 sends compressed scavenging air to a scavenging pipe 13 that leads to the scavenging air receiver 2. Typically, each compressor 7 is provided with a scavenging pipe 13. The scavenging air in the scavenging pipe 13 passes through an intercooler 14 and a water mist catcher 63 to cool the scavenging air.

The engine 100 includes two or more turbochargers 5 and a controller 50. At least one of the turbochargers 5 is a turbocharger 5 that can be selectively activated and deactivated. The controller 50 is configured to deactivate at least one of the selectively activated and deactivated turbochargers 5 when the engine load is below a stop engine load threshold, so that only one turbocharger 5 having an appropriate flow area is activated at low engine load. The controller 50 is also configured to start at least one of the selectively activated and deactivated turbochargers 5 when the engine load exceeds a start engine load threshold. The start engine load and the stop engine load may be the same or different, and the flow area of the activated turbocharger 5 is selected to match the engine load.

Figure 7 shows an embodiment of the engine 100 with two turbochargers 5, each in a separate scavenging path. The turbocharger 5 on the left side of Figure 7 is a selectively operable turbocharger, while the turbocharger 5 on the right side of Figure 7 is always active. The selectively operable turbocharger 5 and the always active turbocharger 5 may have the same capacity or different capacities. In particular, the selectively operable turbocharger 5 may have a smaller capacity than the always active turbocharger 5. The controller 50 is configured to activate and deactivate the selectively operable turbocharger 5 according to the actual operating conditions of the engine, in particular the actual engine load, with a view to achieving an optimal turbocharging efficiency of the engine 100.

An electronically controlled turbine control valve 35 is disposed in a conduit connecting the inlet of the operable/deactivatable turbine 8 of the selectively operable/deactivatable turbocharger 5 to the exhaust 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 through a signal to the turbine control valve 35. The controller 50 opens and closes the flow of exhaust gas from the exhaust receiver 3 to the inlet of the operable/deactivatable turbine 8 by the turbine control valve 35.

An electronically controlled compressor control valve 36 is arranged in a pipe that connects the outlet of the operable/stoppable compressor 7 of the selectively operable/stoppable turbocharger 5 to the scavenging air receiver 2 via the scavenging air cooler 14 and the water mist catcher 63. The compressor control valve 36 is connected to a controller 50, and the position of the compressor control valve 36 is controlled by the controller 50 via a signal to the compressor control valve 36. The controller 50 can open or close the flow of scavenging air from the outlet of the operable/stoppable compressor 7 to the scavenging air receiver 2 via the compressor control valve 36.

At least the selectively operable turbocharger 5 is provided with a rotational speed sensor that generates a signal representative of the rotational speed of the selectively operable turbocharger 5, and this signal is transmitted to the controller 50. The pressure sensor 33 is arranged to measure the pressure at the outlet of the selectively operable 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.

An electronically controlled air bleed valve 37 is arranged between the outlet of the operable compressor 7 and another environment having a pressure, for example atmospheric pressure or substantially equal to atmospheric pressure, such as the exhaust system downstream of the turbocharger 5, or the inlet side of the selectively operable compressor 7, and the air bleed valve 37 is fluidly connected to the outlet of the operable compressor 7 upstream of the compressor control valve 36. Preferably, the air bleed valve 37 is arranged in an air bleed pipe 39 that branches off from a conduit connecting the outlet of the operable compressor 7 to the compressor control valve 36. The air bleed valve 37 is a variable valve that forms a controllable variable restriction on the flow of gas through the air bleed valve 37. The controller 50 thus controls the restriction on the flow of air through the air bleed valve 37 by adjusting the position of the air bleed valve 37.

4 and 5 show the results of an attempt to activate and deactivate the turbocharger 5, which can be selectively activated and deactivated using only the turbine control valve 35 (TCV) and the compressor control valve 36 (CCV). FIG. 4 is a plot showing the scavenging pressure (bar) in the scavenging receiver 2 versus time, and FIG. 5 is a plot showing the opening and closing of the turbine control valve 35 and the compressor control valve 36 versus time, with 0 on the vertical axis corresponding to a fully closed valve and 1 on the vertical axis corresponding to a fully open valve. FIG. 5 also plots the stall margin. The stall margin is an index of how close the compressor is to stalling. In FIG. 5, it is clear that the stall margin becomes negative between about 4 and 13 seconds after the compressor control valve 36 and the turbine control valve 35 are opened, indicating that the compressor is stalling. We tried changing the opening profile and timing of the turbine control valve 35 and the compressor control valve 36, but we were unable to achieve results that allowed us to maintain the surge/stall margin at or above zero while the turbocharger 5, which can be selectively activated and deactivated, was activated and deactivated.

The efficiency of the compressor can be described by a constant efficiency line in a diagram (compressor diagram) where the pressure ratio on the compressor 7 is plotted against the air flow rate through the compressor 7. The constant efficiency line is an elliptical curve on the compressor diagram where the efficiency of the compressor 7 is 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 the atmospheric pressure, which can be assumed to be substantially constant, in order for the controller 50 to determine the pressure ratio on the compressor 7, it is necessary to determine only the pressure at the outlet of the compressor 7, either by measuring (e.g., using a pressure sensor) or estimating (e.g., using a monitoring device). The air flow through the compressor 7 is difficult to measure directly, but in some embodiments, it is determined (calculated) by the controller 50 as a function of the rotational speed of the compressor 7, i.e., the rotational speed of the turbocharger 5.

In some embodiments, for a given turbocharger speed range, the optimum pressure ratio of the turnable and deactivatable compressor 7 that provides the highest compression efficiency for a rotational speed of the selectively turnable and deactivatable turbocharger 5 is stored in the controller 50 as a work line that can be represented, for example, on a diagram in which the optimum pressure ratio is plotted against turbocharger speed.

In another embodiment, since the (atmospheric) pressure at the inlet of the turnable/disable compressor 7 is known and constant, for a given turbocharger speed range, the optimal pressure at the outlet of the turnable/disable compressor 7 that provides the highest compression efficiency for the rotational speed of the selectively turnable/disable turbocharger 5 is stored in the controller 50.

6 is a control diagram for controlling the positions of the turbine control valve 35 (TCV), the compressor control valve 36 (CCV) and the air bleed valve 37 (ARV). The measured or estimated rotation speed of the turbocharger 5 is provided to a target pressure estimator, which may be part of the controller 50 or a separate control unit. The target pressure estimator calculates the optimal pressure at the outlet of the turnable/disable compressor 7 for the actual turbocharger rotation speed, for example using the above-mentioned stored work lines. The target pressure is compared with the measured or determined actual pressure at the outlet of the turnable/disable compressor 7 and the difference between the two signals is determined. This difference is sent to a valve controller, which may be part of the controller 50 or a separate controller. The valve controller adjusts the position of the air bleed valve 37 depending on said difference. For the control of the air bleed valve 37, the valve controller can perform proportional (P) control, or proportional and integral (PI) control, or proportional, integral and differential (PID) control to increase the restriction on the flow provided by the air bleed valve 37 when the pressure at the outlet of the turnable compressor 7 is lower than the target pressure, and to decrease the restriction on the flow provided by the air bleed valve 37 when the pressure at the outlet of the turnable compressor 7 is higher than the target pressure. Thus, the turbocharger speed is used in a first feedback control loop and the compressor outlet pressure is used in a second feedback control loop. Thus, in this embodiment, the control diagram forms a double feedback loop control.

In some embodiments, the valve controller controls the opening and closing of the turbine control valve 35 and the compressor control valve 36 according to a predetermined profile and sequence. The profile or workline for starting the selectively turnable turbocharger 5 and the profile or workline for stopping the selectively turnable turbocharger 5 can be determined by testing or simulation, and these predefined profiles and sequences are stored in the controller 50.

8 shows an example of the results of valve operation over time for turning on and off the selectively deactivatable turbocharger 5 when the engine is operating at 50% engine load (50% of maximum continuous rating). The selectively deactivatable turbocharger 5 is activated, for example, when the engine load rises above an engine load threshold. In this example, the controller 50 is configured to start the selectively deactivatable turbocharger 5 by moving the turbine control valve 35 from fully closed to fully open. The controller 50 is configured to transition the compressor control valve 36 from a fully closed position to a fully open position after a period of time after the turbine control valve 35 is opened. This is not a fixed, predefined period of time. The compressor control valve 36 is opened when the pressure setpoint is no longer increasing. The time at which this occurs is determined by the acceleration of the turbocharger 5. The air bleed valve 37 starts from an open position and closes according to the control method described above, i.e. as a function of the rotational speed of the selectively activatable/deactivatable turbocharger 5 and the pressure at the outlet of the activatable/deactivatable compressor 7. This function is determined by the compressor characteristic, which can be described, for example, by means of a compressor diagram, as explained above. The compressor diagram, in combination with the speed and the outlet pressure of the activatable/deactivatable compressor 7, makes it possible to determine the operating point at which the compressor functions optimally (with high efficiency) or at least without the risk of stalling/surge.

In this embodiment, the compressor control valve 36 opens after the turbine control valve 35. However, this is not necessarily always the case and depends on the circumstances, in particular the acceleration of the turbocharger 5.

The selectively operable turbocharger 5 is deactivated, for example, when the engine load falls below an engine load threshold, which may be different from the engine load threshold for starting the selectively operable turbocharger 5. In this example, the controller 50 is configured to initiate the process of deactivating the selectively operable turbocharger 5 by moving the compressor control valve 36 from fully open to fully closed. The controller 50 is configured to transition the turbine control valve 35 from a fully open position to a fully closed position after a period of time after the turbine compressor control valve 36 is closed. The air bleed valve 37 starts from a closed position and opens according to the control method described above, i.e. as a function of the rotational speed of the selectively operable turbocharger 5 and the pressure at the outlet of the operable compressor 7.

Figure 9 shows the scavenging pressure in the scavenging receiver 2 as a result of the control, the work line setting of the air bleed valve 37, and the actual work line of the air bleed valve 37 versus time. Figure 10 shows the surge margin versus time, and it can be seen that the surge margin is positive both when the turbocharger 5, which can be selectively activated and deactivated, is activated and deactivated, significantly reducing the risk of surge. The surge margin is an indicator of how close the compressor 7 is to surge.

In this way, the controller can adjust the position of the air bleed valve so that the actual pressure at the outlet of the compressor 7, which can be turned on and off, is kept close to the target pressure.

Here the target pressure is based on the peak efficiency of the compressor 7, which can be turned on and off.

The behavior of the selectively operable turbocharger 5 can be predicted based on engine tests on a test bed and/or computer simulations. The appropriate opening curve of the air bleed valve 37 can therefore be based on stored data, without the need to measure or determine in real time the turbocharger speed and/or the outlet pressure of the selectively operable compressor 7. The controller 50 may be provided with one or more worklines for the opening of the pressure relief valve 37. Preferably, each of these curves (worklines) is suited to a specific engine load.

In some embodiments, the compressor control valve 36 is a variable valve that provides a controllable variable restriction to the flow of gas through the compressor control valve 36. In this embodiment, the controller 50 is configured to transition the compressor control valve 36 from closed toward open when starting the selectively operable turbocharger 5 as a function of both the measured or estimated pressure at the outlet of the selectively operable compressor 7 and the measured or estimated rotational speed of the selectively operable turbocharger 5 to assist the air bleed valve 37 in its task of controlling the pressure at the outlet of the selectively operable compressor 7.

11 is a schematic representation of an engine 100 according to another embodiment. The engine 100 comprises two permanent turbochargers 5 and one selectively operable turbocharger 5. In this embodiment, the same components and features as those already described or illustrated are given the same reference numerals as previously used. Except for the additional permanent turbocharger 5, the engine 100 according to this embodiment is essentially the same as the previously introduced engine. However, due to the additional permanent turbocharger, the engine loads at which the selectively operable turbocharger 5 is activated and deactivated are different from those of the previously introduced engine. The engine loads at which the selectively operable turbocharger 5 is activated and deactivated depend on the capacity and characteristics of the respective turbocharger 5.

The method and apparatus have been described with several embodiments. However, upon review of the specification, drawings and claims of this application, one skilled in the art will understand and be able to embody many variations in addition to the described examples in implementing the claimed invention. The words "comprise", "have" and "include" in the claims do not exclude the presence of elements or steps not recited. The absence of a claim expressly stating a plurality of elements does not exclude the presence of a plurality of the elements. The functions of several elements recited in the claims may be performed by a single controller or other unit. The fact that several items are recited in separate dependent claims does not exclude them from being implemented in combination, which may be advantageously implemented in combination.

The signs used in the claims should not be construed as limiting the scope of the invention. Unless otherwise noted, the drawings are intended to be read together with the specification and are an integral part of this disclosure. In the specification, the terms "horizontal," "vertical," "left," "right," "top," and "bottom" merely refer to the orientation of the illustrated structures in the direction of the reader's view.

Claims (13)

A large uniflow type turbocharged two-stroke internal combustion engine,
a plurality of cylinders, each having a scavenging port at a lower end and an exhaust valve at an upper end;
an intake system having a scavenging receiver connected to the cylinder through the scavenging port, through which scavenging air is introduced into the cylinder;
an exhaust system having an exhaust receiver connected to the cylinder through the exhaust valve, through which exhaust gas generated within the cylinder is exhausted;
a plurality of turbochargers each having an exhaust driven turbine coupled to a compressor to power the compressor, an inlet of the turbine connected to the exhaust system, and an outlet of the compressor connected to the intake system for delivering a pressurized scavenging flow to the scavenging receiver;
Equipped with
At least one of the plurality of turbochargers is a selectively operable/shutdown turbocharger, and the selectively operable/shutdown turbocharger is
a turnable and shutable turbine selectively connected to the exhaust receiver via an electronically controlled turbine control valve;
A compressor that can be turned on and off,
having
an outlet of the turnable/disable compressor is selectively connected to the intake system by an electronically controlled compressor control valve and to the outside air by an electronically controlled air bleed valve connected to the outlet of the turnable/disable compressor upstream of the compressor control valve;
the air bleed valve is a variable valve that forms a controllable variable restriction in the flow of gas through the air bleed valve;
The engine further includes a controller coupled to the turbine control valve, the compressor control valve, and the air bleed valve;
The controller further comprises, when starting the selectively operable turbocharger,
transitioning the turbine control valve from a closed state to an open state;
transitioning the compressor control valve from a closed state to an open state;
The air bleed valve,
the measured or estimated pressure at the outlet of the turn-on/turn-off compressor;
- the measured or estimated rotational speed of the selectively operable turbocharger;
A continuous transition from the open state to the closed state as a function of
It is configured as follows :
the controller is further informed of a target pressure at the outlet of the turnable compressor for a given rotational speed of the selectively operable turbocharger, the target pressure corresponding to a pressure at which the turnable compressor has a highest efficiency at the given rotational speed;
institution. When the controller shuts down the selectively operable turbocharger,
transitioning the compressor control valve from an open state to a closed state;
transitioning the turbine control valve from an open state to a closed state;
The air bleed valve,
the measured or estimated pressure at the outlet of the turn-on/turn-off compressor;
- the measured or estimated rotational speed of said selectively operable turbocharger;
to the open state continuously as a function of at least one of
The engine of claim 1 configured to: 2. The engine of claim 1, wherein the function causes the air bleed valve to move to a position where an actual pressure at the outlet of the turnable and deactivatable compressor corresponds to the target pressure for an actual rotational speed of the selectively turnable and deactivatable turbocharger. 2. The engine of claim 1, wherein the target pressure for a given rotational speed of the selectively operable turbocharger is separated by a surge margin from a pressure at which the operable compressor surges at the same given rotational speed of the selectively operable turbocharger. 2. The engine of claim 1, comprising at least one of a pressure sensor configured to provide a signal representative of a pressure at an outlet of the selectively operable compressor, and a speed sensor configured to provide a signal representative of a rotational speed of the selectively operable turbocharger . The engine of claim 5 , wherein the controller is configured to determine the target pressure based on a signal from the speed sensor. 7. The engine of claim 6 , wherein the controller is configured to determine a difference between the target pressure and a signal from the pressure sensor and to determine a setting for the air bleed valve as a function of the difference. 8. An engine as claimed in claim 7 , wherein the controller is configured to determine the setpoints of the turbine control valve and/or the compressor control valve as a function of the difference. The engine of claim 1, wherein the turbine control valve is arranged upstream of the turnable/disable turbine, and/or the compressor control valve is arranged downstream of the turnable/disable compressor, and/or the air bleed valve is arranged in an air bleed pipe downstream of the compressor of the selectively turnable/disable turbocharger and upstream of the compressor control valve. The engine of claim 1, wherein the controller is configured to activate and deactivate the selectively operable turbocharger as a function of operating conditions of the engine. the compressor control valve being a variable valve that provides a controllably variable restriction to the flow of gas through the compressor control valve;
The controller, when starting the selectively operable turbocharger,
the measured or estimated pressure at the outlet of the turn-on/turn-off compressor;
- the measured or estimated rotational speed of said selectively operable turbocharger;
2. The engine of claim 1, configured to move the compressor control valve from a closed state to an open state as a function of two of: 1. A method of operating a large turbocharged two-stroke internal combustion engine of the uniflow type, said engine comprising:
a plurality of cylinders, each having a scavenging port at a lower end and an exhaust valve at an upper end;
an intake system having a scavenging receiver connected to the cylinder through the scavenging port, through which scavenging air is introduced into the cylinder;
an exhaust system including an exhaust receiver connected to the cylinder through the exhaust valve, through which exhaust gas generated within the cylinder is exhausted;
a plurality of turbochargers each having an exhaust driven turbine coupled to a compressor to power the compressor, an inlet of the turbine connected to the exhaust system, and an outlet of the compressor connected to the intake system for delivering a pressurized scavenging flow to the scavenging receiver;
Equipped with
At least one of the plurality of turbochargers is a selectively operable/shutdown turbocharger, and the selectively operable/shutdown turbocharger is
a turnable and shuttable turbine selectively connected to the exhaust receiver by an electronically controlled turbine control valve;
A compressor that can be turned on and off,
having
an outlet of the turnable/disable compressor is selectively connected to the intake system by an electronically controlled compressor control valve and to the outside air by an electronically controlled air bleed valve connected to the outlet of the turnable/disable compressor upstream of the compressor control valve;
the air bleed valve is a variable valve that forms a controllable variable restriction in the flow of gas through the air bleed valve;
The method comprises:
Measuring or estimating at least one of a pressure at an outlet of the turnable and deactivatable compressor and a rotational speed of the selectively turnable and deactivatable turbocharger;
Starting the at least one selectively operable turbocharger,
transitioning the turbine control valve from a closed state to an open state;
transitioning the compressor control valve from a closed state to an open state;
the air bleed valve is switched on during start-up of the at least one selectively operable turbocharger,
the measured or estimated pressure at the outlet of the turn-on/turn-off compressor;
- the measured or estimated rotational speed of said selectively operable turbocharger;
a continuous transition from an open state to a closed state as a function of at least one of
and
comparing the measured or estimated pressure at the outlet of the turnable/disableable compressor with a target pressure at the outlet of the turnable/disabled compressor and controlling the air bleed valve based on the result of the comparison;
wherein the target pressure corresponds to a pressure at which the turnable compressor has highest efficiency at a given rotational speed of the selectively turnable turbocharger . shutting down the at least one selectively operable turbocharger,
transitioning the compressor control valve from an open state to a closed state;
transitioning the turbine control valve from an open state to a closed state;
The air bleed valve,
the measured and/or estimated pressure at the outlet of the turn-on/turn-off compressor,
the measured and/or estimated rotational speed of the selectively operable turbocharger;
a continuous transition from a closed state to an open state as a function of at least one of
13. The method of claim 12 , comprising stopping by:

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