JP2022166819A - Large turbocharged two-stroke internal combustion engine with egr system - Google Patents

Abstract

To accurately control the oxygen concentration in a scavenge gas receiver in order to meet the emission requirements for both NOx and soot in a large turbocharged two-stroke internal combustion engine.SOLUTION: A large turbocharged multi-cylinder two-stroke uniflow internal combustion engine comprises an EGR system for conveying a flow of exhaust gas from an exhaust system to an intake system. The EGR system comprises an EGR blower 29 and an electronically controlled EGR throttling valve (32, 42). An AC drive motor 33 is used for driving the EGR blower 29. The AC drive motor is configured to operate at a predetermined constant speed. A sensor 27 provides a signal representative of the oxygen concentration in a scavenge gas receiver 2, and the signal is received by a controller 50 coupled to the electronically controlled EGR throttling valve. The controller is configured to control the flow of exhaust gas through the EGR system by adjusting the position of the electronically controlled EGR throttling valve as a function of the signal as a primary measure.SELECTED DRAWING: Figure 4

Description

TECHNICAL FIELD The disclosure herein relates to large turbocharged two-stroke internal combustion engines and methods having an exhaust gas recirculation (EGR) system, and more particularly to controlling the operation of the EGR system.

background

Large turbocharged two-stroke internal combustion engines are often used as propulsion systems for large ships and as prime movers in power plants. Its size, weight and power set this type of compression internal combustion engine far apart from other combustion engines and place it in a unique category. These engines are constructed with crossheads to avoid lateral pressure on the pistons, as increased height is of minor concern. Typically, these engines are dual engines and are configured to operate on fuel oil and gas (either natural gas, petroleum gas, methanol or ethane).

Emissions from marine diesel engines are subject to regulation due to awareness of the environmental impact of the emissions. In 2016, Tier III regulations were introduced to limit NOx emissions from marine diesel engines in certain areas. This was previously offered by the International Maritime Organization. Achieving these emission regulations requires the use of techniques to reduce NOx emissions. One such technology is exhaust gas recirculation (EGR). This technology has been used in four-stroke engines in the automotive industry for decades.

The principle of EGR is to recirculate some of the exhaust gas back into the engine's scavenge manifold. This reduces the oxygen level in the scavenging air and thus the formation of NOx gases during combustion. Unfortunately, however, the reduction in oxygen gas during scavenging affects combustion efficiency. Too low oxygen levels in the scavenging air produce undesirable visible smoke.

In a four-stroke automotive engine, there is a positive pressure differential between the exhaust and intake sides. That is, the positive pressure differential recirculates the exhaust into the intake side flow and does not require a blower or the like for recirculation. However, for large turbocharged two-stroke internal combustion engines, there is a negative pressure differential between the exhaust and intake sides. Therefore, simply providing a pipe between the exhaust side and the intake side (as in a 4-stroke automobile engine) causes the supply air to flow to the exhaust side. Therefore, the EGR system of a turbocharged two-stroke internal combustion engine requires a blower or pump to draw some of the exhaust into the charge air. That is, in large turbocharged two-stroke internal combustion engines, the exhaust is recirculated by a blower to overcome the pressure difference between the exhaust system and the intake system.

Thus, in large turbocharged two-stroke internal combustion engines, a blower or pump is required to recirculate the exhaust from the exhaust system to the intake system. In these gigantic engines, very large blowers are required to accomplish this task. And such large blowers require large drive motors to accomplish the task of directing the exhaust from the exhaust system to the intake system.

In order to meet both NOx and soot emission regulations, it is necessary to precisely control the oxygen concentration in the scavenging receiver. This is because if the oxygen concentration is too low, soot formation will be unacceptable, and if the oxygen concentration is too high, NOx emissions will be unacceptable.

Known large turbocharged two-stroke internal combustion engines with EGR have used a controllable, variable speed EGR blower to control the EGR flow to reach the oxygen concentration set point.

Summary

SUMMARY OF THE INVENTION It is an object of the present invention to provide a large turbocharged two-stroke uniflow internal combustion engine which solves or at least alleviates the above mentioned problems.

The above objects and other objects are achieved by the features of the independent claims. More specific implementations will become apparent from the dependent claims, the detailed description of the invention and the drawings.

According to a first conception, a large turbocharged two-stroke uniflow internal combustion engine is provided as follows. This institution
a plurality of cylinders each having a scavenging port at its lower end and an exhaust valve at its 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 generated in the cylinder is discharged;
at least one turbocharger having a turbine in the exhaust system that drives a compressor in the intake system;
a fuel system delivering a flow of fuel to the cylinder;
an EGR system for directing flow of exhaust gas from the exhaust system to the intake system, the EGR system having an EGR blower and an electronically controlled EGR throttle valve;
An AC drive motor associated with the EGR blower to drive the EGR blower, the AC drive motor being directly connected to the AC grid by an electrical switch and configured to operate at a constant speed determined by the AC frequency. When;
a sensor that provides a signal representative of the oxygen concentration within the scavenged air receiver;
a controller adapted to receive said signal and associated with said electronically controlled EGR blower;
wherein the controller operates the EGR system by controlling the position of the electronically controlled EGR throttle valve as a function of the signal as a first criterion for controlling the flow of the exhaust gas through the EGR system. configured to control the flow of said exhaust therethrough;

A controller directly driven by an AC drive motor directly connected to the grid and configured to control the EGR flow without changing the speed of the EGR blower by controlling the position of the electronically controlled EGR valve as a primary criterion. By providing a large turbocharged two-stroke internal combustion engine with an EGR blower having a . By "expensive equipment" is meant variable speed equipment, such as, for example, a variable speed power transmission between an AC drive motor and an EGR blower, or a variable frequency electric drive that powers an AC drive motor. mechanical or electrical drive. The resulting engine is less complex, more reliable, and less expensive.

A load-dependent scavenging air oxygen concentration desired value is predetermined. The actual oxygen concentration is measured or estimated, and by feedback control and/or feedforward control of this measurement, the target value is reached by adjusting the electronically controlled EGR throttle valve.

In one example implementation of the first aspect, the controller causes an electronically controlled EGR valve to move in a closed direction to reduce the flow of exhaust through the EGR system; is configured to move the electronically controlled EGR valve in the opening direction to increase the flow of

In one example implementation of the first aspect, the controller uses an electronically controlled cylinder bypass throttle valve located in a bypass pipe or a Adjusting the opening of the orifice is configured to adjust the flow of exhaust through the EGR system. Here, the bypass pipe is connected to the intake system downstream of the compressor and connected to the exhaust system upstream of the turbine.

In one example implementation of the first aspect, the controller moves the electronically controlled cylinder bypass throttle valve or orifice in a closing direction to increase the flow of exhaust through the EGR system; configured to move an electronically controlled cylinder bypass throttle valve or orifice in a releasing direction to reduce exhaust flow through the EGR system;

In one example implementation of the first aspect, the controller is configured to control the flow of exhaust through the EGR system to maintain an oxygen concentration in the scavenge receiver near a target oxygen concentration. configured to

In one example of implementation of the first aspect, the controller feeds back the signal from the first sensor to maintain the oxygen concentration in the scavenge receiver close to the oxygen concentration target value. /or configured for use in feedforward control. Here, the oxygen concentration desired value is preferably adjusted as a function of the engine load.

In one example of implementation of the first aspect, the AC drive motor is an asynchronous electric motor.

In one example of implementation of the first aspect, the AC drive motor is a synchronous electric motor.

In one implementation of the first concept, the AC drive motor is directly coupled to the drive shaft of the EGR blower.

In one example of implementation of the first concept, the electronically controlled EGR throttle valve is arranged downstream of the EGR blower.

In one implementation example of the first conception, the electronically controlled EGR throttle valve is arranged upstream of the EGR blower.

In one example of implementation of the first aspect, the engine comprises an electronically controlled EGR throttle valve downstream of the EGR blower and an electronically controlled EGR throttle valve upstream of the EGR blower.

In one example of implementation of the first aspect, the AC drive motor is connected to the AC grid without a device for varying frequency and/or voltage.

In one example implementation of the first concept, the EGR blower layout is required to achieve the relevant oxygen target in the scavenge receiver at a given exhaust bypass valve position and cylinder bypass valve position, and Follow the operating point with the lowest compression ratio and volumetric flow covered by the fixed speed of the exhaust recirculation blower. The controller is configured to control the EGR flow as a function of oxygen target value at all other operating points by opening a controlled exhaust bypass valve.

In one example of implementation of the first concept, the layout of the EGR blowers is within the normal operating range of the auxiliary blowers, with one or more auxiliary blowers turned off, and within the scavenge air receiver. The operating point with the lowest compression ratio and volume flow covered by the fixed speed of the exhaust recirculation blower required to achieve the associated oxygen target at .

The controller controls EGR for the above operating points and other operating points by turning off one or more auxiliary blowers and/or throttling the flow of one or more auxiliary blowers. Configured to control flow as a function of oxygen target.

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

The invention will now be explained in more detail with reference to exemplary embodiments shown in the drawings.
1 is a front view of a large two-stroke internal combustion engine in accordance with certain exemplary embodiments; FIG. FIG. 2 is a side view of the large two-stroke internal combustion engine of FIG. 1; 2 is a schematic representation of the large two-stroke internal combustion engine of FIG. 1; 1 is a schematic representation of an embodiment of a two-stroke internal combustion engine with an EGR system; 1 is a schematic representation of another two-stroke internal combustion engine embodiment with an EGR system; 1 is a schematic representation of yet another two-stroke internal combustion engine embodiment with an EGR system;

Detailed explanation

1-3 depict a turbocharged large low speed two-stroke diesel engine. This engine has a crankshaft 8 and a crosshead 9 . FIG. 3 is a schematic representation of a turbocharged large low-speed two-stroke diesel engine with its intake and exhaust systems. In the example, the engine has six cylinders 1 in series. Turbocharged large slow speed two-stroke diesel engines typically have 4 to 14 cylinders arranged in series. These cylinders are carried on a cylinder frame 23 . The cylinder frame 23 is carried by the engine frame 11 . Such an engine can also be used, for example, as a main engine in ships or as a stationary engine for powering generators in power plants. The total engine power can be, for example, 1000 kW to 110000 kW.

The engine in this embodiment is a two-stroke uniflow compression ignition type engine, each cylinder liner 1 being provided with a scavenging port 18 in its lower region and an exhaust valve centrally located at its top. However, the engine does not necessarily have to be compression ignited, and in some embodiments may be spark ignited. In the embodiment presented here, the compression pressure of the engine is high enough to achieve compression ignition. However, the engine may operate at a lower compression pressure and be ignited by a spark or similar means.

The intake system of the engine has a scavenging air receiver 2 . The scavenging air is led through the scavenging air receiver 2 to the scavenging air port 18 of each cylinder 1 . Piston 10 reciprocates between bottom dead center (BDC) and top dead center (TDC) in cylinder liner 1 to compress scavenging air. Fuel is injected from a fuel valve 55 arranged on the cylinder cover 22 . Following the injection of fuel, combustion occurs and exhaust is produced.

The exhaust valve 4 is arranged in the central portion of the cylinder cover 22 . A plurality of fuel valves 55 are arranged around the central exhaust valve. There are preferably two or three fuel valves 55 for each cylinder or type of fuel used. Exhaust valve 4 is actuated by an electrohydraulic exhaust valve actuation system (not shown) controlled by controller 50 . In some embodiments, controller 50 may be an electronic control unit, such as an electronic computer comprising one or more microprocessors, memory, and other hardware necessary for the operation of the control unit. good too. Controller 50 is connected to various sensors and to various devices that affect the operation of the engine. Connections between these sensors and devices and the controller 50 can be in the form of signal lines or wireless connections. To simplify the drawing, these connections are not shown. Controller 50 may be formed by a combination of various control units. Or it may be a single signal control unit.

Fuel valve 55 is part of the fuel supply system. If the engine is a dual or multi-fuel engine, there will be multiple fuel supply systems. In some embodiments, controller 50 is also configured to control operation of fuel valve 55 .

When the exhaust valve 4 is open, the exhaust flows through the exhaust system with exhaust ducts provided in the cylinder 1 to the exhaust receiver 3 and further through the first exhaust pipe 19 to the turbine 8 of the turbocharging system 5. and proceed. From there, the exhaust flows through a second exhaust pipe 25 to the economizer 20 and out the outlet 21 to the atmosphere. Note that in some embodiments, the turbocharging system 5 includes multiple turbochargers.

Turbine 8 of turbocharging system 5 drives compressor 7 via a shaft. Outside air is supplied to the compressor 9 through an air intake 12 . The compressor 7 sends the compressed scavenging air to the scavenging pipe 13 connected to the scavenging receiver 2 . The scavenging air in the scavenging pipe 13 passes through an intercooler 14 for cooling the scavenging air.

The cooled scavenging air passes through an auxiliary blower 16 driven by an electric motor 17 . The auxiliary blower 16 compresses the scavenging air flow when the compressor 7 of the turbocharger 5 cannot provide sufficient pressure for the scavenging receiver 2, ie when the engine is under low or part load. When the engine load is high, the turbocharger compressor 7 can supply sufficiently compressed scavenging air so that the auxiliary blower 16 is turned off and bypassed by the non-return valve 15 .

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

The exhaust produced in the cylinder is exhausted through an exhaust system. The exhaust system comprises an exhaust receiver 3 connected to the cylinder 1 via an exhaust valve 4 .

Referring to the embodiment of Figure 4, the engine is equipped with an exhaust gas recirculation system. The exhaust gas recirculation system comprises an exhaust gas recirculation line 60 connected from the exhaust system to the intake system from a position upstream of the turbine 8 of the turbocharger 5 to a position downstream of the compressor 7 of the turbocharger 5 . Prepare. Thus, exhaust that needs to be recirculated can flow from the exhaust system to the intake system. In this embodiment, structures and features that are similar to structures and features already described or illustrated are labeled with the same reference numerals as before.

The exhaust gas recirculation system comprises a waste recirculation unit 61 configured to process the recycled exhaust gas. To prevent damage to the engine 100, the exhaust used for recirculation typically needs to be cleaned before being allowed into the intake system. For this reason, the exhaust gas recirculation unit 61 typically comprises a wet scrubber using water. In FIG. 4, water inflow and outflow are depicted by horizontal arrows. A water mist catcher 63 removes the water used in the wet scrubber. Thus, relatively clean water is supplied to the exhaust gas recirculation unit 61 and relatively dirty water is discharged from the exhaust gas recirculation unit 61 .

An exhaust recirculation blower 29 is provided to force recirculation gas to flow from the exhaust system to the intake system. The reason why the exhaust gas recirculation blower 29 is necessary is that the exhaust system of a large two-stroke internal combustion engine is normally lower than the charge pressure of the intake system.

The exhaust recirculation blower 29 is driven by an AC drive motor 33 . In some embodiments, AC drive motor 33 is directly connected to EGR blower 29 to drive EGR blower 29 . The AC drive motor 33 is directly connected to the AC grid by an electrical switch 35 . Here the AC grid can be, for example, the AC electrical grid of an ocean-going vessel in which the large two-stroke internal combustion engine 100 is installed, or the AC electrical grid of a building or other facility in which the large two-stroke internal combustion engine 100 is installed. .

The AC drive motor 33 is configured to operate at a constant speed defined by the AC frequency when supplied with AC power from the electrical grid. Since the EGR blower 29 is mechanically directly connected to the AC drive motor 33, the EGR blower 29 is also configured to operate at a predetermined constant speed.

In some embodiments, the drive shaft of AC drive motor 33 is directly coupled to the drive shaft of EGR blower 29 . The AC drive motor 33 is configured to operate at a predetermined constant speed when supplied with constant frequency AC power.

The rotational speed of AC drive motor 33 is determined by the frequency of the AC power supplied to AC drive motor 33 . In some embodiments, the AC power on the grid has a constant frequency, so the rotational speed of the AC drive motor 33 is constant.

In some embodiments, AC drive motor 33 is an asynchronous motor. That is, at steady state, the rotation of the output shaft is just under an integer number of AC cycles of the supplied current.

In some embodiments, AC drive motor 33 is a synchronous motor. That is, in steady state, the rotation of the output shaft is synchronous with the frequency of the supplied current. The rotation period is exactly equal to an integer number of AC cycles.

Therefore, there is no variable mechanical drive or electrical variable drive. For example, there is no variable speed mechanical transmission between the AC drive motor 33 and the EGR blower 29 or a Variable Frequency electric drive (VFD) in the power supply system for the AC drive motor 33 . No device is required to vary the frequency and/or voltage of the current supplied to the AC drive motor 33 from the grid.

In some embodiments, the AC power for the AC drive motor 33 is generated by a generator driven by an engine 100 having a generator that powers the grid. In some embodiments, this AC power is generated by an auxiliary engine that powers the grid (not shown). For example generated by a set of generators. In some embodiments, this AC power is supplied by another source connected to the grid.

In the embodiment of FIG. 4, EGR blower 29 is depicted downstream of EGR unit 61 . However, in some embodiments, EGR blower 29 may be arranged upstream of EGR unit 61 .

An electronically controlled EGR throttle valve 32 is arranged in the EGR path 60 downstream of the EGR blower 29 . Adjustable EGR throttle valve 32 is preferably motorized to open the valve. The EGR throttle valve 32 is also connected to the controller 50 whereby the controller 50 controls the position of the EGR throttle valve 32 through command signals, thereby adjusting the EGR throttle valve 32 opening to be applied to the recirculated exhaust gas flowing through the EGR path 60 . can be commanded to control Accordingly, the controller 50 can increase or decrease the throttle effect of the EGR throttle valve 32 through command signals.

The controller 50 is connected to various sensors to be informed about the operating conditions of the engine 100 (e.g., engine load, engine speed, ambient temperature, scavenging pressure, etc.). It is adapted to receive a signal from a sensor that provides the signal.

The controller 50 controls the flow of exhaust through the EGR system by controlling the position of the electronically controlled EGR throttle valve 32 as a function of said signal as a primary basis for controlling the flow of exhaust through the EGR system. configured to

The controller 50 is preferably configured to control the flow of exhaust through the EGR system in order to maintain the oxygen concentration in the scavenge receiver 2 near a predetermined oxygen concentration target value. In some embodiments, the oxygen concentration target is a function of engine load. or as a function of other operating conditions such as temperature and humidity, scavenging pressure in the scavenging receiver, cylinder pressure, mean effective pressure, emissions regulations applicable to the geographic location in which the engine is operated. be.

Controller 50 uses the signal from sensor 27 for feedback control, and in some embodiments in combination with feedforward control, to maintain the oxygen concentration in scavenge receiver 2 close to a predetermined oxygen concentration target value. configured to

The controller 50 moves the electronically controlled EGR valve 32 in a closed direction (to increase the throttling effect) to reduce the flow of exhaust through the EGR system, and to increase the flow of exhaust through the EGR system. is configured to move the electronically controlled EGR valve 32 in the opening direction (to reduce the throttling effect).

In some embodiments, engine 100 includes cylinder bypass 47 . A cylinder bypass 47 connects downstream of the compressor 7 in the intake system and upstream of the turbine 8 in the exhaust system. Cylinder bypass tube 47 includes electronically controlled cylinder bypass throttle valve 42 and/or electronically controlled orifice 49 . Controller 50 controls the flow of exhaust through the EGR system by controlling the opening of electronically controlled cylinder bypass throttle valve 42 or orifice 49 as the primary basis for controlling the flow of exhaust through the EGR system. configured to

The controller 50 moves the electronically controlled cylinder bypass throttle valve 42 or orifice 49 in the closing direction to increase the flow of exhaust through the EGR system, and the electronic control to decrease the flow of exhaust through the EGR system. It is arranged to move the control cylinder bypass throttle valve 42 or orifice 49 in the opening direction.

In one example implementation of this embodiment, the engine is equipped with an exhaust bypass having an electronically controlled exhaust bypass throttle valve 41 controlled by a controller 50 .

Engine 100 and controller 50 are configured to control EGR flow according to the following scenario.

EGR blower layout is necessary to achieve the relevant oxygen (O ₂ ) target in scavenge receiver 2 with electronically controlled EGR throttle valve 32 open and at a given operating speed of EGR blower 29 Follow the operating point with the highest pressure ratio and volumetric flow covered by the EGR blower 29 . At other engine operating points, EGR flow is controlled by controller 50 as a function of oxygen ( _O2 ) target. This control is accomplished by closing the electronically controlled EGR throttle valve 32 and operating the EGR blower 29 at the proper pressure ratio to achieve the proper flow in the EGR path 60 .

In this scenario, controller 50 is configured to operate according to the following optimization strategy. Depending on engine performance, the electronically controlled cylinder bypass throttle valve 42 or orifice 49 is opened to the allowable extent. This is to lower the operating point at the highest pressure ratio and volumetric flow rate, reducing EGR fluctuations and thus throttle losses.

EGR blower layout is necessary to achieve the relevant oxygen (O ₂ ) target in scavenge receiver 2 with electronically controlled EGR throttle valve 32 open and at a given operating speed of EGR blower 29 The operating point covered by the EGR blower 29 with the electronically controlled cylinder bypass throttle valve 42 or orifice 49 closed follows the lowest pressure ratio and volumetric flow rate. At other engine operating points, EGR flow is controlled by controller 50 as a function of oxygen ( _O2 ) target. This control is accomplished by opening the electronically controlled EGR throttle valve 42 or orifice 49 and operating the EGR blower 29 at the proper pressure ratio to achieve the proper flow in the EGR path 60 . In this scenario, controller 50 is configured to operate according to the following optimization strategy.

Depending on engine performance, electronically controlled cylinder bypass throttle valve 42 or orifice 49 is opened to an acceptable degree. Then, when the allowable degree is exceeded, the EGR throttle valve 32 is used.

FIG. 5 shows an engine embodiment similar to the embodiment of FIG. In this embodiment, structures and features that are similar to structures and features already described or illustrated are labeled with the same reference numerals as before. However, in this embodiment, the valve that throttles the EGR flow within the EGR flow path 60 is located upstream of the EGR blower 29 . Further, the sensor 27 is arranged upstream of the scavenging receiver 2 but downstream of a position in the intake system where the recirculated exhaust gas mixes with the air arriving from the turbine 7 .

In this embodiment, engine 100 and controller 50 are configured to control EGR flow according to the following scenario.

The EGR blower layout is necessary to achieve the associated oxygen (O ₂ ) target in scavenge receiver 2 with electronically controlled EGR throttle valve 43 open and EGR blower 29 at a given operating speed. Follow the operating point with the highest pressure ratio and volumetric flow covered by the blower 29 . At other engine operating points, EGR flow is controlled by controller 50 as a function of oxygen ( _O2 ) target. This control is performed by closing the electronically controlled EGR throttle valve 43 and operating the EGR blower 29 at the proper pressure ratio to achieve the proper flow in the EGR path 60 .

In this scenario, controller 50 is configured to operate according to the following optimization strategy. Depending on engine performance, the electronically controlled cylinder bypass throttle valve 42 or orifice 49 is opened to the allowable extent. This is to lower the operating point at the highest pressure ratio and volumetric flow rate, reducing EGR fluctuations and thus throttle losses.

In this embodiment, the EGR blower layout is required to achieve the relevant _O2 target in the scavenge receiver at a given exhaust bypass valve 41 position and cylinder bypass valve 42 position, and the exhaust recirculation blower Follows the operating point with the lowest compression ratio and volume flow covered by 29 fixed speeds. At all other operating points, the controller 50 keeps the EGR flow at the _O2 target by opening the controlled exhaust bypass valve 41 and operating the EGR blower 29 at the correct pressure ratio to achieve the correct EGR flow. is configured to control as a function of A check valve (not shown) is provided in the EGR flow path 60 for closing the EGR flow path 60 in an emergency. Controller 50 is configured to control cylinder bypass valve 42 as a function of engine performance. It is also configured to use other criteria to reduce EGR variations applicable within the IMO Nox cycle tolerance limits.

In this embodiment, the EGR blower layout is necessary to achieve the relevant _O2 target in the scavenge receiver, with one or more auxiliary blowers worn, and the exhaust recirculation blower 29 Follow the operating point with the lowest compression ratio and volumetric flow covered by the fixed speed. At other operating points, the controller 50 mists the one or more auxiliary blowers, throttles flow through the one or more auxiliary blowers, and controls the EGR blower 29 to achieve adequate flow within the EGR flow path 60. EGR flow is configured to be controlled as a function of the _O2 target value by operating the EGR blower 29 at a value close to the appropriate compression ratio for . The controller 50 may be configured to use additional criteria for proper operation of the EGR blower 29 at the appropriate compression ratio, especially in load ranges where none of the auxiliary blowers 16 are required to maintain scavenging pressure. .

In this embodiment (not shown), the engine 100 includes an electronically controlled EGR throttle valve 32 downstream of the EGR blower 29 and also includes an electronically controlled EGR throttle valve 43 upstream of the EGR blower 29 .

FIG. 6 shows another embodiment of an engine similar to that of FIG. In this embodiment, structures and features that are similar to structures and features already described or illustrated are labeled with the same reference numerals as before. However, in this embodiment, the recirculated exhaust is taken from the low pressure side of the turbine 8 of the turbocharging system 5 and added to the intake system at the low pressure side of the compressor 7 of the turbocharging system 5 . This embodiment therefore operates with exhaust gas recirculation on the low pressure side of the turbocharging system 5 . 4 and 5, on the other hand, operate with exhaust gas recirculation on the high pressure side of the turbocharging system 5 .

A method and apparatus have been described with several embodiments. However, many variations in addition to the described embodiments exist in the practice of the claimed invention by one skilled in the art upon review of the specification, drawings, and claims of this application. understand and be able to implement it. The verbs "comprising," "having," and "including" in the claims do not exclude the presence of elements or steps not recited. The absence of an explicit plural number of an element in a claim does not exclude the presence of a plurality of such elements. The functions of several elements recited in the claims may be performed by a single controller, processor or other unit. The mere fact that certain items are recited in separate dependent claims does not preclude their joint practice, which may be practiced to advantage. Any reference signs used in the claims shall not be construed as limiting the scope of the invention.

Claims (14)

A large turbocharged two-stroke uniflow internal combustion engine,
a plurality of cylinders each having a scavenging port at its lower end and an exhaust valve at its 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 generated in the cylinder is discharged;
at least one turbocharger having a turbine in the exhaust system that drives a compressor in the intake system;
a fuel system delivering a flow of fuel to the cylinder;
an EGR system for directing flow of exhaust gas from the exhaust system to the intake system, the EGR system having an EGR blower and an electronically controlled EGR throttle valve;
An AC drive motor associated with the EGR blower to drive the EGR blower, the AC directly connected to the AC grid by an electrical switch and configured to operate at a predetermined constant speed determined by the AC frequency. a drive motor;
a sensor that provides a signal representative of the oxygen concentration within the scavenged air receiver;
a controller adapted to receive said signal and associated with said electronically controlled EGR blower;
wherein the controller operates the EGR system by controlling the position of the electronically controlled EGR throttle valve as a function of the signal as a primary criterion for controlling the flow of the exhaust through the EGR system. An engine configured to control the flow of said exhaust therethrough. The controller moves an electronically controlled EGR valve in a closing direction to decrease the flow of exhaust through the EGR system and opens the electronically controlled EGR valve to increase the flow of exhaust through the EGR system. 2. The engine of claim 1, configured to move in a direction. The controller adjusts the opening of an electronically controlled cylinder bypass throttle valve or orifice in a bypass pipe as a first or second criterion for adjusting the flow of exhaust gas through the EGR system. wherein said bypass pipe is connected to said intake system downstream of said compressor and connected to said exhaust system upstream of said turbine; or the agency described in 2. The controller moves the electronically controlled cylinder bypass throttle valve or orifice in a closing direction to increase exhaust flow through the EGR system and to decrease exhaust flow through the EGR system. 4. The engine of claim 3, configured to move an electronically controlled cylinder bypass throttle valve or orifice in a releasing direction. The controller is configured to control the flow of exhaust gas through the EGR system to maintain an oxygen concentration in the scavenge receiver near a target oxygen concentration value, wherein the target oxygen concentration value is preferably is adjusted depending on the engine load. the controller is configured to use the signal from the first sensor for feedback and/or feedforward control to maintain oxygen concentration in the scavenge receiver near a target oxygen concentration; 6. An engine as claimed in any one of the preceding claims, wherein the oxygen concentration setpoint value is preferably adjusted as a function of the engine load. 7. An engine as claimed in any preceding claim, wherein the AC drive motor is a synchronous electric drive motor or an asynchronous electric drive motor. 8. The engine of claim 7, wherein the AC drive motor drive shaft is directly coupled to the EGR blower drive shaft. 9. An engine as claimed in any preceding claim, wherein the electronically controlled EGR throttle valve is arranged downstream of the EGR blower. 9. An engine as claimed in any preceding claim, wherein the electronically controlled EGR throttle valve is arranged upstream of the EGR blower. An engine according to any preceding claim, comprising an electronically controlled EGR throttle valve downstream of said EGR blower and an electronically controlled EGR throttle valve also upstream of said EGR blower. An engine as claimed in any preceding claim, wherein the AC drive motor is connected to the AC grid without a device for varying frequency and/or voltage. The EGR blower layout required to achieve the relevant oxygen target in the scavenge receiver at a given exhaust bypass valve position and cylinder bypass valve position is covered by the fixed speed of the exhaust recirculation blower. , according to the operating point with the lowest compression ratio and volume flow, the controller controls the EGR flow as a function of the oxygen target value at all other operating points by opening a controlled exhaust bypass valve. 13. An engine as claimed in any one of claims 1 to 12, configured for: The EGR blower layout is within the range of normal operation of the auxiliary blowers, and with one or more auxiliary blowers turned off, the EGR blower layout required to achieve the relevant oxygen target in the scavenge receiver. , according to the operating point with the lowest compression ratio and volume flow covered by the fixed speed of the exhaust recirculation blower, the controller may turn off one or more auxiliary blowers; 13. Any of claims 1 to 12, configured to control EGR flow as a function of oxygen target value for the above operating points and other operating points by throttling the flow of one or more auxiliary blowers. agency described in

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