Method of supplying fuel to a two-stroke piston internal combustion engine and fuel injection control system for large two-stroke piston engines

Abstract

The present invention relates to a method for supplying fuel to a two-stroke piston internal combustion engine (6), the fuel comprising at least a low-reactive fuel (LRF) as a primary fuel and a high-reactive fuel (HRF) as an ignition-enhancing fuel, the engine (6) comprising at least two cylinders (101), wherein, in the method: 1.1. setting a target engine speed; 1.2. setting a target engine torque to satisfy both the target engine power and the target engine speed; 1.3. monitoring engine performance data; 1.4. determining the HRF of the current combustion event using the engine performance data and the target engine torque. 1.5. Monitor the pressure in each cylinder (101) of the engine (6); 1.6. Obtain the actual peak pressure of the currently ignited cylinder; 1.7. Set a target peak pressure that is common to all cylinders (101) of the engine (6); 1.8. Use the target peak pressure and the actual peak pressure to determine a cylinder-specific LRF correction factor; 1.9. Adjust the LRF amount with the cylinder-specific LRF correction factor to provide a cylinder-specific LRF amount; and 1.10. Use the cylinder-specific LRF amount and the determined HRF amount when controlling the fuel supply in the current combustion event. The invention also relates to a fuel injection control system for a large two-stroke piston engine (6).

Description

Technical Field

[0001] This invention relates to a method for supplying fuel to a two-stroke piston internal combustion engine.

[0002] This invention relates to a fuel injection control system for a large two-stroke internal combustion engine, comprising components for operating the engine. Background Technology

[0003] Large two-stroke internal combustion engines are commonly used as prime movers in large ocean-going vessels. Two-stroke engines can burn various types of fuels, thus reducing the ship's operating costs. Two-stroke engines have relatively high thermal and engine efficiency. They are also reliable in operation. Because two-stroke engines are low-speed engines, they do not require the deceleration or reduction gears needed for propulsion, as is required for higher-rpm four-stroke engines. Traditionally, large two-stroke engines have primarily operated on heavy fuel oils. However, there is a growing interest in reducing emissions of carbon dioxide, nitrogen oxides, and sulfur from combustion engine operation, necessitating alternatives to conventional fuel oils and improved combustion control.

[0004] Patent publication EP3121428B1 discloses a two-stroke crosshead diesel engine with a dual-fuel supply and an engine control system for operating the engine. In gas mode, gaseous gas is mixed with scavenging air to produce a combustible mixture in the combustion chamber of the cylinder. Ignition of the mixture in the cylinder is performed by injecting a small amount of liquid fuel into the combustion chamber of the cylinder. The document discloses that boost air is typically provided by a turbocharger that generates boost pressure, which depends on the engine load and therefore on the engine's power, torque, or speed. For a given scavenging air pressure, the mass of air in the cylinder can be calculated, and then the appropriate amount of gaseous fuel can be determined for the corresponding required drive torque produced by the engine, or for the desired speed. In transitional situations, such as when a ship enters rough seas, a sudden increase in load occurs when the engine load undergoes very sudden, frequent, and heavy load changes. In such cases, the turbocharger system cannot keep up with this rapid change, and the scavenging air cannot be provided at the required pressure, resulting in an overly rich air-gas mixture. The solution based on the aforementioned prior art is to limit the amount of gas supplied to the engine during transient conditions to avoid knocking. To maintain the engine speed or the torque generated by the engine at the desired value, an additional amount of liquid fuel is introduced into the engine in addition to gas during transient conditions. This only applies to special conditions, and because it sets a fixed maximum gas share for the engine, it may not always provide optimal combustion or balance among the individual cylinders.

[0005] One object of the present invention is to provide a method for supplying fuel to the cylinders of a two-stroke piston internal combustion engine, by which engine performance is significantly improved compared with prior art solutions. Summary of the Invention

[0006] The objectives of the invention can be substantially satisfied as disclosed in the independent claims and in other claims that describe various embodiments of the invention in more detail.

[0007] According to a method of supplying fuel to a two-stroke piston internal combustion engine, the fuel comprises at least a low-reactive fuel (LRF) as a primary fuel and a high-reactive fuel (HRF) as an ignition-enhancing fuel, the engine comprising at least two cylinders, wherein: 1. Set the target engine speed; 2. Set the target engine torque to satisfy both the target engine power and the target engine speed; 3. Monitor engine performance data; 4. Use engine performance data and target engine torque to determine the HRF and LRF values ​​of the current combustion event; 5. Monitor the pressure in each cylinder of the engine; 6. Obtain the actual peak pressure of the current ignition cylinder; 7. Set a target peak pressure, which is common to all cylinders of the engine; 8. Use the target peak pressure and the actual peak pressure to determine the cylinder-specific LRF correction factor; 9. Adjust the LRF amount using a cylinder-specific LFR correction factor to provide a cylinder-specific LRF amount; and 10. Use cylinder-specific LRF and determined HRF amounts when controlling fuel supply during the current combustion event.

[0008] This invention enables more precise control of fuel quantity with less and / or easier onboard calibration. In this method, the LRF fuel quantity is the primary feedforward control variable, which allows for precise prevention of premixed fuel pre-ignition. Using cylinder peak pressure as an input variable for adjusting a specific LRF quantity in a cylinder smooths out the torque difference between engine cylinders.

[0009] According to one aspect of the invention, the actual peak pressure is a filtered peak pressure, which is determined using a predetermined number of previous peak pressures in the cylinder. Preferably, the filtered peak pressure is obtained by using the cylinder peak pressures from multiple previous cycles.

[0010] According to one aspect of the invention, the filtered peak pressure of the current ignition cylinder is a sliding average of a predetermined number of previous peak pressures of the cylinder.

[0011] According to one aspect of the invention, upper and lower limits are used for the acceptable peak pressure range, and filtering includes removing individual peak pressures outside the acceptable peak pressure range from the filtering process.

[0012] According to one aspect of the invention, a predetermined number of net values ​​of previous cylinder-specific LFR correction factors are calculated to provide a net total drift, and the net total drift is used to adjust the HRF amount and / or the LRF amount, which are provided using engine performance data and target engine torque for the current combustion event.

[0013] According to one aspect of the invention, scavenging pressure is monitored, and the amount of HRF and LRF of the current combustion event is determined by providing a set of data storage, said set of data storage being configured to provide the relationship between the LRF amount, HRF amount, and engine performance data and target torque.

[0014] The use of LRF as a primary feedforward control variable allows for precise prevention of premixed fuel pre-ignition, which could otherwise occur when the actual in-cylinder air mass deviates from the nominal value (i.e., during heavy propeller operation, rough seas, increased engine load, and tropical environmental conditions).

[0015] According to one aspect of the invention, engine performance data includes engine load, engine speed, and scavenging pressure. Engine performance data arranged in this manner is simple, logical, and easily adjustable. These parameters can be accurately calculated when the engine's mechanical characteristics are known, and can also be corrected for key operating conditions. They can also be easily and finely adjusted during normal shipboard operation without the need for impractical, extensive, and separate test runs in the case of such a large engine. Furthermore, scavenging pressure is a strong indicator of the quality of air trapped in the cylinder; therefore, sudden changes in turbocharger operation, such as sudden load losses (e.g., in a semi-submerged propeller at rough seas), can be immediately detected in the scavenging pressure and taken into account when determining the fuel supply for the next combustion cycle.

[0016] According to one aspect of the invention, the HRF and LRF quantities of a current combustion event are determined by providing a set of data storage devices, said set of data storage devices being configured to provide a model mapping relationship between the LRF quantities, HRF quantities and engine power output by using at least the target engine torque, actual engine speed, and scavenging pressure as inputs to the set of data storage devices.

[0017] In this way, all variables are considered in determining the fuel quantity: target engine torque, actual engine speed, scavenging pressure, and, for example, both tropical and frigid climates are considered in an effective manner. It has been found that scavenging pressure also has a sufficiently strong correlation with ambient air conditions in terms of engine control, and the control information stored in the data memory can also take weather conditions into account when controlling large two-stroke engines.

[0018] According to one aspect of the invention, a target peak pressure is set by providing a predetermined set of data storage devices, said predetermined set of data storage devices being configured to provide the target peak pressure using at least engine performance data as its input variable.

[0019] In this way, the peak pressure is always set to the desired level. The amount of fuel (especially the amount of LRF) can be effectively controlled so that the engine operates very close to advance ignition, in which case the charge in the cylinder ignites at a moment very close to the expected ignition.

[0020] According to one aspect of the invention, a set of data storage is provided for an LFR correction factor, wherein at least the target peak pressure, the actual peak pressure, and the engine performance are used as input variables for the set of data storage.

[0021] According to one aspect of the invention, the HRF and LRF amounts of the current combustion event are determined by the following steps: The HRF torque estimate is calculated based on the LRF quantity, and the LRF torque estimate is also calculated. Calculate the fuel quantity for the HRF corresponding to the estimated HRF torque; The fuel quantity of HRF corresponding to the HRF torque estimate is compared with the predefined physical limit fuel quantity set for the injector used. min The comparison was made, and the fuel quantity of the HRF corresponding to the estimated torque value of the HRF was less than that of the HRF. min In the case of HRF min The LRF torque estimate is corrected by the difference between the fuel quantity of the HRF and the HRF corresponding to the HRF torque estimate; The HRF quantity is calculated using the HRF torque estimate; and The LRF quantity is calculated using the LRF torque estimate.

[0022] As the piston in the cylinder moves toward the TDC, LRF is injected into the engine cylinder, thus providing a premixed charge of air and LRF before ignition, and HRF is injected in the area immediately adjacent to the moment of LRF auto-ignition, which results in the compression ignition of the charge in the cylinder.

[0023] A fuel injection control system for a large two-stroke piston engine includes a controller computer comprising executable instructions. When the fuel injection control system is assembled to the large two-stroke piston engine for use, the executable instructions, when executed by the controller computer, cause the computer controller to perform a method according to the invention for supplying fuel to a two-stroke piston internal combustion engine, wherein the fuel comprises at least a low-reactive fuel (LRF) as a primary fuel and a high-reactive fuel (HRF) as an ignition-enhancing fuel, and the engine comprises at least two cylinders, wherein: 1. Set the target engine speed; 2. Set the target engine torque to satisfy both the target engine power and the target engine speed; 3. Monitor engine performance data; 4. Use engine performance data and target engine torque to determine the HRF and LRF quantities of the current combustion event. 5. Monitor the pressure in each cylinder of the engine; 6. Obtain the actual peak pressure of the current ignition cylinder; 7. Set a target peak pressure, which is common to all cylinders of the engine; 8. Use the target peak pressure and the actual peak pressure to determine the cylinder-specific LRF correction factor; 9. Adjust the LRF amount using a cylinder-specific LFR correction factor to provide a cylinder-specific LRF amount; and 10. Use cylinder-specific LRF and determined HRF amounts when controlling fuel supply during the current combustion event.

[0024] A fuel injection control system for a large two-stroke piston engine includes a controller computer that includes executable instructions that, when executed by the controller computer, cause a computer controller to perform the method according to any one of claims 1 to 12, when the fuel injection control system is assembled into the large two-stroke piston engine for use.

[0025] In general, the present invention can control the ingestion of premixed fuel under the following conditions: engine operating conditions according to reference (ISO) conditions, propeller light / heavy load operation, rough sea mode, engine load transients, engine hardware aging, cylinder-to-cylinder deviation, tropical environmental conditions, changes in LRF fuel type (i.e., LNG, ammonia) and characteristics (i.e., low calorific value, anti-spontaneous combustion), changes in HRF type (i.e., diesel, methanol) and characteristics (i.e., low calorific value, anti-spontaneous combustion), and injector drift.

[0026] Compared to reference ISO operating conditions, this invention can reduce engine emissions and fuel consumption, which would otherwise occur under conditions such as: light / heavy propeller operation, rough sea conditions, transient engine load, engine hardware aging, tropical environmental conditions, extensive variations in LRF fuel type (i.e., LNG, ammonia) and characteristics (i.e., low calorific value, anti-spontaneous combustion), variations in HRF type (i.e., diesel, methanol) and characteristics (i.e., low calorific value, anti-spontaneous combustion), and injector drift.

[0027] This invention can be advantageously combined with upgrades to existing two-stroke engines. According to one aspect of the invention, the upgrade is performed by making an in-situ powertrain modification as disclosed in patent application number PCT / EP2022 / 080336, which is incorporated herein by reference. In this upgrade method, an in-situ modification of the ship's power system is implemented, wherein the power system includes at least one propulsion power system configured to provide thrust to operate the ship at a predetermined first operating profile (e.g., design speed), and the at least one power system includes a multi-cylinder two-stroke piston internal combustion engine, a propeller, and a shaft assembly mechanically connecting the propeller and the engine. The modification includes configuring the at least one power system to provide thrust to operate the ship at a second operating profile having a smaller power requirement than the first operating profile, wherein an existing combustion chamber component, including at least a cylinder liner, cylinder head, piston, and piston rod, is removed from the engine of the at least one power system, and a new combustion chamber component (including a new cylinder liner with an inner diameter smaller than the existing cylinder liner) is assembled to produce a higher specific power than the removed old combustion chamber component. The two-stroke engine is equipped with a fuel injection control system according to the invention, the fuel injection control system including a controller computer, the controller computer including executable instructions that, when the fuel injection control system is assembled into a large two-stroke piston engine for use, cause the computer controller to perform the method according to the invention when executed by the controller computer.

[0028] In this way, the modified engine can be easily test-run and configured to burn fuel efficiently from the outset, and its operation is robust from the beginning. Thus, under the new conditions of the second operating profile, the engine operates in a fuel-efficient manner. Due to the smaller cylinder bore, the engine's operating conditions can be maintained in a manner conducive to complete fuel combustion. Furthermore, the invention is also advantageous in terms of reconstruction, as it requires only a small amount of measurement data from the engine, but is based on an easily calibrated data source.

[0029] In this article, low-reactive fuels (LRFs) can be, for example, natural gas, ammonia, methanol, etc. High-reactive fuels (HRFs) can be, for example, fuel oil, diesel, liquid fuel oil, marine diesel, etc.

[0030] Large two-stroke engines are two-stroke piston internal combustion engines commonly used as main engines in ocean-going vessels. The cylinders can have bores ranging from, for example, 25 cm to 120 cm, and the engine can have power outputs ranging from, for example, 3000 kW to 120,000 kW. Engine speeds are typically in the range of 40 rpm to 250 rpm.

[0031] The exemplary embodiments of the invention presented in this patent application should not be construed as limiting the applicability of the appended claims. The verb "comprising" is used in this patent application as an open-ended limitation, and does not exclude the presence of features not listed. Features described in the dependent claims may be freely combined with each other unless expressly stated otherwise. Novel features considered characteristic of the invention are specifically set forth in the appended claims. Attached Figure Description

[0032] The invention will be described below with reference to the accompanying exemplary schematic diagrams, in which: Figure 1 A large two-stroke crosshead piston internal combustion engine according to an embodiment of the present invention is shown; Figure 2 A block diagram of a control system according to an embodiment of the present invention is shown; and Figure 3 A diagram illustrating the technical effects of the present invention is shown. Detailed Implementation

[0033] Figure 1A schematic cross-sectional view of a two-stroke crosshead piston internal combustion engine 6 is shown, in which the present invention can be applied, typically in large ocean-going vessels. Engine 6 is a large two-stroke multi-cylinder engine for use in or on ships. The engine typically includes 6 to 14 cylinders 101, but of course, the practical application of the invention is not limited to any particular number of cylinders 101 in engine 6. The main components of engine 6 are an engine cylinder block 100, a crankshaft 102 rotatably supported to the engine cylinder block 100, connecting rods 104, a crosshead 106 arranged to be guided by guides 108, piston rods 110, pistons 112 and cylinder liners 114, cylinder head 116, exhaust valves 118, exhaust manifold 120, and a supercharger 122, which typically includes a turbocharger. A flow path, indicated by arrow 126, is arranged in the engine for scavenging between the turbocharger 122 and the scavenging space 124 in the engine. The scavenging air flow path 126 may include, for example, an air cooler. The cylinder liner 114 has an air port 128 at its lower part, which opens to the engine air space 124 and is located in the cylinder above the piston 112, at least when the piston 112 is at its bottom dead center position.

[0034] The engine 6 is provided with at least a first fuel injection system 130 and a second fuel injection system 132, through which the engine can operate by burning two different fuels, specifically low reactive fuel (LRF) as the main fuel and high reactive fuel (HRF) as the ignition-promoting fuel involved in the combustion process of each combustion stage.

[0035] The cylinder head 116, mounted on top of the cylinder liner 114, typically has more than one fuel injection nozzle 115. The fuel injection nozzle 115 is arranged to connect to a first fuel injection system 130. The first fuel injection system includes the necessary components and functions for supplying fuel to the nozzle 115 at a desired pressure and quantity, as is also known. The injection nozzle 115 may be arranged to inject fuel directly into the combustion chamber, or it may be located in a pre-combustion chamber arranged to inject fuel into the cylinder head 116, and this pre-combustion chamber leads to the combustion chamber.

[0036] One or more fuel inlets 134 are arranged to the cylinder liner 114, the fuel inlets being positioned above the air port 128, i.e., on the side of the cylinder head 116. A second fuel injection system 132 is connected to the fuel inlet 136, and it includes a gas inlet valve 134 for controlling the introduction of a second fuel into the engine.

[0037] The engine includes a fuel injection control system 1 configured to operate the engine by supplying fuel to the engine according to the method of the invention. The fuel injection control system includes one or more controller computers 3 and one or more computer programs, which are executed by the controller computers when the engine is running. The execution of the programs causes the fuel injection systems 130 and 132 to operate according to the method of the invention. The fuel injection control system 1 can be integrated into the engine control system, or it can be a separate unit or system arranged to communicate with other control devices arranged in the engine for data transmission. At least the injection nozzle 115 and the gas inlet valve 134 can be electronically controlled by the fuel injection control system 1.

[0038] The aforementioned positions of the fuel injection nozzle 115 connected to the first fuel injection system and the fuel inlet 134 of the second fuel injection system 132 are preferred examples of practical application. Thus, as the piston in the cylinder moves toward the TDC (Transmission Control Center), the second fuel can be injected into the engine cylinder, thereby providing an efficient premixed air-fuel charge before ignition, and the first fuel is injected after the second fuel injection, resulting in compression ignition of the charge in the cylinder.

[0039] The following is combined Figure 1 Explanation function, Figure 1 A large two-stroke engine is disclosed, wherein a first fuel is injected through a direct injection fuel injector 115 disposed in the cylinder head 116, and a second fuel is injected through a fuel inlet 134 disposed in the lower part of the cylinder liner 114. However, it should be noted that the injector 115 can be arranged to inject fuel directly into the combustion chamber or into a pre-combustion chamber disposed in the cylinder head, which leads to the combustion chamber. Correspondingly, the fuel inlet 136 can also be alternatively or additionally disposed in the cylinder head, in which case the fuel inlet 136 can be referred to as a second fuel injector. When disposed in the cylinder head, the fuel inlet 136 can be arranged to inject fuel directly into the combustion chamber or into a pre-combustion chamber disposed in the cylinder head, which leads to the combustion chamber. It is also conceivable to use both locations—through the cylinder head and through the cylinder liner—to inject the second fuel into the combustion chamber.

[0040] According to the present invention, the first fuel is a highly reactive fuel (HRF), and the second fuel is a low-reactive fuel (LRF). The terms "high" and "low" indicate that the reactivity of the two fuels is compared only with each other, and the first fuel has a higher reactivity than the second fuel. Reactivity in this document specifically refers to the ignitionability of the fuel. In some practical applications, the term "high reactivity" may refer to the low auto-ignition temperature value of the fuel, while "low reactivity" may refer to the high auto-ignition temperature of the fuel. The low-reactive fuel (LRF) is used as the primary fuel, while the high-reactive fuel (HRF) is used as the ignition-promoting fuel. Particularly in large ocean-going vessels, the fuel injection control system 1 according to the present invention allows for the efficient upgrading of large two-stroke engines, which were originally designed to burn, for example, heavy fuel oil, to burn both the low-reactive fuel (LRF) as the primary fuel and the high-reactive fuel (HRF) as the ignition-promoting fuel.

[0041] In the following description, some features relating to the engine may not be essential to the invention in its most general sense, but are disclosed for a better understanding of the operation and preferred embodiments of the invention. The engine is provided with one or more pressure sensors 136, which are arranged and configured to monitor the pressure of air in the engine's scavenging space 124. A fuel injection control system 1 communicates 2 with the one or more pressure sensors 136 to receive pressure measurement data from the sensors 136. The scavenging pressure is primarily controlled by the operation of the turbocharger 122, and therefore is highly influenced by and correlated with the actual load on the engine. According to the invention, the scavenging pressure data obtained from the scavenging space 124 is used to estimate the mass of air trapped in the closed combustion chamber or as an indication of the mass of air trapped in the closed combustion chamber. An advantageous feature of the invention is that the fuel control system is configured to operate without requiring measurement of the oxygen concentration in the exhaust gas, and therefore no exhaust gas λ sensor is present in the exhaust manifold.

[0042] A speed sensor 138 is configured to monitor the speed of engine 6, and a load sensor 140 is configured to monitor the load or torque of engine 6. The fuel injection control system 1 communicates with the speed sensor 138 and the load sensor 140 via data transmission 2, 4. These sensors provide the fuel injection control system 1 with engine-related information concerning fuel combustion in all cylinders of the engine. Engine 6 is also equipped with pressure sensors 142 connected to each cylinder of engine 6, thereby monitoring cylinder pressure. The fuel injection control system 1 communicates with pressure sensors 142.1 to 142.N via data transmission 8.1 to 8.N, which are configured to monitor the pressure in each combustion chamber of the engine during operation of engine 6. Pressure sensors 142.1 to 142.N are configured to provide the fuel injection control system 1 with cylinder-specific information, particularly information regarding peak pressure during fuel combustion. Typically, data transmission communication is achieved using physical wires or cables.

[0043] According to one aspect of the invention, the injection or supply of low-reactivity fuel (LRF) as the main fuel and high-reactivity fuel (HRF) as the ignition-promoting fuel into the cylinders of the engine is carried out in a manner that effectively offsets the difference in cylinder-related torque, which is the torque provided to the engine by the combustion of fuel in each individual cylinder when the engine is running. (Reference) Figure 2 The diagram schematically discloses a block diagram of the control system 1, showing that the cylinder 101 is provided with an air port 128, at least one fuel injection nozzle 115, and a fuel inlet 134. This method is used to control the injection quantity of both low-reactive fuel (LRF) as the main fuel and high-reactive fuel (HRF) as an ignition-promoting fuel. The timing of fuel entry can be controlled such that LRF entry occurs when the piston is below the fuel inlet 134, thereby producing a premixed air-fuel mixture. HRF injection has a strong influence on the ignition of the mixture of LRF, HRF, and air, and the HRF is injected such that the fuel in the charge is ignited and burned before the exhaust valve is opened.

[0044] Fuel quantity control is based on current engine performance data 200 and target torque 201, which serve as input values ​​for controlling fuel supply. The target engine torque is set such that the torque will provide sufficient power to move the vessel at the current or desired speed, which is determined by the vessel's operator. In other words, the target engine torque provides the power to meet the target engine speed. Current engine performance data 200 and target torque 201 can be used to determine the HRF and LRF quantities of the current combustion event. The target torque can be obtained such that the target engine speed is first set, and the target engine torque is set to meet the target engine speed. The current combustion event refers to the upcoming combustion that is being prepared. In the cylinder preparing for the combustion event, the piston has passed its bottom dead center and moved toward top dead center, but is still below the position where the fuel inlet can access the combustion chamber (the cylinder space above the piston). The fuel injection control system 1 includes an engine main control unit 202, which provides engine-level HRF and LRF quantities, i.e., control data for all cylinders of the engine, and controls the injection duration of HRF and LRF based on this control data. The main control unit 202 includes a set of data memories 203 configured to provide HRF and LRF quantity commands as feedforward control. The set of data memories 203 includes the relationship between the HRF and LRF quantities, as well as engine performance data 200 and target torque 201. Preferably, a sampling frequency is used to monitor engine performance, which allows the HRF and LRF quantities to be determined individually for each combustion event in each ignition cylinder. Advantageously, the set of data memories 203 includes, or is configured to, provide the relationship between the HRF and LRF quantities as output data, and provide engine load, engine speed, and scavenging pressure as input data related to engine performance. Scavenging pressure can be used as an indication of the quality of air captured in the cylinder. The information in the set of data memories (which may also be referred to as a control chart or fuel chart) includes data preferably initially based on the engine's physical characteristics and fuel characteristics, which can then be easily fine-tuned on board during shipboard operations and in the engine's normal use, such as transporting cargo. Input variables are selected to ensure robustness of engine combustion under all conditions. The use of clear and direct variables based on the engine's clear physical characteristics makes the control system robust to key conditions and easily fine-tunable. This invention also maximizes the proportion of LRF in combustion without entering regions where combustion becomes unstable or incomplete.

[0045] The fuel injection control system 1 also includes a specific program that, if necessary, corrects for the torque supplied by each individual cylinder during each combustion event. For this purpose, the fuel injection control system 1 includes a peak pressure control unit 204 for each cylinder 101 of the engine 6. For cylinder-specific correction of the LRF quantity, the pressure in each cylinder 101 is monitored by corresponding sensors 142.1, 142.2, 142.N. The actual maximum pressure (i.e., peak pressure) is monitored in the specific cylinder and stored by the control system so that the actual peak pressure of the currently ignited cylinder is available to the control system. This provides a series of pressure values ​​for the specific cylinder N: p max, cylN, 1 p max, cylN, 2 p max, cylN, 3 ...and accordingly for each cylinder of the engine. The actual peak pressure used can be the peak pressure previously measured in a particular cylinder. The peak pressure control unit 204 uses the LRF quantity data provided by the main control unit 202 and corrects it using a cylinder-specific LRF correction factor to obtain the cylinder-specific LRF quantity. The target peak pressure (which is common to all cylinders of the engine) is set such that it allows correction to the cylinder-specific LRF quantity to smooth out differences in cylinder-side torque, while the HRF quantity is not directly affected by the peak pressure control unit 204. The cylinder-specific LRF correction factor is determined using the target peak pressure and the actual peak pressure. The cylinder-specific LRF quantity and HRF quantity determined by the main control unit 202 are used to control the fuel supply during the current combustion event. Fuel management is performed using the cylinder-specific LRF quantity and HRF quantity data. In this way, each cylinder operates at its maximum share of LRF while still providing controlled ignition under current conditions. The most advantageous way to provide cylinder-specific LRF values ​​is to sum the LRF value data provided by the main control unit 202 and the cylinder-specific LRF correction factor.

[0046] Figure 2Another specific aspect of the invention is also disclosed, wherein the peak pressure control unit 204 is provided with a filter unit 206 for providing filtered peak pressure data used in the peak pressure control unit 204. The filter unit 206 is configured to filter a predetermined number of cylinder peak pressures, which are measured from specific cylinders and stored for use. Therefore, the actual peak pressure used to determine the cylinder-specific LRF correction factor is the filtered peak pressure. The filtering function can be selected as needed. Advantageously, the filter unit 206 is configured to calculate a moving average of the predetermined number of previous peak pressures of the cylinders. If desired, the moving average can also be a weighted moving average. Additionally, the filter unit 206 can be configured to remove individual peak pressure values ​​outside a predetermined acceptable peak pressure range from the filtering and control process. Therefore, an upper and lower limit of the acceptable peak pressure range is determined, and individual peak pressures that are not valid measurements can be removed from the control process.

[0047] Figure 2 Another aspect of the invention is also disclosed, wherein the peak pressure control unit 204 is provided with an injector model 208 for providing a precise fuel quantity for each fuel combustion event. The injector model 208 is individually calibrated for each fuel port 134 in the engine, taking into account mechanical differences between fuel ports. The injector model provides corrected control data for the fuel ports 134. The injector model can be configured to use fuel temperature and / or pressure as additional input variables, which affect the control data. The injector model can be based on test measurements performed on board or off board.

[0048] As another aspect of the invention, the fuel injection control system includes a drift control unit 210. The drift control unit is arranged to influence the output of the main control unit 222, in other words, to adjust the engine-level HRF and LRF quantity control data. At the level of the drift control unit 210, the main control unit 202 provides feedforward control, but the drift control unit 210 takes into account the net change in the LRF correction factor. The drift control unit is configured to receive cylinder-specific LRF correction factor data from each of the peak pressure control units 204 and calculate a net LRF correction factor from the cylinder-specific LRF correction factor data. The net LRF correction factor is the sum of a predetermined number of previous cylinder-specific LRF correction factors. For example, if the current LRF correction factor and four previous correction factors are used, for fuel quantities of -2g, +2g, +0.5g, and +0.5g per ignition, the net LRF correction factor will be -2 + 2 + 0.5 + 0.5 = 1g. Therefore, the drift control unit 210 uses the thus obtained net LRF correction factor to adjust the output of the main control unit. Advantageously, both the HRF and LRF quantities are adjusted by using a predetermined proportion of the net LRF correction factor. The drift control unit can be equipped with a filter that smooths out sudden and / or large changes in adjustment. This invention enables the engine to maximize the LFR quantity that can be handled under stable combustion conditions. When the LFR is a low-carbon or carbon-free fuel, CO2 emissions are minimized even if the HRF will be, for example, light fuel oil or diesel. This drift compensation allows the cylinders to balance towards the mean fill pressure and further makes it possible to set the ignition pressure to the maximum target pressure for all cylinders.

[0049] However, there are technical limitations to the minimum amount of HRF that the fuel injection nozzle 115 can inject during a single opening or injection, such as mechanical limitations due to the mass of the moving parts of the injector and / or electronic limitations of the solenoid system. To take this into account, the control system 1 includes a fuel quantity correction unit configured to ensure that the HRF quantity is at its minimum level that the injector can mechanically handle. A minimum fuel volume may also be required to prevent fouling and clogging of the HRF fuel injection nozzle 115.

[0050] Figure 3The technical effects of using the fuel injection control system according to the invention in a large two-stroke internal combustion piston engine are disclosed in the figure, which shows a simulated sequence of events. The horizontal axis in the graph represents time, and the status information 40 (off / on) of the peak pressure control unit 204 and the operating status of the engine 41 indicating engine load and marine environment are shown below the graph. In this embodiment, LRF is natural gas and HRF is diesel. The figure shows the following variables: 30: actual amount of gas used in combustion, 31: actual amount of diesel used in combustion, 32: measured gas fraction, 33: estimated gas fraction, 34: target peak pressure, 35: peak pressure measured in an exemplary cylinder of the engine, 36: engine speed, 37: engine load, 38: correction of the LFR amount by the peak pressure control unit 204 to the exemplary cylinder, and 39: average correction of the LFR amount by the drift control unit 210 after the main control unit 202.

[0051] Three different scenarios, A, B, and C, can be seen in the diagram. In scenario A, the engine operates at 50% load, and the peak pressure control unit 204 is not operational (off). The boat is operating in calm water, and there are very small pulses that cause instantaneous load on the engine. When transitioning to scenario B, due to the rough seas, waves are affected by the boat's hull, and the peak pressure control unit 204 is still not operational (off). During scenario B, there are noticeable fluctuations in all the given variables. During scenario C, waves are still affected by the boat's hull, causing pulses acting on the hull that are reflected in the engine load. Now, the peak pressure control unit 204 is on (on), and one can clearly see how the cylinder-specific correction of the LRF quantity smooths out the effects of the rough seas.

[0052] As an additional improvement, the main control unit 202 is configured to continuously register and store LRF and HRF quantities.

[0053] While the invention has been described herein by way of example with respect to embodiments which are presently considered to be the most preferred embodiments, it will be apparent to those skilled in the art that the basic ideas of the invention can be implemented in many ways as technology advances. Therefore, the invention and its embodiments are not limited to the embodiments and samples described above, but may vary within the scope of the patent claims and their legal equivalents. When such a combination is technically feasible, the details mentioned in any of the foregoing embodiments may be used in conjunction with another embodiment.

Claims

1. A method for supplying fuel to a two-stroke piston internal combustion engine (6), said fuel comprising at least a low-reactive fuel (LRF) as a primary fuel and a high-reactive fuel (HRF) as an ignition-enhancing fuel, said engine (6) comprising at least two cylinders (101), wherein: 1.

1. Set the target engine speed; 1.

2. Set the target engine torque to satisfy both the target engine power and the target engine speed; 1.

3. Monitor engine performance data; 1.

4. Using the engine performance data and the target engine torque, determine the HRF and LRF values ​​for the current combustion event; 1.

5. Monitor the pressure in each cylinder (101) of the engine (6); 1.

6. Obtain the actual peak pressure of the current ignition cylinder; 1.

7. Set a target peak pressure, which is common to all cylinders (101) of the engine (6); 1.

8. Use the target peak pressure and the actual peak pressure to determine the cylinder-specific LRF correction factor; 1.

9. Adjust the LRF amount using the cylinder-specific LFR correction factor to provide a cylinder-specific LRF amount; and 1.

10. The cylinder-specific LRF amount and the determined HRF amount are used when controlling the fuel supply in the current combustion event.

2. The method of claim 1, wherein, The actual peak pressure is the filtered peak pressure, which is determined using a predetermined number of previous peak pressures in the cylinder (101).

3. The method according to claim 1 or 2, characterized in that, The filtered peak pressure of the current ignition cylinder is a sliding average of a predetermined number of previous peak pressures of the cylinder (101).

4. The method according to claim 2 or 3, characterized in that, The upper and lower limits are used for the acceptable peak pressure range, and the filtering includes removing individual peak pressures outside the acceptable peak pressure range from the filtering process.

5. The method according to any of the preceding claims, characterized in that, Calculate the net value of a predetermined number of previous cylinder-specific LFR correction factors to provide a net total drift, and the net total drift is used to adjust the HRF amount and / or the LRF amount provided in step 1.

4.

6. The method according to claim 1 or 5, characterized in that, Monitor scavenging pressure; and The HRF and LRF quantities of the current combustion event are determined by providing a set of data storage devices, which are configured to provide the relationship between the LRF quantity, the HRF quantity, and engine performance data and the target torque.

7. The method according to claim 1 or 6, characterized in that, The engine performance data includes engine load, engine speed (6), and scavenging pressure.

8. The method according to claim 6, characterized in that, The HRF and LRF quantities of the current combustion event are determined by providing a set of data storage (203), which is configured to provide a model mapping relationship between the LRF quantity, the HRF quantity and the engine power output by using at least the target engine torque, the actual engine speed and the scavenging pressure as inputs to the set of data storage.

9. The method of claim 1, wherein, The target peak pressure is set by providing a predetermined set of data storage devices, which are configured to use at least the engine performance data as their input variables to provide the target peak pressure.

10. The method of claim 1, wherein, A set of data storage is provided for the LFR correction factor, wherein at least the target peak pressure, the actual peak pressure, and the engine performance are used as input variables for the set of data storage.

11. The method of claim 8, wherein, The HRF and LRF quantities of the current combustion event are determined by the following steps: 11.

1. Calculate the HRF torque estimate and the LRF torque estimate based on the LRF quantity; and 11.

2. Calculate the fuel quantity for the HRF corresponding to the estimated HRF torque value; 11.

3. comparing the fuel quantity of the HRF corresponding to the HRF torque estimate value with a predefined physical limit fuel quantity HRF min set for the used injector, and in case the fuel quantity of the HRF corresponding to the HRF torque estimate value is smaller than HRF min , correcting the LRF torque estimate value based on the difference between HRF min and the fuel quantity of the HRF corresponding to the HRF torque estimate value; 11.

4. Calculate the HRF amount using the aforementioned HRF torque estimate; and 11.

5. Calculate the LRF amount using the LRF torque estimate.

12. The method according to any of the preceding claims, characterized in that, While the piston of the cylinder (101) is moving toward the TDC, LRF is injected into the cylinder (101) of the engine (6) to provide a premixed charge of air and LRF before ignition, and HRF is injected at the moment of automatic ignition of LRF, which results in compression ignition of the charge in the cylinder (101).

13. A fuel injection control system for a large two-stroke piston engine (6), the fuel injection control system comprising a controller computer (3) comprising executable instructions which, when executed by the controller computer, cause the computer controller to perform the method according to any one of claims 1 to 12 when the fuel injection control system is assembled to the large two-stroke piston engine (6) for use.

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