Method for operating large engine and large engine

Abstract

The invention relates to a method for operating a large engine and a large engine. The large engine (20) comprises at least one cylinder (21) having a combustion chamber delimited by a piston (23) movable back and forth along a cylinder axis. The air-fuel mixture is compressed in the combustion chamber by the movement of the piston (23) at a compression ratio, and the operating parameters of the large engine (20) are determined continuously or at regular intervals. An optimized compression ratio for the air-fuel mixture is determined on the basis of the operating parameters, and the compression ratio is adjusted to the optimized compression ratio.

Description

[0001] This application is a divisional application of the patent application filed on April 28, 2020, with application number 202010349046.X and entitled "Method for Operating a Large Engine and a Large Engine". Technical Field

[0002] The present invention relates to a method for operating a large engine having at least one cylinder, and to a large engine. Background Technology

[0003] Large engines, which can be designed as two-stroke or four-stroke engines (such as longitudinally scavenged two-stroke large diesel engines), are commonly used as propulsion units for ships, or even in stationary operations, such as driving large generators to produce electricity. These engines typically operate continuously for considerable periods, placing high demands on operational safety and availability. Therefore, exceptionally long maintenance intervals, low wear, and economical handling of operating materials are central criteria for operators. Large engines typically have cylinders with a bore (cylinder diameter) of at least 200 mm. Currently, large engines with bores up to 960 mm or even larger are in use.

[0004] Different types of large engines are known, each of which can be designed as a two-stroke or four-stroke engine. Alternatives to heavy fuel oils or diesel, traditionally used as fuel for large engines, are also being sought, considering economic and efficient operation, compliance with exhaust emission thresholds, and resource availability. In this regard, two types of liquid fuels are being used: fuels introduced into the combustion chamber in a liquid state; and gaseous fuels, which are introduced into the combustion chamber in a gaseous state.

[0005] Examples of liquid fuels known as alternatives to heavy fuel oils include other heavy hydrocarbons from petroleum refineries, alcohols, particularly methanol or ethanol, gasoline, diesel, or emulsions or suspensions. For example, emulsions known as MSAR (Multiphase Ultrafine Atomized Residue) are known to be used as fuels. A well-known suspension is a suspension of coal dust and water, which is also used as fuel in large engines. Natural gas, such as LNG (Liquefied Natural Gas) or LPG (Liquefied Petroleum Gas), is referred to as a gaseous fuel.

[0006] Another well-known alternative to pure operation using heavy fuel oil is to design large engines that can operate on two or more different fuels, whereby, depending on the operating conditions or environment, the engine may operate on one fuel or another. Such large engines, also known as multi-fuel large engines, can switch during operation from a first mode burning the first fuel to a second mode burning the second fuel, and vice versa.

[0007] Large engines that can operate simultaneously with at least two different fuels are also known. Two different fuels can be burned simultaneously in one or more cylinders, or only the first fuel can be burned in a first set of cylinders, while only a second fuel different from the first fuel is burned in another set of cylinders.

[0008] Known designs of large engines that can operate on two different fuels are engine types currently referred to as "dual-fuel engines." On one hand, these engines can operate in gaseous mode, where a gaseous fuel such as natural gas or methane is introduced into the combustion chamber for combustion; on the other hand, they can operate in liquid mode, where a liquid fuel such as heavy fuel oil or another liquid fuel can be burned in the same engine. These large engines can be two-stroke and four-stroke engines, and in particular, they can also be longitudinally scavenged two-stroke large diesel engines.

[0009] Large engines that can operate with at least two or even more different liquid or gaseous fuels typically operate in different modes depending on the fuel currently in use. In an operating mode commonly referred to as diesel operation, combustion of the fuel usually occurs based on the principle of compression ignition or auto-ignition. In a mode commonly referred to as Otto operation, combustion occurs via spark ignition of an ignitable premixed air-fuel mixture. This spark ignition can occur, for example, via an electric spark using a spark plug, or it can also occur via the auto-ignition of a small amount of fuel injected, which subsequently ignites another fuel. The small amount of fuel used for auto-ignition is typically injected into a pre-combustion chamber connected to the combustion chamber.

[0010] For example, in the aforementioned dual-fuel engine, it is known in the gas mode that gaseous gas is mixed with scavenging air to produce a combustible mixture in the combustion chamber of the cylinder. During this low-pressure process, the mixture in the cylinder is typically ignited by injecting a small amount of liquid, auto-igniting fuel into the combustion chamber or pre-combustion chamber of the cylinder at an appropriate time, which subsequently leads to the ignition of the air-gas mixture.

[0011] In addition, there are hybrid forms known from Otto operation and diesel operation.

[0012] Large engines designed as pure gas engines are also known, that is, engines that operate using only gas as fuel.

[0013] Whether it is a dual-fuel engine or a pure gas engine, the process of introducing gaseous fuel into the combustion chamber of the cylinder and producing an air-gas mixture is crucial for the reliable, low-pollution, and safe operation of such an engine.

[0014] In gas-fuel mode, adjusting the correct ratio of scavenging air to gas, i.e., the air-fuel ratio, is crucial. The air-fuel ratio can be indicated, for example, by a lambda value (λ value), which indicates the ratio of the mass of air captured in the cylinder to the mass of air required for stoichiometric combustion. In large diesel engines, scavenging or boost air is typically provided by a turbocharger, which generates scavenging or boost air pressure that depends on the engine load and therefore on the engine's power, torque, or speed. For a given boost 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 required speed, resulting in an optimal combustion process for that operating condition.

[0015] In particular, when operating in gas mode according to Otto's principle, proper adjustment of the air-fuel ratio is crucial for the engine's low-emission, high-efficiency, and economical operation. If the gas content is too high, the air-fuel mixture becomes too rich. Combustion of the mixture occurs too quickly or too early, which can lead to engine knocking. If the air content is too high, the air-fuel mixture is too lean and may ignite, which of course also negatively impacts the engine's efficient and low-emission operation.

[0016] Therefore, especially for large engines operating in gas mode, efforts are made to keep the λ value within an optimal range between the knock limit on one hand and the no-ignition limit on the other, because otherwise abnormal combustion may occur, potentially damaging the large engine. In the case of large engines operating in gas mode according to Otto's principle, the optimal λ value can be, for example, between 2.0 and 3.0, preferably between 2.3 and 3.0. The limiting values ​​of λ can vary slightly depending on the engine's operating load.

[0017] Large engines are typically designed in such a way that the compression ratio is optimized at the 100% load point, i.e. at full load, and that large engines have the best possible trade-off between combustion behavior and efficiency. This means that large engines are designed in such a way that they have the highest possible thermodynamic efficiency at the 100% load point (i.e. at full load and maximum speed).

[0018] Compression ratio is a geometric value that is the ratio of the first volume of the combustion chamber before the compressed air-fuel mixture to the remaining second volume of the combustion chamber after the compressed air-fuel mixture.

[0019] Optimizing combustion behavior at 100% load means that the efficiency of large engines is no longer optimal at lower loads, such as at lower medium pressures. Summary of the Invention

[0020] Therefore, based on the state of the prior art, the object of this invention is to provide a method for operating a large engine that enables the large engine to achieve optimal efficiency across the entire load range and avoids abnormal combustion. Furthermore, the object of this invention is to provide a corresponding large engine.

[0021] According to the present invention, a method for operating a large engine is thus proposed, the large engine comprising at least one cylinder having a combustion chamber defined by a piston capable of reciprocating along the cylinder axis. An air-fuel mixture is compressed in the combustion chamber by the piston's movement at a compression ratio, and the operating parameters of the large engine are determined continuously or at regular intervals to determine an optimized compression ratio of the air-fuel mixture based on the operating parameters. The compression ratio is adapted to the optimized compression ratio.

[0022] The compression ratio is a purely geometric ratio of the two volumes of the combustion chamber, where the first volume is the combustion chamber volume before the air-fuel mixture is compressed, and the second volume is the combustion chamber volume after the air-fuel mixture is compressed. Therefore, the first volume is the volume of the combustion chamber at the start of compression, while the second volume is the volume of the combustion chamber at maximum compression, i.e., when the piston is at top dead center.

[0023] Because the compression ratio is adjusted to an optimized level, large engines can operate with optimized efficiency across the entire load range. For example, in partial-load operation of a large engine, the compression ratio can therefore be increased compared to full-load operation, thereby increasing the efficiency of the large engine in partial-load operation.

[0024] In embodiments of the present invention, the compression ratio can be controlled or adjusted according to operating parameters. The advantage of controlling the compression ratio is that it can be flexibly adjusted to different environmental conditions, such as changes in fuel quality or variations in the operation of the turbocharger air cooler in a large engine.

[0025] In a very simple embodiment, for example, the optimized compression ratio can be stored in a lookup table as a function of the load operating the large engine. The operating parameter is then the load, and the optimized compression ratio for the corresponding current load for operating the large engine can be seen in this lookup table. The compression ratio is then adjusted to match this optimized compression ratio.

[0026] Several operating parameters are suitable as operating parameters, and based on these operating parameters, it is determined how to change the compression ratio, especially those compression ratios that are known in themselves or determined during the operation of large engines.

[0027] Preferably, the air-fuel ratio is adjusted such that it is between the knock limit and the non-ignition limit.

[0028] Therefore, using the method according to the invention, the compression ratio can be adapted to one or more operating parameters of a large engine, either continuously or at regular intervals. Optimal variation of the compression ratio leads to improved efficiency of the large engine.

[0029] According to a preferred embodiment, the operating parameter is the engine load or the rotational speed at which a large engine is running. The engine load is typically expressed as a percentage of full load.

[0030] According to another preferred embodiment, the operating parameters depend on the transient behavior of the large engine. For this purpose, for example, the transient characteristics of the large engine's torque or speed are determined. Variations in torque or speed can be used as operating parameters or integrated into the operating parameters, for example.

[0031] Another preferred embodiment is that the operating parameters depend on the ignition ratio, which is the ratio of the maximum pressure in the cylinder to the compression pressure in the cylinder. Here, the ignition ratio can be constant or dependent on the engine load or speed.

[0032] Additionally, ignition pressure can be used as an operating parameter. Ignition pressure is the maximum pressure in the cylinder during combustion. Ignition pressure can be constant or dependent on engine load and / or speed.

[0033] According to a particularly preferred embodiment, the ignition pressure or ignition ratio is adjusted to a predetermined value, for example, by means of a lookup table control or by means of a predetermined desired value (target value).

[0034] In embodiments of the invention, the operating parameter may also be an ignition pressure increment, and the ignition pressure increment may be constant or dependent on engine load and / or speed. Preferably, a predetermined maximum value for the ignition pressure increment should not be exceeded.

[0035] Emission parameters can be used as another operating parameter, where the emission parameters are particularly constant or dependent on engine load and / or speed. The compression ratio can also be controlled according to the emission parameters in the form of a predetermined value, or adjusted according to the desired emission value. Emission parameters can be particularly related to nitrogen oxides (NOx) and / or carbon dioxide (CO2) and / or carbon monoxide (CO) and / or oxygen (O2).

[0036] It is also possible that the operating parameters are transient characteristics, which are changes in load or speed, and the compression ratio is adjusted according to the operating parameters.

[0037] Of course, it is understood that more than one operating parameter can be used to change the compression ratio. Another preferred approach is to change the compression ratio if the operating parameter exceeds or falls below its limit value. Here, engine load, speed, ignition ratio, or emission parameters are particularly preferably combined with limit values, especially the ignition pressure increment or the maximum value of the ignition pressure.

[0038] In the method according to the invention, the compression ratio is preferably changed via hardware adaptation of a large engine. In practice, for this purpose, a large engine may include a rotatable crankshaft, wherein a piston is connected to a crosshead via a piston rod, and the crosshead is connected to the crankshaft via a thrust rod. The compression ratio is then changed by displacing the piston rod and / or the piston relative to the crosshead. Of course, other mechanical or hydraulic hardware adjustments known in the art can also be used to change the compression ratio.

[0039] In practice, operating parameters can be continuously or at regular intervals using sensors. For this purpose, sensors can be virtual or real. A virtual sensor is not a real sensor, but rather a simulation of the compliance of a representative measured variable with the target variable. Therefore, the target variable is not directly measured, but rather calculated based on its associated measured variables and relevant models.

[0040] Furthermore, the method according to the invention enables the minimization of vibrations, particularly torsional vibrations, in large engines throughout their entire operating range or load range. Torsional vibrations occur especially in a particular number of cylinders. Torsional vibrations are primarily determined by the cylinder pressure process. Ignition pressure and compression pressure are the decisive factors.

[0041] To achieve the best possible fuel consumption, high ignition and compression pressures are required. However, this leads to increased excitation of torsional vibrations, especially in the low-load range of large engines.

[0042] If the compression ratio is changed as an operating parameter according to the engine load, overall vibration, especially torsional vibration, can be minimized by increasing the compression ratio within a predetermined load range. Preferably, the compression ratio is increased or decreased in advance by control or adjustment at engine loads below or above a certain level, particularly 15% of the engine load.

[0043] Furthermore, the present invention proposes a large engine that operates according to the method of the present invention.

[0044] Preferably, the large engine is designed as a longitudinally scavenging two-stroke large diesel engine.

[0045] Particularly preferably, the large engine is designed as a dual-fuel large diesel engine capable of operating in liquid mode, wherein liquid fuel is introduced into the combustion chamber for combustion, and further capable of operating in gas mode, wherein gas is introduced into the combustion chamber as liquid or gaseous fuel.

[0046] In practice, a large engine may include at least one cylinder having a combustion chamber defined by a piston arranged to move back and forth along the cylinder axis; and a rotatable crankshaft and an inspection device, wherein the piston is connected to a crosshead via a piston rod, and the crosshead is connected to the crankshaft via a thrust rod, and the inspection device includes a thrust device capable of displacing the position of the piston rod and / or the piston relative to the crosshead. Attached Figure Description

[0047] The invention will be explained in more detail below with reference to embodiments and the accompanying drawings, particularly in terms of apparatus and process engineering. The drawings show: Figure 1 This is a schematic cross-sectional representation of an embodiment of a large engine according to the present invention; Figure 2 This is a schematic representation illustrating the dependence of torque on the air-gas ratio in embodiments of a large engine; and Figure 3 It is a schematic representation of the pressure inside the cylinder. Detailed Implementation

[0048] The term "large engine" refers to an engine that is typically used as the main propulsion unit of a ship or for stationary operation, such as driving a large generator to produce electricity. Typically, the cylinders of a large engine each have an inner diameter (cylinder bore) of at least about 200 mm. The term "longitudinal scavenging" refers to the introduction of scavenging or pressurized air into the lower region of the cylinder. Combustion residues, i.e., particularly exhaust gases, are discharged at the upper end of the cylinder.

[0049] In the following description of the invention based on embodiments, reference is made, by way of exemplary nature, to the case of large engines that are particularly important for practice, designed as dual-fuel engines, i.e., engines capable of operating with two different fuels. Specifically, this embodiment of the large engine can operate in liquid mode, in which only liquid fuel is injected into the combustion chamber of the cylinder. Typically, liquid fuel, such as heavy fuel oil or diesel, is injected directly into the combustion chamber at the appropriate time and ignited there according to the self-ignition principle of diesel fuel. The large engine can also operate in gas mode, in which the gas used as fuel, such as natural gas, is ignited in the combustion chamber as a premixed air-fuel mixture. In gas mode, the large engine operates particularly according to a low-pressure method, i.e., the gas is introduced into the cylinder in a gaseous state, wherein the injection pressure of the gas is at most 50 bar, preferably at most 20 bar. The air-gas mixture is spark-ignited in the combustion chamber according to the Otto principle. This spark ignition is typically achieved by introducing a small amount of self-igniting liquid fuel (such as diesel or heavy fuel oil) into the combustion chamber or pre-combustion chamber at the appropriate time, which then self-ignites and causes spark ignition of the air-fuel mixture in the combustion chamber.

[0050] In the embodiments described herein, the large engine is designed as a longitudinally scavenged dual-fuel two-stroke large diesel engine.

[0051] It should be understood that this invention is not limited to this type of large engine and this application, but generally refers to large engines. Therefore, it is also possible that a large engine is designed solely for burning a single gaseous fuel, such as natural gas. This means that a large engine can also be designed as a gas turbine engine. It is also possible that a large engine is designed as a multi-fuel engine, designed for the combustion of two or more fuels, particularly for the simultaneous combustion of two or more different fuels, even in different cylinders.

[0052] Figure 1 One of the cylinders in this embodiment of a large engine, generally indicated by reference numeral 20, is shown in a highly schematic illustration. Inside cylinder 21, piston 23 is arranged in a manner known per se to be able to move back and forth between top dead center and bottom dead center.

[0053] The structure and various components of the large engine 20, such as the injection system for liquid mode, the gas supply system for gas mode, the gas exchange system, the exhaust system or turbocharger system for providing scavenging or boosting air, and the inspection and control system for the large engine, are well known to those skilled in the art in both two-stroke and four-stroke engine designs, and therefore require no further explanation here. Among these components, in Figure 1Only one exhaust valve 24 is shown, as this is sufficient to understand the invention. In modern large engines, the inspection and control system is an electronic system, which typically allows for the adjustment or control of all engine or cylinder functions, particularly injection (initiation and termination of injection) and the actuation of exhaust valves.

[0054] In the embodiment of the longitudinally scavenging two-stroke large diesel engine 20 described herein, scavenging channels 22 are typically located in the lower region of each cylinder 21 or cylinder liner, and are periodically closed and opened by the movement of the piston 23 within the cylinder 21, allowing scavenging air supplied by the turbocharger at the boost air pressure in the intake receiver 26 to flow into the cylinder 21 through the scavenging channels 22, as long as they are open. This is in Figure 1 The figure is indicated by two arrows marked with the reference numeral L. A centrally located exhaust valve 24 is disposed in the cylinder head or cylinder head cover, through which combustion gases are discharged from cylinder 21 into exhaust system 25 after combustion. Exhaust system 25 directs at least a portion of the combustion gases to the turbine (not shown) of the turbocharger, whose compressor provides boost air to the intake receiver 26 under the action of boost air pressure. The boost air pressure is typically regulated via a so-called wastegate valve, which regulates the amount of combustion gases supplied to the turbocharger.

[0055] One or more fuel nozzles (not shown) are provided for introducing liquid fuel into the combustion chamber of cylinder 21, said fuel nozzles being arranged, for example, in the cylinder head and near exhaust valve 24. A gas supply system (not shown) including at least one intake valve with a gas inlet nozzle is provided for gas supply in gas mode. The gas inlet nozzle is typically disposed in the cylinder wall, for example, at a height approximately midway between the top dead center and bottom dead center of piston 23.

[0056] exist Figure 1 Various crank angles are additionally indicated on the left-hand side. The crank angles indicate the crankshaft position and mark the working cycle of the large diesel engine 20 in a manner known per se. The piston 23 is at bottom dead center (BDC) or reversing point at a crank angle of 180°, and at top dead center (TDC) or reversing point at a crank angle of 360°. If designed as a two-stroke engine, the entire working cycle comprises 360°. Starting from a crank angle of 0°—at which point the piston 23 is in the same position as at 360°, i.e., at TDC—the piston 23 moves downward during the expansion stroke until it reaches BDC at 180°, and then moves upward again during the compression stroke until it reaches TDC at 360°. Figure 1 In the illustration, piston 23 is currently in a position corresponding to crank angle 270°.

[0057] The following text will further illustrate the application of large diesel engines as the drive unit of ships through examples.

[0058] Due to legal regulations regarding exhaust emission levels, large diesel engines near the coast today are often required to operate in gas mode, as they would otherwise no longer meet the prescribed limits for exhaust emissions, particularly nitrogen oxides (NOx) and sulfur oxides.

[0059] This invention relates in particular to the operation of a large engine 20 in gas mode.

[0060] In gas mode, the efficiency and combustion of the air-fuel mixture with the lowest possible emissions are sensitively dependent on the ratio of the amount of air to the amount of gas used as fuel. This air-fuel ratio is typically represented by the Lambda value (λ value), which represents the ratio of the mass of air trapped in the cylinder to the mass of air required for stoichiometric combustion.

[0061] Figure 2 A schematic diagram illustrates an exemplary relationship between the air-fuel ratio 1 and the torque 2 generated by the engine propelling the ship. This representation applies to a specific torque corresponding to a specific speed of the ship—or a specific engine speed—when the ship is moving in substantially calm water. In particular, Figure 2 The torque 2 shown is BMEP (Brake Mean Effective Pressure), which is essentially the torque averaged over the working cycle.

[0062] exist Figure 2 The diagram shows two limiting curves for the gas mode: the knock limit (knock curve) 3 and the no-ignition limit (no-ignition curve) 4. In operating conditions outside the knock limit 3, as illustrated, such as at point B, the air-fuel mixture is too rich, meaning there is too little air in the mixture. This overly rich mixture can lead to various problems, such as combustion occurring too quickly (rapid combustion), engine knocking, or the mixture in cylinder 21 starting to burn prematurely (relative to the working cycle) due to the high gas content (pre-ignition). In operating conditions above the no-ignition limit 4, as illustrated, such as at point C, the air-fuel mixture is too lean, meaning there is neither enough gas—or too much air—for optimal combustion in the combustion chamber.

[0063] Therefore, efforts are made to always operate large diesel engines at the optimal air-fuel ratio point of 5, especially in gas mode, i.e. Figure 1 For example, at operating point A. In reality, even at a constant ship rotation speed or constant speed, natural fluctuations in torque or air-fuel ratio 1 cannot be avoided or regulated. Therefore, a tolerance range 6 exists, which is within... Figure 2 The tolerance is defined by two straight lines 7 and 8, within which the air-fuel ratio 1 is allowed to deviate from the optimal point 5.

[0064] Therefore, we always strive to adjust the air-fuel ratio for each torque to ensure that large engines operate within a tolerance range of 6.

[0065] According to the present invention, it is now proposed to continuously or at regular intervals detect the operating parameters of a large engine and determine an optimized compression ratio based on the operating parameters, which enables the highest possible efficiency to be achieved under the current load on which the large engine is operating. For example, within a partial load range, the compression ratio can be increased, resulting in a higher final compression temperature, whereby the air-fuel ratio does not change significantly.

[0066] However, if wastegate margin is available, the air-fuel ratio can be further increased, thereby allowing for further efficiency potential through a further increase in the compression ratio. Exhaust bypass, the mass flow of exhaust gas that bypasses the turbocharger's turbine, is typically regulated or adjusted via a wastegate valve, which can be designed as a similar valve, for example.

[0067] The change in compression ratio is preferably made mechanically by shifting or moving the piston rod and / or piston relative to the crosshead, thereby changing the geometry of the combustion chamber, for example in a crosshead-driven engine.

[0068] In this way, large engines can operate with optimized efficiency across any load range, making them particularly efficient and economical to operate.

[0069] As operating parameters determined continuously or at regular intervals, some parameters are preferred, and these parameters are explained in the non-exhaustive list below.

[0070] For example, the engine load (expressed as a percentage of full load) during the operation of a large engine can be used as an operating parameter. Based on the engine load, the compression ratio can preferably be adjusted to the optimal efficiency within a tolerance range of 6 using a lookup table, or the compression ratio can be controlled accordingly.

[0071] The operating speed of the large engine 20 can also be used as an operating parameter. Depending on the speed, the compression ratio can preferably be adjusted to the optimal efficiency within a tolerance range of 6 via a lookup table, or optionally controlled accordingly.

[0072] Another possibility is to use the ignition pressure within cylinder 21 as the operating parameter. (Reference) Figure 3 Here's an example to explain this situation. Figure 3A schematic diagram of the cylinder pressure p within cylinder 21, depending on the crank angle KW, is shown. At crank angle KW1, exhaust valve 24 is closed and compression begins. At crank angle KW = 360°, the same as crank angle KW = 0°, piston 23 is at top dead center, i.e., the combustion chamber has minimum volume (maximum compression). Exhaust valve 24 opens at crank angle KW2. Curve 10 shows the pressure process in cylinder 21 without combustion, i.e., it represents the "geometric" compression caused solely by piston movement in cylinder 21. Curve 11 shows the pressure in cylinder 21 when combustion occurs. The difference between curves 10 and 11 thus represents the pressure difference caused by the combustion process.

[0073] The maximum value of curve 10 (which naturally lies at crank angle KW = 360°, corresponding to crank angle KW = 0°) is called the compression pressure PC. The maximum value of curve 11, which typically moves to crank angle KW = 360°, is called the ignition pressure PM. The ratio between the ignition pressure PM and the compression pressure PC, i.e., PM / PC, is then designated as the ignition ratio. The ignition ratio is a function of the λ value (i.e., the air-fuel mixture) and the ignition time and compression ratio. Generally, as the λ value increases, the ignition ratio decreases. Therefore, both ignition pressure and ignition ratio can be used as operating parameters.

[0074] Furthermore, the increase of curve 11 in the pressure range above PC (i.e., in the pressure range where combustion occurs) is also related to the air-fuel ratio, so the increase in ignition pressure (i.e., the pressure changes with the crank angle KW) can also be used as a control parameter.

[0075] Of course, it should be understood that more than one operating parameter can be used to change the compression ratio.

[0076] The large engine 20 may include a testing device with a thrust mechanism. If the piston 23 is connected to the crosshead via a piston rod, and the crosshead is connected to a rotatable crankshaft via a thrust rod (neither shown), the thrust mechanism can displace the position of the piston rod and / or piston relative to the crosshead, thereby changing the compression ratio.

Claims

1. A method of operating a large engine (20) comprising at least one cylinder (21) having a combustion chamber defined by a piston (23) movable back and forth along a cylinder axis, wherein an air-fuel mixture is compressed in the combustion chamber by the movement of the piston (23) at a compression ratio, and wherein operating parameters of the large engine (20) are determined continuously or at regular intervals, characterized in that, The optimal compression ratio for the air-fuel mixture is determined based on the operating parameters, and the compression ratio is adapted to the optimal compression ratio.

2. The method according to claim 1, wherein, The compression ratio is controlled based on the operating parameters.

3. The method according to claim 1, wherein, The compression ratio is adjusted according to the operating parameters.

4. The method according to any one of the preceding claims, wherein, The air-fuel ratio is adjusted such that it is between the knock limit (3) and the non-ignition limit (4).

5. The method according to any one of the preceding claims, wherein, The large engine (20) also includes a rotatable crankshaft, and the piston (23) is connected to a crosshead via a piston rod, and the crosshead is connected to the crankshaft via a thrust rod, wherein the compression ratio is changed by displacing the piston rod and / or the piston relative to the crosshead.

6. The method according to any one of the preceding claims, wherein, The operating parameters are engine load and / or speed.

7. The method according to any one of claims 1 to 6, wherein, The operating parameter is the ignition ratio, and the ignition ratio is in particular constant or depends on the engine load and / or speed.

8. The method according to any one of claims 1 to 7, wherein, The operating parameter is ignition pressure, and the ignition pressure is in particular constant or depends on engine load and / or speed.

9. The method according to any one of claims 1 to 8, wherein, The operating parameter is the ignition pressure increment, and the ignition pressure increment is in particular constant or depends on engine load and / or speed.

10. The method according to any one of claims 1 to 5, wherein, The operating parameters are emission parameters, and the emission parameters are in particular constant or dependent on engine load and / or speed.

11. The method according to any one of the preceding claims, wherein, The operating parameters are instantaneous behaviors, which are load changes or speed changes, and the compression ratio is adjusted according to the operating parameters.

12. The method according to any one of the preceding claims, wherein, The large engine (20) operates in gas mode.

13. The method according to any one of the preceding claims, wherein, The operating parameters are detected continuously or at regular intervals by sensors, and the sensors are either virtual or real sensors.

14. A large engine, characterized in that, The large engine (20) operates according to the method according to any one of the preceding claims.

15. The large engine according to claim 14, the large engine comprising at least one cylinder (21) having a combustion chamber defined by a piston (23) arranged to be movable back and forth along the cylinder axis; and a rotatable crankshaft and an inspection device, wherein the piston (23) is connected to a crosshead via a piston rod and the crosshead is connected to the crankshaft via a thrust rod, and the inspection device comprises a thrust device capable of displacing the position of the piston rod and / or the piston (23) relative to the crosshead.

16. The large engine according to claim 14 or 15, wherein the large engine is designed as a dual-fuel large diesel engine, the dual-fuel large diesel engine being capable of operating in a liquid mode in which liquid fuel is introduced into the combustion chamber for combustion, and the dual-fuel large diesel engine being further capable of operating in a gas mode in which gas is introduced into the combustion chamber.

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