Method of operating large-sized engine and large-sized engine

Abstract

To propose a method of operating a large-sized engine.SOLUTION: A large-sized engine 20 comprises at least one cylinder 21. The cylinder 21 has a combustion chamber surrounded by a piston 23 capable of operating in a fore-and-aft direction along a cylinder shaft. An air / fuel mixture is compressed through the operation of the piston 23 while having a compression ratio in the combustion chamber. An operation parameter of the large-sized engine 20 is determined continuously or at fixed intervals. The optimized compression ratio for the air / fuel mixture is determined on the basis of the operation parameter, and the compression ratio is adapted to the optimized compression ratio.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for operating a large engine having at least one cylinder and to a large engine according to the preambles of the independent claims of the respective categories. [Background technology]

[0002] Large engines, e.g. as large longitudinally scavenged two-stroke diesel engines, which can be designed as two-stroke or four-stroke engines, are often used as drive units for ships or even in stationary operation, e.g. to drive large generators for producing electrical energy. The engines usually operate in continuous operation for considerable periods of time, which imposes high demands on the safety and availability of the operation. As a result, particularly long maintenance intervals, low wear and economical handling of the operating materials are central criteria for operators. Large engines typically have a cylinder, the inside diameter (bore) of which is at least 200 mm. Nowadays, large engines with bores of up to 960 mm or even more are used.

[0003] Different types of large engines are known, each of which can be designed as a two-stroke or four-stroke engine. There is also a need to replace the heavy fuel oil or diesel traditionally used as fuel for large engines, with regard to economical and efficient operation, compliance with emission thresholds and resource availability. In this respect, both liquid fuels, i.e. fuels introduced into the combustion chamber in liquid form, and gaseous fuels, i.e. fuels introduced into the combustion chamber in gaseous form, are used.

[0004] Examples of liquid fuels as known alternatives to heavy oils are other heavy hydrocarbons that are residues from oil refining, alcohols, especially methanol or ethanol, gasoline, diesel or emulsions or suspensions. For example, emulsions known as MSAR (Multiphase Superfine Atomized Residue) are known to be used as fuels. A known suspension is a suspension of coal dust and water, which is also used as fuel for large engines. Natural gases, such as LNG (Liquefied Natural Gas) or LPG (Liquefied Petroleum Gas), are known as gaseous fuels.

[0005] Another known alternative to pure operation with heavy fuel oil is to design large engines so that they can be operated with more than one fuel and, depending on the operating situation or environment, the engine can be operated with one fuel or the other. Large engines of this kind are also called large multi-fuel engines and can be switched during operation from a first mode in which a first fuel is burned to a second mode in which a second fuel is burned and vice versa.

[0006] Large engines are also known that can be operated simultaneously with at least two different fuels, where the two different fuels can be burned simultaneously in one or more cylinders, or it is possible that in a first group of cylinders only a first fuel is burned, while in another group of cylinders only a second fuel different from the first fuel is burned.

[0007] A well-known design of large engines capable of operating with two different fuels is the type of engine for which the term "dual fuel engine" is used today. These engines can operate, on the one hand, in a gas mode, where a gas fuel, for example natural gas or methane, is introduced into the combustion chamber for combustion, and, on the other hand, in a liquid mode, where a liquid fuel, such as heavy fuel oil or other liquid fuel, can be burned in the same engine. These large engines can be both two-stroke and four-stroke engines, in particular longitudinally scavenged two-stroke large diesel engines.

[0008] Large engines capable of operating with at least two or more different liquid or gaseous fuels often operate in different modes depending on the fuel currently in use. In the operating mode often referred to as diesel operation, the combustion of the fuel generally occurs according to the principle of compression ignition or autoignition of the fuel. In the mode often referred to as Otto operation, the combustion occurs by spark ignition of a combustible premixed air-fuel mixture. This spark ignition can occur, for example, by an electric spark, for example by means of a spark plug, or by autoignition of a small amount of injected fuel, which then causes the spark ignition of the other fuel. A small amount of fuel intended to autoignite is often injected into a pre-combustion chamber connected to the combustion chamber.

[0009] In the dual fuel engines mentioned above, for example, it is known that for the gas mode, gas in gaseous state is mixed with scavenging air to generate a combustible mixture in the combustion chamber of the cylinder. In this low pressure process, ignition of the mixture in the cylinder usually occurs by injecting a small amount of liquid, self-igniting fuel into the combustion chamber or pre-combustion chamber of the cylinder at the right time, which in turn leads to the ignition of the air-gas mixture.

[0010] Furthermore, there exist mixed forms known from Otto and Diesel operation.

[0011] Large engines which are designed as pure gas engines, i.e. engines which run exclusively on gas as fuel, are also known.

[0012] Whether it is a dual fuel engine or a pure gas engine, the process of introducing gas fuel into the combustion chamber of the cylinder and creating an air-gas mixture is important for the reliable, low-emission and safe operation of this type of engine.

[0013] In gas mode, the regulation of the correct ratio of scavenging air to gas, i.e. the air-fuel ratio, is particularly important. The air-fuel ratio can be indicated, for example, by a lambda value (λ value), which indicates the ratio of the air mass trapped in the cylinder to the air mass required for stoichiometric combustion. In large diesel engines, the scavenging or charge air is usually provided by a turbocharger, which generates a scavenging or charge pressure that depends on the load of the engine and therefore on the power or torque or rotational speed of the engine. For a given charge pressure, the amount of air in the cylinder can be calculated and then for the respective required driving torque generated by the engine or for the desired rotational speed, the appropriate amount of gas fuel can be determined, which leads to an optimal combustion process for this operating condition.

[0014] Especially when the gas mode operates according to the Otto principle, the correct adjustment of the air-fuel ratio is crucial for the most clean, efficient and economical operation of the engine. 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 leads to engine knocking. If the air content is too high, the air-fuel mixture becomes too lean and misfires can occur, which of course also has a negative effect on the efficient and clean engine operation.

[0015] Therefore, especially for large engines in gas mode, an effort is made to keep the lambda value within the optimum range between the knock limit on the one hand and the misfire limit on the other hand, since otherwise abnormal combustion phenomena may occur, which may lead to damage to the large engine. For large engines operating in gas mode according to the Otto principle, the optimum lambda value may be, for example, between 2.0 and 3.0, preferably between 2.3 and 3.0. The limits for the lambda value may vary slightly depending on the load at which the engine operates.

[0016] Large engines are usually designed so that the compression ratio is optimized at 100% load point, i.e. full load, so that they have the best possible compromise between combustion behavior and efficiency, which means that they are designed to have the highest possible thermodynamic efficiency at 100% load point, i.e. full load and maximum speed.

[0017] The compression ratio is a geometric value that is the ratio of a first volume of a combustion chamber before compression of the air-fuel mixture to a second volume remaining in the combustion chamber after compression of the air-fuel mixture.

[0018] Optimizing the combustion behavior at the 100% load point means that the efficiency of large engines is no longer optimal in the lower load ranges, for example at lower and intermediate pressures. Summary of the Invention [Problem to be solved by the invention]

[0019] Starting from the prior art, the object of the present invention is therefore to propose a method for operating a large engine which allows the optimum possible efficiency of the large engine over the entire load range, whilst avoiding abnormal combustion phenomena, and furthermore to provide a corresponding large engine. [Means for solving the problem]

[0020] The subject matter of the invention which meets these objects is characterised by the features of the independent claims of each category.

[0021] Therefore, according to the invention, a method for operating a large engine is proposed, the large engine comprising at least one cylinder having a combustion chamber surrounded by a piston movable back and forth along a cylinder axis, an air-fuel mixture is compressed in the combustion chamber via piston movement with a compression ratio, operating parameters of the large engine are determined continuously or at regular intervals, and based on the operating parameters an optimized compression ratio for the air-fuel mixture is determined, the compression ratio is adapted to the optimized compression ratio.

[0022] The compression ratio is simply the geometric ratio of two volumes of the combustion chamber, the first volume being the volume of the combustion chamber before the compression of the air-fuel mixture and the second volume being the volume of the combustion chamber after the compression of the air-fuel mixture. Hence, the first volume is the volume of the combustion chamber at the beginning of compression and the second volume is the volume of the combustion chamber at maximum compression, i.e. when the piston is at top dead center.

[0023] Due to the fact that the compression ratio is adjusted to an optimized compression ratio, the large engine can be operated with optimized efficiency over the entire load range, for example at partial load operation of the large engine, the compression ratio can thus be increased compared to full load operation, thus increasing the efficiency of the large engine at partial load operation.

[0024] In an embodiment of the present invention, the compression ratio can be controlled or adjusted depending on the operating parameters. Controlling the compression ratio has the advantage that the compression ratio can be flexibly adjusted to different ambient conditions, for example changes in fuel quality or changes in the operation of the charge air cooler in a large engine.

[0025] In a very simple embodiment, for example, the optimized compression ratio can be stored in a look-up table as a function of the load at which the large engine operates. The operating parameter is then the load, and the optimized compression ratio for each current load at which the large engine operates can then be looked up in this look-up table. The compression ratio is then adapted to this optimized compression ratio.

[0026] Some operating parameters qualify as operating parameters based on which it is determined how the compression ratio is varied, in particular parameters that are known per se and are determined during operation of large engines.

[0027] Preferably, the air / fuel ratio is adjusted so that the air / fuel ratio is between the knock limit and the misfire limit.

[0028] Using the method according to the invention, the compression ratio can be adapted continuously or at regular intervals to one or more operating parameters of the large engine, an optimal change in the compression ratio leading to an increase in the efficiency of the large engine.

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

[0030] According to a further preferred embodiment, the operating parameter depends on the transient behavior of the large engine. For this purpose, for example, the transient behavior of the torque or the rotation speed of the large engine is determined. The change in the torque or the rotation speed can then be used as the operating parameter or, for example, can be incorporated into the operating parameter.

[0031] Another preferred embodiment is that the operating parameter depends on the spark ratio, which is the ratio of the maximum pressure in the cylinder to the compression pressure in the cylinder, where the spark ratio can be constant or can depend on the engine load or on the rotational speed.

[0032] Furthermore, the ignition pressure can be used as an operating parameter. The ignition pressure is the maximum pressure in the cylinder during combustion. The ignition pressure may in particular be constant or may depend on the engine load and / or rotation speed.

[0033] According to a particularly preferred embodiment, the ignition pressure or the ignition ratio is regulated to a predefined value, for example controlled by a look-up table or regulated by a predeterminable target value.

[0034] In an embodiment of the invention, the operating parameter may also be the increase in ignition pressure, which may in particular be constant or may depend on the engine load and / or on the rotational speed. Preferably, a maximum value is predetermined for the increase in ignition pressure which must not be exceeded.

[0035] Emission parameters can be used as further operating parameters, whereby the emission parameters are in particular constant or dependent on the engine load and / or on the rotational speed. The compression ratio can also be controlled in dependence on the emission parameters in the form of a predefined value or can be adjusted in dependence on the emission target value. The emission parameters can in particular be nitrogen oxides (NO X ) and / or carbon dioxide (CO2) and / or carbon monoxide (CO) and / or oxygen (O2).

[0036] It is also possible that the operating parameter is a transient behavior, a load change or a rotational speed change, and the compression ratio is adjusted depending on the operating parameter.

[0037] Of course, it should be understood that multiple operating parameters can be used to vary the compression ratio. Another preferred measure is to vary the compression ratio when an operating parameter exceeds or falls below a limit value. Here, it is particularly preferred that engine load, rotational speed, ignition ratio or discharge parameters are combined with limit values, in particular with an increase in ignition pressure or a maximum value for the ignition pressure.

[0038] In the method according to the invention, the compression ratio is preferably varied by hardware adaptation of the large engine. For this purpose, in practice, the large engine may be equipped with a rotatable crankshaft, the pistons being connected to a crosshead via piston rods, and the crosshead being connected to the crankshaft via thrust rods. The compression ratio is then varied by displacing the piston rods and / or the pistons relative to the crosshead. Of course, other mechanical or hydraulic hardware adaptations known from the prior art can also be used to vary the compression ratio.

[0039] In practice, the operating parameters can be detected by sensors, either continuously or at regular intervals. For this purpose, the sensors can be virtual or real sensors. Virtual sensors are not real existing sensors, but simulations of the dependence of representative measurement variables on the target variable. The target variable is therefore not measured directly, but calculated based on the measurement variables correlated with it and a model of the correlation.

[0040] Furthermore, the method according to the invention makes it possible to minimize vibrations in large engines, in particular torsional vibrations, in the entire operating or load range of the large engine. Torsional vibrations are generated in particular by the specific number of cylinders. They are primarily determined by the cylinder pressure course. The ignition pressure and the compression pressure are decisive.

[0041] High ignition and compression pressures are required to achieve the best possible fuel consumption, however, they can also lead to increased excitation of torsional vibrations, especially in the low load range of large engines.

[0042] If the compression ratio varies as an operating parameter depending on the engine load, vibrations in general and torsional vibrations in particular can be minimized by increasing the compression ratio in a given load range. Preferably, it is predetermined by the control or regulation that the compression ratio is increased or decreased below or above a certain engine load, in particular at an engine load of 15%.

[0043] Furthermore, the invention proposes a large engine operated by the method according to the invention.

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

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

[0046] In practice, a large engine may comprise at least one cylinder, a rotatable crankshaft and an inspection device, the cylinder having a combustion chamber surrounded by a piston configured to be movable back and forth along a cylinder axis, the piston connected to a crosshead via a piston rod, the crosshead connected to the crankshaft via a thrust rod, and the inspection device comprising a thrust device capable of displacing the position of the piston rod and / or the piston relative to the crosshead.

[0047] Further advantageous measures and embodiments of the invention result from the dependent claims.

[0048] In the following, the invention, both as regards the device and the method engineering, will be explained in more detail on the basis of an embodiment and with reference to the drawings. [Brief description of the drawings]

[0049] [Figure 1] 1 is a schematic cross-sectional view of an embodiment of a large engine according to the present invention; [Diagram 2] FIG. 1 is a schematic diagram to illustrate the dependence of torque on air-gas ratio in a large engine embodiment. [Diagram 3] FIG. 2 is a schematic diagram of the pressure in a cylinder. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] The term "large engine" refers to an engine such as that normally used as the main drive unit for ships or, even in stationary operation, for example for driving large generators for producing electrical energy. Typically, the cylinders of a large engine each have an internal diameter (bore) of at least about 200 mm. The term "longitudinally scavenged" means that the scavenging or charge air is introduced into the cylinder in a region at the lower end. The combustion residues, i.e. especially the exhaust gases, are exhausted at the upper end of the cylinder.

[0051] In the following description of the invention based on an embodiment, by way of an exemplary nature, reference is made to the case of a large engine, which is of particular importance for the implementation, designed as a dual-fuel engine, i.e. an engine capable of operating with two different fuels. In particular, this embodiment of the large engine can be operated in a liquid mode, in which only liquid fuel is injected into the combustion chamber of the cylinder. Usually, the liquid fuel, for example heavy fuel oil or diesel oil, is injected directly into the combustion chamber at the appropriate time and ignites there according to the diesel principle of autoignition. The large engine can also be operated in a gas mode, in which a gas acting as fuel, for example natural gas, is ignited in the combustion chamber in the form of a premixed air-fuel mixture. In the gas mode, the large engine operates in particular according to the low-pressure method, i.e. the gas is introduced into the cylinder in gaseous state and 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 usually accomplished by introducing a small amount of self-igniting liquid fuel (e.g. diesel or fuel oil) into the combustion chamber or pre-combustion chamber at the right moment, which then self-ignites and causes spark ignition of the air-fuel mixture in the combustion chamber.

[0052] In the embodiment described herein, the heavy duty engine is designed as a longitudinally scavenged dual fuel two-stroke heavy duty diesel engine.

[0053] It should be understood that the present invention is not limited to this type of large engine and this use, but refers to large engines in general. It is therefore also possible that a large engine is designed only for burning a single gas fuel, for example natural gas. This means that the large engine can also be designed as a gas 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, in particular also for the simultaneous combustion of two or more different fuels in different cylinders.

[0054] 1 shows, in a highly diagrammatic view, one cylinder 21 of a plurality of cylinders in this embodiment of a large engine, which is designated as a whole by the reference numeral 20. Inside the cylinder 21 a piston 23 is arranged, in a manner known per se, so as to be movable back and forth between top and bottom dead centre.

[0055] The structure and individual components of the large engine 20, for example the injection system for the liquid mode, the gas supply system for the gas mode, the gas exchange system, the exhaust system or the turbocharger system providing scavenging or charging, and the test and control system for the large engine, both in the design as a two-stroke engine and in the design as a four-stroke engine, are well known to the person skilled in the art and therefore no further explanation is necessary here. Of these components, only one outlet valve 24 is represented in FIG. 1, because this is sufficient to understand the invention. In modern large engines, the test and control system is an electronic system, with which, usually, all engine or cylinder functions, in particular the injection (start and end of injection) and the operation of the outlet valve, are adjustable or controllable or regulatable.

[0056] In the embodiment of the longitudinally scavenged two-stroke large diesel engine 20 described here, scavenging slots 22 are usually provided in the lower region of each cylinder 21 or cylinder liner and are periodically opened and closed by the movement of the piston 23 of the cylinder 21, so that as long as the scavenging slots 22 are open, the scavenging air provided by the turbocharger under the charge pressure of the intake receiver 26 can flow through the scavenging slots 22 into the cylinder 21. This is indicated by two arrows provided with reference L in FIG. 1. In the cylinder head or cylinder cover, an almost centrally located outlet valve 24 is provided, through which the combustion gases can be discharged from the cylinder 21 after the combustion process into an exhaust system 25. The exhaust system 25 directs at least a part of the combustion gases to a turbocharger turbine (not shown), the compressor of which provides the charge air under the charge pressure into the intake receiver 26. The charge pressure is usually regulated via a so-called wastegate valve, which regulates the amount of burnt gases that are fed into the turbocharger.

[0057] One or more fuel injection nozzles (not shown) are provided for introducing liquid fuel into the combustion chamber of the cylinder 21, for example located near the outlet valve 24 in the cylinder head. A gas supply system (not shown) comprising at least one gas inlet valve with a gas inlet nozzle is provided for gas supply in gas mode. The gas inlet nozzle is typically provided in the wall of the cylinder, for example at approximately mid-height between the top and bottom dead centres of the piston 23.

[0058] In FIG. 1, various crank angles are further indicated on the left. The crank angles indicate the position of the crankshaft 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 or reversal point at a crank angle of 180°, and the piston 23 is at top dead center or reversal point at a crank angle of 360°. If designed as a two-stroke engine, the complete working cycle comprises 360°. Starting with a crank angle of 0° - at 0° the piston 23 is in the same position as at 360°, at top dead center - the piston 23 moves downwards during the expansion stroke until it reaches bottom dead center at 180° and then moves upwards again during the compression stroke until it reaches top dead center at 360°. In the drawing of FIG. 1, the piston 23 is currently in a position corresponding to a crank angle of 270°.

[0059] Reference will further be made below to the application, by way of example, where a large diesel engine is the drive unit of a ship.

[0060] Due to legal regulations regarding exhaust gas values, today large diesel engines on shore often have to operate in gas mode, because otherwise there are high risks for exhaust gas emissions, especially nitrogen oxides NO x and because the established limit values ​​for sulfur oxides can no longer be met.

[0061] The present invention is particularly concerned with the operation of the large engine 20 in gas mode.

[0062] In gas mode, the efficiency and combustion of the air-fuel mixture with the lowest possible emissions depends critically on the ratio between the amount of air and the amount of gas used as fuel, usually indicated by the lambda value, which indicates the ratio of the air mass trapped in the cylinder to that required for stoichiometric combustion.

[0063] Figure 2 shows in a schematic diagram an exemplary relationship between the air-fuel ratio 1 and the torque 2 generated by the engine to drive the ship. The drawing applies to a particular torque corresponding to a particular speed of the ship, or to a particular rotational speed of the engine when the ship is moving in substantially calm waters. In particular, the torque 2 shown in Figure 2 is the Brake Mean Effective Pressure (BMEP), which is essentially the torque averaged over the work cycle.

[0064] In the diagram of FIG. 2, two limit curves can be seen for the gas mode, namely the knock limit (knocking curve) 3 and the misfire limit (misfire curve) 4. In operating conditions to the left of the knock limit 3 according to the diagram, for example at point B, the air-fuel mixture is too rich, i.e. too little air is present in the mixture. A mixture that is too rich can lead to various problems, namely that combustion occurs too quickly (fast combustion) or the engine starts to knock or that the mixture in the cylinder 21 starts to burn too early (with respect to the working cycle) (pre-ignition), usually due to a high gas content. In operating conditions above the misfire limit 4 according to the diagram, i.e. for example at point C, the air-fuel mixture is too lean, i.e. there is not enough gas in the combustion chamber for optimal combustion - or there is too much air -.

[0065] For this purpose, in particular in gas mode, an effort is made to always operate large diesel engines at the optimum point 5 for the air-fuel ratio, i.e. for example at the operating point A in figure 2. In practice, natural fluctuations in the torque or the air-fuel ratio 1 cannot be avoided or accommodated even at constant rotational speed or constant speed of the ship, therefore there exists a tolerance range 6, delimited by the two straight lines 7 and 8 in figure 2, within which deviations of the air-fuel ratio 1 from the optimum point 5 are permitted.

[0066] For this reason, efforts are constantly being made to adjust the air-fuel ratio for each torque so that large engines operate within the tolerance range 6.

[0067] According to the invention, it is proposed to continuously or at regular intervals detect the operating parameters of the large engine and, based on the operating parameters, determine an optimized compression ratio, allowing the highest possible efficiency for the current load the large engine is operating in. For example, in the partial load range, the compression ratio can be increased, which results in a higher final compression temperature, whereby the air-fuel ratio does not change significantly.

[0068] However, if a wastegate margin is available, the air-fuel ratio can be increased further and, as a result, further efficiency potentials can be reached by further increasing the compression ratio. The exhaust bypass, i.e. the mass flow rate of the exhaust gases bypassing the turbocharger turbine, is usually regulated or adjusted by a wastegate valve, which can be designed, for example, as a similar valve.

[0069] The change in compression ratio is preferably achieved mechanically, for example in a crosshead driven engine, by displacing or moving the piston rod and / or piston relative to the crosshead, thereby changing the geometric dimensions of the combustion chamber.

[0070] In this way, the large engine can be operated with optimized efficiency over any load range, which allows for a particularly efficient and economical operation of the large engine.

[0071] Several parameters, described in the following non-exhaustive list, are preferred as operating parameters that are determined continuously or at regular intervals.

[0072] For example, the engine load at which a large engine operates, expressed as a percentage of full load, can be used as an operating parameter. Depending on the engine load, the compression ratio can be adjusted, preferably by a look-up table, for optimum efficiency within an acceptable range6, or alternatively can be controlled accordingly.

[0073] One can also use the rotational speed at which the large engine 20 operates as an operating parameter. Depending on the rotational speed, the compression ratio can be adjusted for optimum efficiency, preferably by means of a look-up table, within the tolerance range 6, or alternatively can be controlled accordingly.

[0074] Another possibility is to use the ignition pressure inside the cylinder 21 as the operating parameter. An example of this is explained with reference to FIG. 3. FIG. 3 shows a schematic diagram of the cylinder pressure p inside the cylinder 21 as a function of the crank angle KW. At the crank angle KW1, the outlet valve 24 is closed and compression starts. At the crank angle KW=360°, which is identical to the crank angle KW=0°, the piston 23 is at top dead center, i.e. the combustion chamber has a minimum volume (maximum compression). The outlet valve 24 is opened at the crank angle KW2. Curve 10 shows the pressure course in the cylinder 21 in the absence of combustion in the cylinder 21, i.e. the curve 10 represents that the "geometric" compression occurs solely due to the piston movement in the cylinder 21. Curve 11 shows the pressure in the cylinder 21 in the case that a combustion process occurs in the cylinder 21. The difference between the curves 10 and 11 therefore represents the pressure difference caused by the combustion process.

[0075] The maximum of curve 10 is, of course, at a crank angle KW=360°, which corresponds to a crank angle KW=0°, and is called the compression pressure PC. The maximum of curve 11 is usually displaced from the crank angle KW=360° and 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 the ignition ratio. The ignition ratio is a function of the lambda value, i.e. the air-fuel mixture, as well as the ignition time and the compression ratio. Usually, when the lambda value increases, the ignition ratio becomes smaller. Therefore, both the ignition pressure and the ignition ratio can be used as operating parameters.

[0076] Furthermore, since the increase in curve 11 in the pressure range above PC is also related to the air-fuel ratio, i.e. when combustion occurs, the increase in ignition pressure, i.e. the change in pressure depending on the change in crank angle KW, can also be used as a control parameter.

[0077] Of course, it should be appreciated that a number of operating parameters can be used to vary the compression ratio.

[0078] The large engine 20 may be equipped with an inspection device having a thrust device. If the piston 23 is connected via a piston rod to a crosshead, which in turn is connected via a thrust rod to a rotatable crankshaft (all not shown), the thrust device may displace the position of the piston rod and / or the piston relative to the crosshead so that the compression ratio is changed.

Claims

1. A method for operating a large engine, the large engine (20) comprising at least one cylinder (21) having a combustion chamber surrounded by a piston (23) movable back and forth along a cylinder axis, an air-fuel mixture is compressed in the combustion chamber through the movement of the piston (23) with a compression ratio, 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 based on the operating parameters, and the compression ratio is adapted to the optimized compression ratio, method.

2. The compression ratio is controlled in dependence on the operating parameters. The method of claim 1.

3. The compression ratio is adjusted depending on the operating parameters. The method of claim 1.

4. The air-fuel ratio is adjusted so that the air-fuel ratio is between a knock limit (3) and a non-ignition limit (4).

4. The method according to any one of claims 1 to 3.

5. The large engine (20) further comprises a rotatable crankshaft, the pistons (23) being connected to a crosshead via piston rods, the crosshead being connected to the crankshaft via thrust rods, and the compression ratio being varied by displacing the piston rods and / or the pistons relative to the crosshead.

5. The method according to any one of claims 1 to 4.

6. The operating parameters are engine load and / or rotational speed.

6. The method according to any one of claims 1 to 5.

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

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

9. the operating parameter being the increase in ignition pressure, the increase in ignition pressure being in particular constant or dependent on the engine load and / or on the rotational speed, 9. The method according to any one of claims 1 to 8.

10. the operating parameter is an emission parameter, the emission parameter being in particular constant or dependent on the engine load and / or on the rotational speed, 6. The method according to any one of claims 1 to 5.

11. The operating parameter is a transient behavior, which is a load change or a rotation speed change, and the compression ratio is adjusted depending on the operating parameter.

11. The method according to any one of claims 1 to 10.

12. The large engine (20) operates in gas mode.

12. The method according to any one of claims 1 to 11.

13. The operating parameters are detected continuously or at regular intervals by a sensor, the sensor being a virtual sensor or a real sensor.

13. The method according to any one of claims 1 to 12.

14. The large engine (20) is characterized in that it is operated according to a method according to any one of claims 1 to 13. Large engine.

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

14. A large engine according to claim 13.

16. the large engine is designed as a dual fuel large diesel engine and is operable in a liquid mode where liquid fuel is introduced into the combustion chamber for combustion, and further operable in a gas mode where gas is introduced into the combustion chamber; A large engine according to claim 13 or 14.

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