Large engine

Abstract

To provide a large engine hardly affected by knocking.SOLUTION: In a large engine including at least one cylinder 1 in which a piston 3 is arranged for a reciprocating movement along a cylinder axis A between a top dead center position and a bottom dead center position, the cylinder 1 comprises a cylinder cover 2, the piston 3 has a top face 31, the cylinder cover 2 and the top face 31 of the piston 3 define a combustion chamber for combustion of a fuel, and a cavity 6; 7 opening out into the combustion chamber 4 is provided in the cylinder cover 2. The cavity 6; 7 is configured as a resonance absorber to dampen a resonance frequency of the combustion chamber 4.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to large engines as described in the preamble of the independent patent claims.

Background Art

[0002] Large engines can be configured as large diesel engines that are normally operated with self-ignition of fuel, or as large Otto engines that are normally operated with induced ignition such as spark ignition or pilot ignition. Furthermore, large engines operating in a mixed mode, i.e., operating with both self-ignition and induced ignition of fuel, are known.

[0003] Large engines, designed as two-stroke or four-stroke engines, such as longitudinally scavenged two-stroke large diesel engines, are often used as drive units for ships or in stationary operation to drive, for example, large generators for generating electrical energy. The engines usually operate for a considerable period in continuous operation, which places high demands on operational safety and effectiveness. Therefore, particularly long maintenance intervals, low wear, and economic handling of the operating materials are the main criteria for engineers. Large engines typically have cylinders with an inner diameter (bore) of at least 200 mm. Today, large engines with a bore up to 960 mm or even larger bores are used. Within the framework of this application, the term "large engine" refers to an internal combustion engine having a bore of at least 200 mm, and preferably at least 300 mm, in the cylinders.

[0004] Large diesel engines have been operated with heavy fuel oil for a long time. Under the aspects of economic and efficient operation, compliance with exhaust gas limit values, and resource availability, alternatives to fuel heavy oil are also being sought for large diesel engines. In this regard, both liquid fuels, i.e., fuels introduced into the combustion chamber in a liquid state, and gaseous fuels, i.e., fuels introduced into the combustion chamber in a gaseous state, are used.

[0005] Known examples of liquid fuels as alternatives to heavy fuel oil include other heavy hydrocarbons, particularly those remaining as residues from oil refining, such as alcohols (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 fuel. A well-known suspension is a suspension of coal dust and water, which is also used as fuel for large engines. As for gaseous fuels, natural gas such as LNG (liquefied natural gas), liquefied gas such as LPG (liquefied petroleum gas), or ethane are known.

[0006] Specifically, there are also known large diesel engines that can be operated with at least two different fuels, in which case the engine is operated with one fuel or the other depending on the operating conditions or environment.

[0007] One example of a large diesel engine that can be operated with two different types of fuel is a large diesel engine configured as a dual-fuel large diesel engine. This engine can be operated in liquid mode, in which liquid fuel is introduced into the cylinders for combustion, and in gas mode, in which gas is introduced into the cylinders as fuel.

[0008] Large diesel engines, which can be operated with at least two or more different liquid or gaseous fuels, are often operated in different operating modes depending on the fuel currently in use. In the operating mode often called diesel operation, combustion of the fuel generally occurs according to the principles of compression ignition or autoignition of the fuel. In the mode often called Otto operation, combustion occurs by induced ignition of an easily ignitable premixed air-fuel mixture. For example, this induced ignition may be performed by an electric spark using a spark plug, for example, or by autoignition of a small injection amount of fuel that triggers induced ignition of another fuel. A small amount of fuel intended for autoignition is often injected into a pre-combustion chamber connected to the combustion chamber.

[0009] Furthermore, a hybrid configuration using both Otto and diesel operation is also known.

[0010] Within the framework of this application, the term “large diesel engine” means an engine that can be operated in at least diesel mode. Specifically, the term “large diesel engine” also includes a dual-fuel large engine that can be operated in another mode, such as Otto mode, in addition to diesel mode.

[0011] Therefore, the term "large engine" includes large diesel engines (as described above), large Otto engines, i.e., large gas engines that operate on gaseous fuel, large engines that can be operated solely by Otto operation, and large engines that can be operated in mixed mode. Mixed mode is a mode in which the engine is operated simultaneously by diesel operation and Otto operation.

[0012] Within the framework of this application, the terms “gas mode” or “operation in gas mode” mean using only gas or gaseous fuel as fuel for torque-generating combustion. As already stated, in gas mode for induced ignition of a premixed air-fuel mixture, a small amount of self-igniting liquid fuel, such as heavy oil, is injected to induce ignition; however, the torque-generating combustion process can and is very common to be carried out entirely using gas or gaseous fuel.

[0013] This process of induced ignition through the self-ignition of a small amount of liquid fuel is sometimes called pilot injection. This pilot injection is unrelated to the injection of liquid fuel into the combustion chamber when a large engine is operated in liquid mode. Usually, but not always, a different injection device is used for pilot injection than the one used for liquid fuel injection in liquid mode. In addition, in pilot injection, the small amount of liquid fuel is also often injected into at least one pre-combustion chamber connected to the combustion chamber via a channel, rather than being injected directly into the combustion chamber.

[0014] In particular, in gas mode, avoiding abnormal combustion processes is crucial for economical, efficient, and low-pollution operation, and such abnormal combustion processes occur especially when the ratio of scavenging air to gas, i.e., the air-fuel ratio, is outside a specific range.

[0015] If the gas content is excessively high, the air-fuel mixture becomes excessively rich. Combustion of the mixture may occur excessively rapidly or excessively early, for example, due to autoignition, which can lead to engine knocking. If the air content is excessively high, the air-fuel mixture becomes excessively lean, which can lead to misfires, and this also, of course, has a negative impact on the efficient and low-pollution operation of the engine. Specifically, these two conditions, excessively high gas content and excessively high air content, are designated as abnormal combustion processes. Therefore, in gas mode, efforts should be made to achieve a combustion process that does not involve autoignition of the air-gas mixture. The combustion process should take place within the limits where the air-gas mixture is neither excessively rich nor excessively lean.

[0016] In particular, the combustion process in gas mode is highly sensitive to the air-fuel ratio, making it extremely difficult, or even impossible, to completely avoid the knocking effects typically caused by an excessively rich air-gas mixture. An excessively rich mixture can lead to various problems, namely, combustion occurring too rapidly (rapid combustion), or the mixture, or at least a portion of the mixture, burning too early (in relation to the operating cycle) due to autoignition in the cylinder (premature ignition). Premature combustion of a portion of the compressed air-gas mixture due to undesirable autoignition causes strong pressure fluctuations around the mean cylinder pressure. These pressure fluctuations are detrimental to the engine, consequently increasing the mechanical load on various components of the engine and significantly limiting engine operation, for example, in terms of economical, efficient, and low-pollution operation. [Overview of the project] [Problems that the invention aims to solve]

[0017] Therefore, based on this condition in the art, the object of the present invention is to propose a large engine that is less susceptible to knocking. Accordingly, when knocking occurs, the harmful effects of knocking must be considerably reduced. [Means for solving the problem]

[0018] The subject matter of the present invention, which achieves this objective, is characterized by the structure of the independent patent claims.

[0019] Accordingly, the present invention proposes a large engine comprising at least one cylinder arranged inside such that a piston reciprocates along the cylinder axis between a top dead center position and a bottom dead center position, wherein the cylinder has a cylinder cover, the piston has an upper surface, the cylinder cover and the upper surface of the piston define a combustion chamber for the combustion of fuel, and a cavity leading to the combustion chamber is provided in the cylinder cover. The cavity is configured as a resonance absorber to dampen (attenuate, reduce) the resonant frequency of the combustion chamber.

[0020] For example, it has been found that knocking events occurring in a cylinder due to premature autoignition of at least a portion of the compressed air-gas mixture produce pressure oscillations with significant maximum values ​​within a fairly narrow frequency range. For instance, if the frequency maximum, which is in the range of 1000-1500 Hz, coincides with or is close to the natural frequency of the combustion chamber, the amplitude of the pressure oscillation is considerably increased due to the resonance effect. By providing a cavity configured as a resonance absorber to reduce the resonant frequency of the combustion chamber, the energy associated with the pressure pulsations caused by the knocking event is strongly dissipated, and as a result, the harmful effects of the knocking event are considerably reduced.

[0021] Since the geometry of the combustion chamber is known or can be measured, the resonant frequency of the combustion chamber can be determined with very little effort, for example, by calculation and / or by experimental measurements such as pressure measurements.

[0022] Therefore, a cavity configured as a resonant absorber is matched to the resonant frequency of the combustion chamber, which is either the maximum or close to the maximum in the frequency spectrum of knocking events in the combustion chamber, and as a result, pressure oscillations at this resonant frequency are significantly attenuated or completely suppressed. The resonant frequency of the combustion chamber can be determined by acoustic analysis of the system, which can be performed by measurement and / or calculation and / or simulation. Once the resonant frequency of the combustion chamber is known, the resonant absorber can be designed and configured to reduce pressure pulsations at this resonant frequency. The resonant absorber is configured to reduce the resonant frequency excited by knocking events occurring in the cylinder.

[0023] Naturally, it is also possible to provide multiple cavities, each configured as a resonance absorber to reduce the resonant frequency of the combustion chamber.

[0024] The resonance absorber is preferably configured to reduce the resonant frequency of the combustion chamber when the piston is at or near top dead center. Therefore, the resonant frequency of the combustion chamber is determined with respect to the piston position when the piston is at or near top dead center. Since the geometry of the combustion chamber changes with the movement of the piston, it is advantageous to determine the resonant frequency of the combustion chamber with respect to the piston position where regular combustion should begin. Typically, this is the position where the piston approaches top dead center during the compression stroke.

[0025] In practice, it has been proven advantageous for the resonant absorber to be configured to attenuate the tangential modes of the combustion chamber. Specifically, the resonant absorber is configured to attenuate the first tangential mode.

[0026] The resonance absorber is preferably configured as a Helmholtz resonator having a resonator volume portion and a resonator neck portion connected to the resonator volume portion. In this case, the resonator neck portion is in fluid communication with the combustion chamber. The Helmholtz resonator operates according to a spring-mass system, where the mass is represented by the gas in the resonator neck portion and the spring is represented by the gas in the resonator volume portion. Therefore, the natural frequency of the Helmholtz resonator depends on the geometry of the resonator neck portion and the volume of the resonator volume portion. Therefore, it is extremely easy to match the natural frequency of the Helmholtz resonator to the natural frequency of the combustion chamber.

[0027] According to a preferred embodiment, the cavity is configured to receive a starting air valve for supplying pressurized starting air to the combustion chamber. Therefore, in any case, it is preferable to configure at least one of the cavities provided in the cylinder cover as a resonance absorber. In this embodiment, the cavity in which the starting air valve for starting a large machine is arranged. The volume of the cavity between the starting air valve and the combustion chamber does not form a basis for strong functional limitations. Therefore, it is extremely simple to configure the cavity that receives the starting air valve as a resonance absorber.

[0028] Furthermore, in a preferred embodiment, the cavity is configured as a pre-combustion chamber for pilot combustion that causes combustion in the combustion chamber. In many large engines, especially large engines that can be operated in gas mode, at least one pre-combustion chamber is provided in the cylinder cover. Therefore, it is advantageous to configure the aforementioned pre-combustion chamber as a resonance absorber in order to weaken the resonance frequency of the combustion chamber. Even if the pre-combustion chamber is configured according to the combustion requirements regarding the volume and duration of the high-temperature jet generated by, for example, pilot injection, there are still sufficient free parameters regarding the geometry of the pre-combustion chamber for configuring the pre-combustion chamber as a resonance absorber.

[0029] Pilot combustion preferably causes combustion of the air-gas mixture in the combustion chamber. Therefore, pilot combustion is preferably used when the large engine is operated in gas mode.

[0030] Furthermore, the pre-combustion chamber is preferably configured to receive liquid fuel for self-ignition of the pilot combustion. Alternatively, the pilot combustion can be ignited by a spark.

[0031] According to a preferred embodiment, the pre-combustion chamber has a main volume part for pilot combustion and a tubular volume part for connecting the main volume part and the combustion chamber. The main volume part may be configured as the resonator volume part of a Helmholtz resonator, and the tubular volume part may be configured as the resonator neck part of a Helmholtz resonator.

[0032] According to another preferred embodiment, the pre-combustion chamber is configured as a two-volume Helmholtz resonator having a first resonator volume part, a second resonator volume part, a first resonator neck part, and a second resonator neck part, where the first resonator neck part connects the first resonator volume part and the second resonator volume part, and the second resonator neck part is connected to the second resonator volume part. In this configuration, the main volume part for pilot combustion may constitute the first resonator volume part. The main volume part is connected to a smaller volume part by a channel, and this smaller volume part is approximately spherical and constitutes the second resonator volume part. The channel connecting the main volume part and the smaller volume part constitutes the first resonator neck part. The smaller volume part is connected to the combustion chamber by an outlet that constitutes the second resonator neck part.

[0033] Therefore, with respect to this embodiment, the main volume part is preferably the first resonator volume part, where the tubular volume part has the second resonator neck part.

[0034] [[ID=,19]] The large engine is preferably configured as a large diesel engine.

[0035] The large engine is particularly preferably configured as a two-stroke large diesel engine that is scavenged in the longitudinal direction.

[0036] The large engine is preferably configured as a dual-fuel large diesel engine, which can be operated in liquid mode, in which liquid fuel is introduced into the combustion chamber for combustion, and can also be operated in gas mode, in which gas is introduced into the cylinder as fuel.

[0037] Further advantageous strategies and embodiments of the present invention arise from the dependent claims.

[0038] The present invention will be described in more detail below, based on examples and with reference to the drawings. [Brief explanation of the drawing]

[0039] [Figure 1] This is a schematic diagram of a cylinder in one embodiment of a large engine according to the present invention. [Figure 2] This is the frequency spectrum of a knocking event in a cylinder. [Figure 3] Figure 1 is a cross-sectional view of the pre-combustion chamber of the cylinder shown. [Figure 4] This is a schematic diagram of one embodiment of a pre-combustion chamber configured as a Helmholtz resonator. [Figure 5] This is a schematic diagram of one embodiment of a pre-combustion chamber configured as a two-volume section and a Helmholtz resonator. [Modes for carrying out the invention]

[0040] Figure 1 shows a schematic diagram of a cylinder in one embodiment of a large engine according to the present invention. The cylinder is shown as a whole by reference numeral 1. Cylinder 1 is part of an engine having multiple cylinders 1. The large engine may have 12, or even up to 14, cylinders 1. The large engine is configured, for example, as a two-stroke large diesel engine that is scavenged in the longitudinal direction.

[0041] Cylinder 1 has a cylinder cover 2, and an exhaust valve 5 for discharging exhaust gas from cylinder 1 is provided inside the cylinder cover 2. Inside cylinder 1, a piston 3 is arranged to reciprocate along the axial direction between the top dead center position and the bottom dead center position. The piston 3 has an upper surface 31, which together with the cylinder cover 2 and the cylinder wall or cylinder liner of cylinder 1 defines a combustion chamber 4, in which combustion of fuel takes place.

[0042] The term "large engine" refers to an internal combustion engine typically used in stationary operation as a drive unit for a ship, or, for example, to drive a large generator for generating electrical energy. Typically, the cylinders 1 of a large engine each have an inner diameter (bore) of at least 200 mm. The term "longitudinally scavenged" means that scavenging air or intake air is introduced into the cylinder 1 in the lower end region, and an exhaust valve 5 is located in or on the cylinder cover 2 at the upper end of the cylinder 1.

[0043] In the following description of the present invention, a large diesel engine will be referred to as an example for large engines. It should be noted that the present invention is not limited to large diesel engines and also includes other types of large internal combustion machines, such as large gas engines operated on LNG, for example, Otto engines that can only be operated in Otto mode.

[0044] Large diesel engines are designed as dual-fuel large diesel engines, that is, engines that can be operated with two different types of fuel. Specifically, a dual-fuel large diesel engine can be operated in liquid mode, in which only liquid fuel is injected into the combustion chamber 4 of cylinder 1. Typically, the liquid fuel, such as heavy oil or diesel oil, is injected directly into the combustion chamber 4 at an appropriate time for self-ignition, where it ignites according to the diesel principle of self-ignition.

[0045] Large diesel engines can also be operated in gas mode, in which a gas serving as fuel, such as natural gas (e.g., LNG, or LPG, or ethane), or ethane, is ignited in the combustion chamber in the form of a premixed air-fuel mixture. In gas mode, large diesel engines are preferably operated according to a low-pressure process, i.e., the gas is introduced into cylinder 1 in a gaseous state, thereby the gas injection pressure is at most 50 bar, preferably at most 20 bar, more preferably at most 16 bar, and particularly preferably at most about 10 bar. The air-gas mixture is induced ignition in the combustion chamber 4 according to the Otto principle. This induced ignition is usually caused by introducing a small amount of self-igniting liquid fuel (e.g., diesel oil or heavy oil) into the pre-combustion chamber 6 at the appropriate moment, and then this fuel self-ignites to cause induced ignition of the air-fuel mixture in the combustion chamber 4. In other embodiments, induced ignition is performed by spark ignition.

[0046] Within the framework of this application, as already explained above, the term “gas mode” or “operation in gas mode” should be understood as a large diesel engine operating in gas mode using only gas or gaseous fuel, where, if applicable, a small amount of self-igniting fuel, such as heavy oil or diesel oil, is introduced into one or more pre-combustion chambers 6 simply for the ignition of the air-gas mixture (pilot injection). Self-igniting combustion in the pre-combustion chambers 6 is called pilot combustion.

[0047] Furthermore, a dual-fuel large diesel engine can be operated in mixed mode, in which both liquid and gaseous fuels are injected into cylinder 1. In mixed mode, both the combustion of the self-igniting liquid fuel and the combustion of the induced-ignition gaseous fuel contribute to torque generation. For example, if a dual-fuel large diesel engine is operated in gas mode and the required torque cannot be generated by high-quality combustion of the gaseous fuel alone, an additional amount of liquid fuel is injected into cylinder 1 and burned to generate further torque to achieve the required torque.

[0048] Large engines, such as large diesel engines, are well known in this field, so a detailed explanation is unnecessary. Furthermore, as an example, this application, in which a large diesel engine is the main propulsion unit of a ship or large vessel, should be referenced.

[0049] As is known in the art, the piston 3 is connected to a crosshead (not shown) via a piston rod (not shown), which is connected to a crankshaft (not shown) via a push rod or connecting rod (not shown) so that the motion of the piston is transmitted to the crankshaft via the piston rod, the crosshead, and the connecting rod to rotate it.

[0050] In gas mode, the fuel for combustion is gas. For example, in a low-pressure process, gas is introduced into cylinder 1, preferably approximately midway between the top dead center and bottom dead center positions of the piston 3, through the cylindrical wall, i.e., the lateral region of each cylinder 1, or through the cylinder liner. Inside cylinder 1, the gas mixes with scavenging air during the compression motion of piston 3, thus forming an easily ignitable air-fuel mixture, which is then ignited when piston 3 is approximately at top dead center. Ignition is preferably achieved by injecting a self-igniting fuel, such as heavy oil or diesel fuel, into the pre-combustion chamber 6 of the cylinder. Pilot injection, i.e., injection of liquid fuel in gas mode that functions solely for the ignition of the air-gas mixture in the combustion chamber 4, is preferably performed by one or more pilot injection nozzles 61 distinct from the main injection nozzles that inject liquid fuel into the combustion chamber 4 in liquid mode.

[0051] In other embodiments, induced ignition can be caused by spark ignition, for example, by electrically generating a spark for igniting an air-fuel mixture.

[0052] The pre-combustion chamber 6 for pilot combustion is configured as a cavity within the cylinder cover 2, and the cavity is connected to the combustion chamber 4. The pre-combustion chamber 6 has a main volume section 62 in which pilot combustion takes place, and a tubular volume section 63 that connects the main volume section 61 to the combustion chamber 4.

[0053] During operation in gas mode, the air-gas mixture in the combustion chamber 4 is induced ignition. For the induced ignition of the air-gas mixture, a small amount of self-igniting fuel is injected into the main volume section 62 of the pre-combustion chamber 6 using a pilot injection nozzle 61, where the fuel self-ignites for pilot combustion. The resulting high-temperature jet is guided by a tubular volume section 63 into the combustion chamber 4, where it ignites the air-gas mixture in the combustion chamber 4. The fuel for pilot combustion in the main volume section 62 of the pre-combustion chamber 6 is preferably the same self-igniting fuel used for combustion in the combustion chamber 4 in liquid mode, such as heavy oil or diesel oil.

[0054] In liquid mode, only liquid fuel is injected into the combustion chamber 4 of the cylinder. Normally, the liquid fuel is injected directly into the combustion chamber at the appropriate time and ignites there according to the diesel principle of self-ignition.

[0055] In liquid mode, liquid fuel is supplied to the combustion chamber 4 by the main injection nozzle. As an option, additional liquid fuel can be introduced in liquid mode through the pilot injection nozzle 61. However, the maximum fuel flow rate through the pilot injection nozzle 61 is far too low to operate a large diesel engine in liquid mode on that fuel alone, so this optional measure primarily serves to prevent the pilot injection nozzle 61 from becoming clogged or blocked.

[0056] The structure and individual components of large diesel engines, such as injection systems for liquid mode, gas supply systems for gas mode, gas exchange systems, exhaust systems or turbocharger systems for supplying scavenging or intake air, and monitoring and control systems for large diesel engines, are well known to those skilled in the art for both two-stroke and four-stroke engine designs, and therefore do not need further explanation here.

[0057] In the embodiments of the longitudinally scavenged two-stroke large diesel engine described herein, scavenging air slots are typically located within the lower region of each cylinder 1 or cylinder liner, and these scavenging air slots are periodically opened and closed by the movement of the piston 3 in the cylinder, so that scavenging air supplied by the turbocharger under intake pressure can flow into the cylinder 1 as long as the scavenging air slots are open. An exhaust valve 5, typically located in the center, is provided within the cylinder cover 2, and exhaust gases can be discharged from the cylinder 1 into the exhaust system through the exhaust valve 5 after the combustion process. The exhaust system directs at least a portion of the exhaust gases to the turbocharger turbine, and the turbocharger compressor provides scavenging air, also called intake air, into the intake receiver under scavenging air pressure. The intake receiver is in fluid communication with the scavenging air slots of the cylinder.

[0058] For the introduction of liquid fuel into the combustion chamber 4 during liquid mode, one or more main injection nozzles (not shown) are provided, for example, located within the cylinder cover 2 near the exhaust valve 5. For gas supply during gas mode, a gas supply system (not shown) is provided, having at least one gas inlet valve including a gas inlet nozzle. Typically, the gas inlet nozzle is located on the cylinder wall, for example, at a height approximately midway between the top dead center and bottom dead center of the piston.

[0059] In modern large diesel engines, the monitoring and control systems are electronic systems, and typically, these electronic systems can set, control, or adjust all engine or cylinder functions, specifically injection (initiation and termination of injection) and the operation of the outlet valves.

[0060] Furthermore, cylinder 1 has a cavity 7 located within the cylinder cover 2 and connected to the combustion chamber 4. A starting air valve 8 is located within the cavity 7 to supply pressurized starting air to the combustion chamber 4. Starting large engines, such as large diesel engines, is usually done by injecting compressed air into cylinder 1 to move the piston 3 downward and start rotating the crankshaft. The so-called starting air is continuously supplied to cylinder 1 according to the engine's ignition sequence, but the injection of compressed starting air into the combustion chamber 4 of each cylinder 1 occurs each time the piston 3 is at or just past the top dead center position.

[0061] According to the present invention, at least one of the cavities 7 and 6 leading to the combustion chamber 4, for example, the cavity 7 for the starting air valve 8 or the cavity forming the pre-combustion chamber 6, is configured as a resonance absorber to reduce the resonant frequency of the combustion chamber 4.

[0062] The resonance absorber is preferably configured to attenuate the resonance frequency of the combustion chamber 4, which is either the maximum value or close to the maximum value of the frequency spectrum of the knocking event occurring in cylinder 1. Such knocking events are caused, for example, by undesirable premature autoignition of the air-gas mixture or a portion thereof during operation in gas mode. During the compression stroke of piston 3, it is possible that the compressed air-gas mixture in cylinder 1 may ignite at least partially by autoignition. Such knocking events cause strong pressure oscillations around the mean cylinder pressure in the combustion chamber 4 of cylinder 1.

[0063] Figure 2 shows a typical frequency spectrum of a knocking event in cylinder 1. The horizontal axis is plotted with frequency F, and the vertical axis is plotted with intensity I. It can be seen that there is a significant maximum value at frequency F0. When the aforementioned frequency F0 matches or is close to the resonant frequency of the combustion chamber 4, especially when the piston 3 is near the top dead center position, the pressure oscillation in the combustion chamber is considerably amplified due to the resonance effect. A typical value for frequency F0 is around 1 kHz. F0 is, for example, between 900 Hz and 1500 Hz.

[0064] The cavity 7 and / or pre-combustion chamber 6 are configured to attenuate the resonant frequency of the combustion chamber 4, which is at or near the frequency F0 where the maximum value of the frequency spectrum of the knocking event is located. The sound produced by the knocking event can be recorded and analyzed so that the frequency F0 can be determined.

[0065] The cavity 7 and / or pre-combustion chamber 6 are preferably configured as a Helmholtz resonator having a resonator volume section and a resonator neck section connected to the resonator volume section.

[0066] When the pre-combustion chamber 6 is configured as a Helmholtz resonator, the main volume section 62 of the pre-combustion chamber 6 constitutes the resonator volume section, and the tubular volume section 63 of the pre-combustion chamber 6 constitutes the resonator neck section of the Helmholtz resonator.

[0067] When the cavity 7 that receives the starting air valve 8 is configured as a Helmholtz resonator, the tapered volume section 72 of the cavity 7 adjacent to the starting air valve 8 constitutes the resonator volume section, and the tubular channel 73 of the cavity 7 connecting the tapered volume section 72 and the combustion chamber 4 constitutes the resonator neck of the Helmholtz resonator.

[0068] The following description refers to the pre-combustion chamber 6 configured as a Helmholtz resonator. It should be understood that these descriptions are equally or similarly applicable to the cavity 7 configured as a Helmholtz resonator. In some embodiments of the large engine, only the pre-combustion chamber 6 of cylinder 1 is configured as a Helmholtz resonator to reduce the resonant frequency of the combustion chamber 4. In other embodiments of the large engine, only the cavity 7 is configured as a Helmholtz resonator to reduce the resonant frequency of the combustion chamber 4. In yet another embodiment of the large engine, both the pre-combustion chamber 6 and the cavity 7 are configured as Helmholtz resonators to reduce the resonant frequency of the combustion chamber 4.

[0069] The basic principles of Helmholtz resonators 6 and 7 are well known in the art. Helmholtz resonators are used, for example, as silencers for noise protection or noise reduction. Helmholtz resonators 6 and 7 operate as vibration absorbers according to the principle of a spring-mass system. The mass of this system is represented by the gas in the resonator neck, for example, the tubular volume section 63 or the tubular channel 73. The spring is represented by the gas in the resonator volume section, for example, the main volume section 62 or the tapered volume section 72. Therefore, by adjusting the volume of the resonator volume section and / or the geometry of the resonator neck, the natural frequencies of Helmholtz resonators 6 and 7 can be matched to predetermined or desired values, such as the resonant frequency of the combustion chamber 4 when the piston 3 is at or near top dead center.

[0070] The natural frequencies of the Helmholtz resonators 6 and 7 are adjusted to correspond to the resonant frequencies of the combustion chamber 4 that are at or close to frequency F0, the frequency at which pressure pulsation is caused by knocking events. The pressure pulsation at this natural frequency of the Helmholtz resonators 6 and 7 is considerably reduced.

[0071] Figure 3 shows a more detailed cross-sectional view of one embodiment of the pre-combustion chamber 6 of the cylinder 1 shown in Figure 1. The pre-combustion chamber 6 has a main volume section 62 into which a pilot injection nozzle 61 injects liquid fuel for pilot combustion, and a tubular volume section 63 that connects the main volume section 62 to the combustion chamber 4. The tubular volume section 63 has a spherical volume section 631, a channel 632, and an outlet 633. The channel 632 connects the main volume section 62 and the spherical volume section 631, and the outlet 633 connects the spherical volume section 631 to the combustion chamber 4.

[0072] The configuration of the pre-combustion chamber 6, which has a main volume section 62 for pilot combustion, a channel 632, a spherical volume section 631, and an outlet 633, provides the possibility to optimize the pre-combustion chamber 6 with respect to combustion requirements so that the high-temperature jet generated by pilot combustion in the main volume section 62 of the pre-combustion chamber 6 efficiently and reliably ignites the air-gas mixture in the combustion chamber 4 during operation in gas mode.

[0073] Nevertheless, there are still plenty of free parameters available to adjust the natural frequency of the pre-combustion chamber 6, which is designed as a Helmholtz resonator, to the desired resonant frequency.

[0074] According to the first modification shown in the schematic diagram of Figure 4, the pre-combustion chamber 6 is considered a simple Helmholtz resonator, where the main chamber 62 constitutes the resonator volume section and the tubular volume section 63 constitutes the resonator neck section of the Helmholtz resonator. The geometric dimensions of the pre-combustion chamber 6 are modified insofar as the natural frequency of the pre-combustion chamber 6 corresponds to the desired resonant frequency to be attenuated without compromising reliable induced ignition of the air-gas mixture in the combustion chamber 4. Such calculations are readily available to those skilled in the art.

[0075] According to the second modification shown in the schematic diagram of Figure 5, the pre-combustion chamber 6 is considered to be a two-volume Helmholtz resonator having a first resonator volume section, a second resonator volume section, a first resonator neck section, and a second resonator neck section, where the first resonator neck section connects the first resonator volume section and the second resonator volume section, and the second resonator neck section connects to the second resonator volume section. The main volume section 62 of the pre-combustion chamber 6 constitutes the first resonator volume section, the spherical volume section 631 constitutes the second resonator volume section, the channel 632 constitutes the first resonator neck section connecting the main volume section 62 and the spherical volume section 631, and the outlet 633 constitutes the second resonator neck section connecting the spherical volume section 631 to the combustion chamber 4. Furthermore, in the case of such a two-volume Helmholtz resonator, the natural frequencies are very easy to calculate for a given geometry.

Claims

1. A large engine having at least one cylinder (1), in which a piston (3) is arranged for reciprocating movement along a cylinder axis (A) between a top dead center position and a bottom dead center position, the cylinder (1) having a cylinder cover (2), the piston (3) having an upper surface (31), the cylinder cover (2) and the upper surface (31) of the piston (3) defining a combustion chamber for combustion of fuel, a cavity (6; 7) being provided in the cylinder cover (2) leading into the combustion chamber (4), A large engine, characterized in that the cavity (6; 7) is configured as a resonance absorber for damping the resonance frequencies of the combustion chamber (4).

2. 2. A large engine according to claim 1, wherein the resonance absorber is configured to dampen the resonance frequency of the combustion chamber (4) with the piston (3) at or near the top dead center position.

3. A large engine according to claim 1, wherein the resonance absorber is configured to dampen circumferential modes of the combustion chamber (4).

4. 2. The engine of claim 1, wherein the resonance absorber is configured as a Helmholtz resonator having a resonator volume and a resonator neck connected to the resonator volume, the resonator neck being in fluid communication with the combustion chamber.

5. 2. A large engine according to claim 1, wherein the cavity (7) is adapted to receive a starting air valve (8) for supplying pressurized starting air to the combustion chamber (4).

6. 2. A large engine according to claim 1, wherein the cavity is configured as a pre-combustion chamber (6) for a pilot combustion that initiates the combustion in the combustion chamber (4).

7. 7. A large engine according to claim 6, wherein said pilot combustion initiates said combustion of an air-gas mixture in said combustion chamber (4).

8. 7. A large engine according to claim 6, wherein the pre-combustion chamber (6) is adapted to receive liquid fuel for auto-ignition of the pilot combustion.

9. 7. A large engine according to claim 6, wherein the pre-combustion chamber (6) comprises a main volume (62) for the pilot combustion and a tubular volume (63) for connecting the main volume (62) with the combustion chamber (4).

10. 10. The large engine according to claim 9, wherein the pre-combustion chamber (6) is configured as a two-volume Helmholtz resonator having a first resonator volume, a second resonator volume, a first resonator neck, and a second resonator neck, the first resonator neck connecting the first resonator volume and the second resonator volume, and the second resonator neck connecting the second resonator volume.

11. 11. A large engine according to claim 10, wherein said main volume (62) is said first resonator volume and said tubular volume (63) comprises said second resonator neck.

12. 12. A large engine according to any one of claims 1 to 11, configured as a large diesel engine.

13. 12. A large engine according to any one of claims 1 to 11, configured as a longitudinally scavenged, two-stroke large diesel engine.

14. 12. A large engine according to any one of claims 1 to 11, configured as a dual-fuel large diesel engine capable of being operated in a liquid mode, in which liquid fuel is introduced into the combustion chamber (4) for combustion, and also capable of being operated in a gas mode, in which gas is introduced into the cylinder (1) as fuel.

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