Longitudinal scavenging large engine

Abstract

To provide a longitudinally-scavenged large engine capable of more reliable scavenging.SOLUTION: There is proposed a longitudinally-scavenged large engine having at least one cylinder 10 in which a piston 60 is disposed to be movable back and forth along a cylinder shaft X, and having a cylinder cover 20 which together with the piston 60, defines a combustion chamber 120 for fuel. The large engine is designed for operation in a gas mode in which a premixed air-fuel mixture is burned in the combustion chamber 120, and a plurality of outlet valves 40 are provided inside the cylinder cover 20 to discharge exhaust gas from the combustion chamber 120. In each case, a ridge is provided between two adjacent outlet valves 40 on the cylinder cover 20, and the ridge extends into the combustion chamber 120.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a longitudinally scavenged large engine according to the preambles of the independent patent claims of each category.

Background Art

[0002] Large engines, which can be designed, for example, 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 even in stationary operation for driving large generators for generating electrical energy, for example. Such engines usually operate in continuous operation for a relatively long period of time, and therefore, the requirements for operating safety and availability are high. As a result, in particular, long maintenance intervals, low wear, and economical handling of the operating materials are important criteria for the operator. Large engines usually have cylinders with an inner diameter (bore) of at least 200 mm. Today, large engines with a bore of up to 960 mm or larger are used.

[0003] Another important aspect is energy efficiency, as well as the quality of the exhaust gas, in particular the nitrogen oxide concentration or sulfur load in the exhaust gas. Another problem is unburned hydrocarbons such as methane slip.

[0004] Currently, the legal requirements and limits for corresponding exhaust gas limits are becoming increasingly strict. As a result, in particular in the case of two-stroke large diesel engines, in addition to the combustion of classical heavy fuel oil highly contaminated with pollutants, the combustion of other fuels such as diesel oil or natural gas is also becoming an increasingly problematic issue, because compliance with the exhaust gas limits is becoming increasingly difficult, technically more complex, and thus more costly.

[0005] There is also a demand for a fuel to replace heavy fuel oil, which has been conventionally used as a fuel for large engines, with respect to economical and efficient operation, compliance with exhaust gas limit values, and resource availability. In this regard, both liquid fuels, i.e., fuels introduced into the combustion chamber in a liquid state, and gas fuels, i.e., fuels introduced into the combustion chamber in a gaseous state, are used.

[0006] Examples of liquid fuels as known alternatives to heavy fuel oil are, in particular, other heavy hydrocarbons which are residues from petroleum refining, alcohols, especially methanol or ethanol, gasoline, diesel, or emulsions or suspensions. For example, an emulsion known as MSAR (Multiphase Superfine Atomized Residue) is known to be used as a fuel. These are substantially emulsions of heavy hydrocarbons such as bitumen, heavy fuel oil, or the like, and water, and are produced by a special process. A well-known suspension is a suspension of carbon dust and water, which is also used as a fuel for large engines. Natural gas such as LNG (Liquefied Natural Gas), for example, is known as a gas fuel.

[0007] Another well-known alternative to pure operation with heavy fuel oil is to design large engines such that they can be operated with two or more different fuels and, depending on the operating situation or the environment, the engine is operated with one fuel or the other. Such large engines are also called multi-fuel large engines and can be switched during operation from a first mode in which a first fuel burns to a second mode in which a second fuel burns and vice versa.

[0008] A well-known design of a large engine operable with two different fuels is the type of engine for which the term "dual fuel engine" is used today. These engines are, on the one hand, operable in a gas mode in which a gas fuel, for example, natural gas or methane, is introduced into the combustion chamber for combustion, and on the other hand, operable in a liquid mode in which a liquid fuel such as heavy fuel oil or another liquid fuel is combustible in the same engine. These large engines can be both two-stroke and four-stroke engines, and in particular, can also be longitudinal scavenging two-stroke large diesel engines.

[0009] Large engines are also known that are operable with two different liquid fuels, and usually both fuels are stored, so that the engine is operable with either the first fuel or the second fuel even during operation. Designs are also known in which both fuels are introduced into the combustion chamber in the same operating cycle of the large engine.

[0010] Large engines operable with at least two or more different liquid or even gas fuels are often operated in different operating modes depending on the fuel currently in use. In an operating mode often called diesel operation, the combustion of the fuel generally occurs according to the principle of compression ignition or self-ignition of the fuel. In a mode often called Otto operation, the combustion occurs by spark ignition of a combustible fuel-air mixture. For example, this spark ignition can be caused by an electric spark, for example, by a spark plug, or can also be caused by self-ignition of a small amount of injected fuel that then causes spark ignition of another fuel. In the case of the above dual fuel engine, for example, for the gas mode, it is known to scavenge and mix the gaseous gas in order to generate a combustible mixture in the combustion chamber of the cylinder in this way. In this low-pressure process, the ignition of the mixture in the cylinder is usually achieved by injecting a small amount of liquid fuel into the combustion chamber of the cylinder, or into a pre-combustion chamber, at the appropriate time, which then leads to the ignition of the air-gas mixture.

[0011] Furthermore, a mixed form of Otto operation and diesel operation is also known.

[0012] Furthermore, large engines designed as gas engines are also known. These gas engines are designed only for pure gas operation. For example, a gas engine can be designed such that its operation corresponds to the operation in the gas mode of a dual-fuel engine. Gas engines are usually operated in Otto operation. A preferred fuel for a gas engine is, for example, natural gas.

[0013] Within the framework of the present application, the term "large diesel engine" refers to a large engine that is operable at least in diesel operation. Thus, in particular, the term "large diesel engine" also includes dual-fuel or multi-fuel large engines that are operable not only in diesel operation but also in another operation, for example, Otto operation.

[0014] In a longitudinally scavenged large engine, usually each cylinder has a scavenging opening provided at the lower end of the cylinder or cylinder liner, and at least one outlet valve for discharging exhaust gas provided at the upper end of the cylinder, for example, in a cylinder cover. Through the scavenging opening, fresh scavenging or charging required for the combustion process is supplied to the combustion chamber of the cylinder. Usually, the scavenging opening of the cylinder is opened and closed by the movement of the piston. When the piston approaches the bottom dead center during the working cycle and its downward movement, the scavenging opening is released by the piston so that scavenging or charging can flow into the cylinder. During the next upward movement of the piston, the piston closes the scavenging opening so that further scavenging cannot be introduced into the cylinder.

[0015] This means that during the scavenging of the cylinder, fresh scavenging air flows into the cylinder through the scavenging openings where it is exchanged with the hot exhaust gases remaining in the cylinder from the previous combustion process. These exhaust gases are discharged through the outlet valve. This scavenging process is usually not perfect, i.e., a certain amount of exhaust gas remains in the cylinder. The amount of exhaust gas remaining in the cylinder depends on the flow pattern or flow profile within the cylinder. There is also a partial mixing of the hot exhaust gases with the fresh scavenging air, which heats the air within the cylinder available for the next combustion process.

[0016] In particular, when a large engine is operated in gas mode where a premixed air-fuel mixture is spark-ignited in the combustion chamber, this heating of the air can lead to unwanted self-ignition of the air-fuel mixture within the cylinder, thereby causing a very high mechanical load and a very high increase in exhaust gas values. Furthermore, the increase in the air temperature within the cylinder can have the effect that the spark-ignition combustion process proceeds too fast (high-speed combustion), which also leads to a high mechanical load and high exhaust gas values.

[0017] Therefore, in order to ensure the most efficient and low-emission operation of a large engine, it is important to be able to control, as much as possible, the amount of exhaust gas remaining in the cylinder and the temperature of the scavenging air within the cylinder, especially with respect to the combustion of a premixed air-fuel mixture.

[0018] In a longitudinally scavenged large engine, the flow profile is mainly determined by the scavenging openings and the outlet valve. Although it is already possible to significantly optimize the arrangement and design of the scavenging openings, there is still a clear need for improvement in the area of the exhaust gas outlet. Today, providing an outlet valve is a common design for longitudinally scavenged large engines, and the outlet valve is arranged in the center of the cylinder cover. This centrally arranged outlet valve significantly reduces the flow velocity of the exhaust gas at the center of the cylinder, resulting in a significant amount of exhaust gas accumulating under the outlet valve. When looking across the cross-section of the cylinder, the flow velocity at the center of the cylinder is considerably lower than that in the radially outer region of the cylinder.

[0019] To address this problem, attempts have already been made to provide several outlet valves in the longitudinally scavenged cylinder to create a more favorable flow profile that reduces the amount of exhaust gas remaining in the cylinder. In this regard, there is still room for improvement.

SUMMARY OF THE INVENTION

PROBLEM TO BE SOLVED BY THE INVENTION

[0020] Therefore, starting from this prior art, the object of the present invention is to be able to more appropriately control the amount of exhaust gas remaining in the cylinder, in particular to be able to reduce it without the need for a significant increase in the scavenging amount, thereby enabling a longitudinal scavenging large engine that can operate a large engine as economically as possible with low exhaust gas values.

MEANS FOR SOLVING THE PROBLEM

[0021] The subject matter of the present invention that meets these objectives is characterized by the features of the independent claims.

[0022] Accordingly, according to the present invention, there is proposed a longitudinally scavenged large engine having at least one cylinder arranged such that a piston is movable back and forth along a cylinder axis and having a cylinder cover that defines the boundary of a combustion chamber for fuel together with the piston. The large engine is designed for operation in a gas mode in which a premixed air-fuel mixture is burned in the combustion chamber. A plurality of outlet valves are provided in the cylinder cover to discharge exhaust gas from the combustion chamber. In each case, a ridge is provided between two adjacent outlet valves on the cylinder cover, and the ridge extends into the combustion chamber.

[0023] Due to the combination of a plurality of outlet valves with a bulge disposed therebetween, a particularly favorable flow profile within the cylinder is realized, whereby the amount of exhaust gas remaining within the cylinder can be very significantly reduced. Referring across the cross-section of the cylinder, the flow profile is very flat, or more uniform, which means that within the combustion chamber, areas of very low flow velocity disappear, or at least are significantly reduced. Due to this approximate homogenization of the flow velocity across the cylinder cross-section, the exhaust gas is reliably discharged from all regions of the combustion chamber. Furthermore, the transition region between the fresh scavenging air and the discharged exhaust gas is very narrow or small, i.e., the transition from scavenging air to exhaust gas is very abrupt and does not get soiled. As a result, the heat transfer from the exhaust gas to the fresh scavenging air is also significantly reduced. Due to this very abrupt transition between the fresh scavenging air and the exhaust gas, it is also possible to more appropriately adapt the time for closing the outlet valve to this more abrupt transition region, and thus, overall, more exhaust gas is discharged from the combustion chamber and more fresh scavenging air remains within the cylinder.

[0024] As the heat transfer between the hot exhaust gas and the significantly colder purge air is significantly reduced, two further advantages result. On the one hand, the risk of undesirable self-ignition of the air-fuel mixture is significantly reduced, and on the other hand, due to the higher temperature of the exhaust gas, the effect or efficiency of an exhaust gas purification system such as an oxidation catalyst or an SCR (Selective Catalytic Reduction) device for methane downstream is improved.

[0025] According to a preferred embodiment, the cylinder has four outlet valves disposed within the cylinder cover.

[0026] The four outlet valves are preferably arranged in a rectangular structure.

[0027] To particularly efficiently reduce the areas of low flow velocity within the combustion chamber, it is advantageous for each bulge to extend radially towards the cylinder axis.

[0028] Preferably, each protrusion is designed such that the height of the protrusion measured perpendicular to the radial direction decreases when viewed towards the cylinder axis.

[0029] Furthermore, it is preferable that each protrusion is designed such that the width of the protrusion measured perpendicular to the radial direction decreases when viewed towards the cylinder axis.

[0030] For this purpose, each protrusion is preferably designed as a substantially regular tetrahedron, and the base of the regular tetrahedron is arranged radially outward in each case, and the apex of the regular tetrahedron is arranged radially inward, so that the protrusions are aligned with their respective apexes towards the cylinder axis.

[0031] In a preferred embodiment, a check device for actuating a plurality of outlet valves is provided so as to minimize the amount of exhaust gas remaining in the combustion chamber.

[0032] Furthermore, it is a preferred embodiment that each outlet valve has a valve axis, and at least one outlet valve is arranged such that its valve axis is aligned parallel to the cylinder axis.

[0033] In some embodiments, each outlet valve is arranged such that its valve axis is aligned parallel to the cylinder axis.

[0034] In other embodiments, each outlet valve can be arranged such that its valve axis is aligned obliquely with respect to the cylinder axis. This means that each valve axis forms an angle greater than 0 degrees and less than 90 degrees with the cylinder axis. Such an oblique arrangement may be advantageous especially from an aerodynamic point of view.

[0035] It is also a preferred measure that a plurality of outlet valves are arranged such that the outlet valves are arranged symmetrically with respect to the cylinder axis.

[0036] The longitudinally scavenged large engine is preferably designed as a longitudinally scavenged large diesel engine.

[0037] When the longitudinally scavenged large engine according to the invention is designed as a longitudinally scavenged two-stroke large engine, that is also preferable.

[0038] In particular, the large engine according to the invention can be designed as a longitudinally scavenged two-stroke large diesel engine.

[0039] Particularly preferably, the large engine is designed as a dual-fuel large diesel engine that can be operated in a liquid mode in which liquid fuel is introduced into the combustion chamber for combustion and also in a gas mode in which gas is introduced into the combustion chamber as fuel.

[0040] Even more advantageous measures and embodiments of the invention result from the dependent claims.

[0041] In the following, the invention will be explained in more detail on the basis of embodiments and drawings.

Brief Description of the Drawings

[0042]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0043] FIG. 1 shows in a schematic cross-sectional view an embodiment of a longitudinally scavenged large engine according to the invention, indicated generally by reference numeral 1.

[0044] The large engine 1 comprises at least one, usually several, cylinders 10 in which the combustion process takes place.

[0045] The term "large engine" usually refers to an engine that is used as the main drive unit for ships or, for example, in a stationary operation to drive a large generator for generating electrical energy. Usually, each cylinder 10 of the large engine 1 has an inner diameter (bore) of at least about 200 mm.

[0046] The large engine 1 can be designed as a four-stroke engine or a two-stroke engine. In particular, the large engine 1 can be designed as a large diesel engine, in particular, as a longitudinally scavenged two-stroke large diesel engine. The term "large diesel engine" refers to a large engine 1 that can be operated in diesel operation. In an idealized and limited case, diesel operation is an isobaric process (constant pressure combustion) based on diffusion combustion. In diesel operation, the combustion of the fuel usually occurs according to the principle of self-ignition. Within the framework of this application, the term "large diesel engine" also refers to a large engine 1 that can be operated in Otto operation instead of in addition to diesel operation. In an idealized and limited case, Otto operation is a shared space process (shared space combustion) in which combustion usually occurs according to the principle of spark ignition of the fuel. It is also possible for a large diesel engine to be operable in a mixed form of diesel operation and Otto operation.

[0047] Of course, the term "large engine" also includes engines that are designed as gas engines. These gas engines are designed only for pure gas operation, i.e., they are operated only with gas fuel, for example, natural gas. For example, a gas engine can be designed such that its operation corresponds to the operation in the gas mode of a dual-fuel engine.

[0048] Furthermore, the term "spark-ignition fuel" is used to describe a fuel that burns as intended by spark ignition within cylinder 10, i.e., self-ignition must be avoided as intended. In contrast, the term "self-ignition fuel" refers to a fuel that burns as intended by self-ignition within cylinder 10, such as heavy fuel oil or diesel fuel.

[0049] The term "liquid fuel" refers to a fuel that is introduced into cylinder 10 in a liquid state. The term "gas fuel" refers to a fuel that is introduced into cylinder 10 in a gaseous state.

[0050] In the following description of the present invention, an example of a large diesel engine 1 that is practically important and is designed as a longitudinally scavenged two-stroke large diesel engine and used as a main drive unit for a ship is referred to with exemplary properties. This large diesel engine 1 can be designed, for example, but not necessarily, as a dual-fuel large diesel engine, and thus can be operated with two different fuels, for example, a liquid fuel such as heavy fuel oil and a gas fuel such as natural gas. The dual-fuel large diesel engine 1 can be switched during operation from the combustion of the first fuel to the combustion of the second fuel and vice versa.

[0051] It is understood that the present invention relates to this type of large diesel engine and, without being limited to this use, generally to a longitudinally scavenged large engine 1. It is also possible to design the large engine 1 only for the combustion of a single fuel. For example, the large engine 1 can be designed as a gas engine, which is designed only for operation with gas as fuel. It is also possible to design the large engine 1 as a multi-fuel large engine, which can be operated with a first fuel and at least a second fuel different from the first fuel. Of course, the large engine 1 can also be designed for the combustion of two or more fuels.

[0052] The piston 60 is provided in each cylinder 10 of the large diesel engine 1 in any case, and the piston 60 is arranged to be movable back and forth in the direction of the cylinder axis X between the top dead center and the bottom dead center in any case, and its upper side defines the boundary of the combustion chamber 120 together with the cylinder cover 20.

[0053] The piston 60 is connected to a crosshead (not shown) via a piston rod (not shown) in a manner known per se, and the crosshead is connected to a crankshaft (not shown) via a push rod (not shown). Therefore, the movement of the piston 60 is transmitted to the crankshaft via the piston rod, the crosshead, and the push rod in order to rotate the crankshaft.

[0054] A plurality of outlet valves 40 are provided in the cylinder cover 20, and through them, after the combustion process, the combustion gas can be discharged from the combustion chamber 120 of the cylinder 10 to an exhaust gas collecting pipe (not shown). Each outlet valve 40 extends in the direction of its respective valve axis A. In the embodiment described herein, four outlet valves 40 are provided in each cylinder 10 in any case. This can be referred to in FIG. 2 which shows a plan view of the cylinder cover 20 as seen from the combustion chamber 120. For better understanding, FIG. 3 further shows a perspective cross-sectional view of the cylinder cover 20.

[0055] However, in FIGS. 2 and 3, only the bores 401 that each receive the outlet valve 40 are shown for a better overview, but the outlet valve 40 itself is not shown. When the outlet valve 40 is arranged in each bore 401, each valve axis A is on the respective central axis of the bore 401 in which the outlet valve 40 is arranged.

[0056] In other embodiments, fewer than four or more than four outlet valves 40, for example, two or three outlet valves, or five or more outlet valves, can be provided in each cylinder 10.

[0057] In order to achieve the best possible exhaust of the exhaust gas from the combustion chamber 120, it is preferable that a plurality of outlet valves 40 are arranged symmetrically with respect to the cylinder axis X. In particular, as shown in FIG. 2, the four outlet valves 40 are arranged in a rectangular structure, in particular a square structure. The valve axis A (or the central axis of the four bores 401) is arranged such that the point of passage of its axis into the combustion chamber 120 is on a rectangle (here, a square) through which the cylinder axis X passes through its center.

[0058] In the embodiment described herein, the outlet valves 40 are arranged as such, or the bores 401 are designed such that each valve axis A is aligned parallel to the cylinder axis X. In other embodiments, it is of course possible for one or more valve axes or all valve axes to extend obliquely with respect to the cylinder axis. At that time, each valve axis extending obliquely with respect to the cylinder axis preferably forms an angle greater than 0° and less than 90° with the cylinder axis.

[0059] In a longitudinally scavenged two-stroke large diesel engine 1, for example, the scavenging opening 30 designed as a scavenging slot is provided in the lower region of each cylinder 10 or the cylinder liner in order to supply scavenging air to the cylinder 10. The scavenging opening 30 is periodically opened and closed by the movement of the piston 60 in the cylinder 10. Therefore, the scavenging air provided by the turbocharger (not shown) under the filling pressure of the intake receiver (not shown) can flow into the respective cylinders 10 through the scavenging opening 30 as long as they are open. This is the case when each piston 60 is in the region of its lower dead center.

[0060] Furthermore, at least one fuel injection nozzle 50 is provided in the cylinder cover 20, which is arranged in the center of the cylinder cover 20 such that the central axis of the fuel injection nozzle 50 is on the cylinder axis X in the embodiment described herein. Of course, in other embodiments, more than one fuel injection nozzle 50 can be provided for each cylinder 10.

[0061] The fuel injection nozzle 50 serves to introduce liquid fuel, such as heavy fuel oil or diesel oil, into the combustion chamber 120 of the cylinder 10. This means that, in the liquid mode, the liquid fuel is injected into the combustion chamber 120 of the cylinder 10 by the fuel injection nozzle 50.

[0062] Furthermore, a gas supply system (not shown) is provided, by means of which gas can be introduced into the cylinder 10. The gas supply system is preferably designed as a low-pressure system that introduces gas acting as fuel into the cylinder at a pressure of up to 50 bar (5 MPa), preferably up to 20 bar (2 MPa). The gas supply system comprises at least one gas inlet nozzle arranged on or in the wall of the cylinder. In the direction of the cylinder axis X, the gas inlet nozzle is preferably arranged approximately in the middle between the upper and lower dead centers of the piston 60.

[0063] In the gas mode, gas is introduced into the cylinder 10 by the gas supply system, where it scavenges and mixes and is compressed by the upward movement of the piston 60. By doing so, a pre-mixed air-fuel mixture is created in the combustion chamber 120 and is then spark-ignited at a pre-determinable time or at a pre-determinable crank angle. The spark ignition preferably occurs by injecting a small amount of liquid fuel into the combustion chamber 120 of the cylinder 10 or into a pre-chamber (not shown) at an appropriate time, as a result of which the liquid fuel in the combustion chamber 120 or the pre-chamber auto-ignites and then leads to the ignition of the air-gas mixture in the combustion chamber 120. Some pre-chambers can be provided in a manner known per se, each of which is fluidly connected to the combustion chamber 120. Next, when the auto-ignition fuel is introduced into each of these chambers, the air-fuel mixture in the combustion chamber 120 can be spark-ignited at different points.

[0064] Instead of spark ignition by the introduction of auto-ignition fuel, it is of course also possible to achieve spark ignition by means of electrical ignition, for example by means of an ignition plug.

[0065] The further structure of a large diesel engine and its individual components, such as an injection system, a gas exchange system, an exhaust system or a turbocharger system for providing scavenging or charging, and a check and control system for a large diesel engine, are well known to those skilled in the art in both the design as a two-stroke engine and the design as a four-stroke engine. Therefore, no further explanation is necessary here.

[0066] The check and control system of a modern large diesel engine is an electronic system, whereby, usually, all functions of the engine or cylinder, in particular, injection (start and end of injection), introduction of gas fuel, and operation of the outlet valve, can be adjusted or controlled or regulated. In the embodiment described here, the check and control system comprises a checking device by which each of the outlet valves 40 can be operated for opening and closing. The checking device preferably operates all the outlet valves 40 simultaneously, i.e., synchronously, so that all the outlet valves 40 move as synchronously as possible.

[0067] It is also possible for the checking device to operate each of the outlet valves 40 individually and independently of the other outlet valves 40.

[0068] According to the present invention, in any case, the ridge 7 is provided on the cylinder cover 20 between two adjacent outlet valves 40 or between two adjacent bores 401 for the outlet valve 40. These ridges 7 significantly assist in improving the flow profile within the cylinder 10. The combination of the plurality of outlet valves 40 and each ridge 7 disposed therebetween results in the fact that the regions of very low flow velocity or stagnant regions are at least significantly reduced. The distribution of the flow velocity across the cross-section of the cylinder 10 becomes extremely more uniform. This means that the flow profile becomes flatter. The exhaust gas can be reliably discharged from all regions of the combustion chamber 120. This also results in the fact that the transition region between the new scavenging and the exhaust gas within the cylinder becomes significantly narrower and thus very small. The transition from the new scavenging to the exhaust gas is rather abrupt, and therefore, the heat exchange between the high-temperature exhaust gas and the very cold scavenging also decreases. Compared with the conventional embodiment, this means that the exhaust gas remains at a higher temperature, which is an advantageous aspect regarding the efficiency of the downstream exhaust gas purification system, and the scavenging of the cylinder 10 remains colder, which has a favorable effect regarding unwanted self-ignition or too fast combustion, especially in the gas mode.

[0069] All four ridges 7, each of which is in any case disposed between two adjacent outlet valves 40 or between two adjacent bores 401, extend in any case from the cylinder cover 20 into the combustion chamber 120. According to a preferred embodiment, each ridge 7 extends radially from the cylinder cover 20 towards the cylinder axis X.

[0070] Each ridge 7 is designed such that its height H, which shows an extension in the direction of the cylinder axis X, decreases in the direction of the cylinder axis X from the cylinder cover 20, that is, the height H is maximum at the cylinder cover 20, especially in the radially outer region of the cylinder cover 20, and then preferably decreases continuously.

[0071] Furthermore, an embodiment is preferred in which the width B of each ridge 7 decreases in the direction of the cylinder axis X. The width B means the spread of the ridge in a direction perpendicular to both the radial direction and the cylinder axis X. This direction is the circumferential direction. Thus, the width B of each ridge 7 is maximum in the cylinder cover 20, particularly in the radially outer region of the cylinder cover, and then preferably decreases continuously.

[0072] Both geometric states can be recognized, for example, by the fact that each ridge 7 is substantially designed as a regular tetrahedron, i.e., each ridge 7 consists of four triangles, which, of course, cannot be understood in a strict mathematical sense. The base of the regular tetrahedron is arranged radially outwards on the cylinder cover 20 in any case, and the apex of the regular tetrahedron is arranged radially inwards, so that the ridges 7 are aligned with their respective apexes towards the cylinder axis. Preferably, one "edge" of each regular tetrahedron extends in the radial direction.

Claims

1. having at least one cylinder (10) arranged such that a piston (60) is movable back and forth along a cylinder axis (X), and having a cylinder cover (20) that defines a boundary of a combustion chamber (120) for fuel together with the piston (60), a longitudinally scavenged large engine, the large engine being designed for operation in a gas mode in which a premixed air-fuel mixture is combusted in the combustion chamber (120), a plurality of outlet valves (40) being provided in the cylinder cover (20) for discharging exhaust gas from the combustion chamber (120), in a longitudinally scavenged large engine, a ridge is provided between two adjacent outlet valves (40) on the cylinder cover (20), the ridge extending into the combustion chamber (120), whereby a flow profile in the cylinder is realized, thereby avoiding or reducing an area in the combustion chamber (120) having a low flow velocity, and as a result, reducing the amount of exhaust gas remaining in the cylinder, and the exhaust gas is discharged from all regions of the combustion chamber (120), and heat transfer from the exhaust gas to a new scavenging is reduced, a longitudinally scavenged large engine characterized thereby.

2. the cylinder (10) having four outlet valves (40) arranged in the cylinder cover (20), the longitudinally scavenged large engine according to claim 1.

3. the four outlet valves (40) being arranged in a rectangular structure, the longitudinally scavenged large engine according to claim 2.

4. each ridge (7) extending radially towards the cylinder axis (X), the longitudinally scavenged large engine according to any one of claims 1 to 3.

5. Each projection (7) is designed such that the height (H) of the projection (7) measured perpendicular to the radial direction decreases when looking towards the cylinder axis (X). The longitudinally scavenged large engine according to claim 4.

6. Each projection (7) is designed such that the width (B) of the projection (7) measured perpendicular to the radial direction decreases when looking towards the cylinder axis (X). The longitudinally scavenged large engine according to claim 4 or 5.

7. Each projection (7) is designed substantially as a regular tetrahedron. In each case, the base of the regular tetrahedron is arranged radially outwards, and the apex of the regular tetrahedron is arranged radially inwards, so that the projections (7) are aligned with their respective apices towards the cylinder axis (X). The longitudinally scavenged large engine according to any one of claims 1 to 6.

8. Each outlet valve (40) has a valve shaft (A). At least one outlet valve (40) is arranged such that its valve shaft (A) is aligned parallel to the cylinder axis (X). The longitudinally scavenged large engine according to any one of claims 1 to 7.

9. Each outlet valve (40) is arranged such that its valve shaft (A) is aligned parallel to the cylinder axis (X). The longitudinally scavenged large engine according to claim 8.

10. The plurality of outlet valves (40) are arranged such that the outlet valves (40) are arranged symmetrically with respect to the cylinder axis (X). The longitudinally scavenged large engine according to any one of claims 1 to 9.

11. Designed as a longitudinally scavenged large diesel engine. The longitudinally scavenged large engine according to any one of claims 1 to 10.

12. Designed as a longitudinally scavenged two-stroke large engine, The longitudinally scavenged large engine according to any one of claims 1 to 11.

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

14. Capable of operating in a liquid mode in which liquid fuel is introduced into the combustion chamber (120) for combustion, and further capable of operating in the gas mode in which gas is introduced into the combustion chamber (120) as fuel, designed as a dual-fuel large diesel engine, The longitudinally scavenged large engine according to any one of claims 1 to 13.

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