Cylinder cover for large diesel engine cylinder and method for repairing the cylinder cover

Abstract

To provide a cylinder cover for a cylinder of a large diesel engine capable of significantly reducing at least a risk of crack formation in a region of a nozzle channel in which a nozzle head is extended to a combustion chamber.SOLUTION: A cylinder cover for a cylinder of a large diesel engine has at least one fuel bore for housing a fuel injection nozzle, and a combustion chamber surface defining a combustion chamber having a combustion chamber axis. The fuel bore is extended in a direction of a fuel axis, and opened to the combustion chamber surface. A seat surface for the fuel injection nozzle is disposed on the fuel bore. The seat surface has a symmetric axis matched with the fuel axis, and is connected to the combustion chamber surface by a nozzle channel. The nozzle channel has a length ratio as a ratio of a maximum length of the nozzle channel and a minimum length of the nozzle channel, and the length ratio is equal to 2 in maximum. Further a repair method of the cylinder cover and a large diesel engine are proposed.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a cylinder cover for a cylinder of a large diesel engine and to a method for repairing the cylinder cover according to the preambles of the independent claims of the respective categories. [Background technology]

[0002] Large diesel engines can be designed as two-stroke or four-stroke engines. For example, longitudinally scavenged two-stroke large diesel engines are used as drives for ships or also in stationary operation, for example to drive large generators for producing electrical energy. Since the engines usually run for considerable periods in continuous operation, there are high demands on operational safety and availability. Therefore, among other things, long maintenance intervals, low wear and economical handling of the working materials are important criteria for the operators. Large diesel engines usually have cylinders with an internal diameter (bore) of 200 mm or more. Nowadays, large engines with bores up to 960 mm and more are in use.

[0003] Various types of large diesel engines are known, each of which can be designed as a two-stroke or four-stroke engine. Traditionally, large diesel engines are operated with heavy fuel oil. With regard to economical and efficient operation, compliance with emission thresholds and resource availability, alternatives to heavy fuel oil in large diesel engines are also being searched for. In this respect, both liquid fuels, i.e. fuels which are introduced into the combustion chamber in liquid state, and gaseous fuels, i.e. fuels which are introduced into the combustion chamber in gaseous state, are used.

[0004] Examples of liquid fuels as known substitutes for heavy fuel oil include, inter alia, oil refineries, alcohols, especially methanol or ethanol, gasoline, diesel, or other heavy hydrocarbons left over from emulsions or suspensions. For example, it is known to use emulsions known as MSAR (multiphase ultra-fine spray residue) as fuel. A well-known suspension is a suspension of coal dust and water, which is also used as fuel for large engines. Natural gas, such as LNG (liquefied natural gas), is known as a gaseous fuel.

[0005] Another well-known alternative to pure heavy fuel oil operation is to design large diesel engines to be capable of operation on two or more different fuels, where the engine runs on one fuel or the other depending on the operating conditions and ambient environment.

[0006] Known designs of large diesel engines capable of operating on two different fuels include those currently referred to as "dual fuel engines". These engines are capable of operating in a gaseous mode, on the one hand, where a gaseous fuel, such as natural gas or methane, is introduced into the combustion chamber for combustion, and in a liquid mode, on the other hand, where a liquid fuel, such as heavy fuel oil or other liquid fuel, is burned in the same engine. These large diesel engines may be both two-stroke and four-stroke engines, in particular longitudinally scavenged two-stroke large diesel engines.

[0007] Large engines capable of operating on at least two or more different liquid or gaseous fuels are often operated in various operating modes, depending on the fuel currently being used. In the operating mode often referred to as diesel operation, the combustion of the fuel is generally based on the principle of compression ignition or autoignition of the fuel. In the mode often referred to as Otto operation, the combustion is achieved by spark ignition of an ignitable premixed mixture. This spark ignition is achieved, for example, by an electric spark from a spark plug or by the autoignition of a small amount of fuel, which then leads to the spark ignition of another fuel. A small amount of fuel intended for autoignition is often injected into a prechamber connected to the combustion chamber.

[0008] Furthermore, mixed forms of Otto and Diesel operation are also known.

[0009] Within the framework of this application, the term "large diesel engine" refers to an engine capable of operating at least in diesel operation. In particular, the term "large diesel engine" also includes large dual-fuel or multi-fuel engines which, in addition to diesel operation, can also be operated in a different manner, for example in Otto operation.

[0010] A large diesel engine is comprised of at least one cylinder, but typically multiple cylinders, each with a piston that is movable back and forth between top and bottom dead center, and a cylinder cover that, together with the piston, defines a combustion chamber. During operation, fuel is introduced into the combustion chamber and, depending on the mode of operation, the fuel is spark ignited or auto-ignited when the piston is near top dead center.

[0011] In particular, in the case of diesel operation, for example with heavy fuel oil as fuel, it is a known measure to provide the cylinder head with at least one, and often several, fuel injection nozzles, which inject fuel at high pressure into the combustion chamber. For each fuel injection nozzle, a bore is provided in the cylinder cover, which usually extends into the combustion chamber. This bore is provided with a seating surface in which the fuel injection nozzle sits. That is to say, downstream of the seating surface, the bore is designed as a nozzle channel, the diameter of which is significantly smaller. The fuel injection nozzle has at its end a nozzle head, through which the fuel is injected. This nozzle head extends through the nozzle channel into the combustion chamber, if the fuel injection nozzle is arranged in the bore. This means that the nozzle head projects beyond the wall that defines the combustion chamber. The nozzle head has several nozzle holes, through which the fuel is injected into the combustion chamber in a manner known per se.

[0012] The fuel injection nozzle is usually arranged to extend obliquely relative to the cylinder axis or the combustion chamber axis of the cylinder, which usually coincides with the cylinder axis, and the longitudinal axis of the fuel injection nozzle forms an acute angle with the cylinder axis. Because the available space is very limited, it is usually not possible to arrange the fuel injection nozzle or nozzles at any angle relative to the cylinder axis, but the range of angles that can be achieved is very limited.

[0013] Those areas of the combustion chamber wall, where the nozzle head of the fuel injection nozzle extends into the combustion chamber, are exposed to particularly high thermal loads during the operation of large diesel engines. This applies in particular to the areas located in the outlet region of the nozzle hole, where the fuel enters the combustion chamber. At the ends of the holes, where the nozzle channel leads into the combustion chamber, material removal and therefore dangerous crack formations can occur, which requires complex and expensive repair and maintenance operations. Summary of the Invention

[0014] The present invention therefore aims to propose a cylinder cover for cylinders of large diesel engines, in which the risk of crack formation in the region of the nozzle channel, where the nozzle head extends into the combustion chamber, is at least significantly reduced, and furthermore, to propose a method for repairing the cylinder cover, which at least significantly reduces the risk of future crack formation.

[0015] The subject matter of the invention which achieves these objects is characterized by the features of the independent claims of each category.

[0016] Thus, according to the invention, a cylinder cover for a cylinder of a large diesel engine is proposed, the cylinder cover having at least one fuel bore for accommodating a fuel injection nozzle and a combustion chamber surface defining a combustion chamber with a combustion chamber axis, the fuel bore extends in the direction of the fuel axis and opens into the combustion chamber surface, a seating surface for the fuel injection nozzle is provided in the fuel bore, this seating surface has an axis of symmetry coinciding with the fuel axis and is connected to the combustion chamber surface by a nozzle channel, the nozzle channel having a length ratio which is the ratio between the maximum length of the nozzle channel and the minimum length of the nozzle channel, this length ratio being at most equal to 2.

[0017] Of crucial importance to the invention is the realization that the change in length of the nozzle channel connecting the seating surface of the fuel bore with the combustion chamber is a substantial cause of crack formation in the combustion chamber wall when viewed around the circumference of the nozzle channel. In known designs of cylinder covers, the seating surface in the fuel bore, on which the fuel injection nozzle is located, varies relatively widely in distance from the combustion chamber when viewed around its circumference. This seating surface is at different distances from the combustion chamber when viewed around the circumference of the seating surface. This results in the length of the nozzle channel being significantly shorter at some points around the circumference than at other points. It is now proposed according to the invention to reduce this change in length of the nozzle channel so that the length ratio between the maximum and minimum length of the nozzle channel is at most 2. This reduction in the change in length of the nozzle channel makes it possible to at least significantly reduce the crack formation in the combustion chamber when viewed around its circumference.

[0018] The nozzle channel, which generally extends in the direction of the fuel axis, usually opens into the combustion chamber at an angle different from 90 degrees, i.e. the fuel axis forms an angle different from 90 degrees with the combustion chamber surface. This angle is usually smaller than 90 degrees and larger than 0 degrees. If the fuel axis were perpendicular to the combustion chamber surface, the above problem would not occur trivially, since the distance of the seating surface from the combustion chamber would be constant over the circumference of the nozzle channel. However, in the cylinder cover of a large diesel engine, it is generally not possible, for space reasons, to arrange one or more nozzle channels so that they open perpendicularly to the combustion chamber surface.

[0019] In an ideal case, the ratio of the maximum length to the minimum length is equal to 1, i.e. the maximum length and the minimum length are the same, so that the nozzle channel has a constant length over its entire circumference. However, in many applications, this ideal case is not feasible for practical reasons. However, it has been shown that, in particular, crack formation can be reduced, if not completely, then at least very well, when the length ratio is at most 1.5, preferably less than 1.4.

[0020] In a particularly preferred embodiment, the length ratio is reduced by providing a bead-shaped ridge on the combustion chamber surface that defines a portion of the nozzle channel, allowing the nozzle channel to be extended around its periphery in areas where it would be shorter without the ridge than in other areas. In this embodiment, the nozzle channel is extended in areas where it would be at its shortest length without the ridge.

[0021] Preferably, the raised portion defines the nozzle channel on the side facing the combustion chamber axis, since this region is typically the region where the seating surface is at a minimum distance from the combustion chamber.

[0022] The ridges are preferably designed to reduce the length ratio to a predetermined value. As already mentioned, the minimum value of the length ratio is equal to 1. However, for many applications it is sufficient in practice to adjust the length ratio to a value greater than 1, for example 1.4. The respective desired value of the length ratio is determined by the geometric dimensions of the ridges.

[0023] Since the ridge is primarily intended to reduce or compensate for the difference between the maximum length of the nozzle channel without the ridge and the minimum length of the nozzle channel without the ridge, it is advantageous if the ridge extends over at most half the circumferential length of the nozzle channel when viewed in the circumferential direction of the nozzle channel.

[0024] In order to reduce the length ratio as much as possible, it is advantageous if the height of the ridges varies when viewed in the circumferential direction of the nozzle channel, the height of the ridges referring to their extension perpendicular to the combustion chamber surface.

[0025] It is further preferred that the ridge has a maximum width that is at least as large as half the radius of the nozzle channel, and preferably at least as large as the radius of the nozzle channel, the ridge width being the dimension that indicates how far the ridge of the combustion chamber surface extends from the nozzle channel.

[0026] Another preferred embodiment for reducing the length ratio is to provide a recess in the combustion chamber surface into which the nozzle channel opens.

[0027] This allows the nozzle channel to be shortened along its periphery in areas where, without the recess, the nozzle channel would be longer than in other areas, in this embodiment the nozzle channel is shortened in the area where it has its greatest length without the recess.

[0028] The recess is preferably designed to reduce the length ratio to a predetermined value. As already mentioned, the minimum value of the length ratio is equal to 1. However, for many applications it is sufficient in practice to adjust the length ratio to a value greater than 1, for example 1.5. The respective desired value of the length ratio is determined by the geometric dimensions of the recess.

[0029] Since the recess is primarily intended to reduce or compensate for the difference between the maximum length of the nozzle channel without the recess and the minimum length of the nozzle channel without the recess, it is advantageous if the recess extends over at least half the peripheral length of the nozzle channel when viewed in the circumferential direction of the nozzle channel.

[0030] The recess may also extend around the entire circumference of the nozzle channel when viewed in the circumferential direction of the nozzle channel. The depth of this recess varies in such a way that the maximum length of the nozzle channel when viewed in the circumferential direction of the nozzle channel is at most twice the minimum length of the nozzle channel. Providing a recess around the entire circumference of the nozzle channel has the advantage that sharp edges or very thin areas at the boundaries of the nozzle channel can be avoided.

[0031] The recess extends along at least a portion of the circumference of the nozzle channel and thus has a radius, which is preferably at least twice the radius of the nozzle channel.

[0032] Furthermore, according to the invention, a method for repairing a cylinder cover of a cylinder of a large diesel engine is proposed, the cylinder cover having at least one fuel bore for accommodating a fuel injection nozzle and a combustion chamber surface defining a combustion chamber with a combustion chamber axis, the fuel bore extends in the direction of the fuel axis and opens into the combustion chamber surface, a seating surface for the fuel injection nozzle is provided in the fuel bore, the seating surface having an axis of symmetry coinciding with the fuel axis and connected to the combustion chamber surface by a nozzle channel. The method is characterized in particular in that the combustion chamber surface of the cylinder cover is machined in such a way that the nozzle channel has a length ratio at most equal to 2, the length ratio being the ratio between the maximum length of the nozzle channel and the minimum length of the nozzle channel.

[0033] The method according to the invention is also particularly suitable for cylinder covers in which the fuel axis is not perpendicular to the combustion chamber surface but is arranged at an angle different from 90 degrees on the combustion chamber surface and the nozzle channels open into the combustion chamber surface at an angle different from 90 degrees, preferably less than 90 degrees.

[0034] The realization, crucial to the invention, that the change in length of the nozzle channel connecting the seating surface of the fuel bore with the combustion chamber, when viewed around the circumference of the nozzle channel, is a substantial cause of crack formation in the combustion chamber wall, can also be advantageously utilized in the repair of cylinder covers of large diesel engines, where the combustion chamber surface is machined such that the repaired cylinder cover embodies the cylinder cover according to the invention.

[0035] The length ratio is varied by applying bead-shaped protuberances to the combustion chamber surface or by providing recesses in the combustion chamber surface.

[0036] Furthermore, according to the invention, a large diesel engine, in particular a longitudinally scavenged two-stroke large diesel engine, is proposed having at least one cylinder, the cylinder having a cylinder cover designed according to the invention or repaired by the method according to the invention.

[0037] Further advantageous measures and embodiments of the invention are set forth in the dependent claims.

[0038] In the following, the invention is explained in more detail on the basis of embodiments and with reference to the drawings, both with regard to the apparatus and the process engineering. [Brief description of the drawings]

[0039] [Figure 1] FIG. 1 is a schematic top view of a cylinder of a large diesel engine from the combustion chamber to the cylinder cover, showing a first embodiment of the cylinder cover according to the invention on the left and a prior art cylinder cover on the right. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 3 is a detailed enlarged view of FIG. [Figure 4] FIG. 4 is a cross-sectional view showing a second embodiment of a cylinder cover according to the present invention taken along a cylinder axis. [Diagram 5] FIG. 5 is a detailed enlarged view of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] The term "large diesel engine" refers to engines such as those used as main drives for marine vessels driving large generators for producing electrical energy, or even in stationary operation. Typically, the cylinders of a large diesel engine each have an internal diameter (bore) of at least about 200 mm. The expression "longitudinally scavenged" means that scavenging or charge air is introduced into the cylinder in the region of the lower end.

[0041] In the following description of the invention based on the embodiments, reference is made in an exemplary sense to the case of large engines of particular importance in practice, designed as dual-fuel engines, i.e. engines capable of operating on two different fuels. In particular, this embodiment of a large diesel engine can be operated in 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. Large diesel engines can also be operated in gas mode, in which a fuel gas, for example natural gas, is ignited in the combustion chamber in the form of a premixed mixture. In the gas mode, the operation of the large diesel engine is in particular carried out according to the low-pressure method, i.e. the gas is introduced into the cylinder in gaseous state and the gas injection pressure 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 achieved by introducing a small amount of self-igniting liquid fuel (e.g. diesel or fuel oil) into the combustion chamber or prechamber at the right moment, which then self-ignites and causes a spark ignition of the mixture in the combustion chamber.

[0042] In the embodiment described here, the large engine is designed as a longitudinally scavenged, dual fuel, two-stroke large diesel engine.

[0043] It is understood that the invention is not limited to this type of large diesel engine or its application, but refers generally to large diesel engines. As already mentioned, the term "large diesel engine" also includes engines that can be operated in other operation modes, such as Otto operation, in addition to diesel operation. Of course, a large diesel engine may be designed only for the combustion of a single liquid fuel, such as heavy fuel oil or diesel oil. A large engine may also be designed as a multi-fuel large engine, designed for the combustion of two or more fuels.

[0044] A large diesel engine has at least one, and usually several, cylinders, in each of which a piston is arranged, in a manner known per se, so as to be movable back and forth along the cylinder axis between top and bottom dead centre. The upper side of the piston, together with the cylinder cover 1, defines a combustion chamber 2 into which fuel is introduced and combustion takes place. This combustion chamber usually has a combustion chamber axis A (figure 1) which coincides with the cylinder axis when the cylinder cover 1 is attached to the cylinder. In a manner known per se, the piston is connected via a piston rod to a crosshead which is in turn connected via a pushrod to a crankshaft, so that the movement of the piston is transmitted via the piston rod, the crosshead and the pushrod to the crankshaft to rotate it.

[0045] Figure 1 shows a schematic view from above of the combustion chambers 2, 2' to the cylinder covers 1, 1' of the cylinders of a large diesel engine. For better understanding, figure 1 is divided into two parts, showing on the left a first embodiment of a cylinder cover 1 according to the invention and on the right a conventionally known cylinder cover 1'. The conventionally known designs use reference numbers with dashes and inverted commas, whereas the embodiment according to the invention uses reference numbers without inverted commas.

[0046] FIG. 2 is a cross-sectional view along the combustion chamber axis A of the embodiment of FIG. 1, and similarly shows a first embodiment of a cylinder cover 1 according to the invention on the left and a conventionally known design on the right.

[0047] Figure 3 shows an enlarged detail of figure 2 in order to show the definition of the different dimensions. In figure 3 only a first embodiment of a cylinder cover 1 according to the invention is shown.

[0048] The cylinder cover 1, 1' comprises a central bore 3, 3' housing an outlet valve (not shown) and at least one fuel bore 4, 4' housing a fuel injection nozzle (not shown) capable of introducing fuel, for example heavy fuel oil, into the combustion chamber 2, 2'. In many embodiments, each cylinder cover 1, 1' is provided with a plurality of fuel injection nozzles, for example two or three fuel injection nozzles, and it will be appreciated that each fuel injection nozzle is provided with a separate fuel bore 4, 4'. For the sake of understanding, in the following only one fuel bore 4 is mentioned, but it will be appreciated that in embodiments according to the invention it is possible to have a plurality of fuel bores 4, each housing a fuel injection nozzle.

[0049] An embodiment is also possible in which for each cylinder the cylinder cover has several bores which accommodate several outlet valves, for example three or four outlet valves for each cylinder, and for each of these outlet valves a bore is provided in the cylinder cover 1 or a larger bore is provided in the cylinder cover, accommodating a structural unit which includes several outlet valves.

[0050] The cylinder cover 1, 1' further comprises a combustion chamber surface 5, 5' which defines the combustion chamber 2, 2'. In the embodiment described here, the combustion chamber surface 5 is designed in the shape of a truncated cone. In other embodiments, the combustion chamber surface 5 or 5' may have a spherical shape or a mixed spherical-frustum shape. The central bore 3, 3' which accommodates the outlet valve extends in the direction of the combustion chamber axis A. Here, the combustion chamber surface 5, 5' is a truncated cone-shaped surface and therefore has a truncated cone axis. Generally, a combustion chamber surface has an axis of symmetry. This truncated cone axis or axis of symmetry coincides with the combustion chamber axis A and thus with the cylinder axis when the cylinder cover 1 is mounted on the cylinder. The fuel bore 4, 4', which accommodates the fuel injection nozzle, extends in the direction of a fuel axis B, B' and opens into the combustion chamber surface 5, 5', which usually opens into the combustion chamber surface 5, 5' at an angle different from 90 degrees, preferably less than 90 degrees. The fuel bore 4, 4' is provided with a seat 41, 41' for the fuel injection nozzle, on which the fuel injection nozzle is supported when inserted into the fuel bore 4, 4'. This seat 41, 41' is arranged perpendicular to the fuel axis B, B'. The seat 41, 41' is connected to the combustion chamber surface 5, 5' via a nozzle channel 42, 42'. The nozzle channels 42, 42' are designed in such a manner and with such dimensions that the fuel injection nozzles protrude into the combustion chambers 2, 2', i.e., the fuel injection nozzles extend beyond the ends of the nozzle channels 42, 42', whereby the nozzle holes provided in the fuel injection nozzles that introduce fuel into the combustion chambers 2, 2' are located in the combustion chambers 2, 2', i.e., outside the nozzle channels 42, 42'.

[0051] The bearing surfaces 41, 41' are generally designed with a frustoconical shape, which is only indicated as a hint in the drawings, and therefore have an axis of symmetry, which coincides with the fuel axis B, B'.

[0052] Typically, the fuel axis B, B' and the combustion chamber axis A, A' form an angle different from zero and which may be up to 45 degrees depending on the design of the cylinder cover 1 and the spatial conditions of the cylinder cover 1. In particular, the fuel axis B, B' forms an angle with the combustion chamber surface 5, 5' different from 90 degrees, preferably smaller than 90 degrees and larger than 0 degrees.

[0053] The structure and individual components of large diesel engines, such as the injection system in liquid mode, the gas supply system in gas mode, the gas exchange system, the exhaust system, the turbocharger system providing scavenging and air intake, the check and control system of large diesel engines, whether designed as a two-stroke engine or as a four-stroke engine, are well known to those skilled in the art and will not be described further here. In modern large diesel engines, the check and control system is an electronic system, which is usually able to regulate, control or regulate all engine and cylinder functions, in particular the injection (start and end of injection) and the operation of the outlet valves.

[0054] According to the invention, the nozzle channel 42 has a length ratio at most equal to 2, which is defined as the quotient of the maximum length L1 of the nozzle channel 42 and the minimum length L2 of the nozzle channel, which lengths are explained in more detail below on the basis of FIG.

[0055] Due to the relative arrangement of the fuel bore 4 and the combustion chamber surface 5, it is common that the seating surface 41, whose axis of symmetry is identical with the fuel axis B, is not parallel to the combustion chamber surface 5. The nozzle channel 42, which is part of the fuel bore 4, therefore does not open perpendicularly to the combustion chamber surface 5, but at an angle different from 90 degrees, preferably between 0 and 90 degrees. As a result, the length of the nozzle channel 42, i.e. its extension in the direction of the fuel axis B, changes when moving along the circumference of the nozzle channel 42. This is obviously due to the fact that the nozzle channel 42 does not open perpendicularly to the combustion chamber surface 5 or that the seating surface 41 is not parallel to the combustion chamber surface 5. This means that when moving along the circumference of the nozzle channel 42, its length changes in the direction of the combustion chamber axis B between a maximum length L1, at which the distance of the seating surface 41 from the combustion chamber surface 5 is maximum, and a minimum length L2, at which the distance of the seating surface 41 from the combustion chamber surface 5 is minimum.

[0056] It is essential for the present invention to recognize that the variations in the length of the nozzle channel 42, when viewed over its circumference, are a substantial cause of crack formation in the combustion chamber wall 2, in particular in the combustion chamber surface 5. It is therefore proposed according to the present invention to reduce these variations in the length of the nozzle channel 42 so that the length ratio between the maximum length L1 and the minimum length L2 of the nozzle channel 42 is at most 2. This reduction in the variations in the length of the nozzle channel 42 makes it possible to at least significantly reduce the formation of cracks in the combustion chamber 2, in particular in the combustion chamber surface 5, when viewed over its circumference.

[0057] Furthermore, the nozzle channel 42 is designed or dimensioned to protrude beyond the combustion chamber surface 5 into the combustion chamber 2 when the fuel injection nozzle is inserted into the fuel bore 4, such that the nozzle hole provided in the region of the tip of the fuel injection nozzle that introduces fuel into the combustion chamber 2 is positioned within the combustion chamber 2.

[0058] Ideally, the ratio of the maximum length L1 to the minimum length L2 should be equal to 1, i.e. the maximum and minimum lengths L1, L2 are the same, so that the nozzle channel 42 has a constant length over its entire circumference. However, in many applications, this ideal example is not feasible for practical reasons. However, practice has shown that, in particular, crack formation can be reduced, if not completely, then at least very well, when the length ratio is at most 1.5, preferably less than 1.4.

[0059] In order to reduce the length ratio L1 to L2 to a maximum value of 2, in the first embodiment, a bead-shaped protuberance 6 is provided on the combustion chamber surface 5, which defines a portion of the nozzle channel 42, i.e. forms part of the wall of the nozzle channel 42.

[0060] 1, the ridge 6 does not extend around the entire opening of the nozzle channel 42, but only on the side of the nozzle channel 42 facing the combustion chamber axis A. This ridge 6 preferably extends over a maximum of about half the circumference of the nozzle channel 42.

[0061] As already explained, the main function of the ridge 6 is to reduce the variation in the length of the nozzle channel 42. For this reason, the height H of the ridge 6 preferably varies when viewed in the circumferential direction of the nozzle channel 42. This height H refers to the extension of the ridge 6 perpendicular to the surface 5 of the combustion chamber. In FIG. 3, the height H is depicted where its height is at its maximum. The height H preferably has its maximum where the nozzle channel 42 would have its minimum length without the ridge 6.

[0062] The length of the nozzle channel 42 and the height of the ridge 6 are dimensioned such that when the fuel injection nozzle is inserted, fuel exiting the nozzle hole of the fuel injection nozzle is injected over the ridge 6 rather than against it.

[0063] The ridge 6 also has a maximum width B that is at least half as large as the radius R of the cylindrical nozzle channel 42. This width B is a dimension that indicates how far the ridge 6 of the combustion chamber surface 5 extends from the opening of the nozzle channel 42. The maximum width B is preferably at least as large as the radius R of the nozzle channel 42.

[0064] There are several possible ways of producing the ridges 6. For example, the ridges can be produced integrally with the cylinder cover 1 during its manufacture in a forging or casting process. However, it is also possible to produce the ridges 6 in a separate machining process after the cylinder cover has been manufactured, for example by a welding process such as build-up welding. This last-mentioned measure is particularly advantageous for repairs or maintenance of cylinder covers 1 that are already in use.

[0065] Figures 4 and 5 show a second embodiment of a cylinder cover according to the invention. Figure 4 is a cross-sectional view of the second embodiment along the combustion chamber axis A. Figure 5 is an enlarged view of a detail of Figure 4, similar to Figure 3.

[0066] In a second embodiment, in order to reduce the length ratio between the maximum length L1 and the minimum length L2 of the nozzle channel 42, a recess 7 into which the nozzle channel 42 opens is provided in the combustion chamber surface 5. This recess 7 is preferably designed in the shape of a ring segment or in the shape of a ring and is coaxial with the cylindrical nozzle channel 42, the axis of which is the fuel axis B. The radius of the recess 7 is indicated with the symbol RA.

[0067] This allows the nozzle channel 42 to be shortened along its periphery in areas where the nozzle channel 42 would be longer than in other areas without the recess 7. In this embodiment, the nozzle channel 42 is shortened at least in the area where it has its greatest length without the recess 7.

[0068] 5, in the second embodiment, there is an example of an embodiment in which the maximum length L1 is the same as the minimum length L2, i.e. L1=L2, meaning that the length of the nozzle channel 42 has a constant value when viewed around its circumference, thus resulting in a length ratio equal to 1.

[0069] The recess 7 is preferably designed to reduce the length ratio of L1 to L2 to a predetermined value. As already mentioned, the minimum value of the length ratio is equal to 1. However, for many applications it is quite sufficient in practice to adjust the length ratio to a value greater than 1, for example 1.5. The respective desired value of the length ratio is determined by the geometric dimensions of the recess.

[0070] Since the recess 7 is primarily intended to reduce or compensate for the difference between the maximum length of the nozzle channel 42 without the recess 7 and the minimum length of the nozzle channel without the recess 7, it is advantageous if the recess 7 extends over at least half the circumferential length of the nozzle channel 42 when viewed in the circumferential direction of the nozzle channel 42. The recess 7 may also extend over the entire circumference of the nozzle channel 42 when viewed in the circumferential direction of the nozzle channel 42. The depth of the recess 7 perpendicular to the combustion chamber surface 5 varies in the circumferential direction of the nozzle channel 7 in order to reduce the difference between the minimum length L2 and the maximum length L1 to the desired value.

[0071] The radius RA of the recess 7 is preferably at least twice the radius R of the nozzle channel 42 .

[0072] There are several possible ways of producing the recesses 7. For example, the recesses 7 can be produced integrally with the cylinder cover 1 during its manufacture in a forging or casting process. However, it is also possible to produce the recesses 7 in a separate machining process after the cylinder cover 1 has been manufactured, for example by a machining process such as milling. This last-mentioned measure is particularly advantageous for repairs or maintenance of cylinder covers 1 that are already in use.

[0073] The realization, which is crucial to the present invention, that the change in length of the nozzle channel 42 connecting the seat 41 of the fuel bore 4 with the combustion chamber 2, when viewed around the circumference of the nozzle channel 42, is a substantial cause of crack formation in the combustion chamber wall 2, can also be advantageously used for repairing cylinder covers 1 of large diesel engines.

[0074] The method for repairing a cylinder cover 1 of a cylinder of a large diesel engine according to the invention is characterized in that the combustion chamber surface 5 of the cylinder cover 1 is machined in such a way that the length ratio, which is the ratio between the maximum length L1 of the nozzle channel 42 and the minimum length L2 of the nozzle channel 42, is at most equal to 2.

[0075] For this reason, the length ratio is preferably varied by applying bead-shaped protuberances 6 to the combustion chamber surface 5, for example by a welding process, or by providing recesses in the combustion chamber surface 5, for example by milling.

Claims

1. A cylinder cover for a cylinder of a large diesel engine, comprising at least one fuel bore (4) for accommodating a fuel injection nozzle and a combustion chamber surface (5) defining a combustion chamber (2) having a combustion chamber axis (A), said fuel bore (4) extending in the direction of a fuel axis (B) and opening into said combustion chamber surface (5), said fuel bore (4) is provided with a seating surface (41) for a fuel injection nozzle, said seating surface (41) having an axis of symmetry coinciding with said fuel axis (B) and connected to the combustion chamber surface (5) by a nozzle channel (42), said nozzle channel (42) having a length ratio between a maximum length (L1) of the nozzle channel (42) and a minimum length (L2) of the nozzle channel (42) which is at most equal to 2, said combustion chamber surface (5) being provided with a bead-shaped ridge (6) defining a part of said nozzle channel (42), said ridge (6) being designed to reduce said length ratio to a predetermined value. A cylinder cover characterized by:

2. 2. The cylinder cover according to claim 1, wherein the length ratio is a maximum of 1.

5.

3. 2. A cylinder cover according to claim 1, characterized in that the raised portion (6) defines the nozzle channel (42) on the side facing the combustion chamber axis (A).

4. 4. A cylinder cover as claimed in claim 1 or 3, characterized in that the raised portion (6) extends over a maximum of half the peripheral length of the nozzle channel (42) when viewed in the circumferential direction of the nozzle channel (42).

5. 4. A cylinder cover according to claim 1 or 3, characterized in that the height (H) of the raised portion (6) varies when viewed in the circumferential direction of the nozzle channel (42).

6. 4. A cylinder cover according to claim 1 or 3, characterized in that the raised portion (6) has a maximum width (B) at least as large as half the radius (R) of the nozzle channel (42).

7. 3. The cylinder cover of claim 2, wherein the length ratio is less than 1.

4.

8. 4. Cylinder cover according to claim 1 or 3, characterized in that the ridge (6) has a maximum width (B) at least as large as the radius (R) of the nozzle channel (42).

9. A method for repairing a cylinder cover of a cylinder of a large diesel engine, said cylinder cover having at least one fuel bore (4) for accommodating a fuel injection nozzle and a combustion chamber surface (5) defining a combustion chamber (2) having a combustion chamber axis (A), said fuel bore (4) extending in the direction of a fuel axis (B) and opening into said combustion chamber surface (5), said fuel bore (4) is provided with a seating surface (41) for a fuel injection nozzle, said seating surface (41) having an axis of symmetry coinciding with said fuel axis (B) and connected to the combustion chamber surface (5) by a nozzle channel (42), said combustion chamber surface (5) of said cylinder cover (1) being treated in such a way that a length ratio between a maximum length (L1) of said nozzle channel (42) and a minimum length (L2) of said nozzle channel (42) is at most 2, A method comprising:

10. 10. The method according to claim 9, characterized in that the length ratio is varied by applying bead-shaped protuberances (6) to the combustion chamber surface (5) or by providing recesses (7) in the combustion chamber surface (5).

11. 11. A large diesel engine having at least one cylinder, characterized in that the at least one cylinder has a cylinder cover (1) designed according to any one of claims 1 to 8 or repaired by the method of claim 9 or 10.

12. 12. A large diesel engine according to claim 11, characterised in that the large diesel engine is a longitudinally scavenged, two-stroke large diesel engine.

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