Large diesel engine

Abstract

This invention provides a dual-fuel large diesel engine that reduces the thermal load on the piston rings in gaseous mode. [Solution] A large diesel engine can operate in a liquid mode in which liquid fuel is introduced and in a gaseous mode in which gas is introduced as fuel, and has at least one cylinder 10. A piston is positioned to move axially along the cylinder wall between a lower reversal point UT and an upper reversal point OT, and has an upper surface for defining a combustion chamber 13 within the cylinder. At least one gas introduction opening 4 is provided in the cylinder wall 11, and in gaseous mode, gas is introduced into the cylinder through the gas introduction opening, and this gas introduction ends at the latest at the inlet distance. This inlet distance is the axial distance of the upper surface of the piston from the gas introduction opening and is at least 14% of the stroke S defined by the difference in the position of the upper surface of the piston at the upper reversal point and the lower reversal point.

Description

Technical Field

[0001] The present invention relates to a method for operating a large diesel engine designed as a dual-fuel large diesel engine, and also to a large diesel engine as described in the first part of the independent claims.

Background Art

[0002] Large diesel engines have traditionally operated on heavy fuel oil. Large diesel engines that can be 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, for example, are often used in steady operation to drive large generators for generating electrical energy. The engines usually operate continuously for long periods, and therefore there are high requirements for operating safety and availability. As a result, particularly long maintenance intervals, low wear, and economical handling of operating materials are major criteria for the operator. Large diesel 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 more are in use.

[0003] Also, in terms of economic and efficient operation, compliance with exhaust gas regulation values, and resource availability, alternatives to fuel heavy oil are currently 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.

[0004] Known examples of liquid fuels as alternatives to heavy fuel oil include other heavy hydrocarbons, particularly those remaining as petroleum refining residues, alcohols, especially methanol or ethanol, gasoline, diesel fuel, or emulsions or suspensions. For example, emulsions known as multiphase superfine atomized residue (MSAR) 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. Known gaseous fuels include natural gas such as liquefied natural gas (LNG), liquefied gas such as liquefied petroleum gas (LPG), or ethane.

[0005] In particular, large diesel engines capable of operating on at least two different fuels are known, allowing the engine to run on one fuel or the other depending on the operating conditions or environment.

[0006] One example of a large diesel engine that can operate on two different fuels is a large diesel engine designed as a dual-fuel large diesel engine. This can operate in liquid mode, where liquid fuel is introduced into the cylinder for combustion, and in gaseous mode, where gas is introduced into the cylinder as fuel.

[0007] Large diesel engines, capable of operating on 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 is carried out by spark ignition of a flammable, pre-mixed air-fuel mixture. This spark ignition can be achieved, for example, by an electric spark using a spark plug, or by the autoignition of a small amount of injected fuel, which then triggers spark ignition of another fuel. Often, a small amount of fuel intended for autoignition is injected into a pre-combustion chamber connected to the combustion chamber.

[0008] Furthermore, mixed configurations known for Otto and diesel operation are also known.

[0009] Within the framework of this application, the term “large diesel engine” refers to such an engine that can operate in at least diesel mode. In particular, the term “large diesel engine” also includes dual-fuel large engines that can operate in another mode in addition to diesel mode, such as Otto mode.

[0010] Within the framework of this application, the terms “gas mode” or “operation in gas mode” refer to using only gas or gaseous fuel as fuel for combustion that generates torque. As mentioned above, it is possible and quite common to inject a small amount of self-igniting liquid fuel, such as heavy oil, in gas mode for spark ignition of a pre-mixed air-fuel mixture; nevertheless, the torque-generating combustion process is operated entirely with gas or gaseous fuel.

[0011] This process of spark ignition through the self-ignition of a small amount of liquid fuel is sometimes called pilot injection. This pilot injection is completely unrelated to the injection of liquid fuel into the combustion chamber when a large engine is operating in liquid mode. Pilot injection typically uses a different injection system than that used for injecting liquid fuel in liquid mode. Also, in pilot injection, the small amount of liquid fuel is often injected not directly into the combustion chamber, but into at least one pre-combustion chamber connected to the combustion chamber via a channel.

[0012] Furthermore, it is known that such large diesel engines can be operated in gaseous mode using a low-pressure process, where gas is introduced into the cylinder in a gaseous state, with an injection pressure of up to 50 bar, preferably up to 20 bar. For this purpose, at least one gas inlet opening is provided in the cylinder wall, through which gas is introduced into the cylinder in gaseous mode. In practice, two gas inlet openings are often provided on radially opposite sides with respect to the cylinder axis. The gas inlet openings are positioned at a height between the lower and upper reversal points of the piston motion, such that gas can be introduced into the cylinder during the upward movement of the piston, provided that no compression has yet occurred in the cylinder, or at least no substantial compression has yet occurred.

[0013] The introduction of gas must be completed no later than immediately before the piston passes the gas introduction opening during its upward movement.

[0014] One problem with operation in gaseous mode is that as the compression increases after the outlet valve closes and gas introduction ends, gas is also forced into the region between the piston and the cylinder wall, along which the piston moves during its stroke. This gap between the upper region of the piston and the cylinder wall is defined at the bottom by the piston rings. If multiple piston rings are provided, the first piston ring, i.e., the piston ring located closest to the combustion chamber, defines the gap-type region between the upper region of the piston and the cylinder wall at the bottom. Since this gap-type region is also filled with gas or gaseous fuel, the piston ring or the first piston ring is subjected to a very high thermal load during the combustion process, which increases wear or other heat-induced deterioration of the piston ring. Similar heat-induced problems can occur in or within the piston groove where the piston ring, and in particular the first piston ring, is located. [Overview of the project] [Problems that the invention aims to solve]

[0015] This invention aims to solve this problem.

[0016] Therefore, the object of the present invention is to propose a method for operating a large diesel engine designed as a dual-fuel large diesel engine that can also operate in gas mode, in which the thermal load, particularly the thermal load on the piston rings or the first piston ring, is significantly reduced in gas mode. Furthermore, the object of the present invention is to propose a large diesel engine that operates in such a manner. [Means for solving the problem]

[0017] To achieve these objectives, the subject matter of the present invention is characterized by the configuration of independent claims in each category.

[0018] Accordingly, the present invention proposes a method for operating a large diesel engine designed as a dual-fuel large diesel engine, which can be operated in liquid mode, where liquid fuel is introduced into the cylinder for combustion, and further in gas mode, where gas is introduced into the cylinder as fuel, wherein the large diesel engine comprises at least one cylinder, the piston being positioned to move axially back and forth (i.e., reciprocate) along the cylinder wall between a lower reversal point and an upper reversal point, the piston having an upper surface defining a combustion chamber within the cylinder, and at least one gas inlet opening provided in the cylinder wall, through which gas is introduced into the cylinder as fuel in gas mode, the introduction of gas being terminated at an inlet distance, where the inlet distance is the distance from the gas inlet opening to the upper surface of the piston in the axial direction, and the inlet distance is at least 14% of the stroke defined by the difference in the position of the upper surface of the piston at the upper reversal point and the lower reversal point.

[0019] Therefore, in the method according to the present invention, the introduction of gas into the cylinder is completed very early in the gaseous mode with respect to the piston movement from the lower reversal point to the upper reversal point. The entire process of introducing gas is thus performed very early with respect to the piston position, i.e., when the upper surface of the piston is still away from the gas introduction opening in the axial direction. This means that when the gas introduction is completed, an air cushion still exists between the upper surface of the piston and the injected gas. During the further compression movement of the piston, this air cushion is also compressed, in particular, to prevent gas from being forced into the air gap area between the piston and the cylinder wall. The upper region of the piston, i.e., the upper surface of the piston and the piston groove, as well as the first piston ring, are much better protected by this air cushion from the heat generated during the combustion process. Thus, the first piston ring in particular remains much cooler, thereby greatly reducing heat-induced wear or deterioration.

[0020] The closing of the outlet valve is preferably adapted such that the introduced gas is at least preferably completely prevented from slipping directly from the gas introduction opening through the outlet valve into the exhaust system.

[0021] The optimal inlet distance at which the introduction of the gas is preferably ended at the latest also depends on the specific design and, in particular, on the geometry of the cylinder, such as the piston stroke or the axial distance from the lower reversal point to the gas introduction opening. However, the operating parameters of a large engine, such as the load at which the engine is operated, can also influence the optimal inlet distance. In the following, some preferred limiting values of the inlet distance, which are demonstrated in various application examples, are shown.

[0022] In some application examples of the method according to the present invention, it is advantageous if the inlet distance is at least 18% of the stroke.

[0023] In some application examples of the method according to the present invention, it is advantageous if the inlet distance is at least 20% of the stroke.

[0024] In some application examples of the method according to the present invention, it is advantageous if the inlet distance is at least 23% of the stroke.

[0025] In some application examples of the method according to the present invention, it is advantageous if the inlet distance is at least 26% of the stroke.

[0026] In some application examples of the method according to the present invention, it is advantageous if the inlet distance is at least 29% of the stroke.

[0027] On the other hand, it has also been demonstrated that it is advantageous not to select an overly large inlet distance. The reason is that when the gas is introduced very early, an excessive amount of the introduced gas may be discharged through the exhaust valve together with the exhaust gas by the scavenging process before the exhaust valve closes. This can lead to a problem known as methane slip. Methane is typically contained in gaseous fuels commonly used as fuels in the gaseous mode at a relatively high ratio. When methane enters the exhaust system in an unburned state, the methane concentration in the exhaust gas significantly increases. Since methane is known to be a very environmentally harmful substance, efforts have been made to avoid methane slip as much as possible. Methane is a very powerful greenhouse gas and is known to have a greenhouse effect at least 25 times higher than carbon dioxide, which can have a significant adverse impact on the calculation of the so-called "Energy Efficiency Design Index (EEDI)", and thus has a negative effect from the perspective of efficient and low-emission engine operation.

[0028] Therefore, it is preferable that the inlet distance is at most 35% of the stroke.

[0029] In some applications, it is preferable that the inlet distance is at most 33% of the stroke.

[0030] According to a preferred embodiment, the introduction of the gas starts at an introduction angle, which indicates the crank angle at which the opening of the gas introduction opening starts. The introduction angle is 10° - 25° smaller than the crank angle at which the piston is located at the inlet distance.

[0031] [[ID=1,5]] In some applications, it is preferable that the introduction angle is 15° - 20° smaller than the crank angle at which the piston is located at the inlet distance.

[0032] Another preferred method, particularly advantageous in partial load operation at low or light loads of less than 50% of the full load, is to close the outlet valve for exhausting combustion gases from the cylinder before gas begins to be introduced into the cylinder. In this way, it is possible to avoid the possibility that the introduced gas or a portion of it may be directly discharged into the exhaust system before the combustion process takes place in the combustion chamber.

[0033] Particularly preferably, two gas inlet openings are provided, which are positioned at the same height in the axial direction. Here, it is particularly preferable that the two gas inlet openings are positioned radially opposite each other on the cylinder wall.

[0034] Furthermore, it is preferable that each gas inlet opening is positioned at a height of 40% to 55% of the stroke in the axial direction, and that the height is measured from the position of the top surface of the piston when the piston is at the lower reversal point.

[0035] Furthermore, a large diesel engine operated by the method according to this invention is proposed.

[0036] Preferably, the large diesel engine is designed as a longitudinally scavenging two-stroke large diesel engine.

[0037] Further advantageous means and embodiments of the present invention can be obtained from the dependent claims.

[0038] The present invention will be described in more detail below based on embodiments and drawings. The drawings show the following: [Brief explanation of the drawing]

[0039] [Figure 1] This is a schematic cross-sectional view of a cylinder of one embodiment of a large diesel engine according to the present invention. [Figure 2] This is a schematic cross-sectional view, similar to Figure 1, but with the piston at the inlet distance. [Modes for carrying out the invention]

[0040] The term "large diesel engine" typically refers to an engine used as the main propulsion system for a ship, or even in steady operation to drive a large generator, for example, to produce electrical energy. Typically, the cylinders of a large diesel engine have a bore of at least approximately 200 mm each. The term "longitudinal scavenging" means that scavenging air or intake air is introduced into the cylinder in the lower end region.

[0041] The following description of the present invention refers to a dual-fuel large diesel engine, that is, a large diesel engine designed to operate on two different fuels. In particular, a dual-fuel large diesel engine can operate in liquid mode, where only liquid fuel is injected into the combustion chamber of the cylinder. Typically, liquid fuel, such as heavy 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. A large diesel engine can also operate in gaseous mode, where the gas that acts as fuel, such as natural gas such as liquefied natural gas (LNG), or liquefied petroleum gas (LPG), or ethane, is ignited in the combustion chamber in the form of a pre-mixed air-fuel mixture.

[0042] As already explained above, the terms “gas mode” or “operation in gas mode” should be understood within the framework of this application as a large diesel engine operating in this gas mode with only gas or gaseous fuel, and optionally a small amount of self-igniting fuel, such as heavy oil or diesel oil, being introduced into the combustion chamber or pre-combustion chamber or multiple pre-combustion chambers solely for spark ignition of the air-gas mixture (pilot injection).

[0043] In particular, large diesel engines operate in gas mode according to a low-pressure process, i.e., gas is introduced into the cylinder in a gaseous state, and the injection pressure at which the gas is introduced into the cylinder is a maximum of 50 bar, preferably a maximum of 20 bar. The air-gas mixture is spark-ignited in the combustion chamber according to Otto's principle. Typically, this spark ignition is caused by introducing a small amount of self-igniting liquid fuel (e.g., diesel oil or heavy oil) into the combustion chamber or pre-combustion chamber or multiple pre-combustion chambers at the appropriate moment, and then this fuel self-ignites, causing spark ignition of the air-fuel mixture in the combustion chamber.

[0044] The embodiments described herein refer to a large diesel engine designed as a longitudinal scavenging, twin-fuel, two-stroke, large diesel engine with a crosshead drive.

[0045] In a highly simplified representation, Figure 1 shows one of several cylinders in this embodiment of a large diesel engine, the cylinder as a whole being denoted by reference numeral 10. Inside cylinder 10, a piston 2 is positioned in a manner known to itself, and is movably reciprocated along the cylinder wall 11 in the axial direction A between a lower reversal point UT and an upper reversal point OT. The axial direction A is defined by the cylinder axis of cylinder 10.

[0046] The piston 2, together with the cylinder cover 12, has an upper surface 21 that defines a combustion chamber 13 in which the combustion process takes place. The piston 2 has at least one first piston ring 22 (Figure 2), but typically has multiple piston rings, each of which is positioned in a piston groove 23 that extends around the perimeter of the piston 2.

[0047] As is known in crosshead drive, the piston 2 is connected to a crosshead (not shown) via a piston rod 6, and the crosshead is connected to a crankshaft (not shown) via a push rod (not shown), thereby the movement of the piston 2 is transmitted to the crankshaft via the piston rod 6, the crosshead, and the push rod, causing the crankshaft to rotate.

[0048] The structure and individual components of such large diesel engines, including injection systems for liquid mode (not shown), gas supply systems for gas mode, gas exchange for supplying scavenging or intake air, exhaust systems (not shown) or turbocharger systems (not shown), and inspection and control systems (not shown), are well known to those skilled in the art in both two-stroke and four-stroke engine designs, so no further explanation is needed here.

[0049] For the purpose of understanding the present invention, Figure 1 shows only one of these components, the outlet valve 3, and similarly shows two gas inlet openings 4 into which gas is introduced to act as fuel in the cylinder 10 in gaseous mode. The two gas inlet openings 4 are preferably arranged in the cylinder wall 11 so as to be radially opposite each other. In other embodiments, of course, there may be only one gas inlet opening 4, or three or more gas inlet openings 4. It is also possible to provide multiple gas inlet openings at different heights with respect to the axial direction A.

[0050] In modern large diesel engines, the inspection and control systems are electronic systems that can typically be used to adjust, control, or adjust the functions of all engines or cylinders, particularly injection (initiation and termination of injection) in both gaseous and liquid modes, and the operation of the outlet valves.

[0051] In the embodiment of the longitudinally scavenging two-stroke large diesel engine described herein, scavenging slots 5 are typically provided in the lower region of each cylinder 10 or each cylinder liner, and the scavenging slots 5 are periodically opened and closed by the movement of the piston 2 in the cylinder 10, thereby allowing scavenging air supplied by the turbocharger under intake pressure into an intake receiver (not shown) to flow into the cylinder 10 through the scavenging slots 5 as long as the scavenging slots 5 are open. This is indicated in Figure 1 by two arrows denoted by reference numeral L. The cylinder head or cylinder cover 12 is provided with an outlet valve 3 located approximately in the center, through which combustion gases can be discharged from the cylinder 10 into an exhaust system (not shown) after the combustion process. The exhaust system directs at least a portion of the combustion gases to the turbine (not shown) of the turbocharger, and the compressor of the turbocharger supplies intake air into the intake receiver under intake air pressure.

[0052] One or more fuel injection nozzles (not shown) are provided to introduce liquid fuel into the combustion chamber 13 of the cylinder 10 in liquid mode, and these nozzles are positioned, for example, near the outlet valve 3 in the cylinder cover 12. For example, heavy oil or diesel oil may be burned as liquid fuel in liquid mode.

[0053] For gas supply or introduction in gaseous mode, a gas supply system known by itself is provided, of which only two gas inlet openings 4 are shown in Figures 1 and 2. Preferably, each gas inlet opening 4 is designed as a gas inlet valve equipped with a gas inlet nozzle.

[0054] In Figure 1, the position of piston 2 when it is at the upper reversal point OT is shown by a solid line, and the position of piston 2 when it is at the lower reversal point UT is shown by a dotted line. The distance between the position of the upper surface 21 of piston 2 relative to the axial A when piston 2 is at the upper reversal point OT and the position of the upper surface 21 of piston 2 when piston 2 is at the lower reversal point UT is shown as the stroke S. This distance between the upper reversal point OT and the lower reversal point UT that defines the stroke S can exceed several meters, for example, up to 3 meters, in large diesel engines.

[0055] In Figure 1, various crank angles are additionally shown on the left. The crank angle indicates the position of the crankshaft and, in a way known by itself, characterizes the operating cycle of a large diesel engine. At a crank angle of 180°, piston 2 is at the lower reversal point UT, also called bottom dead center, and at a crank angle of 360°, piston 2 is at the upper reversal point OT, also called top dead center. If designed as a two-stroke engine, the entire operating cycle has 360°. Starting from a crank angle of 0°, with piston 2 in the same position as at a 360° crank angle, i.e., the upper reversal point OT, piston 2 moves downward during the expansion stroke until it reaches the lower reversal point UT at 180°. During the subsequent compression stroke, piston 2 moves upward again, again until it reaches the upper reversal point OT at 360°. Spark ignition or autoignition of the fuel typically occurs during the compression stroke just before piston 2 reaches the upper reversal point OT.

[0056] This invention relates, in detail, to the operation of a large diesel engine in gaseous mode.

[0057] The gas inlet opening 4 is positioned in the cylinder wall 11 at a height H, which is approximately midway between the upper reversal point OT and the lower reversal point UT of the piston 2 with respect to the axial direction A. This height H represents the distance between the gas inlet opening 4 and the upper surface 21 of the piston 2 in the axial direction A when the piston 2 is at the lower reversal point UT. The absolute value of this distance naturally depends on the specific design of the large diesel engine, and in particular on the stroke S, so the height H is expressed as a ratio to the stroke S.

[0058] For example, when the height H is 50%, the gas inlet opening 4 is positioned exactly midway between the position of the upper surface 21 of the piston 2 at the upper reversal point OT and the position of the upper surface 21 of the piston 2 at the lower reversal point UT, with respect to the axial direction A. When the height H is less than 50%, the gas inlet opening 4 is positioned closer to the lower reversal point UT with respect to the axial direction A. When the height H is greater than 50%, the gas inlet opening 4 is positioned closer to the upper reversal point OT with respect to the axial direction A.

[0059] The height H at which the gas inlet opening 4 is positioned in a specific application also depends, in particular, on or near the cylinder 10, on the space available for the gas supply system. It has been demonstrated that positioning the gas inlet opening 4 at a height H that is at least 40% and up to 55% of the stroke S with respect to the axial A is useful in many applications.

[0060] According to this invention, when a large diesel engine is operated in gaseous mode, the introduction of gas is terminated at an inlet distance E, where the inlet distance E is the distance from the gas introduction opening 4 to the upper surface of the piston 2 in the axial direction A, and the inlet distance E is at least 14% of the stroke S.

[0061] This will be explained in more detail below based on the examples shown in Figures 1 and 2.

[0062] In Figure 2, the solid line shows the position of piston 2 at inlet distance E, i.e., the position of piston 2 when the introduction of gas into cylinder 10 has just finished in each operating cycle. This refers to the point after the closing process of the gas introduction opening 4, when the gas introduction opening 4 is just completely closed, thereby preventing any further gas from flowing into cylinder 10. Furthermore, in Figure 2, the dotted line shows the position of piston 2 when it is at the lower reversal point UT.

[0063] If the gas inlet opening 4 is designed as a gas inlet valve comprising a valve body that is lifted from the valve seat by an opening stroke and pushed into the valve seat by a closing stroke, thereby interacting with the valve seat to create a seal, then the inlet distance E is the axial distance A between the upper surface 21 of the piston 2 and the gas inlet opening 4 at the point when the valve body is just fully reinserted into the valve seat, interacting with the valve seat to create a seal, thereby preventing any further gas from flowing into the cylinder 10 through the gas inlet opening 4.

[0064] The start of gas injection refers to the point in time when gas injection into cylinder 10 begins using a similar method, for example, the point in time when the valve body begins to lift from its valve seat due to the stroke motion of the valve body, or the position of piston 2.

[0065] For example, if the maximum stroke of the valve body is 100%, and the 100% stroke corresponds to the position of the valve body where the gas inlet opening 4 is fully open, and the 0% stroke corresponds to the position of the valve body where it interacts with the valve seat and becomes sealed, then the start of gas injection is when the valve body stroke begins to increase from 0%. The end of gas injection is when the valve body stroke takes its value back to 0%.

[0066] The same applies to other designs of the gas inlet opening 4. The start of gas injection is indicated by the point at which the gas flow through the gas inlet opening 4 begins (or the position of the piston 2 as measured by the crank angle). The end of gas injection is indicated by the point at which the gas flow through the gas inlet opening 4 ends (or the position of the piston 2 as measured by the crank angle).

[0067] Therefore, the inlet distance E is the distance from the gas introduction opening 4 to the upper surface 21 of the piston 2 at the end of gas injection.

[0068] According to this invention, the inlet distance E is at least 14% of the stroke S. This means that at the end of gas injection, the upper surface 21 of the piston 2 is still at least 14% of the stroke S away from the gas introduction opening 4. As a result of gas injection into the cylinder 10 being terminated in this way very early in the operating cycle, when gas injection is terminated, there is an air cushion on the upper surface 21 of the piston 2, positioned between the upper surface 21 of the piston 2 and the introduced gas. This air cushion prevents gas from entering the annular gap region between the piston 2 and the cylinder wall 11, which is defined at the bottom by the first piston ring 22, at least over a wide area. Therefore, the air cushion reduces the heat load on both the upper surface 21 of the piston 2 and the first piston ring 22, as well as on the piston groove 23.

[0069] The optimal value of the inlet distance E depends on specific application examples of the method according to the present invention, particularly the design of the large diesel engine operated by the method according to the present invention.

[0070] In practice, several applications of the method according to the present invention have shown that it is advantageous for the inlet distance E to be at least 18% of the stroke S.

[0071] In some applications, it is advantageous for the entry distance E to be at least 20% of the stroke S.

[0072] In some applications, it is advantageous for the entry distance E to be at least 23% of the stroke S.

[0073] In some applications, it is advantageous for the entry distance E to be at least 26% of the stroke S.

[0074] In some applications, it is advantageous for the entry distance E to be at least 29% of the stroke S.

[0075] In practice, it has been demonstrated that selecting an inlet distance E that is too large can lead to significant methane slippage, so it is advantageous not to select an inlet distance E that is too large.

[0076] Therefore, the inlet distance E is preferably 35% of the stroke S.

[0077] In some applications, it is advantageous for the entry distance E to be up to 33% of the stroke S.

[0078] Since it takes time to introduce the amount of gas necessary for combustion into the cylinder 10, it is preferable that the introduction of gas be started at an introduction angle that is preferably 10° to 25° smaller than the crank angle at which the piston 2 is located at inlet distance E. The introduction angle thus represents the crank angle at which the opening of the gas introduction opening 4 begins, i.e., the crank angle at which the introduction of gas into the cylinder 10 begins. As a result, it is preferable that the introduction of gas into the cylinder be carried out over a crank angle range of at least 10° and a maximum of 25°.

[0079] In some applications, it is preferable that the entry angle is at least 15° and up to 20° smaller than the crank angle at which the piston 2 is located at inlet distance E.

Claims

1. A large diesel engine designed as a dual-fuel large diesel engine, the large diesel engine can be operated in liquid mode, in which liquid fuel is introduced into the cylinder (10) for combustion, and can also be operated in gaseous mode, in which gas is introduced into the cylinder (10) as fuel, the large diesel engine having at least one cylinder (10), in which a piston (2) is arranged to reciprocate axially along the cylinder wall (11) between a lower reversal point (UT) and an upper reversal point (OT), the piston (2) having an upper surface (21) for defining a combustion chamber (13) within the cylinder (10), and at least one gas inlet opening (4) is provided in the cylinder wall (11), and in gaseous mode, the gas is introduced into the cylinder (10) as fuel through the gas inlet opening, The large diesel engine is configured in gaseous mode to terminate the introduction of the gas at an inlet distance (E), where the inlet distance (E) is the distance from the gas introduction opening (4) to the upper surface (21) of the piston (2) in the axial direction (A), and the inlet distance (E) is at least 14% of the stroke (S) defined by the difference in the position of the upper surface (21) of the piston (2) at the upper reversal point (OT) and the lower reversal point (UT). A large diesel engine characterized by the following features.

2. The large diesel engine according to claim 1, wherein the inlet distance (E) is at least 18% of the stroke (S).

3. The large diesel engine according to claim 1 or 2, wherein the inlet distance (E) is at least 20% of the stroke (S).

4. The large diesel engine according to any one of claims 1 to 3, wherein the inlet distance (E) is at least 23% of the stroke (S).

5. The large diesel engine according to any one of claims 1 to 4, wherein the inlet distance (E) is at least 26% of the stroke (S).

6. The large diesel engine according to any one of claims 1 to 5, wherein the inlet distance (E) is at least 29% of the stroke (S).

7. The large diesel engine according to any one of claims 1 to 6, wherein the inlet distance (E) is a maximum of 35% of the stroke (S).

8. The large diesel engine according to any one of claims 1 to 7, wherein the inlet distance (E) is a maximum of 33% of the stroke (S).

9. The large diesel engine according to any one of claims 1 to 8, wherein the introduction of the gas is initiated at an introduction angle, the introduction angle being the crank angle at which the gas introduction opening (4) begins to open, and the introduction angle being 10° to 25° smaller than the crank angle when the piston (2) is at the inlet distance (E).

10. The large diesel engine according to claim 9, wherein the entry angle is 15° to 20° smaller than the crank angle when the piston (2) is located at the inlet distance (E).

11. The large diesel engine according to any one of claims 1 to 10, wherein the outlet valve (3) for discharging combustion gas from the cylinder (10) is configured to close before the introduction of the gas into the cylinder (10) begins.

12. A large diesel engine according to any one of claims 1 to 11, wherein two gas inlet openings (4) are provided, which are arranged at the same height (H) with respect to the axial direction (A).

13. A large diesel engine according to any one of claims 1 to 12, wherein each gas inlet opening (4) is positioned at a height (H) of 40% to 55% of the stroke (S) with respect to the axial direction (A), and the height (H) is measured from the position of the upper surface (21) of the piston (2) when the piston (2) is at the lower reversal point (UT).

14. A large diesel engine according to any one of claims 1 to 13, designed as a longitudinal scavenging two-stroke large diesel engine.

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