Internal combustion engine

Abstract

A two-stroke uniflow scavenging crosshead internal combustion engine is disclosed, which includes at least one cylinder, a cylinder cover, a piston, a fuel gas supply system, and a scavenging air system. The two-stroke uniflow scavenging crosshead internal combustion engine is configured to inject fuel gas into the at least one cylinder via the fuel gas supply system, the fuel gas supply system including one or more fuel gas valves for the at least one cylinder at least partially disposed in the cylinder wall. The fuel gas supply system is configured to inject fuel gas into the at least one cylinder during a compression stroke during at least a first fuel gas injection event and a second fuel gas injection event subsequent to the first fuel gas injection event.

Description

Technical Field

[0001] The present invention relates to a two-stroke internal combustion engine and a non-transitory computer-readable medium.

Background Art

[0002] Two-stroke internal combustion engines are used as propulsion engines in ships such as container ships, bulk carriers, and tankers. The reduction of undesirable exhaust gases from internal combustion engines has become increasingly important.

[0003] An effective way to reduce the amount of undesirable exhaust gases is to switch from fuel oil, such as heavy fuel oil (HFO), to fuel gas. The fuel gas can be injected into the cylinder at the end of the compression stroke, where the fuel gas can be immediately ignited either by the high temperature reached when the gas in the cylinder is compressed or by the ignition of a pilot fuel. However, injecting fuel gas into the cylinder at the end of the compression stroke requires a large gas compressor to compress the fuel gas before injection in order to overcome the large pressure in the cylinder.

[0004] However, large gas compressors are expensive and complex to manufacture and maintain. One way to avoid the need for a large compressor is to have a fuel gas valve configured to inject fuel gas at the beginning of the compression stroke where the pressure in the cylinder is significantly lower.

[0005] EP3015679 discloses such a fuel gas valve.

[0006] However, it can be difficult to ensure a rapid and efficient mixing of the scavenging air and the fuel gas in the cylinder.

[0007] Having a non-uniform mixture of fuel gas and scavenging air can result in insufficient combustion of the fuel gas or premature ignition or knocking.

[0008] One possible solution is to inject the fuel gas very early in the compression stroke, allowing the gases to mix over a longer period of time. However, if the fuel gas is injected into the cylinder before the exhaust valve is closed, undesirable fuel gas leakage may occur.

[0009] Therefore, improving the mixing of fuel gas and scavenging air in the cylinder remains a challenge. [Overview of the Initiative]

[0010] According to a first aspect, the present invention relates to a two-stroke uniflow scavenging crosshead internal combustion engine comprising at least one cylinder, a cylinder cover, a piston, a fuel gas supply system, and a scavenging air system, wherein the cylinder has a cylinder wall, the cylinder cover is located on the top of the cylinder and has an exhaust valve, the piston is located to be movable within the cylinder between bottom dead center and top dead center, the scavenging air system has a scavenging air inlet located at the bottom of the cylinder, and the two-stroke uniflow scavenging crosshead internal combustion engine is configured to inject fuel gas into at least one cylinder via the fuel gas supply system, the fuel gas supply system is located at least partially within the cylinder wall and injects fuel gas into the cylinder during the compression stroke to allow the fuel gas to mix with scavenging air and fuel The fuel gas supply system is configured to inject fuel gas into at least one cylinder during the compression stroke of at least a first fuel gas injection event and a second fuel gas injection event following the first fuel gas injection event, under an engine load of at least 50% of the maximum engine load, the first fuel gas valve of the one or more fuel gas valves is configured to inject fuel gas into the cylinder both during the first fuel gas injection event and the second fuel gas injection event, and the maximum flow rate of fuel gas through the first fuel gas valve is higher both during the first fuel gas injection event and the second fuel gas injection event than between the first and second fuel gas injection events.

[0011] Injecting fuel gas during multiple injection events can reduce the impact of the injected fuel gas on the portion of the inner cylinder wall opposite the fuel gas valve. This can result in better mixing of the scavenging air and fuel gas. In addition, the reduced degree of impact can decrease the velocity component of the injected fuel gas along the longitudinal axis of the cylinder, thereby reducing the risk of undesirable fuel gas leakage through the exhaust valve.

[0012] The internal combustion engine is preferably configured to use multiple injections during normal operation, for example, when a container ship is at cruising speed. Thus, the engine may be configured to use multiple injections under engine loads of at least 50%, 70%, 90%, or 100% of the maximum engine load.

[0013] The internal combustion engine is preferably a two-stroke crosshead internal combustion engine with a large, low-speed turbocharger and uniflow scavenging, for propelling a vessel having an output of at least 400 kW per cylinder. The internal combustion engine may include a turbocharger that is driven by the exhaust gases produced by the internal combustion engine and configured to compress the scavenging air. The internal combustion engine may be a dual-fuel engine having an Otto cycle mode when operating on fuel gas and a diesel cycle mode when operating on an alternative fuel, such as heavy oil or marine diesel oil. Such a dual-fuel engine has its own dedicated fuel supply system for injecting the alternative fuel.

[0014] The internal combustion engine preferably comprises a plurality of cylinders, for example, 4 to 14 cylinders. Each of the plurality of cylinders in the internal combustion engine further comprises a cylinder cover, an exhaust valve, a piston, a fuel gas valve, and a scavenging air inlet.

[0015] The fuel gas supply system is preferably configured to inject fuel gas through one or more fuel gas valves under supersonic conditions, i.e., at a speed equal to the speed of sound, i.e., at a constant speed. Supersonic conditions can be achieved when the pressure drop rate across the nozzle throat (the smallest area of ​​the cross-section) is greater than about 2.

[0016] Gas injection can be initiated as long as the pressure in the combustion chamber allows. Thus, one or more fuel gas valves may be configured to initiate fuel gas injection during the final part of the expansion stroke, for example, at -5 degrees from bottom dead center. Thus, fuel gas injection can occur both during the expansion stroke and the compression stroke. Preferably, the fuel gas valve is configured to initiate fuel gas injection after the crankshaft axis has rotated a few degrees from bottom dead center so that the piston passes the scavenging air inlet, in order to effectively prevent a large amount of fuel gas from escaping through the exhaust valve and scavenging air inlet.

[0017] In some embodiments, one or more fuel gas valves are configured to inject fuel gas into the cylinder during a compression stroke within 0 to 160 degrees from bottom dead center, 0 to 130 degrees from bottom dead center, or 0 to 90 degrees from bottom dead center.

[0018] One or more fuel gas valves are positioned at least partially within the cylinder wall between top dead center and bottom dead center, preferably above the scavenging air inlet. One or more fuel gas valves may include nozzles positioned within the cylinder wall for injecting fuel gas into the cylinder. Other parts of the fuel gas valve (other than the nozzles) may be positioned outside the cylinder wall.

[0019] Examples of fuel gases include liquefied natural gas (LNG), methane, ethane, biogas, and liquefied petroleum gas (LPG).

[0020] An internal combustion engine may be equipped with a dedicated ignition system, such as a pilot fuel system, capable of injecting a small amount of pilot fuel, such as heavy fuel oil or marine diesel fuel, precisely measured out so that only the required amount of pilot fuel is used, enabling ignition of the mixture of fuel gas and scavenging air in precisely the right quantity. Such a pilot fuel system would be much smaller in size and therefore more suitable for this purpose compared to dedicated fuel supply systems for alternative fuels, which are not suitable for injecting precise amounts of pilot fuel due to the larger size of their components.

[0021] Pilot fuel can be injected directly into the combustion chamber of an internal combustion engine, or into a pre-combustion chamber fluidly connected to the combustion chamber. Alternatively, a mixture of fuel gas and scavenging air can be ignited by means of a spark plug, laser ignition device, etc.

[0022] The first fuel gas injection event and the second fuel gas injection event may have equal durations. Alternatively, the first fuel gas injection event may have a different duration than the second fuel gas injection event. The fuel gas supply system may be configured to completely shut off the supply of fuel gas to the cylinder between the first fuel gas injection event and the second fuel gas injection event. The fuel gas may be injected using the same one or more fuel gas valves during the first fuel gas injection event and the second fuel gas injection event. Alternatively, the fuel gas may be injected using different fuel gas valves during the first fuel gas injection event and the second fuel gas injection event. For example, the fuel gas may be injected using a first group of one or more fuel gas valves, including a first fuel gas valve, during the first fuel gas injection event, and a second group of one or more fuel gas valves, including a second fuel gas valve, during the second fuel gas injection event.

[0023] The first fuel gas valve may also be configured to inject fuel gas during a portion of the first fuel gas injection event and a portion of the second fuel gas injection event under supersonic conditions.

[0024] In some embodiments, the fuel gas supply system is configured to completely close a first fuel gas valve between a first fuel gas injection event and a second fuel gas injection event.

[0025] In some embodiments, the fuel gas supply system is configured to keep the first fuel gas valve closed between a first fuel gas injection event and a second fuel gas injection event during an idle period.

[0026] As a result, the fuel gas injected during the first fuel gas injection event can be enabled to disperse better in the cylinder before being affected by the fuel gas injected during the second fuel gas injection event.

[0027] In some embodiments, the fuel gas supply system includes a control unit operably connected to the first fuel gas valve, and the control unit is configured to modify the first fuel gas injection event and / or the second fuel gas injection event according to the engine load.

[0028] In some embodiments, the control unit is configured to modify the length of the first fuel gas injection event and / or the second fuel gas injection event according to the engine load.

[0029] As a result, an effective method of controlling the amount of fuel gas injected during the compression stroke is provided. This further enables the control of the fuel gas injection amount without modifying the injection pressure of the fuel gas.

[0030] The injection pressure of the fuel gas can be substantially constant for different engine loads.

[0031] In some embodiments, the control unit is configured to change the number of injection events in which the fuel gas is injected during the compression stroke according to the engine load, such that the number of injection events is greater at lower engine loads where the length of each individual injection event is relatively short than at higher engine loads where the length of each individual injection event is relatively long.

[0032] As a result, the extra time available for fuel injection during low engine loads can be effectively utilized to ensure better mixing of the scavenging air and the fuel gas.

[0033] As a result, the reduced degree of collision of the injected fuel gases may consequently reduce the propagation of the fuel gases to the exhaust valve, allowing the fuel gases to be injected earlier during the compression stroke, which may provide more time for the fuel gases to mix with the scavenging air.

[0034] In some embodiments, the injection direction and / or injection duration differ between the first fuel gas injection event and the second fuel gas injection event.

[0035] In some embodiments, the fuel gas supply system is configured to further inject fuel gas into at least one cylinder during the compression stroke in a third fuel gas injection event following a second fuel gas injection event.

[0036] In some embodiments, one or more fuel gas valves further comprise a second fuel gas valve, the second fuel gas valve configured to inject fuel gas into at least one cylinder during at least two fuel gas injection events.

[0037] At least two fuel gas injection events may be a first fuel gas injection event and a second fuel gas injection event. Alternatively, the at least two fuel gas injection events may also be different from the first fuel gas injection event and the second fuel gas injection event; for example, the at least two fuel gas injection events may not overlap with the first fuel gas injection event and the second fuel gas injection event, or may only partially overlap with them.

[0038] In some embodiments, the first fuel gas valve and the second fuel gas valve are at least partially positioned in the cylinder wall at approximately the same height.

[0039] In some embodiments, the timing of the first fuel gas valve and the second fuel gas valve is asynchronous to produce a more homogeneous mixture of scavenging air and fuel gas.

[0040] In some embodiments, a first amount of fuel gas is introduced into the cylinder through one or more fuel gas valves, and the first and second fuel gas injection events are designed to produce a more homogeneous mixture of fuel gas and scavenging air compared to a situation in which the first amount of fuel gas is introduced into the cylinder during a single fuel gas injection event.

[0041] In some embodiments, the fuel gas supply system is capable of injecting fuel gas into the cylinder through one or more fuel gas valves during the injection period of the compression stroke, and the fuel gas supply system is oversized so that it can deliver at least 120% of the fuel gas required when the two-stroke uniflow scavenging crosshead internal combustion engine is operating at maximum engine load during the injection period, thereby allowing multiple fuel gas injection events to be used even when the two-stroke uniflow scavenging crosshead internal combustion engine is operating at maximum engine load.

[0042] According to a second aspect, the present invention relates to a non-temporary computer-readable medium for storing computer-readable code, wherein the computer-readable code is executable by a control unit of a two-stroke uniflow scavenging crosshead internal combustion engine, the two-stroke uniflow scavenging crosshead internal combustion engine comprising at least one cylinder, a cylinder cover, a piston, a fuel gas supply system, and a scavenging air system, wherein the cylinder has a cylinder wall, the cylinder cover is located on the top of the cylinder and has an exhaust valve, the piston is arranged to move within the cylinder between bottom dead center and top dead center, the scavenging air system has a scavenging air inlet located at the bottom of the cylinder, and the two-stroke uniflow scavenging crosshead internal combustion engine supplies fuel gas to at least one cylinder via the fuel gas supply system. A fuel gas supply system for at least one cylinder comprises one or more fuel gas valves configured to inject fuel gas into the cylinder, at least partially located in the cylinder wall, and configured to inject fuel gas into the cylinder during the compression stroke to allow the fuel gas to mix with scavenging air and to allow the mixture of scavenging air and fuel gas to be compressed before ignition, wherein a control unit is operably connected to a first fuel gas valve of the one or more fuel gas valves, and computer-readable code is configured to control the control unit to control the first fuel gas valve to inject fuel gas into at least one cylinder during the compression stroke during at least a first fuel gas injection event and a second fuel gas injection event following the first fuel gas injection event.

[0043] Different embodiments of the present invention can be implemented in different ways, including two-stroke internal combustion engines and non-temporary computer-readable media, each resulting in one or more of the benefits and advantages described in relation to at least one of the embodiments described above, and each having one or more preferred embodiments corresponding to preferred embodiments described in relation to at least one of the embodiments described above and / or disclosed in dependent claims. Furthermore, it will be recognized that embodiments described in relation to one of the embodiments described herein may be equally applicable to other embodiments.

[0044] The above and / or additional objects, features and advantages of the present invention will be further illustrated by the following exemplary and non-limiting embodiments of the invention, with reference to the accompanying drawings. [Brief explanation of the drawing]

[0045] [Figure 1] A schematic cross-sectional view of a two-stroke internal combustion engine according to an embodiment of the present invention is shown. [Figure 2] A schematic cross-sectional view of a fuel gas valve 200 for a two-stroke internal combustion engine according to an embodiment of the present invention is shown. [Figure 3a] This illustrates different types of injection events according to embodiments of the present invention. [Figure 3b] This illustrates different types of injection events according to embodiments of the present invention. [Figure 3c] This illustrates different types of injection events according to embodiments of the present invention. [Figure 3d] This illustrates different types of injection events according to embodiments of the present invention. [Figure 3e] This illustrates different types of injection events according to embodiments of the present invention. [Modes for carrying out the invention]

[0046] The following description will refer to the accompanying drawings, which illustrate how the present invention may be carried out.

[0047] Figure 1 schematically shows a cross-sectional view of a large, low-speed, turbocharged two-stroke internal combustion engine 100 with uniflow scavenging for propelling a ship, according to an embodiment of the present invention. The engine 100 comprises a scavenging air system 111, an exhaust gas receiver 108, a fuel gas supply system, and a turbocharger 109. The engine has a plurality of cylinders 101 (only a single cylinder is shown in the cross-sectional view). Each cylinder 101 has a cylinder wall 115 and a scavenging air inlet 102 located at the bottom of the cylinder 101. The engine further comprises a cylinder cover 112 and a piston 103 for each cylinder. The cylinder cover 112 is located at the top of the cylinder 101 and has an exhaust valve 104. The piston 103 is positioned to be movable within the cylinder along a central axis 113 between bottom dead center and top dead center. The fuel gas supply system comprises one or more fuel gas valves 105 (shown schematically only) configured to inject fuel gas into the cylinder 101 during the compression stroke, allowing the fuel gas to mix with the scavenging air and the mixture of scavenging air and fuel gas to be compressed before ignition. The fuel gas valves 105 are at least partially located in the cylinder wall between the cylinder cover 112 and the scavenging air inlet 102. The engine further comprises a pre-combustion chamber 114 located at least partially in the cylinder wall 115, the pre-combustion chamber 114 opening into the cylinder through a first opening formed in the cylinder wall, and the pre-combustion chamber is configured to ignite the mixture of scavenging air and fuel gas in the cylinder 101 when the piston is approaching or at top dead center. The pre-combustion chamber may, alternatively, be located in the cylinder cover 112. Alternatively, the engine may be provided with one or more pilot fuel injectors configured to inject pilot fuel directly into the cylinder. One or more pilot fuel injectors may be located in the cylinder wall 115 or cylinder cover 112, and the scavenging air inlet 102 is fluidly connected to the scavenging air system. The piston 103 is shown in its lowest position (bottom dead center). The piston 103 has a piston rod (not shown) connected to the crankshaft via a crosshead and connecting rod.The fuel gas valve 105 is configured to inject fuel gas into the cylinder during the compression stroke, allowing the fuel gas to mix with scavenging air and the mixture of scavenging air and fuel gas to be compressed before ignition. The scavenging air system 111 comprises a scavenging air receiver 110 and an air cooler 106. The fuel gas supply system is configured to inject fuel gas into at least one cylinder during the compression stroke during at least a first fuel gas injection event and a second fuel gas injection event following the first fuel gas injection event.

[0048] By injecting fuel gas during multiple injection events, the impact of the injected fuel gas on the portion of the inner cylinder wall opposite the fuel gas valve can be reduced. This can result in better mixing of the scavenging air and fuel gas. In addition, the reduced degree of impact can decrease the velocity component of the injected fuel gas along the cylinder's central axis 113, thereby reducing the risk of fuel gas leaking undesirably through the exhaust valve.

[0049] The fuel gas valve 105 may be configured to inject fuel gas into the cylinder 101 at the beginning of the compression stroke within 0 to 130 degrees from bottom dead center, i.e., when the crankshaft has rotated 0 to 130 degrees from its orientation at bottom dead center. Thus, both the first and second fuel gas injection events may occur at the beginning of the compression stroke within 0 to 130 degrees from bottom dead center, i.e., when the crankshaft has rotated 0 to 130 degrees from its orientation at bottom dead center. Preferably, the fuel gas valve 105 is configured to begin injecting fuel gas after the crankshaft axis has rotated a few degrees from bottom dead center so that the piston passes the scavenging air inlet 102, in order to prevent fuel gas from escaping through the exhaust valve 104 and the scavenging air inlet 102. The end of the fuel gas injection period is limited by the position of the fuel gas valve 105, i.e., once the piston 103 has passed the fuel gas valve, fuel gas injection is no longer possible.

[0050] The engine 100 is preferably a dual-fuel engine having an Otto cycle mode when operating on fuel gas and a diesel cycle mode when operating on an alternative fuel, such as heavy oil or marine diesel oil. Such a dual-fuel engine has its own dedicated alternative fuel supply system for injecting the alternative fuel. Optionally, the engine 100 further comprises one or more fuel injectors 116 located in a cylinder cover 112 that forms part of the alternative fuel supply system. When the engine 100 is operating on an alternative fuel, the fuel injectors 116 are configured to inject the alternative fuel, such as heavy oil, at the end of the compression stroke under high pressure.

[0051] Figure 2 schematically shows a cross-sectional view of a fuel gas valve 200 for a two-stroke internal combustion engine according to an embodiment of the present invention. The fuel gas valve comprises a valve shaft 201, a valve head 202, a valve seat 203, and a fuel gas nozzle 204 having a nozzle outlet 206. The fuel gas valve may further be provided with an actuator 207 for opening the fuel gas valve. The fuel gas valve may further be provided with a spring (not shown) configured to keep the valve closed in the absence of force from the actuator. The actuator 207 may be operably connected to a control unit 208, which may be configured to send control signals to the actuator to control the actuator to open and / or close the valve. The control unit 208 may be configured to control the fuel gas valve to inject fuel gas into at least one cylinder during the compression stroke in at least a first fuel gas injection event and a second fuel gas injection event following the first fuel gas injection event.

[0052] Figures 3a to 3e illustrate different types of fuel gas injection events performed by a single fuel gas valve according to embodiments of the present invention. The horizontal axis in each figure represents the crank angle, and the vertical axis in each figure represents the mass flow rate.

[0053] Figure 3a shows the first fuel gas injection event 301 and the second fuel gas injection event 302, where both the duration and mass flow rate are the same for both events. There is an idle period between the two fuel gas injection events 301 and 302, where the mass flow rate is 0.

[0054] Figure 3b shows the first fuel gas injection event 301 and the second fuel gas injection event 302, where the durations of the first and second fuel gas injection events 301 and 302 are the same, but the mass flow rate of the first fuel gas injection event 301 is higher than that of the second fuel gas injection event 302. The mass flow rate is zero between the two fuel gas injection events 301 and 302, but there is no idle period.

[0055] Figure 3c shows the first fuel gas injection event 301 and the second fuel gas injection event 302, where the mass flow rate is the same for both fuel gas injection events 301 and 302. The mass flow rate is not zero between the two fuel gas injection events 301 and 302. This indicates that the fuel gas valve is not completely closed between the two fuel gas injection events.

[0056] Figure 3d shows a first fuel gas injection event 301 and a second fuel gas injection event 302, where the mass flow rate is the same for both events, but the duration of the first fuel gas injection event 301 is longer than that of the second fuel gas injection event 302. There is an idle period between the two fuel gas injection events 301 and 302 where the mass flow rate is 0.

[0057] Figure 3e shows the first fuel gas injection event 301, the second fuel gas injection event 302, and the third fuel gas injection event 303, where both the duration and mass flow rate are the same for all three fuel gas injection events 301, 302, and 303.

[0058] While several embodiments have been described and demonstrated in detail, the present invention is not limited thereto and can be embodied in other ways within the scope of the subject matter defined in the following claims. In particular, it should be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention.

[0059] In device claims that list several means, some of these means can be embodied by the same item of hardware. The mere fact that certain measures are described in different dependent claims or illustrated in different embodiments does not imply that combinations of these measures cannot be used advantageously.

[0060] When used herein, the term “equipped with / possessed of” is to be interpreted as specifying the presence of the feature, integer, step, or component being described, but it should be emphasized that this does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. The invention described in the original claims of this application is listed below. [1] A two-stroke uniflow scavenging crosshead internal combustion engine comprising at least one cylinder, a cylinder cover, a piston, a fuel gas supply system, and a scavenging air system, wherein the cylinder has a cylinder wall, the cylinder cover is positioned on the top of the cylinder and has an exhaust valve, the piston is positioned to be movable within the cylinder between bottom dead center and top dead center, the scavenging air system has a scavenging air inlet positioned at the bottom of the cylinder, the two-stroke uniflow scavenging crosshead internal combustion engine is configured to inject fuel gas into the at least one cylinder via the fuel gas supply system, the fuel gas supply system is positioned at least partially within the cylinder wall and injects fuel gas into the cylinder during the compression stroke to allow the fuel gas to mix with scavenging air, and the mixture of scavenging air and fuel gas is compressed before ignition A two-stroke uniflow scavenging crosshead internal combustion engine comprising one or more fuel gas valves configured for at least one cylinder to enable the injection of fuel gas into the at least one cylinder during the compression stroke at an engine load of at least 50% of the maximum engine load, wherein the first fuel gas valve of the one or more fuel gas valves is configured to inject fuel gas into the cylinder both during the first fuel gas injection event and the second fuel gas injection event, and the maximum flow rate of the fuel gas through the first fuel gas valve is higher both during the first fuel gas injection event and the second fuel gas injection event than between the first and second fuel gas injection events. [2] The two-stroke uniflow scavenging crosshead internal combustion engine according to [1], wherein the fuel gas supply system is configured to completely close the first fuel gas valve between the first fuel gas injection event and the second fuel gas injection event. [3] The two-stroke uniflow scavenging crosshead internal combustion engine according to [2], wherein the fuel gas supply system is configured to keep the first fuel gas valve closed between the first fuel gas injection event and the second fuel gas injection event during an idle period. [4] The fuel gas supply system comprises a control unit operably connected to the first fuel gas valve, the control unit configured to modify the first fuel gas injection event and / or the second fuel gas injection event in response to the engine load, the two-stroke uniflow scavenging crosshead internal combustion engine according to any one of [1] to [3]. [5] The control unit is configured to modify the length of the first fuel gas injection event and / or the second fuel gas injection event in response to the engine load, as described in [4], for the two-stroke uniflow scavenging crosshead internal combustion engine. [6] The two-stroke uniflow scavenging crosshead internal combustion engine according to [5], wherein the control unit is configured to change the number of injection events in which fuel gas is injected during the compression stroke in accordance with the engine load, such that there are more injection events at low engine loads where the length of each injection event is relatively short than at high engine loads where the length of each injection event is relatively long. [7] A two-stroke uniflow scavenging crosshead internal combustion engine according to any one of [1] to [6], wherein the one or more fuel gas valves further comprises a second fuel gas valve, the second fuel gas valve configured to inject fuel gas into the cylinder during at least two fuel gas injection events. [8] The two-stroke uniflow scavenging crosshead internal combustion engine according to [7], wherein the first fuel gas valve and the second fuel gas valve are at least partially located in the cylinder wall at substantially the same height. [9] The timing of the first fuel gas valve and the second fuel gas valve is asynchronous to produce a more homogeneous mixture of scavenging air and fuel gas, as described in [8], for the two-stroke uniflow scavenging crosshead internal combustion engine.

[10] The two-stroke uniflow scavenging crosshead internal combustion engine according to any one of [1] to [9], wherein the fuel gas supply system is configured to further inject fuel gas into the at least one cylinder during the compression stroke in a third fuel gas injection event following the second fuel gas injection event.

[11] A two-stroke uniflow scavenging crosshead internal combustion engine according to any one of [1] to

[10] , wherein a first amount of fuel gas is introduced into the cylinder through one or more fuel gas valves, and the first fuel gas injection event and the second fuel gas injection event are designed to produce a more homogeneous mixture of fuel gas and scavenging air compared to a situation in which the first amount of fuel gas is introduced into the cylinder during a single fuel gas injection event.

[12] The fuel gas supply system is capable of injecting fuel gas into the cylinder through one or more fuel gas valves during the injection period of the compression stroke, and the fuel gas supply system is oversized so that the fuel gas supply system can deliver at least 120% of the fuel gas required when the two-stroke uniflow scavenging crosshead internal combustion engine is operating at maximum engine load, thereby allowing multiple fuel gas injection events to be used even when the two-stroke uniflow scavenging crosshead internal combustion engine is operating at maximum engine load, as described in any one of [1] to

[11] .

[13] A non-temporary computer-readable medium for storing computer-readable code, the computer-readable code being executable by a control unit of a two-stroke uniflow scavenging crosshead internal combustion engine, the two-stroke uniflow scavenging crosshead internal combustion engine comprising at least one cylinder, a cylinder cover, a piston, a fuel gas supply system, and a scavenging air system, wherein the cylinder has a cylinder wall, the cylinder cover is located on the top of the cylinder and has an exhaust valve, the piston is movably positioned within the cylinder between bottom dead center and top dead center, the scavenging air system has a scavenging air inlet located at the bottom of the cylinder, and the two-stroke uniflow scavenging crosshead internal combustion engine is configured to inject fuel gas into the at least one cylinder via the fuel gas supply system A non-transient computer-readable medium, wherein the stem comprises one or more fuel gas valves for at least one cylinder, at least partially positioned in the cylinder wall and configured to inject fuel gas into the cylinder during the compression stroke under an engine load of at least 50% of the maximum engine load, allowing the fuel gas to mix with scavenging air and allowing the mixture of scavenging air and fuel gas to be compressed before ignition, the control unit being operably connected to a first fuel gas valve of the one or more fuel gas valves, and the computer-readable code being configured to control the control unit to control the first fuel gas valve to inject fuel gas into the at least one cylinder during the compression stroke during at least a first fuel gas injection event and a second fuel gas injection event following the first fuel gas injection event.

Claims

1. A two-stroke uniflow scavenging crosshead internal combustion engine comprising at least one cylinder, a cylinder cover, a piston, a fuel gas supply system, and a scavenging air system, wherein the cylinder has a cylinder wall, the cylinder cover is positioned on the top of the cylinder and has an exhaust valve, the piston is positioned to be movable within the cylinder between bottom dead center and top dead center, the scavenging air system has a scavenging air inlet positioned at the bottom of the cylinder, the two-stroke uniflow scavenging crosshead internal combustion engine is configured to inject fuel gas into the at least one cylinder via the fuel gas supply system, the fuel gas supply system comprises for the at least one fuel gas valve positioned at least partially in the cylinder wall and configured to inject fuel gas into the cylinder during the compression stroke to allow the fuel gas to mix with scavenging air and to allow the mixture of scavenging air and fuel gas to be compressed before ignition, and the fuel gas supply system performs at least a first fuel gas injection event under an engine load of 50% or more of the maximum engine load. The engine is configured to inject fuel gas into at least one cylinder during a single compression stroke in a second fuel gas injection event following the first fuel gas injection event, the first fuel gas valve of the one or more fuel gas valves is configured to inject fuel gas into the cylinder both during the first fuel gas injection event and the second fuel gas injection event, the maximum flow rate of the fuel gas through the first fuel gas valve is higher during the first fuel gas injection event and the maximum flow rate during the second fuel gas injection event is higher than the flow rate between the first fuel gas injection event and the second fuel gas injection event, the injected fuel gas is non-autoignitable under the conditions present in the cylinder, the internal combustion engine is provided with a dedicated ignition system configured to inject a small amount of autoigniting pilot fuel to ignite a mixture of fuel gas and scavenging air, the fuel gas supply system comprises a control unit operably connected to the first fuel gas valve, the control unit is configured to modify the first fuel gas injection event and / or the second fuel gas injection event in response to engine load,A two-stroke uniflow scavenging crosshead internal combustion engine, wherein the control unit is configured to change the number of injection events in which fuel gas is injected during the compression stroke in accordance with the engine load, such that the number of injection events is greater at low engine loads, where the length of each injection event is relatively short, than at high engine loads, where the length of each injection event is relatively long.

2. The two-stroke uniflow scavenging crosshead internal combustion engine according to claim 1, wherein the fuel gas supply system is configured to completely close the first fuel gas valve between the first fuel gas injection event and the second fuel gas injection event.

3. The two-stroke uniflow scavenging crosshead internal combustion engine according to claim 2, wherein the fuel gas supply system is configured to keep the first fuel gas valve closed between the first fuel gas injection event and the second fuel gas injection event during an idle period.

4. A two-stroke uniflow scavenging crosshead internal combustion engine according to any one of claims 1 to 3, wherein the one or more fuel gas valves further comprises a second fuel gas valve, the second fuel gas valve configured to inject fuel gas into the cylinder during at least two fuel gas injection events.

5. The two-stroke uniflow scavenging crosshead internal combustion engine according to claim 4, wherein the first fuel gas valve and the second fuel gas valve are at least partially positioned in the cylinder wall at substantially the same height.

6. The timing of the first fuel gas valve and the second fuel gas valve are asynchronous so as to produce a more homogeneous mixture of scavenging air and fuel gas, as described in claim 5, for a two-stroke uniflow scavenging crosshead internal combustion engine.

7. The two-stroke uniflow scavenging crosshead internal combustion engine according to any one of claims 1 to 6, wherein the fuel gas supply system is configured to further inject fuel gas into the at least one cylinder during the compression stroke in a third fuel gas injection event following the second fuel gas injection event.

8. A two-stroke uniflow scavenging crosshead internal combustion engine according to any one of claims 1 to 7, wherein a first amount of fuel gas is introduced into the cylinder through one or more fuel gas valves, and the first fuel gas injection event and the second fuel gas injection event are designed to produce a more homogeneous mixture of fuel gas and scavenging air compared to a situation in which the first amount of fuel gas is introduced into the cylinder during a single fuel gas injection event.

9. A two-stroke uniflow scavenging crosshead internal combustion engine according to any one of claims 1 to 8, wherein the fuel gas supply system is capable of injecting fuel gas into the cylinder through one or more fuel gas valves during the injection period of the compression stroke, and the fuel gas supply system is oversized so that the fuel gas supply system can deliver at least 120% of the fuel gas required when the two-stroke uniflow scavenging crosshead internal combustion engine is operating at maximum engine load, thereby allowing multiple fuel gas injection events to be used even when the two-stroke uniflow scavenging crosshead internal combustion engine is operating at maximum engine load.

10. A non-temporary computer-readable medium for storing computer-readable code, the computer-readable code being executable by a control unit of a two-stroke uniflow scavenging crosshead internal combustion engine, the two-stroke uniflow scavenging crosshead internal combustion engine comprising at least one cylinder, a cylinder cover, a piston, a fuel gas supply system, and a scavenging air system, wherein the cylinder has a cylinder wall, the cylinder cover is located on the top of the cylinder and has an exhaust valve, the piston is movably positioned within the cylinder between bottom dead center and top dead center, the scavenging air system has a scavenging air inlet located at the bottom of the cylinder, the two-stroke uniflow scavenging crosshead internal combustion engine is configured to inject fuel gas into the at least one cylinder via the fuel gas supply system, the fuel gas supply system is located at least partially within the cylinder wall and injects fuel gas into the cylinder during the compression stroke under an engine load of 50% or more of the maximum engine load so that the fuel gas mixes with scavenging air. The internal combustion engine is provided with one or more fuel gas valves for at least one cylinder, configured to enable and allow a mixture of scavenging air and fuel gas to be compressed before ignition, the injected fuel gas being non-autoignitable under conditions present in the cylinder, and the internal combustion engine is provided with a dedicated ignition system configured to inject a small amount of autoigniting pilot fuel to ignite the mixture of fuel gas and scavenging air, the control unit being operably connected to a first fuel gas valve of the one or more fuel gas valves, the computer-readable code being configured to control the control unit to control the first fuel gas valve to inject fuel gas into at least one cylinder during a single compression stroke in at least a first fuel gas injection event and a second fuel gas injection event following the first fuel gas injection event, and the computer-readable code being configured such that the number of injection events is greater at low engine loads, where the length of each injection event is relatively short, than at high engine loads, where the length of each injection event is relatively long.A non-transient computer-readable medium further configured to control the control unit to change the number of injection events in which fuel gas is injected during the compression stroke in accordance with the engine load.

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