JP7646482B2 - Internal combustion engine - Google Patents

Description

The present invention relates to a two-stroke uniflow scavenging crosshead internal combustion engine and a pre-combustion chamber.

Two-stroke internal combustion engines are used as propulsion engines in marine vessels such as container ships, bulk carriers, and tankers. The reduction of undesirable emissions from internal combustion engines is becoming increasingly important.

An effective way to reduce the amount of undesirable emissions is to switch from fuel oil, e.g. heavy fuel oil (HFO), to fuel gas. The fuel gas can be injected into the cylinder at the end of the compression stroke where it can be immediately ignited, either by the high temperature that the gas in the cylinder achieves when compressed, or by 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 prior to injection in order to overcome the large pressure in the cylinder.

However, large gas compressors are expensive and complex to manufacture and maintain. One way to avoid the need for a large compressor is to configure the engine to inject fuel gas at the beginning of the compression stroke, when the pressure in the cylinder is significantly lower.

WO2013007863 discloses such an engine. To ensure proper ignition of the fuel gas, a pilot-ignition pre-chamber is provided in the cylinder cover. A quantity of pilot fuel oil is injected into the pilot-ignition pre-chamber, which then self-ignites due to the temperature and pressure in the pilot-ignition pre-chamber. This results in a torch that ignites the fuel gas in the main chamber of the cylinder.

However, injecting a fixed amount of pilot fuel oil increases the amount of undesirable emissions and requires a dedicated fuel oil supply system that makes the engine more complex. Furthermore, in dual-fuel engines that have both a fuel gas supply system and a fuel oil supply system, the added reliability of having two fuel systems is partially lost if the engine cannot function without the fuel oil supply system.

Therefore, it remains a challenge to provide an improved two-stroke internal combustion engine.

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 system, the cylinder having a cylinder wall, the cylinder cover being arranged at the top of the cylinder and having an exhaust valve, the piston being movably arranged within the cylinder along a central axis between bottom dead centre and top dead centre, the scavenging system having a scavenging inlet arranged at the bottom of the cylinder, the fuel gas supply system comprising a fuel gas valve arranged at least partially in the cylinder wall and configured to inject fuel gas into the cylinder during the compression stroke, The engine further includes a pre-combustion chamber and a pilot fuel supply system, the pre-combustion chamber opening into the cylinder through a first opening and including an ignition element, the pilot fuel supply system including a pilot fuel valve configured to inject pilot fuel gas into the pre-combustion chamber during the compression stroke, and the pilot fuel gas being compressed and mixed with air before being ignited to form a combustible mixture in the pre-combustion chamber, the ignition element being configured to ignite the pilot fuel gas in the pre-combustion chamber.

As a result, by using fuel gas as the pilot fuel, any undesirable emissions resulting from the combustion of fuel oil can be avoided. Furthermore, the engine can be designed with fewer fuel supply systems, or, if the engine is a dual-fuel engine, a more reliable engine is provided that can run on fuel gas alone.

The internal combustion engine is preferably a large slow-speed turbocharged two-stroke crosshead internal combustion engine with uniflow scavenging for propelling marine vessels, with a power of at least 400 kW per cylinder. The internal combustion engine may include a turbocharger configured to be driven by exhaust gases generated by the internal combustion engine and to compress the scavenging air. The internal combustion engine may be a dual-fuel engine having an Otto cycle mode when powered by fuel gas and a Diesel cycle mode when powered by an alternative fuel, e.g., heavy fuel oil or marine diesel oil. Such a dual-fuel engine has its own dedicated fuel supply system for injecting the alternative fuel. During compression, either air from the cylinder or a mixture of air and fuel gas formed in the cylinder will flow into the pre-chamber and be mixed with the pilot fuel gas.

The ignition element can be a spark plug, corona/plasma igniter, microwave igniter, glow plug, laser igniter, or jet torch.

The internal combustion engine preferably comprises a plurality of cylinders, for example between 4 and 14 cylinders. The internal combustion engine further comprises a cylinder cover, an exhaust valve, a piston, a fuel gas valve, and a scavenging inlet for each cylinder of the plurality of cylinders.

The fuel gas supply system is preferably configured to inject fuel gas through one or more fuel gas valves under sonic conditions, i.e., at a velocity equal to the speed of sound, i.e., at a constant velocity. Sonic conditions can be achieved when the pressure drop ratio across the nozzle throat (smallest cross-sectional area) is greater than approximately two.

Correspondingly, the pilot fuel supply system may also be configured to inject pilot fuel gas into the pre-combustion chamber via the pilot fuel valve under sonic conditions.

The one or more fuel gas valves are preferably disposed at least partially in the cylinder wall between top dead center and bottom dead center at a location above the scavenging inlet. The one or more fuel gas valves may include a nozzle disposed in the cylinder wall for injecting fuel gas into the cylinder. In some embodiments, the ignition element is configured to generate an approximately instantaneous maximum energy release upon activation.

This can allow for greater control over ignition timing. Examples of ignition elements capable of producing a near instantaneous release of energy upon activation are a spark plug, corona/plasma igniter, microwave igniter, laser igniter, or jet torch.

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

Examples of fuel gases are liquefied natural gas (LNG), methane, ethane, and liquefied petroleum gas (LPG).

In some embodiments, the fuel gas supply system and the pilot fuel supply system supply the same fuel gas.

In some embodiments, the engine further comprises a second pre-chamber, the second pre-chamber opening into the cylinder through a second opening and comprising an ignition element, the pilot fuel supply system comprising a second pilot fuel valve configured to inject pilot fuel gas into the second pre-chamber during the compression stroke, allowing the pilot fuel gas to be compressed before being ignited, and the ignition element configured to ignite the pilot fuel gas in the pre-chamber.

The two pre-chambers may be identical. The two pre-chambers may be arranged opposite each other.

The engine may be provided with more prechambers, for example at least three or four prechambers per cylinder.

In some embodiments, the pilot fuel valve is configured to inject pilot fuel gas into the pre-chamber during the compression stroke within 0 degrees to 160 degrees from bottom dead center, within 0 degrees to 130 degrees from bottom dead center, or within 0 degrees to 90 degrees from bottom dead center.

In some embodiments, the pilot fuel valve is configured to inject pilot fuel gas during a pilot fuel injection period, and wherein the ignition element is configured to ignite the pilot fuel gas in the pre-combustion chamber after the pilot fuel injection period ends.

As a result, by allowing the pilot fuel gas to rest in the pre-chamber before being ignited, a suitable mixture with the charge air can be achieved. The fuel gas and air charge from the main chamber of the cylinder can enter the pre-chamber before the ignition element is ignited. This can reduce the amount of pilot fuel gas injected while still achieving a combustible mixture.

In some embodiments, the pre-chamber is configured to ensure that the air-fuel equivalence ratio λ of the mixture of scavenging air and pilot fuel gas in the pre-chamber is below λ=1.6, λ=1.5, λ=1.4, or λ=1.3 at the time of ignition.

This can be done by controlling the amount of pilot fuel gas injected and by designing the shape of the pre-chamber and the first opening so that the desired amount of fuel gas remains in the pre-chamber.

In some embodiments, the ratio between the cross-sectional area of the pre-chamber opening into the cylinder, measured in m ² , and the volume of the pre-chamber, measured in m ³ , is between 0.5 and 1.2 m ⁻¹ .

As a result, it can be ensured that too much pilot fuel gas does not escape from the pre-combustion chamber before being ignited.

By way of example, if the pre-chamber comprises only a first opening, the surface area of the first opening is 60 mm ² and the volume of the pre-chamber is 0.1 litres, then the ratio is 0.6 m ⁻¹ .

In some embodiments, the engine is configured to ensure that the λ of the mixture of scavenging air and fuel gas in the cylinder is above λ=2.0.

In some embodiments, the pre-combustion chamber further comprises a second ignition element.

Providing a second ignition element in the pre-chamber provides a more reliable engine since it can operate if one of the ignition elements malfunctions.

In some embodiments, the pre-combustion chamber is at least partially disposed in the cylinder wall, and the first opening is formed in the cylinder wall.

In some embodiments, the engine further includes a pre-chamber cooling system for cooling the pre-chamber, the pre-chamber cooling system including a cooling passageway proximate to the pre-chamber for extracting heat from the pre-chamber, the pre-chamber cooling system configured to circulate a cooling fluid through the cooling passageway.

Locating the prechamber on the cylinder wall provides more space for the prechamber cooling system. This may allow the prechamber temperature to be controlled more precisely and with less influence of other engine parameters such as exhaust valve closing timing, engine speed, engine load, etc. More precise control of the prechamber temperature may reduce the risk of misfire and make it more suitable to use pilot fuels that are more difficult to ignite, such as fuel gases such as liquefied natural gas (LNG), methane, ethane, and liquefied petroleum gas (LPG).

In some embodiments, the prechamber cooling system further comprises a control unit configured to control the flow of cooling fluid and/or the inlet temperature of the cooling fluid.

In some embodiments, the control unit is configured to control the flow of cooling fluid and/or the inlet temperature of the cooling fluid in dependence on the engine load, the engine speed, and/or the air-fuel equivalence ratio λ of the mixture of scavenging air and fuel gas.

In some embodiments, the cylinder has a base member and a pre-chamber member, the pre-chamber member is disposed on top of the base member, and the cylinder cover is disposed on top of the pre-chamber member, where the pre-chamber is at least partially disposed in a cylinder wall of the pre-chamber member, and the pre-chamber opens to the cylinder through an opening formed in the cylinder wall of the pre-chamber member.

This allows the pre-chamber components to be specially designed to handle the high temperatures and pressures within the pre-chamber, for example by selecting suitable materials. This may also make it easier to perform maintenance on the pre-chamber.

The pre-chamber member may be bolted together with the base member of the cylinder. Alternatively, the pre-chamber member may be welded together with the base member of the cylinder.

In some embodiments, the pre-chamber member of the cylinder is made of a different material than the substrate member of the cylinder.

In some embodiments, the pre-combustion chamber is at least partially disposed in the cylinder cover, and the first opening is formed in the cylinder cover.

In some embodiments, the engine is a dual fuel engine having an Otto cycle mode when powered by fuel gas and a Diesel cycle mode when powered by an alternative fuel, the engine further comprising a dedicated alternative fuel supply system for injecting the alternative fuel, the alternative fuel supply system comprising one or more fuel injectors disposed in the cylinder cover, wherein the engine is configured to inject the alternative fuel at the end of the compression stroke under high pressure using the one or more fuel injectors when in the Diesel cycle mode, and wherein the engine is configured to repeatedly perform a cleaning operation to clean the pre-chamber when in the Diesel cycle mode.

As a result, the pre-chamber may be protected from combustion by-products resulting from the combustion of the alternative fuel. This may allow the engine to reliably switch back to Otto cycle mode even after being in Diesel cycle mode for an extended period of time.

The alternative fuel may be heavy fuel oil or marine diesel oil. The engine may be configured to perform the cleaning operation every engine cycle. Alternatively, the cleaning operation may be performed less frequently, such as every two engine cycles, every five engine cycles, or once a day. The frequency of the cleaning operation may be determined based on engine parameter settings, such as engine load, and/or sensor data recorded by one or more sensors. The cleaning operation may be performed at any time during the engine cycle.

In some embodiments, the cleaning operation is configured to remove combustion by-products deposited in the pre-combustion chamber and/or prevent combustion by-products from being deposited in the pre-combustion chamber.

In some embodiments, the cleaning operation comprises injection of the first fluid using a pilot fuel valve.

In some embodiments, the first fluid is a fuel gas, atmospheric air, and/or an inert gas.

In some embodiments, the first fluid is air or an inert gas, where the first fluid is used to flush the pre-combustion chamber.

As a result, a simple method of cleaning the pre-chamber is provided by rinsing the pre-chamber.

Cleaning can be performed when the pressure in the cylinder is low, for example at the beginning of the compression stroke. Injection can occur either before the exhaust valve closes or after the exhaust valve closes.

In some embodiments, the first fluid is a fuel gas, and wherein the ignition element is configured to ignite the fuel gas as part of the cleaning operation.

As a result, undesirable by-products from the combustion of alternative fuels in the pre-combustion chamber can be burned off.

In some embodiments, the engine is configured, when in a diesel cycle mode, to repeatedly perform a first type of cleaning operation for cleaning the pre-chamber at a first frequency and a second type of cleaning operation at a second frequency, where the second frequency is less than the first frequency.

In some embodiments, a first type of cleaning operation comprises injecting a first fluid using a pilot fuel valve, the first fluid being air or an inert gas, where the first fluid is used to clean the pre-chamber, and a second type of cleaning operation comprises injecting a fuel gas using a pilot fuel valve, where an ignition element is configured to ignite the fuel gas as part of the second type of cleaning operation.

As a result, the pre-chamber can be kept effectively clean. By injecting fuel gas only as part of the cleaning operation at a low frequency, the pilot fuel supply system can be purged of fuel gas most of the time when the engine is in diesel cycle mode, thereby improving safety. The second frequency can be less than once an hour, once every six hours, once every 12 hours, once a day, once every other day, or once a week.

According to a second aspect, the present invention relates to a pre-chamber for use with a two-stroke uniflow scavenged crosshead internal combustion engine as described in relation to the first aspect, the pre-chamber configured to open into the cylinder through a first opening and comprising an ignition element and a pilot fuel valve configured to inject pilot fuel gas into the pre-chamber during the compression stroke, allowing the pilot fuel gas to be compressed before being ignited, the ignition element configured to ignite the pilot fuel gas in the pre-chamber.

Different aspects of the present invention may be implemented in different ways, including a two-stroke uniflow scavenging crosshead internal combustion engine and pre-combustion chamber as described above and below, each producing one or more of the benefits and advantages described in relation to at least one of the aspects described above, and each having one or more preferred embodiments corresponding to the preferred embodiments described in relation to at least one of the aspects described above and/or disclosed in the dependent claims. Furthermore, it will be recognized that an embodiment described in relation to one of the aspects described herein may be equally applicable to the other aspects.

The above and/or additional objects, features, and advantages of the present invention will be made more apparent from the following illustrative, non-limiting detailed description of embodiments of the present invention, taken in conjunction with the accompanying drawings.

FIG. 1 shows a schematic cross-sectional view of a two-stroke internal combustion engine according to an embodiment of the present invention. FIG. 2 shows a schematic cross-sectional view of a portion of a two-stroke crosshead internal combustion engine with uniflow scavenging according to an embodiment of the present invention. FIG. 3 shows a schematic cross-sectional view of a portion of a two-stroke crosshead internal combustion engine with uniflow scavenging according to an embodiment of the present invention. FIG. 4 shows a schematic diagram of a pre-chamber according to an embodiment of the present invention. FIG. 5 shows a schematic cross-sectional view of a portion of a two-stroke crosshead internal combustion engine with uniflow scavenging according to an embodiment of the present invention. FIG. 6 shows a schematic diagram of a pre-chamber according to an embodiment of the present invention.

In the following description, reference is made to the accompanying drawings, which show, by way of example, how the invention may be put into practice.

1 shows a schematic cross-sectional view of a large slow-speed turbocharged two-stroke crosshead internal combustion engine 100 with uniflow scavenging for propelling marine vessels, according to an embodiment of the present invention. The engine 100 comprises a scavenging system 111, an exhaust gas receiver 108, a fuel gas supply system, and a turbocharger 109. The engine has a number of cylinders 101 (only a single cylinder is shown in the cross-sectional view). Each cylinder 101 has a cylinder wall 115 and comprises a scavenging 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 movably disposed 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 only diagrammatically) configured to inject fuel gas into the cylinder 101 during the compression stroke, allowing the fuel gas to mix with the scavenging air and allowing the mixture of scavenging air and fuel gas to be compressed before being ignited. The engine further comprises a pre-chamber 114 and a pilot fuel supply system, the pre-chamber 114 opening into the cylinder 101 through a first opening and comprising an ignition element (not shown). The pilot fuel supply system comprises a pilot fuel valve (not shown) configured to inject pilot fuel gas into the pre-chamber during the compression stroke, allowing the pilot fuel gas to be compressed before being ignited, the ignition element being configured to ignite the pilot fuel gas in the pre-chamber. The pre-chamber 114 is arranged in the cylinder wall 115 in this embodiment, however, in other embodiments the pre-chamber 114 may be arranged in the cylinder cover 112. The scavenging air inlet 102 is fluidly connected to the scavenging system. The piston 103 is shown in its lowest position (bottom dead center). The piston 103 has a piston rod connected to a crankshaft (not shown). 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 the scavenging air and allowing the mixture of scavenging air and fuel gas to be compressed before being ignited. The fuel gas valve 105 is at least partially disposed in the cylinder wall between the cylinder cover 112 and the scavenging air inlet 102, for example, a fuel gas nozzle of the fuel gas valve 105 may be disposed in the cylinder wall and the remaining part of the fuel gas valve may be disposed outside the cylinder. The fuel gas valve is configured to inject fuel gas into the cylinder 101 at the beginning of the compression stroke within 0 to 130 degrees from the bottom dead center, i.e., when the crankshaft has rotated between 0 to 130 degrees from its orientation at the bottom dead center. Preferably, the fuel gas valve 105 is configured to start injecting fuel gas after the crankshaft axis has rotated a few degrees from bottom dead center so that the piston passes through the scavenging inlet 102 to prevent fuel gas from flowing out through the scavenging inlet 102. The scavenging system 111 includes a scavenging receiver 110 and an air cooler 106.

The engine 100 is preferably a dual-fuel engine having an Otto cycle mode when running on fuel gas and a Diesel cycle mode when running on an alternative fuel, e.g., heavy fuel oil or marine diesel oil. Such a dual-fuel engine has its own dedicated alternative fuel supply system for injecting the alternative fuel. Thus, optionally, the engine 100 further comprises one or more fuel injectors 116 arranged in the cylinder cover 112 forming part of the alternative fuel supply system. When the engine 100 runs on an alternative fuel, the fuel injectors 116 are configured to inject the alternative fuel, e.g., heavy fuel oil, at the end of the compression stroke under high pressure.

2 shows a schematic cross-sectional view of a portion of a two-stroke crosshead internal combustion engine with uniflow scavenging according to an embodiment of the present invention. A cylinder 101, a cylinder cover 112, a piston 103, and an exhaust valve 104 are shown. The piston 103 is arranged at top dead center. The cylinder 101 has a cylinder wall 115 in which a first pre-combustion chamber 114 and a second pre-combustion chamber 116 are provided. The first and second pre-combustion chambers 114, 116 open into the cylinder 101 through openings formed in the cylinder wall 115, and the pre-combustion chambers 114, 116 are configured to ignite a mixture of scavenging air and fuel gas in the cylinder. The engine further comprises a pilot fuel supply system comprising a first pilot fuel valve arranged in the first pre-combustion chamber 114 and a second pilot fuel valve arranged in the second pre-combustion chamber 116, the first and second pilot fuel valves being configured to inject pilot fuel gas into the pre-combustion chambers. The first and second pre-chambers 114, 116 further include an ignition element configured to ignite the pilot fuel gas.

Figure 3 shows a schematic cross-sectional view of a portion of a two-stroke crosshead internal combustion engine with uniflow scavenging according to an embodiment of the present invention. This portion corresponds to the portion shown in Figure 2 with the difference that the cylinder 101 has a base member 117 and a pre-chamber member 118, which is located on top of the base member 117, and the cylinder cover 112 is located on top of the pre-chamber member 118. The first and second pre-chambers 114, 116 are located in the cylinder wall of the pre-chamber member 118. This allows the pre-chamber member to be specially designed to handle the high temperatures and pressures in the pre-chamber, for example by selecting suitable materials.

Figure 4 shows a schematic diagram of a pre-chamber 114 according to an embodiment of the present invention. The pre-chamber 114 is configured to open into the cylinder through a first opening 123 and a second opening 124. The pre-chamber includes an ignition element 119 and a pilot fuel valve 120 configured to inject pilot fuel gas into the pre-chamber during the compression stroke, allowing the pilot fuel gas 121 to be compressed before being ignited. The ignition element 119 is configured to ignite the pilot fuel gas in the pre-chamber, providing a torch 122 for igniting the fuel gas in the cylinder.

5 shows a schematic cross-sectional view of a portion of a two-stroke crosshead internal combustion engine with uniflow scavenging according to an embodiment of the present invention. A cylinder 101, a cylinder cover 112, and an exhaust valve 104 are shown. The cylinder cover 112 is provided with a first pre-chamber 114 and a second pre-chamber 116. The first and second pre-chambers 114, 116 open to the cylinder 101 through openings formed in the cylinder cover 112, and the pre-chambers 114, 116 are configured to ignite a mixture of scavenging air and fuel gas in the cylinder. The engine further comprises a pilot fuel supply system comprising a first pilot fuel valve arranged in the first pre-chamber 114 and a second pilot fuel valve arranged in the second pre-chamber 116, the first and second pilot fuel valves being configured to inject pilot fuel gas into the pre-chambers. The first and second pre-chambers 114, 116 further comprise ignition elements configured to ignite the pilot fuel gas.

6 shows a schematic diagram of the pre-chamber 114 according to an embodiment of the present invention. The pre-chamber 114 is configured to open into the cylinder through a first opening 123 and a second opening 124. The pre-chamber includes an ignition element 119 and a pilot fuel valve 120 configured to inject pilot fuel gas into the pre-chamber during the compression stroke, allowing the pilot fuel gas 121 to be compressed before being ignited. The ignition element 119 is configured to ignite the pilot fuel gas in the pre-chamber, providing a torch 122 for igniting the fuel gas in the cylinder. In this embodiment, the engine is configured to repeatedly perform a cleaning operation to clean the pre-chamber 114 when in diesel cycle mode (and thus not using the pre-chamber 114). In this embodiment, the pilot fuel valve 120 is fluidly connected to both the gas tank 140 and the N2 tank 130. The pilot fuel valve 120 is fluidly connected to the gas tank 140 via a compressor 141 configured to pressurize the gas and a shutoff valve 142. Correspondingly, the pilot fuel valve 120 is fluidly connected to the N2 tank 130 via a compressor 131 configured to pressurize the N2 and a shutoff valve 132. The N2 supply system 130 131 132 may also be used to purge the gas supply system 140 141 142 when the gas supply system is not in use, such as when the engine is in a diesel cycle mode, for example, using one or more blowout tubes (not shown). The cleaning operation may be configured to remove combustion by-products deposited in the pre-combustion chamber and/or prevent combustion by-products from being deposited in the pre-combustion chamber. The cleaning operation may comprise an injection of a first fluid using the pilot fuel valve 120. The first fluid may be N2 supplied from the N2 tank 130, where the first fluid is used to clean the pre-combustion chamber 114. Alternatively/additionally, the first fluid may be fuel gas supplied from the gas tank 140, where the ignition element 119 is configured to ignite the fuel gas as part of the cleaning operation, whereby undesirable combustion by-products may be burned off.

Although several embodiments have been described and illustrated in detail, the present invention is not limited thereto and may 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.

In a device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims or described in different embodiments does not indicate that a combination of these measures cannot be used to advantage.

It should be emphasized that as used in this specification, the term "comprises/comprising" specifies the presence of stated features, integers, steps or components, but does not exclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

The claims as originally filed are set forth below as an addendum.
[1] A two-stroke uniflow scavenging crosshead internal combustion engine (100) comprising at least one cylinder (101), a cylinder cover (112), a piston (103), a fuel gas supply system, and a scavenging system (111), wherein the cylinder has a cylinder wall (115), the cylinder cover is disposed at a top of the cylinder and has an exhaust valve (104), the piston is movably disposed within the cylinder along a central axis (113) between bottom dead center and top dead center, the scavenging system (111) has a scavenging inlet (102) disposed at a bottom of the cylinder, the fuel gas supply system comprises a fuel gas valve (105) at least partially disposed on the cylinder wall and configured to inject fuel gas into the cylinder during a compression stroke, and the fuel gas is supplied to the scavenging system (111) through a scavenging inlet (102) disposed at a bottom of the cylinder. 1. A two-stroke uniflow scavenging crosshead internal combustion engine comprising: a pre-combustion chamber (114) opening into the cylinder through a first opening (123) and comprising an ignition element (119); and a pilot fuel supply system, the pre-combustion chamber (114) comprising a pilot fuel valve (120) configured to inject pilot fuel gas (121) into the pre-combustion chamber during the compression stroke, the pilot fuel gas being compressed before being ignited, and the ignition element (119) configured to ignite the pilot fuel gas (121) in the pre-combustion chamber (114).
[2] The two-stroke crosshead internal combustion engine according to [1], wherein the fuel gas supply system and the pilot fuel supply system supply the same fuel gas.
[3] The two-stroke crosshead internal combustion engine of [1] or [2], wherein the pilot fuel valve (120) is configured to inject the pilot fuel gas (121) into the pre-combustion chamber (114) during the compression stroke within 0 to 160 degrees from bottom dead center, within 0 to 130 degrees from bottom dead center, or within 0 to 90 degrees from bottom dead center.
[4] The two-stroke crosshead internal combustion engine according to [3], wherein the pilot fuel valve (120) is configured to inject the pilot fuel gas (121) during a pilot fuel injection period, and the ignition element (119) is configured to ignite the pilot fuel gas (121) in the pre-combustion chamber (114) after the pilot fuel injection period ends.
[5] The two-stroke crosshead internal combustion engine according to [4], wherein the pre-chamber (114) is configured to ensure that an air-fuel equivalence ratio λ of a mixture of scavenging air and pilot fuel gas (121) in the pre-chamber (114) is below λ=1.6 at the time of ignition.
[6] The two-stroke crosshead internal combustion engine according to [ ^5] , wherein the ratio between the cross-sectional area of the openings (123, 124) of the pre-combustion chamber (114) into the cylinder (101), measured in m2, and the volume of the pre-combustion chamber, measured in m3, is between 0.5 and 1.2 m ^- 1 ^.
[7] The two-stroke crosshead internal combustion engine according to [6], wherein the engine is configured to ensure that the λ of the mixture of scavenging air and fuel gas in the cylinder exceeds λ = 2.0.
[8] The two-stroke crosshead internal combustion engine according to any one of [1] to [7], wherein the pre-combustion chamber (114) is at least partially disposed in the cylinder wall (115), and the first opening (123) is formed in the cylinder wall.
[9] The two-stroke crosshead internal combustion engine according to any one of [1] to [8], wherein the pre-combustion chamber (114) is at least partially disposed in the cylinder cover (112), and the first opening (123) is formed in the cylinder cover (112).
[10] The two-stroke crosshead internal combustion engine according to any one of [1] to [9], wherein the ignition element (119) is configured to generate a near-instantaneous maximum energy release upon start-up.
[11] The two-stroke crosshead internal combustion engine according to any one of [1] to [9], wherein the engine is a dual-fuel engine having an Otto cycle mode when powered by a fuel gas and a Diesel cycle mode when powered by an alternative fuel, the engine further comprising a dedicated alternative fuel supply system for injecting the alternative fuel, the alternative fuel supply system comprising one or more fuel injectors disposed in the cylinder cover, the engine being configured to inject the alternative fuel at the end of the compression stroke under high pressure using the one or more fuel injectors when in the Diesel cycle mode, and the engine being configured to repeatedly perform a cleaning operation to clean the pre-chamber when in the Diesel cycle mode.
[12] The two-stroke crosshead internal combustion engine according to [11], wherein the cleaning operation is configured to remove combustion by-products accumulated in the pre-combustion chamber and/or to prevent combustion by-products from accumulating in the pre-combustion chamber.
[13] The two-stroke crosshead internal combustion engine according to [11] or [12], wherein the cleaning operation comprises injecting a first fluid using the pilot fuel valve.
[14] The two-stroke crosshead internal combustion engine according to [12], wherein the first fluid is a fuel gas, atmospheric air, and/or an inert gas.
[15] The two-stroke crosshead internal combustion engine according to [14], wherein the first fluid is air or an inert gas, and the first fluid is used to clean the pre-combustion chamber.
[16] The two-stroke crosshead internal combustion engine of [13], wherein the first fluid is a fuel gas and the ignition element is configured to ignite the fuel gas as part of the cleaning operation.
[17] The two-stroke crosshead internal combustion engine according to any one of [11] to [16], wherein the engine is configured, when in the Diesel cycle mode, to repeatedly perform a first type cleaning operation for cleaning the pre-combustion chamber at a first frequency and a second type cleaning operation at a second frequency, the second frequency being lower than the first frequency.
[18] The two-stroke crosshead internal combustion engine of [17], wherein the first type of cleaning operation comprises injecting a first fluid using the pilot fuel valve, the first fluid being atmospheric air or an inert gas, the first fluid being used to clean the pre-chamber, and the second type of cleaning operation comprises injecting a fuel gas using the pilot fuel valve, the ignition element being configured to ignite the fuel gas as part of the second type of cleaning operation.
[19] A pre-chamber for use with a two-stroke uniflow scavenging crosshead internal combustion engine according to any one of [1] to [10], wherein the pre-chamber (114) is configured to open into the cylinder (101) through a first opening (123) and comprises an ignition element (119), characterized in that the pre-chamber further comprises a pilot fuel valve (120) configured to inject pilot fuel gas (121) into the pre-chamber (114) during the compression stroke, allowing the pilot fuel gas (121) to be compressed before being ignited, and the ignition element (119) is configured to ignite the pilot fuel gas (121) in the pre-chamber (114).

Claims (17)

A two-stroke uniflow scavenging crosshead internal combustion engine (100) comprising at least one cylinder (101), a cylinder cover (112), a piston (103), a fuel gas supply system, and a scavenging system (111), wherein the cylinder has a cylinder wall (115), the cylinder cover is disposed at a top of the cylinder and has an exhaust valve (104), the piston is movably disposed within the cylinder along a central axis (113) between bottom dead center and top dead center, the scavenging system (111) has a scavenging inlet (102) disposed at a bottom of the cylinder, and the fuel gas supply system includes a fuel gas valve (104) disposed at least partially in the cylinder wall and configured to inject fuel gas into the cylinder during a compression stroke. (105), allowing the fuel gas to mix with scavenging air and allowing the mixture of scavenging air and fuel gas to be compressed before being ignited, wherein the engine further comprises a pre-combustion chamber (114) and a pilot fuel supply system, the pre-combustion chamber (114) opening into the cylinder through a first opening (123) and comprising an ignition element (119), the pilot fuel supply system comprising a pilot fuel valve (120) configured to inject pilot fuel gas (121) into the pre-combustion chamber during the compression stroke, allowing the pilot fuel gas to be compressed before being ignited, and the ignition element (119) configured to ignite the pilot fuel gas (121) in the pre-combustion chamber (114) ,
the pilot fuel valve (120) is configured to inject the pilot fuel gas (121) into the pre-chamber (114) during the compression stroke within 0 to 160 degrees from bottom dead center, within 0 to 130 degrees from bottom dead center, or within 0 to 90 degrees from bottom dead center;
1. A two-stroke uniflow scavenged crosshead internal combustion engine, comprising: a dual fuel engine having an Otto cycle mode when powered by a fuel gas and a Diesel cycle mode when powered by an alternative fuel; the engine further comprising a dedicated alternative fuel supply system for injecting the alternative fuel, the alternative fuel supply system comprising one or more fuel injectors disposed in the cylinder cover; the engine is configured to inject the alternative fuel at the end of the compression stroke under high pressure using the one or more fuel injectors when in the Diesel cycle mode; and the engine is configured to repeatedly perform a cleaning operation to clean the pre-chamber when in the Diesel cycle mode . 2. The two-stroke uniflow scavenging crosshead internal combustion engine of claim 1, wherein the fuel gas supply system and the pilot fuel supply system supply the same fuel gas. 3. The two-stroke uniflow scavenging crosshead internal combustion engine according to claim 1 or 2, wherein the pilot fuel valve (120) is configured to inject the pilot fuel gas (121) during a pilot fuel injection period, and the ignition element (119) is configured to ignite the pilot fuel gas (121) in the pre-combustion chamber (114) after the end of the pilot fuel injection period. 4. The two-stroke uniflow scavenging crosshead internal combustion engine according to claim 3, wherein the pre-chamber (114) is configured to ensure that an air-fuel equivalence ratio λ of a mixture of scavenging air and pilot fuel gas (121) in the pre-chamber ( 114) is below λ=1.6 at the time of ignition. 5. A two-stroke uniflow scavenging crosshead internal combustion engine according to claim ⁴ , wherein the ratio between the cross-sectional area of the first opening (12 3) of the pre-chamber (114) into the cylinder (101), measured in m ² , and the volume of the pre- chamber, measured in m 3 , is between 0.5 and 1.2 m ⁻¹ . 6. A two-stroke uniflow scavenging crosshead internal combustion engine according to claim 5 , wherein the engine is configured to ensure that the λ of the mixture of scavenging air and fuel gas in the cylinder is greater than λ=2.0. The two-stroke uniflow scavenging crosshead internal combustion engine according to any one of claims 1 to 6, wherein the pre- combustion chamber (114) is at least partially arranged in the cylinder wall ( 115 ), and the first opening (123) is formed in the cylinder wall. The two-stroke uniflow scavenging crosshead internal combustion engine according to any one of claims 1 to 7, wherein the pre-combustion chamber (114) is at least partially disposed in the cylinder cover (112), and the first opening ( 123 ) is formed in the cylinder cover (112). The two-stroke uniflow scavenging crosshead internal combustion engine according to any one of claims 1 to 8 , wherein the ignition element (119) is configured to generate an instantaneous maximum energy release upon start-up. 2. The two-stroke uniflow scavenging crosshead internal combustion engine of claim 1 , wherein the cleaning operation is configured to remove combustion by -products accumulated in the pre-combustion chamber and/or to prevent combustion by-products from accumulating in the pre-combustion chamber. 11. A two-stroke uniflow scavenging crosshead internal combustion engine according to claim 1 or 10 , wherein the cleaning operation comprises injecting a first fluid using the pilot fuel valve. 12. The two-stroke uniflow scavenging crosshead internal combustion engine according to claim 11 , wherein the first fluid is a fuel gas, atmospheric air, and/or an inert gas. 13. A two-stroke uniflow scavenging crosshead internal combustion engine according to claim 12 , wherein the first fluid is atmospheric air or an inert gas, and the first fluid is used to wash the pre-chamber. 12. The two-stroke uniflow scavenging crosshead internal combustion engine of claim 11 , wherein the first fluid is a fuel gas and the ignition element is configured to ignite the fuel gas as part of the cleaning operation. 15. A two-stroke uniflow scavenging crosshead internal combustion engine according to any one of claims 1 to 14, wherein the engine is configured, when in the diesel cycle mode, to repeatedly perform a first type of cleaning operation for cleaning the pre-combustion chamber at a first frequency and a second type of cleaning operation at a second frequency, the second frequency being lower than the first frequency. 16. The two-stroke uniflow scavenged crosshead internal combustion engine of claim 15, wherein the first type of cleaning operation comprises injecting a first fluid using the pilot fuel valve, the first fluid being atmospheric air or an inert gas, the first fluid being used to clean the pre-chamber, and the second type of cleaning operation comprises injecting a fuel gas using the pilot fuel valve, the ignition element being configured to ignite the fuel gas as part of the second type of cleaning operation. 10. A pre-chamber for use with a two-stroke uniflow scavenging crosshead internal combustion engine according to any one of claims 1 to 9 , the pre-chamber (114) being configured to open into the cylinder (101) through a first opening (123) and comprising an ignition element (119), characterized in that the pre-chamber further comprises a pilot fuel valve (120) configured to inject pilot fuel gas (121) into the pre-chamber (114) during the compression stroke, allowing the pilot fuel gas (121) to be compressed before being ignited, and the ignition element (119) configured to ignite the pilot fuel gas (121) in the pre-chamber (114).

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