JP7604124B2 - Two-stroke uniflow scavenging crosshead internal combustion engine and method for starting a dual-fuel two-stroke uniflow scavenging crosshead internal combustion engine - Google Patents

Description

The present invention relates to a two-stroke uniflow scavenging crosshead internal combustion engine and a method for starting a dual-fuel two-stroke uniflow scavenging crosshead internal combustion engine.

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 high-pressure compressor to compress the fuel gas prior to injection in order to overcome the high pressure in the cylinder.

However, high pressure gas compressors are expensive and complex to manufacture and maintain. One way to avoid the need for a high pressure 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, it is difficult to ensure proper cooling of the pre-combustion chamber.

Therefore, a challenge remains to provide an improved method for cooling the pre-chamber.

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, a pre-combustion chamber, 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 center and top dead center, 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 on the cylinder wall and configured to inject fuel gas into the cylinder during the compression stroke, the fuel gas being supplied to the scavenging inlet through the scavenging inlet. The pre-chamber is configured to ignite the mixture of scavenging air and fuel gas in the cylinder through a first opening, and the pre-chamber is configured to ignite the mixture of scavenging air and fuel gas in the cylinder, and the engine further includes a pre-chamber temperature regulation system for regulating a temperature of the pre-chamber, the pre-chamber temperature regulation system including a heat exchange flow path adjacent to the pre-chamber for heat exchange with the pre-chamber, and the pre-chamber temperature regulation system is configured to circulate a heat exchange fluid through the heat exchange flow path, and the pre-chamber temperature regulation system further includes a control unit configured to control the flow of the heat exchange fluid and/or the inlet temperature of the heat exchange fluid.

As a result, by providing a dedicated temperature regulation system for the pre-chamber, a secure and efficient ignition in the pre-chamber can be obtained, for example, the temperature of the pre-chamber can be controlled independently of the operation of other cooling systems, such as a cylinder cooling system. The improved control can further allow the temperature of the pre-chamber to be lowered further toward the ignition limit (e.g., the required autoignition temperature of the pilot fuel), thereby reducing NOx gas emissions. The improved control can also reduce the risk of pre-ignition, which not only increases NOx production but also increases engine wear.

The internal combustion engine is preferably a large slow-speed turbocharged two-stroke crosshead internal combustion engine with uniflow scavenging for propelling a stationary power plant or a marine vessel, 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. The internal combustion engine may include a cylinder cooling system. The pre-chamber temperature regulation system may be configured only to regulate the temperature of the pre-chamber (and possibly the engine parts directly or indirectly surrounding the pre-chamber).

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.

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.

The one or more fuel gas valves are preferably located at least partially in the cylinder wall, between top dead center and bottom dead center, at a position above the scavenging inlet. The one or more fuel gas valves may include a nozzle located in the cylinder wall for injecting fuel gas into the cylinder. Other parts of the fuel gas valve (other than the nozzle) may be located outside the cylinder wall.

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

In some embodiments, the engine further comprises a pilot fuel supply system, the pilot fuel supply system comprising a pilot fuel valve disposed in the pre-combustion chamber, the pilot fuel valve configured to inject pilot fuel into the pre-combustion chamber.

The pre-chamber may be configured such that the pilot fuel self-ignites due to the temperature and pressure within the pre-chamber. Alternatively, the pilot fuel in the pre-chamber may be ignited by means of a spark plug or laser ignition device. The pilot fuel may be heavy fuel oil or marine diesel oil, or any other fuel with suitable ignition properties, precisely dosed so that just the right amount can ignite the mixture of fuel gas and scavenging air in the cylinder. Such a pilot fuel system may be much smaller in size and more suitable for injecting a precise amount of pilot fuel compared to a dedicated fuel supply system for alternative fuels, due to the large size of the components that may not be suitable for this purpose. The pilot fuel supply system may be configured to inject a quantity of pilot oil near top dead center, at a suitable crank angle for optimal ignition of the main charge. Ignition of the pilot fuel occurs immediately after injection of the pilot oil, and ignition of the main charge occurs immediately after ignition of the pilot oil.

The pre-combustion chamber may be located in the cylinder wall or cylinder cover.

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

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

In some embodiments, the pre-chamber temperature regulation system is configured to cool the pre-chamber.

The pre-chamber temperature regulation system may be a cooling system configured to cool the pre-chamber, for example, the cooling system may be configured to cool the heat exchange fluid prior to supplying the heat exchange fluid to the heat exchange flow passage. Thus, the heat exchange flow passage may be a cooling flow passage.

Alternatively, the heat exchange passageway may be part of a combined heating and cooling system configured to either cool or heat the pre-chamber, for example, the combined heating and cooling system may be configured to either cool or heat the heat exchange fluid before supplying it to the heat exchange passageway. The combined heating and cooling system may be configured to heat the pre-chamber as part of a gas start procedure, either from a complete engine shutdown or when switching from heavy fuel oil or marine diesel to fuel gas. The combined heating and cooling system may be configured to cool the pre-chamber after the gas start procedure is completed, i.e., during normal gas operation, to prevent damage to the pre-chamber and/or surrounding engine components.

In some embodiments, the heat exchange passageway may be part of a combined heating and cooling system configured to either cool or heat the pre-chamber, where the combined heating and cooling system is configured to heat the pre-chamber when the engine is running at low loads and to cool the pre-chamber when the engine is running at high loads.

As a result, by ensuring that the pre-chamber is sufficiently warm when the engine is running at low loads, combustion stability may be increased and ignition delay may be reduced and stabilized. Furthermore, by cooling the pre-chamber when the engine is running at high loads, damage to the pre-chamber and surrounding engine components may be prevented.

In some embodiments, the combined heating and cooling system is configured to heat the pre-chamber when the engine is operating at a load below a first threshold and to cool the pre-chamber when the engine is operating above a second threshold, where the second threshold is greater than or equal to the first threshold.

The values of the first and second thresholds depend on the particular engine design and may be found via experimentation and/or computer simulation.

Examples of heat exchange fluids are water, air, and system oil.

In some embodiments, the pre-chamber temperature regulation system is further configured to heat the pre-chamber.

In some embodiments, the pre-chamber temperature regulation system is further configured to heat the pre-chamber as part of the engine start-up procedure.

In some embodiments, the engine further comprises a cylinder cooling system comprising a cooling passage proximate to the cylinder for cooling the cylinder, the cylinder cooling system configured to circulate a heat exchange fluid through the cooling passage, and wherein the cylinder cooling system further comprises a control unit configured to control the flow of the heat exchange fluid and/or the inlet temperature of the heat exchange fluid.

As a result, the pre-chamber and the cylinder can both be cooled at least partially independently, for example depending on the values of the engine parameters, whereby better engine performance can be achieved.

The cylinder cooling system is preferably also configured to cool the cylinder cover.

In some embodiments, the cylinder cooling system and the prechamber temperature regulation system are two separate systems that are not fluidly connected.

As a result, the pre-chamber and cylinder can both be cooled completely independently.

In some embodiments, the cylinder cooling system and the pre-chamber temperature regulation system form part of a common engine temperature regulation system comprising a first pressure regulating valve configured to control the inlet pressure of a heat exchange fluid supplied to either the heat exchange passage of the pre-chamber temperature regulation system or the cooling passage of the cylinder cooling system.

As a result, the engine cooling system can be simplified while still providing partially independent control of cylinder and pre-chamber cooling.

In some embodiments, the pre-chamber has a pre-chamber wall, where the heat exchange passage extends within a portion of the pre-chamber wall.

As a result, by having the heat exchange passages located directly inside the pre-chamber wall, the temperature of the pre-chamber can be effectively and precisely regulated.

The portion of the heat exchange passageway that extends into the pre-chamber wall can be formed at the same time that the pre-chamber is formed, for example, using additive manufacturing techniques.

In some embodiments, the engine further comprises a pre-chamber housing, the pre-chamber being disposed in the pre-chamber housing, the pre-chamber having at least a first contact portion and a second contact portion for abutting the pre-chamber housing and securing the pre-chamber to the pre-chamber housing, and wherein the pre-chamber housing has a first insulation volume formed between the first contact portion and the second contact portion for limiting heat exchange between the pre-chamber and the engine.

As a result, by insulating the pre-chamber from the part of the engine in which it is inserted, the temperature of the pre-chamber can be more precisely controlled. This may also allow the parts of the engine in close proximity to the pre-chamber to be made from a material with a lower heat resistance, such as cast iron.

In some embodiments, the pre-chamber further has a third contact portion for abutting the pre-chamber housing, and the pre-chamber housing further has a second insulating volume formed between the second contact portion and the third contact portion.

In some embodiments, the pre-chamber and heat exchange passages are manufactured by a single additive manufacturing process.

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

This allows the pre-chamber member 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 an insert between the base member and the cylinder cover, with or without gasket arrangements towards either one. It may be pre-assembled with the base member before the cylinder cover is fitted.

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

The cylinder base member may be made of cast iron and the pre-chamber member may be made of steel.

In some embodiments, the pre-chamber is connected to the first opening via a flow passage extending along a first axis, where an angle between the first axis and a reference plane disposed perpendicular to the central axis is between 0 degrees and 85 degrees, 0 degrees and 80 degrees, 0 degrees and 60 degrees, 0 degrees and 45 degrees, or 0 degrees and 30 degrees.

As a result, the torch extending from the pre-chamber into the cylinder can come into direct contact with most of the scavenging air and fuel gas mixture.

An engine may be provided with more prechamber members, for example at least two, three, or four prechambers per cylinder.

According to a second aspect, the present invention relates to a method of starting a dual-fuel, two-stroke, uniflow-scavenged, crosshead internal combustion engine having an Otto cycle mode when powered by fuel gas and a Diesel cycle mode when powered by an alternative fuel, the engine comprising at least one cylinder, a cylinder cover, a piston, a fuel gas supply system, a cylinder cooling system, a pre-chamber, and a scavenging system, the cylinder having a cylinder wall, the cylinder cover being disposed at a top of the cylinder and having an exhaust valve, the piston being movably disposed within the cylinder along a central axis between bottom dead centre and top dead centre, the scavenging system having a scavenging inlet disposed at a bottom of the cylinder, the fuel gas supply system being at least partially interposed between the cylinder wall, and a fuel gas valve arranged in the cylinder and 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, a pre-chamber opening into the cylinder through a first opening, the pre-chamber configured to ignite the mixture of scavenging air and fuel gas in the cylinder, wherein the engine further comprises a dedicated alternative fuel supply system for injecting an alternative fuel directly into the cylinder, wherein the pre-chamber is heated as part of the engine starting procedure, and wherein the engine is started directly in a fuel gas mode without first injecting an alternative fuel into the cylinder using the dedicated alternative fuel supply system.

As a result, by heating the pre-chamber, the engine can be started directly in gas mode, lowering unwanted exhaust emissions. This can be particularly beneficial when the engine is started in emission sensitive areas, such as cruise ports located near populated areas.

The institution may be an institution as disclosed in relation to the first aspect of the present invention.

Different aspects of the present invention may be realized in different ways, including a two-stroke uniflow scavenging crosshead internal combustion engine and a method of starting a dual-fuel two-stroke uniflow scavenging crosshead internal combustion engine, 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.

Between two axes, two faces, or an axis and a face, there will always be two angles, a small angle V1 and a large angle V2, where V2=180 degrees-V1. In this disclosure, the small angle V1 will always be specified.

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 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. 5 illustrates a flow chart of a method for starting a dual-fuel, two-stroke, uniflow scavenging, crosshead internal combustion engine in accordance with an embodiment of the present invention. FIG. 6a shows a cross-sectional view of a large slow speed turbocharged two-stroke crosshead internal combustion engine with uniflow scavenging for propelling marine vessels according to an embodiment of the present invention. FIG. 6b shows a cross-sectional view of a large slow speed turbocharged two-stroke crosshead internal combustion engine with uniflow scavenging for propelling marine vessels 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) arranged 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 fuel gas valves 105 are arranged at least partially in the cylinder wall between the cylinder cover 112 and the scavenging air inlet 102. The engine further comprises a pre-chamber 114 arranged in the cylinder wall 115 (shown only diagrammatically). The pre-chamber 114 has a pre-chamber wall and opens into the cylinder through a first opening. The pre-chamber 114 is arranged to ignite the mixture of scavenging air and fuel gas in the cylinder 101. The engine 100 further comprises a pre-chamber thermoregulation system for regulating the temperature of the pre-chamber, the pre-chamber thermoregulation system comprising a heat exchange passage 191 (shown only diagrammatically) in close proximity to the pre-chamber 114 for heat exchange with the pre-chamber 114, the pre-chamber thermoregulation system being configured to circulate a heat exchange fluid through the heat exchange passage 191. The pre-chamber thermoregulation system further comprises a control unit 190 configured to control the flow of the heat exchange fluid and/or the inlet temperature of the heat exchange fluid, for example by controlling a compressor and/or an expansion valve of the pre-chamber thermoregulation system. 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 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 preferably 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 between 0 and 130 degrees from its orientation at 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 the scavenging inlet 102 to prevent fuel gas from escaping through the exhaust valve 104 and 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 positioned 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, each of which is provided with a heat exchange passage (not shown). The first and second pre-combustion chambers 114 116 both open into the cylinder 101 through openings formed in the cylinder wall 115, and the pre-combustion chambers are configured to ignite a mixture of scavenging air and fuel gas in the cylinder.

Figure 3 shows a schematic cross-sectional view of a part of a two-stroke crosshead internal combustion engine with uniflow scavenging according to an embodiment of the present invention. This part corresponds to the part shown in Figure 2 with the difference that the cylinder 101 has a base member 117 and a pre-chamber member 118, which is arranged on the base member 117 and the cylinder cover 112 is arranged on the pre-chamber member 118. The first and second pre-chambers 114, 116 are arranged on 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 a suitable material.

Figure 4 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 first and second pre-chambers 114 116 are arranged in the cylinder cover 112.

5 shows a flow chart of a method for starting a dual-fuel two-stroke uniflow scavenging crosshead internal combustion engine according to an embodiment of the present invention. The engine may be the engine disclosed in connection with FIG. 1. In a first step 501, the pre-chamber of the engine is heated, for example using a heat exchange passage provided in close proximity to the pre-chamber. Then, in step 502, the engine is started directly in fuel gas mode without first injecting alternative fuel into the cylinders using a dedicated alternative fuel supply system. As a result, by heating the pre-chamber, the engine can be started directly in gas mode, lowering the emission of undesirable exhaust gases. This may be particularly beneficial when the engine is started in emission-sensitive areas, such as cruise ports located near residential areas.

6a shows a cross-sectional view of a large slow-speed turbocharged two-stroke crosshead internal combustion engine with uniflow scavenging for propelling marine vessels according to an embodiment of the present invention. The engine is a dual-fuel engine with an Otto cycle mode when powered by fuel gas and a Diesel cycle mode when powered by alternative fuels, e.g., heavy fuel oil or marine diesel oil. Each cylinder has a cylinder wall and is provided with a scavenging inlet located at the bottom of the cylinder (not shown). 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 and has an exhaust valve 104. The piston 103 is movably disposed within the cylinder along the central axis between bottom dead center and top dead center. In the figure, the piston 103 is located at top dead center. The fuel gas supply system comprises one or more fuel gas valves (not shown) configured to inject fuel gas into the cylinder during the compression stroke (when the engine is in gas mode), 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 valves are at least partially arranged in the cylinder wall between the cylinder cover 112 and the scavenging air inlet. The engine further comprises two pilot pre-chamber units 131, each of which comprises a pre-chamber 114, a pilot fuel valve housing 130 and a pilot fuel valve 132 arranged in the pilot fuel valve housing 130. The cylinder has a base member 117 and a pre-chamber member 118, the pre-chamber member 118 being arranged on the base member 117 and the cylinder cover 112 being arranged on the pre-chamber member 118. The pre-chamber 114 is arranged in the cylinder wall of the pre-chamber member 118. The pre-chamber 114 opens into the cylinder through an opening formed in the cylinder wall of the pre-chamber member 118. The scavenging air inlet is fluidly connected to the scavenging system. The piston 103 is connected to the crankshaft (not shown) via a piston rod, a crosshead, and a connecting rod. The pilot fuel valve 132 is configured to inject a small amount of pilot fuel into the pre-chamber 114 at least when the engine is in gas mode. The pilot fuel valve 132 may also be configured to inject a small amount of pilot fuel into the pre-chamber 114 when the engine is running on pure diesel to prevent the pilot fuel valve from sticking. The pre-chamber 114 is configured such that the pilot fuel auto-ignites due to the temperature and pressure within the pre-chamber 114. The pilot fuel oil may be heavy fuel oil, marine diesel oil, or any other fuel with suitable auto-ignition properties.

The engine further comprises one or more fuel injectors 116 arranged in a cylinder cover 112 forming part of an alternative fuel supply system. When the engine 100 is powered by an alternative fuel, the fuel injectors 116 are configured to inject the alternative fuel, e.g. heavy fuel oil, under high pressure at the end of the compression stroke.

6b shows a close-up of the right pilot pre-chamber unit 131 shown in FIG. 6a. The pre-chamber pilot unit 131 comprises a first heat exchange passage 145 for circulating a temperature control fluid having an inlet 136 and an outlet (not shown), where both the inlet 136 and the outlet are arranged in the pilot fuel valve housing 130. The pre-chamber pilot unit 131 further comprises a second heat exchange passage 146 for circulating a temperature control fluid having an inlet 138 and an outlet (not shown), where both the inlet 138 and the outlet are arranged in the pilot fuel valve housing 130. The first and second heat exchange passages 145, 146 extend inside both a portion of the wall of the pre-chamber 114 and a portion of the pilot fuel valve housing 130. The first and second heat exchange passages 145, 146 form part of a pre-chamber temperature regulation system for regulating the temperature of the pre-chamber 114. The pre-chamber temperature conditioning system is configured to circulate a heat exchange fluid through the first and second heat exchange passages 145, 146. The pre-chamber temperature conditioning system further comprises a control unit (not shown) configured to control the flow of the heat exchange fluid, e.g. the flow rate of the heat exchange fluid through the first and second heat exchange passages 145, 146 and/or the inlet temperature of the heat exchange fluid supplied to the first and second heat exchange passages 145, 146. The first and second heat exchange passages 145, 146 comprise a first portion for directing the temperature conditioning fluid towards the first opening 144 of the pre-chamber and a second portion for directing the temperature conditioning fluid away from the first opening of the pre-chamber (only the first portion is visible in this cross-sectional view). The shape of the first portion substantially corresponds to the shape of the second portion. In this embodiment, the pre-chamber member 118 functions as a pre-chamber housing, and the pre-chamber 114 is disposed in the pre-chamber housing, and the pre-chamber 114 has a first contact portion 143 and a second contact portion 142 for abutting against the pre-chamber housing and fixing the pre-chamber to the pre-chamber housing. In this embodiment, both the first contact portion 143 and the second contact portion 142 have a torus shape. The pre-chamber housing has a first insulating volume 141 (e.g., filled with air) formed between the first contact portion 143 and the second contact portion 142 for limiting heat exchange between the pre-chamber 114 and the engine. The pre-chamber further has a third contact portion 147 for abutting against the pre-chamber housing. In this embodiment, the third contact portion 147 has a torus shape. The pre-combustion chamber housing further has a second insulating volume 140 formed between the second contact portion 142 and the third contact portion 147.

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 invention as originally claimed in the present application is set forth 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, a pre-combustion chamber, and a scavenging system, wherein the cylinder has a cylinder wall, the cylinder cover is disposed at a top of the cylinder and has an exhaust valve, the piston is movably disposed within the cylinder along a central axis between bottom dead center and top dead center, the scavenging system has a scavenging inlet disposed at a bottom of the cylinder, the fuel gas supply system comprises a fuel gas valve disposed at least partially on the cylinder wall and configured to inject fuel gas into the cylinder during a compression stroke, allowing the fuel gas to mix with scavenging air, and the mixture of scavenging air and fuel gas is ignited before being ignited. 1. A two-stroke uniflow scavenged crosshead internal combustion engine comprising: a pre-chamber opening into the cylinder through a first opening, the pre-chamber configured to ignite the mixture of scavenging air and fuel gas in the cylinder; wherein the engine further comprises a pre-chamber temperature regulation system for regulating a temperature of the pre-chamber, the pre-chamber temperature regulation system comprising a heat exchange passage adjacent to the pre-chamber for heat exchange with the pre-chamber, the pre-chamber temperature regulation system configured to circulate a heat exchange fluid through the heat exchange passage; and wherein the pre-chamber temperature regulation system further comprises a control unit configured to control a flow of the heat exchange fluid and/or an inlet temperature of the heat exchange fluid.
[2] The two-stroke uniflow scavenging crosshead internal combustion engine according to [1], wherein the control unit is configured to control the flow of the heat exchange fluid and/or the inlet temperature of the heat exchange fluid in dependence on engine load, engine speed, the air-fuel equivalence ratio λ of the mixture of scavenging air and fuel gas, and/or a sensor signal.
[3] The two-stroke uniflow scavenging crosshead internal combustion engine according to [1] or [2], wherein the pre-combustion chamber is at least partially disposed in the cylinder wall, and the first opening is formed in the cylinder wall.
[4] The two-stroke uniflow scavenging crosshead internal combustion engine according to any one of [1] to [3], wherein the pre-combustion chamber temperature adjustment system is configured to cool the pre-combustion chamber.
[5] The two-stroke uniflow scavenging crosshead internal combustion engine according to [4], wherein the pre-combustion chamber temperature regulation system is further configured to heat the pre-combustion chamber.
[6] The two-stroke uniflow scavenging crosshead internal combustion engine of [5], wherein the pre-chamber temperature regulation system is further configured to heat the pre-chamber as part of an engine start-up procedure.
[7] The two-stroke uniflow scavenging crosshead internal combustion engine according to any one of [1] to [6], further comprising a cylinder cooling system comprising cooling passages adjacent to the cylinders for cooling the cylinders, the cylinder cooling system configured to circulate a heat exchange fluid through the cooling passages, and wherein the cylinder cooling system further comprises a control unit configured to control the flow of the heat exchange fluid and/or the inlet temperature of the heat exchange fluid.
[8] The two-stroke uniflow scavenging crosshead internal combustion engine according to [7], wherein the cylinder cooling system and the pre-combustion chamber temperature adjustment system are two separate systems that are not fluidly connected.
[9] The two-stroke uniflow scavenging crosshead internal combustion engine according to any one of [1] to [8], wherein the pre-combustion chamber has a pre-combustion chamber wall, and the heat exchange passage extends inside a portion of the pre-combustion chamber wall.
[10] The two-stroke uniflow scavenging crosshead internal combustion engine according to any one of [1] to [8], further comprising a pre-combustion chamber housing, the pre-combustion chamber being disposed in the pre-combustion chamber housing, the pre-combustion chamber having at least a first contact portion and a second contact portion for abutting against the pre-combustion chamber housing and fixing the pre-combustion chamber to the pre-combustion chamber housing, wherein the pre-combustion chamber housing has a first insulating volume formed between the first contact portion and the second contact portion for limiting heat exchange between the pre-combustion chamber and the engine.
[11] The two-stroke uniflow scavenging crosshead internal combustion engine according to any one of [1] to [10], wherein the heat exchange passage may be part of a combined heating and cooling system configured to either cool or heat the pre-chamber, the combined heating and cooling system being configured to heat the pre-chamber when the engine is running at low load and configured to cool the pre-chamber when the engine is running at high load.
[12] A method of starting a dual-fuel two-stroke uniflow scavenging crosshead internal combustion 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 comprising at least one cylinder, a cylinder cover, a piston, a fuel gas supply system, a cylinder cooling system, a pre-chamber, and a scavenging system, the cylinder having a cylinder wall, the cylinder cover being disposed at a top of the cylinder and having an exhaust valve, the piston being movably disposed within the cylinder along a central axis between bottom dead center and top dead center, the scavenging system having a scavenging inlet disposed at a bottom of the cylinder, the fuel gas supply system being at least partially disposed in the cylinder wall and having a compression stroke. a fuel gas valve configured to inject fuel gas into the cylinder during ignition, 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, the pre-chamber opening into the cylinder through a first opening, the pre-chamber configured to ignite the mixture of scavenging air and fuel gas in the cylinder, wherein the engine further comprises a dedicated alternative fuel supply system for injecting the alternative fuel directly into the cylinder, wherein the pre-chamber is heated as part of an engine starting procedure, and wherein the engine is started directly in a fuel gas mode without first injecting the alternative fuel into the cylinder using the dedicated alternative fuel supply system.

Claims (12)

A two-stroke uniflow scavenging crosshead internal combustion engine comprising at least one cylinder, a cylinder cover, a piston, a fuel gas supply system, a pre-chamber, and a scavenging system, the cylinder having a cylinder wall, the cylinder cover being disposed at a top of the cylinder and having an exhaust valve, the piston being movably disposed within the cylinder along a central axis between bottom dead center and top dead center, the scavenging system having a scavenging inlet disposed at a bottom of the cylinder, the fuel gas supply system comprising a fuel gas valve disposed at least partially on the cylinder wall and configured to inject fuel gas into the cylinder during a compression stroke, 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, the pre-chamber opening into the cylinder through a first opening, the pre-chamber configured to ignite the mixture of scavenging air and fuel gas in the cylinder. 1. A two-stroke, uniflow scavenged, crosshead internal combustion engine, wherein the internal combustion engine further comprises a pre-chamber temperature regulation system for regulating a temperature of the pre-chamber, the pre-chamber temperature regulation system comprising a heat exchange flow path adjacent to the pre-chamber for heat exchange with the pre-chamber, the pre-chamber temperature regulation system being configured to circulate a heat exchange fluid through the heat exchange flow path, wherein the pre-chamber temperature regulation system further comprises a control unit configured to control a flow of the heat exchange fluid and/or an inlet temperature of the heat exchange fluid , wherein the internal combustion engine further comprises a pilot fuel supply system, the pilot fuel supply system comprising a pilot fuel valve disposed in the pre-chamber, the pilot fuel valve being configured to inject a self-ignitable pilot fuel into the pre-chamber, and the control unit being configured to reduce the temperature of the pre-chamber towards the self-ignition temperature of the pilot fuel . The two-stroke uniflow scavenging crosshead internal combustion engine of claim 1, wherein the control unit is configured to control the flow of the heat exchange fluid and/or the inlet temperature of the heat exchange fluid depending on the engine load, the engine speed, the air-fuel equivalence ratio λ of the mixture of scavenging air and fuel gas, and/or a sensor signal. The two-stroke uniflow scavenging crosshead internal combustion engine according to claim 1 or 2, wherein the pre-combustion chamber is at least partially disposed in the cylinder wall, and the first opening is formed in the cylinder wall. The two-stroke uniflow scavenging crosshead internal combustion engine according to any one of claims 1 to 3, wherein the pre-combustion chamber temperature regulation system is configured to cool the pre-combustion chamber. The two-stroke uniflow scavenging crosshead internal combustion engine of claim 4, wherein the pre-combustion chamber temperature regulation system is further configured to heat the pre-combustion chamber. The two-stroke uniflow scavenging crosshead internal combustion engine of claim 5, wherein the pre-chamber temperature regulation system is further configured to heat the pre-chamber as part of an engine start-up procedure. 7. A two-stroke uniflow scavenging crosshead internal combustion engine according to any one of claims 1 to 6, wherein the internal combustion engine further comprises a cylinder cooling system comprising a cooling passage adjacent to the cylinder for cooling the cylinder, the cylinder cooling system configured to circulate a heat exchange fluid through the cooling passage, and wherein the cylinder cooling system further comprises a control unit configured to control the flow of the heat exchange fluid and/or the inlet temperature of the heat exchange fluid. The two-stroke uniflow scavenging crosshead internal combustion engine of claim 7, wherein the cylinder cooling system and the pre-combustion chamber temperature adjustment system are two separate systems that are not fluidly connected. A two-stroke uniflow scavenging crosshead internal combustion engine according to any one of claims 1 to 8, wherein the pre-combustion chamber has a pre-combustion chamber wall, and the heat exchange passage extends inside a portion of the pre-combustion chamber wall. The two-stroke uniflow scavenging crosshead internal combustion engine according to any one of claims 1 to 8, wherein the internal combustion engine further comprises a pre-combustion chamber housing, the pre-combustion chamber being disposed in the pre-combustion chamber housing, the pre-combustion chamber having at least a first contact portion and a second contact portion for abutting against the pre-combustion chamber housing and fixing the pre- combustion chamber to the pre-combustion chamber housing, and wherein the pre-combustion chamber housing has a first insulating volume formed between the first contact portion and the second contact portion for limiting heat exchange between the pre-combustion chamber and the internal combustion engine. 11. A two-stroke uniflow scavenging crosshead internal combustion engine according to any one of claims 1 to 10, wherein the heat exchange passage is part of a combined heating and cooling system configured to either cool or heat the pre-chamber, the combined heating and cooling system being configured to heat the pre-chamber when the internal combustion engine is running at low load and configured to cool the pre-chamber when the internal combustion engine is running at high load. 2. A method of starting a two-stroke uniflow scavenged crosshead internal combustion engine as claimed in claim 1 , having an Otto cycle mode when powered by fuel gas and a Diesel cycle mode when powered by an alternative fuel, the internal combustion engine further comprising a dedicated alternative fuel supply system for injecting the alternative fuel directly into the cylinders, wherein the pre -chamber is heated as part of an engine starting procedure, and wherein the internal combustion engine is started directly in a fuel gas mode without first injecting the alternative fuel into the cylinders using the dedicated alternative fuel supply system, and wherein the internal combustion engine further comprises a pilot fuel supply system, the pilot fuel supply system comprising a pilot fuel valve disposed in the pre-chamber, the pilot fuel valve configured to inject a self-ignitable pilot fuel into the pre-chamber .

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