DK181032B1

DK181032B1 - Internal combustion engine

Info

Publication number: DK181032B1
Application number: DKPA202070397A
Authority: DK
Inventors: Anthony Ramos De Matos Oftedal Michael
Original assignee: Man Energy Solutions Filial Af Man Energy Solutions Se Tyskland
Priority date: 2020-06-17
Filing date: 2020-06-17
Publication date: 2022-10-07
Also published as: CN113803151A; JP2021195953A; JP7286711B2; DK202070397A1; CN113803151B; KR102646089B1; KR20210156789A

Abstract

Disclosed is A two-stroke uniflow scavenged crosshead internal combustion engine comprising at least one cylinder, a cylinder cover, a piston, a fuel gas supply system, and a scavenge air system. The engine further comprises a pilot pre-chamber unit comprising a pre-chamber, a pilot fuel valve housing, and a pilot fuel valve arranged in the pilot fuel valve housing. The prechamber has a pre-chamber wall and opens into the cylinder through a first opening, the pre-chamber being configured to ignite the mixture of scavenge air and fuel gas in the cylinder and wherein the pre-chamber pilot unit further comprises a first heat exchange channel for circulating a heat exchange fluid having an inlet and an outlet, and wherein both the inlet and the outlet is arranged in the pilot fuel valve housing.

Description

DK 181032 B1 1 Field The present invention relates to a two-stroke uniflow scavenged crosshead internal combustion engine and a pilot pre-chamber unit for a two-stroke uniflow scavenged crosshead internal combustion engine. Background Two-stroke internal combustion engines are used as propulsion engines in vessels like container ships, bulk carriers, and tankers. Reduction of unwanted exhaust gases from the internal combustion engines has become increasingly important.

An effective way to reduce the amount of unwanted exhaust gasses is to switch from fuel oil e.g. Heavy Fuel Oil (HFO) to fuel gas. Fuel gas may be injected into the cylinders at the end of the compression stroke where it may be immediately ignited by either the high temperatures which the gases in the cylinders achieve when compressed or by the ignition of a pilot fuel. However, injecting fuel gas into the cylinders at the end of the compression stroke requires high pressure compressors for compressing the fuel gas prior to injection to overcome the high pressure in the cylinders.

The high pressure gas compressors are however expensive and complex to manufacture and maintain. One way to avoid the need of high pressure compressors is to configure the engine to inject the fuel gas in the beginning of the compression stroke where the pressure in the cylinders is significantly lower.

WO2013007863 discloses such an engine. To secure proper ignition of the fuel gas a pilot ignition pre-chamber is provided in the cylinder cover. An amount 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

DK 181032 B1 2 ignition pre-chamber.

This results in a torch which ignites the fuel gas in the main chamber of the cylinder.

Securing proper cooling of the pre-chamber is however difficult.

Additionally, preventing leaking of cooling fluid and enabling easy maintenance may be challenging.

Thus it remains a problem to provide an improved way of cooling pre-chambers.

Summary

According to a first aspect, the invention relates to a two-stroke uniflow scavenged crosshead internal combustion engine comprising at least one cylinder, a cylinder cover, a piston, a fuel gas supply system, and a scavenge air system, the cylinder having a cylinder wall, the cylinder cover being arranged on 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 scavenge air system having a scavenge air inlet arranged at the bottom of the cylinder, the fuel gas supply system comprising a fuel gas valve arranged at least partly in the cylinder wall and configured to inject fuel gas into the cylinder during the compression stroke enabling the fuel gas to mix with scavenge air and allowing the mixture of scavenge air and fuel gas to be compressed before being ignited, wherein the engine further comprises a pilot pre-chamber unit comprising a pre-chamber, a pilot fuel valve housing, and a pilot fuel valve arranged in the pilot fuel valve housing, wherein the pre-chamber has a pre- chamber wall and opens into the cylinder through a first opening, the pre- chamber being configured to ignite the mixture of scavenge air and fuel gas in the cylinder and wherein the pre-chamber pilot unit further comprises a first heat exchange channel for circulating a heat exchange fluid having an inlet and an outlet, and wherein both the inlet and the outlet is arranged in the pilot fuel valve housing.

DK 181032 B1 3 Consequently, by providing the pilot pre-chamber unit with a heat exchange channel where both the inlet and outlet is arranged in a pilot fuel valve housing both effective temperature regulation and easy maintenance is — provided.

The internal combustion engine is preferably a large low-speed turbocharged two-stroke crosshead internal combustion engine with uniflow scavenging for propelling a marine vessel having a power of at least 400 kW per cylinder. The internal combustion engine may comprise a turbocharger driven by the exhaust gases generated by the internal combustion engine and configured to compress the scavenge air. The internal combustion engine may be a dual-fuel engine having a 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 dual-fuel engine has its own dedicated fuel supply system for injecting the alternative fuel.

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

The fuel gas supply system is preferably configured to inject the fuel gas via one or more fuel gas valves under sonic conditions, i.e. a velocity equal to the speed of sound, i.e. a constant velocity. Sonic conditions may be achieved when the pressure drop ratio across the nozzle throat (minimum area of cross section) is larger than approximately two.

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

The one or more fuel gas valves are arranged at least partly in the cylinder wall between top dead center and bottom dead center, preferably

DK 181032 B1 4 in a position above the scavenge air inlet. The one or more fuel gas valves may comprise a nozzle arranged in the cylinder wall for injecting fuel gas into the cylinder. The other parts of the fuel gas valve (other than the nozzle) may be arranged outside the cylinder wall. Examples of fuel gases are Liquefied Natural Gas (LNG), methane, ammonia, ethane, and Liquefied Petroleum Gas (LPG).

The pilot fuel valve may be configured to inject a pilot fuel into the pre-chamber. The pre-chamber may be configured so that the pilot fuel self-ignite due to the temperature and pressure in the pre-chamber.

Alternatively, the pilot fuel in the pre-chamber may be ignited by means comprising a spark plug or a laser igniter. The pilot fuel may be heavy fuel oll or marine diesel oil, or any other fuel with suitable ignitability, accurately measured out so the amount just is able to ignite the mixture of fuel gas and scavenge air in the cylinder. A pilot fuel system may in size be much smaller — and more suitable for injecting a precisely amount of pilot fuel compared to a dedicated fuel supply system for an alternative fuel, which due to the large size of the components may not suitable for this purpose. The pilot fuel valve may be configured to inject an amount of pilot oil at a suitable crank angle for the optimal ignition of the main charge, close to the top dead centre. The pilot fuel ignition immediately follows the pilot oil injection, and the main charge ignition immediately follows the pilot oil ignition.

The pilot pre-chamber unit cnamber unit may be arranged in the cylinder wall or in the cylinder cover. At least a part of the pilot pre-chamber unit may extend out of the part of the engine in which it is inserted e.g. at least part of the pilot pre-chamber unit may extend out of the cylinder wall or the cylinder cover. Both the inlet and the outlet of the first heat exchange channel may be arranged in a part of the pilot pre-chamber unit extending out of the part of the engine in which it is inserted. The pilot pre-chamber unit may be detachably connected to the part of the engine it is inserted into allowing removal of the pilot pre-chamber unit for maintenance purposes.

DK 181032 B1 The first heat exchange channel may be part of a pre-chamber cooling system configured to cool the pre-chamber e.g. the pre-chamber cooling system may be configured to cool the heat exchange fluid before providing the heat exchange fluid to the first temperature regulating channel.

5 The pre-chamber cooling system may comprise a control unit configured to control the flow of the heat exchange fluid and / or the inlet temperature of the heat exchange fluid. The control unit may be configured to control the flow of the heat exchange fluid and / or the inlet temperature of the heat exchange fluid dependent on the engine load, the engine speed and — /or the air—fuel equivalence ratio, A, of the mixture of scavenge air and fuel gas.

Alternatively, the first heat exchange channel may be part of a combined heating and cooling system configured to either cool or heat the pre-chamber e.g. the combined heating and cooling system may be configured to either cool or heat the heat exchange fluid before providing the heat exchange fluid to the first temperature regulating channel. The combined heating and cooling system may be configured to heat the pre- chamber as part of the gas start-up procedure either from a complete engine stop or when switching from heavy fuel oil or marine diesel oil to fuel gas.

The combined heating and cooling system may be configured to cool the pre- chamber after the gas start-up procedure has been completed, i.e. during normal gas operation, to prevent damage to the pre-chamber and / or surrounding engine parts.

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

In some embodiments the first heat exchange channel is extending inside both a part of the pre-chamber wall and a part of the pilot fuel valve housing.

Consequently, by having the first heat exchange channel directly arranged inside the pre-chamber wall, the temperature of the pre-chamber may be effectively and precisely regulated.

DK 181032 B1 6 The part of the first heat exchange channel extending inside the pre-chamber wall may be formed at the same time as the pre-chamber is formed e.g. using additive manufacturing techniques. The part of the first heat exchange channel extending inside the pre-chamber wall and the part extending inside the pilot fuel valve housing may be formed in two separate processes and subsequently connected. Alternatively, the part of the first heat exchange channel extending inside the pre-chamber wall and the part extending inside the pilot fuel valve housing may be formed in a single process e.g. using additive manufacturing. In some embodiments the pre-chamber and the pilot fuel valve housing are two separate elements connected together.

The pre-chamber and the pilot fuel valve housing may be connected using any suitable connection method e.g. using bolted connections or welding. The pre-chamber and the pilot valve housing may be detachably connected or non-detachably connected.

In some embodiments the pre-chamber and the pilot fuel valve housing are formed as one element created in a single process.

The pre-chamber and the pilot fuel valve housing may be formed as one element by being cast together in a single casting process or using additive manufacturing.

In some embodiments the first heat exchange channel comprises a first part for guiding the heat exchange fluid towards the first opening of the pre-chamber and a second portion for guiding the heat exchange fluid away from the first opening of the pre-chamber, wherein the shape of the first portion substantially corresponds to the shape of the second portion.

Consequently, a more uniform temperature regulation of the pilot pre- chamber unit may be achieved. This may secure more effective temperature regulation and prevent tensions within the pilot pre-chamber unit.

In some embodiments the pilot pre-chamber unit further comprises a second heat exchange channel for circulating a heat exchange fluid having an inlet and an outlet and extending through the pilot fuel valve housing and

DK 181032 B1 7 the pre-chamber wall, and wherein both the inlet and the outlet is arranged in the pilot fuel valve housing. Consequently, by having multiple temperature regulating channels a more uniform temperature regulation may be achieved. This may further decrease the required flow speed of the heat exchange fluid which in turn may allow the temperature regulating channels to have a smaller diameter and thereby be arranged even closer to pre-chamber enabling more precise temperature regulation. The second heat exchange channel may comprise a first part for guiding the heat exchange fluid towards the first opening of the pre-chamber and a second portion for guiding the heat exchange fluid away from the first opening of the pre-chamber, wherein the shape of the first portion substantially corresponds to the shape of the second portion. In some embodiments the pilot pre-chamber unit further comprises a — third heat exchange channel for circulating a heat exchange fluid having an inlet and an outlet and extending through the pilot fuel valve housing and the pre-chamber wall, and wherein both the inlet and the outlet is arranged in the pilot fuel valve housing. The third heat exchange channel may comprise a first part for guiding the heat exchange fluid towards the first opening of the pre-chamber and a second portion for guiding the heat exchange fluid away from the first opening of the pre-chamber, wherein the shape of the first portion substantially corresponds to the shape of the second portion. In some embodiments the first, second and third heat exchange channel are arranged rotationally symmetric.

In some embodiments the engine further comprises a pre-chamber housing, the pre-chamber being arranged 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 inthe pre-chamber housing, wherein the pre-chamber housing has a first insulation volume formed between the first contact portion and the second

DK 181032 B1 8 contact portion for limiting heat-exchange between the pre-chamber and the engine.

Consequently, by insulating the pre-chamber from the part of the engine which it is inserted the temperature of the pre-chamber may more precisely be controlled. This may also allow the parts of the engine in proximity of the pre-chamber to be made of materials having lower heat tolerances such as cast iron.

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

In some embodiments the pre-chamber and the temperature regulating channels are produced by in a single additive manufacturing process.

In some embodiments the at least one cylinder has a base member and a pre-chamber member, the pre-chamber member being arranged on top of the base member and the cylinder cover being arranged on top of the pre-chamber member, and wherein the pilot pre-chamber unit is at least partly arranged in the cylinder wall of the pre-chamber member, the first opening is opening into the cylinder through an opening formed in the cylinder wall of the pre-chamber member.

This allows the pre-chamber member to be specifically designed to handle the high temperature and pressure within the pre-chamber, e.g. by selecting suitable materials. This may further make it easier to perform maintenance on the pre-chambers. The pre-chamber member may be an insert between the base member and the cylinder cover, with or without gasket arrangements towards either. It may be pre-assembled with the base member before the cylinder cover is installed.

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

DK 181032 B1 9 The base member of the cylinder 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 channel extending along a first axis, wherein the angle between the first axis and a reference plane arranged perpendicular to the central axis is between 0 degrees and 85 degrees, 0 and 80 degrees, 0 degrees and 60 degrees, 0 degrees and 45 degrees, or 0 degrees and 30 degrees. Consequently the torch extending from the pre-chamber into the — cylinder may come into direct contact with a large portion of the mixture of scavenge air and fuel gas. The engine may be provided with more pre-chamber members e.g. at least two, three or four pre-chambers per cylinder. According to a second aspect the invention relates to a pilot pre- chamber unit for a two-stroke uniflow scavenged crosshead internal combustion engine comprising at least one cylinder as disclosed in connection with the second aspect of the invention, wherein the pilot pre- chamber unit comprises a pre-chamber, a pilot fuel valve housing, and a pilot fuel valve arranged in the pilot fuel valve housing, wherein the pre-chamber has a pre-chamber wall and a first opening for opening into the cylinder, the pre-chamber being configured to ignite a mixture of scavenge air and fuel gas in the cylinder and wherein the pre-chamber pilot unit further comprises a first heat exchange channel for circulating a heat exchange fluid having an inlet and an outlet, and wherein both the inlet and the outlet is arranged in the pilot fuel valve housing.

The different aspects of the present invention can be implemented in different ways including as two-stroke uniflow scavenged crosshead internal combustion engines and pilot pre-chamber units as described above and in the following, each yielding one or more of the benefits and advantages described in connection with at least one of the aspects described above, and each having one or more preferred embodiments corresponding to the

DK 181032 B1 10 preferred embodiments described in connection with at least one of the aspects described above and/or disclosed in the dependant claims. Furthermore, it will be appreciated that embodiments described in connection with one of the aspects described herein may equally be applied to the other aspects.

There will always be two angles between two axes, two planes, or an axis and a plane, a small angle V1 and a large angle V2, where V2=180 degrees-V1. In this disclosure, it will always be the small angle V1 that is specified.

Brief description of the drawings The above and/or additional objects, features and advantages of the present invention, will be further elucidated by the following illustrative and non- limiting detailed description of embodiments of the present invention, with reference to the appended drawings, wherein: Fig. 1 shows schematically a cross-section of a two-stroke internal combustion engine according to an embodiment of the invention.

Fig. 2 shows a schematic cross-section of a part 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-section of a part 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-section of a part of a two-stroke crosshead internal combustion engine with uniflow scavenging according to an embodiment of the present invention.

Fig. 5 shows a schematic drawing of a pilot pre-chamber unit 114 for a two- stroke uniflow scavenged crosshead internal combustion engine according to an embodiment of the present invention.

DK 181032 B1 11 Fig. 6 shows a schematic drawing of a pilot pre-chamber unit 114 for a two- stroke uniflow scavenged crosshead internal combustion engine according to an embodiment of the present invention. Figs. 7a-b show a cross-section of a large low-speed turbocharged two- stroke crosshead internal combustion engine with uniflow scavenging for propelling a marine vessel according to an embodiment of the present invention.

Detailed description In the following description, reference is made to the accompanying figures, which show by way of illustration how the invention may be practiced. Fig. 1 shows schematically a cross-section of a large low-speed turbocharged two-stroke crosshead internal combustion engine with uniflow scavenging 100 for propelling a marine vessel according to an embodiment of the present invention. The engine 100 comprises a scavenge air system 111, an exhaust gas receiver 108, a fuel gas supply system, and a turbocharger 109. The engine has a plurality of cylinders 101 (only a single cylinder is shown in the cross-section). Each cylinder 101 has a cylinder wall 115 and comprises a scavenge air inlet 102 arranged at the bottom of the cylinder 101. The engine further comprises for each cylinder a cylinder cover 112 and a piston 103. The cylinder cover 112 being arranged on top of the cylinder 101 and having an exhaust valve 104. The piston 103 being movably arranged 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 (only schematically shown) configured to inject fuel gas into the cylinder 101 during the compression stroke enabling the fuel gas to mix with scavenge air and allowing the mixture of scavenge air and fuel gas to be compressed before being ignited. The fuel gas valves 105 are arranged at least partly in the cylinder wall between the cylinder cover 112 and the scavenge air inlet 102. The engine further comprises a pilot pre-

DK 181032 B1 12 chamber unit 114 at least partly arranged in the cylinder wall 115 (only schematically shown). The pilot pre-chamber unit 114 comprises a pre- chamber, a pilot fuel valve housing, and a pilot fuel valve arranged in the pilot fuel valve housing, wherein the pre-chamber has a pre-chamber wall and opens into the cylinder through a first opening. The pre-chamber being configured to ignite the mixture of scavenge air and fuel gas in the cylinder

101. The pre-chamber pilot unit 114 further comprises a first heat exchange channel for circulating a heat exchange fluid having an inlet and an outlet. Both the inlet and the outlet of the first heat exchange channel is arranged in the pilot fuel valve housing. The scavenge air inlet 102 is fluidly connected to the scavenge 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 valves 105 are configured to inject fuel gas into the cylinder during the compression stroke enabling the fuel gas to mix with scavenge air and allowing the mixture of scavenge air and fuel gas to be compressed before being ignited. The fuel gas valves 105 are preferably configured to inject a fuel gas into the cylinder 101 in the beginning of the compression stroke within O degrees to 130 degrees from bottom dead center, i.e. when the crankshaft has rotated between O degrees and 130 degrees from its orientation at bottom dead center. Preferably the fuel gas valves 105 are configured to start injecting fuel gas after the crankshaft axis has rotated a few degrees from bottom dead center so that the piston has moved past the scavenge air inlets 102 to prevent fuel gas from exiting through the exhaust valve 104 and scavenge air inlets 102. The scavenge air system 111 comprises a scavenge air 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 dual-fuel engine has its own dedicated alternative fuel supply system for injecting the alternative fuel. Thus optionally the engine 100 further comprise one or more

DK 181032 B1 13 fuel injectors 116 arranged in the cylinder cover 112 forming part of an alternative fuel supply system. When the engine 100 runs on the 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.

Fig. 2 shows a schematic cross-section of a part of a two-stroke crosshead internal combustion engine with uniflow scavenging according to an embodiment of the present invention. Shown is a cylinder 101, a cylinder cover 112, a piston 103, and an exhaust valve 104. The piston 103 is positioned in top dead centre. The cylinder 101 has a cylinder wall 115 — provided with a first a pilot pre-chamber unit 114 and a second a pilot pre- chamber unit 116, the first and second pilot pre-chamber unit 114 116 each comprising a pre-chamber, a pilot fuel valve housing, a pilot fuel valve arranged in the pilot fuel valve housing and a first heat exchange channel for circulating a heat exchange fluid having an inlet and an outlet, where both the inlet and the outlet is arranged in the pilot fuel valve housing. The pre- chamber of the first and second pilot pre-chamber unit 114 116 both opens into the cylinder 101 through an opening formed in the cylinder wall 115, the pre-chambers are configured to ignite the mixture of scavenge air and fuel gas in the cylinder.

Fig. 3 shows a schematic cross-section of a part of a two-stroke crosshead internal combustion engine with uniflow scavenging according to an embodiment of the present invention. The part corresponds to the part shown in Fig. 2 with the difference that the cylinder 101 has a base member 117 and pre-chamber member 118, the pre-chamber member 118 being arranged on top of the base member 117 and the cylinder cover 112 being arranged on top of the pre-chamber member 118. The first and second pilot pre-chamber unit 114 116 being arranged in the cylinder wall of the pre- chamber member 118. This allows the pre-chamber member to be specifically designed to handle the high temperature and pressure within the pre-chamber, e.g. by selecting suitable materials.

DK 181032 B1 14 Fig. 4 shows a schematic cross-section of a part of a two-stroke crosshead internal combustion engine with uniflow scavenging according to an embodiment of the present invention. The part corresponds to the part shown in Fig. 2 with the difference that the first and second pilot pre-chamber unit 114 116 are arranged in the cylinder cover 112.

Fig. 5 shows a schematic drawing of a pilot pre-chamber unit 114 for a two-stroke uniflow scavenged crosshead internal combustion engine according to an embodiment of the present invention. The pilot pre-chamber unit 114 comprises a pre-chamber 134, a pilot fuel valve housing130, and a pilot fuel valve 132 arranged in the pilot fuel valve housing 130. The pre- chamber 134 has a pre-chamber wall and a first opening for opening into a cylinder of the engine. The pre-chamber 134 is configured to ignite a mixture of scavenge air and fuel gas in the cylinder. The pre-chamber pilot unit 114 further comprises a first heat exchange channel 133 for circulating a heat exchange fluid having an inlet 136 and an outlet 137. Both the inlet 136 and the outlet 137 is arranged in the pilot fuel valve housing 130. In this embodiment the pre-chamber 134 and the pilot fuel valve housing 130 are two separate elements connected together. The pre-chamber 134 and the pilot fuel valve housing 130 may be connected using any suitable connection method e.g. using bolted connections or welding.

Fig. 6 shows a schematic drawing of a pilot pre-chamber unit 114 for a two-stroke uniflow scavenged crosshead internal combustion engine according to an embodiment of the present invention. The pilot pre-chamber unit 114 corresponds to the pilot pre-chamber unit disclosed in relation to Fig.

5 with the difference that the pre-chamber 134 and the pilot fuel valve housing 130 are formed as one element created in a single process. The pre- chamber 134 and the pilot fuel valve housing 130 may be formed as one element by being cast together in a single casting process or using additive manufacturing.

Fig. 7a shows a cross-section of a large low-speed turbocharged two- stroke crosshead internal combustion engine with uniflow scavenging for

DK 181032 B1 15 propelling a marine vessel according to an embodiment of the present invention.

The engine is 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.

Each cylinder has a cylinder wall and comprises a scavenge air inlet arranged at the bottom of the cylinder

(not shown). The engine further comprises for each cylinder a cylinder cover 112 and a piston 103. The cylinder cover 112 being arranged on top of the cylinder and having an exhaust valve 104. The piston 103 being movably arranged within the cylinder along a central axis between bottom dead center and top dead center.

In the figure, the piston 103 is arranged at top dead center.

The fuel gas supply system comprises one or more fuel gas valves (not shown) configured to (when the engine is in gas mode) inject fuel gas into the cylinder during the compression stroke enabling the fuel gas to mix with scavenge air and allowing the mixture of scavenge air and fuel gas to be compressed before being ignited.

The fuel gas valves are arranged at least partly in the cylinder wall between the cylinder cover 112 and the scavenge air inlet.

The engine further comprises two pilot pre-chamber units 131 each pilot pre-chamber unit 131 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 top of the base member 117 and the cylinder cover 112 being arranged on top of the pre-chamber member 118. The pre-chambers 114 are arranged in the cylinder wall of the pre-chamber member 118. The pre-chambers 114 opening into the cylinder through an opening formed in the cylinder wall of the pre-chamber member 118. The scavenge air inlet is fluidly connected to the scavenge air system.

The piston 103 is via a piston rod, a crosshead and a connecting rod connected a to a crankshaft (not shown). The pilot fuel valves 132 are configured to at least when the engine is in gas mode inject a

— small amount of pilot fuel into the pre-chambers 114. The pilot fuel valves 132 may also be configured to inject a small amount of pilot fuel into the pre-

DK 181032 B1 16 chambers 114 when the engine is running on pure diesel to prevent the pilot fuel valves to get stuck. The pre-chambers 114 are configured so that the pilot fuel self-ignite due to the temperature and pressure in the pre-chamber

114. The pilot fuel oil may be heavy fuel oil, marine diesel oil, or any other fuel with suitable self-ignitability.

The engine further comprises one or more fuel injectors 116 arranged in the cylinder cover 112 forming part of an alternative fuel supply system. When the engine 100 runs on the 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.

Fig. 7b shows a close-up of the right pilot pre-chamber unit 131 shown in Fig. 7a. The pre-chamber pilot unit 131 comprises a first heat exchange channel 145 for circulating a heat exchange fluid having an inlet 136 and an outlet (not shown), and where both the inlet 136 and the outlet is arranged in — the pilot fuel valve housing 130. The pre-chamber pilot unit 131 further comprises a second heat exchange channel 146 for circulating a heat exchange fluid having an inlet 138 and an outlet (not shown), and where both the inlet 138 and the outlet is arranged in the pilot fuel valve housing 130. The first and second heat exchange channel 145 146 are inside both a part of the wall of the pre-chamber 114 and a part of the pilot fuel valve housing130. The first and second heat exchange channel 145 146 comprises a first part for guiding the heat exchange fluid towards the first opening 144 of the pre-chamber and a second portion for guiding the heat exchange fluid away from the first opening of the pre-chamber (only the first part can be seen in this cross-section). 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, the pre-chamber 114 being arranged in the pre-chamber housing, the pre-chamber 114 having a first contact portion 143 and a second contact portion 142 for abutting the pre-chamber housing and securing the pre-chamber in the pre-chamber housing. In this embodiment both the first contact portion 143 and the second

DK 181032 B1 17 contact portion 142 has an annular shape. The pre-chamber housing has a first insulation volume 141 (e.g. filed 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 athird contact portion 147 for abutting the pre-chamber housing. In this embodiment the third contact portion 147 has an annular shape. The pre- chamber housing further has a second insulation volume 140 formed between the second contact portion 142 and the third contact portion 147.

Although some embodiments have been described and shown in detail, the invention is not restricted to them, but may also be embodied in other ways within the scope of the subject matter defined in the following claims. In particular, it is to be understood that other embodiments may be utilised and structural and functional modifications may be made without departing from the scope of the present invention.

In device claims enumerating several means, several of these means can 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 the term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Claims

DK 181032 B1 18 Requirements:

1. Longitudinally scavenged two-stroke crosshead internal combustion engine (100) comprising at least one cylinder (101), a cylinder head (112), a piston (103), fuel gas supply system and a scavenge air system, wherein the cylinder (101) has a cylinder wall (115), wherein the cylinder head (112 ) is placed on top of the cylinder (101) and has an exhaust valve (104), where the piston (103) is movably placed inside the cylinder (101) along a central axis (113) between bottom dead center and top dead center, where the purge air system has a — purge air inlet (102) arranged at the bottom of the cylinder (101), wherein the fuel gas supply system comprises a fuel gas valve (105) which is located at least partially in the cylinder wall (115) and is configured to inject fuel gas into the cylinder (101) during the compression stroke, enabling for the fuel gas to mix with the scavenge air and — allowing the mixture of scavenge air and fuel gas to be compressed before igniting, the engine (100) further comprising e n pilot prechamber unit (114) comprising a prechamber (134), a pilot fuel valve housing (130) and a pilot fuel valve (132) arranged in the pilot fuel valve housing (130), the prechamber (134) having a prechamber wall and opening into the cylinder through a first opening, where the prechamber (134) is configured to ignite the mixture of purge air and fuel gas in the cylinder (100) and is characterized in that the pilot prechamber unit (114) further comprises a first heat exchange channel (133) for circulating a heat exchange fluid having an inlet (136 ) and an outlet (137), and wherein both the inlet (136) and the outlet (137) — are arranged in the pilot fuel valve housing (130), the engine (100) further comprising a pre-chamber housing (118), the pre-chamber (134) being arranged in the antechamber housing (118), where the antechamber has at least a first contact part (143) and a second contact part (142) to abut against the antechamber housing (118) and secure the antechamber (134) in the antechamber housing (118), where — the antechamber housing (118) hasa first insulating volume (141) formed between

DK 181032 B1 19 the first contact part (143) and the second contact part (142) to limit heat exchange between the pre-chamber (134) and the motor (100).

2. A longitudinally flushed two-stroke crosshead internal combustion engine (100) according to — claim 1, wherein the first heat exchange channel (133) extends both within a portion of the pre-chamber wall and a portion of the pilot fuel valve housing (130).

3. A longitudinally flushed two-stroke crosshead internal combustion engine (100) according to claim 1 or 2, wherein the prechamber (134) and the pilot fuel valve housing (130) are two separate elements connected to each other.

The longitudinally flushed two-stroke crosshead internal combustion engine (100) of claim 1 or 2, wherein the prechamber (134) and the pilot fuel valve housing (130) are formed as one element created in a single process.

The longitudinally flushed two-stroke crosshead internal combustion engine (100) according to any one of claims 1 to 4, wherein the first heat exchange channel (133) comprises a first part for directing the heat exchange fluid towards the first opening of the pre-chamber and a second part for directing the heat exchange fluid away from the — first opening of the antechamber (134), where the shape of the first part essentially corresponds to the shape of the second part.

6. The longitudinally scavenged two-stroke crosshead internal combustion engine (100) of claim 5, wherein the pilot prechamber assembly (114) further comprises a second heat exchange passage (146) for circulating a heat exchange fluid having an inlet and an outlet and extending through the pilot fuel valve housing (130) and the prechamber wall, and wherein both the inlet and the outlet are arranged in the pilot fuel valve housing (130).

A longitudinally scavenged two-stroke crosshead internal combustion engine (100) according to any one of claims 6, wherein the pilot prechamber assembly (114) further

DK 181032 B1 20 includes a third heat exchange channel for circulating a heat exchange fluid which has an inlet and an outlet and extends through the pilot fuel valve housing (130) and the antechamber wall, and where both the inlet and the outlet are arranged in the pilot fuel valve housing (130).

8. A longitudinally flushed two-stroke crosshead combustion engine (100) according to any one of claims 1 to 7, wherein the first, second and third heat exchange channels are arranged rotationally symmetrically.

9. The longitudinally flushed two-stroke crosshead internal combustion engine of claim 1, wherein the prechamber (134) and the heat exchange channels are produced in a single additive manufacturing process.

10. Pilot pre-chamber unit (114) for a longitudinally flushed two-stroke cross-head internal combustion engine (100) comprising at least one cylinder (101) according to any one of claims 1 to 9, characterized in that the pilot pre-chamber unit (114) comprises a pre-chamber (134), a pilot fuel valve housing (130) and a pilot fuel valve (132) arranged in the pilot fuel valve housing (130), the prechamber (134) having a > prechamber wall and a first opening for opening into the cylinder, the prechamber (134) being configured to ignite a mixture of scavenge air and fuel gas in the cylinder (101), and wherein the pre-chamber pilot assembly (114) further comprises a first heat exchange channel (133) for circulating a heat exchange fluid having an inlet (136) and an outlet (137), and wherein both — the inlet (136) and the outlet (137) is arranged in the pilot fuel valve housing (130).