DK180375B1

DK180375B1 - Internal combustion engine

Info

Publication number: DK180375B1
Application number: DKPA201970459A
Authority: DK
Inventors: Hult Johan
Original assignee: Man Energy Solutions Filial Af Man Energy Solutions Se Tyskland
Priority date: 2019-07-11
Filing date: 2019-07-11
Publication date: 2021-02-12
Also published as: JP2022008272A; JP2021014852A; CN115341993A; KR20210008317A; JP6911182B2; KR20220013430A; KR102354285B1; CN112211721A; DK201970459A1; CN112211721B

Abstract

Disclosed is a two-stroke uniflow scavenged crosshead internal combustion engine. The engine comprising at least one cylinder, a cylinder cover, a piston, a fuel gas supply system, 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 fuel gas supply system comprising a fuel gas valve configured to inject fuel gas into the cylinder during the compression stroke enabling the fuel gas to mix with scavenge air. The engine further comprises a pre-chamber and a pilot fuel supply system. The pilot fuel supply system comprising a pilot fuel valve configured to inject a pilot fuel gas into the pre-chamber during the compression stroke enabling the pilot fuel gas to be compressed before being ignited, an ignition element is being configured to ignite the pilot fuel gas in the pre-chamber.

Description

DK 180375 B1 1 Title Internal combustion engine Field The present invention relates to a two-stroke uniflow scavenged crosshead internal combustion engine and a pre-chamber. 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 large gas compressors for compressing the fuel gas prior to injection to overcome the large pressure in the cylinders.

The large gas compressors are however expensive and complex to manufacture and maintain. One way to avoid the need of large 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 180375 B1 2 ignition pre-chamber.

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

Injecting an amount of pilot fuel oil will however increase the amount of unwanted exhaust gases and require a dedicated fuel oil supply system making the engine more complex.

Furthermore, for dual fuel engines having both a fuel gas supply system and a fuel oil supply system, the extra reliability of having two fuel systems is partly lost if the engine cannot function without the fuel oil supply system.

Thus it remains a problem to provide an improved two-stroke internal combustion engine.

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, 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 pre-chamber and a pilot fuel supply system, the pre- chamber opening into the cylinder through a first opening and comprising an ignition element, the pilot fuel supply system comprising a pilot fuel valve configured to inject a pilot fuel gas into the pre-chamber during the compression stroke enabling the pilot fuel gas to be compressed and mixed with air before being ignited to form a combustable mixture inside the pre-

DK 180375 B1 3 chamber, the ignition element being configured to ignite the pilot fuel gas in the pre-chamber. Consequently, by using a fuel gas as the pilot fuel any unwanted exhaust gases resulting from combustion of fuel oil may be avoided.

Furthermore, the engine may be designed with fewer fuel supply systems or if the engine is a dual fuel engine a more reliable engine is provided capable of running solely on fuel gas.

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 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 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 mix with the pilot — fuel gas. The ignition element may be a spark plug, a corona/plasma igniter, a microwave igniter, a glow plug, a laser igniter, or a jet torch. The internal combustion engine preferably comprises a plurality of cylinders e.g. between 4 and 14cylinders. 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.

DK 180375 B1 4 Correspondingly, the pilot fuel supply system may also be configured to inject the pilot fuel gas via the pilot fuel valve into the pre- chamber under sonic conditions.

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 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. In some embodiments the ignition element is configured to generate an approximately instantaneous maximum energy release upon activation.

This may allow even greater control of the ignition timing. Examples of ignition elements capable of generating an approximately instantaneous energy release upon activation are a spark plug, a corona/plasma igniter, a microwave igniter, a laser igniter, or a jet torch.

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.

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 provide 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 a pilot fuel gas into the second pre-chamber during the compression stroke enabling 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.

DK 180375 B1 The two pre-chamber may be identical. The two pre-chambers may arranged opposite to each other.

The engine may be provided with more pre-chambers e.g. at least three or four pre-chambers per cylinder.

5 In some embodiments the pilot fuel valve is configured to inject the pilot fuel gas into the pre-chamber 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.

In some embodiments the pilot fuel valve is configured to inject the 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-chamber after the end of the pilot fuel injection period.

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

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

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

In some embodiments the ratio between the cross-sectional area of the openings of the pre-chamber into the cylinder measured in m? and the volume of the pre-chamber measured in m? is between 0.5-1.2 m™".

Consequently, it may be secured that not too much pilot fuel gas exits the pre-chamber before being ignited.

DK 180375 B1 6 As an example if the pre-chamber only comprises the first opening and the surface area of the first opening is 60mm?2, and the volume of the pre-chamber is 0.1 liter, then the ratio will be 0.6 m”'. In some embodiments the engine is configured to ensure that the A of the mixture of scavenge air and fuel gas in the cylinder is above A=2.0.

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

By providing the pre-chamber with a second ignition element a — more reliable engine is provided as the engine may work if one of the ignition elements malfunctions.

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

In some embodiments the engine further comprising a pre- chamber cooling system for cooling the pre-chamber, the pre-chamber cooling system comprising a cooling channel in proximity to the pre-chamber for extracting heat from the pre-chamber, the pre-chamber cooling system being configured to circulate a cooling fluid through the cooling channel.

Arranging the pre-chamber in the cylinder wall provides more space for a pre-chamber cooling system. This may allow the temperature of the pre-chamber to be controlled more precisely and with less influence of other engine parameters such as exhaust valve closing timing, engine speed, engine load etc. The more precise control of the temperature of the pre- chamber may reduce of risk of misfires making it more suitable to use pilot fuels that are more difficult to ignite such as fuels gases e.g. Liquefied Natural Gas (LNG), methane, ethane, and Liquefied Petroleum Gas (LPG)..

In some embodiments the pre-chamber cooling system further comprises a control unit configured to control the flow of the cooling fluid and — /or the inlet temperature of the cooling fluid.

DK 180375 B1 7 In some embodiments the control unit is configured to control the flow of the cooling fluid and / or the inlet temperature of the cooling 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.

In some embodiments the cylinder has a base member and a pre-chamber member, the pre-chamber member being arranged on top of the base member and cylinder cover being arranged on top of the pre- chamber member, and wherein the pre-chamber is at least partly arranged in the cylinder wall of the pre-chamber member, the pre-chamber 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 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 base member of the cylinder.

In some embodiments, the pre-chamber is at least partly arranged in the cylinder cover and the first opening is formed in the cylinder cover.

According to a second aspect the 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 being configured to open into a cylinder through a first opening and comprising an ignition element and pilot fuel valve configured to inject a pilot fuel gas into the pre-chamber during the compression stroke enabling 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.

DK 180375 B1 8 The different aspects of the present invention can be implemented in different ways including a two-stroke uniflow scavenged crosshead internal combustion engine and a pre-chamber 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 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.

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 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 invention.

Fig. 4 shows a schematic drawing of a pre-chamber according to an embodiment of the invention.

DK 180375 B1 9 Fig. 5 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 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 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 comprises an ignition element (not shown). The pilot fuel supply system comprises a pilot fuel valve (not shown) configured to inject a pilot fuel gas into the pre-

chamber during the compression stroke enabling the pilot fuel gas to be compressed before being ignited, the ignition element being configured to

DK 180375 B1 10 ignite the pilot fuel gas in the pre-chamber. The pre-chamber 114 is in this embodiment arranged in the cylinder wall 115, however, in other embodiments the pre-chamber 114 may be arranged in the cylinder cover

112. 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 arranged at least partly in the cylinder wall between the cylinder cover 112 and the scavenge air inlet 102 e.g. the fuel gas nozzles of fuel gas valves 105 may be arranged in the cylinder wall and the remaining parts of the fuel gas valves may be arranged outside of the cylinder. The fuel gas valves are 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 0 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 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 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 alternative fuel supply system for injecting the alternative fuel. Thus optionally the engine 100 further comprise 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

DK 180375 B1 11 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 pre-chamber 114 and a second pre-chamber 116. The first and second pre-chamber 114 116 opens into the cylinder 101 through an — opening formed in the cylinder wall 115, the pre-chambers 114 116 are configured to ignite the mixture of scavenge 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 valve being configured to inject a pilot fuel gas into the pre-chamber.

The first and the second pre-chamber 114 116 further comprises an ignition element configured to ignite the pilot fuel gas.

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 pre- chamber 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.

Fig. 4 shows a schematic drawing of a pre-chamber 114 according to an embodiment of the invention.

The pre-chamber 114 being configured to open into a cylinder through a first opening 123 and a second opening 124.

DK 180375 B1 12 The pre-chamber comprises an ignition element 119 and pilot fuel valve 120 configured to inject a pilot fuel gas into the pre-chamber during the compression stroke enabling the pilot fuel gas 121 to be compressed before being ignited. The ignition element 119 being configured to ignite the pilot fuel gas in the pre-chamber resulting in a torch 122 for igniting fuel gas in the cylinder.

Fig. 5 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, and an exhaust valve 104. The cylinder cover 112 is provided with a first pre-chamber 114 and a second pre-chamber 116. The first and second pre-chamber 114 116 opens into the cylinder 101 through an opening formed in the cylinder cover 112, the pre-chambers 114 116 are configured to ignite the mixture of scavenge 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 valve being configured to inject a pilot fuel gas into the pre-chamber. The first and the second pre-chamber 114 116 further comprises an ignition element configured to ignite the pilot fuel gas.

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.

DK 180375 B1 13 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 180375 B1 1 Requirements:

A longitudinally flushed two-stroke cross-head internal combustion engine (100) comprising at least one cylinder (101), a cylinder head (112), a piston (103), a fuel gas supply system, a purge air system (111), the cylinder having a cylinder wall (115), the cylinder head is located on top of the cylinder and has an exhaust valve (104), the piston being movably disposed within the cylinder along a central axis (113) between the lower dead center and the upper dead center, the purge air system (111) having a - purge air inlet (102) disposed in the bottom of the cylinder, the fuel gas supply system comprising a fuel gas valve (105) disposed at least partially in the cylinder wall and configured to inject fuel gas into the cylinder during the compression stroke, allowing the fuel gas to mix with purge air and allowing - the purge air mixture and fuel gas is compressed before igniting, the engine further comprising an antechamber (114) and a pilot fuel The pre-supply system (114) opens into the cylinder through a first opening (123) and comprises an ignition element (119), characterized in that the pilot fuel supply system comprises a pilot fuel valve (120) configured to inject a pilot fuel gas (121) into the antechamber during the compression stroke, allowing the pilot fuel gas to compress before igniting, the ignition element (119) being configured to ignite the pilot fuel gas (121) in the antechamber (114).

The long-flush two-stroke cross-head internal combustion engine of claim 1, wherein the fuel gas supply system and the pilot fuel supply system provide the same fuel gas.

DK 180375 B1 2

A longitudinally flushed two-stroke cross-head internal combustion engine according to claim 1 or 2, wherein the pilot fuel valve (120) is configured to inject the pilot fuel gas (121) into the antechamber (114) during the compression stroke within 0 degrees to 160 degrees from the bottom - dead center, within 0 degrees to 130 degrees from the bottom dead center or within 0 degrees to 90 degrees from the bottom dead center.

The long-flush two-stroke cross-head internal combustion engine of claim 3, wherein the pilot fuel valve (120) is configured to inject - the pilot fuel gas (121) during a pilot fuel injection period, and wherein the igniter (119) is configured to ignite the pilot fuel gas (114) in the pilot ) after the end of the pilot fuel injection period.

The long-flush two-stroke cross-head internal combustion engine of claim 4, wherein the antechamber (114) is configured to ensure that the air-fuel equivalence ratio, A, of the mixture of purge air and pilot fuel gas (121) in the antechamber (114) is below A = 1.6 at the time of ignition.

The longitudinally flushed two-stroke cross-head internal combustion engine of claim 5, wherein the ratio of the cross-sectional area of the openings (123, 124) of the antechamber (114) into the cylinder (101) is measured in m? and the volume of the antechamber measured in m? is between 0.5-1.2 m ™.

The longitudinally flushed two-stroke cross-head internal combustion engine of claim 6, wherein the engine is configured to ensure that the A for the mixture of purge air and fuel gas in the cylinder is above A = 2.0.

A longitudinally flushed two-stroke cross-head internal combustion engine according to any one of claims 1 to 7, wherein the antechamber (114) is at least partially

DK 180375 B1 3 placed in the cylinder wall (115), and where the first opening (123) is formed in the cylinder wall.

A longitudinally flushed two-stroke cross-head internal combustion engine according to any one of claims 1 to 8, wherein the antechamber (114) is at least partially disposed in the cylinder cover (112) and the first opening (123) is formed in the cylinder cover (112).

A long-flushed two-stroke cross-head internal combustion engine according to any one of claims 1 to 9, wherein the ignition element (119) is configured to generate an approximately instantaneous maximum energy release upon activation.

An antechamber for use with a longitudinally flushed two-stroke cross-head internal combustion engine according to any one of claims 1 to 10, wherein the antechamber (114) is configured to open into a cylinder (101) through a first opening (123) and comprises an ignition element (119), characterized in that the antechamber further comprises a pilot fuel valve (120) configured to inject a pilot fuel gas (121) into the antechamber (114) during compression stroke which allows the pilot fuel gas (121) to become compressed before ignition, wherein the ignition element (119) is configured to ignite the pilot fuel gas (121) in the antechamber (114).