DK201970460A1

DK201970460A1 - Internal combustion engine

Info

Publication number: DK201970460A1
Application number: DKPA201970460A
Authority: DK
Inventors: Hvidtfeldt Rasmussen Niels
Original assignee: Man Energy Solutions Filial Af Man Energy Solutions Se Tyskland
Priority date: 2019-07-11
Filing date: 2019-07-11
Publication date: 2021-02-26
Also published as: DK202070399A1; DK181408B1; DK180388B1

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 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. The engine further comprises a pre-chamber at least partly arranged in the cylinder wall, the pre-chamber opening into the cylinder through a first opening formed in the cylinder wall, the pre-chamber being configured to ignite the mixture of scavenge air and fuel gas in the cylinder.

Description

DK 2019 70460 A1 1 Title Internal combustion engine Field The present invention relates to a two-stroke uniflow scavenged crosshead internal combustion engine and a pre-chamber member of a cylinder. 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. On 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 ignition pre-chamber. This results in a torch which ignites the fuel gas in the main chamber of the cylinder.

DK 2019 70460 A1 2 Providing the cylinder cover with a pre-chamber is however problematic, since space resources in the cylinder cover may be scarce due to presence of other engine parts such as the exhaust valve and possibly fuel valves for alternative fuel supply systems. Furthermore, it may be difficult to control the temperature of a pre-chamber arranged in the cylinder cover.

Thus it remains a problem to provide an alternative way of igniting the fuel gas. 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 pre-chamber at least partly arranged in the cylinder wall, the pre-chamber opening into the cylinder through a first opening formed in the cylinder wall, the pre-chamber being configured to ignite the mixture of scavenge air and fuel gas in the cylinder.

Consequently, by providing the cylinder wall with a pre-chamber the mixture of scavenge air and fuel gas in the cylinder may be effectively ignited without taking up space in the cylinder cover. This may allow the exhaust valve to be enlarged. Having a pre-chamber arranged in the cylinder wall may also allow the resulting torch to be directed in a more horizontal

DK 2019 70460 A1 3 direction allowing the torch to come into contact with a larger portion of the mixture of scavenge air and 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 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 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

DK 2019 70460 A1 4 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, ethane, and Liquefied Petroleum Gas (LPG).

In some embodiments the engine further comprises a pilot fuel supply system, the pilot fuel supply system comprises a pilot fuel valve arranged in the pre-chamber, the pilot fuel valve being 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 oil 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. Such 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 supply system 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.

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 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

DK 2019 70460 A1 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 5 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.

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 engine further comprises 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 allow the amount of pilot fuel to be reduced and / or make it more suitable to use alternative pilot fuels such as a fuel gas, resulting in the release of fewer unwanted exhaust gases.

In some embodiments the pilot fuel is fuel gas.

In some embodiments the pilot fuel and the main fuel is the same type of fuel gas.

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.

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

DK 2019 70460 A1 6 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 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.

In some embodiments the engine further comprises a second pre-chamber at least partly arranged in the cylinder wall, the second pre- chamber opening into the cylinder through a second opening formed in the — cylinder wall.

The second pre-chamber may be identical to the pre-chamber described above e.g. the second pre-chamber may be provided with pilot fuel valve, it may be provided with a pre-chamber cooling system etc.

The second pre-chamber may be arranged opposite to the first pre-chamber.

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

According to a second aspect the invention relates to a pre- chamber member for a cylinder for a crosshead internal combustion engine — as disclosed in relation to the first aspect the pre-chamber member having a cylinder wall, wherein the pre-chamber member further comprises a pre- chamber at least partly arranged in the cylinder wall, the pre-chamber opening into the pre-chamber member through a first opening formed in the cylinder wall, the pre-chamber being configured to ignite a mixture of scavenge air and fuel gas.

DK 2019 70460 A1 7 The different aspects of the present invention can be implemented in different ways including as two-stroke uniflow scavenged crosshead internal combustion engines and pre-chamber members 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.

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 invention.

DK 2019 70460 A1 8 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.

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 pre-chamber 114 at least partly arranged in the cylinder wall 115, the pre-chamber 114

DK 2019 70460 A1 9 opening into the cylinder through a first opening formed in the cylinder wall, the pre-chamber being configured to ignite the mixture of scavenge air and fuel gas in the cylinder 101. 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 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 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 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

DK 2019 70460 A1 10 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 preferably 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 into the pre- chamber. The pilot fuel supply system may be configured to inject an amount of pilot at the end of the compression stroke via the first and second pilot fuel valve. The pilot fuel may be ignited immediately after being injected by the temperature and pressure in the pre-chambers. This may provide precise control of the ignition timing of the mixture of scavenge air and fuel gas in the — cylinder 101.

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.

— 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

DK 2019 70460 A1 11 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.

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 2019 70460 A1 12

1. 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 pre-chamber at least partly arranged in the cylinder wall, the pre-chamber opening into the cylinder through a first opening formed in the cylinder wall, the pre-chamber being configured to ignite the mixture of scavenge air and fuel gas in the cylinder.

2. A two-stroke crosshead internal combustion engine according to claim 1, further comprises a pilot fuel supply system, the pilot fuel supply system comprises a pilot fuel valve arranged in the pre-chamber, the pilot fuel valve being configured to inject a pilot fuel into the pre-chamber.

3. A two-stroke crosshead internal combustion engine according to claim 1 —or2, wherein 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 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.

DK 2019 70460 A1 13

4. A two-stroke crosshead internal combustion engine according to claim 3, wherein the pre-chamber member of the cylinder is made of a different material than the base member of the cylinder.

5. A crosshead internal combustion engine according to any one of claims 1 to 4 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.

6. A crosshead internal combustion engine according to claim 5, wherein 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.

7. A crosshead internal combustion engine according to claim 6, wherein 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.

8. A crosshead internal combustion engine according to any one of claims 1 to 7, wherein 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 80 degrees, 0 degrees and 60 degrees, 0 degrees and 45 degrees, or 0 degrees and 30 degrees.

DK 2019 70460 A1 14

9. A crosshead internal combustion engine according to any one claims 1 to 9, wherein the engine further comprises a second pre-chamber at least partly arranged in the cylinder wall, the second pre-chamber opening into the cylinder through a second opening formed in the cylinder wall.

10. A pre-chamber member for a cylinder for a crosshead internal combustion engine according to any one of claims 1 to 9, wherein the pre- chamber member has a cylinder wall, the pre-chamber member further comprises a pre-chamber at least partly arranged in the cylinder wall, the pre-chamber opening into the pre-chamber member through a first opening formed in the cylinder wall, the pre-chamber being configured to ignite a mixture of scavenge air and fuel gas.