DK201970373A1

DK201970373A1 - Internal combustion engine

Info

Publication number: DK201970373A1
Application number: DKPA201970373A
Authority: DK
Inventors: Bach Mellergaard Simon
Original assignee: Man Energy Solutions Filial Af Man Energy Solutions Se Tyskland
Priority date: 2019-06-14
Filing date: 2019-06-14
Publication date: 2021-02-24
Also published as: KR20200143652A; KR102678958B1; CN112081687B; KR102285087B1; DK180386B1; JP6946519B2; CN112081687A; CN117090710A; JP2020204326A; KR20210090135A; JP2021181783A

Abstract

Disclosed is a two-stroke uniflow scavenged crosshead internal combustion engine having a plurality of cylinders. The two-stroke uniflow scavenged internal combustion engine is configured to inject into each of the plurality of cylinders a fuel gas via a fuel gas supply system fluidly connectable to a fuel gas tank, the fuel gas supply system comprises for each cylinder a first group of fuel gas valves 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 supply system further comprises for each cylinder a safety valve arranged upstream of the first group of fuel gas valves, the first group of fuel gas valves being fluidly connectable to the fuel gas tank via the safety valve.

Description

DK 2019 70373 A1 1 Title Internal combustion engine Field The present invention relates to a two-stroke internal combustion engine and a valve assembly 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 gas 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 have fuel gas valves configured to inject the fuel gas in the beginning of the compression stroke where the pressure in the cylinders is significantly lower.

EP3015679 discloses such a fuel gas valve.

For a two-stroke uniflow scavenged internal combustion engine this requires the fuel gas valves to be arranged relatively low in the cylinders making failures of the fuel gas valves highly problematic as fuel gas may be released into the scavenging air space below the piston. This may result in too high cylinder pressure causing cylinder cover lift in the next engine cycle or result in misfire or knocking. Furthermore, it may be difficult to detect a leaking fuel gas valve especially if the leakage is small e.g. due to a slightly

DK 2019 70373 A1 2 damaged valve seat area. An undetected small leakage will also increase methane slip being harmful to the environment.

Thus, it remains a problem to provide a safer internal combustion engine.

Summary According to a first aspect, the invention relates to a two-stroke uniflow scavenged crosshead internal combustion engine having a plurality of cylinders, each of the plurality of cylinders has a cylinder wall and a scavenge air inlet arranged in a bottom section of the cylinder, wherein the two-stroke uniflow scavenged internal combustion engine is configured to inject into each of the plurality of cylinders a fuel gas via a fuel gas supply system fluidly connectable to a fuel gas tank, the fuel gas supply system comprising for each cylinder a first group of fuel gas valves arranged at least partly in the cylinder wall and configured to admit 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 from the scavenge air inlet and fuel gas to be compressed before being ignited wherein the fuel gas supply system further comprises for each cylinder a safety valve arranged upstream of the first group of fuel gas valves, the first group of fuel gas valves being fluidly connectable to the fuel gas tank via the safety valve.

Consequently, the delivery of fuel gas to a fuel gas valve may effectively and fast be stopped. Thus the amount of fuel gas allowed to flow through a damaged fuel gas valve may be limited whereby the risk of damage to engine is lowered.

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 combustion engine system may comprise a turbocharger driven by the exhaust gases generated by the internal combustion engine

DK 2019 70373 A1 3 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 and this fuel supply system may also be used for injection of a pilot fuel when operating in the Otto Cycle mode for igniting the mixture of fuel gas and scavenge air.

The internal combustion engine may comprise a dedicated ignition system such as a pilot fuel system being capable of injecting a small — amount of pilot fuel, e.g. heavy fuel oil or marine diesel oil, accurately measured out so the amount just is able to ignite the mixture of fuel gas and scavenge air such that only the necessary amount of pilot fuel is used.

Such a pilot fuel system would in size be much smaller and more suitable for injecting a precisely amount of pilot fuel compared to the dedicated fuel — supply system for the alternative fuel, which due to the large size of the components is not suitable for this purpose.

The pilot fuel may be injected in a pre-chamber being fluidly connected to the combustion chamber of the internal combustion engine.

Alternatively, the mixture of fuel gas and scavenge air may by ignited by means comprising a spark plug or a laser igniter.

Each cylinder may be provided with one or more scavenge air inlets in the bottom of the cylinder and an exhaust outlet in the top of the cylinder.

In some embodiments the safety valve is configured to open before the first group of fuel gas valves is configured to open and to close — after the first group of fuel gas valve is configured to close thereby creating a limited period of time where fuel gas is allowed to flow through the safety valve to the first group of fuel gas valves.

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

DK 2019 70373 A1 4 bottom dead center or within 0 degrees to 90 degrees from bottom dead center.

Examples of fuel gases are natural gas, methane, ethane, and Liquefied Petroleum Gas.

In some embodiments the fuel gas supply system comprises one or more control unit operatively connected to each of the safety valves and configured to for each cylinder keep the safety valves closed for a period of time while the first group of fuel gas valves are closed whereby pressurized gas is captured in the volume between the safety valve and the first group of fuel gas valves.

Consequently, it becomes possible to detect a malfunctioning fuel gas valve early where there only is a minute amount of fuel gas leaking through the fuel gas valve in a closed state e.g. by monitoring the relative small volume between the safety valve and the first group of gas valves for a pressure change or a temperature change.

The volume between the safety valve and the first group of fuel gas valves is defined as the volume downstream of the closing member of the safety valve and the closing member of the first group of fuel gas valves e.g. the volume between the valve plate of the safety valve and the valve plate of the first group of fuel gas valves.

In some embodiments the two stroke internal combustion engine further comprises for each cylinder a first sensor arranged in the volume between the safety valve and the first group of fuel gas valves, the first sensor being configured to detect directly or indirectly a pressure change in — the volume between the safety valve and the first group of fuel gas valves indicative of a malfunctioning fuel gas valve.

Consequently it becomes possible in a reliable manner to detect different types of fuel valve malfunctions.

The first sensor may be a pressure sensor configured to directly detect the pressure change. Alternatively, the first sensor may be another sensor configured to indirectly detect the pressure change, e.g. a

DK 2019 70373 A1 temperature sensor. A second sensor may further be arranged in the volume between the safety valve and the first group of fuel gas valves e.g. the first sensor may be a pressure sensor and the second sensor may be a temperature sensor. The internal combustion engine may further comprise a 5 — control unit operationally connected to the first sensor (and possibly also the second sensor). The control unit may be configured to monitor sensor signal received from the first sensor and issue an alarm if a malfunctioning fuel gas valve is detected e.g. if a pressure drop in the volume between the safety valve and the first group of fuel gas valves is detected indicative of either a damaged valve plate or valve seat, or a stuck valve shaft. The control unit may be configured to take an action responsive to an alarm e.g. the control unit may secure that the safety valve of the malfunctioning fuel gas valve is permanently closed and / or initiate a blow operation to blow out gas from the fuel gas supply system and / or control the engine to switch from a gas mode — to an alternative mode e.g. a Diesel mode.

In some embodiments the control unit is configured to keep the safety valve open until after the first group of fuel gas valves have been closed.

Consequently, the initial pressure of the fuel gas captured in the volume between the safety valve and the first group of fuel gas valves is equal to the injection pressure thereby making it easier to detect small leakages.

In some embodiments the first group of fuel gas valves are arranged along a part of the periphery of the cylinder spanning less than 140 — degrees, less than 90 degrees, or less than 60 degrees.

Consequently, by arranging the fuel gas valve(s) of the first group of fuel gas valves along a small part of the periphery, the piping becomes simpler and the volume between the safety valve and the fuel gas valve(s) of the first group of fuel gas valves may be small.

The first group of fuel gas valves preferably consist of a single fuel gas valve however it may also comprise two or more fuel gas valves.

DK 2019 70373 A1 6 In some embodiments for each cylinder the internal volume of the fuel gas supply system downstream of the safety valve is less than 15 liters, less than 10 liters, or less than 8 liters.

Consequently, by keeping the volume downstream of the safety valve low, the amount of fuel gas allowed to escape through a damaged fuel gas valve may be approximately correspondingly low.

The internal volume of the fuel gas supply system downstream of the safety valve is defined as the internal volume of the fuel gas supply system downstream of the closing member of the safety valve e.g.

downstream of the valve plate of the safety valve.

In some embodiments for each cylinder the first group of fuel gas valves consist of a first fuel gas valve.

Consequently, each fuel gas valve is provided with a dedicated safety valve. This minimizes the volume downstream of the safety valve and — enables fast and precise identification of a malfunctioning fuel gas valve.

In some embodiments the safety valve has a valve housing with an inlet and an outlet, the first fuel gas valve has a valve housing with an inlet and an outlet, and wherein the valve housing of the safety valve is directly connected to the valve housing of the first fuel gas valve so that the outlet of the safety valve is directly connected to the inlet of the first fuel gas valve.

Consequently, the volume downstream of the safety valve may be lowered.

In some embodiments the valve housing of the safety valve and the valve housing of the first fuel gas valve is integral i.e. formed as one element.

In some embodiments the movable parts of the safety valves are identical to the movable parts of the fuel gas valves.

Consequently, maintenance and production may be simpler.

In some embodiments for each cylinder the safety valve is configured to only be open for a predetermined period around the time of injection for the first group of fuel gas valves.

DK 2019 70373 A1 7 In some embodiment the fuel gas supply system further comprises a first main fuel gas supply tube adapted to for each cylinder of a first group of the plurality of cylinders fluidly connect the first group of fuel gas valves to the fuel gas tank, a first main safety valve for fluidly connecting the first main fuel gas supply tube the fuel gas tank, a first blowout valve adapted to fluidly connected the first main fuel gas supply tube to a blowout system, and one or more control units operationally connected to the first main safety valve, the first blowout valve and the safety valve of each cylinder of the first group of cylinders, wherein the one or more control units are configured to for each — cylinder of the first group of cylinders monitor the state of the first group of fuel gas valves and in the event of a malfunction of a fuel gas valve e send a control signal to the safety valve of the malfunctioning fuel gas valve controlling the safety valve to close; e send a control signal to the first main safety valve controlling the first main safety valves to close; and e send a control signal to the blowout valve controlling the blowout valve to open wherein fuel gas supply system is adapted to guide most (e.g. at least 80%, at least 90%, or at least 95%) of the fuel gas present in the fuel gas supply system downstream of the first main safety valve into the blowout system via the main fuel gas supply tube and the blowout valve.

Consequently, by using the same fuel gas tube to supply fuel gas to the fuel gas valves and empty the fuel gas supply system for fuel gas a significantly simpler system results, i.e. there is no longer a need for a dedicate blowout system for receiving fuel gas in the event of an emergency.

In some embodiments, the two stroke internal combustion engine is operable in a first state where the fuel gas supply system provides fuel gas to each of the plurality of cylinders and a second state where the fuel gas supply system is configured to cutoff delivery of fuel gas to at least one cylinder of the plurality of cylinders by keeping the safety valve of the at least one cylinder closed.

DK 2019 70373 A1 8 Consequently, a cylinder may be cutoff for maintenance enabling the two stroke internal combustion engine to be operable in gas mode. According to a second aspect the invention relates to a valve assembly for a fuel gas supply system of a two-stroke uniflow scavenged crosshead internal combustion engine as disclosed in relation to the first aspect, comprising a fuel gas valve and a safety valve, the safety valve has a valve housing with an inlet and an outlet, the fuel gas valve has a valve housing with an inlet and an outlet, and wherein the valve housing of the safety valve is directly connected to the valve housing of the fuel gas valve — so that the outlet of the safety valve is directly connected to the inlet of the fuel gas valve. The valve housing of the safety valve and the valve housing of the fuel gas valve may be directly connected by placing them against each other e.g. so that the valve housing of the safety valve abuts the valve housing of the fuel — gas valve. Alternatively, the valve housing of the safety valve and the fuel gas valve may be directly connected by creating them as an integral element e.g. molding them (or at least a part of them) as a combined single element.

In some embodiments the valve assembly further comprises a pressure sensor arranged in the volume between the safety valve and the fuel gas valves.

The different aspects of the present invention can be implemented in different ways including as a two-stroke uniflow scavenged crosshead internal combustion engine and a valve assembly 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.

DK 2019 70373 A1 9 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 uniflow scavenged crosshead internal combustion engine according to an embodiment of the invention.

Fig. 2 shows schematically a cross-section of fuel gas valve for a a two-stroke uniflow scavenged crosshead internal combustion engine two stroke internal combustion engine according to an embodiment of the invention.

Fig. 3a shows schematically a cross-section of a two-stroke uniflow scavenged crosshead internal combustion engine according to an embodiment of the invention.

Fig. 3b shows schematically a cross-section of a two-stroke uniflow scavenged crosshead internal combustion engine according to an embodiment of the invention.

Fig. 4a shows schematically a part of a two-stroke uniflow scavenged crosshead internal combustion engine according to an embodiment of the invention.

Fig. 4b shows schematically a part of a two-stroke uniflow scavenged crosshead internal combustion engine according to an embodiment of the invention.

Fig. 5 shows a schematic drawing of a valve assembly for a fuel gas supply system of a two-stroke uniflow scavenged crosshead internal combustion engine according to an embodiment of the present invention.

Detailed description

DK 2019 70373 A1 10 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 two-stroke — uniflow scavenged crosshead internal combustion engine 100 for propelling a marine vessel according to an embodiment of the present invention.

The two- stroke internal combustion engine 100 comprises a scavenge air system 111, an exhaust gas receiver 108 and a turbocharger 109. The two stroke internal combustion engine has a plurality of cylinders 101 (only a single cylinder is

— shown in the cross-section). Each cylinder 101 comprises a scavenge air inlet 102 arranged in a lower section of the cylinder for providing scavenge air, a piston 103, an cylinder cover 113 arranged on top of the cylinder, an exhaust valve 104 arranged in the cylinder cover 113 and one or more fuel gas valves 105 (only schematically illustrated). 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 valve 105 is only shown schematically.

The fuel gas valve 105 is arranged at least partly in the cylinder wall between the cylinder cover 113 and the scavenge air inlet 102 and forms part of a fuel gas supply system and is configured to inject fuel gas into the cylinder during the compression stroke enabling the fuel gas to mix with scavenge air from the scavenge air inlet 102 and allowing the mixture of scavenge air and fuel gas to be compressed before being ignited, the fuel gas valve 105 has a fuel gas nozzle, the fuel gas nozzle has one or more nozzle outlets for providing fuel gas to the interior of the cylinder.

The fuel gas supply system is fluidly connectable to a fuel gas tank.

The fuel gas supply system further comprises a safety valve 112 (only schematically illustrated) for each cylinder, where the fuel gas valve 105 is fluidly connectable to the fuel gas tank via the safety valve 112. The safety valve

112 is configured to open a short period of time before the fuel gas valve 105 is configured to open and to close a short period of time after the fuel gas

DK 2019 70373 A1 11 valve 105 is configured to close thereby creating a limited period of time where fuel gas from the main fuel gas supply tube 316 can flow through the safety valve 112 to the fuel gas valve 105. This means that the safety valve 112 at normal operation will be activated just as often as the fuel gas valve 105 as it opens and closes immediately before and after, respectively, the opening period of the gas valve 105 where gas is admitted into the cylinder. The safety valve 112 has a double safety function. Firstly securing that gas admission into the combustion chamber only is possible at the correct admission timing and secondly in the event of failure of a fuel gas valve 105 it — can block gas from entering the combustion chamber, thereby ensuring that only the very small amount of gas in the space downstream of the safety valve will enter the combustion chamber. Another advantage by having a safety valve being activated at each revolution of the engine is that the safety valve 112 will not get stuck which can be a problem for safety valves only activated at the rare event of a failure.

The fuel gas valve 105 may be configured to inject a fuel gas into the cylinder 101 in the beginning of the compression stroke within 0 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 valve 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 exhaust valve is arranged centrally in the cylinder cover and the timing of the exhaust valve may be variable such that the closing and/or opening of the exhaust valve can be optimized e.g. to control the compression ratio and/or the temperature in the cylinder.

Fig. 2 shows schematically a cross-section of fuel gas valve 200 for a two stroke internal combustion engine according to an embodiment of the

DK 2019 70373 A1 12 present invention. The fuel gas valve 200 comprises a valve shaft 201, a valve plate 202, a valve seat 203, and a fuel gas nozzle 204 having a nozzle outlet 206. The valve shaft 201 and the valve plate 202 are movable between a closed position, where fuel gas is prevented to flow through the fuel gas valve 200, and an open position, where fuel gas is allowed to flow through the fuel gas valve 200. The valve shaft 201 and the valve plate 202 are shown in the closed position in Fig. 2. The valve shaft 201 and the valve plate 202 may be movable between the closed position and the open position by means of an actuator (not shown) controlled by a control unit (not shown).

Fig. 3a shows a schematic drawing of a two-stroke uniflow scavenged crosshead internal combustion engine 300 having a plurality of cylinders 301 according to an embodiment of the present invention. The two-stroke uniflow scavenged internal combustion engine 300 is configured to inject into each of the plurality of cylinders a fuel gas via a fuel gas supply system 315 313 316 312305 fluidly connectable to a fuel gas tank 318. The fuel gas supply system 315 313 316 312 305 comprises for each cylinder 301 a first group of fuel gas valves 305 configured to admit a controlled amount of fuel gas into the cylinder 301 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 supply system 315 313 316 312 305 further comprises for each cylinder 301 a safety valve 312 arranged upstream of the first group of fuel gas valves 305, the first group of fuel gas valves being fluidly connectable to the fuel gas tank 318 via the safety valve

312. The fuel gas supply system 315 313 316 312 305 further comprises a — first main fuel gas supply tube 316 adapted to for each cylinder 301 of a first group of the plurality of cylinders fluidly connect the first group of fuel gas valves 305 to the fuel gas tank 318, a first main safety valve 315 for fluidly connecting the first main fuel gas supply tube 316 to the fuel gas tank 318, a first blowout valve 313 adapted to fluidly connected the first main fuel gas — supply tube 316 to a blowout system 314, and one or more control units (not shown) operationally connected to the first main safety valve 315, the first

DK 2019 70373 A1 13 blowout valve 313, and the safety valve 312 of each cylinder of the first group of cylinders. The fuel gas tank 318 may be fluidly connected to the first main safety valve 315 through a compressor 317 configured to compress the fuel gas to the admission pressure e.g. 3-40 bar, preferably 10-25 bar.

Alternatively, the fuel gas stored in the fuel gas tank 318 may be pressurized at the injection pressure whereby there is no need of a compressor between the fuel gas tank 318 and the first main safety valve 315. The one or more control units are configured to for each cylinder 301 of the first group of cylinders, monitor the state of the first group of fuel gas valves 305 and in the event of a malfunction of a fuel gas valve 305 e send a control signal to the safety valve 312 of the malfunctioning fuel gas valve controlling the safety valve 312 to close; e send a control signal to the first main safety valve 315 controlling the first main safety valve 315 to close; and e send a control signal to the blowout valve 313 controlling the blowout valve 313 to open wherein fuel gas supply system is adapted to guide most (e.g. at least 80%, at least 90%, or at least 95%) of the fuel gas present in the fuel gas supply system downstream of the first main safety valve 315 into the blowout system via the main fuel gas supply tube 316 and the blowout valve 313 e.g. by also closing the remaining safety valves 312 and / or the remaining fuel gas valves 305. In this embodiment the first group of the plurality of cylinders consist of all cylinders, however in other embodiments the first group may consist of fever e.g. two or more cylinders. The one or more control unit may also send a control signal to the safety valve 312 and / or the first group of fuel gas valves 305 of the other cylinders in the first group of cylinders to close the valves and / or keep the valves closed. Fig. 3b shows a schematic drawing of a two-stroke uniflow scavenged crosshead internal combustion engine 300 according to an embodiment of the present invention. The engine 300 is similar to the engine shown in Fig. 3a with the difference that the fuel gas supply system further

DK 2019 70373 A1 14 comprises for each cylinder 301 a second group of fuel gas valves 305’, a second safety valve 312° arranged upstream of the second group of fuel gas valves 305’, the second group of fuel gas valves 305° being fluidly connectable to the fuel gas tank 318 via the second safety valve 312’. The fuel gas supply system further comprises a second main fuel gas supply tube 316' adapted to for each cylinder 301 of the first group of the plurality of cylinders fluidly connect the second group of fuel gas valves 305' to the fuel gas tank 318, a second main safety valve 315' for fluidly connecting the second main fuel gas supply tube 316' to the fuel gas tank 318, a second blowout valve 313' adapted to fluidly connected the second main fuel gas supply tube 316’ to a blowout system 314".

Fig. 4a shows schematically a part of a two-stroke uniflow scavenged crosshead internal combustion engine according to an embodiment of the invention. Shown is a cylinder 401 and part of a fuel gas — supply system 412 405. The fuel gas supply system comprises for the cylinder 401 a first group of fuel gas valves 405 configured to inject fuel gas into the cylinder. In this embodiment the first group of fuel gas valves 405 consist of a single fuel gas valve 405. The fuel gas supply system comprises further for the cylinder 401 a safety valve 412 arranged upstream of the fuel gas valve 405 so that the fuel gas valve 405 is fluidly connectable to a fuel gas tank via the safety valve 412. The fuel gas valve 405 is operationally connected to a first control unit 320 configured to open and close the fuel gas valve 405. Correspondingly, the safety valve is operationally connected to a second control unit 319 configured to open and close the safety valve 412.

However, in other embodiments, both fuel gas valves and safety valves may be operationally connected to the same control unit.

Fig. 4b schematically shows a part of a two-stroke uniflow scavenged crosshead internal combustion engine according to an embodiment of the present invention. Shown is a cylinder 401 and part of a fuel gas supply system 412 405 430. The fuel gas supply system comprises for the cylinder 401 a first group of fuel gas valves 405 430 configured to

DK 2019 70373 A1 15 inject fuel gas into the cylinder. In this embodiment the first group of fuel gas valves 405 430 comprises a first fuel gas valve 405 and a second fuel gas valve 430. The fuel gas supply system comprises further for the cylinder 401 a safety valve 412 arranged upstream of the first group of fuel gas valves 405 — 430 so that the first group of fuel gas valves 405 430 are fluidly connectable to a fuel gas tank via the safety valve 412. The first group of fuel gas valves are arranged along a part of the periphery 421, in this concrete embodiment approximately 55 degrees. However, the first group of fuel gas valves may comprise any numbers of fuel gas valves and may be arranged along the — entire periphery e.g. to form a circular nozzle ring. The fuel gas valves may be poppet valves opening inwards or outwards, ball valves, butterfly valves or rotary valves or other suitable valves.

. Fig. 5shows a schematic drawing of a valve assembly 690 for a fuel gas supply system of a two-stroke uniflow scavenged crosshead internal combustion engine according to an embodiment of the present invention. The valve assembly 690 comprises a fuel gas valve 600 and a safety valve 650, the safety valve 650 has a valve housing 655 with an inlet 656 and an outlet 656, the fuel gas valve 600 has a valve housing 605 with an inlet 607 and an outlet 606 formed in a valve nozzle 604. The safety valve 650 comprises a valve shaft 651, a valve plate 652 and a valve seat 653. The valve shaft 651 and the valve plate 652 are movable between a closed position, where fuel gas is prevented to flow through the safety valve 650, and an open position, where fuel gas is allowed to flow through the safety valve 650. The valve shaft 651 and the valve plate 652 are shown in the open position in Fig. 5.

— The fuel gas valve 600 comprises a valve shaft 601, a valve plate 602 and a valve seat 603. The valve shaft 601 and the valve plate 602 are movable between a closed position, where fuel gas is prevented to flow through the fuel gas valve 600, and an open position, where fuel gas is allowed to flow through the fuel gas valve 650. The valve shaft 651 and the valve plate 602 are shown in the open position in Fig. 5. The valve housing of the safety valve 655 is directly connected to the valve housing of the first fuel gas valve

DK 2019 70373 A1 16 565 by forming the valve housing of the safety valve 655 and a part of the valve housing of the fuel gas valve 605 as an integral element. The valve assembly 690 further comprise a pressure sensor 608 arranged in the volume 680 between the safety valve 650 and the fuel gas valve 600.

Moreover, the valve assembly 690 may comprise a position sensor, e.g. an inductive sensor, monitoring the position of the valve shaft 601. An advantage of utilising a pressure sensor compared to an inductive position sensor is that a pressure sensor can verify the tightness of the complete valve assembly and not only the spindle position. Furthermore a single — pressure sensor can monitor the function of both the fuel valve and the safety valve at the same time. A position sensor solution will require two separate sensors for monitoring the two valves.

The pressure monitoring may be used in the control system for adjusting injection parameters and/or in the safety strategy of the engine.

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 70373 A1 17

1. A two-stroke uniflow scavenged crosshead internal combustion engine having a plurality of cylinders, each of the plurality of cylinders has a cylinder wall and a scavenge air inlet arranged in a bottom section of the cylinder, wherein the two-stroke uniflow scavenged internal combustion engine is configured to inject into each of the plurality of cylinders a fuel gas via a fuel gas supply system fluidly connectable to a fuel gas tank, the fuel gas supply system comprising for each cylinder a first group of fuel gas valves arranged atleast partly in the cylinder wall and configured to admit fuel gas into the cylinder during the compression stroke enabling the fuel gas to mix with scavenge air from the scavenge air inlet and allowing the mixture of scavenge air and fuel gas to be compressed before being ignited characterized in that the fuel gas supply system further comprises for each — cylinder a safety valve arranged upstream of the first group of fuel gas valves, the first group of fuel gas valves being fluidly connectable to the fuel gas tank via the safety valve.

2. A two-stroke uniflow scavenged crosshead internal combustion engine according to claim 1, wherein the safety valve is configured to open before the first group of fuel gas valves is configured to open and to close after the first group of fuel gas valve is configured to close thereby creating a limited period of time where fuel gas is allowed to flow through the safety valve to the first group of fuel gas valves.

3. A two-stroke uniflow scavenged crosshead internal combustion engine according to claims 1 or 2, wherein the fuel gas supply system comprises one or more control units operatively connected to each of the safety valves and configured to for each cylinder keep the safety valves closed for a period of time while the first group of fuel gas valves are closed whereby

DK 2019 70373 A1 18 pressurized gas is captured in the volume between the safety valve and the first group of fuel gas valves.

4. A two-stroke uniflow scavenged crosshead internal combustion engine according to claims 1 to 3, wherein the two stroke internal combustion engine further comprises for each cylinder a pressure sensor arranged in the volume between the safety valve and the first group of fuel gas valves.

5. A two-stroke uniflow scavenged crosshead internal combustion engine — according to any one of claims 1 to 4, wherein the first group of fuel gas valves are arranged along a part of the periphery of the cylinder spanning less than 140 degrees, less than 90 degrees, or less than 60 degrees.

6. A two-stroke uniflow scavenged crosshead internal combustion engine according to any one of claims 1 to 5, wherein for each cylinder the internal volume of the fuel gas supply system downstream of the safety valve is less than 15 liters, less than 10 liters, or less than 8 liters.

7. A two-stroke uniflow scavenged crosshead internal combustion engine according to any one of claims 1 to 6, wherein for each cylinder the first group of fuel gas valves consist of a first fuel gas valve.

8. A two-stroke uniflow scavenged crosshead internal combustion engine according to claim 7, wherein the safety valve has a valve housing with an inlet and an outlet, the first fuel gas valve has a valve housing with an inlet and an outlet, and wherein the valve housing of the safety valve is directly connected to the valve housing of the first fuel gas valve so that the outlet of the safety valve is directly connected to the inlet of the first fuel gas valve.

DK 2019 70373 A1 19

9. A two-stroke uniflow scavenged crosshead internal combustion engine according to any one of claims 1 to 8, wherein the fuel gas supply system further comprises a first main fuel gas supply tube adapted to for each cylinder of a first group of the plurality of cylinders fluidly connect the first group of fuel gas valves to the fuel gas tank, a first main safety valve for fluidly connecting the first main fuel gas supply tube the fuel gas tank, a first blowout valve adapted to fluidly connected the first main fuel gas supply tube to a blowout system, and one or more control units operationally connected to the first main safety valve, the first blowout valve and the safety valve of — each cylinder of the first group of cylinders, wherein the one or more control units are configured to for each cylinder og the first group of cylinders monitor the state of the first group of fuel gas valves and in the event of a malfunction of a fuel gas valve e send a control signal to the safety valve of the malfunctioning fuel gas valve controlling the safety valve to close; e send a control signal to the first main safety valve controlling the first main safety valves to close; and e send a control signal to the blowout valve controlling the blowout valve to open wherein fuel gas supply system is adapted to guide most (e.g. at least 80%, at least 90%, or at least 95%) of the fuel gas present in the fuel gas supply system downstream of the first main safety valve into the blowout system via the main fuel gas supply tube and the blowout valve.

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10. A two-stroke uniflow scavenged crosshead internal combustion engine according to any one of claims 1 to 9, wherein the two stroke internal combustion engine is operable in a first state where the fuel gas supply system provides fuel gas to each of the plurality of cylinders and a second state where the fuel gas supply system is configured to cutoff delivery of fuel gas to at least one cylinder of the plurality of cylinders by keeping the safety valve of the at least one cylinder closed.

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11. A valve assembly for a fuel gas supply system of a two-stroke uniflow scavenged crosshead internal combustion engine according to any one of claims 1 to 10, comprising a fuel gas valve and a safety valve, the safety valve has a valve housing with an inlet and an outlet, the first fuel gas valve has a valve housing with an inlet and an outlet, and wherein the valve housing of the safety valve is directly connected to the valve housing of the fuel gas valve so that the outlet of the safety valve is directly connected to the inlet of the fuel gas valve.