Internal combustion engine

Abstract

The invention relates to an internal combustion engine and a method for operating an internal combustion engine. An internal combustion engine (100) having at least one cylinder (101) with an inner diameter of at least 200 mm comprises: a fuel supply system (110), in particular an ammonia supply system, having a main fuel tank (111), a fuel distributor (112); a fuel injection system (120) arranged downstream of the fuel distributor (112); and at least one isolation valve (9) fluidly arranged between the fuel supply system (110) and the fuel injection system (120). The internal combustion engine (100) also includes a fuel purge system (125) having at least a liquid fuel purge system (130). The liquid fuel purge system (130) comprises: a high pressure source (131) of inert gas, preferably N2, preferably having a pressure greater than 30 bar, fluidly connected or fluidly connectable to at least the fuel supply system (110), preferably upstream of the fuel distributor (112); and a collection tank (132) for receiving and storing liquid fuel. The fuel purge system (125) comprises a purge control unit (150) adapted to set a first liquid fuel purge mode for purge of the fuel supply system (110), where the purge control unit is adapted to establish a fluid connection between a high pressure source (131) of inert gas and the fuel distributor (112), and where the purge control unit is adapted to set a second liquid fuel purge mode for purge of the fuel supply system (110). The purge control unit (150) is adapted to establish a fluid connection between the fuel distributor (112) and the collection tank (132) such that inert gas from the high pressure source (131) of inert gas is directed through the fuel distributor (112) and into the collection tank (132).

Description

[0001] The present invention relates to an internal combustion engine having at least one cylinder and to a method for operating an internal combustion engine.

[0002] The present invention particularly relates to an internal combustion engine using ammonia as fuel, in particular as main fuel.

[0003] The present invention preferably relates to an internal combustion engine, such as a large marine or ship engine or stationary engine, the cylinder of which has an inner diameter of at least 200 mm.

[0004] The engine is preferably a two-stroke engine or a two-stroke crosshead engine. The engine can be a diesel or gas engine, a dual fuel or a multi-fuel engine. The combustion of liquid and / or gaseous fuels in such engines as well as compression ignition or forced ignition are possible.

[0005] The internal combustion engine can be a longitudinal scavenged two-stroke engine.

[0006] The term "internal combustion engine" also refers to large engines which are not only capable of operating in Diesel mode, which is characterized by compression ignition of the fuel, but also in Otto mode, which is characterized by forced ignition of the fuel, or in a hybrid of both. Furthermore, the term "internal combustion engine" particularly includes dual fuel engines and large engines, in which the main fuel is ignited with the help of a pilot injection of compression ignition fuel or alternatively by employing a pre-chamber solution.

[0007] The engine speed is preferably below 800 RPM, in particular for four-stroke engines, and more preferably below 200 RPM, in particular for two-stroke engines, which is the identification of low speed engines.

[0008] The fuel can be diesel or marine diesel or heavy fuel oil or emulsions or slurries or methanol or ethanol as well as gaseous fuels, such as liquid natural gas (LNG), liquefied petroleum gas (LPG) and the like.

[0009] Other possible fuels which can be added upon request are: LBG (liquefied biogas), biofuels (e.g. oil made from algae), hydrogen, synthetic fuels made from CO2 (e.g. made from power-to-gas or power-to-liquid).

[0010] With the 2018 International Maritime Organization (IMO) commitment to reduce greenhouse gas emissions from international shipping, ammonia-fueled ships or engines suitable for being driven by ammonia fuel are increasingly developed and built.

[0011] Ammonia is a synthetic product obtained from fossil fuels, biomass or renewable resources (wind, sun, water or heat) and, when produced from renewable resources, will have essentially no carbon footprint or release no CO2, SO X , particulate matter or unburned hydrocarbons when combusted.

[0012] When the fuel is ammonia, it is desirable to minimize the emission of ammonia gas, since ammonia is hazardous and has a pungent smell. This is particularly relevant for the safety of the crew and when the engine is stopped and / or when changing to conventional fuel and / or to a backup fuel and / or when an unexpected event occurs. Therefore, it is known to purge the engine and the piping with an inert gas, such as nitrogen.

[0013] There is a need to purge ammonia to be able to perform maintenance during shutdown, typically to prevent the presence of ammonia in the engine room due to a leak.

[0014] Thus, the risk of events such as ammonia leaking into the engine room is minimized. Such a leak can cause the engine to trip during operation, and an unplanned engine stop can have very serious consequences, e.g. in a sheltered harbor or port and / or during refueling.

[0015] When ammonia is purged, corrosion attack on engine materials can be avoided during operation on a durable backup fuel or during standstill.

[0016] Fuel vapor can be avoided from accumulating in the air chamber / air pocket to the flammable / combustible range.

[0017] During the purging process, some fuel will evaporate into the nitrogen purge stream and thus be discharged from the vessel together with the nitrogen. However, the purged ammonia cannot simply be emitted to the atmosphere / environment.

[0018] WO2022234250 teaches a method of treating an ammonia-containing purge gas stream, wherein the ammonia-containing purge gas stream is passed through a first tank containing water to provide an ammonia-reduced exhaust gas stream.

[0019] DK181016 discloses an aqueous ammonia absorption system for absorbing ammonia supplied through a discharge path into water, thereby forming ammonia water. The ammonia water must be stored and refurbished for further use.

[0020] It is also known to purge fuel nozzles to remove fuel residues. In addition, it is known, for example from EP4155526A1, to cool fuel nozzles. Typically, fuel nozzles require piping for a purging medium and piping for a cooling medium.

[0021] US2015192050 discloses an injector for injecting fuel to heat a post-treatment device, wherein, after fuel injection, an air flow through the nozzle is provided to purge residual fuel and to cool the nozzle to prevent carbon deposition.

[0022] It is an object of the present invention to at least partly prevent the drawbacks of the prior art and in particular to create an internal combustion engine and a method for operating an internal combustion engine which allow a safer and more efficient use.

[0023] This object is achieved by the internal combustion engine, the method for operating an internal combustion engine and the computer program product according to the independent claims.

[0024] The internal combustion engine has at least one cylinder with an inner diameter of at least 200 mm. A piston is arranged in the cylinder for reciprocating movement between a bottom dead center and a top dead center.

[0025] The internal combustion engine can have a scavenge port formed in the cylinder for supplying a scavenge gas into a combustion chamber, which is a space enclosed by the cylinder and an upper surface of the piston.

[0026] The internal combustion engine can be a longitudinally scavenged two-stroke engine, wherein the scavenge gas is introduced into the combustion chamber of the cylinder via a scavenge groove at the bottom of the cylinder when the piston is near its bottom dead center and clears the way for the scavenge gas into the combustion chamber of the cylinder.

[0027] The internal combustion engine can have an exhaust port formed in the cylinder, e.g. in the cylinder head, for exhausting gas out of the combustion chamber. The exhaust port comprises at least one exhaust valve.

[0028] The internal combustion engine comprises a fuel supply system having a main fuel tank, a fuel distribution and preferably a pump fluidically arranged between the main fuel tank and the fuel distributor, which pump is for example arranged in a fuel line connecting the main fuel tank and the fuel distributor.

[0029] In particular, the fuel supply system can be an ammonia supply system. Alternatively, the fuel supply system can be a system for supplying a methanol liquid fuel.

[0030] The main fuel tank can be adapted to store and provide a liquid fuel, e.g. liquid ammonia. Typically, the liquid fuel, e.g. ammonia, can be provided in the main fuel tank at a pressure of up to 25 bar. With the help of the pump, the pressure in the fuel supply system can be increased to 85 bar and due to the design of the fuel injectors, the pressure in the fuel injection system can rise to 500 to 600 bar.

[0031] The main fuel tank can be kept at a lower temperature in order to reduce the storage pressure.

[0032] The internal combustion engine comprises a fuel injection system, in particular an ammonia injection system, which is arranged downstream of the fuel distributor, preferably comprising at least one injection line and at least one injector for each cylinder.

[0033] At least one isolating valve is fluidically arranged between the fuel supply system and the fuel injection system, preferably at least one isolating valve is arranged between the fuel distributor and each fuel injector of the plurality of cylinders. Thus, the fluid connection between the fuel supply system and the fuel injection system, in particular the fluid connection between the fuel distributor and at least one injector, can be interrupted.

[0034] The internal combustion engine further comprises a fuel cleaning system, which has at least a liquid fuel cleaning system.

[0035] The liquid fuel cleaning system comprises a high-pressure source of inert gas, preferably N2, preferably the high-pressure source is for maintaining and / or providing inert gas at a pressure of more than 30 bar, more preferably in the range of 30 to 45 bar.

[0036] The pressure level is determined by the need to avoid boiling of ammonia at the actual fuel temperature in the fuel supply system and the fuel injection system, which can significantly exceed the temperature in the main fuel tank due to heat uptake from the working engine and from air in the engine room.

[0037] The high-pressure source of inert gas is fluidically connected or fluidically connectable to at least the fuel supply system.

[0038] The liquid fuel cleaning system further comprises a collection tank for receiving and storing liquid fuel and inert gas.

[0039] The collection tank can be of the same type as the main fuel tank, but can have a smaller volume. The collection tank can be maintained at a pressure of more than 12 bar, preferably more than 20 bar, preferably in the range of 15 to 20 bar or in the range of 30 to 45 bar. If the pressure of the collection tank is maintained below 30 bar, the pressure can be matched between the fuel supply system and the fuel injection system.

[0040] Preferably, the liquid fuel cleaning system further comprises a first cleaning line fluidically connected or fluidically connectable to the fuel distributor via a cleaning valve for establishing a fluid connection between the fuel supply system and the collection tank. Preferably, the cleaning valve is arranged in the first cleaning line.

[0041] At least one second cleaning line can be connected to the injector, such that a medium directed into the injector can exit the injector through the injector nozzle in order to be injected into the cylinder and / or can exit the injector through the at least one second cleaning line, for example in order to clean the injector. A respective injection valve can be arranged in the injector.

[0042] The fuel washing system comprises a washing control unit adapted to set a first liquid fuel washing mode to wash the fuel supply system. In the first liquid fuel washing mode, the washing control unit is adapted to establish a fluid connection between the high pressure source of inert gas and the fuel distributor and the washing control unit is adapted to establish a fluid connection between the fuel distributor and the collection tank, such that inert gas from the high pressure source of inert gas is directed through the fuel distributor and into the collection tank.

[0043] In this mode, liquid fuel can be purged from the fuel distributor.

[0044] Preferably, in the first liquid fuel washing mode, the washing control unit is adapted to set the isolation valve to close the connection between the fuel supply system and the fuel injection system before establishing the fluid connection between the high pressure inert gas source and the fuel distributor.

[0045] Thus, the high pressure inert gas can be prevented from being directed through the fuel injection system. The fuel injection system can comprise residues of sealing oil that should not be collected in the collection tank. In case of a liquid washing, the fuel will be contaminated, while the fuel vapour will not carry oil. If only liquid fuel and inert gas is collected in the collection tank, the collection tank can be used as a fuel source.

[0046] The internal combustion system can comprise an additional fuel supply system, in particular for a backup fuel, such as diesel, which can at least partially use the same fuel distributor and the same fuel injection system. Alternatively, the additional fuel supply system can comprise a completely separate backup fuel supply system and a completely separate backup fuel injection system.

[0047] The high pressure source of inert gas is preferably fluidly connected or at least fluidly connectable to the fuel supply system upstream of the fuel distributor.

[0048] In the context of the present application, the term "upstream" refers to the conventional direction of fuel flow from the fuel tank to the cylinders.

[0049] In case the high pressure source of inert gas is arranged upstream of the fuel distributor, the fuel distributor can be washed in a downstream direction.

[0050] Alternatively, the high pressure source of inert gas can be fluidly connected or connectable to the fuel supply system downstream of the fuel distributor. In particular, the isolation valve is adapted to not only close the connection between the fuel injection system and the fuel distributor, but also to establish a fluid connection between the high pressure source of inert gas and the fuel distributor.

[0051] The fuel cleaning system can further comprise a gaseous fuel cleaning system. The gaseous fuel cleaning system comprises a low pressure source of inert gas, preferably N2, preferably for maintaining and / or providing the inert gas at a pressure of 3 to 7 bar.

[0052] The low pressure source of inert gas can be fluidly connected or connectable to the fuel injection system.

[0053] The gaseous fuel cleaning system preferably comprises at least one second cleaning line, preferably each second cleaning line is fluidly connected with one of the at least one injector.

[0054] The gaseous fuel cleaning system comprises a cleaning tank for receiving and storing gaseous fuel and inert gas. The cleaning tank can be maintained at a pressure of 2 to 10 bar, preferably 4 to 6 bar, in particular to minimize consumption of inert gas, e.g. nitrogen.

[0055] The gaseous fuel cleaning system can comprise a pressure reduction valve which can be fluidly arranged between the at least one second cleaning line and the cleaning tank.

[0056] When the fuel cleaning system comprises a gaseous fuel cleaning system, the cleaning control unit can be adapted to set a first gaseous fuel cleaning mode to clean the fuel injection system.

[0057] In the first gaseous fuel cleaning mode, the cleaning control unit is adapted to reduce the pressure in the fuel injection system such that fuel in the fuel injection system can evaporate, e.g. by providing to open the pressure reduction valve.

[0058] In the first gaseous fuel cleaning mode, the cleaning control unit is adapted to establish a fluid connection between the low pressure source of inert gas and the fuel injection system and to establish a fluid connection between the fuel injection system and the cleaning tank such that inert gas from the low pressure source of inert gas is guided through the fuel injection system and into the cleaning tank.

[0059] The low pressure source of inert gas can be fluidly connected or connectable to the fuel injection system upstream of the fuel injection system, in particular upstream of the fuel distributor.

[0060] Alternatively, the low pressure source of inert gas can be fluidly connected or connectable to the fuel injection system via an isolation valve. In particular, the isolation valve can be adapted not only to open and close the connection between the fuel injection system and the fuel distributor but also to establish a connection between the low pressure source of inert gas and the fuel injection system.

[0061] The pressure reduction valve of the gaseous fuel cleaning system can be connectable to the low pressure reservoir of inert gas. In the first gaseous fuel cleaning mode, the cleaning control unit can be adapted to reduce the pressure in the fuel injection system by setting the pressure reduction valve to open to the low pressure reservoir of inert gas.

[0062] The low-pressure reservoir of inert gas can be a purge tank or a separate low-pressure reservoir.

[0063] The internal combustion engine can comprise an SCR catalytic converter and an SCR valve fluidly arranged between the at least second purge line and the SCR catalytic converter.

[0064] The purge control unit can be adapted to set the SCR valve to open to: release pressure; and allow gaseous fuel to exit the fuel injection system and enter the SCR catalytic converter. Thus, if the fuel is ammonia, residues of gaseous ammonia can be directed into the SCR reactor, for example before the internal combustion engine is changed to run on a backup fuel.

[0065] The purge control unit can be adapted to set the amount of gaseous fuel entering the SCR catalytic converter. The amount of gaseous ammonia should correspond to the actual NOx emissions so as not to create ammonia slip in the exhaust gas.

[0066] In particular, the purge control unit can be adapted to close the fluid connection between the second purge line and the purge tank so that all gaseous fuel can be directed into the SCR reactor at least during a certain time interval.

[0067] Before purging, the collection tank can be partly filled with liquid fuel, for example ammonia. A mixture of inert gas, for example N2, and fuel, for example ammonia, can accumulate on top. During purging, the purge pressure can rise, mainly due to non-condensable gases. The inert gas can be vented. The mixture can be released into the SCR reactor or into the purge tank.

[0068] The purge control unit can be adapted to set a second liquid fuel purge mode to purge the fuel injection system, in particular simultaneously with or after the first liquid fuel purge mode, wherein the purge control unit is adapted to establish a fluid connection between the high-pressure source of inert gas and the fuel injection system, and wherein the purge control unit is adapted to establish a fluid connection between the fuel injection system and the collection tank and / or into the purge tank.

[0069] In the second liquid fuel purge mode, inert gas from the high-pressure source of inert gas is directed through the fuel injection system and into the collection tank and / or into the purge tank.

[0070] As the fuel injection system can be contaminated with oil, one can not want to purge the oil into the collection tank, as this fuel would be used further.

[0071] However, if the risk of contamination is deemed not high, or if no adverse consequences of contamination are expected, the inert gas and the fuel can be purged into the collection tank.

[0072] The second liquid fuel cleaning mode allows to push liquid fuel out of the fuel injection system, which can be necessary in certain situations, for example during an emergency engine stop or so-called "trip to diesel", i.e. an emergency switch to diesel in case of e.g. a detected ammonia leakage into the engine compartment.

[0073] The first gas fuel cleaning mode can be necessary after the second liquid cleaning mode, because there can be fuel residues left in the system, e.g. liquid droplets on walls, fluid cavities etc., which are difficult to remove in the liquid fuel cleaning mode.

[0074] During an emergency stop, less time is available for cleaning. Liquid fuel, such as ammonia, from the whole system can be flushed quickly, preferably directly into the cleaning tank, instead of being distributed to the collection tank and the cleaning tank.

[0075] The size of the cleaning tank can be chosen to accommodate the full amount of ammonia stored in the cleaning line and the injectors.

[0076] In order to open the connection between the high pressure source of inert gas and the fuel injection system in the second liquid fuel cleaning mode, the cleaning control unit can be adapted to set the isolation valve in order to open or keep open the connection between the fuel supply system and the fuel injection system. In addition, the cleaning control unit can be adapted to establish a connection between the high pressure source of inert gas and the fuel supply system.

[0077] Thus, the high pressure inert gas can enter the fuel injection system via the fuel supply system and the isolation valve.

[0078] Preferably, in the second liquid fuel cleaning mode, the cleaning control unit is adapted to set the cleaning valve in order to close the connection between the fuel distributor and the first cleaning line, so that the high pressure inert gas mainly leaves the fuel distributor through the fuel injection system.

[0079] The cleaning control unit can be adapted to set the second gas fuel cleaning mode to clean the fuel supply system after the first liquid fuel cleaning mode, wherein the cleaning control unit is adapted to establish a fluid connection between the low pressure source of inert gas and the fuel supply system. Thus, fuel residues can evaporate. In the second gas fuel cleaning mode, the cleaning control unit is further adapted to establish a fluid connection between the fuel supply system and the cleaning tank. Thus, gas fuel from the fuel supply system can be guided to the cleaning tank.

[0080] The first cleaning line and the at least one second cleaning line can be merged into one common cleaning line downstream of the fuel supply system and the fuel injection system. The common cleaning line can be adapted to open towards the collection tank or towards the cleaning tank depending on the cleaning mode and depending on the aggregation state of the cleaning fuel.

[0081] The internal combustion engine can comprise a first sensor for providing data indicative of the fuel concentration and / or fuel content in the fuel injection system. The internal combustion engine can comprise a second sensor for providing data indicative of the fuel concentration and / or fuel content in the fuel supply system.

[0082] The cleaning control unit can be adapted to receive data provided by the first sensor and / or the second sensor and can be adapted to decide from the data whether a respective cleaning mode has to be maintained or repeated. The cleaning control unit can be adapted to compare the received data with preset limits.

[0083] The internal combustion engine can comprise more than one cylinder. In the first gaseous fuel cleaning mode, the cleaning control unit can be adapted to clean only a part of the fuel injection system associated with a part of the cylinders, while the other cylinders are still in operation. In this case, the cleaning control unit is adapted to supply the low pressure inert gas downstream of the fuel distributor and only to the injection lines / injectors to be cleaned.

[0084] Additionally or alternatively, in the second liquid fuel cleaning mode, the cleaning control unit can be adapted to clean only a part of the fuel injection system associated with a part of the cylinders. In this case, the cleaning control unit is adapted to supply the high pressure inert gas only to the injection lines / injectors to be cleaned, while for example an isolation valve connecting another part of the injection system to the high pressure inert gas is kept closed.

[0085] The internal combustion engine can comprise a direct connection pipe for directly connecting the collecting tank and the fuel distributor, such that the fuel collected from the collecting tank can be supplied to the fuel distributor, for example via a pump. A direct connection valve can be arranged in the direct connection pipe. When the collecting tank is filled with clean liquid fuel during the cleaning process, this content can be used to operate the engine. This contributes to fuel saving.

[0086] The cleaning tank can contain water for absorbing fuel, in particular ammonia, in use. Additionally or alternatively, the cleaning tank is connected or connectable to an absorption stage containing water.

[0087] In particular, the ammonia / nitrogen mixture can be injected into the water and washed, after which the cleaned nitrogen is released into the environment.

[0088] In particular, the cleaning tank and / or the collecting tank comprises, is connected to or connectable to a fuel trapping system. The fuel trapping system can comprise an acid scraping device and / or an air dilution device.

[0089] The acid scraping can be used, for example together with carbonic acid.

[0090] Furthermore, the ammonia / nitrogen mixture from the collecting tank can be injected into the cylinder at low pressure when the scavenge port is closed.

[0091] Alternatively, the liquid fuel / inert gas mixture can be diluted with a large amount of air until a safe concentration is reached, which can then be emitted into the environment.

[0092] The cleaning tank and / or the collection tank can be connected or connectable to the gas cylinder and / or the SCR reactor.

[0093] The cleaning tank pressure can be increased to 5 bar to enable injection.

[0094] Evaporated gas from the collection tank can be used to compress the gas in the cleaning tank to enable injection into the SCR reactor. The evaporated gas can be preheated in the scavenging air cooler or the exhaust gas economizer of the internal combustion engine.

[0095] When the internal combustion engine is operated with reserve fuel, in particular in diesel mode, the collected fuel, in particular ammonia, can be used as reducing agent. In particular, the ammonia / nitrogen mixture can be injected in small portions into the SCR reactor.

[0096] A cleaning mode can be set between liquid fuel operation and reserve fuel operation, in which the liquid fuel is removed from the fuel supply system and the fuel injection system.

[0097] The internal combustion engine, in particular the fuel supply system and / or the fuel injection system, can comprise a heatable and / or coolable tube, in particular a double-walled tube. The cleaning control unit can be adapted to set the temperature of the tube. In particular, during the first and / or second gaseous fuel cleaning mode, the tube can be heated to accelerate evaporation and reduce the number of cleaning cycles.

[0098] Liquid droplets of the liquid fuel, for example ammonia, must be avoided from boiling in the walls, bends, etc., otherwise there is a risk of subcooling or freezing. The cleaning control unit can be adapted to gradually reduce the pressure in the event that the wall temperature falls below a critical value.

[0099] Evaporation of large amounts of ammonia in the injector or on the tube wall can lead to significant subcooling and thermal mechanical stresses. Therefore, controlled evaporation is necessary.

[0100] In particular, the gaseous fuel cleaning mode can be applied when the internal combustion engine is fueled with ammonia, while the liquid fuel cleaning mode can be applied for example for ammonia fuel or methanol liquid fuel.

[0101] The gaseous fuel cleaning mode is less relevant for methanol liquid fuel, since the methanol vapor pressure is much lower.

[0102] According to another aspect of the present application, the object is also achieved by an internal combustion engine having at least one gas cylinder with an inner diameter of at least 200 mm, the internal combustion engine preferably being an internal combustion engine as described above.

[0103] The internal combustion engine comprises a fuel supply system, in particular an ammonia or methanol supply system, having a main fuel tank, a fuel distributor and preferably a pump fluidically arranged between the main fuel tank and the fuel distributor.

[0104] The internal combustion engine comprises a fuel injection system, in particular an ammonia injection system, arranged downstream of the fuel distributor, preferably comprising at least one injection line and at least one injector for each cylinder.

[0105] The internal combustion engine further comprises an isolation valve fluidically arranged between the fuel supply system and the fuel injection system.

[0106] The internal combustion engine comprises a fuel purging system. The fuel purging system comprises: a source of inert gas, preferably N2, fluidically connected or connectable to the fuel injection system; at least one second purging line, preferably each second purging line is fluidically connected to one of the at least one injector and a purging control unit adapted to set a fuel purging mode. In the fuel purging mode, the purging control unit is adapted to direct the inert gas through the fuel supply system and / or the fuel injection system for purging as described above.

[0107] The fuel purging system can comprise a liquid fuel purging system and / or a gaseous fuel purging system as described above.

[0108] According to this aspect of the present invention, the internal combustion engine comprises an injector cooling system. The injector cooling system comprises: a coolant source, for example a coolant, i.e. a coolant, storage tank; a cooling inlet valve fluidically arranged between the coolant source and the fuel injection system; and a cooling control unit.

[0109] Preferably, the coolant is different from the fuel, the coolant source is different from the fuel source and / or the coolant storage tank is different from the fuel tank.

[0110] The cooling inlet line can be connected downstream of the fuel distributor for directing the coolant from the coolant source directly to the injection system. Alternatively, the cooling inlet line can be connected upstream of the fuel distributor or elsewhere in the fuel supply system.

[0111] The cooling control unit is adapted to implement that the coolant is directed through the fuel injection system, in particular through the at least one injection line and the at least one injector, and through the second purging line when the internal combustion engine is in an idle mode and / or in a reserve fuel mode, for example a diesel mode, and in particular when the purging mode is not active. In particular, the cooling control unit is adapted to set the cooling inlet valve to allow the coolant to enter the fuel injection system.

[0112] During the operation with reserve (diesel) fuel, the fuel injection system is idling (i.e. no injection). Thus, the fuel injection system, in particular the injectors, is not cooled by the injected ammonia. Therefore, a circulation of coolant through the injectors can be arranged in order to cool the injectors.

[0113] The second cleaning line can be fluidically connected or fluidically connectable to a coolant source via the cooling outlet line. Thus, a cooling circuit can be established. The cooling circuit can comprise a heat exchanger to remove heat.

[0114] A limited number of injection actions, in particular at least one injection per time unit or a predetermined number of injections, can be performed during the reserve fuel operation of the engine, when the coolant is circulated through the cooling circuit in order to remove deposits which can be formed and / or accumulated in the injection channel of the injector during the reserve fuel operation of the engine.

[0115] During the switch to the reserve fuel operation, the replacement of the fuel with coolant can be accelerated by the injection during the cooling.

[0116] The coolant can be water or ammonia or a water-ammonia mixture, for example aqua ammonia.

[0117] The cleaning tank and / or the collection tank can be the coolant source, preferably a separate coolant tank is provided.

[0118] In order to remove the coolant from the fuel injection system, a cleaning mode can be set similar to the above described modes, in particular similar to the first gaseous fuel cleaning mode and similar to the second liquid fuel cleaning mode.

[0119] For example, when using an ammonia-based coolant and an ammonia-based fuel, the cleaning tank and / or the collection tank can be used to collect the inert gas for cleaning and the flushed coolant. Alternatively, a further collection tank or coolant storage tank can be connected to the cleaning line.

[0120] For example, for a switch from liquid fuel operation to reserve fuel operation, the injection line can be disconnected from the injector.

[0121] The liquid fuel injection can be stopped and then the injector can be cleaned with an inert gas. Subsequently, a fluid connection between the injection system and a coolant storage tank can be established and the injector can be filled with coolant, for example water. Thus, cooling is started after the cleaning and the coolant can be circulated through the injector between the coolant storage tank and the fuel injection system. Any residue remaining in the fuel injection system after the cleaning can be absorbed and / or removed by the coolant.

[0122] Alternatively, when switching from liquid fuel operation to reserve fuel operation, the fuel supply system can be disconnected from the fuel injection system and liquid fuel injection can be stopped. At least one injection action can be performed before stopping the fuel injection in order to reduce the amount of fuel in the fuel injection system. A fluid connection between the injection system and the coolant reservoir can be established.

[0123] The cooling storage can initially be filled with coolant, e.g. with water, and the cooling can be started directly with the coolant. The coolant can achieve to flush out residues of liquid fuel from the fuel injection system and / or to absorb residues of liquid fuel.

[0124] It should be noted that the coolant can be used to clean the fuel supply system and / or the injection system, thereby supplementing or even replacing the fuel cleaning system.

[0125] Alternatively, the coolant reservoir can be filled first with liquid fuel or with liquid fuel that is flushed during the cleaning process.

[0126] After the injection line has been disconnected from the injector, liquid fuel injection can be stopped, a fluid connection between the injection system and the coolant reservoir can be established and the circulation of coolant, in this case liquid fuel, can be started. Then, within a certain time, the liquid fuel is replaced by another coolant, e.g. water, and the cooling is continued with the other coolant. The other coolant can then achieve to flush out residues of liquid fuel from the fuel injection system and / or to absorb residues of liquid fuel.

[0127] When switching from reserve fuel operation to liquid fuel operation, the fluid connection between the fuel injection system and the coolant reservoir can be disconnected first and then the fuel injection system with the injectors can be cleaned with inert gas (N2). Subsequently, the fuel injection system can be filled with liquid fuel. Then, injection of liquid fuel can be started.

[0128] Alternatively, when switching from reserve fuel operation to liquid fuel operation, the fluid connection between the injection line and the coolant reservoir can be disconnected first and a connection between the fuel injection system and the fuel supply system can be established. Subsequently, injection of liquid fuel can be started.

[0129] It will take some time until the coolant in the fuel injection system is replaced by liquid fuel. During this time, a mixture of coolant and liquid fuel is injected into the cylinder. After this time, the injection system is filled with liquid fuel only and the engine operation can continue on liquid fuel.

[0130] Alternatively, when switching from operation on back-up fuel to operation on liquid fuel, the coolant can gradually be replaced by liquid fuel. The cooling circuit can be operated on liquid fuel, e.g. ammonia, before the fluid connection between the injection line and the coolant storage tank is disconnected. The connection between the injection line and the injector can be established and the internal combustion engine can be operated on liquid fuel, such as ammonia.

[0131] The object of the present application is also achieved by a method for operating an internal combustion engine, preferably an internal combustion engine as described above, having at least one cylinder, the inner diameter of which is preferably at least 200 mm. The internal combustion engine comprises a fuel supply system, preferably an ammonia supply system, having a main fuel tank, a fuel distributor and preferably a pump. The internal combustion engine comprises a fuel injection system, preferably an ammonia injection system, which is arranged downstream of the fuel distributor, preferably comprising at least one injection line and at least one injector for each cylinder.

[0132] The method comprises the steps of: providing a high-pressure inert gas, preferably N2; and guiding the high-pressure inert gas through the fuel distributor into the collection tank and thereby transporting liquid fuel from the fuel supply system into the collection tank.

[0133] In this context, "high pressure" means that the inert gas is provided with a pressure of at least 30 bar, in particular 30 to 45 bar.

[0134] Preferably, the liquid fuel from the fuel supply system is guided into the collection tank via a purge valve fluidly arranged between the fuel distributor and the collection tank.

[0135] Preferably, the method comprises the step of: closing a fluid connection between the fuel supply system and the fuel injection system before guiding the high-pressure inert gas through the fuel distributor. Preferably, the fluid connection is closed by setting an isolation valve fluidly arranged between the fuel supply system and the fuel injection system.

[0136] The method can comprise the steps of: providing a low-pressure inert gas, preferably N2, to the fuel injection system; and guiding the low-pressure inert gas through the fuel injection system into the purge tank via at least one second purge line.

[0137] In this context, "low pressure" means that the inert gas is provided with a pressure of 3 to 7 bar.

[0138] Preferably, each second purge line is fluidly connected with one of the at least one injectors. Vaporized gaseous fuel is thereby transported from the fuel injection system into the purge tank.

[0139] Preferably, the method comprises the step of: reducing the pressure in the fuel injection system before and / or during providing the low-pressure inert gas.

[0140] The method can further comprise the steps of providing a high-pressure inert gas, preferably N2, and guiding the high-pressure inert gas through the fuel injection system into the collection tank. Thereby liquid fuel is transported from the fuel injection system into the collection tank.

[0141] Preferably, before or during the transport of the high-pressure inert gas through the fuel injection system, the fluid connection between the fuel supply system and the fuel injection system is opened, preferably by setting an isolation valve.

[0142] The method can further comprise the steps of providing a low-pressure inert gas, preferably N2, and guiding the low-pressure inert gas through the fuel distributor into the cleaning tank, thereby transporting gas fuel evaporated in the fuel supply system into the cleaning tank.

[0143] Preferably, before and / or during the transport of the low-pressure inert gas through the fuel distributor, the pressure in the fuel supply system can be reduced, so that fuel evaporates in the fuel supply system.

[0144] The method can further comprise the step of pumping liquid fuel from the collection tank, preferably via a direct connection pipe, to the fuel distributor. Thereby, fuel previously purged can be reused.

[0145] When a fuel flow is detected at the inlet of the collection tank, the system refilling is stopped.

[0146] Preferably, the described method for operating an internal combustion engine comprises a cleaning sequence with the following consecutive steps.

[0147] In a first step, a first liquid fuel cleaning mode is set to clean the fuel supply system with a high-pressure inert gas.

[0148] In a second optional step, subsequently a second liquid fuel cleaning mode is set to clean the fuel injection system with a high-pressure inert gas.

[0149] As a further step after the first step, or if the second step has been performed, subsequently to the second step, a first gas fuel cleaning mode is set to clean the fuel injection system with a low-pressure inert gas.

[0150] Finally, a second gas fuel cleaning mode is set to clean the fuel supply system with a low-pressure inert gas.

[0151] The high-pressure inert gas can expel liquid fuel from the respective subsystem. Oil residues can also be expelled.

[0152] The low-pressure inert gas enables the evaporation of fuel from corners and edges, in particular in combination with a prior or simultaneous pressure reduction, so that even from small amounts of residual fuel the respective subsystems can be cleaned.

[0153] This facilitates a more efficient purging of fuel residues from the respective system, since the fuel injectors are arranged above the fuel distributor (relative to the gravitational force).

[0154] The object is also achieved by a method for operating an internal combustion engine, preferably the method as described above, the internal combustion engine preferably being the internal combustion engine as described above, said internal combustion engine having an injector cooling system, having at least one cylinder, the inner diameter of the cylinder preferably being at least 200 mm.

[0155] The internal combustion engine comprises a fuel supply system, the fuel supply system having a main fuel tank, a fuel distributor and preferably a pump.

[0156] The internal combustion engine comprises a fuel injection system, the fuel injection system being arranged downstream of the fuel distributor, preferably comprising at least one injection line and at least one injector for each cylinder.

[0157] Preferably, the method comprises the step of providing a cooling agent to the fuel injection system via a cooling inlet valve (i.e. coolant).

[0158] The cooling agent is guided through the fuel injection system when the engine is in idle mode and / or during backup fuel operation.

[0159] During backup fuel operation, the injectors are not cooled by the injected fuel. During liquid fuel (main fuel) operation, the injectors, in particular the nozzles of the injectors, are cooled by the injected fuel.

[0160] During backup fuel operation, the cooling agent can also help to prevent clogging of the injector holes.

[0161] Typically, a dual fuel internal combustion engine is started at regular intervals in backup fuel (diesel) operation. The operation of the cooling system has to be ready before the engine is started and / or in idle mode (no load).

[0162] In particular, the cooling agent is guided via the injection lines, the injectors and at least one second cleaning line, wherein preferably each second cleaning line is in fluid connection with one of the at least one injectors.

[0163] In order to establish a fluid connection between the cooling agent source and the fuel injection system, the cooling inlet line can be connected downstream of the fuel distributor. In this way, the cooling agent can be guided directly from the cooling agent source to the injection lines.

[0164] Preferably, the fluid connection between the fuel supply system and the fuel injection system is closed, preferably by setting an isolating valve fluidly arranged between the fuel supply system and the fuel injection system, before and / or during the coolant is guided through the fuel injection system.

[0165] Alternatively, the cooling inlet line can be connected upstream of the fuel distributor, such that coolant can be guided through the fuel distributor and subsequently into the fuel injection system.

[0166] For example, if the cooling inlet line is connected upstream of the fuel distributor and water is used as coolant, the injector cooling system can be used for pressure testing. For example, during such a pressure test, for example after maintenance of the engine, the fuel line connecting the fuel tank and the fuel distributor can be filled with water. Possible leaks can be detected without using harmful substances.

[0167] The computer program can comprise program code for performing the steps of the method as described above, when the program is executed on a computer of the internal combustion engine as described above.

[0168] The computer program product, which can be directly loadable into the internal memory of a digital computer, can comprise software code portions for performing the steps of the method as described above, when the program is run on a digital computer of the internal combustion engine as described above.

[0169] The computer program product can comprise instructions for causing the computer of the internal combustion engine, in particular a cleaning control unit and / or a cooling control unit, to perform the steps of the method as described above, when the program is executed on the computer of the internal combustion engine. The cleaning control unit and the cooling control unit can be the same or separate control units, or their functions can be implemented in other control systems, such as an engine control unit.

[0170] The computer-readable medium can store such a computer program product.

[0171] In the following, the application will be further explained by means of the following figures in embodiments:

[0172] Figure 1 A schematic diagram illustrating a first example of an internal combustion engine is shown;

[0173] Figure 2 A schematic diagram illustrating a second example of an internal combustion engine is shown;

[0174] Figure 3 A schematic diagram illustrating a third example of an internal combustion engine is shown.

[0175] Figure 1 A schematic diagram illustrating one example of an internal combustion engine 100 is shown.

[0176] The internal combustion engine 100 is a large engine having at least one cylinder 101 with an inner diameter of at least 200 mm.

[0177] The internal combustion engine 100 comprises a fuel supply system 110, in particular an ammonia supply system, having a main fuel tank 111, a fuel distributor 112 and a pump 113 fluidically arranged between the main fuel tank 111 and the fuel distributor 112.

[0178] The internal combustion engine 100 comprises a fuel injection system 120, in particular an ammonia injection system, arranged downstream of the fuel distributor 112, several injection lines 121 being connected to respective injectors 122.

[0179] The isolation valve 9 is fluidically arranged between the fuel supply system 110 and the fuel injection system 120 of a particular cylinder.

[0180] In the common case that the internal combustion engine comprises a plurality of cylinders 101, each cylinder 101 can have a fuel injection system 120. Each fuel injection system 120 can be fluidically connected to or isolated from the fuel supply system 110 by a respective isolation valve 9.

[0181] The internal combustion engine 100 further comprises a fuel cleaning system 125.

[0182] The fuel cleaning system 125 comprises a liquid fuel cleaning system 130 and a gaseous fuel cleaning system 140.

[0183] The liquid fuel cleaning system 130 has a high pressure source 131 of inert gas, preferably N2, preferably having a pressure of more than 30 bar, more preferably 30 to 45 bar, fluidically connectable to at least the fuel supply system 110 upstream of the fuel distributor 112. The high pressure gas supply line 135 merges into the fuel line 115 connecting the fuel tank 111 and the fuel distributor 112.

[0184] The liquid fuel cleaning system 130 comprises a collection tank 132 for receiving and storing liquid fuel that has been flushed out by the high pressure inert gas.

[0185] A first cleaning line 133 with a cleaning valve 134 is used to fluidically connect the fuel distributor 112 and the collection tank 132.

[0186] The fuel cleaning system 125 comprises a cleaning control unit 150 adapted to set a first liquid fuel cleaning mode to clean the fuel supply system 110. In the liquid fuel cleaning mode, the cleaning control unit is adapted to establish a fluid connection between the high pressure source 131 of inert gas and the fuel distributor 112 by providing an open position of the high pressure gas supply valve 136 in the high pressure gas supply line 135. The cleaning control unit 150 is further adapted to establish a fluid connection between the fuel distributor 112 and the collection tank 132, wherein the cleaning valve 134 is arranged to be open such that inert gas from the high pressure source 131 of inert gas is directed through the fuel distributor 112, through the first cleaning line 133 and into the collection tank 132.

[0187] Advantageously, the first cleaning line 133 can be connected to a lower part of the distributor 112 to drain liquid fuel collected in the lower part of the distributor 112.

[0188] The cleaning control unit 150 can be adapted to set the isolation valve 9 to close the connection between the fuel supply system 110 and the fuel injection system 120 before establishing the fluid connection between the high pressure source 131 of inert gas and the fuel distributor 112, such that only the fuel supply system is cleaned.

[0189] The gaseous fuel cleaning system 140 comprises a low pressure source 141 of inert gas, preferably N2, preferably having a pressure of 3 to 7 bar, fluidly connected or connectable to the fuel injection system 120. In this example, a low pressure gas supply line 146 is used to direct the low pressure inert gas into the fuel distributor 112. Alternatively, the low pressure inert gas can be supplied downstream of the fuel distributor 112.

[0190] The gaseous fuel cleaning system 140 comprises a second cleaning line 142, wherein each second cleaning line 142 is fluidly connected with a respective injector 122.

[0191] The gaseous fuel cleaning system 140 comprises a cleaning tank 143 for receiving and storing gaseous fuel.

[0192] The gaseous fuel cleaning system 140 comprises a plurality of pressure reducing valves 12, 103, 145, wherein one pressure reducing valve 12 is fluidly arranged between at least one second cleaning line 142 and the cleaning tank 143.

[0193] The cleaning control unit 150 is adapted to set a first gaseous fuel cleaning mode to clean the fuel injection system 120 with the low pressure inert gas.

[0194] In the first gaseous fuel purging mode, the purging control unit 150 is adapted to reduce the pressure in the fuel injection system 120 by opening at least one of the pressure reducing valves 12, 145, 103, e.g. the purge tank valve 12, so that fuel in the fuel injection system 120 can evaporate.

[0195] In the first gaseous fuel purging mode, after or during evaporation, the purging control unit 150 is adapted to establish a fluid connection between the low pressure source 141 of inert gas and the fuel injection system 120, and the purging control unit 150 is adapted to establish a fluid connection between the fuel injection system 120 and the purge tank 143. Inert gas from the low pressure source 141 of inert gas is directed through the fuel distributor 112 into the fuel injection system 120 and into the purge tank 143.

[0196] In the first gaseous fuel purging mode, the purge valve 134 can be closed so that inert gas from the low pressure source 141 is forced into the fuel injection system 120.

[0197] One of the pressure reducing valves 145 can be connectable to a low pressure reservoir 144 of inert gas. In the first gaseous fuel purging mode, the purging control unit 150 can be adapted to reduce the pressure in the fuel injection system 120 by setting the pressure reducing valve 145 to open to the low pressure reservoir 144 of inert gas.

[0198] The internal combustion engine comprises an SCR catalytic converter 102, and one of the pressure reducing valves is an SCR valve 103 fluidly arranged between at least the second purging line 142 and the SCR catalytic converter 102. The purging control unit 150 can be adapted to set the SCR valve 103 to open to release pressure and allow fuel to exit the fuel injection system 120 and enter the SCR catalytic converter 102.

[0199] While in the first liquid fuel purging mode high pressure inert gas is directed through the fuel supply system 110, and in the first gaseous fuel purging mode low pressure inert gas is directed through the fuel injection system 120, in the second liquid fuel purging mode high pressure inert gas can be directed through the fuel injection system 120, and in the second gaseous fuel purging mode low pressure inert gas can be directed through the fuel supply system 110.

[0200] In the second liquid fuel purging mode, a fluid connection can be established between the high pressure source 131 of inert gas and the fuel injection system 120, and a fluid connection can be established between the fuel injection system 120 and the collection tank 132.

[0201] The isolation valve 9 can be set to open a connection between the fuel supply system 110 and the fuel injection system 120, in particular the fuel injection system of the particular cylinder 101, so that the high pressure inert gas can enter the fuel injection system 120 via the fuel distributor 112. The purge valve 134 can be set to close a connection between the fuel distributor 112 and the first purge line 133, so that the high pressure inert gas is forced into the fuel injection system 120.

[0202] In the second gaseous fuel purge mode, a fluid connection is established between the low pressure source 141 of inert gas and the fuel supply system 110 and a fluid connection is established between the fuel supply system 110 and the purge tank 143. Preferably, in the second gaseous fuel purge mode, the isolation valve 9 is set to close the connection between the fuel supply system 110 and the fuel injection system 120.

[0203] During the purge process, the purge control unit 150 can be adapted to close a fluid connection between the main fuel tank 111 and the fuel distributor 112, in particular by setting a fill valve 114 arranged in the fuel line 115 accordingly.

[0204] At least one sensor 123 is arranged in the fuel injection system 120 for providing data indicative of a fuel concentration and / or a fuel content in the fuel injection system 120.

[0205] The internal combustion engine 100 comprises a direct connection pipe 2 for directly connecting the collection tank 132 and the fuel distributor 112, so that fuel collected from the collection tank can be supplied to the fuel distributor 112 and liquid fuel collected during the purge process can be used for operating the internal combustion engine 100.

[0206] The first purge line 133 and the second purge line 142 merge into a purge line 126, which divides into a line to the collection tank 132 and a line to the purge tank 143. An upstream side of the purge line 126 is connected or connectable to the first purge line 133 or the second purge line 142 and a downstream side of the purge line 126 is connected or connectable to the collection tank 132 and / or the purge tank 143.

[0207] The purge line 126 comprises several valves for preventing backflow into the fuel injection system 120, the fuel supply system 110 and / or an injector cooling system 300 (see below).

[0208] The internal combustion engine 100 further comprises an injector cooling system 300 comprising a coolant storage tank 303 as a coolant source and a cooling inlet valve 306 fluidically arranged in a cooling inlet line 307 between the coolant storage tank 303 and the fuel injection system 120.

[0209] The injector cooling system 300 comprises a cooling control unit 304 adapted to set the cooling inlet valve 306 and preferably the coolant pump 301 to allow coolant to enter the fuel injection system 120 when the internal combustion engine 100 is in idle mode and / or during reserve fuel operation.

[0210] The coolant can be guided through at least one injection line 121 and at least one respective injector 122 and through the second purge line 142. Since the cooling inlet line 307 can be directly connected to the fuel injection system 120, each fuel injection system 120 can be cooled individually. In particular, the cooling inlet valve 306 can be combined with the isolation valve 9.

[0211] The injector cooling system 300 comprises a cooling outlet line 305 fluidically arranged between the second purge line 142 and the coolant source 303 to establish a coolant circuit.

[0212] The coolant pump 301 can be arranged downstream of the coolant storage tank 303 or anywhere else in the coolant circuit. A heat exchanger is arranged upstream of the coolant storage tank 303 (in this particular context, the terms “upstream” and “downstream” refer to the direction of flow of the coolant). If necessary, the coolant storage tank 303 can be refilled.

[0213] During the cooling process, preferably no purge mode is activated.

[0214] A bleed line is arranged between the fuel distributor 112 and the purge tank 143 and between the cooling inlet line 307 and the purge tank 143. These bleed lines can be closed and opened by corresponding valves.

[0215] The bleed lines can allow to vent inert gas remaining in the system during or after refilling.

[0216] Figure 2 A schematic diagram of a second example of an internal combustion engine 100 is shown. Figure 1

[0217] In the first example according to Figure 1 , high and low pressure inert gas can be guided into the fuel distributor 112 via the fuel line 115. The high and low pressure inert gas is guided essentially in the same way as the liquid fuel, so that the fuel injection system 120 can be purged downstream.

[0218] In contrast, in the second example as shown in Figure 2 , the fuel injection system 120 can be purged with low pressure inert gas in the upstream direction. ​

[0219] Inert gas from the low pressure source 141 can be directed into the fuel injection system 120 via the second purge line 142.

[0220] Inert gas from the low pressure source 141 can be directed directly to the second purge line 142 via a further second purge line 147.

[0221] During the first and second gaseous fuel purge mode, inert gas and gaseous fuel can be directed via the isolation valve 9 to the fuel distributor 112 and from the fuel distributor 112 to the purge tank 143 and / or the SCR catalytic converter 102 (not shown in the figure).

[0222] Figure 3 A schematic drawing of a third example of an internal combustion engine 100 is shown. Figure 1

[0223] The internal combustion engine 100 further comprises an injector cooling system 300 having a coolant storage tank 303, a cooling inlet valve 306 fluidly arranged in a cooling inlet line 307. In this example, the cooling inlet line 307 can be fluidly connected to the fuel line 115, such that coolant is directed through the fuel distributor 112. When the respective isolation valve 9 is open, all fuel injection systems 120 can be cooled simultaneously.

[0224] This arrangement is advantageous in case it is not possible or not allowed to place the cooling inlet valve 306 in the engine room, in the vicinity of the cylinder 101.

[0225] Aspects of the invention are disclosed by the following clauses.

[0226] Clause 1

[0227] An internal combustion engine (100) having at least one cylinder (101) with an inner diameter of at least 200 mm, the internal combustion engine (100) comprising:

[0228] - a fuel supply system (110), in particular an ammonia supply system, having a main fuel tank (111), a fuel distributor (112) and, preferably, a pump (113) fluidly arranged between the main fuel tank (111) and the fuel distributor (112); and

[0229] - a fuel injection system (120), in particular an ammonia injection system, arranged downstream of the fuel distributor (112), preferably comprising at least one injection line (121) and at least one injector (122) for each cylinder (101); ​

[0230] - at least one isolating valve (9) fluidly arranged between the fuel supply system (110) and the fuel injection system (120);

[0231] - the internal combustion engine (100) further comprises a fuel flushing system (125) comprising at least a liquid fuel flushing system (130) having:

[0232] a high pressure source (131) of inert gas, preferably N2, preferably having a pressure of more than 30 bar, more preferably 30 to 35 bar, fluidly connected or fluidly connectable to at least the fuel supply system (110), preferably upstream of the fuel distributor (112);

[0233] a collection tank (132) for receiving and storing liquid fuel;

[0234] a first flushing line (133) fluidly connected or fluidly connectable to the fuel distributor (112) via a flushing valve (134) for establishing a fluid connection between the fuel supply system (110) and the collection tank (132), more preferably the first flushing line (133) comprises a flushing valve (134),

[0235] - the fuel flushing system (125) comprises a flushing control unit (150) adapted to set a first liquid fuel flushing mode for flushing the fuel supply system (110),

[0236] wherein the flushing control unit is adapted to establish a fluid connection between the high pressure source (131) of inert gas and the fuel distributor (112), and

[0237] wherein the flushing control unit (150) is adapted to establish a fluid connection between the fuel distributor (112) and the collection tank (132) such that inert gas from the high pressure source (131) of inert gas is directed through the fuel distributor and into the collection tank,

[0238] wherein preferably the cleaning control unit (150) is adapted to set the isolation valve (9) to close the connection between the fuel supply system (110) and the fuel injection system (120) before establishing the fluid connection between the high pressure source (131) of inert gas and the fuel distributor (112).

[0239] Clause 2

[0240] The internal combustion engine (100) according to clause 1, wherein the fuel cleaning system (125) comprises a gaseous fuel cleaning system (140) having:

[0241] a low pressure source (141) of inert gas, preferably N2, preferably having a pressure of 3 to 7 bar, fluidly connected or fluidly connectable to the fuel injection system (120), in particular via the isolation valve (9);

[0242] at least one second cleaning line (142), preferably each cleaning line (142) is fluidly connected with one of the at least one injector (122);

[0243] a cleaning tank (143) for receiving and storing gaseous fuel;

[0244] preferably at least one pressure reduction valve (12, 145, 103), in particular a cleaning tank valve (12), fluidly arranged in the at least one cleaning line (142) upstream of the cleaning tank (143),

[0245] - and wherein the cleaning control unit (150) is adapted to set a first gaseous fuel cleaning mode to clean the fuel injection system (120),

[0246] wherein the cleaning control unit (150) is adapted to reduce the pressure in the fuel injection system (120) such that fuel in the fuel injection system (120) can evaporate,

[0247] wherein the cleaning control unit is adapted to establish a fluid connection between the low pressure source (141) of inert gas and the fuel injection system (120), and

[0248] wherein the washing control unit (150) is adapted to establish a fluid connection between the fuel injection system (120) and the washing tank (143) such that inert gas from the low-pressure source (141) of inert gas is directed through the fuel injection system (120) and into the washing tank (143).

[0249] Clause 3

[0250] The internal combustion engine (100) according to clause 2, wherein the pressure reduction valve (145) is connectable to a low-pressure reservoir (144) of inert gas, and

[0251] wherein, in a first gaseous fuel washing mode, the washing control unit (150) is adapted to reduce the pressure in the fuel injection system (120) by setting the pressure reduction valve (145) to open to the low-pressure reservoir (144) of inert gas.

[0252] Clause 4

[0253] The internal combustion engine (100) according to clause 2, wherein the internal combustion engine (100) comprises an SCR catalytic converter (102) and an SCR valve (103) fluidly arranged between the at least second washing line (142) and the SCR catalytic converter (102),

[0254] wherein the washing control unit (150) is adapted to set the SCR valve (103) to open to release pressure and to allow fuel to exit the fuel injection system (120) and enter the SCR catalytic converter (102), and in particular to close the fluid connection between the second washing line and the washing tank.

[0255] Clause 5

[0256] The internal combustion engine (100) according to at least one of the preceding clauses, wherein the washing control unit (150) is adapted to set a second liquid fuel washing mode to wash the fuel injection system (120), in particular simultaneously or subsequently to the first liquid fuel washing mode,

[0257] wherein the washing control unit is adapted to establish a fluid connection between the high-pressure source (131) of inert gas and the fuel injection system (120), and

[0258] wherein the cleaning control unit (150) is adapted to establish a fluid connection between the fuel injection system (120) and the collection tank (132) and / or a fluid connection between the fuel injection system (120) and the cleaning tank (143) such that inert gas from the high-pressure source of inert gas (131) is directed through the fuel injection system (120) and into the collection tank and / or the cleaning tank.

[0259] Clause 6

[0260] The internal combustion engine (100) according to clause 5, wherein the cleaning control unit (150) is adapted to set the isolation valve (9) so as to open a connection between the fuel supply system (110) and the fuel injection system (120) and so as to open a connection between the high-pressure source of inert gas (131) and the fuel injection system (120) such that high-pressure inert gas is accessible to the fuel injection system (120) via the fuel supply system (110) and the isolation valve (9), wherein preferably the cleaning control unit (150) is adapted to set the cleaning valve (134) so as to close a connection between the fuel distributor (112) and the first cleaning line (133).

[0261] Clause 7

[0262] The internal combustion engine (100) according to clause 2, wherein the cleaning control unit (150) is adapted to set a second gaseous fuel cleaning mode for cleaning the fuel supply system (110) after the first liquid fuel cleaning mode,

[0263] wherein the cleaning control unit (150) is adapted to establish a fluid connection between the low-pressure source of inert gas (141) and the fuel supply system (110) and

[0264] wherein the cleaning control unit (150) is adapted to establish a fluid connection between the fuel supply system (110) and the cleaning tank (143).

[0265] Clause 8

[0266] The internal combustion engine (100) according to at least one of the preceding clauses, wherein the internal combustion engine (100) comprises a sensor (123) for providing data indicative of a fuel concentration in the fuel injection system (120).

[0267] Clause 9

[0268] The internal combustion engine (100) according to clause 2, wherein the internal combustion engine comprises more than one cylinder (101), and

[0269] wherein, in the first gaseous fuel flushing mode, the flushing control unit (150) is adapted to flush only a part of the fuel injection system (120) related to a part of the cylinders (101), while other cylinders are still in operation.

[0270] Clause 10

[0271] The internal combustion engine (100) according to at least one of the preceding clauses, wherein the internal combustion engine comprises a direct connection pipe (2) for directly connecting the collecting tank (132) and the fuel distributor (112) such that fuel collected from the collecting tank can be supplied to the fuel distributor (112).

[0272] Clause 11

[0273] The internal combustion engine (100) according to at least one of the clauses 2 to 10, wherein the flushing tank (143) contains water for absorbing fuel, in particular ammonia, in use, or the flushing tank (143) is connected or connectable to an absorption stage containing water.

[0274] Clause 12

[0275] The internal combustion engine (100) according to at least one of the clauses 2 to 10, wherein:

[0276] - the flushing tank (143) and / or the collecting tank (132) comprises, is connected to or connectable to a fuel trapping system, such as an acid scrubbing device or an air dilution device, and / or

[0277] - the flushing tank (143) and / or the collecting tank (132) is connected to or connectable to the cylinder (101) and / or an SCR reactor (102).

[0278] Clause 13

[0279] An internal combustion engine (100) having at least one cylinder (101) with an inner diameter of at least 200 mm, the internal combustion engine (100) being preferably an internal combustion engine according to at least one of the preceding clauses, the internal combustion engine (100) comprising:

[0280] - a fuel supply system (110), in particular an ammonia supply system, having a main fuel tank (111), a fuel distributor (112) and preferably a pump fluidically arranged between the main fuel tank (111) and the fuel distributor (112); and

[0281] - a fuel injection system (120), in particular an ammonia injection system, arranged downstream of the fuel distributor (112), preferably comprising at least one injection line (121) and at least one injector (122) for each cylinder (101);

[0282] - in particular, an isolation valve ("9") fluidically arranged between the fuel supply system (110) and the fuel injection system (120);

[0283] The internal combustion engine (100) further comprises:

[0284] - a fuel cleaning system (130) comprising:

[0285] a source (131) of inert gas, preferably N2, fluidically connected or connectable to the fuel injection system (120);

[0286] at least one second cleaning line (142), preferably each cleaning line (142) is fluidically connected with one of the at least one injector (122);

[0287] a cleaning control unit (150) setting a fuel cleaning mode,

[0288] - and the internal combustion engine (100) comprises an injector cooling system (300) comprising:

[0289] a coolant source (303);

[0290] a cooling inlet valve (306) fluidically arranged between the coolant source (303) and the fuel injection system (120);

[0291] a cooling control unit (304) adapted to enable guiding coolant through the fuel injection system (120), in particular through the at least one injection line (121) and the at least one injector (122), and through a purge line (142), in particular when the internal combustion engine (100) is in idle mode or when the internal combustion engine (100) is operated on backup fuel, and to set the cooling inlet valve (301) to allow coolant to enter the fuel injection system (120), in particular when a purge mode is not activated.

[0292] Clause 14

[0293] The internal combustion engine (100) according to clause 13, wherein the injector cooling system (300) comprises a cooling outlet line (305) fluidly arranged between the purge line (142) and the coolant source (301) to establish a coolant circuit.

[0294] Clause 15

[0295] A method for operating an internal combustion engine (100), preferably according to any one of clauses 1 to 14, the internal combustion engine (100) having at least one cylinder (101) with an inner diameter of preferably at least 200 mm, the internal combustion engine (100) comprising a fuel supply system (110), preferably an ammonia supply system (110), having a main fuel tank (111), a fuel distributor (112), and preferably a pump (113), and a fuel injection system (120), preferably an ammonia injection system (120), arranged downstream of the fuel distributor (112), preferably comprising at least one injection line (121) and at least one injector (122) for each cylinder (101),

[0296] The method comprises the following steps:

[0297] - preferably by setting an isolation valve (9) fluidly arranged between the fuel supply system (110) and the fuel injection system (120), preferably closing a fluid connection between the fuel supply system (110) and the fuel injection system (120);

[0298] - providing a high-pressure inert gas, preferably N2;

[0299] - guiding the high-pressure inert gas through the fuel distributor (112) into a collection tank (132) and thereby transporting liquid fuel from the fuel supply system (110), preferably via a purge valve (134) fluidly arranged between the fuel distributor (112) and the collection tank (132), into the collection tank (132).

[0300] Clause 16

[0301] The method according to clause 15, further comprising the steps of:

[0302] - preferably reducing the pressure in the fuel injection system (120);

[0303] - providing a low-pressure inert gas to the fuel injection system (120), the low-pressure inert gas being preferably N2;

[0304] - guiding the low-pressure inert gas through the fuel injection system (120) via at least one purge line (142) into a purge tank (143) and thereby transporting gaseous fuel evaporated in the fuel injection system (120) into the purge tank (143), wherein preferably each purge line (142) is fluidly connected with one of the at least one injector (122).

[0305] Clause 17

[0306] The method according to clause 15 or 16, comprising the steps of:

[0307] - providing a high-pressure inert gas, the high-pressure inert gas being preferably N2;

[0308] - preferably by setting the first purge valve ("9"), preferably opening a fluid connection between the fuel supply system (110) and the fuel injection system (120);

[0309] - guiding the high-pressure inert gas through the fuel injection system (120) into the collection tank (132) and / or the purge tank (143) and thereby transporting liquid fuel from the fuel injection system (120) into the collection tank (132) and / or the purge tank (143).

[0310] Clause 18

[0311] The method according to clause 15, 16 or 17, comprising the steps of:

[0312] - preferably reducing the pressure in the fuel supply system (110) such that fuel evaporates in the fuel supply system (110);

[0313] - providing a low-pressure inert gas, preferably N2;

[0314] - guiding the low-pressure inert gas through the fuel distributor (112) into a washing tank (143), thereby transporting gaseous fuel evaporated in the fuel supply system (110) into the washing tank (143).

[0315] Clause 19

[0316] The method according to any one of clauses 15 to 18, comprising the steps of:

[0317] - pumping liquid fuel from the collecting tank (132), preferably via a direct connection pipe (2), to the fuel distributor (112).

[0318] Clause 20

[0319] A method for operating an internal combustion engine (100), preferably according to one of clauses 15 to 19, the internal combustion engine (100) being preferably according to clause 13, the internal combustion engine (100) having at least one cylinder (101) with an inner diameter of preferably at least 200 mm, the internal combustion engine (100) comprising a fuel supply system (110) having a main fuel tank (111), a fuel distributor (112) and preferably a pump, and a fuel injection system (120) arranged downstream of the fuel distributor (112), the fuel injection system (120) preferably comprising at least one injection line (121) and at least one injector (122) for each cylinder (101),

[0320] The method comprising the steps of:

[0321] - preferably closing a fluid connection between the fuel supply system (110) and the fuel injection system (120) by setting an isolating valve (9) fluidically arranged between the fuel supply system (110) and the fuel injection system (120);

[0322] - providing coolant to the fuel injection system (120), preferably via a cooling inlet valve (306);

[0323] - guiding coolant through the fuel injection system (120), in particular via the injection lines (121), the injectors (122) and at least one washing line (142), while the internal combustion engine is in idle mode, wherein preferably each washing line (142) is fluidically connected with one of the at least one injectors (122).

[0324] Clause 21

[0325] A computer program comprising program code means adapted to perform the steps of the method according to at least one of the clauses 15 to 20 when said program is executed on a computer of an internal combustion engine according to at least one of the clauses 1 to 14.

[0326] Clause 22

[0327] A computer program product directly loadable into the internal memory of a digital computer, comprising software code portions adapted to perform the steps of the method according to at least one of the clauses 15 to 20 when said program is run on a digital computer of an internal combustion engine according to at least one of the clauses 1 to 14.

[0328] Remark:

[0329] Any embodiment described in relation to the apparatus should be similarly applicable to the method and the computer program product. Synergistic effects can result from different combinations of embodiments, even if they can not have been described in detail.

[0330] While the current preferred embodiments of the application have been shown and described, it is to be clearly understood that the application is not limited to the same, but can be otherwise variously embodied and practiced within the scope of the following claims.

Claims

1. An internal combustion engine (100) having at least one cylinder (101) with an inner diameter of at least 200 mm, the internal combustion engine (100) comprising: - Fuel supply system (110), the fuel supply system (110) having a main fuel tank (111) and a fuel distributor (112). - Fuel injection system (120), the fuel injection system (120) being arranged downstream of the fuel distributor (112), the fuel injection system (120) including at least one injection line (121) and at least one injector (122) for each cylinder (101). - Isolation valve (9), said isolation valve (9) being fluidly arranged between said fuel supply system (110) and said fuel injection system (120); and - A fuel cleaning system (125), the fuel cleaning system (125) including a liquid fuel cleaning system (130), the liquid fuel cleaning system (130) having: An inert gas high-pressure source (131) preferably has a pressure greater than 30 bar, and the inert gas high-pressure source (131) is fluidly connected to or can be fluidly connected to the fuel supply system (110) upstream of the fuel distributor (112). Collection tank (132) for receiving and storing liquid fuel; and A first cleaning line (133), which is fluidly connected to or can be fluidly connected to the fuel distributor (112) via a cleaning valve (134), is used to establish a fluid connection between the fuel supply system (110) and the collection tank (132). The fuel cleaning system (125) includes a cleaning control unit (150), which is configured to set a first liquid fuel cleaning mode for cleaning the fuel supply system (110), such that: - Establish a fluid connection between the inert gas high-pressure source (131) and the fuel distributor (112); - Establish a fluid connection between the fuel distributor (112) and the collection tank (132) so that inert gas from the inert gas high-pressure source (131) is guided through the fuel distributor (112) and into the collection tank (132); and - Preferably, the isolation valve (9) is set to close the connection between the fuel supply system (110) and the fuel injection system (120) before establishing a fluid connection between the inert gas high-pressure source (131) and the fuel distributor (112).

2. The internal combustion engine (100) according to claim 1, wherein, The fuel cleaning system (125) includes a gaseous fuel cleaning system (140), which has: An inert gas low-pressure source (141), preferably having a pressure of 3 to 7 bar, is fluidly connected to or can be fluidly connected to the fuel injection system (120). At least one second cleaning line (142), each second cleaning line (142) being fluidly connected to said injector (122); and Cleaning tank (143) for receiving and storing gaseous fuels. The cleaning control unit (150) is configured to set a first gaseous fuel cleaning mode for cleaning the fuel injection system (120), such that: Reduce the pressure in the fuel injection system (120) to cause the fuel in the fuel injection system (120) to evaporate; Establish a fluid connection between the inert gas low-pressure source (141) and the fuel injection system (120); and A fluid connection is established between the fuel injection system (120) and the cleaning tank (143) so that inert gas from the low-pressure inert gas source (141) is guided through the fuel injection system (120) and into the cleaning tank (143).

3. The internal combustion engine (100) according to claim 2, wherein, The pressure reducing valves (12, 145) of the gaseous fuel cleaning system (140) can be connected to the cleaning tank (143) and / or a separate inert gas low-pressure reservoir (144), and In the first gas fuel cleaning mode, the cleaning control unit (150) is configured to reduce the pressure in the fuel injection system (120) by setting the pressure reducing valve (145) to open to the cleaning tank (143) and / or to the separate inert gas low-pressure reservoir (144).

4. The internal combustion engine (100) according to any one of claims 2 to 3, the internal combustion engine (100) comprising an SCR catalytic converter (102) and an SCR valve (103) fluidly disposed between the at least second cleaning line (142) and the SCR catalytic converter (102), wherein, The cleaning control unit (150) is configured to: set the SCR valve (103) to open to release pressure; and set the amount of gaseous fuel leaving the fuel injection system (120) and entering the SCR catalytic converter (102), and in particular, the cleaning control unit (150) is configured to close the fluid connection between the second cleaning line (142) and the cleaning tank (143) so that all gaseous fuel is directed into the SCR catalytic converter (102).

5. The internal combustion engine (100) according to any one of the preceding claims, wherein, The cleaning control unit (150) is configured to set a second liquid fuel cleaning mode for cleaning the fuel injection system (120), particularly simultaneously with or after the first liquid fuel cleaning mode, such that: Establish a fluid connection between the inert gas high-pressure source (131) and the fuel injection system (120); and Establish a fluid connection between the fuel injection system (120) and the collection tank (132) and / or between the fuel injection system (120) and the cleaning tank (143). This causes the inert gas from the high-pressure inert gas source (131) to be guided through the fuel injection system (120) and into the collection tank (132) and / or into the cleaning tank (143).

6. The internal combustion engine (100) according to claim 5, wherein, The cleaning control unit (150) is configured to set the isolation valve (9) to open the connection between the fuel supply system (110) and the fuel injection system (120), and to open the connection between the inert gas high-pressure source (131) and the fuel injection system (120), so that inert gas from the high-pressure source (131) enters the fuel injection system (120) via the fuel supply system (110) and the isolation valve (9), wherein, preferably, the cleaning control unit (150) is configured to set the cleaning valve (134) to close the connection between the fuel distributor (112) and the first cleaning line (133).

7. The internal combustion engine (100) according to any one of claims 2 to 6, wherein, The cleaning control unit (150) is configured to set a second gaseous fuel cleaning mode for cleaning the fuel supply system (110) after the first liquid fuel cleaning mode, such that: Establish a fluid connection between the inert gas low-pressure source (141) and the fuel supply system (110); and Establish a fluid connection between the fuel supply system (110) and the cleaning tank (143).

8. The internal combustion engine (100) according to any one of the preceding claims, wherein the internal combustion engine (100) comprises at least one of the following: - A first sensor (123), the first sensor (123) being used to provide data representing the fuel concentration in the fuel injection system (120); and - A second sensor, the second sensor being used to provide data representing the fuel concentration in the fuel supply system (110), and in, The cleaning control unit (150) is configured to receive the data provided by the first sensor and / or the second sensor, and is configured to determine, based on the data, whether the corresponding cleaning mode must be maintained or repeated.

9. The internal combustion engine (100) according to any one of claims 2 to 8, wherein, The internal combustion engine includes more than one cylinder (101), and In the first gas fuel cleaning mode, the cleaning control unit (150) is configured to clean only a portion of the fuel injection system (120) associated with a subset of the cylinders (101), while the other cylinders remain in operation.

10. The internal combustion engine (100) according to any one of the preceding claims, the internal combustion engine (100) including a direct connection pipe (2) for directly connecting the collection tank (132) and the fuel distributor (112) such that fuel collected from the collection tank can be supplied to the fuel distributor (112).

11. The internal combustion engine (100) according to any one of claims 2 to 10, wherein, The cleaning tank (143) contains water for absorbing fuel during use, or the cleaning tank (143) is connected to or can be connected to an absorption stage containing water.

12. The internal combustion engine (100) according to any one of claims 2 to 10, wherein, - The cleaning tank (143) and / or the collection tank (132) include components connected to or capable of being connected to a fuel capture system, particularly an acid scraper or an air dilution device, and / or - The cleaning tank (143) and / or the collection tank (132) are connected to or can be connected to the cylinder (101) and / or the SCR catalytic converter (102).

13. An internal combustion engine (100) having at least one cylinder (101) with an inner diameter of at least 200 mm, the internal combustion engine (100) preferably being the internal combustion engine according to any one of the preceding claims, the internal combustion engine (100) comprising: - Fuel supply system (110), the fuel supply system (110) having a main fuel tank (111) and a fuel distributor (112). - Fuel injection system (120), the fuel injection system (120) being arranged downstream of the fuel distributor (112), the fuel injection system (120) including at least one injection line (121) and at least one injector (122) for each cylinder (101). - Isolation valve (9), which is fluidly arranged between the fuel supply system (110) and the fuel injection system (120); and - A fuel cleaning system (130), the fuel cleaning system (130) comprising: An inert gas source (131) is fluidly connected to or can be fluidly connected to the fuel injection system (120). At least one second cleaning line (142), each second cleaning line (142) being fluidly connected to an injector (122); and A cleaning control unit (150) is configured to set a fuel cleaning mode. Furthermore, the internal combustion engine (100) further includes: - An injector cooling system (300), the injector cooling system (300) comprising: Coolant source (303); A cooling inlet valve (306) is fluidly disposed between the coolant source (303) and the fuel injection system (120); A cooling control unit (304) is configured to set the cooling inlet valve (301) to allow coolant to enter the fuel injection system (120) in order to guide coolant through the fuel injection system (120).

14. The internal combustion engine (100) according to claim 13, wherein, The internal combustion engine (100) is configured such that when the fuel cleaning mode is not activated, particularly when the internal combustion engine (100) is in idle mode or when the internal combustion engine (100) is operating on standby fuel, coolant can be directed through the at least one injection line (121), the at least one injector (122) and the second cleaning line (142).

15. The internal combustion engine (100) according to any one of claims 13 or 14, wherein, The injector cooling system (300) includes a cooling outlet line (305) which is fluidly arranged between the second cleaning line (142) and the coolant source (303) to establish a coolant loop.

16. The internal combustion engine (100) according to any one of the preceding claims, wherein the internal combustion engine (100) is configured to use ammonia as fuel.

17. A method for operating an internal combustion engine (100), preferably an internal combustion engine (100) according to any one of claims 1 to 16, the internal combustion engine (100) having at least one cylinder (101) with an inner diameter of at least 200 mm, the internal combustion engine (100) comprising: - Fuel supply system (110), the fuel supply system (110) having a main fuel tank (111) and a fuel distributor (112). - A fuel injection system (120) is arranged downstream of the fuel distributor (112), the fuel injection system (120) including at least one injection line (121) and at least one injector (122) for each cylinder (101). The method includes the following steps: - Preferably, the fluid connection between the fuel supply system (110) and the fuel injection system (120) is closed; - Provide a high-pressure inert gas, preferably having a pressure greater than 30 bar; - The high-pressure inert gas is guided through the fuel distributor (112) into the collection tank (132), thereby delivering liquid fuel from the fuel supply system (110) to the collection tank (132).

18. The method of claim 17, further comprising the step of: - Reduce the pressure in the fuel injection system (120) to cause the fuel in the fuel injection system (120) to evaporate; - A low-pressure inert gas is supplied to the fuel injection system (120), the low-pressure inert gas preferably having a pressure of 3 to 7 bar; - The low-pressure inert gas is guided through the fuel injection system (120) into the cleaning tank (143) via at least one second cleaning line (142), thereby delivering the gaseous fuel evaporated in the fuel injection system (120) to the cleaning tank (143), each second cleaning line (142) being fluidly connected to an injector (122).

19. The method according to any one of claims 17 or 18, the method comprising the following steps: - Preferably, the fluid connection between the fuel supply system (110) and the fuel injection system (120) is opened; - The high-pressure inert gas is guided through the fuel injection system (120) into the collection tank (132) and / or the cleaning tank (143), thereby delivering liquid fuel from the fuel injection system (120) to the collection tank (132) and / or the cleaning tank (143).

20. The method according to any one of claims 17 to 19, the method comprising the following steps: - Reduce the pressure in the fuel supply system (110) so that the fuel evaporates in the fuel supply system (110); - Provide a low-pressure inert gas, preferably having a pressure of 3 to 7 bar; - The low-pressure inert gas is guided through the fuel distributor (112) into the cleaning tank (143), thereby delivering the gaseous fuel evaporated in the fuel supply system (110) to the cleaning tank (143).

21. The method according to any one of claims 17 to 20, the method for operating the internal combustion engine (100) according to claims 1, 2, 5 and 7, the method comprising the following sequential steps: - Set the first liquid fuel cleaning mode to clean the fuel supply system (110) with high-pressure inert gas. - Preferably, the second liquid fuel cleaning mode is set to clean the fuel injection system (120) with high-pressure inert gas. - Set the first gaseous fuel cleaning mode to clean the fuel injection system (120) with low-pressure inert gas. - Preferably, the second gaseous fuel cleaning mode is set to clean the fuel supply system (110) with low-pressure inert gas.

22. The method according to any one of claims 17 to 21, the method comprising the following steps: - Liquid fuel is pumped from the collection tank (132), preferably via a direct connection pipe (2), to the fuel dispenser (112).

23. A method for operating an internal combustion engine (100), the method preferably being the method according to any one of claims 17 to 22, the internal combustion engine (100) preferably being the internal combustion engine (100) according to any one of claims 13 to 16, the internal combustion engine (100) having at least one cylinder (101) with an inner diameter of at least 200 mm, the internal combustion engine (100) comprising: - Fuel supply system (110), the fuel supply system (110) having a main fuel tank (111) and a fuel distributor (112). - A fuel injection system (120) is arranged downstream of the fuel distributor (112), the fuel injection system (120) including at least one injection line (121) and at least one injector (122) for each cylinder (101). The method includes the following steps: - Preferably, coolant is supplied to the fuel supply system (110) via a cooling inlet valve (306); - Especially when the internal combustion engine is in idle mode, coolant is directed through the fuel injection system (120).

24. The method according to claim 23, wherein, Coolant is supplied to the fuel injection system (120), and the method includes the following steps: - Before guiding coolant through the fuel injection system (120), shut off the fluid connection between the fuel supply system (110) and the fuel injection system (120).

25. The method according to any one of claims 23 to 24, wherein, The step of guiding coolant through the fuel injection system (120) is performed via the injection line (121), the injector (122) and at least one second cleaning line (142), wherein each second cleaning line (142) is fluidly connected to an injector (122).

26. The method according to any one of claims 23 to 25, the method comprising the following steps: In particular, after maintaining the internal combustion engine (100), the injector cooling system (300) is used for pressure testing.

27. The method according to any one of claims 23 to 26, the method comprising the following steps: In particular, when the internal combustion engine (100) is in idle mode or when the internal combustion engine (100) is operating on standby fuel, coolant is injected into the cylinder (101) through the injector (122).

28. A computer program product comprising instructions that, when executed on a computer of an internal combustion engine according to any one of claims 1 to 16, cause the computer of the internal combustion engine (100) to perform the steps of the method according to any one of claims 17 to 27, wherein the computer is in particular a cleaning control unit (150) and / or a cooling control unit (304).

29. A computer-readable medium on which a computer program product according to claim 28 is stored.

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