Internal combustion engine and methods for operating an internal combustion engine

Abstract

The invention relates to an internal combustion engine (10) having at least one main combustion chamber (12) and a gas supply system (30) for supplying a gaseous fuel (90) to the at least one main combustion chamber (12). The main combustion chamber (12) is delimited by a combustion chamber wall (20), in particular a combustion chamber wall (20) in a cylinder head (14), wherein a spark plug (52) is inserted into an opening (51) in the combustion chamber wall (20). The spark plug (52) is designed as an active pre-chamber spark plug (52) and has a first ignition electrode (22), a second ignition electrode (24), and an electrode gap (26) formed between the ignition electrodes (22, 24). The spark plug (52) further comprises a cap (46) which delimits a pre-combustion chamber (48) in which the ignition electrodes (22, 24) are arranged, wherein the pre-combustion chamber (48) is fluidically connected to the main combustion chamber (12) by at least one outlet opening (42, 43, 44).In addition, the spark plug (52) has a supply device (31) for supplying the gaseous fuel into the pre-combustion chamber (48). The invention further relates to a spark plug (52), a control unit (80) and a method for operating such an internal combustion engine (10).

Description

[0001] The invention relates to an internal combustion engine with a device for the direct supply of a gaseous fuel into a combustion chamber of the internal combustion engine and a pre-chamber spark plug arranged on the combustion chamber, as well as a method for operating such an internal combustion engine according to the preamble of the independent patent claims.

[0002] In principle, internal combustion engines powered by a combustible gas, such as natural gas or hydrogen, are known from the state of the art. Hydrogen-powered vehicles, in particular, have not yet gained widespread acceptance, partly due to the lack of infrastructure for refueling hydrogen. Currently, there is renewed development activity for hydrogen-powered internal combustion engines, which, depending on the system design, can have significantly shorter refueling times than battery-electric vehicles. Furthermore, hydrogen-powered internal combustion engines have significantly lower hydrogen purity requirements than fuel cells, which means that the hydrogen required to power such a vehicle can be produced more easily and cost-effectively. Therefore, vehicles with hydrogen-powered internal combustion engines are viewed as a sensible component of climate-neutral mobility.

[0003] Generally, two different variants of hydrogen-powered combustion engines are known from the state of the art, which differ essentially in the type of mixture formation. On the one hand, there are combustion engines in which hydrogen is injected into the intake tract of the combustion engine. On the other hand, there are engine concepts in which hydrogen is introduced into the combustion chamber by direct injection. Due to the higher ambient pressure and the time available for mixture formation, direct injection requires higher injection pressures than intake manifold injection. However, it has the advantage that the hydrogen injection can be carried out after the end of the intake phase. This allows the intake phase to be optimized with regard to the volumetric efficiency.

[0004] Hydrogen engines with port injection face the challenge of preventing the accumulation of an ignitable hydrogen-air mixture in the intake manifold, thus avoiding the risk of flashback from the combustion chamber and / or an explosion in the intake manifold. Hydrogen engines with direct injection face the challenge of injecting the hydrogen into the combustion chamber at a sufficiently high pressure. This limits possible sealing concepts and is often associated with increased wear when using metallic valve seats and seals. Both port injection and direct injection into the combustion chamber face the challenge that, due to the low density of the fuel, mixing of hydrogen and air is difficult compared to liquid fuel injection, and can lead to inhomogeneities in mixture formation.

[0005] Due to the very wide ignition limits of an air-hydrogen mixture, there is an increased risk of unwanted ignition and / or irregular or knocking combustion. In particular, premature ignition of the mixture due to residual discharge of the ignition coils or glow ignition on hot component surfaces is a problem that must be avoided at all costs.

[0006] To prevent such unwanted ignition of the mixture, very "cold" spark plugs and modified ignition coils are used to prevent pre-ignition. To compensate for the disadvantages in mixture formation, very high charge motion and retracted injectors for injecting the hydrogen, or "jet guiding caps" above the injection nozzle to improve jet shaping, are known. In this case, the injection valve is mounted retracted in its mounting bore, or the exiting jet is masked by a perforated cap to achieve a compact injection jet with a high penetration depth into the surrounding air. In this way, the penetration of the air with hydrogen can be increased and mixture formation can be improved.

[0007] A method for burning hydrogen gas in an internal combustion engine to initiate a diffusion combustion process is known from WO 2023 / 067 117 A2. The internal combustion engine has a piston that is driven by a crankshaft between a lower dead center and an upper dead center to perform a compression stroke, the method comprising the supply of a pilot injection of hydrogen gas into a combustion chamber during the compression stroke, such that the pilot injection of hydrogen pre-mixes with the air and a combustible air-hydrogen gas mixture forms in the vicinity of a spark plug of the internal combustion engine.

[0008] DE 10 2020 003 126 A1 describes an internal combustion engine for a motor vehicle, comprising at least one cylinder having a cylinder axis, which defines a combustion chamber of the internal combustion engine. The cylinder has a prechamber fluidically connected to the combustion chamber via at least one opening, with an injector having a first longitudinal axis, by means of which fuel can be introduced directly into the prechamber. The internal combustion engine further comprises an ignition device, by means of which at least one ignition spark can be generated in the prechamber. The injector is arranged in the center of the combustion chamber, and the longitudinal axes of the ignition device and the injector run obliquely or perpendicular to one another.

[0009] From CN 114183262 A, an internal combustion engine based on a pre-chamber diesel engine is also known, in which hydrogen is directly injected into a pre-chamber of the internal combustion engine, the hydrogen being ignited in the pre-chamber by means of jet ignition.

[0010] The invention is based on the object of optimising the mixture formation and combustion in an internal combustion engine with direct gas injection into the combustion chamber and of overcoming the disadvantages known from the prior art.

[0011] The object is achieved by an internal combustion engine having at least one main combustion chamber and a gas supply system for supplying a gaseous fuel to the at least one main combustion chamber. The main combustion chamber is delimited by a combustion chamber wall, in particular a combustion chamber wall in a cylinder head, wherein a spark plug is inserted in an opening in the combustion chamber wall. The spark plug is designed as an active pre-chamber spark plug and has a first ignition electrode, a second ignition electrode and an electrode gap formed between the ignition electrodes. The spark plug further has a cap which delimits a pre-combustion chamber in which the ignition electrodes are arranged, wherein the pre-combustion chamber is fluidically connected to the main combustion chamber by at least one outlet opening. In addition, the spark plug has a supply device for supplying the gaseous fuel in the pre-combustion chamber.

[0012] An internal combustion engine is an internal combustion engine that converts energy stored chemically in a fuel into mechanical movement by burning the fuel. In particular, an internal combustion engine is a reciprocating piston engine in which the combustion of the fuel produces an oscillating movement of a piston, which is converted into a rotary movement of a crankshaft by known kinematics. A main combustion chamber is a combustion chamber of an internal combustion engine that is connected to an air supply system on the intake side and to an exhaust system on the exhaust side. Such a main combustion chamber is often simply referred to as a combustion chamber.A gas supply system is a system that supplies a gas stored in a reservoir, in particular a liquefied or highly pressurized combustible gas, in particular compressed natural gas (CNG), liquefied natural gas (LNG), or hydrogen, to a combustion chamber of an internal combustion engine. Such a gas supply system may include, in particular, a high-pressure gas reservoir, a pressure control valve, a fuel injection valve, gas lines, and other components. A spark plug, in this context, is an ignition device that can ignite an ignitable air-fuel mixture by means of spark ignition.

[0013] Active or passive pre-chamber spark plugs are used to reduce the tendency to knock in internal combustion engines. When these spark plugs are used, the first part of the combustion takes place in a pre-chamber of the spark plug. The pressure in this chamber then rises and causes the charge contained therein to be pushed through holes into the main combustion chamber. These escaping flame lobes allow the combustion chamber charge to be ignited very quickly, widely and reliably under a wide range of ambient conditions, which leads to a short combustion duration, high combustion stability and a reduced tendency to knock. A distinction is made between active and passive systems. Passive systems have a cap surrounding the electrode gap. In this case, part of the combustion chamber charge is pushed into the pre-chamber by the rising cylinder pressure during the compression phase.Active systems have an additional gas supply device to the pre-chamber, so that the charge composition in the pre-chamber does not have to correspond to the main combustion chamber. Although both systems enable the combustion rate to be increased and thus the tendency to knock and a reduction in cyclic combustion fluctuations, passive pre-chamber spark plugs in particular have the disadvantage that they have an increased residual gas rate in the area of ​​the electrode gap due to poor or no purging of the pre-chamber. This can lead to poor ignition of the mixture, especially at operating points with an increased residual gas rate in the combustion chamber or at very low load. This disadvantage can be avoided by using an active pre-chamber spark plug. In this case, a defined amount of air or an air-fuel mixture is introduced into or removed from the pre-chamber.By purging the prechamber, the residual gas rate in the prechamber can be reduced and the turbulence level in the chamber increased. Both of these factors promote the propensity to ignite and burn through after ignition has been initiated.

[0014] A pre-combustion chamber, also known as a pre-chamber or mixture formation chamber, is a combustion chamber defined by a cap placed on and connected to the spark plug. Such a pre-combustion chamber has a significantly smaller volume than the main combustion chamber. A significantly smaller volume is defined as a volume that corresponds to a maximum of 5% of the volume of the combustion chamber. Furthermore, the volume of the pre-combustion chamber remains constant and does not change due to the movement of a piston that defines the main combustion chamber.

[0015] The internal combustion engine according to the invention therefore makes it possible to reduce the risk of knocking combustion or self-ignition of the combustible gas and to prevent flashback from the combustion chamber into the intake tract of the internal combustion engine. Furthermore, the targeted injection of the gaseous fuel in one or more compact jets allows for thorough mixing of the fresh air and the combustible gas, which contributes to fuel-efficient and low-emission combustion of the combustible gas.

[0016] The additional features listed in the dependent claims enable advantageous improvements and further developments of the internal combustion engine mentioned in the independent claim.

[0017] In a preferred embodiment of the internal combustion engine, the supply device comprises a supply channel that connects a high-pressure reservoir of the gas supply system to the pre-combustion chamber. This allows the gaseous fuel, in particular natural gas or hydrogen, to be introduced into the pre-combustion chamber in a particularly simple manner. This allows the gaseous fuel or an air-fuel mixture in the pre-combustion chamber to be outside the ignition limits, thus reliably preventing spontaneous combustion.

[0018] In a further preferred embodiment of the internal combustion engine, it is provided that an outlet of the supply device, in particular an outlet of the supply channel, is directed towards the ignition electrodes and / or the electrode gap of the spark plug. By injecting the gaseous fuel directed towards the ignition electrodes and / or the electrode gap, an ignitable mixture can be prevented in the critical region of the pre-combustion chamber, since this region is essentially filled with the combustible gas, so that the air / fuel mixture near the electrode gap is outside the ignition limits. Particular attention must be paid to the mixture composition in this region due to the risk of residual discharge of the energy stored in the ignition system.Starting from this area of ​​the pre-combustion chamber, the entire pre-combustion chamber can be filled with the combustible gas, so that no ignitable mixture is present in the pre-combustion chamber during the injection of the combustible gas. The combustible gas then flows through the fluidic connection between the pre-combustion chamber and the main combustion chamber into the main combustion chamber. The shape of the outlet openings in the cap can promote the penetration of the combustible gas into the main combustion chamber and the mixing of the combustible gas with the fresh air in the main combustion chamber.

[0019] In an advantageous embodiment of the internal combustion engine, the supply device comprises a fuel injection valve for injecting the gaseous fuel into the pre-combustion chamber. The fuel injection valve allows the gaseous fuel to be injected under pressure into the pre-combustion chamber, allowing the amount of combustible gas and the timing of injection to be easily controlled.

[0020] In a preferred embodiment of the internal combustion engine, the fuel injection valve is designed as a multi-way valve, in particular as a two-way valve, wherein a first flow path of the multi-way valve connects a valve opening of the multi-way valve opening into the pre-combustion chamber to a high-pressure accumulator of the gas supply system, and a second flow path of the multi-way valve connects a valve opening of the multi-way valve opening into the pre-combustion chamber to an intake tract of the internal combustion engine. This allows the pre-combustion chamber to be easily purged during a compression phase of the internal combustion engine by connecting the pre-combustion chamber to the intake tract, so that the air / fuel mixture flows from the main combustion chamber through the pre-combustion chamber into the intake tract, and an ignitable air / fuel mixture forms in the pre-combustion chamber. In this way, ignition conditions can be easily set in the pre-combustion chamber.Furthermore, by flushing the pre-combustion chamber, turbulence can be generated, which promotes mixing of the gaseous fuel with the fresh air.

[0021] In a preferred embodiment, the internal combustion engine is designed as a hydrogen-powered internal combustion engine. The gaseous fuel is preferably hydrogen. Since the challenges outlined are particularly pronounced in hydrogen engines due to the wide ignition limits, the internal combustion engine described in the previous sections offers the advantages, particularly when using hydrogen, of reliably preventing unwanted spontaneous ignition of the hydrogen and the flashback of a flame front into the intake tract by an open intake valve of the internal combustion engine.

[0022] In an advantageous embodiment of the internal combustion engine, the combustion chamber wall is formed in a cylinder head of the internal combustion engine. The combination of direct gas injection into the combustion chambers of the internal combustion engine and an active prechamber spark plug allows for particularly simple and reliable ignition of a combustible gas, particularly hydrogen. It is advantageous from a structural point of view to arrange the gas injection valve and the spark plug in a cylinder head of the internal combustion engine, which facilitates assembly.

[0023] In a preferred embodiment of the internal combustion engine, the internal combustion engine comprises a plurality of combustion chambers, wherein the combustion chambers are defined by a cylindrical combustion chamber wall, a movable piston, and a cylinder head. This allows a conventional internal combustion engine to be easily converted for operation with a combustible gas, in particular for direct gas injection into the combustion chamber.

[0024] A further aspect of the invention relates to a pre-chamber spark plug with a first ignition electrode, a second ignition electrode, and an electrode gap formed between the first ignition electrode and the second ignition electrode. The spark plug has a cap that delimits a combustion chamber in which the ignition electrodes are arranged, wherein the combustion chamber can be fluidly connected to a main combustion chamber of an internal combustion engine through at least one outlet opening, preferably through a plurality of outlet openings. The spark plug further has a supply device for supplying a gaseous fuel, in particular hydrogen, to the pre-combustion chamber. Such a spark plug makes it possible to reduce the risk of self-ignition of the combustible gas and to prevent flashback from the combustion chamber into the intake tract of the internal combustion engine.In addition, the targeted injection of the gaseous fuel into the pre-combustion chamber of the spark plug can achieve good mixing of the fresh air and the combustible gas, which contributes to fuel-efficient and low-emission combustion of the combustible gas.

[0025] A further aspect of the invention relates to a method for operating an internal combustion engine described in the preceding sections, which comprises the following steps: - Opening at least one intake valve of a main combustion chamber of the internal combustion engine, whereby the main combustion chamber is filled with fresh air, - closing the inlet valve(s) and injecting a gaseous fuel into the pre-combustion chamber, the gaseous fuel flowing through the at least one outlet opening from the pre-combustion chamber into the main combustion chamber, - Compressing the air-fuel mixture in the main combustion chamber, - Ignition of an air-fuel mixture in the pre-combustion chamber, - Opening of an exhaust valve of the main combustion chamber, whereby the burnt air-fuel mixture is expelled into an exhaust system of the internal combustion engine.

[0026] By flushing the electrode with the combustible gas, particularly hydrogen, during the injection process, the advantages of an active pre-chamber spark plug are utilized in an internal combustion engine powered by a combustible gas while simultaneously reducing the risk of unwanted premature ignition. This leads, in particular, to an improved ignition tendency due to a reduced residual gas rate in the pre-chamber and an increased turbulence level in the pre-chamber, improving the ignition and burn-through phases. During the intake phase, the pre-combustion chamber is filled with residual gas from the previous combustion cycle. Therefore, self-ignition is not possible during this phase.By injecting the gaseous fuel after the intake valve closes, it can prevent it from entering the intake tract, thus preventing the risk of explosion in the event of ignition on hot components in the combustion chamber or a flashback into the intake tract. Furthermore, the gaseous fuel is present in the pre-combustion chamber of the spark plug in almost pure form and thus outside the ignition limits.

[0027] In an advantageous embodiment of the method, during compression of the air-fuel mixture in the main combustion chamber, the pre-combustion chamber is connected to a volume with a lower pressure than the combustion chambers in order to flush the pre-combustion chamber. If, through appropriate design of the volumes of the gas supply system and the injection pressure, the pressure upstream of the injection valve is reduced to such an extent that it is below the cylinder pressure near top dead center of ignition (TDC) of the piston, a flow of mixture from the cylinder through the pre-combustion chamber into the gas supply system can occur by briefly opening the injection valve before top dead center of ignition. As a result, the turbulence level in the pre-combustion chamber can be increased shortly before top dead center of ignition, thus improving the ignition tendency and burn-through.This positive effect can be maximized by precise timing of the purge phase, which can be achieved, for example, by an additional, timed purge port that opens into an intake port of the combustion engine. In the configurations implemented, care must be taken to ensure that the mixture near the electrode gap remains outside the ignition limits during the intake and compression phases to avoid pre-ignition caused by residual discharge of the ignition coil. Ideally, an ignitable mixture should only be present at the electrode gap shortly before the ignition point.

[0028] It is particularly preferred if the volume into which the purge channel opens is an intake channel of the internal combustion engine. By activating the opening to the volume, the combustible gas flows from the pre-combustion chamber into the connected volume. This causes effective purging of the pre-combustion chamber and thus a reduction in the residual gas rate and an increase in the turbulence level in the pre-combustion chamber. The combustible gas flowing out into the intake tract is diluted by the fresh air to such an extent that the air-fuel mixture in the intake tract lies outside the ignition limits. In addition, this air-fuel mixture can be fed back into the main combustion chamber in the next combustion cycle by opening the intake valve, thus preventing the gaseous fuel from escaping into the environment.

[0029] Alternatively, the volume can also be part of the gas supply system. In this case, the combustible gas flows from the pre-combustion chamber into a storage volume in the gas supply system, which also leads to efficient venting of the pre-combustion chamber and the generation of turbulence in the pre-combustion chamber.

[0030] In an advantageous embodiment of the method, the gaseous fuel, in particular hydrogen, is injected into the pre-combustion chamber, directed at the ignition electrodes and / or an electrode gap between the ignition electrodes. This allows a particularly rich mixture to be established in this area, ensuring that the concentration of the combustible gas in the area of ​​the ignition electrodes is above the upper ignition limit, thus reliably preventing spontaneous combustion.

[0031] According to a preferred embodiment of the method, the fuel injection valve remains open during compression of the air-fuel mixture to allow the air-fuel mixture to overflow from the pre-combustion chamber into the gas supply system. By opening the fuel injection valve, the pre-combustion chamber is continuously flushed with combustible gas and is outside the ignition limits, thus preventing spontaneous combustion of the gas.

[0032] In an advantageous embodiment of the method, it is provided that the fuel injection valve is opened twice per combustion cycle, wherein during the first opening process a gaseous fuel, in particular hydrogen, is introduced into the pre-combustion chamber and the main combustion chamber, and wherein during the second opening process a purge of the pre-combustion chamber takes place in order to reduce the concentration of the gaseous fuel in the pre-combustion chamber and to produce an ignitable air-fuel mixture.

[0033] A further aspect of the invention relates to a control unit for operating an internal combustion engine described in the preceding sections, wherein the control unit is configured to carry out all method steps of the method according to the invention for operating an internal combustion engine when a computer program is executed by a computing unit of the control unit.

[0034] The various embodiments of the invention mentioned in this application can be advantageously combined with one another, unless stated otherwise in the individual case.

[0035] The invention is explained below in exemplary embodiments with reference to the accompanying drawings. They show: Fig. 1 is a schematic representation of an internal combustion engine according to the invention, operated with a gaseous fuel, having a combustion chamber on which an active pre-chamber spark plug and a fuel injection device are arranged, Fig. 2 a schematic representation of an active pre-chamber spark plug according to the invention with a fuel injection valve into the pre-chamber of the spark plug; Fig. 3 a distribution of hydrogen injected into the combustion chamber, which is injected into the combustion chamber in an engine according to the invention. Fig. 4 shows a cylinder head of an internal combustion engine according to the invention with a first preferred embodiment of an active pre-chamber spark plug with a fuel injection device, Fig. 5 shows a further preferred embodiment of a cylinder head for an internal combustion engine according to the invention with an active pre-chamber spark plug and a fuel injection device, Fig. 6 a flow chart for carrying out a method according to the invention for operating an internal combustion engine with an active pre-chamber spark plug and direct gas injection into the combustion chamber of the internal combustion engine.

[0036] Fig. 1 shows a schematic representation of an internal combustion engine 10 according to the invention, operated with a gaseous fuel 90, having a main combustion chamber 12, on which an active pre-chamber spark plug 52 with a pre-combustion chamber 48 and a fuel injection valve 18 are arranged. The internal combustion engine 10 comprises an engine block 16 and a cylinder head 14, wherein a cylinder 60 is formed in the engine block 16, in which a piston 62 is displaceably arranged. The piston 62 is connected to a crankshaft 72 via a connecting rod 70 in order to translate an oscillating up and down movement of the piston 62 into a rotary movement of the crankshaft. A combustion bowl 66 is formed on the piston 62, which defines the main combustion chamber 12 together with the combustion chamber walls 20. A piston 62 is sealed against the cylinder 60 by piston rings 64.Formed in the cylinder head 14 are an inlet port 55 and an outlet port 57, which can be closed by an inlet valve 56 and an exhaust valve 58, respectively. The inlet valves 56 and the exhaust valves 58 are each actuated by a camshaft 68, which controls the opening times of the inlet valves 56 and the exhaust valves 58, respectively. The main combustion chamber 12 is connected via the inlet port 55 to an intake port 76 of an intake tract 74 of the internal combustion engine 10. The main combustion chamber 12 is further connected via the outlet port 57 to an exhaust system 78.

[0037] Furthermore, a further opening 51 is formed in the cylinder head 14, into which a spark plug 52 is inserted. The spark plug 52 is designed as an active pre-chamber spark plug 52 and comprises a first ignition electrode 22 and a second ignition electrode 24, as well as an electrode gap 26 formed between the first ignition electrode 22 and the second ignition electrode 24. The spark plug 52 further comprises a cap 46, which encloses the ignition electrodes 22, 24 and forms a pre-combustion chamber 48. Outlet openings 42, 43, 44 are introduced into the cap 46 and fluidically connect the pre-combustion chamber 48 to the main combustion chamber 12. Furthermore, a gas supply system 30 is provided on the cylinder head 14, which comprises a high-pressure accumulator 54 and a supply device 31, which connects the high-pressure accumulator 54 to the pre-combustion chamber 48 of the spark plug 52.For this purpose, the supply device 31 comprises a fuel injection valve 18 and a supply channel 32, which opens into the pre-combustion chamber 48 and is configured to inject a combustible gas 90, in particular hydrogen 92, into the pre-combustion chamber 48. An outlet opening 28 of the supply channel 32 is preferably directed toward the ignition electrodes 22, 24 and / or the electrode gap 26 between the ignition electrodes. If the combustible gas 90 is injected into the pre-combustion chamber 48, it is present in high concentration and thus outside the ignition limits in the pre-combustion chamber 48. The combustible gas 90 enters the main combustion chamber 12 in the form of hydrogen jets 50, where the combustible gas 90, in particular hydrogen 92, mixes with the fresh air and forms an ignitable air-fuel mixture 96.The internal combustion engine 10 is operatively connected to a control unit 80, which includes a memory unit 82 and a computing unit 84, as well as a computer program 86 stored in the memory unit 82, which is configured to control the internal combustion engine 10 when the computer program 86 is executed by the computing unit 84. Furthermore, the control unit 80 may have a storage medium 88 on which the computer program 86 is stored.

[0038] In Fig. 2 shows a schematic representation of an end of a spark plug 52 according to the invention facing the main combustion chamber 12. The spark plug 52 comprises a first ignition electrode 22, a second ignition electrode 24, and an electrode gap 26 formed between the first ignition electrode 22 and the second ignition electrode 24. The spark plug 52 further comprises a cap 46 which delimits a pre-combustion chamber 48. Formed in the cap 46 are a plurality of outlet openings 42, 43, 44 which allow hydrogen to escape from the cap into a main combustion chamber 12 (not shown). Furthermore, the outlet openings 42, 43, 44 allow flame jets to escape from the pre-combustion chamber 48 into the main combustion chamber 12 when an ignitable hydrogen-air mixture is ignited in the pre-combustion chamber 48 in order to ignite the hydrogen-air mixture in the main combustion chamber 12.The spark plug 52 has a supply channel 32, which connects a high-pressure hydrogen reservoir 54 to the pre-combustion chamber 48. A fuel injection valve 18 is provided on the supply channel 32 to inject the hydrogen into the pre-combustion chamber 48.

[0039] Fig. Figure 3 shows the propagation of gaseous fuel 90, in particular hydrogen 92, injected into the pre-combustion chamber 48. This fuel passes through the outlet openings 42, 43, 44 in the cap 46 into the main combustion chamber 12 of the internal combustion engine 10 and mixes there with the fresh air. It can be seen that the outlet openings 42, 43, 44 cause the hydrogen jets 50 to break up and mix with the fresh air in the main combustion chamber 12 to produce a combustible hydrogen-air mixture.

[0040] In Fig. 4 shows a preferred embodiment of a cylinder head 14 of an internal combustion engine 10. The cylinder head 14 connects a main combustion chamber 12 of the internal combustion engine 10 to an intake port 76 of an intake tract 74 and an exhaust system 78. Furthermore, a spark plug 52 is inserted into the cylinder head 14, which has a first ignition electrode 22, a second ignition electrode 24, and an electrode gap 26 formed between the first ignition electrode 22 and the second ignition electrode 24. The spark plug 52 further comprises a cap 46, which delimits a pre-combustion chamber 48. Formed in the cap 46 are a plurality of outlet openings 42, 43, 44, which allow hydrogen to escape from the cap into a main combustion chamber 12 (not shown).Furthermore, the outlet openings 42, 43, 44 enable flame jets to emerge from the pre-combustion chamber 48 into the main combustion chamber 12 when an ignitable hydrogen-air mixture is ignited in the pre-combustion chamber 48 in order to ignite the hydrogen-air mixture in the main combustion chamber 12. The spark plug 52 has a supply channel 32 which connects a high-pressure hydrogen reservoir 54 to the pre-combustion chamber 48. A fuel injection valve 18 is provided on the supply channel 32 in order to inject the hydrogen into the pre-combustion chamber 48. The fuel injection valve 18 is designed as a multi-way valve 34 and has a first inlet 36 to a connecting channel 37 to a high-pressure reservoir 54 and a second inlet 38 to a connecting channel 39 to a volume 94, in particular a volume 94 in the intake tract 74. The fuel injection valve 18 further has a connecting channel 40 to the pre-combustion chamber 48.Alternatively, instead of a multi-way valve 34, an additional purge valve may be provided which connects the pre-combustion chamber 48 to the intake tract 74 in order to enable purging of the pre-combustion chamber 48 in the compression phase.

[0041] In Fig. 5 shows a further preferred embodiment of a cylinder head 14 of an internal combustion engine 10. The cylinder head 14 connects a main combustion chamber 12 of the internal combustion engine 10 to an intake port 76 of an intake tract 74 and an exhaust system 78. Furthermore, a spark plug 52 is inserted into the cylinder head 14, which has a first ignition electrode 22, a second ignition electrode 24, and an electrode gap 26 formed between the first ignition electrode 22 and the second ignition electrode 24. The spark plug 52 further comprises a cap 46, which delimits a pre-combustion chamber 48. Formed in the cap 46 are a plurality of outlet openings 42, 43, 44, which allow hydrogen to escape from the cap into a main combustion chamber 12 (not shown).Furthermore, the outlet openings 42, 43, 44 allow flame jets to emerge from the pre-combustion chamber 48 into the main combustion chamber 12 when an ignitable hydrogen-air mixture is ignited in the pre-combustion chamber 48 to ignite the hydrogen-air mixture in the main combustion chamber 12. The spark plug 52 has a supply channel 32 that connects a high-pressure hydrogen reservoir 54 to the pre-combustion chamber 48. A fuel injection valve 18 is provided on the supply channel 32 to inject the hydrogen into the pre-combustion chamber 48. The fuel injection valve 18 is designed as a two-way valve and, in a first switching position, enables the injection of a combustible gas 90, in particular hydrogen 92, into the pre-combustion chamber 48, and, in a second switching position, vents the pre-combustion chamber 48 in order to produce an ignitable air-fuel mixture and combustion-promoting turbulence in the pre-combustion chamber 48.

[0042] In Fig. Figure 6 shows a flowchart for implementing a method according to the invention for operating an internal combustion engine 10. The piston position K is shown over a combustion cycle, i.e., 720°CA. By flushing the electrode with hydrogen 92 during the injection process, the advantages of an active pre-chamber spark plug 52 are demonstrated, namely an improved ignition tendency due to a reduced residual gas rate in the pre-combustion chamber 48 and an increase in the turbulence level in the pre-combustion chamber 48 to improve the ignition and burn-through phase.If, through appropriate design of the volumes of the hydrogen supply line and the injection pressure of the pressure in front of the fuel injection valve 18, the pressure is reduced to such an extent that it is close to ZOT and below the cylinder pressure in the main combustion chamber 12, a flow of mixture from the main combustion chamber 12 through the pre-combustion chamber 48 into the gas supply system 30 can occur by briefly opening the fuel injection valve 18 before ZOT. As a result, the turbulence level in the pre-combustion chamber 48 can be increased shortly before ZOT, thus improving the ignition tendency and combustion. This positive effect can be maximized by precise timing of the purge phase, which can be achieved, for example, by an additional timed purge channel that opens into the intake channel 76.In the configurations implemented, care must be taken to ensure that the mixture near the electrode gap 26 of the spark plug 52 remains outside the ignition limits during the intake and compression phases to avoid pre-ignition due to residual discharge of the ignition coil. Ideally, an ignitable mixture should only be present at the electrode gap 26 shortly before the ignition point.

[0043] To achieve this, a procedure is proposed which includes the following steps:

[0044] In a first phase I, the inlet valve 56 of the main combustion chamber 12 is opened, whereby fresh air flows into the main combustion chamber 12. In this first phase, the pre-combustion chamber 48 is filled with residual gas from the previous combustion cycle, so that ignition is not possible. In a second phase II following the first phase I, the inlet valve 56 is closed and, after the inlet valve 56 has closed, hydrogen 92 is blown into the pre-combustion chamber 48, whereby the hydrogen 92 flows from the pre-combustion chamber 48 through the outlet openings 42, 43, 44 into the main combustion chamber 12. In this second phase II, the pre-combustion chamber 48 is filled with almost pure hydrogen 92, so that the hydrogen concentration in the pre-combustion chamber 48 is outside the ignition limits.By injecting hydrogen 92 after closing the intake valve 56, the ingress of hydrogen 92 into the intake passage 76 can be avoided, which reduces the risk of explosion in the event of ignition, for example at hot valves, or the risk of flame flashback from the combustion chamber into the intake tract 74. Furthermore, the intake phase can be designed for optimal efficiency, since displacement of the intake air mass by the injected hydrogen 92 during the intake phase can be reduced. In a third phase III following the second phase II, the fresh air or the hydrogen-air mixture in the main combustion chamber 12 is compressed after injecting the hydrogen 92 and pushed into the pre-chamber. Alternatively, the fuel injection valve 18 can also be slightly opened to achieve a continuous inflow of hydrogen 92 during compression.If the supply channel 32 opens into the pre-combustion chamber 48 near the electrode gap 26, this results in a hydrogen-air mixture outside the ignition limits in the electrode gap 26, even if fresh air passes from the main combustion chamber 12 into the pre-combustion chamber 48 during compression.

[0045] In a fourth phase IV following the third phase III, the pressure in the combustion chambers 12, 48 increases further due to the progressive compression. As a result, fresh air flows from the main combustion chamber 12 into the pre-combustion chamber 48 and fills it with fresh air, creating an ignitable hydrogen-air mixture in the pre-combustion chamber 48. Furthermore, as the fresh air flows into the pre-combustion chamber 48, it increases the turbulence level in the pre-combustion chamber 48. The filling quality of the pre-combustion chamber 48 and the level of turbulence generated can be increased by a switchable channel opening into the pre-combustion chamber 48, which connects the pre-combustion chamber 48 to a volume 94, for example, the intake port 76, in which a lower pressure level prevails. When this switchable channel is activated, combustion chamber charge flows through the pre-combustion chamber 48 into the connected volume 94.This effectively purges the pre-combustion chamber 48, thus reducing the residual gas rate and increasing the turbulence level therein. The fuel injection valve 18 and the associated gas supply system 30 can function as the previously described purge channel. In the embodiment shown in . Fig. 4, the geometry of the supply line upstream of the fuel injection valve 18 and the injection pressure were designed such that the volume 94 upstream of the fuel injection valve 18 has a pressure below the pressure in the main combustion chamber 12 during the compression phase, so that a renewed opening of the fuel injection valve 18 leads to an overflow of combustion chamber charge through the pre-combustion chamber 48 into the gas supply system 30. From this point on, an ignitable hydrogen-air mixture is present in the pre-combustion chamber 48.

[0046] In a fifth phase V following the fourth phase IV, the hydrogen-air mixture in the pre-combustion chamber 48 is ignited by the ignition electrodes 22, 24 of the spark plug 52. The charge in the pre-combustion chamber 48 burns, causing the pressure in the pre-combustion chamber 48 to rise and leading to the flame lobes typical of pre-combustion chambers being pushed out into the main combustion chamber 12. In a sixth phase VI following the fifth phase V, the hydrogen-air mixture is ignited in the main combustion chamber 12. The flame lobes emerging from the pre-combustion chamber 48 penetrate the main combustion chamber 12 and ignite the cylinder charge located therein, which thereby burns and leads to an increase in pressure in the main combustion chamber 12.

[0047] In a seventh phase VII following the sixth phase VI, the piston 62 is displaced downwards by the expansion of the cylinder charge and transfers mechanical work to the crankshaft 72. In an eighth phase VIII following the seventh phase VII, the exhaust valve 58 is opened and the combusted charge is expelled from the main combustion chamber 12 into the exhaust system 78. The purging of the main combustion chamber 12 with hydrogen 92 during injection leads to a hydrogen filling in the pre-combustion chamber 48. The charge in the electrode gap 26 is therefore outside the ignition limits in this phase, whereby pre-ignition can be avoided. Only in the subsequent purging phase of the pre-combustion chamber 48 does air enter the pre-combustion chamber 48 and thus creates an ignitable mixture that carries a corresponding risk of pre-ignition.This risk can be minimized by a late position of the scavenging phase of the pre-combustion chamber 48, which can be achieved, for example, by controlling the valve connected to the scavenging channel only shortly before the ignition point.

[0048] Alternatively, the Fig.5, a slightly modified method can be carried out. When using a combustion chamber pressure-tight fuel injection valve 18 instead of the two-way valve, the fuel injection valve 18 remains minimally open after the fuel quantity has been injected into the pre-combustion chamber 48 in order to form a low leakage flow during the first part of the compression phase. The injection pressure must be greater than the cylinder pressure in the main combustion chamber 12. If the injection pressure level is selected such that the cylinder pressure rises above the injection pressure during the compression phase, then opening the fuel injection valve 18 from this point onwards causes the combustion chamber charge to flow out into the volume 94 of the gas supply system 30 upstream of the fuel injection valve 18. This state is desired shortly before the ignition point. The fuel injection valve 18 is opened a second time.This creates a purge flow from the main combustion chamber 12 through the pre-combustion chamber 48 into the gas supply system 30, which leads to increased turbulence and an ignitable mixture within the pre-combustion chamber 48. To enable this process, it is necessary to set the injection pressure to a pressure greater than the combustion chamber pressure in phase III in the main combustion chamber 12 and less than the pressure in the main combustion chamber 12 during phase IV. The functionality of this method can depend on the precise setting of the injection pressure. If the injection pressure is too high, this prevents or limits the time window for purging the pre-combustion chamber 48 by opening the fuel injection valve 18 for the second time. If the injection pressure is too low, this limits the possible time window during which a leakage flow can be achieved and thus pre-ignition can be avoided.In this configuration, the time window of the purge phase and thus the presence of an ignitable mixture in the pre-combustion chamber 48 is coupled to the control of the fuel injection valve 18 and the injection pressure.

[0049] Under unfavorable boundary conditions, for example due to premature closing of the injection valve or too low injection pressure in the first injection phase, the leakage flow may end too early, so that sufficient combustion chamber charge flows into the pre-combustion chamber 48 during the compression phase to generate an ignitable hydrogen-air mixture in the pre-combustion chamber 48. This results in the residual risk of premature ignition due to residual discharge of the ignition system.

[0050] In this case, the method according to the invention comprises the following steps: In a first phase, the fuel injection valve 18 is opened after the intake valve 56 has closed to create a lean hydrogen-air mixture in the main combustion chamber 12. In a second phase, a small hydrogen mass flow is continuously injected into the pre-combustion chamber 48 during the compression phase by slightly opening the fuel injection valve 18. This slight leakage flow continuously flushes the pre-combustion chamber 48 with hydrogen 92, thus placing it outside the ignition limits. In order to optimally combust the amount of hydrogen escaping from the pre-combustion chamber 48 during this time, permanent mixing with the combustion chamber charge is necessary. For this purpose, a large-scale flow structure with the main flow direction orthogonal to the outlet openings 42, 43, 44 of the cap 46 delimiting the pre-combustion chamber 48 is advisable. Therefore, a tumble flow should be aimed for during the previous intake phase.The end of the minimum opening of the fuel injection valve 18 lies in a time window in which the pressure in the main combustion chamber 12 is above the pressure in the pre-combustion chamber 48, thus allowing a flow of the combustion chamber charge from the main combustion chamber 12 into the pre-combustion chamber 48 to form an ignitable mixture in the pre-combustion chamber at the time of ignition. Only when the lean hydrogen-air mixture is pushed from the main combustion chamber 12 into the pre-combustion chamber 48 does a pre-combustion chamber mixture within the ignition limits result. In this way, the end of the injection phase and thus of the leakage gas flow can limit the time window during which an ignitable mixture is present in the pre-combustion chamber 48. The robust implementation of this method requires a continuous leakage gas flow during the compression phase, which in turn requires an injection pressure above the cylinder pressure throughout the entire compression phase.For this reason, in this configuration, it is not possible to create a purge flow from the main combustion chamber 12 into the pre-combustion chamber 48 through a second opening window of the fuel injection valve 18. This eliminates the possibility of purging the pre-combustion chamber 48 and increasing the turbulence level therein by opening the fuel injection valve 18 a second time. The possible start of the purge phase, and thus the presence of an ignitable mixture in the pre-combustion chamber 48, is coupled in this configuration to the end of the hydrogen leakage flow phase. With an injection pressure permanently above the cylinder pressure, a leakage flow phase is possible throughout the entire compression phase with a correspondingly long activation of the fuel injection valve 18, which effectively prevents pre-ignition. List of reference symbols 10 Internal combustion engine 12 Main combustion chamber 14 cylinder head 16 Engine block 18 Fuel injection valve 20 combustion chamber wall 22 first ignition electrode 24 second ignition electrode 26 Electrode gap 28 Outlet opening of the supply channel 30 Gas supply system 31 Supply facility 32 supply channel 34 Multi-way valve 36 first entry 37 Connection channel to the high-pressure accumulator 38 second entrance 39 Connection channel to the intake manifold 40 Connection channel to the pre-combustion chamber 42 first exit opening 43 second outlet opening 44 additional exit opening 46 cap 48 Pre-combustion chamber 50 hydrogen jet 51 Opening in the cylinder head 52 Spark plug / active pre-chamber spark plug 54 high-pressure accumulators 55 Inlet opening 56 Inlet valve 57 Outlet opening 58 Exhaust valve 60 cylinders 62 pistons 64 piston rings 66 combustion chamber 68 camshaft 70 connecting rods 72 Crankshaft 74 Intake tract 76 intake duct 78 Exhaust system 80 control unit 82 storage unit 84 computing unit 86 computer program 88 storage medium 90 gaseous fuel 92 Hydrogen 94 volumes 96 air-fuel mixture QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] <h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> WO 2023 / 067 117 A2

[0007] <h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> DE 10 2020 003 126 A1

[0008] <h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> CN 114183262 A

[0009]

Claims

[1] Internal combustion engine (10) with - at least one main combustion chamber (12), - a combustion chamber wall (20) delimiting the main combustion chamber (12), - a gas supply system (30) for supplying a gaseous fuel (90) to the at least one main combustion chamber (12), - a spark plug (52) inserted into an opening (94) in the combustion chamber wall (20), wherein - the spark plug (52) is designed as an active pre-chamber spark plug (52) and comprises the following: ◯ a first ignition electrode (22), a second ignition electrode (24) and an electrode gap (26) formed between the ignition electrodes (22, 24), ◯ a cap (46) which defines a pre-combustion chamber (48) in which the ignition electrodes (22, 24) are arranged, ◯ at least one outlet opening (42, 43, 44) through which the pre-combustion chamber (48) is fluidically connected to the main combustion chamber (12), and ◯ a supply device (31) for supplying the gaseous fuel into the pre-combustion chamber (48). [2] Internal combustion engine (10) according to claim 1, wherein the supply device (31) comprises a supply channel (32) which connects a high-pressure accumulator (54) of the gas supply system (30) to the pre-combustion chamber (48). [3] Internal combustion engine (10) according to claim 1 or 2, wherein an outlet of the supply device (31) is directed towards the ignition electrodes (22, 24) and / or the electrode gap (26). [4] Internal combustion engine (10) according to one of claims 1 to 3, wherein the supply device (31) has a fuel injection valve (18) for injecting the gaseous fuel (90) into the pre-combustion chamber (48). [5] Internal combustion engine (10) according to claim 4, wherein the fuel injection valve (18) is designed as a multi-way valve (34), wherein a first flow path of the multi-way valve (34) connects a valve opening opening into the pre-combustion chamber (48) to a high-pressure accumulator (54) of the gas supply system (30) and a second flow path of the multi-way valve (34) connects a valve opening opening into the pre-combustion chamber (48) to an intake tract (74) of the internal combustion engine (10). [6] Internal combustion engine (10) according to one of claims 1 to 5, wherein the internal combustion engine (10) is designed as a hydrogen-powered internal combustion engine (10). [7] Internal combustion engine (10) according to one of claims 1 to 6, wherein the combustion chamber wall (20) is formed in a cylinder head (14) of the internal combustion engine (10). [8] Pre-chamber spark plug (52), comprising - a first ignition electrode (22), a second ignition electrode (24) and an electrode gap (26) formed between the ignition electrodes (22, 24), - a cap (46) which defines a pre-combustion chamber (48) in which the ignition electrodes (22, 24) are arranged, - at least one outlet opening (42, 43, 44) through which the pre-combustion chamber (48) can be fluidically connected to a main combustion chamber (12) of an internal combustion engine (10), and - a supply device (31) for supplying the gaseous fuel (90) into the pre-combustion chamber (48). [9] Method for operating an internal combustion engine (10) according to one of claims 1 to 7, comprising the following steps: - opening at least one inlet valve (56) of a main combustion chamber (12) of the internal combustion engine (10), wherein the main combustion chamber (12) is filled with fresh air, - closing the inlet valve(s) (56) and injecting a gaseous fuel (90) into the pre-combustion chamber (48), wherein the gaseous fuel (90) flows through the at least one outlet opening (42, 43, 44) from the pre-combustion chamber (48) into the main combustion chamber (12), - Compressing the air-fuel mixture (96) in the main combustion chamber (12), - igniting an air-fuel mixture (96) in the pre-combustion chamber (48), - Opening an exhaust valve (58) of the main combustion chamber (12), whereby the burnt air-fuel mixture (96) is expelled into an exhaust system (78) of the internal combustion engine (10). [10] Method according to claim 9, wherein during the compression of the air-fuel mixture (96) in the main combustion chamber (12), the pre-combustion chamber (48) is connected to a volume (94) with reduced pressure compared to the combustion chambers (12, 48) in order to effect a scavenging of the pre-combustion chamber (48). [11] The method of claim 10, wherein the volume (94) is an intake port (76) of the internal combustion engine (10). [12] Method according to one of claims 9 to 11, wherein the gaseous fuel is blown into the pre-combustion chamber (48) directed onto the ignition electrodes (22, 24) and / or an electrode gap (26) of the spark plug (52) formed between the ignition electrodes (22, 24). [13] Method according to one of claims 9 to 12, wherein the fuel injection valve (18) remains open during compression of the air-fuel mixture (96) to allow overflow of the air-fuel mixture (96) from the pre-combustion chamber (48) into the gas supply system (30). [14] Method according to one of claims 9 to 13, wherein the fuel injection valve (18) is opened twice per combustion cycle, wherein during the first opening process a gaseous fuel (90) is introduced into the pre-combustion chamber (48) and the main combustion chamber (12), and wherein during the second opening process a purge of the pre-combustion chamber (48) takes place in order to reduce the concentration of the gaseous fuel in the pre-combustion chamber (48) and to produce an ignitable air-fuel mixture (96). [15] Control unit (80) for operating an internal combustion engine (10), wherein the control unit (80) is configured to carry out all method steps of a method according to one of claims 9 to 14.

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