Method for operating an internal combustion engine system for a motor vehicle and internal combustion engine system for a motor vehicle

Abstract

Method for operating an internal combustion engine system (1) for a motor vehicle, wherein an internal combustion engine (2) of the internal combustion engine system (1) comprises a main combustion chamber (6) and a pre-chamber (8) associated with said main combustion chamber (6) and fluidically connected to the main combustion chamber (6) by at least one overflow channel (14), wherein according to the method - a fuel-air mixture is delivered into the prechamber (8) by means of an injection device (16) assigned to the prechamber (8) to form a prechamber mixture, - the pre-chamber mixture in the pre-chamber (8) is ignited by means of an ignition device (18), - by means of the ignited pre-chamber mixture passing from the pre-chamber (8) into the main combustion chamber (6) via the respective overflow channel (14), a main chamber mixture (6) formed in the main combustion chamber (6) is ignited, - the fuel-air mixture is taken from a fuel tank (30) of the motor vehicle, and - the fuel-air mixture is removed from the fuel tank (30) by means of a tank ventilation system (28).

Description

The invention relates to a method for operating an internal combustion engine system for a motor vehicle. The invention furthermore relates to an internal combustion engine system for a motor vehicle.Internal combustion engines are frequently used for driving a vehicle. Usually, when designing internal combustion engines (for short: engines), a favorable power-consumption ratio is sought in this case in order to make possible, in particular in the motor vehicle sector (i.e. in automobiles), the smallest possible consumption of fuel with nevertheless satisfactory power yield. For this purpose, there is also the tendency to achieve the most "clean" possible combustion of the fuel, i.e. in particular the least possible pollutant emission. This can be achieved, for example, by as complete a combustion of the fuel as possible, in particular in the case of excess air (based on a so-called stoichiometric ratio between air and fuel), i.e. in the case of a so-called "lean mixture".However, it is problematic when the excess air increases that the mixture formed in the combustion chamber (also: cylinder chamber) of the engine is no longer ignitable from a specific air-fuel mixture ratio, described inter alia by a so-called "combustion air ratio λ" ("lambda value"), and thus no longer burns at all or only incompletely. In the field of motor vehicle engines, in order to avoid this problem, a so-called "stratified charge" is produced in the cylinder chamber as one possibility. This means that different mixture ratios between air and fuel are formed in layers, wherein a comparatively "rich" mixture (i.e. close to the stoichiometric ratio or even with excess fuel) is present in the region of an ignition device serving for ignition (usually a "spark plug"). In the field of (stationary) engines, which are operated in particular with gas, the use of a so-called prechamber is known. This is connected upstream of the actual cylinder space and is filled with more gas (i.e. a richer mixture) than the cylinder space. As a result, there is an ignitable mixture which is ignited and, when it passes into the cylinder chamber, can cause the leaner mixture there to ignite.In particular for gasoline engines, however, such "pre-chamber ignition" cannot be implemented equally easily, since mixture formation in the pre-chamber with the gasoline, which is usually present in liquid form, is complicated. For filling the prechamber, therefore, for example, additional gaseous additional fuels are used. Alternatively, for example, come. Direct Injectors for Use. However, these concepts require additional installation space and / or complex and thus mostly expensive technologies.DE 10 2014 002 905 A1 describes a combustion method for execution with a gas engine. The gas engine is formed with a main combustion chamber and a fuel-flushed prechamber, which is connected to the main combustion chamber via at least one overflow opening. The gas engine is configured for the combustion of a gaseous fuel gas-air mixture in the main combustion chamber. To ignite the gaseous fuel gas-air mixture in the main combustion chamber, a liquid gasoline fuel is injected into the prechamber and ignited therein by means of an ignition device.DE 199 47 080 C1 describes that, for regenerating an activated carbon container which is seated in the tank venting of an internal combustion engine which is operated with air-assisted direct gasoline injection, a pressure regulator is connected to the high-pressure side of the pressure generating unit which generates the compressed air for the injection. Its discharged air is passed through the activated carbon container to regenerate it.DE 25 10 556 B2 describes an internal combustion engine with stratified charge, which has a pre-combustion chamber, which can be supplied with an air-fuel mixture via a rotary distributor in a camshaft bearing part. The air-fuel mixture is injected via an intake passage into a groove or passage in the camshaft and enters the pre-combustion chamber via a flapper valve having a flexible vane opened by the vacuum in the chamber and by a cam, and is ignited there by a spark plug and causes a flame to transition into a main combustion chamber to ignite a leaner mixture therein.AT 410 007 B describes an ignition device for an internal combustion engine, in particular for a multi-cylinder gas internal combustion engine, which has an ignition chamber per cylinder, which can be temporarily connected to the main combustion chamber or a prechamber via a control valve and in which compressed fuel-air mixture is ignited, which enters from the main combustion chamber or the prechamber when the valve is opened. A gas feed channel for feeding a gas or gas mixture opens into the ignition chamber.The object of the invention is to make possible an improved internal combustion engine system.This object is achieved according to the invention by a method for operating an internal combustion engine system having the features of claim 1.The method according to the invention serves for operating an internal combustion engine system for a motor vehicle. The internal combustion engine system comprises an internal combustion engine (for short: engine) having at least one main combustion chamber (also referred to as cylinder chamber) and in each case one prechamber assigned to the respective main combustion chamber, which is connected in terms of flow to the (respective) main combustion chamber by means of at least one overflow duct. According to the method, a fuel-air mixture is discharged into the (respective) prechamber by means of an injection device which is assigned to the respective prechamber or to the respective prechamber and is preferably part of the internal combustion engine system in order to form a prechamber mixture. Subsequently, the pre-chamber mixture located in the pre-chamber is ignited, i.e. brought to combustion, by means of an ignition device (preferably a spark plug) (assigned to the respective pre-chamber). By means of the ignited pre-chamber mixture, which thus expands and which passes via the respective overflow channel from the respective pre-chamber into the (assigned) main combustion chamber, a main chamber mixture formed in the main combustion chamber is ignited.The ignited pre-chamber mixture passes in particular depending on the dimensions of the respective transfer passage "burning" into the main combustion chamber. Alternatively, the pre-chamber mixture passing into the main combustion chamber is closed, but in this case contains at least reactive molecules which cause an ignition reaction with the main chamber mixture. Because of the cross-sectional dimensions of the respective overflow channel, which are preferably significantly smaller than the prechamber, the prechamber mixture entering the main combustion chamber after ignition forms a so-called "torch jet" or "jet". In both cases, the torch jet or jet causes a comparatively high turbulence in the main combustion chamber and also an ignition of the main chamber mixture at a plurality of points. This enables rapid and more complete combustion (in comparison with conventional spark plug ignition in the cylinder chamber), in particular even in the case of lean (and optionally also homogeneously distributed) main chamber mixtures.The term "fuel-air mixture" is understood here and below to mean that the fuel is not introduced "pur" (i.e. without adding air, for example liquid) into the prechamber, but that a preferably vapor mixture is already present. In an optional process variant, this mixture is already itself ignitable. Advantageously, due to the supply of such a fuel-air mixture, for example, a complicated and expensive direct injection of pure fuel for the purpose of mixture formation within the respective prechamber can be dispensed with. In addition, the metering of such a fuel-air mixture is advantageously particularly simple on account of its increased volume (compared to liquid fuel).The term "internal combustion engine system" is understood here and below to mean, in particular, the internal combustion engine and the periphery serving for its operation and connected to it (e.g. control units, fuel lines, possibly present turbochargers and the like).As the fuel for the air-fuel mixture, the same fuel as that of the main chamber mixture is preferably used. This likewise enables simplified engine technology, since no separate (additional) fuel is required for filling (also referred to as "flooding") the prechamber. Consequently, a tank required for such a separate fuel and the associated installation outlay are also dispensed with. Preferably, gasoline is used as fuel, so that the engine is in particular a gasoline (Otto) engine.In principle, it is conceivable within the scope of the invention to flood the respective prechamber only (i.e. exclusively) with the fuel-air mixture. In order, however, to be able to save fuel, in a preferred method variant the main chamber mixture flowing in a compression stroke from the respective main combustion chamber-in particular via the respective overflow duct-into the respectively assigned prechamber (within the prechamber) is enriched with the fuel-air mixture. In this case, the pre-chamber mixture is therefore formed by the part of the main chamber mixture located in the pre-chamber and by the fuel-air mixture added. Expediently, an ignitable mixture is formed (preferably "first"), in particular a mixture in the region around the stoichiometric mixing ratio, which has a mass which is smaller by a multiple and / or a volume which is smaller by a multiple (for example by 80 to 99 times with respect to a so-called compression volume) in comparison with the main chamber mixture in the cylinder space (the compression volume here and below being understood to be the volume remaining in the cylinder space when the piston is arranged at the so-called top dead center, i.e. when the piston is at maximum immersion depth in the cylinder space). As a result, very lean mixtures (for example with a lambda value of about 1.6, i.e. between 1.5 and 1.7, and higher) in the main combustion chamber can in particular also be ignited with little additional outlay and in particular with low pollutant emissions. A mixture having such a combustion air ratio can hardly be ignited in a failsafe manner in the cylinder chamber with a conventional ignition by means of a spark plug; at least in this case (in contrast to the above-described ignition by means of the prechamber mixture), complete combustion usually no longer occurs. In particular, a risk of misfires can thus advantageously be significantly reduced, and the economics of the internal combustion engine system can be increased and its pollutant emissions during operation can be reduced.In order to enable a particularly high (in particular thermal) efficiency, in an advantageous method variant, a lean fuel-air mixture ratio with a combustion air ratio of approximately 1.6 or higher is preferably used for the main chamber mixture at least for normal operation of the engine. In addition, with such a combustion air ratio, in particular with a lambda value higher than 1.6, an emission of nitrogen oxides (NOx) is particularly low-in particular in comparison with a combustion air ratio between 1.05 and 1.4-so that an additional exhaust gas purification can optionally be omitted.According to the invention, the fuel-air mixture is taken from a fuel tank of the motor vehicle. Preferably, the fuel-air mixture is taken as such, i.e. in particular directly, and therefore without further treatment or enrichment with fuel outside the fuel tank. As a result, a separate device for forming a mixture, such as a carburetor, an atomizer, an evaporator or the like, can be advantageously dispensed with, because in the fuel tank in the state (filled with fuel, in particular gasoline), it is recognized that-because of the generally comparatively high volatility of the fuel compared to other liquids-there is already a (approximately saturated) mixture of evaporated (evaporated) fuel and air. Thus, in this method variant, the fuel (vapor) air mixture is already stored and provided, so that a corresponding engine technology can be kept particularly simple and, in particular, implemented cost-effectively. This fuel-air mixture removed from the fuel tank is preferably used to enrich the mixture ratio flowing into the prechamber in the compression stroke to a main chamber mixture, in particular an ignitable mixture ratio. In other words, the fuel-air mixture with the incoming main chamber mixture is "diluted" to the ignitable mixture ratio, particularly since the fuel-air mixture from the fuel tank is regularly too rich for ignition (i.e. lies outside an upper ignition limit). The stoichiometric air-fuel (mass) ratio is about 14.7, while the ratio of the atmosphere in the fuel tank is about 0.68. In addition, in operation, as the main chamber mixture in the main combustion chamber progressively receives more and more lean main chamber mixture flowing into the pre-chamber, the introduction of an amount of the air-fuel mixture required to form the ignitable pre-chamber mixture is preferably adjusted depending on the ignition timing and the composition of the main chamber mixture. The fuel-air mixture is introduced into the prechamber in particular during the compression stroke and / or optionally also before the compression stroke (for example during, in particular towards the end of, an exhaust gas discharge stroke).The fuel-air mixture is removed from the fuel tank by means of a tank venting system. Such a tank venting system is preferably usually present in any case in order to be able to discharge the atmosphere in the fuel tank enriched with fuel vapor (in particular approximately saturated). Thus, an already existing or even prescribed technique is advantageously used to provide the air-fuel mixture. Consequently, additional installation outlay (discharge lines and the like) can be omitted or at least largely reduced (i.e. in particular to the required connection of the injection device to the tank venting system).The internal combustion engine system according to the invention for a motor vehicle is configured in particular for operation according to the method described above. The internal combustion engine system thus comprises the above-described (combustion) engine, which in turn has the at least one main combustion chamber (cylinder chamber). Furthermore, the internal combustion engine system comprises the prechamber assigned to the respective main combustion chamber, which is connected in terms of flow to the assigned main combustion chamber by at least one of the transfer ducts described above. The internal combustion engine system further comprises the injection device assigned to the respective prechamber for discharging the fuel-air mixture into the prechamber, and the respective ignition device.The engine preferably comprises a plurality of, for example three or more, main combustion chambers, each of which is assigned a pre-chamber, an injection device and an ignition device.Since the internal combustion engine system according to the invention is designed for operation according to the method described above, the advantages described above likewise result for the internal combustion engine system.In a preferred embodiment, the injection device is a system for enriching the lean main chamber mixture within the prechamber in order to set a (preferably approximately stoichiometric or even rich) mixture ratio for the prechamber mixture, which in particular enables failsafe ignition.The internal combustion engine system includes the above-described fuel tank venting system. This tank venting system serves to draw the atmosphere enriched with fuel vapor from the fuel tank. By means of this tank venting system, the injection device is connected to the fuel tank of the motor vehicle for the extraction of the fuel-air mixture. The tank venting system and the injection device connected thereto are preferably configured to remove the fuel-air mixture directly (in particular as such) from the fuel tank, so that additional enrichment with fuel (in particular outside the fuel tank) can be dispensed with. The internal combustion engine system can thus be constructed in a particularly simple manner, in particular since a tank venting system is required anyway (i.e. also in the case of an engine without a prechamber).In an expedient development, the tank venting system described above comprises a pumping device, for example a compressor, in order to draw (suck off) the fuel-air mixture from the fuel tank and to apply an injection pressure required for introducing the fuel-air mixture into the respective prechamber. The latter is recognized to vary depending on the time of the discharge of the fuel-air mixture before and / or during the compression stroke, so that a low injection pressure is required in the event of an early discharge and thus a pumping device with comparatively low power can also be used in this case.In an advantageous embodiment, the respective injection device comprises an in particular "simple" or commercially available solenoid valve for metering and dispensing the fuel-air mixture into the prechamber. In this case, the respective injection device expediently also comprises a (preferably passive, for example spring-loaded) nonreturn valve which is connected between the prechamber and the solenoid valve and in this case serves in particular exclusively for sealing the prechamber against the compression and / or combustion pressure. Consequently, in this embodiment, no special injection valve, in particular no direct injection valve, is required. Special valves of this type usually require a control voltage which has a (significantly) increased voltage value compared to the usual voltage value of an on-board voltage of the motor vehicle, since they usually seal independently from the compression and / or combustion pressure. The use of the solenoid valve and the nonreturn valve, which are simpler and more favorable in comparison with a direct injection valve, is advantageously made possible in that a (in particular vapor) mixture is already present, which only has to be metered by means of the injection device and introduced into the prechamber. A comparatively complicated and in particular expensive direct injection, in particular with an accompanying atomization of the fuel for the mixture formation within the prechamber, can thus be dispensed with. In addition, the simplified metering of the (in particular vapor) fuel-air mixture, which has already been described above and is simplified compared to liquid fuel, makes possible a simplified valve technique compared to liquid injection valves. Furthermore, the use of the solenoid valve and of the check valve advantageously requires comparatively little installation space, at least in the immediate vicinity of the prechamber.The internal combustion engine system preferably also comprises control electronics (also referred to as a controller) which is configured to actuate the solenoid valve in particular in a time-controlled manner or (as described above) as a function of the cycle of the engine and / or of the piston arranged in the respective cylinder chamber. In a preferred embodiment, the controller is formed at least in the core by a microcontroller having a processor and a data memory, in which the functionality for controlling the solenoid valve is implemented by programming in the form of operating software (firmware). Alternatively, however, the controller can also be formed by a non-programmable electronic component, e.g. an ASIC, within the scope of the invention.In a further expedient embodiment, the internal combustion engine system comprises a sensor system for monitoring the fuel fraction in the fuel-air mixture. The sensor system is preferably configured for measurement in the tank venting system. This means that the sensor system is configured to pick up a measurement variable in the tank venting system that is characteristic of the fuel fraction, in particular within a (pipe) line of the tank venting system. This detected measured variable is expediently used for controlling the injection device, in particular the solenoid valve. Characteristic here and in the following means that the measured variable contains quantitative information about the fuel fraction, so that it can be read unambiguously from the measured variable. The measured variable can indicate the fuel component directly in this case. However, the measured variable can also be a variable which is directly or indirectly proportional to the fuel component or is in a non-linear ratio.In an expedient development, the tank venting system comprises an air supply into the fuel tank, wherein a tank-side air outlet of this air supply is arranged in the region of a tank base of the fuel tank (and thus preferably below a fuel level in the filled state of the fuel tank). In this case, the air supply is configured in particular (by control technology) to introduce air into the fuel tank as a function of the measured variable detected by means of the sensor system, in particular the ascertained fuel fraction. Due to the fact that the tank-side air outlet is arranged in the region of the tank base, bubbles are thus formed when air is introduced, which bubbles rise in the fuel and thereby lead to an increase in the proportion of fuel in the atmosphere in the fuel tank. As a result, for example, operating- and / or climate-induced fluctuations of the fuel fraction of the atmosphere in the fuel tank can be compensated for.In a preferred embodiment, the volume of the respective prechamber or prechamber is less than 5%, preferably less than 2%, of the compression volume.In order to avoid temperature-induced wear of the prechamber housing even without active (fluid) cooling of a prechamber housing surrounding the respective prechamber, this prechamber housing is made in an expedient embodiment from a material having a high thermal conductivity with at the same time as high mechanical strength as possible (in order to be able to withstand the high pressure values occurring during combustion). High-strength copper alloys (compared to unalloyed copper) or thermally conductive ceramics (in particular compared to steel) are preferably used in this case. As a result, the heat occurring during the combustion can be dissipated in a simple manner into a cylinder head assigned to the engine, in which cylinder head the respective prechamber or the prechamber housing thereof is preferably inserted.Exemplary embodiments of the invention are explained in more detail below with reference to a drawing. Shown therein are: FIG. 1 is a schematic illustration of an internal combustion engine system in a partially enlarged manner, showing a part of an internal combustion engine having a prechamber, FIG. 2 shows a schematic functional diagram of the internal combustion engine system, and FIG. 3 shows a view according to FIG. 2 of a further exemplary embodiment of the internal combustion engine system.Corresponding parts are always provided with the same reference numerals in all figures.FIG. 1 shows a detail of an internal combustion engine system 1. The internal combustion engine system 1 comprises a schematically indicated (internal combustion) engine 2 which is designed as a gasoline spark ignition engine. In the engine 2, a main combustion chamber (referred to as cylinder chamber 6) is disposed inside a cylinder 4. The internal combustion engine system 1 furthermore comprises a prechamber 8, which forms a prechamber combustion chamber surrounded by an associated (prechamber) housing 9 and which is arranged in a cylinder head 10 of the engine 2. The pre-chamber 8 (specifically its pre-chamber combustion chamber) narrows in the direction of the cylinder chamber 6 via a sharp edge 11 to a main channel 12 which at its cylinder-side end is in fluidic communication with the cylinder chamber 6 via a plurality of transfer channels 14 in the form of bores (set obliquely to the main channel 12).The internal combustion engine system 1 also comprises an injection device 16 and an ignition device in the form of a spark plug 18, the latter being inserted into the housing 9 and sealing the prechamber 8 towards the end facing away from the cylinder 4. The injection device 16 comprises a solenoid valve 20 and a check valve 22 connected between the pre-chamber 8 and the solenoid valve 20.The injection device 16 is configured to discharge a fuel-air mixture into the prechamber 8 before and / or during a compression stroke in which a piston 24 (see FIG. 2 ) arranged in the associated cylinder 4 moves in the direction of the cylinder head 10. The solenoid valve 20 is configured to meter the quantity of the fuel-air mixture. The fuel-air mixture accumulates a main chamber mixture compressed in the cylinder chamber 6 in the compression stroke and flowing into the prechamber 8 via the transfer ducts 14 with more fuel. Thus, a richer pre-chamber mixture than the main chamber mixture is formed in pre-chamber 8. The edge 11 creates turbulence upon the inflow of the main chamber mixture into the pre-chamber 8. The main chamber mixture is formed by means of a conventional (direct) injection device in the cylinder chamber 6 from the same fuel as that of the fuel-air mixture and air flowing separately into the cylinder chamber 6 (alternatively, the formation of the main chamber mixture can also be effected by means of a so-called intake duct injection).The pre-chamber mixture is then ignited by the spark plug 18. Due to the combustion, the pre-chamber mixture and / or its (hot) combustion gases expand and enter the cylinder chamber 6 through the transfer ducts 14. Due to the nozzle-like transfer ducts 14, "torch jets" 26 (also referred to as "jets") schematically indicated in the cylinder chamber 6 form, which cause strong turbulences in the cylinder chamber 6 (in particular in comparison to a conventional ignition) and thereby lead to the ignition of the main chamber mixture at many points and thus also to a more rapid and better (almost complete) combustion. In this case, the torch jets 26 can be formed both from (still) burning or from already dissolved prechamber mixture. In the latter case, however, reactive molecules are still contained in the torch jets 26, which lead to an ignition of the main chamber mixture.The volume of the pre-chamber 8 is about 1.6% of the compression volume, i.e. the remaining volume of the cylinder chamber 6, when the piston 24 is arranged at the top dead center. In order to keep a temperature load of the housing 9 of the prechamber 8 as low as possible, the housing 9 is manufactured from a high-strength copper alloy. As a result, the heat introduced into the housing 9 during the burning of the pre-chamber mixture can be dissipated into the cylinder head 10 within a short time.As shown in FIG. 2, the injection device 16 and thus also the prechamber 8 are connected by means of a tank venting system 28 to a fuel tank 30, both of which form part of the internal combustion engine system 1. Via the tank venting system 28, the fuel-air mixture as such is drawn off (suctioned off) directly from the fuel tank 30-specifically from an upper side of the fuel tank 30. That is, no additional enrichment device disposed outside the fuel tank 30 is required to provide the air-fuel mixture. Rather, the air-fuel mixture is already present within the fuel tank 30. The tank venting system 28 comprises a pumping device, specifically a compressor 32, for venting the fuel tank 30 and for generating the required injection pressure.The internal combustion engine system 1 furthermore comprises a sensor system 34 for determining the fuel fraction in the tank venting system 28, In an exemplary embodiment which is not shown in detail, the sensor system 34 is connected to a controller for the injection device 16 in terms of signal transmission. The controller is configured to adjust the dosing of the air-fuel mixture as a function of the fuel fraction in the air-fuel mixture conducted in the tank venting system 28 and of the composition of the main chamber mixture.In a further exemplary embodiment according to FIG. 3, the internal combustion engine system 1 comprises an air supply in the form of a pipeline 36 which leads into the fuel tank 30 and which is provided with an actuatable inlet valve 38. In this exemplary embodiment, control electronics (not shown in more detail) of the inlet valve 38 are connected to the sensor system 34. The control electronics of the inlet valve 38 are configured to introduce air into the fuel tank 30 in the case of a small fuel fraction. The pipeline 36 ends in the region of the tank bottom of the fuel tank 30, so that a large number of bubbles form in the fuel when air is introduced, which bubbles increase the proportion of fuel due to an increase in the surface area of fuel to air.In an exemplary embodiment not shown in more detail, a highly porous or spongy material is arranged in the fuel tank 30, into which material the fuel can penetrate, so that a surface is formed which is many times larger compared to a simple separating surface between fuel and air, which promotes the evaporation of fuel.The subject matter of the invention is not limited to the exemplary embodiments described above. Rather, further embodiments of the invention can be derived from the above description by the person skilled in the art. In particular, the individual features of the invention described on the basis of the various exemplary embodiments and their design variants can also be combined with one another in another manner.List of reference characters1 Internal combustion engine system 2 Engine 4 Cylinder 6 Cylinder chamber 8 Prechamber 9 Prechamber housing 10 Cylinder head 11 Edge 12 Main channel 14 Transfer channel 16 Injection device 18 Spark plug 20 Solenoid valve 22 Nonreturn valve 24 Piston 26 Torch jet 28 Tank venting system 30 Fuel tank 32 Compressor 34 Sensor system 36 Pipeline 38 Inlet valve

Claims

Method for operating an internal combustion engine system (1) for a motor vehicle, wherein an internal combustion engine (2) of the internal combustion engine system (1) comprises a main combustion chamber (6) and a prechamber (8) assigned to this main combustion chamber (6) and connected fluidically to the main combustion chamber (6) by at least one overflow duct (14), wherein according to the method - a fuel-air mixture is emitted into the prechamber (8) by means of an injection device (16) assigned to the prechamber (8), - the prechamber mixture located in the prechamber (8) is ignited by means of an ignition device (18), - a main chamber mixture (6) formed in the main combustion chamber (6) is ignited by means of the ignited prechamber mixture and overflowing from the prechamber (8) into the main combustion chamber (6) by means of the respective overflow duct (14), the air-fuel mixture is taken from a fuel tank (30) of the motor vehicle, and the air-fuel mixture is taken from the fuel tank (30) by means of a tank venting system (28).Method according to Claim 1, wherein the main chamber mixture flowing from the main combustion chamber (6) into the pre-chamber (8) in a compression stroke is enriched with the fuel-air mixture.Internal combustion engine system (1) for a motor vehicle, - having an internal combustion engine (2) which comprises at least one main combustion chamber (6), - having a prechamber (8) which is assigned to the respective main combustion chamber (6) and is connected in terms of flow to the respective main combustion chamber (6) by means of at least one overflow duct (14), - having an injection device (16) for discharging a fuel-air mixture into the respective prechamber (8), - having an ignition device (18) assigned to the respective prechamber (8), and - having a tank venting system (28), wherein the injection device (16) is connected by means of the tank venting system (28) to a fuel tank (30) of the motor vehicle for removing the fuel-air mixture.Internal combustion engine system (1) according to Claim 3, wherein the tank venting system (28) comprises a pumping device (32) for extracting the fuel-air mixture from the fuel tank (30) and for applying a required injection pressure.Internal combustion engine system (1) according to Claim 3 or 4, wherein the injection device (16) comprises a solenoid valve (20) for discharging the fuel-air mixture into the prechamber (8) and a nonreturn valve (22) connected between the prechamber (8) and the solenoid valve (20).Internal combustion engine system (1) according to one of Claims 3 to 5, having a sensor system (34) for monitoring a proportion of fuel in the air-fuel mixture, the sensor system (34) being set up for measurement in the tank venting system (28).Internal combustion engine system (1) according to Claim 6, wherein the tank venting system (28) comprises an air supply (36, 38) into the fuel tank (30), wherein a tank-side air outlet of the air supply (36, 38) is arranged in the region of a tank base of the fuel tank (30), and wherein the air supply (36, 38) is configured to introduce air into the fuel tank (30) as a function of the fuel fraction determined by means of the sensor system (34).Internal combustion engine system (1) according to one of Claims 3 to 7, wherein the pre-chamber (8) has a volume of less than 5%, preferably of less than 2%, of a compression volume.

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