Method for operating a piston engine and piston engine

Abstract

The invention relates to a method for operating a piston engine, in particular a reciprocating piston engine, wherein an ignitable mixture is ignited in a combustion chamber (19) adjacent to a piston (18), which piston (18) is connected to a shaft (20) rotating about an engine axis. To achieve particularly high efficiency, the invention provides that fuel, in particular hydrogen, is introduced into a pre-chamber (1) by means of an injector (13), and that this fuel then spreads from the pre-chamber (1) into the combustion chamber (19) via flow paths (2) connecting the pre-chamber (1) to several positions (5a, 5b) in the combustion chamber (19), after which the fuel mixes with an oxygen-containing gas, in particular air, in the combustion chamber (19) and the ignitable mixture is formed, after which the mixture is ignited in the combustion chamber.The invention further relates to a fuel, in particular hydrogen, which is introduced into a pre-chamber (1) by means of an injector (13) and which subsequently spreads from the pre-chamber (1) into the combustion chamber (19) via flow paths (2) which connect the pre-chamber (1) with several positions (5a, 5b) in the combustion chamber (19), after which the fuel mixes with an oxygen-containing gas, in particular air, in the combustion chamber (19) and the ignitable mixture is formed, after which the mixture is ignited in the combustion chamber.

Description

[0001] The invention relates to a method for operating a piston engine, in particular a reciprocating piston engine, wherein an ignitable mixture is ignited in a combustion chamber which borders a piston, which piston is connected to a shaft rotating about an engine axis.

[0002] The invention further relates to a piston engine, in particular a reciprocating piston engine, comprising a combustion chamber and a movable piston adjacent to the combustion chamber, in order to set a shaft into rotary motion by means of the piston igniting an ignitable mixture in the combustion chamber.

[0003] Methods and engines of the type mentioned above are already known from the prior art.

[0004] A disadvantage of state-of-the-art methods and engines is that only a low efficiency can be achieved.

[0005] This is where the invention comes in. The object of the invention is to provide a method of the type mentioned above with which a particularly high efficiency can be achieved, especially when using hydrogen as fuel.

[0006] Furthermore, such a piston engine should be specified.

[0007] The first problem is solved according to the invention in a method of the type mentioned at the outset, in which fuel, in particular hydrogen, is introduced into a pre-chamber by means of an injector and this fuel then spreads from the pre-chamber into the combustion chamber via flow paths which connect the pre-chamber with several positions in the combustion chamber, after which the fuel mixes with an oxygen-containing gas, in particular air, in the combustion chamber and the ignitable mixture is formed, after which the mixture is ignited in the combustion chamber.

[0008] Within the scope of the invention, it was recognized that prior art methods, and in particular the use of hydrogen as a fuel, achieve low efficiency because direct injection of hydrogen into the combustion chamber leads to an inhomogeneous distribution of the fuel within the combustion chamber. In particular, cryogenic direct injection into the combustion chamber is virtually impossible with prior art methods due to the hot combustion chamber, as the hydrogen begins to vaporize in the front part of the injector even before it reaches the combustion chamber. A further disadvantage of known direct injection methods is that areas with high fuel concentrations and others with low fuel concentrations are created in the combustion chamber, i.e., rich and lean regions, which leads to unwanted pre-ignition and therefore negatively impacts efficiency.

[0009] The invention overcomes these disadvantages by not injecting or blowing fuel directly into the combustion chamber, but rather introducing it into a pre-chamber, preferably at high pressure. From the pre-chamber, the fuel spreads into the combustion chamber via flow paths that connect it to several positions within the combustion chamber and typically include channels. The fuel then mixes with an oxygen-containing gas in the combustion chamber. Thus, mixture formation does not occur directly from a single point in the combustion chamber, where fuel is injected directly into the combustion chamber via an injector as in direct injection, but rather via multiple positions. The fuel introduced into the pre-chamber can then distribute itself throughout the combustion chamber and mix with air, resulting in a very homogeneous mixture.

[0010] Due to direct injection into the pre-chamber, a very high power density is achieved compared to external mixture formation.

[0011] Although the inventive method is preferably implemented in connection with hydrogen, the method can of course also be used with any other gaseous or liquid fuels, for example with gasoline, diesel and / or natural gas.

[0012] This homogeneous mixture formation prevents the formation of rich and lean zones in the combustion chamber, which could lead to unwanted pre-ignition. The fuel injection points and flow paths within the combustion chamber can be arranged to prevent backflow into the intake.

[0013] Furthermore, due to the introduction of fuel into the pre-chamber, it is possible to position the injector in a cooler location, namely opening into the pre-chamber and not into the combustion chamber, which also makes cryogenic direct injection of hydrogen possible without fuel or hydrogen evaporating in the injector.

[0014] By forming a particularly homogeneous mixture in the combustion chamber, for example a mixture with λ=1, ignition and complete combustion of the mixture in the combustion chamber can occur very quickly, resulting in a high efficiency.

[0015] Ignition of the mixture in the combustion chamber can be initiated either in the combustion chamber itself or in the pre-chamber, for example with an ignition device such as a spark plug that opens into the combustion chamber or the pre-chamber. It is also possible for ignition of the mixture to be initiated without a special ignition device; in this case, the engine is designed as a compression-ignition engine.

[0016] Preferably, the fuel is introduced while the piston is at top dead center and / or while the piston is moving from top dead center to bottom dead center during an intake stroke and / or while the piston is moving from bottom dead center to top dead center during a compression stroke.

[0017] Depending particularly on the type of fuel and the pressure at which it is injected, the fuel can spread very rapidly from the pre-chamber into the combustion chamber via the flow paths, forming the mixture within a very short time. This makes it possible, in principle, to introduce fuel even when the piston is at top dead center. Liquid hydrogen, in particular, when injected under high pressure, spreads very rapidly from the pre-chamber into the combustion chamber via the flow paths.

[0018] Additionally or alternatively, it can preferably also be provided that the fuel is introduced while the piston is moving from top dead center to bottom dead center during an intake stroke and / or while the piston is moving from bottom dead center to top dead center during a compression stroke. An intake stroke is understood in particular to be a period during which the piston moves from top dead center to bottom dead center, wherein one or more intake valves are open at least temporarily, and in particular primarily, during the intake stroke. Introducing fuel during the intake stroke, preferably with the intake valve closed and / or in the last third of the intake stroke, can lead to particularly good mixture homogenization, although fuel can also be introduced, in particular additionally, during a compression stroke.

[0019] The compression stroke is understood in particular to be a period of time, preferably immediately following the intake stroke, within which the piston moves from bottom dead center to top dead center, wherein valves, i.e. intake and exhaust valves, are closed at least temporarily, in particular at least mainly, during the compression stroke, so that the mixture in the combustion chamber is preferably compressed.

[0020] The fuel can be introduced in liquid or gaseous form. Particularly when the fuel is hydrogen, it is preferred that the fuel be introduced in liquid form. It is especially preferred that the fuel be introduced into the pre-chamber under high pressure, particularly under a pressure of at least 30 bar, and more preferably under a pressure of at least 500 bar. Preferably, the pre-chamber and the injector are designed separately from each other.

[0021] To achieve particularly good mixture homogenization, it is advantageous for the fuel to be introduced into the combustion chamber at positions that are evenly distributed throughout the combustion chamber. It is particularly preferred that the fuel be supplied to the combustion chamber via flow paths at at least two positions, which are spaced apart by at least 30%, advantageously at least 50%, and most advantageously at least 70% of the combustion chamber diameter.

[0022] Typically, two to 20 positions are provided through which the fuel is introduced from the pre-chamber into the combustion chamber. These positions can, in principle, be located at any point leading into the combustion chamber and are preferably distributed approximately evenly over one or more surfaces of the combustion chamber.

[0023] It is particularly advantageous if the positions are arranged on a cylinder head. The cylinder head, which is preferably made of a metal, can, for example, be multi-part and / or manufactured using a machining process, an additive manufacturing process, a sintering process, or a 3D printing process.

[0024] It has proven advantageous to supply the fuel to the combustion chamber at at least one position which has a distance from a central axis of the combustion chamber of less than 15%, advantageously less than 10% and particularly advantageously less than 5% of a combustion chamber diameter and / or to supply it at at least one position which has a distance from a central axis of the combustion chamber of more than 25%, advantageously more than 35% and particularly advantageously more than 40% of a combustion chamber diameter.

[0025] Fuel is advantageously supplied to the combustion chamber at positions that are close to a central axis and / or far from a central axis in order to achieve uniform fuel supply and distribution and thus good mixture homogenization.

[0026] Preferably, the fuel is supplied to the combustion chamber via the flow paths at at least four, preferably at least eight, positions, which positions preferably open into the combustion chamber in a roughly regularly spaced manner. In this way, a particularly homogeneous distribution of the fuel is achieved.

[0027] The flow paths can be continuous from the pre-chamber to the combustion chamber or branched, so that a channel originating from the pre-chamber opens into the combustion chamber at two or more positions.

[0028] The pre-chamber can, in principle, have any shape. In a reciprocating piston engine, the pre-chamber is preferably rotationally symmetrical about a central axis of the combustion chamber, parallel to which the piston moves translationally.

[0029] The prechamber is particularly preferably lenticular, in the form of an ellipsoid or a sphere.

[0030] Advantageously, the diameter of the pre-chamber in a direction normal to a central axis of the combustion chamber is 5% to 70%, preferably 15% to 60%, particularly preferably 20% to 50% of the combustion chamber diameter.

[0031] Advantageously, the diameter of the pre-chamber in a direction normal to a central axis of the combustion chamber is at least 10%, preferably at least 20%, particularly preferably at least 30% of the combustion chamber diameter.

[0032] It is preferred if the pre-chamber has an extent of max. 50%, preferably max. 30%, particularly preferably max. 20% along the central axis of the combustion chamber, and in particular an extent of the combustion chamber along the central axis at a time when the piston is at top or bottom dead center.

[0033] The volume of the pre-chamber is preferably 1% to 50%, more preferably 2% to 40%, more preferably 10% to 30% of a combustion chamber volume, in particular a combustion chamber volume at a time when the piston is at top dead center or bottom dead center.

[0034] The volume of the pre-chamber is preferably at least 10%, particularly preferably at least 20%, and in particular at least 30% of a combustion chamber volume, especially a combustion chamber volume at a time when the piston is at bottom dead center.

[0035] A compact pre-chamber relative to the combustion chamber has the particular advantage that fuel can be moved quickly and evenly from the pre-chamber into the combustion chamber and thus distributed well, resulting in a particularly homogeneous mixture.

[0036] It is advantageous that the fuel is supplied to the combustion chamber via flow paths of varying lengths. This makes it particularly easy to create a compact pre-chamber while simultaneously ensuring a homogeneous fuel distribution within the combustion chamber.

[0037] The length of a shortest flow path is preferably less than 97%, preferably less than 90%, particularly less than 80%, preferably less than 70%, and particularly preferably less than 60% of the length of the longest flow path.

[0038] In particular, to enable the most simultaneous possible penetration of fuel into the combustion chamber despite differing flow path lengths, it is preferably provided that a portion of the fuel spreading from the pre-chamber into the combustion chamber passes through at least one intermediate chamber along a flow path, wherein this portion of the fuel is slowed down as it passes through the intermediate chamber. Preferably, the at least one intermediate chamber is arranged in a flow path that differs from a flow path of maximum length.

[0039] The intermediate chamber typically reduces the flow velocity, so that by arranging one or more intermediate chambers in the flow paths, different flow path lengths can be compensated for. This is achieved by ensuring that, despite the different velocities at which the fuel flows along the individual flow paths, the flow times are as uniform as possible. As a result, fuel flows into the combustion chamber at approximately the same time at positions further away from the pre-chamber as at positions close to it. This facilitates particularly good homogeneous mixture formation.

[0040] Of course, several intermediate chambers can be provided along a flow path.

[0041] Typically, every flow path that fluidically connects the pre-chamber to the combustion chamber is at least partially formed by a channel. A channel can have a constant, increasing, or decreasing cross-section. Preferably, the channels have approximately circular cross-sections with a diameter of 0.1 mm to 10 mm.

[0042] A reduction in flow velocity is achieved particularly easily with an intermediate chamber if the flow path with the intermediate chamber initially has a channel to which an intermediate chamber connects, after which the intermediate chamber is connected to the combustion chamber via another channel, possibly via another intermediate chamber.

[0043] Typically, the intermediate chamber causes a cross-sectional increase along the flow path from the pre-chamber to the combustion chamber, followed by a reduction in cross-sectional area. Therefore, the cross-section of the intermediate chamber is generally larger than the cross-section of the channels adjoining it.

[0044] The cross-section of the channel or the cross-section of the intermediate chamber is preferably understood to be a cross-section at a position of a flow path running through the respective channel or the respective intermediate chamber, normal to the respective flow path.

[0045] Preferably, the intermediate chamber is designed such that the change in cross-section occurs abruptly. Preferably, the flow cross-section changes at a transition between the channel and the intermediate chamber within a range of less than 10 mm, preferably within less than 5 mm, and particularly preferably within less than 3 mm, along the flow path. A change in cross-section can, for example, mean an increase in cross-section by at least a factor of 1.5, preferably at least a factor of 2, and particularly preferably at least a factor of 3.

[0046] Advantageously, the cross-section narrows abruptly, preferably along the flow path at the end of the pre-chamber or at a transition from the pre-chamber to a channel following the pre-chamber. Such a relatively abrupt change in cross-section significantly reduces the flow velocity, allowing the times within which fuel travels from the pre-chamber to the combustion chamber along the shorter flow paths to be adjusted to those of the longer flow paths. This ensures that the fuel supplied to the combustion chamber via the individual flow paths reaches the combustion chamber at approximately the same time at each point.

[0047] It is advantageous if the cross-section of at least one channel connecting the pre-chamber and the intermediate chamber is larger than the cross-section of one or more channels connecting the intermediate chamber and the combustion chamber. Such a channel can also be designed as a tumble channel and may have a curvature.

[0048] Furthermore, it is advantageous if the cross-section of at least one channel connecting the pre-chamber and the intermediate chamber is larger than the cross-section of one or more of the channels that are assigned to flow paths that do not have intermediate chambers.

[0049] Furthermore, it is advantageous if the cross-section of at least one, preferably all, channels connecting the intermediate chamber and the combustion chamber is smaller than the cross-section of the intermediate chamber.

[0050] Preferably, the maximum cross-section of the intermediate chamber is greater than or equal to the length of the channel of the at least one channel connecting the pre-chamber and the intermediate chamber, and / or greater than or equal to the length of the channel of the at least one channel connecting the intermediate chamber and the combustion chamber.

[0051] It is also advantageous if the pre-chamber is only connected to the combustion chamber via flow paths.

[0052] Preferably, at least one flow path without an intermediate chamber is provided, wherein this flow path is particularly preferably the longest flow path or not the shortest flow path. A flow path without an intermediate chamber is preferably formed entirely by a channel, in particular with a constant cross-section.

[0053] Preferably, the piston engine comprises at least two flow paths without an intermediate chamber, which open into the combustion chamber at a first distance from each other, and at least two flow paths with at least one intermediate chamber, which open into the combustion chamber at a second distance from each other, wherein the first distance is greater, preferably at least twice as large, particularly advantageously at least four times as large and most advantageously at least six times as large as the second distance.

[0054] Preferably, the maximum cross-section of the intermediate chamber is larger than the maximum cross-section of the channel, in particular the maximum cross-section of each channel which opens into the intermediate chamber.

[0055] It is further advantageous if each cross-section of the intermediate chamber is larger than each cross-section of the channel connecting the intermediate chamber to the pre-chamber and / or the intermediate chamber to the combustion chamber.

[0056] The intermediate chamber can, in principle, have any shape suitable for reducing the flow velocity compared to a channel. It is particularly preferred that the ratio of the extent of the intermediate chamber in a direction normal to the flow path to the extent of the channel connecting the pre-chamber and intermediate chamber, normal to the flow path, is at least 1.5, in particular at least 2, and preferably at least 4.

[0057] Preferably, both the channels and the intermediate chambers are designed with a round, in particular an at least nearly circular, cross-section, although other cross-sections, such as oval, square, or rectangular cross-sections, are also possible. Preferably, the ratio of the maximum diameter of the intermediate chamber to the minimum diameter of a channel opening into the intermediate chamber is at least 1.5, more preferably at least 2, and most preferably at least 4.

[0058] Furthermore, it is preferably provided that the channels which connect the pre-chamber to the combustion chamber or the pre-chamber to an intermediate chamber and the intermediate chamber to optionally one or more further intermediate chambers or the combustion chamber have a constant cross-section at least in certain areas, preferably substantially along the entire length of the channels.

[0059] The channels preferably have a diameter of 0.1 mm to 15 mm, preferably 0.5 mm to 5 mm, and particularly preferably 0.8 mm to 3 mm.

[0060] Preferably, it is provided that one or more channels are connected to the intermediate chamber, which connect the intermediate chamber to one or more positions in the combustion chamber, in particular to several spaced-apart positions.

[0061] It can also be provided that the intermediate chamber is connected to a first number of channels, which connect the intermediate chamber to the pre-chamber, and a second number of channels, which connect the intermediate chamber to the combustion chamber, the second number being smaller than the first. For example, the first number can be 1 to 3 and the second number 2 to 8.

[0062] It is preferably provided that the intermediate chamber is connected to the pre-chamber by a channel which has a curved centerline. This introduces a swirl, turbulence, vortex and / or tumble into the flow.

[0063] Furthermore, this can generate a swirl, turbulence, vortex, and / or tumble in the pre-chamber and / or the intermediate chamber, which improves the scavenging of the chambers and / or mixture formation in the chambers. The fuel is therefore preferably supplied to the combustion chamber via at least one flow path, which flow path has a curved centerline at least in some areas, so that a swirl, turbulence, vortex, and / or tumble is introduced into the flow.

[0064] A curved center line may also be provided for channels connecting the intermediate chamber to the combustion chamber and / or for channels connecting the pre-chamber to the combustion chamber. These channels may also be designed as tumble channels.

[0065] The curvature can, in principle, have any orientation. However, it is preferred that the center line is curved around an axis approximately perpendicular to a central axis of the combustion chamber.

[0066] It is preferably provided that the ratio of a combustion chamber diameter to a radius of curvature is more than 0.5, preferably 0.7 to 10, in particular 1.5 to 5.

[0067] It is advantageous if such a channel has a corresponding, in particular constant, curvature up to an entry into the intermediate chamber, preferably along the entire length of the channel.

[0068] It may preferably be provided that at least one channel, in particular a channel connecting the pre-chamber to an intermediate chamber, has a non-circular cross-section, in particular an elliptical cross-section and / or a cross-section with partially parallel side edges. In this way, a particularly effective deceleration of both the flow and the burn-through velocity in the intermediate chamber can be achieved.

[0069] It is advantageous if at least one channel opening into the intermediate chamber enters the chamber off-center, particularly tangentially, in order to achieve a flow field in the intermediate chamber that is at least partially cylindrical. Such a channel with a curved centerline can also be called a tumble channel.

[0070] The tumble channel can have a non-circular cross-section, for example an approximately rectangular cross-section, and a curved centerline, resulting in a cylindrical flow in the intermediate chamber.

[0071] It is particularly preferred that the fuel is supplied to the combustion chamber and / or the mixture to the pre-chamber via the individual flow paths at at least partially different velocities. Particularly preferably, the different velocities correspond to the different lengths of the flow paths, so that fuel enters the combustion chamber at the individual positions essentially simultaneously, and the mixture enters the pre-chamber via the individual flow paths approximately simultaneously, and is in particular forced into it.

[0072] The pre-chamber, connected to the combustion chamber via flow paths, can also be used to ignite the mixture in the combustion chamber at different positions simultaneously. This multiple ignition points result in rapid combustion and a high combustion velocity, enabling a near-thermodynamically ideal constant-volume combustion process and thus achieving exceptionally high efficiency.

[0073] It is therefore preferably provided that ignition of the mixture in the combustion chamber takes place via flame fronts originating from the pre-chamber, which spread into the combustion chamber via the flow paths and ignite the mixture in the combustion chamber at several positions.

[0074] Ignition of the mixture in the flow paths can, in principle, occur at any position along the flow paths. Preferably, the mixture is ignited in the pre-chamber.

[0075] Typically, the flow paths are designed and, if necessary, provided with intermediate chambers, such that lower flow velocities on the one hand and flame propagation velocities on the other are achieved along shorter flow paths than in the longer flow paths, so that the fuel or the flame fronts usually reach the combustion chamber via the individual flow paths at approximately the same time, especially within a period in which the crankshaft is moved by less than 10 degrees.

[0076] Preferably, the flow paths are designed in such a way that a method can be carried out with the piston engine in which, from the discharge of the fuel into the combustion chamber by means of a first fuel front to the discharge of the fuel into the combustion chamber by means of a last fuel front, the shaft is moved by less than 20 degrees, in particular less than 15 degrees, preferably less than 10 degrees.

[0077] Preferably, the flow paths are designed in such a way that a method can be carried out with the piston engine in which, from the ignition of the mixture in the combustion chamber by means of a first flame front to the ignition of the mixture in the combustion chamber by means of a last flame front, the shaft is moved by less than 20 degrees, in particular less than 15 degrees, preferably less than 10 degrees.

[0078] For example, no intermediate chambers may be arranged in the longest flow paths, which connect the pre-chamber with an edge of the combustion chamber, and one or more intermediate chambers may be provided in flow paths that connect the pre-chamber with central areas of the combustion chamber, so that the flow paths are correspondingly shorter in order to achieve approximately the same fuel ejection times and / or burn-through times despite different lengths of the individual flow paths.

[0079] By initiating combustion at multiple points simultaneously, particularly short combustion times are achieved in the combustion chamber, resulting in exceptionally high efficiency. Ignition can be initiated, for example, in the pre-chamber using an ignition device such as a spark plug.

[0080] The further problem is solved according to the invention by a piston engine of the type mentioned at the outset, which has a pre-chamber which is fluidically connected to the combustion chamber at several positions via several flow paths, wherein the flow paths are each at least partially formed by channels, so that the mixture in the combustion chamber can be ignited by igniting an ignitable mixture in the pre-chamber, and has an injector for introducing fuel, in particular hydrogen, into the pre-chamber, wherein the piston engine is configured to form the ignitable mixture in the combustion chamber by introducing fuel, in particular at high pressure, into the pre-chamber, which fuel then spreads via the flow paths in the combustion chamber and mixes with an oxygen-containing gas in the combustion chamber.

[0081] Preferably, the piston engine is configured to carry out a method according to the invention.

[0082] The piston engine can be designed as either a reciprocating piston engine or a rotary piston engine. If the piston is designed as a reciprocating piston engine, it is preferably provided that the pre-chamber, the flow paths, and their positions are arranged in a cylinder head. The same applies if an intermediate chamber is provided to reduce the flow velocity or flame propagation velocity in individual flow paths.

[0083] The cylinder head can be formed in any way known from the prior art, for example in a 3D printing process, for example from a metal.

[0084] Particularly when the piston engine is designed as a reciprocating engine, it is especially preferred that the flow paths open into the combustion chamber at positions which, in a radial direction normal to a central axis of the combustion chamber, are at least partially separated by a distance corresponding to at least 50% of the maximum extent of the combustion chamber in this radial direction. This allows fuel to be introduced into the combustion chamber simultaneously at widely spaced positions, thereby achieving good mixture homogenization and optimal mixture ignition in the combustion chamber.

[0085] In a reciprocating piston engine, the central axis is defined as a straight line parallel to the direction of piston movement within the combustion chamber, and located in the center of the combustion chamber. The central axis can also be a cylinder axis if the combustion chamber is cylindrical.

[0086] If the piston engine is not designed as a reciprocating piston engine, but for example as a rotary piston engine, it is preferably provided that the positions at which the flow paths open into the combustion chamber have a distance from each other in one direction that is at least 50% of the extent of the combustion chamber in that direction, at the time of ignition. The positions can be spaced apart from each other in any direction, in particular in a circumferential direction and / or in a direction of rotation of the rotary piston and / or in a direction parallel to the axis of rotation of the rotary piston.

[0087] It is advantageous if the piston engine is designed to introduce fuel via the injector while the piston is at top dead center and / or while the piston is moving from top dead center to bottom dead center during an intake stroke and / or while the piston is moving from bottom dead center to top dead center during a compression stroke.

[0088] Typically, a piston engine has a control unit which, for example, may be designed to control the injector in a corresponding manner when the piston moves accordingly.

[0089] The intake stroke is usually understood as a period in which the piston moves from top dead center to bottom dead center, during which no combustion takes place and one or more intake valves are at least temporarily open.

[0090] Preferably, at least two positions are spaced apart by a distance of at least 30%, advantageously at least 50%, and particularly advantageously at least 70% of the combustion chamber diameter. This allows fuel to be introduced at widely spaced positions to achieve good mixture formation and homogenization.

[0091] It is particularly preferred that the flow paths have different lengths, wherein at least one flow path, which differs from a flow path with a maximum length, has at least one intermediate chamber into which at least one channel opens, connecting the intermediate chamber to the pre-chamber, the intermediate chamber having a cross-section larger than the cross-section of a channel opening into the intermediate chamber. In this way, an equalization of flow times and combustion times along the individual flow paths can be achieved, which is particularly advantageous with a pre-chamber that is compact compared to the combustion chamber and widely spaced positions. This allows for the approximately simultaneous introduction of fuel via the individual flow paths and the approximately simultaneous ignition of a mixture in the combustion chamber starting from the pre-chamber.

[0092] It is preferably provided that the channel connecting the intermediate chamber to the pre-chamber has a curvature and / or a non-circular cross-section and / or opens tangentially into the intermediate chamber. This results in a cylindrical flow, thereby realizing an advantageous flow path, which in particular achieves an advantageous deceleration of the flow and / or the combustion velocity and / or homogenization of the mixture during backflow.

[0093] It is advantageous if at least one position has a distance from the central axis of the combustion chamber of less than 15%, advantageously less than 10%, and particularly advantageously less than 5% of the combustion chamber diameter, and / or if at least one position has a distance from the central axis of the combustion chamber of more than 25%, advantageously more than 35%, and particularly advantageously more than 40% of the combustion chamber diameter. This allows for the introduction of fuel evenly distributed throughout the combustion chamber and ignition at positions evenly distributed throughout the combustion chamber.

[0094] Typically, an ignition device such as a spark plug is arranged in the pre-chamber and / or in an intermediate chamber, so that the mixture in the combustion chamber can be ignited from the pre-chamber or the intermediate chamber via the flow paths, at several positions in the combustion chamber approximately simultaneously, so that a particularly short combustion time is achieved, which allows for high efficiency.

[0095] If one or more flow paths with an intermediate chamber are provided, it is preferably provided that at least one flow path having the intermediate chamber, and in particular all flow paths with an intermediate chamber, opens into the combustion chamber at a position that is less than 30%, in particular less than 20%, and most advantageously less than 15% of a combustion chamber diameter from the central axis. In particular, if the pre-chamber is arranged centrally or at a small distance from the central axis, flow paths between the pre-chamber and positions near the central axis are preferably shorter than others. Therefore, an intermediate chamber in these flow paths, which connect the positions near the central axis with the pre-chamber, results in lower combustion velocities being achieved here in order to equalize the combustion times through the individual flow paths.

[0096] It is understood that multiple flow paths can have at least one intermediate chamber. Multiple flow paths can also be configured without intermediate chambers. In principle, it is also possible to provide an intermediate chamber in each flow path. Simultaneous ignition of the mixture at different positions in the combustion chamber can then be achieved, for example, by different designs in the individual intermediate chambers.

[0097] Furthermore, it may be provided that flow paths partially run in common channels and split in channels and / or in intermediate chambers.

[0098] The piston engine according to the invention can be manufactured in a variety of ways. For example, it can be provided that those components of the piston engine which have the pre-chamber, the intermediate chamber and the channels, for example the cylinder head, are manufactured using a 3D printing process.

[0099] To achieve the fastest possible combustion through the pre-chamber, it is preferably provided that the pre-chamber has a radial extent of less than 50%, and in particular less than 30%, of the maximum radial extent of the combustion chamber. This makes it possible to ignite the individual channels radiating from the pre-chamber almost simultaneously, thus achieving particularly short combustion times in the combustion chamber.

[0100] Preferably, the flow paths, in particular the channels, open into the pre-chamber in such a way that a turbulent flow, for example a vortex, swirl, and / or cylindrical flow, is achieved in the pre-chamber. Preferably, at least some flow paths, in particular channels, do not open radially into the pre-chamber in a top view, but rather at an inflow angle to a radial direction oriented normal to a central axis, of 10 degrees to 70 degrees, in particular 20 degrees to 50 degrees.

[0101] Preferably, an ignition device, such as a spark plug, is provided in the pre-chamber, advantageously positioned eccentrically within it. An eccentric arrangement is beneficial for creating turbulence in the pre-chamber, thereby achieving a high flame propagation velocity. Furthermore, this ensures that the ignition spark is triggered off-center within a vortex and not at its center, thus improving the ignition of the mixture.

[0102] It is preferably provided that the ratio of the volume of the pre-chamber to the volume of the intermediate chamber is at least 2, preferably at least 4. This allows a particularly advantageous delay in flame propagation and / or flow rate to be achieved.

[0103] The ratio of the cross-section of the pre-chamber to the cross-section of the intermediate chamber is preferably at least 1.5, more preferably at least 2, and in particular at least 4. The cross-section of the pre-chamber can be considered to be a cross-section in a plane normal to the central axis.

[0104] The pre-chamber and the intermediate chamber can, in principle, have any shape. Preferably, the pre-chamber and / or the intermediate chamber are rotationally symmetrical, in particular rotationally symmetrical about a central axis, preferably lenticular or spherical.

[0105] It is advantageous if the intermediate chamber, viewed along the centerline of the combustion chamber, is arranged between the pre-chamber and the combustion chamber, particularly with axial spacing between each chamber. Viewed from above, the intermediate chamber is preferably arranged radially entirely within the pre-chamber. It is particularly advantageous if the at least one pre-chamber, the at least one intermediate chamber, and the flow paths are arranged outside the combustion chamber. Preferably, the pre-chamber is lenticular or approximately in the form of an ellipsoid in which the short axis coincides with the central axis, and the intermediate chamber is spherical. The pre-chamber and / or intermediate chambers can also be annular, particularly if an injector extending along the central axis is provided.

[0106] The pre-chamber, channels, and one or more intermediate chambers can, in principle, be located in any part of the piston engine, for example, in the engine block or the piston. However, it is particularly preferred that the pre-chamber, one or more intermediate chambers, and the channels connecting the pre-chamber to the intermediate chamber(s) and the one or more intermediate chambers to the combustion chamber are located in the cylinder head. This allows existing engines to be retrofitted simply by replacing the cylinder head. Using 3D printing, the cylinder head can be manufactured easily and with virtually any desired geometry.

[0107] Further features, advantages, and effects of the invention will become apparent from the exemplary embodiment described below. The drawings referenced therein show: Fig. 1 a schematic representation of a piston engine according to the invention; Figs. 2 to 4a pre-chamber including flow paths formed by channels and an intermediate chamber connecting the pre-chamber to a combustion chamber, in different views; Fig. 5 A top view from the combustion chamber side of a cylinder head of a piston engine according to the invention, including inlet and outlet valves.

[0108] Fig. 1 Figure 1 shows a schematic representation of a piston engine according to the invention, designed as a reciprocating engine. Visible is a piston 18 connected to a shaft 20 designed as a crankshaft, which is translationally movable along a central axis 6 by combustion of a mixture in a cylindrical combustion chamber 19 in order to set the shaft 20 into a rotary motion about an engine axis.

[0109] As shown, the reciprocating engine has a prechamber 1 and flow paths 2 of different lengths, via which the prechamber 1 is connected to the combustion chamber 19 at different positions 5a, 5b. The prechamber 1 has a smaller diameter in a radial direction 7 and a shorter length along the central axis 6 than the combustion chamber 19, and is therefore more compact than the combustion chamber 19. This results in flow paths 2 of different lengths, which connect the prechamber 1 to positions 5a, 5b distributed around the combustion chamber 19. Positions 5b near the central axis 6 are thus connected to the prechamber 1 via shorter flow paths 2 than positions 5a further out in the combustion chamber 19, which have a greater distance from the central axis 6.

[0110] In order to achieve approximately the same flow times or burn times along the individual flow paths 2 despite their different lengths, an intermediate chamber 4 is arranged in the shorter flow paths 2, which causes a delay in the flow and the flame propagation.

[0111] An injector 13 opens into the pre-chamber 1, through which fuel, in particular hydrogen, can be introduced into the pre-chamber 1 at a high pressure of, for example, several hundred bar. Due to its low specific gravity and the pressure at which it is introduced, the hydrogen can then spread from the pre-chamber 1 into the combustion chamber 19 via the flow paths 2, thus ensuring a homogeneous mixture formation in the combustion chamber 19.

[0112] Furthermore, an ignition device 12, here formed by a spark plug, is provided in the pre-chamber 1, with which the mixture in the pre-chamber 1 can be ignited so that flame fronts emanating from the pre-chamber 1 can ignite the mixture located in the combustion chamber 19 at different positions 5a, 5b via the individual flow paths 2. This allows combustion of the mixture in the combustion chamber 19 to occur within a very short period of time, thereby achieving high efficiency.

[0113] As can be seen, channel 3, which connects the pre-chamber 1 with the intermediate chamber 4, is curved or has a curved centerline 8, so that a tumble flow is achieved, which ensures a particularly advantageous flow. This channel 3 can also be referred to as tumble channel 11.

[0114] Figs. 2 to 4Figures 1 and 2 show a pre-chamber 1 including flow paths 2, which fluidically connect the pre-chamber 1 with positions 5a, 5b in a combustion chamber 19 of a reciprocating engine (not shown), wherein the flow paths 2 are formed by channels 3 and partly by channels 3 and an intermediate chamber 4.

[0115] As can be seen, several flow paths 2 are provided which fluidically connect the pre-chamber 1 to the combustion chamber 19. In the illustrated embodiment, twelve flow paths 2 connect the pre-chambers 1 to positions 5a located further out in the combustion chamber 19, i.e., positions 5a which are further away from a central axis 6 of the combustion chamber 19, while five flow paths 2 are provided which open into an approximately central region of the combustion chamber 19 closer to the central axis 6 at positions 5b and are therefore shorter.

[0116] The flow paths 2 opening into the outer areas of the combustion chamber 19 are formed by four channels 3 opening into the pre-chamber 1, which four channels 3 opening into the pre-chamber 1 subsequently each divide into two channels 3.

[0117] As in the Fig. 4 As can be clearly seen in the top view shown, these four channels 3 do not open radially into the pre-chamber 1, but at an inflow angle 17 of about 40 degrees, so that a flow results in the pre-chamber 1 which has a forced turbulence in the pre-chamber 1, which is advantageous for rapid flame propagation even at low load.

[0118] The five flow paths 2, which open into a central area of ​​the combustion chamber 19, initially run from the pre-chamber 1 through a channel 3, which has a non-circular cross-section, here an approximately rectangular cross-section with rounded corners, and is designed as a tumble channel 11. This channel 3 connects the pre-chamber 1 with an intermediate chamber 4 and also has a curved centerline 8. The centerline 8 is curved about an axis 10, which is approximately perpendicular to a central axis 6 of a cylinder to which the pre-chamber 1 is assigned and which co-defines a combustion chamber 19. This channel 3, which is also referred to as the tumble channel 3, has a curvature with a radius of curvature 9, which is smaller than a combustion chamber diameter in order to achieve favorable turbulence.

[0119] The channel 3, designed as a tumble channel 11, opens into the intermediate chamber 4, not radially, but approximately tangentially, in order to create a cylindrical flow in the intermediate chamber 4, which can be advantageous for deceleration.

[0120] Five channels 3 are connected to the intermediate chamber 4, which connect the intermediate chamber 4 to positions 5b in the combustion chamber 19. These five flow paths 2 thus run together from the pre-chamber 1 to the intermediate chamber 4 in the tumble channel 3 and divide in the intermediate chamber 4 into the five channels 3 that open into the central position 5b in the combustion chamber 19.

[0121] Due to the intermediate chamber 4, a flame propagation speed and a fuel or mixture flow speed along these flow paths 2 are achieved which is lower than the flame propagation speed or flow speed along those flow paths 2 which connect the pre-chamber 1 with the twelve positions 5a located further out in the combustion chamber 19, so that the flame fronts emanating from the pre-chamber 1 and the fuel emanating from the pre-chamber 1 reach the combustion chamber 19 approximately simultaneously despite the different lengths of the individual flow paths 2.

[0122] Accordingly, the mixture that flows back into the pre-chamber 1 before ignition occurs reaches the pre-chamber 1 via the individual flow paths 2 at approximately the same time.

[0123] As in the Figs. 2 to 4The pre-chamber 1 is clearly lenticular in shape, and the intermediate chamber 4 is approximately spherical. The diameter or maximum extent of the pre-chamber 1 in a radial direction 7, which is oriented perpendicular to the central axis 6, is less than 30% of the combustion chamber diameter, resulting in rapid combustion in the pre-chamber 1. The intermediate chamber 4 has an even smaller diameter than the pre-chamber 1. However, the diameter of the intermediate chamber 4 is approximately five times larger than that of the channels 3 opening into the intermediate chamber 4 and than that of the tumble channel 11 between the pre-chamber 1 and the intermediate chamber 4. This results in a favorable reduction of the combustion velocity and the flow velocity in the intermediate chamber 4.As can be seen, the change in cross-section at the transition from channel 3 to intermediate chamber 4 occurs relatively abruptly, in the exemplary embodiment over a few millimeters.

[0124] Prechamber 1 and intermediate chamber 4 are each rotationally symmetrical about the central axis 6 of the combustion chamber 19, although other geometries would of course be possible. This design has proven effective in achieving favorable combustion rates in prechamber 1 and a deceleration in intermediate chamber 4 corresponding to the length differences.

[0125] Fig. 5Figure 1 shows a cylinder head 16 of a piston engine according to the invention in a view from the combustion chamber 19, also showing the intake valves 14 and exhaust valves 15. In this illustration, the different positions 5a, 5b are clearly visible, showing through which fuel is introduced into the combustion chamber 19, from which positions 5a, 5b ignition in the combustion chamber 19 originates, and which positions 5a, 5b are connected to the pre-chamber 1 via the individual flow paths 2.

[0126] As can be seen, six central positions 5b are provided here, which are less far from the central axis 6 than the centers of the intake valves 14 and the exhaust valves 15. Furthermore, positions 5a are provided at which flow paths 2 originating from the pre-chamber 1 open into the combustion chamber 19, which are further away from the central axis 6 in order to introduce fuel into the combustion chamber as evenly as possible and to be able to ignite a mixture located in the combustion chamber 19 at different positions 5a, 5b distributed across the combustion chamber 19.

[0127] In a method according to the invention, a method is preferably used that is located in the Figs. 1 to 5The illustrated engine is operated in such a way that, for example, during an intake stroke, optionally after the intake valves 14 are closed, fuel is introduced at high pressure into the pre-chamber 1, preferably hydrogen in liquid form, after which this fuel spreads from the pre-chamber 1 into the combustion chamber 19 via the flow paths 2 and a mixture is formed in the combustion chamber 19.

[0128] In a compression stroke following the intake stroke, this mixture is thus compressed and forced back into the pre-chamber 1, again via the flow paths 2.

[0129] Subsequently, this mixture is ignited in the pre-chamber 1 starting from the ignition device 12, whereby flame fronts spread via the flow paths 2 from the pre-chamber 1 into the combustion chamber 19 and thus ignite the mixture at the individual positions 5a, 5b approximately simultaneously in the area of ​​the top dead center of the piston 18.

[0130] The working stroke then takes place, whereby the pressure in the combustion chamber 19 increases due to combustion and thereby moves the piston 18 from top dead center towards bottom dead center, driving the crankshaft.

[0131] In a subsequent exhaust stroke, exhaust gas is expelled from combustion chamber 19 or the cylinder. During this exhaust stroke, the pre-chamber 1, including the flow paths 2, can also be purged. The intake stroke then follows.

[0132] With a method according to the invention and a correspondingly designed engine, combustion of hydrogen in particular is possible with particularly high efficiency.

Claims

1. Method for operating a piston engine, in particular a reciprocating piston engine, wherein an ignitable mixture is ignited in a combustion chamber (19) which is adjacent to a piston (18) which piston (18) is connected to a shaft (20) rotating about an engine axis, characterized by the fact that Fuel, in particular hydrogen, is introduced into a pre-chamber (1) by means of an injector (13) and this fuel then spreads from the pre-chamber (1) into the combustion chamber (19) via flow paths (2) which connect the pre-chamber (1) with several positions (5a, 5b) in the combustion chamber (19), after which the fuel mixes with an oxygen-containing gas, in particular air, in the combustion chamber (19) and the ignitable mixture is formed, after which the mixture is ignited in the combustion chamber (19).

2. Method according to claim 1, characterized by the fact thatthe fuel is introduced while the piston (18) is at top dead center and / or while the piston (18) is moved from top dead center to bottom dead center in an intake stroke and / or while the piston (18) is moved from bottom dead center to top dead center in a compression stroke.

3. Method according to claim 1 or 2, characterized by the fact that the fuel is supplied to the combustion chamber (19) via the flow paths (2) at at least two positions (5a, 5b) which have a distance from each other which corresponds to at least 30%, advantageously at least 50% and particularly advantageously at least 70% of a combustion chamber diameter.

4. Method according to any one of the preceding claims, characterized by the fact thatthe fuel is supplied to the combustion chamber (19) at at least one position (5a, 5b) which has a distance from a central axis (6) of the combustion chamber (19) that is less than 15%, advantageously less than 10% and particularly advantageously less than 5% of a combustion chamber diameter and / or is supplied at at least one position (5a, 5b) which has a distance from a central axis (6) of the combustion chamber (19) that is more than 25%, advantageously more than 35% and particularly advantageously more than 40% of a combustion chamber diameter.

5. Method according to any one of claims 1 to 4, characterized by the fact that the fuel is supplied to the combustion chamber (19) via the flow paths (2) at at least four, preferably at least eight, positions (5a, 5b), which positions (5a, 5b) preferably open into the combustion chamber (19) in an approximately regularly distributed manner.

6. Method according to any one of the preceding claims, characterized by the fact thatthe fuel is supplied to the combustion chamber (19) via flow paths (2) of different lengths.

7. Method according to any of the preceding claims, characterized by the fact that a portion of the fuel, which spreads from the pre-chamber (1) into the combustion chamber (19), passes along a flow path (2) at least one intermediate chamber (4), wherein the portion of the fuel is in particular slowed down when passing the intermediate chamber (4).

8. Method according to any one of the preceding claims, characterized by the fact that the mixture formed in the combustion chamber (19) during a compression stroke is forced into the pre-chamber (1) via the flow paths (2), after which ignition of the mixture in the pre-chamber (1) takes place, in particular with an ignition device (12) such as a glow plug or a spark plug.

9. Method according to claim 8, characterized by the fact thata part of the mixture, which is forced from the combustion chamber (19) into the pre-chamber (1), passes along a flow path (2) at least one intermediate chamber (4), wherein the part of the mixture is in particular slowed down when passing the intermediate chamber (4).

10. Method according to any one of the preceding claims, characterized by the fact that Ignition of the mixture in the combustion chamber (19) occurs via flame fronts emanating from the pre-chamber (1), which spread via the flow paths (2) into the combustion chamber (19) and ignite the mixture in the combustion chamber (19) at several positions (5a, 5b).

11. Piston engine, in particular a reciprocating piston engine, comprising a combustion chamber (19), a movable piston (18) adjoining the combustion chamber (19) for setting a shaft (20) into rotary motion by means of the piston (18) igniting an ignitable mixture in the combustion chamber (19), a pre-chamber (1) which is fluidically connected to the combustion chamber (19) at several positions (5a, 5b) via several flow paths (2), wherein the flow paths (2) are each at least partially formed by channels so that the mixture in the combustion chamber (19) can be ignited by igniting an ignitable mixture in the pre-chamber (1), and an injector (13) for introducing fuel, in particular hydrogen, into the pre-chamber (1), wherein the piston engine is configured to form the ignitable mixture in the combustion chamber (19) by introducing fuel, in particular at high pressure, into the pre-chamber (1).which fuel subsequently spreads via the flow paths (2) into the combustion chamber (19) and mixes in the combustion chamber (19) with an oxygen-containing gas, wherein the piston engine is particularly configured to carry out a method according to one of claims 1 to 10.

12. Piston engine according to claim 11, characterized by the fact that the piston engine is configured to introduce fuel by means of the injector (13) while the piston (18) is at top dead center and / or while the piston (18) is moving from top dead center to bottom dead center in an intake stroke and / or while the piston (18) is moving from bottom dead center to top dead center in a compression stroke.

13. Piston engine according to claim 11 or 12, characterized by the fact thatat least two positions (5a, 5b) have a distance from each other which corresponds to at least 30%, advantageously at least 50% and particularly advantageously at least 70% of a combustion chamber diameter.

14. Piston engine according to one of claims 11 to 13, characterized by the fact thatthe flow paths (2) have different lengths, wherein at least one flow path (2) which differs from a flow path (2) with a maximum length has at least one intermediate chamber (4) into which at least one channel (3) opens, which connects the intermediate chamber (4) with the pre-chamber (1), wherein the intermediate chamber (4) has a cross-section which is larger than a cross-section of a channel (3) opening into the intermediate chamber (4), wherein it is preferably provided that the channel (3) which connects the intermediate chamber (4) with the pre-chamber (1) has a curvature and / or a non-circular cross-section and / or opens tangentially into the intermediate chamber (4).

15. Piston engine according to one of claims 11 to 14, characterized by the fact thatat least one position (5a, 5b) has a distance from a central axis (6) of the combustion chamber (19) which distance is less than 15%, advantageously less than 10% and particularly advantageously less than 5% of a combustion chamber diameter and / or that at least one position (5a, 5b) has a distance from a central axis (6) of the combustion chamber (19) which distance is more than 25%, advantageously more than 35% and particularly advantageously more than 40% of a combustion chamber diameter.

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