Piston engine and method for operating a piston engine

Abstract

The invention relates to a piston engine, in particular a reciprocating piston engine, with a combustion chamber (19) into which an ignitable mixture can be introduced in order to set a shaft (22) into a rotary motion about an engine axis (21) by means of a movable piston (18) adjacent to the combustion chamber (19) by means of ignition of the mixture in the combustion chamber (19), and with a pre-chamber (1) which is fluidically connected to the combustion chamber (19) via several flow paths (2), wherein the flow paths (2) are each at least partially formed by transfer channels (3) so that the mixture in the combustion chamber (19) can be ignited by ignition of an ignitable mixture in the pre-chamber (1), wherein the flow paths (2) have different lengths.In order to achieve simultaneous initiation of combustion in the combustion chamber (19) at different positions (5) despite flow paths (2) of different lengths, the invention provides that at least one flow path (2), which differs from a flow path (2) with a maximum length, has an intermediate chamber (4) into which a transfer 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 the transfer channel (3) opening into the intermediate chamber (4).The invention further relates to a method for operating a piston engine wherein an ignitable mixture is ignited in a combustion chamber (19) which borders a piston (18) which piston (18) is connected to a shaft (22) rotating about an engine axis (21) by igniting an ignitable mixture in a pre-chamber (1) which is connected to the combustion chamber (19) via several flow paths (2), after which flame fronts propagate from the pre-chamber (1) via the flow paths (2) into the combustion chamber (19) and ignite the mixture located in the combustion chamber (19), so that the shaft (22) is moved by means of the piston (18) due to a pressure increase in the combustion chamber (19).

Description

[0001] The invention relates to a piston engine, in particular a reciprocating piston engine, with a combustion chamber into which an ignitable mixture can be introduced in order to set a shaft into a rotary motion about an engine axis by igniting the mixture in the combustion chamber by means of a movable piston adjacent to the combustion chamber, and with a pre-chamber which is fluidically connected to the combustion chamber via several flow paths, wherein the flow paths are each at least partially formed by transfer channels, so that the mixture in the combustion chamber can be ignited by igniting an ignitable mixture in the pre-chamber, wherein the flow paths have different lengths.

[0002] The invention further relates to a method for operating a piston engine, wherein an ignitable mixture is ignited in a combustion chamber adjacent to a piston, which piston is connected to a shaft rotating about an engine axis, by igniting an ignitable mixture in a pre-chamber which is connected to the combustion chamber via several flow paths, after which flame fronts propagate from the pre-chamber via the flow paths into the combustion chamber and ignite the mixture located in the combustion chamber, so that the shaft is moved by means of the piston due to a pressure increase in the combustion chamber.

[0003] Engines and methods of the type mentioned above are known from the prior art for initiating ignition of the mixture in the combustion chamber at several positions, particularly in spark-ignition engines, in order to achieve a short combustion time in the combustion chamber. For example, document AT 523836 A4 discloses a reciprocating piston engine with a pre-chamber which is connected to a combustion chamber via several transfer ports in order to achieve ignition of the mixture in the combustion chamber at different positions.

[0004] However, it has been shown that even with the engine disclosed in this document, a thermodynamically non-ideal combustion is achieved, which leads to losses.

[0005] This is where the invention comes in. The object of the invention is to provide a piston engine of the type mentioned above, which can be operated in a particularly efficient manner.

[0006] Furthermore, a method of the type mentioned at the beginning will be specified, with which a particularly high efficiency can be achieved.

[0007] The first problem is solved according to the invention by a piston engine of the type mentioned at the outset, in which 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 overflow channel opens, which connects the intermediate chamber with the pre-chamber, wherein the intermediate chamber has a cross-section which is larger than a cross-section of the overflow channel opening into the intermediate chamber.

[0008] This allows for at least nearly simultaneous ignition of the mixture in the combustion chamber, thereby increasing efficiency.

[0009] Within the scope of the invention, it was recognized that even in a piston engine, in which ignition is initiated from a pre-chamber via transfer ports in several positions in the combustion chamber, the flame fronts reach the combustion chamber at different times due to the different lengths of the transfer ports, so that ignition via the individual transfer ports occurs at noticeably different times.

[0010] According to the invention, this disadvantage is overcome by arranging at least one intermediate chamber in at least one flow path that is not the flow path with maximum length. The intermediate chamber causes a delay in flame propagation in this shorter flow path, so that a lower average flame propagation velocity is achieved in the flow path containing the intermediate chamber than in the longest flow path. Thus, despite the different lengths of the flow paths, the flame fronts reach the combustion chamber at least almost simultaneously, so that, compared to prior art methods, the time difference between the point in time when a first flame front reaches the combustion chamber and the point in time when a last flame front reaches the combustion chamber is significantly reduced.

[0011] The intermediate chamber is preferably designed such that the flow velocity or flame propagation velocity is reduced at the intermediate chamber. The flame propagation velocities in the individual flow paths can be adapted to the lengths of the individual flow paths by one or more intermediate chambers in such a way that identical burn times are achieved along all flow paths and the flame fronts emanating from one or more pre-chambers reach the different positions in the combustion chamber simultaneously.

[0012] A fuel used for mixture formation can be, for example, gasoline, diesel, hydrogen and / or natural gas.

[0013] The cross-section of the overflow 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 overflow channel or the respective intermediate chamber, normal to the respective flow path.

[0014] It is preferably provided that the intermediate chamber, along the flow path from the pre-chamber to the combustion chamber, first causes an increase in cross-sectional area and then a decrease in cross-sectional area.

[0015] 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 overflow 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 by a factor of 2, and particularly preferably by at least a factor of 3. Advantageously, the cross-section tapers abruptly again along the flow path, preferably at the end of the intermediate chamber or at a transition from the intermediate chamber to an overflow channel following the intermediate chamber.Such a relatively abrupt change in cross-section significantly reduces the flame propagation speed, allowing the burn times along the shorter flow paths to be adjusted to those of the longest flow paths, thus achieving the most simultaneous possible ignition of the mixture in the combustion chamber. The intermediate chamber is preferably designed as a retarding chamber, intended to delay flame propagation towards the combustion chamber along the flow path.

[0016] It is advantageous if the cross-section of at least one transfer channel connecting the pre-chamber and the intermediate chamber is larger than the cross-section of one or more transfer channels connecting the intermediate chamber and the combustion chamber.

[0017] Furthermore, it is advantageous if the cross-section of the at least one overflow channel connecting the pre-chamber and the intermediate chamber is larger than the cross-section of one or more of the overflow channels that are assigned to flow paths that do not have intermediate chambers.

[0018] Furthermore, it is advantageous if the cross-section of at least one, preferably all, of the transfer channels connecting the intermediate chamber and the combustion chamber is smaller than the cross-section of the intermediate chamber.

[0019] Preferably, the maximum cross-section of the intermediate chamber is greater than or equal to the channel length of the at least one transfer channel connecting the pre-chamber and the intermediate chamber, and / or greater than or equal to the channel length of the at least one transfer channel connecting the intermediate chamber and the combustion chamber.

[0020] It is also advantageous if the pre-chamber is only connected to the combustion chamber via the flow paths.

[0021] Preferably, the piston engine comprises at least one flow path without an intermediate chamber, wherein this flow path is preferably the longest flow path or not the shortest flow path. A flow path without an intermediate chamber is preferably formed entirely by a transfer channel, particularly one with a constant cross-section.

[0022] 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, advantageously at least twice greater, particularly advantageously at least four times greater and most advantageously at least six times greater than the second distance.

[0023] Preferably, the maximum cross-section of the intermediate chamber is larger than the maximum cross-section of the overflow channel.

[0024] It is advantageous if each cross-section of the intermediate chamber is larger than each cross-section of the overflow channel.

[0025] The intermediate chamber can, in principle, have any shape suitable for reducing the flame propagation velocity compared to a transfer channel. Preferably, the ratio of the intermediate chamber's extent in a direction normal to the flow path to the extent of the transfer channel connecting the pre-chamber and intermediate chamber, normal to the flow path, is at least 1.5, particularly at least 2, and preferably at least 4.

[0026] Preferably, both the overflow 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 an overflow channel opening into the intermediate chamber is at least 1.5, more preferably at least 2, and most preferably at least 4.

[0027] Furthermore, it is preferably provided that the transfer 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 an entire length of the transfer channels.

[0028] The overflow 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.

[0029] Preferably, it is provided that one or more transfer 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 positions spaced apart from each other.

[0030] A piston engine according to the invention can be designed as either a rotary piston engine, for example as a Wankel engine, or a reciprocating piston engine. Preferably, the piston engine is designed such that combustion is initiated at several positions in the combustion chamber, which are distributed throughout the combustion chamber. Due to the different lengths of the flow paths, combustion can advantageously be initiated at particularly widely spaced and / or widely distributed positions in the combustion chamber.

[0031] If the piston engine is designed as a reciprocating engine, it is particularly 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 that corresponds to at least 50% of the maximum extent of the combustion chamber in this radial direction. This allows ignition of a mixture in the combustion chamber to be initiated at widely spaced positions, resulting in short combustion times.

[0032] 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.

[0033] 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.

[0034] It is further preferably provided that at least one flow path, which includes the intermediate chamber, and in particular all flow paths with an intermediate chamber, opens into the combustion chamber at a position which is less than 30%, in particular less than 20%, and most advantageously less than 15% of the combustion chamber diameter from the central axis. In particular, when 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.

[0035] 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.

[0036] Furthermore, it may be provided that flow paths partially run in common overflow channels and split in overflow channels and / or in intermediate chambers.

[0037] 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 transfer ports, for example the cylinder head, are manufactured using a 3D printing process.

[0038] 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 transfer channels radiating from the pre-chamber almost simultaneously, thus achieving particularly short combustion times in the combustion chamber.

[0039] Preferably, the flow paths, in particular the transfer 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 transfer 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.

[0040] Preferably, an ignition device, such as a spark plug, is provided in the pre-chamber, advantageously positioned eccentrically within the pre-chamber. 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.

[0041] In order to delay flame propagation along a flow path which has an intermediate chamber and at the same time ensure good purging of the intermediate chamber, it is preferably provided that the ratio of a volume of the pre-chamber to a volume of the intermediate chamber is at least 2, preferably at least 4.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] Preferably, the prechamber is lenticular or approximately ellipsoidal in shape, with the short axis coinciding with the central axis, and the intermediate chamber is spherical. The prechamber and / or intermediate chambers can also be annular, particularly if an injector extending along the central axis is provided.

[0046] The pre-chamber, transfer ports, 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 transfer ports connecting the pre-chamber to the intermediate chamber(s) and the intermediate chamber(s) 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.

[0047] To achieve a particularly effective delay of flame propagation in an intermediate chamber, it is preferably provided that the intermediate chamber is connected to the pre-chamber by a transfer channel having a curved centerline. This introduces a swirl, turbulence, vortex, and / or tumble into the flow, which causes a delay in flame propagation in the intermediate chamber following the transfer channel with the curved centerline. Furthermore, this can generate a swirl, turbulence, vortex, and / or tumble in the pre-chamber and / or intermediate chamber, which improves the purging of the chambers and / or mixture formation in the chambers.

[0048] A curved center line can also be provided for transfer ports connecting the intermediate chamber to the combustion chamber and / or for transfer ports connecting the pre-chamber to the combustion chamber. These transfer ports can also be designed as tumble channels.

[0049] 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.

[0050] Preferably, the ratio of a combustion chamber diameter to a radius of curvature is greater than 0.5, preferably 0.7 to 10, and particularly 1.5 to 5. It is advantageous if such a transfer channel has a corresponding, and in particular constant, curvature up to its entry into the intermediate chamber, preferably along the entire length of the transfer channel.

[0051] It may preferably be provided that at least one transfer channel, in particular a transfer 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 the combustion velocity in the intermediate chamber can be achieved.

[0052] It is advantageous if at least one overflow 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.

[0053] 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.

[0054] The piston engine can be designed such that mixture formation occurs upstream of an intake valve, so that the combustion chamber is filled with an ignitable mixture during an intake stroke. Alternatively or additionally, fuel can be injected directly into the combustion chamber, so that mixture formation occurs partially or completely within the combustion chamber itself. To achieve an ignitable mixture in the pre-chamber, ignitable mixture can be forced from the combustion chamber into the pre-chamber during a compression stroke. Alternatively or additionally, fuel can be injected into the pre-chamber and / or the transfer ports or one or more intermediate chambers.

[0055] To achieve a particularly ignitable mixture in the pre-chamber, at least one transfer port, especially one in a flow path connecting the combustion chamber to the pre-chamber without an intermediate chamber, can be connected to a channel injector to introduce fuel into the transfer port. During the compression stroke, when the mixture is forced from the combustion chamber into the pre-chamber via the transfer ports and intermediate chambers, fuel can then be injected through this channel injector, resulting in a potentially very rich mixture and / or a mixture with a lambda value less than 1 in the pre-chamber, which is highly ignitable.

[0056] Preferably, the flow paths are designed such that the piston engine can be used to operate a process in which the shaft is moved by less than 20 degrees, particularly less than 15 degrees, preferably less than 10 degrees, from the ignition of the mixture in the combustion chamber by a first flame front to the ignition of the mixture in the combustion chamber by a final flame front. For this purpose, for example, no intermediate chambers may be arranged in the longest flow path(s), which connect, for instance, the pre-chamber to an edge of the combustion chamber, and one or more intermediate chambers may be arranged in flow paths that connect the pre-chamber to central areas of the combustion chamber, so that the flow paths are correspondingly shorter, in order to achieve approximately the same combustion times despite the different lengths of the individual flow paths.

[0057] It is particularly advantageous if an injector leading into the combustion chamber is arranged in such a way that it allows fuel injection into a flow path connected to the pre-chamber, especially during a compression stroke. The injector can then be used, for example, to inject fuel into the combustion chamber at different times during a stroke, such as once during the intake stroke to distribute fuel homogeneously within the combustion chamber, and again during the compression stroke to introduce fuel into the pre-chamber via the transfer port when the gas mixture in the combustion chamber is forced into the pre-chamber. This enriches the mixture in the pre-chamber and / or an intermediate chamber, which is beneficial for rapid combustion in the pre-chamber.To facilitate the introduction of fuel into the pre-chamber via the transfer channel leading into the combustion chamber, where the injector is preferably located adjacent, this transfer channel or flow path adjacent to the injector can have a collection chamber at its end. This chamber is designed and positioned relative to the injector such that it captures the fuel injected by the injector during the compression stroke. The collection chamber can, for example, be designed as an end-end cross-sectional enlargement in the flow path.

[0058] The further problem is solved according to the invention by a method of the type mentioned at the outset, in which at least one flame front, which propagates along a flow path from the pre-chamber into the combustion chamber, which flow path differs from a flow path with maximum length, passes through an intermediate chamber, wherein the flame front is in particular slowed down when passing through the intermediate chamber.

[0059] In this way, the different speeds at which the flame fronts propagate along the individual flow paths equalize the varying lengths of the flow paths, ensuring that the flame fronts reach the combustion chamber at least essentially simultaneously. This allows for approximately simultaneous ignition of the mixture at different positions within the combustion chamber, resulting in a thermodynamically very favorable constant-volume combustion.

[0060] The inventive method is preferably implemented with a piston engine according to the invention, in particular a reciprocating piston engine.

[0061] It is advantageous if the process is implemented in such a way that, 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 wave is moved by less than 20 degrees, in particular less than 15 degrees, preferably less than 10 degrees.

[0062] It is particularly preferred that during a compression stroke, fuel is injected via an injector leading into the combustion chamber, with fuel being injected into a flow path. This results in a rich mixture in the pre-chamber, especially since the additional injection during the compression stroke enriches the mixture that is forced into the pre-chamber. This ensures rapid combustion in the pre-chamber and thus particularly effective ignition of the mixture in the combustion chamber.

[0063] 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; Fig. 2 bis 4 a pre-chamber including flow paths formed by transfer channels and an intermediate chamber connecting the pre-chamber to a combustion chamber, in different views; Fig. 5 a cross-section through a piston engine according to the invention; Fig. 6 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.

[0064] Fig. 1 Figure 1 shows a schematic diagram of a piston engine according to the invention, designed as a reciprocating engine. Visible is a piston 18 connected to a shaft 22 designed as a crankshaft, which is translationally movable along a central axis 6 by combustion of a mixture in a combustion chamber 19 in order to set the shaft 22 into a rotary motion about an engine axis 21.

[0065] Ignition of the mixture in the combustion chamber 19 can be initiated from a pre-chamber 1, in which an ignition device 23 such as a spark plug is provided, via several flow paths 2, which flow paths 2 fluidically connect the pre-chamber 1 to the combustion chamber 19 at different positions 5a, 5b. Positions 5b are located near the central axis 6 and positions 5a are located further away from the central axis 6.

[0066] The flow paths 2 have transfer channels 3 or are formed exclusively by transfer channels 3. In order to achieve the most simultaneous possible ignition of the mixture in the combustion chamber 19 at the different positions 5a, 5b despite the different lengths of the flow paths 2, shorter flow paths 2, which connect the pre-chamber 1 with positions 5b near the central axis 6, have an intermediate chamber 4 in addition to transfer channels 3. This intermediate chamber delays flame propagation. Furthermore, a transfer channel 3, which connects the pre-chamber 1 with the intermediate chamber 4, is designed as a tumble channel 11, so that turbulence is achieved in the intermediate chamber 4.

[0067] To introduce fuel into the combustion chamber 19, an injector 13 is provided. Fuel can also be introduced via the injector 13 during a compression stroke to enrich the mixture in the pre-chamber 1. To ensure that fuel introduced during the compression stroke reaches the pre-chamber 1 particularly reliably, the injector 13 is located near position 5a, where a flow path 2 opens into a collection chamber 20 of the combustion chamber 19. As can be seen, several flow paths 2 can also lead, at least partially, through a single transfer channel 3, here the tumble channel 11, and only separate later, particularly in the intermediate chamber 4.

[0068] Fig. 2 bis 4 Figures 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 transfer channels 3 and partly by transfer channels 3 and an intermediate chamber 4.

[0069] 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-chamber 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 a roughly central region of the combustion chamber 19 closer to the central axis 6 at positions 5b and are therefore shorter.

[0070] The flow paths 2 opening into the outer areas of the combustion chamber 19 are formed by four transfer channels 3 opening into the pre-chamber 1, which four transfer channels 3 opening into the pre-chamber 1 are subsequently each divided into two transfer channels 3.

[0071] As in the Fig. 4 As can be clearly seen in the top view shown, these four transfer 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 promotes forced turbulence in the pre-chamber 1, which is advantageous for rapid flame propagation even at low loads.

[0072] The five flow paths 2, which open into a central area of ​​the combustion chamber 19, initially extend from the pre-chamber 1 via a transfer 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 transfer 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 type of transfer channel 3 can also be referred to as a tumble channel 11. In the exemplary embodiment, the radius of curvature 9 is smaller than the combustion chamber diameter in order to achieve turbulence favorable for rapid combustion.

[0073] The overflow 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.

[0074] Five transfer 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 11 and divide in the intermediate chamber 4 into the five transfer channels 3 that open into the central positions 5b in the combustion chamber 19. Due to the intermediate chamber 4, a flame propagation velocity is achieved along these flow paths 2 which is lower than the flame propagation velocity in the flow paths 2 that 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 reach the combustion chamber 19 approximately simultaneously, despite the different lengths of the individual flow paths 2.

[0075] For ignition of the mixture in the prechamber 1, an ignition device such as a spark plug is preferably connected to or arranged in the prechamber 1, wherein ignition of the mixture in the prechamber 1 preferably takes place eccentrically.

[0076] Furthermore, as shown, a channel injector 12 is provided through which fuel can be injected into the transfer port 3. By injecting fuel into the transfer port 3 during a compression stroke, in which a gas mixture from the combustion chamber 19 is forced into the pre-chamber 1 via the transfer ports 3 or the intermediate chamber 4, the mixture in the pre-chamber 1 can be enriched, making it more easily ignitable.

[0077] As in the Fig. 2 bis 4 The 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 more than five times larger than that of the transfer channels 3 opening into the intermediate chamber 4 and than that of the transfer channel 3 between the pre-chamber 1 and the intermediate chamber 4, which is designed as a tumble channel 11. This results in a favorable deceleration of the combustion rate in the intermediate chamber 4.As can be seen, the change in cross-section at the transition from overflow channel 3 to intermediate chamber 4 occurs relatively abruptly, in the exemplary embodiment over a few millimeters.

[0078] 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.

[0079] Fig. 5 shows a cross-section through an embodiment of a piston engine according to the invention, which is also fundamentally compatible with the one described in Fig. 1 bis 3 The depicted flow network can be combined. Fig. 4 Figure 1 shows a detailed cross-section through the combustion chamber 19 of the piston engine according to the invention, which is designed here as a reciprocating piston engine, showing, among other things, a piston 18 near top dead center and a cross-section through the cylinder head 16. As can be seen, an injector 13 is arranged near the outlet of a flow path 2, and the flow path 2 has a collection chamber 20, i.e., an end-end cross-sectional enlargement, so that fuel introduced by the injector 13 is forced via the collection chamber 20 and the flow path 2 into the pre-chamber 1 to enrich the mixture there.

[0080] Fig. 6 Figure 1 shows the corresponding cylinder head 16 in a further view from the combustion chamber 19, also showing the intake valves 14 and exhaust valves 15. While the pre-chamber and intermediate chamber are visible in this view, the transfer ports 3 opening into the pre-chamber and intermediate chamber are not, as they are not in the plane of the image. It is understood, of course, that corresponding transfer ports 3 are also present here, forming flow paths 2 between the pre-chamber 1 and the combustion chamber 19. One of these flow paths 2 is partially shown.

[0081] In the Fig. 6 On the one hand, the different positions 5a, 5b are clearly visible, through which the ignition in the combustion chamber 19 takes place starting from the pre-chamber 1, or at which positions 5a, 5b the flow paths 2 starting from the pre-chamber 1 lead into the combustion chamber.

[0082] In the Fig. 6 Six central positions 5b are visible 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 be able to ignite a mixture located in the combustion chamber 19 at different positions 5a, 5b distributed over the combustion chamber 19.

[0083] On the other hand, the collection pot 20 is visible here, through which fuel introduced by the injector 13 into the combustion chamber 19 can be captured and transported into the flow path 2. The collection pot 20 is designed as an end-end cross-sectional enlargement in the flow path 2 in order to capture fuel.

[0084] With the in Fig. 5 and 6In the injector 13 shown, injection can take place at different times per cycle, namely on the one hand a main injection for mixture homogenization and on the other hand a secondary injection during the compression stroke to enrich the mixture in the area of ​​the prechamber 1. Fig. 6 Furthermore, the ignition device 23 is also shown, which can cause ignition of the mixture in the pre-chamber 1.

[0085] With the piston engine according to the invention, despite the different lengths of the individual flow paths 2, via which the ignition in the combustion chamber 19 is initiated from the pre-chamber 1, it is possible to initiate the ignition at the different positions 5a, 5b simultaneously, thereby achieving almost uniform combustion.

Claims

1. Piston engine, in particular reciprocating piston engine, with a combustion chamber (19) into which an ignitable mixture can be introduced in order to set a shaft (22) into a rotary motion about an engine axis (21) by means of a movable piston (18) adjacent to the combustion chamber (19) by means of ignition of the mixture in the combustion chamber (19), and with a pre-chamber (1) which is fluidically connected to the combustion chamber (19) via several flow paths (2), wherein the flow paths (2) are each at least partially formed by transfer channels (3) so that the mixture in the combustion chamber (19) can be ignited by ignition of an ignitable mixture in the pre-chamber (1), wherein the flow paths (2) have different lengths, characterized by the fact thatat 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 overflow 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 the overflow channel (3) opening into the intermediate chamber (4).

2. Piston engine according to claim 1, characterized by the fact that a ratio of the extent of the intermediate chamber (4) in a direction normal to the flow path (2) to the extent of the overflow channel (3), which connects the pre-chamber (1) and the intermediate chamber (4) in a direction normal to the flow path (2) is at least 1.5, in particular at least 2, preferably at least 4.

3. Piston engine according to claim 1 or 2, characterized by the fact thatone or more transfer channels (3) are connected to the intermediate chamber (4), which fluidically connect the intermediate chamber (4) to one or more positions (5b) in the combustion chamber (19), in particular to several positions (5b) spaced apart from each other.

4. Piston engine according to one of claims 1 to 3, characterized by the fact that at least one flow path (2) which has the intermediate chamber (4), in particular at least two flow paths (2) with the intermediate chamber (4), opens into the combustion chamber (19) at a position (5b) which has a distance from a central axis (6) of less than 30%, in particular less than 20%, particularly advantageously less than 15% of a combustion chamber diameter.

5. Piston engine according to one of claims 1 to 4, characterized by the fact that a ratio of the volume of the pre-chamber (1) to the volume of the intermediate chamber (4) is at least 2, preferably at least 4.

6. Piston engine according to one of claims 1 to 5, characterized by the fact thatthe pre-chamber (1) and / or the intermediate chamber (4) are rotationally symmetrical, in particular rotationally symmetrical about a central axis (6), preferably lens-shaped or spherical.

7. Piston engine according to one of claims 1 to 6, characterized by the fact that at least one overflow channel (3), in particular the overflow channel (3) which connects the pre-chamber (1) with the intermediate chamber (4), has a curved center line (8).

8. Piston engine according to claim 7, characterized by the fact that a ratio of combustion chamber diameter to radius of curvature (9) is more than 0.5, preferably 0.7 to 10, in particular 1.5 to 5.

9. Piston engine according to one of claims 1 to 8, characterized by the fact thatat least one overflow channel (3), in particular the overflow channel (3) which connects the pre-chamber (1) with the intermediate chamber (4), has a non-circular cross-section, in particular an elliptical cross-section and / or a cross-section with partially parallel side edges.

10. Piston engine according to one of claims 1 to 9, characterized by the fact that at least one overflow channel (3) opening into the intermediate chamber (4) and / or at least one opening into the pre-chamber (1) opens off-center into the intermediate chamber (4) / pre-chamber (1), in particular tangentially, in order to achieve a flow field that is at least partially cylindrical.

11. Piston engine according to one of claims 1 to 10, characterized by the fact thatat least one transfer channel (3), in particular a transfer channel (3) in a flow path (2) which connects the combustion chamber (19) without an intermediate chamber (4) to the pre-chamber (1), is connected to a channel injector (12) in order to be able to introduce fuel into the transfer channel (3), in particular during a compression stroke.

12. Piston engine according to one of claims 1 to 11, characterized by the fact that an injector (13) opening into the combustion chamber (19) is arranged such that the injector (13) makes it possible to inject fuel into a flow path (2) connected to the pre-chamber (1), in particular during a compression stroke.

13. Method for operating a piston engine, in particular a piston engine according to any one of claims 1 to 12, wherein an ignitable mixture is ignited in a combustion chamber (19) adjacent to a piston (18), which piston (18) is connected to a shaft (22) rotating about an engine axis (21), by igniting an ignitable mixture in a pre-chamber (1) which is connected to the combustion chamber (19) via several flow paths (2), after which flame fronts propagate from the pre-chamber (1) via the flow paths (2) into the combustion chamber (19) and ignite the mixture located in the combustion chamber (19), so that the shaft (22) is moved by means of the piston (18) due to a pressure increase in the combustion chamber (19). characterized by the fact thatat least one flame front, which propagates along a flow path (2) from the pre-chamber (1) into the combustion chamber (19) which differs from a flow path (2) of maximum length, passes an intermediate chamber (4), wherein the flame front is in particular slowed down when passing the intermediate chamber (4).

14. Method according to claim 13, characterized by the fact that from the ignition of the mixture in the combustion chamber (19) by means of a first flame front to the ignition of the mixture in the combustion chamber (19) by means of a last flame front, the shaft (22) is moved by less than 20 degrees, in particular less than 15 degrees, preferably less than 10 degrees.

15. Method according to claim 13 or 14, characterized by the fact that Injection is carried out by means of an injector (13) opening into the combustion chamber (19), whereby fuel is injected into a flow path (2), in particular during a compression stroke.

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