Method for the spatial distribution of fuel in the combustion chamber of an internal combustion engine with a specific nozzle and cylinder piston configuration of the internal combustion engine

Abstract

Method for mixture formation in a direct-injection internal combustion engine (100) with at least one cylinder head (40) and at least one cylinder (20) and a rotatably mounted crankshaft, wherein the at least one cylinder (20) has at least one inlet opening on an inlet side for supplying combustion air and at least one outlet opening on an outlet side for removing combustion gases, wherein a combustion chamber (10) is formed which is bounded by a piston crown of a cylinder piston (30) belonging to the at least one cylinder (20), a cylinder inner wall (21) and the cylinder head (40), wherein the longitudinal axis of the cylinder piston (30) is perpendicular to the axis of rotation of the crankshaft,and the fuel is introduced, at least partially, into a piston-head-side omega-shaped recess (ω, M) in the combustion chamber (10) of the at least one cylinder (20) by means of a multi-hole injection valve (50) having injection openings during at least one injection at a predefinable position of the cylinder piston (30) in the cylinder (20), wherein the multi-hole injection valve (50) is arranged in the cylinder head (40) on the opposite side of the piston-head-side omega-shaped recess (ω, M) of the piston head of the cylinder piston (30), characterized in that radial injection openings (S, r ) and at least one axial injection port (S a ) having a multi-hole injection valve (50) • A first partial quantity of fuel is injected onto the bowl collar (31) with a substantially radial orientation to the longitudinal center axis (Z30) of the cylinder piston (30), whereby fuel is partially injected onto straight bowl sections (34) that extend orthogonally outwards from the longitudinal center axis (Z30) of the cylinder piston (30) to the bowl collar (31), and partially onto the strongly inclined or circular bowl walls (32) that adjoin the bowl collar (31), wherein the bowl walls (32) adjoin the bowl collar (31) and initially extend partially outwards from the longitudinal center axis (Z30) of the cylinder piston (30) and undercut the bowl collar (31) and only then extend inwards towards the center of the bowl towards the longitudinal center axis (Z30) of the cylinder piston (30), and • a second fuel fraction with essentially axial orientation to the longitudinal center axis (Z30) of the cylinder piston (30) onto a raised area (M1; 33-1; M2, 33-2) formed as a platform in the center of the omega-shaped bowl (ω1, M1; ω2, M2) is injected into the combustion chamber (10), such that the direction vector of the at least one via the axial injection opening (S a ) directed injected fuel jet (S) after impact changes in such a way that it aligns with the direction vectors of the jet passing over the steeply inclined or circular trough walls (32) via the radial injection openings (S r ) aligned fuel jets (S).

Description

[0001] The invention relates to a method for mixture formation in a direct-injection internal combustion engine with at least one cylinder head and at least one cylinder and a rotatably mounted crankshaft, wherein the at least one cylinder has at least one intake port on an intake side for supplying combustion air and at least one exhaust port on an exhaust side for removing combustion gases. A combustion chamber is formed, which is bounded by the piston crown of a cylinder piston belonging to the at least one cylinder, a cylinder inner wall and the cylinder head, wherein the longitudinal axis of the cylinder piston is perpendicular to the axis of rotation of the crankshaft.

[0002] In this process, the fuel is introduced at least partially into a piston-side omega-shaped recess in the combustion chamber of the at least one cylinder by means of a multi-hole injection valve having injection openings during at least one injection at a predetermined position of the cylinder piston in the cylinder, wherein the multi-hole injection valve is arranged in the cylinder head on the opposite side of the piston-side omega-shaped recess of the piston base of the cylinder piston.

[0003] In a known manner, the crankshaft is articulated to the cylinder piston of at least one cylinder, so that the cylinder piston oscillates along a longitudinal piston axis when the crankshaft rotates around an axis of rotation.

[0004] In direct injection, a fuel injection method used in diesel and gasoline engines, multi-hole injectors (multi-hole nozzles) are used to inject fuel directly into the combustion chamber of the internal combustion engine. This not only injects the fuel but also distributes it very finely. Multi-hole injectors with varying numbers and arrangements of holes are therefore commonplace.

[0005] In direct injection systems, there is very little time available for mixture formation. Therefore, mixture formation processes are needed to support rapid mixture formation and homogenize the fuel-air mixture as much as possible before ignition. This is important for reducing raw pollutant emissions, especially unburned hydrocarbons, carbon monoxide, and particulate matter.

[0006] In the known wall-guided method, the fuel is injected into the combustion chamber in such a way that the injection jets are directed precisely at a wall bounding the combustion chamber, preferably at the edge of a recess provided in the piston crown. In other words, the injection jets are directed concentrically – with respect to the longitudinal center axis of the cylinder piston – onto the wall-side recess collar in the so-called squish gap between the recess collar and the combustion chamber wall. In this procedure, the recess collar of the piston crown borders the wall area of ​​the combustion chamber, which is usually designed as a cylinder. The fuel jet is intended to be split into several partial jets by the partial impact on the recess collar and the wall and deflected in such a way that the fuel jets cover as large an area of ​​the combustion chamber as possible.The described procedure improves combustion because it creates a fuel swirl that is introduced concentrically from the outside, i.e., from the bowl collar, and develops concentrically towards the center of the cylinder piston, contrary to the injection direction. A fuel swirl represents a vortex whose central axis runs parallel to the longitudinal axis of the piston or cylinder.

[0007] It becomes clear that the desired rapid mixture formation is influenced by the use and arrangement of the multi-hole injector nozzle as well as the alignment of the fuel jets with respect to the combustion chamber and the selected combustion chamber geometry.

[0008] Document US 8,800,529 B2 discloses the arrangement of a multi-hole fuel injector in the cylinder head of an engine. The multi-hole fuel injector is mounted in a central position relative to a combustion chamber in a bore in the cylinder head of the cylinder forming the combustion chamber. The combustion chamber contains an omega-shaped recess that is rotationally symmetrical to the longitudinal axis of a piston located in the cylinder. The document reports on the change in fuel distribution, based on the premise that the specific orientation of the fuel injection ports of the multi-hole fuel injector changes with respect to the geometry of the combustion chamber.

[0009] For example, the longitudinal center axis of the multi-hole injector is once positioned centrally along the longitudinal center axis of the cylinder. In another configuration, the longitudinal center axis of the multi-hole injector is offset parallel to the longitudinal center axis of the cylinder. Finally, in a further configuration, the longitudinal center axis of the multi-hole injector is inclined relative to the longitudinal center axis of the cylinder. These variations result in changes to the fuel distribution in the combustion chamber, while maintaining the same geometric design of the rotationally symmetrical omega-shaped recess.

[0010] Document US 4 548 172 A also reveals a cylinder piston with an omega-shaped recess.

[0011] The publication EP 1 234 966 A2 describes the design and a method for maximizing the intensity of pilot fuel ignition in a gas-powered compression-ignition engine. Of particular interest is the design of the piston bowl in the combustion chamber. The piston includes a cavity in its upper surface. This cavity forms two annular chambers, each located laterally on a platform, which is positioned in the center of the cavity. A flat-head screw is located in the platform, such that its flat head acts as a target for the injected fuel, thus reducing wear on the platform. The fuel stream injected by a nozzle strikes the flat head of the screw, which breaks the fuel droplets into smaller droplets. The fuel is then sprayed from the flat head of the screw and reflected into the annular chamber.The spray then swirls through the annular chambers in a highly turbulent manner, maximizing penetration velocity, distribution, and vaporization, thus resulting in improved mixing of the fuel with the supplied air in the combustion chamber. This arrangement and associated method do not use a multi-hole injector, as the aim is to direct the fuel precisely onto the target, i.e., the platform from which the described fuel distribution into the combustion chamber originates.

[0012] Further state of the art is represented by the publications GB 2 097 471 A, DE 39 01 182 A1 and JP S59 - 79 031 A

[0013] Based on known solutions, the invention aims to provide a method for mixture formation and an internal combustion engine for carrying out the method, with which the fuel-air mixture is formed homogeneously in the combustion chamber of the internal combustion engine.

[0014] The invention is based on a method for mixture formation in a direct-injection internal combustion engine with at least one cylinder head, at least one cylinder and a rotatably mounted crankshaft, wherein the at least one cylinder has at least one inlet opening on an inlet side for supplying combustion air and at least one outlet opening on an outlet side for removing combustion gases, wherein a combustion chamber is formed which is bounded by a piston crown of a cylinder piston belonging to the at least one cylinder, a cylinder inner wall and the cylinder head, wherein the longitudinal axis of the cylinder piston is perpendicular to the axis of rotation of the crankshaft.and the fuel is introduced, by means of a multi-hole injection valve having injection openings, at least partially into a piston-side omega-shaped recess in the combustion chamber of the at least one cylinder during at least one injection at a predefinable position of the cylinder piston in the cylinder, wherein the multi-hole injection valve is arranged in the cylinder head on the opposite side of the piston-side omega-shaped recess of the piston head of the cylinder piston.

[0015] According to the invention, a first partial quantity of fuel is injected onto the bowl collar by means of a multi-hole injection valve having radial injection ports and at least one axial injection port, with a substantially radial orientation to the longitudinal center axis of the cylinder piston, whereby fuel is partially injected onto straight bowl sections that extend orthogonally outwards from the longitudinal center axis of the cylinder piston to the bowl collar, and partially onto the strongly inclined or circular bowl walls that adjoin the bowl collar, wherein the bowl walls adjoin the bowl collar and initially extend partially outwards from the longitudinal center axis of the cylinder piston and undercut the bowl collar, and only then extend inwards towards the center of the bowl towards the longitudinal center axis of the cylinder piston.and a second portion of fuel is injected into the combustion chamber with an essentially axial orientation to the longitudinal center axis of the cylinder piston onto a raised platform in the center of the omega-shaped bowl, such that the direction vector of the at least one injected fuel jet directed via the axial injection opening changes after impact in such a way that it coincides with the direction vectors of the fuel jets directed via the radial injection openings over the steeply inclined or circular bowl walls.

[0016] The specific design of the multi-hole injection valve with radial injection ports and at least one axial injection port, and the specific design of the omega-shaped bowl with a platform raised compared to the adjacent bowl areas, advantageously improve the spatial distribution in the combustion chamber of the internal combustion engine. According to the stated objective of the invention, this improved spatial distribution in the combustion chamber of the internal combustion engine results in a more homogeneous fuel-air mixture.

[0017] Preferably, the fuel fractions injected into the combustion chamber via the radial and axial injection ports of the multi-hole injection valve are combined, mixed, and homogenized in a central combustion chamber zone. The invention advantageously allows, in particular, the spatial distribution of the central combustion chamber zone to be influenced, since the radial and axial injection ports, as explained in more detail in the description, are combined and mixed, thereby homogenizing the fuel-air mixture in an improved manner.

[0018] Furthermore, it is preferably provided that the fuel fractions are varied by changing the number and / or size of the radial injection ports and the at least one or more axial injection ports of the multi-hole injector. Advantageously, this allows for simple control and adjustment of the desired fuel fractions.

[0019] Furthermore, it is proposed that the timing of the fuel fractions introduced into the central combustion chamber zone via the radial injection ports and the at least one axial injection port of the multi-hole injector is controlled by adjusting the geometry of the raised platform relative to the adjacent geometry of the omega-shaped recess. In this way, as explained in more detail in the description section, it is also possible to easily determine the point in time at which the fuel fractions meet in the central combustion chamber zone and mix homogeneously.

[0020] In a preferred embodiment, the method is further characterized by the fact that the second fuel fraction injected via the at least one axial injection port of the multi-hole injection valve reaches the central combustion chamber zone of the combustion chamber before the first fuel fraction injected via the radial injection ports.

[0021] Finally, in another preferred embodiment, the method is characterized by the fact that the second fuel fraction injected via the at least one axial injection port of the multi-hole injection valve reaches the central combustion chamber zone of the combustion chamber simultaneously with the first fuel fraction injected via the radial injection ports.

[0022] The structure of the direct-injection internal combustion engine for carrying out the method is characterized in that the internal combustion engine comprises at least one cylinder head, at least one cylinder and a rotatably mounted crankshaft, wherein the at least one cylinder has at least one intake port on an intake side for supplying combustion air and at least one exhaust port on an exhaust side for removing combustion gases, wherein a combustion chamber is formed which is bounded by a piston crown of a cylinder piston belonging to the at least one cylinder, a cylinder inner wall and the cylinder head, wherein the longitudinal axis of the cylinder piston is perpendicular to the axis of rotation of the crankshaft.and the fuel is introduced, by means of a multi-hole injection valve having injection openings, at least partially into a piston-side omega-shaped recess in the combustion chamber of the at least one cylinder during at least one injection at a predefinable position of the cylinder piston in the cylinder, wherein the multi-hole injection valve is arranged in the cylinder head on the opposite side of the piston-side omega-shaped recess of the piston head of the cylinder piston.

[0023] According to the invention, two modifications of the conventional internal combustion engine are provided compared to the prior art, namely firstly, a multi-hole injection valve with radial injection openings and at least one axial injection opening that projects into the combustion chamber, and secondly, a raised area in the center of the omega-shaped bowl, designed as a platform, is formed.The design provides for straight bowl sections extending outwards from the bowl collar, away from the longitudinal center axis of the cylinder piston, and oriented orthogonally to the longitudinal center axis of the cylinder piston. Inwards from the bowl collar, strongly inclined or circular bowl walls extend inwards towards the longitudinal center axis of the cylinder piston, initially extending outwards from the bowl collar partially away from the longitudinal center axis of the cylinder piston, undercutting the bowl collar, and then inwards towards the center of the bowl and the longitudinal center axis of the cylinder piston.

[0024] It becomes clear that the aforementioned relatively easy-to-implement modifications to the internal combustion engine, compared to the state of the art, can provide a method for better spatial distribution of the fuel in the combustion chamber of the internal combustion engine, which enables the desired homogenization of the fuel in a more effective manner.

[0025] In a first embodiment, it is preferably provided that the raised area of ​​the omega-shaped depression, which is designed as a platform, is designed as a straight platform.

[0026] According to the invention, in a second embodiment, the raised area of ​​the omega-shaped depression, which is designed as a platform, is designed as an omega-shaped platform.

[0027] The advantages of the embodiments explained in more detail in the description section make it clear that, while retaining the omega-shaped recess and modifying the pronounced elevation as a straight platform or as an omega-shaped platform in combination with the radial and axial injection of fuel into the combustion chamber, technical changes have been found whose realization represents effective measures for homogenizing the fuel-air mixture.

[0028] The invention is explained in principle and in two embodiments below with reference to the accompanying drawings. These show: Fig. 1 schematically a combustion chamber of a cylinder to illustrate the previous principle of mixture formation by means of a cross-section through the longitudinal center axis of a cylinder piston and a piston base arranged orthogonally to the longitudinal center axis of the cylinder piston with a ω-hole (omega-hole) of the cylinder piston of an internal combustion engine according to the prior art; Fig. 2 schematically the combustion chamber of the cylinder to illustrate the inventive principle of mixture formation by means of a cross-section through the longitudinal central axis of the cylinder piston and a piston crown arranged orthogonally to the longitudinal central axis of the cylinder piston with a modified ω1 recess (omega recess) of the cylinder piston having a straight platform of an internal combustion engine according to the invention in a first embodiment; and Fig. 3 schematically the combustion chamber of the cylinder to illustrate the principle of mixture formation according to the invention by means of a cross-section through the longitudinal central axis of the cylinder piston and a piston base arranged orthogonally to the longitudinal central axis of the cylinder piston with a modified ω2 recess (Omega recess) of the cylinder piston of an internal combustion engine according to the invention in a second embodiment.

[0029] The Fig. Figure 1 schematically shows a combustion chamber 10 of an internal combustion engine 100 to illustrate the previous principle of mixture formation by means of a cross-section through a longitudinal central axis Z30 of the cylinder piston 30 with a piston base of a cylinder piston 30 arranged orthogonally to the piston longitudinal axis, which is designed with a conventional ω-shaped recess (omega recess).

[0030] The combustion chamber 10 is bounded by the top of the cylinder piston 30 and the inner cylinder wall 21 of the cylinder 20 and the bottom of the cylinder head of a cylinder head 40.

[0031] An inlet valve on an inlet side for at least one inlet opening for supplying combustion air and an outlet valve on an outlet side for at least one outlet opening for removing the combustion gases into the combustion chamber 10 are not shown in detail.

[0032] In the cylinder head 40, a multi-hole injection valve 50 is arranged centrally to the piston center of the cylinder piston 30, which is defined by the longitudinal center axis Z of the cylinder piston 30. This injection valve projects into the combustion chamber 10 of the internal combustion engine 100. In this schematic representation, the longitudinal center axis Z50 of the multi-hole injection valve 50 thus coincides with the longitudinal center axis Z30 of the cylinder piston 30.

[0033] The combustion chamber 10 forms a first rotationally symmetric combustion chamber zone I, which, depending on the position of the cylinder piston 30, is limited by the imaginary extension of the bowl collar 31 of the bowl M in the cylinder piston 30 parallel to the longitudinal axis Z of the cylinder piston 30 upwards and by the respective volume between (squish clearance) piston top of the cylinder piston 30 and cylinder head bottom of the cylinder head 40, depending on the position of the cylinder piston 30 in the cylinder 20.

[0034] The combustion chamber 10 forms a second rotationally symmetrical “central” combustion chamber zone II, which, depending on the position of the cylinder piston 30, is limited upwards and downwards by the imaginary extension of the bowl collar 31 of the bowl M parallel to the longitudinal axis of the cylinder piston 30 by the respective volume between the top of the cylinder piston 30 and the bottom of the cylinder head 40 (squish clearance), depending on the position of the cylinder piston 30 in the cylinder 20.

[0035] The combustion chamber 10 forms a third rotationally symmetrical combustion chamber zone III, which, depending on the position of the cylinder piston 30, is bounded downwards by an undercut formed in this area by the imaginary extension of the bowl collar 31 of the bowl M parallel to the longitudinal axis of the cylinder piston 30, wherein the undercut extends from the center of the piston towards the outer wall of the cylinder piston 30.

[0036] The conventional ω-shaped recess M, which delimits the combustion chamber 10, has geometric properties such as a relatively sharp-edged recess collar 31 that is narrowly tapered towards the longitudinal center axis Z30 of the cylinder piston 30. Straight recess sections 34 extend outwards from the narrowly tapered recess collar 31, away from the longitudinal center axis Z30 of the cylinder piston 30, and are oriented orthogonally to the longitudinal axis of the cylinder piston 30. Inwards from these narrowly tapered recess collars 31, steeply inclined, or circular, recess walls 32 extend inwards towards the longitudinal center axis Z30 of the cylinder piston 30. Starting from the recess collar 31, these walls initially extend partially outwards from the longitudinal center axis Z30 of the cylinder piston 30, undercutting the recess collar 31, and only then extend inwards towards the center of the recess towards the longitudinal center axis Z30 of the cylinder piston 30.

[0037] In the center of the conventional ω-trough, i.e., the center of the trough, a relatively pointed elevation 33 is formed, which overall creates the geometric shape typical of omega-shaped sections.

[0038] In this process, several radially oriented injection jets S are injected via injection ports S at a predetermined position of the cylinder piston 30 within the cylinder 20. r The fuel is directed concentrically onto the bowl collar 31 via the multi-hole injection valve 50. This results in fuel being injected partly onto the bowl sections 34 and partly onto the steeply inclined, or circular, bowl walls 32.

[0039] This results in the fuel swirl already explained, in particular through the injection of fuel onto the strongly inclined or circular bowl walls 32, the axis of which runs parallel to the longitudinal axis of the piston Z, as is illustrated by the fuel direction arrows P.

[0040] Through these in Fig. The geometric design of the ω-trough shown in Figure 1 and the multi-hole injection via the multi-hole injection valve 50 ensure good air utilization, overall good mixture formation and combustion through the formation of several radial injection jets S r The fuel is thus atomized or sprayed before ignition, firstly by the multi-hole injection and secondly by the swirl formation in the ω-trough.

[0041] With regard to the position of the ω recess M relative to the multi-hole injection valve 50 (multi-hole injector), which in Fig. 1 and the Fig. 2 and Fig. Figure 3 is only shown in principle and not in all position variants. In one variant, the center of the ω-recess M is placed directly below the multi-hole injector 50. The longitudinal center axis M50 of the multi-hole injector 50 then does not necessarily coincide with the longitudinal center axis Z30 of the cylinder piston 30. This positioning is referred to as the "injector-specific arrangement of the ω-recess".

[0042] In practice, boundary conditions often arise that do not allow the center of the ω-shaped recess M to be positioned exactly centrally under the multi-hole injection valve 50. In such cases, intermediate positions are usually chosen.

[0043] If the longitudinal center axis Z50 of the multi-hole injector 50 coincides with the longitudinal center axis Z30 of the cylinder piston 30, a "piston-specific arrangement of the ω-recess" is present. In this case, the center of the ω-recess does not necessarily lie on the longitudinal center axis Z50 of the multi-hole injector 50.

[0044] If intermediate positions are selected, the center of the ω-recess M lies neither on the longitudinal center axis Z50 of the cylinder piston 30, nor directly on the longitudinal center axis z50 of the multi-hole injection valve 50. However, the offset of the longitudinal center axis Z50 of the multi-hole injection valve 50 or the longitudinal center axis Z30 of the cylinder piston 30 relative to the center of the ω-recess M is in the single-digit mm range and is therefore very small, so that the effect(s) of the invention described below occurs in all positioning cases.

[0045] According to the invention, it is proposed to modify the known rotationally symmetric ω-trough M, for which purpose the following is shown based on the Fig. 2 and Fig. 3 Two embodiments will be explained in detail.

[0046] The structural modification of the ω-trough advantageously leads to an even better homogenization of the fuel-air mixture in the combustion chamber of the internal combustion engine compared to previous methods.

[0047] It has been found that the swirl or turbulence of the fuel, as previously explained, and according to the fuel arrows P in Fig. As shown in Figure 1, although good homogenization of the fuel-air mixture occurs, combustion is initiated from the outside by the swirl and then burns towards the center against the injection direction. In a sense, with radial multi-hole injection, a homogeneous mixture only forms with a delay in the center of the bowl or the combustion chamber 10 via the bowl collar 31, since the injection jets S, which were previously injected exclusively radially into the ω-bowl M, r at least partially, first pass through the third combustion chamber zone III (see figures) and only then enter the second combustion chamber zone II.

[0048] Furthermore, in the center of the combustion chamber 10, a vortex forms due to the asymmetrical inflow of combustion air into the combustion chamber 10, which flows in a circular pattern around the center of the bowl orthogonal to the longitudinal center axis Z30 of the cylinder piston 30, so that a zone with less mixing of the fuel-air mixture and thus less homogenization results in the center of the bowl.

[0049] This disadvantage is overcome according to the invention by providing at least one additional axially oriented injection opening S on the elevation 33-1, 33-2 located in the center of the recesses M1, M2 according to the invention. a The injection jets S are directed in the multi-hole injection valve 50'.

[0050] Preferably, several axially aligned injection ports S are used. aformed in the multi-hole injection valve 50', so that several injection jets S can be injected into the center and deviating from the center into the recesses M1, M2 according to the invention.

[0051] According to the invention, the recesses M1, M2 are modified compared to the pointed elevation 33 of the ω-recess M known from the prior art, as explained below, since the at least one or the several axial injection jets S would otherwise be subject to the swirl directed towards the center of the recess for the homogeneous formation of the fuel-air mixture according to the fuel arrows P in Fig. 1. Counteract.

[0052] For the description of the Fig. 2 and Fig. 3. The reference numerals for those components where structural changes have been made compared to the prior art have been changed. For components that have not undergone structural changes, the reference numerals are retained. In the following, reference is always made to multiple axial injection jets S. However, according to the invention, at least one axial injection jet S is provided, which is defined as at least one axial injection opening S. a is formed in the multi-hole injection valve 50'. It is understood that several axial injection ports S a in the multi-hole injection valve 50' are formed as soon as several axial injection jets S are provided.

[0053] The Fig. Figure 2 schematically shows the combustion chamber 10 of the cylinder 30 to illustrate the principle of mixture formation according to a first embodiment based on a cross-section through the longitudinal center axis Z30 of the cylinder piston 30 and a piston base arranged orthogonally to the longitudinal center axis Z30 of the cylinder piston 30 with a modified ω1 recess M1 (omega recess), which, in contrast to the known recess M, has a raised area 33-1 that is defined as a straight platform.

[0054] The Fig. Figure 3 schematically shows the combustion chamber 10 of the cylinder 30 to illustrate the inventive principle of mixture formation according to a second embodiment by means of a cross-section through the longitudinal center axis Z30 of the cylinder piston 30 and a piston crown arranged orthogonally to the longitudinal center axis Z30 of the cylinder piston 30 with a modified ω2 recess M2 (omega recess), which, in contrast to the known recess M, has a shape designated as ω P(Omega) platform shows a pronounced increase of 33-2.

[0055] In both embodiments according to Fig. 2 and Fig. 3 includes a multi-hole injection valve 50' with radially aligned injection jets S r , which are radially aligned starting from the longitudinal center axis Z50 of the multi-hole injection valve 51, and are directed as before towards the bowl collar 31, and furthermore axially aligned injection openings S a , which is projected onto the raised platform 33-1 of the ω1 trough M1 or onto the one projected onto the ω P (Omega) platform pronounced elevation 33-2 of the ω2 trough M2 are directed.

[0056] According to the two embodiments, the impact of the axially injected second fuel fraction on the respective raised platform 33-1, 33-2 results in the effect that a predetermined fuel fraction of the total fuel quantity to be injected is supplied to the central area of ​​the combustion chamber 10, in particular to the central area of ​​the second combustion chamber zone II, independently of the radially injected fuel guided over the circular bowl walls 32.

[0057] In addition, there is the effect that a homogeneous mixture is formed in the center of the bowl earlier than before, since the respective raised platforms 33-1, 33-2 are closer to the central area of ​​the second combustion chamber zone II according to the invention, so that the central area of ​​the second combustion chamber zone II is filled with fuel earlier than before due to the axial injection.

[0058] Furthermore, another effect is that the respective platform-like elevation 33-1, 33-2 is used for the alignment of the injection openings S a injected axially oriented fuel jets S ensures that the direction vectors of the axially oriented fuel jets S change after impact and coincide with the direction vectors of the fuel jets passing over the circular bowl walls 32 via the injection openings S r injected radially oriented fuel jets S guided first fuel fraction coincide, as indicated by the fuel direction arrows P and P1 according to Fig. 2 and the fuel direction arrows P and P2 according to Fig. 3 illustrate.

[0059] By geometrically varying the height of the respective raised platforms 33-1, 33-2 relative to the lowest point of the circular bowl walls 32, it is possible to determine or adjust the point in time at which the axially injected second fuel fraction combines with the radially injected first fuel fraction. Advantageously, by reducing the height of the respective raised platforms 33-1, 33-2 relative to the lowest point of the circular bowl walls 32, it is possible to ensure that the fuel injected via the injection openings S r injected radially oriented fuel jets S essentially simultaneously with those via the injection openings S a The injected axially aligned fuel jets S guide the second fuel portion to the center of the bowl and thus to the central area of ​​the second combustion chamber zone II.

[0060] In other words, it is possible that the axially oriented fuel jets S contribute to earlier mixture formation via the respective raised platforms 33-1, 33-2 in the center of the bowl, or this effect can be reduced by reducing the height of the respective raised platforms 33-1, 33-2 relative to the lowest point, so that ultimately an essentially simultaneous mixture formation of the radially and axially oriented fuel jets S in the central area of ​​the second combustion chamber zone II can be achieved.

[0061] Furthermore, it is effectively achieved that the injection openings S a injected axially oriented fuel jets S by impact on the raised area 33-1 of the ω1 recess M1 (first embodiment) which is designed as a straight platform or on the area designated as ω P(Omega) platform pronounced elevation 33-2 of the ω2 recess M2 (second embodiment) is also strongly sprayed, thereby also ensuring homogenization of the axially injected second fuel fraction.

[0062] It becomes clear that the measures according to the invention result in a zone in the center of the bowl with improved mixing of the fuel-air mixture and thus improved homogenization of the entire fuel-air mixture in the combustion chamber, particularly in the central second combustion chamber zone II. In other words, the central area of ​​the swirl or vortex in the combustion chamber 10 is improved by the injection openings S a injected axially oriented fuel jets S that strike the respective platform 33-1, 33-2, in relation to the injected radially oriented fuel jets S r homogeneously filled with fuel.

[0063] The radially and axially injected fuel fractions can be controlled by the number and / or size of the injection ports S r , S a be effectively coordinated with each other.

[0064] By comparing the fuel direction arrows P and P1 according to Fig. 2 and the fuel direction arrows P and P2 according to Fig. 3 makes it clear that the ones referred to as ω P (Omega) platform pronounced elevation 33-2 of the ω2 trough M2 due to its geometric omega shape ω PDirectional vectors of the axially oriented fuel jets S are generated, which in the second combustion chamber zone II point more towards the center of the combustion chamber compared to the raised platform 33-1 of the ω1 recess M1. It becomes clear in the figures that the geometric design of the raised platforms 33-1, 33-2 can influence the region within the central area of ​​the combustion chamber 10 of the second combustion chamber zone II in which the radially injected fuel jets S and the axially injected fuel jets S should combine to form a homogeneous mixture. Reference symbol list 100 internal combustion engine 10 Combustion chamber 20 cylinders 21 Cylinder inner wall 30 cylinder pistons 31 trough collars 32 trough walls 33 Heightening with a peak (state of the art) 33-1 Elevation with straight platform according to the invention 33-2 Increase with ω according to the invention P -omega-shaped platform ω P omega-shaped platform 34 trough sections Z Piston longitudinal axis Z30 Longitudinal center axis of the cylinder piston 30 40 cylinder head 50 Multi-hole injection valve (state of the art) 50' Multi-hole injection valve according to the invention Z50 Longitudinal center axis of the multi-hole injection valve 50 M, ω omega-shaped trough (state of the art) ω1, M1 first omega-shaped trough according to the invention ω2, M2 second omega-shaped trough according to the invention I first combustion chamber zone II second combustion chamber zone III third combustion chamber zone S injection jets S r radial injection jets S a axial injection jets

Claims

[1] Method for mixture formation in a direct-injection internal combustion engine (100) with at least one cylinder head (40) and at least one cylinder (20) and a rotatably mounted crankshaft, wherein the at least one cylinder (20) has at least one inlet opening on an inlet side for supplying combustion air and at least one outlet opening on an outlet side for removing combustion gases, wherein a combustion chamber (10) is formed which is bounded by a piston crown of a cylinder piston (30) belonging to the at least one cylinder (20), a cylinder inner wall (21) and the cylinder head (40), wherein the longitudinal axis of the cylinder piston (30) is perpendicular to the axis of rotation of the crankshaft,and the fuel is introduced, at least partially, into a piston-head-side omega-shaped recess (ω, M) in the combustion chamber (10) of the at least one cylinder (20) by means of a multi-hole injection valve (50) having injection openings during at least one injection at a predefinable position of the cylinder piston (30) in the cylinder (20), wherein the multi-hole injection valve (50) is arranged in the cylinder head (40) on the opposite side of the piston-head-side omega-shaped recess (ω, M) of the piston head of the cylinder piston (30), , characterized by , that by means of a radial injection port (S r ) and at least one axial injection port (S a ) having a multi-hole injection valve (50) • A first partial quantity of fuel is injected onto the bowl collar (31) with a substantially radial orientation to the longitudinal center axis (Z30) of the cylinder piston (30), whereby fuel is partially injected onto straight bowl sections (34) that extend orthogonally outwards from the longitudinal center axis (Z30) of the cylinder piston (30) to the bowl collar (31), and partially onto the strongly inclined or circular bowl walls (32) that adjoin the bowl collar (31), wherein the bowl walls (32) adjoin the bowl collar (31) and initially extend partially outwards from the longitudinal center axis (Z30) of the cylinder piston (30) and undercut the bowl collar (31) and only then extend inwards towards the center of the bowl towards the longitudinal center axis (Z30) of the cylinder piston (30), and • a second fuel fraction with essentially axial orientation to the longitudinal center axis (Z30) of the cylinder piston (30) onto a raised area (M1; 33-1; M2, 33-2) formed as a platform in the center of the omega-shaped bowl (ω1, M1; ω2, M2) is injected into the combustion chamber (10), such that the direction vector of the at least one via the axial injection opening (S a ) directed injected fuel jet (S) after impact changes in such a way that it aligns with the direction vectors of the jet passing over the steeply inclined or circular trough walls (32) via the radial injection openings (S r ) aligned fuel jets (S). [2] Method for mixture formation according to claim 1, characterized by , that the radial and axial injection ports (S r , S a) of the multi-hole injector (50') into the combustion chamber (10) partial quantities of fuel are brought together, mixed and homogenized in a central combustion chamber zone (II) of the combustion chamber (10). [3] Method for mixture formation according to claim 1, characterized by , that the fuel fractions are determined by the number and / or size of the radial injection ports (S r ) and at least one or more axial injection ports (S r , S a ) of the multi-hole injector (50') can be changed. [4] Method for mixture formation according to claim 2, characterized by , that the timing of the injection via the radial injection ports (S r ) and the at least one axial injection port (S r , S a) of the multi-hole injector (50') into the central combustion chamber zone (II) of the combustion chamber (10) is adjusted by adapting the geometry of the raised platform (M1; 33-1; M2, 33-2) to the adjacent geometry of the omega-shaped recess (M1, M2). [5] Method for mixture formation according to claim 3, characterized by that the at least one axial injection port (S a ) of the multi-hole injector (50') the fuel partial quantity injected into the central combustion chamber zone (II) of the combustion chamber (10) temporally prior to the injection via the radial injection ports (S r ) injected fuel fraction reached. [6] Method for mixture formation according to claim 3, characterized by that the at least one axial injection port (S a) of the multi-hole injector (50') the fuel partial quantity injected into the central combustion chamber zone (II) of the combustion chamber (10) simultaneously with the fuel injected via the radial injection ports (S r ) injected fuel fraction reached. [7] Direct-injection internal combustion engine (100) for carrying out the method according to claim 1, comprising at least one cylinder head (40) and at least one cylinder (20) and a rotatably mounted crankshaft, wherein the at least one cylinder (20) has at least one inlet opening on an inlet side for supplying combustion air and at least one outlet opening on an outlet side for removing combustion gases, wherein a combustion chamber (10) is formed, which is bounded by a piston crown of a cylinder piston (30) belonging to the at least one cylinder (20), a cylinder inner wall (21) and the cylinder head (40), wherein the longitudinal axis of the cylinder piston (30) is perpendicular to the axis of rotation of the crankshaft,and the fuel is introduced, at least partially, into a piston-head-side omega-shaped recess (ω, M) in the combustion chamber (10) of the at least one cylinder (20) by means of a multi-hole injection valve (50) having injection openings during at least one injection at a predefinable position of the cylinder piston (30) in the cylinder (20), wherein the multi-hole injection valve (50) is arranged in the cylinder head (40) on the opposite side of the piston-head-side omega-shaped recess (ω, M) of the piston head of the cylinder piston (30), , characterized by , that a multi-hole injection valve (50') with radial injection ports (S r ) and at least one axial injection port (S a) projects into the combustion chamber (10) and a platform-shaped elevation (M1; 33-1; M2, 33-2) is formed in the center of the omega-shaped recess (ω1, M1; ω2, M2), wherein straight recess sections (34) extend outwards from the recess collar (31) away from the longitudinal center axis (Z30) of the cylinder piston (30), which are oriented orthogonally to the longitudinal center axis (Z30) of the cylinder piston (30), wherein strongly inclined or circular recess walls (32) extend inwards towards the longitudinal center axis (Z30) of the cylinder piston (30) from the recess collar (31), which initially extend outwards from the recess collar (31) partially away from the longitudinal center axis (Z30) of the cylinder piston (30), undercutting the recess collar (31) and then inwards towards the center of the recess towards the longitudinal center axis Z30 of the cylinder piston 30 run towards. [8] Internal combustion engine (100) according to claim 7, characterized by, that the raised area (33-1) of the omega-shaped depression (ω1, M1) which is pronounced as a platform is pronounced as a straight platform. [9] Internal combustion engine (100) according to claim 7, characterized by , that the raised area (33-2) of the omega-shaped depression (ω2, M2) which is pronounced as a platform is an omega-shaped platform (ω P ) is pronounced.

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