EP4390081A1

EP4390081A1 - Prechamber assembly, cylinder head, piston-cylinder unit and internal combustion engine

Info

Publication number: EP4390081A1
Application number: EP22215376.9A
Authority: EP
Inventors: Wolfgang Fimml; Michael Url; Hubert Winter
Original assignee: Innio Jenbacher GmbH and Co OG
Current assignee: Innio Jenbacher GmbH and Co OG
Priority date: 2022-12-21
Filing date: 2022-12-21
Publication date: 2024-06-26

Abstract

Prechamber assembly (1) for an internal combustion engine, comprising:- at least one prechamber volume (2), wherein the at least one prechamber volume (2) has at least one injector opening (7) with at least one fuel injector (5) partially inserted into or attached to the at least one injector opening (7), preferably for injecting hydrogen, wherein the at least one injector opening (7) or the at least one fuel injector (5) has an injector area (8), and- at least one riser channel (3), wherein the at least one riser channel (3) is connected to the at least one prechamber volume (2), wherein the at least one riser channel (3) has a riser channel area (9), and- at least one nozzle hole (4), wherein the at least one nozzle hole (4) is connected to the at least one riser channel (3), and to a main combustion chamber (12) when the prechamber assembly (1) is in its built-in state in a combustion engine, wherein the at least one nozzle hole (4) has a nozzle hole area,wherein the at least one fuel injector (5) is configured to inject fuel with an injection pressure and that the prechamber assembly (1) is formed such that- the ratio of the injector area (8) over the riser channel area (9) is in the range of 9 to 24, preferably 12 to 18, divided by the value of the injection pressure in bar, and/or- the ratio of the injector area (8) over the nozzle hole area is in the range of 6 to 30, preferably 9 to 21, divided by the value of the injection pressure in bar.

Description

The invention relates to a prechamber assembly for an internal combustion engine, a cylinder head with at least one prechamber assembly, a piston-cylinder unit with at least one prechamber assembly or a cylinder head, an internal combustion engine with at least one cylinder head or at least one piston-cylinder unit, a method for operating an internal combustion engine and a method for designing a prechamber assembly.
Prechamber assemblies are generally used as an ignition intensifier, wherein the fuel-air mixture is ignited inside the prechamber assembly by an ignition device, for instance a spark plug. For instance, it can be used for combustion engines with a lean burn concept, where the fuel-air mixture is less lean in the prechamber assembly to simplify the ignition.
The publication US 7,438,043 B2 discloses a prechamber assembly with an ignition device. No fuel injector is placed in the prechamber assembly such that the prechamber assembly is suitable only for fuel injection into the combustion main chamber or into the intake port (port fuel injection, PFI). Several nozzle holes with a varying length directly connect the prechamber volume to the main combustion chamber. The length of the nozzle holes is varying such that the form of the fuel torches propagating into the main combustion chamber can be adapted. The fuel torches propagating into the main combustion chamber ignite the fuel-air mixture in the main combustion chamber.
The publication WO 2022/226553 A1 discloses a prechamber assembly comprising at least one prechamber volume, wherein the at least one prechamber volume has at least one injector opening with at least one fuel injector partially inserted into or attached to the at least one injector opening, preferably for injecting hydrogen, wherein the at least one injector opening or the at least one fuel injector has an injector area, and at least one riser channel, wherein the at least one riser channel is connected to the at least one prechamber volume, wherein the at least one riser channel has a riser channel area, and at least one nozzle hole, wherein the at least one nozzle hole is connected to the at least one riser channel, and to a main combustion chamber when the prechamber assembly is in its built-in state in a combustion engine, wherein the at least one nozzle hole has a nozzle hole area.
The air-to-fuel ratio or excess air ratio is typically denoted by "lambda" or lambda value. The air-fuel mixture is called rich for lambda smaller than one and lean for lambda larger than one.
A lean (lambda larger than one) combustion concept decreases the production of toxic nitric oxides, but the power is lower than for smaller lambda values. The use of lean mixtures also avoids combustion anomalies, even when the mixture is relatively inhomogeneous. Especially, rich zones which tend to auto-ignite and lead to knocking are avoided by using a lean mixture.
Direct injection, especially at medium injection pressures, causes larger combustion anomalies than, for instance, port fuel injection. The theoretical advantages of medium pressure direct injection over port fuel injection cannot be utilized since medium pressure direct injection can only be used in connection with a relatively lean mixture in order to avoid the combustion anomalies.
In order to increase the power and the performance while utilizing the theoretical advantages of medium pressure direct injection, it can be advantageous to use a less lean combustion concept, especially a configuration where lambda is smaller than three, smaller than two or smaller than 1.5.
Using a less lean mixture also reduces the boost pressure levels for turbochargers or superchargers. The reduced boost pressure demand can be used for further power increase.
As specified above, for less lean mixtures, existing prechamber designs with medium pressure direct injection lead to combustion anomalies.
The object of the invention is to provide a prechamber assembly suitable for medium pressure direct injection which is optimized to avoid combustion anomalies and increase the power of a combustion engine.
The object is solved by the prechamber assemblies of claim 1, the prechamber assembly of claim 3, the cylinder head of claim 9, the piston-cylinder unit of claim 10, the internal combustion engine of claim 11, the method for operating an internal combustion engine of claim 14 and the method for designing a prechamber assembly of claim 15.
A prechamber assembly for an internal combustion engine, comprises at least one prechamber volume, wherein the at least one prechamber volume has at least one injector opening with at least one fuel injector partially inserted into or attached to the at least one injector opening, preferably for injecting hydrogen, wherein the at least one injector opening or the at least one fuel injector has an injector area, and at least one riser channel, wherein the at least one riser channel is connected to the at least one prechamber volume, wherein the at least one riser channel has a riser channel area, and at least one nozzle hole, wherein the at least one nozzle hole is connected to the at least one riser channel, and to a main combustion chamber when the prechamber assembly is in its built-in state in a combustion engine, wherein the at least one nozzle hole has a nozzle hole area.
According to the invention, the at least one fuel injector is configured to inject fuel with an injection pressure.
Further, the prechamber assembly is formed such that the ratio of the injector area over the riser channel area is in the range of 9 to 24, preferably 12 to 18, divided by the value of the injection pressure in bar.
Additionally or alternatively, the ratio of the injector area over the nozzle hole area is in the range of 6 to 30, preferably 9 to 21, divided by the value of the injection pressure in bar.
A prechamber assembly with a geometry calculated according to the invention leads to an improved homogeneous fuel-air mixture when using the prechamber assembly in a combustion engine with the injection pressure. By this, combustion anomalies are minimized.
A secondary advantage of the geometry of the prechamber according to the invention is that the combustion of fuel in the main combustion chamber is amplified. The fuel torches propagating from the nozzle holes into the main combustion chamber are optimally formed.
The areas according to the invention were obtained with a simulation in connection with an optimization. Primarily, the homogeneity of the hydrogen charge was maximized. Secondarily, the form of the fuel torches was optimized for amplification of the combustion in the main chamber.
The riser channel area can be optimized according to at least one of the following criteria:

injection pressure level
injection duration and windows
injector area

The nozzle areas can be optimized according to at least one of the following criteria:

jet penetration length (for instance to avoid liner interaction)
injection pressure level
injection duration and windows
injector area
riser channel area

Preferably, the injection pressure has a magnitude in the range of 20 to 50 bar, preferably 25 to 35 bar, especially preferably essentially 30 bar. This corresponds to the medium pressure range mentioned in the introduction.
The prechamber assembly according to an alternative of the invention is formed such that

the ratio of the injector area over the riser channel area is in the range of 0.3 to 0.8, preferably 0.4 to 0.6, and/or
the ratio of the injector area over the total nozzle hole area is in the range of 0.2 to 1, preferably 0.3 to 0.7.

The prechamber assembly is not necessarily configured to be used at a certain injection pressure.
Preferably, the prechamber assembly is configured to be suitable for an injection pressure of essentially 30 bar.
In a preferred embodiment of the invention the prechamber assembly is configured such that it is suitable for the ignition of an air-to-fuel ratio, preferably air-to-hydrogen ratio, of essentially one.
The ignition properties for this ratio are especially favorable, demanding a minimum of ignition energy. Further, the power of the combustion engine is increased in comparison to leaner mixtures.
In a preferred embodiment the at least one prechamber volume has at least one ignition opening for at least one ignition device, preferably a spark plug.
By this the air to fuel mixture can be ignited in the prechamber. Consequently, fuel torches propagate into the main combustion chamber and ignite the air-fuel mixture there.
In a preferred embodiment the prechamber assembly has at least two nozzle holes, preferably five to twenty nozzle holes. The quantity and the configuration of the nozzle holes influences the homogeneity of the fuel-air mixture in the main combustion chamber. Especially, more than one nozzle hole results in a more homogeneous mixture.
The quantity and configuration of the nozzle holes influences the distribution of fuel-air mixture in the main combustion chamber since the fuel is directly injected into the prechamber volume and the fuel flows into the main combustion chamber through the nozzle holes.
Further, the distribution of the fuel torches propagating into the main combustion chamber after ignition in the prechamber can be influenced. Especially, more than one nozzle hole leads to fuel torches which are more distributed over a larger volume of the main combustion chamber, leading to a better ignition of the fuel-air mixture in the main combustion chamber.
In a preferred embodiment at least one first nozzle hole has a smaller cross-sectional area than at least one second nozzle hole. By choosing a mutually differing area of nozzle holes the flow of fuel from the prechamber into the main combustion chamber can be influenced, especially such that the fuel-air mixture is maximally homogeneously distributed in the main combustion chamber.
Further, the size of the fuel torches is adapted. This can be used to avoid liner interaction of the fuel torches.
Generally, the area influences the jet penetration length of jets propagating from the prechamber into the main combustion chamber.
Preferably, the outlet of the at least one first nozzle hole with the smaller cross-sectional area is arranged at a larger distance from a center of the prechamber assembly than the outlet of the at least one second nozzle hole with the larger cross-sectional area.
In a preferred embodiment at least one first nozzle hole has an orientation which is oblique to the orientation of at least one second nozzle hole. "Oblique" means that there is a non-zero angle of inclination between the orientation of the at least one first nozzle hole and the orientation of the at least one second nozzle hole.
In a preferred embodiment at least one first nozzle hole has a larger inclination with respect to a direction of elongation of the prechamber assembly than at least one second nozzle hole.
Preferably, the at least one first nozzle hole (with the larger inclination) has a smaller cross-sectional area than the at least one second nozzle hole (with the smaller inclination). Thus, interaction with a liner on a cylinder wall is avoided.
In a preferred embodiment the at least one nozzle hole has an orientation which is oblique to the orientation of the at least one riser channel. "Oblique" means that orientation of the at least one nozzle hole has a non-zero angle of inclination with respect to the orientation of the at least one riser channel.
In a preferred embodiment the prechamber assembly has a direction of elongation and wherein the at least one riser channel is oblique to the direction of elongation. "Oblique" means that the direction of elongation has a non-zero angle of inclination with respect to the orientation of the at least one riser channel.
An oblique riser channel which ends asymmetrically in the prechamber volume can be used to cause a tumble stream in the prechamber volume during an exhaust stroke or a compression stroke.
It can be provided that the at least one riser channel is oriented towards the ignition device. With such an orientation of the riser channel, a back-flowing gas from the main combustion chamber (during a compression stroke) can be directed at the ignition device. This can have a cleaning effect on the ignition device, i.e. unwanted deposits in or near the ignition means can be purged or blown away.
A cylinder head according to the invention has at least one prechamber assembly described above.
A piston-cylinder unit according to the invention has at least one prechamber assembly described above or a cylinder head described above.
Further, the at least one fuel injector (of the prechamber assembly of the piston-cylinder unit) is configured to inject fuel with an injection pressure and at least one cylinder is formed such that the ratio of the bore area of the cylinder bore over the injector area is in the range of 20 to 47, preferably 30 to 34 times the value of the injection pressure in bar.
In particular, the injection pressure has a magnitude in the range of 20 to 50 bar, preferably 25 to 35 bar, especially preferably essentially 30 bar.
Additionally or alternatively, at least one cylinder of the piston-cylinder unit is formed such that the ratio of the bore area of the cylinder bore over the injector area is in the range of 600 to 1410, preferably 900 to 1020, wherein the piston-cylinder unit is preferably configured to be suitable for an injection pressure of essentially 30 bar.
By designing the geometry piston-cylinder unit in such a way, the fuel-air mixture is very homogeneous, whereby combustion anomalies are avoided.

The values of the area ratios for different injection pressures are summarized in the following table (rounded to one decimal place in the first two ratio columns):

Injection pressure	Ratio of the injector area over the riser channel area	Ratio of the injector area over the nozzle hole area	Ratio of the cylinder bore area over the injector area
20 bar	0.45 - 1.2, preferably 0.6 - 0.9	0.3 - 1.5, preferably 0.45 - 1.05	400 - 940, preferably 600 - 680
25 bar	0.36 - 0.96, preferably 0.48 - 0.72	0.24 - 1.2, preferably 0.36 - 0.84	500 - 1175, preferably 750 - 850
30 bar	0.3 - 0.8, preferably 0.4 - 0.6	0.2 to 1, preferably 0.3 - 0.7	600 - 1410, preferably 900 - 1020
35 bar	0.26 - 0.69, preferably 0.34 - 0.51	0.17 - 0.86, preferably 0.34 - 0.6	700 - 1645, preferably 1050 - 1190
50 bar	0.18 - 0.48, preferably 0.24 - 0.36	0.12 - 0.6, preferably 0.18 - 0.42	1000 - 2350, preferably 1500 - 1700

An internal combustion engine according to the invention has at least one cylinder head described above or at least one piston-cylinder unit described above.
In a preferred the at least one fuel injector arranged in at least one prechamber assembly of a piston-cylinder-unit is configured to inject 100 % of the fuel, preferably hydrogen, provided to that piston-cylinder-unit per combustion cycle.
Thus 100 % of the fuel flows through the at least one riser channel and the at least one nozzle hole into the main combustion chamber. The geometry of the prechamber assembly according to the invention and, preferably, the adapted bore area of the cylinder lead to a homogeneous distribution of the fuel in the main combustion chamber.
In a preferred embodiment the internal combustion engine is configured such that the air-to-fuel ratio, preferably air-to-hydrogen ratio, is smaller than 3, preferably smaller than 2, especially preferably smaller than 1.5, in particular by adjusting the air intake and the fuel injection amount per combustion cycle.
By using an air-to-fuel ratio smaller than 3, preferably smaller than 2, especially preferably smaller than 1.5, the power of the combustion engine is increased with respect to a leaner mixture. Further, the pressure boost levels can be reduced, and the reduced boost demand can be used for further power increase. Further, the ignition is more efficient.
The geometry of the prechamber assembly or the piston-cylinder unit render the use of such a small air-to-fuel ratio possible, by providing a homogeneous fuel charge.
In a method for operating an internal combustion engine described above according to the invention the combustion engine is operated with the injection pressure, in particular with the injection pressure having a magnitude from 20 to 50 bar, preferably 25 to 35 bar, especially preferably essentially 30 bar.
In a method for designing a prechamber assembly, preferably a prechamber assembly described above, for an internal combustion engine, preferably as described above is used.
The method is characterized by the following steps:

choosing a magnitude of an injection pressure of the at least one fuel injector intended for operation, in particular from the range of 20 to 50 bar, preferably 25 to 35 bar, especially preferably essentially 30 bar, followed by
choosing the ratio of the injector area over the riser channel area from the range of 9 to 24, preferably 12 to 18, divided by the value of the chosen injection pressure in units of 30 bar, and/or choosing the ratio of the injector area over the total nozzle hole area from the range of 6 to 30, preferably 9 to 21, divided by the value of the chosen injection pressure in units of 30 bar,
designing the geometry of the prechamber assembly with the constraint that the area ratios are as chosen in the previous step.

A method for manufacturing a prechamber assembly comprises the steps of the method for designing the prechamber assembly and a further step: manufacturing the prechamber assembly.
A range of a lower boundary to an upper boundary divided by a value means that the boundaries of the range are divided by that value.
The injector area is defined as the smallest cross-sectional area of the at least one injector opening or the at least one fuel injector. If there are at least two injector openings or fuel injectors, the one injector area is defined as the sum of the smallest cross-sectional areas of each respective injector opening, if not indicated otherwise.
Preferably the prechamber assembly has exactly one injector opening.
It is emphasized that the injector opening can be an opening of the fuel injector itself or of an opening of the prechamber assembly. Preferably, the smaller of the two defines the injector opening.
Preferably, the injector opening is an opening of the fuel injector itself, since the prechamber assembly is usually designed such that fuel injector opening is larger than an opening of the prechamber assembly.
For instance, the fuel injector can be an injector valve. In this case the injector opening can be the opening of the injector valve and the injector area can be the cross-sectional area of the injector valve opening.
The riser channel area is defined as the smallest cross-sectional area of the at least one riser channel. If there are at least two riser channels, the riser channel area is defined as the sum of the smallest cross-sectional areas of each respective riser channel, if not indicated otherwise.
Preferably the prechamber assembly has exactly one riser channel.
The nozzle hole area is defined as the smallest cross-sectional area of the at least one nozzle hole. If there are at least two nozzle holes, the nozzle hole area is defined as the sum of the smallest cross-sectional areas of each respective nozzle hole, if not indicated otherwise.
Preferably the prechamber assembly has several nozzle holes.
Further details and advantages of the invention are apparent from the accompanying figures and the following description of drawings:

Fig. 1a: first embodiment of a prechamber assembly
Fig. 1b-d: variants of the first embodiment in a bottom view with a varying arrangement of the nozzle holes
Fig. 2a: second embodiment of a prechamber assembly with at least five nozzle holes
Fig. 2b-d: variants of the first embodiment in a bottom view with a varying arrangement of the nozzle holes
Fig. 3: schematic depiction of a prechamber assembly with areas of the riser channel, injector opening and nozzle holes
Fig. 4: prechamber assembly built onto a cylinder of a piston-cylinder unit

Fig. 1a depicts a first embodiment of a prechamber assembly 1.
The prechamber assembly 1 comprises a prechamber volume 2, wherein the prechamber volume 2 has an injector opening 7 with at least one fuel injector 5 partially inserted into or attached to the at least one injector opening 7, preferably for injecting hydrogen.
The injector opening 7 connects the fuel injector 5 with the prechamber volume 2 such that fuel, especially hydrogen, can be directly injected into the prechamber volume 2. The injector opening 7 can be a channel with a certain length, as depicted in Fig. 1. The injector opening 7 can also be an opening only, for instance when the fuel injector 5 is directly arranged at the prechamber volume 2.
The fuel injector 5 can comprise an injector valve which can be opened or closed depending on the demand for fuel in the prechamber volume 2.
It is conceivable that the fuel injector 5 injects air and/or a fuel/air mixture instead of pure fuel.
The injector opening 7 or the fuel injector 5 has an injector area 8, which can be the cross-sectional area of the fuel injector 5 itself, especially the area of an injector valve. Alternatively, it can be defined as the smallest cross-sectional (effective) area of the injector opening 7 of the prechamber volume 2, especially of a channel connecting the fuel injector 5 with the prechamber volume 2. Preferably, the smaller of the two alternatives is chosen as a definition for the injector area 8.
In general, the injector area 8 is preferably the smallest area the fuel must pass to flow from the injector 5 into the prechamber volume 2.
Further, the prechamber assembly 1 comprises a riser channel 3, wherein the riser channel 3 is connected to the prechamber volume 2. The riser channel 3 has a riser channel area 9 (see Fig. 3), which is preferably defined as the smallest cross-sectional area of the riser channel 3.
The prechamber assembly 1 comprises at least one nozzle hole 4, wherein the at least one nozzle hole 4 is connected to the at least one riser channel 3 and to a main combustion chamber 12 (see Fig. 4) when the prechamber assembly 1 is in its built-in state in a combustion engine. The at least one nozzle hole 4 has a nozzle hole area, wherein the nozzle hole area is preferably defined as the sum of the areas of each the smallest cross-sectional area 16 of each nozzle hole 4 (see Fig. 3).
In operation, fuel is injected into the prechamber volume 2 by the fuel injector 5 and can flow through the riser channel 3 and the nozzle holes 3 into the main combustion chamber 12.
The riser channel 3 is arranged obliquely with respect to a direction of elongation L of the prechamber assembly 1. This means that the direction of the riser channel 3 has a non-zero angle of inclination with respect to the direction of elongation L of the prechamber assembly 1.
By this a tumble stream can be realized in the prechamber volume 2 when air or air-fuel mixture is pressed back into the riser channel 3 during a compression cycle.
The riser channel 3 is directed to the ignition device 6, such that back streaming gas hit the ignition device 6. This can clean the ignition device 6.
Alternatively, the opposite orientation of the riser channel 3. The riser channel 3 can be directed to the fuel injector 5.
The direction of elongation L of the prechamber assembly 1 is preferably parallel to the direction of elongation of the piston-cylinder unit, i.e., the direction of movement of the piston.
The dash-dotted lines show an axis of symmetry of the riser channel 3 and the nozzle holes 4.
In Fig. 1a there are at least two nozzle holes 4 which are shown in the cross section.
In Fig. 1a, both shown nozzle holes 4 are oblique with respect to the riser channel 3, meaning that there is a non-zero angle of inclination between the respective axis of symmetry.
The two shown nozzle holes 4 end up on opposite sides of the tip of the prechamber assembly 1, being arranged in the main combustion chamber 12 in its built-in state. Thus, the fuel injected by the fuel injector 5 distributes well in the main combustion chamber 12. Further, fuel torches propagating out of the nozzle holes 4 into the combustion chamber 12 distribute well in the combustion chamber 12 such that fuel in the combustion chamber 12 is well ignited.
Fig. 1b depicts a bottom view of a variant of Fig. 1a with exactly two nozzle holes.
Preferably, there are more than two nozzle holes 4, which are not visible in the cross-section of Fig. 1. The nozzle holes 4 can be arranged in a nozzle gallery, where several nozzle holes 4 are arranged in different azimuthal angles (with respect to the direction of elongation L). Especially, the nozzle holes 4 can be equally distributed over the whole angular range.
Fig. 1c shows a bottom view of a variant of Fig. 1a with a nozzle gallery with four equally distributed nozzle holes 4.
Fig. 1d shows a bottom view of a variant of Fig. 1a with a nozzle gallery with six equally distributed nozzle holes 4.
More nozzle holes lead to more homogeneous distribution of fuel in the main combustion chamber 12.
Fig. 2a depicts a second embodiment of the prechamber assembly 1. The difference to the first embodiment of Figs. 1a in variants of Figs. 1b, 1c and 1d is the arrangement of the nozzle holes 4.
There are at least five nozzle holes 4 in Fig. 2a. Preferably, the nozzle holes 4 apart from the central nozzle hole 4 are arranged in two nozzle hole galleries.
Fig. 2b depicts a bottom view of the embodiment of Fig. 2a in a first variant with exactly five nozzle holes 4.
Fig. 2c depicts a bottom view of the embodiment of Fig. 2a in a second variant with nine nozzle holes 4. The nozzle holes 4 are arranged in two galleries plus a central nozzle hole 4. The nozzle holes 4 are azimuthally equally distributed.
Fig. 2d depicts a bottom view of the embodiment of Fig. 2a in a third variant with exactly thirteen nozzle holes 4. The nozzle holes 4 are arranged in two galleries plus a central nozzle hole 4. The nozzle holes 4 are azimuthally equally distributed.
In Figs. 2a to 2d it is generally provided that at least one first nozzle hole 4 has a smaller cross-sectional area than at least one second nozzle hole 4 and that least one first nozzle hole 4 has an orientation which is oblique to the orientation of at least one second nozzle hole 4.
Further, at least one first nozzle hole 4 has a larger inclination with respect to a direction of elongation L of the prechamber assembly 1 than at least one second nozzle hole 4. This manifests itself in the existence of several nozzle galleries. Preferably, the at least one first nozzle hole 4 has a smaller cross-sectional area 16 than the at least one second nozzle hole 4.
In other words: Those nozzle holes 4 which are more inclined have a smaller cross-sectional area 16 than those nozzle holes 4 which are less inclined.
The straight central nozzle hole 4 has the largest cross-sectional area 16, whereas the lower gallery has nozzle holes 4 with a larger cross-sectional area 16 than the central nozzle hole 4 and whereas the upper gallery has nozzle holes 4 with a larger cross-sectional area 16 than the nozzle holes 4 of the lower gallery.
In general, the individual nozzle hole area 16 (see also Fig. 3) influences the jet penetration length in the main combustion chamber 12. Thus, the form of the fuel torches propagating into the main combustion chamber 12 can be adapted, be it in the ignition process or in the fuel feeding process.
For instance, the interaction of the fuel torches with a liner on the side wall of the cylinder 13 can be avoided by providing small area nozzle holes 4 in the upper galleries which are more inclined.
Further, a more homogeneous distribution of fuel in the main combustion chamber 12 can be reached by this arrangement of nozzle holes 4.
Fig. 3 shows a schematic representation of the of a prechamber assembly 1 with areas 7, 9, 16 of the riser channel 3, injector opening 7 and nozzle holes 4.
The riser channel area 9 is preferably the smallest cross-sectional area of the riser channel 3.
The injector area 8 is preferably the smallest cross-sectional area of the injector opening 7 or of the fuel injector 5, for instance the injector valve, itself.
The individual nozzle hole areas 16 differ from nozzle hole 4 to nozzle hole 4 as discussed with respect to Figs. 2a to 2d.
The total nozzle hole area is the sum of all individual nozzle hole areas 16.
According to the invention specific ranges of ratios of areas are specified. The optimal ratios depend on the injection pressure, with which fuel is injected into the prechamber volume 2.
Thus, when the at least one fuel injector 5 is configured to inject fuel with an injection pressure, the prechamber assembly 1 is formed such that

the ratio of the injector area 8 over the riser channel area 9 is in the range of 9 to 24, preferably12 to 18, divided by the value of the injection pressure in bar, and/or
the ratio of the injector area 8 over the (total) nozzle hole area (sum of all nozzle hole areas 16) is in the range of 6 to 30, preferably 9 to 21, divided by the value of the injection pressure in bar.

The injection pressure preferably has a magnitude in the range of 20 to 50 bar, preferably 25 to 35 bar, especially preferably essentially 30 bar.
For the preferred case of an injection pressure of 30 bars the ratio of the injector area 8 over the riser channel area 9 is in the range of 0.3 to 0.8, preferably 0.4 to 0.6, and/or the ratio of the injector area 8 over the total nozzle hole area (sum of individual nozzle hole areas 16) is in the range of 0.2 to 1, preferably 0.3 to 0.7.
Fig. 4 depicts a prechamber assembly 1 which is inserted into a piston-cylinder unit of an internal combustion engine having a cylinder 13 with a cylinder bore 14. The piston is not depicted. Especially, the prechamber assembly 1 is inserted into a cylinder head 17, which is arranged on the cylinder 13. The main combustion chamber 12 is inside the cylinder 13.
The cylinder head 13 comprises an intake port 18 and exhaust port 19. Air, preferably air without fuel, is supplied to the main combustion chamber 12 via the intake port 18. After the combustion, the exhaust is removed through the exhaust port 19. Both intake port 18 and exhaust port 19 can be opened and closed by engine valves 20. Preferably, 100 % of the fuel is provided by the prechamber assembly 1, especially by the fuel injector 5.
The cylinder bore 14 has a bore area 15, which is the smallest cross-sectional area of the cylinder bore 14.
It is provided that when the at least one fuel injector 5 is configured to inject fuel with an injection pressure, the at least one cylinder 13 is formed such that the ratio of the bore area 15 of the cylinder bore 15 over the injector area 8 is in the range of 20 to 47, preferably 30 to 34 times the value of the injection pressure in bar, wherein the injection pressure in particular has a magnitude in the range of 20 to 50 bar, preferably 25 to 35 bar, especially preferably essentially 30 bar.
Especially, it is provided that the at least one cylinder 13 is formed such that the ratio of the bore area 15 of the cylinder bore 14 over the injector area 8 is in the range of 600 to 1410, preferably 900 to 1020. In this case the piston-cylinder unit is preferably configured to be suitable for an injection pressure of essentially 30 bar.
The optimized ratios of the areas of riser channel 3, cylinder bore 14, nozzle holes 4 and/or injection opening 7 or fuel injector 5 lead to a surprisingly homogeneous fuel charge, especially hydrogen charge, in the combustion chamber 12 whereby rich zones are avoided, and combustion anomalies are reduced.
Thereby, a smaller air-to-fuel ratio, i.e., lambda value, for example smaller than 3, smaller than 2 or smaller than 1.5 can be used, without the occurrence of combustions anomalies. This increases the power of the combustion engine in a two-fold way: First, the theoretical power yield is larger due to the usage of a less lean mixture and second, there is less demand for boost pressure, which further increases the power.

List of reference signs:

1: prechamber assembly
2: prechamber volume
3: riser channel
4: nozzle hole
5: fuel injector
6: ignition device
7: injector opening
8: injector area
9: riser channel area
11: ignition opening
12: main combustion chamber
13: cylinder
14: cylinder bore
15: bore area of the cylinder bore
16: individual nozzle hole area
17: cylinder head
18: intake port
19: exhaust port
20: engine valve
L: direction of elongation of the prechamber assembly

Claims

Prechamber assembly (1) for an internal combustion engine, comprising:
- at least one prechamber volume (2), wherein the at least one prechamber volume (2) has at least one injector opening (7) with at least one fuel injector (5) partially inserted into or attached to the at least one injector opening (7), preferably for injecting hydrogen, wherein the at least one injector opening (7) or the at least one fuel injector (5) has an injector area (8), and

- at least one riser channel (3), wherein the at least one riser channel (3) is connected to the at least one prechamber volume (2), wherein the at least one riser channel (3) has a riser channel area (9), and

- at least one nozzle hole (4), wherein the at least one nozzle hole (4) is connected to the at least one riser channel (3), and to a main combustion chamber (12) when the prechamber assembly (1) is in its built-in state in a combustion engine, wherein the at least one nozzle hole (4) has a nozzle hole area,
characterized in that the at least one fuel injector (5) is configured to inject fuel with an injection pressure and that the prechamber assembly (1) is formed such that
- the ratio of the injector area (8) over the riser channel area (9) is in the range of 9 to 24, preferably 12 to 18, divided by the value of the injection pressure in bar, and/or

- the ratio of the injector area (8) over the nozzle hole area is in the range of 6 to 30, preferably 9 to 21, divided by the value of the injection pressure in bar.
Prechamber assembly (1) according to the preceding claim wherein the injection pressure has a magnitude in the range of 20 to 50 bar, preferably 25 to 35 bar, especially preferably essentially 30 bar.
Prechamber assembly (1) for an internal combustion engine, preferably according to one of the previous claims, comprising:
- at least one prechamber volume (2), wherein the at least one prechamber volume (2) has at least one injector opening (7) for partially inserting or attaching at least one fuel injector (5), preferably for injecting hydrogen, wherein the at least one injector opening (7) or the at least one fuel injector (5) has an injector area (8), and

- at least one riser channel (3), wherein the at least one riser channel (3) is connected to the at least one prechamber volume (2), wherein the at least one injector opening (7) has a riser channel area (9), and

- at least one nozzle hole (4), wherein the at least one nozzle hole (4) is connected to the at least one riser channel (3), and to a main combustion chamber (12) when the prechamber assembly (1) is in its built-in state in a combustion engine, wherein the at least one injector opening (7) has a nozzle hole area,

characterized in that the prechamber assembly (1) is formed such that
- the ratio of the injector area (8) over the riser channel area (9) is in the range of 0.3 to 0.8, preferably 0.4 to 0.6, and/or

- the ratio of the injector area (8) over the total nozzle hole area is in the range of 0.2 to 1, preferably 0.3 to 0.7,

wherein the prechamber assembly (1) is preferably configured to be suitable for an injection pressure of essentially 30 bar.
Prechamber assembly (1) according to one of the preceding claims wherein the prechamber assembly (1) is configured such that it is suitable for the ignition of an air-to-fuel ratio, preferably air-to-hydrogen ratio, of essentially one.
Prechamber assembly (1) according to one of the preceding claims, wherein the at least one prechamber volume (2) has at least one ignition opening (11) for at least one ignition device (6), preferably a spark plug.
Prechamber assembly (1) according to one of the preceding claims, wherein the prechamber assembly (1) has at least two nozzle holes (4), preferably five to twenty nozzle holes (4).
Prechamber assembly (1) according the preceding claim,
- wherein at least one first nozzle hole (4) has a smaller cross-sectional area than at least one second nozzle hole (4), and/or

- wherein at least one first nozzle hole (4) has an orientation which is oblique to the orientation of at least one second nozzle hole (4), and/or

- wherein at least one first nozzle hole (4) has a larger inclination with respect to a direction of elongation (L) of the prechamber assembly (1) than at least one second nozzle hole (4), preferably wherein the at least one first nozzle hole (4) has a smaller cross-sectional area (16) than the at least one second nozzle hole (4).
Prechamber assembly (1) according to one of the preceding claims,
- wherein the at least one nozzle hole (4) has an orientation which is oblique to the orientation of the at least one riser channel (3), and/or

- wherein the prechamber assembly (1) has a direction of elongation (L) and wherein the at least one riser channel (3) is oblique to the direction of elongation (L).
A cylinder head (17) having at least one prechamber assembly (1) according to at least one of the preceding claims.
A piston-cylinder unit with at least one prechamber assembly (1) according to at least one of the claims 1 to 8 or with a cylinder head (17) according to the preceding claim,
- wherein the at least one fuel injector (5) is configured to inject fuel with an injection pressure and wherein at least one cylinder (13) is formed such that the ratio of the bore area (15) of the cylinder bore (15) over the injector area (8) is in the range of 20 to 47, preferably 30 to 34 times the value of the injection pressure in bar, wherein the injection pressure in particular has a magnitude in the range of 20 to 50 bar, preferably 25 to 35 bar, especially preferably essentially 30 bar, and/or

- wherein at least one cylinder (13) is formed such that the ratio of the bore area (15) of the cylinder bore (14) over the injector area (8) is in the range of 600 to 1410, preferably 900 to 1020, wherein the piston-cylinder unit is preferably configured to be suitable for an injection pressure of essentially 30 bar.
An internal combustion engine having at least one cylinder head according to claim 9 or at least one piston-cylinder unit according to claim 10.
The internal combustion engine of the preceding claim wherein the at least one fuel injector (5) arranged in at least one prechamber assembly (1) of a piston-cylinder-unit is configured to inject 100 % of the fuel, preferably hydrogen, provided to that piston-cylinder-unit per combustion cycle.
The internal combustion engine according to claim 11 or 12, wherein the internal combustion engine is configured such that the air-to-fuel ratio, preferably air-to-hydrogen ratio, is smaller than three, preferably smaller than two, in particular by adjusting the air intake and/or the fuel injection amount per combustion cycle.
Method for operating an internal combustion engine according to one of the claims 11 to 13, wherein the combustion engine is operated with the injection pressure, in particular with the injection pressure having a magnitude from 20 to 50 bar, preferably 25 to 35 bar, especially preferably essentially 30 bar.
Method for designing a prechamber assembly (1), preferably a prechamber assembly (1) according to claims 1 to 8, for an internal combustion engine, preferably according to one of the claims 11 to 13, comprising:
- at least one prechamber volume (2), wherein the at least one prechamber volume (2) has at least one injector opening (7) for partially inserting or attaching at least one fuel injector (5), preferably for injecting hydrogen, wherein the at least one injector opening (7) or the at least one fuel injector (5) has an injector area (8), and

- at least one riser channel (3), wherein the at least one riser channel (3) is connected to the at least one prechamber volume (2), wherein the at least one riser channel (3) has a riser channel area (9), and

- at least one nozzle hole (4), wherein the at least one nozzle hole (4) is connected to the at least one riser channel (3), and to a main combustion chamber when the prechamber assembly (1) is in its built-in state in a combustion engine, wherein the at least one nozzle hole (4) has a nozzle hole area,
characterized by the following steps:
- choosing a magnitude of an injection pressure of the at least one fuel injector (5) intended for operation, in particular from the range of 20 to 50 bar, preferably 25 to 35 bar, especially preferably essentially 30 bar, followed by

- choosing the ratio of the injector area (8) over the riser channel area (9) from the range of 9 to 24, preferably 12 to 18, divided by the value of the chosen injection pressure in bar, and/or choosing the ratio of the injector area (8) over the nozzle hole area from the range of 6 to 30, preferably 9 to 21, divided by the value of the chosen injection pressure in bar,

- designing the geometry of the prechamber assembly (1) with the constraint that the area ratios are as chosen in the previous step.