Piston ring arrangement and piston for a hydrogen engine

Abstract

The present invention relates to a piston ring arrangement for a hydrogen engine, comprising a sealing system piston ring and a compression ring, which are configured to be used over an oil control ring and over an oil scraper ring, wherein the piston ring arrangement is configured to control a pressure increase through blow-by between the sealing system piston ring and the compression ring such that a pressure between the sealing system piston ring and the compression ring, especially in the second part of the work cycle, is between 60° and 450 after ITDC, preferably between 50° and 540° after ITDC, more preferably between 20° and 540° after ITDC and still more preferably between 0° and 540° after ITDC higher than pressure in the combustion chamber of the cylinder, wherein these pressure ratios are achieved at speeds of between 60 and 5000 rpm, preferably 1500 to 4500 rpm, more preferably between 2000 and 4000 rpm, and most preferably between 2500 and 3500 rpm.

Description

[0001] Piston ring assembly and piston for a hydrogen engine

[0002] The present invention relates to a piston ring arrangement and pistons for a hydrogen engine, in particular for a hydrogen internal combustion engine.

[0003] Hydrogen engines encounter the problem of pre-ignition caused by lubricating oil at high power levels, which can lead to self-ignition of lubricating oil droplets during the compression stroke that have entered the combustion chamber between the top compression ring and the cylinder wall during the previous intake stroke. Depending on the injection principle, whether Direct Injection (DI) or Port Fuel Injection (PFI), different combustion conditions can be achieved.

[0004] As with a conventional diesel engine, the compression stroke causes a nearly adiabatic compression of the cylinder charge, which leads to heating of the gas in the combustion chamber. A hydrogen-air mixture has a relatively high autoignition temperature of 585°C, which cannot be achieved with a conventional or even increased compression ratio (without preheating at least the intake air).

[0005] Due to the faster combustion of the hydrogen-air mixture, pressure overlaps occur after ignition further along the crankshaft drive, transporting individual oil droplets to the combustion chamber, which are carried, among other things, by the gas flow. Further disadvantages include the fact that hydrogen engines are expected to consume similar amounts of engine oil to corresponding conventional combustion engines. For an engine with a fuel consumption of approximately 51 / 100km, this would lead to an engine oil consumption of 100ml / 2500km or 4ml / 100km.

[0006] This means that hydrogen engines are almost CO and CO2 free, but not completely.

[0007] It is therefore desirable to further reduce the already very low engine oil consumption of internal combustion engines. According to a first aspect of the present invention, a piston ring arrangement for a hydrogen engine is provided, comprising a piston ring package of three piston rings and an additional sealing system which is extended above a first piston ring of the piston ring package, characterized in that the piston ring arrangement is designed to control a pressure increase due to blow-by below the additional sealing system such that a pressure curve of a pressure above the first piston ring and below the additional sealing system, especially in a second part of a power stroke between 60° after ZOT (top dead center at the time of ignition) and 450° after ZOT, exceeds the combustion chamber pressure curve by at least 80%.

[0008] In a further embodiment of the piston ring arrangement for a hydrogen engine, the additional sealing system comprises one or more sealing system piston rings.

[0009] In another further embodiment of the piston ring arrangement for a hydrogen engine, the ring package is displaced axially towards the crankcase to make room for the additional sealing system.

[0010] In another additional further embodiment of the piston ring arrangement for a hydrogen engine, the additional sealing system is arranged above the original position of the first piston ring of the piston ring package.

[0011] In a further additional embodiment of the piston ring arrangement for a hydrogen engine, the pressure curve of the pressure above the first piston ring and below the additional sealing system always runs above the pressure curves of pressures that exist below the first piston ring of the ring package.

[0012] In another embodiment of the piston ring assembly for a hydrogen engine, the blowby of the first element of the sealing package is increased by a deliberately designed leak, compared to the blowby of a conventional piston ring with low blowby. This can be achieved, for example, by adjusting the end clearance between 0.1 and 5 mm, a deliberate flank leak, or additional design features, such as very large sealing gaps or special undersizing.

[0013] In an exemplary additional embodiment of the piston ring assembly for a hydrogen engine, a volume is increased by an expansion groove. The groove can be placed anywhere on a piston land and increases the resulting volume between the piston and the cylinder wall.

[0014] In an additional exemplary embodiment of the piston ring arrangement for a hydrogen engine, the blowby of a sealing system piston ring is increased by a leak compared to the blowby of a conventional sealing system piston ring with low blowby, which is achieved, for example, by adjusting the end clearance between 0.1 and 5 mm, targeted flank leaks or additional design features.

[0015] In another embodiment of the piston ring assembly for a hydrogen engine according to one of the preceding claims, the pressure is maintained by adjusting the gap. The gap is adjusted here using a gap adjustment device, such as a file.

[0016] In a further additional embodiment of the piston ring arrangement for a hydrogen engine, a height of the first piston ring of the piston ring package under the additional sealing system is reduced in the axial direction in order to reduce inertial forces of the first piston ring.

[0017] In another additional embodiment of the piston ring assembly for a hydrogen engine, at least one piston ring of the ring pack is designed as a rectangular ring with a circumferential groove on the running surface below the pivot point. This piston ring can be designed as a so-called E-line™® ring from Tenneco™®.

[0018] The present invention provides a piston ring arrangement and a combination of a piston ring arrangement and a piston for a hydrogen engine, comprising a sealing system piston ring and a piston ring package with a compression ring, an oil control ring, and an oil control ring. The piston ring arrangement is configured to control a pressure increase due to blowby between the sealing system piston ring and the compression piston ring such that the pressure between the piston rings is always higher than the pressure in the cylinder or combustion chamber from the middle of the power stroke until at least its end. The sealing system piston ring and the compression ring act as a type of valve, trapping blowby gases between the sealing system piston ring and the first piston ring of the ring package shortly after the ignition of the air-fuel mixture.As a result, at least in the lower part of the power stroke, there is always an overpressure compared to the first piston ring, whereby oil that is hanging on the inner cylinder wall is pressed downwards above the first piston ring towards the crankcase by this overpressure. This pressure between the sealing system piston ring and the first piston ring is higher than the pressure in the combustion chamber of the cylinder, especially in the second part of the power stroke, between 60° and 450° after ZOT, 0° preferably between 50° and 540° after ZOT, more preferably between 20° and 540° after ZOT and even more preferably between 0° and 540° after ZOT. As a result of this circumstance, these pressure conditions in these angular ranges mean that less oil can get past the second compression piston ring towards the sealing system piston ring.The now thinner oil film on which the sealing system piston ring slides is so small that the sealing system piston ring could tear oil droplets from this oil film, which could influence the combustion processes of Kb engines, whereby these pressure ratios are achieved in an engine between 60 and 5000 rpm, preferably 1500 to 4500 rpm, more preferably between 2000 and 4000 rpm and most preferably between 2500 and 3500 rpm.

[0019] Here and below, the terms "sealing system piston ring," "upper piston ring of the piston ring assembly," "upper compression piston ring of the piston ring assembly," "first compression ring of the piston ring assembly," and "first piston ring of the piston ring assembly" are used synonymously. Furthermore, the terms "compression ring of the ring pack," "first compression piston ring of the ring pack," "first piston ring of the ring pack," "first piston ring," and "first compression ring" are used synonymously.

[0020] The term "top" is used synonymously with "combustion chamber side" or "toward the combustion chamber." The term "bottom" is used in the sense of "crankcase side" or "toward the crankcase."

[0021] The definition of a speed range appears necessary here, as the pressure losses through the annular gap in slow-rotating internal combustion engines are higher than in fast-rotating engines. This effect is particularly well-known in Wankel engines, which exhibit better combustion chamber sealing and better fuel consumption and emission values ​​at higher speeds than at lower speeds. The specific speed range is specified to give the expert a piston speed and, above all, a time frame within which the overpressure in the space between the sealing system piston ring and the compression ring can be considered when designing the sealing system piston rings and compression piston rings.Here and below, the terms "compression ring" and "sealing system piston ring" are always used in the singular, although it should be noted that two or more sealing system piston rings and two or more compression rings can also be used in the piston ring package. Such embodiments are also within the scope of the claims, as they also each comprise at least one sealing system piston ring and at least one compression ring.

[0022] This design is based on the idea that an additional sealing system, preferably in the form of a sealing system piston ring, is placed upstream of the conventional top ring of a ring pack in the direction of the combustion chamber. This system brings the previous top ring (and thus the previous first compression ring) into an operating range similar to that found in conventional gasoline and diesel engines. Here, too, a controlled blowby of the sealing system piston ring creates an overpressure between the compression piston rings. This overpressure lies above the pressure in the combustion chamber for more than 90°, and at least from 45° after top dead center, already from the second half of the power stroke. This occurs through a pressure drop in the cylinder due to the piston moving downwards during the power stroke. The blowby of the first compression ring is minimized.Furthermore, the sealing system piston ring is optimized for minimal reverse blowby, which traps the initial blowby during the first 90° after top dead center of the power stroke between the sealing system piston ring and the compression piston ring. This allows a higher pressure to exist between the sealing system piston ring and the compression piston ring near the end of the power stroke than in the combustion chamber. This maintains an overpressure above the first compression ring for a longer period, which subsequently helps push oil droplets toward the crankcase.

[0023] In a preferred embodiment of the piston ring assembly, it comprises the features of the embodiments described above. Here, the piston ring designs are also defined as having a pressure retention capacity at a specific operating speed.

[0024] In a further embodiment of the piston ring arrangement, the sealing system piston ring has a lower contact pressure over most of the 4-stroke cycle than the first compression piston ring, wherein the sealing system piston ring in a relaxed state can have an identical average diameter than the compression piston ring and / or the contact pressure of the sealing system piston ring can be smaller or larger than a contact pressure of the compression piston ring, and / or wherein the product of specific contact pressure and a height of the running surface is smaller for the sealing system piston ring than for the compression piston ring.

[0025] Here, the sealing system piston ring seals less tightly than the compression piston ring in order to achieve a relatively rapid pressure increase in the area between the sealing system piston ring and the first compression piston ring. The first compression piston ring mainly serves to counteract a pressure increase in the crankcase. The compression piston ring is planned to be dimensioned much more specifically than is known from previous combustion engines, since increased pressure between the first and second compression piston rings that exists over a longer period has a greater impact on blowby. This is because the higher pressure caused by blowby is not only present during the power stroke, but ideally should be present until the end of the following intake stroke. This means that blowby not only occurs during approx.Blowby, albeit reduced, occurs at the compression ring during a quarter of the four-stroke cycle, but occurs during almost 1 / 4 of the four-stroke cycle, which can lead to an increased pressure rise in the crankcase. Due to the longer period during which blowby occurs at the compression piston ring, the pressure in the crankcase will increase, which can be compensated for by increasing the crankcase ventilation with an oil separator.

[0026] In a further design of the piston ring arrangement, the sealing system piston ring has a larger axial cross-section than the first compression ring. The functions of the piston rings are clearly defined: the upper piston ring acts as a kind of valve, while the first piston ring serves as a pressure barrier from top to bottom. This requires a different inertia force from the compression piston ring compared to the sealing system piston ring, which essentially only serves to seal off any excess pressure against the crankcase.

[0027] In another exemplary piston ring arrangement, the sealing system piston ring is further provided with a DLC (diamond-like carbon) coating at least in the area of ​​one running surface, wherein the first compression ring of the ring pack is preferably also provided with a DLC coating at least on one running surface. DLC, or diamond-like carbon, is a partially amorphous carbon modification comprising large portions of carbon atoms, each bonded by tetrahedral covalent bonds. The bonds are partially arranged at an angle of 109°25', although the entire coating does not form a superordinate diamond lattice over larger distances. Such a DLC coating exhibits particularly high wear resistance, which is particularly beneficial given the particularly thin lubricating film of the sealing system piston ring.

[0028] According to another aspect of the present invention, a piston for a hydrogen internal combustion engine is provided, which comprises four or at least four piston ring grooves, wherein at least one upper piston ring groove is adapted to receive a sealing system piston ring of a piston arrangement as described above and at least one further piston ring groove is adapted to receive a piston ring package with at least one first compression piston ring.

[0029] According to an exemplary embodiment of the piston, it further comprises at least one recess located between the two upper piston ring grooves, increasing the volume between the two upper compression piston rings. These recesses can also be arranged between the ring pack to allow the volumes to be coordinated with one another.

[0030] The objective of the present invention is to maintain, for as long as possible, a positive pressure between the sealing system piston ring and the first compression ring relative to the crankcase pressure, and preferably also relative to the current cylinder pressure. When the intermediate piston ring area is filled during the initial power stroke, a larger volume between the upper two compression rings can help maintain this pressure over a longer period of time while maintaining the same leakage rate.

[0031] In an additional exemplary embodiment of the piston, the plurality of recesses are arranged in a grid in the circumferential direction and in the axial direction. The grid of recesses or depressions forms a type of two-dimensional point grid seal that limits gas movement in the area between the sealing system piston ring groove and the first compression ring groove in both the axial and circumferential directions. This can have a positive effect in other designs. A two-dimensional point grid seal also forms a volume that can maintain an overpressure compared to the combustion chamber and the area below the first compression ring for a longer period of time at the same gas loss rate. The point grid can help mitigate blowby of the annular gap in the circumferential direction. Line grids or hexagonal grids can also be used.According to a further aspect of the present invention, an embodiment of the piston ring arrangement described above is combined with one of the above-described embodiments of a piston according to the invention to be used in a hydrogen engine, wherein the piston is further provided with at least one oil control ring and at least one oil control ring.

[0032] According to another aspect of the present invention, an internal combustion engine having the above combination of piston rings and piston is provided.

[0033] In an additional embodiment of the internal combustion engine, it comprises at least one cylinder, wherein each of these cylinders is provided with a DLC coating in at least one area that can come into contact with the compression piston rings of the at least one piston, and / or wherein the internal combustion engine comprises a crankcase ventilation system with an oil separator. The oil separator is necessary due to the increased blowby of the first compression ring of the piston ring pack toward the crankcase to prevent oil from entering the combustion chamber via the crankcase ventilation and the intake tract, which could lead to premature ignition.

[0034] In the following, the present invention is illustrated by schematic and not-to-scale representations of exemplary embodiments.

[0035] Figure 1 shows a schematic sectional partial view to illustrate an installed piston ring set.

[0036] Figure 2 shows a view of a pressure curve achieved by the present invention with an exemplary piston ring set and an exemplary piston.

[0037] Figures 3 to 5 mainly relate to various embodiments of pistons to be used together with the piston ring sets according to the invention.

[0038] In both the description and the figures, the same or similar terms, designations and symbols are used to refer to the same or similar components and elements.

[0039] Figure 1 shows a partial sectional view of a piston ring set according to the invention in a resting position of, or in, a stationary hydrogen internal combustion engine. In the illustration, a piston is arranged in a cylinder, with the cylinder or the cylinder inner surface represented on the left by a line. A rotational symmetry axis runs parallel to the line, which shows the cylinder inner surface on the right side outside the edge of the image (although, strictly speaking, this only applies to truly rotationally symmetrical components and, strictly speaking, cannot apply to all aspects of an internal combustion engine due to, for example, the annular gap and the piston pin as well as other components and aspects). At the top of Figure 1, as well as in the other figures, is the combustion chamber with the cylinder head (not shown). A crankcase is located below the figure.The piston is provided with four piston ring grooves: a first upper compression piston ring groove, in which a first upper compression piston ring is shown, a second lower compression piston ring groove, in which a second lower compression piston ring is shown, and an oil control piston ring groove, which is provided with an oil control piston ring designed as an eLine ring, as well as an oil scraper groove, which has an oil drainage channel towards the crankcase or an interior of the piston. A piston skirt (not shown) adjoins the oil control piston ring groove. Components such as valve pockets or bowls, piston pins, or other conventional aspects are not shown.

[0040] The radially outer region above the first upper compression piston ring groove is referred to as the top land or also as the “first land” or “land 1”, even though this region may be provided with additional non-land surface structures such as grooves. The intermediate ring region between the first compression piston ring groove and the second compression piston ring groove, or the intermediate compression piston ring region, is also referred to as the “second land” or “land 2”, even though this region may be provided with additional non-land surface structures such as grooves. In the present case, the piston is provided with a constriction in the region of land 2, which is intended to slightly increase the volume of the intermediate ring region.The aim of the present invention is to keep a pressure in the intermediate ring area above a pressure in the crankcase for as long as possible, which is improved with a larger gas volume at the same leakage rate, whereby it should be noted, however, that this gas volume must be kept small or low enough so that the blowby of the upper compression ring is able to achieve a sufficient pressure increase in the intermediate ring area.

[0041] Figure 2 shows a pressure curve of an engine according to the invention, with the different lines each showing the pressure in the combustion chamber, the respective areas between the ring grooves and finally also in the crankcase. The abscissa or X-axis represents the angle of the crankshaft in degrees, with the four strokes covering a total angle of 720° over the two revolutions. The angle value 0° corresponds to the top dead center of the power stroke. The bottom dead center at -180° of the intake stroke represents the beginning of the 4-stroke cycle and the beginning of the diagram. The lowest line with the constant pressure corresponds to the pressure in the crankcase. The line above it corresponds to the pressure of "land four", i.e. the pressure in the area between the oil control ring and the oil control ring.The line running above the pressure in “land four,” which is slightly higher in comparison and leads it in the pressure curve, corresponds to the pressure in “land three,” i.e. the pressure in the area between the second compression piston ring and the oil control ring. These lines do not intersect and are entirely in the range from 0 to 4 bar. The relatively smooth line running above the three lower pressure lines corresponds to the pressure between the sealing system piston ring and the first compression ring, or the pressure in “land two,” i.e. the area between the upper compression ring and the lower compression ring. This pressure curve can be identified by the minimum with the highest pressure value. The pressure in the combustion chamber, or in “land one,” shows the greatest amplitude and the greatest ripple, with the maximum value being reached at or around top dead center.The pressure curve in the combustion chamber shows a second maximum at 360°, in the area where the exhaust valve is already closed and the intake valve is not yet open. Here, the diagram clearly shows that the pressure between the two compression piston rings represents the highest pressure in the system over much of the diagram. This creates a constant blowby at the second compression ring toward the crankcase, which helps minimize the oil film on the inside of the cylinder by forcing excess oil toward the crankcase and the oil control ring due to the excess pressure.

[0042] Figure 3 shows a separate groove in the area between the sealing system piston ring and the first compression piston ring of a pressure reservoir. The groove can also be in the form of a conventional piston ring groove, in which case no piston ring is inserted into this groove.

[0043] Figure 4 shows an embodiment in which the area between the sealing system piston ring and the first compression piston ring, or "land two," is reduced in diameter compared to the top land, or "land one" and "land three," as well as "land four" and land five, or the piston skirt, thus providing a pressure reservoir. Even if land two is set back by just a few tenths of a millimeter, this already results in a significant increase in reservoir volume. Figure 4 also shows that the compression piston rings can have different cross-sections to control the inertia force influences and thus have different axial heights or materials. The second piston ring is preferably reduced in mass compared to the additional sealing element.

[0044] Figure 5 shows another embodiment, in which two sealing system piston rings and two compression rings are used. This design does not feature any modifications to the piston that could create a reservoir volume. The illustrated embodiment has a total of six piston rings and six piston ring grooves, with the top two designed as sealing system piston rings, the middle two as compression rings, the second from the bottom as a standard minute ring, and the bottom one as an oil control ring.

[0045] Furthermore, a piston ring arrangement for a hydrogen engine, comprising a sealing system piston ring and a first compression ring of a sealing package, wherein the sealing system piston ring has a chamfered upper edge between its upper ring flank and its running surface, which increases the blowby in the direction of the crankcase, wherein the sealing system piston ring is configured to twist negatively, and wherein the first compression ring has a chamfer on a radially inner edge of an upper ring flank of the first compression ring, whereby the first compression ring twists positively.

[0046] In a piston ring arrangement according to one of the preceding embodiments, wherein the sealing system piston ring has a lower contact pressure than the first compression piston ring, wherein the sealing system piston ring in a relaxed state has a smaller average diameter than the first compression piston ring and / or wherein a contact force of the sealing system piston ring is smaller than a contact force of the first compression piston ring, and / or wherein the product of specific contact force and a height of the running surface is smaller for the sealing system piston ring than for the first compression piston ring.

[0047] In another piston ring arrangement, the sealing system piston ring has a smaller radial dimension in cross-section than the first compression ring.

[0048] In another piston ring arrangement, the sealing system piston ring has a smaller axial dimension in cross-section than the first compression ring of the sealing package.

[0049] In yet another piston ring arrangement, the first compression ring is provided with a recess between a lower ring flank and a running surface, which extends in a circumferential direction and preferably ends before a respective butt end. In yet another piston ring arrangement according to the invention, the sealing system piston ring is further provided with a DLC layer at least in the region of a running surface, wherein the first compression ring is preferably also provided with a DLC layer at least on one running surface. In another embodiment of the piston ring arrangement, several sealing system piston rings are present and / or the piston ring package has several compression piston rings.

Claims

Claims 1. Piston ring arrangement for a hydrogen engine comprising a piston ring package of three piston rings, and an additional sealing system which is arranged above a first piston ring of the piston ring package, characterized in that the piston ring arrangement is designed to control a pressure increase due to blow-by below the additional sealing system in such a way that a pressure curve of a pressure above the first piston ring and below the additional sealing system, especially in a second part of a power stroke between °60 and 540° after top dead center at the ignition time (TDC), exceeds a combustion chamber pressure curve and is higher than the combustion chamber pressure curve in at least 80% of the defined range.

2. Piston ring assembly for a hydrogen engine according to claim 1, wherein the additional sealing system comprises one or more sealing system piston rings.

3. Piston ring assembly for a hydrogen engine according to claim 1 or 2, wherein the piston ring package is displaced axially toward the crankcase to create space for the additional sealing system.

4. Piston ring assembly for a hydrogen engine according to claim 1, 2 or 3, wherein the additional sealing system is arranged above the original position of the first piston ring of the piston ring package.

5. Piston ring arrangement for a hydrogen engine according to claim 1, 2, 3 or 4, characterized in that the pressure curve of the pressure above the first piston ring and below the additional sealing system always runs above the pressure curves of pressures which are present below the first piston ring of the ring package.

6. Piston ring arrangement for a hydrogen engine according to one of claims 1 to 5, wherein the blowby of a first piston ring of the sealing package is increased by a leak, compared to the blowby of a conventional piston ring with low blowby, which is achieved, for example, by adjusting the end clearance between 0.1 to 5 mm, targeted flank leaks or additional design features.

7. Piston ring assembly for a hydrogen engine according to one of the preceding claims, wherein a volume is increased by an expansion groove.

8. Piston ring arrangement for a hydrogen engine according to one of the preceding claims 1 to 7, wherein the blowby of a sealing system piston ring is increased by a leak (compared to the blowby of a conventional piston ring with low blowby), which can be achieved, for example, by adjusting the end clearance between 0.1 to 5 mm, targeted flank leaks or additional design features.

9. A piston ring assembly for a hydrogen engine according to any preceding claim, wherein the pressure is maintained by adjusting the gap.

10. Piston ring assembly for a hydrogen engine according to one of the preceding claims, wherein the height of the first piston ring of the piston ring pack is axially reduced under the additional sealing system in order to reduce inertia forces of the first piston ring.

11. Piston ring arrangement for a hydrogen engine according to one of the preceding claims, wherein at least one piston ring of the ring package is designed as a rectangular ring with a circumferential groove on the running surface below the pivot point 12. Piston ring arrangement for a hydrogen engine according to one of the preceding claims, with a sealing system piston ring and a first piston ring of the ring package, which is designed as a first compression ring, which are designed to be inserted over an oil control ring and over an oil scraper ring, wherein the piston ring arrangement is designed to control a pressure increase due to blowby between the sealing system piston ring and the first compression ring such that a pressure between the sealing system piston ring and the compression ring, especially in the second part of the power stroke, is between 60° and 450° after ZOT°, preferably between 50° and 540° after ZOT, more preferably between 20° and 540° after ZOT° and even more preferably between 0 0and 540 after ZOT ° with respect to the top dead center of the power stroke is higher than a pressure in the combustion chamber of the cylinder, these pressure ratios being achieved at speeds between 60 and 5000 rpm, preferably 1500 to 4500 rpm, more preferably between 2000 and 4000 rpm and most preferably between 2500 and 3500 rpm.

13. Piston for a hydrogen internal combustion engine comprising at least four piston ring grooves, and configured to receive a piston ring arrangement for a hydrogen engine according to one of the preceding claims, wherein at least one of the upper piston ring grooves is configured to receive a sealing system piston ring and wherein at least one piston ring groove arranged below the at least one upper piston ring groove is configured to receive at least a first piston ring of the piston ring package.

14. Piston according to claim 13, further comprising at least one recess arranged between the upper two piston ring grooves and increasing a volume between the upper two compression piston rings, wherein the recess is preferably designed as at least one expansion groove.

15. Piston according to claim 13 and / or 14, further wherein the at least one recess is designed as a plurality of circumferential grooves which extend in the circumferential direction and form a groove seal, and / or wherein the plurality of recesses form a grid in the circumferential direction and in the axial direction, the grid of the recesses or depressions thereby creating a type of two-dimensional point grid seal which limits gas movement in the area between the upper two compression ring grooves both in the axial direction and in the circumferential direction.

16. A combination of a piston ring arrangement according to any one of claims 1 to 12 and a piston according to any one of claims 1 to 15 for a hydrogen engine, the combination further comprising at least one oil control ring and an oil control ring.

17. Internal combustion engine with at least one piston according to claims 13 to 15.

18. Internal combustion engine according to claim 17, wherein it comprises at least one cylinder which is provided with a DLC coating at least in a region which can come into contact with compression piston rings of the at least one piston, and / or wherein the internal combustion engine comprises a crankcase ventilation system with an oil separator.

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