A piston and an internal combustion engine system

Abstract

The present disclosure relates to piston (3) for an internal combustion engine (10), the piston extending in an axial direction (A) and a radial direction (R), and having an axial top end (16) comprising a piston bowl (6) intended to form part of a combustion chamber, the piston bowl having an axial floor portion (11) with a floor surface (11a) and a circumferential rim portion (20) extending in the axial direction (A) between the floor surface and a top end surface (5) of the axial top end, the circumferential rim portion having at least one fuel impingement portion (60), the piston bowl further having an axial depth (H) defined by an axial distance between the floor surface and the top end surface, the piston bowl further comprising a plurality of spaced-apart protrusions (40, 50) circumferentially distributed around the circumferential rim portion (20), wherein the plurality of spaced-apart protrusions comprises a set of a first type of protrusions (40) and a set of a second type of protrusions (50).

Description

A PISTON AND AN INTERNAL COMBUSTION ENGINE SYSTEMTECHNICAL FIELD[11 The disclosure relates generally to a piston for an internal combustion engine. The disclosure further relates to an internal combustion engine system for a vehicle, wherein the internal combustion engine comprises a piston. The disclosure is applicable on vehicles, in particularly heavy-duty vehicles, such as e.g. trucks. However, although the present disclosure will mainly be described in relation to a truck, the internal combustion engine system may also be applicable for other types of vehicles propelled by means of an internal combustion engine. In particular, the present disclosure can be applied in heavy-duty vehicles, such as trucks, buses, and construction equipment, but also in cars and other lightweight vehicles etc. Further, the internal combustion engine is typically a diesel internal combustion engine, however other fuels may also be possible to use in combination with the piston, such as hydrogen and natural gas. The present disclosure may also be applied in other machines such as power generators and construction equipment. The present disclosure may further be applied in marine vessels or the like.BACKGROUND[2] In the field of internal combustion engine arrangements, numerous efforts are made to accomplish efficient combustion which is also satisfactory in view of residual products, in particular soot particle and NOx emissions, although also carbon monoxide emissions, and hydrocarbon emissions from diesel fuel may naturally be considered.[3] A combustion process in which e.g. diesel fuel is injected directly into the cylinder and is ignited by increased temperature and pressure in the cylinder is generally referred to as a compression ignition combustion process. Another type of ignition process for some gaseous fuels is the spark-ignition combustion process. When the fuel is ignited in the cylinder, combustion gases present in the cylinder undergo turbulent mixing with the burning fuel, so that a mixture-controlled diffusion flame is formed. The combustion of the fuel / gas mixture in the cylinder gives rise to heat generation which causes the gas in the cylinder to expand. The expansion of the gas then causes the piston to move in the cylinder. Depending on a number of parameters, such as the fuel type, the injection pressure of the fuel, the quantity of exhaust gases recirculated to the cylinder, the time of injection of the fuel and theturbulence prevailing in the cylinder, different engine efficiency and emission values are obtained.[41 To control and in particular to reduce emissions from the combustion process in a combustion engine, it has been proposed to utilize the shape of the piston bowl surface facing towards the combustion chamber. The piston bowl surface is part of a piston crown of the reciprocating piston in a cylinder. To this end, the piston bowl surface may be designed so as to affect various parameters inside the combustion chamber such as flame propagation, mixing energy, kinetic energy distribution, and / or swirl.[51 It has also been observed that the shape of the piston bowl may affect combustion and / or mixing of fuels within the cylinder in other types of internal combustion engines, such as gaseous fuel engines, e.g. hydrogen internal combustion engines.[61 Despite the activity in the field, there is a desire for further improving such types of pistons for an internal combustion engine (ICE) system for a heavy-duty vehicle.SUMMARY[7] According to a first aspect of the disclosure, there is provided a piston for an internal combustion engine, ICE, the piston extending in an axial direction A and a radial direction R, and having an axial top end comprising a piston bowl intended to form part of a combustion chamber, the piston bowl having an axial floor portion with a floor surface and a circumferential rim portion extending in the axial direction A between the floor surface and a top end surface of the axial top end, the circumferential rim portion having at least one fuel impingement portion, the piston bowl further having an axial depth H defined by an axial distance between the floor surface and the top end surface, the piston bowl further comprising a plurality of spaced-apart protrusions circumferentially distributed around the circumferential rim portion, each one of the spaced-apart protrusions extending a substantial part in the radial direction towards a center axis AC, and further extending a substantial part in the axial direction from the floor surface towards the top end surface, wherein the plurality of spaced-apart protrusions comprises a set of a first type of protrusions and a set of a second type of protrusions, the set of the first type of protrusions and the set of the second type of protrusions being arranged in an alternate manner along the circumferential rim portion, wherein at least one protrusion of the second type of protrusions is arranged at the at least onefuel impingement portion, so as to redirect a receiving flame to opposite tangential directions and of the circumferential rim portion, and adjacent protrusions of the first type of protrusions are arranged in-between the at least one fuel impingement portion, so as to redirect a circumferential flame progress mainly towards the center axis Ac of the piston, and wherein each one of the first type of protrusions comprises opposite radial side sections and further a flat surface or concave surface extending between the opposite radial side sections, the flat surface or concave surface having a first circumferential extension a at an intersection between the flat surface or concave surface and the floor surface, and further a second circumferential extension b at an axial distance h from the floor surface, the second circumferential extension b being less than the first circumferential extension a.[81 The first aspect of the disclosure may seek to provide an improved piston for an ICE that contributes to reductions in fuel consumption and emissions without compromising on the durability of the piston. A technical benefit may include an enhanced combustion of the fuel by providing the piston with protrusions for facilitating interaction between fuel flames, piston bowl regions and adjacent flames. In addition, the second type of protrusions in combination with the first type of protrusions collectively provide for an enhanced flame circulation during the combustion phase. As such, the combination of the first and second types of protrusions allows for a well-balanced flow situation and an appropriate compromise between combustion performance and heat-load on the ICE system.[9] Moreover, the proposed piston provides for an improved design of the first type of protrusions at a lower area of the piston bowl, which then generally intersects with a dome part of the piston bowl.

[0010] By the provision of having different types of protrusions, the design of the piston contributes to an enhanced combustion process for fuels such as diesel fuel and / or an enhanced mixing of air and fuel for other types of fuels, such as a hydrogen gas fuel. The protrusions may further provide for a sudden change in the side-profile of the protrusion so as to achieve a well-defined flow release location.

[0011] By having protrusions comprising the flat surface or concave surface extending between opposite radial side sections in combination with the provision that the second circumferential extension being less than the first circumferential extension, the piston may better withstand critical fatigue conditions that occur during ordinary use of the piston in heavy-duty vehicles.

[0012] The proposed protrusions are generally provided to enhance fuel flames interaction with the surfaces forming the piston bowl and with adjacent flames. However, whilst the proposed piston can be incorporated in a number of different types of ICE systems, the proposed piston may be particularly suitable for ICE systems fueled by a high-pressure injection of a fuel containing liquid diesel or a pressure injection of a gaseous fuel such as a hydrogen fuel, where the fuel injection duration occurs near the top dead center (TDC). In hydrogen ICE system, the proposed piston design having the above protrusion segment may improve the mixing of hydrogen gas and compressed air prior to an ignition event.[131 Further, by the above arrangement of the first type of protrusions, the first type of protrusions is arranged and configured to guide another receiving flame towards the center axis. The first type of protrusions may also contribute to guide the another receiving flame in the axial direction. The first type of protrusions may also refer to collision protrusions.

[0014] Moreover, by the above arrangement of the second type of protrusions, the second type of protrusions are arranged and configured to redirect a receiving flame to opposite tangential directions of the circumferential rim portion. The second type of protrusions may also refer to dividing protrusions. Hereby, the second type of protrusions (dividing protrusions) contributes to improve the flame-wall flow within the combustion chamber by dividing the flame in a smoother manner in comparison to a similar piston without any dividing protrusions.

[0015] Hence, instead of using kinetic energy / momentum to create turbulence already during the flame-wall event (as provided by a conventional piston without dividing protrusions), the second type of protrusions is thus arranged and configured to provide a smoother flow and to maintain, through the smoother flow, more of the kinetic energy. This may allow for producing increased turbulence (for mixing) later in the combustion cycle in the center of the piston bowl.

[0016] The term “fuel impingement portion”, as used herein, may refer to any one of a spray-fuel impingement portion and a flame-fuel impingement portion. The term “spray” generally refers to fuel in liquid phase, whilst the term “flame” generally refers to the burning gaseous phase, also referred to as a jet. A fuel jet is a gaseous high velocity stream, while the flame is the ignited and burning jet. Accordingly, the term fuel impingement portion may generally cover both an un-ignited flow situation (jet-impingement) as well as an already ignited jet (flame-impingement).

[0017] The piston may be used in any one of a diesel ICE system, a hydrogen ICE system and a methane ICE system.[181 The first type of protrusions may generally be different to the second type of protrusions. In some examples, including in at least one preferred example, optionally the first type of protrusions is different to the second type of protrusions by a difference in geometry. Further, the protrusions can be provided in several different geometries, shapes and disposed at various location along the side section.[191 In some examples, including in at least one preferred example, optionally at least one protrusion of the first type of protrusions may comprise a tip portion facing the center axis, the tip portion may further be defined by an angle of about 40 to 140 degrees. Still preferably, the tip portion may be defined by an angle of about 40 to 120 degrees. Still preferably, the tip portion may be defined by an angle of about 90 to 110 degrees. A technical advantage may be an improved control of the so-called flame-flame event.

[0020] In some examples, including in at least one preferred example, optionally at least one protrusion of the first type of protrusions may comprise a tip portion facing the center axis, the tip portion may be defined by an angle of about 40 to 100 degrees. A technical advantage may be an improved control of the so-called flame-flame event in an ICE system operable on a hydrogen-based fuel, such as a pure hydrogen fuel ICE system.

[0021] In some examples, including in at least one preferred example, optionally a steepness of at least one protrusion of the first type of protrusions in relation to the axial direction is defined by a second angle. A technical advantage may be an improved control of the degree of confinement of the jets in axial direction.

[0022] In some examples, including in at least one preferred example, optionally the second angle is a steep angle or a shallow angle.

[0023] In some examples, including in at least one preferred example, optionally the second angle may be about 10 to 40 degrees. Still preferably, the second angle may be about 15 to 30 degrees. Still preferably, the second angle may be about 20 to 25 degrees. A technical advantage may be an even more improved control of the degree of confinement of the jets in axial direction.

[0024] In some examples, including in at least one preferred example, optionally the at least one protrusion of the second type of protrusions comprises a corresponding tip portion facing the center axis, the corresponding tip portion being defined by an angle of about 80 to140 degrees. Still preferably, the corresponding tip portion may be defined by an angle of about 90 to 130 degrees. Still preferably, the corresponding tip portion may be defined by an angle of about 100 to 120 degrees. A technical advantage may be an improved control of the so-called flame-wall event. The angle provides for an improved control of the point of stagnation. In general, it has been observed that the second type of protrusions allow for improving the possibility of dividing the flow of fuel (flame), thus providing a reduced stagnation within the combustion chamber.[251 In some examples, including in at least one preferred example, optionally the corresponding tip portion may be defined by an angle of less than 100 degrees.[261 In some examples, including in at least one preferred example, optionally a steepness of at least one protrusion of the second type of protrusions in relation to the axial direction is defined by a corresponding second angle. A technical advantage may be an improved control of the degree of confinement of the jets in axial direction.

[0027] In some examples, including in at least one preferred example, optionally the corresponding second angle may be a steep angle or a shallow angle.

[0028] In some examples, including in at least one preferred example, optionally the corresponding second angle may be about 10 to 40 degrees. Still preferably, the corresponding second angle may be about 12 to 30 degrees. Still preferably, the corresponding second angle may be about 15 to 25 degrees. A technical advantage may be an even more improved control of the degree of confinement of the jets in the axial direction.

[0029] In some examples, including in at least one preferred example, optionally a steepness of the circumferential rim portion in-between an adjacent protrusion of the first type of protrusions and an adjacent protrusion of the second type of protrusions defines a side angle SA.

[0030] In some examples, including in at least one preferred example, optionally the side angle may be about 5 to 25 degrees. Still preferably, the side angle may be about 8 to 22 degrees. Still preferably, the side angle may be about 10 to 20 degrees.

[0031] In some examples, including in at least one preferred example, optionally the axial distance h being a quarter of the axial depth H of the piston bowl, and wherein a ratio between the second circumferential extension b and the first circumferential extension a is 0.4 or less. A technical benefit may include a less sensitive design of the protrusions in terms of required fatigue life and required durability. More specifically, by the above configuration ofthe protrusions, the part of the protrusion where there is a low impact on combustion performance is designed so as to minimize the compressive stress at the protrusions in the lower region towards the dome (center of piston) for the temperature load, i.e. compressive stress in the radial direction, whilst also separating the location of the maximum compressive stress due to temperature load from the maximum tensile stress location due to the pressure load. A piston bowl with protrusions where maximum stress regions are separated from each other contributes to increasing the fatigue life of the protrusions and the piston.

[0032] In some examples, including in at least one preferred example, optionally a first radial side section of the opposite radial side sections intersects with the flat surface or concave surface along an intersection edge and a second radial side section of the opposite radial side sections intersects with the flat surface or concave surface along another opposite intersection edge.

[0033] In some examples, including in at least one preferred example, optionally the intersection edges in combination with the first circumferential extension and the second circumferential extension define the extension of the flat surface or the concave surface.

[0034] In some examples, including in at least one preferred example, optionally each one of the intersection edges inclines from the first circumferential extension to the second circumferential extension, respectively, in a linear manner or in a non-linear manner, such as in a curved manner.

[0035] Typically, the intersection edges may incline towards a center region located on the second circumferential extension. By way of example, the intersection edges may incline from the first circumferential extension to the second circumferential extension in a curved manner, as seen in the circumferential direction and in the radial direction.

[0036] In some examples, including in at least one preferred example, optionally the intersection edges in combination with the first circumferential extension and the second circumferential extension define a surface resembling a trapezoid or a triangular shape. Such shapes may further improve the properties of the protrusions in terms of required durability.

[0037] A concave surface substantially extending in the circumferential direction contributes to an improved configuration of the protrusion. The concave surface of the protrusion may generally be the surface of the protrusion that is arranged to face the axial center of the piston bowl. Typically, although strictly not required, a radius of curvature ofthe concave surface may always be essentially perpendicular to the axial center of the piston bowl.

[0038] In some examples, including in at least one preferred example, optionally an extension of the flat surface or the concave surface from the first circumferential extension to the second circumferential extension further comprises a concave axially extending region.

[0039] One advantage with a concave surface in the axial direction is that the portion of protrusion intersecting with the floor surface provides for a smooth transition between the protrusion and the floor portion.

[0040] In some examples, including in at least one preferred example, optionally an extension of the flat surface from the first circumferential extension to the second circumferential extension is defined by a flat surface profile. That is, in the axial direction, the flat surface from the first circumferential extension to the second circumferential extension may be defined by a flat surface profile.

[0041] In some examples, including in at least one preferred example, optionally each one of the opposite radial side sections comprises multiple regions of different convex curved profiles.

[0042] The radial side sections may generally extend in the radial direction. Hence, the radial side sections are radially extending side sections. The radial side section may typically extend from the circumferential rim portion. The radial side section may typically extend from the circumferential rim portion and towards the center axis. The radial side section may typically also extend substantially in the axial direction.

[0043] In some examples, including in at least one preferred example, optionally the spaced-apart protrusions are uniformly circumferentially distributed along the circumferential rim portion.

[0044] The spaced-apart protrusions may be non-uniformly circumferentially distributed along the circumferential rim portion.

[0045] In some examples, including in at least one preferred example, optionally each one of the spaced-apart protrusions extends in the axial direction from the floor surface to the top end surface of the piston top end.

[0046] Each one of the spaced-apart protrusions may extend in the axial direction from the floor surface to the top end surface of the piston top end. In another example, each one of the spaced-apart protrusions may extend in the axial direction from the floor surface to thesecond circumferential extension. As mentioned above, the second circumferential extension is axially located at the axial distance from the floor surface. The axial distance is a quarter of the depth of the piston bowl. In other examples, each one of the spaced-apart protrusions may extend in the axial direction from the floor surface to a given intermediate axial distance being greater than the quarter of the depth of the piston bowl but less than the depth of the piston bowl. In other words, each one of the spaced-apart protrusions may extend in the axial direction from the floor surface towards to a distance in the axial direction between the quarter of the depth of the piston bowl but less than the depth of the piston bowl.

[0047] In some examples, including in at least one preferred example, optionally the flat surface or concave surface extends in the axial direction from the intersection between the flat surface or concave surface and the floor surface and towards the top end surface of the piston top end.

[0048] In some examples, including in at least one preferred example, optionally the flat surface or concave surface extends in the axial direction from the intersection between the flat surface or concave surface and the floor surface to the top end surface of the piston top end.

[0049] In some examples, including in at least one preferred example, optionally the flat surface or concave surface extends in the axial direction from the intersection between the flat surface or concave surface and the floor surface to the second circumferential extension.

[0050] In some examples, the flat surface or concave surface may extend in the axial direction from the intersection between the flat surface or concave surface and the floor surface to the top end surface of the piston top end. In another example, the flat surface or concave surface may extend in the axial direction from the floor surface to the second circumferential extension. By way of example, the flat surface or concave surface extends in the axial direction from the intersection between the flat surface or concave surface and the floor surface to the second circumferential extension.

[0051] As mentioned above, the second circumferential extension is axially located at the axial distance from the floor surface. The axial distance is a quarter of the depth of the piston bowl. In other examples, the flat surface or concave surface may extend in the axial direction from the floor surface to a given intermediate axial distance being greater than the quarter of the depth of the piston bowl but less than the depth of the piston bowl. In other words, the flat surface or concave surface may extend in the axial direction from the floor surface towards toa distance in the axial direction between the quarter of the depth of the piston bowl but less than the depth of the piston bowl.

[0052] In some examples, including in at least one preferred example, optionally each one of the spaced-apart protrusions extends in the radial direction at least partly over the floor portion.

[0053] In some examples, including in at least one preferred example, optionally the first circumferential extension is a maximum circumferential extension of the flat surface or concave surface.

[0054] The first circumferential extension may generally be a maximum circumferential extension of the extension of the flat surface or concave surface, as measured along the circumferential direction. The first circumferential extension is thus a maximum circumferential extension of the flat surface or concave surface. Hence, the first circumferential extension may generally be referred to as the first maximum circumferential extension. One advantage with a protrusion having its maximum circumferential extension at the lowermost portion (near the floor surface of the piston bowl design) is that the tensile stress in the radial direction can be reduced compared to hitherto known designs of piston bowl protrusions. In other words, a wider circumferential extension of the flat surface or the concave surface at the intersection with the floor surface, may generally contribute to reducing the level of tensile stress in the radial direction.

[0055] Each one of the protrusions may extend a substantial part in the axial direction from the floor surface to the piston top end surface.

[0056] The flat surface or concave surface may generally extend in the circumferential direction between the opposite radially extending side sections.

[0057] According to a second aspect of the disclosure, there is provided an internal combustion engine, ICE, system comprising an internal combustion engine for combustion of fuel and having a combustion chamber at least partially delimited by a cylinder and a reciprocating piston according to the first aspect and / or any one of the examples of the first aspect. The reciprocating piston being moveable within the cylinder between a bottom dead center BDC and a top dead center TDC, wherein the piston top end being arranged to form part of the combustion chamber.

[0058] Whilst the present disclosure may be used in any type of ICE system that includes the proposed piston, the present disclosure is particularly useful for a diesel internalcombustion system. Hence, according to at least one embodiment, the ICE system is a diesel ICE system. However, the proposed piston may also be used in a hydrogen ICE system. Hence, according to at least one embodiment, the ICE system is a hydrogen ICE system.[591 According to a third aspect of the disclosure, there is provided a vehicle comprising a piston according to the first aspect and / or any one of the examples of the first aspect and / or an internal engine combustion system according to the second aspect and / or any one of the examples of the second aspect.[601 The disclosed aspects, examples (including any preferred examples), and / or accompanying claims may be suitably combined with each other as would be apparent to anyone of ordinary skill in the art. Additional features and advantages are disclosed in the following description, claims, and drawings, and in part will be readily apparent therefrom to those skilled in the art or recognized by practicing the disclosure as described herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Examples are described in more detail below with reference to the appended drawings.

[0062] Fig. 1 is an exemplary embodiment of the present disclosure, illustrating a side view of a vehicle, in the form of a truck, the vehicle comprising an internal combustion engine (ICE) system according to an example.

[0063] Fig. 2 is a side view of a cylinder and a reciprocating piston of an ICE system according to an example; and

[0064] Figs. 3 A to 3H conceptually illustrate a piston for the ICE system in Fig. 2, according to an example.DETAILED DESCRIPTION

[0065] The detailed description set forth below provides information and examples of the disclosed technology with sufficient detail to enable those skilled in the art to practice the disclosure.

[0066] For a piston internal combustion engine system including a piston with protrusions, there is a challenge to simultaneously achieve reductions in fuel consumption and emissions without sacrificing the durability of the piston. By way of example, some dimensions of theprotrusions are favorable for a decent combustion performance whilst other dimensions may directly have an impact on the durability of the piston.[671 That is, when using protrusions on a piston bowl for a piston intended for an internal combustion engine, ICE, system, such as a diesel ICE system, there is generally also an introduction of stress concentrations on or within the piston. In this context, it has been observed that the lower area of the protrusions, i.e. the area near the floor portion of the piston bowl, is one region among many regions where the impact on combustion performance is relatively low but the impact on the durability is relatively high.[681 The proposed piston thus aims at improving the protrusions of a piston bowl of a piston so as to provide a sufficiently reliable durability in terms of fatigue life, and without compromising any functions of the protrusions relating to combustion of the fuel within the combustion chamber of the cylinder.

[0069] Fig. 1 is an exemplary embodiment of the present disclosure, comprising a side view of a vehicle 1, in the form of a truck, according to an example.

[0070] Whilst the shown embodiment illustrates a truck, the disclosure may relate to any vehicle, such as a car, bus, industrial vehicle, boat, ship, etc., wherein motive power may be derived from an internal combustion engine.

[0071] The vehicle 1 comprises an internal combustion engine system 100. The internal combustion engine system may generally herein refer to the ICE system 10. The ICE, system 100 is arranged in the vehicle so as to provide power to the vehicle and driving the vehicle 1. The ICE system 100 in Fig. 1 also comprises an ICE 10. The ICE 10 is intended for combustion of diesel fuel. However, the ICE 10 may also in other examples be provided in the form of a hydrogen internal combustion engine, i.e. an ICE intended for combustion of hydrogen gaseous fuel. Hence, in one example, the ICE is operable on a hydrogen-based fuel, such as pure hydrogen gaseous fuel.

[0072] In particular, the ICE system 100 is a piston ICE system. The truck is here a vehicle 1 with a single propulsion system where traction power is provided by the ICE system 100. However, the truck may likewise be a hybrid electric vehicle. By way of example, such hybrid electric vehicle may comprise a supporting electric propulsion system having at least one high-voltage battery and at least one traction electric machine, and further the ICE system 100.[731 Moreover, the vehicle 1 may also comprise a controller 90, as depicted in Fig. 1. The controller is here part of a control system. The controller 90 is here an integral part of a main electronic control unit for controlling the vehicle and various parts of the vehicle. The controller 90 is arranged in communication with the components of the ICE system 100, in particular the ICE 10. The controller 90 may be part of the ECU of the vehicle 1. The controller 90 comprises a processing circuitry 91 configured to control the ICE system 100, as described herein.[741 By way of example, the controller 90 is configured to control a controllable fuel injector to inject at least one gaseous fuel jet towards a piston during a fuel injection period. The controller 90 may also be a separate part of the vehicle 1 and communicate with the main electronic control unit for controlling the vehicle 1 and various parts of the vehicle.[751 Turning now to Fig. 2, there is depicted one example embodiment of the ICE system 100 for incorporation in the vehicle 1 as described above in relation to Fig 1. In particular, Fig. 2 is a perspective cross-sectional view of parts of an ICE according to examples of the disclosure. As illustrated in Fig. 2, the ICE 10 comprises at least one cylinder 2. In addition, the ICE 10 has at least one combustion chamber 7 at least partially delimited by the cylinder 2. Moreover, the ICE 10 comprises a piston 3 as disclosed herein, e.g. in Figs. 2, 3 A to 3H.

[0076] The piston 3 is arranged and configured to reciprocate inside the cylinder 2. The piston 3 is arranged to reciprocate inside the cylinder 2 such that the ICE 10 is operated to combust fuel (e.g. diesel), whereby the motion of the piston 3 reciprocating in the cylinder 2 is transmitted to a rotational movement of a crankshaft 4, as shown in Fig. 2. The ICE system 100 thus comprises the crankshaft 4. The piston 3 is connected to the crank shaft 4 by a conventional connecting rod, as illustrated in Fig. 2.

[0077] It is to be noted that whilst Fig. 2 only depicts a single cylinder 2 having the combustion chamber 7 and the reciprocating piston 3 arranged therein, the ICE 10 generally comprises a plurality of cylinders 2 operated to combust fuel (e.g. diesel), whereby the motions of the pistons 3 reciprocating in the cylinders 2 are transmitted to a rotational movement of the crankshaft 4. The crankshaft 4 is further coupled to a transmission (not shown) for providing a torque to driving elements. In case of a heavy-duty vehicle, such as a truck, the driving elements are wheels; however, the ICE system 100 may also be used forother equipment such as construction equipment, marine applications, as power generators, etc.[781 The ICE 10 may advantageously be a four-stroke ICE, comprising a plurality of cylinders 2, each provided with a piston 3, wherein each piston 3 for instance may be connected to a common crankshaft 4. An ICE operable according to a conventional four stroke process performs an intake stroke, a compression stroke, a combustion stroke and an exhaust stroke.[791 Generally, each cylinder 2 is provided with a corresponding piston 3 connected to the crankshaft 4 of the ICE 10. As illustrated in Fig. 2, the piston 3 is arranged in the cylinder 2 for reciprocal movement along a center axis Ac. The piston 3 is mechanically connected to the crankshaft 4 of the ICE 10, so that the piston 3 is movable in the cylinder 2 between an upper dead center position and a lower dead center position. The piston 3 thus reciprocates in the cylinder 2 and is connected to the crankshaft 4 so that the piston 3 is set to reverse in the cylinder 2 at the upper and lower dead center positions. The upper dead center position is denoted as the top dead center, TDC, and the lower dead center position is denoted as the bottom dead center, BDC, as illustrated by the arrows in Fig. 2.

[0080] As also illustrated in e.g. Fig. 2, and further in the other Figures, such as Figs. 3 A to 3H, the piston 3 extends in an axial direction A and in a radial direction R. The piston 3 has a diameter that is less than an inner diameter of the cylinder CD, as shown in Fig. 2. Further, the piston 3 has a circumferential extension along a circumferential direction C. The piston 3 also has a longitudinal center axis Ac, which hereinafter is generally denoted as the axial center axis. The axial center axis Ac of the piston 3 is typically, although strictly not necessary, co-axially arranged with an axial center axis of a gas injector 13, as illustrated in Fig. 2. However, in some examples, the axial center axis of the fuel gas injector 13 may be slightly offset the axial center axis Ac of the piston 3.

[0081] As used herein, the terms “radial” or “radially” refer to the relative direction that is substantially perpendicular to an axial centerline of a particular component. Further, the terms “longitudinal”, “longitudinally”, “axially” or “axial” refer to the relative direction that is substantially parallel and / or coaxially aligned to an axial centerline of a particular component. Also, the terms “longitudinal”, “longitudinally”, “axially” or “axial” refer to a direction at least extending between axial ends of a particular component, typically along the arrangement or components thereof in the direction of the longest extension of thearrangement and / or components. The terms “vertical” and “vertically” generally correspond to the axial direction. The axial direction is generally the same direction as the piston moves within the cylinder. Further, the terms “circumference”, “circumferential”, or “circumferentially” refer to a circumference or a circumferential direction relative to an axis, typically a central axis extending in the direction of the longest extension of the device and / or component.[821 As used herein, the terms "upstream" and "downstream" refer to the relative direction with respect to fluid flow in a fluid pathway. For example, "upstream" refers to the direction from which the fluid flows, and "downstream" refers to the direction to which the fluid flows. Accordingly, in this context, the terms upstream and downstream are generally defined relative to the flow of fuel from a fuel tank to the combustion chamber 7 of the cylinder 2, as illustrated in Fig. 2.

[0083] Similarly, terms such as “upper”, “above” and “top” as well as “floor”, “lower”, “bottom”, “below” generally refer to the relative position of the part or component with respect to the axial direction A.

[0084] Each one of the cylinders 2 defines at least partly a combustion chamber 7. Each one of the cylinders 2 comprises a cavity 2a defining an inner volume. One end of the cylinder cavity is closed by a cylinder head 14. Further, each one of the cylinders 2 has an inner circumferential side wall 29. In a similar vein, the cylinder head 14 has an inner surface 21. These parts together with a combustion chamber facing portion of the piston 3 generally defines the combustion chamber 7. It should be noted that the cylinder head may be provided in several different shapes, and thus not necessarily in the form of a so called pent-roof type, as illustrated in Fig. 2. By way of example, the cylinder head 14 may have an essentially flat bottom inner surface 21. Other examples of cylinder heads are also possible. In addition, the inner wall of the cylinder may be provided by a so called a cylinder liner, as is commonly known in the art.

[0085] As illustrated in Fig. 2, and further in e.g. Figs. 3 A to 3H, the reciprocating piston 3 comprises a piston top end, which herein is denoted as an axial top end 16 of the piston 3. The piston axial top end 16 is here a so-called piston crown. The piston axial top end 16 comprises a piston bowl 6. The piston bowl 6 is thus arranged in an upper axial end portion of the piston 3, as illustrated in Fig. 2. The piston bowl 6 is arranged and intended to form part of the combustion chamber 7. As such, the piston bowl 6 is here the combustion chamberfacing portion of the piston 3. In Fig. 2, there is depicted one example of providing the piston 3 with a piston bowl 6 at its piston axial top end 16, wherein a piston bowl surface 6a of the piston bowl 6 is arranged to define the combustion chamber 7 with the cavity 2a of the cylinder 2. As such, as depicted in Fig. 2, the piston bowl surface 6a forms a combustion chamber 7 with the inner surface 21 of the cylinder head 14, and the circumferential side wall 29 of the cylinder 2.[861 Similar to the piston 3, the piston bowl 6 extends in the axial direction A, in the radial direction R, and having a circumferential extension in the circumferential direction C. In this example, the longitudinal center axis Ac, i.e. the axial center axis, of the piston 3 is coaxial with the axial center axis of the piston bowl 6, as illustrated in Fig. 2.[871 Each cylinder 2 may further comprise at its vertical top end at least one and typically a multiple number of inlet channels having at least one inlet valve 70 for controlling a flow of the inlet air to the combustion chamber 7, and at least one and typically a multiple number of exhaust channels having a least one exhaust valve 60 for controlling discharge of exhaust gases produced from the fuel combustion process taking place within the cylinder 2.

[0088] In particular, in the cylinder head 14, one or more induction ports with corresponding inlet valves 70 are arranged. Accordingly, as depicted in Fig. 2, the ICE system 100 further comprises an intake manifold 72 forming one or more intake guides arranged to guide air to the cylinders 2. In a similar vein, in the cylinder head 14, one or more exhaust ports with corresponding exhaust valves 74 are arranged. Accordingly, as depicted in Fig. 2, the ICE system 100 further comprises an exhaust guide 76 arranged to guide gases from the cylinders 2.

[0089] The cylinder configuration may be e.g. straight, V-shaped or any other suitable kind. The ICE system 100 may also include additional engine components and system components.

[0090] Moreover, in the cylinder head 14, there is disposed at least one fuel injector 13, through which fuel is injected into the cylinder 2 as a fuel spray 51. The fuel is here diesel fuel. In other examples, the fuel is hydrogen fuel. As such, the fuel injector 13 is arranged vertically into the center of the roof of the combustion chamber 7.

[0091] For diesel ICE systems, the fuel is preferably injected with a pressure in the range 600 to 3000 bar. Generally, for an engine system using EGR, about 1000 to 2500 bar may be preferred, without EGR about 800 to 1400 bar. For hydrogen ICE systems, the hydrogen gasfuel may be injected with a low injection pressure of between 15 to 60 bar into the combustion chamber 7 and towards the piston bowl 6. However, for other gaseous ICE systems, the controllable fuel injector may be controllable to inject gaseous fuel into the combustion chamber with an injection pressure of up to about 500 bar.[921 The ignited fuel spray may e.g. form a plume in the combustion chamber 7.[931 The fuel injector 13 may be any suitable type of injector capable of injecting fuel. In general, the fuel injector 13 is arranged in the cylinder 2 and axially above the piston 3. The fuel injector 13 is typically centrally disposed in the cylinder head 14 so that a geometrical center axis A of the fuel injector 13 coincides with a geometrical center axis of the cylinder 2, which is also an axis of reciprocation of the piston 3, and here indicated with reference numeral Ac. Thus, the geometrical center axis of the cylinder 2 and the center axis of the piston 3 may collectively be indicated by the reference Ac.

[0094] The fuel injector 13 is capable of directly injecting fuel into the combustion chamber 7 and towards the piston 3. The fuel injector 13 comprises at least one, preferably a plurality of injection orifices 46 for permitting the pressurized fuel to flow into the combustion chamber 7. The injected fuel will thereby provide kinetic energy into the combustion chamber 7, so as to induce thorough mixing of the fuel with the air contained therein.

[0095] The fuel injector 13 is configured to be controlled by the controller 90 (Fig. 1). Accordingly, the fuel injector is generally a controllable fuel injector 13. The controllable fuel injector 13 can be controllable by several different type of actuators, including, but not limited, to pneumatic actuation control, electronic actuation control, electro-mechanic actuation control, hydraulic actuation control, and a combination thereof.

[0096] The fuel injector 13 is connected and in fluid communication with a fuel tank (not illustrated). The number of fuel gas injectors 13 may be equal to the numbers of cylinders 2 of the ICE 10. The fuel gas injectors 13 are each arranged in fluid communication with the fuel tank.

[0097] For hydrogen ICE systems, the ICE 10 may also comprise an ignition source configured to ignite the injected fuel. The ignition source may be of a conventional type, such as a spark-plug (not illustrated).

[0098] In order to enhance the combustion of injected fuel and air in the combustion chamber 7, the piston 3 further comprises a piston bowl 6 according to any one of theexamples illustrated in the Figs. 3 A to 3H. The piston 3 and its piston bowl design will be described hereinafter in more detail.

[0099] In Figs. 3 A to 3H there is illustrated one example of a piston and piston crown intended for the ICE 10 and the ICE system 100, as described above in relation to Figs. 1 and 2. In particular, Fig. 3 A is a perspective top view of the piston axial top end 16 having a piston bowl 6 according to one example embodiment, Fig. 3B is top view of the piston axial top end in Fig. 3A, whilst Fig. 3C is a perspective cross-sectional view of the piston axial top end 16 in Fig. 3 A, according to one example. Fig. 3D is a cross-sectional view of the piston 3 and its axial top end 16 along the axial direction A and the radial direction R. Fig. 3E is a perspective axial cross-sectional view of the piston 3 along a given axial distance (height) of the piston bowl 6, and along the radial direction R and the circumferential direction C. Fig. 3F is an axial cross-sectional view of the piston 3 along a given axial distance (height) of the piston bowl 6, and along the radial direction R and the circumferential direction C. Fig. 3G is another cross-sectional view of the piston 3 and its axial top end 16 along the axial direction A and the radial direction R. Fig. 3H is another cross-sectional view of the piston 3 and its axial top end 16 along the axial direction A and the radial direction R.

[0100] In the illustrated examples, the piston axial top end 16 forms an integral portion of the piston 3. However, it is also conceivable to provide the piston axial top end 16 as a separate unit, to be attached to one or more piston base portions, so as to form a complete piston 3. The piston axial top end 16 generally amounts to the so-called piston crown. The piston axial top end 16 generally has an axial top end surface 5, i.e. an upper surface, facing the combustion chamber 7 of the cylinder 2 when the piston 3 is arranged in the cylinder 2. The axial top end surface 5 is here the uppermost surface part of the piston 3. For ease of reference, the axial top end surface may simply be denoted as the top end surface 5.

[0101] Figs. 3A to 3E illustrate the piston axial top end 16 in more detail. As shown in e.g. Fig. 3C, the piston bowl surface 6a faces the combustion chamber 7 when arranged in the ICE 10 as the one exemplified in Fig. 2. The piston bowl surface 6a comprises a circumferential rim portion 20 and a floor portion 11 connected to and surrounded by the circumferential rim portion 20. In other words, the piston bowl 6 comprises the circumferential rim portion 20 and the axial floor portion 11, which is connected to and surrounded by the circumferential rim portion 20. The axial floor portion 11 comprises a floor surface I la, as depicted in e.g. 3C.

[0102] The piston bowl 6 can be provided in several different manners. As illustrated in Figs. 3 A to 3E the floor portion 11 is at least partly defined by the piston bowl surface 6a. The floor portion 11 generally has the floor surface 1 la being part of the piston bowl surface 6a. As illustrated in Fig. 2, in conjunction with Figs. 3 A to 3E, the piston bowl 6 is here defined by the circumferential rim portion 20, a central apex 18 and an intermediate section 19. Thus, as may be gleaned from Figs. 3 A to 3E, the floor portion 11 may be generally dome-shaped with the central apex 18 coinciding with the center axis Ac of the piston 3. The floor portion 11 may form dome side surfaces, forming parts of the intermediate section 19, and extending circumferentially from the dome-shape, and forming a dome angle between them. As such, the floor portion 11 may generally have a dome-shaped geometry, at least partly defined by the central apex 18. The floor portion 11 here extends from the circumferential rim portion 20 to the center axis Ac in the center at the central apex 18. The floor portion 11 may align with the circumferential rim portion 20, as illustrated in e.g. Fig.3 A and Fig 3E. This alignment may generally also be defined by a so-called side angle, as further described herein.

[0103] Generally, although strictly not required, the intermediate section 19 extends between the circumferential rim portion 20 and the central apex 18, thereby together forming the piston bowl surface 6a. By way of example, at least the intermediate section 19 and the central apex 18 here together define the floor surface 1 la. In other examples, parts of the rim portion 20, the intermediate section 19 and the central apex 18 together define the floor surface I la, and thus together define the piston bowl surface 6a.

[0104] The circumferential rim portion 20 here also extends in the axial direction A. The circumferential rim portion 20 extends in the axial direction A between the floor surface I la and the top end surface 5 of the axial top end 16.

[0105] The circumferential rim portion 20 is here the radially outermost part of the piston bowl 6, whilst the central apex 18 is the radially innermost part of the piston bowl 6.

[0106] The circumferential rim portion 20, the intermediate section 19 and the central apex 18 collectively form the outwardly opening cavity, as illustrated in e.g. Fig. 3 A. In other piston bowl designs where the top end surface may be an integral part of the piston bowl, the top end surface 5 may be the radially outermost part of the piston bowl 6.

[0107] As depicted in e.g. Fig. 3D, the circumferential rim portion 20 defines at least one fuel impingement portion 60. Generally, the circumferential rim portion 20 comprises anumber of fuel impingement portions 60. The fuel impingement portion 60 will be further described herein.

[0108] The piston bowl 6 has an axial depth H, as depicted in e.g. Figs. 3C, 3D and 3E. The axial depth H of the piston bowl 6 is defined by an axial distance between the floor surface I la and the top end surface 5, as illustrated in Fig. 3D, and also indicated in e.g. Figs. 3C and 3E. Generally, the axial depth H defines the maximum axial distance between the floor surface I la and the top end surface 5. The axial depth H is thus defined as the distance between the lowermost surface part of the floor portion 11 of the piston bowl 6 and the top end surface 5, as illustrated in Fig. 3D.

[0109] In addition, the piston bowl 6 comprises a plurality of spaced-apart protrusions 40, 50, as illustrated in figs. 3 A to 3E. The plurality of spaced-apart protrusions 40, 50 are here disposed on the circumferential rim portion 20. The space-apart protrusions 40 are circumferentially distributed around the center axis Ac. In particular, the plurality of spaced- apart protrusions 40, 50 are circumferentially distributed spaced-apart from each other in the circumferential direction C around the circumferential rim portion 20. Thus, the plurality of spaced-apart protrusions 40, 50 are circumferentially distributed around the circumferential rim portion 20.[HO] In Figs 3 A to 3E, the circumferential rim portion 20 comprises the plurality of spaced-apart protrusions 40, 50. The spaced-apart protrusions 40, 50 are circumferentially distributed around the circumferential rim portion 20 and about the center axis Ac. This way, the plurality of spaced-apart protrusions 40, 50 are circumferentially distributed around the circumferential rim portion 20.[Hl] It follows from the term "protrusion” that the protrusion section must have a certain axial extension in the axial direction A, a certain radial extension in the radial direction R and a certain circumferential extension along the circumferential direction C.

[0112] As such, each one of the spaced-apart protrusions 40, 50 extends a substantial part in the axial direction A from the floor surface I la towards the top end surface 5. In Figs. 3 A to 3E, each one of the spaced-apart protrusions 40, 50 extends in the axial direction A from the floor surface 1 la to the top end surface 5 of the piston top end 16. As such, each one of the spaced-apart protrusions 40, 50 extends in the axial direction A in a continuous manner from the floor surface 1 la to the piston top end surface 15. Other extensions may also be conceivable, as further described below.

[0113] Moreover, as illustrated in e.g. Fig. 3 A, each one of the spaced-apart protrusions 40, 50 extends a substantial part in the radial direction R towards the center axis AC.

[0114] Each protrusion 40, 50 extends from adjacent sides of the circumferential rim portion 20 and towards the center axis Ac of the piston 3, forming an apex towards the center axis Ac. Each one of the protrusion 40, 50 thus faces towards the center axis Ac of the piston 3. The protrusions 40, 50 are disposed on the circumferential rim portion 20.

[0115] As depicted in Figs. 3 A and 3B, the plurality of spaced-apart protrusions comprises a set of a first type of protrusions 40 and a set of a second type of protrusions 50.

[0116] The first type of protrusions 40 is different to the second type of protrusions 50. As illustrated in Figs. 3 A, 3B, 3F and 3G, the first type of protrusions 40 is different to the second type of protrusions 50 by a difference in geometry.

[0117] The set of the first type of protrusions 40 and the set of the second type of protrusions 50 are arranged in an alternate manner along the circumferential rim portion 20, as illustrated in e.g. Figs. 3 A to 3B and Fig. 3F.

[0118] Each protrusion 40 of the first type of protrusions comprises opposite radial side sections 41, 42, as illustrated in e.g. Fig. 3 A. Each one of the radial side sections 41, 42 extends in the radial direction R and from the circumferential rim portion 20. One of the radial side section is a first radial side section 41, whilst the other one of the radial side sections is a second radial side section 42. Each one of the first radial side section 41 and the second radial side section 42 extends in the radial direction R. Hence, the radial side sections may herein also be denoted as radially extending side sections or radially extending radial side sections. The first radial side section 41 and the second radial side section 42 are arranged opposite each other in the circumferential direction C, as depicted in e.g. Fig. 3 A and Fig. 3C.

[0119] As illustrated in Figs. 3 A to 3F, the radially extending side sections 41, 42 are curved convex side sections. In other examples the radially extending side sections 41, 42 may be curved concave side sections. In yet other examples the radially extending side sections 41, 42 may be flat side sections.

[0120] Moreover, in Figs. 3 A to 3F, each one of the opposite radial side sections 41, 42 comprises multiple regions of different convex curved profiles. In Fig. 3C, there is illustrated one example of a protrusion 40 of the first type of protrusions with a first radially extending side section 41 having first and second convex curved profiles 41a, 41b of different curved1 convex profiles and a second radially extending side section 42 having first and second convex curved profiles 42a, 42b of different curved convex profiles. In other examples, the first radially extending side section 41 has a uniform curved convex profile, whilst the second radially extending side section 42 has a uniform curved convex profile.

[0121] Each protrusion 40 of the first type of protrusions here extends in the radial direction R at least partly over the floor portion 11. Further, each one of the spaced-apart protrusions 40 extends in the radial direction R to align with the floor surface 1 la of the floor portion 11. Uli In the illustrated embodiment in Figs. 3 A to 3F, the piston bowl 6 comprises a total of six protrusions 40, equally distributed around the circumference of the piston bowl 6. However, other numbers of protrusions 40 are conceivable, such as four, five and even more protrusions than six protrusions, such as seven, eight and more.

[0123] The first type of protrusions 40 may be distributed around the central axis AC with 45 degrees intervals. Other intervals are also conceivable.

[0124] In Fig. 3 A, the first type of protrusions 40 are uniformly circumferentially distributed around the circumferential rib portion 20. In other design variants, although not shown, the first type of protrusions 40 may be non-uniformly circumferentially distributed on the circumferential rib portion 20.

[0125] As illustrated in Figs. 3 A to 3F, each protrusion of the first type of protrusions 40 further comprises a surface 43 extending between the opposite radially extending side sections 41, 42. In Figs. 3 A to 3F, the surface 43 extends in the circumferential direction C between the opposite radially extending side sections 41b, 42b. Moreover, in Figs. 3A to 3F, the surface 43 is a concave surface 43b. Fig. 3E is a cross sectional view of the concave surface 43b, illustrating the concave profile of the concave surface 43b in greater detail. The radius of the concave profile of the concave surface 43b is selected in view of the intended use of the piston 3. By way of example, the radius of the concave profile of the concave surface 43b follows the radius of the curvature of the circumferential rim portion 20. That is, the radius of the concave curvature of the concave surface 43b corresponds to the radius of the concave curvature of the circumferential rim portion 20. In such examples, a radius of curvature of the concave surface is essentially perpendicular to the axial center of the piston bowl 6. It should, however, be readily appreciated that the radius of the concave profile of the concave surface 43b may have a different concave curvature than the concave curvature ofthe circumferential rim portion 20. By way of example, Fig. 3C illustrates a design where a radius of the concave curvature of the concave surface 43b is different to the radius of the concave curvature of the circumferential rim portion 20. When defining and designing the concavity of the concave surface 43b, the concavity of the concave surface is generally determined in relation to a Cartesian coordinate system (rather than the cylindrical coordinate system), as is also commonly known in the art. In other words, for the concave surface 43b, the radius of curvature is the radius of a circle that best fits a normal section or combinations thereof. The radius of curvature of the concave surface 43b may either be constant in size along the circumferential direction C or slightly change in size along the circumferential direction C.

[0126] In other examples, although not illustrated, the surface 43 may be a flat surface 43a.

[0127] For ease of reference, the following description of the surface 43 will be provided with reference to the concave surface 43b, as illustrated in e.g. Figs. 3 A to 3F. However, the description will likewise be applicable to a surface in the form of the flat surface 43a.

[0128] The concave surface 43b extends a substantial part in the circumferential direction C. As mentioned above, the concave surface 43b here extends between the opposite radially extending radial side sections 41, 42. More specifically, the concave surface 43b extends in the circumferential direction C between the opposite radially extending radial side sections 41, 42. In Figs. 3 A to 3E, the first radial side section 41 of the opposite radial side sections intersects with the concave surface 43b along an intersection edge 45. Analogously, the second radial side section 42 of the opposite radial side sections intersects with the concave surface 43b along another opposite intersection edge 46.

[0129] The concave surface 43b is thus arranged to form a bridging surface between the opposite radial side sections 41, 42.

[0130] The concave surface 43b is also arranged to face towards the center axis Ac of the piston 3.

[0131] In other words, by providing a flat surface 43a or a concave surface 43b between the opposite radial side sections 41, 42, the surface 43, 43a, 43b between the opposite radial side sections is a non-convex surface. The term "non-convex", as used herein means that the surface 43 does not protrude towards the center axis Ac of the piston 3. Rather, the surface43, 43a, 43b is straight or recesses towards a radially outer circumferential surface of the piston 3, as may be gleaned from e.g. Fig. 3E.

[0132] In some examples, as may be gleaned from Fig. 3E, a radial cross-sectional profile through the protrusion 40 resembles a truncated triangle or the like, where the truncated side forms the flat surface 43a or the concave surface 43b.

[0133] The piston bowl 6 is generally obtained by forging. By way of example, the surface 43, 43a, 43b of the piston bowl 6 is forged. The other surfaces of the piston bowl may also be forged.

[0134] Also, the concave surface 43b extends a substantial part in the axial direction A. As illustrated in e.g. Fig. 3 A, and also in Fig. 3E, the concave surface 43b essentially extends in the axial direction A from an intersection 44 between the concave surface 43b and the floor surface 1 la to the top end surface 5 of the piston top end 16. The intersection 44 defines the distinction between the concave surface 43b and the floor surface 1 la. As such, the intersection 44 also defines the distinction between the protrusion 40 and the floor surface I la. The intersection 44 extends in the circumferential direction C. Also, the intersection 44 may generally be an imaginary line illustrating the circumferential extension of the concave surface 43b at its maximum circumferential extension, which in Fig. 3C is illustrated by the reference numeral a.

[0135] As depicted in e.g. Figs. 3 A to 3E, the concave surface 43b has at least an extension between a first circumferential extension, a, at the intersection 44 and a second circumferential extension, b, at an axial distance h from the intersection 44. In this example, the first circumferential extension, a, is larger than the second circumferential extension, b. The first circumferential extension a is larger in the circumferential direction C than the second circumferential extension b.

[0136] Generally, the first circumferential extension, a, is the maximum circumferential extension of the concave surface 43b in the circumferential direction C. That is, the first circumferential extension, a, defines the maximum circumferential extension of the concave surface 43b in the circumferential direction C. In the following description, the first circumferential extension thus generally refers to the first maximum circumferential extension, a.

[0137] In particular, as illustrated in e.g. Figs. 3 A to 3E, the concave surface 43b has the first maximum circumferential extension, a, at the intersection 44 between the concavesurface 43b and the floor surface 11. In addition, as illustrated in Figs. 3 A to 3E, the concave surface 43b has the second circumferential extension b at the axial distance h from the floor surface I la. The axial distance h is a quarter of the piston bowl depth H. The axial distance h and the depth H refer to distances in the axial direction A. In addition, the axial distance h and the depth H refer to distances in the axial direction A as measured in a direction from the floor surface 1 la towards the top end surface 5.

[0138] As illustrated in e.g. Fig. 3 A in conjunction with Fig. 3E, the intersection edges 45, 46 in combination with the first maximum circumferential extension, a, and the second circumferential extension, b, define the extension of the concave surface 43b.

[0139] Further, the second circumferential extension b is less than the first circumferential extension a. Hereby, the piston may better withstand critical fatigue conditions that occur during ordinary use of the piston in heavy-duty vehicles.

[0140] In some examples, a ratio between the second circumferential extension, b, and the first maximum circumferential extension, a, is 0.4 or less. Hereby, each protrusion of the first type of protrusions is designed so as to improve the durability and the fatigue properties of the protrusion during ordinary operation of the piston 3. The first type of protrusions 40 has an improved design withstanding higher fatigue levels in comparison with other designs of piston bowl protrusions. The ratio between the second circumferential extension, b, and the first maximum circumferential extension is herein also denoted as the relative circumferential width ratio.

[0141] In one example, the ratio between the second circumferential extension, b, and the first maximum circumferential extension, a, is 0.4.

[0142] In one example, the ratio between the second circumferential extension, b, and the first maximum circumferential extension, a, is 0.

[0143] In one example, the ratio between the second circumferential extension, b, and the first maximum circumferential extension, a, is 0.26. By way of example, the second circumferential extension, b, is 2,4 mm and the first maximum circumferential extension, a, is 9,3 mm. In this example, the depth H is 18,6 mm.

[0144] In one example, the ratio between the second circumferential extension, b, and the first maximum circumferential extension, a, is 0.25. By way of example, the second circumferential extension, b, is 4,2 mm and the first maximum circumferential extension, a, is 16,8 mm. In this example, the depth H is 19,4 mm.

[0145] In one example, the ratio between the second circumferential extension, b, and the first maximum circumferential extension, a, is 0.17. By way of example, the second circumferential extension, b, is 2,9 mm and the first maximum circumferential extension, a, is 17,5 mm. In this example, the depth H is 18,5 mm.

[0146] In one example, the ratio between the second circumferential extension, b, and the first maximum circumferential extension, a, is between 0.4 and 0. In one example, the ratio between the second circumferential extension, b, and the first maximum circumferential extension, a, is 0.4 or less, but greater than 0. Hence, in one example, the ratio between the second circumferential extension, b, and the first maximum circumferential extension, a, is between 0.4 and 0.05. In one example, the ratio between the second circumferential extension, b, and the first maximum circumferential extension, a, is between 0.4 and 0.1. In one example, the ratio between the second circumferential extension, b, and the first maximum circumferential extension, a, is between 0.3 and 0.15. In one example, the ratio between the second circumferential extension, b, and the first maximum circumferential extension, a, is between 0.26 and 0.17. In one example, the ratio between the second circumferential extension, b, and the first maximum circumferential extension, a, is between 0.25 and 0.17.

[0147] The above relative circumferential width ratio in combination with the configuration of the surface 43 in the form of the flat surface 43 a or concave surface 43b provides an improved design of the protrusions 40 at the lower area of the protrusion, and thus at the lower part of the piston bowl 6. More specifically, by having protrusions 40 comprising the flat surface 43a or concave surface 43b extending between opposite radial side sections 41, 42 in combination with the provision that the ratio between the second circumferential extension, b, and the first circumferential extension, a, is 0.4, or less, the piston 3 has a less sensitive design in terms of required durability. Such design can also better withstand critical fatigue conditions that occur during ordinary use of the piston 3 in heavy- duty vehicles.

[0148] The above configuration of the protrusions is partly based on the observation that a piston operating in a “hot state”, i.e. the piston 3 is exposed to a high temperature load, there is generated high compression stress at the protrusions. When the magnitude of the compression stress exceeds a critical level, at a certain temperature, the material in the area of the protrusion may be subject to stress relaxation. Stress relaxation may e.g. occur as a resultof long-term exposure to high levels of stress that are still below the yield strength of the material. Then, when the vehicle is parked with the ICE turned off, i.e. the ICE is not operating, or at an idling state of the ICE, the piston 3 may cool to a “cold state”, which results in a transformation of the stress from compression stress to tensile stress. When the piston 3 is subsequently exposed to a cylinder pressure load, a fatigue crack may initiate and propagate at a more conventional protrusion due to a cycle of maximum tensile stress from cylinder pressure and maximum tensile stress from stress relaxation.

[0149] The above configuration of the flat surface and the concave surface allows for avoiding, or at least reducing, that critical material regions of the protrusions being exposed to high tensile stress.

[0150] In addition, the relative circumferential width ratio in combination with the configuration of the surface 43 in the form of the flat surface 43 a or concave surface 43b ensure that the part of the protrusion 40 where there is a low impact on combustion performance is designed so as to minimize the compressive stress at the protrusions in the axial lower region for the temperature load occurring during combustion. In addition, the flat surface 43a or concave surface 43b arranged between the radial side sections 41, 42 contributes to separating the location of the maximum compressive stress due to temperature load from the maximum tensile stress location due to the pressure load. A piston bowl 6 with protrusions 40 where maximum stress regions are separated from each other contributes to increasing the durability and fatigue life of the protrusions 40, and thus also the durability of the piston 3.

[0151] As illustrated in Fig. 3E, the convex surface 43b itself provides for a bowl-shaped design of a lower part of the protrusion 40.

[0152] It should be noted that the concave surface 43b may extend further in the axial direction A than to the second circumferential extension b. As illustrated in Figs. 3 A to 3E, the concave surface 43b extends in the axial direction A from the floor surface I la and generally the entire way to the top end surface 5. By way of example, the concave surface 43b extends in the axial direction A from the floor surface I la completely to the top end surface 5. However, in other examples, the concave surface 43b extends in the axial direction A from the floor surface 1 la to a given intermediate axial distance between the quarter of the depth of the piston bowl 6 and the depth H of the piston bowl 6. Accordingly, the concave surface 43b generally extends in the axial direction A from the floor surface I la and towardsthe top end surface 5. By way of example, the concave surface 43b generally extends in the axial direction A from the floor surface I la and towards the top end surface 5, and having an extension in the axial direction A which is greater than the quarter of the depth of the piston bowl 6 but less than the depth H of the piston bowl 6.[1531 Accordingly, as illustrated in e.g. Fig. 3D, an extension of the concave surface 43b from the first circumferential extension, a, to the second circumferential extension, b, further comprises a concave axially extending region. The concave axially extending region here also extends from the floor surface I la and towards the top end surface 5. The protrusion 40 here also comprise an additional upper convex axially extending surface, as illustrated in fig. 3D. The lower concave axially extending region and the upper convex axially extending surface form the shape of an “S”, as depicted in Fig. 3D.[1541 In other examples, the concave surface 43b merely extends in the axial direction A from the floor surface 1 la to the second circumferential extension b. As mentioned above, the second circumferential extension b is axially located at the axial distance h from the floor surface I la. The axial distance h is a quarter of the depth H of the piston bowl 6.

[0155] In an example, as also mentioned above, although not illustrated, where the ratio between the second circumferential extension, b, and the first maximum circumferential extension, a, is zero (0), the concave surface 43b merely extends in the axial direction A from the floor surface I la to the second circumferential extension b. In this way, there is provided a concave surface 43b resembling a triangle, extending in the axial direction A and in the circumferential direction C.

[0156] Hence, the extension of the concave surface 43b is defined by the axially inclined intersection edge 45 and the intersection edge 46 together with the first circumferential extension, a, at the intersection 44 and the second circumferential extension, b, at the axial distance h from the intersection 44. Such extension of the concave surface 43b resembles a trapezoid, i.e. a triangular base shape with a maximum circumferential width at the intersection 44 and a minimum width at the other axial side, i.e. at the second circumferential extension, b. In e.g. Fig. 3C, the concave surface 43b forming a trapezoid surface in the axial direction A and in the circumferential direction C may essentially be designed as a duck-foot. It is to be understood that the term "triangular base shape" also encompasses triangles having rounded comers and even triangles the apex of which is cut, forming an equal-sided trapezoid. Also triangles with non-linear circumferential edges are conceivable.

[0157] As illustrated in Figs. 3 A to 3E, the intersection edges 45, 46 inclines from the first maximum circumferential extension, a, to the second circumferential extension b in a nonlinear manner (curved manner). However, the intersection edges 45, 46 may likewise incline from the first maximum circumferential extension, a, to the second circumferential extension b in a linear manner. The intersection edges 45, 46 inclines towards a center region (in the circumferential direction) located on the second circumferential extension b, as illustrated in Figs. 3 A to 3E. The intersection edges 45, 46 in combination with the first circumferential extension, a, and the second circumferential extension, b, define the overall extension of the concave surface 43, 43a, 43b.

[0158] In a similar vein as the concave surface 43b, the protrusions 40 may extend in the axial direction A in several different manners. As mentioned above, and as illustrated in Figs. 3 A to 3E, each one of the first type of protrusions 40 extends in the axial direction A between the floor surface 1 la of the floor portion 11 and towards the top end surface 5 of the piston top end 16. In particular, each one of the first type of protrusions 40 extends in the axial direction A between the floor surface 1 la of the floor portion 11 and to the top end surface 5 of the piston top end 16. It is to be noted that the intersection edges 45, 46 in Figs. 3 A to 3B may generally extend in the axial direction A between the floor surface 1 la of the floor portion 11 and towards the top end surface 5.

[0159] In another example, each one of the first type of protrusions 40 may merely extend in the axial direction A from the floor surface 1 la to the second circumferential extension, b. As mentioned above, the second circumferential extension, b, is axially located at the axial distance h from the floor surface I la. The axial distance h is a quarter of the depth H of the piston bowl 6. In other examples, each one of the first type of protrusions 40 may extend in the axial direction A from the floor surface 1 la to a given intermediate axial distance, which is greater than the quarter of the depth of the piston bowl 6 but less than the depth of the piston bowl 6. In other words, each one of the protrusions 40 may extend in the axial direction A from the floor surface 1 la towards the top end surface 5 to a distance in the axial direction A between the quarter of the depth of the piston bowl 6 but less than the depth H of the piston bowl 6. In this example, the concave surface 43b generally extends in a similar vein, i.e. from the floor surface I la and towards the top end surface 5 in the axial direction A between the quarter of the depth of the piston bowl 6 but less than the depth of the piston bowl H.[1601 By way of example, the first maximum circumferential extension, a, is 16,8 mm and the circumferential extension E is 26,0 mm. In this example, the second circumferential extension, b, may e.g. be 4,2 mm.[1611 By way of example, the first maximum circumferential extension, a, is 17,5 mm and the circumferential extension E is 27,4 mm. In this example, the second circumferential extension, b, may e.g. be 2,9 mm.[1621 In some examples, each one of the first type of protrusions 40 extends in the radial direction R from the circumferential rim portion 20 to at least the intermediate section 19. In addition, the circumferential rim portion 20 extends in the axial direction A between the floor portion 11 and the piston top end 16, typically between the floor surface 1 la of the floor portion 11 and the top end surface 5 of the piston top end 16.[1631 Hence, as is readily appreciated from the above, the concave surface 43b at least extends in the axial direction A from the first maximum circumferential extension, a, to the axial distance h (H / 4), corresponding to the axial location of the second circumferential extension, b. Depending on the design of the protrusion 40, the concave surface 43b then either terminates at the axial distance h (H / 4), i.e. at the second circumferential extension, b, or extends to a given intermediate axial distance between the quarter of the depth H of the piston bowl 6 and the depth H of the piston bowl 6.

[0164] If the concave surface 43b terminates at the axial distance h (H / 4), i.e. at the second circumferential extension, b, the remaining parts of the protrusion 40 axially above the concave surface 43b are generally formed by an additional surface region together with the radial side sections 41, 42. Analogously, if the concave surface 43b terminates at a given intermediate axial distance between the quarter of the depth H of the piston bowl 6 and the depth H of the piston bowl 6, the remaining parts of the protrusion 40 axially above the concave surface 43b are generally formed by an additional surface region together with the radial side sections 41, 42.

[0165] However, in other examples, as illustrated in Figs. 3 A to 3H, there is no additional surface region. That is, the surface 43 in the form of the concave surface 43b essentially extends to the top end surface 5. Due to the overall design of the protrusion 40, there may generally be a smooth curvilinear transition surface between the concave surface 43b and the top end surface 5, as may be gleaned from e.g. Fig. 3C. Accordingly, the concave surface 43b mates with the top end surface 5 by a smooth curvilinear transition surface between theconcave surface 43b and the top end surface 5, as illustrated in e.g Figs. 3 A to 3D. The additional surface region, i.e. the curvilinear transition surface, here mates with the top end surface 5 in a convex curved manner, as seen in the radial direction R.[1661 Turning now again to the second type of protrusions 50, as illustrated in Figs. 3A and 3B in conjunction with Figs. 3F and 3G. As e.g. depicted in Fig. 3A in conjunction with Figs. 3F and 3G, at least one protrusion of the second type of protrusions 50 is arranged at the at least one fuel impingement portion 60. As such, the at least one protrusion of the second type of protrusions 50 comprises at least one fuel impingement portion 60. As mentioned herein, the fuel impingement portion refers to any one of a spray -fuel impingement portion and a flame-fuel impingement portion. This depends on whether the fuel is in a spray state or in a flame state. A combination of spray and flame state may also be possible for some ICE systems.

[0167] By arranging the protrusion 50 at the fuel impingement area of the piston bowl, the second type of protrusion 50 is arranged to redirect a receiving flame 51, or spray, to opposite tangential directions XR and XL of the circumferential rim portion 20. In this context, the tangential directions XR and XL refer to directions in the circumferential direction C, as also illustrated in Fig. 3F.

[0168] In general, a number of the protrusions of the second type of protrusions 50 is arranged at corresponding fuel impingement portions 60. In the example of Figs. 3 A to 3H, all protrusions of the second type of protrusions 50 are arranged at corresponding fuel impingement portions 60. As such, each one of protrusions of the second type of protrusions 50 comprises a corresponding fuel impingement portion 60.

[0169] Moreover, as depicted in Figs. 3 A to 3B in conjunction with Fig. 3F, adjacent protrusions of the first type of protrusion 40 are arranged in-between the at least one fuel impingement portion 60. By this arrangement, the adjacent protrusions of the first type of protrusions 40 are arranged to redirect a circumferential flame progress mainly towards the center axis Ac of the piston 3.

[0170] As illustrated in Fig. 3F, and as further described herein, each protrusion of the first type of protrusions 40 is arranged and configured to guide another receiving flame 54 towards the center axis Ac. The first type of protrusions 40 thus contributes to guide the another receiving flame 54 in the axial direction A. The first type of protrusions may also refer to collision protrusions.

[0171] Moreover, each protrusion of the second type of protrusions 50 is arranged and configured to redirect a receiving flame 51 to opposite tangential directions XL, XR of the circumferential rim portion 20. The second type of protrusions 50 thus may also refer to dividing protrusions. Hereby, the second type of protrusions (dividing protrusions) contributes to improve the flame-wall flow within the combustion chamber by dividing the flame in a smoother manner in comparison to a similar piston without any dividing protrusions.[1721 Turning now to Fig. 3F, there is illustrated additional details of the design of the first and second types of protrusions 40 and 50.[1731 In Fig. 3F, there is indicated a fuel spray axis 52. The fuel spray axis 52 indicates the direction of fuel 51 from the injector 13 towards the protrusion 50 (second type of protrusion). The fuel 51 hits the protrusion 50 at the fuel impingement portion 60.

[0174] More specifically, the piston bowl 6 is arranged in relation to the injector 13 such that the injector 13 is capable of injecting fuel 51 along the fuel spray axis 51 towards the fuel impingement portion 60 of the protrusion 50. The injector 13 comprises at least one orifice arranged to inject fuel 51 along the fuel spray axis 52 towards the fuel impingement portion 60. The arrangement of the injector 13 in the cylinder and the configuration of injecting fuel towards the fuel impingement portion 60 can be provided in several different ways, as is commonly known in the art, and thus not further described herein.

[0175] Generally, the fuel impingement portion 60 is a surface of the protrusion 50. The fuel impingement portion 60 is at least party defined by an area extending in the axial direction A and in the circumferential direction C.

[0176] In addition, Fig. 3F illustrates a symmetric axis 53, illustrating a radial extension between the protrusion 40 and the axial center axis Ac. For ease of refence, the first fuel spray axis 52 and the symmetric axis 53 extends at least essentially in the radial direction R, and at least between the axial center Ac and the respective protrusions 40, 50.

[0177] In this example, the protrusion 40 of the first type of protrusions 40 comprises a tip portion 80 facing the center axis Ac. In this example, the tip portion 80 is defined at least partly by the radial side sections 41, 42 in combination with the surface 43, e.g. the flat surface 43a or concave surface 43b extending between the opposite radial side sections.

[0178] As illustrated in Fig. 3F, the tip portion 80 is here further defined by an angle CA of about 40 to 140 degrees. Still preferably, the tip portion 80 may be defined by an angle CAof about 40 to 120 degrees. Still preferably, the tip portion 80 may be defined by an angle CA of about 90 to 110 degrees. It has been observed that this type of tip portion contributes to further improve control of the so-called flame-flame event.

[0179] The angle CA is here defined as the angle between the radial side sections 1, 42, as illustrated in Fig. 3F.

[0180] In some examples, each protrusion 40 of the first type of protrusions 40 may comprise a tip portion 80 facing the center axis Ac, wherein the tip portion 80 is defined by an angle CA of about 40 to 100 degrees. A technical advantage may be an improved control of the so-called flame-flame event in an ICE system operable on a hydrogen-based fuel, such as a pure hydrogen fuel ICE system.

[0181] In some examples, as illustrated in Fig. 3D, each one of protrusions 40 of the first type of protrusions 40 in relation to the axial direction A is further defined by a second angle FA.

[0182] In some examples, the second angle FA is a steep angle or a shallow angle. As illustrated in Fig. 3D, the second angle FA is defined in relation to a parallel axis API to the center axis Ac and is a measure of the angle between the floor portion I la and the protrusion 40, more specifically as the angle between the floor portion I la and the surface 43.

[0183] In some examples, the second angle FA is about 10 to 40 degrees. Still preferably, the second angle FA is about 15 to 30 degrees. Still preferably, the second angle is about 20 to 25 degrees.

[0184] The second type of protrusions 50 can be designed in a similar vein, as illustrated in Fig. 3F and 3G.

[0185] Hence, the protrusion 50 of the second type of protrusions 50 here comprises a corresponding tip portion 85 facing the center axis Ac, as illustrated in Fig. 3G. In this example, the corresponding tip portion 85 is defined at least partly by corresponding radial side sections 86, 87 in combination with the surface 88, which is generally a concave surface extending between the opposite radial side sections 86, 87.

[0186] As illustrated in Fig. 3G, the corresponding tip portion 85 comprises the fuel impingement portion 60. Hence, the fuel impingement portion 60 is here defined at least partly by the extension and curvature of the corresponding tip portion 85. By way of example, the fuel impingement portion 60 is defined at least partly by the corresponding radial side sections 86, 87 in combination with the surface 88. In this manner, the concavityprovided by the surface 88 or provided by the radial side sections 86, 87 in combination with the surface 88 provides for redirecting the receiving flame to opposite tangential directions XR and XL.

[0187] The fuel impingement portion 60 may thus be considered to comprise a reflection surface configured to redirect the receiving flame to opposite tangential directions XR and XL. The fuel impingement portion 60 has an extension in the axial direction and an extension in the circumferential direction C. The fuel impingement portion 60 substantially has the shape of a portion of an envelope surface of the protrusion 60. It is implied in the term "surface" that the surface should have at least some extension along the central axis and circumferentially about the central axis. Moreover, the surface in the fuel impingement portion is the surface onto which a spray or flame originating from the orifice in the injector is intended to impinge, causing the spray or flame to be redirected as described above. By affecting the way in which the spray or flame is redirected, the shape of the protrusion 50 comprising the fuel impingement portion 60 will impact the distribution of the kinetic energy inside the combustion chamber.

[0188] It should also be noted that the spray axis 52 will generally form an angle with the central axis Ac. The fuel impingement portion 60 should generally be designed in correspondence with the desired angle of the spray axis 52. The angle of the spray axis 52 is generally dependent, and thus defined in view of the position of the fuel injector 13 which directs the fuel towards the protrusion(s) 50.

[0189] As illustrated in Fig. 3F, the corresponding tip portion 85 is here defined by an angle DA of about 80 to 140 degrees. Still preferably, the corresponding tip portion 85 may be defined by an angle DA of about 90 to 130 degrees. Still preferably, the corresponding tip portion 85 may be defined by an angle DA of about 100 to 120 degrees. The above ranges of the angle DA define a protrusion that has been observed to improve the control of the so- called flame-wall event.

[0190] The angle DA is here defined as the angle between the radial side sections 86, 87, as illustrated in Fig. 3F.

[0191] As such, by arranging the second type of protrusions 50 at the fuel impingement portions 60 in combination with using a design of the protrusions defined by means of the above angle DA, it becomes possible to further improve the control of the point of stagnation.

[0192] In general, it has been observed that the second type of protrusions 60 allow for improving the possibility of dividing the flow of fuel (flame), thus providing a reduced stagnation within the combustion chamber 7.

[0193] In some examples, the corresponding tip portion 85 is defined by an angle DA of less than 100 degrees.

[0194] In some examples, as illustrated in Fig. 3G, each one each one of protrusions 50 of the second type of protrusions 50 in relation to the axial direction A is further defined by a corresponding second angle CFA. Accordingly, a steepness of each one of the protrusions 50 of the second type of protrusions 50 in relation to the axial direction A is defined by a corresponding second angle CFA. A technical advantage may be an improved control of the degree of confinement of the jets in the axial direction A.[1951 By way of example, the corresponding second angle CFA is a steep angle or a shallow angle. The corresponding second angle CFA is defined in relation to a parallel axis AP2 to the center axis Ac and as a measure between the floor portion I la and the protrusion 50, more specifically as the angle between the floor portion I la and the surface 88.

[0196] By way of example, the corresponding second angle CFA is about 10 to 40 degrees. Still preferably, the corresponding second angle CFA may be about 12 to 30 degrees. Still preferably, the corresponding second angle CFA may be about 15 to 25 degrees. Such range of the angle CFA contributes to an even more improved control of the degree of confinement of the jets in the axial direction. A small angle means a steep nose which means more confined jets.

[0197] Moreover, as mentioned above, the circumferential rim portion 20 can be designed in several different ways. Fig. 3H illustrates a cross sectional view across the circumferential rim portion 20 where there are no protrusions, i.e. an area between the first and second protrusions 40 and 50. As depicted in Fig. 3H, a steepness of the circumferential rim portion 20 in-between an adjacent protrusion 40 of the first type of protrusions 40 and an adjacent protrusion 50 of the second type of protrusion 50 defines a side angle SA.

[0198] As depicted in Fig. 3H, the side-angle SA is defined between the circumferential rim portion 20 and the floor surface 1 la, as seen on a portion of the circumferential rim portion 20 extending between an adjacent protrusion of the first type of protrusions 40 and an adjacent protrusion of the second type of protrusion 50. This portion extends in the axial direction and radial direction and is an area avoid of any protrusions. The side angle SAcontrols the direction of the flames in an upward (axial) direction on the way from the adjacent protrusion of the second type of protrusion 50 to the adjacent protrusion of the first type of protrusion 40. The side angle SA should be set to compensate for the relatively strong flow-guiding effects of the second type of protrusion to re-direct the flow downwards.[1991 By way of example, the side angle SA is about 5 to 25 degrees. Still preferably, the side angle SA may be about 8 to 22 degrees. Still preferably, the side angle SA may be about 10 to 20 degrees. As illustrated, the side angle SA is defined as the angle between the floor portion I la and circumferential rim portion 20.[2001 Also, the shape and extension of the flat surface 43a or the concave surface 43b of the first type of protrusion 40 in combination with the surface of the circumferential rib portion 20 creates a cavity, as illustrated in e.g. Fig. 3e. Hereby, the lower part of the flame / jet / fuel 51 will pass over the cavity. The shape of the cavity here contributes to the outgoing flow of the flame / jet / fuel 51 so as to direct the flow more upwards than what is possible with a conventional protrusion without the shape and extension of the flat surface or the concave surface.

[0201] Each protrusion 50 of the second type of protrusions 50 comprises corresponding opposite radial side sections 86, 87, as illustrated in e.g. Fig. 3G. Each one of the radial side sections 86, 87 extends in the radial direction R and from the circumferential rim portion 20. One of the radial side section is a first radial side section 86, whilst the other one of the radial side sections is a second radial side section 87. Each one of the first radial side section 86 and the second radial side section 87 extends in the radial direction R. Hence, the radial side sections may herein also be denoted as radially extending side sections or radially extending radial side sections. The first radial side section 86 and the second radial side section 87 are arranged opposite each other in the circumferential direction C, as depicted in e.g. Fig. 3F.

[0202] By way of example, the radially extending side sections 86, 87 are curved side sections. In other examples, the radially extending side sections 86, 87 may be curved convex side sections. In other examples, the radially extending side sections 86, 87 may be curved concave side sections. In yet other examples, the radially extending side sections 86, 87 may be flat side sections.

[0203] In other examples, each one of the radially extending side sections 86, 87 may comprise a curved concave side profile section and a convex side profile section. Such designs of the sections are illustrated in Fig. 3F, where each one of the opposite radial sidesections 86, 87 comprises multiple regions of different convex curved profiles. Similar to the side sections of the first protrusion 40, the protrusion 50 of the second type of protrusions generally comprises a first radially extending side section 86 having first and second convex curved profiles of different curved convex profiles and a second radially extending side section 87 having first and second convex curved profiles of different curved convex profiles. In other examples, the first radially extending side section 86 has a uniform curved convex profile, whilst the second radially extending side section 87 has a uniform curved convex profile.[2041 Each protrusion 50 of the second type of protrusions 50 here extends in the radial direction R at least partly over the floor portion 11. Further, each one of the spaced-apart protrusions 50 extends in the radial direction R to align with the floor surface 1 la of the floor portion 11.

[0205] In the illustrated embodiment in Figs. 3 A to 3F, the piston bowl 6 comprises a total of six protrusions 50, equally distributed around the circumference of the piston bowl 6. However, other numbers of protrusions 50 are conceivable, such as four, five, seven or even more protrusions.

[0206] The second type of protrusions 50 may be distributed around the central axis AC with 45 degrees intervals. Other intervals are also conceivable.

[0207] In Fig. 3 A, the second type of protrusions 50 are uniformly circumferentially distributed around the circumferential rib portion 20. In other design variants, although not shown, the second type of protrusions 50 may be non-uniformly circumferentially distributed on the circumferential rib portion 20.

[0208] As illustrated in e.g. Fig. 3F, and also in the other Figs. 3 A to 3G, each protrusion of the second type of protrusions 50 further comprises a surface 88 extending between the opposite radially extending side sections 86, 87. In Figs. 3 A to 3G, the surface 88 extends in the circumferential direction C between the opposite radially extending side sections 86, 87. Moreover, in Figs. 3 A to 3G, the surface 88 is a convex surface. Fig. 3F is a cross sectional view of the protrusion 50 illustrating the convex profile of the convex surface 88 in greater detail. The radius of the convex profile of the convex surface 88 is selected in view of the intended use of the piston 3. By way of example, the radius of the concave profile of the convex surface 88 follows the radius of the curvature of the side sections 86, 87. That is, the radius of the convex curvature of the convex surface 88 corresponds to the radius of theconvex curvature of the side sections 86, 87. It should, however, be readily appreciated that the radius of the convex profile of the convex surface 88 may have a different convex curvature than the convex curvature of side sections.[2091 In other examples, the side sections 86, 87 have both convex and concave profiles, where the radius of the convex curvature of the convex surface 88 is similar to the radius of the concave curvature of the side sections 86. 87. By way of example, Fig. 3F illustrates a design where a radius of the convex curvature of the convex surface 88 is different to the radius of the concave curvature of side sections 86, 87. When defining and designing the convexity of the convex surface 88, the convexity of the convex surface 88 is generally determined in relation to a Cartesian coordinate system (rather than the cylindrical coordinate system), as is also commonly known in the art. The radius of curvature of the convex surface 88 may either be constant in size along the circumferential direction C or slightly change in size along the circumferential direction C.

[0210] In Figs. 3A to 3G, the convex surface 88 extends a substantial part in the circumferential direction C. As mentioned above, the convex surface 88 here extends between the opposite radially extending radial side sections 86, 87. More specifically, the convex surface 88 extends in the circumferential direction C between the opposite radially extending radial side sections 86, 87. In Figs. 3A to 3G, the first radial side section 86 of the opposite radial side sections intersects with the convex surface 88 along an intersection edge. Analogously, the second radial side section 87 of the opposite radial side sections intersects with the convex surface 88 along another opposite intersection edge.

[0211] The convex surface 88 is thus arranged to form a bridging surface between the opposite radial side sections 86, 87.

[0212] The convex surface 88 is also arranged to face towards the center axis Ac of the piston 3.

[0213] Also, the convex surface 88 extends a substantial part in the axial direction A. As illustrated in e.g. Fig. 3 A, the convex surface 88 essentially extends in the axial direction A from the floor surface 1 la to the top end surface 5 of the piston top end 16. In some examples, an intersection defines the distinction between convex surface 88 and the floor surface 1 la. As such, the intersection also defines the distinction between the protrusion 50 and the floor surface I la. The intersection extends in the circumferential direction C. Also,the intersection may generally be an imaginary line illustrating the circumferential extension of the convex surface 88 at its maximum circumferential extension.[2141 As illustrated in Figs. 3A to 3G, the convex surface 88 extends in the axial direction A from the floor surface I la and generally the entire way to the top end surface 5. By way of example, the convex surface 88 extends in the axial direction A from the floor surface I la completely to the top end surface 5. However, in other examples, the convex surface 88 extends in the axial direction A from the floor surface 1 la to a given intermediate axial distance. Accordingly, the convex surface 88 generally extends in the axial direction A from the floor surface I la and towards the top end surface 5.[2151 In a similar vein as the convex surface 88, the protrusions 50 may extend in the axial direction A in several different manners. As mentioned above, and as illustrated in Figs. 3A to 3G, each one of the second type of protrusions 50 extends in the axial direction A between the floor surface 1 la of the floor portion 11 and towards the top end surface 5 of the piston top end 16. In particular, each one of the second type of protrusions 50 extends in the axial direction A between the floor surface 1 la of the floor portion 11 and to the top end surface 5 of the piston top end 16.

[0216] Hence, as is readily appreciated from the above, the convex surface 88 at least extends in the axial direction A from the floor surface I la and towards the top end surface 5. Depending on the design of the protrusion 50, the convex surface 88 then either terminates at a given intermediate axial distance between the quarter of the depth H of the piston bowl 6 and the depth H of the piston bowl 6 or mates with the top end surface 5. If the convex surface 88 terminates at a given intermediate distance, e.g. at the axial distance h (H / 4), the remaining parts of the protrusion 50 axially above the convex surface 88 are generally formed by an additional surface region together with the radial side sections 86, 87.

[0217] However, in other examples, as illustrated in Figs. 3 A to 3G, there is no additional surface region. That is, the convex surface 88 essentially extends to the top end surface 5. Due to the overall design of the protrusion 50, there may generally be a smooth curvilinear transition surface between the convex surface 88 and the top end surface 5, as may be gleaned from e.g. Fig. 3G. Accordingly, the convex surface 88 mates with the top end surface 5 by a smooth curvilinear transition surface between the convex surface 88 and the top end surface 5, as illustrated in Figs. 3A to 3G. The additional surface region, i.e. the curvilineartransition surface, here mates with the top end surface 5 in a convex curved manner, as seen in the radial direction R.[2181 It should also be noted that the design of the first and second types of protrusions may also be further determined based on desired number of flames. The number of flames can vary between four to eight, such as six to eight.[2191 To sum up, as illustrated in Figs. 3A to 3H, there is provided a piston 3 for an internal combustion engine, ICE, 10. The piston 3 extends in the axial direction A and in the radial direction R. The piston 3 has an axial top end 16 comprising a piston bowl 6 intended to form part of a combustion chamber, the piston bowl 6 further having an axial floor portion 11 with a floor surface I la and a circumferential rim portion 20 extending in the axial direction A between the floor surface I la and a top end surface 5 of the axial top end 16, the circumferential rim portion having at least one fuel impingement portion 60, the piston bowl further having an axial depth H defined by an axial distance between the floor surface I la and the top end surface 5, the piston bowl 6 further comprising a plurality of spaced-apart protrusions 40, 50 circumferentially distributed around the circumferential rim portion 20.

[0220] Each one of the spaced-apart protrusions 40, 50 extend a substantial part in the radial direction R towards a center axis AC, and further extending a substantial part in the axial direction A from the floor surface I la towards the top end surface 5, wherein the plurality of spaced-apart protrusions comprises a set of a first type of protrusion 40 and a set of a second type of protrusion 50 , the set of the first type of protrusions 40 and the set of the second type of protrusions 50 being arranged in an alternate manner along the circumferential rim portion, wherein at least one protrusion of the second type of protrusions is arranged at the at least one fuel impingement portion 60, so as to redirect a receiving flame to opposite tangential directions XR and XL of the circumferential rim portion.

[0221] In addition, adjacent protrusions of the first type of protrusions 40 are arranged inbetween the at least one fuel impingement portion 60, so as to redirect a circumferential flame progress mainly towards the center axis Ac of the piston 3, and wherein each one of the first type of protrusions 40 comprises opposite radial side sections 41, 42 , and further a flat surface or concave surface extending between the opposite radial side sections, 41, 42 the flat surface 43, 43a or concave surface 43, 43b having a first circumferential extension a at an intersection 44 between the flat surface or concave surface and the floor surface, and further asecond circumferential extension b at an axial distance h from the floor surface, the second circumferential extension b being less than the first circumferential extension a.[2221 The present disclosure also relates to the ICE system 100 comprising a diesel internal combustion engine, as described herein. The ICE system 100 comprises the internal combustion engine 10 for combustion of fuel and having the combustion chamber 7 at least partially delimited by the cylinder 2 and the reciprocating piston 3 according to any one of the above examples in Figs. 3 A to 3H. The reciprocating piston is moveable within the cylinder between the bottom dead center BDC and the top dead center TDC, wherein the piston top end being arranged to form part of the combustion chamber.[2231 The present disclosure also relates to the vehicle 1 comprising the ICE system 100 and the piston 3 according to according to any one of the above examples in Figs. 3 A to 3H. [2241 Moreover, the present disclosure may be exemplified by any one of the below examples.

[0225] Example 1 : A piston 3 for an internal combustion engine, ICE, 10, the piston extending in an axial direction A and a radial direction R, and having an axial top end 16 comprising a piston bowl 6 intended to form part of a combustion chamber, the piston bowl having an axial floor portion 11 with a floor surface I la and a circumferential rim portion 20 extending in the axial direction A between the floor surface and a top end surface 5 of the axial top end, the circumferential rim portion having at least one fuel impingement portion 60, the piston bowl further having an axial depth H defined by an axial distance between the floor surface and the top end surface, the piston bowl further comprising a plurality of spaced-apart protrusions 40, 50 circumferentially distributed around the circumferential rim portion 20, each one of the spaced-apart protrusions extending a substantial part in the radial direction towards a center axis AC, and further extending a substantial part in the axial direction from the floor surface towards the top end surface, wherein the plurality of spaced- apart protrusions comprises a set of a first type of protrusion 40 and a set of a second type of protrusion 50 , the set of the first type of protrusion and the set of the second type of protrusion being arranged in an alternate manner along the circumferential rim portion, wherein at least one protrusion of the second type of protrusions is arranged at the at least one fuel impingement portion 60, so as to redirect a receiving flame to opposite tangential directions XR and XL of the circumferential rim portion, and adjacent protrusions of the first type of protrusion are arranged in-between the at least one fuel impingement portion, so as toredirect a circumferential flame progress mainly towards the center axis Ac of the piston, and wherein each one of the first type of protrusion comprises opposite radial side sections 41, 42, and further a flat surface or concave surface extending between the opposite radial side sections, the flat surface 43, 43a or concave surface 43, 43b having a first circumferential extension a at an intersection 44 between the flat surface or concave surface and the floor surface, and further a second circumferential extension b at an axial distance h from the floor surface, the second circumferential extension b being less than the first circumferential extension a.[2261 Example 2: The piston according to example 1, wherein at least one protrusion of the first type of protrusions comprises a tip portion facing the center axis, the tip portion being defined by an angle CA of about XX 40 to 140 degrees.[2271 Example 3: The piston according to any one of the preceding examples, wherein a steepness of at least one protrusion of the first type of protrusions in relation to the axial direction is defined by a second angle FA.

[0228] Example 4: The piston according to any one of the preceding examples, wherein the second angle is a steep angle or a shallow angle.

[0229] Example 5: The piston according to any one of the preceding examples, wherein the at least one protrusion of the second type of protrusions comprises a corresponding tip portion facing the center axis, the corresponding tip portion being defined by an angle DA of about 80 to 140 degrees.

[0230] Example 6: The piston according to any one of the preceding examples, wherein a steepness of at least one protrusion of the second type of protrusions in relation to the axial direction is defined by a corresponding second angle CFA.

[0231] Example 7: The piston according to example 6, wherein the corresponding second angle is a steep angle or a shallow angle.

[0232] Example 8: The piston according to any one of the preceding examples, wherein a steepness of the circumferential rim portion in-between an adjacent protrusion of the first type of protrusions and an adjacent protrusion of the second type of protrusion defines a side angle SA.

[0233] Example 9: The piston according to any one of the preceding examples, wherein the axial distance h being a quarter of the axial depth H of the piston bowl, and wherein aratio between the second circumferential extension b and the first circumferential extension a is 0.4 or less.[2341 Example 10: The piston according to any one of the preceding examples, wherein a first radial side section 41 of the opposite radial side sections intersects with the flat surface or concave surface along an intersection edge 45 and a second radial side section 42 of the opposite radial side sections intersects with the flat surface or concave surface along another opposite intersection edge 46.[2351 Example 11 : The piston according to example 10, wherein the intersection edges in combination with the first circumferential extension and the second circumferential extension define the extension of the flat surface or the concave surface.[2361 Example 12: The piston according to examples 10 or 11, wherein each one of the intersection edges inclines from the first circumferential extension to the second circumferential extension, respectively, in a linear manner or in a non-linear manner, such as in a curved manner.

[0237] Example 13: The piston according to any one of the preceding examples 10 to 12, wherein the intersection edges in combination with the first circumferential extension and the second circumferential extension define a surface resembling a trapezoid or a triangular shape.

[0238] Example 14: The piston according to any one of the preceding examples, wherein an extension of the flat surface or the concave surface from the first circumferential extension to the second circumferential extension further comprises a concave axially extending region.

[0239] Example 15: The piston according to any one of the preceding examples, wherein an extension of the flat surface from the first circumferential extension to the second circumferential extension is defined by a flat surface profile.

[0240] Example 16: The piston according to any one of the preceding examples, wherein each one of the opposite radial side sections comprises multiple regions of different convex curved profiles.

[0241] Example 17: The piston according to any one of the preceding examples, wherein the spaced-apart protrusions are uniformly circumferentially distributed along the circumferential rim portion.[2421 Example 18: The piston according to any one of the preceding examples, wherein each one of the spaced-apart protrusions extends in the axial direction from the floor surface to the top end surface of the piston top end.[2431 Example 19: The piston according to any one of the preceding examples, wherein the flat surface or concave surface extends in the axial direction from the intersection between the flat surface or concave surface and the floor surface and towards the top end surface of the piston top end.[2441 Example 20: The piston according to example 19, wherein the flat surface or concave surface extends in the axial direction from the intersection between the flat surface or concave surface and the floor surface to the top end surface of the piston top end.[2451 Example 21 : The piston according to example 19, wherein the flat surface or concave surface extends in the axial direction from the intersection between the flat surface or concave surface and the floor surface to the second circumferential extension.

[0246] Example 22: The piston according to any one of the preceding examples, wherein each one of the spaced-apart protrusions extends in the radial direction at least partly over the floor portion.

[0247] Example 23: The piston according to any one of the preceding examples, wherein the first circumferential extension is a maximum circumferential extension of the flat surface or concave surface.

[0248] Example 24: An internal combustion engine, ICE, system 100 comprising an internal combustion engine 10 for combustion of fuel and having a combustion chamber 7 at least partially delimited by a cylinder 2 and a reciprocating piston 3 according to any one of the above examples. The reciprocating piston being moveable within the cylinder between a bottom dead center BDC and a top dead center TDC, wherein the piston top end being arranged to form part of the combustion chamber.

[0249] Example 25: A vehicle 1 comprising a piston according to any one of the examples or an internal engine combustion system according to any one of the examples.

[0250] As used herein, the terms "upstream" and "downstream" refer to the relative direction with respect to fluid flow in a fluid pathway. For example, "upstream" refers to the direction from which the fluid flows, and "downstream" refers to the direction to which the fluid flows.[2511 Also, the term “longitudinal”, “longitudinally”, “axially” or “axial” refer to a direction at least extending between axial ends of a particular component, typically along the arrangement or components thereof in the direction of the longest extension of the arrangement and / or components. The terms “vertical” and “vertically” generally correspond to the axial direction.[2521 The terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting of the disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms "comprises," "comprising," "includes," and / or "including" when used herein specify the presence of stated features, integers, actions, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, actions, steps, operations, elements, components, and / or groups thereof.

[0253] It will be understood that, although the terms first, second, etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element without departing from the scope of the present disclosure.

[0254] Relative terms such as "below" or "above" or "upper" or "lower" or "horizontal" or "vertical" may be used herein to describe a relationship of one element to another element as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present.

[0255] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning consistent with their meaning in the context of thisspecification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.[2561 It is to be understood that the present disclosure is not limited to the aspects described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the present disclosure and appended claims. In the drawings and specification, there have been disclosed aspects for purposes of illustration only and not for purposes of limitation, the scope of the disclosure being set forth in the following claims.

Claims

ClaimsWhat is claimed is:

1. A piston (3) for an internal combustion engine (10), the piston extending in an axial direction (A) and a radial direction (R), and further having an axial top end (16) comprising a piston bowl (6) intended to form part of a combustion chamber, the piston bowl having an axial floor portion (11) with a floor surface (I la) and a circumferential rim portion (20) extending in the axial direction (A) between the floor surface and a top end surface (5) of the axial top end, the circumferential rim portion further having at least one fuel impingement portion (60), the piston bowl further having an axial depth (H) defined by an axial distance between the floor surface and the top end surface, the piston bowl further comprising a plurality of spaced-apart protrusions (40, 50) circumferentially distributed around the circumferential rim portion (20), each one of the spaced-apart protrusions extending a substantial part in the radial direction towards a center axis (AC), and further extending a substantial part in the axial direction from the floor surface towards the top end surface, wherein the plurality of spaced-apart protrusions comprises a set of a first type of protrusions (40) and a set of a second type of protrusions (50), the set of the first type of protrusions and the set of the second type of protrusions being arranged in an alternate manner along the circumferential rim portion, wherein at least one protrusion of the second type of protrusions is arranged at the at least one fuel impingement portion (60), so as to redirect a receiving flame to opposite tangential directions (XR) and (XL) of the circumferential rim portion, and adjacent protrusions of the first type of protrusions being arranged in-between the at least one fuel impingement portion, so as to redirect a circumferential flame progress mainly towards the center axis (Ac) of the piston, and wherein each one of the first type of protrusions comprises opposite radial side sections (41, 42), and further a flat surface (43, 43a) or concave surface (43, 43b) extending between the opposite radial side sections, the flat surface or concave surface having a first circumferential extension (a) at an intersection (44) between the flat surface or concave surface and the floor surface, and further a second circumferential extension (b) at an axial distance (h) from thefloor surface, the second circumferential extension (b) being less than the first circumferential extension (a).

2. Piston according to claim 1, wherein at least one protrusion of the first type of protrusions comprises a tip portion (80) facing the center axis, the tip portion being defined by an angle (CA) of about 40 to 140 degrees.

3. Piston according to any one of the preceding claims, wherein a steepness of at least one protrusion of the first type of protrusions in relation to the axial direction is defined by a second angle (FA).

4. Piston according to claim 3, wherein the second angle is a steep angle or a shallow angle.

5. Piston according to any one of the preceding claims, wherein the at least one protrusion of the second type of protrusions comprises a corresponding tip portion (85) facing the center axis, the corresponding tip portion being defined by an angle (DA) of about 80 to 140 degrees.

6. Piston according to any one of the preceding claims, wherein a steepness of at least one protrusion of the second type of protrusions in relation to the axial direction is defined by a corresponding second angle (CFA).

7. Piston according to claim 6, wherein the corresponding second angle is a steep angle or a shallow angle.

8. Piston according to any one of the preceding claims, wherein a steepness of the circumferential rim portion, extending in-between an adjacent protrusion of the first type of protrusions and an adjacent protrusion of the second type of protrusions, defines a side angle (SA).

9. Piston according to any one of the preceding claims, wherein the axial distance (h) being a quarter of the axial depth (H) of the piston bowl, and wherein a ratio between the second circumferential extension (b) and the first circumferential extension (a) is 0.4 or less.

10. Piston according to any one of the preceding claims, wherein a first radial side section (41) of the opposite radial side sections intersects with the flat surface or concave surface along an intersection edge (45) and a second radial side section (42) of the opposite radial side sections intersects with the flat surface or concave surface along another opposite intersection edge (46).

11. Piston according to claim 10, wherein the intersection edges in combination with the first circumferential extension and the second circumferential extension define the extension of the flat surface or the concave surface.

12. Piston according to claim 10 or claim 11, wherein each one of the intersection edges inclines from the first circumferential extension to the second circumferential extension, respectively, in a linear manner or in a non-linear manner, such as in a curved manner.

13. Piston according to any one of claims 10 to 12, wherein the intersection edges in combination with the first circumferential extension and the second circumferential extension define a surface resembling a trapezoid or a triangular shape.

14. Piston according to any one of the preceding claims, wherein an extension of the flat surface or the concave surface from the first circumferential extension to the second circumferential extension further comprises a concave axially extending region.

15. Piston according to any one of the preceding claims, wherein an extension of the flat surface from the first circumferential extension to the second circumferential extension is defined by a flat surface profile.

16. Piston according to any one of the preceding claims, wherein each one of the opposite radial side sections comprises multiple regions of different convex curved profiles.

17. Piston according to any one of the preceding claims, wherein the spaced-apart protrusions are uniformly circumferentially distributed along the circumferential rim portion.

18. Piston according to any one of the preceding claims, wherein each one of the spaced-apart protrusions extends in the axial direction from the floor surface to the top end surface of the piston top end.

19. Piston according to any one of the preceding claims, wherein the flat surface or concave surface extends in the axial direction from the intersection between the flat surface or concave surface and the floor surface and towards the top end surface of the piston top end.

20. Piston according to claim 19, wherein the flat surface or concave surface extends in the axial direction from the intersection between the flat surface or concave surface and the floor surface to the top end surface of the piston top end.

21. Piston according to claim 19, wherein the flat surface or concave surface extends in the axial direction from the intersection between the flat surface or concave surface and the floor surface to the second circumferential extension.

22. Piston according to any one of the preceding claims, wherein each one of the spaced-apart protrusions extends in the radial direction at least partly over the floor portion.

23. Piston according to any one of the preceding claims, wherein the first circumferential extension is a maximum circumferential extension of the flat surface or concave surface.

24. An internal combustion engine system (100) comprising an internal combustion engine (10) for combustion of fuel and having a combustion chamber (7) at least partially delimited by a cylinder (2) and a reciprocating piston (3) according to any one of the preceding claims, the reciprocating piston being moveable within the cylinder between a bottom dead center (BDC) and a top dead center (TDC), wherein the piston top end being arranged to form part of the combustion chamber.

25. A vehicle (1) comprising a piston according to any one of the claims 1 to 23 and / or an internal engine combustion system according to claim 24.

Images