Abstract: An internal combustion engine piston includes a piston crown, a thrust-side skirt, an anti-thrust-side skirt, a first apron, and a second apron. The first and second aprons are connected to the thrust-side and anti-thrust-side skirts through connecting sections. Each connecting section has a thickness that gradually increases as followed from a proximal longitudinal end to a distal longitudinal end, wherein the proximal longitudinal end is closer to the piston crown, and the distal longitudinal end is closer to a distal longitudinal end of a corresponding one of the thrust-side and anti-thrust-side skirts.

Abstract: A piston for an internal combustion engine includes a piston base material and a film of lubrication coating composition. The coating composition has an inner coating layer formed on a surface of the piston base material and an outer coating layer formed on a surface of the inner coating layer. Each of the inner coating layer and the outer coating layer contains at least one of a polyamide-imide resin, a polyimide resin and an epoxy resin as a binder. The inner coating layer contains 0 to 50 wt % of at least one of graphite and molybdenum disulfide as a solid lubricant, whereas the outer coating layer contains 50 to 95 wt % of at least one of graphite and molybdenum disulfide as a solid lubricant.

Abstract: A steel piston with a piston upper part (12) with combustion chamber recess (11) and ring wall (5), and with a piston lower part (13) with piston body or piston skirt and with connecting rod bearing (8) for internal combustion engines with cylinder crankcases made of lightweight metal alloys, with at least the piston lower part consisting of a steel alloy which has a coefficient of thermal expansion in the range from 13 to 20×10?6 1/K.

Abstract: The present invention relates to a piston (10, 110, 210) for an internal combustion engine, having a first piston component (11) and a second piston component (12), which jointly form a circumferential cooling channel (23) that is open toward the second piston component (12), whereby the first piston component (11) forms at least a part of a piston crown (13) as well as an outer circumferential wall (34) of the cooling channel, characterized in that the outer circumferential wall (34) of the cooling channel (23) has a circumferential projection (32) below the piston crown (13), which projection is provided with a circumferential guide surface (33) for coolant, directed radially inward.

Abstract: A piston of an internal combustion engine, having a crown section. A wear-resistant ring is formed in the crown section to be used for forming a piston ring groove. The wear-resistant ring includes a porous formed body formed of a first material higher in hardness and larger in specific gravity than a base material of the piston, and a second material infiltrated in pores of the porous formed body and containing 20 weight % or more of magnesium.

Abstract: The present invention relates to a piston (10, 110, 210) for an internal combustion engine, having a first piston component (11) and a second piston component (12), whereby the first piston component (11) and the second piston component (12) form a circumferential cooling channel (23) that is open toward the second piston component, which channel is closed off by means of a circumferential closure element. According to the invention, it is provided that the closure element (25, 125, 225) is connected with the first piston component (11) and extends radially in the direction of the second piston component (12), that the second piston component (12) has a circumferential contact flange (26, 126, 226) that extends radially in the direction of the first piston component (11), and that the closure element (25, 125, 225) lies on the contact flange (26, 126, 226) or that the closure element (325) supports itself on a face surface (331) of the contact flange (326) with a circumferential lower edge (329).

Abstract: The piston has a crown forming a piston bowl. The piston bowl has a center portion with a convex spherical shape, a floor having a convex frusto-conical shape adjacent the center portion, and a base having a concave toroidal shape surrounding the floor. The piston bowl also has a cylindrical wall extending tangentially from the base that surrounds the center portion. The piston has a top surface perpendicular to the cylindrical wall along a rim of the piston bowl. A ratio between the piston bowl depth and the cylindrical wall length is less than 4, and a ratio between the piston bowl diameter and the piston bowl depth is 4.7.

Abstract: The present invention relates to a piston (10) for an internal combustion engine having a piston head (11) and a piston skirt (16) with piston hubs (17) which are each connected to a hub bore (18) for receiving a piston bolt, wherein the piston hubs (17) are in the shape of a trapezoidal or step-shaped support in which the inner faces (19) of the piston hubs (17) include an acute angle (?a) with the central axis (M) of the piston. The invention provides that each hub bore (18) is embodied as a shaped bore which is widened at least in its inner area in such a way that the widened portion increases in size in the direction of the inner end (18?) of the hub bore (18) forming facets (120, 220) on the lateral surface (18) of the hub bore (18), and that the facets (120, 220) include an acute angle (?a, ?) with the central axis (M) of the piston.

Abstract: Proposed is a multi-part cooled piston (1) for an internal combustion engine, which piston (1) is composed of an upper piston part (2) and a lower piston part (6). The upper piston part (2) forms an inner annular cooling duct (11) with the lower piston part (6), which cooling duct (11) is covered by an upper region (31) of the lower piston part (6). The region (31) is of thin-walled design in such a way that it can be deformed in the manner of a plate spring.

Abstract: The present invention relates to a method for the production of a piston (10, 110) for an internal combustion engine, having a circumferential cooling channel (24), whereby a blank (11?, 111?) of a lower piston part (11, 111) is forged, and a blank (12?) of an upper piston part (12) is produced, the blanks (11?, 111?, 12?) are pre-machined and joined together to form a piston blank (10?, 110?), which is finished to produce a piston (10, 110). According to the invention, it is provided that at least one depression (25) or at least one recess (135), respectively, is formed into the blank (11?, 111?) of the lower piston part (11, 111) during the forging process, whereby in the finished piston (10, 110), the at least one depression (25) forms an opening (33) for a coolant inflow and/or a coolant outflow, or the at least one recess (135) forms an excavation groove (136) for a pin securing ring, respectively.

Abstract: There is provided an engine in which sliding surfaces of a cylinder and a piston do not tend to seize and the ratio of a lubricating oil to a composite fuel can be reduced. There is also provided a piston that allows the lubricating oil to be intentionally supplied to the surface of the piston that slides along the cylinder or a cylinder liner. In an aspect of the present invention, an engine in which an air-fuel mixture containing a lubricating oil is supplied into a combustion chamber includes supply means for supplying the air-fuel mixture to the interface between an inner wall of a cylinder or a cylinder liner and a tubular portion of a piston (portion between piston rings and/or piston ring portion). The supply means is, for example, through holes passing through the tubular portion of the piston and groove portions.

Abstract: A piston for an internal combustion engine has at least two hub bores for holding a piston pin. The hub bores are formed with a cylindrical inner contour and are provided with a coating comprising a resin with solid lubricant particles embedded therein. The coating forms at least one geometric deviation from the cylindrical inner contour of the hub bores. A method for producing a piston of the type, includes producing bores with a cylindrical inner contour and applying a coating medium comprising a resin with solid lubricant particles embedded therein to the inner faces of the bores by a coating tool, such that the resulting coating forms at least one geometric deviation from the cylindrical inner contour of the hub bores.

Abstract: A piston coating is described that comprises at least one aqueous dispersion selected from among the group including phenolic resins, epoxy resins, polyvinyl butyral, or the condensation products thereof, and at elast one solid lubricant selected from among the group including graphite, MoS2, WS2, and BN. Said coating dispenses with the use of toxic solvents and has a wear resistance and a coefficient of friction similar to those of conventional coatings.

Abstract: The invention relates to a method for producing a piston for an internal combustion engine, wherein a section which in the finished piston has a cooling duct (14) and a piston ring groove is recessed at first, the later cooling duct is then covered, and finally material for accommodating the piston ring is applied, and which is characterized in that the later cooling duct is covered by a wire material which is provided in a length, greater than necessary for one single piston. A device for producing a piston for an internal combustion engine with an at first recessed section that in the finished piston has a cooling duct (14) and a piston ring groove, has a device for attaching a cover on the cooling duct and a device for providing wire material having a length greater than necessary for one single piston.

Abstract: A reinforced piston assembly provides a piston having a corrugated insert supporting an outer piston layer. The corrugated insert can include lateral, concentric or radial corrugations and can include regular or irregular corrugation spacing. The corrugated insert in some embodiments forms a circular disk and can include a plurality of insert holes defined in the disk. A laminated connecting rod having at least two rod layers is pivotally attached to the piston in some embodiments. The laminated connecting rod provides a first end having a diverging section with first and second rod prongs each forming a wrist pin socket. A wrist pin can extend through each socket, and a sleeve is disposed about the wrist pin between the wrist pin sockets. Additionally, one or more flanges can extend from the opposite end of the connecting rod, and a base cap including one or more flange recesses is positioned on the connecting rod for securing the connecting rod to a crankshaft.

Abstract: A multi-part piston for an internal combustion engine has an upper piston part with a piston crown, and a lower piston part with pin boss supports and pin bosses connected with the pin boss supports. The upper piston part and the lower piston part each have an inner and an outer support element, which elements delimit an outer circumferential cooling channel. The inner support elements delimit a cavity that is open toward the pin bosses. The cavity is provided with a separate cooling oil collector that has at least one cooling oil opening.

Abstract: A method for producing a multi-part piston for an internal combustion engine and the piston itself, which has an upper piston part and a lower piston part, each having an inner and an outer support element, which elements delimit an outer circumferential cooling channel and an inner cooling chamber. The inner support element of the upper piston part and/or the inner support element of the lower piston part have at least one recess on their surface. The upper piston part and the lower piston part are connected with one another by pressure welding.

Abstract: A connecting member coupled to four pistons that reciprocate within cylinder bores is coupled to a crankpin of a crankshaft, and a pinion member which integrally rotates with a crankshaft portion is capable of rolling along the inner periphery of an internal gear member and has an outer diameter equal to 1/2 of an inner diameter of the internal gear member. The crankpin executes a reciprocating rectilinear motion through the rotation and revolution of the pinion member, and a journal support member has a bearing for supporting a crank journal so as to rotate positioned between the pinion member and a crank arm, and which is supported by a case member so as to rotate coaxially with an output member.

Abstract: An engine having improved combustion characteristics is provided. The engine includes a fuel injection system that is variable between two operational states. In the first operating state, the fuel injectors provide a fuel spray having first spray pattern characteristics. When the system detects that an operation characteristic exceeds a threshold, the fuel injectors are displaced into a second operating state. In the second operating state, the fuel injectors provide a spray pattern having first spray pattern characteristics. The combustion cycle may be characterized by timing the fuel injection so that the fuel is sprayed into the cylinder early in the compression stroke. Further still, the combustion cycle may be characterized by controlling the fuel pressure so that the fuel pressure is inversely related to the load on the engine.

Abstract: A piston for an internal combustion engine wherein the piston includes a piston body fabricated from a metal and a piston head fabricated from a ceramic or ceramic composite material, the ceramic or ceramic composite piston head is press fit to the piston body and secured by an internal circumferential locking ring.

Abstract: A piston assembly for use in an internal combustion engine is provided by the present disclosure. The piston assembly includes a piston body having an extended piston mantel, a piston face, an internal cavity, and a wrist pin support. Two oil retainer seals are located concentrically about the extended piston mantel near a distal end, each oil retainer seal having an internal groove and being formed of a polymer material. Two compression clips are disposed within the internal grooves of the two oil retainer seals and are adapted to assist the oil retainer seals in establishing contact with an inner wall of a cavity in a cylinder of the internal combustion engine. The piston body is formed of an engineered composite material.

Abstract: With regard to a surface hardening method wherein a surface of an engine member is coated with an alloy layer having high abrasive resistance so as to improve the life of the member and a production method of a piston or the like wherein abrasive resistance of the member is improved by the hardening method, a surface of a metal base material is coated uniformly with a mixture including metal powder, a binder and a solvent so as to form a coat, and the coat is dried and applied thereon with a laser or electron beam so as to be sintered and dispersed for forming an alloy layer on a surface of the metal base material and for bonding the alloy layer to the metal base material.

Abstract: The present invention generally relates to a recess in the top of a piston. More particularly, the present invention relates to a crescent-shaped recess in the top of an expansion piston of a split-cycle engine.

Abstract: Exemplary piston assemblies and methods of making the same are disclosed. An exemplary piston assembly may include a piston crown and a piston skirt that is received in a central opening of the crown. The piston crown may include a ring belt portion defining, at least in part, a cooling gallery. The crown and skirt may each further include corresponding mating surfaces that extend about a periphery of the crown and skirt. The skirt mating surface and crown mating surface may generally be secured to each other that the crown and the skirt cooperate to form a continuous upper combustion bowl surface. The skirt and crown may cooperate to define a radially outer gap about a periphery of the piston crown.

Abstract: A multi-part piston for an internal combustion engine has an upper piston part with a piston crown, and a lower piston part, each of the piston parts having an inner and an outer support element that delimit an outer circumferential cooling channel and an inner cooling chamber. The cooling chamber bottom has an opening. A holding element is disposed in the inner cooling chamber and extends from the underside of the piston crown vertically toward the opening. The holding element carries a closure element that closes the opening and has at least one cooling oil opening.

Abstract: The present invention relates to a multi-part piston (10, 110) for an internal combustion engine, having an upper piston part (11, 111) having a piston crown (13), and a lower piston part (12), whereby the lower piston part (12) has pin boss supports (32) and pin bosses (18) connected with them, whereby the upper piston part (11) and the lower piston part (12) each have an inner (21, 25) and an outer (22, 26) support element, which elements delimit an outer circumferential cooling channel (29). According to the invention, it is provided that the inner support elements (21, 25) delimit a cavity (31) that is open toward the pin bosses (18), and that the cavity (31) is provided with a separate cooling oil collector (35, 135) that has at least one cooling oil opening (37, 38). The present invention furthermore relates to a method for the production of such a piston.

Abstract: A piston construction for an opposed-piston engine accommodates contoured end surfaces of the piston crowns and articulation of the pistons with piston rods. The shape of each piston crown includes a bowl with an adjoining ridge that protrudes axially of the piston. A cooling construction for the piston includes an outer gallery running around the inner surface of the piston sidewall in the vicinity of the crown. The outer gallery girds and is in fluid communication with a central gallery that abuts the deepest part of the bowl. The outer gallery has an asymmetric profile that rises under the ridge and that slants upwardly under a peripheral portion of the bowl. A mechanism for coupling the piston to a piston rod includes a biaxial slipper bearing.

Abstract: A piston and connecting rod assembly wherein the piston includes an inner cooling gallery defined in the body thereof beneath the crown of the piston, an outer cooling gallery defined between the skirt of the piston and the body and beneath the crown. A pin bore is formed in the body. A connecting rod is adapted to interconnect the piston and crankshaft where the connecting rod has at least one end with a bore extending therethrough and adapted to be aligned with the pin bore of the piston. At least one end of the connecting rod is in fluid communication with the inner cooling gallery of the piston and includes a reservoir formed on the end of the connecting rod which is adapted to collect coolant therein.

Abstract: A piston apparatus for an engine, may include a piston pin inserted in a smaller end portion of a connecting rod and having a cross-section changing portion where a cross section changes at a portion of the piston pin, and a fixing member engaging the connecting rod and a piston through the cross-section changing portion to restrain longitudinal movement of the piston pin with respect to the connecting rod.

Abstract: A piston for a piston-cylinder unit, the piston including two pivot bearings for pivotably supporting two connecting rods at the piston about two connecting rod pivot two connecting rod pivot axes extending in parallel to one another and laterally offset from one another; the two pivot bearings provided at a bearing element which is pivotably supported about a bearing element pivot axis at the piston; and the bearing element pivot axis extending parallel to the two connecting rod pivot axes.

Abstract: A piston for an internal combustion engine is provided. The piston has a surface on the combustion side, wherein a depression having a depression edge and a depression floor is arranged in the surface and the depression has a maximum depth of tmax in an axial direction of the piston, measured from the combustion side surface. The combustion side surface furthermore has at least one protrusion that is arranged on a section of the depression edge and has a depth taus, wherein the depth taus of the protrusion is smaller than the depth of the depression tmax in the axial direction of the piston.

Abstract: A multi-part piston for an internal combustion engine has an upper piston part with a piston crown, and a lower piston part, each of the piston parts having an inner and an outer support element that delimit an outer circumferential cooling channel and an inner cooling chamber. The cooling chamber bottom has an opening. A holding element is disposed in the inner cooling chamber and extends from the underside of the piston crown vertically toward the opening. The holding element carries a closure element that closes the opening and has at least one cooling oil opening.

Abstract: The invention relates to a soluble and essentially annular casting core (2) for forming a cooling channel that transitions into two areas (14, 15) which are approximately parallel to the piston axis (16) and are facing away from the piston head (3), via a respective bending of the core (17, 18) in the shape of a quadrant, wherein the second area (14) transitions into a part of the casting core (2) that forms the feed opening (12) of the cooling channel, and the first area (15) transitions into a part of the casting core (2) that forms the discharge opening (13) of the cooling channel. The two areas (14, 15) of the casting core (2) are disposed at a distance from one another, which corresponds at a maximum to two times the cross-sectional diameter of one of the two areas (14, 15). As a result, the throughflow of the cooling oil traversing the cooling channel is accelerated and the cooling of the piston improved.

Abstract: A method for the production of a piston has the following method steps: (a) providing a blank of a piston base body, having an outer joining surface, an inner joining surface and a circumferential lower cooling channel part that runs between the two joining surfaces, (b) providing a blank of a piston ring element, having an outer joining surface, an inner joining surface and a circumferential upper cooling channel part that runs between the two joining surfaces, (c) forming a circumferential widened region on at least one joining surface, the widened region extending toward the related cooling channel part, (d) connecting the blank of the piston base body with the blank of the piston ring element by way of their joining surfaces, by friction welding, to produce a piston blank, and (e) machining the piston blank further and/or finish-machining it to produce a piston.

Abstract: A method for producing a piston for an internal combustion engine, composed of first and second piston components, has the following steps: (a) providing a blank of the first piston component composed of a tempered or precipitation-hardened steel, having at least one joining surface, (b) providing a blank of the second piston component composed of a tempered or precipitation-hardened steel, having at least one joining surface, (c) tempering or precipitation-hardening the blanks, (d) friction-welding the joining surfaces of the blanks to produce a piston blank, with the formation of at least one friction-welding seam and a heat influence zone in the region of the at least one friction-welding seam, (e) annealing or low-stress annealing of the piston blank, thereby obtaining the heat influence zone(s), (f) re-machining and/or finishing the piston blank to produce a piston. A piston so produced is also provided.

Abstract: A method for the production of a piston for an internal combustion engine has the following steps: producing an upper piston part having at least one joining surface, b) producing a lower piston part having at least one joining surface, c) producing a direct contact between the at least one joining surface of the upper piston part and the at least one joining surface of the lower piston part, d) heating the upper piston part and the lower piston part by induction or by a direct flow of current over the joining surfaces in the region of the joining surfaces that have been brought into direct contact, e) connecting the upper and lower piston parts with one another to produce a piston by a pressing process, and machining the piston to finish it.

Abstract: A piston for an internal combustion engine has an upper part and a lower part. The upper part has a collar with a ring rib and the lower part has a wall and a contact part radially within the wall. When the upper part is connected with the lower part by friction welding, the face surfaces of the ring rib, the collar, the wall, and the contact part form friction-welding surfaces and form a cooling channel and a cooling cavity between them. To supply the cooling channel and the cooling cavity with cooling oil, radial bores are introduced into the ring rib, which bores connect the cooling channel with the cooling cavity. In this way, it is guaranteed that a sufficient residual amount of oil collects in the cooling channel and in the cooling cavity, which amount is constantly renewed, and leads to good cooling of the piston crown.

Abstract: A piston and method of construction is provided. The piston includes a top part fixed to a bottom part. The top part has an uppermost surface with annular inner and outer upper joining surfaces depending therefrom. The bottom part has a pair of pin bosses with pin bores aligned with one another along a pin bore axis; a pair of upwardly extending annular inner and outer lower joining surfaces and a combustion bowl wall. Inner and outer weld joints fix the inner and outer upper and lower joining surfaces to one another. An annular cooling gallery is formed laterally between the upper and lower joining surfaces. The inner weld joint joining the top part to the bottom part is located within the combustion bowl wall and configured to minimized the compression height of the piston.

Abstract: A piston for an internal combustion engine has a lower piston part and an upper piston part disposed on the lower piston part. The upper piston part has a top land that runs around its circumference, and a ring belt that runs around its circumference. At least the upper piston part consists of a sintered material.

Abstract: A method for producing a piston for internal combustion engines includes the following steps: a first part is pre-fabricated by hot forging and a recess which has an undercut is formed in the first part during pre-fabrication by forming on the first part a projection, to which projection a lateral force is applied to form the undercut; a second part is pre-fabricated by hot forging and a projection is formed on this second part whose dimensions are matched to the dimensions of the recess; the two parts are joined together so that the projection on one part engages in the recess in the other part; and a compressive force is applied to the two parts which is sufficiently large and so aligned that the material of the projection on one part flows into the recess in the other part and completely fills it to connect the parts by positive fit.

Abstract: A piston for an internal combustion engine has an upper and a lower piston part. The upper piston part has a cooling cavity on its underside, and the lower piston part has a ceiling element with a cover hood, which closes off the cooling cavity. The cover hood is securely attached on the ceiling element if the central part of the cover element has an oil drain opening, the top of which is formed as a neck, the upper edge of which neck has a circumferential bead having an underside configured as a circumferential undercut, and if the cover hood has a centrally located opening, the edge of which has slits that are distributed over the circumference and lie radially. The cover hood is attached on the neck so that the sheet-metal tabs are snapped in below the undercut, between the slits, and form a secure snap-in connection with the neck.

Abstract: A multi-part piston for an internal combustion engine has an upper piston part and a lower piston part. The upper piston part and the lower piston part each have an inner and an outer support element, which elements delimit an outer circumferential cooling channel and an inner cooling chamber, whose cooling chamber bottom has an opening. The opening is closed off with a separate closure element, which has at least one cooling oil opening.

Abstract: A piston for an internal combustion engine includes a piston base material including a pair of skirt portions opposed to each other in a radial direction of the piston base material. The piston includes a multiple-layer coating formed on at least one of surfaces of the pair of skirt portions. The piston further includes marks provided to respective layers of the multiple-layer coating at locations different from each other.

Abstract: A double-layer lubrication coating composition is made up of an upper-layer coating composition and a lower-layer coating composition. The upper-layer coating composition is made up of 50 to 70 wt % of an epoxy resin or a polyamide-imide resin, 5 to 20 wt % of boron nitride, and 15 to 30 wt % of silicone nitride or alumina. The lower-layer coating composition is made up of 50 to 70 wt % of an epoxy resin or a polyamide-imide resin, 15 to 30 wt % of polytetrafluoroethylene and 5 to 20 wt % of molybdenum disulfide and may include graphite as required.

Abstract: A piston for an internal combustion engine is disclosed. The piston body has two pin bores for receiving a piston pin. At least one rib is disposed on the second side and extends outwardly therefrom. The at least one rib is aligned laterally between the two pin bores in a direction along the piston pin axis. The at least one rib has a longitudinal axis extending generally perpendicular to both the reciprocation axis of the piston and the piston pin axis. A piston having a boss extending approximately within the piston pin radius of the piston pin axis, and a piston having a boss generally following the contour of the piston pin are also disclosed. An engine having the piston is also disclosed.

Abstract: A piston for an internal combustion engine, has a lower piston part and an upper piston part disposed on the lower piston part. The upper piston part has a top land that runs around its circumference, and a ring belt that runs around its circumference. At least the upper piston part consists of a sintered material.

Abstract: A piston 2 includes a piston upper body 8 made up of a crown portion 3 for receiving combustion pressure and a land portion 7 having piston ring grooves 4, 5, and 6, as well as a skirt portion 9 formed on the lower side of the piston upper body 8, and a pin boss portion 11 for supporting a piston pin 10. The land portion 7 also includes an outer peripheral surface 16 of the aforementioned piston upper body 8. The land portion 7 is referred to as the outer peripheral surface 16 of the piston upper body 8. In the piston 2, reference numeral 12 denotes a thrust side, and reference numeral 13 denotes an anti-thrust side. The piston 2 is formed such that the piston upper body 8 is off-centered toward the anti-thrust side 13 with respect to a center line 14 of the piston 2.

Abstract: A piston seat method and apparatus for a differential-stroke cycle combustion engine, the combustion engine including one or more two-part pistons, each two-part piston having a first piston part and a second piston part. The apparatus comprising: a piston seat cover operatively associated with the first piston part, the piston seat cover being adapted for abutting engagement with the second piston part; wherein, upon abutting engagement, the seat cover is adapted to move relative to the first piston part, thereby at least partially absorbing impact forces applied between the first piston part and the second piston part.

Abstract: A piston-type internal combustion engine is formed of a high performance synthetic resin material. The cylinders and pistons have an octagonal profile. Two or three rows of pin roller bearings are positioned in transverse semi-cylindrical grooves formed on the cylinder walls, to afford smooth, low-friction rolling contact and to seal the compression from leaking around the piston. There are angle support pieces fitted within the annular channels at respective vertices or corners, and are adapted for rotationally supporting the ends of adjacent pin roller bearings.

Abstract: A piston for a direct injection engine is provided, the piston having a bowl at an upper end, the bowl forming a portion of a combustion chamber. The bowl includes an inner surface that defines a volume configured to receive a fuel-air mixture, the inner surface of the bowl including a generally concave portion including a flat bottom surrounding a central protruding dome. The relatively flat bottom portion is bounded by two radial concave surface portions which are disposed below two convex separation features for the injected fuel spray. Such surface geometries may reduce soot and improve fuel-air mixing.