A combustion chamber for an opposed-piston engine has a rotationally skewed shape in a longitudinal section that is orthogonal to a chamber centerline, between diametrically-opposed openings of the combustion chamber through which fuel is injected. The rotationally skewed shape interacts with swirl to generate a tumble bulk charge air motion structure that increases turbulence.

A piston with an improved bowl geometry includes a piston body having a generally planar crown and a skirt extending from the crown. An oval or multi-lobed bowl rim of a combustion bowl that is recessed in the crown so that the sides of the bowl rim are provided with increased material to resist fatigue along the pin plane, optionally along the thrust/antithrust plane and generally optionally along other planes between the pin plane and the thrust/antithrust plane.

A reentrant combustion chamber is disclosed. The reentrant combustion chamber includes a profile forming the inlet of the combustion chamber that is a projective surface formed inward in the combustion chamber and the bottom of the combustion chamber that is a recessed space that is recessed outward under the inlet in the combustion chamber, a cone formed in a truncated cone shape continuing from the profile and protruding to the central space in the combustion chamber, and a top end for expanding the space of the combustion chamber by expanding the top of the combustion chamber at the inlet of the combustion chamber.

An internal combustion engine comprises a fuel injector 31, a spark plug 16, a piston 14 having a cavity 91, a swirl control device 95, and a control system 70. The cavity is formed so as to change in distance from the fuel injector to a side wall surface of the cavity, in the circumferential direction. The system performs ignition assist control for successively performing injections of main fuel and ignition assist fuel, makes an air-fuel mixture formed by the ignition assist fuel burn by flame propagation by the spark plug, and makes the remaining fuel burn by pre-mix compression self-ignition. The system controls the swirl control device during the ignition assist control so that when the engine load is high, the fuel sprayed heads toward parts of the side wall surface which are short in distances from the fuel injector.

A piston with an improved bowl geometry includes a piston body having a generally planar crown and a skirt extending from the crown. An oval or multi-lobed bowl rim of a combustion bowl that is recessed in the crown so that the sides of the bowl rim are provided with increased material to resist fatigue along the pin plane, optionally along the thrust/antithrust plane and generally optionally along other planes between the pin plane and the thrust/antithrust plane.

A piston crown is provided for a piston in an internal combustion engine arrangement that includes a cylinder, the piston crown having a piston bowl surface adapted for facing a combustion chamber in the cylinder, wherein the piston bowl surface including a circumferential rim portion, a floor portion connected to and surrounded by the circumferential rim portion, a plurality of circumferentially spaced protrusions in the circumferential rim portion, at least one spray impingement portion, located between two adjacent protrusions. The spray impingement portion includes a reflection surface, being defined by that each possible normal to the reflection surface is directed towards a central axis of the piston, and forming an angle being within a range of a constant angle 10 with the central axis, wherein the constant angle is at least 50.

A piston may include an outer peripheral surface and a crown. The outer peripheral surface may include first and second openings spaced about and extending through the outer peripheral surface. The crown may include a recess at least partially defined by a first lobe in fluid communication with the first opening and a second lobe in fluid communication with the second opening. Each of the first and second lobes may be recessed relative to an adjacent portion of the recess of the crown.

Cooperatively shaped piston and cylinder head arrangements for internal combustion engines are disclosed. The piston may have a domed head with one or more curved exhaust channels and inlet channels formed therein. The piston cylinder may have curved surfaces that are exact or close inverse or negative counterparts to the curved surfaces of all or part of the domed head, including the exhaust channels, and/or inlet channels formed on the piston.

A piston has a piston crown portion forming at least one arcuate indent in aligned fashion with a fuel jet discharged into a combustion chamber. Each arcuate event forms lobes, which separate the fuel jet into portions, or is tiered, to accommodate fuel jet portions being discharged into the combustion chamber at different times. Each lobe or tier includes an entry surface, a recirculation surface and a wall to separate it from adjacent lobes or tiers, respectively.

An opposed piston engine may include a first housing, first and second pistons, and first, second, and third fuel injector nozzles. The first housing may define a first passage extending along a first longitudinal axis. The first and second pistons may be slidably disposed within the first passage. The first, second, and third fuel injector nozzles may be in fluid communication with the first passage. At least one of the first, second, and third fuel injector nozzles may be angularly offset from another one of the first, second, and third fuel injector nozzles by an oblique angle about the first longitudinal axis.