Asymmetrically-Shaped Combustion Chamber For Opposed-Piston Engines

A two-stroke, direct injection, opposed-piston engine including a cylinder with a bore, piston-controlled exhaust and intake ports near respective ends of the cylinder, and a pair of pistons disposed in opposition in the bore, in which each piston has a crown with an end surface and a sidewall, the end surface and sidewall meeting at a circular peripheral edge centered on an axis of the piston, and the end surface defining a combustion chamber in the cylinder bore with the end face of the other piston when the pistons are near top center locations in the bore;

• wherein,
• the combustion chamber has an asymmetrical shape defined between first and second end surface ridges positioned on either side of a chamber centerline that extends between diametrically opposing points of the bore;
• the asymmetrical shape includes a maximum distance R1 from the chamber centerline to one side of the combustion chamber;
• R1 is positioned a distance L along the chamber centerline on either side of a centerline midpoint;
• and,
• the asymmetrical shape has polar symmetry with respect to a point on a longitudinal axis of the bore in a plane that is transversel to the longitudinal axis and that bisects the combustion chamber.

A piston for an opposed-piston engine, the piston including a longitudinal axis and comprising:

• an end surface having a shape that defines a combustion chamber with the end surface of an opposing piston in a cylinder bore of the opposed-piston engine;
• a circular sidewall centered on the piston axis and extending from the end surface;
• a circular peripheral edge where the sidewall meets the end surface;
• notches in the peripheral edge at respective ends of a diameter of the peripheral edge, through which fuel is injected into the combustion chamber;
• and,
• the shape of the end surface includes at least one elongated ridge that extends between the notches and projects through a reference plane that is transverse to the longitudinal axis and contains the peripheral edge;
• the elongated ridge including an outer wall that faces the peripheral edge and an inner wall that faces the diameter;
• in which the inner wall of the ridge is asymmetrically curved in the plane of reference with respect to the diameter of the periphery;
• and,
• in which the curvature of the inner wall in the plane of reference is polar-symmetric with the curvature of an inner wall of an opposing ridge.

A piston for an opposed-piston engine, in which the piston has a cylindrical sidewall centered on a longitudinal axis and a crown with an end surface including a peripheral edge where the sidewall meets the end surface, comprising:

• the end surface including opposed curved ridges that is surrounded by the peripheral edge and that protrude outwardly away from the crown through a cut plane that is transverse to the longitudinal axis of the piston and contains the peripheral edge;
• each curved ridge including an inner wall that transitions to an elongated cleft in the end surface that extends along a diameter of the piston between opposed notches that are aligned with the diameter and that open through the peripheral edge into respective ends of the cleft;
• the cleft having an asymmetrical shape with respect to the diameter that includes a maximum distance R1 from the diameter to each inner wall, in which R1 is positioned a distance L along the diameter on either side of the longitudinal axis:
• and
• the curvature of each inner wall in the plane of reference being polar-symmetric with the curvature of the other inner wall.

A piston for an opposed-piston engine, in which the piston has a cylindrical sidewall centered on a longitudinal axis and a crown with an end surface including a peripheral edge where the sidewall meets the end surface, comprising:

• the end surface including a curved ridge that is surrounded by the peripheral edge and that protrudes outwardly away from the crown through a cut plane that is transverse to the longitudinal axis of the piston and contains the peripheral edge;
• the curved ridge including an inner wall that transitions to an elongated trench in the end surface that extends along a diameter of the piston between opposed notches that are aligned with the diameter and that open through the peripheral edge into respective ends of the trench;
• and,
• the trench having an asymmetrical shape with respect to the diameter that includes a maximum distance R1 from the diameter to the inner wall, in which R1 is positioned a distance L along the diameter on either side of the longitudinal axis.

A method for operating an opposed-piston engine including a cylinder, a pair of opposed pistons in the bore of the cylinder and spaced-apart intake and exhaust ports controlled by the pistons, by:

• introducing swirling charge air into the cylinder between end surfaces of the pistons;
• moving the pistons toward each other in a compression stroke;
• forming a combustion chamber between end surfaces of the pistons, the combustion chamber having an asymmetrical shape with respect to a chamber centerline that extends between diametrically opposing openings of the combustion chamber, wherein the asymmetrical shape includes a maximum distance R1 from the chamber centerline to one side of the combustion chamber, R1 is positioned a distance L along the chamber centerline on either side of a midpoint of the centerline, and the asymmetrical shape is polar symmetric with respect to the midpoint;
• and,
• injecting opposing spray patterns of fuel into swirling charge air in the combustion chamber through the opposing openings.