Swirl-conserving combustion chamber construction for opposed-piston engines

An opposed-piston engine, comprising:

• at least one cylinder with longitudinally-separated exhaust and intake ports;
• a pair of pistons disposed in opposition to one another in a bore of the cylinder, each piston operable to move from a respective bottom center (BC) position to a respective top center (TC) position in the bore during a compression stroke, in which:
• the pistons have shaped end surfaces that form a combustion chamber having an elongated, bilaterally symmetrical shape referenced to a plane of symmetry that includes an injection axis of the combustion chamber and a pair of injection ports located on the injection axis when the pistons are near respective top center positions;
• the combustion chamber is defined between a bowl in the end surface of a first piston of the pair of pistons and a generally convex portion of the end surface of a second piston of the pair of pistons that comprises outwardly protruding mirrored ridges and a cleft between the outwardly protruding mirrored ridges, as the bowl in the end surface of the first piston receives the convex portion and covers the cleft;
• when the end surface of the second piston is viewed in plan, each ridge includes a central portion that curves toward a periphery of the end surface of the second piston and which transitions to flanking portions that curve away from the periphery;
• and,
• the cylinder includes a pair of diametrically opposed fuel injector ports with which the injection ports of the combustion chamber align when the first and second pistons are near the respective top center positions.

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 the pistons;
• moving the pistons toward each other in a compression stroke;
• forming a combustion chamber between a bowl formed in a first piston of the pair of pistons and a generally convex portion of the end surface of a second piston of the pair of pistons that comprises outwardly protruding mirrored ridges and a cleft between the outwardly protruding mirrored ridges, as the bowl in the end surface of the first piston receives the convex portion and covers the cleft;
• concentrating swirling charge air in a central, partially spherical portion of the combustion chamber between the end surfaces of the pistons as the pistons move toward respective top center positions in the bore;
• generating tumble in charge air in respective lateral portions of the combustion chamber;
• and
• injecting fuel into the combustion chamber through the lateral portions.