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A combustion chamber construction for opposed-piston engines includes an elongated, bilaterally symmetrical shape referenced to a major axis and a pair of injection ports located on the major axis when the pistons are near respective top center positions. The combustion chamber is defined between a

A combustion chamber construction for opposed-piston engines includes an elongated, bilaterally symmetrical shape referenced to a major axis and a pair of injection ports located on the major 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 a pair of pistons and mirrored ridges protruding from the end surface of a second piston of the pair. 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. The ridge configuration imparts a substantially spherical configuration to a central portion of the combustion chamber where swirling motion of charge air is conserved.

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1. A combustion chamber construction for an opposed-piston engine including at least one cylinder with a bore and longitudinally-separated exhaust and intake ports and a pair of pistons disposed in opposition to one another in the bore of the cylinder, in which: the pistons have shaped end surfaces

1. A combustion chamber construction for an opposed-piston engine including at least one cylinder with a bore and longitudinally-separated exhaust and intake ports and a pair of pistons disposed in opposition to one another in the bore of the cylinder, 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 in the cylinder;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 transitions to respective flanking portions that curve away from the periphery; and,the cylinder includes a pair of 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. 2. The combustion chamber construction of claim 1, in which the central portions of the mirrored ridges define a combustion chamber volume having a substantially spherical or spheroidal shape when the combustion chamber is formed. 3. The combustion chamber construction of claim 2, in which each end surface includes a peripheral edge, an annular surface running inside the peripheral edge, and diametrically-opposed notches formed in the annular surface, wherein the notches on the end surface of the first piston align with the notches on the end surface of the second piston to form the pair of injection ports when the first and second pistons are near the respective top center top center positions. 4. The combustion chamber construction of claim 3, in which the first piston controls the exhaust port and the second piston controls the intake port. 5. The combustion chamber construction of claim 1, in which the first piston controls the exhaust port and the second piston controls the intake port. 6. The combustion chamber construction of claim 1, wherein: the cleft has an elongated, bilaterally symmetrical shape referenced to the plane of symmetry that includes the injection axis of the combustion chamber; andthe bowl in the end surface of the first piston has a concave surface that curves away from a periphery of the piston toward the interior of the piston. 7. 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. 8. The opposed-piston engine of claim 7, in which the central portions of the mirrored ridges define a combustion chamber volume having a substantially spherical or spheroidal shape when the combustion chamber is formed. 9. The opposed-piston engine of claim 8, in which each end surface includes a peripheral edge, an annular surface running inside the peripheral edge, and diametrically-opposed notches formed in the annular surface, wherein the notches on the end surface of the first piston align with the notches on the end surface of the second piston to form the pair of injection ports when the first and second pistons are near the respective top center positions. 10. The opposed-piston engine of claim 9, in which the first piston moves past the exhaust port and the second piston moves past the intake port. 11. The opposed-piston engine of claim 7, in which the first piston moves past the exhaust port and the second piston moves past the intake port. 12. 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; andinjecting fuel into the combustion chamber through the lateral portions. 13. The method of claim 12, in which injecting fuel into the combustion chamber includes injecting the fuel along an injection axis of the combustion chamber. 14. The method of claim 13, in which injecting fuel into the combustion chamber includes injecting opposing sprays of the fuel along the injection axis. 15. The method of claim 12, in which generating tumble includes generating respective counter-rotating tumble motions in the lateral portions of the combustion chamber. 16. The method of claim 15, in which injecting fuel into the combustion chamber includes injecting opposing sprays of fuel along an injection axis of the combustion chamber. 17. The method of claim 12, further including generating opposing inward squish flows of charge air as the combustion chamber is formed. 18. The method of claim 17, in which generating tumble includes generating respective counter-rotating tumble motions in the lateral portions of the combustion chamber. 19. The method of claim 18, in which injecting fuel into the combustion chamber includes injecting the fuel along an injection axis of the combustion chamber. 20. The method of claim 19, in which injecting fuel into the combustion chamber includes injecting opposing sprays of fuel along the injection axis. 21. The method of claim 19, further including igniting the fuel in response to compression of charge air in the combustion chamber.