Opposed-piston engine

An opposed-piston engine, comprising:

• a cylinder;
• a one-side piston disposed inside the cylinder on one side in an axial direction;
• and
• an other-side piston disposed inside the cylinder on another side in the axial direction,
• wherein a top surface of the one-side piston has a one-side cavity recessed in a central portion,
• wherein a top surface of the other-side piston has an other-side cavity recessed in a central portion,
• wherein an outer peripheral edge of the one-side cavity is at least 0.1D1 away from an outer peripheral edge of the top surface of the one-side piston over the entire circumference,
• where D1 is a diameter of the top surface of the one-side piston,
• wherein an outer peripheral edge of the other-side cavity is at least 0.1D2 away from an outer peripheral edge of the top surface of the other-side piston over the entire circumference, where D2 is a diameter of the top surface of the other-side piston,
• wherein the one-side piston has a one-side fuel injection groove extending from the outer peripheral edge of the one-side cavity to the outer peripheral edge of the top surface of the one-side piston, and
• wherein the one-side fuel injection groove has a higher groove height on an upstream side in a flow direction of a swirl flow formed inside the cylinder than on a downstream side in the flow direction of the swirl flow.