An internal combustion engine to reduce abrasion with a piston while retaining oil film on an upper portion of a cylinder includes: a cylinder block that includes a cylinder, and a piston that is stored in the cylinder in a manner capable of reciprocating along an axis line of the cylinder, in which the cylinder includes a multi-bulging inner circumference portion in which a diameter in a thrust-anti thrust direction is a minimal diameter.

An internal combustion engine comprising an engine block comprised of a main cavity, an intake plenum, and an exhaust plenum; a crankshaft supported within the main cavity of the engine block; a rotating piston assembly contained within the main cavity of the engine block and comprised of a rotatable cylinder housing having a housing axis of rotation and comprised of a plurality of pistons contained in combustion cylinders; and a rotating valve ring contained within the engine block and surrounding the rotating piston assembly, and comprised of intake ports, ignition energy ports, and exhaust ports corresponding to each of the plurality of combustion cylinders. The rotatable cylinder housing has an axis of rotation that is parallel to and offset from the crankshaft axis of rotation.

An internal combustion engine comprising an engine block comprised of a main cavity, an intake plenum, and an exhaust plenum; a crankshaft supported within the main cavity of the engine block; a rotating piston assembly contained within the main cavity of the engine block and comprised of a rotatable cylinder housing having a housing axis of rotation and comprised of a plurality of pistons contained in combustion cylinders; and a rotating valve ring contained within the engine block and surrounding the rotating piston assembly, and comprised of intake ports, ignition energy ports, and exhaust ports corresponding to each of the plurality of combustion cylinders. The rotatable cylinder housing has an axis of rotation that is parallel to and offset from the crankshaft axis of rotation.