The ornamental design for an internal-combustion engine, as shown and described.
FIG. 1 is a front view of an internal-combustion engine.
FIG. 2 is a back view of the internal-combustion engine.
FIG. 3 is a left view of the internal-combustion engine.
FIG. 4 is a right view of the internal-combustion engine.
FIG. 5 is a top view of the internal-combustion engine; and
FIG. 6 is a perspective view of the internal-combustion engine.
The broken line showing portions of an engine is included for the purpose of illustrating environmental structure and forms no part of the claimed design.