There is provided a combustion engine and an electric generator. The combustion engine comprises an engine housing, a cylindrical member configured to rotate about an axis within a cavity of the engine housing, a piston, and an engagement section for engaging the piston. The piston is mounted to the engine housing and the engagement section is mounted to the cylindrical member, or the piston is mounted to the cylindrical member and the engagement section is mounted to the engine housing, such that the piston and the engagement section periodically rotate past one another as the cylindrical member is rotated within the engine housing. The piston engages the engagement section as they rotate past one another, the engagement forcing the piston to compress gases in a combustion chamber, which fire to drive the rotation of the cylindrical member. The electric generator may be driven by the combustion engine.