Internal combustion engines and methods of operating an internal combustion engine are provided. The engine may include double-ended pistons such that power strokes can be applied to drive the double-ended piston in both directions along the axis along which the piston reciprocates. In some engines, multiple pistons may be connected to a single piston shaft and arranged inline such that the motion thereof is in the same direction at all times along the piston axis of motion. In one engine, the double-ended piston divides a cavity of the engine block or cylinder wall into two separate compression chambers. Each compression chamber has its own fuel inlet. Each fuel inlet is coupled to a different fuel source such that one fuel may be combusted in one of the compression chambers and a different fuel is combusted in the other one of the compression chambers.