An engine is described for operation on a fuel expanding about adiabatically in a power stroke of the engine. To aid the power stroke efficiency, the rotary engine contains one or more of a rotor configured to rotate in a stator, the rotor offset along both an x-axis and a y-axis relative to a center of the stator, a vane configured to span a distance between the rotor and the stator, where the inner wall of the stator further comprises at least one of: a first cut-out in the housing at the initiation of the power stroke, use of a build-up in the housing at the end of the power stroke, and/or use of a second cut-out in the housing at the completion of rotation of the rotor in the engine. The engine yields a cross-sectional area expanding during a portion of the power stroke at about the Fibonacci ratio.