An asymmetric complete-expansion thermodynamic engine cycle is provided by an engine which compresses an air/fuel mixture to a given ratio, ignites and combusts the mixture, and expands the products through a power stroke to a volume substantially larger than the compression volume before being vented and purged to the atmosphere. This cycle is performed by a non-axisymmetric main rotor revolving within a cylindrical housing. Sealing means associated with the main rotor provide for the varied compression and expansion volumes. The cylindrical housing also contains means for air intake, fuel injection, venting, and spent gas exhaust porting.