Steam powered engine

A rotary engine and method having a housing with a bore defining a cavity. A rotatable rotor in the cavity has a plurality of protuberant lobes with respective distal ends moving along the bore. Each of a plurality of vanes has a distal end biased to engage a perimeter of the rotor. The rotor rotates between neutral rotor positions where all of the lobes are simultaneously rotationally aligned with the vanes, and a plurality of different power stroke rotor positions between consecutive neutral rotor positions incrementally increasing in size a like plurality of volumetrically equivalent working fluid expansion chambers that are each in fluid communication with a respective working fluid inlet intersecting the bore and, in turn, incrementally decreasing in size a like plurality of volumetrically equivalent working fluid exhaust chambers each in continuous fluid communication with a respective working fluid outlet intersecting the bore.