An epitrochoidal Stirling type engine operating on a Carnot cycle. The engine has a hot end and a cool end. Each end has a three-lobed rotary piston or rotor eccentrically mounted. Each rotor is in a four-lobed housing. There are connections for fluid flow between pairs of lobes with regenerators in the connections. The thermodynamic cycle corresponds to that of the Stirling engine. Heat is applied to one end of the engine and heat is discharged at the other end. As each rotor moves in and out of the housing lobes, a hydrodynamic fluid film of gas is produced between the rotor and the housing which keeps the rotor from contacting the housing.