This research study a numerical analysis on the oscillatory flow and temperature distribution inside a gamma type Stirling engine with ideal gas as working fluid. The CFD code used in the investigation for modeling is ESI-CFD. In this study, a 2-D mathematical model is formulated for a full scale gamma-configuration Stirling engine with single and dual power pistons. Variation of time, piston volume with pressure and temperature are presented. The calculated temperature distribution results compare well with experimental results from the other research in our group. Also, a preliminary study for an initial thermal equilibrium porous-media model used in CFD codes for simulation of Stirling regenerators is presented.