A 2D Stirling engine numerical model that includes the expansion space, heater, regenerator, cooler, simplified “spider” and compression space was studied. Two 2D Stirling engine models were examined for different boundary conditions: One is the wall boundary without thickness or heat capacity, and one is wall boundary with thickness and heat capacity around the engine. The model dimensions were scaled from the STC 55 W Stirling engine. No experimental results were available for this scaled engine. The simulation results were examined to avoid round-off error, temporal discretization error and grid independence. The comparison between the 2D numerical simulation results and 1D model simulation results show some agreement for several major parameters. 2D-model for three different amplitudes of power piston were also simulated and simulation results for power output show same trend with the experimental results of STC 55 W Stirling engine. This investigation provided helpful information for future work on Stirling engine numerical model development. The studies also indicated that the numerical model for porous media (regenerator section of Stirling engine) needed improvement for accurately modeling the oscillatory flow and heat transfer in a Stirling engine regenerator section.