Three-dimensional flow simulations of the full cycle for four-valve direct-injection Diesel engine have been carried out with different meshes. The aim of the present study is to establish an extensive CFD investigation of in-cylinder aero-thermal flow of a direct-injection Diesel engine. The ICE-CFD solver is used to examine the unsteady behavior of a realistic engine configuration. Moreover, a layering approach and dynamic mesh model are adopted to generate the grid. The predicted radial velocity and swirl ratio for four different meshes are compared with Laser Doppler Velocimetry measurements and with numerical results from the literature. The comparison shows that the obtained results with the fine mesh present a good agreement with the experimental measurements along the compression phase and at the start of the expansion phase. In addition, these results are more accurate than the predicted results reported in the literature. Furthermore, CFD analysis is presented for the whole cylinder volume with regard to several parameters such as velocity field, swirling, tumble flow, pressure and temperature distributions. These results prove that in-cylinder CFD simulation gives reasonably accurate results that enable enhanced knowledge of the aero-thermal flow of full engine cycle.