This investigation delivers the results of the study in two dimensions of the influence of the geometry at the entrance of the diffuser of a ramjet engine using the ANSYS-Fluent software. Initially, the isentropic, thermal and gas dynamics flow calculations were performed in order to obtain the ramjet operational parameters; from these results, different geometries at the entrance of the diffuser were proposed, which in this particular case has a central core, whose main function is the generation of oblique shock waves in order to make the diffusion process gradually without generating great amount of losses. The proposed geometries were simulated through the ANSYS -Fluent software in order to know their influence on the isentropic flow behavior. Finally, it was possible to verify that the variation of the wedge angle is given between 7º-14º without affecting the behavior of the ramjet diffuser.