The thesis work started during an internship at Leonardo Engineers for Integration Srl. The study was focused on the development and the optimization of a range extender engine, suitable for the use in a hybrid propulsion system. To obtain acceptable results, the optimization has been achieved by the use of simulations. The task of this study is to determine an appropriate working condition of the engine because the problems that can occur are different and it's essential to avoid them. How was a proper engine configuration achieved? The engine, subject of the study, has been considered as a 1-D model using WAVE software developed by Ricardo Software.