This thesis project is a combustion modelling study and development of a natural gas engine by means the support of a CFD (Computational Fluid Dynamics) software called CONVERGE. The sophisticated software used introduced a new concept of an automatically mesh generation, useful to save time, with a complex code which can also refine the grid locally basing on particular rules. The project supports an European research, named Gas-on, with the specific aim to reduce the engine emissions trough the usage of alternative fuels, such as methane (CH4) and methane with the addition of percentages of hydrogen (H2), in order to reduce the carbon pollutant generated by engines.