The project is aimed at the development of an accurate and efficient CFD model of the 1.4 liter CNG engine in CONVERGE, by means of thorough calibration and validation against the experimental data available at Politecnico di Torino. The project is focused on the combustion simulation by using the SAGE detailed chemistry model, coupled to a suitable reaction mechanism among some found in literature. The different mechanisms are validated with experimental data found in literature for the matter of ignition delay and laminar flame speed, and compared as part of engine simulations, under several mesh settings and fuels. Mechanisms reduction (both dynamic and through Chemistry Module) is also carried out.