This thesis is the result of a work carried by the candidate within a collaboration project between the Energy department of Politecnico di Torino, and FPT Industrial. The focus of the project is on the renewal of a FPT Heavy Duty Spark Ignition engine concept, evaluating its performance as the fuel whereby it is supplied is switched from compressed natural gas to alternative fuels. Developed in the preliminary phase of the project, the present work deals with the calibration of a 0D entrainment-based combustion model, directly implemented on GT-Power commercial software. For such a purpose, FPT industrial provided a detailed engine model that initially implemented a Wiebe function to model combustion process, calibrated upon 42 engine points spacing 9 ranges of engine revolution speed, and featuring Break Mean Effective Pressure and Spark Advance sweeps for each speed.