A Multidimensional Performance Model of a Spark Ignition Engine Characterized by a Single Step Reaction to Equilibrium Abstract-A new multidimensional model of a spark ignition engine has been developed. The main features of this model are its two-dimensional computational scheme, the assumption of equilibrium conditions for the thermodynamical properties, and the automatic determination of the initial conditions.This approach enables the number of free parameters to be considerably reduced with respect to similar programs currently available, thus ensuring an overall increase in the reliability of the entire computational scheme.