The mathematical modeling and simulation of an SI engine combustion cycle has contributed for its development, leading to the improvement of the engine purpose to convert the chemical energy of a fuel into mechanical energy through the movement of a piston. The simulation of this models allows the efficiency evaluation of the fuel combustion by generating performance parameters. The Matlab® software, a high-level language and interactive environment, were used for the creation of an add-on based on graphical user interface (GUI), capable of simulating the combustion cycle of a SI engine fuelled by wet ethanol with user-supplied initial parameters. A two-zone model with adaptive heat transfer correlations, including the correlations of Woschni, Hohenberg, Sitkei, Annand and Eichelberg, were implemented for the calculations of the combustion cycle, considering an “unburned” zone, in which the fuel-air mixture has not yet reacted, and a “burned” zone, which consists in the combustion products. The resultant add-on, called ExpEngine (for Experimental Engine), is capable of simulating pressure and temperature gradients as a function of the crank angle, alongside with indicated performance parameters such as IMEP, power, torque, fuel specific consumption, thermal efficiency and volumetric efficiency. The wet ethanol can be set as five different fuel blends: hydrous ethanol fuel (E95W5) and mixtures of ethanol and water in the proportions of 90 % (E90W10), 80% (E80W20), 70 % (E70W30) and 60 % (E60W40) by volume of ethanol.