Increasingly stringent vehicle pollution requirements, problems related to oil reserves are forcing the use of alternative fuels and additives in vehicles fueled by internal combustion engines. In this paper, was developed a single-cylinder gasoline engine model with port fuel injection. With this model were examined additions of n-butanol (5%, 10% and 15% by volume) to net gasoline and their influence on brake power, exhaust gas temperature, in-cylinder pressure, volumetric efficiency, CO, CO2 and unburned HC emissions.