This diploma thesis deals with the changes of individual components of the heat balance in the petrol engine with combustion for ethanol fuel. The work is divided into two parts. The first part, the theoretical one deals with the im-pact of the current state of internal combustion engines on the environment and are also dis-cussed alternative fuels. In the second part is described the methodology of experimental measurements, which were carried out on this topic in the engine testing laboratory of Mendel University in Brno. From the obtained values the final heat balance of the petrol engine run-ning on fuel containing ethanol is evaluated and compiled.