The paper discusses the issues of the influence of the fuel spray formation on the generation of self-ignition spots and the development of pre-flame processes in the cylinder of a model diesel engine. The investigations were carried out with the use of 8-hole piezoelectric injectors for a standard diesel fuel and three other types of fuel that were mixtures of: ethanol, butanol and gasoline in a variety of proportions. By applying optical methods of analysis the authors determined the geometrical indexes of the forming of fuel spray and of fuel mass distribution in the longitudinal and transverse cross-section of the fuel spray during the injection process. The location and number of the self-ignition spots in the combustion chamber were evaluated on the basis of a comparison under the swirl vs. no swirl conditions.