Nowadays, the research and development activities performed in the area of internal combustion engines are focused on the LTC technologies, especially on the HCCI technology. It is so because these innovative technologies are characterized by high operational efficiency as well as by low emissions of nitrogen oxides (NOX) and particulate matter (PM). The combustion process LTC is able to utilize various fuels. The kind of fuel, together with its physical and chemical properties have a major influence on engine power output and gaseous emissions. The presented scientific contribution deals with analysis of an experimental engine operating with the HCCI combustion, specifically it deals with operational influences of several selected fuel mixtures. There is investigated an influence of the fuel mixtures, which consist of different components with various properties, on the engine power output and on the gaseous emissions. These experimentally applied fuels were created as the mixtures of isooctane and n-heptane using different mixing ratios. The obtained results offer a global view on a real effect of the fuel components applied in the fuel mixtures.