The performance and combustion emissions of diesel engine can be modified using various chemical fuel additives. Fuel additives consist of a variety of chemical compounds. It contains chemical elements such as: hydrocarbons, C11-C14, C10-C13, n-alkanes, isoalkanes, cyclics aromatics, cycloalkane, 2-ethylhexyl nitrates. Analysis has been conducted on diesel fuel and diesel fuel and additives blends. Fuel additives No.1, No.2 and No.3 consisting of these chemical elements have been analysed. The obtained results show, that the amounts of carbon monoxide emissions at low engine loads (IMEP = 0.32 MPa) increases up to 35% compared to pure diesel fuel. While using additives, the hydrocarbons emissions at low engine loads almost doubles compared to pure diesel fuel. The break specific fuel consumption with the engine powered by pure diesel fuel was lowest in all modes. The highest increase on in cylinder pressure 11% was only determined with the fuel additive No.3 at the maximum load of 1.12 MPa at the speed of 1800 rpm.