The study aims to investigate the effects of operational parameters such as nozzle opening pressure and fuel injection timing on exhaust emissions of a single cylinder diesel engine fuelled with distilled marine fuels. Tests were performed on a single cylinder, 13 kW, natural aspirated, direct injection and air cooled diesel engine at 1600 RPM constant engine speed. The tests were conducted for three different nozzle opening pressures (20, 22 and 24 MPa) and 3 different nozzle opening pressures (25° bTDC, 20° bTDC and 15° bTDC). The experiments were repeated at least three times to increase the reliability of the results. The results of the study show that increasing nozzle opening pressure increases the BTE and NOx emissions whereas decreases CO emissions, specific fuel consumption and exhaust gas temperature. Advancing fuel injection timing reduces the CO emissions but increases NOx emissions. The paper provides detailed test results, explanations and discussion.