The present study investigates the effect of water emulsion and ZnO nanoparticle on the emissions pattern of a diesel engine running with SB. Test fuels were prepared based on the different percentage of water and mass fractions of nanoparticle, and the emission characteristics were compared with SB. The physicochemical properties were measured based on EN14214 standards, and the characteristics of nano-fuels were examined using SEM, EDS and UV-visible absorption spectrum. Experiments were carried out in a computerized, single-cylinder, four-stroke diesel engine with an eddy current dynamometer. The experimental results reveal that SB20W emulsion fuel promotes a drop of 41.4% and 28.3% in NOx and smoke emissions at BP of 2.56 kW compared to SB, respectively. SB10W emulsion fuel promotes an improvement of 40% and 33.3% in HC and CO emissions compared to SB at 2.56 kW BP, respectively. An inclusion of ZnO nanoparticle in SB20W emulsion fuel significantly reduces the NOx, HC, CO and smoke emissions irrespective of load conditions, and an increase in the mass fraction of nano particle further reduces the emissions level. At 2.56 kW BP, SB20W100ZnO emulsion fuel reduces the NOx, HC, CO and smoke emissions by 7.1%, 40%, 33.3% and 15.1% compared to SB20W emulsion fuel, respectively. (C) 2019 Elsevier Ltd. All rights reserved.