The current work aims at assessing the single cylinder, diesel engine fueled with nano-emulsion of orange peel oil biodiesel. The orange oil was elicited from orange peels through solvent extraction method then converted into methyl ester. By using the solvent extraction method, the orange peel oil (Limonene) yield was achieved up to 823%. Later, nanofluid was prepared in two different concentrations by doping 50 and 100 ppm of TiO2 nanoparticles. The orange oil biodiesel nano-emulsions namely OOME-T50 and OOME-T100 were prepared with the proportion of 88% of pure orange oil methyl ester, 10% of TiO2 nanofluid and 2% of span-80 as a surfactant. Experiments were performed with prepared fuels (pure OOME, OOME-T50 and OOME-T100) in a test engine and its results were discussed. The BTE of the engine increased up to 1.4% and 3.0% with OOME OOME-T50 and OOME-T100 fuels when correlated with pure OOME fuel. However, neat diesel fuel indicates maximum BTE at peak load condition. Significant reduction of about 24.2%, 9.7%, 18.4%, 16.0% in smoke, NOx, CO and HC were observed for OOME-T100 nano-emulsion fuel as correlated to pure OOME at peak load. Also, it can be noted that the cylinder peak pressure and heat release rate were increased for OOME nano-emulsion fuels when compared to pure OOME at greatest power output. (C) 2019 Elsevier Ltd. All rights reserved.