The present experimental work aims at investigating the effect of zinc oxide and titanium dioxide nanoparticles addition in Calophyllum inophyllum biodiesel in twin cylinder water cooled direct injection four stroke diesel engine. The nanofluids have been prepared from 50 ppm and 100 ppm concentrations of titanium dioxide and zinc oxide with distilled water through ulrasonication process. Four different Calophyllum inophyllum nano emulsions have been prepared with the proportions of 93% of Calophyllum inophyllum biodiesel, 5% of nanofluids of zinc oxide and titanium dioxide and 2% of span 80 using mechanical stirrer. The compression ignition engine characteristics were examined with all four Calophyllum inophyllum nano emulsions and the results were compared with conventional diesel and pure Calophyllum inophyllum biodiesel under various engine loads. The diesel engine operation with CIME nano emulsions improves brake thermal efficiency by 5-17% compared to pure CIME fuel at maximum brake power due to large surface to volume ratio of nanoparticles which exhibit rapid evaporation and better atomization. Further, the CO and HC emissions were reduced drastically for CIME nano emulsions compared to pure biodiesel and conventional diesel fuel. The NOx emission was lower than pure Calophyllum inophyllum biodiesel for all CIME nano emulsions but slightly higher than conventional diesel fuel. The smoke emission of diesel engine was reduced drastically for all CIME nano emulsions compared to both pure biodiesel and diesel fuels at all engine loads. Combustion characteristics of in cylinder gas pressure and heat release rate were increased by the addition of nano particles with pure Calophyllum inophyllum at all engine loads. Finally, it can be observed that the doping of nano particles with biodiesel has a very good effect on performance characteristics with notable improvement in performances and minimum emissions. (C) 2017 Elsevier Ltd. All rights reserved.