The developments in the field of nano-additives have increased in the recent years due to the desire to reduce the level of exhaust emissions in diesel engines. The soot characteristics of particulate matter (PM) and nitrogen oxides (NO_X) were experimentally investigated using two concentrations of titanium dioxide (TiO₂) as nano-additives (25 ppm and 40 ppm) blended with C20D (composed of 20% castor oil methyl ester and 80% diesel fuel) and 30% exhaust gas recirculation (EGR). The combustion of C20D + TiO₂ increases brake thermal efficiency (BTE) by 2.8% in comparison with neat C20D, while a significant reduction was obtained in BSFC 6.5% and NO_X emissions were maintained at a level parallel with diesel. The results indicated that the technique involving a high EGR rate and the addition of 25 ppm and 40 ppm of TiO₂ nanoparticles to the C20D exhibits better reductions in NO_X emissions by 17.34% and 21.83%, respectively, compared to the technique comprising the use of C20D + TiO₂ and C20D. The reduction in the total concentration of PM via the addition of TiO₂ nanoparticles to the C20D was 26.74% greater than neat C20D and diesel. In contrast, the incorporation of a high rate of EGR with C20D +TiO₂ increased the PM concentrations by 16.85% compared to the technique without EGR. Furthermore, the high concentrations of TiO₂ nanoparticles (40 ppm) in the C20D produced 19 nm smaller soot nanoparticles compared to the 23 nm larger soot nanoparticles produced from the low concentrations of TiO₂ nanoparticles (25 ppm) added into the C20D. The current investigation reveals that the reduction in NO_X emissions and the production of soot nanoparticles notably improved due to the synergic effect of EGR, the TiO₂ nanoparticles, and biodiesel.