The present research work aims at investigating the effect of newly developed multifunctional additive with diesel and Calophyllum Inophyllum biodiesel on compression ignition engine characteristics. A newly developed hydrocarbon based multifunctional fuel additive named as “Thermol-D” which comprises of various ingredients at suitable composition like surfactant, demulsifier, lubricity enhancer, dispersant, cetane improver, antioxidant and combustion catalyst. In this present study, the Thermol-D has been doped with conventional diesel and Calophyllum Inophyllum biodiesel at 0.5 ml, 1 ml and 2 ml concentrations. Moreover, the Thermol-D addition with diesel and biodiesel has shown remarkable stability at all concentrations without any phase separation issues. All the fuel comparative analysis is carried out using all the fuel samples at same operating conditions under load variation from No load to full load at constant engine speed. It has been noticed that the doping of Thermol-D with diesel and biodiesel has increased the brake thermal efficiency by 21% and 43% at 100% loading conditions due to the presence of combustion catalyst and cetane improver in the additive. The multifunctional additive presence in the fuel blends is reduced the carbon monoxide and unburnt hydrocarbon emissions by 32–36% and 20% respectively. Furthermore, the oxides of nitrogen emission has also reduced at significant rate in the range of 18–20.5% for 2% Thermol-D addition with diesel and biodiesel. The Thermol-D contains slight fraction of antioxidant and cetane improvers which has resulted in combustion temperature. All the combustion characteristics are improved by the addition of Thermol-D with diesel and biodiesel. © 2020 Elsevier Ltd