Abstract Calophyllum inophyllum biodiesel is seems to be a potential alternative fuel for diesel engine applications due to its non-edible form, easily cultivable nature and abundant availability everywhere in the world. Isobutanol is the next generation biofuel which can be used as partial substitute to petroleum diesel or biodiesel due to its better solvency character. In the present study, a comparative assessment on diesel engine characteristics is carried out using isobutanol as an additive with diesel and biodiesel in the form of binary and ternary blends. Five blends are prepared by 20% of isobutanol with diesel and biodiesel as D80IB20 and B80IB20 along with three ternary blends of diesel-biodiesel-isobutanol using 10%, 15% and 20% concentrations of isobutanol. Experimental study in a diesel engine revealed that the brake thermal efficiency is improved by 3.19% for 10% isobutanol addition in diesel-biodiesel blends with significant improvement in brake specific fuel consumption when compared to biodiesel. All binary and ternary blends of isobutanol reduce CO emission by 13–59% than that of diesel fuel with substantial penalty in HC emission. Meanwhile, when compared to biodiesel, the oxides of nitrogen emission is decreased by 8.16% for isobutanol addition with diesel and biodiesel in terms of binary and ternary blends but higher than that of conventional diesel fuel. Furthermore, momentous improvement is observed in heat release rate during isobutanol addition for B80IB20, D70B10IB20, D70B15IB15 and D70B20IB10 fuel blends when compared to pure biodiesel. Finally, it is noted that isobutanol would be a feasible additive for the partial replacement of diesel and biodiesel in the blends for diesel engine applications.