In this study, optimised ternary fuel blend for diesel, mahua biodiesel, n-heptane/fusel alcohol and engine load are established for improved performance, combustion and emission parameters on a compression ignition (CI) engine by experimental and statistical approach. The diesel-biodiesel blend (30%) with either n-heptane (5%, 10% and 15%) or fusel alcohol (5% and 10%) were studied at engine loads (25%, 50%, 75% and 100%). From L27 engine experiments, predictions and optimisation were done using desirability-based response surface methodology (RSM). The optimal engine parameters were found to be 9.5% n-heptane or 8.4% fusel alcohol along with M30 biodiesel blend at 78.6% and 80.2% load, respectively. The best engine's output parameters generated by considering due weightages based on the implication are peak CP: 71.30 bar, HRR:65.10 J/°CA, BTE :32.71%, BSFC: 0.2383 kg/kWh, CO: 0.0754%, CO2: 8.9%, HC: 63.11 ppm, smoke: 11.43 N, and NOx: 921.54 ppm for 9.5% n-heptane with M30 blend. Validation of the numerical data has been done through actual engine experimental trials. The results suggest that ternary blends will serve as a feasible alternative for CI engines.