The present study attempts to study the influences of piston geometry, butanol fumigation, EGR, injection pressure and injection timing upon the performance and emissions of a light-duty DI diesel engine fuelled with diesel, Jatropha methyl ester (JME) and 20% by voL of n-butanol/diesel blends. Experiments were designed based on Taguchi L-18 orthogonal array that considered main fuel injection timing, EGR, premixing ratio of n-butanol with diesel, injection pressure, secondary injection timing, piston geometry, main injection fuel and secondary injection fuel as factors and NOx emission, smoke opacity and BSFC as responses. The best combination of the above factor levels were predicted by using desirability function. Results indicated that B20 injected at 20 degrees CA bTDC with an injection pressure of 200 bar under 10% EGR alongside 40% by vol. of butanol/diesel fumigation with a premixing ratio of 20% at 9 degrees CA aTDC in the engine fitted with a torroidal piston was predicted to deliver 359.13 ppm of NOx emissions, 74.83% of smoke opacity with 1.127kg/kWh of BSFC. The tests revealed that the predictions by using desirability function were within a reasonable accuracy of 10%. (C) 2019 Elsevier Ltd. All rights reserved.