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This study applies L9 orthogonal array of Taguchi design to obtain an optimum combination of oxygenated additive, its blending proportion with diesel and injection timing in a naturally aspirated, direct-injection diesel engine with an objective to achieve maximum reduction in smoke emissions with minimum increase in NOx emissions and minimum decrease in brake thermal efficiency (BTE) at various load conditions. Experiments are designed based on design of experiments (DOE) method to reduce the number of trials. Multi-response signal-to-noise ratio (MRSN) technique is incorporated into the conventional taguchi design to obtain the optimum level of factors according to the set objective. Confirmation experiment is conducted to verify the predicted optimum combination of factors and the results were compared in the same engine operated with baseline diesel fuel injected at its original injection timing. The results indicated that the response variables presented significant improvements with the predicted combination, thus validating the use of Taguchi method in reducing emissions and improving performance simultaneously. Keywords: Diesel engine, Optimisation, Emission control, NOx, Smoke, Taguchi method