One of the most important features of the biodiesel fuels to be used in diesel engines is decreasing engine emissions. In the present research, the emissions of an OM 924 Diesel Engine were modeled based on the response surface methodology under the effects of alga biodiesel as well as engine load and rotational speed to find the minimum of those amounts. The obtained quadratic models to predict the effect of input variables on the response surface were statistically significant at 1 % probability level. The amount of CO and HC emissions decreased by increasing the biodiesel percentage compared to that of pure diesel fuel. Biodiesel percentage of 65.6 and 62.6 % were the best blends in terms of minimizing CO and HC emissions, respectively. By increasing the percentage of biodiesel in the blended fuels, CO2 and NOX emissions increased and the lowest amounts of those were observed for pure diesel fuel and B6, respectively. Also, an increase in biodiesel percentage in the blended fuels caused to decrease in smoke opacity and high biodiesel percentages were the best in terms of minimizing smoke opacity. The results of multi-objective optimization showed that the lowest CO, CO2, HC, NOX, and smoke opacity emissions happened for 66.6 % biodiesel at the engine load and rotational speed of 36.9 % and 1527 RPM, respectively.
