Optimal fuel utilization in internal combustion engines plays a key role in improving fuel economy, reducing emissions, and consequently mitigating environmental impacts. In this study, the combustion chamber geometry of a common-rail diesel engine is optimized with the aim of lowering fuel consumption and exhaust emissions while maintaining the engine’s current power output. For this purpose, a closed-cycle engine model was first developed in AVL FIRE software and validated at an operating speed of 2000 rpm. During the optimization process, ISFC, NOx, and Soot were defined as the main objective functions. The geometric parameters of the piston bowl, with specified upper and lower bounds, were used as inputs to the multi-objective genetic algorithm (MOGA). CFD outputs, including NOx and Soot levels for each design configuration, were evaluated, and the variations of emissions throughout the optimization process were analyzed. A total of 240 design cases were generated by the algorithm. Among the five initially selected designs, two were discarded due to power reduction. From the remaining three designs, one was finally chosen. In this selected case, Soot and ISFC changes were negligible; ISFC increased by only 0.052%, which is almost identical to the baseline, whereas NOx emissions were reduced by approximately 2%. Overall, the optimization process resulted in a piston bowl design that produces the lowest NOx and Soot emissions while maintaining fuel consumption close to that of the baseline combustion chamber.