This thesis presents a new bowl-in piston design, called "Double Step", for the combustion chamber of a light-duty Diesel engine and its analysis through a three-dimensional Computational Fluid Dynamics (3D-CFD) study. The case study was developed in collaboration with Stellantis, which provided all the experimental data obtained from engine test bench activities necessary to set up the study. The primary aim of this work is to investigate and understand how the new bowl geometry influences in-cylinder turbulence, engine efficiency, and pollutant emissions compared to the baseline design. A secondary objective is the development of a set of prototype pistons based on the new geometry and the evaluation of their performance through engine dynamometer testing.