In this research the modelling of the reactive sprays process within the compression ignition CI engine combustion chamber is performed. Several engine operating conditions are researched and thoroughly analyzed. Usually, the spray process is modeled with the Euler Lagrangian approach which has limited validity in the dense spray region near the nozzle exit. In the presented research a new method has been developed and used within the 3-D RANS CFD modeling framework. The spray process is modelled with the Euler Eulerian size-of-classes model used for reliable interphase momentum transfer. Furthermore, the combustion process is modelled by taking into account chemical kinetics solving the general gas phase reaction equations. The new method is incorporated into the commercial Computational Fluid Dynamics (CFD) code FIRE®, and it was used in combination with the previously validated spray sub-models. The results are extensively validated against the available experimental data, and a very good agreement of the mean pressure, temperature, rate of heat release and ignition delay trends are achieved. The compared results imply that the developed method is suitable for modeling various engineering applications where reactive multiphase processes occurs.