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The extremely important objective reducing pollution produced by internal combustion engines in order to prevent further climate changes which threaten all mankind as well as the need to reduce fuel consumption which will ultimately lead to the exhaustion of fossil fuel demand for more efficient combustion processes. Increasing operating pressure and temperature of internal combustion engines is widely known way of enhancing combustion efficiency, this is a trend which has been followed by the large majority of engine manufacturers, extending to all kind of internal combustion engines, from diesel engines to rocket engines. However, as pressure and temperature in the combustion chamber increase, also increases the likelihood of reaching or exceeding the thermodynamic critical point of the working fluids and consequently the process of fuel injection may happen at such conditions. As the critical point is achieved the thermodynamic properties of fuels and oxidizers dramatically change dramatically, and the models once used to calculate internal flows and fuel injection of combustion engines may no longer be accurate. Previous works attempted to evaluate the applicability of a numerical variable density approach, originally developed for the modeling of turbulent, isothermal, gaseous jets, to the study of cryogenic nitrogen jets under transcritical and supercritical conditions. The obtained results proved the potential of such approach. However, this approach didnt take in consideration the real fluid thermodynamics or the heat transfer in the flow. To address these limitations the energy equation as well as real fluid thermodynamics were integrated in the existing numerical approach. were assumed as constants. The approach was employed in the modeling the injection of cold nitrogen through a round injector, into a chamber filed with gaseous nitrogen at supercritical conditions. The results were compared experimental data of Mayer et al. with good agreement.