Numerical simulation of filling process of cryogenic propellants with inert gas purge

Abstract

The cryogenic filling process is a complex phenomenon with a combination of thermal and flow transients, especially in the case of inert gas purge during the start-up of liquid rocket engines. A 7-Equation two-fluid model is proposed in this work by adding an extra mass conservation equation for the purging gas compared with the conventional 6-Equation model. And the conservation equations for mass and energy are in the differential form, while the momentum equations are given in quasi-steady state. The model is programmed in Modelica language based on the idea of modular modeling. A two-step rising pressure in the supply system of a real engine shown by the experimental data is also predicted by the model. Then the reason for the pressure surge is analyzed by the numerical results. Finally, the numerical study is carried out to examine the effect of inlet pressure and purging pressure on filling characteristics in the supply system. The results show that within the range of parameter considered, the magnitude of pressure surge in the oxygen dome increases with increase in inlet pressure and purging pressure. The filling rate of liquid oxygen in the dome changes in a positive way with inlet pressure while in a negative way with purging pressure.