Numerical investigation on pressurization behaviors of methane propellant by submerged helium injection

In this article, a three-dimensional numerical model is developed to investigate submerged helium (GHe) pressurization in a methane tank, incorporating turbulent flow, phase change, species transport, and gas-liquid-solid phase heat transfer. The model is validated against experimental data from submerged GHe pressurization tests. A key contribution lies in the systematic quantification of differences between submerged and unsubmerged GHe pressurization processes, alongside the discovery and elucidation of the three-stage characteristics of the submerged GHe pressurization and dominant influential factors governing each stage. Furthermore, parametric investigations into the effects of initial liquid methane (LCH4) temperature (94.5–111.5 K), GHe temperature (268–308 K), and GHe mass flow rate (0.09–0.25 kg/s) on pressurization behaviors are systematically conducted, providing quantitative insights into their impacts. The results reveal that: (i) Compared with unsubmerged pressurization, submerged pressurization results in a lower pressurization rate, average ullage temperature, high-temperature LCH4 volume, and ullage pressure decay rate after pressurization cessation, with reduction of 58.20%, 31.03%, 98.56%, and 53.86%, respectively. (ii) The submerged pressurization process can be divided into three stages: initial, transition, and stable. The dominant influential factors governing pressure variation in these stages are the reduction of ullage volume, the combined effect of ullage heat transfer and GHe injection, and GHe injection alone, respectively. (iii) Increasing the initial LCH4 temperature promotes ullage pressure rise (maximum increase of 34.38%) but significantly increases both the high-temperature LCH4 volume and the evaporation rate (up to 31.36 times and 57.90 times, respectively). Increasing the GHe mass flow rate significantly enhances the ullage pressure rise (maximum increase of 200.13%) but has little effect on the high-temperature LCH4 volume. (iv) The effect of GHe temperature on pressurization behaviors and high-temperature LCH4 volume is negligible. This study provides a valuable theoretical basis for the engineering optimization of submerged GHe pressurization systems in liquid oxygen-methane reusable launch vehicles, contributing to a shorter launch cycle while maintaining propellant quality.