Li−SF 6 combustion in stored chemical energy propulsion systems

Abstract

Appropriate thermodynamic models and thermo-chemical data for multicomponents and immiscible phases have been incorporated into a code for the computation of chemical equilibrium of the reactants used in a stored chemical energy propulsion system. The reactants considered are molten lithium fuel and gaseous sulfur hexafluoride oxidant. Extensive equilibrium state relationships as a function of mixture fraction have been presented over a temperature range of possible operating conditions. They were subsequently employed to predict the complex flow structure of a choked, turbulent, reacting SF6 gas jet submerged in a molten lithium bath. Detailed profiles of velocity, temperature, void fraction and mass fraction of all phases in the jet have been presented. The results show that the reaction is completed within a short distance from the injector but the plume jet penetrates farther beyond due to significant evaporation of lithium fuel in the hot temperature plume, and subsequent condensation of the evaporated fuel and reaction products in the later part of the plume. The effect of lithium subcooling on flow structure has also been examined. It is found that lowering the degree of subcooling by raising the fuel bath temperature increases fuel evaporation, decreases the entrainment rate, delays the completion of reaction and lengthens greatly the jet penetration distance. Finally, for practical use, a simple correlation of the jet penetration length as a function of subcooling has also been presented.