Computational Realization of Popping Impinging Sprays of Hypergolic Bipropellants by a Eulerian-Lagrangian Approach

Abstract

This work adopts a Eulerian-Lagrangian approach to simulate the spray impingement of MMH (Monomethyl hydrazine)/NTO (nitrogen tetroxide), which are prevalent rocket engine bipropellants for deep space missions and satellite orbital maneuvers. The emphasis of this work is to computationally realize the popping phenomenon and to study its parametric dependence on liquid and gas-phase reaction rates. The liquid-phase reaction of MMH/NTO is realized based on the extended spray equation, incorporating the additional independent variable, propellant mass fraction, to account for the mixing droplets. The popping can be reproduced over wide ranges of Damköhler numbers for both liquid- and gas-phase reactions. Furthermore, the computational results have been validated through qualitative comparison with experimental images and quantitative comparison with experimental frequencies. The present results verify our hypothesis that the heat release from the liquid-phase reaction enhances the evaporation so that the intense gas-phase reaction zone around the impingement point periodically separates the sprays to cause the popping phenomenon. This phenomenon can be suppressed by reducing the Damköhler numbers of liquid-phase reaction and therefore to suppress the evaporation. This work provides valuable understanding for avoiding the off-design popping phenomenon that may reduce combustion efficiency and increase the risk of combustion instability in rocket engines.

Keywords: Hypergolic Bipropellants, Monomethylhydrazine, Nitrogen tetroxide, Spray equation, Popping phenomenon