Transient Oxygen Droplet Combustion in a Hydrogen Atmosphere: A Numerical Approach
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In liquid rocket propulsion oxygen normally enters the combustion chamber as a dispersed phase, as the hydrogen fuel more rapidly evaporates into a continuous, vapor phase. The foundational configuration considered here is a single liquid oxygen droplet surrounded by gaseous hydrogen. This project employs computational techniques to model the coupled oxidizer/fuel mixing, ignition, and combustion behaviors of the liquid oxygen/gaseous hydrogen system. For simplicity the problem is modeled with spherical symmetry, consistent with microgravity conditions. Conservation equations are implemented within the OpenFOAM platform to calculate species concentrations, temperatures, and heat release rates as functions of time and space. The OpenFOAM software package allows for calculations to be run in a sophisticated run-time environment. Both single-step and six-step chemical reaction models are employed for simulating oxygen-hydrogen combustion. Numerical simulations of both chemical models show diffusion, ignition, and the subsequent formation of three distinct flame zones. These include premixed flames in both the fuel and oxidizer sides of the diffusion flame at the stoichiometric interface. The premixed flame zones weaken as a quasi-steady combustion state is achieved in both cases. The global-chemistry reaction simulation is run until near total consumption of the oxygen occurs. A number of suggestions are presented based off these results for improving future simulation accuracy and efficiency.