Numerical Simulation of Liquid Oxygen Droplet Combustion in Hydrogen under Microgravity Conditions

Abstract

This work presents an efficiently lean, custom-built numerical simulator developed to study the combustion of a liquid oxygen (LOX) droplet combusting in Hydrogen gas (H2) under microgravity conditions. Motivated by drop-tower tests conducted at ZARM (The Center for Applied Space Research and Microgravitation) in Bremen, Germany, the quasi-static evaporation framework reproduces key coupled processes– flame dynamics, Stefan flow, droplet regression, and surface ice formation– within a computationally minimalist yet physically faithful model. The governing reaction-diffusion equations were solved using finite-difference methods incorporating time-dependent, spatially homogeneous Stefan velocity fields generated by real-time evaporative feedback from the flame. The simulation achieves strong quantitative agreement with experimental and computational benchmarks, reproducing flame stand-off ratios (F/D ≈ 2–3.5) and peak adiabatic flame temperatures (Tpeak ≈ 3000 K) consistent with previous work. Diffusive heat transfer dominates the total energetic flux, contributing 80–85% of the total heat input (Qmax ≈ 0.3–0.5 W), while radiative effects remain secondary, in accordance with previous estimates. Parametric sweeps over surface ice coverage fraction ψ reveal compensating feedback between evaporative impedance and geometric flame shape contraction. A single predominant global reaction mechanism, augmented by equilibrium radical generation at the reactive flame front, suffices to reproduce thin flame-sheet behavior within the high-Damkoehler limit. The resulting simulator balances interpretability, stability, and physical fidelity, requiring no HPC infrastructure and running interactively accessibly in Google Colab. Beyond LOX–H2 combustion, this framework offers a transparent, extensible platform for general coupled parabolic PDEs, bridging the gap between high-overhead CFD and simplistic static equilibrium tools.