Numerical investigation of the combustion of liquid oxygen droplets in an environment of hydrogen under microgravity conditions

Abstract

To develop more effective and better cryogenic powered liquid rocket engines, it is vital to undertake further studies to better understand the behavior of the LOX/LH2 system. This work studies the configuration of a single liquid oxygen droplet surrounded by gaseous hydrogen diluted with helium. A numerical model using OpenFOAM as well as a coupled droplet evaporation model based on combining OpenFOAM results with the existing theoretical models have been developed to understand the species and temperature profiles near the droplet surface. The coupled droplet model estimates the droplet evaporation rate and droplet lifetime by achieving an energy balance between the calculated heat transfer from the flame to the latent heat associated with the simulated droplet evaporation. To reduce the computational complexity, spherical symmetry is assumed while modelling the droplet, consistent with microgravity conditions. OpenFOAM was employed to solve the conservation equations to calculate species concentrations and temperature profiles. Single-step, four-step, and six-step chemical reaction models were employed for simulating oxygen-hydrogen combustion. The global-chemistry reaction simulation was run until steady-state flame condition was achieved. Based on the numerical simulations for these chemical species, a blowing velocity of 0.0853 m/s for a fuel composition of 30% H2 and 70% He was determined to be optimal parameters as it provides a solution to balancing the evaporation rate with the heat transfer. The temperature gradient was determined using the probe tool in Paraview. Using this as an input to the coupled droplet evaporation model developed using MATLAB, the mass balance equation was satisfied. The droplet lifetime was estimated using the D2 Law. Suggestions are made based off these results for improving future simulation accuracy and efficiency.