Simulation of homogeneous ethanol condensation in supersonic nozzle flows using DSMC

When a liquid rocket engine operates in the space environment, droplets have been observed in the thruster plume that can cause contamination of spacecraft surfaces. Condensation can add to this contamination by contributing to the formation and growth of liquid particles in the flow. The condensation process has been modeled using the direct simulation Monte Carlo method (DSMC). Models have been developed and incorporated into the DSMC code for the processes involved in condensation, which include nucleation, condensation, evaporation, coalescence, and non-sticking collisions. The models are applied to simulate the flow of ethanol in dry air, which has been used to model hydrazine in contamination studies in a vacuum chamber and has been used in several studies of condensation in a supersonic nozzle. Simulations are conducted of the internal flow in the divergent portion of a supersonic nozzle. The results show reasonable agreement with experimental data for the mass fraction of condensed ethanol along the nozzle axis, but the simulations give a lower value in all cases. The simulation results for the point of condensation onset show good agreement with experimental data. The results are shown to be sensitive to the nucleation and evaporation rates, as well as the inclusion of the carrier gas.