Green propellants are the future of in-orbit rocket engines, a promising combination is cryogenic oxygen and methane. Due to a required active ignition of this combination, the understanding of the cold flow mixture is very important. Reliable ignition is absolutely critical for achieving the respective mission goals. Low initial pressures lead to flash evaporation inside the injector as well as spray flash evaporation in the combustion chamber. A valuable tool for the development and understanding are numerical simulations. This work presents the development of two different numerical methods, in order to describe the flash evaporation of cryogenics inside the injector and of the superheated spray in the chamber. Implementation of the flash evaporation inside the injector into a CFD-solver is based on the Homogeneous Relaxation Model. The inter-phase heat transfer plays an important role, the results show that the implemented methods can adequately describe this phenomenon including the increased evaporation time-scale in these thermal non-equilibrium flows. The achievable mass flow is strongly effected by the evaporation due to a choking of the nozzle. The simulation results show an excellent agreement with a corresponding experiment, it fails however for very short nozzles with a sharp inlet due to different flow characteristics not taken into account by the models. A comparison with a classical cavitation model shows, that the thermal effects can not be neglected, since the cavitation model cannot predict the correct mass flow. The implementation of the droplet flash evaporation model for spray calculations is based on the Adachi correlation. Results reproduce the typical bowl-shaped spray. Spray angle and width agree with a reference experiment, an excellent agreement can be achieved with temperature measurements along the centerline. A second test case studies the addition of a highly underexpanded coaxially injected gaseous methane jet. The supersonic methane leads to containment of the spray and results in delayed flashing and jet breakup. Although the chamber pressure rise is underpredicted the resulting spray agrees well with the experiment. The developed methods therefore allow the computation and characterization of flashing for cryogenic liquid propellants in in-orbit rocket engines.    «

Green propellants are the future of in-orbit rocket engines, a promising combination is cryogenic oxygen and methane. Due to a required active ignition of this combination, the understanding of the cold flow mixture is very important. Reliable ignition is absolutely critical for achieving the respective mission goals. Low initial pressures lead to flash evaporation inside the injector as well as spray flash evaporation in the combustion chamber. A valuable tool for the development and understand...    »