Numerical Simulation of Hybrid Rockets Liquid Injection and Comparison with Experiments

摘要

In this paper, CFX is used to simulate different hybrid rocket configurations applying liquid N_2O as the oxidizer and paraffin wax as the fuel. This work is intended as the prosecution of a previous study about hybrid rockets with diaphragms of different geometries inside the combustion chamber, where N_2O was injected in a gaseous phase. In this work, liquid injection is introduced, together with droplets vaporization and their coupling with the Eulerian gas phase, in terms of both heat and momentum exchange. The main objective is the description of the numerical models to be applied when liquid is injected. To validate computational fluid dynamics output, experimental results coming from a laboratory scale engine have been used. The different geometries studied include an engine with a cylindrical grain having no diaphragm and the same rocket with a four-hole diaphragm at 24% of the grain length. The simulations are steady state, and combustion derives from a single-phase chemical reaction. Liquid injection is fully simulated for the oxidizer, but paraffin entrainment is neglected for the fuel. Computational fluid dynamics results show a good agreement with the corresponding experiments, concerning the ballistic parameters of interest in this study: chamber pressure, efficiency, and characteristic velocity C~*. Computational fluid dynamics predicts (both for gas and liquid injection) a higher efficiency for the rocket geometries provided with a diaphragm compared to the same geometries without a mixing device, and this is in accord with experiments.