Meso and Micro Scale Propulsion Concepts for Small Spacecraft

摘要

Combustion of liquid nitromethane and RK315A was experimentally studied in a meso-scale combustor with a volume of 108 cubic mm and diameter of 5 mm. The meso-scale combustor utilized a vortex combustion concept, which has been demonstrated to be useful for stabilizing combustion of gaseous hydrocarbon air mixtures in small volumes. The monopropellants were injected tangentially from the backend of the cylindrical combustor and the combustion products exited the chamber tangentially at the other end. Stable and complete combustion of nitromethane was achieved at chamber pressures above 350 psi. The chemical power input was 230W for all the cases investigated. To complement the experiments, a comprehensive numerical analysis was developed to study the combustion of liquid monopropellant in a small-volume vortex chamber based on a two-phase flow analysis using the level-set approach. The model allows for a detailed investigation of the liquid-film motion and gas-phase flow development. In addition, a small scale electrolytic igniter was developed, tested, and found to ignite RK315A. A series of fundamental combustion studies was performed with gaseous micro diffusion flames. For ethylene/air mixtures, these flames had characteristic dimensions of 200-300 micrometers and were found to be momentum driven. Their small size indicates the potential for even smaller combustors than previously studied. Finally, detailed numerical modeling studies on the generation of vortex flows, which are used in the mesoscale combustors, have been performed. These studies have produced a mapping for the conditions required to achieve vortex breakdown as well as the type of vortex breakdown produced. The interactions between combustor flowfield and flame structures are also studied in detail.