Weakly Buoyant Spherical Diffusion Flames: Properties of Hydrogen-CO/Ethylene Flames

Abstract

Flame structure is strongly dependent upon the environment in which the flame is situated, in particular Earth’s gravity. In a microgravity or microbuoyancy environment, natural convection due to the unidirectional gravity vector is largely suppressed. As buoyant effects are minimized, spherical symmetry of a fundamentally spherical phenomenon can be achieved. In particular, spherical flames present a unique opportunity for studying flame phenomena, as the spherical symmetry reduces complexity in analysis and interpretation of the controlling physical processes. In this study, weakly buoyant spherical flames were generated using a low pressure and low density fuel environment and a spherical porous copper burner. Flame testing focused on mixtures of hydrogen and another fuel reacting with diluted oxygen. Ethylene-based fuels were first used, as ethylene is a more complex hydrocarbon than methane and exhibits sooting behavior. Syngas was also explored, for its potential in clean-burning technology. Five fuel mixtures were tested: hydrogen-methane, hydrogen-ethylene, helium-ethylene, nitrogen-ethylene and hydrogen-carbon monoxide. Through observation of flame shape and luminosity, the flames were tested for variations with pressure, oxidizer concentration, fuel concentration and flow rate. Computational studies were also conducted to elucidate experimental results.