Radiative extinction of gaseous spherical diffusion flames in microgravity

Extinguishing flames were considered experimentally and numerically. The experiments involved microgravity spherical diffusion flames burning ethylene and propane at 0.98 bar. Both normal and inverse flames were considered, with nitrogen supplied in either the fuel or the oxidizer. Flames were observed that ignited and extinguished within the 2.2 s available test time. Diagnostics included color video and thin-filament pyrometry. The computations simulate flow from a porous sphere into a quiescent environment, include detailed chemistry, transport and radiation, and yield both steady-state and transient results. Transient radiative extinction was observed and modeled. Extinction time, peak temperature, and radiative loss fraction were found to be independent of flowrate except at low flowrate. Radiative heat losses were found to be dominated by combustion products outside the flames and to scale with flame surface area.