Transport effects on flame spread over thick solid fuel beds in microgravity and Earth gravity environments

The effects of radiation heat transfer in microgravity compared to convection heat transfer in Earth gravity for opposed-flow (downward) and the effects of heat and mass transfer for concurrent-flow (upward) over thermally-thick fuel using low density foam fuel were investigated.; Microgravity experiments on flame spread over thermally-thick fuels were conducted using foam fuels to obtain low density and thermal conductivity, and thus large flame spread rate. And thereby valid microgravity results were obtained even in 2.2 second drop-tower experiments. Contrast to the conventional understanding, it was found that steady flame spread can occur over thick fuels in quiescent microgravity environments, especially when radiatively-active diluent gases such as CO2 were employed. This is proposed to result from radiative heat transfer from the flame to the fuel surface, and this radiation effects are more significant at microgravity conditions because the flame is thicker and thus the volume of radiating combustion products is larger as well. These results suggested that helium may be a better inert agent on both a mass and a mole bases at microgravity even though CO 2 is much better on a mole bases at Earth gravity.; In building fires, combustion may occur under poorly ventilated circumstances causing the air to become partially depleted of oxygen and to contain combustible gases such as CO and hydrocarbon. Tests have been done using thermally-thick fuels, and added gaseous fuels help the fuel burn faster than the one without it and the gaseous fuel lowers the extinction limit of the solid thick fuel even it is quite small.; Buoyancy-driven upward flame spread experiments using thermally-thick fuel were conducted. It is of another great practical importance because it is a paradigm for the main mechanism of fire spread in most building fires. Unlike thermally-thin fuel tests using papers, unsteady behaviors such as "hopping," "walking" mode of flame spread was observed for narrow, wider samples respectively. These behaviors were found to occur for a wide range of fuel types and test conditions.