On the effects of opposed flow conditions on non-buoyant flames spreading over polyethylene-coated wires – Part II: Soot oxidation quenching and smoke release

Smoke release in the limited volume of a spaceship poses a major threat to the life of astronauts in long range exploration missions. If the absence of buoyant flows fundamentally affects combustion mechanisms, the possibility of atmospheric design in spacecraft environment provides a new leverage, not usually available on Earth. Investigating a non-buoyant flame spreading over the polyethylene coating of an electrical wire in an opposed laminar flow, the previous paper highlighted how flow conditions, namely oxygen content, flow velocity, and ambient pressure, affected spread rate and soot formation rate. The implementation of the Broadband Modulated Absorption/Emission (B-MAE) technique provided mappings of soot temperature and volume fraction in the spreading flames during parabolic flights. In this second paper, the link between these microscopic observations and new macroscopic findings regarding the influence of flow conditions on the smoke production of a flame in the same configuration is presented. Taking into account other requirements of space exploration, atmospheric conditions below normoxic values present a clear interest from a fire safety perspective. In the process, a threshold temperature at which soot oxidation reactions are frozen is identified. The value of 1400 K brought forward conforms with past measurements performed at normal gravity, while discrepancies with previous microgravity measurements are addressed. Given the broad capability of human lungs to adapt to various conditions, the overall mapping of smoke production as a function of flow conditions is a valuable tool for atmospheric design considerations.