AC plasma retarded flame spread over thin solid fuels in a simulated microgravity environment

Abstract

The flame spread over thin solid fuels in a narrow channel by the action of AC plasma was first proposed and reported to show a trade-off between the flame instability produced by ionic wind and the kinetic enhancement stimulated by energetic and chemically active species. The 6 mm height narrow channel apparatus has been demonstrated the ability to suppress buoyant flow in horizontally spreading flames, and can successfully simulate a microgravity environment. Plasma acted on flame spread over thin solid fuels led to a confined behavior not typically seen in previous researches, which was investigated by integrated studies of experiment and supporting analysis using BOLSIG+. Four primary variables including flow velocity, reduced electric field, oxygen concentration and electrode length were considered. Among them, the reduced electric field and the oxygen concentration were found the crucial factors affecting the flame spread and further the flammability limit. The experimental results showed the affected field of the flame spread matched the field acted by AC discharge, which suggested a one-to-one correspondence between AC plasma action and flame slowing down or extinguishing. The results also showed that the narrow channel apparatus could capture the essential features of the flame spread in a simulated microgravity, for example the flame-lets phenomenon. The dependence of ionic wind on the reduced electric field was additionally investigated by solving the electron energy deposition into different excited channels and the electron energy distribution function (EEDF), which was essentially in agreement with the experimental observations. This study would develop a new and successful tool with rapid control of spacecraft fire and response to future exploration vehicles.