Implications of Spread Rate and Temperature Measurements in Flame Spread Over a Thin Fuel in a Quiescent, Microgravity, Space-Based Environment

Abstract

Results and analysis of the data acquired in an experiment on laminar flame spreading at microgravity conducted on a recent Space Shuttle mission are presented. In the experiment, a thin fuel (ashless filter paper) was burnt in a quiescent environment in a 50% O₂/50% N₂ mixture at a total pressure’ of 152 kPa (1·5 atm). The entire experiment from ignition to extinction was recorded using two 16 mm cine-cameras, and the temperature of the fuel surface and at two locations in the gas phase were measured using Pt/Pt-Rh thermocouples.

The flame spread rate was found from a frame-by-frame analysis of the film. The spread rate and temperature measurements are used to extract information on the fuel pyrolysis process and the different modes of heat transfer between the gas and the solid phase. Analysis of the experimental data and close inspection of the film reveal the following: i) Unlike normal gravity flames, the microgravity flame shows significant radiative heat transfer between the gas and the solid phase, ii) Following the flame spread process a substantial amount of potentially pyrolyzable fuel remains such that a stationary flame near the end of the fuel sample persists for some time. iii)The remaining solid fuel undergoes surface reaction as fresh oxygen diffuses back to and products diffuse away from the fuel surface. iV) Commonly used first-order Arrhenius pyrolysis kinetics that result in rapid and complete fuel vaporization near the leading edge of the flame provide for inconsistencies between observations ii) and iii) here and measured temperature and computed solid density profiles.