Ignition Delay of Combustible Materials in Space Exploration Atmospheres

Material flammability is an important factor in determining the pressure and composition (fraction of oxygen and nitrogen) of the atmosphere in the habitable volume of exploration vehicles and habitats. The method chosen in this work to quantify material flammability is by its ease of ignition and the minimum (critical) radiant heat flux for ignition. Piloted ignition delay tests were conducted in the Forced Ignition and Spread Test (FIST) apparatus subject to various atmospheric pressures and oxygen concentrations. The ignition delay time was measured as the time it takes a combustible material to ignite after it has been exposed to an external heat flux. In these tests, polymethylmethacylate (PMMA) was exposed to an oxidizer flow velocity of 1 m/s and a range of externally applied heat flux levels from 8 to 14 kW/m². Tests were conducted at standard atmospheric pressure and oxygen concentration as well as at the proposed exploration environment of lower pressure (58.6 kPa) and high oxygen concentration (32%). It was found that the ignition time in the proposed space exploration atmosphere was reduced by 27% compared to standard conditions. This finding indicates that materials will be more susceptible to ignition (shorter ignition delay) in exploration atmospheres when an external heat flux is applied.