Modeling Microgravity and Normal Gravity Opposed Flame Spread over Polymer/Glass Composites

Abstract

Experimental data of opposed -flow flame spread obtained both in microgravity and normal gravity is used to validate the predictions of an analytical model for opposed -flow flame spread r ate. The model is based on a balance between heat -transfer controlled flame spread and kinetically controlled flame spread. The model predicts that the flame spread rate increases with opposed flow velocity, reaches a maximum, then decreases until extincti on. The fuels examined are thermally thick polymethylmethacrylate (PMMA) and polypropylene glass fiber composite (PPG). The microgravity flame spread experiments were conducted on NASA’s KC -135 research aircraft in the Forced Ignition and Flame Spread Test (FIST) at opposed -flow velocities lower than can be achieved in ground -based tests due to buoyancy -induced flow. In order to apply the analytical model to predict the experimental data, four model parameters need to be calibrated. Once this is done, excel lent agreement between the model and the data is achieved. The model predicts that for some conditions and fuels, flame spread in microgravity occurs in the heat transfer dominated regime subject to low velocity flow while that in normal gravity in the kin etically controlled regime. Consequently, there is a maximum in the flame spread rate at velocities lower than those generated by buoyancy in normal gravity. These results, which are supported by the experimental measurements, are relevant for fire safety in spacecraft since ground bas ed tests may under predict microgravity flame spread rates of materials intended for use on spacecraft.