Effect of oxygen concentration, pressure, and opposed flow velocity on the flame spread along thin PMMA sheets

The flame spread of thin PMMA sheets has been studied both in opposed configuration under microgravity (9.3 s drop tower) and in downward configuration under normal gravity conditions. The position of the flame front has been determined with the help of an infrared camera. Propagation rates have been measured over a range of 30–200 mm/s forced opposed flow (only microgravity), 60–101.3 kPa ambient pressure, and oxygen concentrations of 21–35.4 vol. %, which corresponds to real environmental conditions on spacecraft. In addition to variations along the normoxic curve with constant oxygen partial pressure, the parameters oxygen and pressure were examined independently of each other in order to be able to determine their respective effects. The variation of the flow velocity was carried out at 60 kPa and 35.4 vol. % oxygen. The results for both microgravity and normal gravity are discussed separately on the basis of the respective atmospheric effect. Along the normoxic curve, a significant increase in the flame spread rate was found with increasing oxygen concentration and correspondingly decreasing pressure. This results in a significant increase in the risk of fire with regard to future exploration missions. The effect of the flow velocity cannot be neglected in the investigated velocity range and was linked to the influencing parameters in a correlation. Based on this parameterization, a linear function is given that reflects both the downward and the opposed results well. This function can be used to predict the flame spread in the given parameter space. Under normal gravity, the tested samples show a slightly increased propagation rate in most cases. This can essentially be attributed to the difference in velocity between the buoyant flow and the forced flow in µg.