Combustion and Flammability Characteristics of Solids at Microgravity in very Small Velocity Flows

AT MICROGRAVITY IN VERY SMALL VELOCITY FLOWS C. Sanchez-Tarifa1and M. Rodriguez2, 1 & 2ETSI Aeronauticos, Propulsion Dept., Plaza del Cardenal Cisneros, No. 3, 28040 Madrid (Spain). e-mail1: cstarifa@lmf.dmt.upm.es. e-mail:2: mrf@lmf.dmt.upm.es INTRODUCTION Fires still remain as one of the most important safety risk in manned spacecraft. This problem will become even more important in long endurance non orbital flights in which maintenance will be non existing or very difficult. The basic process of a fire is the combustion of a solid at microgravity conditions in O2/N2 mixtures. Although a large number of research programs have been carried out on this problem, especially on flame spreading, several aspects of these processes are not yet well understood. It may be mentioned, for example, the temperature and characteristic of low emissivity flames in the visual range that take place in some conditions at microgravity; and there exists a lack of knowledge on the influence of key parameters, such as convective flow velocities of the order of magnitude of typical oxygen diffusion velocities. The “Departamento de Motopropulsion y Termofluidodinamica” of the “Universidad Politecnica de Madrid, Escuela Tecnica Superior de Ingenieros Aeronauticos” is conducting a research program on the combustion of solids at reduced gravity conditions within O2/N2 mixtures. The material utilized has been polymethylmethacrylate (PMMA) in the form of rectangular slabs and hollow cylinders. The main parameters of the process have been small convective flow velocities (including velocity angle with the direction of the spreading flame) and oxygen concentration. Some results have also been obtained on the influence of material thickness and gas pressure. The experimental program has been continuously supported by ESA, including three parabolic flight campaigns in the NASA KC-135 and one in the ESA Caravelle; a MiniTexus sounding rocket launched in 1995 and a Texus launching that would be carried out in November/December of this year.