FPE Seminar Series: Flammability of Materials in Spacecraft Environments
Speaker: Carlos Fernandez-Pello, Professor, Dept. of Mechanical Engineering @ University of CA, Berekeley
Title: Flammability of Materials in Spacecraft Environments
Understanding the flammability of combustible materials inside a spacecraft is important for fire safety applications because the conditions in spacecraft environments can greatly differ from those on earth. They include microgravity, low velocity flows induced by the spacecraft ventilation, and potentially low pressure (~60 kPa) and elevated oxygen concentration (~34%). These ambient conditions are referred to as space exploration atmospheres (SEA) and are designed to reduce preparation time for space walks, while keeping the partial pressure of oxygen acceptable for human respiration. However, because in a gravity field there is a flame-induced buoyancy, it is very difficult to reproduce on earth the environmental conditions of a spacecraft, particularly the low velocity flows. The spacecraft ventilation system induces flows with velocities that are of the order 100 mm/s, while in earth gravity the buoyant flows induced by a compartment fire have velocities of the order of 300 mm/s to 600 mm/s. Thus, fire testing of materials to be used in spacecraft requires either a reduced gravity facility, or alternative approaches to reduce buoyancy. Experimental testing in space is difficult and expensive. However, reducing buoyancy by decreasing ambient pressure is a possible approach to simulate on-earth the burning behavior inside spacecraft environments. The objective of the work presented here is to verify that possibility by studying the effect of pressure and oxygen concentration, and consequently buoyancy, on flame spread, and by comparison with microgravity data, observe up to what point low-pressure can be used to replicate flame characteristics observed in microgravity. Experiments in normal gravity were conducted in a pressure vessel that simulates the combustion chamber in the Combustion Integrated Rack (CIR) of the International Space Station (ISS). Microgravity experiments were conducted during NASA’s Spacecraft Fire Experiment (Saffire), on board the Cygnus spacecraft and in the Microgravity Science Glovebox (MSG) in the ISS Destiny Lab. The study provides information about the similitudes of the flame spread process in variable pressure, oxygen concentration, flow velocity and gravity environments, providing guidance for potential ground-based testing for fire safety design in spacecraft and space habitats.
Carlos Fernandez-Pello is an Endowed Chair Professor in the Department of Mechanical Engineering at the University of California, Berkeley. He received degrees of Doctor Aeronautical Engineer from the University of Madrid, Spain, and a Ph.D. in Engineering Sciences from the University of California, San Diego. He was a Postdoctoral Fellow at Harvard University working on the Home Fire Project, and a Research Fellow at Princeton University working on the flammability of liquid and solid fuels. He joined the University of California, Berkeley in 1980, where he teaches courses in thermal-sciences with emphasis on combustion. His research has emphasized material flammability on earth and in spacecraft environments, smoldering and transition to flaming, spot ignition of wildfires by sparks and embers, and micro-scale combustion. He also had several administrative appointments including Associate Dean of the U.C. Berkeley Graduate Division, where he supervised several units related to university wide graduate studies. In 2009 he was named the Almy C. Maynard and Agnes Offield Maynard Endowed Chair of Mechanical Engineering. Professor Fernandez-Pello is co-author of the book Fundamental of Combustion Processes and of five book chapters on material flammability. He has published over 250 papers in archival technical journals and over 250 hundred non-archival papers. His research is or has been funded by NASA, NSF, NIST, DARPA, DOE and ARO.