Paper # 070LT-0365 Topic: Laminar Flames 8 th U. S. National Combustion Meeting Organized by the Western States Section of the Combustion Institute and hosted by the University of Utah May 19-22, 2013 Characteristics of Laminar Diffusion Flames in a Quiescent Microgravity Environment Fumiaki Takahashi 1* , Nicholas Hennigan 2 , Dennis P. Stocker 3 , Paul V. Ferkul 1 , Viswanath R. Katta 4 1 National Center for Space Exploration Research, Cleveland, OH 44135 2 NASA Undergraduate Student Research Program (USRP) 3 NASA Glenn Research Center, Cleveland, OH 44135 4 Innovative Scientific Solutions, Inc., Dayton, OH 45440 Burning characteristics of low-speed (~1 mm/s order) methane and ethylene laminar diffusion flames formed over a porous cup burner in a quiescent microgravity environment were studied experimentally and computationally. The experiment was conducted at the NASA 2.2 s drop tower. The video images showed that the luminosity of the hemispherical blue flame zone peaked near the flame base (edge) and gradually decreased toward the centerline. The temporal radiometer output signal reflected the transient flame size variation and captured the partial flame extinction. A time-dependent, axisymmetric, full-chemistry computation with radiation and transport processes was performed to reveal the diffusion flame structure. The calculated heat-release rate peaked in the flame base consistent with the observed flame luminosity. Although the initial fuel injection velocity was small, the flow accelerated by thermal expansion passed through the flame zone. Therefore, the calculated flame zone continued to expand outwardly, except for very low fuel injection velocity cases, for which nearly stationary flames were obtained. 1. Introduction The Burning Rate Emulator (BRE) experiment [Zhang et al., 2013] is in development to be conducted on board the International Space Station to improve spacecraft fire safety. The purpose of the BRE experiment is to gain fundamental understanding of spacecraft materials flammability by simulating condensed fuels combustion using gaseous fuels in a quiescent microgravity (g) environment. By using fuels that share similar properties, gaseous flames can emulate the burning of condensed fuels such as paper, plastic, and alcohol. Currently, the selection of materials intended for use in the habitable environments of US spacecraft is based on pass-or-fail flammability testing based on upward flame spread in a quiescent normal earth-gravity (1g) environment [Anon., 1998]. However, microgravity testing has shown that some fuels burn in microgravity but not in normal gravity. Laminar diffusion flames over a porous plate, through which a gaseous fuel is injected, have long been used to simulate the gas phase part of condensed fuel burning experimentally, analytically, and numerically [Emmons, 1956; de Ris, 1969; Hirano et al., 1974; Ohki and Tsuge, 1974; Fernandez-Pello and Williams, 1977; Wichman and Williams, 1983; Quintiere, 1981; Ramachandra and Raghunandan, 1984; Chen and T’ien, 1986]. Fires on Earth are always associated with surrounding air flow (wind or natural convection) and, in spacecraft, there is an air current (typically up to 20 cm/s) due to the environmental control and life support system. Therefore, the majority of investigations in the past have considered flame-flow interactions (e.g., opposed or concurrent flame spread), while studies on flames in a purely quiescent g environment are limited [Ross, 2001]. Brahmi et al. [2005] burned ethane in a porous burner with relatively low-velocity oxidizer flow (10-150 mm/s) in g and observed three flame shape regimes: elliptical, parabolic, and flat flames. * Corresponding author. E-mail: fumiaki.takahashi-1@nasa.gov