Fire safety in space - Investigating flame spread interaction over wires

A new rig for microgravity experiments was used for the study flame spread of parallel polyethylene-coated wires in concurrent and opposed airflow. The parabolic flight experiments were conducted at small length- and time scales, i.e. typically over 10 cm long samples for up to 20 s. For the first time, the influence of neighboring spread on the mass burning rate was assessed in microgravity. The observations are contrasted with the influence characterized in normal gravity. The experimental results are expected to deliver meaningful guidelines for future, planned experiments at a larger scale. Arising from the current results, the issue of the potential interaction among spreading flames also needs to be carefully investigated as this interaction plays a major role in realistic fire scenarios, and therefore on the design of the strategies that would allow the control of such a fire. Once buoyancy has been removed, the characteristic length and time scales of the different modes of heat and mass transfer are modified. For this reason, interaction among spreading flames may be revealed in microgravity, while it would not at normal gravity, or vice versa. Furthermore, the interaction may lead to an enhanced spread rate when mutual preheating dominates or, conversely, a reduced spread rate when oxidizer flow vitiation is predominant. In more general terms, the current study supports both the SAFFIRE and the FLARE projects, which are large projects with international scientific teams. First, material samples will be tested in a series of flight experiments (SAFFIRE 1-3) conducted in Cygnus vehicles after they have undocked from the ISS. These experiments will allow the study of ignition and possible flame spread in real spacecraft conditions, i.e. over real length scale samples within real time scales. Second, concomitant research conducted within the FLARE project is dedicated to the assessment of new standard tests for materials that a spacecraft can be composed of. Finally, these tests aim to define the ambient conditions that will mitigate and potentially prohibit the flame spread in microgravity over the material studied.

[1]  A. Claverie,et al.  Interactions between soot and CH∗ in a laminar boundary layer type diffusion flame in microgravity , 2007 .

[2]  G. Legros,et al.  Soot volume fraction fields in unsteady axis-symmetric flames by continuous laser extinction technique. , 2012, Optics express.

[3]  B. Porterie,et al.  Transport mechanisms controlling soot production inside a non-buoyant laminar diffusion flame , 2009 .

[4]  H. W. Emmons,et al.  The Film Combustion of Liquid Fuel , 1956 .

[5]  Robert Friedman,et al.  Fire Safety in Spacecraft , 1996 .

[6]  Osamu Fujita,et al.  Solid combustion research in microgravity as a basis of fire safety in space , 2015 .

[7]  Kenichi Ito,et al.  Effect of low external flow on flame spread over polyethylene-insulated wire in microgravity , 2002 .

[8]  Takashi Kashiwagi,et al.  The USML-1 wire insulation flammability glovebox experiment , 1995 .

[9]  Kenichi Ito,et al.  Effective mechanisms to determine flame spread rate over ethylene-tetrafluoroethylene wire insulation: Discussion on dilution gas effect based on temperature measurements , 2000 .

[10]  J. Torero,et al.  Three-Dimensional Recomposition of the Absorption Field Inside a Non-Buoyant Sooting Diffusion Flame , 2005 .

[11]  Osamu Fujita,et al.  Flame spread over electric wire in sub-atmospheric pressure , 2009 .

[12]  Jose L. Torero,et al.  Scaling-Up fire , 2013 .

[13]  F. A. Williams,et al.  Combustion of vertical cellulosic cylinders in air , 1969 .

[14]  O. Fujita,et al.  Flame spread over electric wire with high thermal conductivity metal core at different inclinations , 2015 .

[15]  Hiroyuki Takeuchi,et al.  Observation of Flame Spreading over Electric Wire under Reduced Gravity Condition Given by Parabolic Flight and Drop Tower Experiments , 2010 .

[16]  A. Fernandez-Pello,et al.  SOOTING BEHAVIOR DYNAMICS OF A NON-BUOYANT LAMINAR DIFFUSION FLAME , 2007 .

[17]  J. Torero,et al.  Influence of g-jitter on a laminar boundary layer type diffusion flame , 2005 .

[18]  Fengshan Liu,et al.  Numerical study of the effects of gravity on soot formation in laminar coflow methane/air diffusion flames under different air stream velocities , 2009 .

[19]  Jose L. Torero,et al.  Fire safety in space – beyond flammability testing of small samples , 2015 .

[20]  J. Torero,et al.  Three-dimensional recomposition of the absorption field inside a nonbuoyant sooting flame. , 2005, Optics letters.

[21]  J. Sato,et al.  Physical model analysis of flame spreading along an electrical wire in microgravity , 2002 .

[22]  Robert Friedman,et al.  Fire Safety in the Low-Gravity Spacecraft Environment , 1999 .

[23]  Jose L. Torero,et al.  Phenomenological model of soot production inside a non-buoyant laminar diffusion flame , 2015 .

[24]  C. Megaridis,et al.  Soot-field structure in laminar soot-emitting microgravity nonpremixed flames , 1996 .

[25]  Kenichi Ito,et al.  Experimental study on flame spread over wire insulation in microgravity , 1998 .

[26]  Kalyan Annamalai,et al.  Flame Spread Over Combustible Surfaces for Laminar Flow Systems Part I: Excess Fuel and Heat Flux , 1979 .

[27]  Sandra L. Olson,et al.  Buoyant low-stretch diffusion flames beneath cylindrical PMMA samples , 2000 .