: SPOT FIRE IGNITION OF WILDLAND FUEL BEDS BY HOT METAL PARTICLES
Speaker: Prof. Carlos Fernandez-Pello
From: Department of Mechanical Engineering, USA
Date: May. 6, 2015 9:30~11:00
CV of the Speaker:
Dr. Carlos Fernandez-Pello is Professor of the Department of Mechanical Engineering, the Almy C. Maynard and Agnes Offield Maynard Endowed Chair of Mechanical Engineering. He received degrees of Doctor Aeronautical Engineer (1971) from the University of Madrid, Spain, and a Ph.D. in Engineering Sciences (1975) from the University of California, San Diego.
From 1975 to 1977 he was a Postdoctoral Fellow at Harvard University, and from 1977 to 1980 a Research Fellow at Princeton University. He joined the University of California, Berkeley in 1980, where he has been a Full Professor since 1986. Since July 2003 to December 2012 he was also Associate Dean of the U.C. Berkeley Graduate Division.
Professor Fernandez-Pello teaches courses in thermosiences with emphasis on combustion His recent research emphasizes material flammability in earth and spacecraft environments, wildland fire spotting and development, smolder propagation, pyrpolysis, micro-scale power generation, electromagnetic effects on flames and solar energy storage.
His research is or has been funded by NASA, NSF, NIST, DARPA, DOE and ARO. He has published over 200 papers in peer reviewed technical journals and over 300 hundred non-archival papers. He is a member of the Royal National Academy of Engineering of Spain and a Fellow of ASME International. He is, or has been, in the Editorial Advisory Boards of the Combustion Institute, Combustion Science and Technology, Combustion and Flame, and Progress in Energy and Combustion Science. He is a member
of the NSTAC advising committee and has been a member of NASA Advisory Committee for the International Space Station, and of the USRA/NASA Microgravity Science and Applications Science Council. He is, and has been, a consultant for government and industry in the USA and abroad.
Wildland and Wildland/Urban interface fires are a serious problem in many areas of the world. It is expected that with global warming the wildfire and wildland/urban nterface fire problem will only intensify.
The ignition of natural combustible material by hot metal particles or embers is an important fire ignition pathway by which wildland and urban spot fires are started. There are numerous cases reported of wild fires started by hot metal particles from clashing power-lines, or from sparks generated by machines or engines. Similarly there are many cases reported of industrial fires caused by grinding and welding sparks.
Despite the importance of the subject, the topic remains relatively unstudied. The problem of spot fire ignition can be separated in three independent processes: the generation of particles; their flight by plume lofting and/or wind drag; and the ignition of the fuel bed after the landing of the particle. In this presentation a comprehensive summary of that work to date by the author is provided. The work includes experimental and theoretical modeling of the ability of hot metal particles and embers to cause the ignition of wildland fuel beds.
The metal particles studied are representative of clashing conductors (aluminum and copper) and those produced by machine friction and hot work such as welding (stainless steel and brass). Five fuel beds were tested: alpha-cellulose in strips and as a powder, barley grass and pine needles and powders formed by grinding the grass or needles. These fuel beds are representative of thermal insulation (cellulose strips) litter (grass, needles), and duff (powders. The overall results show a hyperbolic relationship between particle size and temperature, with the larger particles requiring lower temperature to ignite the fuel bed than the smaller particles. An important finding is that although particle energy is important in the capability of the particle to ignite the fuel, both energy and temperature are determining factors of the particle ignition capabilities. The thermal properties of the metal play a lesser role with the exception of the energy of melting if it occurs. It also appears that the controlling ignition mechanisms by large particles are different than those from the small particles. The former appear to be determined primarily by the particle surface temperature while the later by the particle energy and surface emperature. From the experiments it was also found that pure cellulose beds ignite at lower temperatures than grass blend beds. This suggests that the lignin and more complex chemical structure of actual natural fuels deter their ignition when compared with pure cellulose fuels. It was also found that when the fuel is in powder form it ignites at a lower temperature than in strip/grass form. This confirms that the geometry of the fuel is also an important factor in the easiness of ignition of the fuel, and that as the fuel is thinner ignition is easier.. To provide further information about the fire spot ignition process both analytical and numerical modeling are used and compared with the experimental results. Although the models provide qualitative predictions further development is necessary to reach quantitative predictive capabilities