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NSF: Tackling CFD Modeling of Flame Spread on Practical
Solid Combustibles
This three year (September 2007 – September 2010) project is funded by the Combustion, Fire, and Plasma Systems program of the National Science Foundation under Award Number 0730556, "Tackling CFD Modeling of Flame Spread on Practical Solid Combustibles." The principal investigator is Prof. Carlos Fernandez-Pello. Project personnel include Chris Lautenberger (post-doctoral researcher) and Sonia Fereres (Ph.D. student).
The work that will be conducted as part of this NSF Award is intended to help overcome the challenges currently associated with “accurate” prediction of large scale fire development/flame spread/fire growth.
The objective is to develop improved computer models to predict real-scale fire behavior (flame spread and fire growth) with data obtained from laboratory-scale tests. Enhancing the current available computer models to predict real-scale fire behavior can be interesting for many different applications:
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Forensic fire reconstruction.
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Heat release rate estimation of large fuel packages (for example: rail vehicles, ships, aircraft, etc.) as an alternative to burning them at full scale which involves substantial cost and size.
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Alternative to full scale fire testing required by building codes and/or for material certification.
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Base to extrapolate normal gravity flammability data to microgravity or partial gravity environments (for use in the Space Shuttle, the International Space Station- ISS or other spacecraft).
The primary tasks that will be completed are:
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Continued development of a broadly applicable pyrolysis model that can simulate the pyrolysis and gasification of a variety of practical materials encountered in fires. The model will be capable of simulating materials ranging in complexity from traditional laboratory fuels (noncharring polymers and wood) to real-world fuels (foams and upholstery, charring and intumescent polymers, carpet, composites, materials with layered structure, etc.), with an emphasis on the latter. This is an extension of the generalized pyrolysis model developed by Lautenberger [1]. We are currently in the process of cleaning up the existing code and making it publicly available. See http://code.google.com/gpyro for details.
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Continued development of techniques to extract the material properties needed for pyrolysis modeling from bench-scale experimental data (thermogravimetric analysis, differential scanning calorimetry, and flammability tests such as Cone Calorimeter and Fire Propagation Apparatus). These techniques will be based on earlier work [2, 3] involving the application of genetic algorithms as an optimization tool, although alternate optimization methods may be explored.
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Coupling of the pyrolysis model to NIST’s Fire Dynamics Simulator (FDS) Version 5, including full solid/gas interactions to account for consumption of oxygen by oxidative condensed-phase reactions (e.g., char oxidation). Since radiative flame heat transfer dominates flame spread rates at hazardous scales, a previously-developed model for soot formation and oxidation [4] will be extended and inserted into FDS. Its predictive capabilities with regard to prediction of radiative flame heat fluxes will be assessed by comparison of model calculations to flame heat fluxes from turbulent gaseous diffusion flames.
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Comparison of coupled pyrolysis/CFD model calculations to experimental data for flame spread on real-world fuels. The coupled code will be used to simulate flame spread on practical solid combustibles over a range of length scales, including fully turbulent large-scale flame spread. However, the CFD model’s predictions of temperatures, velocities, turbulence statistics, and heat fluxes will first be compared to experimental data for “gas burner” type problems that do not involve a burning condensed-phase. Depending on the outcome of this exercise, modifications to the gas-phase CFD code may be implemented to improve its predictions before the coupled pyrolysis/CFD model is used to simulate flame spread on practical fuels.
This project is in its initial stages, and this web page will be updated as new results become available. Check back soon! Questions or comments? Email Chris Lautenberger (clauten(at)me.berkeley.edu).
References
[1] Lautenberger, C., “A Generalized Pyrolysis Model for Combustible Solids,” Ph. D. Dissertation, Department of Mechanical Engineering, University of California, Berkeley, December 2007
[2] Lautenberger, C., Rein, G. & Fernandez-Pello, A.C., “The Application of a Genetic
Algorithm to Estimate Material Properties for Fire Modeling from Bench-Scale Fire Test Data,” Fire Safety Journal 41: 204-214 (2006).
[3] Rein, G., Lautenberger, C., Fernandez-Pello, A.C., Torero, J.L. & Urban, D.L., “Application
of Genetic Algorithms and Thermogravimetry to Determine the Kinetics of Polyurethane Foam in Smoldering Combustion,” Combustion and Flame 146: 95-108 (2006).
[4] Lautenberger, C., de Ris, J., Dembsey, N.A., Barnett, J.R. & Baum, H.R., “A Simplified
Model for Soot Formation and Oxidation in CFD Simulation of Non-premixed Hydrocarbon Flames,” Fire Safety Journal 40: 141-176 (2005).
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