Fully Coupled Three-Dimensional Simulation of Downward Flame Spread over Combustible Material

Area of Science:

• Combustion Science
• Materials Science
• Computational Fluid Dynamics

Background:

• Understanding flame propagation on materials is crucial for fire safety.
• Polyurethane's thermal decomposition and flame spread behavior require detailed investigation.

Purpose of the Study:

• To simulate and analyze downward laminar flame spread on a rigid polyurethane slab.
• To compare simulation results with experimental data and identify key influencing factors.

Main Methods:

• Utilized three-dimensional simulations with ANSYS Fluent for gas-phase and Pyropolis for solid-phase modeling.
• Incorporated finite-rate volatile oxidation, soot dynamics, and radiative heat transfer.
• Developed a kinetic model for material decomposition based on microscale combustion calorimetry data.

Main Results:

• Examined transient flame and pyrolysis zone behavior, and spatial distributions of heat flux, temperature, and burning rates.
• Identified material thermal property variations, emissivity, and reradiation as critical factors.
• Distinguished between thermal and kinetic flame spread modes, with propagation velocity governed by heating or burning velocity, respectively.

Conclusions:

• Simulation results show favorable agreement with measured flame propagation velocities.
• Accurate modeling necessitates considering dynamic changes in material properties and radiative effects.
• The identified thermal and kinetic modes provide insight into flame spread mechanisms.