Abstract
Building polymers implemented into building panels and exterior façades have been determined as the major contributor to severe fire incidents, including the 2017 Grenfell Tower fire incident. To gain a deeper understanding of the pyrolysis process of these polymer composites, this work proposes a multi-scale modelling framework comprising of applying the kinetics parameters and detailed pyrolysis gas volatiles (parent combustion fuel and key precursor species) extracted from Molecular Dynamics models to a macro-scale Computational Fluid Dynamics fire model. The modelling framework was tested for pure and flame-retardant polyethylene systems. Based on the modelling results, the chemical distribution of the fully decomposed chemical compounds was realised for the selected polymers. Subsequently, the identified gas volatiles from solid to gas phases were applied as the parent fuel in the detailed chemical kinetics combustion model for enhanced predictions of toxic gas, charring, and smoke particulate predictions. The results demonstrate the potential application of the developed model in the simulation of different polymer materials without substantial prior knowledge of the thermal degradation properties from costly experiments.
Highlights
Fire risks associated with lightweight building materials have continuously threatened building occupants, the environment, and properties [1,2]
A multi-scale modelling approach was proposed to address this significant knowledge gap by applying the kinetics parameters and detailed pyrolysis gas volatiles extracted from Molecular Dynamics (MD) to enable a more realistic detailed chemistry combustion in Computational Fluid Dynamics (CFD) fire model. This multiscale modelling is a potential technique for the simulation of combustible polymer materials, as it allows to describe them without the need of performing costly experiments
The key properties associated with the burning behaviour of pure polyethylene (PE) and polyethylene with aluminium trihydroxide (PE/ATH) were analysed by molecular dynamics simulations
Summary
Fire risks associated with lightweight building materials have continuously threatened building occupants, the environment, and properties [1,2]. Molecular dynamics (MD) simulations with a reactive force field (ReaxFF) have significant potential to be applied to gain a more in-depth knowledge of pyrolysis breakdown of material and extract the key input data required for fire modelling. Chen et al [29] characterised the pyrolysis process of three common engineered polymers (high-density polyethylene, poly (methyl methacrylate) and high impact polystyrene) through ReaxFF simulations, obtained detailed pyrolysis kinetics and char formation that was in good agreement with the experimental result. TThe ddata wwere applied as inputs into a three-diimmeennssiioonnaall LLEESS ffiirree mmooddeell comprising of (i) solid pyrolysis, (ii) gas-phase combustion, (iii) radiation heat exchange between fire source, walls, and gaseous products, (iv) soot formation, and (v) sub-grid scale (SGS) turbulence models. FFiigguurree1133..NNuummeerriiccaallrreessuullttssffoorrHH22O mass fraction profifille froomm ccoonnee ccaalorimetry under a heat flflux ooff3355 kW//mm ffoorrppoolylyeeththyylelenneewwitihthalaulmuminiinuimumtrithriyhdyrdorxoixdied(eP(EP/EA/TAHT)Hca)sceawseitwh i(tih) p(iu)rpeuCr2eHC4 2H4 ((eetthhyylelennee))aanndd(i(ii)i)vvoolaltaitlielsesgagsasmmixitxutruerefrformommmoloecleucluarladrydnyanmaimcsic(sM(DM)Dsi)msiumlautliaotnioans athsethpearpeanrtefnutel. fuel
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