Polytetrafluorethylene (PTFE) burn characteristics and toxicant formation in an oxidizer cross-flow via laser absorption tomography.

A two-dimensional solid-fuel combustion experiment for fire-resistant polymers under forced convective cross-flow was developed to assess burn characteristics and toxicant formation using advanced laser absorption diagnostics that enable in situ species and temperature measurements near the fuel surface. The method was used to examine the thermochemical flow-field structure near the surface of polytetrafluoroethylene (PTFE) exposed to a well-defined solid-fuel pilot flame burning polymethyl methacrylate (PMMA). Infrared diode and quantum cascade lasers were used to probe rovibrational absorption transitions of hydrogen fluoride (HF) and carbon monoxide (CO), respectively, at the exit plane of a heterogeneous cylindrical fuel grain from which temperature and mole fraction could be inferred. A laser absorption tomography (LAT) technique with a Tikhonov-regularized Abel inversion was applied to reconstruct radially-resolved profiles in the axisymmetric reacting flow which, when compiled across a range of fuel lengths, provided a two-dimensional image of the near-surface reaction layer. Thermochemical data and reaction rate parameters from existing fluorocarbon chemistry models were used to generate high-temperature simulations of product species concentrations and temperature as a function of oxidizer-to-fuel ratio to elucidate observed trends and identify key reactions relevant to the novel dataset. The geometry and scale of the composite fuel experiments is intended to be tractable for reactive multi-physics models, enabling quantitative comparison of combustion characteristics and ultimately improved predictive capability of toxicant quantities resulting from fluoropolymer combustion in fire environments.