Quantifying the Combustion Characteristics of Hydrofluorocarbons

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Halogenated hydrocarbons are extensively used as refrigerants and fire suppressants. Compounds that are currently used by the industry have large global warming potential and/or ozone depletion potential. Environmentally friendlier alternatives that have been identified are hydrofluorocarbons, which are flammable and pose fire risks. Some of these hydrofluorocarbons are already in use as refrigerants even though their combustion behavior is not well-characterized. Candidate fire suppressants that were tested were found to promote combustion instead of inhibiting it. This project aims to quantify the reactivity of hydrofluorocarbons through novel experiments. Furthermore, computations will be performed to investigate the fire risk associated with these compounds in the case of accidental leakage and subsequent ignition. The results from these studies are expected to play an important role in the selection and adoption of hydrofluorocarbons in the industry and the development of safety protocol. The project will not only advance the understanding of the combustion behavior of these exotic compounds but also of other fundamental combustion aspects such as gravity-induced acceleration of flames. The proposed project will also create opportunities for undergraduate students to have hands-on, experimental research experience and will result in the development of education modules, which will be used to strengthen courses as well as inspire K-12 students.Hydrofluorocarbons are mildly flammable compared to hydrocarbons, which makes quantifying their reactivity challenging. Flame speeds will be measured by overcoming challenges associated with buoyancy-induced flow and radiation heat loss, using a lab-scale drop tower experiment and detailed computational models, respectively. Judiciously performed parametric studies will enable the elucidation and quantification of their reactivity, dominated by reactions of fluorine-based radicals, and create archival data valuable for the development of chemical kinetic models. Due to their mild reactivity, gravity-driven instability growth is expected to significantly influence the dynamics of hydrofluorocarbon/air flames. Direct Numerical Simulations will be performed to investigate the effect of instability growth on flame dynamics, the coupling between the gravity-driven and intrinsic flame front instabilities resulting from thermal expansion and non-equidiffusion, and the resulting flame acceleration.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.