Numerical and Experimental Studies of Extinguishment of Cup-Burner Flames by C6F12O
Fumiaki Takahashi, Viswanath R. Katta, Valeri I. Babushok, Gregory T. Linteris
The extinguishment processes of cup-burner flames by adding a halon-replacement fire-extinguishing agent C6F12O (Novec 1230) to coflowing air in normal gravity have been studied computationally and experimentally. The time-dependent, axisymmetric numerical simulations with a detailed reaction mechanism (up to 141 species and 2206 reactions), molecular diffusive transport, and a gray-gas radiation model, reveal a unique two-zone flame structure. The peak reactivity spot (i.e., reaction kernel) at the flame base stabilizes a trailing flame, which is inclined inwardly by a buoyancy-induced entrainment flow. As the volume fraction of the agent in the coflow air is increased gradually, the total heat release increases up to three times due to the additional exothermic reactions to form HF and CF2O, thus resulting in a two-zone diffusion flame structure; whereas at the base, the flame-anchoring reaction kernel weakens (the local heat release rate decreases) and eventually the flame blows off. A numerical experiment, in which the C6F12O agent decomposition reactions are turned off, indicates that for addition of inert C6F12O, the maximum flame temperature decreases rapidly due to its large heat capacity and the blow-off extinguishment occurs at ≈1700 K, a value identical to that for inert gases previously studied, while the reaction kernel is still burning vigorously. The calculated minimum extinguishing concentrations of C6F12O in a propane flame are 4.2 % (with full chemistry), and 4.3 % (without agent decomposition) which is in fairly good agreement with the measured value of 5.1 %.
, Katta, V.
, Babushok, V.
and Linteris, G.
Numerical and Experimental Studies of Extinguishment of Cup-Burner Flames by C6F12O, Proceedings of the Combustion Institute, [online], https://doi.org/10.1016/j.proci.2020.05.053
(Accessed December 3, 2023)