Evaluations for Fire-Suppression Abilities and Inhibition Reaction Mechanisms of Halon Replacements in Low-Temperature Combustion

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In this research project, the evaluations for fire-suppression abilities and the inhibition reaction mechanisms of hydrofluorocarbons, which are ones of the halon replacements, have been investigated at temperatures lower than 1000 K. A rapid compression machine was newly manufactured for this research project, in addition to a shock tube and a turbulent flow reactor.In the ignitions of isobutane, the induction periods for ignition monotonically decreased with temperature. When HFC-227ea (2H-heptafluoropropane, CF_3CHFCF_3) was added in the mixtures of isobutane and air, the ignitions were suppressed. However, this inhibition effect was not caused by the deactivation of chain-carriers by fluorine atoms, because fluorine-free propane had the same inhibition effect as HFC-227ea.In the ignitions of n-heptane, a negative temperature coefficient (NTC)region, where the induction periods increased with temperature, was observed. The addition of HFC-227ea gave the promotion for the n-heptane ignitions, in contrast to the isobutane ignitions. In the NTC region, oxygen molecules are added to alkyl radicals formed from fuel, so that alkylperoxy radicals (ROO) are produced. The alkylperoxy radicals are changed to hydroperoxyalkyl radicals (R'OOH) by the migration of H atoms. If HFC-227ea is added, the alkylperoxy radicals abstract H atoms from HFC-227ea to become peroxides. The peroxides docompose into OH radicals which are among the important chain-carriers in combustion, leading to the promotion of ignitions.