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

本研究项目在低于1000 K的温度下，对哈龙替代品之一的氢氟碳化合物的灭火能力和抑制反应机理进行了评价。除了激波管和湍流反应器外，还为本研究项目新制造了一台快速压缩机。在异丁烷点火过程中，点火诱导期随温度的升高而单调减小。在异丁烷和空气的混合物中加入HFC-227ea (2h -七氟丙烷，CF_3CHFCF_3)，抑制了点火。然而，这种抑制作用不是由氟原子使链载体失活引起的，因为无氟丙烷与HFC-227ea具有相同的抑制作用。在正庚烷的点火过程中，观察到一个负温度系数（NTC）区域，该区域的诱导期随着温度的升高而增加。与异丁烷相比，HFC-227ea的加入促进了正庚烷的点火。在NTC区，在燃料形成的烷基自由基上加入氧分子，生成烷基过氧自由基（ROO）。烷基过氧自由基通过氢原子的迁移转变为羟基过氧烷基自由基（R'OOH）。如果加入HFC-227ea，烷基过氧自由基从HFC-227ea中提取H原子成为过氧化物。过氧化物分解成OH自由基，OH自由基是燃烧过程中重要的链载体之一，促进着火。

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.