Droplet-combustion experiments with normal-alkane fuels, carried out onboard the International Space Station, have shown that, after radiative extinction of a droplet burning with an ordinary hot flame, often quasi-steady burning is initiated and sustained by a chemical-kinetic mechanism associated with cool flames. This second, cool-flame combustion stage occurs in a partial-burning regime in which both fuel and oxygen leak through a reaction zone that is controlled by the low-temperature chemistry of cool flames. This second stage persists for an appreciable period of time, after which it is terminated by cool-flame extinction, often at a measurable non-zero droplet diameter. This extinction diameter depends on the fuel and on the composition of the ambient atmosphere. Experiments involving large fuel droplets of different initial diameters indicate that the value of this cool-flame extinction diameter may vary with the initial droplet diameter and with the ignition energy imparted by the hot-wire igniters, even though the cool flame lies well within the region described as the inner quasi-steady zone, where flame structures are independent of initial conditions. These observations imply that the effective ambient atmosphere during the second stage likely depends on the previous combustion history. In the present contribution, evaluations are reported concerning possible influences of the ignition process, of the first-stage hot-flame combustion, and of prior cool-flame combustion on the effective atmosphere in which the second-stage combustion and extinction occur. It is concluded that analysis of influences of fuel leakage and condensation may be needed.

在国际空间站上进行的正构烷烃燃料液滴燃烧实验表明，在普通热火焰燃烧的液滴辐射熄灭后，通常通过化学动力学机制引发和维持准稳态燃烧与冷火焰有关。第二个冷火焰燃烧阶段发生在部分燃烧状态，其中燃料和氧气都通过由冷火焰的低温化学控制的反应区泄漏。第二阶段持续相当长的一段时间，之后它被冷火焰熄灭终止，通常在可测量的非零液滴直径处。该消光直径取决于燃料和环境大气的成分。涉及不同初始直径的大燃料液滴的实验表明，这种冷火焰熄灭直径的值可能会随着初始液滴直径和热线点火器赋予的点火能量而变化，即使冷火焰正好位于该区域内描述为内部准稳态区，其中火焰结构与初始条件无关。这些观察结果意味着第二阶段的有效环境大气可能取决于之前的燃烧历史。在目前的贡献中，报告了关于点火过程、第一阶段热火焰燃烧和先前冷火焰燃烧对发生第二阶段燃烧和熄灭的有效气氛的可能影响的评估。