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On The Validity Of Quasi-steady Assumption In Transient Droplet Combustion

机译：瞬态液滴燃烧中准稳态假设的有效性

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摘要

A study on droplet combustion in unsteady force convection at high pressure under microgravity conditions was performed. The hysteresis loop of the instantaneous burning rate of a single suspended 1-butanol droplet was observed for the first time. Results showed that the classical quasi-steady film model cannot describe droplet combustion in an unsteady flow. Based on precise experimental observation and by utilizing dimensional analysis of the energy conservation equation, a new criterion is herein proposed for the condition in which the quasi-steady assumption is valid and for that in which it is not. The dimensional analysis led to formulation of a new time scale. Based on the time scale which we call the response-time-scale, a new Damkoehler number, termed the response-Damkoehler-number was formulated. Using the definition of the new time scale and that of the Damkoehler number, unsteady behaviors of droplet combustion under conditions of various pressures and varying force convection were examined. Finally, using the response-Damkoehler-number and the deviation factor between the actual instantaneous burning rate and the burning rate predicted by the quasi-steady theory, droplet combustion was categorized into four specific regimes. This study is also of fundamental interest in terms of the effects of turbulence on droplet evaporation and combustion in spray flames.
机译：在微重力条件下，进行了高压非定常对流中的液滴燃烧研究。首次观察到单个悬浮的1-丁醇液滴瞬时燃烧速率的磁滞回线。结果表明，经典的拟稳态膜模型不能描述非稳态流中的液滴燃烧。在精确的实验观察的基础上，利用能量守恒方程的维数分析，为准稳态假设有效和不成立的条件提出了新的判据。维度分析导致制定了新的时间尺度。基于我们称为响应时间尺度的时间尺度，制定了一个新的Damkoehler数，称为响应Damkoehler数。使用新的时间标度和Damkoehler数的定义，研究了在各种压力和不同力对流条件下液滴燃烧的不稳定行为。最后，使用响应-Damkoehler数和实际瞬时燃烧速率与准稳态理论预测的燃烧速率之间的偏差因子，将液滴燃烧分为四个特定的状态。就湍流对喷雾火焰中的液滴蒸发和燃烧的影响而言，这项研究也具有根本的意义。

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