开展微重力环境下多组分单液滴的蒸发及自着火的研究, 对于在喷雾燃烧模拟中, 提高实际燃料液滴蒸发模型的准确性, 表征实际燃料燃烧特性是十分重要的。该文构建了考虑气液相传热传质的, 且适用于多组分单液滴蒸发及自着火的数值模拟方法, 并对比了多组分正烷烃混合物与单组分正烷烃单液滴的模拟结果。模拟发现, 多组分燃料中高挥发性组分先蒸发、低挥发性组分后蒸发的现象和液相内有限的传质速率相耦合, 导致了低挥发性组分在液滴表面积累, 降低了燃料整体挥发性, 延长了液滴着火延迟时间和液滴燃烧寿命。因此, 已有研究中仅依据实际燃料整体物化性质而构建的, 较少组分的燃料模型, 可能无法表征实际燃料中组分挥发性差异, 因而在数值模拟中表现出不同的液滴蒸发及自着火性质。该文指出了较少组分燃料模型在描述多组分单液滴蒸发及自着火过程中的不足, 为针对实际燃料用于喷雾燃烧模拟的液滴模型的深入研究奠定了基础。

Objective: Understanding how multicomponent fuel droplets combust in microgravity environments is crucial for characterizing real fuels during spray combustion. Constructing surrogate fuels that represent real fuels is significant, balancing the need for accurate representation of complex, multicomponent fuels with acceptable computational costs. Existing surrogate fuels often match the overall properties of real fuels; however, this can lead to inaccuracies due to differences in how components vaporize due to their volatility. This article aims to study the differences in droplet evaporation and autoignition behaviors among hydrocarbon fuels with various carbon numbers and volatilities in both single- and multi-component scenarios. Methods: We developed a numerical simulation model for single droplet combustion under the assumption of spherical symmetry for multicomponent fuels. This model solves the one-dimensional convective diffusion equation for heat and mass transfer and the continuity equation for gas and liquid phases. We examined single-component n-alkanes with carbon numbers ranging from 9 to 13 and four multicomponent mixtures with an average carbon number of 10, designed to represent surrogate fuels. For single-component fuels, our analysis focused on the zero-dimensional ignition delay time, ignition delay time for droplet combustion, and droplet radius changes over time. For multicomponent fuels, we also studied component distribution in the gas and liquid phases to understand the coupling relationship between evaporation, diffusion, and reaction during droplet combustion. Our quantitative analysis of ignition delay time involved simulating zero-dimensional ignition time under local temperature and composition throughout the droplet combustion process and the entire space. Results: The results showed that although zero-dimensional ignition delay times did not differ significantly among components with different carbon numbers, fuel droplets with lower carbon numbers had shorter ignition delay times because of higher volatility. In multicomponent mixtures, despite similar molecular structures, average carbon numbers, and ignition delay times in zero-dimension reactors between the four mixtures and n-decane, there were significant differences in droplet ignition delay times and droplet radius evolution. The analysis revealed that in multicomponent fuels, high-volatility components evaporate first, and low-volatility components evaporate later. With limited liquid mass transfer rates, low-volatility components accumulate on the droplet surface. This accumulation reduces volatility, extends the ignition delay time, and prolongs the droplet combustion lifetime. Our quantitative analysis found that droplet evaporation influences ignition in two ways: it mixes components and propagates the reaction, and it accelerates the ignition process through continuous fuel evaporation. Both processes are closely related to preferential vaporization. Conclusions: Therefore, surrogate fuel models that match the overall physical and chemical properties of real fuels may exhibit different droplet combustion properties compared with real fuels. This finding highlights the importance of accurately modeling the complex evaporation and combustion processes of multicomponent fuels in microgravity environments to improve spray combustion simulation accuracy.