微重力条件下的液滴燃烧, 尤其是单液滴燃烧的研究工作, 对于丰富液滴燃烧理论具有重要意义, 也为航空发动机等喷雾燃烧系统的设计提供了重要参考。该文首先阐述了单液滴燃烧的基础理论——液滴直径平方定律及其影响因素, 并介绍了单液滴燃烧实验方法, 着重分析悬挂纤维丝对液滴燃烧的影响; 接着介绍了液滴燃烧过程中可能出现的碳烟壳、火焰熄灭现象、冷火焰等情况; 此外分析了高压环境对燃烧特性的影响, 进一步讨论了多组分液滴燃烧时可能出现的微爆等特殊现象, 并对实际燃料与相应的表征燃料建模相关研究进行介绍, 最后总结了目前微重力条件下单液滴燃烧研究中存在的挑战。

Significance: Single droplet combustion in a microgravity environment is an important model for understanding spray combustion. This study aims to enrich the theory of droplet combustion, providing crucial insights for practical applications such as engine design of aerospace and other spray combustion systems. Progress: By combining single droplet combustion experiments in microgravity with numerical simulations, this study discusses unique phenomena and analyzes the influence of various uncertainties, such as experimental methods and environmental conditions, on combustion characteristics. This study begins by explaining the D² law, a fundamental theory of single droplet combustion, and its influencing factors. Then, it focuses on the suspending fiber wire technique, analyzing how it affects droplet combustion characteristics. This study examines soot shell formation, flame extinction phenomena, and cool flames during droplet combustion, discussing the mechanisms behind soot shell generation and its influence on the combustion process. The single-droplet flame, a typical diffusion flame, is affected by radiation extinction and diffusion extinction. The cool flame is controlled by the low-temperature oxidation reaction of hydrocarbon fuel, leading to a complex multistage ignition process in droplet combustion. In addition, this study reviews how high-pressure environments affect combustion characteristics and explores phenomena such as preferential evaporation and possible microexplosions during multicomponent droplet combustion. Finally, research on alternative fuels and biofuels reveals that biofuels produce considerably lower soot emissions than conventional hydrocarbon fuels. Conclusions and Prospects: By combining experiments and numerical simulations, this study expanded basic combustion theory through new phenomena observed in microgravity experiments, offering new ideas for developing microgravity experiments and improving numerical models. These experiments on single-droplet combustion in a microgravity environment made several important contributions: using new phenomena to address gaps in droplet combustion theory; revealing fundamental characteristics of autoignition, quasi-steady-state combustion, and extinction of different liquid fuels through experiments under reduced buoyancy convection conditions; and establishing a novel theoretical framework for droplet combustion based on multistage reaction flame structures. However, the experimental and theoretical aspects of single-droplet combustion in the microgravity environment still face several challenges: deficiencies in optical diagnostics for high-pressure combustion experiments, the lack of a large amount of experimental data to support relevant theories in high-pressure environments, the controversy of the pressure effect in microexplosions, insufficient experimental data for practical fuel surrogates, the difficulty in accurately using simple models with few components to develop representations of complex surrogates for practical fuels, and the lack of research data on new liquid fuels (e.g., biodiesel). Addressing these challenges can provide theoretical support for developing new combustion technologies and facilitate the transition to green and low-carbon energy solutions.