烃类燃料的微重力燃烧是太空环境中研究燃烧过程的重要领域之一。本文从理论模型、检测手段以及重力对碳烟生成量及分布区域的影响3个方面总结了微重力条件下C1-C4烃类燃料燃烧生成碳烟的研究进展。详细阐释了目前数值模拟采用的碳烟模型及其优缺点, 分析了应用于微重力条件下的碳烟检测/诊断手段的优势及不足, 介绍了已有研究中揭示的重力对碳烟生成量及分布区域的影响规律, 并对微重力条件下碳烟生成过程的未来研究方向进行展望。

Significance: The combustion of hydrocarbon fuels is a significant element in energy conversion and utilization, and it involves complex chemical reactions and physical phenomena. The formation of soot is a critical phenomenon in this process. In addition to environmental pollution, the formation of soot in engines may induce safety risks. An excessive amount of soot may accumulate and block the nozzle of an aerospace engine, resulting in flight accidents. Therefore, it is critically important to control soot formation to ensure flight safety and thus reduce environmental pollution. To effectively control soot, an extensive analysis of the formation mechanism of soot is required. Under normal gravitational conditions, the combustion process may be significantly affected by natural convection, which intensifies the complexity and instability of combustion. This further constrains the analysis of soot formation. However, under microgravity conditions, the intrinsic nature of the combustion phenomena is more pronounced, and the combustion and flow problems are simplified. Furthermore, compared with normal gravity conditions, the flame structure is more stable and symmetrical, which can be attributed to the reduction or even elimination of buoyant convection. Additionally, factors such as residence time, concentration, and particle size exhibit obvious increases, facilitating the investigation of the soot formation process. However, due to the current limitations of microgravity facilities in terms of time and space, existing research on soot formation under microgravity conditions is not comprehensive. Therefore, it is important to summarize the progress made in the current research on soot formation under microgravity conditions and evaluate the limitations of these experiments in these conditions. This may promote the development of soot-formation research under microgravity combustion. Progress: In terms of soot models, soot growth models primarily involve acetylene single-equation and acetylene/benzene two-equation soot models, which are optimized and improved in accordance with experimental measurements for soot nucleation, growth, and oxidation, in addition to radiation models (optical thin radiation model). These models can help to analyze the variation in soot formation location, particle size, and nucleation and oxidation processes to some extent. However, there are still significant discrepancies between the numerical and experimental microgravity results. In terms of diagnostic techniques, soot diagnostic methods operating under microgravity conditions include intrusive and non-intrusive techniques, which can be used to measure parameters such as soot morphology, structural size, and concentration distribution. Because of the significant disturbances caused by intrusive techniques in the combustion flow field, nonintrusive optical diagnostic techniques have garnered more attention for use in experiments. With the improvement and development of microgravity facilities, experimental detection techniques have evolved from one-dimensional to multi-dimensional measurements, and comprehensive results are obtained. However, existing research on multi-dimensional measurements under microgravity conditions is limited. In accordance with the impact of gravity on soot formation, numerical and experimental methods are often combined to explore soot formation characteristics in drop towers, space stations, and parabolic flights by considering small-molecule hydrocarbons as fuel sources. The main purpose of these investigations was to analyze the impact of buoyant convection on soot formation pathways, distribution areas, and soot morphology and structural characteristics. Conclusions and Prospects: Although numerous experiments and numerical simulations have been conducted to study the formation of soot under microgravity conditions, there is a lack of extensive research. Future research directions for microgravity soot studies may focus on multi-dimensional measurements of experimental parameters under microgravity conditions to obtain more precise experimental results, which may help optimize soot models, improve predictive accuracy, and deeply explore the intrinsic mechanisms of soot formation.