为了提高燃烧效能，实现对燃烧过程的有效控制，需要针对单个油滴的非均相燃烧过程及瞬时燃烧特性展开深入研究。本文以RP-3航空煤油为研究对象，基于单个油滴燃烧实验系统，深入研究了微油滴燃烧过程中气泡演化机理，为进一步提高航空煤油燃烧效能奠定基础。首先，研究了油滴内气泡产生的动力学机理，发现影响微油滴和微气泡力学行为的主要因素是表面张力。通过设计V型挂丝结构，提高了油滴尺寸的精度，扩大了产生油滴的尺寸范围，有效控制了油滴成像位置和成像清晰度。分析了油滴蒸发燃烧过程，发现仅有背光不足以保证成像的清晰度。通过设计主动式复合光路照明系统，并调控光场、视场及油滴成像位置，精确捕捉到燃烧微油滴中气泡和凹坑等的清晰图像，可供图像颜色特征差异性识别和解析。其次，分析了RP-3喷气燃料的馏分组成和化学组成。基于含量和沸点分析，燃料油滴在温度升高时，先蒸发的是正庚烷而不是水。为精准地捕捉微油滴的燃烧过程，分别搭建了可制备480～2200μm直径油滴的挂滴装置，初速度为零的弹丝飞滴装置，滴液直径为80～600μm的一体式和组装式喷射飞滴装置。通过对光场和视场相关设备进行标定，分析了油滴取样误差、成像误差、透镜效应误差、图像处理的误差和图像测量不确定性。然后，在微尺度挂滴燃烧过程中，利用高速显微摄像技术，捕捉到油滴内部微气泡萌生核化、生长、聚并和溢出全过程，发现了油滴内部蒸发的气泡周期性暴涨/碎裂过程，以及油滴表面的气膜/气囊结构及其相互转换现象。进而分析了表面张力在微油滴燃烧中所起的作用，阐释了燃烧微油滴中气泡的演化机理。实验证实：挂滴实验油滴炸裂的临界尺寸在2.5～5.0μL。最后，为消除挂丝对油滴传热和黏附效应等的影响，开展了喷射飞滴和弹丝飞滴实验，通过对平面火焰的调控，满足了喷射飞滴误差和一致性检验要求，构建了稳定的飞滴蒸发燃烧环境。捕捉到油滴表面凹坑、油滴内部气泡及油滴表面气膜/气囊结构，发现了小油滴炸裂和大油滴不炸裂等现象。
In order to improve the combustion efficiency and effectively control the combustion process, it is necessary to detailedly study the heterogeneous combustion process and the characteristics of instantaneous combustion of single oil droplet. Based on the single oil droplet combustion experiment system, the objective of this thesis is to deeply research and analyze the bubbles evolution mechanism of micro oil droplet combustion process for RP-3 aviation kerosene, which can lay a foundation for further improving the combustion efficiency of aviation kerosene.Firstly, the dynamic mechanism of bubbles generation inside micro oil droplet was studied. It was noted that the main influence factor of the mechanical behavior of micro oil droplet and micro-bubbles was surface tension. By designing the V-type hanging wire structure, the measuring accuracy and the range of the oil droplet size are improved. The position and sharpness of the oil droplet imaging are effectively controlled. Moreover, the process of the oil droplet evaporation and combustion was analyzed. It is difficult to obtain high sharpness imaging with the backlight only. Hence, by adopting an active compound light path illumination system, adjusting the light field and the view field, and the oil droplet imaging position, a clear image of bubbles and scallops in the burned oil droplet can be accurately captured, which can be used to identify the difference in image color characteristics.Secondly, the composition of RP-3 jet fuel were analyzed. Based on the analysis of composition and boiling point, n-heptane is evaporated before water with the increasing of fuel droplet temperature. In order to accurately capture the combustion process of the micro oil droplet, a suspend droplet device which can prepare a droplet with diameter from 480 μm to 2200 μm, an elastic wire flying droplet device with an initial velocity of zero, and an integral type and assembly with a oil droplet diameter from 80μm to 600 μm were constructed respectively. By calibrating the light field and field-of-view equipment, the oil droplet sampling error, imaging error, lens effect error, image processing error, and image measurement uncertainty are detailedly analyzed.Then, in the micro-scale suspend droplet combustion process, the high-speed microscopic imaging technology was used to capture the entire process of the initiation, growth, coalescence and overflow of the micro-bubbles inside the oil droplet, The cyclical explosion/fragmentation process of bubbles evaporating inside the oil droplet, as well as the gas-film/balloon structure and its mutual transformation phenomenon on the oil droplet surface were found. Further, the role of surface tension in the combustion of micro oil droplet was analyzed, and the evolution mechanism of bubbles in micro oil droplet was interpred. The experiments confirmed that the burst critical size of the oil droplet was 2.5 μL to 5.0 μL in the suspend droplet test. Finally, eliminating the effect of the hanging wire on oil droplet heat transfer and adhesion, jet droplets and elastic fly droplet experiments were conducted. Through the regulation of the planar flame, the requirements of spray droplet error and consistency inspection were met, and a stable flying droplet evaporation combustion environment was obtained. The scallops on the surface droplet and the bubble inside droplet and the gas-film/balloon structure on droplet surface were captured, Moreover, it was found that small droplet burst and large droplet did not burst.
