A Study on Spray Combustion in Supercritical Environments

对超过液体燃料临界点的加压加热环境气体即超临界环境中喷雾燃烧机理进行了基础研究。目前的研究主要包括以下三个方面：(1)射流混合式喷雾燃烧器的蓝焰燃烧；(2)超临界环境下喷雾燃料蒸气浓度和平均液滴直径；(3)超临界环境下热壁上液滴蒸发和燃烧。主要实验结果如下：(1)通过火焰内温度分布的测量和火焰内燃烧成分的采样分析，探讨了蓝色火焰燃烧的机理。蓝色火焰燃烧时喷嘴周围的氧浓度和温度高于黄色火焰燃烧时。火焰中乙炔浓度在黄色火焰中值较高。(2)采用重建全息图图像处理技术测量了超临界环境下喷注的燃油蒸气浓度。燃油蒸气浓度的径向分布在喷淋中心和喷淋边缘处较低，在喷淋中心和喷淋边缘处最大。通过夫琅和费衍射光的光学分析，测量了喷雾的平均液滴直径。随着环境温度的升高，平均液滴直径先增大一次，然后减小。(3)在压力容器中观察了超临界环境下燃料滴在壁面上的蒸发和燃烧过程。在相同壁温下，在空气中的蒸发寿命短于在氮气中的蒸发寿命。当环境压力超过燃料临界压力时，燃烧结束时间在刚好低于燃料临界温度的壁面温度范围内增加，在其他温度范围内减少。

A basic research was conducted on mechanisms of spray combustion in pressurized and heated ambient gas beyond the critical point of liquid fuel, that is, supercritical environments. The current research includes the following three items : (1) Blue Flame Combustion in a Jet-Mixing-Type Spray Combustor (2) Fuel Vapor Concentration and Mean Drop Diameter in a Spray Injected into Supercritical Environments (3) Drop Evaporation and Combustion in Supercritical Environments on a Hot Wall.The principal results of the experiments listed above are as follows: (1) Mechanisms of blue flame combustion were investigated by the measurement of temperature distribution in a flame and the sampling analysis of combustion contents in a flame. Oxygen concentration and temperature around a nozzle in blue flame combustion were higher than in yellow flame combustion. Acetylene concentration in a flame showed higher value in a yellow flame. (2) Fuel vapor concentration in a spray injected into supercritical environments was measured by the image processing technique of a reconstructed hologram. The radial distribution of the fuel vapor concentration showed a low value at the center and the edge of the spray, and took a maximum between them. Mean drop diameter of the spray was measured by the optical analysis of the Fraunhofer diffraction light. The mean drop diameter increased once, then decreased with an increase of the ambient temperature. (3) Evaporation and combustion processes of a fuel drop in supercritical environments on a wall were observed in a pressure vessel. The evaporation lifetime in air was found to be shorter than that in nitrogen at the same wall temperature. As the ambient pressure increased beyond the critical pressure of the fuel, the end of combustion time increased in the wall temperature range just below the critical temperature of the fuel, and in the other temperature range it decreased.