A Study on Spray Combustion in Supercritical Environments

对液体燃料临界点，即超临界环境下加压和加热环境气体的喷雾燃烧机理进行了基础研究。本文的研究内容包括以下三个方面：(1)喷射混合式喷雾燃烧室内的蓝色火焰燃烧；(2)超临界环境下喷雾中的燃油蒸汽浓度和平均液滴直径；(3)超临界环境下的液滴蒸发和热壁燃烧。蓝色火焰燃烧时喷嘴周围的氧气浓度和温度均高于黄色火焰燃烧。火焰中的乙炔浓度在黄色火焰中表现出较高的值。(2)用再现全息图的图像处理技术测量了超临界环境下喷雾中的燃油蒸汽浓度。燃油蒸汽浓度的径向分布在喷雾中心和喷雾边缘处表现出较低的值，并在两者之间出现最大值。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，液滴的平均直径先增大后减小。(3)在压力容器中观察了超临界环境下油滴在壁面上的蒸发和燃烧过程。在相同壁温下，空气中的蒸发寿命比氮气中的短。当环境压力超过燃料的临界压力时，在壁面温度略低于燃料临界温度的温度范围内，燃烧结束时间增加，而在其他温度范围内，燃烧结束时间缩短。

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.