A Study on Spray Combustion in Supercritical Environments

本文对超临界环境中的喷雾燃烧机理进行了基础性研究。本研究包括以下三个方面：（1）射流混合型喷雾燃烧室中的蓝焰燃烧;（2）超临界环境下喷雾中的油蒸气浓度和平均液滴直径;（3）热壁上超临界环境下液滴的蒸发和燃烧。（1）通过对火焰温度分布的测量和对火焰中燃烧成分的取样分析，研究了蓝焰燃烧的机理。蓝焰燃烧时喷嘴周围的氧浓度和温度高于黄焰燃烧时。火焰中的乙炔浓度在黄色火焰中显示出较高的值。(2)利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气浓度。燃油蒸气浓度的径向分布在喷雾中心和边缘处均呈现出一个低值，在中心和边缘之间出现一个最大值。喷雾的平均液滴直径通过夫琅和费衍射光的光学分析来测量。随着环境温度的升高，液滴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中燃料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。随着环境压力增加超过临界压力的燃料，燃烧结束时间增加的壁面温度范围内的临界温度的燃料以下，并在其他温度范围内，它减少。

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.