Evaporation and Ignition of Liquid Fuels at Critical Pressure Regime.

在高压高温环境下测量了燃料液滴的点火时间。悬浮的正庚烷、正辛烷、正癸烷和正十六烷液滴直径为0.35至1.4mm，在高达950℃的温度下迅速浸入电炉中。液滴的附着，炉膛的运动和点火的测量在一个空气容器中进行，压力从大气压到超过临界压力。在大气压下测量的小液滴在高压下无法观察到相对较长的点火时间，并且对于本研究中使用的每种燃料，液滴不点燃的直径随着压力的增加而变小。点火时间随压力单调减小，即使在超临界压力下，点火时间行为也没有太大变化。与燃烧过程不同的是，在点火过程中没有发生剧烈的性质变化。这主要是因为在液滴点火现象中，与液滴燃烧现象相比，液滴的表面温度要低得多。在第二阶段的研究中，研究了正癸烷和正十六烷在高压环境下悬浮燃料液滴阵列中的火焰传播现象。7个大小相同的液滴以等距水平排列。在0.1 ~ 2.0MPa的环境压力下，利用带图像增强器的高速摄像机检测到直径为0.50、0.75和1.0mm的液滴的OH发射历史，测量火焰的传播速率。结果表明，随着液滴间距的减小，火焰蔓延速度增大，并在一定间距处达到最大值。由于汽化潜热较大，液滴间距的进一步减小使扩散速率降低。火焰蔓延速率随压力的增大而减小，超过临界压力时没有火焰蔓延。这是由于火焰直径随着压力的增加而迅速减小。少

Ignition times of a fuel droplet were measured in a high-pressure high-temperature ambient. Suspended n-heptane, n-octane, n-decane, and n-hexadecane droplets with diameters of 0.35 to 1.4mm were quickly immersed in an electric furnace at temperatures up to 950. Attachment of a droplet, movement of the furnace and measurement of ignition were carried out in an air vessel with pressures from atmospheric pressure to over the critical pressure.Relatively long ignition times of small droplets measured under atmospheric pressure could not be observed at high pressures and the diameter below which a droplet does not ignite became smaller with pressure for every fuel used in this research. Ignition time decreased monotonously with pressure, and even at supercritical pressures, the ignition time behavior did not change much. Being different from the case of combustion, it is suggested that drastic change of properties did not take place in ignition processes. This is basically because the surf … More ace temperature of the droplet is much lower for droplet ignition phenomena in comparison with the droplet burning.At the second stage of the research, flame spread phenomena in a suspended fuel droplet array were investigated for n-decane and n-hexadecane in a high-pressure ambience. Seven droplets of the same size were arranged horizontally at equal spacings. Flame spread rates were measured based on OH emission histories detected by a high-speed video camera with an image intensifier for droplet diameters of 0.50,0.75, and 1.0mm at ambient pressure from 0.1 to 2.0MPa.Results showed that, as droplet spacing became smaller, flame spread rate increased and had a maximum value at a certain spacing. A further decrease in droplet spacing caused the spread rate to decrease due to the large latent heat of vaporization. Flame spread rate decreased with pressure and no flame spread was observed at the pressure over the critical pressure. This is due to the rapid decrease in flame diameter with pressure. Less