Evaporation and Ignition of Liquid Fuels at Critical Pressure Regime.

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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