Transcritical phenomena of autoignited fuel droplet at high pressures under microgravity |
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Authors: | Daisuke Segawa Tomoki Kajikawa Toshikazu Kadoka |
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Affiliation: | 1. Department of Mechanical Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Sakai, 599-8531, Osaka, Japan
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Abstract: | An experimental study has been performed under microgravity to obtain the detailed information needed for the deep understanding
of the combustion phenomena of single fuel droplets which autoignite in supercritical gaseous environment. The microgravity
environments both in a capsule of a drop shaft and during the parabolic flight of an aircraft were utilized for the experiments.
An octadecanol droplet suspended at the tip of a fine quartz fiber in the cold section of the high-pressure combustion chamber
was transferred quickly to be subjected to a hot gaseous medium in an electric furnace, this followed by autoignition and
combustion of the fuel droplet in supercritical gaseous environment. High-pressure gaseous mixture of oxygen and nitrogen
was used as the ambient gas. Temporal variation of temperature of the fuel droplet in supercritical gaseous environment was
examined using an embedded fine thermocouple. Sequential backlighted images of the autoignited fuel droplet or the lump of
fuel were acquired in supercritical gaseous environment with reduced oxygen concentration. The observed pressure dependence
of the ignition delay and that of the burning time of the droplet with the embedded thermocouple were consistent with the
previous results. Simultaneous imaging with thermometry showed that the appearance of the fuel changed remarkably at measured
fuel temperatures around the critical temperature of the pure fuel. The interface temperature of the fuel rose well beyond
the critical temperature of the pure fuel in supercritical gaseous environment. The fuel was gasified long before the end
of combustion in supercritical gaseous environment. The proportion of the gasification time to the burning time decreased
monotonically with increasing the ambient pressure. |
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