The experiments were conducted by using the drop shaft of JAMIC (Japan Microgravity Center) at Hokkaido. The oil-in-water emulsion which consisted of n-hexadecane as a base fuel, distilled water and a trace of surfactant was tested. Photographic observation and temperature measurement were made of the suspended emulsion droplet during the heating-up and combustion processes under microgravity. The primary attention was toward the phase-separation in the droplet, and the time histories of droplet temperature and the amount of water in the droplet, during the period of time prior to disruptive microexplosion. The effects of the emulsion properties on the onset rate of microexplosion were also revealed by using statistical analysis.

The primary conclusions reached in the present study are as follows;

(1) The phase-separation occurs in the emulsion droplet. This results in the formation of a single water droplet enveloped by a shell of the base fuel prior to the microexplosion under microgravity.

(2) Selective evaporation of the base fuel would occur after the phase-separation. The volume of the base fuel decreases while the water volume does not change.

(3) The droplet temperatures at the start and the end of the phase-separation do not change with water content.

(4) The droplet temperature at the microexplosion decreases with water content.

(5) The microexplosion would occur after the phase-separation.

　

Fig. 13 Estimated onset rate of droplet microexplosion.

　

ACKNOWLEDGMENTS

　

This study was performed under the management of the Japan Space Utilization Promotion Center as a part of the R&D project of "Advanced Combustion Science Utilizing Microgravity" supported by NEDO (New Energy and Industrial Technology Development Organization). The authors also thank Kao Corporation for preparing the surfactant used in this study.

　

REFERENCES

　

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