LIF Thermometry of a Fuel Droplet Burning Under Microgravity in a Drop Shaft

The achievement of the combustion research under microgravity depends substantially on the availability of diagnostic systems. The non-intrusive diagnostic systems are potentially applicable for providing the accurate, realistic and detailed information on momentum, mass and energy transport, complex gas phase chemistry, and phase change in the combustion field under microgravity. The non-intrusive nature of optical instruments is essential to the measurement of combustion process under microgravity which is very nervous to any perturbation. This has resulted in the increased interest in the development of the non-intrusive diagnostic systems available for the combustion experiments under microgravity. Although extensive efforts have been directed toward this subject, the diagnostic system remains largely undeveloped. The laser-based non-intrusive diagnostic systems have been successfully employed to the research of various combustion processes under the terrestrial condition. However, the application of the non-intrusive diagnostics to the combustion experiments under microgravity is accompanied by several constraints which happen to be crucial. A very limited space is only available for constructing a highly sophisticated system which is so sensitive that it is easily affected by the magnitude of gravitational force, vibration and heterogeneous field of temperature and density of the environments. Usually, the system should be properly adjusted prior to the experiment. It is quite difficult to tune the instruments during measurements. The programmed sequence of operation should also be provided. The flame under microgravity tends to be highly sooty. The strong black body radiation from soot in the flame often causes the hazardous noise in various optical measurements. This paper describes a part of the recent results obtained in a series of the research program on the development of non-intrusive diagnostic systems available for combustion experiments under microgravity. An attempt has been made to solve the above problems for developing a compact non-intrusive diagnostic system to do the instantaneous measurements of the temperature of a fuel droplet burning under microgravity in a drop shaft on the basis of the laser induced fluorescence thermometry which has been reported to be successfully applied for a single fuel droplet and a cloud of fine droplets in a fuel spray under the terrestrial condition.