| Summary: | 博士 === 國立成功大學 === 航空太空工程學系 === 103 === Coaxial injector is mainly used in large-scale liquid rocket engines. By utilizing optical methods, this research studies the effects of gas to liquid velocity ratio (2.9 to 60), gas layer thickness (1.2 mm to 2.4 mm), and liquid physical properties (surface tension and viscosity) on the breakup and atomization of coaxial liquid jet spray. The spray angles, droplet size (SMD, SMD0.1) distributions as well as the breakup processes at different experimental conditions are observed and analyzed.
The results reveal that the significance of the breakup of coaxial jet spray is the surrounding high speed air confines the spray spatially, and forces the inherent unstable liquid column into spiral-type turning, then elongates into ligament before instantaneous breakup. Once the liquid jet has broken up, the outer high speed air appears to have no further effect on the spray. Due to this controlling breakup process, the spray angle appears to be increased with increasing velocity ratio but decreased with increasing gas layer thickness, and the droplet size distribution of coaxial jet spray appears to be uniform, concentrated, and invariant after jet has broken up.
Coaxial jet with a lower liquid surface tension apparently shows more branching fiber growth from the liquid column surface that induces smaller droplets stripping from main wavy jet. Increasing liquid viscosity in this study shows an intense effect on coaxial jet spray. With higher viscosity, the liquid ligament is stretched wider to penetrate the liquid and gas boundary before disintegration. Hence, the liquid ligament could utilize more energy of surrounding high speed air for liquid atomization, thus to produce larger spray angle and smaller droplet sizes as observed in the experiments.
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