(Theoretical Studies on Evaporation and Combustion for Single Droplets and Sprays)

• Main Authors: Jeng-Shien Shieh, 謝政憲
• Other Authors: Keh-Chin Chang
• Format: Others
• Language: en_US
• Published: 1995
• Online Access: http://ndltd.ncl.edu.tw/handle/76451523106261280537

博士 === 國立成功大學 === 航空太空工程學系 === 83 === The first part of this study regards the combustion of single droplets. The present simulations were performed under the same test conditions as those of Kobayasi(1955) except that buoyancy effects were neglected. The primary objective of this theoretical analysis centers on the thermal radiation from the droplet flame. Radiation absorption of liquid fuel and gas mixture are therefore considered here. The results show that the consideration of flame radiation on droplet combustion in the post-ignition period leads to some differences in droplet regression rate predictions. The prediction for the opaque droplet burning rate is slower than that for the semitransparent case. The second part of the study is a theoretical analysis of evaporating and combusting sprays. Nearly complete measurements of dilute, polydisperse methanol sprays have been provided by McDonell and Samuelsen (1990). Droplet turbulent kinetic energy predictions are in good agreement with the measurements. Two separated flow methods, one deterministic and one stochastic, are examined. The results show that the dispersion effects are predicted well by the stochastic method for small droplets. The other test case focuses on the dilute, monodisperse methanol spray burnt in a turbulent buoyant methane flame which was also experimental studied by Shuen et al. (1985b). The major contribution of the present study is that internal heating and circulation of droplet are considered. Instead of the thin-skin approximation, a spherically symmetrical conduction equation for droplet is solved. Thus, the predicted droplet lifetime of the present study are longer than those predicted by Shuen et al.(1985b). However, some deviations from the measurements still exist for some liquid-phase properties.