Effects of droplet diameter on instantaneous burning rate of isolated fuel droplets in argon-rich or carbon dioxide-rich ambiences under microgravity

• Published in: Proceedings of the Combustion Institute 2013, Vol.34 (1), p.1601-1608
• Main Authors: Nakaya, Shinji, Fujishima, Kotaro, Tsue, Mitsuhiro, Kono, Michikata, Segawa, Daisuke
• Format: Article
• Language: English
• Subjects: Argon; Carbon dioxide; Droplet combustion; Microgravity; Soot formation
• ISSN: 1540-7489; 1873-2704
• DOI: 10.1016/j.proci.2012.05.086

The burning characteristics of isolated fuel droplets for ethanol, 1-butanol and n-decane were experimentally examined in carbon dioxide-rich or argon-rich environments under microgravity. The ambience consisted of oxygen, nitrogen, carbon dioxide and argon. The concentration of oxygen was fixed to be 21% in volume percentage, and that of carbon dioxide or argon was varied from 0% to 60% in volume percentage. Detailed measurements of the droplet surface areas were conducted using a high speed video camera and the effective droplet diameter squared were calculated. The instantaneous burning rates were calculated from the evolutions of the droplet diameter squared. When the soot production was limited, the instantaneous burning rate increased with time. Variations of the instantaneous burning rate with the instantaneous droplet diameter squared were obtained. The results indicated that the instantaneous burning rate was correlated with the droplet diameter squared after the initial heating period and that was approximated by the first order linear function. From the function, an indicative burning rate and the dependence of the burning rate on the droplet diameter squared were obtained. The indicative burning rate increased with increase in the argon concentration and decreased with increase in the carbon dioxide concentration. They were well related to the thermal diffusivity of the ambient gas regardless of the gas components. The existence of other factors influencing the burning rate was inferred as well. On the other hand, the dependence of the instantaneous burning rate on the droplet diameter squared was attributed to the fuel properties.