On the combustion and the microexplosion of biodiesel/alcohol droplet in microgravity
Date Issued
2015
Date
2015
Author(s)
Hsieh, Chih-Wei
Abstract
In the present work, combustion of a multi-component droplet, blended with biodiesel and alcohol (methanol, ethanol and 2-propanol, respectively), was studied in a gravity-reduced environment. A “drop tower” facility was utilized to achieve the microgravity condition, and the falling time was about 0.68 s. Droplets of different sizes, i.e., 0.5 mm and 0.38 mm in diameter, respectively, were initially produced by a droplet generator. They were suspended at the crossing point of two ultra-thin fibers and ignited by a pair of electrical hot wires. The droplets then underwent a convection-free combustion, leading to formation of spherically symmetric flame. It was found that the existence of internal inhomogeneity directly contributed to occurrence of microexplosion. Via observation by using a CCD camera, explosion was yielded when a bubble was heated during the burning period to sufficiently high temperature. Furthermore, influence of different relative humidity of the environment was tested. The results revealed its little relevance to the formation of inhomogeneity in the droplet that was suspected to be caused by absorption of water on the surface. The stochastic nature of microexplosion was then found to correlate with the size of droplets, with a lower possibility of explosion in smaller ones. The maximum frequency occurred at 50% mass fraction of alcohol in all sizes of droplets, resulting in the corresponding highest averaged burning rate in the same proportion. In the meantime, the addition of alcohol into biodiesel showed significant enhancement of burning rate in the cases without explosion, with largest increment created when the mixture included 25% alcohol.
Subjects
microgravity
droplet combustion
biodiesel
alcohol
microexplosion
Type
thesis
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