Flame dynamics and spread in atomizing multicomponent droplets of biodiesel and ethanol doped with graphene oxide
Sepehr Mosadegh, Sina Kheirkhah
Abstract
The effects of heterogeneous and homogeneous atomizations on combustion dynamics and flame spread rates of multi-droplets are experimentally investigated. The utilized fuel is biodiesel, which is blended with ethanol and doped with graphene oxide. Scanning Electron Microscopy, Raman spectroscopy, and X-ray diffraction experiments were conducted to characterize the utilized graphene oxide. Stable fuel suspensions are prepared. Either one droplet is positioned at the intersection of three thin fibers or an array of three droplets is positioned along a horizontal line and at the intersections of the fibers. For the latter configuration, either the droplet at the center or that on the right-hand-side is ignited. Simultaneous and time-resolved flame chemiluminescence and shadowgraphy techniques are utilized for imaging the flame and droplets, respectively. It is observed that, for a single droplet combustion of biodiesel, relatively low frequency (about 10 Hz) dynamics appear in the second half of the droplet life-time, which is due to heterogeneous atomizations. Blending with ethanol leads to homogeneous atomizations with dynamics featuring frequencies smaller than 50 Hz and at the beginning of the droplet lifetime. For all tested multi-droplet configurations, independent of the graphene oxide doping concentration and blending with ethanol, the most dominant frequency of flame chemiluminescence oscillations is about 10–15 Hz. It is observed that the heterogeneous atomizations lead to a flame spread rate of about 6 mm 2 / s . Compared with that for heterogeneous atomizations, the flame spread rate for homogeneous atomizations are significantly larger (10–40 mm 2 / s ) and feature a positive relation with the root-mean-square of the main droplet’s flame chemiluminescence oscillations. Overall, the results of the present study underline the important role of atomizations on the flame dynamics and how fast the flame spreads in multi-droplet configurations. • Flame oscillations of homogeneous atomizations were larger than heterogeneous ones. • Flame spread rates were higher in ethanol–biodiesel blends than those for biodiesel. • Modes of flame spread among multi-droplets affected by atomizations were identified. • Doping with graphene oxide had small impact on flame spread of low-volatility fuels.