Self-tuning and topological transitions in a free-falling nanofuel droplet flame

Pandey, K and Basu, S and V, G and Potnis, A and Chattopadhyay, K (2020) Self-tuning and topological transitions in a free-falling nanofuel droplet flame. In: Combustion and Flame, 220 . pp. 144-156.

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Abstract

In the present study, flame dynamics of free-falling contactless burning fuel droplets (pure and nanofuel) is investigated. A droplet under free fall undergoes acceleration resulting in progressive increase of its velocity (increase in Reynolds Number, Re) along the path. The consequent dynamic external relative flow induced along the drop trajectory allows self-tuning of the flame through a series of transitions. At low Re, the droplet flame transitions from an initial fully enveloped buoyant diffusion flame to a premixed wake flame structure. It is shown that this transition occurs due to flame extinction at the droplet forward stagnation point when critical strain rate is exceeded due to the external flow. Subsequently the wake flame topology undergoes significant variations with further increase in Reynolds number. The flow conditions necessary for wake-flame stabilization are characterized. Using a round-jet analogy, a linear relationship between the flame height and Reynolds number is established which shows that topological transitions are predominantly hydrodynamic in nature. Droplet burning rate for all functional droplets exhibits minimal change due to reduced energy input from the wake flame. However, for nanofuel droplets, the global heat release is lowered due to the reduction in gasification rate brought about by the in-situ formation of porous structure by the agglomeration of nanoparticles. Furthermore, for particle laden droplets, absence of sufficient energy input from the flame suppresses internal heterogeneous boiling as found in most pendant droplet experiments. © 2020

Item Type:	Journal Article
Publication:	Combustion and Flame
Publisher:	Elsevier Inc.
Additional Information:	Copyright for this article belongs to Elsevier Inc.
Department/Centre:	Division of Interdisciplinary Sciences > Interdisciplinary Centre for Energy Research Division of Mechanical Sciences > Mechanical Engineering Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	11 Nov 2021 11:49
Last Modified:	11 Nov 2021 11:49
URI:	http://eprints.iisc.ac.in/id/eprint/66077

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