Abstract
Understanding the combustion characteristics of fuel droplets laden with energetic nanoparticles (NP) is pivotal for lowering ignition delay, reducing pollutant emissions and increasing the combustion efficiency in next generation combustors. In this study, first we elucidate the feedback coupling between two key interacting mechanisms, namely, secondary atomization and particle agglomeration; that govern the effective mass fraction of NPs within the droplet. Second, we show how the initial NP concentration modulates their relative dominance leading to a master-slave configuration. Secondary atomization of novel nanofuels is a crucial process since it enables an effective transport of dispersed NPs to the flame (a pre-requisite condition for NPs to burn). Contrarily, NP agglomeration at the droplet surface leads to shell formation thereby retaining NPs inside the droplet. In particular, we show that at dense concentrations shell formation (master process) dominates over secondary atomization (slave) while at dilute particle loading it is the high frequency bubble ejections (master) that disrupt shell formation (slave) through its rupture and continuous outflux of NPs. This results in distinct combustion residues at dilute and dense concentrations, thereby providing a method of manufacturing flame synthesized microstructures with distinct morphologies.
Highlights
(1) ejection impact parameter αlocal,max (t) and (2) droplet void fraction ξ(t)
The total area swept by centroid motion during the droplet lifetime is an order higher at dilute PLRs compared to dense PLRs (A is confined to a small region surrounding the initial centroid (x0, y0))
Significant effort is directed towards understanding the combustion behavior of nanofuel droplets with a motive of enhancing the exothermicity, energy density, ignition probability and auto ignition properties of conventional hydrocarbon fuels while reducing their soot forming potential
Summary
Understanding the combustion characteristics of fuel droplets laden with energetic nanoparticles (NP) is pivotal for lowering ignition delay, reducing pollutant emissions and increasing the combustion efficiency in generation combustors. First we elucidate the feedback coupling between two key interacting mechanisms, namely, secondary atomization and particle agglomeration; that govern the effective mass fraction of NPs within the droplet. Secondary atomization of novel nanofuels is a crucial process since it enables an effective transport of dispersed NPs to the flame (a pre-requisite condition for NPs to burn). (1) ejection impact parameter αlocal,max (t) and (2) droplet void fraction ξ(t) Physical interpretation of these parameters and the classification of ejection modes[6,8] based on these parameters is detailed in references[6,7,8]. We explain physically how the interplay between two key mechanisms affects the global atomization behavior of burning nanofuel droplets i.e. the frequency of ejections f(t) and the shell formation by NP aggregation.
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