The effect of fine droplets on laminar propagation speed of a strained acetone-methane flame: Experiment and simulations
Journal article
Authors | Fan, Luming, Tian, Bo, Chong, Cheng Tung, Jaafar, Mohammad Nazri Mohd, Tanno, Kenji, McGrath, Dante, Oliveira, Pedro M.de, Rogg, Bernd and Hochgreb, Simone |
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Abstract | In this study, we investigate the effect of the presence of fuel droplets, their size and concentration, on stretched laminar flame speeds. We consider premixed strained methane/air mixtures, with the addition of small acetone droplets, and compare the flame velocity field behaviour to that of the fully vaporized mixture. An impinging stagnation flame configuration is used, to which a narrowly distributed polydisperse mist of acetone droplets is added. Total acetone molar concentrations between 9% and 20% per mole of methane are used, corresponding to 18.6% and 41.4% of the total fuel energy. The Sauter Mean Diameter (SMD) of acetone droplets is varied from 1.0 to 4.7 μm by carefully tuning the air flow rate passing through an atomizer. The droplet size distribution is characterized by a Phase Doppler Anamometry (PDA) system at the outlet of the burner. The flame propagation speed is measured using Particle Image Velocimetry (PIV) for overall equivalence ratios ranging from 0.8 to 1.4 at various strain rates, and the result is compared with a reference case in which acetone was fully vaporized. Unlike the fully vaporized flame, a two-stage reaction flame structure is observed for all droplet cases: a blue premixed flame front followed by a reddish luminous zone. Comparison of the results between gas-only and droplet-laden cases shows that the mean reference burning velocity of the mixture is significantly enhanced when droplets are present under rich cases, whereas the opposite is true for stoichiometric and lean cases. The mean droplet size also changes the relationship between flame speed and strain rate, especially for rich cases. The result suggests that with typical conditions found in laminar strained flames, even for the finest droplets that may have been vaporized before reaching the flame front, the resulting inhomogeneities may lead the flame to behaves differently from the well-premixed gaseous counterpart. Simulations at similar conditions are performed using a two-phase counterflow flame model to compare with experimental data. Model results of reference velocities do not compare well with observations, and the possible reasons for this behaviour are discussed, including the difficulties in determining the pre-vaporization process and thus the boundary conditions, as well as the fidelity of the current point-source based 1D model. |
Keywords | Aerosol Sprays; Laminar flame; PIV |
Year | 2021 |
Journal | Combustion and Flame |
Journal citation | 229, p. 111377 |
Publisher | Elsevier |
ISSN | 00102180 |
Digital Object Identifier (DOI) | https://doi.org/10.1016/j.combustflame.2021.02.023 |
Web address (URL) | http://hdl.handle.net/10545/625746 |
hdl:10545/625746 | |
Publication dates | 31 Jul 2021 |
Publication process dates | |
Deposited | 30 Apr 2021, 08:33 |
Accepted | 19 Feb 2021 |
Rights | © 2021 The Combustion Institute. Published by Elsevier Inc. All rights reserved. |
Contributors | University of Derby and University of Cambridge |
File | File Access Level Open |
https://repository.derby.ac.uk/item/9352x/the-effect-of-fine-droplets-on-laminar-propagation-speed-of-a-strained-acetone-methane-flame-experiment-and-simulations
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