The effect of fine droplets on laminar propagation speed of a strained acetone-methane flame: Experiment and simulations
Mohd Jaafar, MN
de Oliveira, PM
Combustion and Flame
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Fan, L., Tian, B., Chong, C., Mohd Jaafar, M., Tanno, K., McGrath, D., de Oliveira, P., et al. (2021). The effect of fine droplets on laminar propagation speed of a strained acetone-methane flame: Experiment and simulations. Combustion and Flame, 229 https://doi.org/10.1016/j.combustflame.2021.02.023
In this study, we investigate the e ffect 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 eld behavior to that of the fully vaporized mixture. An impinging stagnation flame con figuration 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 m by carefully tuning the air ow 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 signi cantly 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 di fferently from the well-premixed gaseous counterpart. Simulations at similar conditions are performed using a two-phase counter flow 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 di culties in determining the pre-vaporization process and thus the boundary conditions, as well as the fi delity of the current point-source based 1D model.
The authors gratefully acknowledge the nancial support from Universiti Teknologi Malaysia under grant number RG84263, and a UK Newton Advanced Fellowship (NA160115) for C. T. Chong.
University of Malaya (UM) (unknown)
Universiti Teknologi Malaysia (UTM) ()
Royal Society (NA160115)
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External DOI: https://doi.org/10.1016/j.combustflame.2021.02.023
This record's URL: https://www.repository.cam.ac.uk/handle/1810/317973
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