The paper presents a transient, axisymmetric numerical simulation of combustion of methanol droplets in a nearly quiescent environment (with ambient temperature of 1200 K, ambient pressure of 1 atm., and Reynolds number of 10−2). The focus is on the combustion process of droplet sizes applicable in a practical spray. A gradual transition from kinetically controlled combustion to diffusion controlled combustion is found with the increase in droplet sizes. Droplets smaller than ≈ 60 μm are influenced more by chemical kinetics due to the reaction zone broadening and a concomitant reduction in flame temperatures. In this kinetically controlled regime, the burning rate of an individual droplet first increases to a maximum, and then decreases. In this regime, the average of droplet burning rate over its life time is bounded by an upper bound of thin flame-sheet burning rate (large Damköhler number limit), and a lower bound of pure evaporation rate (small Damköhler number limit). The actual average burning rate lies between the two values, determined by the droplet size. For droplets smaller than ≈ 60 μm, the flame stand-off ratio varies throughout their lifetime. The analysis underlines the importance of accurate chemical kinetics modelling for small droplets.
Combustion Characteristics of Small Isolated Methanol Droplets
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Awasthi, I, Gogos, G, & Sundararajan, T. "Combustion Characteristics of Small Isolated Methanol Droplets." Proceedings of the ASME 2012 International Mechanical Engineering Congress and Exposition. Volume 7: Fluids and Heat Transfer, Parts A, B, C, and D. Houston, Texas, USA. November 9–15, 2012. pp. 405-415. ASME. https://doi.org/10.1115/IMECE2012-86165
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