Ethanol Spray Combustion under a MILD Condition: A Chemical Kinetic Study
2019
Karimi Motaalegh Mahalegi, Hamed | Mardani, Amir
Moderate or intense low-oxygen dilution (MILD) combustion of liquid fuels has attracted attention because of its advantages in industrial burners and gas turbine applications. Here, numerical investigation has been conducted on an experimental MILD turbulent spray burner. The H∥ flame of Delft spray in a hot co-flow burner is selected, and the Reynolds averaged Navier–Stokes/eddy dissipation concept framework with 40 species/180 reversible reactions through a skeletal chemical mechanism is used in addition to unsteady Lagrangian tracking of spray droplets to investigate the flame structure and chemical kinetic of reacting flow field. At first, current numerical results were compared with experimental measurement data and also quantitatively compared with previous numerical works. Overall, the trends of the experimental result are well predicted, although there are some deviations in maximum temperature and prediction of fine droplets. Subsequently, after inspection of thermal and velocity fields, as well as heat release, five distinct zones have been distinguished. Each zone is analyzed by an equivalent perfectly stirred reactor, and ethanol consumption pathways are studied. They unravel specific characteristics of ethanol consumption under MILD combustion. It was revealed that high co-flow temperature and distributed heat release can strengthen the endothermic direct decomposition route of ethanol to ethylene and weaken the exothermic production of C₂H₅O isomer radicals which are dominant in ordinary combustion. Furthermore, stable intermediates such as ethylene, acetaldehyde, and methane accumulate under fuel-rich and moderately high-temperature conditions of the internally reacting region because of the absence of loss routes in the chemical pathways.
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