Abstract
Generating energy from combustion is prone to pollutant formation. In energy systems working under non-premixed combustion mode, rapid mixing is required to increase the heat release rates. However, local extinction and re-ignition may occur, resulting from strong turbulence–chemistry interaction, especially when rates of mixing exceed combustion rates, causing harmful emissions and flame instability. Since the physical mechanisms for such processes are not well understood, there are not yet combustion models in large eddy simulation (LES) context capable of accurately predicting them. In the present study, finite-rate scale similarity (SS) combustion models were applied to evaluate both heat release and combustion rates. The performance of three SS models was a priori assessed based on the direct numerical simulation of a temporally evolving syngas jet flame experiencing high level of local extinction and re-ignition. The results show that SS models following the Bardina’s “grid filtering” approach (A and B) have lower errors than the model based on the Germano’s “test filtering” approach (C), in terms of mean, root mean square (RMS), and local errors. In mean, both Bardina’s based models capture well the filtered combustion and heat release rates. Locally, Model A captures better major species, while Model B retrieves radicals more accurately.
Highlights
Combustion of fossil fuels is still the main source of energy production
Many engineering applications take the advantage of such turbulent combustion, which enhances the mixing of fuel and oxidizer
Since the formation rates of both major and minor species are provided by direct numerical simulation (DNS), it is interesting to assess the models in predicting species formation rates of both major and radical species
Summary
Combustion of fossil fuels is still the main source of energy production. generating energy from combustion of conventional sources is prone to pollutant formation and emissions. In the context of LES of reactive flows, DesJardin and Frankel [11] proposed to use the SS idea to close the filtered formation rate of species ω k (φ) in Equation (1) They reported both a priori and a posteriori assessments of the method using a two-dimensional spatially developing non-premixed jet DNS database with one-step chemistry. The selected SS models were employed in a more challenging test case employing large filter widths (∆/∆DNS = 8, 12, 18) to assess their capabilities in the prediction of combustion and heat release rates along with the extinction and re-ignition phases of a temporally evolving syngas jet flame for which a DNS database is available.
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