2016 Has correction 2016-6-29**Abstract:** Accurate computation of molecular diffusion coefficients in chemically reacting flows can be an expensive procedure, and the use of constant non-unity Lewis numbers has been adopted often as a cheaper alternative. The goal of the current work is to explore the validity and the limitations of the constant non-unity Lewis number approach in the description of molecular mixing in laminar and turbulent flames. To carry out this analysis, three test cases have been selected, including a lean, highly unstable, premi…

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“…This is because the species Lewis numbers vary relatively little through the flame even when using mixture-averaged formulation. 31 Extension of these conclusions to other conditions, such as lean hydrogen/air flames, where thermo-diffusive instabilities occur, is unclear and should be the subject of future work.…”

confidence: 99%

“…This is because the species Lewis numbers vary relatively little through the flame even when using mixture-averaged formulation. 31 Extension of these conclusions to other conditions, such as lean hydrogen/air flames, where thermo-diffusive instabilities occur, is unclear and should be the subject of future work.…”

confidence: 99%

“…11,30 Constant non-unity Lewis numbers were employed, 31 and the species Lewis numbers are the same as those listed in the work of Savard and Blanquart. 12 The chemical and transport models were compared against experimental data and numerical results using full transport (mixture-averaged formulation).…”

confidence: 99%

“…They reported that methane, n-heptane, iso-octane, and toluene flames have similar normalized turbulent flame speeds and fuel burning rates when neglecting differential diffusion, but flames using the nonunity Lewis number approximation underpredict the normalized flame speed when including differential diffusion due to reduced burning rates [3]. Building on these results, Burali et al [2] evaluated the relative accuracy of the nonunity Lewis number assumption relative to mixture-averaged diffusion for lean, unstable hydrogen/air flames; lean, turbulent n-heptane/air flames; and ethylene/air coflow diffusion flames. Their results demonstrated that the relative error associated with the nonunity Lewis number assumption could be minimized with careful selection of the Lewis number vector for a wide range of flames [2].…”

confidence: 94%

“…This is because calculating diffusion fluxes requires point-wise knowledge of the multicomponent diffusion coefficient matrix, which scales with the number of chemical species squared [1]. The unity Lewis number, non-unity Lewis number, and mixture-averaged diffusion assumptions have been used to reduce the costs associated with mass diffusion by approximating the full diffusion coefficient matrix as a constant scalar value, a constant vector, and a matrix diagonal, respectively [1][2][3][4]. In addition, several approaches, such as those used by Warnatz [5] and Coltrin et al [6], further reduce the system's complexity by approximating multicomponent diffusion processes in terms of equivalent Fickian processes.…”

confidence: 99%