Modeling of radiation and nitric oxide formation in turbulent nonpremixed flames using a flamelet/progress variable formulation

A model for the prediction of the nitric oxide (NO) formation in turbulent nonpremixed flames is proposed. Since the NO formation has a strong temperature sensitivity, the accurate prediction of the flame temperature under the consideration of radiative heat losses is required. The first part of the paper addresses the extension of a flamelet-based combustion model to account for radiative heat loss effects by introducing enthalpy as an additional parameter. A transport equation for enthalpy is solved, and the radiative sink term in this equation is obtained from unsteady flamelet solutions. The model is applied to a large-eddy simulation (LES) of Sandia flame D, and the importance of the interaction between turbulence and radiation on temperature and mixture fraction is investigated. Based on the radiative flamelet formulation, a consistent model for the prediction of NO formation is developed in the second part of the paper. In this model, an additional transport equation for the NO mass fraction is solved, and the chemical source term is obtained from a flamelet library. Since the consumption rate is dependent on the NO mass fraction, this term requires modeling, which is discussed in this paper. By employing a scale similarity argument, a closure model for application in LES is presented. After the analysis of the proposed model for the thermal, nitrous oxide, and prompt pathways for NO formation, the NO model is integrated into the extended flamelet/progress variable model and applied in LES of Sandia flame D and a Pratt & Whitney aircraft engine combustor configuration. (C) 2008 American Institute of Physics.