Assessment of existing and new modeling strategies for the simulation of OH* radiation in high-temperature flames

Four methods to calculate OH* radiation from numerical simulations of flames above 2700 K are presented: (1) A state-of-the-art chemiluminescence model: OH* emission is assumed to be proportional to the concentration of an excited sub-species OH*. OH* is implemented in the detailed chemical reaction mechanism. (2) A spectral model: emission and absorption are computed and integrated on a line-by-line basis from the HITRAN data base. (3) An equilibrium filtered radiation model: it provides a very simple way to compute OH* emissivity in a post-processing step. This is a simplification of the chemiluminescence model suitable for high-temperature flames. (4) An extension of the latter model to approximate the influence of self-absorption. The advantages and limitations of all approaches are discussed from a physics-based perspective. Their performances are assessed in a laminar hydrogen–oxygen jet flame at varying pressure. The importance of self-absorption for OH* radiation is analyzed and emphasized. Recommendations for the model selection are given.