Prediction and measurement of a non-equilibrium turbulent diffusion flame

Superequilibrium radical concentrations in a turbulent CO/H2/N2 jet diffusion flame are computed using a two-scalar pdf model and directly measured using single pulse laser saturated OH fluorescence. The model is based on the averaged Navier-Stokes equations and the k∈l turbulence model. Non-equilibrium chemistry is accounted for by including CO in the partially equilibrated oxyhydrogen radical pool. Two scalars (mixture fraction and eaction progress suffice to describe the thermochemical system. Laser saturated fluorescence is used to directly measure the mean and fluctuating components of OH concentrations and thus the radical pool. Measurements and model both find mean OH concentrations which are four to six times larger than equilibrium with rms values of OH concentration also reasonably predicted. Superequilibrium effects are predicted to lower the mean temperature by as much as 250 K in agreement with experiments. Evidence of the breakdown of partial equilibrium was found in cool fuel-rich zones where predictions of temperature and OH concentration were too high. Extensions of the model to predict thermal NO formation and CO burnout are discussed.