Linear-Eddy Modeling of Turbulent Transport. Part 4. Structure of Diffusion Flames

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Abstract
A simulation model of the axial structure of turbulent jet diffusion flames is formulated for the purpose of interpreting flame-structure measurements. The model, based on the linear-eddy approach, incorporates spatial and temporal variation of the air entrainment rate, reflecting buoyancy effects, and an implementation of turbulent mixing using a novel stochastic representation of convective stirring in conjunction with Fick's law governing molecular diffusion. Simulation results are compared to axial profiles of mixing-cup density measured in propane flames. The comparisons suggest that the measured Froude-number dependences reflect the combined effect of finite-rate mixing and the transition from forced to natural convection. Predictions for hydrogen flames are presented in order to assess the generality of inferences based on the propane results.