Geometry characterization and thermal radiation prediction of buoyant square and line diffusion flames based on 3D flame reconstruction

Abstract

This paper presents an experimental study on the instantaneous and mean geometrical features and radiation properties of buoyant square and line diffusion flames with heat release rates (Q˙) of 5.0–30.0 kW using the visual hull reconstruction method. Equal fuel exit areas were selected for the square and linear burners to reveal the effect of fire source shape on the combustion process. Results show that the reconstructed three-dimensional (3D) instantaneous flames could well reflect the temporal evolutions of the square and line flames. The instantaneous flame surface area and volume exhibit excellent synchronization with time. Consistent with the predictions based on the turbulent mixing concepts, the mean flame surface area and volume of the square flame are lower than the line flame under equal Q˙. The heat release rates per unit surface area remain unchanged, and the heat release rates per unit volume decrease slightly with Q˙ for the square and line flames. The mean beam lengths, calculated from the mean flame surface area and volume of the 3D flame shape, increase with Q˙ steadily for the two types of flames. A 3D flame radiation model is developed based on the reconstructed 3D instantaneous flame shape. It could accurately predict the instantaneous and time-averaged radiative heat fluxes in the near-field and far-field for axisymmetric and non-axisymmetric flames.