Reaction rates, air entrainment and radiation in turbulent fire plumes

Abstract An improved version of the k - ϵ - g model of turbulence is applied to the case of buoyancy controlled turbulent diffusion flames. The model accounts for the generation of turbulence due to the gravity field and describes the fluctuations of a conserved scalar quantity by introducing a polynomial probability density function (PDF). A combustion model is assumed which postulates infinitely fast chemical kinetics and determines the local burning rate by solving for the source term the fuel conservation equation in which convection and diffusion of fuel have been determined from calculated profiles of mean fuel mass fraction. The local emission of radiation by the luminous flames considered in the study is assumed to be proportional to the local volumetric burning rate. Predictions of the radiation emitted by horizontal slices of the flame agree with experimental measurements. While flame heights are correctly predicted, the model underestimates the lateral spread of the flame, despite the fact that total agreement between experiment and model predictions was obtained in an earlier study for a nonreacting thermal plume. Model predictions of an effective flame radius, which is representative of the net width of the region where reaction is taking place, agree with the same quantity obtained from radiation measurements. Calculated values of the amount of oxygen entrained in the plume are presented and the implications of the result on simpler fire plume models are discussed.