FLAMELET-MODELING OF TURBULENT SPRAY DIFFUSION FLAMES BASED ON A LAMINAR SPRAY FLAME LIBRARY

The present paper investigates the structure of turbulent spray diffus ion flames by means of numerical simulations. The flamelet model for t urbulent diffusion flames has recently been extended to turbulent spra y diffusion flames. The model is suitable for considering detailed che mical reactions through use of a laminar flame library consisting of s tructures of laminar gas diffusion flamelets that are characterized by the mixture fraction and its scalar dissipation rate. The focus of th e present paper is the implementation of laminar spray diffusion flame s for use in turbulent flame computations. Since the structure of lami nar spray flames is considerably different from that of their gaseous counterparts, new criteria need to be developed for the implementation of these structures. The present paper presents characteristics of la minar spray flames and their consideration in turbulent flame computat ions. Both the model predictions (using either laminar gas flames or l aminar spray flames) are compared to experimental results of a turbule nt, axisymmetric free jet where an air-assisted methanol spray is inje cted into air. The new model is free of parameters that need to be adj usted to predict experimental data, and it correctly predicts the prin cipal structure of the turbulent spray flame. Two reaction zones are i dentified where the turbulent model using laminar gas flames needs an artificial cut-off temperature to predict the low temperature regime w here liquid is present. Thus, the use of laminar spray flames is requi red for the prediction of turbulent spray flame characteristics within the vaporization zone.