Detailed soot modeling in turbulent jet diffusion flames

Abstract

An approach for modeling the interaction between the formation and oxidation of soot, the radiative heat loss, and the flowfield in turbulent jet diffusion flames is presented. These interactions are modeled by the flamelet library approach in the framework of prescribed probability density functions (PDFs). The formation and oxidation of soot is calculated from a detailed chemical soot model. The laminar flamelet concept is applied to model the rates of soot particle inception, soot volume dependent surface growth, and oxidation, as well as species and temperature fields, Radiative heat transfer from the soot particles and the gas-phase species, CO2 and H2O, decreases the peak flame temperature, which in turn influences the flamelet structures. Experiments from Young et al. on a turbulent ethylene diffusion flame are used to validate the modeling approach. The calculated fields of mean mixture fraction, temperature, and soot volume fraction are found to be in agreement with the experimental data. The spatially resolved rates of soot inception, surface growth, and oxidation are presented. The maximum rates of the surface independent production occur in the fuel-rich region at a radial position of about 10 mm. In contrast, the maximum rates of surface growth and oxidation are found on the centerline with the oxidation occurring at a higher location in the flame. The total rate has its maximum on the centerline, whereas soot formation and destruction balances on the slightly rich side near the stoichiometric contour. This shows the strong interaction of soot formation and oxidation in the flame. A sensitivity analysis of the calculated soot volume fraction on different model parameters is presented. The rate coefficient of the heterogeneous surface growth reaction is the most sensitive parameter. A 20% increase of this rate leads to a 65% increase of the calculated maximum soot volume fraction.