Detailed modeling of soot formation and turbulence-radiation interactions in turbulent jet flames.

摘要

Detailed radiation modeling of turbulent sooting flames faces a number of challenges. Principal among these have been been a lack of good models for predicting soot formation and effective means to capture turbulence-chemistry interactions in soot subprocesses. Uncertainties in measurement and prediction of soot properties has also been a problem. Radiative heat transfer becomes important in combustion environments due to the very high temperatures encountered and has not yet been studied in sufficient detail in the case of luminous (i.e., sooting) flames. A comprehensive approach for modeling turbulent reacting flows, including detailed chemistry, radiation and soot models with detailed closures for turbulence-chemistry interactions (TCI) and turbulence-radiation interactions (TRI) is developed in this work. A review of up-to-date literature on turbulent combustion modeling, turbulence-radiation interactions and soot modeling is given. A transported probability density function (PDF) approach is used to model turbulence-chemistry interactions and extended to include soot formation. Nongray gas and soot radiation is modeled using a photon Monte Carlo (PMC) method coupled with the PDF method. Soot formation is modeled based on the method of moments (MOM) approach with interpolative closure.;Optimal soot submodel parameters are identified based on comparison of model predictions with experimental data from various laminar premixed and (opposed) diffusion flames. These parameters (including gas-phase chemistry) are applied to turbulent flames without further "tuning." Six turbulent jet flames with Reynolds numbers varying from 6700 to 15000, varying fuel types---pure ethylene, 90% methane-10% ethylene blend and different oxygen concentrations in the oxidizer stream from 21%O2 (air) to 55%O 2, are simulated. The predicted soot volume fractions, temperature and radiative wall fluxes (when available) are compared with experiments. All the simulations are carried out with a single set of parameters for all models involved, without specific adjustments. Very encouraging agreement is found for most of the quantities, representing a significant step forward in modeling turbulent sooting flames. A detailed analysis of the radiation characteristics of these flames is also undertaken. It is found that emission TRI was generally important for all the flames. In the laboratory scale flames, including TRI increases the radiative loss from the flame by up to 90%. Absorption TRI is found to be unimportant in laboratory-scale flames, but becomes important in the large (industrial scale) flame that was studied numerically.