Ansys Fluent provides five models for the prediction of soot formation in combustion systems. The predicted soot concentration can be coupled with radiation absorption for the P-1, discrete ordinates, or discrete transfer radiation models with a variable absorption coefficient.
Ansys Fluent predicts soot concentrations in a combustion system using one of the following available models:
the one-step Khan and Greeves model [301], in which Ansys Fluent predicts the rate of soot formation based on an empirical relation. This is a default soot formation model in Ansys Fluent.
the two-step Tesner model [410], [652], in which Ansys Fluent predicts the formation of nuclei particles and computes soot formation on the nuclei. In this and previous models, combustion of the soot (and particle nuclei) is assumed to be governed by the Magnussen combustion rate [410]. This assumption limits the use of these models to turbulent flows. The detailed chemistry and physics of soot formation are quite complex and both of these models are empirically-based and can be used to approximate soot formation process in combustion systems. The results yielded by these models should be considered as qualitative indicators of the system performance, unless validated by experimental results.
the Moss-Brookes model [81], in which Ansys Fluent predicts soot formation for methane flames (and higher hydrocarbon species, if appropriately modified) by solving transport equations for normalized radical nuclei concentration and the soot mass fraction. This model has less empiricism and should theoretically provide better accuracy than the Khan and Greeves and Tesner models.
the Moss-Brookes-Hall model [228], which is an extension of the Moss-Brookes model and is applicable for higher hydrocarbon fuels (for example, kerosene). The Hall extension provides further options for modeling higher hydrocarbon fuels. Note that the Moss-Brookes-Hall model is only available when the required species are present in the gas phase species list.
the Method of Moments model [192], in which Ansys Fluent predicts soot formation based on the soot particle population balance methodology. The Method of Moments considers a soot size distribution where the diameters of the soot particles are dynamically evolving. This approach uses fewer empirical constants for modeling of various soot formation sub-processes, such as nucleation, coagulation, and the surface growth kernels.
The following restrictions apply to soot formation models:
You must use the pressure-based solver. The soot models are not available with either of the density-based solvers.
The Khan and Greeves model and the Tesner model can model soot formation only for turbulent flows whereas the Moss-Brookes model, the Moss-Brookes-Hall model, and the Method of Moments model can be used with both laminar and turbulent flows.
The soot model cannot be used in conjunction with the premixed combustion model.