Assessment of Turbulence-Chemistry Interaction Models in MILD Combustion Regime

The present paper reports on the assessment of different turbulence-chemistry interaction closures for modeling turbulent combustion in the Moderate and Intense Low oxygen Dilution (MILD) combustion regime. 2D RANS simulations have been carried out to model flames issuing from two burners i.e. Delft-Jet-in-Hot-Coflow (DJHC) burner and Adelaide JHC burner which imitate the MILD combustion. In order to model these flames, two different approaches of turbulence-chemistry interaction models, i.e. Eddy Dissipation Concept (EDC) and PDF based models, are considered; while in the PDF based modeling, two different variants are invoked to understand the applicability of the PDF based models in the MILD regime: one is based on presumed shape PDF (i.e. steady flamelet (SF) model) approach and the other one is transported PDF approach. For transported PDF method, two different solution approaches namely, Lagrangian solution method (LPDF) and Multi-Environment Eulerian PDF (MEPDF) model are considered. A comprehensive study has been carried out by comparing the results obtained from these different models. For the DJHC burner, the computations are carried out for a jet speed corresponding to Reynolds numbers of Re = 4100, whereas the Adelaide JHC burner computations are performed for a jet speed corresponding to Reynolds number of Re = 10000. The effects of molecular diffusion on the flame characteristics are also studied by using different micro-mixing models. In the case of DJHC burner, it has been observed that the mean axial velocity and the turbulent kinetic energy profiles are in good agreement with the measurements. However, the temperature profiles are over-predicted in the downstream region by both EDC and the PDF based models. In the context of Adelaide JHC burner, the profiles of the temperature and the mass fraction of major species (CH4, H-2, O-2, H2O, CO2) obtained using LPDF approach are in better agreement with the measurements compared to those obtained using EDC model; although, both the solution approaches fail to capture CO and OH radical profiles.