  In this paper we report results of a numerical investigation of turbulent
natural gas combustion for jet in a coflow of lean combustion products in the
Delft-Jet-in-Hot-Coflow (DJHC) burner which emulates MILD (Moderate and Intense
Low Oxygen Dilution) combustion behavior. The focus is on assessing the
performance of the Eddy Dissipation Concept (EDC) model in combination with
two-equation turbulence models and chemical kinetic schemes for about 20
species (Correa mechanism and DRM19 mechanism) by comparing predictions with
experimental measurements. We study two different flame conditions
corresponding to two different oxygen levels (7.6% and 10.9% by mass) in the
hot coflow, and for two jet Reynolds number (Re=4100 and Re=8800). The mean
velocity and turbulent kinetic energy predicted by different turbulence models
are in good agreement with data without exhibiting large differences among the
model predictions. The realizable k-e model exhibits better performance in the
prediction of entrainment. The EDC combustion model predicts too early ignition
leading to a peak in the radial mean temperature profile at too low axial
distance. However the model correctly predicts the experimentally observed
decreasing trend of lift-off height with jet Reynolds number. A detailed
analysis of the mean reaction rate of the EDC model is made and as possible
cause for the deviations between model predictions and experiments a low
turbulent Reynolds number effect is identified. Using modified EDC model
constants prediction of too early ignition can be avoided. The results are
weakly sensitive to the sub-model for laminar viscosity and laminar diffusion
fluxes.
