Eddy Dissipation Concept Combustion Model Research Articles

Numerical Simulation of Delft-Jet-in-Hot-Coflow (DJHC) Flames Using the Eddy Dissipation Concept Model for Turbulence–Chemistry Interaction

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.

A NUMERICAL INVESTIGATION OF A LIFTED H2/N2 TURBULENT JET FLAME IN A VITIATED COFLOW

Numerical calculations of a lifted H2/N2 turbulent jet flame in a vitiated coflow of hot gases are presented. The calculations are performed using Magnussen's Eddy Dissipation Concept (EDC) for turbulent combustion, and are an extension to previously reported EDC modeling results presented by Cabra et al. (2002). Four different turbulence models are employed to investigate in more detail the turbulence modeling effect on the EDC combustion model with detailed chemistry. A series of simulations are presented that indicate the extent to which turbulence models influence the predicted lift-off height with the EDC combustion model. Several flow conditions were tested. For all calculations, EDC predicts more lift-off by using the standard k-ϵ model than by using Reynolds-stress-equation (RSE) models, whereas a modified k-ϵ model predicts less lift-off than the RSE models. The reason for the lower predicted lift-off with the modified k-ϵ model is because a modified turbulence Prandtl or Schmidt number in the scalar equations in the modified k-ϵ model allows an earlier mixing of the hot coflow with the fuel jet. All models overpredict the lift-off height for the standard flow conditions. Recent experiments and numerical calculations by others have shown that the vitiated coflow flame is extremely sensitive to variations in the coflow temperature. The present calculations show that this sensitivity is captured by the EDC combustion model, however to a smaller degree than that previously reported. Calculations with variations in coflow temperature and jet flow velocity indicate that for each flow condition, the various turbulence models predict the same percentage increase or decrease in lift-off height. These EDC calculations show that the turbulence model effect on the EDC predicted lift-off height is important and that a better flame structure is predicted with the RSE model by Jones and Musonge than with the other turbulence models.