Kinetic and fluid dynamic modeling of ethylene jet flames in diluted and heated oxidant stream combustion conditions

This paper reports the results of a numerical investigation of several turbulent nonpremixed ethylene jet flames, either undiluted or diluted with hydrogen, air or nitrogen, which have been experimentally studied using a jet in hot coflow (JHC) burner. The fuel jet issues into a hot and highly diluted coflow at two O2 levels (3% or 9%) and a temperature of 1100 K. These conditions emulate those of moderate or intense low oxygen dilution (MILD) combustion. The attention is mainly focused on assessing the performance of different models for the turbulence chemistry-interaction. The model predictions are compared to experimental measurements. The Eddy dissipation concept (EDC), flamelet and PDF transport models were used in combination with a two-equation turbulence model (k-ε) and two different kinetic mechanisms (GRI-Mech 3.0 and POLIMI). The effect of the oxygen concentration in the coflow is well captured by all models. A modified version of the EDC model, recently proposed for the modeling of methane MILD combustion conditions, is also used. This model significantly improves the predictions of the EDC in the case of the ethylene flames studied in this paper. The agreement between measurements and predictions of the flamelet model is generally not as good as the PDF transport and modified EDC models, whose predictions are in good agreement with the measurements, and are improved especially for the apparent liftoff heights and the peak flame temperature. The effect of the fuel composition on the CH2O formation is also discussed, showing generally good agreement.