The effects of composition on the burning velocity and NO formation in premixed flames of C2H4+O2+N2

Experimental measurements of the adiabatic burning velocity and NO formation in C2H4 + O-2 + N-2 flames are presented. The oxygen content in synthetic air varied from 18% down to 14%. Non-stretched flames were stabilized on a perforated plate burner at 1 atm. A heat flux method was used to determine the burning velocities under the conditions when the net heat loss of the flame is zero. Adiabatic burning velocities of ethylene + nitrogen + oxygen mixtures were found in good agreement with the modeling. Sampling measurements were performed at 10-20 mm from the burner and concentrations of stable species, CO, CO2, O-2 and NO, were recorded. The concentrations of CO, CO2 and O-2 were compared with the modeling to reveal that the range of the flame conditions was less affected by the ambient air entrainment. The dependencies of [NO] as a function of equivalence ratio clearly possess two maxima: in stoichiometric mixtures due to Zeldovich thermal-NO mechanism and in rich mixtures at equivalence ratio close to 1.4 due to Fenimore prompt-NO mechanism. Dilution by nitrogen decreases [NO] at any equivalence ratio. Numerical predictions of the concentrations of NO in a post-flame zone of lean and stoichiometric flames are in good agreement with the experiments when downstream heat losses to the environment were taken into account. The predictions of the Konnov mechanism in rich ethylene flames reproduce trends of the experimental data with an under-prediction of about 10-15 ppm. (C) 2007 Elsevier Inc. All rights reserved.