Probe sampling measurements and modeling of nitric oxide formation in ethane + air flames

Burning velocity and probe sampling measurements of the concentrations of O2, CO2, CO and NO in the post-flame zone of ethane + air flames are reported. The heat flux method was used for stabilization of laminar, premixed, non-stretched flames on a perforated plate burner at 1 atm. Axial profiles of the concentrations of the major species were used to assess interaction of the flame with the burner surface and conversion of the sampling gases in the probe. Tests performed with the probes of different inlet diameters showed negligible CO–CO2 and NO–NO2 conversion within the experimental accuracy. Two kinetic models, the GRI-mech. 3.0 and in-house modified detailed reaction mechanism, were tested. Both kinetic mechanisms accurately reproduce laminar burning velocities and concentrations of the major species, CO, CO2 and O2, in these flames. Numerical predictions of the concentrations of NO in a post-flame zone of lean and stoichiometric flames are in good agreement with experiment when downstream heat losses to the environment were taken into account. The GRI-mech. 3.0 over-predicts the [NO] by about 30 ppm at the equivalence ratio of 1.4. The predictions of the in-house mechanism in rich flames are closer to the experimental data with an under-prediction of about 15 ppm. The influence of the assumed temperature gradient downstream the flame front on the calculated flame structure was also assessed.