Raman-LIF measurements of temperature, major species, OH, and NO in a methane-air bunsen flame

Abstract

Nonintrusive measurements of temperature, the major species (N 2, O 2, H 2, H 2O, CO 2, CO, CH 4), OH, and NO in an atmospheric pressure, laminar methane-air Bunsen flame were obtained using a combination of Raman-Rayleigh scattering and laser-induced fluorescence. Radial profiles were measured at three axial locations for an equivalence ratio of 1.38. Measurements along the centerline of the flame, for equivalence ratios of 1.38, 1.52, and 1.70, were also obtained. The measurements indicate that the inner unburned fuel-air mixture experiences significant preheating as it travels up into the conical flame zone surrounding it. Consequently, the centerline axial temperatures were typically 100–150 K higher than predicted by adiabatic equilibrium for reactants at an initial temperature of 300 K. Because the amount of preheating increases with the equivalence ratio (due to the increased inner flame height), the maximum temperatures (2000 K) in a Bunsen flame were rather insensitive to the stoichiometry. We observed a 20% reduction of the maximum NO concentrations (80 ppm) in a Bunsen flame by increasing the equivalence ratio from 1.38 to 1.70. We also find that using a one-dimensional premixed laminar flame model incorporating finite-rate chemistry, satisfactorily predicts properties such as the temperature, CO, OH, and NO concentrations at the inner flame.