A study of carbon monoxide in a series of laminar ethylene / air diffusion flames using tunable diode laser absorption spectroscopy,

Tunable diode laser absorption spectroscopy has been used to map carbon monoxide concentrations and temperatures in a series of laminar ethylene/air, axisymmetric diffusion flames. As the quantity of soot increased, temperatures near the tip of the flames were observed to decrease. Carbon monoxide concentration profiles were found to depend on soot levels with the most dramatic differences apparent along the centerline beyond the stoichiometric surface. These measurements were combined with literature data to calculate oxidation rates for both soot and carbon monoxide. It was found that the oxidation rate for CO low in the flames was larger than that near the visible flame tip, which is attributable to both lower hydroxyl radical concentrations and temperatures at the tip. Further, soot oxidation, which is believed to form CO, occurs at a faster rate than CO oxidation processes at the visible flame tip, thus leading to carbon monoxide emission from the flame.