Measurement of atomic oxygen and nitrogen oxides in jet-stirred combustion

Abstract

Direct spectroscopic measurement of continuum chemiluminescence at 3500 Å, due presumably to the reaction CO+O→CO2+hv, was used to determine super-equilibrium atomic oxygen concentrations in situ for near-homogeneous, continuous-combustion of either carbon monoxide or methane with 133% theoretical air in a jet-stirred reactor operated near blowout, at atmospheric pressure. Reactor CO and NOx concentrations were measured by gas sampling. The motivation for this initial optical spectroscopic examination of the jet-stirred reactor was the elucidation of NOx formation in high-intensity, backmixed combustion. Measured gas temperatures were in the ranges T=1350 to 1500°K for carbon monoxide combustion, and T=1400° to 1800°K for methane combustion. Peak atom oxygen concentrations occurred just prior to reactor blowout. Partial equilibrium was indicated for the reactions CO+OH⇆CO2+H and O2+H⇆O+OH, at throughput rates sufficiently less than reactor blowout. Atomic oxygen measurements were used to compare NOx measurements with values predicted for plausible NOx kinetic formation mechanisms, considering only O, OH, and H as reaction radical intermediates. Agreement between the comparisons was obtained only for carbon monoxide combustion, indicating that nitrous oxide probably acts as an intermediate in NOx formation in the presence of super-equilibrium concentrations of atomic oxygen.