CO and Temperature Measurements in a Flat Flame by Laser Ab orption Spectroscopy and Probe Techniques

Abstract

Carbon monoxide and temperature have been measured in the post-flame region of laminar, pre-mixed methane/air flat flames at atmospheric pressure using both laser absorption spectroscopy and conventional probe techniques. The laser absorption measurements employed a tunable diode laser to record fully resolved absorption lines in the fundamental band of CO near 4.7 microns. Probe measurements were made with thermocouples and sampling microprobes (uncooled quartz and water-cooled stainless steel). The extracted gases were analyzed for CO and CO₂ using NDIR instruments. The laser absorption measurements of CO in rich flames were in good agreement with chemical equilibrium calculations based on metered fuel and air flow-rates and measured local temperature. In lean flames, measured levels of CO exceeded equilibrium values, as expected, due to incomplete reaction of CO to CO₂ near the flame front. Temperatures inferred from the relative absorption in lines from different vibrational levels were in good agreement with thermocouple measurements. The sampling measurements in all flames yielded total carbon consistent with input stoichiometry, but indicated some conversion of CO to CO₂ in both probes, with the extent of conversion depending on pressure in the probe.