Modeling and Measurement of Sample Probe Effects on Pollutant Gases Drawn from Flame Zones

Abstract

The oxidation of NO toNO₂ and CO to CO₂ in quartz gas-sampling microprobes drawing gases from fuel-lean flames of CH₄/air and CO/air has been modeled and measured. The kinetic model includes surface recombination of O- and H-atoms. Confirming measurements were obtained by gas-sampling a jet-stirred reactor. It was predicted that as the gas sample was rapidly quenched sufficient levels of HO₂ were formed within the probe to oxidize NO to NO₂. The transient HO₂ concentration limited the NO₂ formation to ca. 25 ppm. Ozone may have exerted a similar influence. Carbon monoxide tended to oxidize to CO2 due to reaction with OH in the warmer regions of the probe. Modeling indicated that sample distortions could be eliminated at probe pressures below 10 torr.