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Obtaining and Interpreting Near-Infrared Wavelength Modulation Absorption Signals From Hot Fire Gases: Practical Issues.


pdf icon Obtaining and Interpreting Near-Infrared Wavelength Modulation Absorption Signals From Hot Fire Gases: Practical Issues. (418 K)
Blevins, L. G.; Peterson, B. W.

Chemical and Physical Processes of Combustion, Fall Technical Meeting. Proceedings. Combustion Institute/Eastern States Section. October 13-19, 1999, Raleigh, NC, 85-88 pp, 1999.

Keywords:

carbon monoxide; fiber optics; fire measurements; infrared spectroscopy; instrument design; lasers

Abstract:

Near-infrared tunable diode laser absorption spectroscopy (TDLAS) shows promise for measuring concentrations of several gaseous species important in fires, including CH4, 02, C2H2, C2H4, CO, CO2 and H2O. Researchers at NIST are presently studying the possible application of near-infrared TDLAS for rapid measurement of CO concentration in and around fires. Near-infrared diodes are compact, spectrally narrow, and rapidly tunable, and the potential exists to deliver diode light into and out of real-scale fires using rugged and readily-available silica fiber optics. The goal of the NIST project is to develop a diode laser sensor capable of measuring CO concentration at temperatures between 300 K and 1200 K in fire gases partially obscured by soot. This abstract describes some practical signal interpretation issues found to be important during sensor development. Previous studies on the use of near-infrared diodes for CO measurement have focused on determining CO amounts in room-temperature absorption cells with controlled gas composition. Some recent studies of CO in combustion gases employed rapid probe sampling with a multi-pass cell/diode laser arrangement, and an in situ measurement of CO concentration in the hot exhaust of a premixed methane/air flame was recently reported. Near-infrared TDLAS has been used in fire research to quantify hydrogen fluoride concentration in post-flame gases following fire suppression.