Quantifying the CO and CO2 Mole Fraction in the Plume of an Aerosol-Based Fire Extinguishing Agent Using 4560 nm and 4320 nm QCLs

Abstract

We demonstrate tunable diode laser spectroscopy (TDLS)-based absolute measurements of the mole fraction of carbon monoxide (CO) and carbon dioxide (CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) in the plume of an aerosol-based fire extinguishing agent. The mole fraction values of CO and CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> in the plume for two different compositions of the aerosol-forming compound are measured to study the effect of chemical composition on gas emission during controlled discharge of aerosol. The aerosol plume from the first composition contained 336 ± 39 ppm CO and 1389 ± 99 ppm CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> on an average while that from the second composition contained 691 ± 56 ppm CO and 1971 ± 118 ppm CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . These measurements show that the CO content in the plume can be reduced by more than 50% if the chemical composition of the aerosol-forming compound is properly chosen. The technique can be readily extended to measure other species (such as nitrogen oxides) that are often present in fire-extinguishing aerosol plumes. Two mid-infrared continuous-wave distributed-feedback quantum cascade lasers are used to interrogate the rotational-vibrational transitions of CO at 4559.217 nm and CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> at 4319.30 nm. The mole fractions of CO and CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> are extracted by a digital signal processor from least-squares fit of a simulated Voigt lineshape to the gas absorption line obtained using direct absorption spectroscopy.