Application of an all-solid-state diode-laser-based sensor for carbon monoxide detection by optical absorption in the 4.4 ? 4.8 µm spectral region
of the carbon monoxide (CO) molecule has been developed and demonstrated. The single-mode, tunable
output of an external-cavity diode laser (ECDL) is difference-frequency mixed (DFM) with the output of a
550-mW diode-pumped cw Nd:YAG laser in a periodically-poled lithium niobate (PPLN) crystal to
produce tunable cw radiation in the mid-infrared. The wavelength of the 860-nm ECDL can be coarse
tuned between 860.78 to 872.82 nm allowing the sensor to be operated in the 4.4 ? 4.8 µm region. Results
from single-pass mid-IR direct absorption experiments for CO concentration measurements are discussed.
CO measurements were performed in CO/CO2/N2 mixtures in a room temperature gas cell that allowed the
evaluation of the sensor operation and data reduction procedures. Field testing was performed at two
locations: in the exhaust of a well-stirred reactor (WSR) at Wright-Patterson Air Force Base and the
exhaust of a gas turbine at Honeywell Engines and Systems. Field tests demonstrated the feasibility of the
sensor for operation in harsh combustion environments but much improvement in the sensor design and
operation was required. Experiments in near-adiabatic hydrogen/air CO2-doped flames were performed
featuring two-line thermometry in the 4.8 µm spectral region. The sensor concentration measurement
uncertainty was estimated at 2% for gas cell testing. CO concentration measurements agreed within 15%
of conventional extractive sampling at WSR, and for the flame experiments the repeatability of the peak
absorption gives a system uncertainty of 10%. The noise equivalent CO detection limit for these
experiments was estimated at 2 ppm per meter, for combustion gas at 1000 K assuming a SNR ratio of 1.
Advisor:Caton, Jerald A.; Lucht, Robert P.; Phares, Denis; Welch, George R.
School:Texas A&M University
School Location:USA - Texas
Source Type:Master's Thesis
Keywords:optical sensor laser spectroscopy frequency conversion carbon monoxide infrared sources
Date of Publication:12/01/2004