In situ measurements of CO concentration were recorded with tunable diode-l
aser absorption spectroscopy techniques in both the exhaust and the immedia
te post-flame regions of an atmospheric-pressure flat-flame burner operatin
g on ethylene air. Two room-temperature cw single-mode InGaAsSb/AlGaAsSb di
ode lasers operating near 2.3 mu m were tuned over individual transitions i
n the CO first overtone band(nu' = 2 <-- nu" = 0) to record high-resolution
absorption line shapes in the exhaust duct [79 cm above the burner, simila
r to 470 K; R(15) transition at 4311.96 cm(-1)] and the immediate postflame
zone [1.5 cm above the burner, 1820-1975 K; R(30) transition at 4343.81 cm
(-1)]. The CO concentration was determined from the measured absorption and
the gas temperature, which was monitored with type-S thermocouples. For me
asurements in the exhaust duct, the noise-equivalent absorbance was similar
to 3 X 10(-5) (50-kHz detection bandwidth, 50-sweep average, 0.1-s total m
easurement time), which corresponds to a CO detection limit of 1.5 ppm m at
470 K. Wavelength modulation spectroscopy techniques were used to improve
the detection limit in the exhaust to similar to 0.1 ppm m (similar to 500-
Hz detection bandwidth, 20-sweep average, 0.4-s total measurement time). Fo
r measurements in the immediate postflame zone, the measured CO concentrati
ons in the fuel-rich flames were in good agreement with chemical equilibriu
m predictions. These experiments demonstrate the utility of diode-laser abs
orption sensors operating near 2.3 mu m for in situ combustion emission mon
itoring and combustion diagnostics. (C) 2000 Optical Society of America. OC
IS codes: 300.1030, 300.6260, 300.6340, 300.6380, 280.1740, 280.3420.