Abstract

A diode-laser sensor system, comprised of a tunable external-cavity diode laser (ECDL) operating near 2.0 μm and fiber-optic components, has been developed to measure the gas temperature and the concentrations of CO₂ and H₂O in the combustion and exhaust regions of a flat-flame burner (C₂H₄/air) using absorption spectroscopy techniques. The present system extends the techniques developed previously 1-4 for the measurement of H₂O and CO₂ by probing relatively stronger vibrational bands and thus offers higher measurement sensitivity. Measurements of individual transitions (1-cm⁻¹ scans) were recorded by adjusting the internal grating to particular center wavelengths and by applying a 6-volt sawtooth voltage waveform at a 1.25-Hz repetition rate to the wavelength modulation input. Temperature may be determined either from the ratio of measured H₂O (ν₁+ ν₂, ν₂ + ν₃ bands) or CO₂ (ν₁+2ν₂+ ν₃ band) absorbances. Species (H₂O, CO₂) concentrations were determined from the measured temperature and absorbances of appropriate transitions recorded by tuning the ECDL wavelength across selected transitions within the 250 cm⁻¹ laser tuning range centered at 2.02 μm.

© 1998 Optical Society of America