S. Li, A. Farooq, R.K. Hanson
Measurement Science and Technology, 22, 125-301, (2011)
Making use of a newly available rapid-tuning diode laser operating at
wavelengths up to 2.9 ¬µm, an absorption-based temperature sensor was
developed for in situ measurements in low-pressure flames. Based on the
systematic analysis of H 2 O vapor transitions in the fundamental
vibrational bands (ŒΩ 1 and ŒΩ 3 ) of H 2 O in the range of 2.5‚Äì3.0
¬µm, an optimal closely-spaced spectral line pair near 2.9 ¬µm was
selected for its temperature sensitivity in the range of 1000‚Äì2500 K.
The narrow-linewidth room-temperature laser was scanned repetitively
across these spectral features at 5 kHz, enabling fast, accurate
temperature sensing. Use of the temperature sensor was investigated in
low-pressure flames supported on a McKenna burner at 15, 25 and 60 Torr.
To avoid absorption by the cold gases in the flame edges and the
recirculation region between the burner and the vacuum chamber wall, a
variable-path in situ probe was designed and an optimal path length was
determined to accurately measure the flame centerline temperature.
Different flame conditions were investigated to illustrate the potential
of this sensor system for sensitive measurements of combustion
temperature in low-pressure flames.