In Situ Flame Temperature Measurements Using a Mid-Infrared Two-Line H₂O Laser-Absorption Thermometry

ABSTRACT

A mid-infrared two-line thermometry based on H₂O absorption was developed for in situ and sensitive temperature measurements of laminar flames. The H₂O absorption lines in v₃ fundamental band were systematically investigated and a new promising line pair (4029.52 cm^–1 and 4030.73 cm^–1) was selected to achieve strong absorption line-strength and high-temperature sensitivity over the temperature range of 1000–3000 K. This line pair was readily assessed by a single current scan of a distributed feedback laser near 2.5 μm. The scanned-wavelength laser absorption strategy was adopted for temperature measurements for both laminar sooting and non-sooting flames. This optical sensor was applied in measuring various flame conditions including CH₄/air and C₂H₄/air premixed flames (Ф = 0.8–1.2), C₂H₄/air sooting flames (Ф = 1.78–2.38), and partially premixed flames. Our measurements were in good agreement with thermocouple measurements for all the flame conditions. In addition, numerical simulations using the detailed chemical kinetic mechanisms (CH₄ flame: GRI 3.0, C₂H₄ flame: USC 2.0) were conducted to validate the experimental results.

KEYWORDS:

• Flame temperature
• Laminar flame
• Laser absorption
• Two-line thermometry

Acknowledgment

The authors gratefully acknowledge the National Supercomputing Center (Shenzhen) for providing CHEMKIN-Pro (15131) software and computational facilities.

Funding

This research is supported by the National Natural Science Foundation of China (NSFC; 11502222) and Research Grants Council of the Hong Kong Special Administrative Region, China (CUHK14234116).

Additional information

Funding

This research is supported by the National Natural Science Foundation of China (NSFC; 11502222) and Research Grants Council of the Hong Kong Special Administrative Region, China (CUHK14234116).