Improved Method for Quantitative Measurement of OH Radicals Based on Absorption Spectroscopy

Area of Science:

• Combustion diagnostics
• Laser spectroscopy
• Chemical kinetics

Background:

• Hydroxyl radical (OH) concentration measurements are crucial for understanding combustion processes.
• Traditional OH-Planar Laser-Induced Fluorescence (OH-PLIF) methods face challenges due to high temperature sensitivity and unreliable calibration constants.

Purpose of the Study:

• To develop an explicitly temperature-corrected OH radical concentration inversion model.
• To improve the accuracy and applicability of OH-PLIF measurements in high-temperature environments.

Main Methods:

• Combined absorption spectroscopy with dual-line temperature inversion.
• Simultaneously acquired PLIF images and absorption spectrum data.
• Incorporated temperature-dependent absorption cross-section (σ(ν,T)) and calculated equivalent absorption path length.

Main Results:

• The temperature-corrected model significantly reduced systematic errors caused by temperature variations.
• Calibration constant (C) fluctuation was reduced to less than ±5% across different operating conditions.
• Optimized constant Copt = 0.01844, with average relative errors controlled within 4-6%.

Conclusions:

• The developed model effectively mitigates temperature-induced errors in OH concentration measurements.
• The optimized model demonstrates broad applicability and improved accuracy compared to uncorrected methods, reducing overall error from 9.1% to 5.2%.