Quantitative Diagnostics of Hydroxyl (OH) Radicals in Methane-Air Flames Using Wavelength Modulation Spectroscopy...

Area of Science:

• Combustion diagnostics
• Spectroscopy
• Chemical kinetics

Background:

• Fossil fuel combustion produces exhaust gases, contributing to pollution and climate change.
• Hydroxyl (OH) radicals are crucial flame indicators, but current measurement techniques like laser-induced fluorescence (LIF) are complex for industrial use.
• Accurate combustion diagnostics are vital for improving efficiency and reducing environmental impact.

Purpose of the Study:

• To develop and validate a practical method for measuring OH radical concentrations in combustion environments.
• To address the challenge of spectral interference from water vapor in OH radical measurements.
• To enable reliable, real-time combustion monitoring for industrial applications.

Main Methods:

• Utilized wavelength modulation spectroscopy (WMS) with a near-infrared laser at 1.49 μm to detect OH radicals.
• Employed a wavelength division multiplexer (WDM) for simultaneous laser operation at 1.49 μm (OH) and 1.39 μm (H₂O, temperature).
• Corrected spectral interference from H₂O and validated results against direct absorption spectroscopy (DAS) and CHEMKIN simulations.

Main Results:

• The dual-laser WMS system accurately quantified OH radical concentrations in methane/air flames across various equivalence ratios.
• The method effectively corrected for spectral interference from water vapor.
• Comparisons with thermocouple temperature measurements and CHEMKIN simulations confirmed the technique's reliability.

Conclusions:

• The proposed WMS-based dual-laser system offers a robust and interference-corrected method for OH radical quantification.
• This technique shows significant potential for practical implementation in industrial burner systems for combustion monitoring.
• The study advances the development of efficient and reliable combustion diagnostic tools.