Two-line jointly optimized tomographic absorption spectroscopy for flame measurement with adaptive hybrid...

Area of Science:

• Combustion science
• Spectroscopy
• Optical diagnostics

Background:

• Accurate measurement of temperature and species concentration in combustion fields is crucial for understanding and controlling combustion processes.
• Traditional methods often struggle with non-uniformities and measurement noise, leading to inaccuracies.

Purpose of the Study:

• To develop and validate an improved tomographic absorption spectroscopy (TAS) method for accurate reconstruction of temperature and H2O mole fraction distributions in combustion fields.
• To enhance the robustness of TAS against artifacts and noise using advanced regularization techniques.

Main Methods:

• Utilized two absorption lines of H2O (7185.597 cm⁻¹ and 7444.352 cm⁻¹) for two-line thermometry.
• Implemented an adaptive hybrid regularization approach to jointly solve for absorption coefficients, balancing smoothness and gradient preservation.
• Compared the proposed method against Algebraic Reconstruction Technique (ART) and Tikhonov regularization.

Main Results:

• The improved TAS method reduced reconstruction errors by approximately 50% compared to ART and Tikhonov regularization in numerical tests.
• Experimental validation on a McKenna CH4/air flame showed good agreement with thermocouple measurements (mean deviation of 13.2 K in the core region).
• Successfully recovered the expected top-hat temperature profile in the experimental flame.

Conclusions:

• The developed adaptive hybrid regularization approach significantly improves the accuracy and robustness of TAS for combustion diagnostics.
• This advanced TAS method is effective for reconstructing temperature and H2O distributions in non-uniform combustion environments.
• The findings contribute to the advancement of optical diagnostic techniques for detailed combustion analysis.