Temperature measurement by two-line laser-saturated OH fluorescence in flames

Area of Science:

• Physical Chemistry
• Spectroscopy
• Combustion Science

Background:

• Accurate temperature measurement is crucial for understanding and controlling combustion processes.
• Traditional methods like thermocouples can be intrusive and have limitations in harsh combustion environments.
• Optical techniques offer non-intrusive alternatives but require robust methodologies for reliable temperature determination.

Purpose of the Study:

• To introduce and validate a novel two-line laser-saturated fluorescence (LSF) technique for measuring combustion temperatures.
• To determine the rotational temperature of the hydroxyl radical (OH) as a proxy for flame temperature.
• To assess the accuracy and precision of the developed LSF method in realistic combustion scenarios.

Main Methods:

• Utilized two-line laser-saturated fluorescence targeting specific rotational transitions within the OH A(2)Sigma(+)-X(2)II (0,0) band.
• Saturated two distinct rotational transitions using laser excitation.
• Measured fluorescence emission originating from the laser-pumped upper rotational levels and calculated temperature from the intensity ratio.

Main Results:

• Successfully demonstrated temperature profile measurements in subatmospheric H(2)/O(2)/Ar flat flames.
• Achieved temperature measurements with an accuracy of 3-5% and exhibited low random error.
• Corroborated results by comparing LSF measurements with coated thermocouples, OH absorption, and chemical kinetics code predictions.

Conclusions:

• The proposed two-line LSF technique is a reliable and accurate non-intrusive method for combustion temperature measurements.
• The technique provides high-fidelity temperature data, suitable for validating combustion models and understanding flame dynamics.
• LSF offers a significant advancement in optical diagnostics for combustion research due to its accuracy and low error.