Diode-Laser Absorption Sensor for Line-of-Sight Gas Temperature Distributions

Area of Science:

• Applied Physics
• Laser Spectroscopy
• Fluid Dynamics

Background:

• Accurate temperature measurement is crucial for understanding and controlling non-uniform gas flows.
• Traditional methods often struggle with complex flow fields and require multiple sensors.
• Line-of-sight absorption techniques offer non-intrusive measurement capabilities.

Purpose of the Study:

• To develop and demonstrate a novel line-of-sight laser absorption technique for temperature measurements in nonuniform-property flows.
• To leverage the broad wavelength-scanning capabilities of vertical cavity surface-emitting lasers (VCSELs) for multi-transition interrogation.
• To create a VCSEL-based sensor for mapping oxygen gas temperature distributions.

Main Methods:

• Utilized a vertical cavity surface-emitting laser (VCSEL) with broad wavelength-scanning abilities (>1.7 nm).
• Interrogated multiple oxygen absorption transitions in the A band near 760 nm along a single line of sight.
• Scanned the VCSEL over ten transitions in the R branch and optionally six in the P branch.
• Applied atmospheric-pressure air with known temperature distributions (200-700 K) for validation.

Main Results:

• Successfully demonstrated temperature distribution measurements in nonuniform flows.
• Inferred temperature information based on the unique temperature dependence of probed absorption line strengths.
• Achieved a fast time response of approximately 30 ms.
• Measurement accuracy and resolution are dependent on line strength temperature dependence and number of scanned lines.

Conclusions:

• The developed VCSEL-based sensing strategy effectively measures temperature distributions in nonuniform gas flows.
• The technique's fast response and adaptability to various species and conditions show significant promise for industrial applications.
• Further optimization and theoretical prediction of sensor performance are possible.