Quantitative planar temperature imaging in turbulent non-premixed flames using filtered Rayleigh scattering

Area of Science:

• Combustion science
• Laser-based diagnostics
• Thermometry

Background:

• Accurate temperature measurements are crucial for understanding turbulent non-premixed flames.
• Traditional Laser Rayleigh Scattering (LRS) requires knowledge of the scattering cross-section, which can vary.
• Filtered Rayleigh Scattering (FRS) offers a potential pathway for single-measurement thermometry.

Purpose of the Study:

• To demonstrate the application of FRS for quantitative temperature measurements in turbulent non-premixed jet flames.
• To investigate the feasibility of using targeted fuel tailoring for single-point FRS thermometry.
• To validate FRS temperature measurements against traditional LRS.

Main Methods:

• Utilized filtered Rayleigh scattering (FRS) and laser Rayleigh scattering (LRS) for simultaneous temperature measurements.
• Employed targeted fuel tailoring with specific CH4/H2/Ar mixtures to establish a unique FRS signal-temperature relationship.
• Performed simulations using laminar, counterflow flame calculations to verify the FRS signal's proportionality to temperature.
• Conducted experiments on turbulent non-premixed jet flames at various Reynolds numbers (Re=10,000, 20,000, 30,000).

Main Results:

• Demonstrated that a unique relationship between the FRS signal and local temperature is achievable for select fuel mixtures across diverse flame conditions.
• Showed that the mixture-averaged Rayleigh scattering cross-section is nearly constant for the optimized fuel, enabling LRS as a reference.
• Presented simultaneous LRS-FRS measurements in turbulent jet flames, revealing good agreement between the two techniques.
• Confirmed accurate instantaneous temperature fields and statistical quantities using both methods.

Conclusions:

• The developed FRS thermometry approach, combined with targeted fuel tailoring, provides accurate temperature measurements in turbulent non-premixed flames.
• The unique FRS signal-temperature proportionality simplifies quantitative temperature mapping in complex combustion environments.
• The study validates FRS as a reliable diagnostic tool for combustion research, comparable to established LRS methods.