Fiber-bundle-based 2D Raman and Rayleigh imaging for major species and temperature measurement in laminar flames

Area of Science:

• Combustion Science
• Optical Diagnostics
• Spectroscopy

Background:

• Accurate measurements of temperature and species concentrations are crucial for understanding flame dynamics and improving combustion efficiency.
• Existing optical diagnostic techniques often face limitations in spatial resolution, temporal response, or the number of species that can be simultaneously quantified.
• Developing advanced imaging systems is essential for detailed flame characterization.

Purpose of the Study:

• To introduce and validate a novel fiber-bundle-based 2D Raman and Rayleigh imaging system.
• To enable simultaneous, spatially resolved measurements of major species mole fractions and temperature in flames.
• To demonstrate the system's capability in characterizing hydrogen-air diffusion flames.

Main Methods:

• A fiber-bundle-based imaging system utilizing a cascade of dichroic mirrors and bandpass filters to separate Raman signals.
• Simultaneous detection of four major species (N2, O2, H2, H2O) using a single back-illuminated CCD camera.
• Integration with a pulse-burst laser (10 kHz) and a 10 kHz optical shutter for high-speed flame measurements.

Main Results:

• Successful characterization of the novel imaging system using a McKenna burner.
• Demonstration of 2D measurements of temperature and major species mole fractions in a hydrogen-air diffusion flame stabilized over a Santoro burner.
• First-ever reported 2D measurements of N2, O2, H2, and H2O mole fractions and temperature in H2-air diffusion flames at atmospheric pressure.

Conclusions:

• The developed fiber-bundle-based 2D Raman and Rayleigh imaging system offers a unique capability for simultaneous flame measurements.
• This technology provides a significant advancement in optical diagnostics for combustion research, enabling detailed flame analysis.
• The system's successful application to H2-air diffusion flames highlights its potential for broader use in various combustion environments.