Hybrid Femtosecond/Picosecond Coherent Anti-Stokes Raman Scattering for Gas-PhaseTemperature Measurements of Counterflow Flames at Elevated Pressures

Well-controlled laboratory experiments using reactors with canonical geometries, such as counterflow burners, can be used to evaluate the ability of chemical-kinetic mechanisms and transport properties to predict combustion processes. Although counterflow diffusion flames have been employed previously to explore the validity of chemical kinetic mechanisms near flame extinction, measuring temperature and local strain rate with sufficient accuracy to obtain validation data is a challenge. For this thesis, femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps CARS), a laser-based spectroscopy technique, has been used to quantify gas temperature in a counterflow diffusion flame at atmospheric and elevated pressures.

To enable this study, a three-axis stage system was developed to translate the CARS measurement location relative to the flame while maintaining precise spatial and temporal overlap of the laser pulses utilized to generate the CARS signal. An additional challenge addressed was maintaining the stability of multiple beam positions over the 40 ft propagation distance between the laser system and the counterflow burner. The success of employing fs/ps CARS in large-scale combustion environments relies on mitigating alignment and stability challenges identified during this study. Methods used to align fs/ps CARS and improve system stability are presented in the current work.