Spatially and Temporally Resolved Temperature and Species Concentration Measurements in High-Pressure Combustors using fs-CARS

The objective of the proposed Phase-I research effort is to develop femtosecond (fs) laser-based coherent anti-Stokes Raman scattering (CARS) spectroscopy for providing quantitative high-speed (1-10 kHz) temperature and species concentration measurements in unsteady reacting flows. The initial frequency-spread dephasing rate of the Raman coherence induced by the ultrafast (~85 fs) Stokes and pump beams will be used to measure gas-phase temperature for high-pressure combustion. This initial frequency-spread dephasing rate of the Raman coherence is completely independent of local molecular collisions and depends only on the frequency spread of the Raman transitions at different temperatures. Single-shot CARS thermometry will be performed by obtaining time-resolved CARS spectra from chirped probe pulse. A simple theoretical model based on the assumption of impulsive excitation of Raman coherence will be developed to interpret and extract high-speed, single-shot temperature from the interaction of a chirped probe-pulse with the Raman coherence. During the Phase-I research effort measurements will be performed in laboratory flames. Successful implementation of the proposed technique will pave the way for the application of fs-CARS for high-speed temperature and species concentration measurements in high-pressure gas-turbine test rig and augmentor at Wright-Patterson Air Force Base (WPAFB) during the Phase-II research effort.