Dual-pump dual-broadband CARS for exhaust-gas temperature and CO2-O2 -N2 mole-fraction measurements in model gas-turbine combustors

Application of dual-pump, dual-broadband (DPDB) coherent anti-Stokes Raman scattering (CARS) for the measurement of temperature and multiple-species mole fractions is presented for the first time in a liquid-fueled combustor of practical interest. In this system pure rotational transitions of O2–N2 and the ro-vibrational transitions of CO2–N2 are probed using two narrowband pump beams, a broadband pump beam, and a broadband Stokes beam. This technique permits highly accurate temperature measurements at both low and high temperatures as well as mole-fraction measurements of two molecules with respect to N2 from each laser shot. Single-shot measurements of temperature and mole-fraction ratios of CO2/N2 and O2/N2 in the exhaust stream of a swirl-stabilized, JP-8-fueled, model gas-turbine combustor are presented for equivalence ratios ranging from 0.45 to 1.0. Agreement between mean rotational and ro-vibrational temperatures is within ~3%, and mean measurements of CO2/N2 and O2/N2 mole-fraction ratios are within ~15% of equilibrium theory. To illustrate the ability of the current measurement system to track multiple scalar statistics in turbulent reacting flows, histograms and scatter plots of temperature and species mole fractions are presented within the potential-core and turbulent-shear-layer regions of the exhaust stream.