Temperature response of an acoustically-forced turbulent lean premixed flame: a quantitative experimental determination

Temperature measurements have been taken on an acoustically-forced lean premixed turbulent bluff-body stabilised flame. The burner used in this study is a test-bed to investigate thermo acoustic instability in gas-turbine engines at the University of Cambridge. Numerous experiments have been performed on the burner, one of which used two-line OH planar laser induced fluorescence to measure temperature. Here, we employ vibrational coherent anti-Stokes Raman scattering (CARS) of nitrogen as an alternative to measure temperature, circumventing the limitations of the former method. The use of nitrogen CARS avoids the problem of probing regions of the flame with low OH concentrations that resulted in erroneous temperature. Such an application of CARS showed that the results from previous efforts were systematically biased up to 47% close to the bluff-body. We also critically review the limitations of CARS used in our experiments, pertaining to spatial resolution and associated biasing further downstream from the bluff-body. Using the more accurate results from this work, more up-to-date CFD models of the burner can be validated, with the aim of improved understanding and prediction of thermo acoustic instability in gas turbines.