CROSSED-BEAM CORRELATION TECHNIQUE FOR TURBULENT-FLAMES MEASUREMENTS

Emission-absorption spectroscopy methods for flame diagnostics have mostly been limited to axisymmetrical laminar flames. The development of tunable lasers with extremely narrow bandwidth has made possible the determination of time-averaged mean values of temperature and species concentration in axisymmetrical turbulent flames. In this work, a new method is presented to allow the measurement of both time-averaged mean values and fluctuation intensities of temperature and species concentration in turbulent flames. With this method, turbulent flames -irrespective of their geometries- may be investigated. The possibilities of these measurements using the crossed-beam correlation technique are studied and presented. The correlation between the fluctuation values of received radiation density of two laser beams crossed at a certain point in the turbulent flame gives information about the mean and fluctuation components of the spectral absorption coefficient at that point. Measurement of the absorption coefficient leads to determination of temperature and species concentration. The fluctuation intensities are measured using crossed laser beams having the same wavelength, whereas time-averaged mean values are determined when the wavelengths of the laser beams are different.