SCANNED-WAVELENGTH AND FIXED-WAVELENGTH ABSORPTION DIAGNOSTICS FOR COMBUSTION MEASUREMENTS USING MULTIPLEXED DIODE-LASERS

A multiplexed diode-laser sensor system comprising two diode lasers an d fiber-optic components has been developed to nonintrusively monitor temperature and species mole fraction over a single path using both sc anned- and fixed-wavelength laser absorption spectroscopy techniques. In the scanned-wavelength method, two InGaAsP lasers were current tune d at a 2-kHz rate across H2O transitions near 1343 mn and 1392 mn in t he 2 nu(1) and nu(1) + nu(3) bands. Gas temperature was determined fro m the ratio of single-sweep integrated line intensities. Species mole fraction was determined from the measured line intensity and the calcu lated line strength at the measured temperature. In the fixed-waveleng th method, the wavelength of each laser was fixed near the peak of eac h absorption feature using a computer-controlled laser Line-locking sc heme. Rapid measurements of gas temperature were obtained from the det ermination of peak line-intensity ratios. The system was applied to me asure temperature and species concentration in the postflame gases of an H-2-O-2 flame. The good agreement between the laser-based measureme nts obtained using scanned- and fixed-wavelength methods with those re corded with thermocouples demonstrates the flexibility and utility of the multiplexed diode-laser sensor system and the potential for rapid, continuous measurements of gasdynamic parameters in high-speed or tra nsient flows with difficult optical access.