Diode laser sensor for gasdynamic measurements in a model scramjet combustor

A sensor for simultaneous and continuous measurements of water vapor densit y, temperature, and velocity has been developed based on absorption techniq ues using room temperature diode lasers (InGaAsP) operating at 1.31 mu m. L aboratory calibrations of density and temperature were acquired in a variab le temperature absorption cell and on a H-2-air flat flame burner from 500 to 2200 K. Laboratory determinations showed absolute accuracies of 5% in te mperature and 10% in molecular density for a 0.3-Hz bandwidth. An optical s ystem was developed for integrating the sensor to a model scramjet combusto r at the U.S. Air Force Research Laboratory, Wright-Patterson Air Force Bas e. Preliminary measurements in the Mach 2.1 flowfield at expanded temperatu res of 540, 650, and 740 K across an 18-cm pathlength resulted in temperatu re measurements that agreed with theoretical predictions to within 7-11%, D ensity measurements agreed with predictions to within 17-56%. Velocity meas urement precision was compromised by beam steering effects, although result s in reasonable agreement with predictions were observed at the lowest enth alpy condition.