Studies on Laser Induced Fluorescence in Subsonic and Supersonic Jet Using Ketone Tracers

Abstract

The present work focuses on the study of LIF from ketone based tracers for gas flow visualization. For all these studies a frequency quadrupled, Q switched, Nd:YAG laser (266 nm) was used as an excitation source. The quenching effect of oxygen on LIF of acetone, Methyl Ethyl Ketone (MEK) and 3-pentanone was studied quantitatively at low pressures (~700 torr) with oxygen partial pressures upto 450 torr. Nitrogen was used as a bath gas into which these molecular tracers were added in different quantities according to their vapor pressure at room temperature. Further Smoluchowski theory was used to calculate the quenching parameters and compared with the experimental results. The molecular density distribution measurement in turbulent nitrogen jet (Re 3X103), using acetone and MEK tracers was demonstrated. Emitted fluorescence images of subsonic jet flow field were recorded on CMOS camera. The dependence of PLIF intensity on acetone vapor density was used to convert PLIF image of nitrogen jet into the density image on pixel by pixel basis. Instantaneous quantitative density image of nitrogen jet, seeded with acetone was obtained. Arrow head shaped coherent turbulent structures were observed in our experiments. PLIF imaging was used for supersonic jet, using acetone as molecular tracer. For supersonic jet, the fluorescence images were recorded on ICCD camera. Significant decrease in the PLIF intensity due to the presence of oxygen was clearly observed. The dependence of PLIF intensity on binning of images and air pressure was studied. It was demonstrated that even with the presence of the condensation of acetone, one can obtain good quality PLIF images. It was also shown that binning and Gaussian image processing of steady state jet PLIF images can further improve the image quality for quantitative analysis.