PLANAR LASER-INDUCED-FLUORESCENCE IMAGING MEASUREMENTS OF OH AND HYDROCARBON FUEL FRAGMENTS IN HIGH-PRESSURE SPRAY-FLAME COMBUSTION

Planar laser-induced fluorescence images of OH have been obtained in l iquid-fueled spray flames burning heptane, ethanol, and methanol over a range of pressures from 0.1 to 1.0 MPa. In addition to the OH fluore scence, a nonresonant fluorescence interference that increased rapidly with pressure was detected. Examination of the spectrum of this inter ference indicates that it arises from hydrocarbon fuel-fragment specie s in the fuel-rich zones of the flame. The pressure dependence of the fluorescence signal is examined in both steady-state and time-dependen t analyses, and a model for evaluation of pressure effects and quenchi ng variations in quantitative imaging measurements in nonpremixed flam e environments is presented. The results indicate that increased combu stor pressure results in a rapid rise of the volume fraction of hydroc arbon fragments and a decrease in the OH volume fraction.