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 liquid-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 fluorescence, a nonresonant fluorescence interference that increased rapidly with pressure was detected. Examination of the spectrum of this interference indicates that it arises from hydrocarbon fuel-fragment species in the fuel-rich zones of the flame. The pressure dependence of the fluorescence signal is examined in both steady-state and time-dependent analyses, and a model for evaluation of pressure effects and quenching variations in quantitative imaging measurements in nonpremixed flame environments is presented. The results indicate that increased combustor pressure results in a rapid rise of the volume fraction of hydrocarbon fragments and a decrease in the OH volume fraction.