LASER-INDUCED FLUORESCENCE MEASUREMENTS OF NO AND OH MOLE FRACTION INFUEL-LEAN, HIGH-PRESSURE (1-10ATM) METHANE FLAMES - FLUORESCENCE MODELING AND EXPERIMENTAL VALIDATION

A method for quantifying laser-induced fluorescence (LIF) signals and planar laser-induced fluorescence (PLIF) images of the OH and NO radic als in high pressure flames is presented. The fluorescence signal per unit radical mole fraction is modeled as a function of temperature, pr essure, overall flame stoichiometry and laser spectral bandwidth. A re cently developed model (JQSRT, 51, 511; Appl. Phys. B, 57, 249)(1,2) f or electronic quenching cross-sections of OH and NO is utilized to exp ress the fluorescence yield as a function of these parameters. The mod els are confirmed using single-point measurements in the burnt gas reg ion of a flat flame burner at up to 10 atm. The measurements are perfo rmed at points in the flame where the temperature, pressure, OH and NO mole fraction are all known. For fuel-lean flames at elevated pressur e, interference from the O-2 Schumann-Runge system was found with NO A <-- X (0, 0) fluorescence measurements. This interference must be con sidered when selecting an appropriate NO transition in this type of en vironment.