A 2-D fuel/oxygen equivalence ratio imaging system has been developed. The technique exploits the efficient quenching of the fluorescence of organic molecules by molecular oxygen in order to determine the fuel and oxygen partial pressures simultaneously. Following pulsed planar laser excitation of fluoranthene—a specially selected fluorescent dopant—two images of the fluorescence were recorded, with the second image being delayed by several nanoseconds. Use of a rapid lifetime determination algorithm yielded first a fluorescence lifetime image, and subsequently, with the assumption of Stern-Volmer quenching, an intensity image corrected for quenching. Images of the air pressure, fuel pressure, and the equivalence ratio were obtained. The technique, which uses dual gated intensifiers coupled to a sensitive CCD camera, requires only two integrated fluorescence intensities to calculate the fluorescence lifetime accurately. In the current work, images of the turbulence-induced mixing of a methane jet into quiescent air are displayed. Images can also be obtained in flames, but the analysis of the data is uncertain because the fluorescence lifetime of fluoranthene is temperature dependent.
T. Q. Ni and L. A. Melton, "Fuel Equivalence Ratio Imaging for Methane Jets," Appl. Spectrosc. 47, 773-781 (1993)