A technique for acquiring two-dimensional soot-volume-fraction measurements in laminar flames has been demonstrated. The technique provides a map of very low noise concentration over a range of wavelengths (250–1100 nm). A noise level of 0.0007 in extinction and a spatial resolution of 30–40 μm for soot concentration were achieved with an arc lamp source that was filtered to provide greater spatial coherence and a CCD detector. The broadband arc lamp source also allowed us to avoid the added noise resulting from speckle with coherent laser sources. Beam steering, due to refractive-index gradients in the flame, was measured and compared with theoretical predictions. The optical arrangement to minimize the effect of beam steering is described. As a result the beam steering had no effect on the soot measurements in the flames examined. Flame-transmission maps obtained with this system in an ethylene/air laminar diffusion flame are presented. Tomographic analysis from use of an Abel inversion of the line-of-sight data to obtain radial profiles of soot concentration is described.
[Optical Society of America ]
(110.0110) Imaging systems : Imaging systems
(110.4280) Imaging systems : Noise in imaging systems
(120.0120) Instrumentation, measurement, and metrology : Instrumentation, measurement, and metrology
(120.1740) Instrumentation, measurement, and metrology : Combustion diagnostics
David R. Snelling, Kevin A. Thomson, Gregory J. Smallwood, and Ömer L. Gülder, "Two-Dimensional Imaging of Soot Volume Fraction in Laminar Diffusion Flames," Appl. Opt. 38, 2478-2485 (1999)