Effect of soot self-absorption on color-ratio pyrometry in laminar coflow diffusion flames.

This Letter reports on the effect of self-absorption on measured temperature for color-ratio soot pyrometry with a color camera. A series of increasingly nitrogen diluted atmospheric pressure ethylene/air laminar coflow diffusion flames are studied, providing flames with different optical path lengths, soot loading, and soot optical properties. Numerical calculations are used to simulate the change in collected flame emission signal with and without light attenuation using experimentally measured maps of the soot absorption coefficient.

Boundary condition thermometry using a thermographic-phosphor-coated thin filament.

Thermographic phosphors (TPs) exhibit a temperature sensitive emission spectrum when excited with ultraviolet radiation. In this study, 14 μm diameter SiC fibers are coated with ZnO or Dy:YAG using a ceramic binder to a total diameter of 70±9 μm. ZnO and Dy:YAG fibers were used to measure fiber temperatures in the range of 294-450 K and 450-1245 K, respectively.

Use of high dynamic range imaging for quantitative combustion diagnostics.

High dynamic range (HDR) imaging is applied to quantitative combustion diagnostics in coflow laminar diffusion flames as a way to improve the signal-to-noise ratio (SNR) and measurement sensitivity. The technique relies on the combination of partially saturated frames into a single unsaturated image; in this work, the effectiveness of the HDR approach is demonstrated when applied to two-color ratio pyrometry. Specifically, it is shown than an increase in SNR results in more precise temperature measurements for both soot and thin filament pyrometry.

Absorption-ablation-excitation mechanism of laser-cluster interactions in a nanoaerosol system.

The absorption-ablation-excitation mechanism in laser-cluster interactions is investigated by measuring Rayleigh scattering of aerosol clusters along with atomic emission from phase-selective laser-induced breakdown spectroscopy. For 532 nm excitation, as the laser intensity increases beyond 0.16  GW/cm^{2}, the scattering cross section of TiO_{2} clusters begins to decrease, concurrent with the onset of atomic emission of Ti, indicating a scattering-to-ablation transition and the formation of nanoplasmas.

Quantitative Rayleigh thermometry for high background scattering applications with structured laser illumination planar imaging.

This work demonstrates structured laser illumination planar imaging (SLIPI) for Rayleigh thermometry with high background scattering. Two coherent laser beams were crossed to produce an interference pattern, from which the modulated Rayleigh signal was collected. The modulated signal serves as a signature that identifies information about Rayleigh scattering from the probe volume against additional contributions in the image from background scattering.

Use of Rayleigh imaging and ray tracing to correct for beam-steering effects in turbulent flames.

Laser Rayleigh imaging has been applied in a number of flow and flame studies to measure concentration or temperature distributions. Rayleigh cross sections are dependent on the index of refraction of the scattering medium. The same index of refraction changes that provide contrast in Rayleigh images can also deflect the illuminating laser sheet.