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We present a novel framework and experimental method for the quantification of spatial resolution of a tomography system. The framework adopts the "black box" view of an imaging system, considering only its input and output. The tomography system is locally stimulated with a step input, viz., a sharp edge. The output, viz., the reconstructed images, is analysed by Fourier decomposition of their spatial frequency components, and the local limiting spatial resolution is determined using a cut-off threshold. At no point is an observer involved in the process. The framework also includes a means of translating the quantification region in the imaging space, thus creating a spatially resolved map of objectively quantified spatial resolution. As a case-study, the framework is experimentally applied using a gaseous propane phantom measured by a well-established chemical species tomography system. A spatial resolution map consisting of 28 regions is produced. In isolated regions, the indicated performance is 4-times better than that suggested in the literature and varies by 57% across the imaging space. A mechanism based on adjacent but non-interacting beams is hypothesised to explain the observed behaviour. The mechanism suggests that, as also independently concluded by other methods, a geometrically regular beam array maintains maximum objectivity in reconstructions. We believe that the proposed framework, methodology, and findings will be of value in the design and performance evaluation of tomographic imaging arrays and systems.

In this paper we discuss the development and application of 2D imaging methods for the study of fuel-air mixing and the in-situ measurement of soot in flames. Fuel imaging is based on planar laser-induced fluorescence (PLIF) with pulsed U V lasers. Fuel concentrations may be estimated from the fluorescence of common fuel components or through the addition of a fluorescent species or seed. PLIF of fuel is shown to be applicable to both premixed and non-premixed combustion. The choice of fluorescent seed and the role of interfering species, such as combustion derived polyaromatic hydrocarbons (PAH) and laser-induced incandescence from soot, are discussed. The application of the method is illustrated with an example of an isothermal mixing study in a gas turbine combustor sector rig and measurements in a simple flame. The results demonstrate that PLIF can achieve high spatial resolution, circa 0.4mm, in a combustor with dimensions of order of 400mm. The dynamic range of the measured intensities exceeds 1500 with typical signal-to-noise ratios of better than 100: I . A major source of interference in PLIF studies of non-premixed flames is laser-induced incandescence (LII) from soot particles. We discuss the role of LII both as an interference in PLIF imaging and as an imaging method for soot volume fraction. A detailed analysis of the physics of LII is presented on a theoretical model developed. Results from the model and supporting experimental data are presented. LII images from a highly turbulent sooting flame indicate that soot structures, probably in the form of thin sheets as small as 100 pm across, are formed through vortex mixing. E 8450The derivation of temperatures of gas phase media from spectra generated by DFWM, induced by frequency scanned narrow linewidth lasers, is briefly reviewed. The technique of multiplex or broadband DFWM is described, by which spectra, and hence temperatures, may be obtained by a single shot of a novel broadband "modeless" laser. Experimental measurements of broadband DFWM lineshapes from OH are briefly described and compared with theoretical predictions. Results of temperature measurements in premixed methanelair flames using broadband DFWM spectra are reported. Systematic errors arising from the effect of absorption are discussed, improvements to and applications of the technique to turbulent media are briefly considered.Optical methods for measuring temperatures in hostile environments are attractive since they allow remote sensing and are inherently non-invasive. These features are especial-ly useful for diagnostics of combustion processes where physical probes may perturb the medium. Laser based techniques have been developed using linear and nonlinear scat-

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