Publications

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Four-dimensional (x, y, z, t) x-ray computed tomography was demonstrated in an optically complex spray using an imaging system consisting of three x-ray sources and three high-speed detectors. The x-ray sources consisted of high-flux rotating anode x-ray tube sources that illuminated the spray from three lines of sight. The absorption, along each absorption path, was collected using a CsI phosphor plate and imaged by a high-speed intensified CMOS camera at 20 kHz. The radiographs were converted to a quantitative equivalent path length (EPL) of liquid using a variable attenuation coefficient to account for beam hardening. The EPL data were then reconstructed using the algebraic reconstruction technique into high-speed time sequences of the three-dimensional liquid mass distribution.

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Trajectories of unique particles were tracked using spatially and temporally interlaced single-shot images from multiple views. Synthetic data were investigated to verify the ability of the technique to track particles in three-dimensions and time. The synthetic data was composed of four images from unique perspectives at four instances in time. The analysis presented verifies that under certain circumstances particle trajectories can be mapped in three dimensions from a minimal amount of information, i.e. one image per viewing angle. These results can enable four-dimensional measurements where they may otherwise prove unfeasible.

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Knowledge of soot particle sizes is important for understanding soot formation and heat transfer in combustion environments. Soot primary particle sizes can be estimated by measuring the decay of time-resolved laser-induced incandescence (TiRe-LII) signals. Existing methods for making planar TiRe-LII measurements require either multiple cameras or time-gate sweeping with multiple laser pulses, making these techniques difficult to apply in turbulent or unsteady combustion environments. Here, we report a technique for planar soot particle sizing using a single high-sensitivity, ultra-high-speed 10 MHz camera with a 50 ns gate and no intensifier. With this method, we demonstrate measurements of background flame luminosity, prompt LII, and TiRe-LII decay signals for particle sizing in a single laser shot. The particle sizing technique is first validated in a laminar non-premixed ethylene flame. Then, the method is applied to measurements in a turbulent ethylene jet flame.

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two-color, volumetric laser-induced fluorescence (TC-VLIF) was demonstrated for three-dimensional, tomographic imaging of the structural properties of the OH radical and temperature field in a turbulent hydrogen-air flame. Two narrow-band laser sources were tuned to the Q_i(5) and Q_i(14) transitions of the (1,0) band in the A²E<—X²II system and illuminated a volumetric region of the flame. Images from eight unique perspectives collected simultaneously from each of the two transitions were used to reconstruct overlapping 011 fields with different Boltzmann fractions and map the 3D temperature distribution with nanosecond precision. Key strategies for minimizing sources of error, such as detector sensitivity and spatial overlap of the two fields, are discussed.

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