Browsing by Author "Geigle, Klaus Peter"

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    Investigation of laminar pressurized flames for soot model validation using SV-CARS and LII
    (ELSEVIER, 2005) Hadef, R; Geigle, Klaus Peter; Michael, S
    Quasi-simultaneous measurements of temperature and soot volume fraction in pressurized and atmospheric flames are presented. A dual-flame burner concept yielded stable laminar flames for a variety of equivalence ratios, pressures, and fuels, and permitted the investigation of flames without the influence of soot oxidation. A CARS-based technique (shifted vibrational CARS) for temperature measurements, which offers high accuracy over the entire relevant temperature and soot concentration range, is described. Comparison of temperature measurements in the nonsooting part of a laminar diffusion flame at atmospheric pressure by SV-CARS and conventional N2 Q-branch CARS yielded excellent agreement. This new technique was applied to quasi-1D laminar flames with soot concentrations up to 10 ppm and pressures up to 5 bar. The temperature profiles measured in these flames were combined with soot concentration measurements using LII; calibration and correction for signal trapping yielded quantitative soot volume fraction data. The temperature and soot concentration data were combined to generate a comprehensive dataset for the validation of an improved kinetic soot model for the prediction of soot formation in premixed combustion at elevated pressure.
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    The concept of 2D gated imaging for particle sizing in a laminar diffusion flame
    (Springer, 2013) Hadef, Redjem; Geigle, Klaus Peter; Zerbs, Jochen; Sawchuk, Robert A.; Snelling, David R.
    Abstract In this work, time-resolved laser-induced incandescence (TiRe LII) has been employed to measure primary particle diameters of soot in an atmospheric laminar ethylene diffusion flame. The generated data set complements existing data determined in one single location and takes advantage of the good spatial resolution of the ICCD detection. Time resolution is achieved by shifting the camera gate along the LII decay. One key input parameter for the analysis of time-resolved LII is the local flame temperature. This was determined on a grid throughout the flame by coherent anti-Stokes Raman scattering. The accurate temperature data, in combination with other published data from this flame, are well suited for soot model validation purposes while we showed feasibility of a shifted gate approach to deduce 2D particle sizes in the chosen standard flame.
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    Visualization of soot inception in turbulent pressurized flames by simultaneous measurement of laser-induced fluorescence of polycyclic aromatic hydrocarbons and laser-induced incandescence, and correlation to OH distributions
    (Springer, 2015) Geigle, Klaus Peter; O’Loughlin, William; Hadef, Redjem; Meier, Wolfgang
    Distributions of polycyclic aromatic hydrocarbons (PAH) and their correlation with soot formation were studied in ethylene–air swirl flames stabilized in a gas turbine model combustor at increased pressure. The combustor can be operated with secondary air injection to study the influence of soot oxidation. We employed PAH laserinduced fluorescence using UV excitation simultaneously with IR-excited laser-induced incandescence to identify soot. PAH signatures typically appear discontinuous unlike OH, yet similar to soot but exhibit more uniform intensity and larger size. The correlation of both diagnostics allowed identification of a wide range of soot formation progress, including isolated soot or PAH, as well as PAH transitioning into soot. The occurrence of soot, PAH and OH and their spatial variations are strongly dependent on the properties of the flow field. In the bottom part of the inner recirculation zone and for the reference case, a rich flame with additional oxidation air, soot levels are relatively high, while PAH intensities in this region are minimal. This correlates well with high temperatures in this region published recently, which are unfavorable for soot formation as the precursors, PAH, decompose. Consequently, soot presence here is attributed to transport. In contrast to OH and soot distributions which change significantly upon addition of secondary air downstream of the primary combustion zone, PAH distributions for both cases look relatively similar. This is attributed to a downstream consumption of PAH by different processes. Without oxidation air, PAH completely transform into soot, while additional oxidation air leads to their oxidation.