Application of a beam homogenizer to planar laser diagnostics

Pfadler, Sebastian; Beyrau, Frank; Löffler, M.; Leipertz, Alfred

doi:10.1364/oe.14.010171

Cited by 61 publications

(19 citation statements)

References 17 publications

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“…Further ongoing studies using temporally and spatially high resolving laser-based techniques will provide a deeper understanding of the underlying physics and chemistry involved in the process. For this purpose, particle image velocimetry (PIV) for velocity field characterization [18], planar laser induced fluorescence (PLIF) to determine radical concentrations [19] as well as linear Raman scattering for the measurement of major species concentrations [20] and coherent anti-Stokes Raman scattering (CARS) for the measurement of temperatures [21], will be applied. …”

Section: Discussionmentioning

confidence: 99%

Technical Feasibility of Electric Field Control for Turbulent Premixed Flames

et al. 2010

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The utilization of electric fields for the control of technical combustion processes (EFCC, Electric Field Controlled Combustion) provides an interesting approach in present-day discussions regarding reductions in CO 2 emission levels and improved fuel efficiency. The technical feasibility of electric field control of turbulent premixed flames is demonstrated for the first time at technically relevant operating conditions. The technical criteria addressed include the efficiency of control at thermal powers above 50 kW, operating pressures in the order of 10 bar, air preheating, increased mixture exit velocities as well as swirl-stabilized flames. Capacitive coupling of electric fields is explored against the background of preferably non-intrusive integration into existing gas turbine systems. It is demonstrated that electric fields can be transmitted through ceramic burning chamber walls using capacitive coupling by electrodes deposited as coatings on the walls, thus avoiding sensitive mechanical parts as weak spots within the combustion chamber. No reasonable limitations are observed that might hinder a possible realization of flame control for technical combustion processes using EFCC. IntroductionThe influence of electric fields on flames is known for almost 200 years and was mentioned for the first time in 1814 [1]. In the 1960's and 1970's, several different studies attempted to characterize the observed effects and to utilize them for technical applications. The two main effects observed that are of technical importance are an increase in flame stability and a reduction of pollutant emissions. Therefore, the utilization of electric fields for the control of technical combustion processes (EFCC, Electric Field Controlled Combustion) provides an interesting approach in present-day discussions regarding reductions in CO 2 emission levels and improved fuel efficiency.Most of the previous studies in the area were limited to simple atmospheric laboratory flames with low thermal power and laminar or low-turbulence flow fields [2][3][4][5][6][7][8][9][10][11]. In order to extend the scope of research to technically relevant conditions, a new study was recently begun, dealing with the technical feasibility of flame control by electric fields in stationary gas turbine combustors. This study was conducted at the Institute for Engineering Thermodynamics (LTT) at the FriedrichAlexander-University of Erlangen-Nuremberg in close cooperation with the Siemens AG company within the framework of the research initiative "Power Plants for the 21 st Century" (KW21). It was shown that the application of electric fields for flame control can broaden the regime for stable operation as well as decrease overall pollutant emissions at relevant operating conditions, i.e., increased pressure, high exit velocity and air preheating as well as swirl stabilization. Moreover, in order to avoid the requirement for the installation of metallic electrodes inside the combustion chamber, the coupling of an electric field in a capacitive manner t...

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Section: Discussionmentioning

confidence: 99%

Technical Feasibility of Electric Field Control for Turbulent Premixed Flames

et al. 2010

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“…To illuminate the complete coated surface and also to decrease the gradient in the laser fluence along the investigated plate due to the Gaussian beam distribution, the laser beam was expanded using a spherical diverging lens (f = − 30 mm). Instead of a more complex beam homogeniser (Pfadler et al 2006), we applied a simple UV diffusor with a diffusion angle of 5° (48-515, Edmund Optics) positioned in the path of the expanding beam to obtain a smoother laser fluence distribution. The laser pulse energy was monitored and kept constant during the performed experiments using an online energy monitor from LaVision at approximately 44 mJ for plate A, which resulted in an average fluence of ~ 1 mJ/cm 2 .…”

Section: Setup For Surface Thermometrymentioning

confidence: 99%

Planar measurements of spray-induced wall cooling using phosphor thermometry

et al. 2018

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The wall cooling induced by spray impingement is investigated using phosphor thermometry. Thin coatings of zinc oxide (ZnO) phosphor were applied with a transparent chemical binder onto a steel surface. Instantaneous spatially resolved temperatures were determined using the spectral intensity ratio method directly after the injection of UV-grade hexane onto the surface using a commercial gasoline injector. The investigations showed that 2D temperature measurements with high spatial and shot-to-shot precision of, respectively, 0.5 and 0.6 K can be achieved, allowing the accurate resolution of the cooling induced by the spray. The presence of a liquid film over the phosphor coating during measurements showed no noticeable influence on the measured temperatures. However, in some cases a change in the intensity ratio at the spray impingement area, in the form of a permanent "stain", could be observed after multiple injections. The formation of this stain was less likely with increasing annealing time of the coating as well as lower plate operating temperatures during the injection experiments. Finally, the experimental results indicate a noticeable influence of the thickness of the phosphor coating on the measured spray-induced wall cooling history. Hence, for quantitative analysis, a compromise between coating thickness and measurement accuracy needs to be considered for similar applications where the heat transfer rates are very high.

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“…Larger variations must be avoided, by using for example a beam homogeniser (see, e.g. Pfadler et al 2006). In this regard, we also note that the spatial variation in laser fluence caused by refractive index gradients is difficult to correct for.…”

Section: Discussionmentioning

confidence: 97%