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Lind S.,Erlangen Graduate School in Advanced Optical Technologies SAOT | Trost J.,Erlangen Graduate School in Advanced Optical Technologies SAOT | Zigan L.,Friedrich - Alexander - University, Erlangen - Nuremberg | Leipertz A.,Erlangen Graduate School in Advanced Optical Technologies SAOT | Will S.,Erlangen Graduate School in Advanced Optical Technologies SAOT
Proceedings of the Combustion Institute | Year: 2015

The present study introduces an advanced measurement technique for multi-parameter imaging in optically accessible IC engines which is based on two planar laser-induced fluorescence (PLIF) techniques. A LIF tracer mixture consisting of triethylamine (TEA) and acetone is used to investigate the simultaneous determination of air/fuel-ratio, temperature and exhaust gas/air concentration in a direct-injection spark-ignition (DISI) engine with exhaust gas recirculation (EGR). The approach is based on applying a two-wavelength excitation scheme of acetone for temperature and concentration measurement and employing single-wavelength excitation of TEA for the determination of AFR utilizing the effect of oxygen quenching. At first the spectral properties of the tracer mixture are studied to show the separability of the fluorescence signals of both tracers and to identify possible tracer interactions. For calibration and IC engine measurements the focus is put on the tracer acetone for the determination of temperature and air concentration. Fluorescence calibration at IC engine conditions is conducted with pure acetone and with an acetone/TEA mixture to visualize possible interactions. The tracer mixture is then applied in an optically accessible IC engine for temperature determination, which is compared with results of the commonly used successive application of the two individual techniques. The results suggest the suitability of this measurement technique for the simultaneous determination of air/fuel-ratio, air concentration and temperature in combustion devices like IC engines, which helps in the optimization of mixture formation and the subsequent processes such as ignition and pollutant formation. © 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved. Source


Spyropoulos G.D.,Friedrich - Alexander - University, Erlangen - Nuremberg | Kubis P.,Friedrich - Alexander - University, Erlangen - Nuremberg | Li N.,Friedrich - Alexander - University, Erlangen - Nuremberg | Baran D.,Friedrich - Alexander - University, Erlangen - Nuremberg | And 8 more authors.
Energy and Environmental Science | Year: 2014

Organic solar cell technology bears the potential for high photovoltaic performance combined with truly low-cost, high-volume processing. Here we demonstrate organic tandem solar modules on flexible substrates fabricated by fully roll-to-roll compatible processing at temperatures <70 °C. By using ultrafast laser patterning we considerably reduced the "dead area" of the modules and achieved geometric fill factors beyond 90%. The modules revealed very low interconnection-resistance compared to the single tandem cells and exhibited a power conversion efficiency of up to 5.7%. Bending tests performed on the modules suggest high mechanical resilience for this type of device. Our findings inform concrete steps towards high efficiency photovoltaic applications on curved, foldable and moving surfaces. © The Royal Society of Chemistry 2014. Source


Manhart M.T.,Friedrich - Alexander - University, Erlangen - Nuremberg | Kowarschik M.,Angiography and Interventional X Ray Systems | Fieselmann A.,Friedrich - Alexander - University, Erlangen - Nuremberg | Deuerling-Zheng Y.,Angiography and Interventional X Ray Systems | And 5 more authors.
IEEE Transactions on Medical Imaging | Year: 2013

Tissue perfusion measurement using C-arm angiography systems capable of CT-like imaging (C-arm CT) is a novel technique with potentially high benefit for catheter guided treatment of stroke in the interventional suite. However, perfusion C-arm CT (PCCT) is challenging: the slow C-arm rotation speed only allows measuring samples of contrast time attenuation curves (TACs) every 5-6 s if reconstruction algorithms for static data are used. Furthermore, the peak values of the TACs in brain tissue typically lie in a range of 5-30 HU, thus perfusion imaging is very sensitive to noise. We present a dynamic, iterative reconstruction (DIR) approach to reconstruct TACs described by a weighted sum of basis functions. To reduce noise, a regularization technique based on joint bilateral filtering (JBF) is introduced. We evaluated the algorithm with a digital dynamic brain phantom and with data from six canine stroke models. With our dynamic approach, we achieve an average Pearson correlation (PC) of the PCCT canine blood flow maps to co-registered perfusion CT maps of 0.73. This PC is just as high as the PC achieved in a recent PCCT study, which required repeated injections and acquisitions. © 1982-2012 IEEE. Source


Koch H.,Friedrich - Alexander - University, Erlangen - Nuremberg | Kageler C.,Erlangen Graduate School in Advanced Optical Technologies SAOT | Kageler C.,Bayerisches Laserzentrum GmbH | Otto A.,Friedrich - Alexander - University, Erlangen - Nuremberg | And 2 more authors.
Physics Procedia | Year: 2011

Welding of zinc coated sheets in zero gap configuration is of eminent interest for the automotive industry. This Laser welding process would enable the automotive industry to build auto bodies with a high durability in a plain manufacturing process. Today good welding results can only be achieved by expensive constructive procedures such as clamping devices to ensure a defined gad. The welding in zero gap configuration is a big challenge because of the vaporised zinc expelled from the interface between the two sheets. To find appropriate welding parameters for influencing the keyhole and melt pool dynamics, a three dimensional simulation and a high speed imaging system for laser keyhole welding have been developed. The obtained results help to understand the process of the melt pool perturbation caused by vaporised zinc. © 2011 Published by Elsevier Ltd. Source


Eichmann S.C.,Lehrstuhl fur Technische Thermodynamik LTT | Kiefer J.,Erlangen Graduate School in Advanced Optical Technologies SAOT | Kiefer J.,University of Aberdeen | Kiefer J.,University of Bremen | And 5 more authors.
Measurement Science and Technology | Year: 2014

We propose a gas sensor, based on spontaneous Raman scattering, for the compositional analysis of typical biogas mixtures and present a description of the sensor, as well as of the calibration procedure, which allows the quantification of condensable gases. Moreover, we carry out a comprehensive characterization of the system, in order to determine the measurement uncertainty, as well as influences of temperature and pressure fluctuation. Finally, the sensor is applied at different locations inside a plant in which biogas is produced from renewable raw materials. The composition is monitored after fermenting, after purification and after the final conditioning, where natural gas is added. The Raman sensor is able to detect all the relevant gas components, i.e. CH4, CO2, N2 and H2O, and report their individual concentrations over time. The results were compared to reference data from a conventional gas analyzer and good agreement was obtained. © 2014 IOP Publishing Ltd. Source

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