Research Outputs

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Now showing 1 - 10 of 17
  • Publication
    Experimental Investigation and Benchmark Study of Oxidation of Methane–Propane–n-Heptane Mixtures at Pressures up to 100 bar
    (MDPI, 2019) ;
    Ramalingam, Ajoy Kumar 
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    Minwegen, Heiko 
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    Heufer, Karl Alexander 
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    Winter, Franz 
    Dual fuel combustion exhibits a high degree of complexity due to the presence of different fuels like diesel and natural gas in initially different physical states and a spatially strongly varying mixing ratio. Optimizing this combustion process on an engine test bench is costly and time consuming. Cost reduction can be achieved by utilizing simulation tools. Although these tools cannot replace the application of test benches completely, the total development costs can be reduced by an educated combination of simulations and experiments. A suitable model for describing the reactions taking place in the combustion chamber is required to correctly reproduce the dual fuel combustion process. This is why in the presented study, four different reaction mechanisms are benchmarked to shock tube (ST) and rapid compression machine (RCM) measurements of ignition delay times (IDTs) at pressures between 60 and 100 bar and temperatures between 671 and 1284 K. To accommodate dual fuel relevant diesel-natural gas mixtures, methane–propane–n-heptane mixtures are considered as the surrogate. Additionally, the mechanisms AramcoMech 1.3, 2.0 and 3.0 are tested for methane–propane mixtures. The influence of pressure and propane/n-heptane content on the IDT based on the measurements is presented and the extent to which the mechanisms can reflect the IDT-changes discussed.
      145  1Scopus© Citations 15
  • Publication
    Performance Comparison between Extruded and Printed Ceramic Monoliths for Catalysts
    (EUCASS, 2017-07)
    Koopmans, Robert-Jan 
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    Bartok, Tobias 
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    Batonneau, Yann 
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    Maleix, Corentin 
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    Beauchet, Romain 
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    Schwentenwein, Martin 
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    Spitzbart, Manfred 
    This paper presents the first results of monopropellant decomposition tests obtained from monolithic ceramic catalysts produced by means of additive layer manufacturing techniques and using ceramic precursors. The purpose is to compare the performance of printed monoliths with traditionally manufactured catalysts with respect to decomposition of highly concentrated hydrogen peroxide. Small holes with a pitch larger than 0 are generally difficult to manufacture. Holes with a diameter of 1.25 mm are difficult to manufacture when the pitch is larger than 2. ecomposition tests revealed that the manufacturing process does not influence the transient pressure performance but is noticeable in the transient temperature performance. However, the influence is only present during part of the transient phase. For optimum transient performance the surface area-to-volume ratio should be maximised.
      121  2
  • Publication
    Efficient Blue-Light-Emitting Polymer Heterostructure Devices: The Fabrication of Multilayer Structures from Orthogonal Solvents
    (Wiley, 2010)
    Sax, Stefan 
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    Rugen-Penkalla, Nicole 
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    Neuhold, Alfred 
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    Zojer, Egbert 
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    List, Emil J. W. 
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    Müllen, Klaus 
    An all-solution processed organic light-emitting diode with enhanced device efficiency based on an additional methanol-soluble polyfluorene layer (see figure) with nonionic ethylene glycol side chains is presented. Due to an asymmetric shift of the energy levels at the polymer/polymer interface, significant efficiency enhancements were obtained.
      117  1Scopus© Citations 92
  • Publication
    A Novel Dual Fuel Reaction Mechanism for Ignition in Natural Gas–Diesel Combustion
    (MDPI, 2019) ;
    Frühhaber, Jens 
    ;
    Lauer, Thomas 
    ;
    Winter, Franz 
    In this study, a reaction mechanism is presented that is optimized for the simulation of the dual fuel combustion process using n-heptane and a mixture of methane/propane as surrogate fuels for diesel and natural gas, respectively. By comparing the measured and calculated ignition delay times (IDTs) of different homogeneous methane–propane–n-heptane mixtures, six different n-heptane mechanisms were investigated and evaluated. The selected mechanism was used for computational fluid dynamics (CFD) simulations to calculate the ignition of a diesel spray injected into air and a natural gas–air mixture. The observed deviations between the simulation results and the measurements performed with a rapid compression expansion machine (RCEM) and a combustion vessel motivated the adaptation of the mechanism by adjusting the Arrhenius parameters of individual reactions. For the identification of the reactions suitable for the mechanism adaption, sensitivity and flow analyzes were performed. The adjusted mechanism is able to describe ignition phenomena in the context of natural gas–diesel, i.e., dual fuel combustion.
      129  1Scopus© Citations 10
  • Publication
    Bond Wire Fatigue of Au, Cu, and PCC in Power LED Packages
    Bond wire failure, primarily wire neck breakage, in power LED devices due to thermomechanical fatigue is one of the main reliability issues in power LED devices. Currently, the standard testing methods to evaluate the device’s lifetime involve time-consuming thermal cycling or thermal shock tests. While numerical or simulation methods are used as convenient and quick alternatives, obtaining data from material lifetime models with accurate reliability and without experimental fatigue has proven challenging. To address this issue, a mechanical fatigue testing system was developed with the purpose of inducing mechanical stresses in the critical region of the bond wire connection above the ball bond. The aim was to accelerate fatigue cracks at this bottleneck, inducing a similar failure mode as observed during thermal tests. Experimental investigations were conducted on Au, Cu, and Pd-coated Cu bonding wires, each with a diameter of 25 µm, using both low- and high-frequency excitation. The lifetime of the wire bond obtained from these tests ranged from 100 to 1,000,000 cycles. This proposed testing method offers material lifetime data in a significantly shorter timeframe and requires minimal sample preparation. Additionally, finite element simulations were performed to quantify the stresses at the wire neck, facilitating comparisons to conventional testing methods, fatigue test results under various operating conditions, material models, and design evaluations of the fine wire bond reliability in LED and microelectronic packages.
      19  285
  • Publication
    Simulation of a Magnetocaloric Heat Pump in Building Technology
    Increased quality of building envelopes in the last decades leads to decreased heating demands of new buildings and therefore heating devices with lower heating powers are needed. !ere is a lack of suitable solutions in the heating market in the small power range, which can cover small heating loads decentral without distribution losses. In the presented study, the potential of magnetocaloric heating is investigated. Apart from the advantage that no climate-relevant gases are used compared to commonly used compression heat pumps, this technology is suitable for covering low heating requirements. A cornerstone of the investigation is the development of a programme for simulating the behaviour of a building-integrated magnetocaloric heat pump. Target is to determine the effect of the change in basic properties such as the nature of the magnetocaloric material, the magnetic flux density, the working frequency, etc., but also to determine the influence of building parameters on the overall efficiency of the heating system.
      126  766
  • Publication
    Impact of Catalyst Length and Preheating on Transient Catalytic H2O2 Decomposition Performance
    (American Institute of Aeronautics and Astronautics, 2015)
    Krejci, David 
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    Koopmans, Robert-Jan 
    ;
    Scharlemann, Carsten 
      115  2Scopus© Citations 5
  • Publication
    Modeling the Pilot Injection and the Ignition Process of a Dual Fuel Injector with Experimental Data from a Combustion Chamber Using Detailed Reaction Kinetics
    (SAE International, 2018-09-10)
    Peter, Andreas 
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    Wensing, Michael 
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    Frühhaber, Jens 
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    Lauer, Thomas 
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    Winter, Franz 
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    Priesching, Peter 
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    Pachler, Klaus 
    The introduction of the so called Emission Controlled Areas within the IMO Tier III legislation forces manufacturers of maritime propulsion systems to adherence to stringent emission thresholds. Dual fuel combustion, which is characterized by the injection of a small amount of fuel oil to ignite a premixed natural gas air mixture, constitutes an option to meet this target. At high diesel substitution rates and very short pilot injection events, the injector is operated in the ballistic regime. This influences spray penetration, mixture formation and ignition behavior. In the present work, a seven-hole dual fuel injector was measured in a combustion chamber to provide data for the generation of a CFD model using the commercial code AVL FIRE®. The liquid and the vapor phase of the fuel spray were quantified by Mie-scattering and Schlieren-imaging technique for different chamber conditions. Based on the measured spray characteristics, a methodology was developed to imprint a velocity profile to the initial droplets in the CFD model, to depict the spray penetration for small injection durations. To characterize the ignition process and the flame propagation, measurements of the OH* emission and the natural luminosity of the flame were carried out. A detailed reaction mechanism, which is able to predict both diesel and dual fuel combustion, was integrated in the CFD model. The ignition delay was fitted to the experimental data by adapting the reaction mechanism for different chamber temperatures. The influence of the presence of natural gas on the ignition behavior was validated using data from a rapid compression machine. Even for low temperatures and high pressures, similar to the start of injection under engine operating conditions, a good correlation could be achieved. The developed knowledge will be transferred to an engine model to investigate the limits of dual fuel combustion processes.
      114  2Scopus© Citations 8