Verloeschen in instationaeren Vormischflammen bei Druckabsenkung Abschlussbericht

SIGLETIB: FR 4085 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Zur Untersuchung des linearen Tragverhaltens von Faserverbundkonstruktionen mittels numerischer Methoden

In order to apply a proper method for the numerical analysis of composite structures they need to be classified with respect to their material ingredients. The technical term 'composites' covers a wide range of material combinations, like concrete-steel, foam-metal, epoxy-carbon, rubber-rayon, etc. All composed materials can be seen as reinforced matrix materials. But their load-carrying behaviour might differ significantly with respect to the fiber-matrix materials. But their load-carrying behaviour might differ significantly with respect to the fiber-matrix combination chosen. For the analysis of fiber-reinforced composites it is widely accepted to homogenize the mechanical properties of the individual constituents in order to be able to apply an orthotropic material formulation. With this at hand a ply can be viewed as a smeared material which can be numerically treated easily. But we have to pay for with loosing informations about the individual structural response of the matrix and the fibers, respectively. Moreover it has been observed that for specific material combinations, e.g. reinforced-rubber composites, the assumption of material homogenization generates artificial numerical stiffness which is not physically motivated. Thus, wrong numerical results are produced. The present report clarifies the problem. In addition, a classification of composite materials is proposed. Furthermore, a strategy will be developed in order to overcome the deficiencies when applying the classical homogenization technique. The work serves as a contribution for bringing together different activities in numerical structural analysis of composites. (orig.)Available from TIB Hannover: RR 7409(1996,1)+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Vorausberechnung der Zuendstabilitaet von turbulenten Diffusionsflammen

SIGLECopy held by FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Heterodyne frequency shift laser doppler anemometer

Laser Doppler anemometry is a non-intrusive method for the study of flow processes by measuring the velocity of tracer particles carried in the flow. The direction, as well as the magnitude of the flow velocity can be obtained if frequency shift techniques are employed. Conventional techniques involve a single laser source and a beam splitter to generate two LDA beams which cross in the measuring volume. A frequency shift is then introduced into one of these two beams. The alternative approach presented here involves the use of two independent laser sources, which differ in their emission frequency by a set value, giving the frequency shift. The emission line width and stability of the laser frequencies directly affect the bandwidth of the measuring signal. We show that such effects can be eliminated by correlating the measuring signal with a reference signal. The reference signal consists of a beat signal of the two laser sources which is processed to produce a reference signal pair with a phase difference of 90 between the two components. By mixing the measuring signal with this reference signal pair we obtain a sine-cosine quadrature signal which is modulated only by the Doppler frequency. This quadrature signal is independent of the shift frequency and its fluctuations. The requirements for the stability and emission line width of the laser sources are therefore significantly reduced. The quadrature signal demodulation then allows directional measurements of quasi-static flow processes with velocities of less than 0.05 m/s corresponding to very small Doppler frequencies of 10 kHz or less. (orig.)Available from TIB Hannover: RO 3132(53) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Einfluss der Struktur des Strahlrandes auf die thermische Stickoxidbildung in Freistrahldiffusionsflammen Abschlussbericht

TIB: FR 4086 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Numerische Simulation der elementarkinetischen Vorgaenge im DI-Dieselmotor und im nachgeschalteten Plasmareaktor Abschlussbericht

The attempt to use microwave induced N_2-O_2 plasmas for reducing NO_x-emissions of direct injecting gasoline and Diesel engines reaching the limits of the EURO 4 exhaust gas standards is of special interest. It was attempted to explore the fundamental plasmachemical reaction paths for NO_x-kinetics in hot thermal and cold non-thermal plasmas. To reach this aim a numerical parameter study was done to determine theoretical possible NO_x-reduction potentials. The principal analogy of plasma free jets and turbulent jet flames was the reason to choose the theory of laminar diffusion flamelets for non-premixed turbulent combustion for the turbulent reacting flow. The turbulent flow was modelled by a k-#epsilon# model of the commercial CFD solver FLUENT. The mechanism of chemical reactions consists of reactions for all ground states and electric and vibrational excited states. The results of the studies show that thermal plasmas with an oxygen part more than 5% are not able to reduce NO_x-emissions. On the one hand reduction potentials were found at temperatures more than 6000-8000 K. On the other hand a real plasma jet always consists of a hot center and a cooler zone around the center where heavy NO_x-producing is taking place. The results for non-thermal plasmas show theoretical reduction potentials of about 80% at temperatures of about 2000 K. This shows a good agreement with latest experimental studies. (orig.)Im Rahmen nachmotorischer Prozesse ist der Versuch, mit mikrowelleninduzierten N_2-O_2-Plasmen NO_x-Emissionen direkteinspritzender Otto- und Dieselmotoren derart zu reduzieren, dass sie die Grenzwerte der kommenden Abgasvorschrift EURO 4 erfuellen, von besonderem Interesse. Im Rahmen des Teilprojektes 17 wurde der Versuch gemacht, fundamentale Wirkketten der NO_x-Kinetik in heissen, thermischen und kalten, nicht-thermischen Plasmen offen zu legen. Dazu wurde eine numerische Studie der wichtigsten physikalischen Parameter des Plasma-Jet-Reaktors durchgefuehrt, um theoretisch erzielbare NO_x-Reduktionspotentiale zu berechnen. Die prinzipielle Analogie eines Plasma-Freistrahls mit einer turbulenten Freistrahlflamme legte es nahe, die Theorie laminarer Diffusionsflamelets fuer die nicht-vorgemischte, turbulente Verbrennung als Modell fuer die turbulente, reaktive Mischung zu waehlen. Zur Modellierung der turbulenten Stroemung wurde das k-#epsilon#-Modell des kommerziellen Loesers FLUENT benutzt. Der Mechanismus elementarer, chemischer Reaktionen besteht aus Reaktionen der Grundzustaende und der elektrisch und vibrational angeregten Komponenten. Die Ergebnisse der Untersuchungen zeigen, dass thermische Plasmen mit einem Sauerstoffanteil von mehr als 5% nicht in der Lage sind, NO_x-Emissionen zu reduzieren. Zwar werden fuer Temperaturen oberhalb von 6000-8000 K Reduktionspotentiale gefunden. Doch ein realer Plasma-Freistrahl besteht aus einem heissen Kern und einer kuehleren, umgebenden Zone, in der es zu erheblicher NO_x-Bildung kommt. Die Ergebnisse fuer nicht-thermische, kalte Plasmen zeigen, dass bei Temperaturen von etwa 2000 K theoretische Reduktionsgrade von bis zu 80% erzielt werden koennen. Dies deckt sich mit juengsten experimentellen Studien. (orig.)SIGLEAvailable from TIB Hannover: DtF QN1(91,10) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung, Berlin (Germany)DEGerman

Experimentelle Untersuchung magerer Zuendgrenzen und Flammengeschwindigkeiten unter hohem Druck und Mikrogravitation Schlussbericht

Available from TIB Hannover: F98B642 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman