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Ettlingen, Germany

Kuznetsov M.,Karlsruhe Institute of Technology | Friedrich A.,Pro Science | Stern G.,Pro Science | Kotchourko N.,Pro Science | And 2 more authors.
Journal of Loss Prevention in the Process Industries

A series of medium-scale experiments on vented hydrogen deflagration was carried out at the KIT test side in a chamber of 1×1×1m3 size with different vent areas. The experimental program was divided in three series: (1) uniform hydrogen-air mixtures; (2) stratified hydrogen-air mixtures within the enclosure; (3) a layer deflagration of uniform mixture. Different uniform hydrogen-air mixtures from 7 to 18% hydrogen were tested with variable vent areas 0.01-1.0m2. One test was done for rich mixture with 50% H2. To vary a gradient of concentration, all the experiments with a stratified hydrogen-air mixtures had about 4%H2 at the bottom and 10 to 25% H2 at the top of the enclosure. Measurement system consisted of a set of pressure sensors and thermocouples inside and outside the enclosure. Four cameras combined with a schlieren system (BOS) for visual observation of combustion process through transparent sidewalls were used. Four experiments were selected as benchmark experiments to compare them with four times larger scale FM Global tests (Bauwens et al., 2011) and to provide experimental data for further CFD modelling. The nature of external explosion leading to the multiple pressure peak structure was investigated in details. Current work addresses knowledge gaps regarding indoor hydrogen accumulations and vented deflagrations. The experiments carried out within this work attend to contribute the data for improved criteria for hydrogen-air mixture and enclosure parameters to avoid unacceptable explosion overpressure. Based on theoretical analysis and current experimental data a further vent sizing technology for hydrogen deflagrations in confined spaces should be developed, taking into account the peculiarities of hydrogen-air mixture deflagrations in presence of obstacles, concentration gradients of hydrogen-air mixtures, dimensions of a layer of flammable cloud, vent inertia, etc. © 2015 Elsevier Ltd. Source

Kuznetsov M.,Karlsruhe Institute of Technology | Redlinger R.,Karlsruhe Institute of Technology | Breitung W.,Karlsruhe Institute of Technology | Grune J.,Pro Science | And 2 more authors.
Proceedings of the Combustion Institute

Effects of elevated temperatures (up to 573 K) and pressures (up to 72 bar) on the laminar flame velocity of hydrogen-oxygen-steam mixtures were studied both experimentally and computationally. Stoichiometric hydrogen-oxygen mixtures diluted with steam up to 85% (mol.) have been tested in a spherical explosion chamber with an inner diameter of 25 cm using the pressure method and high speed shadow cinematography. The experimental data on the laminar burning velocity were compared with numerical calculations that used different H/O reaction mechanisms based on the Lutz, GRI-Mech 3.0, Li and Warnatz schemes. The calculations were performed with three codes: INSFLA, Cantera (for unstretched planar flames) and our own FP-code (based on the PREMIX code). Nonmonotonic pressure dependence and strong suppressing effect of steam dilution on laminar flame velocity was found both experimentally and numerically. The best consistency with the experimental measurements of the laminar flame velocity at elevated pressures and temperatures in presence of high steam concentrations was found for the Lutz H/O mechanism. © 2010 Published by Elsevier Inc. on behalf of The Combustion Institute. All rights reserved. Source

Veser A.,Pro Science | Kuznetsov M.,Karlsruhe Institute of Technology | Fast G.,Karlsruhe Institute of Technology | Friedrich A.,Pro Science | And 4 more authors.
International Journal of Hydrogen Energy

Experiments on flame propagation regimes in a turbulent hydrogen jet with velocity and hydrogen concentration gradients have been performed. Horizontal stationary hydrogen jets released at normal and cryogenic temperatures of 290, 80 and 35 K with different nozzle diameters and mass flow rates have been investigated. Sampling probe method and laser PIV techniques have been used to evaluate the distribution of hydrogen concentration and flow velocity. High-speed photography combined with a Background Oriented Schlieren (BOS) system was used for the visual observation of the turbulent flame propagation. In order to investigate different flame propagation regimes the ignition position was changed along the jet axis. It was found that the flame propagates in both directions, up- and downstream of the jet flow if hydrogen concentration is >11%, whereas in case [H2] < 11%, the flame propagates only downstream. This means that at normal temperature the flame is able to accelerate effectively only if the expansion ratio σ of the H 2-air mixture is higher than a critical value σ (*) = 3.75 defined for a closed geometry. © 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. Source

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