On polyhedral structures of lean methane/hydrogen Bunsen flames: Combined experimental and numerical analysis |
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| Institution: | 1. Technical University of Darmstadt, Department of Mechanical Engineering, Simulation of reactive Thermo-Fluid Systems, Otto-Berndt-Str. 2, 64287 Darmstadt, Germany;2. Darmstadt University of Applied Sciences, Laboratory for Optical Diagnostics and Renewable Energies, Schoefferstr. 3, 64295 Darmstadt, Germany;3. Technical University of Darmstadt, Department of Mechanical Engineering, Reactive Flows and Diagnostics, Otto-Berndt-Str. 3, 64287 Darmstadt, Germany;4. Department of Mechanical and Aerospace Engineering, Sapienza University of Rome, via Eudossiana 18, 00184 Rome, Italy;1. Institute of Technical Thermodynamics, Karlsruhe Institute of Technology, Engelbert-Arnold-Str. 4, Karlsruhe 76131, Germany;2. Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, China;3. Dalian National Laboratory for Clean Energy, Dalian 116023, China;1. Institut für Technische Verbrennung, Universität Stuttgart, Pfaffenwaldring 31, Stuttgart 70569, Germany;2. Institut für Verbrennung und Gasdynamik (IVG), Universität Duisburg-Essen, Carl-Benz Straße 199, Duisburg 47057, Germany;3. Simulation reaktiver Thermo-Fluid Systeme (STFS), TU Darmstadt, Otto-Berndt-Straße 2, Darmstadt 64287, Germany;4. Reaktive Strömungen und Messtechnik (RSM), TU Darmstadt, Otto-Berndt-Straße 3, Darmstadt 64287, Germany;1. Technical University of Darmstadt, Department of Mechanical Engineering, Simulation of reactive Thermo-Fluid Systems, Otto-Berndt-Straße 2, 64287 Darmstadt, Germany;2. Engler-Bunte-Institute, Karlsruhe Institute of Technology, Engler-Bunte-Ring 7, 76131 Karlsruhe, Germany;3. Steinbuch Centre for Computing, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany;1. University of Applied Sciences Darmstadt, Department of Mechanical and Plastics Engineering, Optical Diagnostics and Renewable Energies, Germany;2. University of Duisburg-Essen, Department of Mechanical and Process Engineering, Institute of Combustion and Gas Dynamics, Germany;3. Technical University of Darmstadt, Department of Mechanical Engineering, Reactive Flows and Diagnostics, Germany;4. Norwegian University of Science and Technology, Department of Energy and Process Engineering, Trondheim, Norway;5. University of Applied Sciences Darmstadt, Department of Chemical Engineering and Biotechnology, Chemical Reaction Engineering, Germany |
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| Abstract: | In premixed flame propagation of lean hydrogen or hydrogen-enriched blends, both hydrodynamic and thermo-diffusive instabilities are governing the flame front shape and affect its propagation velocity. As a result, different types of cellular patterns can occur along the flame front in a laminar scenario. In this context, an interesting phenomenon is the formation of polyhedral flames which can be observed in a Bunsen burner. It is the objective of this work to systematically characterize the polyhedral structures of premixed methane/hydrogen Bunsen flames in a combined experimental and numerical study. A series of lean flames with hydrogen content varying between 20 and 85% at two equivalence ratios is investigated. The experiments encompass chemiluminescence imaging together with Planar Laser-induced Fluorescence (PLIF) measurements of the OH radical. Characteristic cell sizes are quantified from the experiments and related to the characteristic length scales obtained from a linear stability analysis. In the experiments, it is observed that the cell sizes at the base of the polyhedral Bunsen flames decrease almost linearly with hydrogen addition and only a weak dependence on the equivalence ratio is noted. These trends are well reflected in the numerical results and the length scale comparison further shows that the wavelength with the maximum growth rate predicted by the linear stability analysis is comparable to the cell size obtained from the experiment. The correlation between the experimental findings and the linear stability analysis is discussed from multiple perspectives considering the governing time and length scales, furthermore drawing relations to previous studies on cellular flames. |
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