Identification of combustion mode under MILD conditions using Chemical Explosive Mode Analysis |
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| Authors: | NAK Doan S Bansude K Osawa Y Minamoto T Lu JH Chen N Swaminathan |
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| Institution: | 1. Department of Mechanical Engineering and Institute for Advanced Study, Technical University of Munich, Garching, Germany;2. Department of Mechanical Engineering, University of Connecticut, Storrs, USA;3. Department of Mechanical Engineering, Tokyo Institute of Technology, Meguro-ku, Japan;4. Combustion Research Facility, Sandia National Laboratories, Livermore, CA, USA;5. Department of Engineering, University of Cambridge, Cambridge, UK |
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| Abstract: | Direct Numerical Simulations (DNS) data of Moderate or Intense Low-oxygen Dilution (MILD) combustion are analysed to identify the contributions of the autoignition and flame modes. This is performed using an extended Chemical Explosive Mode Analysis (CEMA) which accounts for diffusion effects allowing it to discriminate between deflagration and autoignition. This analysis indicates that in premixed MILD combustion conditions, the main combustion mode is ignition for all dilution and turbulence levels and for the two reactant temperature conditions considered. In non-premixed conditions, the preponderance of the ignition mode was observed to depend on the axial location and mixture fraction stratification. With a large mixture fraction lengthscale, ignition is more preponderant in the early part of the domain while the deflagrative mode increases further downstream. On the other hand, when the mixture fraction lengthscale is small, sequential autoignition is observed. Finally, the various combustion modes are observed to correlate strongly with mixture fraction where lean mixtures are more likely to autoignite while stoichiometric and rich mixtures are more likely to react as deflagrative structures. |
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