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Optimization of the Eddy Dissipation Concept (EDC) model for turbulence-chemistry interactions under hot diluted combustion of CH4/H2

Mardani, A ; Sharif University of Technology | 2017

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  1. Type of Document: Article
  2. DOI: 10.1016/j.fuel.2016.11.056
  3. Publisher: Elsevier Ltd , 2017
  4. Abstract:
  5. Moderate or Intense Low-oxygen Dilution (MILD) combustion which known as a combustion under highly preheated and diluted condition is a relatively new combustion regime including many differences in comparison with the traditional one. Among many distinguished disparities between combustion modeling of conventional and MILD ones, turbulent-chemistry interaction modeling is an open field of study. Current knowledge on modeling this combustion regime shows that the eddy dissipation concept (EDC) model could be successfully used for modeling of this combustion regime. In this paper, it has been tried to propose some guidelines to modify the semi-empirical constants of the original EDC model for MILD combustion. In this way a parametric study of the EDC model constants for a nonpremixed MILD burner is done in terms of accuracy of prediction while the responses of the model to its constants are focused on the basis of physical arguments. Burner of Dally et al. (JHC) is modeled using the RANS approach in a 2D axisymmetric computational domain for different oxygen levels and fuel jet Reynolds numbers when a reduced detail chemical mechanism of DRM-22 is used to represent the chemical mechanism. Moreover using a well-stirred–reactor analysis and extracting the chemical reactions pathways, discussions are completed. Results show that reducing the CD2 constant which leads to a decrease in time scale and volume fraction constants of the model would improve the performance of the model for MILD condition. Prediction of flame lift-off and minor OH species has been improved by changing default model constants of Cτ and Cγ to around 0.0893 and 1.0, respectively, especially for lower oxygen levels. Indeed reaction pathway analysis and dimension of reaction zone showed that reducing scales of the defined reactor in the EDC model (i.e. fine structure) to the Kolmogrov or smaller scales might push the reactions inside each structure toward the non-equilibrium condition and enlargement of overall reaction zone and make the EDC model more compatible with MILD combustion characteristics. Reduction in the length and time scales of the fine structure led to improvement in Temperature, OH, and CO profiles inside of MILD region of the JHC burner, although for CO, disagreement is still considerable. Considering error analysis of five checked parameters (i.e. H2O, CO2, OH, CO, and temperature) at both MILD and conventional regions of the JHC burner may conduct us toward that the defaults setting of the model still works reasonably on the whole when it is used at both regions. © 2016 Elsevier Ltd
  6. Keywords:
  7. EDC ; Hydrogen ; Methane ; MILD combustion ; Turbulence-chemistry interaction ; Turbulent non-premixed combustion ; Atomic physics ; Carbon dioxide ; Combustion ; Fuel burners ; Oxygen ; Reaction kinetics ; Reynolds number ; Turbulence ; Chemical mechanism ; Computational domains ; Diluted combustion ; Eddy dissipation concept ; Nonequilibrium conditions ; Turbulence-chemistry interactions ; Chemical analysis
  8. Source: Fuel ; Volume 191 , 2017 , Pages 114-129 ; 00162361 (ISSN)
  9. URL: https://www.sciencedirect.com/science/article/pii/S0016236116311577