Modeling homogeneous ignition processes of clustering solid particle clouds in isotropic turbulence

Fuel, vol. 371, pp. 132054

Abstract

The objective of this study is to numerically investigate the ignition and combustion of pulverized solid fuels in turbulent conditions and to assess different modeling strategies relevant to large-eddy simulations (LES). The investigations show that due to the high Stokes number of solid particles, they do not necessarily follow the flow. At Stokes numbers around unity, particle–turbulence interactions can lead to particle clustering and change the ignition behavior. According to observations, ignition is most likely to happen outside the formed clusters, where suitable thermo-chemical conditions exist. To study this behavior, direct numerical simulations (DNS) of reactive particles in turbulent conditions employing detailed kinetics for solid and gas phases were performed. Pulverized fuel combustion was modeled using the point-particle approximation to represent the dispersed phase in an Eulerian–Lagrangian framework. Isotropic turbulence was employed to investigate the influence of particle clustering on the ignition process. After investigating the physical aspects of the ignition process, the DNS dataset was used as a benchmark for evaluating the reduced-order flamelet models usually employed in LES of pulverized fuel combustion during the ignition process. The flamelet model performance in predicting the selected quantity of interest was compared to the DNS data. An error decomposition was performed using the optimal estimator concept. Finally, the prediction accuracy of presumed PDFs is evaluated by calculating the errors in predicting the quantity of interest using different PDFs compared to the predictions using the accurate sub-filter joint distribution of the DNS data. • DNS of clustering pulverized solid fuel ignition and combustion is performed. • The ignition origins were investigated with respect to particle clustering. • A systematic model assessment using the optimal estimator method was performed. • Effects of changing FPV input parameters in the model performance were studied. • The presumed marginal PDF assumption was compared to the joint PDF distribution.

Authors 7

1. Pooria Farmand corresponding Aachen Faculty of Mechanical Engineering Institute for Combustion Technology

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University, Faculty of Mechanical Engineering, Institute for Combustion Technology, Templergraben 64, 52056 Aachen, Germany

2. Hendrik Nicolai

   Technische Universität Darmstadt

   Affiliation as printed

   Technical University of Darmstadt, Department of Mechanical Engineering, Simulation of reactive Thermo-Fluid Systems, Otto-Berndt-Straße 2, 64287 Darmstadt, Germany

3. Lukas Berger Aachen Faculty of Mechanical Engineering Institute for Combustion Technology

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University, Faculty of Mechanical Engineering, Institute for Combustion Technology, Templergraben 64, 52056 Aachen, Germany

4. Antonio Attili

   University of Edinburgh

   Affiliation as printed

   University of Edinburgh, School of Engineering, Institute of Multiscale Thermofluids, The King’s Buildings, Mayfield Road, Edinburgh, EH9 3FD, United Kingdom

5. Michael Gauding Aachen Faculty of Mechanical Engineering Institute for Combustion Technology

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University, Faculty of Mechanical Engineering, Institute for Combustion Technology, Templergraben 64, 52056 Aachen, Germany

6. Christian Hasse

   Technische Universität Darmstadt

   Affiliation as printed

   Technical University of Darmstadt, Department of Mechanical Engineering, Simulation of reactive Thermo-Fluid Systems, Otto-Berndt-Straße 2, 64287 Darmstadt, Germany

7. Heinz G. Pitsch Aachen Faculty of Mechanical Engineering Institute for Combustion Technology

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University, Faculty of Mechanical Engineering, Institute for Combustion Technology, Templergraben 64, 52056 Aachen, Germany