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UID:event-32@tuemeche.nl
DTSTAMP:20261007T234656Z
DTSTART;TZID=Europe/Amsterdam:20261021T110000
DTEND;TZID=Europe/Amsterdam:20261021T123000
SUMMARY:Why do iron particles fail to burn? Numerical investigations into
  the interaction of turbulence and iron powder combustion
DESCRIPTION:Speaker: Shyam Hemamalini\nHost: Xiaocheng Mi\n\nIndustrial i
 ron powder combustors represent a highly promising carbon-free renewable 
 energy technology\, but their practical application is frequently hindere
 d by combustion inefficiency\, specifically the presence of unoxidized pa
 rticles. To understand if such flames can be self-sustaining\, an investi
 gation into the observed inefficiency is necessary. This investigation hi
 nges on two fundamental questions:\n\n1. Can all particles be ignited in 
 the first place?\n2. If particles are successfully ignited\, can they que
 nch midway through their combustion?\n\nIn real combustors\, the flow is 
 inherently turbulent\, which drives the fluid dynamic phenomenon of prefe
 rential concentration. This phenomenon results in particle clustering\, w
 hich could have a detrimental effect on the combustion process. In order 
 to understand precisely how preferential concentration affects the overal
 l combustion of the particles and to deduce whether turbulence interactio
 n could be an answer to the posed questions\, a dedicated numerical frame
 work to simulate turbulent\, particle-laden iron flames is developed. The
  framework is based on a two-way coupled Eulerian-Lagrangian approach\, t
 racking the iron particles with the point-particle assumption and employi
 ng the “switch-type” kinetics from the oxide-layer model by Mi et al.
  to model particle reactions. This framework is implemented in the high-f
 idelity solver NTMIX-CHEMKIN to perform robust Direct-Numerical-Simulatio
 ns (DNS) and in the commercially-available OpenFOAM to test large-scale c
 apabilities with Large-Eddy-Simulations (LES).\n\nUsing this framework\, 
 iron particle combustion in a Homogeneous Isotropic Turbulence (HIT) fiel
 d is first analyzed using DNS [3]. The results demonstrated that preferen
 tial concentration causes massive localized oxygen depletion\, which can 
 elongate particle burn times by up to eight times compared to isolated pa
 rticles. However\, the most critical message from this study is that alth
 ough the combustion time is significantly elongated by clustering\, the f
 lame does not quench\; the particles smoothly complete their oxidation.\n
 \nThis behavior is further confirmed by the DNS of a turbulent mixing lay
 er\, which also showed the extension of combustion time and underscored t
 he critical importance of oxygen depletion in particle-dense regions. The
  mixing layer study additionally revealed that while small particles (und
 er 20 μm) maintain the laminar structure of the flow\, larger particles 
 (over 28 μm) possess the momentum to actively perturb the mixing layer a
 nd induce turbulent-like behavior. Because particles do not quench once i
 gnited\, the primary focus for solving combustion inefficiency should be 
 strictly on the ignition phase of the combustion process.\n\nExperimental
  results from pilot burners\, such as those analyzed by Niek van Rooij an
 d Jesse Hameete\, highlight that iron particles can completely fail to ig
 nite\, possibly due to the gradual growth of the oxide layer and subseque
 nt hindering effects on ignition. Hence\, accurately predicting ignition 
 becomes the most vital part of the numerical modeling of turbulent iron f
 lames. The jet-in-hot-coflow burner developed by Jesse Hameete is numeric
 ally modeled as LES in OpenFOAM. Two distinct reaction models—the first
 -order Damköhler model and the oxide-layer model—are compared against 
 experimental data. Ultimately\, neither numerical model is currently able
  to perfectly capture the observed ignition behavior. While the first-ord
 er model overpredicts ignition percentages\, the oxide-layer model exhibi
 ts the same trend in percentages as seen in the experimental results\, al
 beit with a substantial error in critical temperature. However\, this stu
 dy confirmed that particles do not partially oxidize in such large-scale 
 flames\; rather\, they fail to ignite.\n\nCan preferential concentration 
 enhance ignition? A numerical study on ignition in three-dimensional sphe
 rical suspensions shows that a clustered particle distribution has a subs
 tantially lower ignition temperature than a random Poisson distribution i
 n space. Hence\, partial clustering before particle injection could lead 
 to better ignition in large-scale combustors.\n\nUltimately\, this resear
 ch establishes that the combustion inefficiency in industrial turbulent i
 ron flames is primarily a failure of ignition rather than mid-combustion 
 quenching. While preferential concentration significantly delays oxidatio
 n through localized oxygen depletion\, it does not inherently extinguish 
 ignited particles\; conversely\, clustering may actually lower the therma
 l threshold required for initial ignition. These findings shift the parad
 igm for optimizer strategies toward the pre-ignition phase. Future resear
 ch must bridge the gap between current kinetic models and experimental re
 ality\, specifically investigating how multi-stage turbulent mixing dynam
 ics can be leveraged to optimize combustion efficiency and improve the ov
 erall performance of large-scale iron powder combustors.
LOCATION:Atlas 0.710
URL:https://tuemeche.nl/peoplepages/event.php?id=32
CATEGORIES:PhD Defense
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