Numerical determination of iron dust laminar flame speeds with the counter-flow twin-flame technique

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Abstract

Iron dust counter-flow flames have been studied with the low-Mach-number combustion approximation. The model considers full coupling between the two phases, including particle/droplet drag. The dispersed phase flow strain relations are derived in the Stokes regime (Reynolds number much smaller than unity). The importance of solving a particle flow strain model is demonstrated by comparing three different cases: a free unstrained flame, a counter-flow flame where slip effects are neglected and a counter-flow flame where slip effects are included. All three cases show preferential diffusion effects, due to the lack of diffusion of iron in the fuel mixture, e.g. DFe,m= 0. The preferential diffusion effect causes a peak in the fuel equivalence ratio in the preheat zone. On the burned side, the combined effect of strain and preferential diffusion shows a decrease in fuel equivalence ratio. Inertia effects, which are only at play in the counter-flow case with slip, counteract this effect and result in an increase of the fuel equivalence ratio on the burned side. A laminar flame speed analysis is performed and a recommendation is given on how to experimentally determine the flame speed in a counter-flow set-up. Novelty & Significance We introduce a novel model to include particle flow strain in a dispersed counter-flow set-up. For the first time, the impact of particle flow strain on the flame structure of iron dust is studied with a one-dimensional (1D) model. Two major effects that modify the flame structure and burning velocity are identified: preferential diffusion and inertia of the particles. Preferential diffusion effects are found to be always present in (iron) dust flames. Inertia effects play a role in the counter-flow case with slip. Due to the inertia of the particles, the particle flow strain is lower than the gas flow strain. As a consequence, higher particle concentrations are reached compared to the other cases. Furthermore, it is shown that each particle size experiences a different particle flow strain rate, which is important when doing experiments as it implies that the PSD at the flame front will be different than at the inlet.

Original languageEnglish
Article number113524
Number of pages13
JournalCombustion and Flame
Volume266
DOIs
Publication statusPublished - Aug 2024

Keywords

  • Burning velocity
  • Counter-flow
  • Dispersed-phase flame
  • Iron
  • Particle flow strain

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