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Behavior of Premixed Sooting Flame in a High-Pressure Burner

Author: Dr. Ahmad Saylam

Document type: Published open-access journal article

Journal: Reactions

Publication details: Volume 4, Issue 1, pages 155–170, 2023

Publication date:

Scientific status: Numerical CFD study combining three-dimensional screening and justified two-dimensional analysis. The work evaluates burner-induced flow and soot-formation effects under the simulated atmospheric- and elevated-pressure conditions.

DOI: 10.3390/reactions4010009

Abstract

The study numerically investigates how burner optical ports, edge inter-matrices and pressure influence soot formation and the behaviour of premixed sooting flames in a high-pressure burner.

Three-dimensional CFD simulations of premixed C2H4/air flames at 1.01 and 10 bar were first performed using a one-step chemistry approach. Their purpose was to assess whether prospective axisymmetric two-dimensional and one-dimensional representations could adequately capture the burner-flow behaviour relevant to the study.

The resulting two-dimensional analysis indicates that edge inter-matrices can generate axial vorticity. At elevated pressure, strong thermal expansion of the burned gases can generate multiple axial vortical structures. These structures produce multiple axial sooting regions that correspond qualitatively to luminous soot streaks observed experimentally.

Relatively low-temperature regions below approximately 1800 K, together with enhanced mixing around and above the edge inter-matrix location, can promote conditions favourable to soot formation. The calculated influence on the centreline soot-volume fraction nevertheless remained limited: below about 3% for the atmospheric-pressure flame and below about 10% for the 10 bar flame.

Increasing mixture reactivity—by reducing the rich equivalence ratio or increasing pressure—promoted earlier soot-precursor formation and shifted the sooting region upstream under the investigated conditions.

Technical contribution

The work links specific high-pressure-burner design features to local flow structures and spatial soot behaviour. It shows that optical access and internal support structures can influence the flame even when their effect on the centreline soot-volume fraction is comparatively modest.

The study also establishes a modelling workflow in which three-dimensional simulations are used to test geometric effects before adopting a computationally less demanding axisymmetric representation for more detailed analysis.

Principal findings

  • Burner optical ports and edge inter-matrices can disturb the local flow field and should not automatically be treated as negligible.
  • Edge inter-matrices can generate axial vortical structures and locally enhance species and thermal mixing.
  • Elevated pressure increases flame reactivity and can strengthen thermally driven flow structures.
  • Multiple local sooting zones can arise even when the centreline soot response remains relatively limited.
  • More reactive conditions shift soot-precursor formation and the sooting region closer to the burner.

Scope and application boundary

The conclusions apply to the investigated burner geometry, premixed ethylene–air flames, pressures, equivalence ratios, boundary conditions and modelling assumptions. They should not be transferred unchanged to a different burner or fuel.

The three-dimensional screening calculations used one-step chemistry. Such chemistry can support flow-field assessment but does not resolve the detailed pathways governing soot-precursor formation and particle evolution.

Axisymmetric modelling can represent only geometric and flow features compatible with rotational symmetry. Fully three-dimensional optical ports, manufacturing asymmetries and non-axisymmetric instabilities may require explicit three-dimensional treatment.

Quantitative application to another facility should include geometry-specific meshing, grid-independence assessment, validated heat-loss and radiation treatment, detailed chemistry and soot modelling, boundary-condition uncertainty and comparison with measured temperature, velocity, species and soot fields.

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Licence and reuse

The article is distributed under the Creative Commons Attribution 4.0 International licence .

The licence permits sharing and adaptation, including commercial reuse, provided appropriate attribution is given, a link to the licence is supplied and any changes are indicated.

Citation

Saylam, A. (2023). Behavior of Premixed Sooting Flame in a High-Pressure Burner. Reactions, 4(1), 155–170. https://doi.org/10.3390/reactions4010009