Numerical study of sooting flames: from strain rate sensitivity to turbulence-chemistry interaction models

Student thesis: Doctoral Thesis


Soot prediction from combustion systems is still a major challenge in high-fidelity simulations of reactive flows, especially in turbulent conditions. Among the critical aspects, due to its slow characteristic formation times, soot sensitivity to strain rate and turbulence-chemistry interaction models for combustion closure can be found. Starting from the laminar problem, Soot Formation (SF) and Soot Formation Oxidation (SFO) counterflow flames are studied, allowing assessment of the roles of the different underlying phenomena concurring at soot formation with varying strain rates, depending on their relevance in each configuration. Attention is devoted to the inception model, which always regulates the onset of soot formation, and entirely determines the soot sensitivity to strain rate in the SF configuration through nucleation and condensation. Besides, surface growth and oxidation are analyzed in the SFO configuration, where they are predominant. The corresponding models are fine-tuned and generalized, and improved predictions are obtained in both configurations. Afterwards, a 2-points flame-controlling continuation method with soot module inclusion is developed to build a tool capable of flamelets generation inclusive of soot effects on the gas phase. The implementation is first tested discussing general features of the S-curve and verifying the consistency with previous works. The tool is finally used to compute the S-curve of ethylene pressurized sooting flames. The models and tools developed are incorporated into an OpenFOAM-based solver to perform Computational Fluid Dynamic (CFD) simulations of sooting turbulent flames. These are studied in pressurized, highly turbulent environments, to validate the soot model at a fundamental level but with practically relevant operative conditions. The numerical results are found to satisfactorily depict the soot volume fraction (SVF) formation, even though a few quantitative and qualitative discrepancies are discussed. Furthermore, soot intermittency and pressure scaling are analyzed. Finally, an alternative turbulence-chemistry interaction model for combustion closure is explored. A generalized partially-stirred reactor model is developed which accounts for all chemical times in a consistent manner. While the applicability of available models is confined to specific turbulence-chemistry interaction regimes, the incorporation of detailed chemistry description in the proposed approach improves synergistic predictions of all species and makes it suitable for systems with characteristic times very different from each other, such as soot and NOx.
Date of AwardOct 31 2022
Original languageEnglish (US)
Awarding Institution
  • Physical Sciences and Engineering
SupervisorHong G. Im (Supervisor)


  • Soot modelling; Strain rate; Method of moments; Counterflow flames; Soot Formation; Soot Formation Oxidation; S-curve; Turbulent sooting flames; Turbulence-chemistry interaction; PaSR model

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