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    Numerical Investigation of Soot Formation in Non-premixed Flames

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    ThesisAbdelgadirJune2017.pdf
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    Description:
    Dissertation _ Ahmed Abdelgadir
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    Type
    Dissertation
    Authors
    Abdelgadir, Ahmed Gamaleldin cc
    Advisors
    Bisetti, Fabrizio cc
    Committee members
    Roberts, William L. cc
    Knio, Omar cc
    Haworth, Daniel C.
    Program
    Mechanical Engineering
    KAUST Department
    Physical Science and Engineering (PSE) Division
    Date
    2017-05
    Embargo End Date
    2018-06-15
    Permanent link to this record
    http://hdl.handle.net/10754/625044
    
    Metadata
    Show full item record
    Access Restrictions
    At the time of archiving, the student author of this dissertation opted to temporarily restrict access to it. The full text of this dissertation became available to the public after the expiration of the embargo on 2018-06-15.
    Abstract
    Soot is a carbon particulate formed as a result of the combustion of fossil fuels. Due to the health hazard posed by the carbon particulate, government agencies have applied strict regulations to control soot emissions from road vehicles, airplanes, and industrial plants. Thus, understanding soot formation and evolution is critical. Practical combustion devices operate at high pressure and in the turbulent regime. Elevated pressures and turbulence on soot formation significantly and fundamental understanding of these complex interactions is still poor. In this study, the effects of pressure and turbulence on soot formation and growth are investigated numerically. As the first step, the evolution of the particle size distribution function (PSDF) and soot particles morphology are investigated in turbulent non-premixed flames. A Direct Simulation Monte Carlo (DSMC) code is developed and used. The stochastic reactor describes the evolution of soot in fluid parcels following Lagrangian trajectories in a turbulent flow field. The trajectories are sampled from a Direct Numerical Simulation (DNS) of an n-heptane turbulent non-premixed flame. Although individual trajectories display strong bimodality as in laminar flames, the ensemble-average PSDF possesses only one mode and a broad tail, which implies significant polydispersity induced by turbulence. Secondly, the effect of the flow and mixing fields on soot formation at atmospheric and elevated pressures is investigated in coflow laminar diffusion flames. The experimental observation and the numerical prediction of the spatial distribution are in good agreement. Based on the common scaling methodology of the flames (keeping the Reynolds number constant), the scalar dissipation rate decreases as pressure increases, promoting the formation of PAH species and soot. The decrease of the scalar dissipation rate significantly contributes to soot formation occurring closer to the nozzle and outward on the flames wings as pressure increases. The scaling of the scalar dissipation rate is not straightforward due to buoyancy effects. Finally, a new scaling approach of the flame at different pressures is introduced. In this approach, both Reynolds number and Grashof number are kept constant so that the effect of gravity is the same at all pressures. In order to keep Gr constant, this requires the diameter of the nozzle to be changed as pressures vary. This approach guarantees a similar non-dimensional flow field at all pressures and rules out the effect of hydrodynamics and mixing, so that only the effect of chemical kinetics on soot formation can be studied.
    Citation
    Abdelgadir, A. G. (2017). Numerical Investigation of Soot Formation in Non-premixed Flames. KAUST Research Repository. https://doi.org/10.25781/KAUST-4699F
    DOI
    10.25781/KAUST-4699F
    ae974a485f413a2113503eed53cd6c53
    10.25781/KAUST-4699F
    Scopus Count
    Collections
    PhD Dissertations; Physical Science and Engineering (PSE) Division; Mechanical Engineering Program

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