On the prediction of combustion products and soot particles in compartment fires

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Copyright: Yuen, Anthony Chun Yin
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Abstract
In fire simulations, one of the most critical challenges is the incorporation of detailed chemical description for the combustion process where intermediate chemical products are formed through a series of elementary reactions. It is essential to apply a comprehensive reaction scheme that fully describes the oxidation processes of the parent fuel and the formation processes of major intermediate chemical species. A novel in-house fire field model based on Large Eddy Simulations (LES) approach incorporating fully coupled subgrid-scale (SGS) turbulence, combustion, soot formation and radiation models for the interactive and non-linear nature of the turbulent reacting flow in compartment fire phenomena has been developed in this dissertation. It uniquely embraces the detailed reaction mechanisms for the chemical processes involved during combustion. Since the modelling of hydrocarbons by-products are enabled when considering the full chemical profile, the formation of soot particles can be related to the concentration of main incipient such as acetylene, which provides an appropriate representation of nucleation, surface growth processes. Furthermore, two alternative SGS turbulence models: Vreman model (VM) and Wall-Adapting Local Eddy Viscosity model (WALEM) are incorporated and examined for compartment fire simulations. Parametric studies have been performed in two large-scale compartment fire tests. It is found that the turbulent Prandtl and Schmidt numbers of 0.3 respectively and the Smagorinsky constant of 0.2 should be applied to correctly model the flow and thermal diffusivities. Furthermore, temperature and velocity field predications accuracies are enhanced using WALEM, owing to the wall adaptive features and the consideration of both strain and rotational rates of the turbulent field. The importance of incorporating the detailed reaction mechanisms in compartment fire simulations has been confirmed by comparing with experiments. It is discovered that species concentrations especially CO2 and CO are more accurately predicted by the detailed scheme comparing to the multi-step scheme, since the formation of hydrocarbons and nitrogen oxides are considered. This also improves the replication of the flame structure as the fire is chemically-driven within the combustion zone. In addition, the evaluation of soot particle content is also enhanced with the consideration of acetylene as the precursor.
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Author(s)
Yuen, Anthony Chun Yin
Supervisor(s)
Yeoh, Guan Heng
Timchenko, Victoria
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Publication Year
2014
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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