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Abstract: A new soot model is presented, which has been developed for CFD applications, combining accuracy and efficiency. While the chemical reactions of small gas phase species are captured by a detailed chemical kinetic mechanism, polycyclic aromatic hydrocarbons (PAHs) and soot particles are represented by sectional approaches. The latter account for important mechanisms such as the formation of sections, their oxidation, the condensation of acetylene, and the collisions between sections. The model has been designed to predict soot for a variety of fuels with good accuracy at relatively low computational cost. Universal model parameters are applied, which require no tuning in dependence of test case or fuel. Soot predictions of ethylene, propylene, kerosene surrogate, and toluene flames are presented, which show good agreement with the experimental data. Furthermore, the importance of the correct choice for thermodynamic data of PAHs and soot is highlighted and the impact of heat radiation is discussed. [Copyright &y& Elsevier]

Abstract: In this paper a new soot formation model for gas turbine combustor simulations is presented. A sectional approach for the description of Polycyclic Aromatic Hydrocarbons (PAHs) and a two-equation model for soot particle dynamics are introduced. By including the PAH chemistry the formulation becomes more general in that the soot formation is neither directly linked to the fuel nor to C2-like species, as it is the case in simpler soot models currently available for CFD applications. At the same time, the sectional approach for the PAHs keeps the required computational resources low if compared to models based on a detailed description of the PAH kinetics. These features of the new model allow an accurate yet affordable calculation of soot in complex gas turbine combustion chambers. A careful model validation will be presented for diffusion and partially premixed flames. Fuels ranging from methane to kerosene are investigated. Thus, flames with different sooting characteristics are covered. An excellent agreement with experimental data is achieved for all configurations investigated. A fundamental feature of the new model is that with a single set of constants it is able to accurately describe the soot dynamics of different fuels at different operating conditions. [Copyright &y& Elsevier]

Abstract: An extension of the turbulent flame speed closure model rendering the model applicable to multiphase flow and ignition is presented. As formerly no coupling between reaction progress variable and enthalpy was existent, except through the temperature dependency of the laminar flame speed, an adaptation is proposed which offers an interface to initiate the combustion process. The modification to incorporate multiphase conditions is achieved by substituting the mixture fraction variable as representation of the composition in the original implementation of the turbulent flame speed closure model with independent species. Source terms to correlate the species progress to the reaction progress variable are derived in this work. The additional transport equations serve a higher generality of the model and enable the proper treatment of vaporizing fuel droplets. It is demonstrated that limitations which arise in the standard formulation of the model, stemming from differences in the transport equation for the reaction progress variable and the mixture fraction, are addressed and resolved by the new approach. Regarding the initiation of the flame, an additional source term for the reaction progress variable is introduced, which relates the reaction progress to the auto-ignition time. This allows the development of the flame without imposing artificial boundary conditions. The correct model behavior is established by means of a series of widely used test cases. The results of these simulations show that the model’s potential to predict flame growth and more generally the flame evolution as a function of time and space is preserved. At the same time more sophisticated test case boundary conditions involving multiphase conditions and variable inflows in terms of composition can be incorporated. As a thorough assessment of the extended model capabilities, a multiphase lab scale set-up, which provides a comprehensive data set, is presented. The good agreement of the obtained results underline the range of applicability of the extended model and its accuracy, albeit its simplicity, for multiphase conditions. [Copyright &y& Elsevier]