Large eddy simulations of biodiesel spray flames using a cost-effective Flamelet Generated Manifold methodology
(2024) 27th “Journées d’étude” of the Belgian Section of the Combustion Institute — Location: Brussels (3.April.2024)
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- Spray combustion is encountered in numerous technological applications, notably in the trans-port and energy sectors. Advancements in combustion modeling, numerical methods and computer technology have enabled detailed simulations of spray flames of conventional fuels, such as diesel fuel and its surrogates. However, nowadays societies strive to curb the consumption of fossil fuels in order to mitigate the effects of climate change. To this end, alternative, carbon-neutral fuels (biofuels) are promising candidates to replace fossil fuels in internal combustion engines. Nevertheless, the combustion properties of such fuels have been studied to a much lesser extent than those of conventional fuels.In order to fill this gap, new modeling approaches and robust numerical methods for the simulation of spray combustion of alternative fuels have been implemented. This implies detailed numerical simulations of the flows of interest under realistic engine conditions. More specifically, an improved methodology for turbulence-chemistry interactions based on the Flamelet Generated Manifolds (FGM) approach is proposed in particular for biofuels. These models also encompass the description of the secondary breakup of the droplets using a modified version of the well-known Taylor Analogy Breakup (TAB) model. All of this allows for an accurate prediction of dynamic features of spray flames, such as ignition delay time (IDT) and flame lift-off length (FLOL). Further, we employ these new modeling and associated numerical tools to perform detailed simulations of spray flames of biofuels such as biodiesel and ethanol.We are performing Large Eddy Simulations (LES) of spray flames of the Karanja Methyl Ester(KME) biodiesel. Our numerical setup follows closely the well-known “Spray A” configuration which is relevant to operating conditions of engines with exhaust gas recirculation. With regard to the numerical methodology, we employ the Eulerian approach for the gaseous phase,combined with Lagrangian particle tracking for the motion of the fuel droplets. In terms of chemical kinetics, we employ a compact combustion mechanism of a surrogate blend composed of n-dodecane and methyl butanoate, with the latter one representing the ester content of the biodiesel. This mechanism is tabulated and turbulence-chemistry interactions are computed via the FGM methodology. Herein we employ a new and cost effective FGM tabulation based on4 control variables (mixture fraction, progress variable, and their variances). Additionally, for increased accuracy, the temperature is not computed from the FGM database but via numerical integration of the energy equation.
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Ponet, A., & Papalexandris, M. (2024). Large eddy simulations of biodiesel spray flames using a cost-effective Flamelet Generated Manifold methodology. 27th “Journées d’étude” of the Belgian Section of the Combustion Institute, Brussels. https://hdl.handle.net/2078.5/268837