LES of biodiesel spray flames using a cost-effective Flamelet Generated Manifold methodology*

In this talk we report on Large Eddy Simulations 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. The breakup of fuel droplets is accounted for via a modified version of the Taylor Analogy Breakup model. 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 Flamelet Generated Manifold (FGM) methodology. Herein we employ a new and cost effective FGM tabulation based on 4 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. In this talk we present results for global flame properties, such as ignition delay time, flame lift-off length and flame temperature. We also analyze the mass fractions of species that are indicative of combustion efficiency, such as OH, CH2O and C2H2. Finally we compare our numerical predictions with earlier experimental and numerical results for standard diesel fuel and its surrogates.