Numerical simulations of flame structure and soot formation of biodiesel spray combustion*

We report on Large Eddy Simulations of spray flames of the Karanja Methyl Ester biodiesel. Our numerical setup follows the well-known “Spray A” configuration which is relevant to operating conditions of diesel engines with exhaust gas recirculation. We employ the Eulerian approach for the gaseous phase, combined with Lagrangian particle tracking for the motion of the droplets. In terms of chemical kinetics, a compact combustion mechanism of a surrogate blend composed of n-dodecane and methyl butanoate is used, 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 methodology. Herein we use a new and cost effective FGM tabulation based on 4 control variables (mixture fraction, progress variable, and their variances). A popular soot model is also included in the kinetics scheme. In this talk, we first present results for certain global flame properties, such as ignition delay time, flame lift-off length and maximum flame temperature. Then, we analyze the mass fractions of species indicative of combustion efficiency and soot production, as well as soot concentration. Finally, we compare our numerical predictions with experimental and numerical results for diesel fuel and its surrogate n-dodecane.