Turbulent Non-premixed Combustion of Rapeseed Methyl Ester in a Free Shear Swirl Air Flow

Turbulent nonpremixed combustion of rapeseed methyl ester (RME) in a free shear swirl air flow was modeled by solving the governing conservation equations of mass, momentum, energy, and equations representing the droplet breakup, dispersion, movements, vaporization, and the combustion (i.e., formation, reaction and transport of gaseous species) and then validated via experimentations. A surrogate combustion mechanism for RME including 419 reactions and 101 species was employed for handling the combustion chemistry. The flamelet concept is used to relate the instantaneous composition of gaseous species to the mixture fraction. The turbulent gas mixture velocity across the flame was numerically resolved by Reynold Average Navier Stokes (RANS) and the turbulence fluctuations of scalar variables (i.e., mixture fraction, heat loss, and scalar dissipation) is averaged and taken into account by weighting with an assumed shape probability density function (PDF). The heat radiation was modeled via discrete ordinates to increase the reliability of simulation in prediction of temperature and gaseous specious, especially thermal NO. The atomization, ignition, evolution of flame, in cylinder temperatures, and local concentrations of regular pollutants (CO, NO, NO2, CO2, and O-2) of turbulent RME flame are studied and compared with experimentation. Results reveal that numerical modeling satisfies criteria of simulated flame being able to accurately predict the temperature and formation pollutants. However, some discrepancies between the model and experimental data exist, especially in the post-flame-zone and for NO emission because the flamelet concept cannot perfectly capture the slow chemistry reactions such as thermal NO formation and absence of prompt NO formation in the combustion mechanism which was employed for biodiesel fuel.