Application of Large Eddy simulation to Gasoline Engine and Comparison against RANS

The work presented is a comparative analysis between Reynold’s Averaged Navier Stokes (RANS) and Large Eddy simulation (LES) description of turbulence to capture the in-cylinder flow structures. Simulations are performed using RNG k - € RANS model and LES one equation eddy viscosity model with Werner and Wengle wall model. ECFM combustion model has been used to achieve the desired rate of heat release when compared against the experiments. KH-RT spray model has been used to define the primary and secondary breakup of parcels. A Renault engine operating on Miller cycle has been chosen for this study. Consecutive perturbation method (CPM) available in Converge has been used to take the advantage of availability of higher number of cores to reduce the effective CPU time. Results of RANS simulation indicates that increase in valve overlap results in faster tumble decay compared to LES. Moreover, it is also found that LES required lesser tuning of flame stretch due to turbulence and a single value can be applied across different valve lift conditions. A quantitative comparison of standard deviation of IMEP between test and the simulation results has been made. An analysis on fast and slow burning cycles has been performed which showed that velocity plays a major role in affecting the burning speed. Furthermore, additional results obtained from the multiple cycles of LES are analyzed.